Color Cosmos Oculus: Vision, Color, and the Eye in Jacopo Zabarella and Hieronymus Fabricius ab...

COLOR, COSMOS, OCULUS: VISION, COLOR, AND THE EYE IN JACOPO ZABARELLA AND

HIERONYMUS FABRICIUS AB AQUAPENDENTE

Tawrin Baker

Submitted to the faculty of the University Graduate School in partial fulfillment of the requirements

for the degreeDoctor of Philosophy

in the Department of History and Philosophy of Science Indiana University

November 2014

Accepted by the Graduate Faculty, Indiana University, in partial fulfillment of the requirements for the degree of Doctor of Philosophy.

Doctoral Committee

Date of Defense: October 3, 2014

________________________________ William Newman, Ph.D.

________________________________ Domenico Bertoloni Meli, Ph.D.

________________________________ Jutta Schickore, Dr.phil

________________________________Rega Wood, Ph.D.

________________________________Sven Dupré, Ph.D.

ii

Copyright © 2014Tawrin Baker

iii

Acknowledgements

I would like to first thank Bill Newman, my advisor, for setting me on my initial

scholarly path and guiding me down it. After writing a paper for your Francis Bacon class in my

first semester you mentioned that little research had been done on pre-Newtonian color theory —

a tantalizing morsel for a first year graduate student, the necessary first sustenance from which

this dissertation developed. You set a powerful example as a scholar. I am indebted to all I have

been able to learn, and you have done for me. A tremendous thanks also to Nico Bertoloni Meli,

who has been immensely supportive and encouraging throughout my time at IU. You have

guided this dissertation, and my growth as a scholar, in more ways than I can mention. It is

impossible to imagine what sort of historian I would be without either of you.

A warm thanks also to Sven Dupré, whom I met at a key moment as I was beginning my

dissertation proper. Working with you at the MPIWG opened up many doors, and your example

broadened both my knowledge and methods as a scholar. A heartfelt thanks to Karin Leonhard: I

cannot express the importance of your encouragement. I would also like to give my appreciation

to Jutta Schickore and Rega Wood, whose support, advice, and scrutiny helped me enormously.

Also crucial to this dissertation is Carl Pearson. Without your classes on Aristotle, or exposure to

your historical sensibility, my research would be greatly impoverished. Thank you. Finally, to

Jim Capshew, Sandy Gliboff, Amit Hagar, Lisa Lloyd, Jordi Cat, and Colin Allen: you have all

shaped my thinking, and it has been a pleasure to be a student surrounded by such a rare

combination of intellects.

The quality and character of one’s fellow graduate students is nearly as important as one’s

professors, and I have been incredibly lucky. Scott Hyslop, Emil Sargsyan, Steve Laurie, and

iv

Laura Seger were with me from the beginning. Karin Ekholm, Evan Ragland, Joel Klein, and

Allen Shotwell were examples to strive towards. Patrick McNeela, Klodian Coco, Ashley

Inglehart, and Nicolas Bamballi have all helped me work through ideas in this dissertation.

Benny Goldberg and Peter Distelzweig at Pitt have supported and inspired my work. To all, your

friendship made grad school possible.

Many of the dissections in this dissertation were done in collaboration with Bradley

Barger. Thank you so much for your help, and I hope we can anatomize together again. Maybe

some ears next time?

Part of my dissertation research was made possible by a generous grant from the Gladys

Krieble Delmas Foundation. I would also like to thank the Lilly Library and its staff.

A shout out to $, Squishy, Scooter, Sharky, Sarah B., Aa-Lo, damiandamiandamian,

Nomi, Ekers, Gordo, L-D, Sloze, Slick Ricky, Sarah C., etc. You know who you are and what

you have done.

To Juana: my love and gratitude, always.

Lastly, none of this would be possible without the love and support of my parents,

Murray and Janice. There are traces of you in all I am and do, including this weird thing below.

v

Tawrin Baker

COLOR, COSMOS, OCULUS: VISION, COLOR, AND THE EYE IN JACOPO ZABARELLA AND HIERONYMUS FABRICIUS AB AQUAPENDENTE

The seventeenth century saw radical changes to theories of vision, light, color, matter, and

knowledge about animal bodies. Understanding vision in the sixteenth century is essential to

grasp these changes, but here many lacunae exist. Histories of vision have focused on

mathematical optics and neglected color in natural philosophy and medicine. Historians of

medicine have not sufficiently analyzed works on vision and color by physicians. Finally,

historians of philosophy have produced few analyses of color theory from antiquity until 1600.

My dissertation analyzes two highly important works on vision that have yet to be examined in

detail by modern scholars: the natural philosopher Jacopo Zabarella's De visu, first published in

his natural philosophy textbook De rebus naturalibus in 1590, and the physician and anatomist

Hieronymus Fabricius ab Aquapendente's De visione, first published in 1600. Both taught at the

University of Padua, at the time Europe's most prestigious medical school, and their stature and

influence was considerable.

Chapter 1 provides the history of one widely held theory of what color is and how it arises,

which I dub the condensation theory of the origin of color. This theory arises from the

Aristotelian commentary tradition with significant influences from astronomy, optics, and

anatomy. This theory of color was closely intertwined with an Aristotelian cosmology, and is

found in fully developed form in Averroës. Chapter 2 analyzes book 1 of Zabarella's De visu,

where we find the most rigorous and complete explication of this theory in its history. Chapter 3

is an analysis of Fabricius's De visione, which combines anatomy, natural philosophy, and

mathematical optics. Chapter 4 examines the shared, novel theory of vision held by Zabarella

and Fabricius, and argues that they interacted across disciplinary lines in forming it. Chapter 5

demonstrates Zabarella’s and Fabricius’s influence on highly important figures for seventeenth-

century optics and visual theory, such as Johannes Kepler, François Aguilón, and Christoph

Scheiner; it argues for a revision to current narratives about the reception of the retinal theory of

vision; and it addresses some major misconceptions about transformations to theories of vision

and sensation in the seventeenth century.

vii

Table of Contents

Introduction 1

§ 0.1 Historical Aims 6

§ 0.2: Historiographical Issues 13

§ 0.3: The Three al-Ḥasans 22

§ 0.4: Appendices 24

Chapter 1: Color & Cosmos 26

§ 1.0: Introduction 26

§ 1.1 Aristotelian Background 29

§ 1.2: Ancient Commentators 41

§ 1.3: Optics: Density, Rarity, and Color in Ptolemy and Ibn al-Haytham 51

§ 1.4: Averroës and the Articulation of the Condensation Theory 68

§ 1.5: Medieval Appropriation of the Condensation Theory 76

§ 1.6: Conclusion 90

Chapter 2: Vision and the Rise of Autonomous Natural Philosophy: Zabarella’s De visu 95


§ 2.1: Zabarella’s Life and Works 99

§ 2.2: Historiographical Review: Zabarella and “Scientific Method” 106

§ 2.3: Light, Color, and Transparency in De Visu 109

§ 2.4: The Definition of Color 113

§ 2.5: Generation of Real Colors 116

§ 2.6: Real versus Apparent Colors 125

§ 2.7: Intentional or “Spiritual” Species 128

§ 2.8: Lux and Lumen 131


viii

Chapter 3: Vision and Philosophical Anatomy: Fabricius ab Aquependente’s De visione 141


§ 3.1: Fabricius’s Life and Career 146

§ 3.2: Historiographical Review 150

§ 3.3: A Brief History of Humors and Tunics in the Sixteenth Century 156

§ 3.4: The Meaning of Dissection in Fabricius’s Philosophical Anatomy 175

§ 3.5: Transparency and Complexion in Historia 180

§ 3.6: Fabricius on the Action of the Eye 194

§ 3.6-1: Genre and Textual Authority 194

§ 3.6-2: The Nature of Light and Color according to Fabricius 197

§ 3.6-3: Glowing Meat, Shining Eyes, and the Nature of the Transparent 206

§ 3.7: Fabricius on the Utilitas of the Most Godlike of the Instruments 211


Chapter 4: The Visual Theory of Zabarella and Fabricius 219


§ 4.1: Zabarella’s and Fabricius’s Refutations of Atomistic Theories of Vision 222

§ 4.2: Zabarella Contra Galen 1: Refutation of the Extramission Theory 226

§ 4.3: Zabarella Contra Galen 2: Arguments from the Exceedingly Skillful Construction of the Eye 232

§ 4.4: Fabricius on the many Utilitates of Diaphaneity (or, How to Graft Optics onto Anatomy at the End of the Sixteenth Century) 249

§ 4.5: Utilitas of the Cornea: Fabricius’ Treatment of Refraction 259

§ 4.6: Fabricius’s Appropriation of Pecham 264

§ 4.7: Fabricus on the Utilitas of the Crystalline and Vitreous Humors 275


Chapter 5: Light, Color, and the Eye in the Early Seventeenth Century 283


§ 5.1: Kepler 284

ix

§ 5.2: François d’Aguilón 297

§ 5.3: The Clarity and Color of the Crystalline Humor and Retina in the Seventeenth Century 310

§ 5.4: Some Revisions to the Historiography of Seventeenth-Century Vision and Sensation 325


Conclusion 340

§ 6.1: Summary 340

§ 6.2: Color and Cosmos Revisited 345

Appendix 1: Glossary 349

Appendix 2: Translation Of Chapter 1 of Zabarella’s De visu 351

Appendix 3: Zabarella On the Nature and Generation of Color 352

Bibliography 355

Primary Sources 355

Primary Sources in Translation 360

Secondary Sources 365Curriculum Vitae

x

Introduction

Have you considered how lavish the maker of our senses was in making the power to see and be seen?

I can’t say I have.Well, consider it this way. Do hearing and sound need another

kind of thing in order for the former to hear and the latter to be heard, a third thing in whose absence the one won’t hear or the other be heard?

No, they need nothing else.And if there are any others that need such a thing, there can’t

be many of them. Can you think of one?I can’t.You don’t realize that sight and the visible have such a need?How so?Sight may be present in the eyes, and the one who has it may

try to use it, and colors may be present in things, but unless a third kind of thing is present, which is naturally adapted for this very purpose, you know that sight will see nothing, and the colors will remain unseen.

What kind of thing do you mean?I mean what we call light.

Plato, Republic VI, 507 c-e.1

Plato’s dialogue from the Republic shows starkly the distance between the ancient and modern

understanding of vision. Today, we think of sight as occurring when light of various wavelengths

within the visible spectrum interacts with photoreceptors in our retinas; in humans, there are

typically three types of receptors (cones) responsible for color vision whose peak sensitivity

occurs at three different wavelengths and one type (rods) responsible for peripheral and low-light

1

1 Translation by G.M.A. Grube, rev. C.D.E. Reeve. From Plato, Plato: Complete Works, ed. by John M. Cooper (Indianapolis: Hackett Publishing Company, 1997), 1128.

monochromatic vision. The particular wavelengths that we see and, in some sense, attribute to

the things we see themselves can result from a dizzying array of causes: the spectrum of

wavelengths of the light source or sources, the absorption spectrum the things seen (due itself to

many causes), the kind and degree of scattering occurring at the surface of things, constructive

and destructive interference, the degree of translucency and the complicated effects that can

arise, as well as incandescence, chemoluminescence, fluorescence, the effect of refraction, and

selective absorption in the medium. We don’t however, see the wavelengths of light or their

spectra per se: an immensely complex series of neurological processing at various places

(beginning in the retinal ganglion cells) gives rise to our perception of color (as well as shape,

size, distance and so on) and this perception is influenced by a great number of contextual factors

such as the degree and color of the illuminating light (that is, to some extent our perceptual

mechanism automatically “corrects” the color of a body when seen under colored lights) or color

contrasts in the field of vision. Research on physical, physiological, and psychological aspects of

color is ongoing, and there is much yet to be discovered.

Yet, according to the predominant way of talking about color today, we say that we see

light, and that color is, or arises from, some property of light. It is its wavelength or the spectrum

of wavelengths of light that are supposed to be the initial cause of our perception of color, and it

is not uncommon to hear someone speak (perhaps erroneously) about the color of light. The

notion that color is an affection of light only rose to prominence in the seventeenth century, and

before that, light and color were typically considered distinct — though perhaps related — entities

or properties. As Plato says, light is a third factor that allows us to see color. This distinction is

crucial for understanding premodern theories of vision, and yet the history of color as a property

2

distinct from light has barely been sketched. The history of vision prior to Newton has focused

almost entirely on light, and pre-Newtonian physical color theory, in particular, has been little

studied.2

Investigating color, particularly among the many Aristotelianisms in the Middle Ages and

Renaissance, reveals a dense web of connections between what might otherwise seem disparate

topics, and it enriches our understanding of anatomy, natural philosophy, and mathematical

optics in surprising ways. Without understanding color, sixteenth-century theories of vision and

developments in the anatomy of the eye cannot be well understood. Furthermore, because color

has been largely neglected by historians and philosophers, many of the great transformations in

the seventeenth century are not fully understood. This includes the (at least seemingly) radical

reconceptualization of sensation and the sensible qualities in the seventeenth century, including

the so-called primary-secondary quality distinction; the adoption of the retinal theory of vision;

changes to the understanding of matter, its properties, and how mixture works; the understanding

of generation and corruption, including animal generation; and, to some extent, the momentous

shift from a geocentric to a heliocentric conception of the cosmos. The association between

3

2 There are many aspects to the history of color, and the category “color” is an unwieldy subject of historical analysis. Much foundational work tracing the connections between color in art, philosophy, and science has been carried out by John Gage. John Gage, Color and Culture: Practice and Meaning from Antiquity to Abstraction (Boston: Little, Brown and Company, 1993). John Gage, Color and Meaning: Art, Science, and Symbolism (University of California Press, 2000). The work of Alan Shapiro is also essential for understanding color in the seventeenth century, particularly in connection with Newton and the history of optics. See especially Alan E. Shapiro, “The Evolving Structure of Newton’s Theory of White Light and Color,” Isis 71, no. 2 (June 1, 1980): 211–35; Alan E. Shapiro, “Artists’ Colors and Newton’s Colors,” Isis 85, no. 4 (December 1, 1994): 600–630. Finally, although it is a superficial treatment of the topic, one of the few works in the history of science to treat physical color theory without subsuming the history of color under the history of light or mathematical optics, is Henry Guerlac, “Can There Be Colors in the Dark? Physical Color Theory before Newton,” Journal of the History of Ideas 47, no. 1 (January 1, 1986): 3–20. The seeds of several key research questions found in this dissertation can be found there.

structure of the eye and the structure of the cosmos was commonly made prior to the seventeenth

century. For example after comparing the eye to an egg, Andreas Vesalius writes:

In quite the same way one could describe the parts of the universe, either from the earth to the water, air, fire, lunar heaven, and so on to the furthest heaven, or from that heaven to the center of the universe, the Earth. The fabric of the eye can be compared to the universe or an egg in its construction.3

Yet we will see, prior to the seventeenth century the connection between the eye and the cosmos

involved far more than a mere analogy or aid to memory. One of the dominant theories in the late

Middle Ages and Renaissance about how color arises out of the fundamental stuff of the universe

— what I call the condensation theory of the origin of color — had at its very center the problem

of how vision can comprehend both the incorruptible, etherial heavens and the ever-changing,

gross matter beneath the lunar sphere. Note that I use the term “origin” here in a scholastic sense,

and in this context it refers primarily to the material and formal conditions for substances to be

colored instead of uncolored, and only secondarily how the conditions of that substance cause or

otherwise relate to our perception of color. After the rise in the mechanical philosophy in the

seventeenth century opacity is in a sense basic, while transparency requires an explanation: how

do light particles or mechanical impulses that constitute light make their way through air, water,

or glass without colliding or being impeded by the medium? In the scholastic view (or at least

according to the most common scholastic view in the later Middle Ages), to be uncolored is to be

transparent, and transparency, or the capacity for transparency, was in some sense fundamental: it

naturally existed in elemental fire, air, water, as well as the celestial aether, and the lack of

transparency in elemental earth was the exception.

4

3 Andreas Vesalius, The Fabric of the Human Body: An Annotated Translation of the 1543 and 1555 Editions of “De Humani Corporis Fabrica Libri Septem,” 2 vols. (Basel: S Karger Ag, 2013), 1306.

This dissertation focuses on color, vision, and the eye in two highly influential, but thus far

largely neglected, works on vision by two professors at the University of Padua who flourished

in the second half of the sixteenth century: the logician and natural philosopher Jacopo Zabarella

(1533–1589) and the surgeon, physician, and anatomist Hieronymus Fabricius ab Aquapendente

(c. 1533–1619). Zabarella’s De visu libri duo, or Two Books on Sight, was first published in his

natural philosophy textbook De rebus naturalibus libri XXX in Venice in 1590. This work was

reprinted many times throughout Europe, and was also published in his posthumous De anima

commentary. (For a more extensive biography and historiographical review of Zabarella, see

Chapter 2 sections 1 and 2, hereafter written as §§ 2.1–2.) There Zabarella gives perhaps the

most comprehensive and systematic account of light, color, and vision in the Peripatetic

tradition. Fabricius’s De visione, or On Vision, was first published in 1600 along with his works

on speech and hearing — De voce and De auditu, respectively. This text is remarkable in that it is

the first anatomy text to seriously attempt the integration of anatomy with a natural-philosophical

account of light, color, and vision, along with an account of the refraction of rays culled from

works in mathematical optics. That is, it is the first anatomical text to both give an accurate

portrayal of the size, shape, and optical density of the three clear humors of the eye, and to use

this empirically-derived eye (rather than the idealized one used in the genre of mathematical

optics) to understand how rays of light and color progress through the eye. (A lengthier

biography along with a historiographical review is in found in §§ 3.1–2.)

This dissertation has three primary historical aims and two notable historiographical ones,

which are outlined below.

5

§ 0.1 Historical Aims

The fundamental historical purpose of this dissertation is to carefully analyze Zabarella’s De visu

and Fabricius’s De visione. These works were immensely popular and influential when they were

first published, and they also provide insight into what these two professors would have taught

their many international students. These students include William Harvey (a student of Fabricius)

and the writer of the most popular scholastic natural philosophy textbooks in the seventeenth-

century, Johannes Magirus (whose text was used, among others, by Isaac Newton when he was a

student at Cambridge).4 If one wishes to understand how physicians, philosophers, and the

learned in general would have understood vision at the end of the sixteenth and the beginning of

the seventeenth centuries, these two works are indispensable. They also have yet to be carefully

investigated.5 This is in part because they do not easily fit into older narratives of scientific

progress, and insofar as they have been incorporated into scientific revolution or other

6

4 Johann Magirus, Physica peripatetica ex Aristotele, eiusque interpretibus collecta, et in sex libros distincta: in usum Academiae Marpurgensis Studio & opera Johannis Magiri Doctoris Medici & Physiologiae (Frankfurt: Palthenius, 1597). Its many subsequent editions are usually titled Physiologiae Peripateticae. Among other things, this textbook was still used in Cambridge when Isaac Newton was a student. On its popularity and influence, see Mary Reif, “Natural Philosophy in Some Early Seventeenth Century Scholastic Textbooks” (PhD Dissertation, Saint Louis University, 1962), 20; Charles H. Lohr, “Renaissance Latin Aristotle Commentaries: Authors L-M,” Renaissance Quarterly 31, no. 4 (1978): 532–603.5 A translation of De visione into German has been made in three parts: Hieronymus Fabricius ab Aquapendente, Die Augenanatomie des Fabricius ab Aquapendente (1537-1619): Übersetzung von“Oculi dissecti historia” mit Kommentar, trans. Walter Birchler (Zurich: Juris Druck + Verlag, 1979). Hieronymus Fabricius ab Aquapendente, Die Abhandlung über das Sehen von Hieronymus Fabricius ab Aquapendente (1537-1619): Übersetzung von “De actione oculorum” mit Kommentar (Zurich: Juris Druck + Verlag, 1984). Heironymus Fabricius ab Aquapendente, Die spezielle Physiologie des Auges von Hieronymus Fabricius ab Aquapendente (1533-1619): Übersetzung ausgewählter Kapitel des 3. Buches von “De visione” mit Kommentar, trans. Jeannette Scharpf-Paravicini (Zurich: Juris Druck + Verlag, 1991). The commentary in the above works, however, is scant, the historiography outdated, and the authors do little to put the work in context or revise the predominant attitude towards the work. See also Erwin De Nil and Mark De Mey, “Hieronymus Fabricius d’Aquapendente: De Visione, Ending of the Perspectivist Tradition,” in Optics and Astronomy: Proceedings of the XXth International Congress of History of Science (Brepols, 2001), 51–65. The scholarship in this essay, however, is poor; in addition to recapitulating the received view of De visione, the authors make basic mistakes in their interpretation and translation of key parts of the text, rendering their analysis unreliable.

discontinuity narratives they are placed on the pre-revolution side. One exception to this are

theses about the “School of Padua” and experimental method centered on Zabarella — which are

now largely discredited. Zabarella and Fabricius were not thought to embody the new approach

to science in the seventeenth century, and thus their works were not carefully examined. This is

particularly true with respect to visual theory. They wrote just prior to Kepler’s development of

the retinal theory of vision in his Ad Vitellionem paralipomena (Frankfurt 1604), they did not

appear to contribute to the rise of mechanical philosophy and its account of sensation and

sensible qualities, and far from being put in the “mathematization of nature” camp, many

historians and philosophers have criticized them for not sufficiently recognizing the role of

mathematics in natural philosophy.6 During the crucial formation of the history of science as a

discipline they were not believed to be a part of the “Scientific Revolution,” and their retrograde

approach to nature supposedly prevented them from making discoveries that should have been

within their grasp (a charge leveled at Fabricius in particular). For many historians, then, these

two have served as foils for understanding more well-known seventeenth century figures such as

Kepler and Descartes. One problem is that Zabarella and Fabricius approached vision in a way

that is quite alien to modern understandings and sensibilities, and many of the key terms that

they employ — such as density and rarity, object and subject, light and color — do not refer to the

same things they do today, and thus their elaborate and sometimes subtle arguments are, more

often than not, misunderstood by modern scholars. By using these two professors as mere

contrast cases for seventeenth century developments, twentieth-century historians have not felt

the need to analyze the works carefully; or rather, because the errors of these two professors

7

6 See §§ 2.2, 3.2 below.

seemed obvious in retrospect their arcane treatises were deemed not worth the trouble of wading

through. They are well worth the trouble, and is time for these works to be looked at closely.

Chapter two of my dissertation analyses Book I of Zabarella’s De visu, in which he gives

what he sees as the correct theory of vision according to Aristotle. This includes definitions of

color and visibility, an account of real versus apparent color, an account of what transparency is,

an account of what intentional species are, an account of lux and lumen, the relationship between

lux, lumen, color, and transparency, and finally, an account of the structure and purpose of the

eye and its parts. According to Zabarella, all of this is merely to explicate what Aristotle means

when he says that any explanation of vision must include (1) the object of sight, (2) the

intermedium, and (3) the instrument of sight. Chapter 2 should be thought of as an analysis of

vision in the context of the rise of natural philosophy as an autonomous discipline in Northern

Italy. I treat to Book II of Zabarella’s De visu in Chapter 4. Chapter 3 analyzes Fabricius’s De

visione. This chapter includes important background on the history of ocular anatomy and its

connection to visual theory in the sixteenth century. I look at the Galenic structure of his treatise,

his relationship to Aristotle and Aristotelianism, and analyzes how he understands the categories

of dissectio (dissection), historia (history), actio (action), and utilitas (usefulness). Thus, Chapter

3 is an account of vision in the context of sixteenth-century anatomy and medicine. Chapter 4

compares the two works, and shows that the natural philosopher and the anatomist held the same,

novel theory of vision. This chapter examines their attacks on competing theories, analyzes their

shared theory of vision, and argues that in some crucial ways this novel theory of vision departed

from all previous theories about the functioning of the eye. Chapter 5 includes an analysis of the

influence of this theory of vision, particularly on Johannes Kepler and François d’Aguilón.

8

Chapter 5 also sketches a revised account of the reception of the retinal theory of vision in the

first half of the seventeenth century, and with the benefit of a solid grasp of Zabarella’s and

Fabricius’s approach to vision it revisits key issues involved in seventeenth-century changes in

sensible qualities, sensation, and the overall approach to vision.

My second goal, historically speaking, is to give some account of physical color theory in

the sixteenth century among the medical and, primarily, philosophical traditions; I also use this

understanding of pre-modern physical color theory to reevaluate seventeenth century changes in

accounts of vision, light, color, ocular anatomy, and sensation. Sixteenth-century figures

typically emphasized that color and light were distinct (though related) entities. Although there is

a great deal of secondary literature on light, there is relatively little on color, and this disparity

results in some misunderstanding of the history of vision, sensation, and ocular anatomy. By

color theory, however, I do not primarily refer to which colors produce others when mixed, or

how colors were thought to relate to and interact with each other in painting. These were not the

main concerns of physicians, philosophers, or writers on optics in the sixteenth century, and so

they are not mine. (I do, however, hope that this work will be useful to art historians and others

interested in color histories more broadly understood.) Rather, I focus on descriptions, by

physicians and natural philosophers primarily, of what color is in a body, in what way color

exists in a transparent medium, what it is to perceive color, and especially what the origins of

color are — that is, what fundamental properties of matter underly the color of a body itself.

Scholastic answers to the last issue were usually one of the following: that color is

directly tied to the four elements (earth, air, fire, and water), that it is fundamentally tied to the

four elemental qualities (hot, cold, wet, and dry), that it is given by the substantial form of a

9

body, or that it arises from the density and rarity of a body. These four explanations of the origin

of color were not strictly speaking incompatible. One could hold that the origin of color was

density and rarity, but that the elements and/or the elemental qualities effect those changes in

density and rarity; or that color was tied to the four elements, but that when mixed the substantial

form of the newly generated substance is the cause of its color, and furthermore that the new

color of a body need not take into account the ratio of the original elemental ingredients; and so

on. Zabarella held that the origin of color was density and rarity, and this appears to have been

one of, if not the, dominant explanation of the origin of color in the late Middle Ages and

Renaissance. For this reason I focus on the history of what I call the condensation theory of the

origin of color in Chapter 1.

There was a great ferment in the Renaissance regarding color and color theory. Yet the

sixteenth century in particular has scarcely been analyzed, and especially the great number of

scholastic Aristotelian works on the subject have hardly been examined. As I will show, the

condensation theory of color was closely intertwined with an Aristotelian cosmology. This came

to the Latin West in two main ways. One way was through the commentaries on Aristotle by Ibn

Rushd, or Averroës, who outlines the condensation theory of the origin of color primarily in his

commentary on Aristotle’s De caelo (On the Heavens) and his treatise De substantia orbis (On

the Substance of the Heavenly Spheres). Another main font consists of works typically classified

within mathematics, especially the optics of Ibn al-Haytham and Ptolemy but also astronomical

works (including Ptolemy’s Mathematike Syntaxis or Almagest). In astronomical works, the

refraction causing changes in the apparent positions of the stars was typically explained in terms

of the difference in density between the heavens and the sublunar realm. However, mathematical

10

texts, both optical and astronomical, largely just assumed that rare substances were transparent,

and that both color as well as refraction were caused by the condensation of fundamentally

transparent substances; they did not give a physical or philosophical account of how exactly this

worked. The long development of the condensation theory of the origin of color, from Aristotle

through the Middle Ages occupies Chapter 1. This serves as the background for my analysis of

the sixteenth century in subsequent chapters, in particular color and vision in Zabarella and

Fabricius. Furthermore, it must be noted that “density” meant something quite different from

what it means today, and this has caused some misunderstanding in the secondary literature.

Chapter 1, therefore, contains significant discussion of premodern concepts of density (or

thickness or coarseness) and rarity (or subtlety, thinness, tenuity, or fineness). (See the glossary

in Appendix 1.)

Because color has been largely absent from histories of vision in the Renaissance, many

of the shifts in visual theory that have occurred in the seventeenth century are not properly

understood. Thus, in addition to understanding sixteenth-century color theory, another purpose of

my investigation into physical color theory is to reevaluate the shifts in light, color, and vision in

the seventeenth century, and to suggest new ways to look at the adoption of the retinal theory of

vision. From Galen, at least, until the seventeenth century the crystalline humor — what is now

called the crystalline lens or just the lens of the eye — was thought to be the site of visual

sensation. Because they have neglected to account for color, historians and philosophers have not

yet seriously enquired into what would have been involved in abandoning one of (if not the)

central aspect of the Aristotelian framework for vision: that the sensitive part of the eye must be

potentially any color, meaning that it must be itself uncolored; that is, that sight must take place

11

in a transparent part of the eye. One of the greatest shifts in visual theory in the history of

western science is at present only partially understood, and neither the criticism of the retinal

theory of vision by Kepler’s contemporaries nor its appropriation by seventeenth-century

Aristotelians has received much attention.

My third historical aim is to better understand the “Paduan scene” at the end of the

sixteenth century. Important seeds of change concerning natural philosophy, medicine, and

anatomy were being sown in Northern Italy during the Renaissance, and the University of Padua

was particularly fertile ground. Natural philosophy as an autonomous discipline — not one

subservient to either theology or medicine — was on the rise in Northern Italy from the middle of

the fifteenth century through the end of the sixteenth century.7 Thanks to figures like Giovanni

Battista da Monte the importance of clinical medicine in the curriculum grew dramatically while

at the same time becoming more systematic and sophisticated.8 The sixteenth century saw the

publication of Vesalius’s monumental De fabrica humani corporis, the rise of medical

humanism, the creation of the first permanent anatomy theatre in Padua by Fabricius, the growth

of a culture of public dissection generally, and the rise of the prestige and importance of the

faculty of anatomy at Bologna and Padua.9 These developments were not all independent of one

12

7 Charles H. Lohr, “The Sixteenth-Century Transformation of the Aristotelian Natural Philosophy,” in Aristotelismus Und Renaissance (Harrassowitz, 1988), 89–100. David A. Lines, “Natural Philosophy in Renaissance Italy: The University of Bologna and the Beginnings of Specialization,” Early Science and Medicine 6, no. 4 (January 1, 2001): 267–323. David A. Lines, University Natural Philosophy in Renaissance Italy: The Decline of Aristotelianism? (Brill, 2002). Heikki Mikkeli, “The Foundation of an Autonomous Natural Philosophy: Zabarella on the Classification of Arts and Sciences,” in Method and Order in Renaissance Philosophy of Nature (Ashgate, 1997), 211–28.8 Jerome Bylebyl, “The School of Padua: Humanistic Medicine in the Sixteenth Century,” in Health, Medicine, and Mortality in the Sixteenth Century, ed. Charles Webster (CUP Archive, 1979), 345–52; Maria Muccilo, “Da Monte, Giovanni Battista, Dettò Montano,” in Dizionario Biographico Degli Italiani, vol. 32, 1986, 365–67; Paul F. Grendler, The Universities of the Italian Renaissance (JHU Press, 2004), 341–2.9 Bylebyl, “The School of Padua,” 345–352. Arturo Castiglioni, A History of Medicine (A. A. Knopf, 1958), 442-443.

another, however. In Chapter 4, I show that Zabarella and Fabricius held the same, novel theory

of vision, and through a comparison of their texts I argue that the two almost certainly interacted

in some fashion in forming their theory. Thus, despite disciplinary boundaries that produced, at

times, fierce rhetoric aimed at physicians by natural philosophers and vice versa, intellectual

exchange appears to have been common.

§ 0.2: Historiographical Issues

One persistent problem with the history of vision before the seventeenth century, and which is to

some extent a broader problem with the history of science, is that historians have not sufficiently

looked at the relationship between works in natural philosophy, works in medicine and anatomy,

and works in mathematics (in this case mathematical optics). In part this is just the old problem

that nineteenth- and twentieth-century categories of science do not map easily onto the past, but

when the histories of science, medicine, and philosophy became professionalized in the first half

of the twentieth century the guiding research questions were affected by contemporary categories

within science. This problem has been to some extent exacerbated by continuing disciplinary

divisions within academia. Historians of medicine, historians of the mathematical sciences, and

historians of philosophy have all each treated the figures I discuss here, but each with different

interests, and as a result scholars have carved out and analyzed particular portions of treaties on

vision without understanding them as a whole, and without carefully comparing works written by

natural philosophers, by physicians, and by mathematicians.

Proof of this lack of integration can be found in how Fabricius’s De visione has been

variously described. Andrew Cunningham, in a seminal essay on Fabricius’s “Aristotle Project”

13

wrote that, if we understand Fabricius’s own reasons for investigating the nature of animal

bodies, “we might be able to recognize that some things were not in fact ‘staring him in the face’

after all; that, by the criteria of what he was actually doing, his answers were competent answers

to his questions”.10 Cunningham gives a short exposition of Fabricius’s discovery and account of

the ostiola (or little doors) in the veins, and shows that for Fabricius the discovery of the

circulation of the blood, for example, would not have been staring him in the face.11 He does not,

however, say much at all about Fabricius’s De visione, and some scholars still ask how Fabricius

could have done such careful work on ocular anatomy without coming to the conclusion that the

retina was the site of visual sensation.12 Among historians of medicine Huldrych Koelbing sums

up the predominant attitude towards Fabricius’s De visione.

Mais que fait-il de toutes ces observations? A peu pres rien! Fabrice a bien contribué à l’essor de l'anatomie du XVIe siècle, mais ses connaissances approfondies ne lui servent qu'à confirmer des doctrines anciennes, et plus particulièrement la théorie de la vision d'Aristote et d'Alhazen...13

Koelbing also writes:

Et, bien entendu, dans son texte, il attribute toujours au cristallin un position au centre du globe oculaire, quoiqu’il ait observè lui-même que c’est faux. C'est difficile à comprendre: son observation, personnelle et nouvelle, de la vrai position du cristallin, immédiatement derrière la pupille, n'influence en aucune manière les idées de Fabrice sur le fonctionnement de l’œil! Son commentaire se

14

10 Andrew Cunningham, “Fabricius and the ‘Aristotle Project’ in Anatomical Teaching and Research at Padua,” in The Medical Renaissance of the Sixteenth Century, ed. Andrew Wear, Roger Kenneth French, and Iain M. Lonie (Cambridge University Press, 1985), 222.11 Cunningham, “Fabricius and the ‘Aristotle Project,’” 206–209.12 E.g., Erwin De Nil and Mark De Mey, “Hieronymus Fabricius d’Aquapendente: De Visione, Ending of the Perspectivist Tradition,” in Optics and Astronomy: Proceedings of the XXth International Congress of History of Science (Brepols, 2001), 51–65.13 Huldrych M. Koelbing, “Anatomie de L’œil et Perception Visuelle, de Vésale À Kepler,” in Le Corps À La Renaissance. Actes Du XXXe Colloque de Tours 1987 (Paris, 1990), 395.

limite à la seule phrase qu'il ajoute à son dessin: “Les investigateurs des œuvres de la nature auront donc beaucoup à méditer.”14

As I will show, Koelbing’s assessment is incorrect, and in fact Fabricius rejects crucial aspects of

both Aristotelian and medieval Perspectivist theories of vision — although he does so without

making a fuss, and without overturning Aristotle and Alhazen tout court. It seems that, because

Fabricius did not do what Kepler did, he does not require careful analysis. Thus Koelbing takes

Fabricius’s statements that the crystalline humor is the “middle humor” (i.e., that it is between

the aqueous and vitreous humors) to mean that it is in the geometrical center of the eye; this is a

mistake that others have made and can be easily dismissed. More insidious, and much more

difficult to rectify, is that Koelbing and many others appear to fault Fabricius for failing to

develop a retinal theory of vision. One larger purpose of my dissertation is to make good sense of

Zabarella and Fabricius’s crystalline-centered theory of vision, and to show why Kepler’s retinal

theory of vision would have been considered highly problematic on both natural-philosophical

and empirical grounds. The desire for our historical actors — especially when they are intelligent

and diligent observers of nature, as Fabricius and Zabarella both were — to come to the “correct”

conclusions is perhaps inevitable, but it is obvious that this presentist impulse must be curbed.

Historians of science studying the history of visual theory have looked very carefully at

works in mathematical optics to the neglect of works of medicine, anatomy, and natural

philosophy, particularly in the sixteenth and early seventeenth centuries. This is despite the fact

that education in medicine and the arts (i.e., philosophy) was far more common than education in

mathematics. If one wishes to get a sense of what a literate person would have understood about

vision in the Renaissance, works by physicians and natural philosophers must be examined

15

14 Koelbing, “Anatomie de L’œil,” 365.

carefully.15 Thus, for example, after discussing the anatomists Colombo, Bartisch, Estienne,

Fabricius, Jessenius, Varolio, and Laurens on ocular anatomy, David Lindberg writes: “None of

the post-Vesalian authors that I have mentioned made significant alterations in visual theory.”16

Although Fabricius’s De visione was first published in 1600, Lindberg does not seem to realize

this and only cites the 1614 edition, so it is not surprising that he does not examine it carefully in

a book aimed towards understanding Kepler's Paralipomena.17 A. C. Crombie has also written

on Fabricius, saying: “His visual theory was essentially a combination of the formulations of the

problem by Aristotle and Galen with a version of the optical scheme with which Alhazen had

prevented the reversal of the image as the visual cone passed through the transparent media.”18

Largely dismissing the anatomists, Crombie says: "It was the mathematicians who came to

reform visual theory by proceeding through an optical analysis of ocular physiology, exploiting

the models of eyeglasses and the camera obscura, and thus reformulating the problem itself.”19

As I will show, this picture is not correct. The work of mathematicians cannot be discounted, but

16

15 The extremely important issue of how vision was understood vision apart from the intellectual elite, which includes artists, those involved in practical mathematics, and the population in general, is beyond the scope of this dissertation. On this, see Gage, Color and Culture; Gage, Color and Meaning; Shapiro, “Artists Colors”; James S. Ackerman, “On Early Renaissance Color Theory and Practice,” Memoirs of the American Academy in Rome 35 (January 1, 1980): 11–44; Samuel Y. Edgerton, “Alberti’s Colour Theory: A Medieval Bottle without Renaissance Wine,” Journal of the Warburg and Courtauld Institutes 32 (1969): 109–34; Joy Allen Thornton, “Renaissance Color Theory and Some Paintings by Veronese” (PhD Dissertation, University of Pittsburgh, 1979); Sven Dupré, Renaissance Optics: Instruments, Practical Knowledge and the Appropriation of Theory (Max-Planck-Inst. für Wissenschaftsgeschichte, 2003). Andrea Feeser, Maureen Daly Goggin, and Beth Fowkes Tobin, The Materiality of Color: The Production, Circulation, and Application of Dyes and Pigments, 1400-1800 (Ashgate Publishing, Ltd., 2012).16 David C. Lindberg, Theories of Vision from Al-Kindi to Kepler (Chicago: University of Chicago Press, 1976), 175.17 Lindberg, Theories of Vision, 173.18 A. C. Crombie, “Expectation, Modelling, and Assent in the History of Optics: Part I. Alhazen and the Medieval Tradition,” Studies in the History and Philosophy of Science 21, no. 4 (1990): 629. This statement and others about Fabricius are repeated verbatim in A. C. Crombie, Styles of Scientific Thinking in the European Tradition: The History of Argument and Explanation Especially in the Mathematical and Biomedical Sciences and Arts, 3 vols. (London: Duckworth, 1994), 1120.19 Crombie, “Expectation: Part I,” 630.

the foundation for the radical changes in visual theory that took place in the seventeenth century

was the integration of anatomy, mathematical optics, and natural philosophy. The works of

Zabarella and Fabricius exemplify this interdisciplinary confluence, and I argue that they

themselves had some direct influence on seventeenth-century changes. If one wishes to identify a

revolution in visual theory around this time, Kepler should be placed somewhere in the middle,

not at the beginning or end. (He nevertheless remains, in my estimation, the most important

figure in this transformation.)

Finally, twentieth-century disciplinary isolation has resulted in a failure by historians of

philosophy to carefully examine Zabarella’s and Fabricius’s works on vision, among others. Thus

while Zabarella’s logic has been carefully analyzed,20 his disputes with fellow professors and his

relationship to medical humanism regarding method treated at length,21and his influence among

Northern European Protestants mapped out, his work on vision has not been the primary subject

of any study whatsoever. It is notable that a dissertation on Zabarella’s psychological works was

made in 1971 by Jorge Soler, but he skipped over Zabarella’s De visu because, he says, it did not

fit into the general character of his dissertation.22 Certainly De visu raises different issues and

requires a different sort of background knowledge compared to the rest of Zabarella’s

psychological works. Only two articles, to my knowledge, have given De visu much attention.

Charles B. Schmitt, with typical perspicuity, recognized the influence of anatomy on

psychological works by philosophers in the sixteenth century, and on De visu in particular. In a

17

20 William F. Edwards, “The Logic of Iacopo Zabarella” (PhD Dissertation, Columbia University, 1960).21 Heikki Mikkeli, An Aristotelian Response to Renaissance Humanism: Jacopo Zabarella on the Nature of Arts and Sciences (SHS, 1992).22 Jorge Leoncio Soler, “The Psychology of Iacopo Zabarella (1533 - 1589)” (Ph.D., State University of New York at Buffalo, 1971), 16.

footnote to his seminal “Experience and Experiment” essay he says that he plans to “treat this

topic in greater length elsewhere.”23 Unfortunately, whatever work he did on the topic has not

been published. More recently, in a very interesting essay on anatomy in connection with De

anima commentaries around 1600, Simone De Angelis refers to both Zabarella and Fabricius.

However, De Angelis points to a passage in De visu (Book I Chapter 8) where Zabarella cites

Galen’s De usu partium, and takes this to mean that Zabarella was referring his readers to Galen

for further elucidation.24 In fact, Zabarella rejects Galen's account of the eye, and is highly

critical of both the ancient doctor's skills of observation and philosophical acumen. (See §§ 4.1–

2.) Furthermore, De Angelis contrasts Fabricius with Kepler, not realizing the connection

between the two through Fabricius’s student Jan Jessenius. (See § 5.1.) De Angelis, is not,

strictly speaking, a historian of philosophy — and in fact if anything he exemplifies the

interdisciplinary combination of history of science, medicine, and philosophy needed to

understand this crucial period, and he raises compelling questions. The mistakes and omissions

in his recent essay occur largely because Zabarella’s De visu and Fabricius’s De visione have not

yet been given the detailed treatment they deserve.

In addition to the integration of the histories of medicine, optics, and philosophy, another

historiographical issue that I focus on concerns the notion of disciplinary boundaries at the end

of the sixteenth century. Zabarella and Fabricius certainly present their works in different ways,

18

23 Schmitt points out Zabarella’s personal anatomical observations of the eye, which Zabarella uses as evidence against the Galenic theory vision. He writes: "This is by no means a unique example of the use of information learned from anatomical dissections in arguments concerning natural philosophy and sensory psychology during the I6th and early I7th centuries. I plan to treat this topic in greater detail elsewhere." Charles B. Schmitt, "Experience and Experiment: A Comparison of Zabarella’s View With Galileo’s in De Motu," Studies in the Renaissance 16 (January 1, 1969): 97, n. 40.24 Simone De Angelis, “From Text to the Body: Commentaries on De Anima, Anatomical Practice and Authority around 1600,” in Scholarly Knowledge: Textbooks in Early Modern Europe (Librairie Droz, 2008): 205–28.

and a superficial reading of their works might lead one to the conclusion that there were

significant barriers erected between the logician and natural philosopher on the one hand and the

physician, surgeon, and anatomist on the other. They certainly have allegiance to different

authorities. Zabarella, as an interpreter of Aristotle at perhaps the most respected medical school

in Europe, is adamant that natural philosophy — that is, Aristotelian natural philosophy based on

a thorough analysis of the original Greek texts and the subsequent two thousand years of

commentary — should form the foundation of medical knowledge. As such, Zabarella thoroughly

criticizes Galen at every opportunity.25 (See §§ 4.2–4.3.) Fabricius, on the other hand, retains

both Galen and Aristotle as authorities, and his attitude throughout is one of respect for the

ancient doctor, even when he rejects his opinions for the same reasons as Zabarella. (See §§

3.6-2, 4.7.) Fabricius successfully raised the status of anatomy and surgery (along with his

salary) by integrating anatomy with natural philosophy, and his approach should be considered

“Galeno-Aristotelian.”26 Zabarella and Fabricius wrote in distinctly different genres — the natural

philosophy textbook versus the anatomy book. However, a careful analysis of their texts reveals

remarkable similarities in their reasons for rejecting Galen’s theory of vision and Galen’s

description of the structure and purpose of the parts of the eye. They also give nearly identical

accounts of certain aspects of dissection. Finally, I argue that they present, in their two texts, the

same theory of vision, one which is new with them and which had considerable influence. (See

Chapter 4, especially § 4.7.) Thus while they frame their works, in a sense, in opposition to one

another, and while each author argues that the methods of their discipline provide the most

19

25 See also Mikkeli, An Aristotelian Response.26 Peter Distelzweig, “Fabricius’s Galeno-Aristotelian Teleomechanics of Muscle,” in The Life Sciences in Early Modern Philosophy, ed. Ohad Nachtomy and Justin E. H. Smith (New York: Oxford University Press, 2014), 232.

secure knowledge about the natural world, nevertheless behind the veil of this textual animosity

there was, I argue, significant and fruitful interaction. Zabarella almost certainly went to

Fabricius’s dissections, and whether in a formal or informal setting they exchanged knowledge in

a way that was mutually beneficial. The disciplinary boundaries were porous, although this was

not something that they could not readily admit in print.

Above I have described the main historiographical issues that have impeded our

understanding of the two works of vision that are at the center of my dissertation. My attempt to

overcome them and, ultimately, provide a better picture of theories of vision in general around

1600 consists of reading the texts carefully, attributing — initially, at least — any confusion

arising therein to my own ignorance rather than some fault in my historical subjects. It also

involves reading their predecessors to understand background knowledge and assumptions, as

well as their contemporaries to get a sense of the reception and interpretation of their texts at the

time. These are not groundbreaking historiographical methods, but the goal — to know what they

knew by reading who they read — is extraordinarily difficult to achieve; I have surely not

succeeded fully, and I wait to be corrected by others. Somewhat more novel, although it should

not be, is the issue of historical replication.27 (See Chapter 4.) In tandem with reading the texts

and images themselves, have also replicated many ocular dissections and experiments described

by Zabarella and Fabricius. Fabricius’s De visione, after all, was at least in part intended to be

read alongside dissections of the eye, especially his own. (See § 3.4.) My historical replications

20

27 For an overview of the practice of historical replication, see Luigi Belloni, “The Repetition of Experiments and Observations: Its Value in Studying the History of Medicine (and Science),” Journal of the History of Medicine and Allied Sciences XXV, no. 2 (1970): 158–67. Heinz Otto Sibum, “Reworking the Mechanical Value of Heat: Instruments of Precision and Gestures of Accuracy in Early Victorian England,” Studies in History and Philosophy of Science Part A 26, no. 1 (March 1995): 73–106. Paolo Palmieri, Reenacting Galileo’s Experiments: Rediscovering the Techniques of Seventeenth-Century Science (Edwin Mellen Press, 2008).

are still ongoing, but I hope to show that what Zabarella and Fabricius might have seen in their

dissections and experiments on the eye are not always what we would expect. On the one hand,

once ocular dissections are performed with specific questions in mind some features seem to be

obvious while others are not. Every sensible aspect of the humors and inner tunics — shape, size,

relative position, color, clarity, texture, refractive power — is significant for understanding how

the eye works. However, the key issue seems to be whether a controversy or question arises in

the first place. For example, if the relative volumes of the anterior humor (the aqueous) and the

posterior humor (the vitreous) do not matter for one’s theory of vision, it is by no means obvious

that their relative volumes will be noted. On the other hand, if — as Galen says — the vitreous

humor is supposed to be somewhere between the color of blood and the transparency of the

crystalline humor, performing enough dissections on fresh eyes will likely convince a diligent

observer that Galen was wrong. Finally, if one tries to interpret the diagrams of the eye found in

most medieval and many renaissance works of mathematical optics as relating, in any essential

aspects, to actual eyes seen under dissection it is highly unlikely that one will come to the

conclusion that the scheme of the eye described in medieval perspectivist works was abstracted

from observation. The key point, it seems, is that the investigator must have these questions in

mind during dissection for these discrepancies to be at all noticeable. One point I make is that, in

Padua in the second half of the sixteenth century, natural philosophy, mathematical optics, and

anatomy were for the first time integrated in such a way such that vision, as treated within all

three disciplines, took as a fundamental empirical basis the eye as revealed through careful

dissection. (A possible exception to this is Galen, but by the end of the sixteenth century Galen’s

anatomy is heavily criticized.)

21

Taking the eye as personally witnessed through careful anatomical dissection as a

foundation for visual theory, these Paduan figures brought together and diligently considered the

many concerns from each discipline, and the controversies therein were resolved through some

combination of empirical evidence and scientific methodology. Many discrepancies among the

various disciplines were directly addressed (in print at least) for the first time, and methods of

reconciling different accounts and deciding right from wrong became necessary. Zabarella and

Fabricius, particularly the latter, were instrumental in working out how to combine the concerns

from these three, formerly separate, textual traditions. That the “scientific methodologies” of

Zabarella and Fabricius are somewhat alien to those of the later seventeenth century, not to

mention those of today, has obscured this fact. The integration of these various disciplines

involved the conviction that mathematical optics and natural philosophy must both base their

accounts on the eye as revealed through careful dissection, and that dissection can resolve

questions and tensions arising within and among the various practices . This, I argue, is a highly

significant turning point in the history of vision, and it appears first in Padua at the end of the

sixteenth century in the works of Zabarella and, especially, Fabricius. The integration of these

three traditions was also considered by Kepler, who had a different approach for how to reconcile

various discrepancies among authorities. However, I argue that Kepler’s approach would have

been less convincing to his contemporaries than the approaches of Zabarella or Fabricius. (See §

5.1.)

§ 0.3: The Three al-Ḥasans28

22

28 Or, as Nicolas Bamballi suggests, Alhazen Trismegistus.

Throughout this dissertation I use Ibn al-Haytham, Alhacen, and Alhazen to refer to three

substantially different texts. I use the first when referring to Abū ʿAlī al-Ḥasan ibn al-Ḥasan ibn

al-Haytham, the 10th century polymath and author of the Arabic Kitab al-Manazir or Book of

Optics.29 Following A. Mark Smith, I refer to Alhacen as the “author” of the manuscript

translated into Latin in the 12th century which was usually called De aspectibus or Perspectiva.

The Latin text differs from the Arabic not only because of many translation issues — it seems that

there were multiple translators involved and thus that some Arabic terms are translated

inconsistently, including those related to density and rarity — but also because the first three

chapters of the first book are missing from the Latin manuscript. These chapters provided much

of the experimental and, for lack of a better word, phenomenological grounding for what

follows. Furthermore, after Book III Chapter 3 the translation turns into something of a

paraphrase. As a result of all of this, the Latin version has not only different content but quite a

different character than the Arabic original.30 Finally, a version based on two Latin manuscripts

was printed 1572. This was edited by Friedrich Risner and titled Opticae thesaurus, and while

the spelling “Alhazen” does not appear to be the most common variant before Risner’s edition,

afterwards it became the dominant rendering of his name in the West. Furthermore, as A. Mark

Smith has shown, Risner happened to use manuscripts that diverged quite far from the family of

manuscripts that have come down to us.31 The printed text was also bound together with a short

treatise De crepusculis et nubium ascensionibus (On Twilight and Dawn) falsely attributed to Ibn

23

29 The first three books were translated into English as Ibn Al-Haytham and A. I. Sabra, Optics of Ibn Al-Haytham, 2 vols. (Warburg Institute, University of London, 1989).30 Ibn al-Haytham and Sabra, Optics vol. 2, lxxiii–lxxix. Alhazen and A. Mark Smith, Alhacen’s Theory of Visual Perception: A Critical Edition, with English Translation and Commentary, of the First Three Books of Alhacen’s De Aspectibus, the Medieval Latin Version of Ibn Al-Haytham’s Kitāb Al-Manāẓir (American Philosophical Society, 2001), xix–xxi31 Alhazen and Smith, De aspectibus, xxiii, clxi-clxvii.

al-Haytham, as well as the Polish mathematician Witelo’s treatise on optics. Edited significantly

by Risner, this edition was arranged into a series of theorems or propositions, and corresponding

sections in Witelo’s treatise are provided after each proposition (and vice versa). This makes the

work seem much more similar to Witelo’s, the latter of which follows a Euclidean deductive

model of definitions followed by theorems, rather than the more inductive and experimental

foundation that the original Arabic text had. Perhaps most significantly, the text of the

propositions or theorems that head each of the sections in Risner’s edition were added by Risner

himself. These are substantial additions, often extrapolations and interpretations of the

manuscript text, and at times they pronounce with authority what is only hinted at in the main

body. These propositions tend to reflect sixteenth-century concerns, and are frequently cited by

later authors who thus occasionally take “Alhazen” to have proved things that one would be hard

pressed to find in the original. Due to Risner’s clear influence in both content and character, I

write “Alhazen” when referring to this work.

§ 0.4: Appendices

There are three appendices to the main body of the dissertation. Appendix 1 is a glossary of

important terms. One reason that the analysis of pre-modern treaties on vision and sensation is so

difficult, and mistakes so easily made, is that many common terms have changed their meaning

dramatically. Thus opacity, density and rarity, subject and object, have all undergone substantial

changes since the Renaissance. Throughout I attempt to use the terms as my historical actors

used them, and thus a glossary of these terms is helpful. There are also some specialized

vocabulary and terms for parts of the eye that are included. Appendix 2 is a translation of the

24

proemium to Zabarella’s De visu and the first paragraph of Fabricius’s De visione. Appendix 3 is

a schematic outline of Zabarella’s rather intricate account of light and color, along with some

diagrams to help the reader visualize his framework for light, color, and vision.

NB: Because I make frequent references to various parts of the eye in this dissertation, I am

including here a modern depiction of the eye with the various parts labeled.

Figure 0.1: A typical twentieth-century representation of the interior of the eye.

25

Chapter 1: Color & Cosmos

§ 1.0: Introduction

This chapter is an examination of an important, but largely forgotten, theory of the origin of

color that was commonplace before the seventeenth century. What I call the condensation theory

of the origin of color closely intertwined the concept of density (or thickness) and rarity (or

tenuity) with light, color, and the material properties of the eye. Although it is difficult to judge

precisely what proportion of philosophers held the theory in the late Middle Ages and

Renaissance, it was certainly one of the more prevalent explanations for the origin of color. It is

mentioned in passing by the well-known writer on art an architecture Leon Battista Alberti,

indicating that knowledge of the theory was not confined to academic circles.1 The principal

source of this theory, at least in the form held by many in the Latin West, was Averroës. In

constructing his theory of the origin of color Averroës synthesized a number of ideas about

density and rarity, mixture, vision, and the nature of the heavens, and he also appears to have

integrated ideas and examples developed in the traditions of mathematical optics and astronomy

in his commentaries on Aristotle, although in this he seems to have been continuing a trend in the

Arabic-speaking intellectual world rather than forging a new path. His theory was appropriated

in different ways by later writers, but there are a number of stable and easily identifiable features

of the condensation theory of the origin of color. According to this theory, color was

26

1 “Lasciamo stare quella disputa de i philosophi, ne laquale si cercano i primi nascimenti de i colori. Perchioche, che giova al pittore il sapere, in che modo sia fatto il colore da i mescolamenti de raro, & del folto, del caldo, & del secco, o del freddo, & de l’humido?” Alberti, Leon Battista, La pittura (appresso Gabriel Giolito de Ferrari, 1547), 9v.

fundamentally tied to both assumptions about the substance of the heavens as well as the nature

of matter at the smallest level. Succinctly, the theory states that four of the five primary bodies

that constitute the universe — elemental water, air, fire, and the celestial aether — are naturally

transparent, while the remaining element earth lacks all transparency and is thus black. Through

the condensation or thickening of transparent substances the color white is generated, and all the

remaining species of color arise from a mixture of white and black, or perhaps more properly

from light and dark. Color, then, arises from the transparency or non-transparency of a body, and

transparency in turn is the result of the rarity or density of the body. This account in some sense

applies — though usually not without some subtle distinctions — to the celestial realm as well as

the terrestrial realm. It should be stressed, however, that what was understood by density and

rarity is quite different than today; precisely what these terms meant is not easy to explicate, and

doing so is a major task of this chapter. The outline of the condensation theory and its history in

this chapter will provide the necessary background for understanding theory of color and vision

given by Zabarella in his De visu libri duo, the subject of the next chapter.

The primary constraint for Peripatetic philosophers adopting the condensation theory of

the origin of color is the need to harmonize Aristotle’s numerous, often conflicting, comments on

color, light, vision, transparency, density and rarity, and the nature of the cosmos, but it seems

that the influence of works on mathematical optics, stemming form Ptolemy especially, is a

crucial ingredient in the mix as well. Other influences, e.g., from Stoic physics and Kalam

atomism, might be important as well, but they will remain unexplored in my analysis. Indeed, I

can only give a broad sketch of its development and the main philosophical features that were

27

adopted by Averroës onwards, and no doubt further studies on Greek, Arabic, and medieval Latin

works will give a more fine-grained picture of this tradition.

The first part of this chapter (§ 1.1) looks at the Aristotelian background for the

condensation theory of the origin of color. Aristotle sets the stage for its full development in

Averroës, but the theory itself can’t be found in anything like its full form in Aristotle’s writings

alone. The next section (§ 1.2) looks at Aristotle’s statements on color and density and rarity as

interpreted by the ancient commentators; there I show that there are some tentative developments

among them that end up feeding into the condensation theory of the origin of color, particularly

by Simplicius, but on the whole one can’t say that any ancient commentator held the

condensation theory. We then turn to the understanding of color and density and rarity in Ptolemy

and Ibn al-Haytham (§ 1.3). In Ptolemy we see a clear connection between color and density

within his Stoic-influenced extramission theory of vision. Notably, density and rarity are also

used to account for refraction from at least Ptolemy onwards in optics and astronomy, and this

dual explanatory role that density plays — accounting for both color or darkness as well as

refraction — is an important strand in the history of physical color theory. Ibn al-Haytham

follows Ptolemy’s use of density and rarity in both his astronomy and his optics, but in

appropriating it for his extramission theory of vision the notion of density and rarity is

reconfigured in subtle but important ways. In section 4 I look at the full development of the

condensation theory of the origin of color in Averroës’s De caelo commentary and his De

substantia orbis (§ 1.4). Finally, in the last section I look at the appropriation of this theory in

two highly influential Latin scholastics, Roger Bacon and Albertus Magnus (§ 1.5). This chapter

treats over 1,600 years of history and can hardly do justice to the works and figures analyzed.

28

My aim is primarily to provide background to Zabarella and Fabricius’s understanding of color.

Because the history of color, particularly physical color theory, has been relatively neglected

there are currently no broad narratives in intellectual history to draw from. The account I give

here is bound to be improved upon should specialists in the history of science and philosophy of

ancient Greek, early Arabic, and medieval Latin periods pursue the matter further.

§ 1.1 Aristotelian Background

The Aristotelian corpus provides the fundamental framework for the philosophical discussion of

color in all of the works discussed in this chapter.2 For most of the figures that I will discuss,

vision was given an intromissionist account in which the forms of the colors in bodies propagate

through a transparent medium into our eyes. However, it should be noted that Aristotle is not

entirely consistent in his account of vision, and thus the following account is based primarily

upon Aristotle’s De anima and De sensu, which most intromissionist followers of Aristotle

looked to for the basis of their visual theory.

According to Aristotle, visual perception occurs when our visual faculty takes on the

form/essence (eidos), or formula (logos) of the color inhering in the surfaces of those things we

see.3 In this sense, perception is necessarily mediated — perception is not direct physical contact.

29

2 For a more detailed account of vision, color, and light in Aristotle, see Richard Sorabji, “Aristotle on Colour, Light and Imperceptibles,” Bulletin of the Institute of Classical Studies, 47 (2004): 129–140. For recent in-depth treatments of Aristotle on perception, see: T. K. Johansen, Aristotle on the Sense-organs, Cambridge Classical Studies (New York: Cambridge University Press, 1997); Stephen Everson, Aristotle on Perception (New York: Oxford University Press, 1999).3 On sensation in general, see DA 416b33-418a6, and especially 424a17-b20. At the latter we read that “a sense is that which has the power of receiving into itself the sensible forms (eidos) of things without the matter, in the way in which a piece of wax takes on the impress of a signet ring without the iron or the gold; what produces the impression is a signet of bronze or gold, but not qua bronze or gold: on a similar way the sense is affected by what is coloured or flavoured or sounding not insofar as each is what it is, but insofar as it is of such and such a sort and according to its form (logos)”. All translations are from the Barnes edition.

However, under normal conditions the forms of color (the proper, or special, sensibles with

respect to vision) that are impressed upon the visual faculty are accurate representations of the

forms as they exist in the bodies themselves. In order for color to propagate through a transparent

medium, however, the transparent medium must be actualized, and thus the role of light for

Aristotle is to turn a dark, potentially transparent medium (such as air or water) into a bright,

actually transparent medium. Light, in a sense, switches on the transparency in the air, instantly

removing the darkness that prevented the colors at the surfaces of bodies from issuing forth and

affecting our eyes. Color, then, can be thought of in two ways: either with respect to the material

and formal conditions at the surface of a visible body, or with respect to the power that the body

has to issue forth its form (later understood as its species) if the proper conditions are met.

Vision, then, occurs when three conditions are met: the presence of a colored body, an

illuminated, actually transparent medium, and an animal with a functioning eye.

Aristotle’s main discussions of vision and color occur in On the Soul, On Sense and

Sensible Objects, Meteorology III, and On the Parts of Animals, with some important comments

as well in On the Generation of Animals and the Metaphysics — not to mention the pseudo-

Aristotelian treatise On Colors, which was believed to be genuine by many (but not all)

commentators in the Middle Ages and Renaissance. Aristotle gives a hylomorphic account of

sensation, and this hylomorphic account pertains to both the objects of sense and the organs of

sense — both the perceiver and the perceived are analyzed in terms of a composite of matter and

form. Sensitive beings (i.e., animals) consist of matter suitably organized for the task of

sensation. The sensitive part of the sense organs are simple or homeomerous parts, meaning that

their underlying matter is an immediate (uncompounded) mixture of elemental earth, air, fire,

30

and water, together with their elemental qualities hot, cold, wet, and dry. (Along with the

sensitive parts of the sense organs, other homeomerous parts include bone, flesh, and sinew.4) In

the case of vision, Aristotle does not seem to differentiate between the various tunics and humors

of eye, but merely says that the sensitive, homeomerous part of the eye is necessarily made of

transparent matter, i.e., that it is predominantly composed of water and is cold and wet as a

result.5 By the time of Galen, at least, the sensitive part was considered to be the crystalline

humor or ice-like humor (glacialis), now called the crystalline lens (or just the lens), and the

other parts of the eye existed to aid the crystalline humor in its function. (For reference to a

modern depiction of the eye, see figure 0.1; for a sixteenth-century one, see figure 3.1.) One

crucial point is that in order for the crystalline humor to potentially receive any color it must

itself be uncolored, that is, transparent. Additionally, this material substrate must be combined

with a sensitive soul or faculty of vision — i.e., the form of the eye. Animal spirits were

frequently assigned the task of carrying the impressions upon the crystalline humor back to the

common sense. After Galen this was located in the brain (contra Aristotle, who placed it at or

near the heart). The special or proper object of vision, the sense quality that is grasped by vision

alone, is color. Vision, then, takes place when our sense perception receives the forms of the

colors of a substance (i.e., the accidents inhering in the surface of a substance) without that

31

4 PA 646a13-25, 647a3-25.5 On the account of the eye as a heterogeneous organ made up of homeomerous parts see PA 657a25- 658b25. That the eye is water: SS 438a13-25. Later authors will point to his comments in Generation of Animals to argue that vision takes place at the covering of the crystalline lens, called the aranea. These comments occur at GA 780a25-b1. See § 3.5.

substance’s underlying matter.6 Whether we additionally receive anything beyond an array of

color impressions, such as species of the common sensibles, species of more abstract forms such

as beauty, or indeed species of the substantial forms of the bodies themselves, was a commonly

addressed topic in medieval and renaissance treatises on vision, although at least after the

thirteenth century this was usually denied.

We can summarize some of the philosophical principles (as opposed to anatomical ones,

which are discussed in later chapters) that most writers following Aristotle, and particularly those

under the influence of Avicenna, Ibn al-Haytham, and Averroës, adhered to.7 These included: (1)

that sensation involves the sense perception becoming in some way similar to its objects of

perception (i.e., the proper sensibles such as color, flavor, sound, etc.), although the sensible and

the sense perception remain unlike some way as well;8 (2) that sense perception involves the

32

6 This outline is simplified and incomplete. In addition to intromissionist accounts, which were generally speaking Peripatetic, extramissionist theories of vision persisted to some extent, even after Ibn Sina and Ibn al-Haytham established the dominance of the intromissionist account. Among Christian writers from Augustine until the translation movement in the 12th century vision was almost always though to be extramissionist. Some figures, Roger Bacon most notably, combined intromisison and extramission theories. Additionally, according to some (again Roger Bacon is notable) there were also species of specific forms that multiplied outwards; these, however, could not be perceived by the visual faculty (though they could be received by higher mental faculties). For a more detailed account, see: David C. Lindberg, Theories of Vision from al-Kindi to Kepler (Chicago: University of Chicago Press, 1976); Roger Bacon and David C. Lindberg. Roger Bacon’s Philosophy of Nature: a Critical Edition, with English Translation, Introduction, and Notes, of De Multiplicatione Specierum and De Speculis Comburentibus (St. Augustine’s Press, 1998).7 For a more detailed account of these constraints and their relevance to scholastic theories of vision, see Alison Simmons, “Explaining Sense Perception: A Scholastic Challenge,” Philosophical Studies: An International Journal for Philosophy in the Analytic Tradition, 73 (1994): 257–275. Note that Simmons primarily analyzes Jesuits, and thus her analysis of scholastic theories of vision does not apply straightforwardly to figures such as Zabarella.8 DA 417a20. There is a vigorous debate on whether, according to Aristotle, the eye becomes actually colored during vision, and this has been pointed to as reviving interest in Aristotle among philosophers of mind. The works that originally incited the debate are Richard Sorabji, “Aristotle on Demarcating the Five Senses,” The Philosophical Review, 80 (1971): 55–79, and Myles Burnyeat, “Aristote voit du roughe et entend un “do”: combien se passe-t-il de choses? Remarques sur “De anima” II, 7-8.,” Revue Philosophique de la France et de l’Étranger, 183 (1993): 263–280. More recently, see the works in n. 2 above and Allan Silverman, “Color and Color-Perception in Aristotle’s de Anima,” Ancient Philosophy, 9 (1989): 271–292; Joseph M. Magee, “Sense Organs and the Activity of Sensation in Aristotle,” Phronesis, 45 (2000): 306–330.

assimilation of the form or formula of the objects of sensation without the matter of the bodies in

which those qualities reside, somehow analogous to how a signet-ring makes an impression on

wax;9 (3) that sensation is passive in some manner and active in another; (4) that sensation is a

type of alteration, and alteration requires physical contact, but nevertheless at the same time (5)

sensation does not involve direct contact, and thus the alteration must be mediated; (6) that

contraries, such as black and white, cannot exist simultaneously in the same matter. This last

point becomes problematic in the case of sight, because one needs to explain how two people

whose lines of sight happen to cross can see different colors through the same space of air. Let’s

say one person is looking at a red wall and the other at a green wall, and that their lines of sight

cross. If the alteration of the medium produces green for one person, and red for the other, that

means that some portion of the intervening medium ought to be green and red at the same time,

and yet neither of the viewers will perceive the colors as mixed. Thus, the notion of qualitative

alteration in the medium requires some explication, and later on this problem was dealt with

through the notion of intentional or spiritual species. Species here literally means “appearance,”

and is not to be confused with species in the biological sense or the Porphyrian sense of genera,

differentia, and species. Species of color in the medium did not have the same material existence

that they do in a body, but a spiritual or intentional existence, and this perhaps ad-hoc mode of

existence was supposed to solve this problem. The meaning of “spiritual” or “intentional” in this

context, however, could vary considerably.10

33

9 DA 424a20.10 See Katherine H. Tachau, Vision and Certitude in the Age of Ockham (Brill Archive, 1988). Alison Simmons, “Explaining Sense Perception.” On the closely related notion of intelligible species and its connection to sensible species, see Leen Spruit, Species Intelligibilis: From Perception to Knowledge. Volume 1: Classical Roots and Medieval Discussions (BRILL, 1994); Leen Spruit, Species Intelligibilis: From Perception to Knowledge. Volume 2: Renaissance Controversies, Later Scholasticism, and the Eliminatinon of the Intelligible Species in Modern Philosophy (BRILL, 1995).

Moreover, Aristotle’s discussion of color and vision is far from uniform across his works.

Whereas his discussion of the rainbow in Meteorology III seems to invite an extramissionist

reading of vision, most everywhere else Aristotle says that vision occurs by reception, not

emission. Aristotle also appears to give two different definitions of color. In De anima the nature

of color is said to be “the power to set in movement what is actually transparent.”11 A little

further in De anima Aristotle suggests that the proper sensibles (color, sound, smell, taste, and

touch) can only really affect sensitive beings, and that the sensibles affect other things (such as

the intervening media in the case of vision) only insofar as those insensitive bodies are given the

power to affect an animal with sense perception.12 This seems to define color as merely the

power that visible objects have to affect things that have the faculty of vision. Color, on this

account, causes a motion in air and water, but this motion is merely the power to affect the

functioning eyes of a living animal, and therefore exists only in relation to the sensitive soul. In

Metaphysics IV Aristotle could be interpreted as affirming this, and thus he says that the powers

of color and the other proper sensibles would be destroyed if there were no beings endowed with

sensitive souls — yet he is not explicit that colors, odors, and so on just are their powers to affect

sense organs, and indeed can be interpreted as denying this.13 Note that not every author agrees

34

11 DA 418b1.12 “The problem might be raised: Can what cannot smell be said to be affected by smells or what cannot see by colors, and so on? Now a smell is just what can be smelt, and if it produces any effect it can only be so as to make something smell it, and it might be argued that what cannot smell cannot be affected by smells and further that what can smell can be affected by it only in so far as it has in it the power to smell (similarly with the proper objects of all the other senses). Indeed that this is so seems clear as follows.” DA 424b6-18. However, the argument that follows is ambiguous and has been interpreted in many ways.13 “And, in general, if only the sensible exists, there would be nothing if animate things were not; for there would be no faculty of sense. The view that neither the objects of sensation nor the sensations would exist is doubtless true (for they are affections of the perceiver), but that the substrata which cause the sensation should not exist even apart from sensation is impossible. For sensation is surely not the sensation of itself, but there is something beyond the sensation, which must be prior to the sensation; for that which moves is prior in nature to that which is moved, and if they are correlative terms, this is no less the case.” Metaph. IV, 1010b30–1011a2.

that Aristotle, strictly speaking, gives a definition of color in De anima. On the other hand, in De

sensu Aristotle explicitly defines color as “the limit of the transparent in a determinately bounded

body.”14 In this treatise, all bodies are said to be transparent to some degree, and color is what

you get when the transparency in a body ends. The particular color of a body itself is determined

by a mixture of the fundamental color-contraries white and black (or light and dark), and in De

sensu Aristotle gives three ways of producing other colors from black and white: juxtaposition of

black and white particles, the effect when one color is seen through another, as when a painter

applies a semi-transparent wash over an underlying color, and the combination of black and

white in a true Aristotelian mixture, i.e., mixture as is described in On Generation and

Corruption.15 Although Aristotle gives preference to the last account, he seems to affirm that the

other two kinds of color mixture do give rise to the perception of different colors, at least. That

is, the juxtaposition of invisibly small black and white particles does, indeed, give rise to colors

other than gray for Aristotle. Those colors are merely apparent because they not exist at the

smallest level or under every condition of viewing.16

What is common throughout the Aristotelian corpus, however, is the clear distinction

between light and color. While modern science attributes the sensation of color to light itself,17

35

14 SS 439b11.15 SS 439b19-440b25. For the Aristotelian problem of mixture and its interpretation by later commentators, see Rega Wood and Michael Weisberg, “Interpreting Aristotle on mixture: problems about elemental composition from Philoponus to Cooper.” Studies in History and Philosophy of Science 35 (2004): 681–706.16 “It is plain that when bodies are mixed their colours also are necessarily mixed at the same time; and that this is the real cause determining the existence of a plurality of colours — not superposition or juxtaposition. For when bodies are thus mixed, their resultant colour presents itself as one and the same at all distances alike; not varying as it is seen nearer or farther away.” SS 440b13-18. 17 Or perhaps more accurately, that color in humans is a phenomenon dependent upon the wavelengths of light together with their interaction with (generally speaking) three types of photoreceptors, which themselves are sensitive to a range of wavelengths but whose peak sensitivities differ among one anther.

prior to the seventeenth century it was generally accepted that color was not a property of light,

but a separate accident with its own being; color required a material substrate for its existence,

and since light was not considered to be a material body it could not act as a substrate for color.

(Note that the issue becomes more complicated with the medieval distinction between real color

and the spiritual or intentional species of color.) It should be mentioned that late medieval and

renaissance writers usually made a clear distinction between light as the property of a luminous

body, which they termed lux, and light as the effect of a luminous body on other things, which

they called lumen. This was frequently understood in terms of intentional species, with lumen

being the species of lux propagated through transparent media and onto the surfaces of bodies.

These monumental differences in the understanding of light and color between the premodern

and the modern period must be kept in mind when analyzing theories of vision in the Aristotelian

tradition.

The above is only a brief outline of some of the issues involved in color and vision for

Aristotle and his interpreters. Furthermore, almost every aspect of this account was explicated in

a dizzying number of ways — from the nature and origin of color, to the relationship between

light, color, and transparency, to the structure and action of the eye, and what the sensitive soul is

and how it works. The period between 1500 and 1650, in particular, saw more commentaries on

Aristotle’s works than the previous thousand years combined, most of which have yet to be

carefully examined by modern scholars.18

In addition to the question of the proper definition of color and an account of its nature,

the issue of the origin of color and transparency themselves had enormous implications for the

36

18 Charles H. Lohr, “Renaissance Latin Aristotle Commentaries: Authors A-B,” Studies in the Renaissance 21 (January 1, 1974): 228.

understanding of vision in the broadest sense. In short, what is transparency, what is color, and

what is light? How are each of these connected to the elements, the elemental qualities, or the

nature of matter in any fundamental sense? Aristotle never specifies what the precise connection

is, although there are several statements that interpreters had to work with. In several places

Aristotle mentions a connection between the transparency of air and water with the transparency

of the incorruptible celestial body, but this connection is rather unclear. For example, in Book II

of De anima he writes:

Now there clearly is something which is transparent, and by 'transparent' I mean what is visible, and yet not visible in itself, but rather owing its visibility to the colour of something else; of this character are air, water, and many solid bodies. Neither air nor water is transparent because it is air or water; they are transparent because each of them has contained in it a certain substance which is the same in both and is also found in the eternal upper body.19

As mentioned above, in De sensu Aristotle is explicit that transparency is present in every body

to some degree, and thus it appears that for Aristotle transparency is a property present

throughout the entire universe, in both the supra- and sub-lunar realms, and that transparency is

distinct from and perhaps not reducible to, the elements of tangible reality. Additionally, Aristotle

mentions that there is some relationship between light, transparency, and the color white, as well

as some relationship between darkness, opacity, and the color black. Precisely what that

relationship consists in is unclear.20 The contraries of black/dark and white/bright were supposed

to be the source for all the other colors. Unlike with the contraries of tangible reality. i.e., hot-

cold and wet-dry, which are treated at length in On Generation and Corruption, Aristotle does

37

19 DA 418b5.20 For example, immediately after defining color in De sensu he writes: “Now, that which when present in air produces light may be present also in the transparent; or again, it may not be present, but there may be a privation of it. Accordingly, as in the case of air the one condition is light, the other darkness, in the same way the colours white and black are generated in determinate bodies.” SS 439b15–17.

not specify how transparency and its privation relate to one another nor precisely how they relate

to white and black, and thus it was left to his commentators to develop a detailed account and

harmonize it with the rest of his corpus.

The above are only some of the issues later Peripatetics wrestled with, but not all of them

are of equal importance for understanding the development of the condensation theory of the

origin of color. I will summarize here five key opinions about color in the Aristotelian corpus

that, based on my initial research, were worked into condensation theories.

The first is light and color are distinct qualities — holders of the condensation theory had

a dualistic account of light and color. Light serves to actualize a potentially transparent medium

— or perhaps more accurately, light just is the state of a medium in actual transparency (although

this identity of light and actual transparency is rendered problematic with the near-universal

acceptance of the lux-lumen distinction in late medieval and renaissance Aristotelianism). Color,

in turn, is not a property of light, but a separate quality with the power to alter vision.21

Second is that vision occurs through the intromission of colors into our eyes. This form of

intromission generally took color, and not light, to be the proper object of sight, although there

were some who allowed both to be the special objects of vision. Color, then, sends its form or

similitude through actually transparent media, thus not only altering the intervening air or water

but also the transparent, visually sensitive part of our eyes. In several places where he treats

vision Aristotle unambiguously holds to an intromission theory of vision, which includes the

opinion that sensation cannot occur outside of our body and that nothing needs to be emitted

from our eyes in order for vision to take place. Nevertheless, one obstacle to calling the

38

21 Richard Sorabji, “Aristotle on Colour,” 129–140.

Aristotelian theory of vision intromissionist tout court is Aristotle’s own analysis of the rainbow

in Meteorology III, in which he uses an extramission account, as he says, according to the

science of optics.22

The third important Aristotelian borrowing in the condensation theory of vision is that

color is defined as “the limit of transparency in a bounded body.” All bodies are supposed to be

transparent to some degree, and color is just what you get when the transparency in a body ends.

The fourth component is that black and white (or dark and light, or shade and clarity) are

color contraries. The mixture of black and white does not just lead to shades of gray; rather,

specific colors arise from specific ratios of black and white. Furthermore, the three types of

mixture of black and white that Aristotle mentions in De sensu become relevant to the real-

apparent distinction discussed by many Peripatetics.23

The last major Aristotelian component to condensation theories of color is his statement

that transparency is something that both air and water share with the celestial body.24 Because the

celestial body lacks the qualities of hot, cold, wet, and dry that underly substantial change in the

sublunar realm, it seems that transparency cannot be tied to the elements or the elemental

qualities themselves. However, it should be noted that although Peripatetics who adopted the

condensation theory of color took special note of this fact, nevertheless this is in tension with the

account of the origin of color in the Pseudo-Aristotelian De coloribus, which was believed by

many to be genuine. (Zabarella, notably, does not believe it is genuine.)

39

22 Metr. Book III, 372a30-31. Other places where commentators have read an extramission theory of vision into Aristotle occur in Problems Book XXXI, 959b5-12, and On Dreams, 459b25ff.23 SS 440a31-b23.24 DA 418b5.

Many of the “physiologists” whose theories Aristotle examines and refutes at the

beginning of most of his works took changes in density and rarity to be one of, if not the,

fundamental kind of alteration. Although Aristotle rejects this, nevertheless he frequently

explains changes in the natural world in terms of condensation and rarefaction. This is somewhat

problematic because he never seems to define density and rarity explicitly, and his use of the

terms appear to be equivocal.25 Faced with these difficulties, condensation theories about the

origin of color pulled three main facets from Aristotle’s discussions of density and rarity. The

first is that true density and rarity does not involve voids or interstitial spaces. The rarity of an

uncompressed sponge versus a compressed one does indeed involve interstitial matter, but this is

different from the rarity of air compared to water.26 In the Categories Aristotle puts rarity in the

category of situation, not quality,27 and it appears to be this sort of density and rarity that he

frequently appeals to in Meteorology books I-III.28 In other places he refers to a density and

rarity that is quite different from that of a sponge, a sort of thickening and thinning of the

substances themselves. Here density and rarity does appear to be in the category of quality: it is a

40

25 Harold Joachim, for example, in his influential commentary on DG says that, for Aristotle, density and rarity does not involve pores or interstices; “We must rather conceive of ὕλη as a material capable of filling space with all possible degrees of intensity, or capable of expanding and contracting without a break in its continuity.” However, he also says that Aristotle uses the terms dense and rare (πυκνόν-µανόν) to mean coarse and fine (παχύ-λεπτόν), and he never reconciles these two interpretations of density and rarity. Aristotle, and Harold Henry Joachim. Aristotle on Coming-to-be and Passing-away (De Generatione Et Corruptione): A Revised Text with Introduction and Commentary (Olms., 1922), 124, 204, 225-6.26 Phys. 216b23ff.27 “‘Rare’ (µανόν) and ‘dense’ (πυκνόν) and ‘rough’ and ‘smooth’ might be thought to signify a qualification; they seem, however, to be foreign to the classification of qualifications. It seems rather to be a certain position of the parts that each of them reveals. For a thing is dense because its parts are close together, rare because they are separated from one another; smooth because its parts lie somehow on a straight line, rough because some stick up above others.”Cat. 10a17-24. 28 One particularly relevant passage occurs in Meteorology III, 377b5ff, where Aristotle discusses the optical phenomena of rods: he attributes the colors of rods to a cloud with variable density and rarity, and then connects this to the size of the reflecting particles in the clouds.

second quality, like hardness or softness, that arises from the mixture of the four elements and

the mutual interaction of the first qualities hot, cold, wet, and dry.29

The second is the notion that condensation and rarefaction precedes all generation or

corruption, but is not itself generation or corruption. Aristotle’s statements about this in book 7

and 8 of the Physics are brief, and it is possible that he gives this position only for the sake of

argument; nevertheless the question posed a challenge to later commentators.30 Furthermore, in

much of his discussion of mixture and substantial change Aristotle relies heavily on the notion of

thickening, coagulation, and condensation and rarefaction, combined at times with references to

the small parts of substances, and thus density and rarity was believed by many later

commentators to be the most fundamental of the second qualities.

The third is that a dense medium is one that is not easily divided.31 Again, Aristotle’s

comment is not explained in any detail, but it became significant for later writers.

§ 1.2: Ancient Commentators

There are a few aspects to ancient Aristotelian commentaries that are relevant for the history of

the condensation theory of color generation. The first is that, despite the importance of

condensation for Ptolemy’s understanding of color and transparency (and for Stoic ideas on the

same), ancient Greek commentators did not emphasize this connection between condensation

and color. Alexander of Aphrodisias and Simplicius do discuss density and rarity in connection

with the heavens in their De caelo commentaries, and no doubt this influenced later Arabic

41

29 See Aristotle’s discussion of the three levels of composition in PA book 2, 646a13-25.30 Phys. 7.3, 246a4-10; 8.7, 260b8-15.31 “Now the medium causes a difference because it impedes the moving thing, most of all if it is moving in the opposite direction, but in a secondary degree even if it is at rest; and especially a medium that is not easily divided, i.e. a medium that is somewhat dense (παχύτρον).” Physics 4.8, 215b1-10.

writers, but there does not seem to be anything like a complete system for understanding the

origin of color grounded in density and rarity. Here my analysis includes the De sensu and De

anima commentaries of Alexander of Aphrodisias as well as a few extant fragments of his De

caelo commentary; Porphyry’s commentary on the Categories; Priscian’s On Theophrastus On

Sense-Perception; Simplicius’s commentaries on the Categories, De anima, and De caelo, and

Philoponus’s commentary on De anima.

In the De anima and De sensu commentaries, the primary focus for the most part was on

indeterminate versus determinate transparency. Determinate transparency was said to give rise to

color, while indeterminate transparency allowed for the propagation of the forms of colors to our

eyes. Thus air, water, and pure fire (in contrast to the flames we see in burning matter) are

transparent precisely because they lack an internal principle due to which the body’s boundaries

are fixed, and are instead limited by surrounding bodies. Whether a body is transparent or else

colored seems to be connected to the solidity or fluidity of a body. The principle of self-

boundedness in bodies, according to these commentators, arises from the presence of earth. As

Aristotle says In On Generation and Corruption, “moist is that which, being readily adaptable in

shape, is not determinable by any limit of its own; while dry is that which is readily determinable

by its own limit, but not readily adaptable in shape.”32 Thus ancient commentators tended to set

up a transparency–color contrariety, with the least self-bounded substances (fire, in the terrestrial

realm at least) on one extreme and the most self-bounded (earth) on the other. Where on this

scale the color of a mixed body falls is due to the degree of earth in the mixt, but because the

power of confining itself within its own limits is due to the nature of the dry, color might

42

32 329b29-33.

ultimately be said to be tied to elemental qualities. Note that it is not transparency and opacity (in

the modern sense of opacity; see Appendix 1) that are contrasted with each other, and it is better

to say that transparency is opposed to non-transparency. If a body cannot be seen through, this is

because there is a limit to its transparency arising from an elemental make-up that causes it to

have a well-defined limit to its substance. According to this way of thinking a white body that

cannot be seen completely through is nevertheless the most transparent of bounded bodies, while

black bodies are the least transparent. Pure elemental earth is (supposedly) black precisely

because it lacks all transparency, i.e., does not admit light into its body whatsoever. This might

seem to be contradicted by experience with solid — and thus seemingly earthy — transparent

bodies such as crystal and glass. Nevertheless many ancient commentators claim that, on the

contrary, this demonstrates that glass and transparent stones have a high proportion of water in

their mixture.33 According to some ancient commentators, transparency is a supremely reliable

indicator of the elemental composition of a body, and is appears to be more reliable than the

solidity of the body.

The ability of a substance to admit light into its substance determines the transparency /

non-transparency contrariety. Whether or not light is actually present in such a substance is due

to the quality of luminosity, and a body can be shining due to its own nature or else illuminated

from outside. As we will see, this is picked up in the Latin tradition as well, where opacitas

means primarily shade or darkness, i.e., a lack of illumination, rather than the fact that one

43

33 E.g., Alexander writes that “one would discover that all those <bodies> which are transparent and which seem to be <constituted> out of earth, are <constituted> of water to a greater degree.” Alexander of Aphrodisias, On Aristotle’s ‘On Sense Perception’, trans. by Alan Towey (Cornell University Press, 2000), 52. Although less explicit, see similar statements at: Priscian and Simplicius, On Theophrastus on Sense-perception with Simplicius On Aristotle’s On the Soul 2.5-12, trans. by Pamela M. Huby and Carlos G. Steel (Cornell University Press, 1997), 16, 163.

cannot see through it. Opacity, then, can be caused by either the paucity of a source of light, or

else the lack of a body to admit any light whatsoever, and therefore darkness and blackness are

strongly related, while whiteness and transparency are likewise related.34 In this sense, what is

often translated as “opaque” might be better rendered as “murky.” (See the entry for “opacus” in

Appendix 1.) The redefinition of opacity to mean a body that does not allow the transmission of

light occurs primarily in the seventeenth century, and this is discussed at length in the final

chapter (§ 5.2).

The focus on surface in ancient commentators’ discussions of color certainly has a

precedent in Aristotle,35 but it also seems likely that Neoplatonic (and perhaps also Pythagorean)

ideas about epiphaneia or surface were at play.36 In his De sensu Aristotle combats the

Pythagoreans, whom he says named the surfaces of bodies “hue,” by arguing that while color is

actually present on the surface it is also potentially present in the depths of the body:

But it is manifest that, when the transparent is in determinate bodies, its bounding extreme must be something real; and that colour is just this something we are plainly taught by facts — colour being actually either at the limit, or being itself that limit, in bodies. (Hence it was that the Pythagoreans named the superficies of a body its hue.) For it is at the limit of the body, but it is not the limit of the body;

44

34 Peter Adamson supports this analysis, although he introduces the idea that al-Kindi reverses the notion of visibility as transparency to that of visibility as blocking sight (and thus, that black bodies are the most visible bodies), and that he does so under the influence of Ptolemy. However, al-Kindi seems to be unique among pre-seventeenth century writers in holding this view. Peter Adamson, “Vision, Light and Color in Al-Kindi, Ptolemy and the Ancient Commentators,” Arabic Sciences and Philosophy, 16 (2006): 207–236.35 For example, in addition to the passages cited above, in his discussion of the meaning of the phrase “that in virtue of which” in Metaphysics V, 1022a14–24, Aristotle writes: “‘That in virtue of which’ has several meanings, (1) the form or substance of each thing, e.g. that in virtue of which a man is good is the good itself, (2) the proximate subject in which an attribute is naturally found, e.g. colour in a surface. ‘That in virtue of which’, then, in the primary sense is the form, and in a secondary sense the matter of each thing and the proximate substratum of each.”36 Jean Christensen de Groot, “Philoponus on ‘De Anima’ II.5, ‘Physics’ III.3, and the Propagation of Light,” Phronesis, 28 (1983): 194.

but the same natural substance which is coloured outside must be thought to be so inside too.37

For most ancient commentators, the potential color in the interior of the body is merely the

potential for the interior to become a surface, and it is the degree of self-boundedness of the body

that determines its color. As we will see, in the condensation theory of color the density of the

substance determines where on the transparency–color axis it lies, and the surface conditions

merely relate to its visibility — a rather different interpretation of this passage by Aristotle. The

distinction is important: whether color is a condition of a body that exists without reference to

vision is at issue, and the debate over this question tends to center around the two different

accounts of color given in De anima and De sensu. Among those who make the distinction

between color and visibility, the De anima definition is usually said to be the definition of

visibility (or at least some account of it), and the De sensu definition that of color. Alexander

does not make this distinction between color and visibility, and thus denies that phosphorescent

bodies are colored precisely because we see them only in the dark — that is, we see them when

the transparent medium is not activated. He says that “colour is what is capable of producing

change in that which is actively transparent.”38 On the other hand, Philoponus does make the

distinction between color and visibility. He says Aristotle gives the proper definition of color in

De sensu, and the “definition” in De anima is merely a “definition of colour that points it out by

what is incidental and peculiar, not by its substance.”39 Nevertheless Philoponus emphasizes,

perhaps more than any of the other ancient commentators, that the power of color to affect vision

45

37 SS 439a30-440b1.38 Alexander of Aphrodisias, On the Soul: Part I: Soul as Form of the Body, Parts of the Soul, Nourishment, and Perception, trans. by Victor Caston (Bloomsbury Academic, 2012), 67. 39 John Philoponus and William Charlton, On Aristotle’s ‘On the Soul 2.7-12’, Ancient Commentators on Aristotle (Ithaca, N.Y.: Cornell University Press, 2005), 5.

(i.e., its visibility) arises only from the surface of bodies. He says that even in colored,

translucent bodies such as gemstones the power to affect our vision arises only from the surface

of those bodies, not their depths; similarly, when looking at an insect entombed in amber we see

the surface of the insect only if the strength of its color is greater than that of the surface of the

amber.40

Another feature of the ancient commentaries is that, with the exception of Philoponus,

there is little discussion of mathematical optics in the commentaries on De anima and De sensu

themselves.41 On why the eye is made of water instead of air (both of which possess the required

transparency for an Aristotelian theory of vision) Alexander writes that, unlike air, water is

“appearance-making” (emphanês) because of its “fine nature.” On the difference between air and

water, he writes that that “it is sufficient if that through which we see is transparent, but that with

which we see must be appearance-making and such as to be able to admit and preserve the forms

of the <bodies> seen."42 Alexander seems to be harkening back to an earlier notion that Aristotle

attributes to Democritus: that the observable image formed in the pupil by reflection is essential

to the process of vision. In Aristotle and Alexander’s Greek the small reflected image visible to

an observer is a korê, literally a “little girl” or doll-like image, and this term was translated into

the Latin pupilla. The latter term soon came to mean the opening in the iris rather than the image

46

40 Ibid., 4-6.41 On Philoponus’s account of light and vision, see S. Sambursky, “Philoponus’ Interpretation of Aristotle’s Theory of Light,” Osiris, 13 (1958): 114–126.42 Alexander of Aphrodisias, On Aristotle’s ‘On Sense Perception’, trans. by Alan Towey (Cornell University Press, 2000), 36. See also n. 127 in ibid.,166. Alexander is even more explicit in his On the Soul. Just after mentioning the reflected image in the eye, Alexander writes that eyes “are in turn also able to receive a reflected image themselves because they are both smooth and transparent. [...] For the interior of the eye is composed of water, for the following reason. Of the transparent [materials] that lack a definite shape, water straight off can retain the modification produced in it by colour, because of its density and consistency; for air is not like this.” Alexander of Aphrodisias, On the Soul: Part I: Soul as Form of the Body, Parts of the Soul, Nourishment, and Perception, trans. by Victor Caston (Bloomsbury Academic, 2012), 68. See also ibid., 161 n. 392; 162 n. 393.

produced there (the English pupil comes from Latin via Old French).43 Aristotle denies this

Democritean explanation on the grounds that the perceived image in the pupil is not in the eye

itself, but rather dependent on another person observing the image in the eye (what would later

be called a virtual image), and Aristotle says that Democritus did not understand mathematical

optics sufficiently to give a true account of this phenomenon.44 Aristotle’s opinion that this image

in the eye is insignificant for vision will have consequences for the theory of vision held by

Zabarella and Fabricius, as we will see later (§ 4.1). Furthermore, Alexander’s attribution of the

“appearance-making” power of the eye to its fine nature should be contrasted with the account

given by those who hold the condensation theory of the origin of color. As we will see, according

to the latter it is the density (and thus in some sense the coarse nature) of the crystalline humor

that is contrasted with the rarity of air, and this density is essential for vision.

Although he wrote after Ptolemy it is curious that Alexander did not appeal to

mathematical optics in order to reject this reflection-account of vision.45 As will be clear later in

this chapter, it was the confluence of mathematical optics and Aristotelian natural philosophy in

the Islamic world that provided the context for the condensation theory of color generation.

These two fields seem to have been less well integrated in the Ancient Greek commentary

tradition than in the Arabic one. Philoponus’s deeper engagement with mathematical optics, as

47

43 SS 438a5-16. Plato in Alc. I 133A, also seems to have Socrates endorse a theory in which vision takes place by the formation of a virtual (reflected) image in the eye. Also see the discussion by Caston in Alexander of Aphrodisias, On the Soul: Part I: Soul as Form of the Body, Parts of the Soul, Nourishment, and Perception, trans. by Victor Caston (Bloomsbury Academic, 2012), 161 n. 392.44 SS 438a5-438a12.45 See, however, what is referred to as his “mantissa,” parts of which may not have been written by Alexander himself. Alexander of Aphrodisias, Supplement to “On the Soul,” trans. R. W. Sharples (Cornell University Press, 2004).

well as his far more extensive account of the eye and its parts, was possibly also influential for

the blending of optics and natural philosophy in the Arabic tradition.46

The analysis of density and rarity by these ancient commentators likewise shows a

different set of assumptions than those which will make their way into the condensation theory

of the origin of color in Averroës. For example, Porphyry holds that density and rarity are not

qualities but “species of relative position.”47 Of the commentators mentioned, only Simplicius

says that density and rarity are something other than the position of the parts.48 In his

commentary on the passage in Aristotle’s Categories that mentions density and rarity, Simplicius

says that density and rarity belongs both in the category of position (or situation) as well as the

category of quality.49 However, his position differs somewhat from later Aristotelians holding the

condensation theory of color generation, who tend to say there are there are two kinds of density

48

46 Peter Adamson, “Vision, Light and Color in Al-Kindi”; Richard Sorabji, ”John Philoponus” in Philoponus: And the Rejection of Aristotelian Science, ed. Richard Sorabji (London: Duckwork, 1987), 26-27.47 Porphyry, On Aristotle’s Categories, Ancient Commentators on Aristotle (Ithaca, N.Y: Cornell University Press, 1992), 147. Note that while Alexander of Aphrodisias’s commentary on the Categories was thought to be lost, one of the works contained in the famous Archimedes Palimpsest is a Cateogries commentary, and Robert Sharples suggests that this may be Alexander’s. However, the text revealed so far only refers to 1a20-1b24. See <http://archimedespalimpsest.org/about/scholarship/commentary-aristotle.php>48 I have, however, not consulted Philoponus’s commentary on the Categories; an English translation is scheduled for publication in 2015.49 “In my opinion it is worth noting that perhaps rarity and density, and smoothness and roughness are qualities according to their character, as warmth and coolness are, and also display some position according to the arrangements of their parts. There is nothing surprising about putting the same thing in different categories in different respects, as is the opinion of Aristotle and his commentators.” Simplicius, On Aristotle’s ‘Categories 7-8’, The Ancient Commentators on Aristotle (Ithaca, N.Y: Cornell University Press, 2002), 124. Also see Simplicius’s comments on Physics 260b7-15, where Aristotle says (perhaps only for the sake of argument) that condensation and rarefaction precede all generation and corruption: “In this way white and sweet would fall under the heading of rarity because like heat they seem to tend to separate the perceptions relative to them, and their opposites seem to be kinds of density. It is clear that 'condensation' and 'rarefaction' are 'combination' and 'separation', being different names for the same thing.” Simplicius, On Aristotle’s ‘Physics 8.6-10’, The Ancient Commentators on Aristotle (Ithaca, N.Y: Cornell University Press, 2001), 36. Simplicius’s analysis overall does not lead one to the conclusion that rarity or density are used equivocally, but rather that they are in one sense in the category of quality, in another sense in the category of situation or position.

and rarity, one in the category of situation and one in the category of quality. Further

complicating matters, Averroës and some others following him will say that density and rarity are

used equivocally when describing the heavens and the earth, but this equivocal use does not

necessarily correspond to the previously mentioned two uses. We must therefore keep in mind

four possible uses of density and rarity: in the category of situation, in the category of quality, as

applied to the heavens, and as applied to the sublunar realm.

Simplicius also discusses density and rarity in connection with the moon in his De caelo

commentary. In his discussion of 290a24–9, where Aristotle says that it is evident that the stars to

not roll because the same face of the moon is always visible, Simplicius reviews several accounts

of the cause of moon-spots. (Aristotle himself is silent on the cause of the moon-spots.) Of most

relevance to our discussion is his commentary to 289a11–19, where Aristotle discusses the

substance of the heavens. Simplicius says that just because some parts of the heavens are visibly

different than others does not mean that they are composed of a different substance. He quotes

Alexander of Aphrodisias’s De caelo commentary; this commentary is now lost in the original

Greek and only partial translations into Arabic appear to have been made.50 Alexander asks why

there is such apparent difference between the parts of the heavens. “If they differ entirely

because of denseness and rareness or because of color or some other properties of this kind, how

can they be called simple or not subject to affection, since affections occur because of these

differences and these differences are affections?”51 As Simplicius relates, Alexander concludes

that this is possible because differences in density and rarity there are inherent, and not due to

49

50 Goulet-Aouad, “Alexandros d’Aphrodisias,” in Dictionnaire Des Philosophes Antiques, vol. I, 1989, 125–39. H. Hugonnard-Roche, “L’Organon. Tradition Syriaque et Arabe,” in Dictionnaire Des Philosophes Antiques, vol. I (1989), 502–28.51 Simplicius, Simplicius: On Aristotle On the Heavens 2.1-9, trans. Ian Mueller, NIPPOD edition (Bristol Classical Press, 2014), 91. (436,5.)

being affected. That is, the qualities are set and static, and thus the density and rarity in the

heavens are not contraries, properly speaking, because no change from dense to rare or vice

versa can or will take place. “For <the heavenly bodies> are not free of affection without

qualification; rather they do not suffer ‘any of the difficulties to which mortals are suspect.’”52

Alexander, then (according to Simplicius) argues that it is possible for density and rarity, and

thus variation in brightness, to occur in the heavens, but he does not appear to be committed to it.

Likewise, after quoting Alexander’s text Simplicius argues the same, although he seems more

committed to the idea that differences in density and rarity are present in the heavens.

Nor does the denseness in the heaven fight with the rareness there, nor does standing still there fight with motion there, because their substrata are different in nature.... And, for example, the sun and the stars, which are thought to be dense, and the bodies in the heaven which resemble rare things, do not change into one another because the nature of the substratum is always such as to be related to one and the same form and because of the unchanging substance of the form, which results directly from an unmoving cause.53

Clearly, then, it was common in antiquity to ascribe density and rarity to the heavens in order to

account for the diversity in the heavens, and if (as we will see shortly) Ptolemy is any indication

this could have been due at least in part to Stoic influences. However, neither Alexander nor

Simplicus appear committed to this explanation, nor do they connect their discussion of the

density and rarity in the heavens to an account of transparency and color formation in the

sublunar realm.

Many of the key aspects of the condensation theory of the generation of color are lacking

in the ancient Aristotelian commentaries: that all transparent bodies are so because they are rare;

50

52 Ibid., 92. (436,15.)53 Ibid., 93. (437,20.) At another point Simplicius asks “why, even if the body of the sun is large and dense, does the contact with respect to the motion of the heavenly body with the sublunary in the region of the part involve more resistance”. Ibid., 96. (440,20.)

that density and rarity ultimately reduces to the size of the parts (or the potential minima) that

make up a body; that whiteness arises from the condensation of a transparent body (and thus that

density, in some sense, accounts for what it is to be colored); that color cannot be ultimately

grounded in the elements or the elemental qualities because of the visible differences in the color

of the heavens; and that the color of a body has two aspects: one in relation to vision, or the

visibility of a body, and one in relation to itself, or color considered absolutely.

§ 1.3: Optics: Density, Rarity, and Color in Ptolemy and Ibn al-Haytham

In ancient and medieval mathematical optics since Ptolemy, at least, density and rarity were

frequently invoked to account for the transparency or non-transparency of a body, its refractive

power, as well as its color. This is not to mention the solidity versus fluidity, of a body, which

was also linked to density and rarity. From a modern perspective the explanatory power of

density and rarity is overburdened, and it seems inevitable that a single cause would not be able

to account for such diverse effects. But for this criticism to have force one must understand what

was meant by density and rarity in these optical works. This is a difficult task because optics was

a science subordinate to geometry, and thus was ultimately a mathematical genre. Due to this fact

natural-philosophical explanations for density and rarity, color, and so on were not analyzed at

length in works on optics by the major writers in the ancient and medieval tradition (e.g.,

Ptolemy, Ibn al-Haytham, Roger Bacon, Witelo, and Pecham). Few modern scholars have

addressed the connection between color, refraction, and density, and most who do simply admit

51

their perplexity or, worse, treat this as a mistake that will be inevitably corrected in later eras.54

As perplexing as it may be to us, that density and rarity underlay these seemingly diverse

phenomena seemed perfectly reasonable to some of the most influential thinkers in the history of

science, and treating it as a mistake only obscures the meaning of the terms and their important

(and changing) connection to systems of thought, to experimental practice, and to quotidian

experiences with materials and material transformations in cooking, artisanal work, and so on.

For the most part scholars have treated color and refraction separately. Lindberg has

written an important article on the physical causes of refraction in medieval optics, but he does

not mention color at all, nor does he investigate the nature of density and rarity (or coarseness

and fineness, thickness and thinness, etc.) in any detail. Because of this he notes “the rather

surprising extent to which Alhazen and his Western followers ignored traditional Neoplatonic

and Aristotelian modes of explanation and dealt with refraction in mechanistic terms”, and he

also notes that Alhazen does not employ Aristotelian hylomorphism and all its attendant

categories and principles in his account of the cause of refraction.55 As we will see, although Ibn

al-Haytham does not rush immediately to “Aristotelian” categories and metaphysical principles

in his accounts (and, it should be noted, neither does Aristotle), his overall framework can be

called Aristotelian. Furthermore, Lindberg overstates the degree to which Ibn al-Haytham’s

52

54 E.g., see David C. Lindberg, “The Cause of Refraction in Medieval Optics,” The British Journal for the History of Science, 4 (1968): 26, where he writes that Ibn al-Haytham’s principle that the cause of refraction as related to the coarseness of the medium and the subsequent ease of the traversal of light (he fails to include color) “is false and, moreover, that Alhazen and his followers should have recognized its falsity with ease.” See also Alhacen and A. Mark Smith, “Alhacen on Refraction: A Critical Edition, with English Translation and Commentary, of Book 7 of Alhacen’s ‘De Aspectibus,’ the Medieval Latin Version of Ibn Al-Haytham’s ‘Kitāb Al-Manāzir.’ Volume One. Introduction and Latin Text,” Transactions of the American Philosophical Society, New Series, 100 (2010): lvi–lxiii. Although he doesn’t say that Alhacen “should have” recognized the problem with their use of density, he concludes “Most of the problems discussed to this point arise because of Alhacen’s failure to specify what he means by density in the first place.” Ibid., lxi.55 David C. Lindberg, “The Cause of Refraction,” 34.

account is mechanistic — which in any case is a problematic category for historical analysis of

this time period. More recently, Mark Smith writes of Alhacen’s De aspectibus that “Although

this terminological confusion about densitas, grossities, spissitudo, soliditas, subtilitas, and

raritas in the Latin text is not necessarily reflected in the Arabic text, it none the less bespeaks an

underlying conceptual confusion about the various connotations and implications of density and

rarity that is common to both texts.”56 Smith also seems to connect density and rarity with

solidity and fluidity, specific gravity, and the coarseness and fineness of actual, discrete particles,

but does not work out the details of this connection.57 If we do not fully understand what Alhacen

and others meant, the conceptual confusion might well be ours.

Ptolemy’s Optics was one of the most important ancient sources that posited a connection

between density and rarity (or, perhaps more accurately, thickness versus tenuity) and color. This

work was perhaps known to the Arabic speaking world since the time of the first great translation

movement in the ninth century; Lejeune gives the composition of al-Kindi’s De aspectibus (c.

873) as a terminus ante quem, but this not entirely certain.58 Unfortunately, all Greek and Arabic

manuscripts are now lost, and the only extant copies stem from a Latin translation of the Arabic

version by Eugene of Sicily (c. 1130-1203), likely during the second half of the twelfth century.59

The text we have is disordered and contains many lacunae, and furthermore reconstructing the

Greek and Arabic terms, not to mention deciphering what they would have indicated in that

53

56 Alhacen and Smith, “Alhacen on Refraction,” lxii.57 Alhacen and Smith, “Alhacen’s Theory of Visual Perception,” lvi–lv; Alhacen and Smith, “Alhacen on Refraction,” lx.58 Ptolemy, L’Optique de Claude Ptolémée Dans La Version Latine D’après L’arabe de L’émir Eugène de Sicile. Edited by Albert Lejeune. Université de Louvain. Recueil de Travaux D’histoire et de Philologie, 4. Sér fasc. 8. Louvain: Bibliothèque de l’Université, Bureaux du recueil, 1956, 29*. Cf. Ptolemy and A. Mark Smith, Ptolemy’s Theory of Visual Perception: An English Translation of the Optics (American Philosophical Society, 1996). 55ff.59 Ptolemy, L’Optique, 9*-13*; Ptolemy and Smith, Ptolemy’s Theory of Visual Perception, 7-8.

context, is problematic. Whether translations of terms such as density and rarity were affected by

earlier or contemporaneous translations, and whether additions or omissions in such passages

were made considering such works, is particularly important. Neoplatonic influences could have

asserted themselves in the translation from Greek to Arabic, but from what we have seen the late

antique commentators had little to say about density and rarity that relates to theories of the

origin of color. Also, given what we know of Eugene of Sicily it seems unlikely that his

translation of Ptolemy’s work would have been influenced by, for example, Ibn al-Haytham’s

optics (which was translated later). Finally, while it is certain that Ptolemy’s characterization of

density and rarity, and its relationship to color and vision, influenced later thinkers, what that

influence consisted in is difficult to say, and what follows should be considered in light of such

uncertainties. In spite of this, I propose that many of the key concepts that connect density and

rarity with color and vision derive from the tradition of mathematical optics as well as its

connection to astronomy, and specifically from Ptolemy’s works on both subjects.

According to Ptolemy’s stoic-influenced extramission theory of vision, things that are

both luminous and compact or thick are intrinsically capable of being sensed by our visual rays.

Those [things] therefore that are truly seen are thick shining [bodies]. For things subject to vision ought to be shining to some degree, either from itself or from another, since this is the special characteristic of the visual sense, and thick in substance to retain vision, in order that the power [of vision] may penetrate them and not pass through without inscribing an effect.60

The Latin text has spissitudo for what might be variously translated as compactness, density, or

thickness. Indeed all three English terms fall short of the multitude of meanings found in the text,

54

60 Book II , § 4. "Que ergo uere uidentur, sunt lucida spissa. Res enim uisui subiecte debent esse quomodocumque lucide, aut ex se aut aliunde, cum hoc sit proprium uisibili sensui, et spisse in substantia ad retinendum uisum, ut uirtus penetret eas et non transeat sine effectu incidenti." Ptolemy, L’optique, 12. All translations from the Latin are mine, but I have consulted Smith, “Ptolemy’s Theory of Visual Perception.”

and given that the English terms are difficult to separate from more modern notions of matter and

vision I will use the Latin.61

Since color is the special object of vision, by impeding the visual flux the spissitudo of a

body determines whether a body is colored. If vision passes through without effect, a body is

transparent; if it does not, it is seen and therefore colored, and so non-transparency and color are

synonymous. Colors are “primarily seen” (primo videntur) even though they are “not visible per

se without illumination.”62 (What colors are per se, absent illumination, is not discussed.63)

Conversely, “things that have no spissitudo (i.e., are extremely tenuous) and have no color are

neither sensed nor judged to be bodies according to vision.”64 All other properties of things are

secondarily visible by means of the sensation of illuminated color. Ptolemy’s Peripatetic

influences are shown in his discussion of the relationship between illumination and color. For

example, after stating that color “truly inheres” in compact bodies and “belongs to them by

nature” he says that it is as if lumen gives form to the matter (“yle”) of color,65 an analogy that

many later figures such as Albertus Magnus and Zabarella will also use. Although darkness

55

61 Determining what the Greek and Arabic terms might have been is beyond the scope of this dissertation, but the Arabic terms are likely similar to those used by Ibn al-Haytham. See the Latin-Arabic glossary entries for densus, rarus, and spissitudo in: Ibn Al-Haytham and A. I. Sabra, Optics, vol. 2. (Warburg Institute, University of London, 1989), 179,195, 198.62 Book II, § 5; Lejeune, L’Optique, 13. 63 It is likely that Ptolemy’s use of per se here is informed by Aristotle’s discussion of kath’ hauto in the Posterior Analytics and Metaphysics Z. Additionally, given that Ptolemy later suggests that lumen gives the form (yle) to the matter of color, it is possible that Ptolemy had in mind that “illuminated color” is essentially, or per se, visible because the form / matter composite is complete. Following Aristotle in 1029b22ff, “illuminated color”, then, would have an essence in the sense that “white man” does not. Nevertheless, Ptolemy only seems to be using the form-matter distinction as an analogy, and not an absolute statement about the ontological status of un-illuminated color. On the other hand, Albertus Magnus, for one, held that lumen was indeed the form for the matter of color in a real sense. See the discussion below in § 1.5.64 Book II, § 6; Lejeune, L’Optique, 13.65 Book II, § 16. "Manifestum est ergo per ea que diximus, quod color uere inest his, et de natura eorum est, et non uidetur nisi lumine cooperante uisui ad effectum.... [Lumine] Communicat autem sibi ipsi [colori], ut forme coloribus quoque ut yle." Lejeune, L’Optique, 18.

(tenebra) is an absence of color, and thus is not strictly speaking seen (just as silence is not really

heard), black bodies do appear to be truly seen, and thus black is a color contrary along with

white.66 However, this Aristotelian influence is tempered with strong Stoic elements: colors are

seen by means of a passion in the visible flux, which is generated by the “relationship and

reasoning” between the governing faculty and the illuminated body.67

Within Ptolemy’s Stoic-influenced extramission theory it makes intuitive sense for

spissitudo to simultaneously indicate the refractive power, the compactness or thickness of

substance, and whether it is colored: just as compact substances block our hands from feeling

what is beyond it, likewise such bodies stop visual rays from “feeling” ahead any further, thus

causing the sensation of the special object of vision, i.e. color. If the thickness only impedes the

visual flux somewhat, its thickness nevertheless alters its path. This notion of vision “feeling

ahead” can be seen in Galen’s statement that the Stoics believe (wrongly, according to him) that

“we see by means of the surrounding air as with a walking-stick.”68 For the most part that which

is spissior in color has greater corporeity, although Ptolemy qualifies this equivalence with the

examples of milk and glass.69 Beyond statements like this, the extant Latin text never gives a

precise definition for spissitudo.70 At various places, spissitudo is invoked to account for the fact

56

66 Book II § 21, 24; Lejeune, L’Optique, 21, 23-4.67 Book II § 22. “Nec passio et acidens quod ei accidit, in omni uisu existunt a uirtue regitiva. Nec uere fit hoc ex rebus uidendis tantum, uerum etiam per relationem et rationcinationem inter illas factam et id quod diuiditur et procedit a uirtute regitiua.” Ptolemy, L’Optique, 22.68 Galen, On the Doctrines of Hippocrates and Plato: Books VI - IX. trans. by Phillip De Lacy, Corpus medicorum Graecorum (Akademie-Verlag, 1980), 475. (Book VII, Chapter 7.)69 Book II § 25. "Videtur autem illud cuius color est spissior, habere maiorem corporalitatem, quamvis non tale sit, ut lac ad comparationem uitri." Ptolemy, L’Optique, 25.70 See Lejeune at ibid, 12, n. 4: “Dans ce qui nous reste de l'Optique, cette notion de compactité n'est définie nulle part et rest fort vague; cependant elle sert à ramener à l'unité plusieurs propriétés lumineuses. Selon son degré de compactié ou de raréfaction, un corps ou un milieu est ou bien opaque, et s'il est en autre poli, réfléchissant, ou bien transparent et plus ou moins réfringent.”; Ptolemy and Smith, Ptolemy’s Theory of Visual Perception, 71 n. 3, 81 n. 43, 229 n. 1.

that we see color rather than seeing through a body, for the presence of what we would call

translucency or light-scattering, for why things are “tenuously colored” (such as thin clouds or

shavings of horn),71 and perhaps most importantly for refraction. Moreover, while the text

assumes that the spissitudo of a body is (for the most part) the reason it lacks transparency, and

as well assumes that all colors are derived from the Aristotelian color contraries black and white,

nowhere does the text say why black, white, or some intermediate color should arise from the

spissitudo of a body, nor does it explain what exactly it means for black and white to be mixed.

The text we have gives one pair of contraries in order explain why the visual flux either passes

through a body, is only partially affected by it, or else stops at it and is affected by its color.

Presumably this spissitudo also accounts for the reason that light passes through a body or else

activates its color at its surface, but the text is not explicit about this. Color is simply described as

an accident whose two extremes are white and black, and color is never reduced to or derived

from any other properties of bodies.72 Although such parts may have been lost or omitted during

one of the translation steps, this failure to investigate the natures of and relationships between

spissitudo, color, and light nevertheless makes sense if we remember that Ptolemy’s main

purpose was to treat vision mathematically, not physically. The treatise primarily aims to account

for potential visual deception.73 According to the genre conventions of such treatises, the author

would be expected to either establish such physical principles in order to provide a basis for the

57

71 “Lejeune, L’Optique, 109.72 E.g, at Book II, § 24, we see: “Manifestum est ergo ex his que diximus, quod uisus congnoscit colorem per colorationem accidentem; et congnoscit albedinem, uerbi gradi, quia dealbat, et nigredinem quia denigrat, et sic singulos colores medios.” Ptolemy next rejects the notion that white is caused by a spreading out of the visual rays, and black a contraction of them. Ptolemy, L’Optique, 23-4.73 See, e.g., A. Mark Smith, “What Is the History of Medieval Optics Really About?” Proceedings of the American Philosophical Society 148, no. 2 (June 2004): 180–194; Ptolemy and Smith, Ptolemy’s Theory of Visual Perception, 18-19.

mathematical analysis, or else take them from other works; yet, the ultimate philosophical (or

empirical) ground for those principles need not be fully explicated. However, one important

point connected to density and rarity that is relevant for understanding Ibn al-Haytham, as well

as Arabic Peripateticism connected with these issues generally, is Ptolemy’s statement at the

beginning the Mathematike Syntaxis (or Almagest). There he says there that the celestial body,

among all bodies, “the one with the constituent parts which are finest and most like each other.”74

Ptolemy’s works were hugely important for Ibn al-Haytham. In his Discourse On Light,

written after his Kitab al-Manazir, Ibn al-Haytham says (like Ptolemy) that the celestial body is

the most transparent body in the universe, which fact he connects to the subtlety of the parts of

the celestial body.75 Throughout this treatise Ibn al-Haytham identifies the subtlety of a body’s

form with its optical density or rarity, and in the course of his discussion he uses a concept of

minima that is very similar to that of Averroës.76 Although this work was never translated into

Latin, nevertheless the Latin translators of Ibn al-Haytham’s De aspectibus, Ptolemy’s Optics,

and many other works (such as Averroës’s commentaries) would not necessarily have needed his

Discourse on Light in order to grasp the use of his terms in his optics. It is primarily we moderns

— bringing with us radically different notions of density and rarity, matter and its properties,

58

74 Ptolemy, Ptolemy’s Almagest, trans. J. G. Toomer (Princeton, N.J.: Princeton University Press, 1998), 40. I thank William R. Newman for pointing out this passage. For Ptolemy on the mathematical details of atmospheric refraction, see A. Mark Smith, “Ptolemy, Alhacen, and Ibn Mu’adh and the Problem of Atmospheric Refraction.” Centaurus 45, no. 1–4 (2003): 100–115.75 Roshdi Rashed, “Le ‘Discours de La Lumière’ d’Ibn al-Haytham,” Revue d’histoire des sciences, 21 (1968): 220-23. 76 On the notion of minima naturalia, see John E. Murdoch, “The Medieval and Renaissance Tradition of Minima Naturalia,” in Late Medieval And Early Modern Corpuscular Matter Theories, ed. Christoph H. Lüthy, John E. Murdoch, and William R. Newman (BRILL, 2001), 91–131. Ruth Glasner, “Ibn Rushd’s Theory of Minima Naturalia,” Arabic Sciences and Philosophy 11, no. 01 (2001): 9–26. Unfortunately, because they were published in the same year Murdoch’s and Glasner’s articles seem not to have the benefit of each other’s analyses.

light, color, and transparency, etc. — who gain the most from the explicit statements that he

makes here.

Ibn al-Haytham divides transparent bodies into two classes: one containing the celestial

body, which is a single substance, and the other the sublunar bodies.77 The celestial body is the

most transparent body in the world, but — as we will see below — it is nevertheless not perfectly

transparent in the mathematical sense.78 The sublunar bodies are themselves divided into three

kinds: the class of air, which is the most subtle and thus the most transparent; that of water

(which includes the humors of the eye and egg whites), which is less transparent than air; and the

class of transparent stones. Each class has variation within it, as is evident from differences in

refraction and, perhaps, differences in color as well.79

Most interesting for our discussion, however, is the explicit link between the size of the

parts of a body and the degree of transparency. Ibn al-Haytham gives a mathematical “proof” of

59

77 "Ceci étant admis, revenons à notre propos sur les corps transparents; nous disons donc que la transparence est un forme dans le corps transparent car elle est transmettrice de lumière. Les corps transparents se divisent en deux parties ou corps cèlestes et corps sublunaires. Les corps célestes étant tous d'une même substance forment une seule espèce mais les sublunaires parmi les corps transparents se subdivisent en trois partes: l'une qui est l'air; la deuxième, l'eau, les humeurs transparentes tels le blanc d'œuf, les couches transparents de l'œil et ainsi de suite; la troisième, les pierres transparentes come le verre, le cristal, les pierres précieuses transparentes — toutes ces espèces forment l'ensemble des corps transparents. Ces corps diffèrent de par leur transparence et, excepté le corps céleste, chaque espèce a sa propre transparence. L'air en effet a une transparence différente selon qu'il est épais ou subtil, épais comme le brouillard et la fumée, air mêlé de poussière ou de fumée, subtil comme les courants d'air entre les murs, l'air proche du céleste, l'air pur de tout mélange. L'air subtil a un plus grande transparence comme c'est le cas pour l'eau courante comparée à leau mêlée de teintures. Il en est de même pour les humeurs transparentes dont les unes sont plus transparentes que les autres; de même pour les pierres transparentes, le cristal est plus transparent que les rubis; de toutes ces choses non sens peuvent témoigner. Mais aucune différence n'apparaît dans les corps célestes qui sont seulement transparentes: ceci est évident car l'œil perçoit tous les astres malgré la différence de leurs distances à la Terre et de leurs positions dans la voûte céleste." Roshdi Rashed. “Le ‘Discours de La Lumière’ d’Ibn al-Haytham.” Revue D’histoire Des Sciences 21 (1968), 215-16.78 Ibid. 220-23. 79 Ibn al-Haytham might, however, simply be referring to the differing degrees of refraction rather than color, given that, e.g., by modern measurements quartz has an index of refraction of approximately 1.46 and ruby that of about 1.76.

the fact that the celestial body is not perfectly transparent, which he attributes to the

mathematician Abu Aa'd al'Ala' Ibn Sahl (c. 940–1000). This involves the fact that “virtual” or

mathematical angles can be divided indefinitely.80 Although he presents the argument as Ibn

Sahl’s, he seems to supplement Ibn Sahl’s mathematics with his own commentary on the

physical implications of the proof. Thus he says that because the air has a more subtle form than

water, if some bit of water is divided into parts beyond the physical minimum allowed by its

form then that water must pass away and become air. The body with, he says the most subtle

form is the celestial aether, but mathematically speaking it is not perfectly transparent. This is

because the degree of refraction from a ray traversing a boundary between two media depends on

the relative densities of those two media. (See figure 1.1) A ray is passing from a less dense into

a more dense medium will refract towards the normal. One can imagine increasing the rarity of

the initial medium, thus causing the ray to refract more at the boundary. Physically, according to

Ibn al-Haytham, this involves dividing the first medium into smaller and smaller parts (or,

perhaps, increasing its potential divisibility by increasing the subtlety of its form). At this point

the argument is not entirely explicit, but I believe that Ibn al-Haytham assumes that the parts of

the celestial body must have some finite size — that is, that the heavens cannot be composed of

indivisible points — and thus that even the substance of the heavens must have a finite potential

minimum size to its parts in order for the form of the celestial body to inhere. Even the form of

60

80 Rashed, “Le ‘Discours de La Lumière’ d’Ibn al-Haytham,” 198–224.

the celestial body is not perfectly subtle.81 In most

versions of kalām composition by indivisible,

dimensionless points was a fundamental tenet,82

but Ibn al-Haytham appears to be following book 6

of the Physics where Aristotle holds actual

composition by indivisibles to be physically

impossible.

The upshot of this thought experiment is that

we can imagine a virtual angle of refraction greater

than that which occurs between the sphere of fire

and the celestial body. Thus, while the celestial

body is the most subtle physical body possible, it

is not perfectly transparent in the mathematical

sense. Ibn al-Haytham concludes the following:

Les deux doctrines [of the geometers and

61

81 “Les corps dans lequel ils se trouvent qui est limité par ce qu'il est — le corps dans lequel on suppose l'angle — ne peut être divisé à l'infini car tout corps physique ne peut être divisé que dans une certaine limite. Il est limité par sa forme et s'il était divisé ensuite, il s'en déferait por en revêtir une autre. Par exemple, l'eau divisée jusq'à l'extrême, ne peut aller au-delà d'une limite où la plus petite partie de l'eau si elle était encore divisée se déferait de la forme de l'eau pour revêtir cell de l'air. De même si l'air était divisé en sa partie la plus infime et devait être divisé encore, il se déferait de la forme de l'air et revétirait celle du feu. Mais si le feu était divisé en sa partie la plus infime, il ne pourrait être divisé par-delà cette limite car il n'existe aucune forme plus subtile que celle du feu. Et si la forme du corps céleste est plus subtile que celle du feu et qu'il soit possible au feu de devenir du genre du corps céleste, la plus infime partie du feu pourrait alors être divisée et le feu devenir de la substance du corps céleste. Cependant le corps céleste n'est guère divisible et si l'on supposait sa division elle [sic] s'arrêterait à la plus infime des ses parties après quoi il n'y aurait nulle division car il n'existe pas de forme plus subtile que celle du corps céleste. Si l'on suppose après cela une division — si celle-ci était possible — on peut supposer qu'elle ne concernerait que les dimensions du corps et non sa substance. Et si l'on suppose la division de la substance du corps celle-ci concernerait notre représentation et non la réalité.” Ibid., 222–2382 Alnoor Dhanani, The Physical Theory of Kalām: Atoms, Space, and Void in Basrian Muʻtazilī Cosmology, Islamic Philosophy, Theology, and Science, v. 14 (Leiden  ; New York: E.J. Brill, 1994).

Figure 1.1: An adaptation of a figure found in Ibn al-Haytham’s Discourse On Light. As a ray of light from E crosses from the celestial realm into the upper atmosphere CDB at D, it is refracted towards the normal FI, giving ray DA. If the celestial substance were rarified, however, the ray would refract through a greater angle DAʹ. We can imagine the “virtual” ray DAʹ as the result of a ray entering the atmosphere from a perfectly transparent medium. Because the celestial substance must have some minimal size for its form to inhere, DAʹ is not physically possible, and thus the celestial substance is not perfectly transparent. Modified from Rashed, “Le ‘Discours de La Lumière’ d’Ibn al-Haytham,” p. 222.

C BIϴ

Aʹ

F

D

E

A

the physicists] sont justes: que la transparence n'a pas de limite dans la représentation et qu'elle en a une dans les corps physiques laquelle est la transparence du corps céleste. Ces choses que nous avons rappelées concernent la transparence et les corps transparents; elles forment l'ensemble de ce qu'il faut savoir de leurs conditions.83

Note Ibn al-Haytham’s conclusion: that this is all we need to know about the conditions of

transparency and transparent bodies. The account that Ibn al-Haytham gives here of “subtlety”

requires more analysis that I can give, and in particular comparing it with statements by his

contemporaries, predecessors, and immediate readers in Arabic would illuminate this passage

greatly. However, rarity here seems to be clearly connected to some concept of minima: that the

form of a body cannot inhere once it is divided into parts smaller than some limit. Interestingly,

Ibn al-Haytham equates rarefaction and the division of the parts of a body; he might be thinking

that heating water divides it through the motion of its fluid parts, and thus if this division passes

a certain limit it turns to air. Whether this also causes an expansion of the body, or whether

expansion due to rarefaction was only of secondary importance, is difficult to say. It is interesting

to note that Santorio Santorio, an early, influential (and understudied) seventeenth-century

champion of corpuscular explanations, assumes that divisibility and rarefaction are identical, and

uses this fact to attack Zabarella’s theory of color. Expansion due to rarefaction is a secondary

concern. (See the following chapter.)

Scattered throughout his Kitab al-Manazir (Book on Optics) are many statements about

transparency, opacity, and color and their relationship to density and rarity. Although he has

much more to say about color, nowhere in his Optics is he as explicit as he is in his Discourse on

Light about what is ultimately meant by density and rarity. Similar to the account in Ptolemy, for

Ibn al-Haytham density and rarity account for refraction, color, translucency, as well as the

62

83 Rashed, “Le ‘Discours de La Lumière’ d’Ibn al-Haytham”, 223.

consistency of a body.84 The passage that demonstrates this most succinctly occurs when he

describes the crystalline humor, in Book I, Chapter 6, section 64. In Sabra’s translation of the

Arabic we read:

And we saw that this humour has some transparency and some density, and for this reason it is likened to ice. Thus because it is somewhat transparent it receives the forms and these pass through it on account of the transparency that is in it; and because it is somewhat dense it resists the forms and hinders them from passing through it on account of the density that is in it, and the forms are fixed in its surface and its body on account of that density. Similarly with every transparent body that is somewhat dense: when it is illuminated, the light passes through it according to the transparency that is in it, and the light is fixed in its surface according to its density — just as light is fixed in the surfaces of opaque bodies. Light is also fixed in the whole of the body which it penetrates on account of the density of that body; thus light appears on the surface and in the whole of the body in as much as it is fixed in it.85

In the Latin translation it is called the humor glacialis, or ice-like humor rather than the

crystalline humor, and as with Ptolemy the term used for density is spissitudo. In later chapters I

will show that this comparison to ice is highly important for later writers, in particular Zabarella

and Fabricius, and moreover that this similarity was perhaps observable in dissection given the

conditions of sixteenth-century dissection practices in Northern Italy. However, given that we

don’t know the extent to which Ibn al-Haytham was familiar with careful ocular dissection we

cannot assume that this density, which will be interpreted as a sort of cloudiness in the humor

63

84 See the introductory notes in: Alhacen and A. Mark Smith, “Alhacen’s Theory of Visual Perception: A Critical Edition, with English Translation and Commentary, of the First Three Books of Alhacen’s ‘De Aspectibus’, the Medieval Latin Version of Ibn al-Haytham’s ‘Kitāb al-Manāẓir’: Volume One.” Transactions of the American Philosophical Society 91, no. 4 (January 1, 2001), lv; Ibn al-Haytham and Sabra, Optics vol. 2, 22.85 Ibn al-Haytham and Sabra, Optics of Ibn Al-Haytham, 83. Note that the Latin translation does not use the word “opacus”: "Et iam predictum est quod in isto humore est aliquantule diafonitatis una pars et aliquantule spissitudinis, et propter hoc assimulatur glaciei. Quia ergo est in ea aliquantule diafonitatis, recipit formas, et pertranseunt in ea cum eo quod est ex ea de diafonitate; et quia in ea est aliquantule spissitudinis, prohibet formas a transitu in ea cum eo quod est ex ea de spissitudine. Et figuntur forme in eius superficie et corpore. Et similiter quodlibet corpus diafonum in quo est aliquid spissitudinis, quando super ipsum oritur lux, pertransibit in eo secundum id quod est in eo de diafonitate, et figitur lux in superficie eius secundum quod est in eo de spissitudine." Alhacen and Smith, “Alhacen’s Theory of Visual Perception,” 50-51. See also a similar passage at 1.7.9.

later on, was due to observation of the humor for Ibn al-Haytham. Nevertheless, whatever Ibn al-

Haytham saw or imagined about the crystalline humor, the key idea that he introduces is that

crystalline must have a quite specific degree of density in order both receive the forms of things

as well as retain them. This property of the crystalline humor — which I call a species-fixing —

will have great ramifications for theories of vision as well as anatomical observation up through

the first half of the seventeenth century, at least.

For our present purposes, then, the importance of this passage is the dichotomy between

transparency and non-transparency, with the degree of density (again, spissitudo in the Latin) or

rarity accounting for this difference. Note that Ibn al-Haytham sometimes uses the term

“coarseness” (grossities in the Latin version) as well.86 However, in the Latin version spissitudo,

densitas, and soliditas alone are employed where Sabra uses “opacity,” and Smith in his

introduction and commentary uses opacity, density, and solidity more or less interchangeably as

well.87 The Latin opacus and related terms originally meant dark or shaded rather than opaque in

the modern sense of blocking the passage of light, and this was the dominant meaning, it seems,

until the seventeenth century. (See Appendix 1.) Sabra’s use of the term opacity fails to make a

connection between the physical constitution of a body — namely the fineness of its parts — and

its optical properties, a connection that, as we have seen in his Discourse on Light, Ibn al-

Haytham clearly had in mind.

64

86 On this, see David C. Lindberg, “The Cause of Refraction,” 23–38. Lindberg casts this accounting for refraction by the grossities of the media a “mechanical approach,” but such a description stretches the term “mechanical” too far in my opinion.87 See Alhacen and Smith, “Alhacen’s Theory of Visual Perception,” liv, 404 n. 59. It seems that soliditas is at times used interchangeably with spissitudo and densitas, but more often it is used for solid bodies that are not fully transparent. See, for example, Alhacen’s use of soliditas at III.3.21, III.5.10, III.6.16, III.7.151, III.7.163; the exception to this is III.7.89. It is interesting to speculate whether Ibn al-Haytham thought of density and rarity and its relationship to transparency as working somewhat differently among his three species of transparent bodies given in his Discourse on Light (i.e., air, water, and stones). The Latin De aspectibus, however, provides no clues.

The important contrast with transparency is the degree to which a body can receive and

interact with illumination: that is, for the illumination to mingle with the color of the body and

for the two to propagate together in all directions. The first three chapters in Book I are notably

missing from the Latin translation, and it is in these sections that Ibn al-Haytham is most explicit

about this relationship. At Book I, Chapter 2, section 12 (hereafter as: I.2.12) we read:

We also find that sight does not perceive any visible object unless the object is opaque or has some opacity in it. For when a body is extremely transparent (such as rarefied air) sight does not perceive it but perceives what is behind it. Sight does not sense a transparent body unless it is denser than the intermediate air between itself and the eye. But every opaque body has a colour or something like colour, such as the light of the stars and the forms of [self-]luminous bodies. Similarly, no transparent body with any opacity in it can be devoid of colour.88

Note that the Arabic term for “opacity” here is likely kathāfa, meaning density or thickness.89

Thus, at I.6.107 we are told that every medium has some density to it, and that the color

propagating from a body to our eyes is always altered by this mixing — although in most cases

this tainting is slight and imperceptible.90

That light and color are separate entities, but nevertheless that they must mingle and

propagate together in order for vision to take place is shown by a great number of carefully

considered experiments in Book I Chapter 3 of the Arabic version. If sunlight is allowed to enter

through a wide hole in a small dark chamber with white walls, and if that light lands upon a

strongly colored body, then the walls will show the form of that color. If a white body is put in

65

88 Ibn al-Haytham and Sabra, Optics vol 1, 9.89 Ibn al-Haytham and Sabra, Optics vol 2, 198.90 Ibn al-Haytham and Sabra, Optics vol 1, 97. “Et hoc est quod promisimus declarare in fine capituli tertii, et declaratum est modo quod colores quos comprehendit visus ex rebus visis non comprehendit ipsos nisi admixtos cum formis lucis que sunt in eis et admixtos cum omnibus formis orientibus super ipsos ex coloribus corporum oppositorum. Et si in corpore diafono quod est medium inter ipsos et visum fuerit aliqua spissitudo, admiscebitur color eius etiam cum eis, et visus non comprehenditilium colorem singularium." Alhacen and Smith, “Alhacen’s Theory of Visual Perception.” 64-65.

the path of the sunlight, the room will be illuminated, while if a black body is put in its place, the

room will darken. At I.3.121 we read:

It is therefore evident from this experiment that colour radiates from an illuminated coloured body and extends in all directions just as the light in this body does, both being always together; that the form of colour is mingled with the form of light; and that the form of the colour extending along with the form of the light is weaker than the colour itself, and the farther it is from the coloured body the weaker it becomes — as is the case with light.91

This seeming “rebounding” of light and color, however, is not considered to be a reflection

because, unlike the images in a mirror, the color itself does not change its position as the

observer moves. Rather, this is understood in terms of Ibn al-Haytham’s idea of “primary lights”

and “accidental lights”; the former are self-luminous bodies such as the sun or flames, while the

latter are bodies that are luminous only because they are illuminated by another self-luminous

body. Modern categories in which things are either specular or diffuse reflectors does not

coincide precisely with Ibn al-Haytham’s categories: diffuse reflection (caused by reflection from

a rough body) is different from Ibn al-Haytham’s accidental illumination on a basic ontological

level, and this stems in great part from the Neoplatonic-influenced Peripateticism that shapes his

thinking. Although he never addresses the issue directly, it is clear that light is not a body, and

thus does not literally rebound off the solid surface of things. Thus we read:

The sense of sight perceives no visible things that are not in a body. Bodies combine many properties, and there occur in them many properties. The sense of sight perceives in bodies many of the properties that inhere or occur in them. Now colour is one of the properties that inhere in bodies, and light is one of the properties that [either] inhere in bodies or occur in them.92

66

91 Ibn al-Haytham and Sabra, Optics vol. 1, 45.92 Ibn al-Haytham and Sabra, Optics vol. 1, 126. "Sensus quidem visus nichil comprehendit de rebus visibilibus nisi in corpore. In corpore autem multe res congregantur et accidunt ei multe res, et visus comprehendit de corporibus multas res que sunt in eis et que accidunt illis. Et color est unum eorum que accidunt corporibus, et similiter lux, et sensus visus comprehendit utrumque istorum in corporibus." Alhacen and Smith, “Alhacen’s Theory of Visual Perception,” 97

The two primary properties that we perceive are light and color, but as he says the “forms” of the

two are distinct (here forma in Latin, sura in Arabic).

Undoubtedly, Ibn al-Haytham was influenced by trends in Islamic Peripateticism, by

Kalam, and perhaps by other Stoic-influenced sources apart from Ptolemy, but in the main his

work is modeled after Ptolemy’s, and he pulls together, refines, and rethinks many of Ptolemy’s

statements of the relationship between the density or thickness of a body and its transparency,

translucency (that is, the degree to which a body “fixes” light within it), color, and refractive

power. Notably, he repurposes these notions to suit an intromission theory of vision. The intuitive

notion from Ptolemy, that the physical density of a body would block a visual ray from feeling

ahead, does not lend support to Ibn al-Haytham’s theory of vision in the same way it does for

Ptolemy, and thus the identification of physical and optical density is more theoretical and

abstracted from experience. A particularly interesting point is that, along Ibn al-Hatham’s

appropriation of the visual cone while at the same time reversing the direction of vision, Ibn al-

Haytham also takes the qualities that Ptolemy says are required of substances in order for us to

be able to see them and applies them the crystalline humor. Not only is it the case that things

“that are truly seen are thick shining [bodies]”, as Ptolemy says, but according to Ibn al-Haytham

that which we see with also needs to be a somewhat thick, shining body. To repeat the quote

analyzed above, Ptolemy writes “For things subject to vision ought to be shining to some degree,

either from itself or from another ... and thick in substance to retain vision, in order that the

power [of vision] may penetrate them and not pass through without inscribing an effect.”93 With

only a few substitutions we can derive Ibn al-Haytham’s account of the crystalline humor: “For

67

93 Ptolemy, L’optique, 12.

the seat of sensation ought to be shining to some degree, not from itself but from another ... and

thick in substance to retain visible objects, in order that the power [of the visible objects] may

penetrate the crystalline humor and not pass through without inscribing an effect.”

Moreover, Ibn al-Haytham’s use of density and rarity was also influenced by the need to

explain the refraction of starlight when passing from the aether to upper atmosphere, and the

notion of a hierarchy of subtlety as a sort of hierarchy of perfection of the basic constituents of

the universe no doubt was widespread. Finally, while Ibn al-Haytham also retains the distinction

between color and light found in the Aristotelian tradition, he says that “the form of color is

always mixed with the form of light (lumen)” and that they are never perceived individually.94

After Ibn al-Haytham, this joining or mixing of light and color seems to become the typical way

to characterize the relationship between the two, rather than — as in Aristotle and Alexander of

Aphrodisias — the notion that light only or primarily activates the intermedium and not the

colored surfaces of bodies. After Ibn al-Haytham, the mathematical analysis of rays in optical

works should be interpreted as an analysis of the path of the joint propagation of light and color

and not merely one or the other. This is an important step towards the unification of light and

color that we will see in Fabricius and which became dominant later in the seventeenth century.

§ 1.4: Averroës and the Articulation of the Condensation Theory

68

94 Alhacen and Smith, “Alhacen’s Theory of Visual Perception,” 22-23; see also sections 1.3.123, 128 (extant in the Arabic MSS only) in Ibn al-Haytham and Sabra, Optics, 44, 47.

Ibn Rushd, or Averroës in the Latin West, seems to have been particularly attentive to unresolved

questions about color, light, and transparency in the Aristotelian corpus.95 (Although, there was

certainly precedent for this in Arabic philosophy, starting as early as al-Kindi.96) All of the

previously mentioned sources, and many more, were known to Averroës. Curiously, Averroës

addresses the origin of color and its relationship to transparency most directly in his commentary

on Aristotle’s De coelo and in an independent treatise, On the Substance of the Celestial Sphere

— curious, that is, because Aristotle himself does not address color or transparency in De coelo.

Given this fact, it seems likely that Averroës was at least prompted to discuss color here by

Simplicius’s discussion of the moon-spots in his De anima commentary, but Averroës goes much

further than any of the authors before him. Averroës’s scheme for the generation of color appeals

to density and rarity, which he uses in a manner much like that of Ptolemy and Ibn al-Haytham.

However, he does so in the role of a commentator, and thus with the aim of resolving the many

difficulties and puzzles found in the Aristotelian corpus. Addressing the issue of the substance of

the celestial body in Book II of De caelo, Aristotle says that the stars produce light and heat

because of “the friction set up in the air by their motion.”97 This is a notoriously unsatisfactory

conclusion, and Averroës rejects the friction account because the Sun and many other stars do not

touch the upper atmosphere. In its place, he gives a short explanation for the cause of celestial

69

95 For an analysis of Averroës’s color theory in his commentaries on De anima and De sensu, see Helmut Gätje, “Zur Farbenlehre in der muslimischen Philosophie,” Der Islam; Zeitschrift für Geschichte und Kultur des Islamischen Orients, 43 (1967): 280-301. Note, however, that Gätje fails to make the connection between color and those works and Averroës’s discussions in De substantia orbis and his De caelo commentary.96 Otto Spies, “Al-Kindi’s Treatise on the Cause of the Blue Colour of the Sky,” Journal of the Bombay Branch of the Royal Asiatic Society, no. 13 (1937): 7–19. Adamson, “Vision, Light and Color in Al-Kindi,” 207–36. On color in the Islamic speaking world, also see Eric Kirchner and Mohammad Bagheri, “Color Theory in Medieval Islamic Lapidaries: Nıshābūrı, Tūsı and Kāshānı,” Centaurus 55, no. 1 (2013): 1–19.97 De coelo, 289a20.

light and heat in which he appeals to density and rarity,98 but he treats this at greater length in De

substantia orbis.

A full explication of what Averroës has to say about celestial accidents is beyond the

scope of this chapter, and so I will merely summarize his arguments for positing a relationship

between transparency, density, and illumination.99 At the point in his discussion where he

discuses density and rarity in the celestial body Averroës takes it as proven that the celestial

realm cannot undergo substantial change (i.e., generation and corruption) and therefore, he says,

only “those accidents, the change of which does not involve an alteration in the substance of the

underlying subject, are common to the celestial and the terrestrial bodies.” These include

locomotion, transparency and non-transparency, as well as “those qualities to which the latter

accidents are subsequent — I have in mind the rare qualities and the dense qualities — for it seems

70

98 Aristotle and Averroës, Aristotelis De Coelo; De Generatione et Corruptione; Meteorologicorum; De Plantis Libri Cum Averroës Cordubensis in Variis Eosdem Comentariis, vol. 5, Opera Omnia (Venice: Giunta, 1562). For example on p. 127r he writes that the celestial bodies “habent communicationem cum elementis in diaphaneitate, et illuminatione, & obscuritate.” On p. 125v, we read: “sed attribuit hoc [that is, light and heat] stellae quia pars orbis, in qua est stella, facit hanc operationem per stellam, quae est in ea, quae stella est pars eius, & potentia totius orbis est congregata ex potentiis partium. quoniam, quemadmodum virtutum corporalium, successio & additio unius post alteram est secundùm successionem corporum in magnitudine, & parvitate, sic erit successio, & additio virtutum coelestium corporum aequalium eiusdem speciei secundùm suam successionem in densitate, & raritate.”99 See also the introduction to Averroës and Arthur Hyman, Averroës on the Substance of the Celestial Sphere: Critical Edition of the Hebrew Text with English Translation and Commentary, ed. Arthur Hyman (Medieval Academy of America, 1986). This is a critical edition of the Hebrew text with an English translation from the Hebrew, but in the passages I have examined in this section do not differ in any significant way between the Latin version and the English translation.

that density and rarity are the cause of transparency and non-transparency.”100 (Note the

uncertainty in phrase “it seems,” as Zabarella will say this as well.) For Averroës, given that the

celestial body is a single, homogenous substance, transparency, darkness (obscuritas in Latin),

and luminosity in the heavens cannot differ for the reason that different parts of the heavens are

made from different stuff. Averroës is particularly adamant that the celestial body is a unity, and

that the planets and stars do not differ in species. Because of this, Averroës appeals to a variation

in the density and rarity of the parts of the celestial sphere.101 This agrees with the scheme of

density and rarity that Ptolemy and Ibn al-Haytham use to understand transparency and its

absence in bodies. That the condensation of a transparent substance produces the color white

almost certainly received a some confirmation from experience — such as the fact that air, when

condensing into water, produces clouds or fog, or the fact that the densest part of the body, the

bones, are white. However, Averroës does not ground his theory on induction or experience.

71

100 English translation is from Averroës and Hyman, On the Substance, 91-2. On the difference between the celestial and sublunar bodies: "Differunt in natura passiva, quae dicitur altero, & conveniunt secundum accidentia, secundum quae non transmutatur substantia. haec enim alteratio, secundum quam transmutatur substantia alterati, videtur esse propria corporibus, quorum substantiae admiscentur potentiae, & sunt corpora generabilia, & corruptibilia. Accidentia vero, quae non transmutant substantiam deferentis, sunt communia utrique corpori. Et primum istorum est motus localis, & diaphaneitates, & qualitates, quas sequuntur ista, scilicet raritas, & densitas. Videtur enim que raritas, & densitas causae sint ferè diaphaneitatis, & non diaphaneitatis. Sed tamen dicuntur utraeque in utroque corpore secundum prius, & posterius, sicut dicitur corporeitas.” Averroës, Averrois Cordubensis Sermo De Substantia orbis; Destructio destructionem philosophae Algazalis; de animae beatudine, seu epistola de intellectu. Vol. 9. Omnia Quae Extant (Venice: Iuntas. 1562), 7v col. 1–2. Also see Augustino Nifo's commentary: Nifo, Agostino. Commentationes in Librum Averrois de Substantia Orbis (Venice, 1546), 29r ff.101 On luminosity, he writes, that, unlike in the terrestrial sphere where luminosity occurs when fire acts upon a dense body, “it seems that the cause of the luminosity of the parts of the celestial bodies, that is, the stars, is the density of that particular part of the celestial sphere occupied by the star that is transparent in actuality. And that the stars are the dense part of the celestial sphere becomes even more apparent through the density existing in the planets which, as a result of this density, eclipse one another, and the most obvious evidence is provided by what occurs in the case of the moon” Averroës and Hyman, On the Substance, 92-93. “Et similter conveniunt in illuminatione, & obscuritate. sed haec magis videntur dici aequivoce, quàm secundum prius, & poserius. Lux enim videntur fieri in hoc corpore igneo diaphano simplici, quod est in concavo orbis Lunae, quando agit in corpore denso, & admiscetur cum eo. at causa illuminationis partium corporis caelestis, scilicet stellarum videntur esse densitas illius partis diaphanae in actu ex orbe. & hoc apparet in stellis, quae eclipsant se adinvicem, & hoc bene apparet in Luna." Averroës, Sermo de substantia orbis, 7v, cols. 1–2.

Rather, it is a deduction based on (to him) more secure metaphysical principles combined with a

sort of process of elimination: density and rarity are the only proper candidates to account for

difference in the heavens. Furthermore, Averroës knew Ibn al-Haytham’s works, and it is likely

that Averroës is modifying the scheme of condensation and rarefaction present in Ptolemy and

Ibn al-Haytham, a scheme which in any case seems to have been a common notion among

Islamic intellectuals.

Importantly, Averroës concludes that the qualities of density and rarity, as well as

transparency, are predicated “in respect to priority and posteriority.” That is, the heavens don’t

require the activation of light to become transparent (they are, by nature, transparent in act),

whereas transparent substances below do (they are potentially transparent until illuminated).102

Furthermore, luminosity and obscurity are not the same species of quality above and below, and

so the terms “luminosity” and “obscurity” (“obscuritas”) as applied to the two realms are

equivocal.103 While luminosity in the sublunar region arises when "the fiery element acts upon a

heavy and dense body," in the celestial sphere luminosity is generated from the greater density of

some portion of that transparent body.104 In addition to their differing causes, Averroës further

distinguishes celestial and terrestrial heat on the basis of their actions:

72

102 “Yet, even though the celestial and terrestrial bodies have the attributes of rarity and transparency in common, these terms are predicated of the two bodies in respect to priority and posteriority, as is the case with the predication of ‘corporeity which exists in both of them.” Ibid., 92. See also Hyman’s comment at Ibid., n. 67. Note that this has a precedent in (Ps-) Simplicius’s De anima commentary. “For the celestial body is at once a source of light and transparent. Therefore, even if some portion of it is prevented by the cone of the earth from being illuminated by the sun's light, still it is not in darkness because of its own light. Where there is potentially light, as in air, there is not only light but also darkness.” Priscian, and Simplicius, On Theophrastus on Sense-perception with Simplicius On Aristotle’s On the Soul 2.5-12, trans. by Pamela M. Huby and Carlos G. Steel (Cornell University Press, 1997), 163.103 Averroës and Hyman, On the Substance, 92.104 Ibid., 92.

For the calefactory action of fire damages and destroys things — especially the kind of fire which produces light — while the calefactory action of the celestial bodies produces generation and bestows vegetative and animal life. This is the reason there are two kinds of calefaction: that which is a passive quality changing the substance of the subject in which it inheres, and that which is not a passive quality. The case of calefaction is akin to the case of transparency and non-transparency, that is, there is the kind of transparency and non-transparency that is the result of a passive quality and there is the kind that is not.105

The calefactory power of the celestial body is due to the luminosity of the stars, and he says that

the ancient commentators noticed that “light, insofar as it is light, is perceived to produce heat

upon being reflected,” and that this is “an accident common to the celestial bodies and fire.”106

How this seemingly empirical observation about the nature of light simpliciter is squared with

the equivocal use of luminosity between the celestial and terrestrial realms is not clear.

Thus, the stars and planets are condensed parts of the heavens, and as such they have

powers that are analogous to those of condensed matter on earth, but nobler in its effects. Most

importantly, for Averroës there is an ontological distinction between not just the material basis of

heaven and earth, but the transparency, rarity, and the density of their substances, and thus an

ontological divide between the properties, such as illumination and the power to heat, that arise

due to condensation and rarefaction.107 In explaining the heaven’s ability to heat without itself

being hot, as well as the fact that the heavens are transparent without requiring activation via

73

105 Ibid., 95. “calor enim ignis corrumpit, & destruit entia, & maxime ignis immuinantis, calor vero corporum coelestium largitur vitam vegetibilem, sensibilem, & animalem. Et secundum hoc calor erit duobus modis, calor qui est de qualitatibus passivis, quae transmutant substantiam, in qua sunt, & calor, qui non est de qualitatibus passivis, sicut est dispositio in diaphaneitate, & non diaphaneitate, scilicet quòd quaedam sequitur qualitatem passivam & quaedam non.” Averroës, Sermo de substantia orbis, 8r col. 1.106 Averroës and Hyman, On the Substance, 94. “Et expositores dant secundam cauam, scilicet illuminationem, dicunt enim quod lux, in eo quod lux, videtur calefacere, quando reflectitur, & dicunt quod non est de accidentibus propriis igni, sed de accidentibus communibus igni, & coelesti corpori.” Averroës, Sermo de substantia orbis, 8r col. 1. Among the more important figures in the commentary tradition to say this is Philoponus. Philoponus and Charlton, On Aristotle’s ‘On the Soul 2.7-12’, 13-14.107 Averroës and Hyman, On the Substance, 97-98.

illumination, Averroës draws an analogy with the first mover: while the primium mobile moves

without itself moving, those bodies that are moved by it cannot in turn move other bodies

without themselves being moved; likewise, the heavens produce heat without themselves being

hot (or susceptible to heat), and produce illumination that renders potentially transparent bodies

actually transparent without themselves needing to be activated by illumination.108 This

presumably means that any colored body in the heavens would be able to transmit its form of

color through the heavens — right up to the inner concavity of the lunar sphere — without the

heavenly media requiring activation. This condition of perpetual actual transparency is in-

principle unobservable — a curious and seemly superfluous notion apart from its metaphysical

necessity. Additionally, the precise difference between celestial and terrestrial color (particularly

whiteness), isn’t entirely clear. His most direct statement about this is rather obscure: “And the

parts of the celestial bodies differ in respect to transparency and non-transparency, so that there is

generated in them something like color, an example of this being the Milky Way.”109 How

something that is actually seen could only be “like color” seems hard to explain, and Averroës

does not do so here.

Finally, Averroës has an interesting comment about color mixture. He uses the example of

color mixture to support the idea that the substantial forms of the elements themselves can be

mixed, and thus rather strikingly he seems to ground his theory of physical mixture upon a

theory of color mixture. It is also worth noting that this statement, which was often quoted by

medieval Latin writers, occurs in his De caelo commentary:

74

108 “The celestial body, according to this opinion, is transparent in actuality in virtue of itself, this being contrary to the case of the transparent bodies here below, which are transparent in actuality only at a time when light is present.” Averroës and Hyman, On the Substance, 93. 109 Ibid., 93. “Et partes diversantur in hoc in diaphaneitate, & non diaphaneitate, ita quòd in eis fit aliquid simile colori, sicut in galatia.” Averroës, Sermo de substantia orbis, 7v col. 2.

We say that the substantial forms of these elements are diminished in respect of perfect substantial forms; they are as it were an intermediate between forms and accidents. Therefore it is not impossible that their elemental substantial forms should be mixed in such a way that another form should arise from their commingling, as many intermediate colors are made from the mixture of white and black.110

We have, then, all of the components for the condensation theory of the origin of colors

mentioned above. Nevertheless, how exactly this thickening or condensation is to be understood

is not altogether clear. Rather than a notion of density that is perhaps more familiar to us — the

compression of a given quantity of matter into a smaller volume — Aristotle's description in

Meteorology IV of the thickening of substances (such as boiled honey when placed in cold

water) comes to mind. However in Meterology IV as well as the biological works Aristotle's

explanations using condensation generally rely on the action of the active qualities hot and cold,

which are for Averroës are absent from the heavens. Averroës is likely thinking of the potential or

actual size of the contiguous parts of a substance, in line with that described by Ibn al-Haytham,

but precisely why the tenuity of a substance, understood in terms of the small size of its parts,

should result in transparency, why the thickness of it, understood in terms of large size of its

parts, should result in color, or why condensation should give rise to luminosity, is nowhere

explicated.111 On the one hand, it might seem that Averroës backed himself into a corner within

his elaborate development of Aristotelian cosmology and its relationship to generation and

corruption, and that he simply chose the only plausible mechanism left at his disposal. Yet his

75

110 “Dicemus quod formae istorum elementorum substantiales sunt diminutae à formis substantialibus perfectis, & quasi suum esse est medium inter formas, & accidentia, et ideo non fuit impossibile ut formae eorum substantiales admiscerent, et proveniret ex collectione earum alia forma, sicut cum albedo, & nigredo admiscent, fiunt ex eis multi colores medii.” Aristotle and Averroës, Aristotelis De coelo; De generatione et corruptione; Meteorologicorum; De plantis libri cum Averroës Cordubensis in variis eosdem comentariis (Venice: apud Iuntas, 1562), 227r col. 2.111 On Averroës’s use of minima naturalia in his physics commentaries, see Glasner, “Ibn Rushd’s Theory of Minima Naturalia.”

choice of density and rarity to account for the origin of color likely had wide support at the time,

Rather than a strained explanation, it would appear that, according to the standards of the time,

the pieces all fit quite easily.

§ 1.5: Medieval Appropriation of the Condensation Theory

This use of density and rarity to account for the differing luminosity of the heavens was taken up

by Roger Bacon in both his Opus maius and his De multiplicatione specierum (On the

Multiplication of Species), and so we see that a key figure in the development of medieval

theories of vision in the Latin West also propagated the condensation theory of the origin of

color. In part II, chapter I of his section on mathematics in the Opus Maius, Bacon cites both

Averroës’s commentary on De coelo as well as De substantia orbis, and explicitly follows him in

attributing the cause of the luminosity of the stars to the density of the transparent aether.112 He

also has many passages where he explains transparency and its contrary by appealing to the

rarity or density of the medium, the most explicit of which occurs in his treatise De

multiplicatione specierum:

Now, ‘diaphanous’... and ‘rare‘ — all these terms have the same meaning as far as the thing [itself] is concerned, but differ according to certain [other] considerations. For ‘rare’ designates the disposition of a body absolutely, according as its parts are widely separated from each other, as in air and water and the like. The other terms are employed in relation to sense or sensible objects, according as their species are able to pass through [the medium so designated], as we observe in water, air, the sphere of fire, and the planetary spheres apart from

76

112 “Therefore they make a mistake who judge that the sphere of fire is naturally luminous, just as here below, and especially since it is rarer than air, and therefore less visible, and on this account less fitted for light, because density is a cause of illumination, as Averroës states in the second book of the Heavens and the World, and in the book on the Substance of the Sphere.” Roger Bacon. The Opus Majus of Roger Bacon. Translated by Robert Belle Burke. Vol. 1. (Thoemmes Press, 2000), 149.

the bodies of the planets; for sight penetrates all of these, as do the species of [visible] things.113

What exactly Bacon means here by the parts being “separated from each another” (remote

iacent) is not entirely clear, especially considering the Aristotelian denial of void space that

Bacon follows.114 Some manuscript variants, moreover, omit this phrase.115 Furthermore, it is

clear that density and rarity, for Bacon, are not equivalent to anything like the mass or the weight

of the object, nor is density to be confused to the hardness or solidity of the object. For him,

density or rarity (which are again a disposition of the parts of a body) produce sensible effects

primarily upon vision, rather than touch (through either solidity or weight). Thus “density” and

“optical density” are more or less synonymous. See, for example, Part II Chapter 5 of De

multiplicatione specierum, where he writes: “It must be recognized, in the first place, that neither

reflection nor refraction is produced by hardness and solidity, but only by density and rarity.”

Because species are able to pass through glass and crystal, he says the following:

Therefore glass is rare; and crystal and the like are somewhat (but not perfectly) dense, and yet they are sufficiently rare to permit the species of light to pass through them. However, a substance is not called ‘hard’ and ‘solid’ from the closeness of its parts, but from its stability and firmness and fixity, owing to its dry nature, from which hardness and solidity derive, as Aristotle says in De generatione, book ii.116

77

113 “Dyaphanum enim ... et rarum: hec omnia idem significant secundum rem, sed differunt secundum considerationes aliquas. Nam rarum dicit dispositionem corporis absolute, secundum quod partes eius remote iacent, ut est aer et aqua et huiusmodi. Alia dicuntur per comparationem ad sensum vel sensibile secundum quod species eorum potest transire, ut patet in aqua et aere et spera ignis et orbibus planetarum extra corpus earum; nam visus penetrat hec omnia, et species rerum penetrant ipsa.” Roger Bacon Roger Bacon’s Philosophy of Nature: a Critical Edition, with English Translation, Introduction, and Notes, of De Multiplicatione Specierum and De Speculis Comburentibus. St. Augustine’s Press, 1998, 96-7.114 For Roger Bacon’s position on the void, see Edward Grant, Much Ado About Nothing: Theories of Space and Vacuum from the Middle Ages to the Scientific Revolution (Cambridge University Press, 1981), especially p. 87-8.115 See Lindberg’s notes at the bottom of Bacon, Philosophy of Nature, 96.116 Bacon, Roger Bacon’s Philosophy of Nature, 131.

The importance of this passage for us is that rarity in the sense of transparency is, according to

Bacon, a consequence of the rarity of matter in the sense of a disposition of parts.117 Rarity is a

condition of a body considered absolutely, and thus it is not a property that involves any

relationship to other bodies; other properties follow upon the density or rarity of the body, such

as how the body interacts with light or affects our sense perception. But it needs to be stressed

that, for Bacon, density and color are not one and the same. Density is a necessary, but not

sufficient condition for the perception of color, at least. Bacon makes a distinction between color

considered absolutely and visibility, or the perception of color (although he is not always careful

in making this distinction). For the perception of color, illumination and a transparent medium

are also necessary. Furthermore, Bacon seems to say that the visibility of a body — or the power

of lux and color to alter the medium, our eyes, and our sense perception — is a nature that is

something more than the mere density and rarity the body, although he does not spell out

precisely what the relationship is.118 Furthermore, just as Bacon models his account of the causal

interaction of nature as a whole — his doctrine of the multiplication of species — on the analogy

of light and visual perception, likewise for him density and rarity not only relate to the

transparency and non-transparency of a body with respect to lumen and color, they also relate to

transit or non-transit of every species through intervening media. Thus the multiplication of

substantial forms, such as fire, as well as accidental forms such as color, are affected by the

78

117 It is possible that Roger Bacon considered density and rarity to fall within the category of situation rather than quality; further research on this question is required, but unfortunately I cannot investigate this in greater detail here.118 “and therefore a dense substance is not seen as a result of its absolute nature, for its visibility depends on the transparent medium.... Therefore the existence of colour and light requires density, so that sight will be terminated at the colour and light (lux). And light and colour are seen as a result of their own nature producing species; and they are perceived before density is perceived....” Bacon, Roger Bacon’s Philosophy of Nature, 39.

density and rarity of the substances that the species encounter.119 In a certain cense, his notion of

density and rarity, which has received little attention from scholars, occupies a key place in his

entire philosophy of nature.

Albertus Magnus provides the most detailed, and perhaps the most widely read, version

of the condensation theory of color generation among medieval Latin writers. He refers to color

in his commentaries on De caelo, Meteorology, De anima, and De sensu — as well as in his

introductions (Isogogae) to these various subjects.120 In addition to his influence via manuscripts,

all of the previously mentioned works were published in many editions throughout the sixteenth

century, and had significant influence in published form. In his De caelo commentary, Albertus

poses the question of whether the heavens can be altered according to rarity and density (rarum

et spissum). He says that, according to the opinion of the Peripatetics, the celestial orbs are

denser in some parts than others, and that this is possible because the essence of the heavens is

not dependent on the density and rarity of its parts.121 Here Albertus points to book 8 of his own

Physics commentary, where he says that he has shown that the essence of the heavens is not

made (facere) by parts variously dense and rare.

Like Averroës, Albertus concludes that rarity and density are equivocal terms when

applied to the heavens and terrestrial elements. In the latter heat rarefies and cold condenses, and

79

119 See, for example, Ibid., 210-11, 258-9, 264-5.120 For convenience I have used the late ninteenth-century editions of Albertus Magnus’s works, published in Paris and edited by Augusti Borgnet. These in turn are based on the mid seventeenth-century Jammy editions.121 "Est autem adhuc dubium, utrum corpus coeli alteretur secundum rarum et spissum. Scimus enim sententiam esse Peripateticorum, quod orbis in una parte spissor est quam in alia: et sic videtur non esse inconveniens, quin alteretur secundum rarum et spissum: essentia enim orbis non seipsam fecit secumdum partes diversas rarum, et spissam, sed oportet quod aliquid aliud sic eam faceret, sicut et probavimus in VIII Physicorum." Albertus Magnus. Opera Omnia. ed. Augusti Borgnet, vol. 4 (Paris: Ludovicum Vivès 1890), 34-5.

thus sublunar density or rarity follows from the elemental qualities (although it is unclear from

this passage whether Albertus thinks that this is the only way to effect density and rarity in the

sublunar realm). Elemental processes are not at work in the heavens; instead, the differences in

density are set by God during creation, an opinion, he notes, that Avicenna and Averroës follow

in their Sufficientia caeli et mundi and De natura orbis (i.e., De substantia orbis), respectively.122

However, while Averroës did indeed write the latter, the text that Albertus attributes to Avicenna

was not, in fact, written by him (and it is also far less explicit about the relationship between

rarity-density and transparency, luminosity, and color).123 Later in his commentary Albertus

reiterates this distinction between celestial and terrestrial density and rarity: the transparency, and

thus rarity, of air and water is due to the parts being small and fluid, and able to pass one over the

other, while the transparency/rarity of the heavens is due to the spiritual nature of the body, in

80

122 "Si autem propter hoc dicatur, quod rarum et spissum sunt primae qualitates ex parte naturae: et ideo quod alteratur secundum rarum et spissum, alteratur secundum alias qualitates, et transmutatur in substantia, sicut nos videmus quod materia ignis raritate praeparatur ad huc ut sit calida, et materia terrae spissitudine praeparatur ad hoc ut sit frigida: et sic etiam coelum alterabitur secundum istas qualitates. Dicendum videtur, quod rarum et spissum in coelo aequivoce sunt ad rarum et spissum etiam elementorum. In elementorum enim materia calorem rarificat, et frigus inspissat: sed in coelo non, sed potius, ut diximus in VIII Physicorum, creator: et creator primus partes orbis produxit in diversa raritate et spissitudine, et fecit corpus medium sphaerarum comprehensible, et extensibile, ut plenum sit quod est inter sphaeras: et haec est sententia duorum Philosophorum, scilicet Avicennae in sufficientia caeli et mundi et Averroës in libro <37> de Natura orbis. Si quis autem dicat quod non sunt in coelo diversi orbes continentes se invicem, sed totum est unum est et continuum, illenescit quid dicit, et est ignarus coeli, sicut probabimus inferius: figura autem descripta es hic in qua sufficiunt circuli tres super diversa centra existentes: quia quod accidit in tribus, accidit in omibus, etiam si mille esse ponerentur. " Ibid., 36-37.123 Oliver Gutman, “On the Fringes of the Corpus Aristotelicum: The Pseudo-Avicenna ‘Liber Celi Et Mundi’.” Early Science and Medicine 2, no. 2 (January 1, 1997): 109–128. Pseudo-Avicenna, and Oliver Gutman. Liber Celi Et Mundi: Introduction and Critical Edition (University of Oxford, 1996).

virtue of which the heavens possess a tenuity not possible in the elemental realm.124 There he

also states that a diversity of density and rarity in the heavens is necessary to accomplish a

diversity of effects in the inferior realm. For Albertus it is not merely differences in color and

lumen that arise from density and rarity, but indeed the intensity of every celestial power that

affects the terrestrial ream is due to the degree of density or rarity of that body.125 All generation

and corruption on earth is, in some sense, affected by the diversity of density and rarity in the

heavens. As we have seen, at the center of this scheme, from Averroës onwards, was the problem

of how to account for the visible differences in the heavens given that they are homogeneous and

incorruptible, but to do so in a way that provides some link between the terrestrial and celestial

qualities and processes, particularly with respect to transparency and luminosity. Differences in

celestial powers are also of paramount importance, but the appeal to density and rarity here

follows, it seems, from a scheme originally used to understand the visibility of the heavens, not

the reverse.

In this section Albertus discusses the nature of transparency — he consistently uses the

Greek-derived term diaphaneitas, which is also the term used in the Latin translation of

81

124 "Similiter autem diaphaneitatis dispositio non est propria aeris, vel aquae, vel ignis: sed haec elementa habent eam ex convenientia communi cum coelo, sicut etiam dixit Aristotelis in secundo de Anima: sed participatio ipsius in coelo et in materia est valde diversa et aequivoca: quia in elementis videmus expresse, quod calidum dissolvens facit eam, vel ad minus frigus non totum exprimens humidum mobile, cuius una pars fluit ab alia, cum male sit terminabile in seipso, sicut causatur diaphaneitas sive perspicuitas in aqua ... In coelo autem diaphaneitas non causatur ex aliquo solventes partes, vel ex hoc quod una pars fluit ab alia: sed potius ex ipsa natura spiritualitatis corporis huius, quod sicut diximus, determinatur forma separata, cuius subiectum est indivisibile et simplex per naturam: et advenit ei quantitas, non potest afferre ei proprietates ignobiles: et ideo remanet tenue et perspicuum” Albertus Magnus. Opera Vol 4, 124-125.125 "Et similiter est de raro et spisso, quod habet non ex qualitatibus activis vel passivis facientibus constare vel distare partes materiae, sed potius omnia ista sunt consequentia formas separatas quae motum coeli explicant per lumen et perducunt ad effectum: et ideo necesse est coelum esse spissus et minus spissum, ut diversetur suum instrumentum quod est lumen: et ita per consequens diversimode moveat materiam ad diversas formas generatorum et corruptorum: haec autem infra latius exequamur. Sed haec dicta sunt secundum sententiam Avicennae et Averrois et aliorum Philosophorum, ut sciatur per tales formas orbis non subjici alicui passioni vel alterationi." Ibid., 125.

Averroës’s De coelo and De substantia orbis. He highlights Aristotle's statement in De anima

that transparency is not a special (propria) characteristic of air or water, but is a property

common to both these elements as well as the heavens. Like density and rarity, however, the

word transparency as applied to the heavens and the earth are equivocal. In the elements,

transparency is due to the parts being mobile and able to flow past one another, which is caused

either by heat dissolving the parts or a lack of the congealing power of cold; this transparency is

not perfect, which is evidenced by the fact that the depths of the sea are dark. In the heavens,

however, the parts don't flow past one another. Instead, transparency arises "from the nature of

the spiritual body" which is simple and indivisible. He says that "ignoble" properties cannot be

present in the heavens, and thus darkness — which after all is merely a state of an imperfect

transparent substance — cannot be present there. The stars arise from condensed portions of this

82

"tenuous and perspicuous" body, and these areas are strengthened and exhibit greater powers

than the rest of the parts of the orb.126

Some of the stars shine with their own light, while others shine due to their "participation

in the solar lumen". In the former, the cause of the shining is their condensation (spissitudo). In

the latter some stars shine by receiving the solar lumen in their depths, while others (such as the

galaxia or milky way, which he says is really just a multitude of small stars) merely diffuse the

lumen from their surface. In either case, Albertus makes it clear that the celestial orbs partake of

lumen differently than inferior bodies. Thus we need to distinguish darkness as a property of a

transparent body, which is an imperfection that is removed once the transparent body is activated

by lumen, from blackness, which is the property of the surface of a body.

Albertus holds that density and rarity are equivocal terms when applied to the heavens

and the earth, and thus he gives second scheme tying density and rarity to transparency on earth,

83

126 "et ubi non est tenue et perspicuum, sicut in stellis, hoc contingit in illo quod confortetur motus eius quod movet forma corporali materiam activorum et passivorum: eo quod stella in orbe est amplioris efficaciae quam caeterae partes orbis: et cum moveat per quantitatem et lumen suum, oportet quod ibi confortetur actus sui instrumenti, et per illud inspissatur ibi sicut patet: quia nisi essent non diaphanae stellae, una non eclipsaret aliam. Hoc totum expressius videtur in luna quam in aliqua aliarum: sed nos de inferius tractabimus in loco ubi de stellis orbis faciemus inquisitionem. Et eodem autem modo dicimus de illuminatione: quia lumen non est proprietas ignis, sed potius accidit igni, siduc [sic] Alexander Peripateticus, cum commiscetur corpori diaphano spissato per aliquam causam: et ideo lumen etiam est forma communis et coelo et quibusdam corporibus non simplicibus: et idoe lumen etiam in quibusdam partibus invenitur, et in quibusdam non: extra stellas enim non lucet orbis, sed lucet in stellis, et in stellis lucet ex participatione lucis solis: et causa lucis in stellis est spissitudo earum: et lumen quidem in aliquibus recipitur secundum profundum ipsarum, et in quibusdam diffunditur in superficie, et in quibusdam recipitur in profundum, et efficiuntur luminaria sicut stellae lucentes et candelae. In quibus autem diffunditur in superficie, efficiuntur candidae et quasi lacteae, sicut est via quae lactea vocatur, quae galaxia dicitur, eo quod ibi sipssior est orbis per multitudinem stellarum parvarum: et sic iterum patet, quod aliter orbis participat lumen quam inferiora corpora. Et similiter est de raro et spisso, quod habet non ex qualitatibus activis vel passivis facientibus constare vel distare partes materiae, sed potius omnia ista sunt consequentia formas separatas quae motum coeli explicant per lumen et perducunt ad effectum: et ideo necesse est coelum esse spissus et minus spissum, ut diversetur suum instrumentum quod est lumen: et ita per consequens diversimode moveat materiam ad diversas formas generatorum et corruptorum: haec autem infra latius exequamur. Sed haec dicta sunt secundum sententiam Avicennae et Averrois et aliorum Philosophorum, ut sciatur per tales formas orbis non subjici alicui passioni vel alterationi." Ibid., 124.

one which is connected to the elemental qualities of hot and cold and their powers to cause

dissolution or prevent it through congelation. Transparency in the elemental bodies is a result of

the parts being able to flow past one another, or to stand together or apart (constare vel distare).

Here we should not necessarily think of density and rarity as primarily related to specific gravity

or even to the idea that more matter is packed into a smaller space. Albertus stresses the mobility

of the parts of a rare substance, and thus constare and distare should be thought of as the parts

standing together as one continuous substance, or being merely contiguous and thus, while

touching, existing more separately.

In his De caelo commentary Albertus also talks about the relationship between heat and

light. Heat, he says, does not always come into being due to something that is essentially hot —

motion and the reflection of rays in burning mirrors are examples where the cause of heat is not

essentially hot.127 (Note that the latter case is shown, he says, in Euclid's Perspectiva.) An

objection from a statement that he attributes to Plato, that "everything generated, is generated by

another similar in species or genera," does not affect his position, because he says this only

applies to the generation of substances, not accidents.128

84

127 "Caliditas enim et lumen deprehensa in stellis non sunt causae quare debent dici igneae: quia caliditas non semper provenit ex hoc quod essentialiter est calidum, cum aliquando proveniat ex motu, et aliquando ex reflexione radiorum ad locum unum, sicut apparet in speculis comburentibus in libro quem Euclides de talibus speculis in sua Perspectiva ascripsit. Cum tamen motus et radii et lumen non essentialiter sint calidi, propter hoc Antiqui fallaci et convertibili crediderunt signo." Ibid., 167-8128 "omne generatur, a sibi simili specie vel genere generari.... Cum autem accidentia generatur, quorum non est per se et proprie generatio, non oportet ista salvari: quia videmus nigredinem aliquando generari a calido, aliquando a frigido: cum igitur calor sit accidens sicut lumen, non oportet hic a sibi similibus specie vel genere produci." Ibid., 168.

Motion, he says, generates heat only in bodies in which motion can loosen part from part

by means of friction.129 That is to say, motion rarefies the body — but again, it seems that

rarefaction is merely to be understood as a fluidity of the parts with respect to one another, along

with the size of those fluid parts; this is the opposite of thickness (spissitudo). In the terrestrial

realm, this loosening of the parts can cause earth, water, and air to lose their form once the

dissolution goes beyond a certain minima, or the minimum size in which the substantial form of

those elements can inhere. Fire is the most subtle of the elements and the one with the smallest

minima, and thus when either friction or fire acts on a body such as air and dissolves it, then the

form of fire can be induced if the dissolution is sufficient. On the other hand, none of this can

occur in the celestial realm, because its nature does not allow the possibility of such a

dissolution.

Albertus holds that the influence of the heavens is not due merely to their motion (which

is one reading of Aristotle), nor to the effects of lumen. One effect of lumen that he says is

manifest to sense is that heat is vigorously created where there is a great deal of reflected lumen,

which is shown by burning mirrors. Here we should note the great influence that the pseudo-

Euclidian text De speculis, and the tradition of burning mirror treatises generally, had on

understanding the relationship between light and heat. In this tradition, heat is generated by the

85

129 "sed tamen motus non habet ubique inducere calorem, sed potius in corpore quod dissolvit motus per confrictionem partis ad partem: propter hoc enim quod dissolvit partes eius, rarefacit eas et disponit ad ignem et calorem: et cum dissolvuntur ultra quam debitum sit formae aeris, vel aquae, vel terrae, tunc dispositio fit necessitas, et inducit igneitatem. Quando autem motus est in subiecto quod dissolvi non potest per motum, tunc non inducit calorem neque igneitatem: et tale corpus est coeli, sicut probatum est in libro superiori." Ibid., 169.

reflection or refraction of many rays directed to a single point.130 Albertus also talks about the

oblique rays in the winter not producing heat when they reflect. Fundamentally, lumen causes

heat by a motion that moves and dissolves material and "moves the body as a whole to a

form”.131 Lumen is not essentially hot, however:

[Lumen] operates through the special effect proper to it, which is to dissolve [what is] capable of being illuminated. But to dissolve is in one way the effect of motion, and in another the effect of lumen: motion indeed dissolves by friction and by weakening part from part; lumen however is in some way the first form of the moving body as a whole, because [lumen] is not disposed by the quality towards which it moves.132

Lumen heats in a different way than, say, friction or fire, insofar as it excites a body’s natural

disposition to heat, and it also excites any spiritual formative virtue that might be contained in

any seminal principle contained in the body.133 Therefore, if the body (such as water) is itself not

disposed to heat to begin with, lumen will not heat that body, and in this way the heat of the stars

differs from terrestrial forms of heat. This notion, it is important to note, recurs in Zabarella and

Fabricius’s account of the purpose of the vitreous humor. (See §§ 4.3, 4.7.)

86

130 "Reflexio autem est causa calores, et quod in reflexione multi radii diriguntur ad punctum unum, ubi proper multiplicatum calorem, aut calet locus, aut in toto incenditur, sicut apparet in berillo vel crystallo, vel forte vitro bene et impleto aqua frigida, quae opposita sibi fortissima illuminatione illuminat unum locum post ipsum: et ad illum fit reflexio radiorum, in quo etiam accenditur ignis, si ponatur pannus combustus et bene siccus, nisi sit ventus impediens fixionem caloris, et remanentiam super idem punctum: vel nisi sit nimis obliquus radius solis incidens in corpus reflectens ipsum, sicut est in hyeme." Ibid., 173.131 “Ad hoc autem quod quaeritur, utrum lumen ex motu vel ex se sit causa caloris? Dicendum videtur, quod non ex motu quo movetur, sed poitius ex motu quo movet et dissolvit materiam et movet eam universaliter ad formam, quia lumen coeli secundum quod huius movet ad omnem forma.” Ibid., 174.132 "[lumen] operatur ipsum per proprietatem effectus sui proprii, qui est dissolvere illuminata passibilia: et quia iste effectus est etiam motus, et ideo motus operatur calorem. Sed dissolvere aliter est effectus motus, et aliter est effectus luminis: motus enim dissolvit fricando et concutiendo partem ad partem, lumen autem est sicut forma prima universaliter moventis corporis, quia non disponitur qualitate ad quam movet." Ibid., 174.133 “Sed lumen coeli vel stellarum super ista vel illa figura respectus stellarum conjunctum cum virtute formativa spirituali quae est in calore excitato per lumen, movet ad hanc speciem aut illam: et ideo dicit Aristoteles in libro de Animalibus, quod in semine est triplex calor, hoc est, elementaris, coelestis, et animae informantis ad virtutem seminis formativam.” Ibid., 74.

Another thing to note is that in the section in his Isagoge to De Caelo et Mundo Albertus

states that the heavens are not colored, because colors are caused by the qualities of the elements.

He either seems to be referring to colors other than white, or perhaps does not include luminous

white as a color properly speaking. In either case his statement would seem to apply to the color

of Mars, for example. The apparent color of heavenly bodies, he says, appears in the same way

that different elemental effects are caused by different celestial bodies, even while those bodies

do not themselves possess those qualities — e.g., in the "manifest" effect that the moon has on

humidity, especially with respect to the tides.134

In his De anima commentary Albertus claims that color has a double being (esse): one

material, and one formal. Some important reasons that he makes this distinction are the

experiments of Avicenna and Avempace: if we are in the dark, while some colored body is

illuminated, we can see the colored body; however, the reverse is not true. This is confirmed with

experiences with mirrors: if the mirror is in the dark, but we are illuminated, we can see

ourselves — but we cannot if the mirror is illuminated but we are not. Thus, it appears that only

the colored body needs to be illuminated, not the medium.135 On the other hand, he points out

that Alexander of Aphrodisias and Averroës (interpreting Aristotle) say that color is per se

87

134 "Videmus, enim, quòd quando luna habet plenitudinem sui luminis, tunc mare excrescit, et in decremento lunae mare descrescit. Unde patet, quòd luna est mater & causa omnis humiditatis. Praeterea dicit Aristoteles in libro de proprietatibus elementorum, quòd quando omnes planetae fuerunt coadunati in signo piscium, factum est diluvium: quando autem coadunati fuerunt in signo geminorum, facta est magna mortalitas Item patet ex praedictis, quòd caelum non est coloratum: quia color causatur ex qualitatibus elementorum." Albertus Magnus, Philosophiae naturalis isagoge, (Vienna 1514), 13-14135 "Experimentum autem est: quia nos videmus, quod vidente existente in tenebris & aere tenebroso iuxta videntem, et tantum colore illuminato fit visio. Si autem e converso fiat color in tenebris, & videns in lumine stet, & aer sit illuminatus, non fiet visio. Similiter autem speculo posito contra lumen, & facie in tenebra, non resultabit imago in speculo. Si autem e converso fiat, statim in speculo videbitur facies. Ista igitur sunt qua moverunt istos, & quaedam alias his similia." Albertus Magnus, Opera, vol 5, 246.

visible, and thus that "the entire cause of vision will be due to [color's] own particular essence,

and not therefore due to admixture of lumen."136

Albertus's dual esse to color is meant to resolve this: the material esse of color exists on

account of the "transmuting qualities" of hot, cold, wet and dry, which affect how the surfaces of

bodies "terminate" with respect to sight. That is, the mixture of the elements determines a body’s

degree of transparency, which appears to be equivalent to how determinate its limit is. The

various ways in which surface-boundaries are determined cause various colors to be induced.

Thus, Albertus’s material esse to color is a way of explaining Aristotle’s definition of color in De

sensu as “the limit of the transparent in a bounded body”, and according to this material esse

colors exist in the dark. However, in order to move the diaphanous, a formal esse of color is

required as well, and this is provided by lumen. Lumen, he says, is the "hypostasis" of color,

which is formed when lumen has penetrated into the extreme boundaries of the perspicuous. In a

determinately transparent body, lumen is mixed together with the opacitas or darkness of the

surface of the body, which causes color to exist in an active sense, i.e., as the movement of a

transparent medium. Thus, Albertus’s formal esse of color accounts for Aristotle’s De anima

“definition” of color. The elemental make-up of a body determines its density and rarity, which

provides the material being of color, while lumen provides the formal being of color. Albertus

writes: "from whence it is clear that lumen is the substance of color, and not heat or cold or the

88

136 “E converso autem Alexander et Averroes innitentes vel intendentes dictis Aristotelis, dicunt colorem esse per se visibile: ergo erit tota causa visionis per essentiam suam propriam: non igitur per admixtionem luminis.” Ibid., 246. Note that Albertus is likely getting his account of Alexander here through Averroës.

rest of the qualities which cause [color] in the subject materially, but do not constitute the

essence itself [of color]."137

89

137 "Nos autem quantum intelligere possumus, utrosque secundum aliquam partem utrum dicere arbitramur: et ut hoc intelligatur, videtur dicendum quod color habet duplex esse, scilicet materiale et formale. Materiale autem dicimus quod sit per qualitiates transmutantes materiam, quae sunt calidum, frigidum, humidum, & siccum: haec enim diversmode variantia superficiem corporis terminati, diversos inducunt & causant colores, licet nihil istorum sit de essentia coloris: et secundum hoc esse colores actu sunt in tenebris, sed non movent diaphanum: quia, sicut superius diximus, sensibile non agit nisi secundum simplicem formam, quando multiplicat se ad medium & ad sensum. Habet autem aliud esse formale, et hoc est a lumine: quia, sicut optime dicit Philosophus, lumen est colorum hypostasis, et hoc causatur ab hoc quod lumen influitur extremitati perspicuis terminatione enim corpus est perspicuum. Sed duplex est perspicuum: quoddam enim est perspicuum totum quod non terminat, sed per se transducit visum, sicut aer, et ignis, et aqua, et vitrum, et crystallus, et quaedam alia simila. Quoddam autem est perspicuum terminatum, et hoc non in toto sed in sua superficie est perspicuum, et ideo terminat & non transducit visum: et secundum quod corpus est perspicuum, ita recipit luminis habitum: quod enim in toto est perspicuum, *non* recipit lumen in superficie et in profundo: quod autem non in toto sed in superfice tantum est perspicuum, non recipit lumen nisi in superficie: & ibi lumen permixtum opacitati corporis, causat colorem. Et haec fuit causa quare Pythagorici colorem vocabant epiphanum: quia videbant eum esse diffusionem luminis in superficie corporis terminati: epiphanum enim est superficie tenus operans: unde patet lumen esse de substantia coloris, & non calidum & frigidum & caeteras qualitates, quae causant ipsum materialiter in subiecto, & non ingrediuntur essentiam ipsius." Ibid., 246–7. Note the “non” flagged with asterisks above is not present in the Jammy edition, and is certainly incorrect. Albertus Magnus, Opera omnia, ed. Petrus Jammy, vol. 3 (Lyon, 1651), 80.

§ 1.6: Conclusion

Io rispuosi: «Madonna, sì devotocom' esser posso più, ringrazio luilo qual dal mortal mondo m'ha remoto. Ma ditemi: che son li segni buidi questo corpo, che là giuso in terrafan di Cain favoleggiare altrui?». Ella sorrise alquanto, e poi «S'elli erral'oppinion», mi disse, «d'i mortalidove chiave di senso non diserra, certo non ti dovrien punger li stralid'ammirazione omai, poi dietro ai sensivedi che la ragione ha corte l'ali. Ma dimmi quel che tu da te ne pensi».E io: «Ciò che n'appar qua sù diversocredo che fanno i corpi rari e densi». Ed ella: «Certo assai vedrai sommersonel falso il creder tuo, se bene ascoltil'argomentar ch'io li farò avverso».

I replied to her: “Lady, I thank Him who has raised me from the mortal world, as devoutly as I can, but tell me what are those dark marks on this planet, that make the people down there on earth make fables about Cain?” She smiled a moment, and then said: “If human opinion errs, where the key of the senses cannot unlock it, the arrows of amazement should certainly not pierce you, since you see that Reason’s wings are too short, even when the senses can take the lead. But tell me what you yourself think about it.” And I: “I think what appears variegated to us up here, is caused by dense and rare bodies.” And she: “You will see that your thought is truly submerged in error, if you listen attentively to the argument I will make against it.”

Dante, Paradiso 2.46–63.138

Dante’s suggestion in the Paradiso that the moon’s blemishes arise from differing density and

rarity was common during his time, and it was an opinion that he himself put forth earlier in his

Convivio, composed between 1304 and 1307.139 There he writes that moon-spots are “nothing

but the rarity of its substance in which the rays of the Sun cannot terminate and be reflected back

as in its other parts”.140 Dante changed his mind before he wrote his Divine Comedy, and in effect

90

138 Translation by A. S. Kline.139 Tamara Pollack, “Light and Mirror in Dante’s “Paradiso”: Faith and Contemplation in the Lunar Heaven and the Primo Mobile,” (unpublished Ph.D., Indiana University, 2008), 145–148.140 Dante, The Convivio 2.13.9. Translation by Richard Lansing.

we are given the reasons for this when he has Beatrice, using the conventions of a scholastic

disputation, correct his initial opinion. Scholars have looked at the issue of density and rarity

with respect to the moon in some depth. Edward Grant has studied this most carefully within

medieval natural philosophy, and several Dante scholars have also addressed this problem.141

However, this analysis is usually restricted to the moon. Grant, who analyzes the terms density

and rarity at some length, writes “For [the medieval scholastics], density was equated with

heaviness and hardness, whereas rarity was identified with lightness and softness. Thus density

and rarity involved three pairs of opposite or contrary qualities.”142 Yet Grant’s summary does

not do justice to the variety of accounts given for density and rarity. The connection to gravity

and levity is not always stressed, and at times this connection is abandoned when, for example

glass is said to be rare because of its transparency. For all his thoroughness, Grant has not

plumbed the depths of this important medieval issue. The connection between density and rarity

and vision before the seventeenth century, and in particular to the question of how color arises in

bodies, has not been carefully studied, but there was indeed a link between the cosmological

question of how to account for difference in the heavens and theories of color and vision. The

issue of density and rarity, furthermore, was in some way connected to almost every aspect of

natural philosophy. What precisely was meant by density and rarity within the long Aristotelian

tradition is still not well understood, and as a result it is sometimes confused with modern

concepts of density and rarity.

91

141 Elizabeth R. Hatcher, “The Moon and Parchment: Paradiso II, 73-78,” Dante Studies, with the Annual Report of the Dante Society (1971): 55–60. Tamara Pollack, “Light and Mirror in Dante’s ‘Paradiso’,” 141–183. Edward Grant, Planets, Stars, and Orbs: The Medieval Cosmos, 1200-1687 (Cambridge University Press, 1996), 428-33, 198-99. This is also treated briefly by Pierre Duhem. For example, see Pierre Duhem, Medieval Cosmology: Theories of Infinity, Place, Time, Void, and the Plurality of Worlds (University of Chicago Press, 1987), 486-7.142 Grant, Planets, 198

We have seen that the belief that the origin of colors is found in the condensation and

rarefaction of matter was not always stressed in ancient Aristotelian commentaries, but was

assumed (although not worked out in any detail) in treatises on mathematical optics. After

Averroës forged the condensation theory using material from these two traditions, this

condensation theory of the origin of color was taken up in the West by some of the most

influential early scholastics, including Roger Bacon and Albertus Magnus. Although there was

some room to maneuver within the condensation theory, its characteristic traits are the following.

(1) That transparency in a body exists due to its rarity, and (at least usually) that rarity in this

sense is not merely the relative position of the parts as Aristotle says in Categories 10a17-24

(i.e., such rarity is not the rarity of a sponge). (2) That the heavens are supremely rare, and fire,

air, water, and earth are successively less rare; the first four are therefore naturally transparent to

varying degrees, while earth is not transparent. (3) That what we see is color, and therefore

because we see difference in the heavens there must be some underlying difference accounting

for the difference in color and luminosity. (4) Since, in the heavens, this difference cannot

involve differences in qualities that give rise to generation and corruption, differences in color (at

least with respect to the presence or absence of the color white) and luminosity appear to be due

to variation in the density and rarity of the heavens. (5) Therefore, the color white is formed from

the condensation of a transparent body, while lux is also formed from the condensation of the

heavens (and, according to some, from the condensation of elemental fire as well). (6) That

darkness in a medium is due to a lack of illumination, and that the color black is due to a lack of

transparency at the boundary of a determinate body. That is, earth is naturally black because it

does not admit illumination into its substance. (7) That the mixture of black and white bodies

92

produces the remaining colors (and not merely gray), and that the ratio of black and white

determines the specific color of a body.

Many other issues remained indeterminate within this tradition, such as the nature and

role of illumination for vision, the precise ontological status of colors in the dark, how exactly

color was propagated through the medium and what its ontological status in that medium was,

how exactly visual perception was supposed to work (both with respect to both the organ of

vision and the visual faculty), and so on. Furthermore, this is not the only explanation for the

origin of color among the scholastics. Another major explanation involved tying the colors to the

elements themselves in some way, particularly in a manner influenced by the pseudo-Aristotelian

De colorbus. Finally, another tactic (following Avicenna and, it seems, Aquinas, rather than

Averroës) appealed to the substantial form of a body as the cause of its color, although this could

also be combined with the condensation theory of color or the elemental theory of color. Much

later Daniel Sennert, for example, will follow Zabarella in appealing to density and rarity in

order to account for the color of the celestial body, the elements, and imperfect mixts, while

resorting to substantial forms in order to account for the color of perfect mixts such as gems,

metals, and the homogenous parts of living beings.

It is not clear how much debate existed over the origins of color within medieval

philosophy, largely because this issue has not been the focus of much scholarship. In the

sixteenth century, however, it is clear that many of these issues were given significant attention.

For example, in the sixteenth century a large number of commentaries on Averroës’s De

substantia orbis were published, including those by some of the most influential natural

93

philosophers at the time.143 It seems that, in the sixteenth century, commentaries on Aristotle’s

De caelo and Averroës’s De substantial orbis most clearly addressed the condensation theory of

color, but in these commentaries only a partial account of color is given; another account would

be given in De anima commentaries, a third in commentaries to De sensu, and so on. The rise of

the natural philosophy textbook in the sixteenth century, however, meant that the questions about

vision and color could be culled from these various commentaries, and be resolved in a single

location.

94

143 For example: Cajetanus Thienaeus, Johannes van Gent and Aristoteles. Super libros de anima. Questiones de sensu agente: de sensibilibus communibus: ac de intellectu. De substantia orbis Joannis de Gandavo cum questionibus ejusdem. per Gregorius de Gregoriis (1505); Agostino Nifo. Commentationes in Librum Averrois de Substantia Orbis (Venice, 1508); Averroës and Ioannem Baptistam Confalonerium, Libellus de substantia orbis ... expositus per Ioannem Baptistam Confalonerium. Eiusdem Io. Baptiste Confalonerii opuscula (In aedibus Francisci Bindoni & Maphei Pasini, 1525); Johannes de Janduno and Averroës, In libros Aristotelis De Coelo & Mundo quaestiones subtilissimae; quibus nuper consulto adiecimus Averrois sermonem de substantia orbis (Apud Hieronymum Scotum, 1552); Averroës and Marco Antonio Zimara, Averrois Cordubensis Sermo de Substantia Orbis: M. Antonij Zimarae in Sermonem de Substantia Orbis Contradictionum Solutiones (Junctae 1562); Niccolò Vito di Gozzi, Commentaria in Sermonem Aver. de Substantia Orbis et in Propositiones de Causis (Iunta, 1580).

Chapter 2: Vision and the Rise of Autonomous Natural Philosophy: Zabarella’s De visu

Yet soon he healed; for Spirits that live throughoutVital in every part, not as frail manIn entrails, heart of head, liver or reins,Cannot but by annihilating die;Nor in their liquid texture mortal woundReceive, no more than can the fluid air:All heart they live, all head, all eye, all ear,All intellect, all sense; and, as they please,They limb themselves, and color, shape, or sizeAssume, as likes them best, condense or rare.1


In 1603 the physician and natural philosopher Santorio Santorio first published his Methodi

vitandorum errorum omnium qui in arte Medica contingunt, or The Methods of Avoiding all the

Errors Touching the Medical Art. In his discussion of the color of humors he criticizes the theory

of color generation held, he says, by Albertus Magnus and Jacopo Zabarella, a theory which

hinges on the idea that transparent bodies are so because they are rare or tenuous, and that

condensing transparent bodies generates the color white, one of the two color-contraries that, in

the Aristotelian framework, are fundamental for color mixture. His criticism, then, is aimed

precisely at the condensation theory whose history was sketched in the last chapter. Santorio

would eventually secure a chair in theoretical medicine at the University of Padua in 1611, but in

1603 his corpuscular and experimental approach to medicine and philosophy marked a

significant shift from most traditional sorts of Galenism and Aristotelianism found in Italian

universities. Santorio writes:

95

1 Milton, Paradise Lost, Book VI, 344–353.

Jacopo Zabarella, in De visu book 1 Chapter 3, says that the diaphanous is made from a tenuous body, and for instance he has the following words: “since the perspicuous is a medium carrying colors to vision it is constituted of these two parts: of a tenuous body as matter, and of lumen as form.” But the opinions of these distinguished men are most manifestly opposed to experience (experimenti). Who does not see that crystal and diamond are exceedingly dense, and not rare or tenuous — and yet they are transparent, and diaphanous. Indeed if crystal or diamond is reduced to a most tenuous powder, is it not the case that the substance of the crystal or diamond, turned into this most tenuous powder, will be more rare, and tenuous? Therefore (if the opinion of Albertus or Zabarella is true, namely that the diaphanous consists of a rare or tenuous material) then the powdered crystal should be more transparent, which is opposed to sense. In addition, if clear, transparent water is agitated until it becomes foam, is it not made more rare? But yet it loses perspicuity. What is more, smoke is exceedingly rare, and nevertheless dark (opacus). Therefore neither rarity, nor tenuity will constitute the diaphaneity of a body.2

Santorio’s own explanation is that color is light itself refracted or debilitated in various ways, a

version of the modification theory of color common among seventeenth-century figures before

Newton.3 Yet what are we to make of his criticism of Zabarella, Albertus and the condensation

theory of the origin of color in general? Santorio received his medical degree in 1582, and

Zabarella was one of Santorio's professors in natural philosophy at Padua. Although Zabarella

96

2 “Iacobus Zabarella libro 1. de visu cap. 3. à corpore tenui fieri diaphanum, habet enim haec verba, "perspicuum quatenus est medium deferens colores ad visum à duobus his partibus constitui, à corpore tenui tamquam à materia, & à lumine tamquam à forma;" quorum excellentium virorum sententiae manifestissimè reluctantur experimentis; quis enim non videt crystallum, & adamentem esse densissima, & non rara, & tenuia, attamen esse transparentia, & diaphana, quinimmo si crystallum, vel adamans in tenuissimum pulverem redegeris, an ne crystalli, seu adamantis substantia facta pulvis tenuissimus erit rarior, & tenuior? ergo (si vera esset sententia Alberti, vel Zabarellae, quod scilicet diaphanum constituatur à raritate, vel tenuitate materiae) pulvis crystalli esset transparentior, quod sensui adversatur: Praeterea aqua transperens, & splendida, si eo usque agitetur quousque spumescat, non ne fit rarior? attamen perspicuitatem amittit: ad haec fumus est rarissimus, attamen est opacus, quare nec raritas, vel tenuitas corporum constituent diaphanum;” Santorio Santorio. Methodi Vitandorum Errorum Omnium Qui in Arte Medica Contingunt Libri Quindecim (Geneva: apud Petrum Albertum, 1603), 112v. Santorio’s quote is from Zabarella, De rebus naturalibus libri XXX, “De visu liber primus”, Cap. III. 3 Discussion of the seventeenth-century modification theories of color can be found in Hideto Nakajima. “Two Kinds of Modification Theory of Light: Some New Observations on the Newton-Hooke Controversy of 1672 Concerning the Nature of Light.” Annals of Science 41, no. 3 (1984): 261–278; and Alan E. Shapiro “Artists’ Colors and Newton’s Colors.” Isis 85, no. 4 (December 1, 1994): 600–630. Contra Shapiro and others, I argue that it is a confusion to label most Aristotelian theories of color modification theories, which are light-centric theories (i.e., color is modified light). Rather, Aristotelian theories of color such as Zabarella’s are mixture theories, and are body-centric.

died in 1589, his posthumous natural philosophy textbook De rebus naturalibus libri XXX

(Venice, 1590) was popular and influential when this criticism was published. Santorio’s one-

time teacher was not only among the most respected natural philosophers in the Peripatetic

tradition, but, as many have pointed out, he was willing to part with Aristotle if experience

demanded it.4 Yet Santorio’s attack was repeated by nearly every seventeenth-century advocate

of the corpuscular or mechanical philosophy. Most notably, Gassendi, Descartes, and Boyle all

considered it devastating to the scholastic account of color generation. How, then, are we to

make sense of Santorio’s easy dismissal of Zabarella’s theory of color generation? How could

Zabarella, especially, have overlooked this apparently simple and obvious empirical refutation of

their ideas?

In his treatise De visu libri duo, first published posthumously in his scholastic textbook

De rebus naturalibus libri XXX as well as in his De anima commentary, Jacopo Zabarella

appropriates the condensation theory of the origin of light and color and its cosmological

motivation. He was certainly influenced by Averroës, Roger Bacon, and Albertus Magnus —

indeed he cites and criticizes them all. However, unlike his predecessors he presents scheme

linking tenuity, color, and illumination for all visible phenomena in a single location, rather than

scattering it across a number of different commentaries. He is also much less certain about the

distinction between celestial and terrestrial light and heat that was important for many

commentators. At times Zabarella suggests that there is no equivocation in the use of these terms:

although the celestial aether is distinct from the elements, nevertheless transparency,

97

4 Charles B. Schmitt, “Experience and Experiment: A Comparison of Zabarella’s View With Galileo’s in De Motu.” Studies in the Renaissance 16 (January 1, 1969): 80–138. Paolo Palmieri, “Science and Authority in Giacomo Zabarella.” History of Science 14 (2007): 404–427.

illumination, and density and rarity all appear to be ontologically identical in both realms.5 His

account of the generation of color is perhaps, therefore, more general than most of his

predecessors in that a single scheme applies to the entire universe. Because his discussion occurs

in the rising genre of the natural philosophy textbook, his account is not scattered across a

number of commentaries to Aristotle’s many works or Peter Lombards Sentences.6 Moreover, his

account is more comprehensive and systematic than that given previous authors. Finally,

although it is thoroughly scholastic, Zabarella’s treatment is also in important respects

humanistic: his discussion relies upon Aristotle’s Greek, incorporates the works of the newly-

available ancient commentators, medieval Arabic sources, and a great number of medieval and

renaissance Latin texts.7 He perhaps as many sources to draw upon as a modern scholar, and his

familiarity and understanding of those texts arguably equals or surpasses that of any era, in part

because he was among the last generation of scholars to take nearly all of Aristotle’s natural

philosophical works as describing nature truly. He stands at the pinnacle of Aristotelianism as a

vital philosophical and cultural force, and his life ended just before many cracks in the

Aristotelian foundation become obvious in the seventeenth-century.

98

5 Note that Zabarella does make a distinction between two kinds of heat in a living body: the one is an elemental head due to the temperament of the elements in a mixed body, and the other is a vital heat due to the animal soul. In book 2, section 3 of the Generation of Animals Aristotle says that the vital heat is “analogous to the element of the stars,” and for this reason Zabarella also refers to this as celestial heat. However, for Zabarella (and unlike many scholastics) elemental and vital heat do not correspond to heat generated by elemental fire and heat generated by heavenly light, respectively. Zabarella, Giacomo, De rebus naturalibus libri XXX, quibus quaestiones, quae ab Aristotelis interpretibus hodie tractari solent, accurate discutiuntur (Venice: Paulus Meiettus, 1590), 278-9, 473, 512.6 Charles B. Schmitt, “The Rise of the Philosophical Textbook,” in The Cambridge History of Renaissance Philosophy, ed. C. B. Schmitt et al. (Cambridge: Cambridge University Press, 1988), 792–804.7 On the availability of ancient texts for Zabarella, see Anthony Grafton, “The Availability of Ancient Works,” in The Cambridge History of Renaissance Philosophy, ed. C. B. Schmitt et al. (Cambridge: Cambridge University Press, 1988), 763–91.

The sixteenth-century was, arguably, the period in which Aristotelian natural philosophy

was at its most vigorous, and if we wish to understand the still-understudied tradition of

renaissance natural philosophy Zabarella’s works are essential. David Lines has shown the

growth in the proportion of the budget given to the natural philosophy faculty at Italian

universities from the fifteenth through the sixteenth centuries, a growth that coincided with an

increase in the prestige and autonomy of its faculty.8 Zabarella is a particularly important

example of the scholastic specialist in natural philosophy that emerged in the sixteenth century.

My primary aim in this chapter is to analyze book 1 of Zabarella’s De visu. I have given a

brief sketch of Zabarella’s life and works and situated him historically and historiographically in

the introduction, but I flesh this out in greater detail below in §§ 2.1 and 2.2. I then give

Zabarella’s account light, color, transparency, and their relationship (§ 2.3), his discussion of the

definition of color (§ 2.4), the generation of real colors (§ 2.5), the distinction between real and

apparent colors (§ 2.6), the meaning he gives to intentional or spiritual species (§ 2.7), and the

relationship between lux, lumen, color, and the eye (§ 2.8). I then return to Santorio’s criticism of

Zabarella, presented at the beginning of the last chapter, and provide some remarks about the fate

of Zabarella’s account of color due to the interlocking changes to concepts of color, light, density

and rarity, vision and the eye, matter, and cosmology in the seventeenth century.

§ 2.1: Zabarella’s Life and Works

99

8 David A. Lines, "Natural Philosophy in Renaissance Italy: The University of Bologna and the Beginnings of Specialization". Early Science and Medicine 6, Nr. 4 (January 1, 2001): 267–323.

Bibliographical details have been presented most recently by William Edwards, Antonio Poppi,

and Heikki Mikkeli,9 and of the three Edwards’s is the most in-depth and original (although at

times his account is marred by a hagiographic tendency). The main sources for Zabarella’s life

come largely from the seventeenth century, but these are not always trustworthy. For example,

Jacopo Filippi Tomasini’s 1630 book on notable Paduans — the Illustrium virorum elogia —

cannot, for obvious reasons, always be trusted.10 A funeral oration for Zabarella by Antonio

Riccoboni, printed in 1590, gives us further information, but nevertheless is limited in its scope

and must be interpreted with caution. According to William Edwards the most reliable

information about Zabarella comes from Luigi Lollino (1557–1624), who wrote down his

recollections of professors at Padua towards the end of his life; this only exists in manuscript,

however, and as I have not been able to consult it I must rely on Edwards’s reading.11 Finally,

because he was born into one of the oldest and most noble Paduan families Zabarella’s

genealogy is well documented. These sources combine to give an official portrait of Zabarella,

but seeing behind this public persona is difficult: there appear to be no extant letters to family or

acquaintances, for example, that might give us a sense of the person beyond his role as a public

interpreter of Aristotle and a member of a noble Paduan family. We know that he rarely left

Padua, and that he spoke with a stutter and thus shied away from public disputations that were an

100

9 William F. Edwards, “The Logic of Iacopo Zabarella” (unpublished PhD Dissertation, Columbia University, 1960) 1-82. Antonino Poppi, La dottrina della scienza in Giacomo Zabarella (Antenore, 1972). Heikki Mikkeli, An Aristotelian Response to Renaissance Humanism: Jacopo Zabarella on the Nature of Arts and Sciences (SHS, 1992).10 Giacomo Filippo Tomasini, Illustrium virorum elogia iconibus exornata (Pasquardus, 1630), 136-140; Giacomo Filippo Tomasini, Gymnasium Patavinum Iacobi Philippi Tomasini Episcopi Aemoniensis Libris V (Udine: Nicolaus Schirattus, 1654).11 Edwards, “The Logic of Iacopo Zabarella,” 13. Although approved for publication, Lollino’s accounts of professors at Padua (ten in all) never were published, and exists only in manuscript form. Ibid., 13. I have not consulted this.

important part of university life, but such tidbits are hardly enough to build a substantial portrait.

In histories of science and philosophy Zabarella is often taken as one of the key exemplars of late

renaissance Aristotelianism, and thus whether his public persona — which is primarily constituted

by his published works — can be taken for the man himself is an important question. I will return

to this topic shortly, but first I will provide a rough sketch of Zabarella from the sources that

have come down to us.

Jacopo (or Giacomo) Zabarella was born on September 5, 1533 in Padua.12 He completed

his doctorate in arts from Padua in 1553, and took up the first chair of logic there in January of

1563 at a salary of 60 florins, succeeding his teacher Bernardo Tomatino.13 What he did in the

interim is not entirely clear, although we find him involved in several literary societies at this

time. He also became a member of the Sacred College of Philosophers and Physicians

immediately after completing his doctorate, and through this he was involved in the University

of Padua in several ways, including being present in the conferring of degrees.14 Zabarella also

inherited the title of count palatine from his father, and from this he had the privilege of

conferring degrees on his own15 (although I am unaware of any evidence that he did so). In 1568

he was appointed second extraordinary chair in natural philosophy, at a salary of 130 florins; in

1577 he moved to the first extraordinary chair in natural philosophy at a salary of 260 florins,

which was increased to 350 florins in 1584; and finally in 1585 he became second ordinary chair

in natural philosophy at a salary of 410 florins, and remained there at the same salary until his

101

12 According to Tomasini he was born at almost half-past noon on September 9, with mercury in a favorable position, which he says explains his mental faculties. Tomasini, Illustrium virorum elogia, 138.13 Edwards, “The Logic of Iacopo Zabarella,” 29; Tomasini, Gymnasium Patavinum, 331. Note that, aside from his birth and death, for many of these dates the sources do not all agree.14 See Edwards, “The Logic of Iacopo Zabarella,” 24-5. 15 Paul F. Grendler, The Universities of the Italian Renaissance (JHU Press, 2004), 183-6.

death in 1589.16 That Zabarella never received the first ordinary chair in natural philosophy can

be explained in part by his being a native Paduan: to prevent nepotism and recruit the best

professors to the University the Venetian senate created statutes prohibiting native Paduans and

Venetians from occupying the first ordinary chairs (although it appears to have been strictly

enforced only for the more prestigious positions).17

His main teachers were Bernardino Tomitano (1517-1576) in logic and his uncle

Marcantonio Genua (1491-1563) in natural philosophy. Sources also say that he studied

mathematics under Pietro Catena (1501–1576), and Lollino says Lazzaro Bonamico was his

teacher in Greek, while others mention Giovanni Fasolo.18 Whatever the case, it is clear that

Zabarella’s thorough engagement with Aristotle and the ancient commentators in Greek

profoundly affected his interpretation of Aristotelian logic and natural philosophy.19 Regarding

mathematics, Tomasini mentions that Zabarella held optics and astrology in high esteem, that he

cast horoscopes for his nine children, and that he also predicted his own death by interpreting the

stars.20 Zabarella’s interest in astrology is highlighted by all other contemporary sources,

including Lollino’s manuscript21 and Riccoboni’s funeral oration. In the latter Riccoboni

102

16 Edwards, "The Logic of Iacopo Zabarella," 30. Note that extraordinary positions were less prestigious and less well-paid than ordinary ones, the title originally referring to whether the professor taught on ordinary days or not. In Padua the actual difference, besides prestige and salary, was that extraordinary professors usually taught during the less desirable afternoon hours. Grendler, The Universities, 144-6. 17 Jerome Bylebyl, “The School of Padua: Humanistic Medicine in the Sixteenth Century,” in Health, Medicine, and Mortality in the Sixteenth Century, ed. by Charles Webster (CUP Archive, 1979), 343–344.18 Edwards, “The Logic of Iacopo Zabarella,” 13-26.19 E.g., see Edwards, “The Logic of Iacopo Zabarella,” 23-24.20 “Opticam enim, & Astrologiam in deliciis habuit, cuius mihi testes praedictiones ipsius variae, quae iam suos eventus feliciter sortitae sunt.” Tomasini, Gymnasium Patavinum, 136-7. “Quibus omnibus ex Natali syderum constitutione vitam, & eventus (quatenus per artem licet) antèquam interiret praedixit...” Ibid., 138. Edwards, writing in 1960, tries to minimize this interest of Zabarella’s, and writes, for example: “Zabarella did not practice astrology in the undesirable sense of that word, the only predictions alluded to by his biographers being those he perhaps only half seriously made for his children, and this is surely nothing reprehensible.” Edwards, “The Logic of Iacopo Zabarella,” 51.21 Edwards, “The Logic of Iacopo Zabarella,” 50.

highlights Zabarella’s study of astrology while describing how he excelled in all parts of

philosophy, and he mentions both Zabarella’s successful prediction of future events as well as the

observation and contemplation of the motion of the stars and planets.22

Although the sources we have often point to Zabarella’s interest in mathematical optics, it

is difficult to say if his knowledge extended much beyond John Pecham’s Perspectiva communis

— which was the typical introductory text in optics at the time, and was published many times

throughout the sixteenth century. He certainly demonstrates nothing original to this field in his

published works. However, Zabarella's account of vision is constrained by his role as a university

professor: his job, he says, is to illuminate and interpret the texts and philosophy of Aristotle.23

As we have seen in the last chapter, reconciling Aristotle's statements on color and vision is

fraught with difficulty, and professing to follow Aristotle as closely as possible does not preclude

innovation. Throughout De rebus Zabarella stresses that he follows Aristotle as far as possible by

proceeding ad mentem Aristotelis. Such a declaration was common at the time (and was made by,

among others, William Harvey), but unlocking what those who made it intended by the phrase is

a complex task. For Zabarella it means, according to Paolo Palmieri, according to Aristotle’s

103

22 "Cumque in omnibus Philosophiae partibus excellentissimum se ostenderit: dici tamen non potest, quantum excelleret in Astrologia, & futurorum eventuum praedictione, quoad incerta rei natura, & Catholicae fidei praescriptum pateretur: quantum in observatione illorum ignium sempiternrum, quae sydera, & stellae nuncupantur: quantum in cognoscendo motu illarum stellarum errantium, quas non immerito Fridericus I maximus Imperator familiae Zabarellae pro Insigni concescit, ut maxiums eius splendor significarentur; quasque merito Iacobus Zabarella contemplabatur, tamquàm in familiae suae Insigni sibi propositas contemplandas, ad principatum celeri gradu currens in Rep. litteraria, familiae Zabarellae maxime congruentem, etiam per Leonem, etiam per Aquilam in eodem Insigni egregie significatum." Antonius Riccobonius, In Obitu Iacobi Zabarellae Patavini Antonii Riccoboni oratio (Padua: Apud Paulum Meiettum, 1590), 6v.23 See Antonino Poppi, “Zabarella, or Aristotelianism as a Rigorous Science,” in The Impact of Aristotelianism on Modern Philosophy, ed. by Riccardo Pozzo, Studies in Philosophy and the History of Philosophy, 39 (Washington, D.C.: The Catholic University of America Press, 2004), 35–63; Dal Pra, Mario, “Una Oratio Programmatica Di Giacomo Zabarella,” Rivista critica di storia della filosofia, 21 (1966), 286–90; Paolo Palmieri, “Science and Authority,” 404–427.

scientific principles.24 This means that when he addressed subjects that Aristotle did not treat, or

where Aristotle is unclear, Zabarella was free to decide what Aristotle might or ought to have

said given the scientific framework developed by the Stagirite. The “scientific framework” of

Aristotle was primarily given in the Posterior Analytics, on which Zabarella made a long and

detailed commentary.25 Additionally, on some points (such as the nature of space) Zabarella

comes to conclusions that certainly go against the letter of Aristotle’s texts, and these seem to be

instances of Zabarella quietly correcting Aristotle. Zabarella appropriated Aristotle's texts and

reconciled them with the knowledge and concepts current in the late Renaissance; he negotiated

Aristotle's sometimes conflicting statements on a topic and attempted to come to a resolution

with the help of the most important auctoritates; and in some cases he rejected Aristotle's

specific solution to a problem in favor of one that he found more appropriate to both Aristotle's

overall scheme and the facts of nature. Proceeding ad mentem Aristotelis thus gave Zabarella a

degree of leeway and potential for novelty.

Zabarella’s major works published before his death are his Opera logica (1578) and a

commentary on Aristotle's Posterior Analytics (1582); he also published some logical tables in

1580 and a response to criticism (primarily by Francisco Piccolomini and Bernardino Petrella) of

his ideas on method in his De doctrinae ordine apologia (1584). His other two works of primary

importance, the natural philosophy textbook De rebus naturalibus libri XXX and a commentary

on Aristotle's De anima, were both published posthumously; the former work, first published in

1590 in Venice, went through at least eleven editions, and the latter, first published in 1596 in

104

24 Palmieri, “Science and Authority,” 404–427.25 First published in 1582 in Venice, and republished individually or as a part of his Logic at least eight times throughout Europe.

Basel, went through at least seven.26 His treatise on vision, De visu libri duo, was published in

both of these popular posthumous works, and thus was widely read.27 Finally, his commentaries

on Physics I, II, and VIII were published in 1601, and republished along with commentaries on

On Generation and Corruption and Meterolology I and IV in 1602. These last works are, to my

knowledge, almost entirely unstudied.

Although it was common at the time for professors in natural philosophy to have medical

degrees, especially at universities with a reputation for medicine such as Bologna and Padua,

Zabarella only had a degree in arts (that is, philosophy). In contrast his rival in natural

philosophy Francisco Piccolomini (1523-1607), who held the first chair in natural philosophy at

Padua from 1565-1598, did.28 Nevertheless, in many ways Zabarella’s career was defined by his

stance towards the art of medicine: Edwards writes that his work De methodis, the most

substantial part of Zabarella’s first publication Opera Logica, was entirely “an attack on the

methodological theory of the medici.”29 As we will see, the second book of De visu is also

primarily an attack on the visual theory of contemporary physicians, and so Zabarella’s

engagement with contemporary medicine and his struggle against many aspects of Galenism

occurred throughout his career and in many different levels, from specific theories to

foundational scientific principles.30

105

26 Charles H. Lohr, "Renaissance Latin Aristotle Commentaries: Authors So–Z," Renaissance Quarterly 35, no. 2 (July 1, 1982): 233 ff.; Edwards, "The Logic of Iacopo Zabarella," 368-373.27 Note that there is one minor difference in the text of De visu as published in the De anima commentary versus De rebus. At the end of Book I Chapter 2, Zabarella discusses Philoponus’s opinion on situations where a body is partly colored and partly transparent. The text in the De anima commentary is shorter, omitting an example clarifying Philoponus’ position.28 Charles H Lohr, “Renaissance Latin Aristotle Commentaries: Authors Pi-Sm.” Renaissance Quarterly, 33 (1980), 626.29 Edwards, “The Logic of Iacopo Zabarella,” 27.30 This is a major theme in Heikki Mikkeli, An Aristotelian Response to Renaissance Humanism: Jacopo Zabarella on the Nature of Arts and Sciences (SHS, 1992).

Zabarella has been of some interest to historians and philosophers of science primarily

for his work in logic. Yet his works in natural philosophy were highly influential, and his

importance north of the Alps in particular has been well established.31 He is perhaps most well

known today for his discussion of the regressus method — a combination of demonstrative and

resolutive methods used in investigating natural phenomena — and the bitter controversy between

him and Francesco Piccolomini concerning the order and classification of the sciences.32 Also

notable is his placement of the science of the soul at the pinnacle of natural philosophy rather

than considering it an intermediary between physics and metaphysics,33 and that Zabarella argues

against using metaphysical principles as the basis of natural philosophy.

§ 2.2: Historiographical Review: Zabarella and “Scientific Method”

Largely due to the claims made by John Herman Randall, Jr., Zabarella has been an important

figure in debates over the origins of the scientific method.34 The question concerns to what extent

Paduan professors in medicine and natural philosophy (Randall’s “School of Padua”) contributed

106

31 Emily Michael, “Daniel Sennert on Matter and Form: At the Juncture of the Old and the New,” Early Science and Medicine 2, no. 3 (1997): 272-299; Ian Maclean, ‘“Meditations of Zabarella in Northern Germany, 1586-1623,” in La presenza dell’Aristotelismo Padovano nella filosofia della prima modernità, ed. by Gregorio Piaia (Roma-Padova, 2002), 173–198; Sachiko Kusukawa, “Meditations of Zabarella in Northern Europe: The Preface of Johann Ludwig Hawenreuter,” in La presenza dell’Aristotelismo Padovano nella filosofia della prima modernità, ed. by Gregorio Piaia (Roma-Padova, 2002), 199–214.32 On the latter, see Nicholas Jardine, “Keeping Order in the School of Padua: Jacopo Zabarella and Francesco Piccolomini on the Offices of Philosophy” in Method and order in Renaissance Philosophy of Nature, ed. by Di Liscia, Kessler, and Methuen (Ashgate, 1997), 183–209.33 Heikki Mikkeli, "The Foundation of an Autonomous Natural Philosophy: Zabarella on the Classification of Arts and Sciences," in Method and Order in Renaissance Philosophy of Nature. (Ashgate, 1997) 220.34 John Herman Randall, “The Development of Scientific Method in the School of Padua,” Journal of the History of Ideas, 1 (1940), 177–206; John Herman Randall, The School of Padua and the Emergence of Modern Science (Editrice Antenore, 1961). Note that Randall’s thesis greatly influenced William Edwards and is followed by William A. Wallace. Schmitt attributes the thesis originally to Ernst Cassirer, Erkenntnisproblem in Der Philosophie Und Wissenschaft Der Neuren, (Berlin 1922), 136-143.

to, or hindered, seventeenth-century scientific methodology, particularly with respect to Galileo’s

writings about scientific method as well as his actual scientific practice. Randall made the strong

claim that Zabarella was just one step away from Galileo and the modern scientific method.

“There was but one element lacking in Zabarella's formulation of method: he did not insist that

the principles of natural science be mathematical, and indeed drew his illustrations largely from

Aristotle's biological subject-matter.”35 Today, in light of the enormous historical and

philosophical literature on the scientific revolution and the scientific method since, Randall’s

claims seem anachronistic and perhaps even quaint. Although it has had some defenders, a

number of direct attacks on his thesis has made it highly questionable.36 Nevertheless, questions

remain concerning the continuity or discontinuity between Zabarella’s teachings and

seventeenth-century thinkers, especially on many specific points of natural philosophy.

Texts have been the main sources when investigating notions of continuity or

discontinuity surrounding the so-called Scientific Revolution, but the conclusions drawn from

these textual analyses are often extended to the mind of the historical actor, and the line between

the content of the texts themselves and the personal views of their authors is often crossed. At

one point in the history of science at least, analyses of texts were, explicitly or implicitly, taken

to be histories of ways of thinking, and thus notions such as incommensurability related to the

minds of the actors themselves. Given Zabarella’s status as an exemplar for late-renaissance

Aristotelianism, it is important to explore how his role as a professor in logic and natural

107

35 Randall, “The Development of Scientific Method,” 204.36 Apart from William Edwards, William A. Wallace has been the most active defender of at least some parts of Randall’s thesis. Against it (to varying degrees) see: Charles B. Schmitt, ‘Experience and Experiment”; Antonino Poppi, “Zabarella, or Aristotelianism as a Rigorous Science”; Nicholas Jardine, “Galileo’s Road to Truth and the Demonstrative Regress,” Studies in History and Philosophy of Science Part A 7, no. 4 (1976): 277–318.

philosophy affected his literary output. Of primary note is that Zabarella took his role as a

professor that of a public interpreter of Aristotle, and in this regard his stated role was precisely

not to be an original thinker.37 Clearly, however, this does not preclude novelty; any claims that

one is following Aristotle as closely as possible cannot be taken at face value, and indeed the

history of philosophers “recovering the authentic Aristotle” can be seen precisely as a means to

give authority to new ideas and theories.

It is known that Zabarella had interests that went beyond his published works. Later on I

will attempt to pierce beyond the veil of the published text and see, at least to some extent,

Zabarella as someone who was curious and interested in the active investigation of nature. By all

accounts it appears that, in his stated method for scientific demonstration (derived from

Aristotle’s Posterior Analytics), experience was largely used to confirm what was already known

via demonstration from first principles. It is also clear that being a public interpreter of Aristotle

looks very different from our notions of modern science. But it does not necessarily follow that

his notion of natural philosophy should be directly opposed to that of later thinkers such as

Galileo any more than a modern epistemologist, philosopher of science, or Aristotle scholar

today should be opposed to modern science.

Nevertheless, to the extent that he believed that natural philosophy is an entirely

theoretical or speculative discipline, that using the methods of demonstration outlined in

Aristotle’s Posterior Analytics are more certain than any practical art, and that the proper goal of

108

37 In this I agree with Paolo Palmieri’s argument that “Zabarella achieved a lucid separation between allegiance to reason and allegiance to Aristotle’s authority, within the constraints of the Aristotelian framework. Zabarella, in other words, fully realized that he could freely practice natural science [scientia naturalis] according to Aristotle’s mind [ad mentem Aristotelis], suspending the question of whether Aristotle’s pronouncements could be reconciled with the truth of the matter.” Palmieri, “Science and Authority,” 404.

natural philosophy, which is knowledge itself, is more noble than any practical art — to this

extent Zabarella is certainly against the spirit of later thinkers such as Galileo and Francis Bacon.

Active investigation and manipulation of nature was not prohibited by Zabarella. In fact he

actively investigated nature himself and was attuned to the growing body of experiment and

observation in the sixteenth century, particularly, as we will see, in anatomy. For Zabarella,

experiment was another thing altogether from natural philosophy, the latter being a

demonstration of the truths about the natural world and not a method for discovering them. One

final issue that is closely related to this is the question of Zabarella’s attitude towards practical

disciplines, in particular medicine and anatomy.38 I will treat this in chapter four, which focuses

on the relationship between anatomy and visual theory in Zabarella and Fabricius.

While it is almost certainly true that Zabarella cannot be considered a forerunner of

modern science, whether he should be considered hostile to the Scientific Revolution (however

defined), or retrograde in some other sense, is another issue. The interpretation, appropriation, or

rejection of his works by later thinkers, on the one hand, and how his teachings fit into his own

context, on the other, should be the subject of separate analyses. The latter is my primary focus in

this chapter, but I will address to the former in the conclusion to this chapter and, at greater

length, in Chapter 5.

§ 2.3: Light, Color, and Transparency in De Visu

109

38 For example, in the Complete Dictionary of Scientific Biography we read the following: “He was an orthodox Aristotelian who defended the scientific status of theoretical natural philosophy against the pressures emanating from the practical disciplines, that is, the art of medicine and anatomy.” Heikki Mikkeli, “Zabarella, Jacopo (Giacomo),” in Complete Dictionary of Scientific Biography, vol. 25 (Detroit: Charles Scribner’s Sons, 2008), 387.

As mentioned, Zabarella’s writings on natural philosophy have not been sufficiently analyzed by

modern scholars, and apart from a tantalizing note by Charles Schmitt Zabarella’s De visu has

been largely neglected.39 Zabarella's treatise on vision consists of two books. De visu is found

both in his natural philosophy textbook De rebus naturalibus, first published in 1590, as well as

in his De anima commentary, which was first published only after his death by his son Francesco

Zabarella in 1606.40 This commentary also includes several other books related to the soul taken

from De rebus, likely included by Francisco with the aim of perfecting the unfinished

commentary.41 These books are inserted just after his commentary on similar sections of

Aristotle’s De anima, and thus the content often overlaps. In addition to the two books of De visu

(inserted after Zabarella’s commentary on 419b4, in which Aristotle discusses vision), these

books are De mente humana (inserted after 413a9) De partitione animae (413b24), De

facultatibus animae (415a14), De sensu agente (418a6), De speciebus intellibibilibus (429b10),

De mente agente (430a25), and De ordine intelligendi. The last book follows immediately after

De mente agente, with no further commentary in between and with no commentary afterwards.

Zabarella’s De anima commentary, therefore, ends with the issues raised in Aristotle’s

notoriously cryptic passage in III.5 on that part of the rational soul which is impassive, immortal

110

39 In a footnote in his oft-cited article "Experience and Experiment," Schmitt points out Zabarella’s personal anatomical observation of the eye, which he uses as evidence against the Galenic theory vision. He writes: "This is by no means a unique example of the use of information learned from anatomical dissections in arguments concerning natural philosophy and sensory psychology during the I6th and early I7th centuries. I plan to treat this topic in greater detail elsewhere." Charles B. Schmitt, "Experience and Experiment,” 97, n. 40. However, he never appears to have followed up on this.40 Zabarella, Jacopo, Commentarii Jac. Zabarellae Patavini, In III. Aristot. Libros de Anima: Nvnc Demvm a Mendis Qvamplvrimis Typographicis, quae priore editione irrepserant, summo labore purgati, & in Germania commodioribus & distinctioribus typis in Studiosorum vtilitatem editi. Cvm Indice Qvaestionvm Dvbiarvm, Propositionum, Rerum & Verborum locupletissimo, apprimeque necessario (Frankfurt: Zetznerus, 1606).41 Jorge Leoncio Soler, “The Psychology of Iacopo Zabarella (1533 - 1589)” (Ph.D. Dissertation, State University of New York at Buffalo, 1971), i-ii,

and unmixed with matter. Although I will not treat the topic here, it is important to remember

that Zabarella’s treatment of vision was ultimately a part of understanding psychology and the

rational soul, of which the most important and controversial issue among scholastics was the

mortality of the rational soul.42

The aim of the first book of De visu, Zabarella says, is to present Aristotle's true opinion

on vision, while the aim of the second is to defend this account against other theories, especially

those of Galen and Plato but also the ancient atomists. As previously mentioned, the second book

will be treated in Chapter 5. The rest of this chapter is an analysis of book 1.

After a brief proemium,43 Zabarella notes that any treatment of vision must account for

three intertwined aspects, namely the object of vision, the transparent medium, and the organ of

vision.

Concerning Aristotle’s thoughts (sententia) themselves that will be shown [below], we will preserve this order: namely, since he himself judged that vision is made through [1] the action of the object [2] in the organ of vision [3] through a transparent medium, we will treat all these one by one, and we will resolve every one of the difficulties that arise, so that in the end we will understand, according to Aristotle, how vision takes place from the conjunction of those three. Therefore first the object, which is color, will be treated according to the instruction (praeceptio) of Aristotle, understanding the nature and generation of it, in order to better recognize why, and in what way the medium and the sensitive organ is affected by color.44

111

42 A more complete account of this is Soler, “The Psychology of Iacopo Zabarella.”43 See Appendix 2 for a translation of De visu, book 1, Chapter 1.44 “In ipsa autem Aristotelis sententia delcaranda hunc ordinem servabimus: quum enim ipse existimaverit visionem fieri per actionem obiecti in organum visus per medium perspicuum, de his omnibus singillatim agemus, & eas, quae in singulis orientur, difficultates solvemus; ut tandem quomodo ex eorum trium concursu secundùm Aristotelem visio fiat intelligamus. Primùm igitur de obiecto, qui color est, iuxta Aristotlelis praeceptionem dicendum est; ut eius naturam, & generationem intelligentes, melius cognoscere possimus, cur, & quomodo à colore medium, & organum sensus afficiatur.” Jacopo Zabarella, De rebus naturalibus libri XXX, quibus quaestiones, quae ab Aristotelis interpretibus hodie tractari solent, accurate discutiuntur (Venice: Paulus Meiettus, 1590), 600.

Note that the technical term object here, obiectum, comes from the verb obiico, obiicere — to

throw before, oppose, or present. Considering color as an object of vision, then, implies its status

in relation to a perceiver, rather than its nature considered in itself (and one certainly should not

interpret “object” here with it’s more common modern meaning as any visible or tangible thing

itself). As we will see Zabarella will treat color both per se and according to its relationship to

the perceiver. This is a common distinction made by scholastics, but one that seventeenth-century

opponents of scholasticism, as well as scholars of the seventeenth-century, often mischaracterize.

Moreover, this consideration of the three aspects of vision — color, the transparent medium, and

the eye — is significant because Zabarella claims that a failure to attend to the eye itself has led

many of his predecessors to give faulty accounts of light, color, transparency, and their

relationship. Finally, I would like to point out the phrase iuxta Aristotlelis praeceptionem —

according to the instructions of Aristotle — that Zabarella uses here, which shows Zabarella

embracing his role as a public explicator of Aristotle. Zabarella’s preface here conceals the fact

that in many ways he is moving well beyond what Aristotle himself says. This includes the use of

the lux/lumen distinction throughout his analysis, the adoption of the condensation theory of the

origin of color, and an explication Aristotle’s definition(s) of color in which he says, in the end,

that Aristotle did not give a definition of color per se, but an account of color that is only partly

per se and partly with respect to vision.

The most significant way in which Zabarella moves beyond the text of Aristotle,

however, is Zabarella’s careful attention to recent developments in ocular anatomy, the results of

which are central to his treatise on vision. Zabarella himself emphasizes that Aristotle had not

112

treated ocular anatomy in any detail.45 In Chapter 4 I will argue that Zabarella likely followed

Fabricius in his account of the parts of the eye. Because the two Paduan professors shared not

only the same account of the parts of the eye but also the same theory of vision (both of which

are original to them, although embraced by many of their students and readers), there must have

been some interaction between the two that resulted in their shared theory. Zabarella treats the

eye and its relationship to visual theory at much greater length in book 2, in the course of

showing that Galen was wrong about both the anatomy of the eye and his theory of vision. Here I

am merely interested in showing how Zabarella uses ocular anatomy — again, about which

Aristotle himself fails to give any detailed account — in his argument for what the correct

“Aristotelian” positions on light, color, transparency, and vision should be. Thus, acting

“according to the instructions of Aristotle” means, in this context, primarily following Aristotle’s

prescription that a full analysis of vision must include accounts of the object, the medium, and

the eye.

§ 2.4: The Definition of Color

At the beginning of book 1, Chapter 2 Zabarella notes that Aristotle appears to give two

definitions of color. This is an issue that is frequently raised by commentators, a problem whose

resolution can have significant ramifications for the ontological status of color and the other

113

45 De visu 1.8: “apud Aristotelem vero nihil tale notare aliquis quantumvis lividus advesarius eius potest, qui semper à rebus alienis abstinuit: & non modo illa, quae ad aliam disciplinam, sed etiam quae ad alium eiusdem disciplinae librum perinent, tractare veritus est: quod quidem est manifestissimum in tractatione ab eo facta de visu, & facultate visua: diligentem enim oculi, & constructionis eius declarationem apud Arist. nullibi legimus, licet oculus ex pluribus humoribus, & pluribus tunicis, aliisque partibus mirabili structura, atque artificio constitutus sit: nihil enim aliud de oculi fabrica ab eo scriptum habemus, nisi eum aqueam esse debuisse, non quidem aquam puram, sed excessu aqueum, quim enim in 1, cap. 2. libri de Partib. animal. dixerit organa sensuum debere esse similatia, totus autem oculus sit corpus dissimilare, Aristoteles praecipuam oculi partem respexit, quae est humor, crystallinus, in quo tanquam in vero visus istrumento species coloris recipitur, & ab anima iudicatur.” Zabarella, De rebus, 613.

sensible properties.46 As Zabarella relates, in De anima Aristotle says that color is a motion of the

actualized transparent: “color est motivus perspicui, quod sit actu.”47 That is, a potentially

transparent medium, such as air or water, becomes actually transparent due to the presence of

lumen, after which point a certain kind of change in the transparent medium, which is called

color, can be brought about. De anima commentaries sometimes mention this as a definition of

color — that color just is a body’s ability to move the actualized transparent and affect vision (an

almost Pythagorean stance) — but as far as I can tell this is nearly always rejected.48 Zabarella,

likewise, rejects this De anima account as a definition or a description of the essence of color,

and claims that Aristotle did not intend it to be one. He points to Book III of the Physics where

Aristotle analyzes what the nature of motion is. There Aristotle distinguishes between something

“being” simpliciter and that thing “being as”: it is one thing for some mass of bronze to be, and

another for it to be a potential statue. This distinction is used to understand the difference

between something being, and for that something to potentially be in motion. “We can

distinguish between the two [i.e., being simpliciter and being “as”] — just as colour and visible

are different — and clearly it is the fulfilment of what is potential as potential that is motion.”49

114

46 Note that Zabarella does not believe that the De coloribus, now believed to be pseudonymous, was written by Aristotle, and as evidence for this he points out that there is no definition of color in De coloribus. Before him Julius Caesar Scaliger, at least, held this as well (believing that it was written by Theophrastus) but the authenticity of De coloribus was far from being universally questioned.47 Zabarella, De rebus, 601. This comes from DA 2.7, 418a27–b3. “Whatever is visible is colour and colour is what lies upon what is in itself visible; ‘in itself’ here means not that visibility is involved in the definition of what thus underlies colour, but that that substratum contains in itself the cause of visibility. Every colour has in it the power to set in movement what is actually transparent; that power constitutes its very nature.” 48 For example, this is mentioned (though not advocated) in: Conimbricenses and Aristotle, Commentarii Collegii Conimbricensis Societatis Iesu, In Tres Libros De Anima Aristotelis Stagiritae (Cologne: Zetznerus, 1603), col. 222 A. Two figures often cited on this question are Pythagoras in connection to color being an epiphany and Avempace’s opinion (as related by Averroës) that there are no colors in the dark.49 Phys, 201b5.

Visibility, then, is color insofar as it has a potential to be seen. The De anima “definition” is,

Zabarella says, an aptitude of color, which (citing Themistius and Simplicius) he calls visibility

or the ratio of the visible. Visibility is an accidens proprium of color: it is a property invariably

united to something but not a part of its essential definition, such as the capacity for laughter in

humans. Color as “a motion of the actualized transparent” is therefore a description of a power of

color, a power relative to the medium and to vision.

Thus visibility is an aptitude of color considered with respect to the faculty of sight, and

it cannot be the absolute nature of color.50 For Zabarella, color does indeed have an absolute

nature, and this exists in a body regardless of whether that particular patch of color in it is

currently affecting a transparent medium or vision itself. In contrast with the account given in De

anima, Aristotle's account in De sensu is, Zabarella says, a true definition: color is the limit (or

border) of the bounded transparent: "color est extremitas perspicui terminati". Later on Zabarella

will clarify this further; while being as outwardly uncritical towards Aristotle as possible, he will

say that even what Aristotle gives in De sensu is not, strictly speaking, a definition of color

considered absolutely, but rather a definition of visible color with respect to itself.51 This last,

115

50 “per hanc proprietatem definiri colorem, non quidem absolutè ut color est, sed ut visum respicit, & visibilis dicitur; ideò si ea est vocando definitio, non est talis definitio, per quam absolutè sumpta coloris natura declaretur, sed est descriptio quaedam tradita per posteriora, & pro occasione sufficiens; quum enim non alia ratione ibi de colore agatur, quàm ad declarandam ex sua operatione facultatem animae visuam, satis fuit declarare nomen coloris prout visum respicit, & quatenus visibilis est;” Zabarella, De rebus, 601.51 “Non est autem ignorandum definitionem hanc partim dici posse coloris absolute considerati, partim ad visionem relati: ipsae nanque secundùm se nullum respecum notat, nam dicere extremitatem perspicui terminati non est respicere visum; dicitur tamen ea ratione definiri cum respectu, quatenus color absolutè sumptus non minus in profundo esse videtur, quàm in superficie, ut albedo non minus in profunditate substantiae lactis, quàm in eius extremitate; attamen non est visibilis nisi color superficiei; hunc igitur solum definit ibi Aristotelis: buum enim ibi in sensuum consieratione versetur, ad eum non pertinebat definire alium colorem, quàm eum, qui visibilis est; definit ergo colorem visibilem, sed definit ipsum secundùm se, & absolutè consideratum, non tamen alio consilio, quàm gratia visus; quodcirca est modo aliquo definitio respectiva, & dicere possumus notari in ea respectum ad visum, sed respectum remotum;” Zabarella, De rebus, 605.

rather subtle, distinction relies on Zabarella’s explication of color considered absolutely, which is

a property that exists as much in the depths of a body as it does at its surface.52 Notably, there

appears too little to draw upon in Aristotle’s works themselves for constructing such a definition,

and thus we can see how Zabarella understands his job as a public explicator of Aristotle. After

beginning with an analysis of Aristotle’s De anima and De sensu considered in light of the

Posterior Analytics, he draws upon the Aristotelian tradition (especially Averroës) in order to

give the best “Aristotelian” understanding of color, after which he squares Aristotle’s text with

his own conclusion. We will return to Zabarella’s final analysis of the definition of color later on;

for now, we merely need to note that this distinction between absolute color and visibility

provides Zabarella with a basis for his analysis of the origin of color and the real-apparent

distinction. In the hands of some authors, the real versus apparent distinction can be arcane, but

understanding Zabarella on this issue is rather straightforward once his account of color is

understood.

§ 2.5: Generation of Real Colors

Taking the De sensu definition of absolute color as his starting point, Zabarella then makes the

distinction between real and apparent (or spiritual) color, beginning with the definition of real

color. He rejects the notion that colors come from the elemental qualities of hot, cold, wet and

dry. He does so because the celestial body, which lacks these qualities (and so is not susceptible

to generation and corruption) is nevertheless visible, and because the object of vision is color the

stars and planets are therefore colored. Zabarella takes for granted that the heavens are

116

52 Note Zabarella’s discussion of this precise point is addressed at length by Justin Broackes, “Aristotle, Objectivity, and Perception,” in Oxford Studies in Ancient Philosophy (Oxford: Oxford University Press, 1999): 57–113.

immutable, that color is the object of vision (and thus that vision is only affected insofar as there

is color), and that color is the limit of the transparent; it follows, then, from the fact that we see

heavenly bodies, that color cannot be exclusively tied to the elementary qualities or the elements

alone. The celestial and terrestrial realms, however, have the property of perspicuity in common.

Zabarella thus describes how color is generated from perspicuous matter:

Indeed, because the perspicuous is that which, on account of the tenuity of its parts (partium tenuitatem), vision passes through and does not terminate, from whence it is called indeterminate, it is necessary that, if the perspicuous should be thickened (incrassetur) and condensed (condensetur), such that vision ceases to pass through, and is terminated, and vision is not allowed to extend further through its interior substance, then the perspicuous being lost, [vision] should receive color from that place in its surface which terminates and moves vision.53

Zabarella clearly follows the condensation theory of the origin of color that was outlined in the

last chapter; however, his account is more thorough and systematic, and his discussions of all the

relevant aspects of color and vision occur at one place. This is a consequence of the textbook

format that he adopted, and thus the move away from commentary format as the natural

philosophy gained autonomy as a discipline makes it easier to find and understand an author’s

position in such a work.54 This has implications for the way in which Aristotelian natural

philosophy would be read and criticized later on in the seventeenth century.

As with some of the authors discussed in the previous chapter, Zabarella holds a

peculiarly material explanation for perspicuity. Both color and perspicuity arise from a

117

53 "quoniam enim perspicuum illud est, quod propter partium tenuitatem transparet, nec visum terminat, unde etiam interminatum appelatur; necesse est ut, si perspicuum incrassetur, & condensetur, ita ut definat transparere, & visum terminet, nec sinat ulterius per intimam eius substantiam porrigi, tunc amissa perspicuitate colorem loco eius recipiat in superficie, quo moveat ac terminet visum:" Zabarella, De rebus, 602.54 Charles B. Schmitt, “The Rise of the Philosophical Textbook,” in The Cambridge History of Renaissance Philosophy, ed. C. B. Schmitt et al. (Cambridge: Cambridge University Press, 1988), 792–804; Lines, David A., “Natural Philosophy in Renaissance Italy: The University of Bologna and the Beginnings of Specialization,” Early Science and Medicine, 6 (2001); 267–323; Lines, David A., University Natural Philosophy in Renaissance Italy: The Decline of Aristotelianism? (Brill, 2002).

disposition of the parts that make up a body. This differential thickness or compactness can also

occur in the aether, a homogeneous body that is not capable of undergoing substantial change.

Zabarella says that the heavens are made thick (fit densum), and they differ only by greater and

lesser density or rarity. Not all colors arise from this celestial thickening, but only degrees of

shining white, which, says Zabarella, just is lux.55 Thus the moon, in addition to being the least

condensed and therefore the most perspicuous of the heavenly bodies, is also the least self-

luminous.

Zabarella criticizes previous authors, and Averroës in particular, for not clearly pointing

out that density and rarity are used in two senses. In Chapter 9 of De accretione, & nutritione in

De rebus he takes Averroës to task for apparently contradicting himself in the use of density and

rarity — although Zabarella does not mention that in his commentaries Averroës is merely

following Aristotle’s conflicting accounts.56 Zabarella also rejects the opinion, given by the

Paduan natural philosopher Marcus Antonius Zimara (d. 1475/6), that density and rarity are in

fact only in the category of quality, and that changes in quantity are merely a consequence of

condensation and rarefaction. Zabarella’s opinion is that in one meaning of the terms density and

rarity are in the category of quality, which consist of a “tenuity of substance, not a distance of the

parts among themselves, and is numbered among the second qualities following from heat and

118

55 "ex una enim & eadem corporis natura constant coelestia omnia, nec differunt, nise per maiorem, vel minorem raritatem, seu densitatem: & quo densiora sunt, eo magis colorata sunt, hoc est, magis lucida; nullus enim alius est coelestium color, quam albedo splendens, quae dicitur lux, & quo densiora sunt, eo magis alba, ac lucentia sunt." Zabarella, De rebus, 602.56 "Averroës enim variis in locis de raritate loquens varia, & inter se pugnantia pronuciare visus est: nam illo comment. 84. inquit, rarum & densum esse contraria in quantitate; tamen in comment. seq. 85. ait raritatem & densitatem non esse de essentia quantitatis. In 7. autem Physic. comment. 15. inquit, raritatem & densitatem esse qualitates. Sed in 1 Metaphys. comment. 15. easdem locavit in Categoria situs, quae videtur etiam Aristotelis sententia fuisse, in lib. Categoriarum, cap. de Qualitate. At in comment. 77. libri 8. Phys. dixit rarefactionem & densationem esse motus locales. Magna igitur est horum locorum discrepantia, quum Averroës motum ad raritatem modo dicat esse ad quantitatem, modo ad qualitatem, modo ad situm, modo ad ubi." Zabarella, De rebus, 548.

cold”.57 The other use of density and rarity refers to the distance of the parts of a substance

among themselves, and thus requires interstitial matter filling such void spaces; this is the

density and rarity of a sponge, and this is in the category of situation.58

In addition to the aether, three of the elements are naturally perspicuous to varying

degrees, with water being the least perspicuous and fire, which is "exceedingly fine (tenuissimus)

and invisible," the most. (See Appendix 1.) These substances can themselves undergo

condensation only if they are combined with some other dark, dense material — that is, with earth

or with some substance that contains earth. Zabarella distinguishes between the generation of

color due to imperfect mixture and that due to perfect or true Aristotelian mixture. When

condensed (presumably with only a minimal amount of earth in the mixture) water and air

become white, while fire, on account of its greater tenuity, becomes not only white but bright and

shining (lucidis et splendens).59 The degree of natural tenuity prior to condensation is thus linked

with how shining, i.e., lumen-producing, the condensed product is: aether is the most lumen

generating, fire less so. These considerations recall Aristotle's Meteorologica IV, and perhaps to a

lesser extent Aristotle's material considerations in De partibus animalibus and De generatione

119

57 "omnis enim rarefactio est transitus ad maiorem quantitatem, seu potius ad maiores terminos quantitatis, non tamen primario, sed secundario, & per quandam comitantiam, seu consequutionem; per se autem, & primo non est ad quantitatem, sed ad aliquod aliud, quod maior quantitas consequitur. In reliquis autem puto deceptum esse Zimaram, quia non animadvertit duplicem esse raritatem, & duplicem densitatem; quarum una est proprie in Cagegoria qualitatis, quia consistit in tenuitate substantiae, non in distantia partium inter se, & est de numero secundarum qualitatum consequens calorem & frigus, ut ait Aristoteles in libro secundo de Partib. anim. cap I & Averroës in 7. Physic. comment. 15 & in 2 de Generat. 15 & ibidem Ioann. Grammaticus in context. 17.” Zabarella, De rebus, 549.58 "Altera est raritas, quam non videtur animadvertisse Zimara, quae non consistit in tenuitate substantiae, sed in distantia partium inter se; quemadmodum spongiam raram esse dicimus, quia partes habet invicem distantes per spatium vacuum interpositum, non quidem vere vacuum, quod omni corpore careat, sed quod alio tenui, in insensili corpore plenum est;" Zabarella, De rebus, 549.59 Zabarella, De rebus, 602.

animalibus.60 Additionally, a good number of the explanations for phenomena in the upper

atmosphere are attributed to condensation in chapters 4 and 5 of Meterology I; Zabarella cites

these sections of Meteorology later in De visu, and thus it almost certainly had an impact on his

description here. The odd additional factor, however, is the link between tenuity, transparency,

and luminosity — that a naturally tenuous body, once condensed, gives rise to lux. This suggests a

sort of material link between the nature of the celestial body and the nature of fire, a similarity in

terms of configuration or disposition even though they are composed of fundamentally different

substances.61 Given that this explanation extends through both the celestial and terrestrial realms,

specifying what sort of qualitative change occurs between transparency and whiteness, rarity and

density, tenuity and lux, is difficult. It is not easy to bring it in line with Aristotle's Categories,

120

60 For a discussion of the connection between material necessity and the relationship between Meterology IV and Aristotle's biological works, see: Gill, Mary Louise. "Material Necessity and Meteorology IV“. In Aristotelische Biologie, edited by Sabine Follingerand and Wolfgang Kullmann (Stuggart: Franz Steiner Verlag, 1997), 145–161.61 In book 1, Chapter 3 (“De perspicuo”) Zabarella writes: "Quod ad partem materialem attinent, ea nihil aliud est, quam corpus aptum recipere in sua substantia, & lumen, & aliarum rerum colores: praestare autem hoc non potest, nisi sit pervium, idque est id, quod vocamus perspicuum sive transparens, pervium autem esse non potest, nisi habeat substantiae tenuitatem, ut per eam possit lumen intima penetrare, nam tenuitati opponitur crassities, ac densitas, quae impedimento est receptioni luminis, & coloris introrsum, quia facit terminationem, & colorationem in superficie." Zabarella, De rebus, 606.

for example, and it also not easy to reconcile with some statements in De caelo.62 This latter

point is interesting given that Zabarella rejects Aristotle's position, which the latter presents in De

caelo and De generatione, that the Sun generates heat and light only through the friction of the

celestial bodies upon the sub-lunary regions.63 (Zabarella’s account of how lumen produces heat,

an essential topic for his account of the function of the parts of the eye, will be dealt with in §

4.3.)

In addition to whiteness and lux being generated through condensation, the elements can

also generate color through their combination, either through composition (that is, juxtaposition

of discrete parts) or through true mixture (i.e., as described in Aristotle's De generatione and

Meteorology IV).64 Zabarella's exemplar of color-by-composition is a candle flame, which allows

one to observe the gradations of color and lux that arise due to both the commingling of the

121

62 For example, at 270a15 Aristotle writes: "It is equally reasonable to assume that this body [of the heavens] will be ungenerated and indestructible and exempt from increase and alteration, since everything that comes to be comes into being from its contrary and in some substrate, and passes away likewise in a substrate by the action of the contrary into the contrary, as we explained in our opening discussions. Now the motions of contraries are contrary. If then this body can have no contrary, because there can be no contrary motion to the circular nature, seems justly to have exempted from contraries the body which was to be ungenerated and indestructible. For it is in contraries that generation and decay subsist. Again, that which is subject to increase increases upon contact with a kindred body, which is resolved into its matter. But there is nothing out of which this body can have been generated. And if it is exempt from increase and diminution, the same reasoning leads us to suppose that it is also unalterable. For alteration is movement in respect of quality; and qualitative states and dispositions, such as health and disease, do not come into being without changes of properties. But all natural bodies which change their properties we see to be subject without exception to increase and diminution. This is the case, for instance, with the bodies of animals and their parts and with vegetable bodies, and similarly also with those of the elements. And so, if the body which moves with a circular motion cannot admit of increase or diminution, it is reasonable to suppose that it is also unalterable." See also 289a20: "The warmth and light which proceed from them are caused by the friction set up in the air by their motion." Zabarella, on the other hand, rejects this explanation of celestial heat.63 Zabarella’s rejection of Aristotle on this point is discussed in Palmieri, Paolo. "Science and Authority in Giacomo Zabarella". History of Science 14 (2007): 415-17.64 “vel enim per solam compositionem sine vera mistione, vel cum vera mistione, quae est mutatio naturam elementorum in naturam misti” Zabarella, De rebus, 602. For an overview of the problem of mixture in the Aristotelian commentary tradition, see Rega Wood, and Michael Weisberg. "Interpreting Aristotle on mixture: problems about elemental composition from Philoponus to Cooper." Studies in History and Philosophy of Science 35 (2004): 681–706.

elements as well as condensation and rarefaction. At the base of the flame, Zabarella says, the

earthy vapors are crowded together with fire, although the vapors have not been fully changed

(mutatur) into fire, and the flame is therefore turbid and less white; he compares this to hot coal

or iron, in which bits of fire are interspersed through a material of great thickness. A composition

consisting of dark earth and shining white fire gives rise to luminous colors different from black

and white. At the upper part or tip of the flame, the fumes eventually pass away and are changed

into fire. This part of the flame is also condensed by the surrounding cold, and thus because it is

less rare, and more pure, the flame becomes more white, and more shining.65

On the other hand, in a true mixture the nature of the elements is not conserved, but

rather changed (mutantur) into the nature of the mixt. The fire that forms an ingredient in such a

mixture loses its capacity to generate lux upon being condensed, and for this reason Zabarella

says that such perfect mixts attain color, not splendor. Nevertheless, something of the nature of

fire can remain, and this explains the shining eyes of animals and other glow-in-the-dark things

that Aristotle mentions in book 2 of De anima.66 In this rather unclear passage in Aristotle

discusses weakly luminescent bodies that are visible in the dark but that, nonetheless, do not

cause any other bodies to become visible, and that furthermore have a color different from that

which appears in daylight. There are two primary ways that this passage was read. Aristotle says

that such phenomena are “something like color.” One reading of this passage takes the role of

light to be only the activation of the transparency of the intermedium. If such bodies produced

122

65 Zabarella, De rebus, 603.66 "Quando autem fit vera vera elementorum mistio, in qua non servantur elementorum naturae, sed mutantur in naturam misti, ignis non amplius splendet, quia desinit esse ignis, quare mistum adipiscitur colorem non splendentem, contingit tamen in aliquibus, ut, licet veram habeant mistionem, tamen aliquid lucis retineant ex igni commisto, cuiusmodi sunt oculi quorundam animalium, & noctilucae, & alia, quorum mentionem facit Aristot. context. 72. lib. 2. de anima, quae, quum noctu luceant, videntur in tenebris;" Zabarella, De rebus, 603.

light they should cause other bodies to be visible, or at least should cause that body’s own proper

color, observable in daylight, to become visible. Because this is not the case, this reading holds

that Aristotle had a difficult time explaining these phenomena, and that he is forced to include

such shining bodies as second special objects of vision in addition to color, and that such shining

bodies (whose shine, according to De sensu 437b1-15, arises from their smoothness) are indeed

visible in the absence of light.67 Zabarella follows the second way of interpreting this passage,

and he does not consider these phenomena to be a reason to posit a second special object of

vision in addition to color. Rather, he attributes it to what happens when the ingredients of a mixt

body have some fire but very little earth: a faint lux is formed from the condensation of the fire,

but this shining is overwhelmed in daylight and thus is only seen in the dark. Furthermore, this

lux is not seen as purely white because it is weak, and so it does not reveal the true color of the

body; it is for this same reason that some stars appear other than white.68 It is worth noting that

this seemingly trivial question was a cause of some consternation at the time. The fact that

Zabarella himself spends almost three-hundred lines (three and a half double-column folio pages)

in his De anima commentary making sense of noctilucae (things that glow in the dark) seems to

indicate a weak spot arising from the strict distinction between color and light in the Aristotelian

123

67 From De anima 418a26: “The object of sight is the visible, and what is visible is colour and a certain kind of object which can be described in words but which has no single name; what we mean by the second will be abundantly clear as we proceed.” Later, at 419a1-10, Aristotle writes “Not everything that is visible depends upon light for its visibility. This is only true of the ‘proper’ colour of things. Some objects of sight which in light are invisible, in darkness stimulate the sense; that is, things that appear fiery or shining. This class of objects has no simple common name, but instances of it are fungi, horns, heads, scales, and eyes of fish. In none of these is what is seen their own proper colour. Why we see these at all is another question.” Also note that Aristotle mentions this in De sensu, 437b1-15, where he says “Things which are smooth have the natural property of shining in darkness, without, however, producing light.” This passage is, like the above, rather incomplete and open to many interpretations.68 Jacopo Zabarella, Commentarii Jac. Zabarellae Patavini, In III. Aristot. libros de anima (Frankfurt: Zetznerus, 1606), cols. 584C-585C.

framework for vision. Zabarella exerts some effort to smooth over these cracks.69 (Fabricius is

preoccupied with noctilucae as well, which we will see in the next chapter, and they play an

important role in seventeenth-century changes to accounts of light and color.)

Zabarella concludes from this account of the generation of color that lux, white, and the

perspicuous are therefore of the same nature — a nature that is shared across the three elements as

well as the celestial aether. The condensation of substances with this nature causes that nature to

be expressed in different ways. Likewise, darkness (tenebra), black, and the opaque are of the

same nature, as they all terminate sight. Lux and tenebra are contraries, as are white and black. A

mixture of the elements — whether perfect or imperfect — gives rise to the variety of colors we

experience, including luminous ones. This mixture occurs through both the condensation of the

perspicuous (aided by the admixture of earth) as well as due to the mutation that results as a

result of the perfect mixture of substances possessing the contraries perspicuous/white and

opaque/black. This process results in the real colors that exist at the visible surfaces of bodies.70

In an interesting aside, Zabarella says that Parmenides confirms the idea that black or opacity is

natural to earth, while white and perspicuity are natural to the other elements. Zabarella is, it

seems, deriving this from Aristotle’s Physics book 1, part 5. There we read “All thinkers then

124

69 Zabarella, In de anima, cols. 581-7. Zabarella’s solution is as follows: “Dicimus ergo, has omnes differentias prvenire à natura perspicui, variis enim modis acceptum haec omnia facit, nam si purum sit, & interminatum, & vere perspeicuum, sic est receptivum luminis, & coloris in tota sua substatnia: hoc idem sit condensetur, desinit esse transparens, & fit terminatum, proinde coloratum, & loco perspicuitatis colorem adipiscitur, cumque vel non lucentem (si condensatio perspicui fiat sine mistione cum opaco) vel lucentem (si fiat sine admistione opaci, vel saltem cum pauci opaci admistione) & hic videtur esse duplex, alius enim est ita lucens, ut ex se sine externo limine illuminet alia; alius vero non ita fit lucens, sed per externi luminis receptionem lucidus fit, & rutilans, quae differentia oritur ex diversitate naturarum elementorum.” Ibid, cols. 582F-583B. For a broad but superficial history of luminescence, see Edmund Newton Harvey, A History of Luminescence from the Earliest Times Until 1900 (American Philosophical Society, 1957). 70 “Haec igitur est illorum colorum generatio, qui solent appelari reales; album enim & nigrum sunt proprii colores elementorum, & per elementa competunt mistis, tum ipsimet colores extremi, tum omnes medii, qui ex elementorum reali commistione oriuntur in mistis.” Zabarella, De rebus, 604.

agree in making the contraries principles, both those who describe the All as one and unmoved

(for even Parmenides treats hot and cold as principles under the names of fire and earth) and

those too who use the rare and the dense.”71

§ 2.6: Real versus Apparent Colors

Given this account of the generation of color in bodies, Zabarella’s discussion of real versus

apparent color is relatively straightforward. Just as mixture of the contraries black and white can

occur in bodies, likewise a mixture of visible species can occur in the medium; these colors are

truly colors, but they are not real colors because the colors that are created through the mixture of

species might not represent the colors inhering in the surface of a body. The real versus apparent

distinction does not hinge on any deception of the eye, because in both cases the eye truly

receives the species of color that it appears to receive — and indeed, the eye receives nothing

except species of lux and color (although we only perceive lux, i.e., lumen, insofar as it is joined

with the color white). The real versus apparent distinction is merely relevant to a judgment about

the color of bodies themselves that are seen: real colors inhere in determinate bodies, and if the

form (or ratio) of the color perceived turns out to be the same as the body that appears to be

colored then we say that we perceive a real color; it the color we perceive arises from a mixture

of visual species in the medium then we say that we perceive an apparent color. In either case,

however, we are accurately perceiving the species that is presented to our visual faculty, even, it

seems, in the case of a jaundiced eye: if the species of color entering the eye are mixed with

yellow within the eye itself, it is indeed this mixed species that is presented to the faculty of

125

71 188a19–26.

vision, and so our faculty of vision itself does not err. This is not a question about reliability of

the faculty of vision or the inherent deceptiveness of one ontologically distinct class of color, but

about the faculty of judgment and the circumstances in which is reliable. It must be stressed that

it is decidedly not a question about the ontological status of the color as it is received by the eye.

Many prominent seventeenth-century opponents of Aristotelianism, as well as some recent

scholars of the seventeenth century who are too trusting of their historical actors,72 have either

mischaracterized the scholastic position or have taken the Jesuit account of this distinction as

representing all scholastics. For the Jesuit account we can look at François d’Aguilón (Franciscus

Aguilonius), whose influential Opticorum libri Sex (Antwerp, 1613) seemed to have set the stage

for later accounts and criticism of the real-apparent distinction. There he writes that there are

three kinds of colors. True and real (veri ac reali) colors are those in a body arising either from a

mixture of the elements or according to the specific form of a substance. Intentional or notional

colors, emanate (emanare) from a self-luminous body and are carried across a medium (like heat

propagating from a fire). These are extremely tenuous compared to the first kind of colors, and

are propped up by the first kind. Fantastical or apparent colors, finally, come together in the

medium, and Aguilonius says that apart from lumen there is no truth (“praeter lumen nullam

aliam veritatem habeant.”). Rainbows and the like are in this third category.73 Aguilonius’s

discussion of the truth and falsity of colors themselves seems to have been common to the

Jesuits, but as far as I can tell was not typical apart from them, and I have not been able to

decipher what is intended by the statement that apparent colors “hold no truth apart from lumen.”

126

72 Most recently, see Ofer Gal and Raz Chen-Morris, Baroque Science (University of Chicago Press, 2013). This is developed at length in § 5.4 below.73 François de Aguilón, Francisci Agvilonii E Societate Iesv Opticorvm Libri Sex (Ex officina Plantiniana, 1613), 45.

Seventeenth-century figures such as Descartes often read the Jesuits as typical of all scholastics,

and he certainly seems to have done so here (and may have misinterpreted the Jesuits as well).

Whether figures such as Descartes did so deliberately, merely through carelessness, or perhaps

due to something like the incommensurability of scholastic and mechanistic approaches, is an

important question. (Certainly, that Descartes was educated by Jesuits does much to account for

his understanding of scholastic theories of light, color, and sensation.) I will briefly point out the

implications of this at the end of this chapter, and will take up the historiographical issues this

raises in some detail in my concluding chapter.

Zabarella's primary example of the distinction between real and apparent (or spiritual)

colors is not the rainbow or the neck of a pigeon, which are sometimes discussed in this context,

but the sun at sunset. The sun is truly white, but at sunset it appears red because the species of

white coming from the sun are mixed with the opacity contained in the dark, earthy fumes

present in the air; we are not deceived insofar as we see red, but only insofar as we judge the sun

itself to be red.74 The difference between the real and apparent distinction also relates to the

colored body that moves the medium into producing color, that is, the ultimate cause of the

species of color. The color of wine is a real color because it is the limit of the transparent in the

wine itself that causes the intermedium to take on the color of red. When we see it directly, we

see its real color. If one shines light through a phial of wine so that a red color is projected on a

white linen sheet, when we look at that red spot, according to Zabarella, it is not the white sheet

itself that is the agent of color change in the medium and in our eyes. Rather, the agent causing

127

74 "non ideo dicitur apparens: quia falsa sit illa apparentia, nam visus non decipitur, dum iudicat se rubedinem recipere: rubedo enim revera est, quae recipitur, & est genita ex commistione specierum, quemadmodum diximus: quod si iudicaret ex ea visione Solem esse rubeum, utique deciperetur, quia non est in Sole color ille, sed generatur in aere ex commistione luminis Solis cum aere atro, & participe tum opacitatis, tum perspicuitatis." Zabarella, De rebus, 604.

the red color that we perceive is still the wine, which projects a species (or spiritual color) onto

the linen.75 This is shown by the fact that a change in position of the wine, but not the linen,

causes the red image to move, and no matter how long that red species is projected onto the linen

the physical color of the linen itself is unchanged. This, according to Zabarella, is the distinction

between a “spiritual” or intentional quality and a real quality: if one were to heat up the linen, a

real quality would be transferred to it, and if it were heated sufficiently the real heat transferred

would cause it to ignite. Similar to how our eyes receive spiritual species of color, if we touch a

hot body the spiritual quality of heat is transferred through our nerves into the common sense in

the brain. When this happens, however, the nerves, the brain, and the common sense do not

become actually hot, just as the linen does not become actually red. That our flesh might actually

become hot is, in some sense, incidental to the sensation of heat itself.

§ 2.7: Intentional or “Spiritual” Species

The issue of intentional species in medieval philosophy is exceedingly complicated. I will

discuss this only briefly here,76 and in what follows I rely mainly on James B. South’s analysis of

Zabarella on intentionality and Jorge Soler’s PhD dissertation on Zabarella’s account of

psychology.77 The notion of intentional objects appears to have been introduced into the Latin

128

75 “Differt autem realis color à spirituali, quia realis pendet omnino à subiecto, in quo est, & ad eius motum movetur, ut color vini, & color lactis, & color sanguinis; at color spiritalis pendet ab agente, à quo producitur, nec movetur ad motum subiecti, in quo recipitur, ut color in linteo panno productus à vini in phiala existentis, ad motum enim phialae movetur, sed non ad motum panni lintei: in hoc autem exemplo patet colorem spiritalem, quando recipitur in corpore aliquo terminato, posse in medio speciem suam producere, & per se videri; sic enim fit per se terminativus visus.” Zabarella, De rebus, 604.76 For a general discussion of intentional or spiritual species, see: Katherine H. Tachau, Vision and Certitude in the Age of Ockham (Brill Archive, 1988); Dominik Perler, Ancient and Medieval Theories of Intentionality (BRILL, 2001).77 James South, “Zabarella and the Intentionality of Sensation,” Rivista di storia della filosofia (2002): 5-23; Soler, Jorge Leoncio, “The Psychology of Iacopo Zabarella,” 131-147.

West through Avicenna,78 but the exact meaning of “intentionality” ever since has been a matter

of heated debate. Zabarella discusses intentional or spiritual species in his Liber de sensu agente,

placed just before his De visu libri duo in De rebus (and present in his De anima commentary as

well). In it he rejects the notion that an external agent sense is needed to turn sense objects (e.g.,

colors present in bodies and in the medium) into sensed objects (e.g., perceptions of colors) in a

manner similar to how an agent intellect is needed to turn objects of the imagination into objects

of the intellect.79 The notion of an agent sense was introduced by Averroës over the worry that a

lower, more material form could cause the existence of a higher, more immaterial or spiritual

form — that the material objects of sense could cause the existence of the more spiritual objects

of cognition. Zabarella argues that the animal faculties have all the powers necessary for

sensation to occur, and that animals do not need an external power to “spiritualize” these

material objects. Furthermore, he also rejects Thomas Aquinas’s notion that intentional species in

the medium are “immaterial” or “spiritual” in the sense that they are more like separated spiritual

substances, or beings that do not require a material substrate for their existence, i.e., God and the

angels. In Thomas’s scheme, it would be absurd to believe that a lower, material accident could

generate a being so metaphysically elevated that it has less dependence on matter than its cause.

Zabarella resolves this dilemma by saying that the objects of sense produce likenesses of

themselves that are “spiritual” or “immaterial” in the sense that they are debilitated entities

(minor entitas) compared to their causes, and that they are “tenuous things” (res). Thus, the use

of “spiritual” to describe intentional species on the one hand and angels on the other is equivocal.

129

78 Richard Sorabji, “From Aristotle to Brentano: The Development of the Concept of Intentionality” in Aristotle and the Later Tradition, ed. by Henry Blumenthal and Henry Robinson, Oxford Studies in Ancient Philosophy (Oxford: Clarendon Press, 1991), 236–37.79 The notion of an agent intellect was introduced in response to comments by Aristotle in Book III, Chapter 5 of De anima.

This tenuousness of the sensible species is best understood in through the case of sound:

species of sound are not emanations of matter, nor are they merely the air between the object and

our ears, as is shown by the fact that wind does not destroy our ability to hear. Species of sound

are thus not material in the sense that they inhere in a particular body. Nevertheless, species of

sound are a kind of movement — a vibration (tremor) — of matter and so require a material

substrate.80 Odors are the most material, while colors are the most spiritual, and thus the most

tenuous, of sensible species: they have the most debilitated being and thus are both least affected

by wind and also have the least effect on the matter in which species of colors exist. (Recall the

impermanent effect of the red species of wine on the white linen, which is in stark contrast to the

permanent effect of spilling that wine on the linen.) Zabarella also points to the sensation of heat:

if a small flame is very briefly allowed to heat a piece of iron the change in warmth will be

nearly imperceptible, but if that same flame is brought to our hand we will instantly feel it, even

if the warmth of our hand itself (a measured by another hand) changes imperceptibly. Zabarella

concludes that, in addition to the real heat generated by the flame, an “immaterial” (that is,

extremely tenuous) species of heat is also impressed.81

The “intentional” aspect of species, for Zabarella, has to do with the soul. Intentionality

here means a “turing towards” the object by the soul, its attention (attentio). The soul, by

attending to the species of color present in the eye, is itself the cause of the objects of

imagination in the soul (including color, shape, etc.). The sensitive soul does not just passively

suffer the impressions of the objects of sense (as Aristotle seems to portray sensation), but it

actively creates those sensations by turning its attention to the subtle activity occurring in the

130

80 Soler, “The Psychology of Jacopo Zabarella,” 144.81 Soler, “The Psychology of Jacopo Zabarella,’ 137.

sense organs. The activity in the crystalline humor is merely the occasion for soul to generate an

entity in the soul that represents the objects presented to it, but this mental object is different

from the image in the crystalline humor numerically, specifically, and generically. The soul, it

seems, is like a painter creating a representation of something presented to it. Zabarella does not

seem to specify how exactly this works, however. If this representation is not a passive

impression but an active generation, what does it generate this representation from if not

something impressed upon it? What is the efficient cause of the sensation in the soul? Zabarella

says that the efficient cause is the soul itself judging the species,82 and he points to the fact that,

when distracted by our thoughts, we often fail to see what is happening before us (that is, we fail

to attend to the transient effects on the matter in our eyes). Perhaps more importantly, Zabarella

does not specify what guarantees the veridicality of this representation. In an account where

species impress their forms on a passive sense faculty, as for Aristotle himself, this veridicality

seems more straightforward.83 In Zabarella’s philosophy, it seems that what it means to represent

or be a likeness of something cannot be further unpacked: there just are representations or

likenesses, i.e., things that intrinsically refer to other things.

§ 2.8: Lux and Lumen

The majority of the rest of Book I is taken up with the distinction between lux and lumen and the

question of whether lumen is required for the sake of the medium (that is, to turn the dark,

131

82 “Primum enim ab actione obiecti matetrialis sit in organo receptio speciei, ut coloris in oculo; secundo anima iudicium profert, et ita agere dicitur; tertio recipitur iudicium in toto composito, nempe organo animato, et ita anima tanquam eius pars dicitur pati.” Zabarella, De rebus, 598.83 For an overview of these issues, see: Peter King, “Rethinking Representation in the Middle Ages: A Vade-Mecum to Medieval Theories of Mental Representation,” in Representation and Objects of Thought in Medieval Philosophy, ed. by Henrik Lagerlund (Ashgate, 2007), 81–100.

potentially perspicuous medium into actually perspicuous medium) or for the sake of the colors

themselves (to excite colors into sending their species through the medium). After presenting a

multitude of arguments pro and con on the various positions — primarily discussing Averroës’s

commentary on De anima, Avempace’s position (via Averroës’s commentary), and the position

of Albertus Magnus, Zabarella presents his own view. He reconciles the various solutions and

argues that lumen is necessary for both the color of the body and the medium — and that it is also

necessary for a third item: the eye itself. What unites these three things that are necessary for

vision is that they all partake in perspicuity. Real colors inhere in the determinate perspicuous,

while spiritual or apparent colors inhere in the indeterminate perspicuous. The indeterminate

perspicuous (i.e., the medium) cannot receive (or, as Zabarella says, “suffer”) the species of color

without lumen — but similarly, the determinate perspicuous cannot move the perspicuous unless

it is joined to lumen.84 In each case, lumen is the perfection of the transparent. In addition to

Zabarella’s ability to negotiate a position among the various authorities, as well as his need to

reconcile Aristotle’s conflicting statements on a topic, here we also see a desire for symmetry in

his account of nature, a trait that he displays elsewhere.

Again, we see Zabarella reconciling reason, authority, and experience. There are several

examples from experience that, Zabarella implies, any theory of vision needs to take into

account. The first is the fact that, when some surface of a body is in darkness while the

surrounding air is illuminated — for example, when the surface of a body is parallel to the source

132

84 "ita neque terminatum potest habere colorem motiuum perspicui, nisi iunctum habeat lumen" Zabarella, De rebus, 617.

of illumination — then the colors are not seen.85 This is used to argue that lumen in the medium

alone is insufficient, and that the colors themselves require illumination. The second is that,

when looking out through a dark cave, the colors of bodies outside penetrate into the darkness of

the cave, even when the darkness is such that the walls of the cave are entirely invisible for lack

of light. Combined with the first, this seems to imply that the air itself does not require the

activation of lumen. Zabarella also relates an experience he attributes to Avicenna:

This opinion is confirmed by an experience from Avicenna: if one is in a very dark place where there is a hole, one sees through the hole those external colors; therefore those [colors] pass through the dark air, for which reason lumen is not required for the illumination of the medium, but it is enough if colors themselves are in lumen.86

These experiences suggest the position of Avempace, that lumen is required for color alone. On

the other side, the arguments Zabarella marshals for the view that lumen is required for the

medium alone rely either upon authority (most prominently statements by Aristotle in De anima),

133

85 “De colore ostendendum manet quòd ipsum quoque illuminari oporteat, si debeat esse motivus perspicui; hoc quidem satis per experientiam manifestum esse videtur: nam si totus intermedius aer illuminatus esse statuatur, & color sit in tenebris, non videbitur; contrà verò si color sit illuminatus, videbitur ab oculo in spelunca in tenebris existente, & per multum quoque aeris medii tenebrosi: num autem hoc argumento ostendatur solam coloris illuminationem ese necessarium, ut putavit Avempace, ita ut absque medii illuminatione vision fieri possit;” Zabarella, De rebus, 619.86 “Confirmatur haec opinio ab Avicenna per experientiam; si quis enim sit in aliquo obscurissimo loco, ubi sit foramen, videt per foramen illud externos colores, igitur illi transeunt per aerem tenebrosum, quare non requiritur lumen ad medium illuminandum, sed satis est si colores ipsi in lumine sint;” Zabarella, De rebus, 614. Note that, although this might suggest an experience similar to a camera obscura, not only are the terms themselves lacking from this passage, but indeed it is not about projection of color against a wall. Rather, Zabarella describes the observer looking directly out through the hole. This will be discussed at length in later chapters.

upon previously accepted demonstrations about the nature of light, or upon arguments from the

nature or definition of color. On this point, at least, he does not appeal to experience.87

Zabarella’s final account is a reconciliation of these two positions, which, he says, is

similar to Albertus’s position with the additional requirement that lumen is necessary for the sake

of the organ of sight as well as the medium and the colored surface. In Zabarella's account of

Albertus’s position, lumen is formally joined to the surface of a body, thus giving the colored

surface a new form and causing color to propagate through the medium — that is, lumen gives

color new properties, causing it be more like lumen. As we saw in the last chapter, For Albertus

the matter of color is the density and rarity of a body, while the form of color is the illumination

by lumen. In Zabarella’s own account, rather, lumen is united with color at the surface and

propagates together with color through the medium and into the darkness of the eye. Color and

lumen, however, have each their own form, and so color and lumen are not joined as matter and

form, but merely joined and propagated together. In this sense it is quite similar to Alhacen’s

account of how color and light are joined. This union allows for color and lumen to be distinct

entities, a requirement that both experience and authority demand from Zabarella, but it also

allows him to account for the example of the cave, the dark room with a hole, and the eye itself,

134

87 At ibid., p 615 he presents the position of Averroës, who according to Zabarella accepts Aristotle's account of color in De anima as a true definition, and argues that color is per se visible because visibility is included in the definition of color in secundo modo dicendi per se. The basic idea here is that, in De anima, color is defined as a motion of the actualized transparent, but that such a motion (as Aristotle says) only has the power of either affecting the sense of vision, or else affecting another body such that it affects vision. Thus, the definition of the predicate is included in the subject, and color is per se visible in secundo modo. He also presents the opinion of Albertus Magnus, who argues that color has a dual being (esse): one material, and one formal. The material being is brought about through a mutation of matter which occurs during a mixture of the four elements. This material being is not, however, able to effect a change in the medium on its own. The formal being of color, which is the ability to move the transparent medium, is acquired when lumen is joined to this material surface. As I explain below, this position of Albertus is similar to Zabarella's own, but not exactly.

all the while avoiding some of the problems associated with color itself acquiring a new form, or

color itself not having the characteristic of affecting a transparent medium..

In the middle of his discussion of the nature of lux and lumen and their relationship to

color, Zabarella has a chapter (Chapter 8) titled “On the Instrument of Vision.” Here he briefly

describes the shape, size, arrangement, and clarity of the parts of the eye, in which he relies on

accurate, up-to-date anatomical observations on the eye. He goes into an account of the purpose

of the parts of the eye at greater length in book 2 of De visu, and my treatment of this in Chapter

4 will likewise be more in-depth, but it is necessary to point out how Zabarella relies an accurate

description of the eye in order to demonstrate conclusions about the nature of light and color. The

primary reason Zabarella introduces this here is to show that the sensitive part of the eye, the

crystalline humor, is analogous to a person standing in a dark cave. Thus, for Zabarella the

primary model of the interior of the eye is not the projected image inside a camera obscura, but

rather that of a body endowed with the faculty of vision placed in the middle of a dark room or

cave, looking out upon the light and color of the world. We will see that the darkness of the eye

and its interior surfaces play a crucial role in Zabarella's account of the usefulness of the parts of

the eye, an account that is similar in many of its particulars to the one Fabricius gave ten years

after De rebus was published. They both have in mind a dark room with a hole through which the

colors of the world stream forth, but this is a very different sort of dark room compared Kepler’s

camera obscura. For now, however, we should emphasize that Zabarella introduces an account

of the eye in order to show how previous philosophers have failed to give a complete account of

light, color, and vision according to Aristotle: they expound upon on the object of vision and the

transparent medium, but they neglect the instrument of vision, the eye. As he writes at the very

135

beginning of his treatise, “since he [Aristotle] himself judged that vision is made through [1] the

action of the object [2] in the organ of vision [3] through a transparent medium, we will treat all

these one by one, and we will resolve every one of the difficulties that arise, so that in the end we

will understand, according to Aristotle, how vision takes place from the conjunction of those

three.” (See § 2.3 above.) The eye that he treats in this chapter, however, is an eye that has been

thoroughly informed by the developments in dissection and anatomy that were currently taking

place in Padua. He therefore uses detailed, cutting-edge knowledge of anatomy to resolve

abstruse debates about the nature of color, lumen, and perspicuity.

§ 2.9: Conclusion

With the eventual collapse of the Aristotelian cosmos during the seventeenth century the initial

motivation for the condensation theory of color generation disappeared. Furthermore, the radical

rethinking of matter that arose from many quarters — from alchemy/chymistry, mechanics and

the study of falling bodies, and the mechanical philosophy — rendered the color scheme

advocated by Zabarella difficult to follow, at the least. In particular, terms like density and rarity

underwent radical changes throughout the seventeenth century, and stable, well-defined (and

more nearly modern) senses of the terms seem to settle down only after Newton. We still have

vestiges of usage with the specific terms optical density and rarity, which are now divorced from

the usage that refers to either specific gravity or thickness of substance. The notion we have of

optical density and rarity, however, was once the more primary sense of the terms, being both

ontologically (on the Aristotelian account) and experientially more fundamental. With continuing

experiments and refinements in concepts of matter, however, it seems inevitable that so many

136

diverse phenomena would fail to be captured by a single term. Perhaps equally important was the

radical shift in not only the configuration, but especially the matter of the heavens. It was no

longer relevant to show how a homogenous substance incapable of generation or corruption can

give rise to a variety of manifest qualities (not to mention varied occult astrological powers).

Without this key cosmic aporia positioned at the center of theories of color, the remaining pieces

no longer fit so neatly; the whole apparatus seems to have turned cumbersome, ad hoc, and

perhaps even unintelligible. Indeed, although parts of both Zabarella’s account of vision were

compatible with later theories — particularly with respect to unification of light and color and the

incorporation of the latest results in anatomy — his account of color generation was to be roundly

rejected in the seventeenth century in favor of a corpuscular theory of color. Francis Bacon,

Gassendi, Descartes, Hobbes, Boyle, and Hooke, and many others all rely on a modification

theory of light, wherein light, which is by default white, becomes colored once the light iteslf is

altered through its interaction with matter due to reflection and refraction.88

We can now return to Santorio’s criticism of the condensation theory of color. Unlike

Santorio and, it seems, the majority of writers on the origin of color until Newton, Zabarella and

Albertus did not take the examples of foam and crushed glass as paradigmatic for the origin of

color. Yet they were far from ignorant of these examples. They would have encountered the

essentially the same description of the whiteness of foam and ground glass in two of their most

important authorities: Aristotle and Avicenna. In the On the Generation of Animals 2.2, we read:

It is not only the liquids composed of water and earthy matter that thicken, but also those composed of water and air; foam, for instance, becomes thicker and

137

88 For modification theories of light and color, see: Hideto Nakajima, “Two Kinds of Modification Theory of Light: Some new observations on the Newton-Hooke controversy of 1672 concerning the nature of light.” Annals of Science 41, Nr. 3 (1984): 261–278. Alan E. Shapiro “Artists’ Colors and Newton’s Colors.” Isis 85, Nr. 4 (1994): 600–630.

white, and the smaller and less visible the bubbles in it, the whiter and firmer does the mass appear. The same thing happens also with oil; on mixing with air it thickens, wherefore that which is whitening becomes thicker, the watery part in it being separated off by the heat and turning to air (pneuma).89

Even more similar to Santorio’s description is that found in Avicenna, who uses the same

examples of foam and crushed glass, and just like Santorio he also says that whiteness here arises

from a multitude of small reflections:

Therefore every traversable or diaphanous body, when mixed with air and reduced to somewhat small parts, will be made white — such as when froth occurs and when glass is crushed and similar things. This happens because the entering light falls upon many small surfaces which do not appear when they are separated [from one another], but appear when they are conjoined.90

However, his purpose is quite different than Santorio’s: for Avicenna, this an example of an

apparent color, one which is formed from an arrangement of small parts. The quality of

whiteness does not inhere in the substance of the glass or water, and what one sees is the

whiteness of the source of light itself, not the whiteness of the body. Although Avicenna does not

analyze this in terms of density and rarity, he does put this change in the category of situation,

which, as we have seen in Zabarella, was only one form of density and rarity. Santorio’s

dismissal of the condensation theory of the origin of colors, then, is due to his rejection of the

kind of density and rarity that the scholastics cared most about, which is also the only kind of

density and rarity possible in the Aristotelian celestial realm. Santorio, in fact, explicitly states

138

89 735b8-30. On Aristotle’s use of pneuma in this passage, see the introduction and appendix to Aristotle, Generation of Animals, trans. by Arthur Leslie Peck (London; Harvard University Press: Cambridge, Mass., 1943).90 “Si ergo omne corpus pervium vel diaphanum, quando admiscetur ei aer et reducitur in partes modicas, efficitur album, sicut aqua quando fit spuma et vitrum quando conteritur et similia, fit istud propterea quod lux penetrans cadit super multas superficies parvas quae non apparent quando sunt separatae, et apparent quando sunt coniunctae, et continuatur visus rei separatae eo quod penetrat lux in pervio ad superficies interiores et reflectuntur ab eo et quiescunt super eo, et non transcendit lux in eis proper multitudinem reflextionis luminis earum retro, quia pervium clarum est in quo transcendit visus et fit ab eo retrogradatio luminis retro, non apparet pervium ubi fit retrogradatio radiorum. Quando ergo non apparet pervium, videtur habere colorem qui est albus." 79-80” Avicenna, Liber Quartus Naturalium: De Actionibus Et Passionibus Qualitatum Primarum (Brill, 1989), 79-80.

that density and rarity is a change in situation and nothing more, and moreover he cites

Aristotle’s discussion in the categories for support.91

For both Zabarella and Santorio, the perception of color in bodies, under normal viewing

conditions, is caused in some sense by the disposition of matter and its interaction with light.

However, what is meant by color, light, a disposition of matter — and in some respects

perception itself — changes radically. The seventeenth century saw redefinitions of color, light,

and density and rarity, but the meanings of the terms appears to have been highly dynamic and

variable, and this doesn’t seem to have settled down until after Newton, at least. Corpuscular

philosophers adhered to theories that, in all major aspects, were identical to what we have seen in

Santorio — from Descartes to the self-styled Epicureans Gassendi and Walter Charleton to the

experimental philosophers Boyle and Hooke. The reasons for this are complicated. Not only

Santorio, but every figure just mentioned invokes the examples of foam and ground glass to

explain the generation of whiteness from transparency, and like Santorio most present it as an

obvious, matter-of-fact refutation of Scholastic theories of the origin of color. However, their

appeals to such commonplace experiences are best seen as an extension of the literary

experientia in the scholastic tradition rather than an a refutation of it on empirical or

experimental grounds. The examples of ground glass and foam were scholastic topoi, and

scholastics certainly had the tools to account for these phenomena: in foam and ground glass

scholastics saw a demonstration of the juxtaposition of the small parts of two bodies, and

combining the two merely changes the situation of the two bodies with respect to one another.

What they would claim not to have seen are examples of the more fundamental type of mixture:

that is, perfect, homogenous, Aristotelian mixture, in which color is consequent on a change in

139

91 Santorio, Methodi Vitandorum Errorum, 157v.

density according to the category of quality. One major factor in the demise of such condensation

theories of the origin of color seems to be the dissolution of the Aristotelian cosmos. Soon after

Santorio wrote of “the error of Albertus and Zabarella on the nature of the transparent”, and

especially due to Galileo’s observations of the moon and the satellites of Jupiter, fewer and fewer

struggled with questions about how light and color can at once arise from an unchanging,

homogenous, divine substance as well as the corruptible, mixed, tangible stuff below. They no

longer had to answer how, given this radical divide in the universe, our eyes are suited to

perceive both. With the dissolution of the Aristotelian cosmos we also see the loss of a central

motivation for those holding such a condensation theory of the origin of color: the connection

between the heavens surrounding us and the crystalline humor inside our eyes. Indeed, running

parallel to this cosmological shift is a change in the site of vision, from the crystalline humor to

the retina. In next two chapters we will see that the condensation of the crystalline humor is the

cause of both an increase refractive power as well as a loss of transparency. Anatomists and

philosophers writing on the eye from Ibn al-Haytham onwards, at least, pointed to the density of

the crystalline humor as the essential reason why it can simultaneously receive and retain colors.

This density was essential to its functioning, and many, including Zabarella, it mirrored the

condensation of the stars.

140

Chapter 3: Vision and Philosophical Anatomy: Fabricius ab Aquependente’s De visione

It is likewise the most simple, pure, and sincere body imaginable: wherein all the parts of the Chicken do abide in potentiâ, but none, actu: nature seeming to have afforded to it the same privledge which men commonly ascribe to the materia prima, or first Matter, for which all things spring; namely, to be capable of all formes, potentially, but to possess none, actually. So the Crystalline humor of the Eye, to the intent that it may be susceptible of all Collours, is it self void of all: and in like manner the Mediums, or organs of each particular sense, are quite destitute of the qualities of sensible things, or objects: namely the Organs of Hearing and Smelling, and the Aire which is subservient unto them, are without all Sound or Odor: so likewise the moisture of the tongue and mouth, is of it self insipid. And upon this Argument chiefly they rely, who constitute Intellectum possibilem incorporeum, a Potential Understanding which is incorporeal, namely, because it is susceptible of all formes without matter; and as the Hand is called Organum Organorum, the instruments of instruments, so they affirm that to be formam formarum, the Form of forms, having no matter at all, but being altogether Incorporeal, and therefore they assert it to be Possibilis, Potential, but not Passibilis, passible.1


Above William Harvey describes the “Colloquamentum Crystallinum,” the primagenial or

radical moisture out of which “the first particle of the foetus, namely the Blood, and all the post-

genit parts do arise, as out of their Root.”2 It shows quite dramatically the dense web of

associations in which Aristotelian accounts of sensation, and the crystalline humor in particular,

were embedded. The first Latin edition of Harvey’s Exercitationes de generatione animalium

141

1 William Harvey, Anatomical Exercitations Concerning the Generation of Living Creatures to Which Are Added Particular Discourses of Births and of Conceptions, &c. (London  : 1653), 463. This is a quite literal translation from: William Harvey, Exercitationes de Generatione Animalium Quibus Accedunt Quaedam de Partu, de Membranis Ac Humoribus Uteri & de Conceptione (Londini: Typis Du-Gardianis, 1651), 252–53.2 Harvey, Anatomical Exercitiationes, 462.

was published in 1651, and thus it also shows how far into the seventeenth century one could

simply assert that the crystalline humor was the chief author of vision. William Harvey, of

course, was Fabricius’s most famous student.

In the last chapter we saw how Zabarella conceived of the relationship between color,

light, transparency, matter, the soul, and the cosmos. His work can be seen as a culmination of

much that had proceeded him in the Peripatetic tradition, but he scarcely could have known that

he was writing at the end of a long tradition of discussion and debate on these topics. Zabarella's

endorsement of the condensation theory of the origin of color is tied to a very specific

understanding of the world — from the structure of the universe to the nature of motion or change

— and our relationship to it through our senses. He composed one of the most detailed,

comprehensive, and unified expositions of light, color, and vision in the Peripatetic tradition, and

he did so as a natural philosopher at a time when natural philosophy had been, over the course of

more than a hundred years before him, successfully establishing its place in northern Italian

universities as an autonomous discipline.

Here I examine his colleague at Padua, the physician, surgeon, anatomist, and de-facto

natural philosopher Hieronymus Fabricius ab Aquapendente (c. 1533-1619).3 They were exact

142

3 On Fabricius’s interest in giving causal explanations in the manner of Aristotle, see Andrew Cunningham, “Fabricius and the ‘Aristotle Project’ in Anatomical Teaching and Research at Padua,” in The Medical Renaissance of the Sixteenth Century, ed. by Andrew Wear, Roger Kenneth French, and Iain M. Lonie (Cambridge University Press, 1985), 195–222. On his appropriation of natural philosophy in conformation with Zabarella’s notions of the proper relationship between philosophy and medicine, particularly in connection with Fabricius’s desire to raise the status of anatomy and the anatomy faculty at the University of Padua, see Nicholas Jardine, “Keeping Order in the School of Padua: Jacopo Zabarella and Francesco Piccolomini on the Offices of Philosophy,” in Method and Order in Renaissance Philosophy of Nature, ed. Di Liscia, Kessler, and Methuen (Ashgate, 1997), 204–207. On Fabricius and the teaching of natural philosophy at the anatomy theatre, see Cynthia Klestinec, Theaters of Anatomy: Students, Teachers, and Traditions of Dissection in Renaissance Venice (Johns Hopkins University Press, 2011). On Galen’s statement that anatomy is a form of natural philosophy, see Galen, Galen on the Usefulness of the Parts of the Body. De Usu Partium, trans. Margaret Tallmadge (Cornell University Press, 1968), Book I, 15, 18–19.

contemporaries: likely born in the same year, Fabricius was officially appointed to a

professorship in surgery at Padua in 1565 by the Venetian Senate, only two years after Zabarella

was appointed to the chair in logic. As a physician and anatomist he had an allegiance to Galen,

but he also famously revived Aristotle’s anatomical project.4 As we will see, his Aristotelianism

was of quite a different sort than Zabarella’s, and this is revealed in his treatment of light, color,

transparency, and vision in his 1600 treatise De visione (On Vision).

This chapter analyzes the three sections of his work on vision titled historia, actio, and

utilitas (the significance of these terms is explained below in § 3.4).5 The last section on the

utilitas of the parts of the eye will be treated only briefly in this chapter, mainly in order show

how it fits into the structure of his Galenic-styled anatomical treatise. How Fabricius engaged

with the works of Alhazen, Witelo, and Pecham, and the tradition of mathematical optics in

general in his utilitats section is reserved for the next chapter, where I show that Fabricius and

Zabarella held an identical, novel theory of vision, and where I also argue that there was a mutual

influence between the professor of anatomy and the professor of natural philosophy. As I

mentioned in the introduction, the previous chapter can be seen as an analysis of vision —

Zabarella’s theory of vision specifically — in the context of the rise of an autonomous natural

philosophy in the sixteenth century. This chapter analyzes vision in the context of sixteenth-

century anatomy and medicine; it focuses on Fabricius’s Galeno-Aristotelian philosophical

143

4, Cunningham, “Fabricius and the ‘Aristotle Project,’” 195–222; Andrew Cunningham, The Anatomical Renaissance: The Resurrection of the Anatomical Projects of the Ancients (Scolar Press, 1997).5 An excellent analysis is of these terms, their use by Fabricius, and their connection to Aristotle can be found in Peter Distelzweig, “Fabricius’s Galeno-Aristotelian Teleomechanics of Muscle,” in The Life Sciences in Early Modern Philosophy (New York: Oxford University Press, 2014), 65–84. See also Nancy Siraisi, “Historia, Actio, Utilitas: Fabrici E Le Scienze Della Vita Nel Cinquecento,” in Il teatro dei corpi: le pitture colorate d’anatomia di Girolamo Fabrici d’Acquapendente, ed. by Maurizio Rippa Bonati and Jose Pardo-Tomas (Milano: Mediamed, 2004), 63-73.

anatomy, and analyzes his De visione in order to see how Fabricius integrates theories of matter,

color, light, transparency, and sensation into his anatomical project. While this chapter and the

previous one lay out the anatomical and natural-philosophical basis for vision, the chapter after

this investigates visual theory itself, including the often neglected topic of sixteenth-century

extramissionism.6 In addition to understanding how the various components analyzed in this and

the previous chapter are integrated into their theory of vision, the next chapter will also explore

how mathematical optics informed their works.

This chapter has seven main parts plus a conclusion. First is an account of Fabricius’s life

and career (§ 3.1), and this is followed in the second part by a review of his current place in the

history of science and medicine and a brief look at the historiographical issues in which

Fabricius’s works, and especially his De visione, have been treated (§ 3.2). The following section

looks at medieval and renaissance accounts of the eye, and especially the main controversies

treated in sixteenth-century anatomical works and the eventual consensus reached on the shape,

size, and location of the humors at the end of the century (§ 3.3). Here I point to Vesalius’s key

role in establishing the trajectory for accounts of the eye, even while both his textual descriptions

as well as his images of the eye were arguably less empirically grounded than the anatomists that

came before him. After Vesalius most anatomists responded to and criticized his treatment of the

eye while largely ignoring (in print, at least) pre-Vesalian anatomical works. Additionally, images

of the eye in later texts mostly copied and corrected the diagrams in the Fabrica. In a sense,

Vesalius reset the debate over the structure of the eye, and due to the controversies that ensued

144

6 Sixteenth-century extramissionism among physicians is touched upon in Katrien Vanagt, “Early Modern Medical Thinking on Vision and the Camera Obscura. V.F. Plempius’ Ophthalmographia,” in Blood, Sweat and Tears - The Changing Concepts of Physiology from Antiquity into Early Modern Europe, ed. Claus Zittel, Manfred Horstmanshoff, and Helen King (Brill Academic Publishers), 569–293.

his Fabrica led to more sophisticated accounts of not only the structure of the eye among

anatomists and physicians, but of visual theory as well. In the fourth section I turn to Fabricius’s

De visione in the light of late sixteenth-century Galenism and Aristotelianism (§ 3.4). There I

examine the text’s tripartite structure of historia, actio, utilitas and Fabricius’s attempt to use this

Galenic form, combined with Aristotelian principles, to elevate anatomy to an acceptable version

of natural philosophy. Here I also highlight his important, though overlooked, insistence that

dissectio (dissection) and historia are, properly speaking, distinct parts of anatomical

investigation. Although his philosophical accounts are largely Aristotelian, it is particularly

interesting that Fabricius makes no claim to be an orthodox Aristotelian, nor does he claim that

his account of vision is the definitive Peripatetic account. Aristotle is one authority among many,

and when Fabricius differs from Aristotle he makes no attempt to bend the Stagirite to his own

position. In some sense, then, his Aristotle is more historicized than Zabarella’s. In the fifth

section I look at his history (historia) of the eye, to understand Fabricius’s account of

transparency, consistency, density and rarity, and color of the parts of the eye — in short, their

complexion or temperament — as well as their shape and size (§ 3.5). In the sixth section I

examine the action (actio) section of De visione, in which Fabricius gives his account of light

and vision (§ 3.6). This part is divided into three subsections: the first is a look at the literary

genre of De visione and Fabricius’s relationship to his ancient and modern sources, which is of

particular relevance for understanding his section on the actio of the eye (§ 3.6-1); the second is

an analysis of Fabricius’s account of light, color, and transparency in the actio (§ 3.6-2); and the

third examines Fabricius’s discussion of phosphorescent meat, which was cited frequently by

later authors (§ 3.6-3). Finally, in the seventh section I outline Fabricius's account of the utilitas

145

— the usefulness or purpose — of the eye in general, and show how it fits into Fabricius's overall

program of philosophical anatomy (§ 3.7).

§ 3.1: Fabricius’s Life and Career

Hieronymus Fabricius ab Aquapendente (c. 1533-1619) was most likely born the same year as

Zabarella. His career at Padua lasted over fifty years, and today he is mostly remembered for his

anatomical discoveries (particularly his discovery of the ostiola, or "little doors," in the veins),

for creating the first permanent anatomy theater in Padua in 1594, which still stands today,7 and

for having trained and greatly influenced William Harvey.8 During his time at Padua Fabricius

elevated the position of anatomy within the University (along with his salary) in part by recasting

anatomy as a form of Aristotelian natural philosophy. He was also a prominent physician and

surgeon, and treated members of the Medici family as well as Galileo and Paolo Sarpi.9

Adelmann gives the most complete account in English of Fabricius life in his preface to

The Embryological Treatises of Hieronymus Fabricius of Aquadenpente.10 Adelmann, in turn,

largely follows Giuseppe Favaro’s accounts, which Adelmann has confirmed with his own

146

7 According to Cynthia Klestinec the anatomy theater that still stands today is technically the second permanent anatomy theater. The first was also built at the behest of Fabricius, in 1584, and the history of the two anatomy theaters is illuminating. Nevertheless, it’s “permanence” was relatively temporary, and so I follow most everyone else and refer to the currently existing anatomy theater as the first permanent one. Cynthia Klestinec, “A History of Anatomy Theaters,” Journal of the History of Medicine and Allied Sciences 59, no. 3 (2004): 375–412.8 "Aristotelem ex antiques; ex recentioribus verò Heronymum Fabricium ab Aquapendente, sequor; illum, tanquam Ducem; hunc, ut Praemonstratorum." William Harvey, Exercitationes de Generatione Animalium, C3v.9 Hieronymus Fabricius and Howard Bernhardt Adelmann. The Embryological Treatises of Hieronymus Fabricius of Aquadenpente (Cornell University Press, 1967), 28.10 Fabricius and Adelmann, Embryological Treatises, 6-22.

investigation of the primary material.11 The main contemporary sources of Fabricius’s life are

Tomasini’s book of biographies of famous Paduans and his history of the University of Padua, a

published funeral oration, as well as the records of the transalpine student nation in Padua,

published by Antonio Favaro in 1911.12 This last source was used recently by Cynthia Klestinec

to greatly enrich our picture of the relationship between Fabricius and his students, the

importance of manual skill for the anatomist, and some crucial aspects of public versus private

anatomical instruction.13

Fabricius was born to an old and respected family in the town of Acquapendente, now in

the province of Viterbo. The date of his death is well attested. There is some uncertainty of the

date of his birth, but 1533 or thereabouts seems fairly certain. He went to Padua around 1550,

and graduated from the University there with a degree in medicine and philosophy, probably in

1559 around the age of twenty-six. His teachers at Padua included the famous anatomist

Gabrielle Falloppio (1523–1562) in anatomy and medicine. In 1565 Fabricius assumed the chair

of anatomy, which had had only temporary appointments since the death of Falloppio in 1562,

and he held this post until his death in 1619.

147

11 These sources are: Giuseppe Favaro, “L’insegnamento anatomico Di Girolamo Fabrici d’Acquapendente,” in Monografie storiche sullo studio di Padova, contributo del R. Instituto Veneto di Scienze, Lettere ed Arti alla celebrazione del VII centenario della Università di Padova (Venice, 1922), 109-136. Giuseppe Favaro, “Contributi Alla Biografia Di Girolamo Fabrici d’Acquapendente,” in Memorie E Documenti per La Storia Della Università Di Padova, vol. 1 (Padova, 1922).12 Ioannes Thuilius, Funus Perillustris, & Excellentissimi Viri, D. Hieronymi Fabricii Ab Aquapendente Medicinae Doctoris, Equitis D. Marci, & in Celeberrimo Gymnasio Patavino (Padova: Typis Petri Pauli Tozzii, 1619). Giacomo Filippo Tomasini, Illustrium Virorum Elogia Iconibus Exornata (Pasquardus, 1630). Tomasini, Giacomo Filippo, Gymnasium Patavinum Iacobi Philippi Tomasini Episcopi Aemoniensis Libris v (Udine: Nicolaus Schirattus, 1654). Antonio Favaro, Atti Della Nazione Germanica Nello Studio Di Padova, 2 vols. (Venice, 1911). I have examined the above sources. For more biographical details and further sources, see Maria Muccilo, “Fabrici d’Acquapendente, Girolamo,” in Dizionario Biographico Degli Italiani, vol. 43, 1993.13 Cynthia Klestinec, “Civility, Comportment, and the Anatomy Theater: Girolamo Fabrici and His Medical Students in Renaissance Padua,” Renaissance Quarterly, 60 (2007), 434–63. Klestinec, Theaters of Anatomy.

Fabricius’s first published anatomical work was a collection of three treaties in folio,

collectively titled De visione, voce, auditu. It was first published in 1600 in Venice as a single

bound book, although the treatises were also published separately in pamphlet form for the

convenience of students, who were expected to bind together these with his later treatises as they

were published.14 These works begin his plan for a philosophical anatomy, the Totius animalis

fabricae theatrum or the “Theatre of the Whole Animal Fabric,” an anatomical-philosophical

investigation into not just man, but the nature of the animal body and ultimately the animal

soul.15 The aim of this investigation was not to understand the differences and similarities among

species in the way that modern comparative anatomy does, but with the goal of understanding

Nature herself through the diversity of her works. Considered in this way anatomy is a subset of

natural philosophy rather than medicine. As a speculative science its aim is knowledge; the aim

of anatomy is neither for the sake of some action (e.g., to increase health as many natural

philosophers would, following Aristotle, classify the aim of medicine), nor is the aim the

production of physical objects (as in the science of house building, for example) as in the factive

sciences.16 Although Fabricius in no way abandoned Galen, nevertheless the ancient doctor

became merely one authority among many. Indeed, thanks to anatomists such as Berengario da

Carpi and, especially, Vesalius, Galen was known to be fallible on points of anatomy, which

148

14 Hieronymus Fabricius ab Aquapendente, Hieronymi Fabrici ab Aqvapendente Anatomici Patavini de venarvm ostiolis (ex typographia Laurentij Pasquati, 1603), i. 15 He describes this project at greatest length in his dedication to Jovanni Delfino at the beginning of De auditu. This project analyzed in, Andrew Cunningham, “Fabricius and the ‘Aristotle Project.’” See also the collected volume of essays Maurizio Rippa Bonati and José Pardo Tomás, Il teatro dei corpi: le pitture colorate d’anatomia di Girolamo Fabrici d’Acquapendente (Mediamed, 2004).16 On the categorization and division of the sciences in the Renaissance, see Walter R. Laird, “The ‘Scientiae Mediae’ in Medieval Commentaries on Aristotle’s ‘Posterior Analytics’” (Ph.D., University of Toronto (Canada), 1983).Walter. R. Laird, “The Scope of Renaissance Mechanics,” Osiris, 2nd Series, 2 (January 1, 1986): 43–68.

includes what is often viewed as Galen's “physiology,” although this label is anachronistic.

Furthermore Zabarella, among other natural philosophers, fiercely attacked Galen’s scientific

methodology, and thus the philosophically astute Fabricius would have been keenly aware of

many kinds of criticism of Galen. It has been argued that Zabarella was an influence on Fabricius

in at least three respects: (1) his classification of the sciences, (2) Fabricius’s decision to cast

anatomy as a form of natural philosophy, and (3) Fabricius’s emphasis and understanding of the

soul.17 However this connection is based on a gross similarity between Zabarella’s and

Fabricius’s attitudes towards these issues, and little direct evidence for this influence has been

put forth. I argue that it is likely that the influence was mutual, and as we will see in this chapter

and the next not only are there are similarities in their classification of the sciences and their

account of the soul, but there are also striking similarities in matters of substance — particularly

the detailed account of the size of the humors, the action of the eye, and most importantly the

unique purpose they both ascribe to the vitreous humor.

Fabricius’s status and pay increased dramatically over his lifetime, from 100 florins

annually at the time of his first appointment to the chair of surgery in 1565, to 600 florins when

he was accorded all the privileges of a first ordinary professor in medicine in 1584, to 1100

florins at his fifth reappointment to the chair of surgery in 1594, to 1000 scudi for life when he

was made Professor supraordinarius in anatomy in 1600 (he later also became Supraordinarius

in surgery in 1603).18 The case has been made that Fabricius increased his status and pay by

recasting the discipline of anatomy as theoretical science, and that he did this by taking (as

149

17 Nicholas Jardine, “Keeping Order,” 204-207. Simone De Angelis, “From Text to the Body: Commentaries on De Anima, Anatomical Practice and Authority around 1600,” in Scholarly Knowledge: Textbooks in Early Modern Europe (Librairie Droz, 2008), 205–28.18 Fabricius and Adelmann, Embryological Treatises, 7-8.

mentioned above) the domain of anatomy to be not merely the human body, as Galen and most

other anatomists did, but the total or universal animal. Nicholas Jardine, for example, writes:

Fabricius’s new anatomy can thus be seen to appropriate that very portion of natural philosophy judged by his natural philosopher colleagues to be fundamental to all sound medical teaching and practice. In effect, this new anatomy is presented as an alternative to natural philosophy as the foundation of medicine; and this alternative is offered in a university in which the primary role of natural philosophers is the training of medical students.19

This appears to me to be substantially correct, but Jardine does not offer much evidence. Below I

will support this reading of Fabricius’s anatomical project and compare it with Zabarella’s

statements on the proper natural-philosophical grounding for medicine whenever appropriate.

§ 3.2: Historiographical Review

Perhaps the most influential and comprehensive work on the history of vision from antiquity

through the early modern period is David Lindberg’s Theories of Vision from Al-Kindi to Kepler.

This work privileges mathematical aspects of visual theory, and as a consequence in his chapter

on renaissance anatomy Lindberg writes that artists and anatomists before Kepler “rarely

deviated from the fundamentals of medieval visual theory”20 and that anatomical work on the eye

was “only slightly germane to visual theory.”21 He says that the debate over the role of the

aranea in visual perception — and indeed whether it might be the seat of vision instead of the

crystalline humor — is of little importance precisely because the question did not affect

mathematical accounts of vision. However, questions about which material body serves as the

150

19 Nicholas Jardine, “Keeping Order,” 207.20 David C. Lindberg, Theories of Vision from Al-Kindi to Kepler (Chicago: University of Chicago Press, 1976), 166.21 Ibid., 169.

site of visual perception point back to what color is exactly, and because of this a wealth of

different conceptions of the world are implicated in the shift in the site of visual perception.

Philosophically minded anatomists such as Fabricius were certainly attuned to this relationship

between anatomy and accounts of light, color, and perception. Furthermore, as I will argue in this

and the next two chapters, anatomical developments had a clear and significant impact on visual

theory, and on a few issues there is a direct connection between the developments in anatomy

and visual theory occurring in Padua on the one hand and Kepler's new account of vision on the

other. When discussing Fabricius, Lindberg references only a later, 1614 edition of De visione,

voce, auditu — yet the first edition was published in 1600, and so it is not surprising that he does

not examine Fabricius carefully in a book ultimately aimed towards understanding Kepler’s

theory of vision.22

A. C. Crombie has also written on Fabricius, saying: “His visual theory was essentially a

combination of the formulations of the problem by Aristotle and Galen with a version of the

optical scheme with which Alhazen had prevented the reversal of the image as the visual cone

passed through the transparent media.”23 Crombie writes, not necessarily inaccurately, “With

some concessions to optical science, he [Fabricius] remained firmly within the medical

tradition.”24 Yet this comes as a sort of fault, one that held Fabricius back from discovering the

retinal theory. In the same way that Fabricius supposedly “failed” to grasp the purpose of the

ostiola or little doors in the veins, and so was held back from the discovery of the circulation of

the blood; so too Fabricius supposedly “failed” to grasp the importance of refraction in the eye,

151

22 Ibid., 173.23 A. C. Crombie, “Expectation, Modelling, and Assent in the History of Optics: Part I. Alhazen and the Medieval Tradition” in Studies in the History and Philosophy of Science, 21 (1990), 629.24 Ibid., 629.

and so despite his accurate anatomy Fabricius, occluded by his Galenism and Aristotelianism,

was held back from discovering the retinal theory of vision.25 It also neglects the important role

Fabricius had in synthesizing anatomy, natural philosophy, and mathematical optics, in the

process setting an important precedent for later writers on vision. Rather than the anatomists,

Crombie writes “It was the mathematicians who came to reform visual theory by proceeding

through an optical analysis of ocular physiology, exploiting the models of eyeglasses and the

camera obscura, and thus reformulating the problem itself.”26 Few scholars since Lindberg and

Crombie have challenged this account, and thus little scholarship has been done on works by

physicians dealing with ocular anatomy, visual theory, and the connection between the two.

Three main points need to be addressed concerning this. First is that not all histories of

vision need to be Kepler-centric: it is worthwhile to study renaissance theories of vision for their

own sake, and thus Fabricius’s De visione, a substantial work by the most celebrated anatomist

of his day, deserves more than a cursory examination. Second, the history of vision is not just the

history of mathematical optics. Even if physicians did not reform visual theory as significantly as

mathematicians, their work deserves to be studied, especially given the enormous reach and

influence their teachings had on students, on readers through their published works, and

generally through their heavy representation in scientific academies and the republic of letters.

Of particular interest is the attention to Plato’s and, especially, Galen’s theory of vision in the

sixteenth century due to the influence of humanism. The careful reading of ancient texts and the

152

25 This attitude is expressed even more clearly in Huldrych M. Koelbing, “Anatomie de L’œil et Perception Visuelle, de Vésale À Kepler,” in Le Corps À La Renaissance. Actes Du XXXe Colloque de Tours 1987 (Paris, 1990), 389–98. Erwin De Nil and Mark De Mey, “Hieronymus Fabricius d’Aquapendente: De Visione, Ending of the Perspectivist Tradition,” in Optics and Astronomy: Proceedings of the XXth International Congress of History of Science (Brepols, 2001), 51–65.26 Crombie, “Expectation: Part I,” 630. See also the discussion at § 0.2.

appropriation of the ideas and attitudes contained within appears to have led to a revival of the

extramission theory of vision by physicians in the sixteenth-century. In response to this

extramissionist revival came attacks on Galenic and Platonic theories; these attacks drew

primarily upon Aristotle but also on perspectivist works stemming from Ibn al-Haytham’s

Optics. Thus, there was a newfound attention to visual theory in connection with medicine and

anatomy in the sixteenth century — although little attention has been paid to this, in part due to

the dominance of Lindberg’s narrative and his contention that the extramission theory of vision

was dispatched for good by Ibn Sina and Ibn al-Haytham. These two points will be developed at

length in Chapter 4. A third point, which will be argued in the next two chapters, is that

developments in mathematical optics in the seventeenth century in fact took for granted accurate

descriptions of the eye, and indeed for the first time works of mathematical optics employed an

eye that was abstracted from accurate anatomical dissection; they did not, as the medievals did,

conform the structure of the eye to the demands of geometric visual theory. Fabricius, it seems,

the first person to attempt to fully integrate the traditions of mathematical optics, natural

philosophy, and anatomy, and to say that all three disciplines treat the same eye and so should

base their accounts on an accurate understanding of every aspect of the eye as revealed through

meticulous and skillful dissection. This was a crucial influence on later developments in

seventeenth century visual theory. Late-sixteenth century developments in the shape and size of

the humors, their refractive power, and the connection between the tunics and nerves were all

relied upon by seventeenth-century reformers of vision; mid-sixteenth century accounts would

have been unable to provide the support needed for the mathematical analyses given by Kepler

and Descartes, and as we will see a great deal happened in the years between Vesalius’s Fabrica

153

and Fabricius’s De visione. Moreover, as I will outline in Chapter 5, in the first half of the

seventeenth century the retinal theory of vision was largely adopted within a scholastic

Aristotelian framework, and thus accurate knowledge of the color and complexion of the humors

were crucial for accounting for how the retinal theory of vision worked, as least before Descartes

and the mechanical theory of light and vision rendered color a much less significant factor in

theories of vision. Furthermore, although Fabricius (or Zabarella, who held substantially the

same theory of vision) did not achieve what Kepler did, Kepler knew their theory of vision very

well, and I will argue in the next chapter that Kepler’s analysis was facilitated by knowledge of

their account of the eye and their model for vision. Although it is impossible to say what Kepler

would have written had he not been exposed to their theory of vision (through Fabricius’s student

Johannes Jessenius), he would have had many additional obstacles to overcome had he only

relied on Felix Platter’s anatomical work and the medieval Perspectivists such as Alhazen and

Witelo.

In a highly influential article Andrew Cunningham makes the case that anatomists in

Padua, led by Fabricius, were writing about, teaching, and doing anatomy with a very specific

purpose — they were “recreating the research programme of Aristotle in anatomy.”27 He revisits

this theme in Chapter 6 of his book The Anatomical Renaissance, although here he restricts his

claims to Fabricius and its implications for understanding his student William Harvey’s work.28

His basic argument is that sixteenth century anatomy should not be thought of as a monolithic

enterprise to which various practitioners made contributions. In the case of Fabricius, anatomy

was a way of doing natural philosophy; its subject matter was the animal (not merely man), and

154

27 Andrew Cunningham, “Fabricius and the ‘Aristotle project,’” 195-222.28 Andrew Cunningham, The Anatomical Renaissance, 195.

his “programme” was explicitly modeled on Aristotle’s biological works and the Stagirite’s

conception of the soul, particularly as interpreted by the ancient Aristotelian commentator

Alexander of Aphrodisias. This seems to capture a great deal of the overall structure and purpose

of Fabricius’s works, but it doesn’t necessarily illuminate their details. In the case of the eye,

anatomical knowledge was greatly advanced from the account that Aristotle gave, and by the

sixteenth century the philosophical questions involved in theories of color and vision could not

be decided upon by reference to Aristotle alone. It is therefore of interest to see how Fabricius

reconciled these distinctly sixteenth-century problems in his “Aristotical” anatomy, and as we

will see at times he does so by refuting Aristotle on specific points of natural philosophy.

Cynthia Klestinec’s recent work fleshes out the Paduan medical scene, in particular with

her emphasis on the powerful role students played in Padua, her analysis of the various ways that

anatomy was taught at Padua, the importance of manual skill for students and for the reputation

of the professors, and the culture and politics at Padua during the time of Fabricius.29 Following

Cunningham, she stresses how public anatomical investigation under Fabricius was a

demonstration of natural philosophy, and how this context shaped what was “seen” (which, she

argues, was a significantly aural performance, rather than unmediated visual observation, in

Fabricius’s public anatomy theatre). She contrasts public dissection with private anatomical

demonstrations and the technical and practical skills emphasized in the latter. Both practices, she

argues, were necessary for the tradition of learned medicine. However, she does not discuss the

philosophical content presented by Fabricius in detail — we are simply given a picture of him as

a follower of Aristotle and Galen. Furthermore, while she is likely correct to deflate the notion of

155

29 Klestinec, “A History of Anatomy Theaters in Sixteenth-Century Padua”; Klestinec, “Civility, Comportment, and the Anatomy Theater”; Klestinec, Theaters of Anatomy.

anatomical theatre as a place where students learned the kind of knowledge and manual skill that

was necessary for surgery, or indeed that they would have learned many of the finer points of

dissection technique itself, this doesn’t mean that the anatomy theatre was not a place for the

exchange of significant, even new, knowledge about the body and its processes. The privileged

front-row area of the anatomical theatre was reserved, at least in part, for fellow professors, and a

public dissection could be the occasion for disputations the structure of parts of the body, its

physiology (less anachronistically, what was called actio and utilitas; more on this below), or

indeed broader questions touching natural philosophy.30 Thus Klestinec’s work does not exhaust

the possibilities of the anatomical theater as a site of knowledge creation and exchange.

§ 3.3: A Brief History of Humors and Tunics in the Sixteenth Century

The eye degrades rapidly, contains many fluid parts, and can differ greatly both across species as

well as within an individual over the course if its life. Aristotle did not describe the eye in much

detail, and while Galen’s extramissionist account of vision was endorsed by some physicians

(and anatomists) in the sixteenth century, his account of the shape, size, color, connection, and

purpose of the parts of the eye came under significant attack. In the sixteenth-century almost

every sensible aspect of the parts of the eye — including color, clarity, texture, firmness, size,

position, and connection — was potentially significant for understanding vision, and all are

unstable in a decaying body under dissection. During the course of the sixteenth century

anatomists became increasingly sensitive to minute details of the eye, in part it seems due to an

156

30 To get a sense of the huge range of controversies in natural philosophy that were connected to the anatomy of the eye, see the Paduan physician, surgeon and anatomist Julius Casserius’s (1552-1616) work on vision, where he treats fifty-two disputed questions on light, color, and vision, perhaps the most exhaustive list of such scholastic questions ever treated in a single work. Julius Casserius, Pentaestheseion, hoc est de quinque sensibus liber (Venice, 1609), 296-323;

increased concern with visual theory.

Anatomists were not unified in the

theory of vision they either professed

or, when not explicitly presenting a

view, that they implicitly favored.

Nevertheless, some basic facts about

the structure of the eye gained the

consent of nearly all anatomists,

while some others did not. Here I

will describe two points on which a

general consensus was reached, and

one where controversy lingered: the

place of the crystalline humor in the

eye, the shape of the crystalline

humor, and whether the tunica

aranea (or spider-web-like tunic)

was continuous with the retina. All three had important ramifications for visual theory.

There are three clear humors that make up the interior of the eye: the aqueous humor,

located towards the front of eye; the crystalline humor (now called the crystalline lens or just the

lens), which is next, and the vitreous humor, which is at the rear of the eye. (See figure 3.1) The

aranea, now called the lens capsule, was described as a subtle, clear membrane covering at least

the front end of the crystalline humor, although later in the sixteenth century it was found to

157

Figure 3.1: Diagram of the eye with superimposed legend. Note that the aranea, surrounding the crystalline humor I and continuous with the retina F, is not labeled. Julius Casserius, Tabulae anatomicae LXXIIX (Deuchinus, 1627), 95r.

AA: Nervus opticusBB: Dura oculi tunica (Sclera)C: CorneaDD: Uvea tunicaE: Foramen uveae tunicaeF: Retiformis tunicaG: Adnata oculi tunicaH: Aquea I: Crystallini K: Vitrei

cover both sides of the crystalline. Galen’s three main discussions of the eye are found in On the

Usefulness of the Parts, On the Doctrines of Hippocrates and Plato, and On Anatomical

Procedures; the section in On Anatomical Procedures where the anatomy of the eye is described,

however, was until recently only extant in Arabic manuscript, and thus sixteenth-century

anatomists in the West did not have access to it.31 In none of these does Galen give a clear

description of either the relative size of the three humors or the precise location of the crystalline

humor within the eye.32 Furthermore, Galen says that the aranea only covers the anterior of the

crystalline, not the posterior.

Medieval perspectivists as well as many pre-Vesalian anatomists placed the crystalline

humor towards the front of the eye. Alhacen, Witelo, and Pecham describe only the front of the

crystalline as lenticular, although their characterization of the shape of this humor is not

altogether clear. At times Alhacen, and Pecham following him, refers to the crystalline and the

vitreous together as a single humor (usually called the humor glacialis, or ice-like humor); the

rear of the crystalline is never given real consideration, and the diagrams accompanying

medieval texts often show a flat boundary between the two (figure 3.2) or else present the

vitreous as largely spherical, giving the crystalline humor a crescent shape (see figure 4.7 in the

158

31 It did, notably, influence Hunain ibn Ishaq among others. Galen, Galen on Anatomical Procedures: The Later Books, ed. M. C. Lyons and B. Towers, trans. Wynfrid Laurence Henry Duckworth (Cambridge University Press, 2010), xi-xiv. On Galen in the sixteenth-century, see: Andrew Wear, “Medicine in Early Modern Europe, 1500–1700,” in The Western Medicial Tradition: 800 B.C. – 1800 A.D. (Cambridge University Press, 1995), 250–264, 270–273. On the availability of Galen in the Renaissance, see Richard J. Durling, “A Chronological Census of Renaissance Editions and Translations of Galen,” Journal of the Warburg and Courtauld Institutes 24, no. 3/4 (July 1, 1961): 230–305; Stefania Fortuna, “The Latin Editions of Galen’s Opera Omnia (1490-1625) and Their Prefaces,” Early Science and Medicine 17, no. 4 (January 1, 2012): 391–412.32 Galen, Usefulness, 464-503; Galen, On the Doctrines of Hippocrates and Plato: Books VI - IX., trans. by Phillip De Lacy, Corpus medicorum Graecorum (Akademie-Verlag, 1980), 459.

next chapter).33 The Perspectivae all also seem to put the crystalline towards the front of the eye

rather than in the geometrical center. The degree to which any of them witnessed dissections, or

refer to parts of the eye that they think one should expect to see in a dissection, is unclear,

although Witelo does say that the lenticular shape of the front end of the crystalline humor “is

obvious from the [conclusions of] those considering the eye’s anatomy.”34 Finally, Alhacen,

Witelo, and Pecham all describe the retina and the aranea as a single tunic surrounding the entire

glacialis, i.e. the crystalline-vitreous composite.35 It must be remembered that the eye described

by these works, which were considered as sciences subalternate to geometry, was largely

theoretical. The structure of the eye that they present serves a geometric account of vision, and

the description of the interior humors in particular does not (and perhaps were not intended) to

correspond to a real, observable eye under any dissection conditions that I can imagine.36 That is,

their descriptions of the eye are largely determined by the demands of their mathematical

account; information gathered from dissection of actual eyes does not appear to have been used

as the basis for, or constraints upon, this geometrical scheme.

Mondino de Luzzi (ca. 1270 – 1326), the medieval anatomist who was the main authority

before the works of Galen were translated and republished during the late fifteenth and early

159

33 Alhacen and A. Mark Smith, “Alhacen’s Theory of Visual Perception: A Critical Edition, with English Translation and Commentary, of the First Three Books of Alhacen’s ‘De Aspectibus’, the Medieval Latin Version of Ibn Al-Haytham’s “Kitāb Al-Manāẓir”: Volume One,” Transactions of the American Philosophical Society, 91 (2001), 12; Witelo and Sabetai Unguru, Witelonis Perspectivae Liber Secundus et Liber Tertius, Studia Copernicana, XXVIII (Ossolineum, 1991), 105-111/294-297; John Peckham, John Pecham and the Science of Optics: Perspectiva Communis, ed. by David C. Lindberg (University of Wisconsin Press, 1970), 114/115. 34 Witelo and Unguru, Witellonis perspectivae, 107/297. 35 Alhacen and Smith, “Alhacen’s Theory of Visual Perception,” 12/349; Pechkam, John Pecham and the Science of Optics, 115. Witelo, Witelonis perspectivae, 107/296.36 There are many interesting issues at play here. On whether the eye described by Perspectivists is “real” or “theoretical,” see Alhacen, “Alhacen’s Theory of Visual Perception,” xlix, lxxviii-lxxix; Lindberg’s note in Peckham, John Pecham and the Science of Optics, 247 n. 83; Unguru’s note in Witelo, Witelonis perspectivae, 210 n. 2.

sixteenth century, writes that the aranea covers the front of the crystalline and is connected to the

retina, and that the crystalline humor has “a round or spherical figure, but with a certain flatness

in the anterior part, and this humor is more toward the anterior than the vitreous in which it is

placed.”37 The anatomist Berengario da Carpi (c. 1460–c. 1530) also describes the retina and

aranea as connected, and that they both arise from the optic nerve. However, he says that often

“they are reckoned as one,” but “whether they are one or two, as also the other tunics, is of little

concern to physicians.”38 Berengario also says “the vitreous humor is far larger than the

crystalline.”39 Alessandro Benedetti (c. 1450–1512), writing somewhat earlier than Berengario,

joins the aranea with the retina and says they have the “same nature.”40 He also describes the

front of the crystalline as being more flattened, and importantly he also describes the rear as well,

saying that it is more globular.41 The main authorities in anatomy before Vesalius, then, describe

the crystalline as having a flattened anterior (but not a flattened posterior), put the crystalline in

the front part of the eye and thus have the vitreous humor fill the bulk of the eye, and connect the

aranea (which is only said to cover the front of the crystalline) with the retina.

160

37 "Post istas est tuncia Aranea circumdans christallinum versus partem anteriorem, cui in parte posteriori continuatur tunica rhetina, et in medio istarum continuetur humor vitreus in medio cuius est humor christallinus rotundus sive figurae spericae, cum quadam planitie in parte anteriore, et hic humor vitreus in quo locatur, et ideo hic humor vitreus factus est ad christallinum locandum et ad ipsum nutriendum." Carpi, Jacopo Berengario da Carpi and Mondino, Carpi Commentaria cum additionibus super anatomia mundini vna cum textu eiusdem in pristinum et verum nitorem redacto (per Hieronymum de Benedictis, 1521), 462r.38 Jacopo Berengario da Carpi, A Short Introduction to Anatomy (Isagogae Breves) (University of Chicago Press, 1959), 152. 39 Ibid., 152. Beringario’s description, although more extensive, is fundamentally the same in his lengthy commentary to Mondino. Berengario da Carpi and Mondino, Carpi Commentaria, 467v ff.40 “Alia item membranula quam tenuissima, qua quarta inter priores annumeratur, quae arachnoides sive amphiblestroides vocatur: quae cum posteriore naturae eiusdem habetur cui coniungitur, eam reticularem tantum vocari putant.” Alessandro Benedetti, Historia corporis humani, sive Anatomice, ed. Giovanna Ferrari (Giunti, 1998), 278.41 “Gutta ipsa in partem priorem magis vergit, quae in parte postrema rotunda est, in priore leviter plana, cuius videndi potentia in cerebro primum sita est, vel in corde principali origine.” Ibid., 280.

Two other prominent anatomists

were less conclusive about the shape and

location of the humors. Gabriele Zerbi (1445 –

1505) has a long treatment of the eye in his

anatomical text.42 Each part of the eye is

described under the following categories:

substance, complexion, color, figure, quantity,

number, situation, manner (modus),

connection (colligantiam), support (iuvant,

roughly the function or purpose the part

serves), and passiones (or diseases associated

with the part). Not every category is used for

every part, but frequently most are used.

Overall, the text follows medieval precedents,

and appears untouched by the style, sensibility,

and resources of renaissance humanism. Zerbi

describes the retina and aranea as being

connected. The crystalline is described as

being compressed in the front, and being

smaller in quantity than both the aqueous and

the vitreous humor. However, the aqueous humor (which he calls the albugineous or egg-white-

161

42 Gabriele Zerbi, Opus Preclarum Anathomie Totius Corporis Humani et Singulorum Membrorum Illius (Bonetus, 1533). 122r–133r. The first edition was published in 1502.

Figure. 3.2: "A drawing of the eye according to manuscripts of the Perspectiva". From Witelo, and Sabetai Unguru, Witelonis Perspectivae Liber Secundus et Liber Tertius, Studia Copernicana, XXVIII (Ossolineum, 1991), 109.

like humor) is said to be “greater than the rest of the humors of the eye,”43 while at the same time

the vitreous humor is said to be greater in bulk than the crystalline as well as the aqueous.44 On

the latter point Zerbi appeals to Galen’s short treatise On the Anatomy of the Eye, which is in fact

pseudonymous. (About which more below.) Niccolò Massa (1485–1569) in his introductory

anatomy text described the aranea and the retina as to parts of a single tunic containing the

crystalline and vitreous humors. However his only comment about the sizes or shapes of the

humors is that the vitreous is much greater in quantity than the crystalline.45 Massa, it should be

noted, seems unconcerned with visual theory: he says nothing about the purpose of the various

tunics and humors, and he does not give the site of visual sensation as almost all anatomists

did.46

The pseudo-Galenic Liber de oculis (Book on the Eye, sometimes also called Galeni liber

de oculis translatus a Demetrio) was in fact a translation of a work by Hunayn ibn Ishaq (known

as Johannitius to the Latins). Ibn Ishaq’s work on the eye was published under Galen’s name in

many Opera beginning early in the sixteenth century, and it was often believed to be genuine.47

In this text we read that the crystalline humor “is not entirely round, but somewhat flattened” and

162

43 “Quantitate est hic humor amplior ceteris oculi humoribus.” Zerbi, Anathomie, 131r. 44 “Quantitate est maior vitriformis cristalloyde. fere enim amplectitur ab eo; et maior albugineo. sic docente Ga.[lenus] in libello de anathomia oculorum cum dicebat vitriformis humor efficit molem oculi primes parte suam repletionem:” Zerbi, Anathomie, 131r45 Nicolo Massa, Liber introductorius anatomiae siue dissectionis corporis humani. (Francisci Bindoni ac Maphei Pasini, 1536), 92r–93v.46 My treatment of these renaissance anatomists is brief. The best introduction to late fifteenth- and early sixteenth-century anatomy is now Allen Shotwell, “The Revival of Anatomical Practices and Techniques in the Renaissance” (PhD Dissertation, Indiana University, Bloomington, 2013).47 Max Meyerhof. “New Light on Hunain Ibn Ishaq and His Period.” Isis 8, no. 4 (October 1, 1926): 685–724. This treatise was included in printings of Galen’s Opera into the seventeenth century at least, although after some point was labeled spurious. It was also published as Liber de oculis Constantini Africani in Omnia opera Ysaac, (Lyon, 1515).

that it is “located in the middle of the eye.”48 Thus the text also does not describe any asymmetry

to the flattening. “Located in the middle” could be interpreted as “the center of the eye” or

simply “the middle humor,” but a shortly thereafter the text says that the crystalline is “located in

the middle so that the rest of the parts might serve it,” and then finally that it is between the other

two humors.49 The text does not give estimates of their sizes, and thus it would be easy to read it

as saying that that the crystalline humor was indeed in the center of the eye, and not just the

middle humor. Finally, in the pseudo-Galenic Anatomia vivorum (Anatomy of the Living), a very

popular text which was also commonly believed to be genuine in the first half of the sixteenth

century, we read that the crystalline humor is “called grando glacialis by Aristotle, because it

resembles a hailstone in form and color.” The crystalline is “placed in the depth and in the

middle” because it is safest there and so that the other parts can nourish it, although the text does

not refer to the relative sizes of the humors.50 It also says that the crystalline is flattened in the

front, but spherical in the back, and that the aranea and retina are connected, although the retina

is somewhat strangely said to be between the crystalline and the vitreous humors.51

One last figure that must be discussed before Vesalius is Avicenna, whose Cannon of

Medicine — perhaps the most important and widely known book on medicine in the Late Middle

Ages and Renaissance — contains some influential statements about the dissection of the eye.

163

48 “Crystallinus est humor albus, splendidus, licidus, non omnino rotundus, sed aliquantulum planus, qui locatus est in medio oculorum.” Later he writes “I refer to the seventeenth-century Giunta edition of Galen’s works, at which point it was recognized as not being written by Galen. Claudius Galenus, Galeni Opera ex octaua Iuntarum editione., vol. 9 (apud Iuntas, 1609), 186r.49 “In medio locatus, ut caeterae partes sibi ministrent;” Galen, Galeni Opera ex octaua Iuntarum editione, vol 9, 186r.50 George W. Corner, Anatomical Texts of the Earlier Middle Ages: A Study in the Transmission of Culture (Carnegie Institution of Washington, 1927), 98. On the history and analysis of this text, see ibid., 35 ff.51 Corner, Anatomical Texts, 98–99.

Book 3, Fen 3, Tract 1, Chapter 1 is on the anatomy of the eye.52 There we read about the

glacialis (or ice-like humor), otherwise known as the crystalline humor.

the middle [humor] is the glacialis, and indeed the humor itself is clear in the same way as a hailstone. The glacialis is in truth round, of which a compression of it diminished the rotundity on its anterior part. [...] And this humor indeed is placed in the middle, since this is the suitable (dignior) spot...53

We see that while the crystalline is clearly asymmetrical according to Avicenna, the issue of

whether it is merely the middle humor or in fact in the center of the eye is open to interpretation.

On the vitreous we read that the vitreous is similar to melted glass, “and the color of melted glass

is clear, and inclines somewhat towards red.”54 Following Galen, he says that the vitreous

nourishes the crystalline, and because of this it must be clear for the sake of the crystalline, but it

is red because it came from blood. Finally, the aranea is generated from the retina, and thus they

are connected and of the same substance. (In the next chapter I will address the notion that

crystalline resembles a hailstone, and there I will also address the notion that the color of the

vitreous is reddish like molten glass.)

Rather than following his recent predecessors in anatomy such as Berengario, or even the

standard medieval text Mondino, in placing the crystalline towards the front of the eye, Vesalius

locates the crystalline in the direct center of the eye, and he gives the vitreous and the aqueous

164

52 I have used Avicena, Liber canonis: De medicinis cordialibus  ; et Cantica, ed. Benedetto Rinio (Basel: per Ioannes Heruagios, 1556), 405f. I have also consulted the French translation of certain sections of the Arabic found in Abū Bakr Muḥammad ibn Zakarīyā Rāzī, ’Ali Ibn Al-’Abbās, and ’Ali Ibn Sīnā, Trois traités d’anatomie arabes, trans. P. De Koning (Brill, 1903). 660ff. On Avicenna and the Cannon in the Renaissance, see Nancy G. Siraisi, Avicenna in Renaissance Italy: The Canon and Medical Teaching in Italian Universities after 1500 (Princeton University Press, 1987).53 “quorum medius est glacialis: & ipse quidem est humor clarus, sicut grando: glacialis vero est rotundus, cuius minuit rotunditatem compresso ipsius ab anteriore parte eius ... & hic quidem humor est positus est in medio, quoniam est dignior locis.” Avicenna, Liber canonis, 405A.54 “Hic autem humor similis es vitro liquefacto: & color vitri liquefacti est clarus, & declinat ad parvam rubedinem: clarus vero est, quoniam nutrit clarum: parvae autem est rubedinis, quoniam est ex substantia sanguinis: & ipse non convertitur ad similitudinem eius, quod nutritur integre.” Avicenna, Liber canonis, 405A

humors the same volume.55 (See figure 3.3.) In his treatment of the eye Vesalius cites both On

the Usefulness of the Parts and On the Doctrines of Hippocrates and Plato. Although he does not

cite the two pseudo-Galenic works mentioned above, it is in my opinion quite possible that he

relied in particular on the Hunayn Ibn Ishaq’s On the Eye, generally known at the time as Galeni

liber de oculis translatus a Demetrio. As we have seen, reading this text is quite easy to think

that the crystalline humor was in the geometrical center of the eye, and this text is also one of the

165

55 Andreas Vesalius De humani corporis fabrica libri septem (per Ioannem Oporinum, 1555), 799-806.

Figure 3.3: Cross-sectional images of the human eye in three anatomical texts, showing the position of the crystalline humor and the relative sizes of the three humors, above, with accompanying representations of the crystalline humor. Note that Vesalius's diagram is the same in the 1543 edition.

Vesalius 1555 Valverde 1556 Platter 1583

few that fails to make a distinction between the shape of the anterior and posterior of the

crystalline humor.

One important issue regarding the placement of the crystalline humor is Galen's

insistence that, in addition to the aqueous humor that one observes in dissection, there is also a

region around the pupil filled with "an etherial pneuma of the nature of light."56 Galen says that

after death this part is "empty and the surrounding tunics become lax," and thus "it is clear that

the space was filled with some pneuma, or liquid, or both."57 Galen later emphasizes this point:

in living animals you see that the eye is exactly extended, every part being filled, and that no part of it is shriveled or lax, whereas if you care to dissect a dead diligently considered animal, you will see even before you do so that the eye is already somehow more shriveled than it is in its natural state.58

Galen's insistence that the front of the eye contains an etherial pneuma is used as confirmation of

his extramission theory of vision, and thus the fact that the size and placement of the humors of a

living eye differs from what is seen in dissection is a crucial piece of knowledge indicating

extramission and not intromission. However, Galen's insistence that the eye is more lax after

death is perhaps due to the fact that he did not dissect a fresh eye. In my own dissections of cow

eyes this laxness that Galen mentions is readily apparent after several days if the eye is kept cool,

and the eye becomes lax more quickly if kept at a warm temperature. When dissecting a cow’s

eye only several hours after slaughter, however, I was unable to detect much laxness of the eye,

166

56 Galen, Usefulness, 475.57 Ibid., 476.58 Ibid, 476. Later, Galen writes "If, then, when the animal is still alive, it is possible to see that both membranes [the iris and the cornea] are stretched and that when one eye is closed, the pupil of the other is enlarged, and if, when the animal is dead, you can see that the membranes are already lax even before the thin humor is emptied out and that they become extremely lax after emptied, it is clear that while the animal was living they were filled with both humor and pneuma. Now one of these [the pneuma], being thinner and less substantial, is easily evacuated before dissection, but the humor still remains because it needs an evacuation that is perceptible." Ibid, 476-477.

although I might not be as sensitive to this as Galen. It is possible, then, that Galen's insistence

on the difference between the amount of humor in the anterior chamber in a living eye compared

to a dead eye is due to his failure to examine eyes immediately after the death of the animal; this

is perhaps confirmed by Galen's description of the color of the vitreous humor, discussed below.

Vesalius appears to follow Galen in the belief that living eyes contain a subtle pneuma in

the anterior chamber. This would account for Vesalius’s textual description and visual depiction

that the aqueous humor and the vitreous humor are equal in size, and consequently for the

crystalline humor being in the center of the eye rather than, as most previous anatomists had

indicated, towards the front. Vivian Nutton has recently analyzed Vesalius’s notes in the margins

of his 1555 Fabrica. These notes seem to have been made in preparation for a revised third

edition that was never published, and they confirm the notion that Vesalius was following Galen

rather than primarily drawing from his own, careful dissections of the eye. In his notes Vesalius

offers no correction to the shape of the crystalline humor, but he does mention that only a small

amount of aqueous humor comes out of the eye upon dissection compared to the vitreous. He

gives two possibilities for this, the first is that in a living eye “one must conclude that it [the

aqueous] is largely composed of a sort of spirit and aerial substance” which supposedly

dissipates after death. As we have seen above this is Galen's position. After this Vesalius writes:

“perhaps someone [might say] that the vitreous humor occupies a larger space in the eye than the

rear portion and thus that the lens along with the vitreous humor [is placed] off-center in the front

167

part of the eye.”59 Vesalius’s language gives the

impression that he prefers the first explanation: he writes

that "one must conclude" the former, while "perhaps" the

latter is the case.60 He offers no correction to his accounts

elsewhere of the size of the various humors or the

placement of the crystalline humor, and although he does

give notes indicating corrections to some of his diagrams

does not indicate changes to his diagrams of the eye. In

any case his comments and corrections regarding the other

parts of the body do not seem to be based on new

observations made through dissection.61

Vesalius also described the crystalline humor as lenticular and symmetric, again here

seeming to follow following Galen’s somewhat ambiguous description as well as the Liber de

oculis falsely attributed to Galen. In a marginal illustration and accompanying text, Vesalius says

that its shape can be understood by removing a slice from the middle of a sphere, thus giving a

168

59 Vivian Nutton, “Vesalius Revised. His Annotations to the 1555 Fabrica,” Medical History, 56 (2012): 435. Translation his. In a footnote Nutton mentions that a referee points out that it would be difficult to determine the place of the crystalline humor once the aqueous humor had leaked out and the bulbous collapsed. My dissections with fresh and corrupted cow’s eyes lead me to strongly disagree: the place of the crystalline humor and the volume of the vitreous are obvious, especially if one is dissecting with the intent to discover this. Nutton also notes that earlier anatomists also divided the eye into two equal cavities, which is largely incorrect. I would like to thank Gideon Manning for bringing this article to my attention.60 "Quia vero huius humoris dum oculum dissecamus parva & vitrii humoris mole vix comparanda occurrit portio, colligendum est illam magna ex parte spiritu quodam aereaque substantia constatre eam sedem occupante, quam aqueo humori inter crystallinum et corneam tunicam pelucendtem alioquin vulgo tribuimus. Quamvis enim forte quispiam humorem vitreum ampliorem oculi sedem {implere} quam posteriorem implere hincque crystallinum simul cum vtreo extra centri regionem in anteriori..." Vivian Nutton, “Vesalius Revised,” 435 n. 48.61 Note that Nutton concludes that there is no explicit mention by Vesalius that he had dissected a new corpse, and that most of his other corrections are not based on new anatomical knowledge. Ibid., 434-5.

Figure 3.4: Marginal figure showing how to derive the shape of the crystalline humor from a sphere. Vesalius 1555, 801.

precise geometrical description of its symmetry (figure 3.4). In Galen, on the other hand, we find

many statements that the crystalline is a flattened sphere, but the cause of this is either because a

flattened front is better for vision, or else that a perfect sphere would tend to rotate within the eye

while a flattened sphere is more secure. Galen never explicitly refers to the shape of the rear of

the humor, and never says whether the crystalline is symmetrically flattened or not.62 The great

majority of Vesalius’s predecessors in anatomy — including Avicenna, Mondino, Zerbi,

Berengario, Benedetti, as well as the Anatomia vivorum — describe the crystalline as asymmetric

with a flattened front, and thus it is curious that Vesalius gives such a precise account of a

symmetrical, lenticular shape.

Vesalius seems to have made definite what is somewhat ambiguous in works by (or

thought to be by) Galen, and to have done so in opposition to, or ignorance of, statements by

both previous anatomists and perspectivists. The case of the eye provides an interesting

complement to Bylebyl’s statement that “Galen’s anatomy was so much more sophisticated, in

terms of both detailed content and dissection technique, that it effectively rendered obsolete even

the best of what are usually called pre-Vesalian anatomists.”63 Although Vesalius’s account of the

eye was for the most part longer and more “sophisticated” than the anatomists reviewed above,

Vesalius’s approach to the eye differed from his anatomical predecessors due to his close reading

of Galen. Picking up Galen’s insistence that the eye contains a pneuma or spirit in the front

chamber which dissipates immediately upon death, and Vesalius appears to assume that the size

and configuration of the humors as revealed through dissection is not representative of a living

169

62 Galen, Usefulness, 467-8, 479; Galen, On the Doctrines, 459.63 Jerome Bylebyl, “The School of Padua,” 357. On problems with Galen’s understanding of the eye from a modern point of view, see Galen, Usefulness, 467 n. 10.

eye. Drawing heavily on Galen, Vesalius appears to reconstruct what is the case in a living eye.64

Although they may have likewise attempted to reconstruct the shape, size, color, and

configuration of the humors in a living eye, his predecessors did not do so with a Galenic theory

of vision in mind, and in any case appeared to assume that fewer changes occur to the eye upon

death.

Vesalius's work is titled De humani corporis fabrica, and so it is no surprise that for the

most part it only explicitly treats the fabric (or structure, or history) of the eye. Nevertheless it is

not "theory neutral," but rather shows a bias towards a Galenic extramission theory of vision.

Moreover, at the very beginning of his chapter on the eye he creates an analogy between the eye

and the cosmos:

We review the eye in exactly the same way that the parts of the world [are considered], either from earth to water, air, fire, the heaven of the moon, and so on to the outermost heaven, or else from the heaven toward the center of the world. In fact the fabric of the eye, looked at with respect to [its] arrangement, can be compared to the world and to an egg. We will conveniently deal with this; in order to deliver precisely, and afterwards to stick most securely in memory, I will first remove [the parts] from the center to the outer surface, and afterwards from the latter to the former.65

While Vesalius's comparison is not original, it is nevertheless a striking image, and I have not

found an anatomical work in which the analogy between the cosmos and the eye is so explicit.66

170

64 On problems with Galen’s understanding of the eye from a modern point of view, see Galen, Usefulness, 467 n. 10.65 “pari prorsus nimirum modo, quo mundi partes, vel à terra ad aquam, aerem, ignem, lunae coelum, ac sic deinceps ad extimum usque coelum, vel ab hoc coelo versus mundi centrum, recenseremus. Mundo namque & ovo, oculi fabrica, quod ad constructionem spectat, conferri potest. Quam, ut exactiùs tradatur, ac postmodum memoriae firmiùs haereat, à centro primùm ad eximam superficiem, & postmodum ab hac ad illud opportunè pertractabimus.” Vesalius, Fabrica, 801. 66 In connection with this, particularly because Vesalius might have been drawing upon Hunayn Ibn Ishaq's work on vision, see Bruce Stansfield Eastwood, “The Elements of Vision: The Micro-Cosmology of Galenic Visual Theory according to Ḥunayn Ibn Isḥāq,” Transactions of the American Philosophical Society, 72 (1982): 1–59. Cf n. 35 above.

This cosmic model of the eye, combined with the Galenic idea that the front chamber of the eye

is more copious in a living eye, appear to have together contributed to Vesalius’s representation

of the humors of the eye.

Another possible reason for Vesalius’s idiosyncratic depiction might be due to his

dissection techniques, which were geared towards spectacular public displays rather than close,

private investigation. In my own reconstructions of ocular dissections and experiments, cow, pig,

and sheep eyes dissected within several hours of slaughter are not particularly lax, and the

conclusion that the crystalline humor is placed towards the front of the eye is difficult to avoid. I

was, however, aware that this was the case; I surmise that this could have slipped Vesalius’s

notice only if he either did not dissect an eye with the intent to discover whether the crystalline

humor is placed towards the front of the eye or in the geometrical center. That Vesalius did not

do so seems to imply that Vesalius did not take not of his anatomical predecessors on this point,

or that he ignored them and assumed, with Galen, that a dead eye differers structurally from a

living eye.

I have also dissected cows eyes that were left to degrade (though sealed in plastic) for

seven days at an ambient temperature that ranged between 5 and 20 degrees centigrade. Despite

the corruption that occurred it was difficult to believe that one could conclude, during a

reasonably careful dissection of the eye, that the aqueous and the vitreous had anything close to

the same volume. After such corruption the vitreous, now somewhat looser and less congealed,

nevertheless held its position within the eye and the crystalline was securely attached to it

towards the front of the eye. Dissecting the eye by making a cut along the largest circle

perpendicular to the axis of vision, as Vesalius himself (along with most anatomists at the time)

171

describes, it was clear that the crystalline is positioned well in front of this great circle. After

detaching the crystalline from the vitreous the flattened front and protruding, gibbous anterior of

the crystalline were also clearly observable. When describing the interior of the uvea Vesalius

quite clearly describes what is now called the tapetum lucidum, an iridescent reflective

membrane behind the retina on some animals (not humans) that improves night vision by

reflecting light back to the retina.67 Colombo attacks Vesalius for this, noting that the uvea is

completely black in man and that this iridescence of the uvea occurs only in certain animals

(which includes cows and sheep, but not pigs). Colombo therefore accuses Vesalius of dissecting

beasts and attributing what was found therein to humans, the very sin of which Vesalius accuses

Galen.68 Indeed, both at the very beginning and at the end of his section on the eye Colombo

vehemently attacks Vesalius, and thus his treatment of the eye framed by a criticism of Vesalius.

The tapetum lucidum, however, was not commonly noticed before Vesalius, and so Vesalius

seems to have observed some aspects of the eye with care. Overall, however, his investigation of

the eye appears somewhat casual and sloppy compared to his contemporaries.

Vesalius’s public anatomical demonstrations were spectacular events where the large

structures of the body were emphasized, while the human eye is a small organ whose parts

cannot be easily shown in a crowed pubic dissection. The eye would have been dissected late in

172

67 "Caeterùm interna uveae superficies diversis, sed omnibus interim hominibus iisdem, interstinguitur coloribus. In posteriori enim oculi sede, qua haec tunica primùm pronascitur, subalba est: mox viridis, & dein caerulea iridisin modum efficitur. atque hos colores adhuc in posteriori oculi sede interna haec superficies possidet, in anteriori autem oculi sede universa impense nigricat.” Vesalius, Fabrica, 804.68 “Uveae nomen fortita est, eo quòd uvea granum videatur esse, cui capulus ademptus fuerit. in hac, ut dicebam, magna colorum varietas spectatur. in hominis namque uvea nigrum colorem cernes, puniceum, ceruleum, rubrum: at in bove, preater hos viridem & cianeum.” Realdo Colombo, De re anatomica libri XV (Venice: ex typographia Nicolai Builacquae, 1559), 218. At the beginning of his treatment of the eye Colombo accuses Vesalius of attributing structures in the eyes of beasts to men: “Scito praeterea neminem ante me hominis oculum descripsisse, sed omnes belvinum oculum descripsere, magno & turpi errore, in quem ipse quoque Vessalius incidit, in eius inversa pene formatione cum aliis Anatomicis deceptus.” Ibid., 215-16.

his program if at all. Given the importance of public dissection for Vesalius, and that visual

theory was not a contested topic among anatomists and physicians at the time, the most likely

reason for Vesalius’s anomalous description of the eye is that he never carefully dissected one.

The surviving notes on Vesalius's 1540 dissection in Bologna suggest this. The student Hessler

writes:

And he cut the eye through the middle with a razor, and he shook out into the hand the substance of the eye: the first humor, he said, is the albugineus one, the second is the vitreous and the third is the crystallinous humor, by which properly the vision occurs, and it is hard like a jewel. All this, he said, anybody can see for himself at home.69

Along with many of Vesalius’s critics later in the century, I am left wondering if Vesalius ever

did carefully see this for himself at home.

Vesalius’s depiction of the humors quickly came under criticism, perhaps most famously

by Realdo Colombo at Padua, and subsequent anatomists generally placed the crystalline humor

towards the front of the eye.70 Rather than building on pre-Vesalian works, later anatomists gave

textual descriptions of both the position of the crystalline humor and the proportional volume of

the three humors in explicit opposition to Vesalius: the proportional volume of the vitreous

humor increased, the crystalline humor was moved to the front of the eye, and the asymmetry of

173

69 Baldasar Heseler and Ruben Eriksson, Andreas Vesalius’ First Public Anatomy at Bologna: 1540 (Almqvist & Wiksell, 1959), 290–291.70 “Erroresque Vessalii in historia de oculo nullo negocio deprehendes: quem mirum est in membrani adeo nobilis descriptione tantopere lapsum esse: nam non modo in musculis & membranis, sed in humoribus quoque decipitur, & tota errat via, existimans cristallinum humoremque in centro oculi exquisite situm esse; item tantum humoris aquei, quantum vitrei reperiri." Colombo, De re anatomica, 220. Colombo also accuses both Galen and Vesalius of introducing errors by using the eyes of beasts in place of human eyes: “Scito praeterea neminem ante me hominis oculum descripsisse, sed omnes belvinum oculum descripsere, magno & turpi errore, in quem ipse quoque Vessalius incidit, in eius inversa pene formatione cum aliis Anatomicis deceptus. quod verum esse facile perspcies, si Galeni, Vessalii, aliorumque Anatomicum historiam de oculo cum nostra contuleris & profecto non leveter hi homines accusandi sunt, Galenus praesertim, & post ipsum Vessalius, qui tantam rem, tam illustrem, tam optatam, tam negligenter scribendam putarent, belvinum oculum pro humano dissecantes.” Ibid., 215-6. See also Lindberg, Theories of Vision, 173-174.

crystalline humor was acknowledged. These changes were also mirrored in changes in visual

depictions of the eye, most of which were not original compositions but rather modifications of

Vesalius’s diagrams in Fabrica. (See figure 3.3.)

The aranea, on the other hand, was described as continuous with the retina by almost all

sixteenth-century anatomists with the important exception of Felix Platter, whose images and

descriptions Kepler drew upon in his 1604 Ad Vitellionem paralipomena. Platter says that the

retina ends at the ciliary process (a name that Platter seems to have coined for the circular frill

behind the iris, formed from the choroid and extending to the crystalline humor).71 As we will

see in the next chapter, the growing consensus on these two points of anatomy had important

ramifications for understanding not just the structure of the eye, but the visual process as a

whole. This is especially because the importance of those shapes was considered in light of

Vesalius’s portrayal of anatomy: according to him, anatomy is at once a scientia and an erudite

activity that demands the analysis of ancient texts along with the body.72 Additionally, in the next

chapter we will see that Platter’s break from the dominant opinion that the aranea was of the

same substance of the retina was used by Kepler to strengthen his claim that the retina, and not

the crystalline humor, was the seat of visual sensation.

Vesalius, then, seems to be the catalyst for developments in ocular anatomy, and as a

consequence in visual theory, in two opposing ways. Later anatomists formed their consensus of

174

71 "Hic ... Accumbit uveae membrae immediatè, non tamen illi nectitur, atque ultrâ medium oculi usque ad ciliares processus, ubi desinit”. Felix Platter, De corporis humani structura et vsu (ex Officina Frobeniana, per Ambrosium Frob., 1583), 187.72 Nancy G. Siraisi, “Vesalius and Human Diversity in De Humani Corporis Fabrica,” Journal of the Warburg and Courtauld Institutes 57 (January 1, 1994): 65-66; Nancy G. Siraisi, “Vesalius and the Reading of Galen’s Teleology,” Renaissance Quarterly 50, no. 1 (April 1, 1997): 1–37; Andreas Vesalius, The Fabric of the Human Body: An Annotated Translation of the 1543 and 1555 Editions of “De Humani Corporis Fabrica Libri Septem,” 2 vols. (Basel: S Karger Ag, 2013), 4.

the shape and size of the humors of the eye by refuting Vesalius (and, to some extent, Galen)

rather than building upon pre-Vesalian medieval and renaissance texts. Additionally, the

importance of those changes was considered in light of Vesalius’s claims about the relationship

between anatomy and natural philosophy. The revival of not just Galenic anatomy and all that it

entailed (including account of structure, action, and the use of the parts), but Galenic logic,

Galenic theories of method and teaching, and Galenic natural philosophy overall had a large

impact on sixteenth-century medicine and anatomy. Although no careful survey has been made to

date, the humanistic revival of Galen’s works seems to have led to an increase in the number of

sixteenth-century physicians that professed an extramission theory of vision. Along with this was

a renewed attention to visual theory among physicians, including those, like Fabricius, who went

to great effort to refute Galenic and Platonic extramission theories of vision.

§ 3.4: The Meaning of Dissection in Fabricius’s Philosophical Anatomy

Fabricius’s first paragraph in his first anatomical work of his ambitious Theatrum totius animalis

fabricae (The Theatre of the Whole Animal Fabric) begins with the following.

Our discussion will be in three parts. First we will reveal the entire fabric and structure of the eye. Then we will proceed to the action of the eye, that is, to vision itself. Finally, we will contemplate the utilitates of the eye, not only according to the eye as a whole (in universum), but also [the utilitates] of the individual parts of the eye themselves. In general, moreover, we hunt all these things through dissection. Indeed, dissection (if one judges correctly) has the advantage (usum) that it makes evident not only those things which belong to the eye — that is, structure and history — but it also leads to an acquaintance with the

175

actions or faculties, and finally it uncovers and declares the utilitates, of the eye. We begin, however, to dissect the eye exactly as it presents itself to sight.73

Contained in this brief outline for his work is a powerful statement about dissection: that it leads

one to understand actions and faculties of a living body, not just the structures in a dead one, and

that it uncovers the utilitates, or the final causes of the existence of the parts of the eye. Anatomy

reveals the universal part, not merely the particular individual under dissection. It is an empirical

investigation, but at the same time a philosophical one seeking causes. In his preface to De voce,

which was published with De visione, Fabricius says that one can consider four parts to anatomy:

in addition to actio and utilitas, what is referred to as historia is more properly divided into two:

dissectio and historia.74 Through dissection the organs are brought forth and shown, but this is

done for the sake of comparing, and this is so that the other three (history, action, and use) can be

brought to light. Although he doesn’t elaborate on what comparing here means, we can gather

from his works that he refers to both comparing several animals of the same kind in order to

discern what is accidental and what is not about a part or organ under consideration, and also to

comparing one type of animal to another in order to understand what is the same and what is

different across different kinds of animals. This comparison, it must be remembered, is always

done on the level of the part and the organ to which that part belongs (and, perhaps, what we

176

73 “Triparta erit nostra haec disputatio. Primò enim totus oculi fabricam structuramque patefaciemus. Deinde agemus de oculi actione, hoc est de visione ipsa. Postremò tum oculi in universum, tum singularum ipsius oculi partium utilitates contemplabimur. Haec autem omnia ferè per dissectionem venabimur. dissectio enim (si quis recte aestimet) eum habet usum, ut tum ea, quae oculis insunt, hoc est structuram & historiam, manifestet: tum in actionis facultatisve notitiam deducat: tum denique oculi utilitates aperiat atque declaret. Incipiemus autem oculum dissecare, prout sese nobis offert aspectui.” Fabricius, De visione, 1.74 The first important analysis of Fabricius’s use of historia, actio, utilitas is in Cunningham, “Fabricius and the ‘Aristotle Project,’” especially p. 216. Cunningham also adds a fourth part, demonstratio, but he does not notice the distinction between dissectio and historia. See also Benjamin Isaac Goldberg, “William Harvey, Soul Searcher: Teleology and Philosophical Anatomy” (PhD Dissertation, University of Pittsburgh, 2012), 90–104; Peter Distelzweig, “Fabricius’s Galeno-Aristotelian Teleomechanics.”

might call the system as well), and the aim is to understand the universal part or organ.

Dissection and history, he says, are exemplified by Aristotle’s History of Animals and Galen’s On

Anatomical Procedures. Next historia (strictly considered) reveals what belongs to the organ: the

temperament of the parts within the organ, and what follows from temperament. Thus, historia

includes an account of the elemental composition of the part, and it connects Aristotle’s History

of Animals with the discussion at the beginning of Book II of On the Parts of Animals, where

Aristotle talks about the three levels of composition that must be accounted for in the description

of an organic part. From this historia the actio or action of the organ and its parts is then

revealed, which Fabricius calls the office or function (munus seu functio) of each organ. It is, in

short, what the organ does, the movement or activity of the organ or part, including actions

produced by natural faculties; with respect to his three works in De visione, voce, auditu,

Fabricius relates actio to Aristotle’s On the Soul and On the Generation of Animals, as well as

Galen’s On the Natural Faculties and On the Doctrines of Hippocrates and Plato. Finally, after

understanding the actio of the part or organ its usefulness or utilitas is discovered, which he says

is nothing other than the reason for the action; that is, the utilitas is the for-the-sake-of-which, or

the final cause, of the action. This step corresponds to Aristotle’s On the Parts of Animals and

Galen’s On the Usefulness of the Parts. It is interesting to note that not only does this method

aim at a teleological explanation, but this process of investigation and exposition is itself

177

teleological, with each step being for the sake of the next level of analysis.75 The activity of

dissection, then, ultimately contributes to an understanding of the final cause, the utilitas, of the

parts, organs, and perhaps systems of an animal; dissection is not performed to pile up

particulars, or to discover new parts absent an account of their purpose.76 It is in this sense that

Fabricius “hunts” all things concerning the eye through dissection.

Unlike the other three stages essential for his Galeno-Aristotelian philosophical anatomy,

the dissection stage stands largely outside the text itself — although it is represented in part

through his anatomical plates, and the reader is also guided by Fabricius’s remarks on how to

dissect the eye in part 1, section 10. Dissection lies in the realms of both investigation and

teaching: the anatomist might discover new parts or structures, but the process is not over until

these things can be easily shown, and explained, to students and the public (and, ultimately,

when the utilitates of the parts are given). Dissection also involves manual skill and technique,

which no text can convey on its own. In Chapter 10 of his historia in De visione, Fabricius has a

short treatment on how to dissect the eye, which he says he demonstrates in his public lectures as

178

75 “Quod si ex tribus hisce partibus prima dividatur; ut aucto iam earum numero fiant quatuor, Dissectio, Historia, Actio, Usus: nihil reprehendo. Video enim & veteres quosdam id fecisse, & fieri non incommodè posse; cum re vera, exactè si distinguas, aliud sit Dissectio, aliud Historia. Dissectio primùm rationem dissecandi organi tradit, quotque modis ea fieri & possit, & debeat, ostendit. est autem ad hunc finem comparata, ut reliqua tria, videlicet historiam, actionem, & utilitatem patefaciat. Historia autem ea exponit, quae organo insunt, nimirum, temperamenta quae consequuntur, quaeque accidunt; quae omnia aperiuntur dissectione; qua eadem innotescit etiam Actio, ut & Galenus testatur, & nos in Anatomica methodo demonstravimus. Est autem Actio uniuscuiusque organi munus seu functio. Utilitas verò nihil aliud, quam id, cuius gratia tributa cum ipsa actio, tum ea, quae insunt. Atque has quatuor tametsi distinctas reipsa videmus esse partes; tamen ita inter se apta sunt & cohaerent, separari omninò ut non queant.” Fabricius, De voce, ii.76 For more on sixteenth-century uses of historia, and historia anatomica in particular, see Gianna Pomata, “Praxix Historialis: The Uses of Historia in Early Modern Medicine,” in Historia: Empiricism and Erudition in Early Modern Europe, ed. by Gianna Pomata and Nancy G. Siraisi (Cambridge (Mass.); London: MIT Press, 2005), 105–46. A brief account of Fabricius’s use of historia, actio, and utilitas is found in Siraisi, “Historia, Actio, Utilitas.” A more thorough account, and its relationship to William Harvey, can be found in Peter Distelzweig, “Descartes’s Teleomechanics in Medical Context: Approaches to Integrating Mechanics and Teleology in Hieronymus Fabricius Ab Aquapendente, William Harvey, and René Descartes” (unpublished PhD Dissertation, Pittsburgh, PA: University of Pittsburgh, 2013).

well. He gives two ways to “dissect the tunics, humors, and nerves of the eye” (he omits the

muscles): one involves cutting the eye longitudinally (from back to front) and the other

transversely, or perpendicular to the visual axis. The fat, muscle, and tendons must be denuded

from the eye, leaving only the sclera and cornea visible, and to dissect the eye the “sharpest of

179

Figure 3.5: Table 4 from Fabricius’s De visione (Venice 1600). Note figure 29, which depicts the retina (protruding from the eye) pulled together into a mass after the vitreous and crystalline humors were removed. Witnessing the actual retina in this way was supposed to convince the viewer that the retina is of the same substance as the cerebrum, although the force of this demonstration is lost in the engraving. This is one indication that this text were meant to be performed, rather than read passively.

knives” (acutissima cultri) must be used. His instructions allow one to reproduce that which he

shows in table 4, figure 29 at the end of the historia section, and thus his images can be seen as

not only a naturalistic representation of the eye, but perhaps more importantly as a guide for

one’s own dissection. (See figure 3.5.) This chapter and its relationship to the plates is a reminder

that the text was intended not just to be read. The dissections were meant to be reenacted and

performed so that the "reader" fully understands the shape, size, position, and most importantly

complexion of the parts under investigation. This expectation of personal visual and tactile

experience on the part of the reader is often appealed to later, when Fabricius attempts to

convince the reader of his conclusions in the actio and utilitas sections.

Note that Kepler, in his Paralipomena, says that he has never seen a dissection of an eye.

That he gives an account of the utilitas of the crystalline and the retina without having

experienced the colors and complexion of the humors personally would certainly have reduced

the epistemic reliability of his account of sensation for both Galenic physicians as well as natural

philosophers. This will be discussed at length in § 5.1, and is a major theme in Chapter 5 overall.

§ 3.5: Transparency and Complexion in Historia

We now turn to section 1 of De visione. After presenting his mini-manifesto on anatomy,

Fabricius then discusses the substance of the eye in general terms. He says that the eye comes

from the expansion and enlargement of the optic nerve, whose three parts correspond to the three

primary substances of the brain.77 The outer part of the eye, known as the sclera (sclerodes tunica

in Latin, from the Greek skleros meaning hard) is the same substance of the thick (crassa), tough

180

77 “Oculi tunicae ex nervo expanso atque amplificato resultant, qui cum ad constituendum oculum devenit, statim expanditur: & prout tres substantias seu distincta corpora vervus, optinet, sic tres varias ac diversas tunicas expansus constituit porrigitque.” Fabricius, De visione, 1-2.

outer membrane of the optic nerve known as the dura mater. (See figure 3.1.) The sclera, in turn

is continuous with the transparent cornea. The tunic beneath the sclera, the dark-colored choroid

(choroides tunica), is according to Fabricius an expansion of the substance of the pia mater, the

second, inner membrane of the optic nerve, and the choroid gives rise to the uvea at the front of

the eye. Fabricius also calls this the tenuis meninx. Finally, the retina is of the same substance as

the innermost part of the optic nerve, what he later calls the marrow of the nerve (nervi medulla),

which is the same substance as the innermost part of the brain. Importantly, he also says that the

retina is connected to the aranea (today called the lens capsule) that surrounds the crystalline

humor.78 With the exception of whether the aranea and the retina are connected (as mentioned

above in connection with Kepler and Platter) the above description of the eye was

uncontroversial at the end of the sixteenth century.

As we saw in the last chapter, Zabarella considered the question of the origin of color to

be fundamental to a theory of vision. Although Fabricius never addresses this issue specifically,

it is relevant to his theory of vision, and so his position on this matter must be sought in the

various places where he reveals some aspect of it. In his treatise on the formation of the egg and

chick, De formatone ovi et pulli (Padua, 1600), Fabricius mentions that the eyes are one of the

first structures to emerge in the formation of the chick in the egg. He follows Galen in comparing

the creation of the fetus to that of a ship: just as the keel is laid down first, so too is the spine

181

78 Note that modern anatomy describes the optic nerve as having three meningeal layers in addition to the inner optic nerve: the dura mater, the arachnoid layer, which Fabricius does not recognize, and the pia mater, all of which connect to their respective layers surrounding the brain. Modern anatomy does consider the sclera to be an extension of the dura mater that also surrounds the brain, and considers the retina to be an extension of the inner nervous substance — i.e., an extension of the optic nerve proper. However, modern anatomy does not consider the choroid (primarily a vascular layer) to be an extension of the pia mater; instead the choroid comes from various arteries that pierce the sclera at several points. These arteries are easy to miss in a dissection of the eye given that they are small, drained of most of their blood, and surrounded by muscles and fat (and thus scraped away during the initial denuding process).

among the first structures to be formed.79 However, because the spinal cord lies inside the spinal

column, it is necessary that the spinal cord, and along with it the brain, be formed first. Note that

this is in contrast to both Aristotle and, later, William Harvey, who both claim that the heart is the

first structure to be created.80 In addition to the spine, brain, and the bones, the eyes are formed

very early, and are also large and conspicuous. Many, he says, have wondered why this is the

case, and Fabricius gives several possible reasons for the early formation of the eye.81

First, he says, it is perhaps because the interior parts of the eye are diaphanous, and

because they cannot be generated from red-colored blood, that they must be principally

generated from diaphanous bodies such as chalazae (the small stringy parts that suspend the yolk

of an egg in the albumen). As a result Nature can only form them slowly. This relates to an

important point that will be covered in the next chapter about the usefulness of the vitreous

humor. For Galen, the vitreous humor must provide nutrition to the all-important crystalline

humor precisely because, if blood were assigned this task, then the transparency of the crystalline

would be marred in the process. Zabarella finds this explanation not only unnecessary (because it

places limits on Nature which other examples of nourishment do not bear out, e.g., blood turning

into semen) but he claims that it creates a number of other problems. While Fabricius also rejects

Galen’s account of the usefulness of the vitreous, and does so for many of the same reasons, he

does not, as Zabarella does with zeal, impugn the ancient doctor’s competence in observation or

philosophizing in the process. The first solution Fabricius gives for why the eye is formed early

in fetal development, then, contradicts his own opinion presented in De visione about the ability

182

79 Fabricius and Adelmann, Embryological Treatises, 200-202. 80 Ibid., 733 n. 133.81 Adelmann lists a number of discussions of this. Ibid., 732, n. 129.

of Nature to turn blood into completely clear and untainted substances such as the crystalline

humor during nourishment. The inclusion of this argument, and the fact that he does not reject it

outright, points to Fabricius’s overall strategy of reconciling his account with Galen’s whenever

possible.

Fabricius’s second reason considers the case that a good deal of blood does in fact

participate in the generation of the eye, a position that implicitly rejects Galen’s statement that

blood is incapable of directly providing nutrition to a transparent substance without marring it. It

may be surmised that this is the argument Fabricius prefers, and that the others are included for

the sake of completion. In the case of blood generating and nourishing the eye directly, nature

must generate parts with contrary properties immediately next to one another: “namely dark,

black, and fleshy (corpulentae) parts like the uvea and the choroid, and from very diaphanous,

white, loose-textured (rarissimae), and pure parts like the crystalline, aqueous, and vitreous

humors, and also the cornea, conjunctiva, retina, and aranea.”82 Although within the power of

Nature, this difficult task takes a good deal of time, and therefore the process must be started

early on.

The last reason for the early development of the eye that Fabricius includes is that eyes

are necessary for the life of an animal once they are born, and thus Nature must begin at once in

order to perfect these organs. This argument seems appended without conviction; it applies to

183

82 “Quòd si concurrerere multum sanguinis dicamus, omnino alio nomine oculi priùs, & gignuntur, & perficiuntur: proptereà quòd oculi ex diversis admodum, & inter se contrariis partibus conflantur, opacis scilicet, nigrisque, & corpulentis, ut uvea tunica, & choroide: & ex diaphanis albissimis, rarissimis, & purissimis, nimirum crystallino, aqueo, & vitreo humor: item cornea, coniunctiva, retina, aranea.” Adapted from Adelman’s translation. Hieronymus Fabricius, Hieronymi Fabrici ab Aqvapendente olim anatomici patavini celeberrimi de formatione ovi, et pvlli tractatvs accvratissimvs (Padua 1621), 44.

other parts of the body more forcefully than the eyes, especially since not all animals are born

with eyes open (such as cats, dogs, and most rodents).

While Fabricius’s treatment of many parts of the eye in De visione are tangential to our

purposes (including his treatment of the muscles, the bones of the orbit, the eyelids and lashes,

and the tear ducts), some discussion of the tunics of the eye is necessary. First, it should be noted

that Fabricius is as complete as possible in his discussion. There was a good deal of controversy

over how many distinct tunics are in the eye, with answers ranging from seven to two with every

number in between. The solutions depended upon two factors: what criteria were employed for

deciding whether one body part was a different substance from another, and whether being called

a tunic implies that the part performs the task of protecting the inner parts of the eye. For

example, the sclera and cornea are continuous with one another, and are identical in almost every

property apart from the transparency of the cornea versus the whiteness of the sclera. Does this

difference in transparency mean that they are different substances, thus making them two tunics

instead of one? Likewise, should the retina be disqualified as a tunic because it does not protect

the inner humors in the way that the sclera and choroid do? Here we see Fabricius’s tendency for

reconciliation: he sidesteps the question entirely, arguing that an accurate account if the structure

of the parts combined with determination of their usefulness is all one needs.

Fabricius describes the cornea as protruding from the eye, which not all previous writers

described or depicted. Galen says that nature made the cornea “grow thinner and at the same

time denser, and, gradually bringing it forward, she ended by making the very middle of it

extremely thin and dense.”83 For Galen the protrusion does not have a purpose in itself, but is

184

83 Galen, Usefulness, 470.

merely the means to stretch thin the sclera and make it transparent; Galen gives an account from

material necessity rather than final cause. Most notably Vesalius fails to describe it as protruding

in his text, and in his image the cornea is depicted as not deviating from the sphere described by

the sclera.84 Vesalius’s image was copied in many anatomical works, and while many aspects

were changed in these depictions (e.g., the position and shape of the crystalline described above)

the protuberance of the cornea was not always added to these depictions. (See figure 3.3.) Lastly,

it should be noted that while none of the three al-Ḥasans (i.e., ibn al-Haytham, Alhacen, and

Alhazen) describes the protuberance of the cornea, many of the Latin perspectivists whom he

influenced did, although the diagrams accompanying their texts are often ambiguous.85

Fabricius describes the cornea as “tough, dense, thin (tenuis), polished, and diaphanous,

but of a different diaphaneity and more dense than air....”86 An accurate and relatively

standardized vocabulary was key for anatomists and physicians, and Fabricius spends a good

deal of time scrutinizing ancient terms and descriptions of parts. Fabricius would therefore have

an interest in being clear about how terms like dense (densa), thin (tenuis), and diaphanous

(diaphana) are related to one another, how these properties relate to the material composition of

the part, and how exactly these properties were determined through either dissection and optical

experiment. We see his careful attention to these terms most clearly in the distinction he makes

later on between several different kinds of density or transparency and their effects (§ 4.4).

185

84 Vesalius, Fabrica, 804-5.85 That is, Ibn al-Haytham, Alhacen, or Alhazen. See: Alhacen and A. Mark Smith, “Alhacen’s Theory of Visual Perception,” xxxviii-xxxviii, 350, 400 n. 34. Also note the diagram in Risner’s edition in Alhazen and Witelo, Opticae Thesaurus, ed. by Friedrich Risner (Basel, 1572), 5.86 It is “dura, densa, tenuis, perpolita ac diaphana, diaphano quidem ab aere diverso, ac densiore...” Fabricius, De visione, 5.

Optical experiments played a somewhat limited, but nevertheless important, role in

determining the properties, activity, and ultimately usefulness of the parts of the eye for

Fabricius, and these experiments also put the treatise in a certain dialogue with works in the

optical tradition, particularly with Alhazen. This engagement with Alhazen and the optical

tradition, however, is a complicated one, and this shows in the terminology used to describe the

parts of the eye and what sort of optical effects these terms point to, including those of refraction,

reflection, and the capturing of images (in the way that a translucent or cloudy body might

appear to “capture” images). In Riser’s edition of Alhazen we read that the cornea is a “tunica

fortis, alba, diaphana....”87 Literally, this might be rendered as a strong, white, and transparent,

but “fortis” here almost certainly means tough or durable, while “alba” is likely a reference to the

lack of tint to the cornea and not that it is the color of milk, for example. Alhazen says that the

cornea is so called because of the similarity to how horn can be made “bright/untainted and

clear” (alba et clara), and in this description he is almost certainly following Galen.88

Horn was used for a variety of purposes from antiquity on. Producing transparent horn —

which can be quite transparent indeed — could involve a process of months-long soaking in order

to separate the core from the outer part; the outer cone is then cut, heated and flattened under

pressure, and then scraped thin to produce transparent sheets.89 These sheets were used for a

186

87 Alhazen, Opticae thesaurus, 3. 88 Galen writes: “You will think it wonderfully like horn that has been cut thin. Hence those skilled in anatomy, thinking the name hornlike [tunic] appropriate, have called it this, and the name has always remained to this day. For this hornlike tunic, being made thin, hard, and dense, must straightaway become clear also, so as to be the most suitable for transmitting light, just as horn is, that has been carefully thinned down and polished.” Galen, Usefulness, 470.89 This process is described in Isaac Smith Homans, A Cyclopedia of Commerce and Commercial Navigation (Harper, 1858), 991. Given the relatively unsophisticated techniques used, it is not unreasonable to assume that the artisanal process used antiquity is the same or similar to the nineteenth-century one given here.

variety of purposes, including windows, lantern covers, and, from the middle ages on at least,

transparent book covers or hornbooks. Thus, the term “cornea” establishes a direct analogy with

the combination of toughness and transparency present in commonly used horn products that are

the result of a long artisanal process.

Fabricius, like Galen, says that the cornea is made thin (tenuis) in order to make it

diaphanous. Nevertheless, despite its thinness he says that the cornea is not simple, but rather is

composed of three to four layers that can be discerned by separating them with scissors or a

knife.90 These layers, Fabricius says, are like several coats of laminate that are applied one over

the other. However, tenuity or thinness here does not seem to be used in the same way that the

thinness or subtlety of air is supposed to explain its transparency.91 He appears to be simply

saying that, like horn, if the measurable thickness of the body becomes too great the passage of

light is hindered. However, it is certainly possible that the term tenuis is doing double duty here.

We must turn to Fabricius’s discussion of the humors of the eye to determine the use of

these terms and their relevance for the issues at stake. Chapter 5 of the historia is on the retina

(or net-like tunic) and aranea (or web-like tunic). Fabricius considers these to be a single,

continuous tunic that arises from the marrow of the optic nerve (nervi medulla), which is of the

substance of the brain. Fabricius relates a common observation that goes back to Galen at least:

187

90 Fabricius, De visione, 5. Note that modern science distinguishes between at least five layers in humans, and four in some other animals. Just recently, however, a claim to the discovery of a sixth layer has been made: Harminder S. Dua, Lana A. Faraj, Dalia G. Said, Trevor Gray, and James Lowe, “Human Corneal Anatomy Redefined: A Novel Pre-Descemet’s Layer (Dua’s Layer),” Ophthalmology, 120 (2013): 1778–1785.91 This is made clear when Fabricius gives the final cause of the tenuity of the cornea. “Oportuit verò eandem tenuem esse. Nam etsi multiplex est, hoc est ex quatuor ferè tunicis conflata: tenuis tamen est; ne fortè dura densaque cum sit, simul crassior existens, lucis transitum praepediret, uti evenit crassiori cornu, ac vitro triangulo, quod lucem tantum solis primam transire permittit, reliquas verò ut candelae, ac secundas luces obscurissimè pertransire sinit.” Fabricius, De visione, 67. Note Fabricius’s intriguing mention of triangular glass, although he doesn’t make much of it. Also note that according to modern measurements, in most places the sclera is about twice the thickness of the cornea.

if one removes the vitreous humor from the eye and collects the retina together in one mass, it is

easily seen that the retina is of the same substance of the brain. This determination is supposed to

be obvious, needing no further demonstration than the testimony of sight and, perhaps, touch.

Fabricius depicts this observation in his plate 4 (see figure 3.5). The black and white engraving,

however, cannot convince the viewer of this conclusion, and neither in my opinion, does the

colored version in the Marciana library.92 I suggest that the image is present primarily to offer the

viewer an example of how to replicate this observation in one’s own dissection, and through this

to determine the similarity of the substance of the retina and the brain personally. Here we see

dissection as a crucial aspect of the anatomical method. The goal of anatomy is to demonstrate

knowledge about the body scientifically. Unlike the other steps to the anatomical method,

dissection occurs outside the book and must be supplied by attending a dissection or, preferably,

performing dissections oneself.

The aranea is compared to the subtlety of a spider’s web because it is “exceedingly

slight, thin, dense, and pellucid.”93 The portion covering the anterior of the crystalline is “denser

and thicker” (densior, & crassior) than the rear, which for Fabricius explains why it is easy to

miss — particularly the portion covering the rear of the crystalline humor which, he says, was not

observed by Galen. (Vesalius omitted it as well.) While Fabricius faults Galen here, he does not

fault Aristotle. Fabricius interprets Aristotle’s statements that vision occurs at the pupil as being

188

92 Rari 120. Note that the Marciana would not grant me any pictures or reproductions of Fabricius’s colored plates. Although most of these have been beautifully reproduced in Il grande teatro dei corpi: le pitture anatomiche di Girolamo Fabrici d'Acquapendente (Torino : UTET, 2011) this plate was not one of them. This might be because it is one of the least aesthetically pleasing of Fabricius’s colored anatomical pictures, and to my knowledge it has never been reproduced. Il grande teatro is also inaccessible, and I have been unable to locate a copy in North America, or in fact anywhere other than the Marciana Library itself.93 “Nam tunica evadit levissima, tenuissima, densissima, & pellucida, quae cum nulli meliùs quàm tenuibus aranearum telis, in subtilitate comparari potuerit....” Fabricius, De visione, 10.

about the aranea at the anterior of the crystalline humor.94 Fabricius points to a passage in book

5 Chapter 1 of On the Generation of Animals as evidence for this. There Aristotle writes:

Not only the above-mentioned facts are causes of seeing keenly or the reverse, but also the nature of the skin upon what is called the pupil. This ought to be transparent, and it is necessary that the transparent should be thin and white and even, thin that the movement coming from without may pass straight through it, even that it may not cast a shadow by wrinkling (for this also is a reason why old men have not keen sight, the skin of the eye like the rest of the skin wrinkling and becoming thicker in old age), and white because black is not transparent, for that is just what is meant by “black,” what is not shone through, and that is why lanterns cannot give light if they be made of black skin.95

Fabricius’s interpretation is not implausible, but because Aristotle provides only vague

statements about the eye elsewhere, and nowhere enumerates its parts explicitly, we should not

take the his reading as definitive.

Fabricius’s discussion of the aqueous humor in his historia is largely a discussion of what

ancient authors have reported — perhaps because he could find no fault with their description, but

perhaps also because Fabricius will not use any new knowledge about this humor later on when

giving his theory of vision. The one exception to this mere note-taking attitude is that Fabricius

rejects the notion that this humor is filled with animal spirits. Such spirits were supposed to

cause the pupil to contract or dilate as “Galen and all ancient physicians conclude.”96 He

mentions that Galen calls this humor “χαϑαρός, that is, pure, and shining” and also “λεπτός, that

is tenuous.”97 The term aqueous is important because it carries with it the notion that the eye is

primarily watery, about which Fabricius sides with Aristotle against Plato, who believed that the

189

94 For the ancients the pupil referred to the location of the small reflected image in the eye; see § 1.2.95 GA, 780a25-b1.96 Fabricius, De visione, 11.97 “Dicitur quoque hic humor à Galeno χαϑαρός id est purus, & nitidus. Ultimò λεπτός hoc est tenuis denominatur.” Fabricius, De visione, 11.

eye was fiery. That the crystalline humor is sometimes called the glacialis, or ice-like humor, and

that the posterior humor is the vitreous, or glass-like humor, reinforces the watery nature of the

eye: ice is congealed water, while glass can be liquefied into water and poured. Because the

aqueous is λεπτός or tenuous, it flows easily and is easily moved (moveri) — but whether being

easily moved is meant in the sense of color causing a movement of the transparent in the sense

given in Aristotle’s De anima is not clear.

Fabricius describes the crystalline humor in great detail. Although he does so elsewhere

in his historia, here in particular he uses many tactile analogies, and one gets a visceral sense of

what it is like to handle the crystalline humor, a point that I only fully realized once I dissected

eyes and handled the crystalline humor myself.

The crystalline, then, is in the first place a solid (concretus) and thick (crassus) humor, yet it is not of such a thickness that the diaphanous nature withdraws from it. Indeed it allows the passage of light, because the diaphanous is a neighbor to whiteness, and for this reason when the diaphaneity of it is destroyed, which happens when it is cooked, the crystalline humor is rendered most white of all — certainly due to a more pure (purior) and more tenuous (tenuior) airy or watery part, which brings about the diaphanous itself, being exhaled. Furthermore white is similarly brought about when it is condensed (condensare) and thickened (crassescere), which we often observed in old oxen, seeing that the aqueous and airy parts are conquered by the terrestrial parts. Yet it is so thick that indeed it might be compared to the great softness of wax, although while [the humor is] soft the slight pliancy [of wax] is not added. The result is that, touching it with one’s fingers, it very much emulates how wax and glue stick.98

190

98 “Crystallinus igitur primo quidem concretus humor est & crassus: crassities tamen tanta non est, ut diaphanam ei naturam adimat. Luci enim transitum praebet. Quia vero diaphanum albo vicinius est, propterea diaphano ejus pereunte, quod contingit, cum decoquitur, albissimus redditur omnis crystallinus, exhalatis scilicit purioribus, tenuioribus & aëreis, aut aqueis partibus, quae ipsum diaphanum efficiebant: sic otiam [sic: etiam] dum impensius condensatur & crassescit, albus similiter efficitur, quid in senscentibus bobus saepe observavimus, superantibus silicet terreis partibus, aqueas & aëreas: ita tamen crassus est, ut vel summam cerae mollitiem adaequet, cui cum mollitie lentor non exiguus adjungitur: quò fit ut digitis contrectatus, impensiùs quam cera adhaereat glutinumque ferè aemuletur." Fabricius, De visione, 12.

Fabricius’s point about the crystalline humor being somewhat thick (crassus), but not so much

that its diaphaneity is lost, is crucial point related to his theory of vision, and this will be

investigated at length in the next chapter. For now our focus is on the relationship between

transparency, tenuity, thickness, and the material composition of the humor. Fabricius’s statement

that transparency and whiteness are neighbors is highly significant, and intersects with scholastic

beliefs about color that we saw exemplified in Zabarella in the last chapter. Fabricius’s

explanation for the loss of transparency of the crystalline humor due to boiling or old age, on the

other hand, is something we don’t see in Zabarella, and perhaps shows the influence of his

medical training. The statement itself is compatible with either of the two theories of the origin

of color discussed in Chapter 1: that condensation and rarefaction are ultimately responsible for

color, or that colors are fundamentally tied to the elements or the elemental qualities.

The last transparent body discussed in his section on historia is the vitreous, or glass-like,

humor. This humor is so called not because it is similar to hot, liquid glass, but rather to glass

that has cooled, and “exactly resembles the most pure and pellucid glass.”99 Fabricius here

censures Galen for supposing that the vitreous humor is less pure and less diaphanous than the

crystalline: when placed next to one another, Fabricius says that its transparency surpasses that of

the crystalline, and this is because it is just as pure, but more fine or tenuous (tenuis), than the

crystalline.

In his treatise De formatione ovi et pulli (On the Formation of the Chick and the Egg) we

find more clues to Fabricius’s position on the relationship between the elements, density and

191

99 “Unde Latinè vitreus Graecè ὑαλοειδὴϛ est appellatus: cui non tantum liquato & ferventi, sed etiam refrigerato similis est. etenim purissimùm pellucidumque vitrum exactè imitatur: quam ob causam purissimùm etiam apparet diaphanum: quod sanè crystalloidi collatum, non hoc à crystallino, ut Galenus censet, sed contra potiùs ab hoc crystallinum superari dixeris: cuius rei, quod purum similiter sed tenuius crystallino sit, causa est.” Fabricius, De visione, 14.

rarity, and color. There we find two main positions: that whiteness in the body is a consequence

of a cold and dry temperament, and that yellow or red colors in a living body are a result of a hot

temperament. This is why the yolk is yellow, why eggshells are usually white, and also why the

albumen of the egg is “white.”

For as I have said elsewhere, everything red in the animal body is hot, but everything white is cold. Hence I cannot willingly agree with the opinion of Aristotle when he writes that the yolk is more earthy than the albumen; for if the albumen is colder, more viscid (tenacius), and heavier, it follows that it is more earthy. Nor does its whiteness, suggesting as it does a transparent, rare (aëreo) body, constitute an objection, when bones, too, besides being very white are also especially earthy, because the more tenuous portions have evaporated from them, a fact which Aristotle confirms by the example of ashes, which turn white when smoke, the coloring agent, has been released from them.100

Fabricius’s statement that redness in an animal body always signifies heat, and white cold,

suggests that Fabricius is following a theory in which colors are tied to the elemental qualities,

rather than a theory in which color is tied to the elemental bodies themselves or else arises solely

from condensation. Earthiness is better signified by heaviness and solidity (or, in a liquid,

viscosity) than by color; although transparency suggests that air contributes greatly to the

albumen’s make-up, this is outweighed by the fact that whiteness and transparency are

neighbors, and that bones and ashes are both white.

This last statement is a reference to the pseudo-Aristotelian De coloribus (at 791a5),

which shows that Zabarella’s belief that the treatise was not written by Aristotle was not

universal. It also might explain Fabricius’s somewhat conflicting statements on the relationship

between color and the elements: as we have seen in Chapter 1, De coloribus is difficult to

reconcile with Aristotle’s statements in De anima, De sensu, and De generatione animalium. It is

192

100 Fabricius and Adelmann, Embryological Treatises, 220.

an interesting question, but to my knowledge an unexamined one, whether physicians at the time

were more likely to take the De coloribus as genuine than natural philosophers. De coloribus is

certainly easier to combine with a scheme in which color is tied specifically to the elements or

the elemental qualities. In the medical tradition the color of a body and its parts were important

signs of their complexion or temperament (i.e., the ratio of the elements in the mixture forming

the parts of a body or the humors) as well as an imbalance of the humors. Because of this it

seems likely that physicians would refer to the De coloribus and that they would resist labeling it

as spurious. Complexion and temperament were crucial concepts for the diagnosis of disease, the

determination of whether certain drugs would be beneficial for a patient, for giving dietary

advice, and so on. Nevertheless there seems to be no reason that, using a bit of scholastic

gymnastics, a physician couldn’t reduce an elemental theory of the origin of color to a

condensation one, or even that they both could be held simultaneously — a hybrid or eclectic

theory. In Fabricius’s writings both theories do seem to be present, and there also seems to be

some tension between these two ideas: at times Fabricius invokes condensation, and at other

times he appeals directly to the elements themselves to account for the presence of color in a

body. Evidence of such a hybrid explanation for color can be seen in Fabricius’s discussion of

the color of semen:

If, however, all semen is white, it is therefore cold, since I have repeatedly said that everything white in the body of an animal is cold. This, however, is to be understood only of the corporeal substance of the semen. For since the semen is foamy and also spirituous and airy, by the same token it possesses much innate heat. Indeed, this heat is lodged in a cold substance, because if it had been placed in a warm one it would easily be dissipated and pass away before the animal was formed from it, and this the coldness prevents.101

193

101 Fabricius and Adelmann, Embryological Treatises, 221.

Only the bodily substance of the semen is cold; the spirituous part of the semen is responsible for

the initial stages of the generation of the offspring, and thus it must necessarily be hot and active.

It should be noted that Fabricius attributes the whiteness itself to the presence of cold; in

contrast, many writers — including Aristotle, Avicenna,102 and just about every seventeenth-

century proponent of the corpuscular philosophy — attribute this whiteness to a combination of

airy and watery parts producing bubbles that cannot be individually detected by the eye. That is,

from Aristotle onwards the whiteness of semen, sea-foam, and other bodies that were combined

with transparent parts too small to see individually (but combined imperfectly, that is, not

forming a true Aristotelian mixt) was explained by its texture rather than its elemental make-up.

That Fabricius does not do so is a sign of the influence of the medical tradition.

§ 3.6: Fabricius on the Action of the Eye

§ 3.6-1: Genre and Textual Authority

In the last chapter we saw Zabarella emphasis that an Aristotelian theory of vision requires an

account of three things: the object of sight, the transparent medium, and the instrument of vision.

He says that previous philosophers had neglected the eye, or the instrument of vision, in forming

their theories of light and color. Zabarella’s opinion on the role of lumen in sight relied on first-

hand anatomical knowledge about the structure of the eye: because the sensitive part of the eye

— the crystalline humor — is situated as if it were in a dark cave, colors propagating from bodies

to our eyes must be joined with lumen in order for those colors to penetrate the darkness of the

194

102 Aristotle discusses this in On the Generation of Animals, 735b8-36: “It is not only the liquids composed of water and earthy matter that thicken, but also those composed of water and air; foam, for instance, becomes thicker and white, and the smaller and less visible the bubbles in it, the whiter and firmer does the mass appear.” Avicenna mentions this in Liber Quartus Naturalium: De Actionibus Et Passionibus Qualitatum Primarum. Brill Archive, 1989, 79-80.

eye. Fabricius likewise emphasizes the object, medium, and instrument, of vision, but his

phrasing of the issue indicates that his task is not to explicate Aristotle’s theory of vision, rather

to provide his own. Aristotle appears as one of Fabricius’s main authorities, although Alhazen

perhaps surpasses Aristotle in this — but Fabricius’s treatise is not ultimately concerned with

expounding or defending either. Rather, Fabricius is looking ultimately towards the third and

most important section of his treatise where he gives the utilitates of the various parts, or the

Galeno-Aristotelian teleological explanation for all that is involved in vision, whose ultimate

purpose is the preservation of animal life. The structure of Fabricius’s text is modeled after

Galen’s On the Usefulness of the Parts, but the context of sixteenth-century anatomy and natural

philosophy significantly transformed the “Galenic” structure. For example, Fabricius needed to

be much more thorough than his ancient model in order to usurp the authority of Vesalius and

surpass his colleagues, and therefore Fabricius is far more meticulous than Galen in accounting

for every sensible property of every part of the eye in the historia section, and in giving a

teleological explanation of every one of those properties in the utilitas section. The actio section

serves as a bridge between the sensible properties of the eye and an account of their purpose;

Fabricius does this primarily by locating exactly where the sensitive faculty resides in the eye,

and to do so he needed an account of light, color, and transparency that would stand up to much

greater scrutiny than Galen’s. Finally, while Fabricius uses Galen’s (quite limited) incorporation

of mathematical optics into his account of the eye to justify his own engagement with optics, the

higher level of mathematical knowledge among a far greater proportion of his audience meant

that Fabricius’s mathematical treatment had to be much more thorough that Galen’s. At times

195

Fabricius seems to treat Galen’s section on the eye in Usefulness as a few rough notes from

which Fabricius produced polished final draft.

Compared to Zabarella, on the other hand, Fabricius has much more freedom in his

account of light and color: as an anatomist he is not acting as a public interpreter of Aristotle, and

his successful efforts to elevate anatomy to a branch of natural philosophy meant that he was

writing in a genre — we might call it philosophical anatomy — that was relatively new, and which

therefore did not have to align itself with any particular author or tradition. His position is in-

between natural philosophy and anatomy. Early and mid sixteenth-century anatomical authors, in

particular Vesalius, gave little emphasis to the action and, especially, the usefulness of the parts,

which were the very things that Fabricius used to elevate anatomy to natural philosophy. Thus

Fabricius’s relationship to past anatomical texts can be highly critical. Yet while there was great

precedent in anatomy for criticizing Galen’s conclusions regarding any specific point of

structure, action, or use, Fabricius is constrained by the ultimate goal of anatomy: providing a

final causal explanation of organs and their parts. As we saw, in De visione Fabricius corrects

many of Galen’s observations about the structure of the eye, and we will see him reject the

ancient doctor’s theory of vision and with it his account of the action of the eye entirely;

furthermore, in the next chapter we will see that he gives entirely different accounts of the

utilitas of many of the key parts of the eye. All of this, however, he does while remaining

Galenic — or, perhaps more properly, Galeno-Aristotelian.

In addition to this, when grappling with the philosophical aspects of vision, such as the

nature of light, color, and transparency, Fabricius can be agnostic on some issues where a natural

philosopher would not have been allowed to be: if the ultimate account of the usefulness of the

196

parts of the eye does not hinge on how precise his definition of color is, he is free to be a bit

looser in it; if the actio and utilitas of the crystalline humor does not rely on making a subtle

distinction between lux and lumen, then he can deny the distinction, at least for the sake of his

analysis; and if he feels sympathy with some un-Aristotelian ideas about the nature of light, then

he has the luxury of presenting a few speculations without needing to defend them rigorously.

We see Fabricius’s relatively flexible attitude towards textual authority, especially

compared to Zabarella, in his adherence to the tripartite account necessary for an Aristotelian

theory of vision. Fabricius interprets the Stagirite much more freely, and for example he can

open up a certain space for his own views by relating Aristotle’s ideas imprecisely:

For Aristotle recognized that in vision three essential things, at least, must be produced: the eye or nerve, the body which is seen; and third, that which is placed in between each of these. The fact that, if you should remove one of these vision would by no means take place, will be revealed most clearly.103

Fabricius suggests that perhaps, only the nerve of the eye is needed for vision, whereas Aristotle

does not mention the ocular nerve, but merely insists that the sensitive part of the eye must be

transparent; he has Aristotle saying that merely a body, rather than color (the object of vision for

Aristotle), be present; and that something be in between the two. On each of these points

Fabricius will coordinate his account with Aristotle’s, more or less, but form the start he draws

the outlines for an Aristotelian theory of vision as widely as possible.

§ 3.6-2: The Nature of Light and Color according to Fabricius

197

103 “Nam cum in visione efficienda tria ad minimùm necessaria esse nosset Aristoteles: oculum sivè nervum, corpus quod videtur; & tertium quod inter utrumque interponitur, quorum unum si tollas, nequaquàm fieri visionem, clarissimè patebit.” Fabricius, De visione, 39.

Fabricius ends his chapter on “The Way of Seeing According to Aristotle” by stressing the

Aristotle’s understanding of the transparent medium: air carries color not because it is air, but

because it is diaphanous and illuminated, and “truly it will be the medium by means of which we

are supposed to be able to see the things themselves.”104 His interpretation of how (according to

Aristotle) the medium is supposed to be activated is that the sun causes the whole of the air to be

illuminated by “affecting and beating” (contingens & verberans) the air with its light and

splendor; after this happens then the colors themselves can “beat” the air and alter it, and thus, on

Fabricius’s account of Aristotle, colors use the illuminated air as a vehicle.105 Immediately after

this description the anatomist presents “Modo visionis et propria sententia”, his own account of

how vision takes place. He breaks with Aristotle on several points. The first is that he considers

light to be the carrier of all sensible qualities, and is responsible for them being “formed and

impressed” (efformatum et consignatum) in the eye.

Light (lux), and this alone, steps forth, which, if it touches the color of a body, becomes colored; if it receives magnitude itself, or number, or figure, it carries these things in the same manner.106

This highly significant: the strong distinction between light and color is arguably an essential

tenet of Aristotelian theories of vision, and the reduction of color to an affection of light has

major ramifications for seventeenth century developments in optics and natural philosophy. For

Aristotle, color cannot be an accident of light because light just is the activity of some part of a

198

104 “Quòd si aer, non t aer, sed ut diaphanum, & illuminatum corpus à coloribus alteratur: meritò quoque aqua & ipsa diaphana cum fit, praeterea à sole contacta, etiam lucida efficiatur; verum erit medium, per quod res ipsas videre possimus.” Fabricius, De visione, 40. 105 “Ut enim Sol lucis suae splendore aerem contingens & verberantes, eum totum colllustrat: ita & colores aerem verberantes, eum immutant & afficiunt, eoque veluti accommodato vehiculo utuntur.” Fabricius, De visione, 40106 “Atque haec sola, lux existit, quae si colorem corporis attingat, coloratur; si magnitudinem, ipsam suscipit, si numerum, si figuram, haec itidem refert.” Fabricius, De vision, 40

transparent medium. If one accepts Aristotle’s definition of color in De sensu — that color is “the

limit of the transparent in a bounded body” — it is nonsense to say that light is colored: light is

the state of actual transparency in a body, and thus it cannot itself be a body (it is an activity).

More importantly a logical contradiction arises: color cannot be a both the non-transparent (i.e.,

the limit of the transparent) and a property of the actually transparent (i.e., light), at least not in

the same way. Fabricius’s conception of light and color are thus significant departures from

Aristotle. It is a break from the perspectivists as well. According to Alhazen, even though they

are always joined color and light are distinct.107 Likewise for Witelo and Pecham.108 For

Fabricius, the vehicle for color is not the illuminated medium, but rather light itself: by coming

into contact with a colored body, light becomes tinged with that color and is then able to transmit

this to our eyes. Light is neither itself a body nor an activity of a body, but Fabricius never makes

clear what it is exactly.

One important consequence of saying that light is the vehicle for the propagation of color,

and thus that color can be an affection of light, is that color has a more robust existence in the

medium than many of the more traditional interpretations of visual species. Light was nearly

always given independent (i.e., non-relational) existence by Aristotelians: just as the soul,

defined as the first actuality of the organized body, truly exists for Peripatetics, so too does light,

as the actuality of a potentially transparent body, truly exist. Color, however, was a trickier

matter. As we have seen, many commentators, including Averroës and Zabarella, held a twofold

199

107 Dignius ergo est, ut non sit sensus visa coloris rei visae, nisi ex forma coloris venientis ad ipsum visum cum lumine, & forma colores semper est admixta cum forma lucis, & non est distincta ab ea. Visus ergo non sentit lumen, nisi admixtum cum colore. Dignius ergo est, ut non sit sensus visus coloris rei visae & luminis, quod est in ea, nisi ex forma admixta cum cum lumine & colore veniente ad ipsum ex superficie rei visae.” Alhazen, Opticae thesaurus, 7. Cf. Alhacen and Smith, “Alhacen’s Theory of Visual Perception,” 22-23. See also Smith’s comments at liv-lv. 108 John Peckham, John Pecham and the Science of Optics, 62-63, 86-89.

account of color. In their condensation theory of color, color considered in itself exists absolutely

in body, and in some sense it is reducible to the density or rarity of the body (however “density

and rarity” ought to be understood). Visibility, on the other hand, was a power of color to affect

sight, and was thus in some sense relational; it was a power that only has potential existence until

all three criteria for vision are met: color (here considered absolutely, i.e., some ratio of density/

shade/black and rarity/light/white) present at the surface of a body, an illuminated medium, and a

functioning eye. Colors in the medium only have a “spiritual” or intentional existence in the

medium, and for Zabarella this means that they are tenuous entities with diminished being; while

these tenuous entities possess the same ratio of dark/black to light/white of the colored bodies

that caused them, their presence is entirely dependent on the cause (the colored body) being

present. Moreover, by affecting vision species do not trigger the sensitive soul to generate a

representation of themselves in the sense faculty, but rather a representation of that which caused

them. In other words, for Zabarella and many scholastics intentional species of colors have such

a diminished existence that we do not even, technically speaking, sense them; they merely trigger

us to sense that which caused them.

Colors have a more robust existence for Fabricius. He considers color at the surface of a

body to have actual existence regardless of its relationship to sensitive beings, although because

of the nature and scope of his treatise he does not give a full explication of what this means.

Additionally, by considering color in the medium to be an affection of light, color is granted a

more robust ontological status in transit. Thus, immediately after describing his view of light

Fabricius explains how light carries sensible qualities in the medium:

For whether you call it a simulacrum, or a form, or a species, or an apparition, is of no importance, only whether you understand that which alone represents the

200

thing. And light is of this nature, that whether the eye be present or not, not only is [light] affected by all these things [i.e., color, shape, size, etc.], and transformed (immuteretur), but also in a moment of time [light] carries these things into the furthest possible space, though in proportion to one another. Moreover light rightly becomes just like the matter of each of these species, since each essence inheres in light, just as in matter. The result is that species are nothing other than affected light.109

Light is explicitly said to act like matter: the medium is not the vehicle for visible species, light

is. He makes the consequences of this for the status of sensible “species” explicit as well: color,

magnitude, shape, number, and the rest of Alhazen’s sensible intentions have an observer-

independent existence in the medium, just as those qualities do in tangible bodies. Nevertheless,

he follows Aristotle in saying that light propagates instantaneously, and because of this that it is

incorporeal and not a tangible body.110 The text contains a marginal reference to Alhazen, book 1

proposition 23, corresponding to Risner’s 1572 edition. There in Alhazen’s optics we read the

following:

And it has already been shown that forms of light and color are continually generated in air and in all [other] transparent bodies, and these forms continually extend through the air, as well as through [other] transparent bodies, in various directions, whether the eye is present or not.111

201

109 “quam sivè simulachrum, sive formam, sive speciem, aut spectrum appelles, nihil refert: si modò id solùm, quod rem repreaesentat, intelligas. estque huius naturae lux, ut sive oculus fuerit praesens, sive non; non modò ab his omnibus afficiatur, immutereturque: verùm etiam haec omnia momento temporis in longissimum spatium sibi tamen proportionatum deferat. Quae porrò lux, meritò harum omnium specierum veluti materia existit quandoquidem in luce tamquam in materia omnem essentiam adipiscuntur: quo fit ut species nihil aliud sit quam lux affecta.” Fabricius, De visione, 41.110 Fabricius cites De sensu Chapter 7; in modern editions this corresponds to the end of Chapter 6, 446b30-447a10.111 Translation from Alhacen and Smith, Alhacen’s Theory of Visual Perception, 372, which corresponds to section 6.54 in the Arabic. Risner’s edition reads: “Etiam declaratum est quòd formae lucis & coloris semper generentur in aere, & in omnibus corporibus diaphanis, & semper extendantur in aere, & in corporibus diaphanis ad partes oppositas, sive oculus fuerit praesens, sive non.” Alhazen, Opticae thesaurus, 14.

Here Alhazen is referring back to book 1, Chapter 3 of the Arabic version. Since the first three

chapters were omitted in the Latin translation Fabricius could not have read what Alhazen claims

to have shown here. This appears, then, to be an appeal to authority by Fabricius. The passages in

the Arabic showing this (1.3.114), however, reference common and continually cited,

experiences such as that white clothing is colored green when standing under a tree.

In this section Fabricius cites Plotinus’s Ennead 4, book 5 Chapter 6, and this might

provide a clue to the impetus for Fabricius’s account of light. Fabricius says that light is a

quality, and therefore requires a material substrate. In standard fashion he says that air, water,

fire, the heavens, as well as glass, crystal, and horn (playing upon the transparent parts of the eye

that were named after three things) all share in the nature of the diaphanous. He says that

Aristotle’s position is that, because “light is the activity of the diaphanous, and produces its

form” this indicates that the diaphanous alone is the material substrate for light; a consequence of

this is that, if the diaphanous is removed, then light could neither exist nor go forth.112 However,

he adds that, “just as Plotinus wisely said, the air or other things [are only material substrates for

light] per accidens, for the reason that that they intervene [between the body seen and the

eye].”113 Fabricius concludes this by saying that “only light and the diaphanous are of necessity

required to conduct visible forms: light, which receives and carries the forms in a moment, and

also the diaphanous, as the matter for light.”114 This is also the very reason that the eye is made

202

112 “ideò solùm diaphanum illud est, quod lucis est materia, id, quod nobis etiam significavit Aristoteles dùm lucem esse actum, formamque diaphani prodidit. hinc fit, ut ablatò diaphano nusquam lux consistat, aut progrediatur.” Fabricius, De visione, 41113 “Aer autem ac reliqua, per accidnes, ob id videlicet, quod interveniunt, uti à Plotino sapienter dictum est: materia lucis existimanda sunt.” Fabricius, De visione, 41.114 “Iam igitur ex dictis patere potest, lucem solam, ac diaphanum ad visilium [i.e., visibilium] formarum traductionem necessariò requiri: lucem quidem, quae formas momento recipiat deferatque, diaphnanum autem, ut lucis materiam.” Fabricius, De vision, 41. Note that Fabricius often uses the term visilis for visibilis.

up of the most pure and perspicuous substance in every type of animal, be it bird, quadruped, or

fish: so that light, after having been endowed with visible forms, can enter the eye and ultimately

alter the sensitive spirits present in the nerves and produce vision.115

It is not easy to interpret how much we should make of Fabricius’s reference to Plotinus

here. What Fabricius means by diaphanous bodies being the substrate light only per accidents is

especially tricky: when Plotinus says this, he means that the diaphanous intermedium is a

substrate for light only because such a body happens to be there; if there were a void, light would

nevertheless act across the void, and thus a diaphanous body is not an essential component of

vision. The passage that Fabricius points to, Ennead IV, Book 5, Chapter 6, includes the

following:

But could light also occur if there was no air, as when the sun shines upon the surfaces of bodies, if the intermediary was void — end even as things are the intermediary is illuminated incidentally, because it is there? But if light resulted from an affection of air and the other [translucent bodies], and light had its substantial existence through the air — for it would be an affection of it — the affection could not exist without something to be affected. Now, first of all light does not belong primarily to air, nor to air in virtue of its intrinsic character; for it belongs also to each and every fiery body: there are even stones of this kind with a shining surface. But could that which passes to something else from a thing which has a surface of this kind exist if air did not? But if it is only a quality, and a quality of something, since every quality is a quality is in a substrate, one must look for a body in which light will be. But if it is an activity from something else, why should it not exist and travel to what lies beyond without the existence of an adjoining body, but with a kind of void in between (if that is possible).116

Plotinus endorses the view that light is an activity, and the position that is rejected above — in

which a diaphanous body is indeed an essential requirement for vision — is Aristotle’s. Fabricius

203

115 Fabricius, De visione, 42.116 Plotinus, Ennead IV, trans. by A. H. Armstrong, Loeb Classical Library, Rev (Cambridge, Mass: Harvard University Press, 1984), 301-303. Also see: Eyjólfur Kjalar Emilsson, Plotinus on Sense-Perception: A Philosophical Study (Cambridge; New York: Cambridge University Press, 1988), 36-62.

certainly seems to side with Aristotle, but the influence of Plotinus can be seen in many ways. As

was mentioned before, Fabricius’s first discussion of the three requirements for vision include

the eye or nerve, that which is seen, and that a vague “something” is between the two. Plotinus

seems to admit that some space must exist between the two,117 but given his statements this can

be empty space, and thus “something” includes void. Although Fabricius says that both light and

the diaphanous are necessary for vision, and furthermore says that light is a quality — the very

position that Plotinus rejects in the passage above — he seems to cast as wide a net as possible in

his initial philosophical descriptions, perhaps as a way to give Plotinus’s position as much space

as possible.

Even if he doesn’t accept Plotinus’s opinion on the nature of light and sensation outright,

the influence of the Enneads is nevertheless important, and this shines through particularly in

Fabricius’s interpretation of Aristotle here. As we have seen in the last chapter, Zabarella arrives

at “Aristotelian” answers to questions about the nature of light, color, transparency, and

intentional species by combining a deep reading of Aristotle’s own texts, a thorough knowledge

of the nearly two-millennia long commentary tradition, and both personal and textual

experiences. On the other hand — at least on questions of the nature of light, color, and the role of

the transparent medium — Fabricius seems to read Aristotle’s opinion on these issues with the

help of Plotinus’s characterization of Peripatetic theories of vision. For example, while certainly

well-versed in Aristotle’s own writings, Fabricius’s Aristotle has not been “updated” using

concepts and distinctions absent from the Stagirite’s own writings, at least not to the extent that

someone like Zabarella, speaking ad mentem Aristotelis, would have done. For example,

204

117 See Ennead IV, book 5, Chapter 2: “...for warming is by contact, but in acts of seeing there is no contact; this is the reason why the sense-object does not produce sight when it is placed on the eye....” Plotinus, Ennead IV, 289.

Fabricius’s Aristotelianism does not rely on the lux/lumen distinction or the notion of intentional

species. Furthermore, the anatomist chooses to part with Aristotle whenever his more historicized

version of the Stagirite does not seem adequate. For example, Zabarella says lumen and color are

always joined in the medium, thus honoring Aristotle’s opinion that light and color are separate.

Fabricius’s Aristotle, on the other hand, is of the opinion that that light only activates the

transparent medium, and that light and plays no role in activating color at the surface of bodies.

Though he doesn’t advertise it, Fabricius rejects this and holds that color is an affection of light.

In terms of a ray analysis of light and color, Zabarella and Fabricius’s accounts are

indistinguishable, yet only Zabarella claimed to be a faithful interpreter of Aristotle. Fabricius,

perhaps, presents a more historicized Aristotle than many of his contemporaries, but this is

beyond the scope of this dissertation.118

Fabricius’s reading of Aristotle compared to Zabarella’s reflects important disciplinary

boundaries, but we must be careful not to apply this boundary distinction thoughtlessly. As we

will see in the next chapter, both Fabricius and Zabarella present theories of vision that are

identical in their description of both the parts of the eye in their analysis of the usefulness or

purpose of the parts of the eye. Furthermore, while their accounts of light, color, species, and

aspects of psychology differ — at times radically — nevertheless their descriptions of the path of

the rays of light and color in the eye are identical. The natural philosopher and the anatomist give

identical descriptions of the fabric of the eye, usefulness of its parts, as well as a structurally

identical description of the action of the eye. Nevertheless, Zabarella claims his theory of vision

as the true Aristotelian account, while Fabricius positions his account as distinct from Aristotle’s.

205

118 On the historicization of Aristotle in the sixteenth century, see Craig Martin, Subverting Aristotle: Religion, History, and Philosophy in Early Modern Science (JHU Press, 2014).

§ 3.6-3: Glowing Meat, Shining Eyes, and the Nature of the Transparent

Fabricius says that since light is a quality of a body, the amount of light in something follows

from its temperament, that is to say from the precise mixture of the elements in that body. (Note

that he says that this does not apply in the heavens, although he doesn’t say how color arises

there.) All bodies participate in the nature of light, and since the color white is close to the nature

of light, if something becomes whiter it will have a greater disposition for light.119 Once again,

we find Fabricius appealing to a mixture of the elements and the elemental qualities to account

for color rather than condensation and rarefaction.

In this context he recounts an experience he had with glowing meat, a passage that was

frequently cited by later authors, including Thomas Bartholin in the seventeenth century and

Joseph Priestly in the eighteenth.120 Yet after the seventeenth century no author relates

Fabricius’s reason for giving the account: that is to understand the relationship between

temperament, transparency, and light or luminescence.121 Fabricius writes that in 1592, during

the Easter celebration, three young, noble, studious Romans bought a lamb for the feast. After

some had been eaten they stored the rest, and later noticed that the lamb would shine (collucere)

like candles. They sent some of the meat to Fabricius, who observed the phenomenon carefully.

It is noteworthy that Fabricius is keen to mention that not only he and the three noble Romans

206

119 “Etenim cum lux qualitas quaedam sit, temperamentum seu corporis proprietatem consequens quod de omnibus lucidis corporibus (coelesti excepto) intelligas; fit ut corpus omne, naturae lucis cuiusdam particeps sit, cuiusque plus obtineat, quo albo colore qui luci propior est, magis fuerit affectum.” Fabricius, De visione, 44.120 Thomas Bartholin, De Luce animalium libri III, admirandis historiis rationibusque novis referti (Ex officina F. Hackii, 1647), 183-4. Priestley, Joseph, The History and Present State of Discoveries Relating to Vision, Light, and Colours, by Joseph Priestley (J. Johnson, 1772), 563. 121 Priestley strips Fabricius’s own concerns in his retelling, as does Edmund Newton Harvey, A History of Luminescence from the Earliest Times until 1900 (American Philosophical Society, 1957), 87-8.

observed this, but also many other citizens of Padua; Fabricius is aware of the importance of

citing reliable testimony. The meat and fat were "glowing (nitere) with a certain silvery luster."

The lamb had touched the meat of a goat that was stored along with it, and the part of the goat

that had touched the lamb was also glowing. Furthermore, the shine would cling to the fingers of

anyone who touched the lamb. Fabricius then uses this example to investigate the relationship

between diaphaneity and luminescence.

It was observed that although the meat was bright (splendida), it was not diaphanous; but nevertheless while the glowing was apparent, it seemed as if it were indeed diaphanous, just as if the [property of being] diaphanous were perpetually joined with the splendor, although the diaphanous did not actually appear in the daylight. In addition, the meat’s own illumination (proprium lumen) entirely withdrew in the daylight, and just as it glowed in the most obscure darkness, so too as daylight approached the splendor was obscured little by little. It was likewise observed that the most splendid meat was that which was soft to the touch, that is, [the splendor] did not have any hard subject, which was evidence (indicium) that the diaphanous was present in connection with air. Also, this was observed in vesicles (vesicula) filled with air. In sum, those parts that were perspicuous by candlelight were completely luminous in the dark. But those things that were opaque (opaca) — the meat on account of its depth, or bone it’s subject — continued without illumination in the dark.122

The relationship between the diaphanous and luminosity is emphasized in the passage above, but

there is also an elemental component in Fabricius’s discussion. Parts that were harder, denser —

and thus, according to typical medical theory at the time, contained a greater proportion of earth

— both lacked transparency and did not become luminescent. (Note as well that Fabricius

207

122 "Notabatur, quòd quamvis caro esset splendida, non autem dipahana: attamen cum splendor apparebat, videbatur etiam quasi diaphana, ità ut cum illo splendore conjungeretur perpetuò diaphanum, quamvis revera diaphanum in diurno lumine non appareret. Praeterea in diurno lumine prorsus delitescebat dictae carnis proprium lumen, quod sicuti in obscurissimis tenebris splendebat, ità sensim, & sensim, accedente diurno lumine obscurabatur splendor. Observatum itidem est, splendidam maximè eam carnem esse, qua contactu mollis persentiebatur, id est, durum subjectum aliquid non habebat, quod erat indicium, diaphanum aereum inibi adesse. hoc idem observatum est, in vesicula quaedam aere plena. In summa ea pars, quae ad candelae lumen perspicua erat, tota in tenebris erat luminosa. Quae verò caro propter ipsius profunditatem, aut os subiectum opaca erat, sinè lumine in tenebris permanebit." Fabricius, De visione, 45.

describes a white body, bone, as being opacus, an indication that the shift from the term meaning

murky to meaning opaque in the modern sense is present in Fabricius.) Degrees of luminescence

are here used as an indicator of degrees of transparency, a property that is not always

immediately perceptible in a body on account of its depth and the effect of daylight. This

transparency is then correlated with the elemental make-up of the parts of the bodies. However,

this connection between transparency and luminosity introduces a problem for Fabricius’s theory

of vision: one of his goals in this chapter is to refute Plato’s (and Galen’s) emission theory of

vision, and so the possibility that the clear, untainted (clara, alba) parts of the eye could be

luminous is problematic. Fabricius addresses this by saying that, although the humors of the eye

are diaphanous, nevertheless they are not self-luminescent. Contra Plato and Galen, any such

light would be a nuisance to vision rather than aid it, and to support this notion he cites the

second proposition of Alhazen’s De aspectibus which points out that after staring at brightly lit

bodies one can barely see things in a dark room.123 Elsewhere in the treatise Fabricius also

rejects the possibility that any of the humors are themselves luminous. For instance, in the third

section of De visione, when discussing the usefulness of the iris of the eye, he accounts for the

typical example that the eyes of cats glow in the dark by concluding that only their irises shine at

night — and indeed, he says, if one carefully observes cats in the dark one sees (according to him)

that the pupil itself is black, and thus that the humors within are not themselves luminous.124

Part his criticism of Galen and Plato’s theory of vision is his rejection of a sympathetic

account of sensation in favor of the Aristotelian potency/act model. He says that Galen holds that

208

123 Fabricius, De visione, 46. Alhazen, Opticae thesaurus, 1–2.124 Fabricius, De visione, 89. This eyeshine is largely due to the presence of a tapetum lucidum in these animals, a reflective coat behind the retina that reflects light, giving increased night vision by, in effect, doubling the chance that a photon will strike a receptor. However, the irises of cats do also reflect light, and so Fabricius not entirely incorrect.

the instruments of the senses must be made from the same substance as that which that move the

senses: the olfactory organ needs to composed of vapor because it is moved by vapor, the organ

of hearing is airy because it is moved by air, and taste is humid and thus the tongue is also

humid.125 Sight, however, is a bit different for Galen: the organ of sight is diaphanous because

sight is moved by light, and the substance that underlies light is the diaphanous. Fabricius cites

book 7 of On the Doctrines of Hippocrates and Plato, where we Galen writes: “We shall say,

therefore, that it was needful that the organ of sight be luminous, the organ of hearing airy, that

of smell vaporous, that of taste moist, that of touch earthy. It was not possible for them to be

otherwise, for they required the alteration caused by similars.”126 In other words, for Galen like

affects like, the very doctrine that Aristotle sought to replace with the notion that the organs of

sense must be potentially like, but actually unlike, their respective objects of sense.127

Fabricius’s argument against Plato and Galen here is curious. He puts forth the familiar

question of whether light (lux) or color is the proper object of vision, and he answers that, if

color was indeed the proper object of sight, then Plato would be right about the eye containing an

inner light. Fabricius holds that color is an affection of light — “the true matter of the species of

color is light alone” — and thus if color alone affected the eye, then color would need to be

transferred to another light. That is, the eye would need its own innate light in order to be

209

125 Fabricius, De visione, 46-7.126 Galen, On the Doctrines, 463. Galen here claims to be following not only Hippocrates and Plato, but also quotes Empedocles to support this view: “By earth we shall perceive earth; by water, water; / air by shining air; and consuming fire by fire.” Ibid. See also Plato at 45b-46a: “Accordingly, whenever there is daylight round about, the visual current issues forth, like to like....” But at night “the visual ray is cut off; for issuing out to encounter what is unlike it, it is itself changed and put out....” Plato, Timaeus, trans. by Francis Macdonald Cornford (New York: Macmillan Publishing Company, 1959), 42-3.127 De sensu 438b15-439a5; De Anima 417a1ff;

receptive of color.128 But this is an error, he says. Not color, but light itself moves vision; strong

light, and not strong color, undermines and destroys sight; and color, in the dark and without

light, cannot effect vision. Yet light, insofar as it affects and perfects vision, does so with the

forms of colors.129 It is worth emphasizing Fabricius’s strange argument: having concluded to his

satisfaction that species of color are nothing but tinged (or despoiled) light, if the orthodox

Aristotelian position that color is the primary object of sight is true, then Plato must be correct

about the eye having an innate light. Yet Plato and Galen are mistaken about the innate light of

the eye. Therefore Aristotle is correct that the eye does not emit light, but not that the primary

object of vision is color. Fabricius does not advertise the fact that he is breaking with Aristotle,

specifically, on this point, although most of his readers (and certainly his colleagues at Padua)

would see him as doing so. In fact, in my reading he never criticizes Aristotle directly in this

treatise; the closest he gets is to devote one chapter to “The Way of Seeing according to

Aristotle’s Opinion” and a subsequent one to “The Way of Seeing and [The Author’s] Own

Opinion.” Unlike his antagonistic references to Galen and Plato, Aristotle’s works are never cited

in the margins for the sake of criticism, only support. Fabricius also does not explicitly criticize

Alhazen and Witelo, and in this sense he seems to invest them with the same authority as

Aristotle, although their authority is in a different domain. One way to interpret this is that, as a

210

128 “Res autem, quae visum movet, hoc est obiectum ipsius visus; duplex constitui potest. aut enim lux est, aut color; si color, verissima est Platonis sententia, scilicet visus sensorium esse lucidum. etenim quod à colore afficitur, nil aliud, quam lux est, quae sicuti à veriis coloribus tingitur, ac faedatur; sic omnes coloris species recipit, atque conservat. ut proindè vera specierum colorum materia sola lux sit, siquidem in luce tamquam in materia omnem essentiam fortiuntur. Quod si lucem tanquam subiectum aut materiam coloris statuamus: iam hoc pacto argumentari licet.” Fabricius, De visione, 47.129 “quando quidem uti supra dictum est, non color, sed lux est, quae visum movet, & afficit. Etenim lux non modò visum movet, & afficit, verùm etiamsi valens sit, labefactat, & corrumpit, quorum neutrum color in tenebris & sinè luce efficere potest: quò fit, ut verum, propiumque visus obiectum, quod visum qiudem movet, & afficit; affectione tamen quae magis perficit, quàm corrumpit; lux quidem sit; at non omnis, sed tantummodo affecta: affecta inquam, non alia re quàm colorum formis.” Fabricius, De visione, 49.

physician and anatomist in the late sixteenth-century, Galen had already been thoroughly

assimilated into Fabricius’s discipline; criticizing Galen results in no loss of authority to his

work, and indeed if done the right way it might enhance it. However, Fabricius’s innovation in

his overall anatomical project is the appropriation of Aristotle and the revival of an “Aristotelian

programme” in anatomy (as Cunningham puts it). His further innovation in his treatise on vision

is not only to incorporate the perspectivist tradition, but indeed to declare that only anatomy can

provide the empirical foundation for mathematical optics, at least with respect to the structure,

action, and utilitas of the parts of the eye (see §§ 4.4–7 in the next chapter). If he wished to

convince philosophers and mathematicians of the merits of his approach, Fabricius could not

well afford to criticize their authorities.

Another way of interpreting this is that Fabricius would not dream of trying to surpass

Aristotle, and that he was not competent enough a mathematician to surpass Alhazen and Witelo.

As we will see below, his aim is indeed to surpass Galen.

§ 3.7: Fabricius on the Utilitas of the Most Godlike of the Instruments

A more in-depth account of Fabricius’s section on utilitas in De visione is given in the next

chapter, but here I wish to outline Fabricius’s overall aim and motivation in this section.

Fabricius adds a lengthy proemium to the third section of De visione in which he makes three

main points that are relevant to our discussion. First is that he says that, in explicating the

usefulness of the eye and its parts, he will attempt to outdo the work of the admirable Galen

himself in his On the Usefulness of the Parts of the Body, and further that neither Galen nor any

other man has seen and understood the infinite wisdom of God in constructing the eye.

211

Fabricius’s ambition is on full display, but he nevertheless says that Galen is preferable to others

(presumably here referring to Vesalius, and perhaps Colombo and Fallopio) who have written on

the eye and vision because Galen passes beyond the fabric of the eye to investigate action and

use, and crucially that Galen included a mathematical account of vision as well. Fabricius does

not present himself as rejecting Galen, but rather surpassing him.130

A second point that Fabricius highlights is that, following Galen, he will not shy away from

a mathematical account of vision. He mentions Galen’s famous dream in Chapter 10 of

Usefulness, where the ancient physician says that at first he thought it best to omit a

mathematical account of the eye because of the difficulties it would pose for many for his readers

(although Galen’s mathematics are quite basic — an indication of the low level of mathematical

education among the learned at the time). A sort of divine intervention changed Galen’s mind:

“Afterward I dreamed that I was being censured because I was unjust to the most godlike of the

instruments, and was behaving impiously toward the Creator in leaving unexplained a great work

of his providence for animals, and so I felt impelled to take up again what I had omitted and add

it to the end of the book."131 Fabricius uses the fact that Galen gave a mathematical discussion of

vision in an anatomy text as a classical precedent for his own integration of perspectiva with

anatomia, something that perhaps no anatomist had done since (in Latin, at least). However,

Fabricius says that he has shown in his previous section that Galen was not correct on the actio

212

130 "Conabor tamen ita huiusmodi usus explicare; ut quivis possit spem capere, aliquando vel ipsum etiam admirabiliem Galenum in usibus partium disquirendis posse superari. neque id mirum, cùm infinita Dei Sapientia haec omnia effinxerit, construxeritque, quam neque Galenus, neque hominum quispiam mentis acie pervidere aut intelligenta capere potuit. Quanquam fateri aequum est, caeteris omnibus de visione, & de oculis scripserunt, Galenus longè praeferendum esse, quòd in huius rei tractatione magis reliquis omnibus laboraverit, diligentiamque singularem adhibuerit, cùm de visione libros tres conscripserit, De usibus verò partium oculi, librum integrum, qui decimus est de usu partium." Fabricius, De visione, 55.131 Galen, Usefulness, 490-91.

of the eye, and for this reason he claims that he can determine the utilitas of the parts of the eye

better than Galen. A key component to this utilitas is a mathematical account of vision: the

reason why the parts are individually shaped and collectively configured as they are, the reason

why they are of such and such a color or of such and such a degree of transparency, and the

purpose for them being composed of predominantly this element (here water) rather than any

other is crucially related to the behavior of rays of colored light in the eye. In fashioning the parts

of the eye, Nature had to take into account how light would be reflected and refracted in it, and

also how light and images are collected, captured, and dispersed. Understanding this is the job of

mathematical optics, and therefore this discipline must be drawn upon in order to understand the

final cause of the various shapes, sizes, transparencies, etc. of the parts of the eye.

This is a third point that Fabricius stresses in the proemium. All of the parts of the eye are

created for the ultimate purpose of vision. Because the crystalline humor is sensitive to light and

its affections, many of the parts exist, in fact, for the sake of the crystalline humor. On this point

he implicitly criticizes Galen for not giving a good account of the fabric of the eye.132 All things

that can be observed through dissection about the parts of the eye are to be accounted for with

respect to the action of the crystalline and the behavior of light, thanks to which a final cause can

be given. Fabricius gives a short example of how this works with the cornea: its usus is first to be

diaphanous to let in light, second to be round to improve vision, third to be tough to protect the

crystalline, and so on — an account that is more complete, precise, and well-structured than what

213

132 “Attamen cùm rerum omnium opifex, oculum non ex crystallino tantum, sed ex aliis multis partibus efformarit: ideo dicendum est, non frustrà reliquis oculi partes positas esse, sed ad utilitatem, & commodum actionis, idest visionis crystallinique, procreatas fuisse.” Fabricius, De visione, 55-56.

Galen gives.133

§ 3.8: Conclusion

De visione, voce, auditu was Fabricius’s first published example of his philosophical anatomy.

Unlike his sixteenth-century predecessors, his goal was not just to provide a structure or natural

history of the body, but to connect that structure to the elemental composition through an

analysis of temperament, on the one hand, and to use this to eventually demonstrate the final

cause of the parts, organs, and systems of the body on the other. Furthermore, as he says, “we

hunt all of this through dissection.” In connection to this it is instructive to look at Zabarella’s

comparison of natural philosophy with medicine. In 1586 Zabarella published his first foray into

natural philosophy with De naturalis scientiae constitutione, which was later included as the first

book in his De rebus naturalibus. In Chapter 32, Zabarella says that anatomists should not

imitate Aristotle’s History of Animals, but rather his Parts of Animals. Two things, he says, are

required for complete knowledge of the part: first, its operation or activity (operatio) combined

with role the part plays in service of animal life (it’s officium or office), and second what mixture

of the elements, and temperament of the primary qualities, are needed for each part to perform its

office. In other words, material and final causes, respectively. Determining this is the province of

natural philosophy, and only once this speculative knowledge is perfectly known can the art of

214

133 “propterea nunc omnium eorum, quae ipsis oculis inesse conspiciuntur, cuius gratia, seu finalis cause est afferenda. Quae verò ipsis oculis insunt, per dissectionem potissimùm manifestantur; ideoque mirandum non est, si rursus à dissectione sumemus exordium, oculique fabricam patefaciemus. Dixi autem potissimùm per dissectionem, quoniam certè nonnulla, etsi perpauca, quae ad oculos pertinent, sine dissectione conspectui se se offerunt. haec autem sunt, quae ad totum oculum spectant, quamvis neque omninò sine dissectione perfectè intelligi possunt, ut positio, magnitudo, numerus, figura, conexio, & eiusmodi, de quibus omnibus nunc erit agendum.” Fabricius, De visione, 56.

medicine, the most noble application of natural philosophy, be perfected.134 Zabarella maintained

a strict separation between medicine and natural philosophy based on the ends of the two

disciplines. The purpose of medical knowledge and skill is to heal, and because it aims at action

it cannot be a speculative or theoretical discipline. The purpose of natural philosophy is

knowledge for its own sake, and because its aim is purely contemplative and not productive it is

a speculative discipline. The theoretical sciences are more noble than the productive or practical

sciences, and many practical sciences, medicine in particular, depend on natural philosophy by

taking its principles and conclusions for granted. It must be emphasized that Zabarella strictly

demarcates the disciplines of natural philosophy and medicine; he is not making a strict

demarcation between natural philosophers and physicians. Even if part of his purpose in making

such a distinction was to carve out a privileged place at the University of Padua (and society in

general) for natural philosophers such as himself, nothing precludes a physician or anatomist

from doing natural philosophy . In fact, Zabarella’s point is that anatomy should be done as

natural philosophy. It should not, as Vesalius in his Fabrica most conspicuously does, concern

itself with structure alone. Rather, it should ground those accounts of structure in an analysis of

the elemental composition of the parts, and furthermore describe the final cause of those parts.

215

134 “Post libros igitur de historia ponendi statim sunt quatuor libri de partibus animalium, de quorum divisione in partes non est quod in praesentia dicamus: satis sit hoc annotare, Aristotelem in iis libris demonstrativè de partibus agere, quod in prioribus de historia libris non fecerat; singularum enim partium causas assignat finales, nam finis cuiusque partis est propria operatio, & proprium munus, ad quod singulam partem tanquàm instrumentum ad finem natura direxit; sunt enim omnes animalis partes instrumenta animae ad varias edendas operationes, instrumenti autem natura optime ex eius fine declaratur. Ex hac potissimum naturalis philosophiae parte sumit ars medica partem illam, qua physiologica dicitur, in qua de humano corpore, ac de eius partibus sermo fit, quum Medico illas curaturo necessaria penitus sit earum cognitio; ob id Medici, qui artificiosam, ac fructuosam facere volunt humani corporis anatomen, imitari Aristotelem debent, non in libris de historia, sed in libris de partibus methodicè de ipsis partibus agentem: duo namque omnino cognoscenda sunt ad perfectam ipsarum partium notitiam habendam; unum est proprium cuiusque partis officium, propriaque operatio; alterum vero, quod ex illo deducitur, ea, quae in singula parte requiritur elementorum commistio, & primarum qualitatem temperies; horum enim altero ignorato, non potest aliqua humani corporis pars dici perfecte cognita.” Jacopo Zabarella, De rebus naturalibus (Venice 1590), 63.

As Zabarella says, Aristotle’s History of Animals are a preparation for the rest of the books on

animals. All knowledge begins with sensation, and thus historia is necessary to give us the quod

sit, or that which is the case. Yet the goal of dissection and animal research is not merely to

describe what is in the body, but to give the propter quid, the reason why the various parts of the

body are there, and why Nature made them as they are.135

Even if Fabricius was not drawing upon Zabarella specifically in forming his anatomical

program, it matches Zabarella’s prescriptions exactly. As we have seen, anatomy for Fabricius

starts with dissection, which gives us that which is the case. Following Aristotle’s dictum that all

knowledge comes through the senses, it follows that to truly understand anatomy one must

perform dissections oneself, or at the very least be present at a dissection. Fabricius’s anatomical

works were meant to be used, their contents meant to be performed and not passively accepted.

Dissectio is done for the sake of historia, which for Fabricius includes an account of the

temperament of the various parts. Thus, his account in the historia is already worked-over to

some extent: it is not a mere account of what one senses, an autopsia, but also what one judges

the composition of the parts to be. It is important to note that it is not just vision that gives us

information during dissection. The sense of touch, in particular, is crucial for analyzing

complexion, or the mixture of the elements and the elemental qualities. Historia understood in

this sense puts the anatomy on the road to natural philosophy, and this historia is for the sake of

actio, the activity or movement involved with the organ and its parts. Finally, this actio is for the

sake of the final cause, the utilitas or officium of the parts, the organ, and the system. Fabricius

216

135 "Itaque libri de historia sunt praeparatio quaedam ad alios omnes de animalibus libros; tradunt enim cognitionem, quod ita sit; alii veri frequentes earundem rerum causas declarant, & docent propter quid; ideo illi iure fuerunt appellati historici, quum reliqui non historici, sed scientiales potius sint appellandi." Zabarella, De rebus, 62.

thus fulfills Zabarella’s requirements for philosophical anatomy. Moreover framing his project in

this way certainly contributed to an increase in his status and pay at the University.

Heikki Mikkeli, one of the foremost experts on Zabarella, writes:

While discussing the principles of medical art Zabarella compares the anatomical principles with the principles derived from natural philosophy. In his view only the philosophy of nature, not anatomy, can provide a solid basis for medical practitioners. In this respect Zabarella cannot be considered as a forerunner of modern experimental science.136

I do not wish to argue that Zabarella was a forerunner of modern experimental science, but

Mikkeli misses (or at least fails to emphasize) the fact that Zabarella is not making a strong

distinction between anatomy and natural philosophy, but rather criticizing those who, like

Vesalius, perform anatomy imperfectly. The former would seem antithetical to the development

of modern science, while the latter hardly seems so. Even if Zabarella used the term anatomia in

a narrow sense to mean merely the cutting apart of bodies and presenting them to the senses (and

I don’t think he does), his point is that the proper aim of dissection should be to imitate

Aristotle’s Parts of Animals, in which Aristotle gives both the elemental composition (the

material cause) of the part and the role it serves in the life of the animal (the final cause).

“Precisely for this reason those medici, who wish to make a skillful and fruitful anatomy of the

human body, should imitate Aristotle — not in his books on historia, but in his books on the parts

[of animals].”137 This, as we have seen, was precisely Fabricius’s project. Zabarella was critical

of contemporary anatomists and physicians, not anatomy or medicine per se.

Within the natural-philosophical framework for anatomy that Fabricius constructed,

217

136 Heikki Mikkeli, An Aristotelian Response to Renaissance Humanism: Jacopo Zabarella on the Nature of Arts and Sciences (SHS, 1992), 171.137 “ob id Medici, qui artificiosam, ac fructuosam facere volunt humani corporis anatomen, imitari Aristotelem debent, non in libris de historia, sed in libris de partibus methodicè de ipsis partibus agentem.” Zabarella, De rebus, 63.

however, the anatomist had significantly more room to maneuver than a public expositor of

Aristotle such as Zabarella. Although grounded in the texts of Galen and Aristotle, Fabricius’s

philosophical anatomy was a new sort of genre, or at least a transformed one. As such it was less

constrained by the restrictions, requirements, and other baggage constraining works in scholastic

natural philosophy. As we have seen in the example of his opinion that color as an affection of

light, Fabricius was willing and able to make significant alterations to fundamental tenets of

Peripatetic theories of vision, and he was eager to reject the Galenic model of vision entirely.

Although most scholars is no longer consider it plausible to cast Zabarella as a forerunner of

modern experimental science, is perhaps possible to see Fabricius and his fellow anatomists in

this role.

In the next chapter we will examine the visual theory of Zabarella and Fabricius and their

analysis of the utilitas of the humors and tunics of the eye in connection with the history of

mathematical optics.

218

Chapter 4: The Visual Theory of Zabarella and Fabricius


To this point the chapters above have, to some extent, proceeded along two separate lines.

Chapter 1 outlines the history of one particular physical color theory as well as many related

notions, and chapter two analyzes at the full flowering of that theory in book 1 of Zabarella’s De

visu. Chapter 3, on the other hand, looks at the history of ocular anatomy and its connection to

color, light, and vision in Fabricius’s De visione, but as we saw Fabricius was not committed to

the condensation theory of the origin of color as Zabarella was, and as an anatomist and a

physician he held some opinions related to vision that break with Aristotle in ways the natural

philosopher would likely have censured. This chapter brings these two lines together. As I will

show, Zabarella and Fabricius held the same theory of vision, supported by the same, remarkably

specific observations about the size and other properties of the humors, and they appeal to the

same experiments on the eye. I have been unable to find any earlier proponents of this theory,

and it was recognized by later anatomists, at least, as being unique to Fabricius. Zabarella,

however, does not attribute this theory to Fabricius, and in any case he published it ten years

before Fabricius. I therefore consider it a shared theory to which, in all likelihood, they both

made contributions.

While their theory of vision was hardly revolutionary, it is distinctive enough to be

recognized in the history of visual theory. Moreover, it did influence later figures at least

somewhat, and I make the case in the next chapter that their theory of vision influenced Kepler in

219

particular (although Fabricius’s general anatomical findings are the more decisive influence).

Notably, the theory identifies the crystalline humor with a burning lens (an artificial instrument,

if you like) whose action Nature frustrates by placing behind it a large chamber filled with

watery vitreous humor. Apart from the act of sensation itself, the functioning of their eye is

exactly like a dead one, and so dissection and experiment reveals the eye’s secrets. These aspects

are supposed to be original to Kepler: that the eye as an artificial, even “mechanical,” device, and

the eye that is the subject of mathematical analysis is a “dead” eye whose sensitive powers in no

way affect ray analysis. This is certainly present in Kepler, but it is clearly there in Fabricius, as

well. Most importantly, however, is that the visual theory held by Zabarella and Fabricius

represents a momentous but overlooked transition in the history of vision. Since Galen (and

perhaps Ptolemy), the histories of mathematical optics, natural philosophy, and especially

anatomy had proceeded along largely separate paths, such that eye of the medieval perspectivists,

the eye of the natural philosophers, and the eye of the anatomists were not one and the same. The

mathematicians constructed their geometrical eye using the a priori constraint that the front

surfaces of the cornea and crystalline humor be concentric. They did not abstract from skillfully

performed anatomies. The eye of the natural philosopher was an entity with certain necessary

properties, but it had no well-defined structure such that changes to that structure would

fundamentally alter their arguments or conclusions. The eye of the anatomists, finally, was

almost entirely concerned with structure (structura, fabrica, or historia). This structure was at

times carefully observed and noted, at times not; some anatomical authors meticulously

compared their dissections with the accounts and terms used by their forebears, while others

concerned themselves with only what was before their eyes, and did not coordinate this with a

220

mountain of authoritative texts. Occasionally, the eye was endowed with the properties

appropriate to a theory of vision, Galenic or Perspectivist-Aristotelian in broad terms, but never

with the notion that a meticulous observation of the eye might seriously challenge the visual

theory of these past giants. This changed with Zabarella and, especially, Fabricius.

In § 4.1 I look at Zabarella’s and Fabricius’s refutations of atomistic theories of vision,

which however were made without resorting their anatomical findings about the eye. § 4.2

presents Zabarella’s refutation of Galen’s extramission theory of vision in book 2, chapters 2–4

of De visu. Here Zabarella uses philosophical arguments to attack Galen and, especially, the

many Galenic theories of vision held by contemporary physicians. In these chapters he doesn’t,

however, employ his experiences with ocular dissection. In § 4.3 I examine De visu book 2,

chapters 5 and those that follow, where he does indeed do so. In the process Zabarella gives his

own, anatomically grounded theory of vision whose defining characteristic is the presence of a

burning lens in the eye which dissipates and destroys the incoming lumen so that the crystalline

humor does not constantly see the retina and uvea behind it. Zabarella’s eye is the eye as

revealed through skillful anatomical dissection, and this has many consequences for his

philosophical arguments (for some of these, see also § 2.8). In this section I also present some of

my results from the recreations of renaissance and early modern anatomical dissections and

experiments; these experiments inform the rest of the sections as well. § 4.4 looks at Fabricius on

the purpose Nature had in mind by thickening the transparent parts of the eye in various ways.

Giving the utilitas of this diversity of diaphaneity is a way for Fabricius to join the previously

separate textual traditions of optics and anatomy. § 4.5 examines his account of the utilitas of the

cornea, and § 4.6 looks carefully at his appropriation of the Perspectivae communis by John

221

Pecham, in particular. Finally, § 4.7 looks at Fabricius’s version of the theory of vision shared by

him and Zabarella, and there I argue that, in some way, the two interacted to form this shared

theory. I address some historiographical concerns in the conclusion.

§ 4.1: Zabarella’s and Fabricius’s Refutations of Atomistic Theories of Vision

Zabarella begins his second book on vision with the following:

Everything that has been said to this point was concerned with revealing Aristotle’s opinion on vision; it follows that we might also weigh the opinions of others on these matters, and compare them with the opinion of Aristotle, and strive to vindicate it [i.e., Aristotle’s opinion] from the objections of others.1

As he says, his second book is a defense of Aristotle’s theory of vision against competing

theories. He first treats what he calls the opinion of Democritus, although his version of

Democritus’s theory of vision is drawn entirely from Aristotle’s texts, and so is his refutation.

His primary goal in this book is not to refute atomistic theories of vision, but rather Galenic-

influenced extramission theories held by many physicians at the time. The second book of De

visu is concerned with Zabarella’s contemporaries, and he is not just wrestling with a dead

author’s opinions, i.e., a historicized reconstruction of Galenic theories of vision; he is

combatting living opinions, the Galenic theories of contemporary medici. That extramissionism

had a lively following is rarely mentioned by modern scholars, but Zabarella’s and Fabricius’s

treatises cannot be fully understood apart from that context. The Democritean theory of vision

that Zabarella begins with — Aristotle’s version of Democritus given in De sensu — did not have

notable adherents at the time. However, the idea that reflection is an important phenomenon to be

222

1 Omnia, quae hactenus dicta sunt, ad delcarandam Aristotelis de visione sententiam pertinuerunt: sequitur ut aliorum quoque hac de re opiniones perpendamus, & cum Aristotelis sententia conferamus, & eam ob aliorum obiectionibus vindicare nitamur.” Zabarella, De Rebus naturalibus libri XXX (Venice: Paulus Meiettus 1590), 623.

accounted for in a theory of vision can be found in many contemporary works touching upon

visual theory.2 Zabarella’s refutation appears to have been undertaken in part for completeness

sake — Aristotle had done so, and thus so shall he — but perhaps also to combat the still-

commonly held notion that reflection plays an important role in seeing.

Zabarella says that Democritus takes vision to be a reception of species or images on the

surface of the eye rather than in the substance of the eye itself, and this interpretation is derived

from Aristotle and his ancient commentators alone, and not, for example from the much more

detailed account and refutation given by Theophrastus in his De sensu.3 Vision according to this

view involves the reception and reflection of images on the surface of the eye, or at least the

surface of some part of the eye. That the eye acts like a mirror is essential for Democritus’s

theory of vision — or, we should say, for Aristotle’s reconstruction of Democritus’ theory, as

“reflection” and “image” for Democritus and Aristotle likely had very different meanings.4

Zabarella denies that vision occurs due to reflection by making a distinction found in Aristotle:

223

2 For example, this statement in Book II of Francis Bacon The Advancement of Learning was typical: “Are not the organs of the senses of one kind with the organs of reflection, the eye with a glass, the ear with a cave or strait, determined and bounded? Neither are these only similitudes, as men of narrow observation may conceive them to be, but the same footsteps of nature, treading or printing upon several subjects or matters.” Francis Bacon, The Works of Francis Bacon, ed. James Spedding, Robert Leslie Ellis, and Douglas Denon Heath (Boston,: Brown and Taggart, 1860), 221.3 SS 438a5-16. “Democritus, on the other hand, is right in his opinion that the eye is of water; not, however, when he goes on to explain seeing as mirroring. The mirroring that takes place in an eye is due to the fact that the eye is smooth, and it really has its seat not in the eye, but in that which sees. For the case is one of reflexion. But it would seem that in his time there was no scientific knowledge of the general subject of the formation of images and the phenomena of reflexion. It is strange, too, that it never occurred to him to ask why the eye alone sees, while none of the other things in which images are reflected do so.” See also G. S. Kirk and J. E. Raven, The Presocratic Philosophers; a Critical History with a Selection of Texts (Cambridge [Eng.]: University Press, 1957), 421–424; C. C. W. Taylor, The Atomists, Leucippus and Democritus: Fragments  : A Text and Translation with a Commentary (University of Toronto Press, 1999), 108-10, 119-20, 208-11; Hermann Diels and Walther Kranz, Die Fragmente der Vorsokratiker, griechisch und deutsch, 3 vols. 7th ed. (Weidmann, 1954).4 Kurt Von Fritz, “Democritus’ Theory of Vision,” in Science, Medicine, and History: Essays on the Evolution of Scientific Thought and Medical Practice, Written in Honour of Charles Singer, ed. by E. A. Underwood (London, 1953), 83–99, especially 92-5.

“to have this image (imago) in the eye is not to see, but to be seen by another.”5 Furthermore, the

appearance of a reflected image in the eye were indeed the same as seeing it, then any polished

body could be said to see. Rather, it is the reception of the image in the inner substance of the

eye, not its surface, that constitutes vision:

For in fact [the inward substance of the eye] is watery, and perspicuous, and somewhat dense, in order to receive the species of colors, and be able to retain them, so that by appearing (inexistente) [they] might be judged by the faculty of the soul, and thus be called sensed (sentiri) and recognized (cognosci).6

That the eye must be somewhat dense in order to simultaneously receive and retain species of

color will be analyzed shortly ; although it has not been given much prominence in histories of

visual theory its importance cannot be overemphasized. For now I wish to note Zabarella’s

emphatic opinion, repeated several times, that images (imagines) are received in the inner

substance of the eye rather than just at its surface. Although this is derived from Aristotle’s

remarks in De sensu,7 Zabarella takes this further than his source. Not only is the reflected image

that one sees in the eye of another not physically present in their eye, but Zabarella strikingly

contrasts the external surface with inward substance, indicating a concern with dimensionality of

the objects of sense and the instruments of sense. The relevance of this distinction will be clear

224

5 “Putavit Democritus visionem fieri per receptionem quidem speciei in oculo, non tamen in ipsa oculi substantia introrsum, sed in superficie, apparet enim in oculo impressa imago alterius tanquam in speculo: quum enim superficies oculi sit laevis, ac tersa, recepit imagines rerum praesentium, quo fit, ut quisque certnat imaginem suam in oculis aliorum intueri solemus; ea namque nihil aliud est, quam refractio speciei tanquam in speculo, quoniam superifices oculi instar speculi tersa ac laevis est: hanc igitur imaginem (inquit Arist.) in oculo habere non est videre, sed videri ab alio, non emim ille videt, qui in oculis habet imaginem, sed alius, qui imaginem in oculo alterius intuetur;” Zabarella, De rebus, 623.6 “vera autem speciei receptio est illa, quae ab Aristotele ponitur, qui dicit speciem recipi in ipsa oculi substantia intrinsecus; ea namque aqeua est, & perspicua, & aliquantum densa, ita ut recipere speciem coloris, ac retinere possit, ut ab inexistente facultate animae iudicetur, & ita sentiri, & cognosci dicatur....” Ibid., 623.7 “The soul or its perceptive part is not situated at the external surface of the eye, but obviously somewhere within: whence the necessity of the interior of the eye being transparent, i.e. capable of admitting light.” SS 438b7–15.

when we look at Kepler’s theory of light, color and vision, which involves the reception of two-

dimensional species at the surface of the retina. (See § 5.1.)

Zabarella’s concerns can be contrasted with Fabricius’s. The latter’s first refutation of

competing theories of vision is the “modo visionis ex Stoicorum, & Epicuri.” Epicurus’s

atomism took advantage of Aristotle’s criticisms, and perhaps because he was able address

Aristotelian attacks on Democritean atomism Epicurus does not claim reflection (however

understood) to be essential to vision.8 In Epicurean theories of vision images or eidôla made up

of thin films of atoms flow from the surface of bodies into the eye, and so in some way we sense

actual parts of the bodies under consideration. Our Paduan anatomist cites Alexander of

Aphrodisias’s dismissal of the Epicureanism on the grounds (1) that bodies would continually

diminish, (2) that atoms physically emitted from the object would take time to reach our eyes,

and (3) that these thin films of atoms would not retain their shape through the air.9 Comparing

the two, we can note that Zabarella’s criticism of Democritus is not a criticism of atomistic

theories of vision per se, while Fabricius’s criticism is. This is perhaps an indication that

Zabarella did not find Epicureanism, which at the time was becoming culturally relevant in part

due to the popularity of Lucretius’s De rerum natura, to be serious enough to deserve a

refutation, but it might simply come from the fact that Zabarella here sticks closely to Aristotle’s

225

8 From the Letter to Herodotus, 46–53: “And we must indeed suppose that it is on the impingement of something from outside that we see and think of shapes. For external objects would not imprint their own nature, of both colour and shape, by means of the air between them and us and them, or by means of rays or of any effluences passing from us to them, as effectively as they can through certain delineations penetrating us from objects, sharing their colour and shape, of a size to fit into our vision or thought, and travelling at high speed, with the result that their unity and continuity then results in the impression, and preserves their co-affection all the way from the object because of their uniform bombardment from it, resulting from the vibration of the atoms deep in the solid body.” A. A. Long and D. N. Sedley, The Hellenistic Philosophers, Vol. I (Cambridge: Cambridge University Press, 1987), 73.9 Hieronymus Fabricius ab Aquapendente, De visione, voce, auditu (Venice, 1600).38. Fabricius’s citation corresponds to Alexander of Aphrodisias, On Aristotle’s ‘On Sense Perception’, trans. by Alan Towey (Cornell University Press, 2000), 60-61.

texts. Regardless, this difference in which version of ancient atomistic theories of vision is

attacked does seem to indicate that Fabricius takes his philosophical domain to be greater than

the rather narrow compass claimed by Zabarella and other writers of scholastic natural

philosophy textbooks.

§ 4.2: Zabarella Contra Galen 1: Refutation of the Extramission Theory

Zabarella’s attack on Galenic theories of vision occurs primarily in three chapters of book 2. His

Chapter 4 has to do with mostly philosophical objections on the nature of light and sensation,

Chapter 5 uses evidence from anatomy against Galen, and Chapter 6 deals with the substance of

the eye, specifically arguing against the notion that the eye is fiery rather than watery. In Chapter

4 Zabarella presents several of Galen’s arguments against Aristotle’s theory of vision, primarily

that Aristotle’s intromission account has a problem with determining magnitudes of bodies. For

ancient extramissionists, beginning arguably with Euclid, vision was accomplished through (or at

least described by) a visual cone whose apex is inside the eye and whose base is on the thing

seen. One key postulate for Euclid and the ancient perspectivists is that the angle subtended by

the observed body within the visual cone determines its apparent size.10 Aristotle offers no

account of how the image of something the size of a mountain can be reduced such that it enters

the pupil of the eye, or indeed how or why such an image is transmitted simultaneously to

multiple observers. Galen not only criticizes Aristotle’s intromission theory, but claims that

226

10 Euclid, “The Optics of Euclid,” Journal of the Optical Society of America, ed., trans. by Harry Edwin Burton, 35 (1945): 357–72; David C. Lindberg Theories of Vision from Al-Kindi to Kepler (Chicago: University of Chicago Press, 1976), 11-17.

Aristotle himself recognized the absurdities produced by it and, when performing the business of

actually analyzing vision mathematically, that Aristotle resorted to an extramission theory.11

As mentioned earlier, Zabarella’s refutation of Galen involves more than a detached

intellectual dispute with an ancient authority. Throughout he mentions that Galen’s theory of

vision is also that of many medici, and so it seems that the revival of Galenism in the sixteenth

century brought along with it a resurgence of extramissionism. The appropriation of Galen’s

account of vision included the use of Galen’s arguments against Aristotle’s theory of vision.

Although extramission accounts by physicians were rarely fleshed out in anatomical or medical

works, it doesn’t seem that the medici were merely parroting Galen, and a variety of ways in

which visual spirits emitted something (light, spirit) seem to have been put forth. Sixteenth-

century extramissionism in general is an overlooked topic, perhaps because Lindberg’s

influential Theories of Vision barely mentions extramission theories after the Roger Bacon

synthesized the visual theories of Alhacen and Aristotle in the thirteenth century.12 The neglect of

extramissionism is not Lindberg’s fault, however: his synthesis of a huge amount of material

spanning millennia left little room for exceptions to the dominant trends in visual theory, and

227

11 “But it is even less possible for the size of an object to enter the pupil; yet this point, which refutes their [Aristotle’s and Epicurus’] views, they pass by as a small matter. They [the followers of Aristotle and Epicurus] try to devise verbal quibbles in regard to distance and position but neglect to explain how size is discerned, even though it overturns their views completely. And yet Aristotle appears to me to have recognized in his reasoning the absurdity of his statement about the reflection, that it comes to us from the sense-objects, as he nowhere ventures to use it but always drags it along with him as something unconvincing. For when he explains how the rainbow is formed, and the halo around the sun and moon, and the counter-suns and mock suns, as they are called, and when he discusses the things seen through mirrors, he refers them all to the reflection of the visual ray, saying that it makes no difference whether we suppose that the visual ray is reflected, or that the alterations produced by the visual object in the air around us are reflected.” Galen, On the Doctrines of Hippocrates and Plato, trans. by Phillip De Lacy, Corpus medicorum Graecorum (Akademie Verlag, 2005), 471-3. See also Rudolph E. Siegel, Galen on Sense Perception: His Doctrines, Observations and Experiments on Vision, Hearing, Smell, Taste, Touch and Pain, and Their Historical Sources (Karger, 1970).12 Lindberg, Theories of Vision, 107-116.

Lindberg offers the caveat that after the Baconian synthesis “physicians clung to their Galen, and

defenders of the Platonic and Euclidean theories, although exceedingly scarce, were not

altogether lacking.”13 Still, these “exceptions” were more important than Lindberg lets on.

Extramissionism was not only common among physicians. As Sven Dupré shows, there was a

group of mathematicians in the sixteenth century for whom extramission and intromission could

each be be held when speaking variously according their role as a mathematician following

Euclid or their role as a natural philosopher following Aristotle.14

Unfortunately there is no room for a full exploration of sixteenth-century

extramissionism here, but the effort spent by Zabarella and Fabricius to refute Galen’s theory of

vision needs to be understood in the context of a widespread allegiance to Galenic

extramissionism by many sixteenth-century physicians. These attacks on extramissionism

occurred alongside battles over disciplinary hierarchy waged by Zabarella — and, in a slightly

different manner and context by Fabricius — against the professors of medical theory and

practice. Making a direct connection between our figures and these physicians is not easy: none

of the famous professors of medicine at Padua, such Gian Battista da Monte or Eustachio Rudio,

published works dealing with vision explicitly, and there are no obvious references to this

controversy in their works on medicine. Yet other notable physicians do side with Galen on the

issue. For example Francisco Vallés (1524–1592) endorsed Galen’s extramissionism in his

228

13 Lindberg, Theories of Vision, 116.14 Sven Dupré, “Kepler’s Optics Without Hypotheses,” Synthese, 185 (2012): 501–25.

Controversiarum medicarum et philosophicarum libri decem, pointing out the problems that

Aristotle’s theory has with determining apparent distances.15

Chapter 4, Book II of Zabarella’s De visu corresponds to arguments, outlined in the last

chapter, that Fabricius makes against Galen on the actio of the eye, but unlike Fabricius

Zabarella explicitly directs his attack towards both Galen and the many versions of Galenic

extramission put forth by the medici. He writes that Galen’s theory, although easy to attack and

contrary to reason, nevertheless is an annoyance to Aristotelians because it is not easy to

understand what Galen meant, and that this latter point is shown by the variety of opinions that

physicians following Galen have adopted.16 Zabarella’s strategy is to move back and forth

between Galen’s ambiguous statements and their various interpretations by contemporary

physicians. By refuting the many extramissionist opinions held by physicians he aims to dispatch

the full range of interpretations the ancient doctor’s theory of vision. Zabarella can be seen

demonstrating the futility of the Galenic approach overall by arguing (1) that Galen’s theory of

vision is susceptible to the very problems that Galen attributes to Aristotle’s theory, and

furthermore (2) that these problems are even more intractable under Galen’s theory, or at least

under certain interpretations of Galen’s extramission theory.

Zabarella’s first argument against Galen turns on the problem of determining magnitude:

without the use of a visual cone cast forth from our eyes, how is vision supposed to determine

229

15 Franciscus Valles de Covarrubias, Controversiarum medicarum et philosophicarum libri decem (Andreas Wechelus, 1582), 104-107. First printed in 1556, it was a highly popular work and was reprinted many times throughout the second half of the sixteenth century and the first half of the seventeenth.16 “Haec Galeni sententia, quanquam facillima impugnatu est, ut quae est omnino absona rationi, tamen propter varia, & pugnantia Galeni dicta magnum nobis negotium facessit, quum eam plene intelligere non facile esse videatur; quo factum est, ut eam plures Medici ad varios sensus, ut ipsam tuerentur, extorserint; nam si Galenum praesentem haberemus, quem interrogare, & vicissim respondentem audire nobis licere, magis eius sententiam assequi, & assequuti reprehendere, atque impugnare facilius possemus:” Zabarella, De rebus, 626.

the apparent magnitude of bodies? Stars, after all, certainly look much smaller than a person

standing close to us. Responding to this critique, Zabarella asks whether this judgment of the

magnitude of bodies occurs outside the eye or within it. In fact, he says, Galen assumes judgment

to occur within the eye, which is why Galen says that the crystalline humor is transparent and

clear. That is, Galen assumes that the crystalline is susceptible to the reception and subsequent

alteration by colors; the objects of vision do not receive the visual faculty, rather the faculty of

vision, located in the eye, receives the objects of vision. Galen poses the question of how,

according to Aristotle, the colored image of something as large as a mountain is supposed to

enter into our eyes. But having established that, according to Galen, the eye is created by nature

with the capacity to receive impressions of color, Zabarella points out that if vision worked by

sending out rays which then return the objects of vision to the eye, vision would return the

magnitude of the objects of vision along with their color. This is precisely the problem that Galen

imputed to Aristotle: that the magnitude of the actual bodies cannot be returned to the eye. At

best Galen’s extramission account is superfluous, in that the objects of vision must in any case be

received in our eyes without their original magnitude; at worst, Galen believes that sensation and

judgment occur outside the eye, with the objects of vision (that is, colored bodies) themselves

receiving the faculty of vision. According to Zabarella this consideration negates the very

advantage that the extramission of a visual cone is supposed to have: that the apparent magnitude

of things is determined by the angle subtended by the visual rays striking what we are looking at,

and not by its actual size. Implicit in Zabarella’s attack on Galen here seems to be the knowledge

of Alhazen’s or later works on Perspectivist optics, which, by recasting the visual cone as a tool

230

for intromission theories, leveled the playing field on this point.17 Zabarella, however, does not

mention this.

Zabarella asks what, on extramissionist accounts, is supposed to be sent out from the eye.

Is the eye luminous, as many medici seem to think? Experience teaches us that the emission of

lumen causes things to be seen, not to see. Just as the eye must be uncolored in order to see

colors, so too it must lack illumination in order to be receptive of lumen. Like Fabricius (see §

3.6-3), Zabarella argues that any inner light produced by the eye would be a hinderance to vision

rather than an aid, “for every small light is obscured by a great one.”18 Is spirit sent out, or does

the eye cause the air to change into the nature of visual spirt? Galen, given his statements about

how visual spirits dilate the pupils, seems to think so. But animal spirits are corporeal according

to Galen, and this results in numerous insoluble problems. Wouldn’t these spirits move in the

wind? Wouldn’t the body be drained after a few hours of seeing, similar to one losing blood?

Finally, Galen himself says in the seventh book of On the Doctrines of Hippocrates and Plato

that the brain is the primary instrument of all sensation, whose office is performed via nerves

sent throughout the body. Touch, taste, smell, and hearing unquestionably work through

intromission. Therefore if vision occurs through emission, the senses would not be contained

under one univocal nature stemming from one temperament of the primary instrument (the

brain), and thus sensation in toto would not be reduced to one faculty. Zabarella demands that

any account of sensation be systematic and operate according to one underlying set of principles:

231

17 Lindberg, Theories of Vision, 85.18 “omnia namque parva lumina à magnis luminibus obfuscantur, idcirco interdiu non lucent, noctu autem lucent, & videntur, quia tunc à nullo maiori lumine opprimuntur, Galenus tamen de oculorum lumine, quod debilissimum est; asserit contrarium: interdiu enim dum externus aer à sole illuminatur, inquit emitti ab oculis nostris lumen, & externo lumini iunctum reddere aerem visus instrumentum idoneum;” Zabarella, De rebus, 628.

if one sense operates by suffering the reception of its objects of sense, the rest must function

likewise.

§ 4.3: Zabarella Contra Galen 2: Arguments from the Exceedingly Skillful Construction of the Eye

In Book 1, Chapter 8 of De visu Zabarella introduces the anatomy of the eye as a way to

adjudicate between conflicting notions about the nature of light, color, and transparency. Because

the sensitive part of the eye — the crystalline humor — is situated as if in a dark cave, it is not

enough to say that lumen activates the intermedium alone. Lumen is also necessary to activate

and propagate color at the surface of bodies and, crucially, it is necessary for the instrument of

sight, the eye. As we saw in Chapter 2 (§ 2.8), according to Zabarella lumen activates the

transparent medium causing it to be receptive of color; it also activates color — or the limit of the

transparent in a bounded body — and as a result of this color and lumen are joined at the surface

of bodies and propagate together into the darkness of the eye. This lumen coming from the

bodies we are looking at activates the transparency of the crystalline humor, allowing the faculty

of vision to receive the species of color that are joined to that light. In Book 1 Chapter 8, he

writes that the officium — the task or purpose — of most of the parts of the eye is to protect or aid

the crystalline humor in its function as the seat of vision.19 We also read, next to a marginal index

declaring “the error of Galen on the vitreous humor,” the following:

For when looking at [the vitreous humor] I am able to judge that it is perhaps four, or even five times greater [than the crystalline]. But it is clear (clarus) in the highest degree, and bright (albus), and on this matter it is manifest that Galen is

232

19 “quum illatum officium non sit videre, sed inservire crystallino, ut in eo fieri visio possit, aliae namque ad ipsum protegendum, alia ad nutriendum, alia ad movendum totum oculum pertinent.” Zabarella, De rebus, 613.

deceived, when in the tenth book of On the Usefulness of the Parts he says the color of this [humor] is somewhat dark (subnigrum), just as if a bit of black were mixed with much white. Indeed I most manifestly saw that this vitreous humor had no blackness, nor to be less bright than the crystalline — although [it was] not solid, but soft and fluid, from which it is called glassy due to its similarity to melted glass. And furthermore Galen was deceived when he said the that office of this humor is to nourish the crystalline. Indeed, we will show this to be false in its proper place.20

This proper place is De visu, book 2, Chapter 5, titled “Other arguments against Galen from the

substance of the eye.”

Zabarella offers arguments against Galen based on four main observations of the eye: the

substance of the crystalline humor, the figure of the crystalline humor, the office of the vitreous

humor, the color of the uvea. Zabarella begins with an argument from the substance of the

crystalline humor:

Galen asserts this to be solid and hard, and moreover clear (albus), and shining (splendidus), and perspicuous: but apart from the avowal (confessione) of Galen all these things are manifest from the anatomy and inspection of the construction of the eye. [...] Indeed it is clear (albus) in the highest degree, and shining, but what kind of shining [is it]? Is it of such a kind that, from its own lux, it illuminates another? By no means, and this is asserted by the most persevering of men, and denied manifestly by sense. No, it shines from another lumen, which it receives. Likewise in crystal and other solid perspicuous [bodies] we examine, when not made shining (lucentia) by receiving the lumen of another, but in the dark, are destitute of all lumen. However, splendor is made in such solid, perspicuous, and dense [bodies], which on account of their perspicuity receive lumen internally, and on account of their density retain it, and unite it, and give it

233

20 “nam ut ego iudicare videns potui, est fortasse quadruplo, vel etiam quintuplo maior, sed maxime clarus, & albus, & in hoc manifestissimum est, deceptum esse Galenum, qui in decimo de usu partium dixit huius colorem esse subnigrum, veluti si quis parum nigri cum multo albo commiscuerit; ego enim apertissime vidi vitreum hunc humorem nihil habere nigredinis, nec minus crystallino album esse, non tamen ita solidum, sed molliorem, & fluentem, unde apellatus est vitreus, ad similitudenem vitri liquifacti: deceptus etiam in eo est Galenus, quod dixit huius humoris officium esse, ut ex eo crystallinus nutriatur; hoc enim falsum esse ostendemus loco suo.” Zabarella, De rebus, 613. Note Zabarella’s term “subnigrum.”

back it more intensely. Therefore it is established that the crystalline humor is suitable for the reception of lumen, not for emitting it.21

Note Zabarella’s praise for the “most persevering of men,” no doubt a reference to contemporary

Paduan anatomists including Fabricius, the most illustrious anatomist at the time this was

written. It is crucial that we keep some terminology in mind as we simultaneously stress two

things: the great sensitivity to optical qualities that Zabarella and his contemporaries had, and

which are different from the ones we might be sensitive to; and the fact that the categories they

employed, and thus the meaning of the terms, were quite different from today. The term albus or

bright here should be thought of as contrary to opacus, dark or shade. Contrary to what Francis

Bacon will write several decades later — “that whiteness and blackness are most incompatible

with transparence”— for Zabarella whiteness is not opposed to transparency in the same way that

blackness is.22 Indeed, they are explicitly of the same nature according to Zabarella.

Furthermore, these are not Zabarella’s idiosyncratic notions: I have sketched a history of how

these properties were understood in the long history of optics and Peripatetic philosophy, and

234

21 “hunc asserit Galenus solidum esse, ac durum, & praeterea album, & splendidum, & perspicuum; sed absque Galeni confessione haec omnia sunt manifesta ex anatome, & inspectione constructionis oculi; [...] in substantia habet ita solidam, ut sublata etiam aranea tela, qua totus investitur, consistentiam habeat, & figuram suam retineat, nec modo ullo fluat [...] albus etiam maximè est, & splendens, sed quo splendore? an tali, ut ex propriam lucem habens illuminet alia? nequaquam, & hoc asserere pertinacissimi hominis esset, & negantis res sensui manifestas; sed splendens est alieno lumine, quod receperit: idque etiam in crystallo, & aliis solidis perspicuis cernimus, recepto non alieno lumine fiunt lucentia, sed in tenebris omni prorsus lumine destituta sunt; fit autem splendor talis in perspicuis solidis, ac densis, qua propter perspicuitatem recipiunt lumen introrsum, & propter densitatem retinent, atque uniunt, & intensius reddunt, factus igitur est crystallinus aptus ad lumen recipiendum, non ad emittendum;” Zabarella, De rebus, 631.22 From the Valerius Terminus, in Francis Bacon, The Works of Francis Bacon, Vol. 6, ed. by James Spedding, Robert Leslie Ellis, and Douglas Denon Heath (Boston: Brown and Taggart, 1860), 55-6. Likewise, it is also worth noting that in his Novum Organum, when discussing the benefits of attending to what he calls a Migratory Instance, or natures that can be generated or destroyed by a simple operation, Francis Bacon writes that one should not be deceived by these migratory instances into thinking that “whiteness is produced only by transparent bodies.” Francis Bacon, The Instauratio Magna. Part 2, Novum Organum and Associated Texts, ed. Graham Rees and Maria Wakely, vol. XI, The Oxford Francis Bacon (Oxford New York: Clarendon Press  ; Oxford University Press, 2004), 277.

most of Zabarella’s contemporaries used these terms similarly.23 (See Appendix 1.) What is

important for the property albus is not that it blocks light, but that it has no trace of opacus,

which would render the body either shaded or colored depending on how dark and light were

mixed.

What these terms meant — albus, opacus, perspicuous, splendidus — in the context of

optics and natural philosophy (and perhaps generally) underwent a significant shift in the

seventeenth century, and it is a difficult question whether we can fully understand what Zabarella

and his contemporaries intended by their descriptions without having grown up in a culture with

the same, very precise sensitivity to such optical phenomena. Yet we can make significant

progress by reproducing their ocular

dissections, especially if the

relevant conditions under which

they were performed are replicated.

We can, to at least some degree, see

what they saw. Of course, there are

significant questions that arise with

such an attempt to successfully “go

native” and thereby understand how

another culture’s visual experiences

of their world and the textual

descriptions they produced

235

23 Note, however, that the shift from “opacus” meaning dark or shaded to meaning non-transparent was already underway in the late-sixteenth century. One marker for this is whether the phrase “opaque white” would be considered an oxymoron.

Figure 4.1: Graph of the intensity of transmission (Itr) and scattering (Isc) of visible light through the crystalline lens of a calf. The critical temperature Tcat (where Itr is 90% of maximal intensity) is about 19º C. Note that the two curves are plotted on different, arbitrary intensity scales. Taken from M Delaye, J I Clark, and G B Benedek, “Identification of the Scattering Elements Responsible for Lens Opacification in Cold Cataracts,” Biophysical Journal, 37 (1982): 647–56.

interrelate. Nevertheless, some small attempts at progress can be greatly instructive.

At the University of Padua, as at many Italian universities, public dissections were not

only an important part of the medical curriculum, but were significant civic events. Public

dissections were held in the colder winter months in part to delay the rate of decomposition of

the bodies. As it turns out temperature affects the crystalline humor, and what are now known as

cold cataracts develop at temperatures below about 19º C (see figure 4.1). If we assume that

temperatures in Padua during the late-sixteenth and early-seventeenth centuries were not wildly

different from the more recent past, we can see that during the months of November, December,

January, and February it would have been cold enough to significantly affect the transmission of

light through the crystalline humor, resulting in a high degree of scattering even on relatively

warm winter days (figure 4.2). To get a sense of what this might have looked like, see figure 4.3.

236

Figure 4.2: The average high and low temperatures in degrees Celsius for Padua. Data obtained from http://www.climate-charts.com/Locations/i/IY16095.php#data. Data originally from the National Oceanic and Atmospheric Administration (NOAA) via World Meteorological Organization, and National Climatic Data Center (U.S.), 1961-1990 Global Climate Normals, Version 1.0 [CD-ROM] (Asheville, NC: The Center  : NCDC Climate Services Branch, 1998).

-6

0

6

12

18

24

30

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

-1.4 0.53.5

7.411.6

15.317.5 16.9

13.88.8

3.7-0.4

5.78.8

13.117.5

22.426.0

28.4 27.924.5

18.8

11.56.5

30-Year Average Temperatures for Padova, Italy 1961-1990

I will go into more depth below, but we know that Zabarella attended at least one dissection of

the eye, which could have been performed in either public or private. He also mentions

personally witnessing the liver during a dissection, and overall it seems that Zabarella was no

stranger to anatomical demonstrations.

From the shape of the crystalline humor it is obvious to Zabarella that it is not designed

to emit light, but receive it. The rear of the humor is gibbous or bulging where it meets the

vitreous humor (with the aranea in between) while it is more flattened in the front. The

flattening, he says, is so that it can receive more rays, while the protruding rear aids the vitreous

humor in performing its function, “in whose imputed office it is manifest that Galen was

deceived.”24 According to Galen in On the Usefulness of the Parts, the purpose of the vitreous

humor is to nourish the crystalline, and therefore color of the vitreous is somewhere in between

that of blood and the transparency of the crystalline humor. This is so that it doesn't mar the

clarity that is essential for the action of the crystalline humor when the vitreous nourishes it.25 As

we have seen in § 3.3, Avicenna, among others, also follows Galen on this point. Note, however,

that Galen does not give this account in On the Doctrines of Hippocrates and Plato, where both

the crystalline and the vitreous are described as “perfectly clear, transparent, and bright,” which

indicates, perhaps, that he changed his views on this point.26

Zabarella says that, contra Galen in Usefulness, the vitreous is not only clear, but in fact

more clear (albissimus) than the crystalline, and Galen’s description is adversatur sensui, or

237

24 “in cuius officio assignando deceptum fuisse Galenum ita manifestum est, ut nihil esse possit clarius, & hoc intellecto patebit receptione visionem fieri, non emissione.” Zabarella, De rebus, 631–2.25 Galen, Galen on the Usefulness of the Parts of the Body. De Usu Partium. Translated from the Greek with an Introduction and Commentary by Margaret Tallmadge May., trans. by Margaret Tallmadge (Cornell University Press, 1968), 464.26 Galen, On the Doctrines, 459.

238

Figure 4.3: The crystalline lens of a cow at approximately 10º C, taken from above and the side, and in front of a colored background (left) and graph paper with four squares per inch. Observe the clouding of the central region, corresponding to the description by Zabarella and Fabricius (among others) as being both not tinted, and also having a certain transparency to receive light and color while at the same time a certain density or thickness to retain, delay, and fix the light and color in the humor.

Figure 4.4: Quartz crystal (left) and ice (in this case a hailstone), the two objects from which the crystalline humor or glacialis received its name. Nearly every author since antiquity also remarks on the similarity of the humor to crystal and ice (or hail) in terms of transparency, color, and clarity.

opposed to sense. Thus, he says, if Galen’s account of the usefulness of the vitreous were correct

then its transparency would be superfluous.27 Nature, Zabarella notes, can turn blood into any

number of substances — nerves, milk, and semen, for example — and yet is always able to

generate the resulting color without difficulty. Indeed, if blood can be turned into the vitreous

humor, which is more transparent than the crystalline, nothing prevents nature from directly

nourishing the crystalline directly.28 Furthermore, the sheer amount of the vitreous causes a

problem with Galen’s account:

It is also inharmonious to reason that the vitreous humor, which is of such a great mass, should deliver nutrition to the crystalline: for the vitreous is much greater that the crystalline, and, if we believe the senses, it is four, or perhaps five times greater. In all things, however, we see nourishment to be far less in quantity than the thing nourished. And this is altogether necessary, because, since the nourishment is at first contrary [to the nourished body], and since it fights the thing nourished, if it is greater it would overwhelm [the thing nourished] rather than nourish it — being as powerful as it is, since to a greater body belongs a greater strength. Thus the nature of the crystalline humor would be changed into the nature of the vitreous, rather than the reverse. 29

In these arguments Zabarella was relying upon a quite recent (post-Vesalian) consensus in

anatomy regarding the position, shape, and relative bulk of the humors of the eye. (See § 3.3.)

Thus Zabarella’s criticism of Galen’s account of the vitreous humor and crystalline humors is

threefold: (1) if the usefulness of the vitreous humor was to provide nutrition for the crystalline,

nature would be acting without purpose in making the vitreous humor clear; (2) nature would

239

27 Zabarella, De rebus, 632.28 Zabarella, De rebus, 632.29 "quia mutatur in ea generatione color in colorem conveniente rei generandae, vel nutriendae, quod praestare sagacissima natura, quando ita expedit, facile potest. Est etiam absonum rationi, quòd tanta moles, quanta est humor vitreus, crystallino ad eius nutritionem tradita sit: nam multo maior est crystallino vitreus, ac, si sensui credimus, est quadruplo, & fortasse quintuplo maior, videmus autem in omnibus alimentum esse re nutrenda longe minoris quantitatis, idque omnino necessarium est: quia, quum alimentum in principio sit contrarium, & cum re alenda pugnet, si maius esset, opprimeret eam potius, quam aleret, tanquam validius, quoniam in maiori corpore vis maior inest; potius igitur natura crystallini in naturam vitrei mutaretur, quam è contrario." Zabarella, De rebus, 632.

also be acting against its own ends by making far too much of the stuff; and finally (3), the

crystalline humor, in particular the rear, would be shaped as it is for no reason. We can see here

an implicit accusation that, on Galen’s account, nature would be acting without foresight. Not

coincidentally, this is Galen’s favorite argument against earlier anatomists, such as Erasistratus,

whom Galen attacked for claiming (yet failing) to follow in Aristotle’s footsteps.30 Zabarella also

repeatedly says that the shape, size, and transparency of the humors is clear to sense, thus

impugning not only Galen’s reasoning but also, it seems, his skill at anatomical observation.

Rejecting Galen’s account of the office of the vitreous, Zabarella offers another account

which he says is, after it is diligently considered, “so evident, so that nothing can be clearer.” For

Zabarella, the purpose of the vitreous humor is to put distance between the crystalline humor and

240

30 See H. Von Staden, “Teleology and Mechanism: Aristotelian Biology and Early Hellenistic Medicine,” in Aristotelische Biologie, ed. W Kullmann and S Föllinger (Franz Steiner, 1997), 183–208.

Figure 4.5: Crystalline and vitreous humors of a cow. The black fringes are remnants of the ciliary body, flecks of which can also be seen in the liquid (the aqueous humor) in which the two sit.

Figure 4.6: Crystalline humor of a cow. The faint line shows where it was previously connected to the ciliary body. Note the difference in shape between the anterior (left) and posterior surfaces.

the colored tunics at the rear of the eye. The crystalline has to be transparent for it to be receptive

of lumen and color, but this also entails that lumen passes beyond the humor. If the body

immediately behind the crystalline were not transparent, light would return to the crystalline

tinged with the color of that body, and as a result the crystalline humor would perpetually receive

the color of the tunic behind it.31 The purpose of vision is not to perpetually see our retinas, and

therefore, not only is a certain space necessary, but the light progressing through the crystalline

needs to be dispersed or otherwise prevented from reflecting back. For this reason, says

Zabarella, in addition to acting as the seat of sensation, the rays of lumen are refracted upon

exiting the crystalline humor, uniting into a point just behind it. Zabarella compares this with

what "experience teaches" us with glass placed over a hole into a cave or cavity: the lumen

behind it is formed into a cone, the point of which can kindle a flame. Beyond this point the

lumen is weakened, and he says "the cone, extending to a peak, does not go past a certain

determinate point."32 Thus, focusing lumen together into a point ultimately weakens the lumen

241

31 “quum enim necessarium sit ut per crystallinum tanquam perspicuum transeat lumen, & color receptus, certe nisi aliquis alius humor in parte posteriore inter tunicas, & crystallinum intercessisset, lumen illud ad tunicas in illa parte pervenisset, & quum soleat lumen à solidis corporibus reflecti, fuisset iterum reflexum à tunicis ad crystallinum unà cum colore tunicarum, est autem secunda tunica colorata colore subnigro, ideo imbutus fuisset, perpetuò crystallinus colore illo, quod quidem visioni maximum impedimentum attulisset; [...] fuit ergo necessarium ut inter tunicas, & crystallinum in posteriore oculi parte humor vitreus poneretur, isque magnus, & magnae profunditatis, ut in eius medio posset linearum visualium angulus fieri, & inde earum conus exinaniri, neque ad tunicas pervenirent, ne ab earum colore crystallinus per reflexionem luminis coloraretur: hoc est absque dubio vitrei humoris officium;” Zabarella, De rebus, 632.32 "nam experientia docet, lumen transiens per vitreum aliquod cavum uniri in illa cavitate, & permeans ultra vitrum in quadam certa ab eo distantia facere conum, in cuius extremetate intensissimum lumen apparet, sed minimae quantitas instar milii, nempè si in illa certa distantia ponatur corpus aliquod solidum, in quod angulus impingat; nam si propinquius vitro corpus illud ponatur, maiore eius pars illuminabitur, & eo maior, quo sit propinquius vitro; at si paulatim removeatur, minuetur continuè donec ad minimam superficiei illuminatae quantitatem perveniat, ideò in illa minima quantitate ita est unitum & validum illud lumen, ut etiam accendat, & urat, quoniam ibi definit conus, & angulus à concursu radiorum productus; ideo si adhuc magis removeatur corpus illud, nullum amplius lumen ab illo vitreo ad ipsum pervenit, sed exinanitum, quia quum ad conum, & ad acumen tendat, non praetergreditur quoddam determinatum punctum:" Ibid., 632-3.

beyond that point, which experience with burning lenses (he says) shows. Note that the

crystalline humor is not merely analogous to a burning instrument, it is one. It is frustrated,

however: the actual production of fire is prevented because the cone of lumen comes to a point in

a watery substance, the vitreous humor. Furthermore, the “experience” that Zabarella describes

in many ways resembles a camera obscura: light is described entering an aperture and being

united by a glass lens within a dark room. However, Zabarella does not mention image

formation; he is describing an investigation of burning lenses, not the projection of images in a

camera obscura. This distinction is important, and will be discussed at length further on.

Not only does Zabarella compare the crystalline humor to a glass lens, but he also

mentions a dissection demonstrating these properties of the eye:

I saw the crystalline separated from the other humors in a dissection of the eye, which when placed near a small lit candle was made to shine all over, and gleamed just as if imbued with the lumen of the candle on account of its perspicuity. And the lumen traveled across the entire substance of the crystalline humor, and in the posterior part of the crystalline humor it turned into a cone, and into a peak not much beyond the bulge of the crystalline humor, so that that peak and the running together of the lines stood apart very little from the crystalline humor — indeed almost seemed to touch [the crystalline humor] itself. Therefore it is certain that the peak of that cone is exhausted (exinaniri) in the vitreous humor, which has a great depth, and thus is not able to reach the posterior tunics.33

When Zabarella speaks of the crystalline humor “gleaming just as if imbued with the lumen of

the candle on account of its perspicuity” we can, from the perspective of modern science, say

that he was seeing a crystalline humor that had developed a cold cataract, thus causing light to

242

33 "ego igitur in oculorum sectione vidi crystallinum ab aliis humoribus separatum, cui quum accensa candelula apponeretur, totius fiebat lucidus, & splendens tanquam candelae lumine imbutus ob suam perspicuitatem, & trans totam crystallini substantiam meabat lumen, & in posteriore crystallini parte transibat in conum, & in acumen non multo post intimam crystallini gibbositatem, ita ut acumen illud, & linearum concursus parum distaret à crystallino, immò ipsum fere attingere videretur; ideo certum est illius coni acumen exinaniri in humore vitreo, qui magnam habet profunditatem, ideoque ad posteriores tunicas pervenire non posse." Zabarella, De rebus, 633.

scatter as it passed through. Zabarella, however, did not view this as an accidental property of the

humor — a deviation from the more pure transparency of a properly functioning humor — but

rather as an essential property of the humor, without which vision itself would not occur. I call

this property that of species-fixing. Furthermore, for him this was not a case of light scattering,

but rather of the humor becoming luminous from the light of another, which he contrasts with the

Platonic/Galenic idea that the eye is self-luminous. The distinction between the humor scattering

light versus becoming luminous from the light of another is a subtle but important one, but it

reveals fundamental ontological assumptions involved in scholastic notions of lumen,

assumptions that differ greatly from seventeenth-century corpuscular, as well as more modern,

ideas of light. According to Zabarella’s account of sensible or intentional species, qualities

inhering in a body have a robust existence, while the species of such qualities exist in a medium

and have a diminished existence. Lumen for Zabarella is the species or image (imago) of lux in a

transparent medium, while lux is a property of the surface of bodies that shine or produce lumen.

Therefore, on this account the crystalline humor acquires the property lux, a brilliance or shining,

from a separate self-luminous body; the crystalline has a disposition for such shining, and when

exposed to species of lux (i.e., lumen) it acquires the property of lux and begins to put forth

lumen. However, in an important sense this lux and lumen are not its own: the crystalline humor

is not the ultimate cause of its shining because the lux in the crystalline humor requires being

continually exposed to the lumen of a nearby luminous body, and indeed the very shining present

in the crystalline humor is the image of the shining present in the self-luminous body it is

exposed to. Importantly for perception itself, this account holds not just for light, but for color as

well. The colors of bodies within one’s field of vision are “fixed” in the crystalline humor, a

243

process that cannot occur in more perfectly rare and transparent bodies such as air. Like the

projection of the red color of a vial of wine onto a white cloth, the colors induced in the

crystalline humor are entirely dependent on the external body causing them — the existence of

color in the crystalline is tenuous and relational — but at the same time colors find more purchase

in the somewhat dense crystalline humor than they would in pure air. It is only due to this

species-fixing property that light and color are “shown” within the eye, and this is a prerequisite

for the act of judgment by the visual faculty to take place. A quite precise degree of density in the

eye is thus necessary for sensation to occur within the eye. (I treat this at greater length in § 4.4.)

In contrast, according to later views this distinction between qualities and species of qualities

disappears, and thus it often said that what we see is light itself. In post-scholastic vision, light

either goes into the crystalline humor or perhaps some impulse is transmitted to the crystalline

humor, as according to Descartes. Some of this light or some proportion of this impulse is

scattered in different directions.

Returning to the quote above, this reference to dissection is not the only one in

Zabarella’s De rebus. In book 2, Chapter 6 of De visu he says that the opinion that the eye is of a

fiery temperament is “countered by the dissection of the eye and by sense itself.”34 Later on in

Book 2, Chapter 7 Zabarella will use arguments from the tangible properties of the crystalline

humor during dissection to show that the temperament of the eye is watery. The eye can be

considered in two ways, “taken in one way through that body which is observed by the senses

through anatomy” which clearly reveals it to be watery. The other way is an analysis of its innate

heat and the spirits sent to the crystalline by the brain. One might argue that the heat and spirits

244

34 “Attamen huic sententiae dissectio oculi, & sensus ipse refragatur;” Zabarella, De rebus, 634.

present in a living eye are fiery while a dead eye under dissection loses this heat as the spirits

dissipate, but Zabarella rejects this. Apart from the fact that Aristotle everywhere denies that the

eye is fiery, if the crystalline is a perfect mixt then after death its elemental composition does not

immediately change.35 (Note that Zabarella’s account of putrefaction is at issue here.36) Thus, as

we have seen in Fabricius, dissection is a reliable means of directly assessing the elemental

composition of the parts of a living body. Also note that here Zabarella adds an argument that

contradicts Aristotle’s account in Meteorology III of a man whose sight was so weak that the air

itself acted as a mirror. Zabarella says that the sight of the old is not weak because of a weakness

of the soul — the soul itself is not debilitated with age — but only because the organ acquires

impurities over time making it more earthy and less perspicuous, and less capable of receiving

light and color.37. An entirely separate reference to dissection is offered in Zabarella’s book On

the Division of the Soul Chapter 9 in De rebus. Here he also uses dissection to refute Galen on

the question of whether the brain or the heart is the “principle organ” (praecipuo membro).

Arguing the Aristotelian position that the heart is the primary organ, Zabarella says that many

arteries connect the heart to the liver, a confirmation that the liver is subject to the primary

245

35 “oculus duobus modis considerari potest, uno modo sumi potest pro illo corpore, quod per anatomen sensu conspicitur, sic autem aqueus est, patet enim crystallinum humorem esse aqueum; secundo modo pro calido innato, quo ut instrumento crystallinus utitur, nempe pro spiritu animali illuc misso à cerebro, & hac ratione oculus est igneus, ideo Aristoteles utrunque respiciens variè loquutus est. Sed vana est haec consideratio, quoniam Aristoteles in libro de sensu & sensilibus oculum sumit animatum, atque perfectum, siquidem anima destitutum negat esse oculum appellandum, sed illum solum, qui facultatem videndi habeat; hic autem non est sine spiritibus, & calore innato, eum tamen Aristoteles negat esse igneum tum ibi, tum in quinto libro de ortu animalium capite primo, & apertè asserit esse aqueum, scilicet ratione excessus, quia aliquam ignis quoque portionem in crystallino esse quis negare potest, si crystallinus est corpus mistum, & perfectum mistum? non est ergo credendum Aristotles alibi ex propria sententia loquentem appellare oculum igneum.” Zabarella, De rebus, 635-6.36 Sachiko Kusukawa, “Nature’s Regularity in Some Protestant Natural Philosophy Textbooks 1530-1630,” in Natural Law and Laws of Nature in Early Modern Europe, ed. by Lorraine Daston and Michael Stolleis (Ashgate Publishing, Ltd., 2008), 118-9.37 Zabarella, De rebus, 637. This is an argument that Fabricius also uses, though it was likely commonplace among physicians at the time.

agency of the heart. He writes “Let the Doctors explain why the liver is filled with arteries, as

anybody can verify through anatomical dissections.”38 Zabarella is clearly writing within a

culture where anatomy is commonplace.

While a living eye is sensitive, nevertheless a dead eye does not lose its temperament

immediately, and the crystalline humor in particular retains two important properties: it retains

and “reveals” the light and the colors it receives from its field of vision, and it also acts like a

burning glass by uniting the lumen into a point just behind the crystalline humor. But what are

we to make of Zabarella’s statement that the peak of the cone is “exhausted” in the crystalline

humor, and what are the other consequences of the eye possessing a miniature burning lens? We

can make some sense of the first question by looking at Zabarella’s explanation for why lumen

from the Sun heats the earth. Earlier in De rebus, in Chapter 10 (titled “In What Way Lumen

Heats”) of his book On Celestial Heat, Zabarella gives the “true opinion” of how lumen from the

sun generates heat on earth without the sun itself being hot. He writes that “experience shows”

that heat from lumen is insensible unless the rays of lumen are duplicated. When a ray of lumen

strikes a body perpendicularly and reflects directly back there will be a ray ascending and a ray

descending, and “from the collision of the two rays the air is thinned and made more hot.”39 This

duplication is important, and it explains why, he says, summer is hotter than winter. Earlier in On

Celestial Heat in Chapter 3, titled “In What Way Motion Generates Heat,” a marginal note states

246

38 Zabarella, De rebus, 519. Translation from Jorge Leoncio Soler, “The Psychology of Iacopo Zabarella (1533 - 1589)” (PhD Dissertation, State University of New York at Buffalo, 1971), 32. 39 "ita enim lumen in solo aere attritionem facit, neque quodlibet lumen, sed mangum, at vehemens: experientia enim docet, nullum à lumina candela accensae produci calorem, ob eius luminis parvitatem, ac debilitatem; immò nec astrorum, nec Solis lumen quanvis maximum esse videatur, producere calorem videtur, vel saltem debilem admodum, & insensilem producit, nisi duplicetur, & ita per duplicationem validus reddatur; proiecti nanque radii Solis in terram resiliunt à terra refracti, & in aere duplicantur, nimirum descendentes, atque ascendentes, & ex radiorum inter se collisione extenuatur aer, & calidior fit: credendum quidem est radios Solis etiam rectà proiectos, ac simplices aliquid caloris efficere” Zabarella, De rebus, 402.

“Heat is the cause of rarity, not rarity the cause of heat.” Here Zabarella writes that motion per se

is not the cause of heat. It is only the cause of heat when motion rarefies substances, and only

certain ones. Involved in this is a subtle problem about the direction of causation, for heat

manifestly rarefies (e.g., in boiling water) but it also seems from experience that rarefaction can

cause heat: in addition to Zabarella’s above example of lumen giving rise to heat through

rarefaction, Zabarella also interprets friction as a case of motion causing rarefaction, and so

interprets Aristotle’s notorious example of lead tips of arrows melting in flight in De caelo II, as

well as shooting stars, “torches,” and “goats” occurring in the upper atmosphere in Meteorology I

as examples of rarefaction causing heat. Are cause and effect, in this case, reciprocal? Zabarella

has a nuanced answer, and says that only in simple bodies (the four elements) are cause and

effect reciprocal, in which case “just as an effect is given with a given cause, so too a cause is to

be given with a given effect; nor for this reason does it happen so that the effect should be the

cause of its own cause [i.e., that a vicious circle of causation occurs], but that [the effect] is a

preparation for [the cause] in the subject that is to receive [the cause].”40 Reciprocal, in this

sense, merely means that heat follows from rarefaction, not that rarefaction alone is the cause of

heat. Rarefaction of air by means of a burning glass therefore prepares the air to receive the form

of heat. Rarefaction is only the cause of the conditions necessary for the form of heat to arise;

only after the form of heat is generated in the body can a flame can be induced, and this flame is

caused by the form of heat itself and not by rarefaction. In mixed bodies, on the other hand, this

reciprocality cannot be taken for granted, and it only occurs in bodies with a built-in capacity to

247

40 “dico calorem, & raritatem se mutuo consequi ut causam & effectum reciprocabiles, dum considerantur in simplicibus, de his enim loquimur, non de mistis, quorum alia est ratio ob contrariorum elementorum concursum; igitur ubi causa & effectus reciprocantur, quemadmodum posita causa ponitur effectus, ita & effectu posito ponitur causa, nec propterea fit ut effectus sit causa suae causae, sed est praeparatio ad eam in subiecto recipiendam:” Ibid., 391-2.

receive heat through motion and rarefaction. In a thick (densum) body such as water this cannot

occur, and indeed Zabarella says that firing an arrow into water does not produce heat. At the

marginal note reading “Why water is not made hot by motion” Zabarella gives the reason why

stagnant water is often hotter than rapidly flowing water in rivers: water is a naturally cold, dense

substance, and so does not receive heat through motion; stagnant waters are not per se more apt

to receive heat, but they are in more constant contact with air which itself (and not the water) is

made hot through the “percussion of the rays of the sun.”41

In scholastic treatises and works on burning mirrors it was extremely common to describe

burning mirrors as causing a flame by acting on the air and not by giving heat to the solid body

that the rays reach. Thus in Pecham’s Perspectivae communis, the most widely read book on

optics in medieval and renaissance Europe, we read that a burning glass brings the rays of light

together and “when these rays have been assembled and the air rarefied, fire is kindled [just]

beyond the terminus of their species.”42

Returning to the vitreous humor, we can see that the converging rays in the vitreous are

debilitated through collision, but because they collide in water (which, unlike air, is not naturally

receptive to heat) no heat or flame is generated. The watery temperament of the eye, and in

particular the vitreous humor, is thus required for the organ to work properly. To summarize,

Zabarella describes the officio of the vitreous humor as having three parts. (1) The vitreous

248

41 Ibid., 392.42 John Peckham, John Pecham and the Science of Optics: Perspectivae Communis, ed. by David C. Lindberg (University of Wisconsin Press, 1970), 230-1. As evidence of the great shift occurring in the seventeenth century, see Boyle’s remarks about why black bodies, compared to white ones, are easier to ignite using burning mirrors. Robert Boyle, Experiments and Considerations Touching Colours First Occasionally Written, among Some Other Essays to a Friend, and Now Suffer’d to Come Abroad as the Beginning of an Experimental History of Colours, Early English Books Online (London: Printed for Henry Herringman, 1664), 103-4.

humor is capacious so, that the rear tunics are far away from the crystalline humor. (2) It is more

transparent than the crystalline, and combined with the fact that Nature has made the rear of the

crystalline humor protrude this causes the lumen at the crystalline-vitreous boundary to be united

immediately behind it; this debilitates the lumen and prevents it from reaching the rear tunics and

returning their color to the crystalline humor. (3) The vitreous humor watery so that the

crystalline-humor-as-burning-glass does not kindle a flame in the eye. All of this — the great size

of the vitreous humor, the relative transparencies of the humors, the shapes of the humors, and

the complexion of the vitreous — would be to no purpose if Galen’s extramission theory were

correct.43

Zabarella’s final argument from the substance of the eye, which I will treat only briefly,

concerns the uvea or grape-like tunic, the dark membrane in between the outermost sclera and

the innermost retina. Why is it dark? Galen says that shining, bright bodies hurt the eye, while

dark grey (subnigrum) or blue (caerulum) bodies help the eye rest and give it strength, and this is

the reason why it is dark colored.44 Zabarella says the same thing as Galen does, but argues that

this only supports intromission.

§ 4.4: Fabricius on the many Utilitates of Diaphaneity (or, How to Graft Optics onto Anatomy at the End of the Sixteenth Century)

The first chapter in section three of Fabricius’s De visione, after the proemium (which was

discussed in § 3.7), is on the utilitas of the whole eye. Fabricius begins his discussion with the

249

43 Zabarella, De rebus, 633.44 Though Zabarella does not cite a passage, here, he is almost certainly thinking of Galen’s account in On the Usefulness of the Parts. To give support for his opinion that the uvea is dark in order to “furnish for tired eyes a corrective object to look at,” Galen cities Xenophon’s account of soldiers suffering from the brilliance of snow and the practice of painters looking at grey or dark objects in order to rest their eyes. Galen, Usefulness, 473-4.

temper (temperies) of the eye. He says it is cold and humid, and because it is free of blood in

nearly all its humors and membranes it has only a small amount of heat.45 That the eye is

fundamentally watery is crucial because Fabricius, just like Zabarella, argues that the eye acts as

a burning glass, and a watery nature is necessary to prevent the vitreous humor from igniting.

Determining the temperament of the parts of the eye involves direct tactile experience and

therefore, as Fabricius emphasized in the proemium, a determination of the utilitas of the parts is

impossible without dissection.

Why is the eye watery? Fabricius repeats Aristotle’s assertion that both air and water are

naturally pellucid, and that Nature made the eye from water because water is easier to contain

than air. This explanation has more to do with convenience — that water is merely the best

possible material available. One gets the impression that, because this explanation doesn’t touch

on the essential activities involved with vision, Fabricius does not find it entirely satisfying. He

goes beyond Aristotle and says that not only is water more easily to be contained within the eye

than air, but also that water itself can contain the visible forms of things better than air.

“Therefore,” he says, “in order that [the inner substance of the eye] should be contained, and in

turn contain, it is of necessity made watery.”46 For support he draws upon Albertus Magnus, who

250

45 Fabricius, De visione, 56.46 "Atque hic videtur illa Aristotelis quaestio locum habere: cur scilicet oculus ex aqua magis quàm aera natura consistet: cum duo tantum in universa rerum natura pellucida corpora reperiantur, aer & aqua: cetera verò horum admixtione & beneficio diaphana sint & dicantur. Nam terreum elementum quis neget opacum esse? Ignis verò quo utimur, turbidus certè & opacus est. Huic igitur quaestioni satisfacit Aristoteles, cum ait optima ratione aqueum constitutum esse oculum non aereum, quoniam aqua ominium pellucidorum facillimè conservari potest; aer verò neque contineri intra oculum, neque continere visilium formas posset. Igitur, ut contineatur, vicissimque contineat, necessariò aqueus factus est." Fabricius, De visione, 57. C.f. Aristotle, De sensu, 438a13–24.

says that the forms of color are not retained in transparent air unless it has been thickened

(crassescere) into water, and adds a few lines of Catullus as a literary flourish.47

All of this is in a sense preliminary. His primary account of the utilitas of the eye being

watery considers the way in which water, specifically, can be transparent, and he spends several

pages explicating this. Being composed of water not only means that light will refract when it

leaves air, but it also allows light to interact with different parts of the eye in several ways. Both

the degree and the type of thickening is a factor, and Fabricius expands on this point:

Thus the eye is watery so that it might be thickened in various ways. Yet to thicken in various ways admits of two uses. The first is so that various refractions of light occur, and how this adds to vision will be made clear shortly. The second is so that light in one place passes through, in another place is shown (firmare), and in another disappears. For it will be declared in its proper place [that light] proceeds through the aqueous humor, is shown in the crystalline, [and] finally vanishes in the vitreous.48

This passage is significant for a number of reason. First, it is the earliest place I have been able to

find — whether in works on optics, natural philosophy, or anatomy — that unambiguously

distinguishes two kinds of condensation or thickening of the transparent: the first sort affecting

what we would call the optical density or the refractive power of the transparent body, the other

what we might today call its translucency, cloudiness, or degree of light-scattering. As we have

seen above, these terms require care. “Optical density” as it is used today is a legacy of an earlier

251

47 Catullus 70. He only includes portion highlighted below. Nulli se dicit mulier mea nubere malle quam mihi, non si se Iuppiter ipse petat. dicit: sed mulier cupido quod dicit amanti, in vento et rapida scribere opertet aqua.48 "Igitur aqueus est oculus, ut vario modo crassescat. Vario autem modo crassescere: duos praebet usus. primus est, ut varia lucis fiat refractio, quae quantum visioni conferat, paulò post patebit. alter est, ut lux alibi quidem permeet, alibi firmetur, alibi denique evanescat. Nam suo loco dicetur, per aqueum humorem lucem progredi; in Crystallino firmari; in vitreo tandem delitescere." Fabricius, De visione, 58. This point is reiterated in his discussion of the utilitas of the cornea, p. 97.

understanding of light, color, and refraction that has been the subject of this dissertation so far,

but as used today the phrase implies that one already has in mind a sharp distinction between this

and density in the sense of specific gravity (now the default meaning) or density in the sense of

the thickness of a fluid. That is, “optical density” as a common phrase arose only after density (or

thickness) and refractive power came to be understood as very distinct concepts, a process which

Fabricius stands at or near the beginning of; to apply this term to Fabricius is anachronistic and

likely might confusion, and thus I will employ the more neutral term refractive power. Moreover,

while today “optical density” is typically used to mean refractive power, in some disciplines such

as spectroscopy it means spectral absorbance, or the measure, for some wavelength, of the ratio

between the light incident upon some material and the light transmitted through it.

More importantly, the thickening of the transparent in the second sense has no clear

analogue in modern science. The modern distinctions that every schoolchild learns between

between transparency, translucency and opacity does not map onto the premodern terms from

which they derive. Translucent and transparent — translucens and transparens — were often used

interchangeably in Fabricius’s time, although the former (along with diaphanus) implies the

passage of light while the latter the passage of sight. The notion of light scattering that our

current use of the term “translucent” brings to mind would not necessarily have been endorsed

by Fabricius and others at the time. Those in Peripatetic-perspectivist tradition that I have been

examining would not typically have said of a condensed or somewhat cloudy body that some of

the light is reflected from it while some of it passed through. As we have seen above (§ 4.3) the

issue is a complicated one. In this context it also involves the distinction between perfect and

imperfect mixts. Fabricius holds that the crystalline humor was a perfect mixt — a homogeneous

252

body as described at the beginning of book 2 of Aristotle’s On the Parts of Animals. Because

there are not supposed any small parts of the crystalline that differ in some way from others, light

cannot not be reflected or scattered by some parts of the crystalline humor but not others. Rather,

we should recall Zabarella’s vivid image of his experience with a dissection of the eye and seeing

the humor “gleaming just as if imbued with the lumen of the candle on account of its

perspicuity.”

When Fabricius says that light is “shown” in the crystalline humor he uses the Latin verb

firmare. In addition to to show, declare, confirm or establish it can also mean to strengthen or

make firm and also to support in the physical or metaphorical sense. I call this property species-

fixing. What Fabricius means here is that species of light, along with the colors which with it is

tinged, quite literally show up and announce themselves due to the thickened transparency of the

crystalline humor. This is clear when he discusses the utilitas of the crystalline humor in Chapter

7. There he repeats the observation that this humor is “not fluid like water, but compact, just like

water which is to some extent congealed into ice.”49 Its transparency here is broken down and

understood in several different respects. “First, the Crystalline is made diaphanous so that it can

be altered and transformed by light, and made clear, and to not possess any natural color.”50 If it

were red or yellow, we would always see red or yellow. Second, it’s transparency differs from the

aqueous humor — “diversum ab aqueo humore” — so that a new refraction of light is made at the

transition. Third, the “diaphaneity of the Crystalline is denser than the diaphaneity of the aqueous

253

49 Because the crystalline is the seat of vision, he concludes “Igitur aqueus est primo Crystallinus, non tamen fluidus ut aqua; sed compactus, ut aqua quae mediocriter in glaciem sit concreta.” Fabricius, De visione, 96. His description here is nearly identical to that on p. 58, “Crystallinus verò aquam imitatur, quae mediocriter sit in glaciem concreta;”50 “Quocirca, primùm quidem diaphanus Crystallinus est factus, ut à luce alteretur, immuteturque ac lucidus fiat, neque colorem aliquem naturalem obtineat.” Fabricius, De visione, 97.

humor so that light is refracted towards the perpendicular at its surface, in order that the greatly

united and strengthened light affect it.”51 Finally, its density causes light and color to appear in

the crystalline humor rather than passing through without affecting it. Following Alhazen, he

says that if the crystalline were “an exceedingly rare diaphanous [body]” the forms of things

would pass through them, and the species would not be felt or apprehended. “For this reason, in

the same place the author [Alhazen] says that light and color do not appear in a diaphanous body,

unless there happens to be a certain thickness (spissitudo) in it.”52 That is, light’s visible presence

— it’s showing up in the way that species don’t in clear air, and what I term species-fixing —

indicates that the crystalline humor is physically altered in a stronger sense than clear air or water

are, and it is on account of this presence that light and color are able to be sensed. This

relationship between density or thickness is an important one, and Fabricius brings all of his

authorities in the optical tradition to bear on it. (Fabricius’s cited passages are compared in table

1.)

Fabricius’ spends nearly a page in his discussion of the thickness or density of the

crystalline and how light is impressed and delayed there — to how species cling to (adhaerescere)

and are retained (continere) due to this density. Furthermore, this density that gives rise to

species-fixing is the first and most important quality of the crystalline humor that he discusses

and whose utilitas he analyzes. As we have seen, this kind of thickening is distinct from that

which gives rise to refractive power, and it is also distinct from its lack of color, and therefore he

254

51 “Tertio, diaphanus diaphano aqueo humore densiore; ut lux in eius superficie ad perpendicularem refringatur, in qua perpendiculari, uti dictum est, lucem impensiùs uniri robararique contingit.” Fabricius, De visione, 97.52 “Dicebat enim idem Alhazen, quòd si Crystallinum esset diaphanus rarissimus, pertransirent rerum formae, & non pateretur ab eius passione ex genere doloris, ac proinde species non apprehenderet. Quare idem auctor dicit, non apparere lucem, & colorem in corpore diaphano, nisi in eo fit aliqua spissitudo.” Fabricius, De visione, 97.

gives a separate account of the utilitas of each of these qualities. Moreover, all the other

properties of the crystalline humor — its ability to refract, its clarity, its shape, size, and position

within the eye — are there to improve vision. They are, strictly speaking, not essential. That the

crystalline humor is rare enough to let light enter and pass through, but nevertheless thick enough

to be affected by light, is the essential property of the humor. Every other property of the eye is

there to aid or perfect the essential functioning of the eye that arises due to this property of

species-fixing.

This property of species-fixing that is described variously as delaying, retaining, and

declaring is foreign to our modern understanding of light and vision but was central to pre-

255

Table 1: Statements about species-fixing in the crystalline humor, or the precise density and transparency needed for vision to occur, according to Alhazen (from Risner’s Opticae Thesaurus), Witelo (also from Risner’s edition) and Pecham (from the Cologne edition). Alhazen is referenced according to book, chapter, and proposition (B C.P), followed by the page number. The numbers in brackets provide a cross-reference to Smith’s edition. Witelo is referenced according to book and proposition, with page numbers to Unguru’s edition in brackets. Pecham is referred to by book and proposition.

Alhazen (1572) Witelo (1572) Pecham (1592)

“& est aliquantulum diaphanus, ut recipiat formas lucis & coloris, & ut penetranseant per ipsum lux & color: & est aliquantulum spissus, ut remaneant in eo diu formae lucis & coloris, ita ut appareat virtuti sensibili forma lucis & coloris, quae figebantur in eo.”

I 6.33, 21 [I, 7.5]

“Et non apparet lux & color in corpore diaphano, nisi sit in eius diaphanitate aliquid spissitudinis: & propter hoc non est glacialis in fine diaphanitatis, neque in fine spissitudinis.”

II 1.6, 27 [II 2.18]

“est enim in glaciali aliqua diaphanitas, propter quam recipit formas, & aliqua spissitudo prohibens transitum formarum: in ob hoc figuntur formae in eius superficie & corpore.” III 7, 88 [p. 114,

302]

“Nihil enim potest esse coloratum aut luminosum, nisi densum. Nec visibile glacialem movere posset, si magis medio esset perlucidum. Item sine luce nihil videtur, ut patet ex XLVII, huius, si autem illud quod videtur, perspicuum esset, sicut aêr, lux in eo consistere & figi non posset: non ergo videretur. Omne itaque visibile, ut videatur, medio densius esse opportet.”

I 52.

modern Peripatetic-perspectivist theories. Unfortunately it has not been treated adequately. Mark

Smith consistently translates Alhacen’s spissus in this context as “opaque,” which is

unfortunate.53 As we have seen, for most pre-seventeenth century authors the term opacus is best

understood as meaning dark or shaded, and white bodies such as bone or eggshell would not be

called opacus because white is the nearest color to the diaphanous. White bodies admit light to a

greater degree than any other colored body, and black bodies are black precisely because they do

not admit species of light whatsoever. We must not assume that people believed that some

quantity of light or energy must be preserved when light reaches a black body; for many the

activity of light just isn’t able to penetrate the body and so ends there. Smith’s interpretation of

spissus here as “opaque” is no doubt meant to help the reader understand Alhacen’s scheme, but

instead the reader is misled. In his introduction Smith writes that “Opacity (densitas or soliditas)

is the gauge of an object’s ability to block light” and “once they have absorbed incoming light,

opaque bodies become luminous sources in their own right, radiating light in precisely the same

way as self-luminous bodies, although more weakly.”54 However, it is precisely the fact that the

crystalline humor is not opaque in the sense of dark, but rather bright and close to white, that

allows it to show light and color in a way that neither a purely transparent body nor a purely

opaque, i.e. black, body does. In a purely transparent body both light and color are allowed to

pass through, but neither show up, while in an opaque body light is not admitted whatsoever and

256

53 E.g.: see Alhacen and A. Mark Smith, “Alhacen’s Theory of Visual Perception: A Critical Edition, with English Translation and Commentary, of the First Three Books of Alhacen’s ‘De Aspectibus’, the Medieval Latin Version of Ibn Al-Haytham’s ‘Kitāb Al-Manāẓir’: Volume Two,” Transactions of the American Philosophical Society, 91 (2001): 388, 423; A. Mark Smith, ‘“Alhacen on Refraction: A Critical Edition, with English Translation and Commentary, of Book 7 of Alhacen’s ‘De Aspectibus,’ the Medieval Latin Version of Ibn Al-Haytham’s ‘Kitāb Al-Manāzir.’ Volume One. Introduction and Latin Text,” Transactions of the American Philosophical Society, New Series, 100 (2010): cxi, n. 54. See also his discussion at lxi-lxii.54 Alhacen and Smith, “Alhacen’s Theory of Visual Perception,” liv.

so color cannot possibly show up. While this might seem like a minor point, it reveals an

enormous gap between the ontology of the sensible qualities, certain epistemological issues such

as how representation and intentionality function, as well as what dissection reveals about the

crystalline humor for Zabarella and Fabricius. Smith notes in his introduction to “Alhacen’s

Theory of Visual Perception” that transparency is the absence of opacity, but he understands

opacity as preventing the direct passage of light, rather than not admitting light whatsoever. He

writes that “Although this terminological confusion about densitas, grossities, spissitudo,

soliditas, subtilitas, and raritas in the Latin text is not necessarily reflected in the Arabic text, it

nonetheless bespeaks an underlying conceptual confusion about the various connotations and

implications of density and rarity that is common to both texts.”55 Smith is correct that density

and rarity referenced several things that we now mark as distinct, but it is quite a leap to say that

Ibn al-Haytham and every subsequent medieval natural philosopher had a confused

understanding of these concepts, especially when Smith has failed to grasp their intended

meaning. Note that I only stress Mark Smith’s mistake here because he is one of the few scholars

that discusses these important issues at any length.

Conflating opacity with non-transparency fails to capture the scheme in which

transparency, white, and light are all of the same nature, while opacity, dark, and black are also

of the same nature. Zabarella is the most consistent in applying this framework (see § 2.5 as well

as Appendix 3). For Zabarella, the contraries dense-rare only partly overlap with the contraries

bright-opaque: the thickening of the heavens, of air, or of water does not make these things dark

or opaque, but rather visible. In fact, opaque bodies are technically invisible in that darkness and

257

55 Alhacen and Smith, “Alhacen on Refraction,” lxii.

blackness indicate a lack of color, the proper sensible

of vision; darkness and blackness are “seen” as a

privation of sight. The mixture of air, fire, or water

with naturally opaque/black earth performs two

functions: it thickens or condenses the composite body

causing it to lose its transparency, and it also darkens

it causing it to become colored. Although these two

actions are not entirely decomposable, the conceptual

latitude provided allows one to account for colored

transparent bodies such as stained glass or wine, and

for dense, non-transparent yet brightly colored bodies

such as bone. Smith’s slight mistranslation (which,

insofar as this is discussed at all, seems to be

commonplace) not only affects the reader’s ability to

understand fundamental concerns of pre-modern

actors, but also to grasp what they conceived of as one

of the basic differences that can occur in matter,

whether it be the heavens or the elements: that of

density and rarity. What the visible properties of the

basic constituents of the universe are, how these constituents interact during mixture, and how

the changes due to mixture are perceived were also at the heart of medical diagnosis, that is,

determining the temperament of the body and its parts. Finally, this mistranslation is a subtle but

258

Figure 4.7: The Perspectivist visual cone in many sixteenth-century editions of Pecham’s Perspectiva. Note the refraction of the rays, funneling the image into the hole in the optical nerve, typical of the perspectivist account of perception. The tunics and humors are represent from outward in: consolidativa, cornea, uvea (the dark semicircle), crystalline (with aqueous in between the cornea/uvea and the crystalline), and vitreous in the center. The points, from top to bottom, represent the centers of: (1) the cornea and crystalline, (2) the vitreous, and (3) the consolidativa. From Peckham, Johannes, Perspectivae communis (Cologne, 1592), 13v. The source of this image is found in the 1504 Venice edition, 6r.

radical importation of later notions onto the pre-modern period, and thus it obscures the ability to

discern some crucial changes to these notions in the seventeenth century.

Fabricius’s account of these processes is, however, not as conceptually neat as Zabarella’s,

and he does mention that condensation leads to a greater darkening of a body. Thus in his

discussion of the density of the cornea in the context of refraction, he writes that “light always

delights in the diaphanous, and seeks after it, in order to exist; it flees from the dark [opacum].”56

He explains:

light is the act of the diaphanous, and therefore the diaphanous is the matter of light, without which light can neither exist nor carry anything ... and insofar as the diaphanous is connected with corporeal being, and hence participates in darkness [opacitas], it will be affected by greater or less corpulence, that is to say retarded; which makes it so that light does not always progress directly, but is refracted.57

Opacity is caused by corpulence or the thickness of matter (as opposed to the rarity of, say, spirit

or the celestial body). As such, corpulence is contrary to light, and this gives the fundamental

cause for refraction. Note, however, Fabricius’s decomposition of thickening into its two distinct

forms, quoted at the beginning of this section: thickening that causes refraction and, ultimately,

opacity; and thickening that causes species-fixing, that is, whiteness and the “showing up” of

light and color. I have discussed the latter kind at length. I now move on to the thickening that

results in refraction.

§ 4.5: Utilitas of the Cornea: Fabricius’ Treatment of Refraction

259

56 “Etenim lux gaudet semper diaphano, ipsumetque appetit, ut consistat: contra opacum refugit.” De visione, 69.57 “lux enim actus diaphanous est, diaphanum igitur lucis est materia, sine qua lix neque consistere neque vehi ullo pacto potest propterea quatenus diaphanum lux assequitur, per ipsum statim pervadit: at quatenus diaphanum esse corpus contigit, ac proinde opacitatis particeps, à corpulentia magis minusve afficitur, ne dicam retardatur: quo fit ut non semper recta progredi lix possit, sed frangatur:” Fabricius, De visione, 69.

Chapter 2, on the utilitas of the cornea, is the longest chapter in this section devoted to a single

part, and this is largely because it provides Fabricius with his first opportunity discuss refraction.

For this reason I will give a more in-depth synopsis of this chapter than the later ones. Fabricius

lists the following properties that must be accounted for concerning the cornea: that it is tough,

dense, thin/subtle, polished, and transparent ("dura, densa, tenuis, perpolita, & diaphana").58 It is

with this discussion of the cornea, then, that we can sort out how Fabricius uses these various

terms and how the properties relate to one another.

He starts with durability or toughness, whose purpose is to protect the interior parts of the

eye (chiefly the crystalline humor) from air, smoke, dust, cold, agitation, contusion, and fire.

However, the crystalline is tough without being fragile like glass, which would be disastrous for

the eye as a whole. The cornea is also dense, which protects itself from being eroded by the same

forces listed above, and its density also prevents the subtle aqueous humor from escaping. While

the cornea is tough and dense, Fabricius also says that it is tenuis or subtle rather than crassa or

thick, as the latter would hinder the passage of light. The cornea is polished (perpolita) to allow

species and similitudes into the eye accurately. That is, the cornea is polished rather than rough

or uneven (aspera), so that the minute extrusions and cavities in the surface wouldn't deform

light and images on their way to the crystalline humor. Furthermore, if the cornea were rough we

would constantly feel as though there were debris between the cornea and the eyelid, causing

both discomfort and erosion over time. This same reasoning is also why the cornea is stretched

taught (tensa) as opposed to wrinkled (corrugata). All this is a part of his meticulous accounting

for the final cause of every observable property of every part of the eye.

260

58 Fabricius, De visione, 67.

The major section on the cornea explains the usefulness of the diaphaneity of the cornea:

compared to only a single page for all the previous qualities, Fabricius devotes over four folio

pages to this alone, and he devotes five more to the shape and position of the cornea in

combination with its refractive power. Accounting for the utilitas of the diaphaneity of the cornea

gives Fabricius his first chance to discuss diaphaneity in general, treating both mathematical

considerations (refraction, most importantly) and considerations from natural philosophy, all of

course in a teleological framework that gives the for-the-sake-of, i.e. the final cause, of the parts

being as they are. His sections on the diaphaneity of the aqueous, crystalline, and vitreous

humors are considerably shorter because they rely on his discussion here.

Principally, the cornea is diaphanous so that light can be admitted, and so that the eye is

pervious to the visible forms of things. Light is refracted because the cornea is of a different

diaphaneity than the air, and its transparency is formed by nature according to a specific purpose.

Here he mentions Galen's mathematical discussion in Usefulness, which (as Fabricius relates)

Galen was compelled to include because of a dream. Fabricius repeats his assertion that he will

relate the mathematical details of vision at greater length and, perhaps, in a more beautiful

fashion than Galen.59 In doing so he relies heavily on Alhazen, Pecham, and Witelo. Although he

refers to Alhazen first, nearly twice as many marginal citations are made to Pecham. As we will

see he (or perhaps the publisher) copies a number of diagrams from certain sixteenth century

printed editions of his Perspictivae communis, and he also quotes Pecham at length. Witelo, on

the other hand, is only cited once in this section.

261

59 “Sed fortassè hoc loco magis nobis utendum erit illa excusatione Galeni, qua ipsa x. de usu partium cap. xii. usus est, ubi dicit se somnio perpulsum ut admirabilia in oculo non reticeret, & mathematica non omitteret. Nos etenim omninò difficilia proponere aggredimur, & longè plura ac fortè etiam pulchriora quàm Galenus proposuerit.” Fabricius, De visione, 68.

Fabricius’s primary goal here is to reveal nature’s purpose in making the cornea different

from the air in diaphaneity. The optici, he says, teach three ways that light can progress: directly,

by reflection, or by refraction. Reflection is caused by polished surfaces, but refraction occurs

when light advances across bodies that differ in diaphaneity. Fabricius writes “in the eye [light]

advances by no way other than refraction.”60 This reinforces the point made earlier that we

shouldn’t interpret the shining of the crystalline as an instance of light scattering. Here he cites

book 7 proposition 37 in Riser’s edition of Alhazen, where we likewise read “we say that it is

universal, that everything that is comprehended by sight is comprehended through refraction,

whether sight and the seen are in the same diaphanous [body] or in different ones, or whether the

seen [body] is in opposition to sight, or is comprehended by reflection.”61 Immediately after this

Alhazen makes his famous distinction between rays that enter the cornea obliquely and those that

enter orthogonally. Direct rays, being stronger, are the rays that are primarily perceived, and in

this way a one-to-one correspondence between every in our visual field and a point in the

crystalline humor is established. Oblique rays are involved in peripheral vision only, not direct

vision. I call this requirement that only rays that enter the eye perpendicularly the orthogonality

hypothesis. (By refraction, then, Alhazen apparently means the refraction that occurs in the

crystalline-vitreous boundary, as well as the twisting refraction that occours in the optic nerve.

262

60 Fabricius, De visione, 69.61 “dicamus universaliter, quòd omnia, wuae comprehenduntur à visu, comprehenduntur refractè, sive visus & visum fuerint in eodem diaphano, sive in diversis, sive visum sit in oppositione visus, sive comprehendatur ab ipso reflexè.” Alhazen, and Witelo, Opticae Thesaurus, ed. by Friedrich Risner (Basel, 1572), 269. Note that Risner made sure the terms reflexus and refractus were used consistently in his edition, and his use corresponds to our modern terms reflection and refraction (indeed, Risner was instrumental in standardizing these terms). Earlier manuscripts often used the terms with the meaning inverted, but this use was not entirely consistent and thus context played a large role in determining meaning. Mark Smith’s critical edition of the Latin manuscripts reads “sive comprehendatur ab ipso reflexive” in the final clause, which he translates as “refraction.” Alhacen and Smith, “Alhacen on Refraction,” Vol. 1, 106; “Alhacen on Refraction,” Vol. 2, 301. I find Risner’s interpretation as meaning reflection in the modern sense more convincing.

See boo II, sections 6–862.) For the

orthogonality hypothesis to work,

however, Alhazen and the perspectivists

that follow him (such as Witelo, Pecham,

and Roger Bacon) had to construct an

idealized, mathematical eye in which rays

orthogonal to the outer cornea are also

orthogonal to the crystalline. Only in this

way could the visual pyramid of Ptolemy

and the ancient extramissionists be

retained. Through this pyramid a one-to-

one correspondence between the eye and

the visual field is established, without

which there would be no accounting for a

coherent image in the eye.63 This scheme

is neatly captured in the some sixteenth-

century editions of Pecham’s Perspectivae

communis. (See figure 4.7.) At this point Fabricius does not talk about the visual pyramid, and

his discussion of refraction here merely leads him to the conclusion that the refraction of light in

263

62 Ibn Al-Haytham and A. I. Sabra, Optics of Ibn Al-Haytham, 2 vols. (Warburg Institute, University of London, 1989), 115–116; Alhacen, “Alhacen’s Theory of Visual Perception,” 81–83; Alhazen, Opticae thesaurus, 27–29.63 Lindberg, Theories of Vision.

Figure 4.8: The two types of refraction. Peckham, Johannes, Perspectivae Communis Libris Tres (Cologne: Apud Haerades Arnoldi Birckmanni, 1592), 7r-7v.

Figure 4.9: The two types of refraction in De visione, 71.

the eye brings rays together and thus strengthens sight.64 He gives two diagrams, copied it seems

(although somewhat improved) from Pecham’s Perspectivae communis. From the editions that I

have seen, Fabricius’s diagrams here and elsewhere most closely resemble those of the 1580

Cologne edition (republished in 1592).65 (See figures 4.8 and 4.9.)

§ 4.6: Fabricius’s Appropriation of Pecham

Fabricius does bring up the visual pyramid a little later when giving the final cause for why the

cornea is round and protrudes from rest of the sphere of the eye. He pays lip service to Galen’s

explanation in Usefunness that it is safer and more convenient if the cornea lacks sharp edges or

protruding angles, but again Galen’s explanations here don’t seem to satisfy Fabricius. Rather,

Fabricius gives three primary reasons dealing with vision itself. The cornea is round and

protruding because (1) it allows the eye to see more than it would otherwise, (2) because it

causes light to unite and become strengthened, and (3) because it allows more visible species to

enter through the pupil. To emphasize this last point he draws upon Pecham’s Perspectivae and

copies diagrams from the Cologne editions, most likely. In figure 4.10 we have a comparison

between a sixteenth-century edition of Pecham’s Perspectivae with Fabricius’s images. These T-

diagrams are rather idiosyncratic, and for the 1542 Nuremberg edition of Pecham’s Perspectivae

264

64 Fabricius, De visione, 71.65 John Peckham, Perspectivae Communis Libris Tres (Cologne: Apud Haerades Arnoldi Birckmanni, 1580, 1592). These images follow, though with some alterations, those found in an earlier 1504 Venice edition, but small differences suggest that the images in De visione follow the Cologne editions. There is at least two other editions with distinct diagrams. One was “carefully and diligently emended, and purged of endless blemishes which sprung forth, and also with a restoration of demonstrations which were deficient, by George Hartman.” John Peckham, Perspectivae communis, ed. by George Hartman (Nurenburg: apud Iohan. Petreium, 1542). Another was published also in 1504, though with images quite different than the Venice edition. John Peckham, Perspectiua Joannis pisani anglici viri religiosi vulgo cmmmunis appellata rationes visus in radiationibus ac lineis visualib[us]. atq[ue] speculares formas imagines. In florentissimo gymnasio Liptzensi emendatum atq[ue] in figuris rectificata (Venice, 1504). Neither edition appears to have influenced De visione.

illustrates this with a simple rectangle. Pecham’s proposition 29, which this diagram corresponds

to, says “The eye would not be suited to seize a quantity (of rays) if it were not round.”66 The

square in the center of the left-most diagram in figure 4.10 represents what would happen if the

cornea were flat: vision would only be able to grasp the rays that are both within and parallel to

CA and DB. Essentially, there would be no peripheral vision, and the central field of vision

would be limited to a region the size of the surface of the eye. A round eye, represented by the

surrounding circle, gives a much wider field of vision. Fabricius provides a copy of the original

image in the Cologne edition, but also decomposes the argument into two further diagrams: the

right-most image in 4.10 shows precisely the narrow field of vision that would result from a flat

cornea, while figure 4.11 shows the effect of a round cornea. In the accompanying text Fabricius

writes:

Since distinct vision is made solely by direct rays — that is, [rays] arriving perpendicular to the surface of the eye — if the surface of the eye were flat, clearly no perpendicular [rays] would come to the eye unless they were themselves level with the surface.67

Fabricius here embraces the orthogonality hypothesis introduced by Ibn al-Haytham, but in a

somewhat weaker sense than the perspectivists. Ibn al-Haytham admitted that, in addition to

direct vision which occurs by rays that enter both the cornea and the crystalline humor

orthogonally, we also see via indirect or peripheral vision. In indirect sight our visual faculty

does, in fact, sense the rays that enter the eye obliquely, but these rays are weaker and this is why

265

66 Peckham, Perspectivae communis libris tres (Cologne: In officina Berkmannica, sumptibus Arnoldi Mylii, 1592), 11r.67 “Quoniam enim visio distincta, solùm fit per lineas radiosas rectè, hoc est perpendiculariter ad superficiem oculi pervenientes; si oculi superficies esset plana, clarum est nullas perpendiculares ad eum venturas, nisi à superficie sibi aequali.” Fabricius, De visione, 73-4.

our vision is weaker outside the central region of our visual field.68 Yet Ibn al-Haytham’s

pointwise analysis, as well as that of Witelo and Pecham, is only used to explain part of vision,

and thus we should not imagine that pre-Keplerian optics involved a little picture or image of the

outside world actually appearing in the crystalline humor.69 Lindberg’s statement that, in the

scheme developed by Ibn al-Haytham and appropriated by the Latin perspectivists,

“perpendicular rays alone must be responsible for sight” is, if not misleading, at best an

266

68 Mark Smith makes this point in Alhacen and Smith, Alhacen’s on Refraction, vol. 1, xxxv-xxxviii, lxvii-lxx.69 See especially Mark Smith’s discussion about the Hockney-Falco thesis, in which he argues against the notion that Perspectivist optics, in the tradition of Ptolemy and Ibn al-Haytham, was suited to analyze real, projected images. “Not only were real images beyond the conceptual pale of Perspectivist optics, but the structure of Perspectivist ray-analysis, centered as it was on viewpoints rather than focal points, was ill-suited to explain the phenomenon [of image projection] in any meaningful way.” A. Mark Smith, “Reflections on the Hockney-Falco Thesis: Optical Theory and Artistic Practice in the Fifteenth and Sixteenth Centuries,” Early Science and Medicine, 10 (2005): 177.

Figure 4.10: Images accompanying explanations for why the cornea is round. The left image is from the 1592 Cologne edition of Pecham’s Perspectivae, 11v; center and right images are from De visione, 74. Rays from the visible body CD enter the cornea, represented by the curved line AB. Note Fabricius’s diagram on the right, which makes explicit the notion that, if the cornea were flat, then only rays that are directly in front of the cornea would enter the eye perpendicularly; thus direct vision would only apprehend a section of a body equal to the size of our cornea. Compare to figure 4.11.

overstatement.70 This is because the

orthogonality hypothesis accounts

only for a portion of vision at the

center of our visual field. It is

difficult to say what proportion of our

visual field is comprehended by the

orthogonal cone of rays, but it

appears to have been quite small. As

we will see, for Fabricius distinct

vision comprehends quite a small

angle indeed.

The difference between the orthogonality hypothesis as used by the perspectivists and

Fabricius is that the Paduan does not require the rays that contribute to direct vision to be

orthogonal upon entering the crystalline humor — they only need to be orthogonal upon entering

the cornea. In discussing how the shape of the cornea allows for a greater field of vision

Fabricius repeats his citation of Alhazen’s passage in book 7, proposition 37, this time quoting

the proposition “Distinct vision is made by straight lines from the visible [body] perpendicular to

sight.”71 He also cites and quotes book 2 proposition 8, which is on peripheral vision achieved

via oblique rays. This text reads, “Vision through the [central] axis of the optic pyramid is most

267

70 Lindberg, Theories of Vision, 74. On p. 76 Lindberg says that the account given in book 7, in which Ibn al-Haytham says that oblique rays do indeed contribute to vision, is “a theory wholly at variance with that of book 1 and that he allows the inconsistency to stand suggests that he was not able to resolve the problem to his own satisfaction.” It is far more reasonable to assume that for Ibn al-Haytham the orthogonality hypothesis only accounted for direct vision, and that 71 “Visio distincta fit rectis lineis à visibili ad visum perpendicularibus. Et visio omnis sit refractè.” Book 7, prop 37. p. 268. Fabricius’s quotation is at Fabricius, De visione, 76.

Figure 4.11: Fabricius’s depiction of the increase in the field of vision due to the rotundity of the cornea. (Compare to the rightmost image in figure 4.10.) Fabricius, De visione, 75.

certain; but through other lines it is that much more certain the closer it is to that same [central]

axis.”72 It is crucial to note that he cites Risner’s edition, which has additional text at the head of

what Risner has grouped into “propositions.” Thus both of the quoted propositions above are not

found in the original Arabic or Latin manuscripts. The substantial text labeled “propositions” that

head the many sections of Risner’s edition are Risner’s own interpolations; the 1572 Alhazen is

not the same as the Alhacen of the medieval manuscripts (who, in turn, is not the same as the

Arabic Ibn al-Haytham; see § 0.3). Lindberg expresses puzzlement about how to rectify the issue

268

72 “Visio per axem pyramidis opticae certissima est: per aliam verò lineam tantò certior, quantò eidem axi propinquior fuerit.” Book 2, prop. 8. p. 29. Fabricius’s quotation is at Fabricius, De visione, 76. C.f. Alhacen and Smith, “Alhacen on Refraction,” p. 106; Alhacen and Smith, “Alhacen’s Theory of Visual Perception,” 93. It is quite likely that the interpolated propositions by Risner here were influenced by Pecham’s Perspectivae. See below.

Figure 4.12: Depictions of the visual pyramid in Fabricius’s De visione as interpreted through Risner’s edition of Alhazen and Pecham’s Perspectivae. The left image shows the visual pyramid. The center shows the cornea DD and the pupil F (the central circle). Rays C are perpendicular to the cornea and enter the enter pupil rectilinearly, whereas rays G on either side (carrying the species from points A and B) do not enter the pupil unless they are refracted at the surface of the cornea. The image on the right shows the rays failing to pass through the pupil in the hypothetical situation where refraction does not occur. Fabricius, De visione, 76-7.

of direct versus oblique rays, but Lindberg relies upon Risner’s edition and points out the quoted

passage above — i.e., Risener’s interpolation — that asserts that rays closer to the central axis are

more “certain” than others. The issue that Lindberg points to is thus confined to Alhazen, and is

not necessarily present (or as pronounced) in Ibn al-Haytham or Alhacen.73 It also underscores

the fact that Lindberg and others have failed to recognize that many readers of the Perspectivists,

Fabricius included, cared little about the problem of securing a one-to-one correspondence

between every point on the visible object and some part of the eye.

Just after his citations to Alhazen, Fabricius emphasizes the importance of non-orthogonal

rays by citing and quoting Pecham, book 3 proposition 15: “By means of refraction many [rays]

beyond the visual pyramid affect sight.”74 The visual pyramid, which gives rise to direct, distinct

vision, therefore only contains those rays that are both perpendicular to the cornea and are able to

enter the pupil; many other rays affect sight, but these “are seen weakly and imperfectly.”75 (see

figures 4.12 and 4.13.) Therefore, without refraction occurring at the cornea our visual pyramid

would be extremely narrow. It is possible, as Lindberg and most modern commentators do (as

well as Witelo to some extent) to make sense of Ibn al-Haytham/Alhacen/Alhazen’s theory of

vision by stressing punctiform analysis, in which one describes a point-wise, one-to-one map

between the visual field and some part of the eye. However, given the texts that Fabricius’s takes

as authoritative on these matters, his interpretation — which minimizes the role of the

orthogonality hypothesis and punctiform analysis — seems accurate and rather straightforward. It

also might very well have been the norm for the period. Distinct vision, on this account, covers a

269

73 Lindberg, Theories of Vision, 75–6.74 “Per fractionem multa extra pyramidem radiosam videri.” Pecham, Perspectivae 1592, 45. Fabricius, De visione, 77.75 Ibid., 77.

very small area in the visual field, and occurs only through rays that do not refract at the cornea;

indistinct or weak vision occurs through refracted rays, and it covers a much greater area.

Fabricius did not worry about the issue of punctiform analysis, and some important questions

about the the history of medieval perspectivism still remain. First, to what degree did all of the

Perspectivists themselves, particularly Pecham, make punctiform analysis the lynchpin of their

theory of vision? According to many modern historians this difficulty in accounting for both

distinct vision (via orthogonal rays) and indirect vision (via oblique rays) somehow shows that

the perspectivists were inconsistent or confused; if the orthogonality hypothesis plays a less

important role in their theory of vision, the conflict between distinct vision made by orthogonal

rays alone and indistinct vision made by all rays is less of an issue. Second, to what extent did

people at various points in time, especially non-mathematicians, emphasize the orthogonality

hypothesis in their reading of perspectivist works? Kepler, certainly, cared deeply about the

problem of punctiform analysis and the corresponding problem with rectifying distinct and

indistinct vision in the Perspectivists, but he may well have been an anomaly in this respect.

Lindberg and others likewise emphasize the orthogonality hypothesis and seem to consider it to

be the essential feature of perspectivist optics. Yet it is entirely possible that Lindberg and others

have read both the Perspectivists as well as pre-seventeenth century readers of mathematical

optics with post-Keplerian lenses. Further studies of how perspectivist optics were read and

interpreted prior to the seventeenth century are needed to resolve these issues.

Fabricius’s scheme incorporating distinct and indistinct portions of the visual field is

summarized and highlighted in an image that combines the results of the movement of the eyes

and head on the field of vision. In figure 4.13, which depicts the field of vision seen from above,

270

we see how small the area labeled “distinct vision without the motion of the eye” is. As I have

just shown, according to Fabricius distinct vision is the only part of vision to which the

orthogonal hypothesis applies. This is also true for Pecham and, to some extent, Risner’s

Alhazen. The lines labeled “indistinct vision without the motion of the eye” form the limits of

the visual pyramid, but these rays enter the pupil according to the image in 4.12. Most historical

271

Figure 4.13: The visual field from above according to Fabricius. De visione, 118.

analyses of Perspectivist optics have failed to recognize that, in the sixteenth century at least (and

likely before) the application of the orthogonal hypothesis to only a very small fraction of the

visual pyramid appears to have been the norm.76

For Fabricius, the rays that enter the cornea orthogonally was quite a narrow cone; whether

it was significantly more narrow than the Perspectivists is difficult to say, as none of the works

272

76 C.f. Lindberg, Theories of Vision, especially chapters 5 and 9; A. C. Crombie, “Expectation, Modelling, and Assent in the History of Optics: Part I. Alhazen and the Medieval Tradition,” Studies in the History and Philosophy of Science, 21 (1990): 612-614

Figure 4.14: Fabricius’s abstract diagrams of the cross-section of human and sheep eyes along the visual axis. These diagrams are explicitly intended help investigators of mathematical optics uncover the refractions occurring within the eye more precisely. Note his determination of (1) the center of the eye, (2) the aranea (and thus the anterior surface of the crystalline humor), and (3) the cornea in both human and sheep eyes, and especially that the centers occur in different places in the two animals. Fabricius almost certainly is referencing (and silently criticizing) the diagrams found in Pecham’s Perspectivae communis, e.g., the centers of curvature given by the three points in figure 5.7 above. Fabricius, De visione, 105.

allow for a precise mathematical determination of the angle of the central pyramid involved in

distinct vision. Certainly, Fabricius’s sensitivity to the actual size of the pupil in an eye is a

reason why the central cone of distinct vision was so narrow, and the Perspectivists reliance on a

theoretical, mathematical eye might have constrained the angle of direct vision in the way that

the real eye did for Fabricius. Regardless, Fabricius does deviate from the Perspectivists quite

clearly by discarding the orthogonality hypothesis when it comes to the crystalline humor. This

fact can be seen in his cross-sectional diagrams of the eye (see figure 4.14). In terms of the size,

shape, and placement of the humors and tunics, these diagrams give a far more accurate cross-

sectional diagram of the eye than any of his predecessors.77 Fabricius almost certainly intended

them to supersede Vesalius’s diagrams and those derived from them, but he also explicitly

wished for writers of mathematical optics to use these diagrams in their analyses of refraction

occurring in the eye. Fabricius proudly writes:

But so that those who produce works of optical science can accurately observe the diverse progression of rays, which are called visual, while they cross over from one humor into another; and [so that] they can accurately measure off the angles of refraction, and thence grasp the innumerable utilitates of the parts: we provide, with the most exact care, human and sheep eyes divided through the middle. And the whole magnitude and that of the individual parts, including their situations and figures, are described, and the place that each of their centers occupy is revealed, and everything is outlined in tables below.78

273

77 See, for example, the opinion of optometrist turned historian Hirschberg, J., The History of Ophthalmology (Bonn: J. P. Wayenborgh, 1982), Vol 2.78 “Ut autem qui Opticae scientiae operam dant, accuratè obervare possint, progressum varium radiorum, quos visuales appellant, dum ab uno in alium humorem transeunt; atque angulos refractionis dimetiri, & inde innumeras utilitates partium excepere: curavimus exactissima diligentia, oculum humanum & ovilem per medium secari, & magnitudinem totius, ac singularum partium, nec non earundem situs, & figuras describi, & loca qua eorum centra obtinent inveniri, & omnia in subiecta tabella delineari.” Fabricius, De visione, 105.

Immediately below the diagrams, he writes, as a sort of punctuation and challenge, “Diligent

investigators of the works of nature will have much to contemplate, where they are able.”79 Here

Fabricius is implicitly criticizing the diagrams of the eye that he would have found in Pecham’s

Perspectivae, the diagrams in Riser’s edition of Alhazen, and the diagrammatic cross-sections

found in Vesalius’s Fabrica and the numerous images derived from it. Fabricius’s determination

of the centers of curvature for the eye as a whole, for the aranea and thus also the anterior

surface of the crystalline, and for the cornea, is particularly important. It reveals a reference to

(and a criticism of) the diagrams found in Pecham’s Perspectivae, and the editions Fabricius was

intimately familiar with give a set of points sharply at odds with Fabricius’s. In figure 4.7 above

we can see three dots. Going form top to bottom, the first dot is the center of the cornea and

sclera (note that, in Ibn al-Haytham and Pecham, the cornea does not bulge). The second dot is

the center of the vitreous, whose eccentricity is partly responsible for the refraction of visual rays

depicted. The third is the center of the consolidativa (the outer, white, part of the eye).

Fabricius’s diagrams, a fusion of careful anatomical observation and sensitivity to mathematical

abstraction and analysis, are radically different from the diagrams in works of mathematical

optics prior to him. Most importantly for visual theory, the cornea and the anterior surface of the

crystalline are not concentric (most easily visible in the human eye). Fabricius therefore discards

one central aspect of Perspectivist optics: that the primary visual rays leading to distinct vision

must enter both the cornea and the crystalline humor perpendicularly. But also note that

Fabricius’s attention to many types of animal — his drive to understand the fabric the universal

animal and its parts — leads him to put the centers of the various tunics and humors in different

274

79 “Habebunt enim curiosi indagatores operum naturae, ubi multa contemplari possint.” Fabricius, De visione, 105.

places for different animals. The entire Perspectivist scheme that relies upon concentric spheres

is untenable. It is, after Fabricius, contrary to anatomical experience, and any scheme involving

some precise geometrical concentricity of spheres would fail to account for all animals. This,

most of all, is why “investigators of the works of nature will have much to contemplate.”

Unfortunately, for many reasons this important moment in the dismantling of medieval optics has

been entirely overlooked by historians.

§ 4.7: Fabricus on the Utilitas of the Crystalline and Vitreous Humors

The same account of the purpose of the vitreous humor given by Zabarella (see § 4.3) was also

advanced by Fabricius. He discusses the vitreous humor at length in part III, Chapter 10 on the

utilitas of the vitreous. He rejects the accounts of Alhazen and Witelo, in which vision is

perfected only once the image enters an aperture in the optical nerve, as “obscure” (obscurum);

he is thus implying that here are both conceptual as well as anatomical problems with the

account,80 and elsewhere he denies the optical foramen. He rejects Galen's belief that the vitreous

humor merely nourishes the crystalline, and this is because the vitreous is, he says, the most

pellucid of all the parts.81 On the contrary, Fabricius says that one office of the retina is to

prohibit contact between the choroid tunic (or uvea) and the vitreous humor, and this is to

prevent the choroid from spoiling the “purissima vitrei substantia” with its darkness.82 He is,

then, modifying Galen’s own argument in order to use it against him — it is not the vitreous that

must prevent blood from spoiling the pure substance of the crystalline, but instead the retina that

275

80 Fabricius, De visione, 107.81 Ibid., 105.82 Ibid., 106.

prevents the uvea from spoiling the pure substance of the vitreous. Fabricius’s opinion on the use

of the vitreous humor is nearly identical to Zabarella’s, and he argues this using a thought

experiment. He writes, "my opinion can be easily followed, if first it is imagined that the vitreous

humor, or something diaphanous, were not next to [the crystalline humor]."83 If this were the

case, something colored would be in contact with the crystalline. It would be like shining a light

against a colored wall, and the light would return to the crystalline humor tinged with the color

of the tunic. Nature, therefore, had to place some distance between the posterior surfaces of the

eye and the crystalline humor so that light passing through the crystalline would "disperse and

disappear, and be prevented from reflecting back."84 This is why the vitreous humor is so large,

and the crystalline humor so far away from the retina. Additionally, the reason why the posterior

of the crystalline humor protrudes is, just as with Zabarella, so that light can be united in the

vitreous directly behind the crystalline humor, thereby debilitating the light.85 Fabricius writes:

What, therefore, will be the proposed usefulness of the roundness [of the posterior of the crystalline humor]? It is surely, in my opinion, so that the light carried past the crystalline should be united into itself and not progress very far from the crystalline, but cease in the vitreous, and in a certain way perish.86

276

83 "Id autem mea sententia facile assequemur, si primo vitreum, aut eius diaphanum non adesse imaginemur. Quod si diaphanum post crystallinum non esset positum, necessario opacum collocari corpus oporteret (etenim necessario omnino haec enunciatio est, neque medium ullum inter haec duo intercedit) igitur retinam, & Choroidem, crystallinum attingere necessarium esset: indeque lux crystallinum transgressa, & has tunicas, quasi coloratum parietem pertingens, pertundensque ac tunicarum coloribus, ob contactum affecta, foedataque denique retro ad crystalloidem reflexa crystallinum potius tunicarum nativis coloribus afficeret, quam extrinsecus assumptis, sine ulla sensus videndi utilitate." Ibid., 10784 "Neque hoc loco illud est astruendum in crystallino, lucem dispergi, & evanescere, & ita reflexum prohiberi, quoniam lux per longissimam spatium sibi tamen proportionatum omnia diaphana permeat." Ibid., 10785 "Crystallini postica extuberantia, quae lucis unionem in vitreo prope Crystallinum finiri cogit." Ibid., 11086 “Quae igitur erit propositae rotundus utilitas? Ea certe, mea sententia, ut lux crystallino transvecta, tum in seipsa uniatur, tum longius à crystallino non progediatur, sed in vitreo cesset, ac quodammodo commoriatur." Ibid., 102-103.

Thus we see that in De visione the notion that the rays of light do not merely come together and

then disperse, but are in fact debilitated and disappear, is perhaps even stronger than in Zabarella.

Both also think of this process as an instance of a burning lens. Zabarella, we have seen, makes

the argument that the collision of rays of lumen produces heat in air but not water because the

former is hot by nature, the latter cold. Likewise, as we have seen for Fabricius one of the crucial

reasons why the eye is made of water rather than air is precisely to prevent the kindling of flame

in the eye.87

§ 4.8: Conclusion

Zabarella and Fabricius stayed in Padua almost their entire lives, and they certainly interacted in

some capacity. Given that Zabarella is not known to have travelled beyond Venice, and even

there only rarely, it is certain that he observed his dissections in Padua, and because Fabricius

was the public lecturer in anatomy from 1566 onwards it is likely that Zabarella attended one or

several of Fabricius’s public demonstrations. As Cynthia Klestinec points out, in these public

dissections Fabricius focused on natural philosophy rather than the art of dissection.88

Furthermore Fabricius’s interest in visual theory, and certainly his heavy citation of the

perspectivae, was rare for an anatomist of his time. The common points in their theory of vision

that I have been unable to find in any previous author are as follows: (1) that the vitreous is four

or perhaps five times the size of the crystalline (which is in fact incorrect); (2) that the rays of

light need to refract into a cone just behind the crystalline humor, which is why nature has made

277

87 “Aqueus deinde est non aereus; ut intus facilè contineri vicissimque continere visilium formas possit, neque lux vehemens intus in oculo ignem accendere valeat.” Ibid., 6088 Cynthia Klestinec, Theaters of Anatomy: Students, Teachers, and Traditions of Dissection in Renaissance Venice (Johns Hopkins University Press, 2011).

the rear round and protruding; (3) that the vitreous is more transparent and thus less optically

dense than the crystalline in order to cause this cone; (4) that, contra Galen, the vitreous is clear

because otherwise the color of the vitreous would reflect back and interfere with the crystalline

humor; (5) that the uniting of rays into a cone debilitates and exhausts light; (6) that there is such

a great quantity of vitreous humor in order to provide large chamber for this cone to occur, and

so that the colored retina and uvea are far from the crystalline; (7) that there a sort of burning

glass in the eye, and (8) thus the primary reason that the complexion of the vitreous watery is to

prevent a kindling of flame in the eye. Furthermore, both have the visual faculty make an active

judgment at the aranea that is carried back through the retina and optical nerve, rather than

having the visual spirits be passively impressed with an image.

It is possible that one developed a theory of vision independently and the other copied it

without attribution. On the other hand they may have developed the theory together (even if not

consciously), perhaps with the involvement of others present in Padua during discussion and

public disputation. Disputatio, it should be emphasized, was an expected part of public

anatomical demonstrations.89 Their theory of vision could have been formed between them

privately as well. Finally, it is possible that there is some earlier source that both Zabarella and

Fabricius are drawing upon and which neither acknowledged. Absent further evidence it is by far

most likely that the theory arose out of their interaction: Zabarella clearly attended many

different anatomical demonstrations, and these were most likely performed by Fabricius. Indeed,

as a fellow professor Zabarella would have been granted front row access to the annual

dissections. Any common source for their theory would need to have been a contemporary who

278

89 Klestenec, Theaters of Anatomy, 46–47, 69.

did not discuss their theory in print, and whose anatomical knowledge was as up-to-date as

theirs. Zabarella, as we have seen, says that many physicians followed Galen's extramission

theory, and so the pool of potential sources excludes many physicians and anatomists. In all

likelihood this was a Paduan theory, developed within a culture of anatomical demonstration and

public disputation (on to of any informal exchange of ideas), and perhaps held by other

professors as well. Nevertheless, Zabarella and Fabricius have the best claim to it. Although

Zabarella revealed it in print ten years before Fabricius, what Fabricius was teaching around

1590 is in all probability revealed through Jessenius’s account of the eye in his Anatomiae

Pragensis (see § 5.1 below), which does not deviate from the main features of Zabarella’s and

Fabricius’s theory of vision. Absent further evidence it seems most appropriate to consider it a

shared theory. Indeed, they both had a hand in disseminating it throughout Europe via their texts

as well as their students, although Fabricius seems to have been more influential in this regard.

To borrow an image from Francis Bacon, the activity of Zabarella and Fabricius neither

resembles the behavior of ants, piling up natural histories and experiments without purpose, nor

that of spiders, spinning webs from themselves alone. Whether they might reflect Bacon’s ideal,

the bee — gathering material from nature and digesting it into a philosophical honey — perhaps

depends on whether one considers their ruminations to be proper digestion.

A great deal has been written on Zabarella's regressus method in connection to Galileo

and the development of the so-called modern scientific method, and I don't wish to delve too far

into the issue here. (See § 2.2.) Rather than focusing on the abstract notion of scientific method

or the slippery distinction between experience and experiment, I have presented some specific

ways that Zabarella applied his experiences with anatomy, and in the next chapter I will show

279

that the theory of vision he endorsed, and likely helped to create, had some influence. Putting

aside Zabarella's opinion on the proper method of demonstration and the influence of his

regressus method, we can see that he was clearly connected to important empirical work on the

animal body being carried out in Padua. He relied on this new knowledge to argue for specific

philosophical positions on light, color, and sensation in De visu book 1 (see § 2.8), to argue

against theories of vision that were in competition with Aristotelian ones in De visu book 2, and

to formulate a new theory compatible with both Aristotle and his experiences with dissection (§

4.3).

As a member of the arts faculty at Europe's most prestigious medical school, Zabarella

argued that Aristotelian natural philosophy and logic are the true foundations for medicine. As an

anatomist and physician, Fabricius's methods of investigation and argumentation were of a

different sort: his Aristotle was not so much that of the Posterior Analytics, but of the History of

Animals, the De anima, and the Parts of Animals understood alongside Galen's Anatomical

Procedures, On the Natural Faculties, and On the Usefulness of the Parts. These three pairs of

texts were packaged, respectively, into the framework of historia, actio, and utilitas.90 Fabricius's

Aristotle was in substantial harmony with Galen, whereas Zabarella's Aristotle was irreconcilable

with Galen on nearly every issue: on questions of logic and demonstration,91 on a theory of

vision and everything that goes into it, and on foundational anatomical and “physiological”

issues. Yet behind this disciplinary divide Zabarella and Fabricius presented the same theory of

vision. They gave identical accounts of the structure of the eye. Their theory of light differed:

280

90 See the introduction to Fabricius, De voce.91 Not addressed here, but see William F. Edwards, “The Logic of Iacopo Zabarella” (PhD Dissertation, Columbia University, 1960).

light and color progressed in tandem according to Zabarella, whereas light alone, but tinged with

color, progressed according to Fabricius. But their analysis of the path of rays in the eye was

identical. They gave the same account of the action of the eye — that is, where vision takes place

and by what means, including the notion that the visual faculty makes an active judgment at the

aranea. Finally, they centered their theory of vision around the same things and for the same

reasons: a novel account of the usefulness of the vitreous humor, an identical (qualitative)

analyses of the path of light in the eye, and the presence of a burning glass in the eye. Their

treatises on vision are not easily accommodated within recent historiography on the role of

experience and experiment and the rise of the experimental method in the sixteenth and

seventeenth centuries, a historiography which has tended to privilege the exact sciences.92 More

importantly, the treatises on vision by these two Paduans reveals some inherent limitations of this

historiographical approach. Discussions by historical actors about the proper form of

demonstration, the precise relationship between sensory experience and universal knowledge,

and the admissibility of singular events and contrived experiments into natural philosophy all

ought to be taken into account. However, doing so does not fully map the historical terrain.

Although Fabricius likely incorporated Zabarella’s opinion about the proper grounding of

medicine and natural philosophy in the creation of his philosophical anatomy (§§ 3.1, 3.8),

Zabarella spent much of his career fighting against precisely the Galenic methods of

281

92 See especially Peter Dear, “Jesuit Mathematical Science and the Reconstitution of Experience in the Early Seventeenth Century,” Studies in History and Philosophy of Science Part A 18, no. 2 (June 1987): 133–75; Peter Dear, “The Meanings of Experience,” in The Cambridge History of Science: Early Modern Period, ed. Lorraine Daston and Katherine Park, vol. 3 (Cambridge, 2006), 106–31. The former is particularly relevant as it looks at the development of experiment in mathematical optics. A comparison between the use of experience and experiment in works on vision written by anatomists and physicians with those written by mathematicians would be particularly fruitful. I see little reason to privilege the latter over the former, as has thus far been the case.

investigation and demonstration that Fabricius’s held allegiance to.93 Fabricius’s harmonization

of Galen and Aristotle was anathema to Zabarella. Moreover, Zabarella adopted perhaps the

strictest interpretation of the Posterior Analytics and the methods of proper demonstration

possible, and if we take this to be his approach to the investigation of nature the two appear to be

worlds apart.94 Yet despite the disciplinary barriers, and behind the official, highly formalized

accounts of the relationship between demonstration, experience, and experiment that they give,

their accounts of vision were in many ways identical, and a fruitful interaction between the two

highly likely. The explicit statements about experience, experiment, and scientific method by

historical actors can be deceptive. Analyses of such must be tempered by detailed historical

investigations into the content of written works — the often difficult and unyielding texts

themselves — and with other methods, such as historical replication, that reveal in concrete ways

the past practices and actions of historical subjects.

282

93 Heikki Mikkeli, An Aristotelian Response to Renaissance Humanism: Jacopo Zabarella on the Nature of Arts and Sciences (SHS, 1992). For example, Mikkeli writes: “When Zabarella speaks about the relationship of medicine to natural philosophy in the middle of the work on methods, [William] Edwards takes his methodology as a starting-point for his interpretation. If we realize, however, that the methodology is used only in order to illustrate the basic difference between these two kinds of disciplines, we end up with a different conclusion. It can be said that Zabarella agreed with Leoniceno, for example, in pointing out that Galen did not speak about research methods, but about orders of presentation in his Ars medica. Yet this approach misses the whole intention of Zabarella's treatment, which shows that his fundamental assumptions about the nature and role of theoretical and practical knowledge were quite different from those of the anatomists or medical practitioners.” Ibid., 171.94 See especially Antonino Poppi, “Zabarella, or Aristotelianism as a Rigorous Science,” in The Impact of Aristotelianism on Modern Philosophy, ed. Riccardo Pozzo, Studies in Philosophy and the History of Philosophy 39 (Washington, D.C.: The Catholic University of America Press, 2004), 35–63. See also Stefan Heßbrüggen-Walter, “Problems with Rhubarb: Accommodating Experience in Aristotelian Theories of Science,” Early Science and Medicine (forthcoming). I would like to thank Stefan for allowing me to read this draft version and for a stimulating discussion about Zabarella.

Chapter 5: Light, Color, and the Eye in the Early Seventeenth Century


In this chapter the results of my investigation into the works of Zabarella and Fabricius, and the

relationship between, color, vision and the eye in anatomy, natural philosophy, and optics in

general, are applied to the seventeenth century. In the first section I demonstrate the influence of

Fabricius’s anatomical results and his theory of vision on Kepler, as conveyed through

Fabricius’s student Johannes Jessenius. I also argue that Kepler’s account of vision overall

contained some highly problematic aspects from the point of view of many of Kepler’s

contemporaries, rendering the retinal theory of vision, as presented by Kepler, less attractive to

them than most scholars assume. In section 5.2 I look at François d’Aguilón’s optical treatise. I

point out some important seventeenth-century shifts in the meaning of terms found there, and

highlight some important differences in the treatment of color by Aguilón compared to Zabarella;

I also suggest that, to some extent, these differences reflect ones between northern Italian natural

philosophers and Jesuits generally. I also show that Fabricius influenced Aguilón in some

important ways. In section 5.3 I sketch out a new account of the adoption of the retinal theory of

vision in the first half of the seventeenth century, particularly in the works of Christoph Scheiner

and Vopiscus Fortunatus Plempius. The advantages of Kepler’s account were by no means

obvious, and I argue that the important initial diffusion and acceptance of the retinal theory

occurred in due to the appropriation of Kepler’s theory within various forms of Aristotelianism.

Contrary to the accepted view in the history of science, the retinal theory did not, at least

initially, contribute the demise of Aristotelian ideas of sensation or to Aristotelianism generally;

283

on the contrary, the transformation of the retinal theory into Aristotelian theory of vision was

instrumental during its initial period of diffusion and acceptance. Finally, in section 5.4 I suggest

many revisions to the current historiography of the seventeenth century. I do this by taking Ofer

Gal and Raz Chen-Morris’s recent book Baroque Optics as an example of problematic narratives

that arise from a lack of attention to the history of physical color theory, to late-renaissance

accounts of sensation, and in particular to Zabarella and Fabricius’s treatises on vision.

§ 5.1: Kepler

In his Anatomia Pragensis of 1601 Johannes Jessenius (Jan Jesenský, 1566–1621) draws heavily

on Fabricius, his teacher in anatomy during his time in Padua. (His medical studies were in

Rome and Padua from 1588–1593.)1 Indeed, his section on the eye functions as a paraphrase of

Fabricius’s De visione — from the description of the shape and clarity of the humors, to the

usefulness of the vitreous humor, and even the statement that the vitreous humor is four times the

size of the crystalline.2 Jessenius writes, at the beginning of his section of the eye, “my teacher,

the Paduan Anatomist D. Hieronymus Aquapendente, always seemed to me to reign supreme in

the anatomy of the eye.”3 Given how closely together De visione and the Anatomia Pragensis

were published, it is quite likely that Jessenius's account of the eye is based on notes from

284

1 Unfortunately, apart from Czech or Slovak sources biographical information for Jessenius is rather slight. I have used David Kachlik et al., “A Biographical Sketch of Johannes Jessenius: 410th Anniversary of His Prague Dissection,” Clinical Anatomy 25, no. 2 (March 1, 2012): 149–54. Although I have not consulted it, see also Friedel Pick, Joh. Jessenius de Magna Jessen, Arzt Und Rektor in Wittenberg Und Prag Hingerichtet Am 21. Juni 1621. Ein Lebensbild aus der Zeit des 30jährigen Krieges, in Studien Zur Geschichte Der Medizin vol. 15 (Leipzig: Ambrosius Bbarth, 1926).2 Johannes Jessenius, Iohannis Jessenii a Iessen, Anatomiae, Pragae, anno M.D.C. abs se solenniter administratae historia: accessit eiusdem de ossibus tractatus (excudebat Laurentius Seuberlich, 1601), 113r-126v. 3 “Praeceptor meus, D. Hieronymus Aquapendentius, Anatomicus Patavinus, in oclulorum anatome, regnum tenere mihi semper visus est.” Jessenius, Anatomia, 113v.

Fabricius's anatomical demonstrations rather than Fabricius's recently published text. Jessenius

arrived in Prague in 1600 and performed a public anatomy there in June of that year, which his

Anatomia celebrates and upon which he says it is be based. Fabricius’s dedication in his De

visione, on the other hand, is dated December 1600, and so was published after Jessenius’s

anatomical demonstration. Kepler arrived in Prague in October of 1600 and so missed

Jessenius’s dissection, and in his 1604 Paralipomena he also writes that he did not have access to

a copy of Fabricius’s De visione. Thus if Jessenius did acquire a copy of De visione after his

public anatomy (and indeed almost immediately after De visione was published in Venice) and

used it to enhance the text of his Anatomia, it seems odd that Kepler would not have known

about this copy in Prague or have had access to it. It is reasonable to asume, then, that Jessenius’s

treatment on the eye in the Anatomia Pragensis was based largely on notes from Fabricius’s

anatomical lectures and demonstrations. Apart from its brevity and the relatively diminished

incorporation of mathematical optics, Jessenius follows Fabricius to a remarkable degree — and

indeed I can find no notable contributions from Jessenius, or any deviation whatsoever from

Fabricius’s De visione on points of structure, action, or use. Thus it appears that we have a sort of

record of what Fabricius would have taught about the eye in his own lectures and anatomical

demonstrations circa 1588–1591 — the only record of his anatomies of which I am aware. A

detailed comparison between the two texts could be quite instructive, but for the purposes of this

dissertation I only compare points relavent to my discussion.

Jessenius and Kepler knew each other well, and in his Paralipomena Kepler mentions

that he gathered all his knowledge of ocular anatomy from Felix Platter’s De corporis humani

structura et usu and the Anatomia Pragensis of his friend Jessenius. Kepler refers to the latter in

285

part because of Jessenius's own anatomical efforts, but also because “he professed chiefly to

follow Aquapendente.”4 The shapes of parts of the eye, the relative optical densities of the two

humors, and the crossing of rays in the vitreous humor are all critical for Kepler’s theory of

vision, yet Kepler claimed that he “never before had been either spectator or performer” at an

anatomical dissection of the eye, trusting instead in the expertise of Platter and Jessenius.5 Much

of what Kepler takes for granted about the structure and complexion of the eye is absent from

Platter's work, and so the visual theory of Zabarella and Fabricius had some influence on

Kepler’s revolutionary treatise via Jessenius, contrary to the frequent dismissal of the role played

by anatomists and scholastic natural philosophers regarding visual theory.6

Comparing the theory of vision given in the last two chapters to Kepler's reveals

important continuities and some crucial differences. Kepler provides the physical and causal

foundation for his theory in the first chapter of the Paralipomena and an appendix to it; there he

develops his own novel theory of color and light and gives a discussion and attack on Aristotle’s

theory of light and color. Importantly, he refutes Aristotle himself, and does not seriously engage

with the much more complex Aristotelian accounts given by contemporary natural philosophers

like Zabarella. Kepler’s keen attention to the shape of the posterior of the crystalline humor, and

the importance of the fact that the vitreous is less dense and thus more transparent than the

286

4 Johannes Kepler, Optics: Paralipomena to Witelo & Optical Part of Astronomy, ed. William H. Donahue (Green Lion Press, 2000), 171-172; Johannes Kepler, Ad Vitellionem Paralipomena, Quibus Astronomiae Pars Optica Traditur   (apud Claudium Marnium & haeredes Ioannis Aubrii, 1604), 159. All translations are from Donahue. Throughout I cite both the recent translation and the original; the page numbers in KGW can be found via citation to the original publication.5 Kepler Optics, 171-2; Kepler, Paralipomena, 158-159.6 To give one more recent example: “No anatomical discoveries fed into this [i.e., Kepler’s] model: a 17th century anatomist’s knowledge of this organ did not differ significantly from that of a 15th century artist-anatomist like Leonardo da Vinci (1452-1519).” Wolfgang Lefèvre, “Exposing the Seventeenth-Century Optical Camera Obscura,” Endeavour 31, no. 2 (June 2007): 55-56. See also §§ 0.2, 3.2.

crystalline, was clearly derived from Jessenius (whose account is entirely from Fabricius) rather

than Witelo or Platter. In Witelo the shape of the rear of the crystalline is unclear, while Platter

says that the posterior of the crystalline is "sphaericus," which Kepler does not follow.

Furthermore, Platter only says that the vitreous is “equally as splendid as the crystalline, but

softer.”7 Platter never explicitly refers to the density or rarity, thickness or thinness, or degrees of

transparency of the crystalline in the vitreous in a way that can be clearly understood in terms of

refractive power. He does mention that the crystalline humor acts as a sort of magnifying glass,

but from the point of view of mathematical optics this is a confused account, and Kepler is

critical of Platter on this point.

Jessenius’s Anatomia Pragensis contains no images, and so Kepler famously reproduced

images from Platter. However, besides these anatomical plates Platter’s anatomy contains only

four (folio) pages of text spread out in diagrammatic form, and thus relatively little detail about

either the action or utilitas of the parts of eye. Jessenius has far more text on the eye, and we can

observe Kepler following Jessenius's much more detailed account of the shape of the humors,

their translucency, and their refractive powers. Concerning the posterior of the crystalline humor,

Kepler writes, “Jessenius reports that [the posterior of the crystalline] is not spherical, as Platter

asserts, but that it protrudes greatly (valdè protuberare), and is made oblong, as if rising into a

cone”.8 Kepler uses this to argue (again, without having seen a dissection) that the posterior is a

hyperbolic conoid, a shape that satisfies the requirements of his mathematical account. In the

Anatomia Pragensis Jessenius, speaking of the usus of the crystalline, does indeed say that it

287

7 "aequè splendidus ac crystallinus, sed mollior" Felix Platter, De corporis humani structura et vsu Felicis Plateri (ex Officina Frobeniana, per Ambrosium Frob., 1583), 187.8 “Sic enim refert Jessenius, non sphaericum esse, quod Platterus aiebat, sed valdè protuberare, & oblongum fieri, quasi in conum assurgat: anteriore verò facie, depresse esse rotunditate;” Kepler Paralipomena, 167.

“protrudes greatly” but he adds that this is “so that the light transmitted through the crystalline

should be united into itself and not progress very far from the crystalline, but disappear at the

crystalline, and in a certain way perish.”9 This account is exactly what we read in Fabricius’s De

visione, and thus we see that the very text that Kepler cites on the shape of the crystalline humor

has its source in Fabricius, and that it conveys a novel aspect of his and Zabarella's theory of

vision. Certainly, Kepler’s combination of experience with optical devices, his Neoplatonic

concept of light, and his mathematical acumen led him to reject the notion that the light

“perishes” just behind the crystalline. From this it follows that light and color would be cast upon

the retina — the very thing that Zabarella, Fabricius, and Jessenius wished to avoid. However,

among all of Kepler’s sources only Jessenius describes rays of light forming a cone within the

vitreous due to the difference in refractive power of the humors. Kepler cites the 1589 edition of

della Porta’s Magia naturalis, where both the camera obscura and vision are separately

discussed, but he laments della Porta’s failure to connect the two.10 In fact, in his De refractione

(of which Kepler says he was unable to find a copy) della Porta assumes that vision takes place

at the anterior of the crystalline humor, and he ignores what happens beyond.11

288

9 “ita posteriùs valdè protuberat, eo fine ut lux crystallino transmissa, cùm in seipsa uniatur, tum longius à crystallino non progressa, illicò in crystallino evanesceret, & quasi commoreretur.” Jessenius 1601, 117v. This account of what happens to light is repeated and emphasized at 124v–125r, where we read “Vitreus humor ideò post crystallinus collocatus, ne lux crystallinum transvecta à coloratis & opacis oculi parietibus reflexa, crystallinum foedaret: id quod per vitrei diaphanum perficitur. Accedit autem ad hanc lucis obliterationem, crystallini quoque, diversum à vitreo, diaphanum, unde novam in vitreo fieri refractionem contingit, & consequenter aliquam lucis debilitationem.” By comparison, Fabricius’s has “Quae igitur erit propositae rotundus utilitas? Ea certe, mea sententia, ut lux crystallino transvecta, tum in seipsa uniatur, tum longius à crystallino non progediatur, sed in vitreo cesset, ac quodammodo commoriatur." Fabricius, De visione, 102–3.10 Kepler, Optics, 224-226; Kepler, Paralipomena, 209-211. 11 Giambattista della Porta, De refractione optices parte (Apud Io. Iacobum Carlinum & Antonium Pacem, 1593), 83-86; Thomas Frangenberg, “Perspectivist Aristotelianism: Three Case-Studies of Cinquecento Visual Theory,” Journal of the Warburg and Courtauld Institutes 54 (1991): 153. For the account given by Francesco Maurolico in his Photismi, see Ibid, 147-150.

It is well accepted that Platter's belief that the retina is visually sensitive influenced

Kepler's theory of vision. But accurate knowledge of the shapes and sizes of the humors, and that

the difference in their refractive powers cause incoming rays to cross within the eye, are crucial

features in Kepler's theory of vision. For this information he relies entirely on his anatomical

authorities. Apart from the shape of the crystalline (about which Kepler explicitly follows

289

Figure 5.1: Simplified representation of three main theories of the refraction of rays in the eye: perfection in the aperture of the optical nerve (A), weakening and dispersion in the vitreous (B) and the double-cone retina model. Note that no attempt was made to accurately portray the shape of humors in (A) — that is, the visual theory of Alhacen, Witelo, Peckham, and their followers. Nor was any attempt made to accurately render the refraction of rays due to the various humors in (C).

Jessenius), Platter says nothing about these things, and so Kepler's source for this empirical

information is Jessenius — and thus ultimately Fabricius.

Importantly, Zabarella and Fabricius (and following them Jessenius) believe that the

refraction that occurs within a living eye can be discovered by doing experiments on a dead eye.

This is a significant break from nearly all past writers. As we have seen, for the Perspectivae the

visual faculty actively intervenes, so that the colored image passing through the crystalline is

kept upright and sent precisely through the optical foramen. According to Galen and those who

follow his account of vision, there was a luminous pneuma filling the front of the eye which

immediately dissipates upon death, and thus the position of the humors cannot be accurately

determined by dissection on a dead eye.12 Alan Shapiro emphasizes the fact that “Kepler treated

the eye as an optical instrument without any active powers — a ‘dead’ eye."13 We can see

Zabarella and Fabricius doing the same . Furthermore, their eye, on which they witnessed or

performed experiments, was not merely a passive eye as for Kepler, but it was literally a dead

eye in front of them. The separation of the refractive and other passive properties of the eye from

the activity of the sensitive faculty is obvious in their works: sensation does not interfere with

refraction or with the reception of color and light in a living eye. However, for our Paduans this

“dead eye” involved the refraction of rays coming to a point in the vitreous in the manner of a

290

12 Although vivisection seems impractical, the many ophthalmologists that performed surgery on the eye might have had a better sense of the size and constitution of the aqueous humor in a living eye; however, those performing cataract surgery, especially, typically lacked a medical degree, were less well-educated, and were of a lower social standing than physicians. There appears to have been little circulation of knowledge between ophthalmologists and physicians up through the sixteenth century, at least. See J. Hirschberg, The History of Ophthalmology (Bonn: J. P. Wayenborgh, 1982), Vol 2. 13 Shapiro 2008, Alan E. Shapiro, “Images: Real and Virtual, Projected and Perceived, from Kepler to Dechales,” Early Science and Medicine 13, no. 3 (2008): 310. See also A. C. Crombie, “Expectation, Modelling, and Assent in the History of Optics — II. Kepler and Descartes,” Studies in History and Philosophy of Science 22, no. 1 (1991): 96.

burning glass; for Kepler this refraction of the rays results in the projection of an inverted pictura

upon the retina.14 A. C. Crombie states that Kepler’s camera obscura model of vision

enabled him to isolate the geometrical optics of the eye as an immediately soluble physical problem to be treated first and apart from all questions of sensation and perception. With this new conception of the subject-matter he could reduce physiological optics to inanimate physics and banish from this passive physical mechanism any active sensitive power to look at an object or to receive stimuli selectively.15

With Zabarella and Fabricius’s model for vision in mind, I would put this somewhat differently.

The difference was not so much between mechanical and non-mechanical approaches to vision,

but rather a redefinition of what geometrical optics is about and what is meant by sensation

itself. That is, I argue that Kepler’s “new conception of the subject-matter” was not the cause for

the separation of the inanimate physics of vision (including image formation) from issues about

sensation or the sensitive soul. This separation was already present in Zabarella and Fabricius.

Like Kepler, the two Paduans isolated geometrical optics from sensation, but what “optics” and

“sensation” meant for them was entirely different. Kepler’s geometrical optics of picture

formation involved the distinction between an imago (images that seem to be in mirrors and

glass spheres and so forth) and a pictura (a projected image in the manner of a camera obscura);

this reframed the entire problem of geometrical optics, although Kepler himself did not carry this

291

14 On this crucial point, Sven Dupré writes that, prior to the sixteenth century, the “punctum inversionis was not used in the perspectivist tradition of optics. Rather, this point was regarded as either the point of inversion or the point of combustion, but it fell outside the conceptual framework of perspectivist optics that this point could possibly be the locus of both.” Sven Dupré, “Kepler’s Optics Without Hypotheses,” Synthese 185, no. 3 (2012): 515. For more on the conceptual framework of medieval and renaissance perspectivists and their failure to treat image projection, see A. Mark Smith, “Reflections on the Hockney-Falco Thesis: Optical Theory and Artistic Practice in the Fifteenth and Sixteenth Centuries,” Early Science and Medicine 10, no. 2 (2005): 163-186.15 A. C. Crombie, “Expectation, Modelling, and Assent in the History of Optics — II. Kepler and Descartes,” Studies in History and Philosophy of Science 22, no. 1 (1991): 96.

shift in out fully in his works.16 Kepler’s potentially visible pictura changed what seeing was all

about, and thus Keper gave a new conception of what is, in fact, sensed. (Note that Kepler

insisted that this pictura should be actually visible, but did not witness this; it was proven to be

actually visible thanks to Scheiner and others.) Only after such a precise point-to-point map

between sensible objects and the instrument of sense was conceived and given a plausible

mathematical account did the images (imaginis), which were thought to appear in the crystalline

humor according to previous writers, appear inadequate. The “problem” of image formation prior

to Kepler was redefined after the appearance Kepler’s solution. Although historically

intertwined, if one wishes to trace the precise contours of seventeenth century change to visual

theory this issue should not be conflated with the mechanization or mathematization of nature.

Most analyses of Kepler’s Paralipomena stress the analogy of the eye to a camera

obscura, and this is no doubt justified. Using this analogy and applying his expertise in

mathematics Kepler was able to account for not only a single ray originating from each point in

the object, as had past perspectivists, but an innumerable quantity of rays issuing forth from

every point on the visible body into the eye in the form of a cone. These cones (or pencils of

rays) then combine again through refraction into a single point on the retina resulting in an

inverted, and reversed picture there. This is Kepler's double cone model, taken up by Scheiner,

Plempius, and Descartes, and it is the basis for modern visual theory. (See figure 5.1.)

Furthermore, Kepler’s experience with the camera obscura led him to make a distinction

between a pictura, or a real projected image, and an imago, a perceived image that is the product

292

16 See Alan E. Shapiro, “Images: Real and Virtual, Projected and Perceived, from Kepler to Dechales,” Early Science and Medicine 13, no. 3 (2008): 270–312.

of the imagination (e.g., the image seen in a mirror or crystal ball).17 However, in placing the seat

of vision at the retina Kepler had a problem: the retina is, he says, colored.18 Without the

elaborate theory of light and color developed in Kepler's first chapter — a theory that is finely

tuned to solve this problem — the possibility that a colored body could be the seat of visual

sensation would have been ridiculous. As Kepler presents it, however, his solution to the problem

of the colored retina appears ad hoc. He writes that the retina "is said to resemble the substance

of the cerebrum, but to be more mucous and reddish (bluish, according to Jessenius), whence one

concludes that it seems to be above all a diluted white tinged with redness or blueness."19 After

describing how each point of an object is resolved into a single point on the retina, he refers his

reader to his first chapter. There Kepler writes:

There follows hence a kind of corollary to Props. 30 and 31: that the rays that have flowed to black surfaces are perceived most distinctly, and to white ones most evidently; and if a surface be a mean between black and white, such as blue, white washed with red, and the like, they will stand about equally in rendering both the individual colors and their differences.20

What would otherwise be an embarrassing lack of cooperation by nature as revealed through

anatomical observation is reframed four chapters earlier, in the foundational matter of his optics,

by positing a theory of light and color in which surfaces tinted either red or blue are ideally

suited to image projection. If the retina turns out to be reddish, as Platter says, or bluish, as

according Jessenius, no matter — either color will do just fine. Kepler also conveniently chose

Platter's position that the aranea and the retina are not connected. The "entire opinion [that the

crystalline is the seat of sensation] ... is knocked down when the crystalline is cut off from the

293

17 Shapiro, “Images”; Dupré “Kepler’s Optics Without Hypotheses.”18 Kepler, Optics, 185; Kepler, Paralipomena, 175.19 Kepler, Optics, 178; Kepler, Paralipomena, 166.20 Kepler, Optics, 38-39; Kepler, Paralipomena, 25.

nerve and from the retina, and joined with the uvea, as was shown from Platter."21 Kepler was no

authority on this matter, and to his contemporaries it could very well seem that, without good

justification, he simply ignored authorities that did not support his theory.

Unfortunately there is no space to fully analyze Kepler’s account of light, color,

transparency, and density and rarity here, but a brief account of Kepler’s similarities and

differences compared to his predecessors is instructive.22 In Chapter 1 proposition 17 Kepler

writes: “The opaque is something that is broken up into many surfaces, and something that

possesses great density, and something that possesses much color, whether in quantity or quality.

For the opaque is that which does not transmit rays.”23 Just after this, however, he invokes the

passage in De sensu where Aristotle says that every body has some degree of transparency:

“Further, that nothing is absolutely opaque, Aristotle also allows in the book on perceptibles.”

Color for Kepler is related the diaphanous itself:

Color is light (lux) in potentiality, light entombed in a pellucid material, if it now be considered apart from vision. Different degrees in the arrangement of matter, by reason of rarity and density, or of pellucidity and darkness, and likewise, different degrees of the spark of light, which is condensed into matter, bring about the distinction of colors.24

294

21 Kepler, Optics, 219; Kepler, Paralipomena, 204.22 The fullest account is David C. Lindberg, “The Genesis of Kepler’s Theory of Light: Light Metaphysics from Plotinus to Kepler,” Osiris 2 (January 1, 1986): 4–42. However, he neglects the degree to which Kepler’s theory of color, transparency, density and rarity, and so on relate to his contemporaries. 23 Kepler, Optics, 25; “Opacum est & id, quod multis superfiebus confragosum est, & id, quod multam obtinet densitatem, & id, quod multum colorem vel in quantitate, vel in qualitate obtinet. Opacum enim est, quod lucis radios non transmittit.” Kepler, Paralipomena, 13.24 Kepler, Optics, 25; “Color est lux in potentia, lux sepulta in pellucidi materia: si iam extra visionem consideretur; & diversi gradus in dispositione materiae, causâ raritatis & densitatis, seu pellucidi & tenebrarum; diversi item gradus lucula, quae materiae est concreta, efficiunt discrimina colorem. Cum enim colores, qui cernuntur in iride, sint ex eodem genere, unde & colores in rebus; eadem erit utrorumque origo.” Kepler, Paralipomena, 11.

Just before this, in proposition 12, he writes that it is no impediment for pellucid bodies to be

colored, “for pellucid bodies should be so.”25 A few things should be noted: as seen above, colors

are lux in potentia, and they receive their activity through illumination. They must be

“entombed” in a diaphanous body rather than a completely non-transparent one, otherwise the

activity of lux would not be able to reach and activate color. Furthermore, Kepler rejects Aristotle

and holds that light plays no role in the activation of the transparent medium, because for Kepler

the transparent medium requires no activation, only color does.26 However, Kepler conceived of

the activity of the objects of vision — i.e., light and color — as points that have become super-

rarefied into two-dimensional surfaces, propagating outwards from luminous and colored bodies

in all directions instantaneously.27 These sense objects are not received by a three dimensional

body, but ultimately by super-rarefied spirits at a two dimensional boundary.28 Kepler rectifies

the seemingly three-dimensional, corporeal account of color given in the passage above with the

two-dimensional nature of light using an idiosyncratic account of density and rarity. Dense

bodies are “bodies of which many parts of matter fill a small solidity.”29 (Note that this is a

significant break from the notion of density and rarity we have seen in Zabarella and his

sources.) Kepler then introduces the notion of surface density: density, as an affect of matter,

belongs to three dimensions, but two dimensional surfaces “participate in the density of bodies

according to their measure.”30 The two dimensional character of light and color is thus preserved,

295

25 Kepler, Optics 23; Kepler, Paralipomena, 10.26 Kepler, Paralipomena, 37.27 Kepler, Paralipomena, 6-25; Lindberg, “Genesis of Kepler’s Theory of Light,” 4–42.28 Kepler, Paralipomena, 170, 204, 220-221.29 Kepler, Optics 23; “Densorum corporum, seu quarum multae partes materiae angustam implent soliditatem, superficies etiam densa sunt quodammodo, respectu scilicet eo, quo lux & corpora se mutuo afficiunt.” Kepler, Paralipomena, 11.30 Kepler, Optics, 23; Kepler, Paralipomena, 11.

and the relationship between density and rarity, transparency, color, and refraction is also

preserved . However, Kepler’s reasoning might be considered less an argument than an assertion,

and his conclusion would no doubt be considered dubious by some of his contemporaries. All of

this is in a sense directed towards his account of vision, in which the “opaque (opacus) wall of

the eye” has picturae of the external world projected upon it.

For Kepler, the retina is not purely white — it is either reddish or blueish, and so “opacus”

here seems to be referring to both the stoppage of rays and the lack of brightness. To complicate

matters further, in a lengthy marginal note to proposition 15 we read that “White and black

appear to be opaque in its highest degree; the rest can be pellucid in its highest degree as

well....”31 Kepler, then, seems to be using “pellucid” and “opaque” simultaneously as a term

suited to the analyses of both natural philosophy and mathematical optics. That is, he uses them

to refer to a the degree of receptivity to the activity of light of a body (or surface!) — and he cites

Aristotle for support in this. He also uses the terms to refer to whether a body allows the

transmission of rays or not, and thus whether we can see through it. Kepler’s account is at once

eclectic, syncretic, and original. It must also have seemed, I suggest, unsatisfactory to some of

his contemporaries. Whether or to what degree this is true deserves a detailed analysis of its own,

but we can get some sense of it by the way in which the retinal theory of vision was

appropriated. Early adopters such as Scheiner, Plempius, and Descartes abandoned much of

Kepler’s account of light, color, density and rarity, and transparency when they took up the

retinal theory.

296

31 Kepler, Optics 24; “Videntur albus & niger Opaci in summo suo gradu: reliqui pellucido etiam in summo gradus inesse possunt.” Kepler, Paralipomena, 12.

In addition to solving the problem of how the colored surface of the retina can act as the

seat of sensation, Kepler claimed that his characterization of light as two-dimensional also gave a

better causal understanding of reflection and refraction.32 What Kepler demanded of his readers,

however, was to abandon their previous understanding of transparency, light, and color; to

discard the philosophically well-grounded notion that two-dimensional surfaces are

mathematical abstractions, not physical entities, and thus to accept that two-dimensional beings

can, somehow, interact with our three dimensional bodies via our retinas; and finally, to abandon

the principle at the heart of previous theories of visual perception — that color, the object of

vision, can only affect that which is potentially colored, i.e., uncolored, i.e., transparent. Kepler’s

mathematical account of vision must have been appealing to those that were capable of wading

through it, but there were many aspects that would have appeared problematic, especially to

those that were not already inclined to accept a mathematical description of nature that was

grounded in physics in a more traditional sense. It is extremely difficult to look at treatises of

vision during this period without the conceptual lens of modern visual theory, a tool that Kepler

himself helped to create. However, an accurate assessment of this period requires it.

§ 5.2: François d’Aguilón

Throughout I have tended to stress the similarities between Zabarella and Fabricius on vision and

the eye, but one item of note is unique to Fabricius. Along with a geometrical diagram of a

human eye, Fabricius also gives one for a sheep's eye, and notably the position of the centers of

297

32 Kepler, Paralipomena, 13-21; Stephen Straker, “Kepler’s Optics: A Study in the Development of Seventeenth-Century Natural Philosophy” (PhD Dissertation, Indiana University, 1970), 503-506, 509-520.

curvature occur in different places within the eyes. (See figure 4.14; compare to figure 4.7.) On

these diagrams he writes:

But so that those who produce works of optical science can accurately observe the diverse progression of rays, which are called visual, while they cross over from one humor into another; and [so that] they can accurately measure off the angles of refraction, and thence grasp the innumerable utilitates of the parts: we provide, with the most exact care, human and sheep eyes divided through the middle. And the whole magnitude and that of the individual parts, including their situations and figures, are described, and the place that each of their centers occupy is revealed, and everything is outlined in tables below. Diligent investigators of the works of nature will have much to contemplate, where they are able.33

Throughout his treatise Fabricius's discussion of rays is merely qualitative, but here we see the

expert at investigating animal bodies handing over his results to experts in optics. What Fabricius

provides, however, is not merely the scheme for one individual eye, or even one kind of eye, but

two kinds of animal eyes. He poses the problem of solving, geometrically, the question of vision

in two different kinds of animal. Each animal has humors of different relative sizes, and in his

diagrams the surfaces of the sclera, the cornea, the anterior of the crystalline have different

centers of curvature. At play here is the problem of vision in animals as a whole, which shows

Fabricius’s appropriation of the “Aristotelian programme” of the universal animal and its parts.34

Notably, because the centers of curvature of the cornea and the crystalline are not identical, and

furthermore are not in the same place in the two animals, the visual theory of Alhazen and the

rest of the perspectivists becomes impossible on empirical grounds. Jessenius did not include

298

33 “Ut autem qui Opticae scientiae operam dant, accuratè obervare possint, progressum varium radiorum, quos visuales appellant, dum ab uno in alium humorem transeunt; atque angulos refractionis dimetiri, & inde innumeras utilitates partium excepere: curavimus exactissima diligentia, oculum humanum & ovilem per medium secari, & magnitudinem totius, ac singularum partium, nec non earundem situs, & figuras describi, & loca qua eorum centra obtinent inveniri, & omnia in subiecta tabella delineari. Habebunt enim curiosi indagatores operum naturae, ubi multa contemplari possint.” Fabricius, De visione, 105.34 Andrew Cunningham, “Fabricius and the ‘Aristotle Project’ in Anatomical Teaching and Research at Padua,” in The Medical Renaissance of the Sixteenth Century, ed. Andrew Wear, Roger Kenneth French, and Iain M. Lonie (Cambridge University Press, 1985), 195–222.

corresponding images or any descriptions of them in his text, and Kepler approached the

problem Fabricius points out quite differently by extrapolating from the refraction of a sphere

and applying these results to the eye.35 However, at least two important writers on optics were

influenced by Fabricius in this respect. Franciscus Aguilonius (François de Aguilón) relied

almost entirely on Fabricius for his anatomy of the eye in his 1613 Optica. Aguilonius uses the

knowledge that the centers of curvature of the cornea and the anterior of the crystalline humor

occur in different places in the eye to argue against Alhazen and Witelo. From this he generates

his own, new crystalline-centered theory.36 Additionally, in his Oculus of 1619 the Jesuit

mathematician and natural philosopher Christoph Scheiner quoted this very passage, expressed

his delight in reading it, and took up the challenge in his retinal theory of vision.37

The Jesuit Aguilonius cites Fabricius several times in his Opticorum libri sex, and his

account of the structure and utilitates of the eye and its parts is essentially a paraphrase of De

visione.38 Aguilonius also gives the same account of shape of the crystalline and the size vitreous

causing the rays of light cross and perish in the vitreous.

The vitreous however is arranged after the crystalline by nature, so that whatever lumen will have progressed past the crystalline, it should be weakened in it, and

299

35 Shapiro, “Images: Real and Virtual.”36 François de Aguilón, Francisci Agvilonii E Societate Iesv Opticorvm Libri Sex (Ex officina Plantiniana, 1613), 11–12, 119-125. Note that he nevertheless reverses the order of the centers of the cornea and crystalline compared to Fabricius, which has a significant effect on his analysis of vision.37 Christoph Scheiner, Oculus, Hoc Est, Fundamentum Opticum, 1619, 20.38 Aguilón, Opticorum libri sex, 1–6. On Aguilón’s life, see August Ziggelaar, François de Aguilón, S.J. (1567-1617), Scientist and Architect (Institutum Historicum S.I., 1983). Catherine Chevalley, “L’optique Des Jésuites et Celle Des Médecins: A Propos de Deux Ouvrages Récents,” Revue D’histoire Des Sciences 40, no. 3/4 (July 1, 1987): 377–82.

not, as was just said, reflect defiled from the opaque and colored retina to the crystalline.39

This is precisely the account first given by Zabarella and Fabricius, and thus their theory of

vision found a home in a highly influential text on geometrical optics. Aguilonius’s Opticorum

libri sex is an enormous and impressive volume, and it devotes six books, over seven-hundred

pages, to direct vision alone. (Two more volumes on reflected and refracted vision were planned,

but never published.) Although it came out after Kepler’s 1604 Paralipomena and his 1611

Dioptrics, Aguilonius notably did not embrace the retinal theory.40

His work is also well-known for the six images by Rubens that adorn the title pages of

each of the books, and for his treatment of color mixture that embraced the painters primaries of

yellow, red, and blue as basic in addition to the traditional black and white.41 (See figure 5.2.)

These five species of simple colors, he says, are not those proper to the elements nor are they

generated from the first qualities (hot, cold, wet, and dry) or their combination.42 Rather,

Aguilonius takes as simple colors those which act as the elements for all other colors — that is, he

sidesteps the problem of the origin of color (i.e., why color rather than no-color) and simply

300

39 "Vitreum autem post crystalloidem natura collocavit, ut si quid luminis crystallinum praetergressum fuerit in eo hebetetur, ne, ut iam antè dictum est, ab opaco coloratoque retinae corpore foedatum ad crystallinum reflectatur." He also says that crystalline is dense and protrudes in the rear "ut lux in ipso commoriatur, ne longiùs progressa vitreumque praetervecta, ad retinam redeat, ab eaque ad crystallinum resiliens nova affectione visum perturbat." Aguilón, Opticorum libri sex, 6.40 Johannes Kepler, Dioptrice seu Demonstratio eorum quae visui & visibilibus propter conspicilla non ita pridem inventa accidunt: Praemissae Epistolae Galilaei de iis, quae post editionem Nuncii siderii ope Perspicilli, nova & admiranda in coelo deprehensa sunt. Item Examen praefationis Ioannis Penae Galli in Optica Euclidis, de usu Optices in philosophia (typis Davidis Franci, 1611). It is unlikely that Aguilón saw a copy of the Paralipomena prior to completing his own work. See Ziggelaar, François de Aguilón.41 On the influence of the painterly tradition on natural philosophy and color mixture, see Alan E. Shapiro, “Artists’ Colors and Newton’s Colors,” Isis 85, no. 4 (December 1, 1994): 600–630; John Gage, Color and Culture: Practice and Meaning from Antiquity to Abstraction (Boston: Little, Brown and Company, 1993), 153–190. On Aguilón’s color theory see ibid., 95, 154, 229–232. On Aguilón and Rubens, see Martin Kemp, The Science of Art: Optical Themes in Western Art from Brunelleschi to Seurat (Yale University Press, 1990), 99–105. 42 Aguilón, Opticorum libri sex, 38–39.

states that color is a property of opaque bodies, by which he means bodies that cannot be seen

through. Colors are not considered in the context of their relationship to fundamental physical

properties or changes. Instead, the simple colors are those that cannot be analyzed further, and

which, through composition, can generate all other colors. This scheme appears to be based on

the notion of analysis and synthesis found in alchemy (and he does have a few references to

chymical experiments and tests), and in particular the “negative-empirical concept” in which the

primary constituents of matter are those that cannot be resolved further by laboratory

techniques.43 Here, however, Aguilonius divorces color from its material substrate, and takes the

painter’s palette as his “laboratory,” exemplifying the notion of the painter’s primary and

secondary colors.44 He gives an interpretation of Aristotle’s account in De sensu on the three

types of mixture: through juxtaposition of discrete parts, through overlay as when painters use a

semitransparent wash, and true physical mixture (see § 1.1). However, he links this to a

classification of color in a manner that differs from previous writers, or at least those that I am

familiar with. True mixture, or mixture of colors in themselves, results in real colors, and the

paradigm for this process is the way in which painters mix pigments on the palette. What he calls

intentional mixture is exemplified by the technique of overlaying in painting, and in this case the

species of colors are truly mixed in the medium. Finally, he has a third category of “notional”

colors arise from juxtaposition of colored bits; in this case the colored bits each propagate

301

43 William R. Newman, Atoms and Alchemy: Chymistry and the Experimental Origins of the Scientific Revolution (University of Chicago Press, 2006), 95–9944 Note, however, that this idea of painters primary secondary colors was abstracted from their experiences, and not so much a reflection of their practice. John Gage, Color and Culture: Practice and Meaning from Antiquity to Abstraction (Boston: Little, Brown and Company, 1993), 154, 177–179, 229; Alan E. Shapiro, “Artists’ Colors and Newton’s Colors,” Isis 85, no. 4 (December 1, 1994): 600–630.

species of colors separately, but these colors are confused in the eye when seen at a sufficiently

far distance.45

He has a lengthy discussion of this, but the upshot is that there are three kinds of colors,

which however correspond only loosely to the three types of mixture given above.46 First, true

and real (veri ac reali) colors are those in a body arising either from a mixture of the elements or

according to the specific form of a substance. Thus, although he never gives an account of the

relationship between his simple colors and the underlying material conditions, Aguilonius

nevertheless grounds the ontological status of real colors in either their elemental constitution or

their specific form. Second, intentional or notional colors, emanate (emanare) from a self-

302

45 Aguilón, Opticorum libri sex, 39–40.46 Ibid., 40–45.

Figure 5.2: Aguilón’s diagram of color mixture indicating an influence from the painting tradition. The five species of simple colors, from left to right, are white, yellow, red, blue and black. The composite colors (colores compositi) are gold, green, and purple. Note that the precise hue indicated by the Latin terms might not correspond precisely to what we would consider as exemplars for the corresponding English terms. Aguilón, Opticorum libri sex, 40.

luminous body and are carried across a medium like heat propagating from a fire. These are

extremely tenuous compared to real colors, and are propped up by the first kind. It appears, then,

that he is grouping two of Aristotle’s kinds of color mixture, arising from overlay and

juxtaposition, into this category of color, and thus both intentional and notional mixture would

correspond to the ontological status of Zabarella’s intentional or “spiritual” colors. They might

also correspond to Zabarella’s instances of apparent colors for which we are liable to make a

mistake in judging that a sensation represents the real color of a body (see § 2.6). Third,

Aguilonius gives fantastical or apparent colors, which he says “hold no truth apart from

lumen.”47 These colors come together in the medium, and rainbows and the like are in this third

category.

A full analysis of Aguilonius’s treatment of color is beyond the scope of this dissertation,

but a few important points should be noted. First, as was shown in §§ 2.5–6, Zabarella’s

distinction between real and apparent colors was not connected to the ontological status of the

colors themselves. For Zabarella, the ontological distinction was between colors considered in

themselves and the visibility of colors. The former arise from the material conditions of density

and rarity in a body, and they exist regardless of the presence of sensitive beings whatsoever. The

latter are colors considered with respect to a visually sensitive being; they are the ability of color

to alter actually transparent media in order to affect sight, and are an accidens proprium of color

considered absolutely. Separate from this, Zabarella also makes a distinction between real and

apparent colors, but this distinction is entirely to do with judgment. If we put on red-colored

glasses, things that aren’t red will appear to be so. In this case we actually sense the color red,

303

47 “quòd praeter lumen nullam aliam veritatem habeant.” Aguilón, Opticorum libri sex, 45.

however, so our visual faculty is not mistaken, and the colors we sense are not false. It is merely

an error in judgment if we attribute the color red to things which, in fact, are not red (i.e., do not

have the material conditions, or the precise ratio of density and rarity, that gives rise to red in the

body). Aguilonius, on the other hand, seems to confuse or combine these ontological and

epistemological issues. For him, real colors are grounded in the elements or the substantial form

of a body (although he remains agnostic about how this works). Both intentional and notional

colors, on the other hand, have a tenuous existence in the medium only, and thus have different

ontological status from real colors. Aguilonius does not mention the issue of judgment in

connection with this category of colors, and indeed earlier he notes that notional colors arise

from a mixture of species in the eye itself, opening the door to the possibility that the faculty of

vision itself combines species which otherwise might not be combined. Nevertheless, despite

their tenuous, existence intentional and notional colors have a clear cause and ultimately do

reflect the material conditions of some body or bodies. Aguilonius’s third category of qualities,

however, is more difficult to understand.

To a third genus look to fantastical or apparent colors, so called because they hold no truth apart from lumen; they are separated from the two kinds of colors above above all by deficiency. Moreover they are appropriate to [transparent] media, because they dwell only in the perspicuous body, nor at any time subsist or are able to be discerned apart from lumen.48

Aguilonius’s first type of colors, then, is the color of a body, while the second refer back to or is

caused by some color in a body, even if that color is altered or mixed on the way to our eyes (or

indeed by our visual faculty itself). On the other hand the third type of color — Aguilonius’s

304

48 “Ad tertium genus spectant colores phantastici seu apparentes, ita vocati, quòd praeter lumen nullam aliam veritatem habeant; quo potissimùm defectu à superioribus duobus colorum generibus discriminantur: conveniunt autem cum mediis, quòd in solo corpore perspicuo versentur, nec umquam à lumine secreti subsistere aut cerni possint.” Aguilón, Opticorum libri sex, 45.

apparent colors — seem in no way to be caused by any real, physical color of a body. It is, in

some sense, just modified light itself (although I am not sure how this is supposed to work when

light and color are still distinct entities). Aguilonius’s scheme has its precedent in previous Jesuit

writers, and for example in the Coimbra commentary on Aristotle’s De anima, first published in

1592, there is a section heading telling us that “Apparent colors are not distinguished from

lumen; true [colores] are distinguished.”49 It seem, then, that for many Jesuits apparent colors are

inherently epistemically unreliable on account of their peculiar ontological status. How to work

this out, and whether there was a sort of Jesuit hegemony on this issue, requires more

investigation than I can give here.

Thus three important differences are found in Aguilonius (and perhaps many Jesuits)

compared to Zabarella and other Averroës-influenced scholastics in general, especially those

from northern Italy. First is the notion that apparent colors are in some sense false while real

colors in bodies are true.50 This is a distinction that Zabarella directly opposes, insisting instead

that sensations cannot be false, and that the faculty of vision does not make a mistake concerning

the species of color presented to it. According to Zabarella and many others, only judgments

about which bodies are colored can be true or false. The second important difference found

Aguilonius and others with a similar classification scheme is the idea that apparent colors are

somehow themselves lumen or caused by lumen, and for this reason exist only in transparent

305

49 “Articulus II: Apparentes colores à lumine non distingui; veros distingui.” Conimbricenses and Aristotle, Commentarii Collegii Conimbricensis Societatis Iesu, In Tres Libros De Anima Aristotelis Stagiritae (Cologne: Zetznerus, 1603), 222. 50 Explicating what they mean by calling certain colors true and others not true is no simple matter. The Coimbra commentary, for example, devotes several pages to this question, and in the end the question seems to be where those colors originally reside: if the colors we sense are caused by and accurately represent a determinate body, then they are real and true colors; if they arise only in an indeterminate body such as air or water, then they have no “truth” apart from lumen and are apparent. Conimbrincenses, In De anima, 218–225.

media, while real and true colors are caused by bodies with a determinate limit with respect to

vision. For Zabarella lumen and color cannot be the same because, if they were, then every

illuminated medium would impede the reception of different colors. In fact, he says, our

experiences tell us the opposite: it is illumination that allows for the medium and our eyes to

receive different colors; illumination does not impede this ability. Color, therefore, cannot arise

from lumen in the medium because lumen is a different kind of entity from color altogether.51 In

the case of apparent colors, such as the red sun at sunset, it is the color (in this case white)

propagating along with the lumen that is altered in transit, not the lumen itself. According to

Zabarella’s scheme, for a color to have no truth apart from lumen makes no sense — lumen is a

prerequisite for the existence of species of color in the medium, nothing more. Finally, the last

important difference between Zabarella and Aguilonius (as well as other Jesuits, it seems) is that

the latter tends to give a twofold scheme for the origin of color: in simple and imperfectly mixed

bodies color arises in connection with the primary qualities hot, cold, wet, and dry. In perfect

mixts, however, color is due to the substantial form of a body. Zabarella, following Averroës,

tends to downplay the importance of substantial forms, whereas the Jesuits, following Thomas

Aquinas, tend to emphasize the unity of substances and the importance of substantial forms.

One last important shift that we see fully actualized in Aguilonius is the meaning of the

term opacus. As we have seen, the Latin term opacus was at first not equivalent to the modern

term opaque — opacus did not mean something through which light cannot pass. Rather, it meant

dark or shaded, and originally it referred to the murky character of a thick forest. Zabarella was

careful to keep this use of the term opacus, and so both un-illuminated air and un-illuminable

306

51 Zabarella, De rebus, 618.

elemental earth were both opacus. On the other hand, a bright white body, such as a cloud or

white linnen, is not opacus precisely because such white bodies are extremely close to the nature

of the transparent; although they have a determinate boundary with respect to sight, such white

bodies in fact admit lumen to the highest degree. The key test as to whether this shift in meaning

has occurred is whether the phrases “luminous opaque” or “opaque white” are contradictions. If

dictionaries are any indication, such statements in Latin, from antiquity through the Renaissance,

would have been contradictory. (See Appendix 1.) At some point, however, opacus came

primarily to mean non-transparent, and it seems that Aguilonius’s work marks a reversal in the

dominant meaning of the term. In Julius Caesar Scaliger’s Exotericarum exercitationum, on the

occasion of attacking Cardano’s account of the rainbow, we read, “The opaque is truly that which

is in shadow, or is shadow itself, according to Cicero; and that which does not transmit rays: such

as is earth.”52 Over time the second of these two meanings became dominant, and thus the entry

in Rudolph Goclenius’s 1613 Philosophical Lexicon quotes Scaliger, but arranges the quote such

that Scaliger’s second notion of opacus (as not transmitting rays) becomes the primary

definition:

Opaque is opposed to transparent. And it is that which does not transmit rays, such as is earth. Scal.ex.80.s.1.sic. The opaque is that which is in shadow, or shadow itself according to Cicero, and that which does not transmit rays.53

In Aguilonius this shift in the terms is even more complete, and there are no traces that opacus

means dusky, shaded, or lacking illumination. Indeed, according to Aguilonius opacity is the

307

52 “Est enim opacum, quod in umbra est, aut umbra ipsa, apud Ciceronem: & illud, quod radios non transmittit: qualis terra est.” Julius Caesar Scaliger, Exotericarum exercitationum liber quintus decimus, de subtilitate, ad Hieronymum Cardanum (ex officina typographica Michaelis Vascosani, 1557), 124. Ex. 80.53 “Opacum opponitur Transparenti. Estque quod radios non transmittit, qualis est terra. Scal.ex.80.s.1.sic. Est opacum, quod in umbra est, aut umbra ipsa apud Ciceronem, & illud, quod radios non transmittit.” Rudolph Goclenius, Lexicon philosophicum (Becker, 1613), 276.

necessary condition for lux itself as well as color, and his Theorem 31 is titled “Lux and color are

the special characteristics (proprietates) of opaque bodies.”

In addition if we wish to roam through singulars, we will find that every body, which either shines itself with brilliance, or which is imbued with any color, is opaque. And no opaque body stands forth which is not clearly visible due to either lux or color. Thus it is that “shining” and “colored” are reciprocal with “opaque.”54

He gives this specifically to refute those who say that light (lux) exists in the diaphanous, while

color exists in the opaque. As we have seen, for Aguilonius the simple colors yellow, red, and

blue do not arise from a mixture of white and black. Thus the long-held scheme, laid out so

meticulously by Zabarella, is rejected in part through a redefinition of terms. For Zabarella, light,

white, and the transparent are of the same nature, while shade (tenebra), black, and the dark

(opacus) are of the same nature. When this set of contraries are present in a determinately

bounded body one gets a scale from white to black with all the colors in-between, and,

depending what kind of body was condensed to achieve that determinate-boundedness, one

might also get lux. When these contraries are set in an indeterminately bounded body, one gets a

scale from perfect illuminated transparency to un-illuminated darkness. But Aguilonius is not

concerned with getting all of the colors out of a mixture of white/bright and black/dark, and so, it

seems, he has no motivation to retain this scheme. That opaque should mean “that which does

not allow the transmission of rays” is natural to a writer in mathematical optics. On the other

hand, for a natural philosopher such as Zabarella the notion of opaque is linked to the presence of

illumination as an activity, not a ray. Thus, the opaque is “that which is not illuminated,” while

308

54 Praetereà si per singula discurrere velimus, comperiemus omne corpus, quod vel proprio nitet fulgore, vel quod colore aliquo infectum est, opacum esse; nullumque corpus opacum extare, quod non vel luce, vel colore conspicuum sit. Ita ut lucidum & coloratum cum opaco recprocentur.” Aguilón, Opticorum libri sex, 32.

“not being illuminated” could be due either to a lack of illumination or else because the body

possesses a gross, earthy nature that does not admit illumination into its substance.

Two likely reasons for the shift in the meaning of “opaque” are thus (1) that light was

increasingly being thought of primarily as a ray rather than an activity of the transparent, and (2)

that white/bright and black/dark were less and less considered to be the fundamental color-

contraries, the mixture of which gives rise to all species of color.55 Tracing the precise contours

and causes of this shift would be a difficult task, however, and it is beyond the scope of this

dissertation to come to a definitive answer as to precisely how or why it happened. The most

important point I wish to make is that it did happen, and that this shift signals a key

reconfiguration of some of the most fundamental constituents of visible reality. Recognizing that

this shift did, indeed, occur ought to change the way we read, understand, and translate works of

the past. In many ways it signals the shift from medieval and renaissance scholasticism to

seventeenth-century conceptions of light, color, vision, and the and scope of mathematical optics.

As we have seen, Fabricius’s use of opacus is not entirely consistent, and at times he uses it to

refer to things dark in color while at other times (e.g., when speaking of refraction) to refer to

how rays are transmitted through a body. We also saw (§ 5.1) that Kepler’s use of opacus follows

the trend in works of mathematical optics by using it to mean “not-transmitting rays,” but that he

also retained the sense from the natural philosophy tradition: that the diaphanous or pellucid was

that which admits the activity of light, and at times he seems to use the term opacus to refer to

dark or shaded things.

309

55 For the latter, see especially Alan E. Shapiro, “Artists’ Colors and Newton’s Colors,” Isis 85, no. 4 (December 1, 1994): 600–630.

Aguilonius, however, is explicit and consistent in his use of opacus. The shift in the

meaning of opacus was, perhaps, first fully accomplished not by later proponents of the

mechanical philosophy such as Descartes, but by a Jesuit architect and mathematician in a

thoroughly scholastic treatise on optics. Aguilonius also rejects the condensation theory of the

origin of color. He argues that, because changes in density and rarity come before all generation

and corruption, and because the latter is obnoxious to the heavens, that density and rarity cannot

be the underlying cause of the generation of lux and color.56 Furthermore, he argues that density

and rarity never cause a change in the species of color, but merely its intensity.57 In many

important respects, then, compared to Zabarella Aguilonius endorses the opposite opinion to

many key positions on the nature of light and color, while nevertheless remaining within the

scholastic framework.

§ 5.3: The Clarity and Color of the Crystalline Humor and Retina in the Seventeenth Century

In important ways, from Ibn al-Haytham onwards the notion that the crystalline humor must

have just the right amount of density to allow species fixing defined medieval and renaissance

visual theory. The sensitive part of the eye needed to be transparent enough to accept color and

illumination, but just dense enough to retain and fix the images of light and color propagating

forth from the bodies under our vision. (See §§ 1.3, 4.3, 4.4.) Species-fixing was a property that,

at least for Zabarella, Fabricius, and their followers, arose from the material composition of the

crystalline humor, arising from the condensation of the watery crystalline humor, and was

310

56 Aguilón, Opticorum libri sex, 422.57 Ibid., 35.

unaffected by the powers of the sensitive soul. Although this density was imposed upon the

humor by Nature for the sake of sensation, this species-fixing property nevertheless existed

separately from the sensitive soul and was thus observable upon dissection. This description of

the crystalline humor carries along with it a great many assumptions about the nature of light,

color, transparency, density and rarity, and their relationship. Providing a detailed picture of this

is a one of the primary purposes of my dissertation. It is perhaps surprising, then, that this

species-fixing property of the crystalline humor survived the transition to the retinal-centered

theory of vision, at least in the first half of the seventeenth century. This property was transposed

to the retina, and many descriptions, based upon dissection, that were characteristic of the

crystalline humor prior to the retinal theory were subsequently “seen” and described as

belonging to the retina. At the same time the species-fixing property vanished from the

crystalline humor, and accounts of the transparency of the crystalline humor — again based on

personal dissection — changed radically. Thus descriptions of what we would call the

translucency of the crystalline disappeared from anatomical works. The crystalline humor was

suddenly perfectly clear; the analogy to ice and hail was at times retained, but some authors said

explicitly that the analogy was to that of supremely clear ice, and not cloudy ice or snow-like

hail. The crystalline was still called the densest of the humors, but suddenly this density implied

only an increase in its refractive power. As we have seen, this distinction between various types

of thickening or condensation had a precedent in Fabricius (§ 4.4), but over the seventeenth

century there was an growing divide between what was meant by optical density or refraction

and what was meant by the thickness of a body which made it either more viscous, more solid, or

not easily divisible. Furthermore the meaning of density as “the quantity of matter in a given

311

volume” (with continual refinements in the meaning of “matter” up until Newton) was

increasingly appealed to. After a certain point, each of the notions above ceased to implicate the

other, and so the initial appropriation of the retinal theory by authors holding to more traditional

accounts of light, color, and sensation gives us an important clue concerning the retention of the

terms even while this conceptual divide took place. What was both seen and described underwent

some important transpositions, but at least at first — particularly, it seems, within the relatively

conservative medical community — the retinal theory was accommodated within a roughly

Aristotelian or Galeno-Aristotelian framework. Traditional authorities were not outright

rejected, but reinterpreted. I will look at the first influential adherents of the retinal theory of

vision, Christoph Scheiner (c. 1573–1650) and Vopiscus Fortunatus Plempius (or Plemp, 1601–

1671). Finally, I will look very briefly at Descartes’s treatment of the clarity of the humors for a

perspective from the mechanical philosophy. First, however, a look at Kepler’s account of the

humors is necessary.

Although he professes to have never seen a dissected eye himself, Kepler is not above

dispensing advice, and writes that “anatomists should consider the cause of the name” of the

aranea or web-like tunic, which he says applies to the both the crystalline covering as well as the

ciliary process, and thus the term aranea is apt because “the crystalline humor is suspended in

the center of the ciliary processes, by means of threads drawn inwards to the center on all

sides.”58 Kepler pays close attention to the shapes and sizes of the humors: he claims that the rear

of the crystalline humor is a “hyperbolic conoid,” that the front is spherical or spheroidal, and

that “the anterior roundness of the cornea and the crystalline humor [are] perceptibly similar,

312

58 Kepler, Optics, 178–179; Kepler, Paralipomena, 167.

their diameters being in a ratio of 4 to 3.”59 The crystalline humor, the most dense (densissmus)

of the three humors is simultaneously, and against the description of Jessenius, “perfectly

pellucid” (pellucidissimi). I cannot say where Kepler is getting his precise shapes and ratios, as

they are not to be found in his acknowledged sources, but the fact that the cornea and the

crystalline have different curvatures is found in Jessenius, and as was mentioned earlier this

contradicts the visual theory of Witelo and the perspectivists. In Fabricius we saw the first real

effort, with the possible exception of Galen, to base a theory of vision on skillful dissection and

meticulous observation of actual eyes: Fabricius the anatomist “hunts all things through

dissection” (see § 3.4). Kepler, on the other hand, never witnessed a dissection, and furthermore

he never performed the experiment in which an inverted picture is seen at the rear of a dissected

eye. He seems to have determined the mathematical structure of vision first, to have picked his

empirical evidence from among his anatomical authors to some extent, and to have assigned

shapes and properties to the humors a priori.

Fabricius’s approach to the problem of vision was mirrored most manifestly by Christoph

Scheiner. There are many differences between the approach to vision between the two authors,

and Scheiner says that he only read Fabricius’s De visione once he had begun both his

dissections of the eye and his analysis of vision based upon them. Nevertheless, Scheiner’s

project complements Fabricius’s, and we can see this in the advertisement in Scheiner’s title

itself: The Eye, that is, The Fundament of Optics in which, from the Accurate Anatomy of the Eye

313

59 Kepler, Optics, 179; Note that I have corrected Donahue’s translation here, as he renders “dimetientes” as “dimensions.” The original passage reads: “figuram accepit aut sphaericam, aut sphaeroidis lenticularis portionem, circumducta ellipsi, per axem divisa, manente recto latere: a posterior parte, quae ab iisdem ciliaribus processibus determinata, vitreo immergitur; figura ipsa est conoides hyperbolica, hyperbola circa axem circumducta. Sic enim Iessenius, non sphaericum esse, quod Platterus aiebat, sed valdè protuberare, & oblongum fieri, quasi in conum assurgat: anteriore verò vacie depressa esse rotunditate; & similes, ad sensum, esse, corneae, & crystallini humoris, rotunditatem anteriorem: dimetientes verò, ut 4 ad 3.” Kepler, Paralipomena, 167.

and from Recondite Experiences Painstakingly Performed...”60 and so on. To be sure, Scheiner’s

work is not an anatomical text. It is an optical treatise, although a truncated one in which most of

the typical topics treated in later books on optics are intentionally not pursued. He also performs

and emphasizes experimentation to a much greater degree than Fabricius. As an optical treatise it

has a different scope, character, and expected readership compared to an anatomical work like

Fabricius’s; the textual structure has only a loose correspondence to Fabricius’s Galenic one, and

the Galeno-Aristotelian goal of demonstrating knowledge about nature through final causes is

not emphasized. Nevertheless the approach of taking dissection as the starting point of

investigation, of determining the shapes and properties of the humors empirically, and of using

the eye that is revealed through dissection as the basis for both mathematical optics and a

philosophical treatment of vision, is the same.

The local context of Scheiner’s dissections, however, were quite different. As I have

argued, Fabricius’s dissections, both public and private, would typically have been performed in

the winter months in Padua, and from the point of view of modern science this led to visible

“cold cataracts” in the crystalline humor (See the images in § 4.3; also see the analysis in §§ 4.3–

4.7). For Fabricius, this visible “cloudiness” fit perfectly with a long textual tradition involving

both descriptions of the humor — its historia — as well as the properties deemed necessary for the

proper functioning of the eye — its actio and utilitas. Indeed, this material cloudiness was

necessary for species-fixing, which together with to the presence of a sensitive soul were the

314

60 The full title reads: Oculus hoc est: fundamentum opticum, in quo ex accurata oculi anatome, abstrasarum experientiarum sedula perstigatione, ex invisis specierum visibilium tam everso quam erecto situ spectatulis, nec-non solidis rationum momentis radiius visualis eruitur; sua visioni in oculo sedes decernitur; anguli visorii in genium aperitur; difficultates veteres, novae, innumerae experiuntur, abstrusa, obscura, curiosa plurima in medium proferuntur; plura depromendi occasio harum rerum studiosis datur: opus multorum votis diu expetiturm; philosophis omnibus, praesertim qui naturae vim in Medicina, Physica aut Mathesi addiscenda rimantur, neque inutile neque ingratum, imò necessarium futurum. (Oeniponti [Innsbruck]: Agricolum, 1619).

fundamental prerequisites for vision itself. Scheiner, on the other hand, not only adopted the

retinal theory of vision, but as a mathematician rather than a teacher of anatomy he wouldn’t

have been as likely to perform his dissections in the cold months. He could simply stop by the

butcher any time without regard for anual demonstrations or class schedules. As Paul Grendler

writes:

In the seventeenth century anatomical study continued to be essential to medical research and education. But the public anatomy, which Vesalius used so effectively to promote the new anatomy, diminished in importance and value ... [Seventeenth century] anatomical research was best done in an intimate private setting, far from the open and sometimes carnivalesque atmosphere of the public anatomy.61

It is possible, then, that Scheiner literally did not see what Fabricius would have seen, and thus

that the different contexts of their dissections yielded a different empirical basis for their

theories.

Scheiner’s descriptions of the crystalline and retina shows a transference of the species-

fixing property, and all (or at least most) of the attendent visible characteristics, from the

crystalline humor to the retina. Thus at a marginal note that reads “the retinal tunic is

diaphanous” we find the following.

All tunics apart from the sclera, uvea, and choroid are diaphanous: the cornea above all the rest, the retina less [than the rest], of which alone it is possible to doubt whether it is at all diaphanous; but this is manifestly proven by experience (experientia) and thenceforth deduced according to reason.62

315

61 Paul F. Grendler, The Universities of the Italian Renaissance (JHU Press, 2004), 341.62 Omnes Tunicae praeter Sclerodem, Uveam, & Choroidem sunt diaphanae: ultra mediocritatem Cornea, minus Retina, de quâ solâ dubium esse posset, an omninò pellucida esset; sed probatur manifestâ experientiâ & ratione inde deducta:” Scheiner, Oculus, 6.

The experience he points to is the fact that the tint from the choroid can be seen through the

retina: the bottom of the choroid can be seen in a bull to be blueish, and to be yellowish in cats.63

Scheiner’s description of the retina is in stark contrast to Fabricius, who writes that the retina is

not sensitive precisely because it is not diaphanous in the correct way.64

Of all the humors, Scheiner says, the crystalline is the most pellucid. Later in his treatise

he will determine the refractive power of the humors by experiment, and conclude that the

crystalline is most refractive as well. Thus the degree of transparency (or, to use his term, how

pellucid it is) here does not implicate refraction — transparency and refractive power have been

divorced from one another conceptually, and the latter must be analyzed carefully in a separate

experiment. As we have seen, according to previous writers the density of the crystalline resulted

in both refractive power as well as species-fixing; it was interpreted according to visual

inspection as a translucent white or “cloudiness” by many writers, including Zabarella and

Fabricius, and was experimentally shown by the fact that it gleams when exposed to light.

Recall, however, that Fabricius distinguishes between several kinds of condensation or

thickening: one kind results in the cloudiness or species-fixing property of the eye, and the other

a difference in refractive power (see § 4.4). However, it suits the retinal theory of vision for the

crystalline to refract species of light and color only, and Scheiner interprets its density in this

way alone, and ge also interprets references to the density of the crystalline by past authorities as

referring exclusively to its refractive power. This need not be interpreted cynically — i.e., that the

authors took what suited them best and were in opportunistic observers. There certainly was a

316

63 Presumably he is referring to a dissection of the eye from the front with the vitreous still in place and thus the retina as well; the choroid is indeed conspicuous in this case. He might also be referring to simply looking into the pupils of these animals, living or dead.64 Fabricius, De visione, 106.

degree of theory ladenness to the observations of all concerned (which should be distinguished

from opportunistic observation), but given the different conditions of dissection between

Zabarella and Fabricius on the one hand and Scheiner on the other it may well be a case of two

very careful sets of observations, but observations of different things due to differing local

conditions.

In his opening section on the anatomy of the eye Scheiner mentions that color and

opacity necessarily accompany one another: “color alone prohibits the flux of light, and only an

opaque body cannot be illuminated, from which it follows whatever is stained with color has less

transparency.”65 Later in his section on refraction he says that the “retinal tunic is smooth and

pellucid, therefore it admits rays into itself.”66 The uvea behind the retina is opaque so that “the

entry should very much be forbidden to light and species” and thus that light doesn’t reflect back

to the retina.67 The uvea also turns the eye into a dark chamber which, as is shown in the

experience of a camera obscura, is more suited to receive visible species of things. Furthermore,

the retina is “more opaque-white than diaphanous” in order to avoid drinking in the species of

the uvea itself. We see, then, the same issues found in many traditional perspectivist treatises, as

well as a concern with what happens to light after it passes through the semitransparent seat of

sensation that we saw in Fabricius and Zabarella— that is, the problem of seeing the interior of

one’s own eye . Scheiner gives the same or similar solutions as well, but with the parts

rearranged. He even gives a detailed account of refraction within the retina, his seat of sensation,

317

65 “lucis enim fluxum solus color prohibet, & solum corpus opacum illuminari nequid, unde quo quid colore tinctius est, hoc transparentiae minus habet.” Scheiner, Oculus, 7.66 “Tunica Retina laevis, & pellucida est, igitur radios in se admittit. Consequentia clara est.” Ibid., 70.67 “Uvea igitur tunica opaca est, ut luci & speciebus ingressum nimium interdicat sinumque intimum tenebricosum reddat:” Ibid., 7.

which can be read in some sense as a transference, to the retina, of the issues involved in the

refraction of rays in the crystalline humor found in crystalline-centered theories of vision.68

This transfer of the vision-causing qualities, that were once attributed to the crystalline

humor, to the retina, as well as a transformation of the accounts of the crystalline and the retina

as revealed through dissection, are seen perhaps more clearly in Vopiscus Fortunatus Plempius’s

Opthalmographia, sive tractatio de oculi fabricâ, actione, & usu, praeter vulgatas hactenus

philosophorum ac medicorum opiniones (Amsterdam 1632).69 His subtitle translates as “contrary

to the opinions of philosophers and physicians until now,” and indeed his is the first treatise in

the genre of anatomy (or medicine) to embrace a retinal theory of vision.70 Plempius studied in

Louvain, Leiden, as well as Padua, and at Padua his teacher was Adriaan van den Spiegel or

Spigelius, the successor to Fabricius in anatomy and Casserius in surgery. Plempius cites

Kepler’s Paralipomena many times throughout his work, particularly in his sections On Color,

On the True Manner of Vision, On the Office of the Retina, and On the Office of the Crystalline.71

He also uses the term pictura just as Kepler does. On the crystalline, which he says “all the

medical writers celebrate with encomia,” we read:

This humor is called crystalloid, or crystalline, or ice-like (glacialis); not because it is similar in every way to crystal or ice (indeed [it is] not [similar] in hardness), but because it is translucent or perspicuous. Avicenna likens it to a hailstone, where “hailstone” is not to be understood as those arriving white and snow-like,

318

68 Ibid., 70ff, 114ff.69 Vopiscus Fortunatus Plempius, Ophthalmographia, sive Tractatio de oculi fabrica, actione, & usu praeter vulgatas hactenus philosophorum ac medicorum opiniones. (Sumptibus Henrici Laurentii bibliopolae, 1632).70 Apart from Felix Platter, that is. However, Platter’s account provides no real justification for the action of the crystalline, which he thinks enlarges the visual image just like a magnifying glass. As Kepler recognizes, this betrays his ignorance of mathematical optics. By retinal theory of vision, then, I mean one that is tied to a mathematical account of image projection on the retina that would have been considered reasonably plausible at the time — essentially a post-Keplerian account.71 Plempius, Ophthalmographia, 88, 127, 172, 183 (respectively).

but transparent and frozen, as when in the summer they are accustomed to descend from our skys: and this [the crystalline humor] sufficiently recalls with accuracy.72

Plempius asserts that Avicenna meant not just any hailstones, but particularly transparent ones.

He also interprets the attribution of white or “alba” by past writers to the crystalline humor,

saying that “alba” is understood in two ways: in one sense it is a color, in another it is the

capacity to receive all colors. The “alba” of the crystalline only of the latter.73 In his discussion of

the use or office of the crystalline, he rejects all past medical writers on the topic and argues for

Kepler’s theory presented in the Paralipomena. At one point he singles out Fabricius’s account

of vision, where one purpose of the crystalline is to unite the rays of light behind it upon which

they cease and disappear. “To unite [light], indeed thus. However, to cease and stop, by no

means.”74

On the historia of the retina, Plempius writes “it is a soft, mucous-like white mixed with

red; opaque not diaphanous. Yet it participates to a certain extent in perspicuity, for the bottom of

the uvea shines through ... yet the best evidence testifies that it has much more opacity than

transparency.”75 He mentions that Fabricius says the retina is “opaque and corpulent,” and that

the utilitates of this is to prevent whatever light that doesn’t perish in the vitreous from

rebounding back to the crystalline. This opacity also disqualifies it as site of sensation according

319

72 “Vocatur humor hic crystalloides, & crystallinus, & glacialis; non quod omnifariam crystallo & glaciei similis sit, (non enim duritie) sed quod translucens sit seu perspicuus. Avicenna grandini aequiparat, ubi per grandinem, non illa alba & nivie intelligenda venit, sed transparens & glaciata, in aestate de nostrati caelo quando discendere solita: & hanc satis exactè refert.” Ibid., 44.73 Ibid., 45.74 Ibid., 184.75 Reliqua est ex tunicis ea, quae retiformis dicitur, officiosissima in oculo pars.” 40. “Est tunica mollis, mucosa, alba mixa rufedina, opaca non diaphana. participat tamen aliquatenus etiam perspicuitatem, nam uvea fundus per retinam tralucet: ad eum ferò modum, quo scriptae litterae per superimpositam tenuissimam scriptoriam chartam transparent. plus tamen multò opacitatis quam perluciditatis obtinere testatissimum.” Ibid., 40.

to Fabricius. Arguing against Fabricius on this point, Plempius says that according to Aristotle all

bodies participate in perspicuity.

In fact if you pursue the matter carefully, you will not be able to deny that an even greater and more impressed opaque will be affected by light. For the transparent transmits approaching lumen and allows it to escape; in the opaque however it [i.e., lumen] is fixed in it, and [lumen] thrusts out its strength into it. In just this way, therefore, lumen and the sparks of light (lucula) of objects going through the pupil pierce the humors of the eye until striking into the retina, and fixed in that very place exercise their operations.76

Although Plempius follows Kepler in many ways, including here using “lucula” or “sparks of

light” to refer to color, nevertheless he does not follow Kepler on the two-dimensional nature of

light and, consequently, does not adopt Kepler’s opinion that light is impressed on the two-

dimensional surface of the “opaque wall of the retina.” Rather, Plempius retains the traditional

explanation in which species of light and color are fixed in a body only if that body has the right

degree of transparency. For Plempius the degree of transparency ought to be much less, and the

opacity much more, than what Zabarella and Fabricius would have, yet the principle is

essentially the same, as is the notion that a completely transparent body is not suited to be the

seat of sensation.

Both Scheiner and Plempius accommodated the retinal theory within a more or less

scholastic Aristotelian framework for light and color. Scheiner’s account of light, color, and

320

76 “Quin si perpense rem agites, opacum magis atque impressius à luce affici non poteris diffiteri: quippe transparens allapsum lumen transmittit & finit elabi; in opaco autem figitur id ipsum, atque in eodem vires suas exerit. Similiter ergò, lumen & obiectorum visibiles luculae pupillam ingressae humores oculi trajiciunt, donec in retinam impingant, & ibidem fixae suam exerceant operationem.” Ibid., 173. Note that “lucula,” a diminutive form of lux, appears to be a term coined by Kepler, which Donahue translates as “sparks of light.” According to Kepler the degree of the “sparks of light” trapped in matter determines its color, and this color, entombed in matter, is activated and released when light reaches it. Thus “sparks of light” here probably refer to color. Kepler, Optics, 24 n. 26. Plempius uses “lucula” liberally, another indication of Kepler’s influence.

species has been treated elsewhere, so I will simply make some summary remarks.77 For

Scheiner, we do not see representations of pure light, nor are they phaenomina mere apparent

colors enclosed in air and caused by light mixed and altered in darkened media alone. We see

species of real colors.78 These species must show up in the body of some semi-transparent part of

the eye, and not merely at its surface. However, because his treatise is primarily a mathematical

work, Scheiner does not have much to say on the nature of color itself. Plempius, on the other

hand, has a long discussion of the nature of color, discussing Aristotle’s two “definitions” of

color in the manner of the scholastics. Here he cites Julius Caesaer Scaliger, the Jesuit Antonio

Rubio, and Aguilonius among others as attacking the notion that color is nothing other than

lumen, and he himself attacks the notion that the colors are tied to the primary qualities. He

writes “I think colors to be a certain proportion of the bright (lucidus) perspicuous and the

opaque within a body, painting the air with its species until causing vision,”79 and he has great

sympathy with Kepler’s definition of color as “light entombed in pellucid body.” He mentions

Zabarella’s statement that colors are generated from the from the condensation of the

perspicuous, and he reluctantly rejects a man of Zabarella station “because the empress truth

commands us to serve.”80 Since colors are a mixture of the diaphanous and the opaque, real or

“true” (veri) colors are seen when, e.g., white shows up as white regardless of the change in

illumination. Apparent or fantastical colors are seen when various changes in the incoming light

produce various colors. Plempius also has a quite lengthy discussion of visible species. In short,

321

77 Isabelle Pantin, “Simulachrum, Species, Forma, Imago: What Was Transported by Light into the Camera Obscura? Divergent Conceptions of Realism Revealed by Lexical Ambiguities at the Beginning of the Seventeenth Century,” Early Science and Medicine 13, no. 3 (January 1, 2008): 245–69.78 Scheiner, Oculus, 132–33.79 “Colorem esse puto certam perspicui lucidi & opaci proportionem corpori insitam, suâ specie pingentem aerem ad visionem faciendam.” Plempius, Ophthalmographia, 88.80 Ibid., 89.

Plempius gives an eclectic, but for the most part a scholastic Aristotelian account of light, color,

and species. He aims to incorporate some recent challenges — such as those put forth by Kepler

— within traditional accounts, but he does not adopt any coherent and systematic theory that

would fundamentally challenge the (still-dominant) scholastic opinions on light, color,

transparency, sensation, and so on. Thus he claims to adopt an Aristotelian theory of vision

— “vision is made, as Aristotle rightly [teaches], through the species and forms of things

received within [the eye]” — but this is an Aristotle as interpreted by Kepler.81 Plempius nowhere

mentions Kepler’s radical characterization of light as an essentially mathematical, two-

dimensional entity, and consequently that sensation ought to occur at the two-dimensional

interface at the wall of the retina. He presents Kepler’s ray analysis stripped of Kepler’s own

physics and metaphysics, and thus he retains all the scholastic issues and concerns with light, and

color that Kepler seems to have wished to discard.

Finally, a comparison with Descartes is in order. Descartes advocated the retinal theory of

vision in his Dioptrique, first published in French in 1537, prefaced by the Discourse on Method

and followed by his Geometry and Meteorology.82 Descartes is usually posited as one of the

primary advocates of the retinal theory of vision and a major reason for its acceptance.

Consequently, the retinal theory of vision is commonly thought of as a mechanical theory of

vision, or else deeply connected with the mechanization of nature. For example, Stephen Straker,

322

81 “Igitur visio fit, ut rectè Aristoteles, per species rerumque formas intus susceptas. At verò non est hic, quod plerique solent, ignavius subsistentdum; perquirendum porrò est, ubi illae formae recipiantur seu in quà pare, & potissimùm quànam id fiat ratione. Hoc negotio tam laudabiliter perfunctus est Clarissimus Joannes Keplerius, ut non tantùm supra omnes sese antecedentes existat, sed posterius etiam omnem magis accurandi spem sustulisee videatur.” Ibid., 127.82 René Descartes, Discours de la methode pour bien conduire sa raison, & chercher la verite dans les sciences. Plus la dioptrique. Les meteores. Et la geometrie. Qui sont des essais de cete methode (de l’imprimerie de Ian Maire, 1637). Throughout I quote the translation by Paul Olscamp.

in his highly influential PhD dissertation, says of Kepler’s theory of vision: “Briefly, it is the first

large step toward that mechanization of light and vision which would soon capture the

imagination of Descartes and emerge as the dominant natural philosophy of the 17th century.”83

As I have been arguing, Kepler’s work appears as such only after the fact, and if only the

traditional cast of Scientific Revolutionaries are examined in any detail. Most of Kepler’s

readers, before Descartes, did not adopt Kepler’s approach to the mathematization nature, much

less his “mechanization of nature,” which in any case does not seem to be applicable to Kepler.

But Descartes did take up Kepler’s approach to the mathematization of light and vision and,

indeed, applied it to a true mechanization of light and vision. Although it is generally assumed to

be the case, whether Descartes was in fact a decisive reason for the eventual dominance of the

retinal theory is an open question, and little work has

been done to trace the precise contours of the history of

the retinal theory in the first half of the seventeenth

century. The literature on Descartes is vast, and so I will

only point out his characterization of the humors and

tunics, hitherto considered to be of little importance

because they were unimportant for Descartes.

In the first book of his Dioptrique Descartes

explains why he begins with light before treating the eye

— indicating that his readers would have expected the

reverse order found both in traditional Perspectivist

323

83 Stephen Straker, “Kepler’s Optics: A Study in the Development of Seventeenth-Century Natural Philosophy” (PhD Dissertation, Indiana University, 1970), 37-8.

Figure 5.3: Descarte’s first image of the eye in the Dioptrique. Descartes, Dioptrique, 26.

works as well as discussions of vision in anatomical treatises. Famously, after introducing his

blind figure who “sees” by feeling ahead with a stick, Descartes says

I would have you consider light as nothing else, in bodies that we call luminous, than a certain movement or action, very rapid and very lively, which passes toward our eyes through the medium of the air and other transparent bodies, in the same manner that the movement or resistance of the bodies that this blind man encounters is transmitted to his hand through the medium of his stick.84

We see when bodies “receive light and reflect it against our eyes.” Descartes then treats

refraction in the second book, including his famous derivation of the sine law of refraction on the

assumption that the impulse of light travels slower in a looser body (i.e., a rarer material) than in

a hard body (a denser material).85 On the parts of the eye (see figure 5.3), Descartes writes:

ZH is the optic nerve, which is composed of a great number of small fibers whose extremities are extended throughout the space GHI where, mingling with an infinity of small veins and arteries, they compose a sort of extremely tender and delicate flesh, which is like a third membrane that covers the entire inside of the second.86

Furthermore, after describing how to turn the eye of an ox into a mini camera obscura, Descartes

mentions that “you cannot doubt that an entirely similar one is formed in the eye of a live man ...

and even that it is formed much better there, because its humors, being full of spirits, are more

transparent and have more exactly the shape which is requisite to this effect.”87 The crystalline

humor “causes almost the same refraction as glass or crystal” while the other two humors refract

324

84 René Descartes, Discourse on Method, Optics, Geometry, and Meteorology, trans. Paul J. Olscamp (Indianapolis, IN: The Bobbs-Merrill Company, 1965), 67.85 A. I. Sabra, Theories of Light, from Descartes to Newton (CUP Archive, 1981). Descartes’s theory of refraction in the context of seventeenth century kinematic theory of light can be found in Alan E. Shapiro, “Kinematic Optics: A Study of the Wave Theory of Light in the Seventeenth Century,” Archive for History of Exact Sciences 11, no. 2/3 (December 31, 1973): 140.86 Descartes, Discourse, 84.87 Ibid., 97.

light less, approximately as much as ordinary water.88 He says that the ciliary process is

completely black and “seems to be like a small muscle which can contract and enlarge” thus

changing the shape of the crystalline humor so that we can focus on things closer or further

away.89 He describes how the pupil can enlarge or contract, and how the muscles of the eye cause

the eye to rotate in its orb. Then he writes: “I purposely omit many other details which can be

observed about this matter, and with which the anatomists swell their books. For I believe that

those I have presented here will suffice in order to explain everything relevant to my subject, and

that the others which I could add, while in no wise improving your understanding, would only

serve to divert your attention.”90 This is about as far from Fabricius’s project to meticulously

account for the fabric, activity, and purpose of every sensible part of the eye, a project founded

on the Galeno-Aristotelian conviction that nature does nothing in vain. Descartes’s treatise is not

aimed to understand Nature’s works in every minute detail, but to strip that which needs

accounting for to a minimum. The colors, complexions, and intricate relationships between most

of the parts of the eye are not purposeful creations whose secrets can be unlocked though skill,

observation, experience, and reasoning. They are distractions. Shape, size, refractive power, and

the rectilinear impulses of light are all that need to be comprehended.

§ 5.4: Some Revisions to the Historiography of Seventeenth-Century Vision and Sensation

There is still a great deal of confusion surrounding the many important changes to accounts of

color, vision, and sensation in general in the seventeenth century. I illustrate this with a critique

325

88 Ibid., 84. 89 Ibid., 85.90 Ibid., 86.

of a major, recently published work in the history and philosophy of science, Ofer Gal and Raz

Chen-Morris’s Baroque Science.91 My critique is not of their account per se, but only insofar as

they recapitulate a number of misreadings of seventeenth century sources that are typical of

scholarship in the history and philosophy of science. I restrict my analysis to their first chapter,

titled “Science’s Disappearing Observer: Baroque Optics and the Enlightenment of Vision.” This

chapter is an expanded version of an article of the same name in The Journal of the History of

Ideas three years prior.92 In the account they give in the book, therefore, they had the potential to

respond to questions and concerns put forth by scholars in the intervening period; to the extent

that any problems persist I consider such misapprehensions to reflect those within the history and

philosophy of science in general.

Their first chapter undergirds many of their arguments later in the book. As they

succinctly conclude, in chapter one they attempt to show:

The naturalization of vision led to the estrangement of nature. Confidence in images from the very far away cast fundamental doubt on our sense of the immediate. Scientific observation entailed the disappearance of the observer. This is the optical paradox that Kepler’s “enlightenment” of optics created and that Descartes’ skepticism articulated as the fundamental epistemological conundrum of the Baroque.93

As usual, Kepler stands alone at the head of many important seventeenth-century

transformations, but in their analysis only Francesco Maurolico (1494– 1575) stands between

Kepler and the medieval Perspectivists of Alhazen, Pechan, and Witelo. (Note, however, that his

work Photismi de lumine et umbra was only published in 1611.) Like Lindberg and Crombie,

326

91 Ofer Gal and Raz Chen-Morris, Baroque Science (University of Chicago Press, 2013).92 Ofer Gal and Raz Chen-Morris, “Baroque Optics and the Disappearance of the Observer: From Kepler’s Optics to Descartes’ Doubt,” Journal of the History of Ideas 71, no. 2 (April 1, 2010): 191–217.93 Gal and Chen-Morris, Baroque Science, 51.

then, the focus is on sixteenth century mathematicians, and physicians and natural philosophers

are not in the picture. On Gal and Chen-Morris’s account, the inaccessibility of the Aristotelian

heavens created an “epistemological rift” which Kepler bridged through a “new agent,” light.

It was light that created images, bouncing off ‘‘an opaque medium’’ and falling on an ‘‘opaque screen.’’ If the screen happened to be the eye, ‘‘vision is produced,’’ but there was nothing unique to the eye: any screen would do.

With light as the sole agent of all optical phenomena, there is no fundamental epistemological difficulty with observing the distant celestial phenomena.... And with light, there is no epistemological difficulty with artificosa observationes.94

Gal and Chen-Morris, however, do not give an account of the objects of vision before Kepler. As

we have seen, most authors considered them to be either color alone or else both light and color .

Typical of most accounts, because they fail to contrast Kepler with his contemporaries what is

supposed to be new about Kepler’s “new agent” is not well articulated. They stress that light is

essentially mathematical according to Kepler, but why this should bridge the “epistemological

rift” between the heavens and the earth better than an account using species of light and color is

not explained. Species of color, as we have seen, were believed to behave mathematically, they

just weren’t essentially mathematical entities. In line with mechanization of nature narratives

(exemplified for Keper’s optics by Straker), they claim that “Light optics dissolved the

dichotomy between instrument and eye, between mediated and direct observation, and set the

stage for a new type of observation”.95 But as we have seen, no such dichotomies existed in

Zabarella and Fabricius, at the very least. Gal and Chen-Morris point out that, prior to Kepler,

vision was essentially teleological, and that this teleology was characterized by the use of visual

species. For support, however, they cite Leon Battista Alberti, Robert Grosseteste, and Roger

327

94 Ibid., 20. See also Gal and Chen-Morris, “Baroque Optics,” 196.95 Ibid., 20.

Bacon.96 Although Bacon, in particular, was highly influential, none of these authors typified the

understanding of vision and visual species during the middle ages, much less in Kepler’s day.

They write, “Visual rays guaranteed the veracity of vision, and the geometrical analysis of their

propagation was always subsidiary to the assumption of their intentionality and their consequent

indubitability.”97 But this fails to capture what was meant by intentional species, particularly in

the sixteenth century. As we have seen in Zabarella, the “intentionality” of species in the medium

indicates two things: that species have a diminished being compared to their cause, and that

intentional species turn our attention towards the cause of those species, the colors themselves. In

what sense are species “indubitable,” as they claim? For Zabarella (and many others), only in

two ways: that we cannot doubt that we do, indeed, perceive the sensations that we perceive; and

that those sensations have a cause that corresponds to these sensations in some formal or

representational aspect. However, this only applies to the proper objects of perception, which is

color in the case of vision, and furthermore there is nothing preventing species of color from

changing on their way to our eyes, leading to the possibility of mistaken judgments about the

color of a body. In both Zabarella and Fabricius, visual sensation is, moreover, an active

judgment made by the visual power in the eye: this act of judgment looks upon the tenuous and

physical effect of species of color in the crystalline humor, and from this creates a new entity, the

sensation itself. That is to say, Zabarella’s theory of sensation bottoms out at the notion of

representation: he takes as a foundational principle, without demonstration, that such

representation is possible, and that the visual faculty has the power to create a representation of

the soul of the colors present in the crystalline humor. But this by no means implies that the

328

96 Ibid., 21.97 Ibid., 22.

accuracy of sensations are somehow guaranteed, only that, under ideal conditions, accurate

sensations are possible. Moreover, such representation applies to the proper species of vision, the

visibility of color, which is an accidens proprium of a body with some specific ratio of density

and rarity. Even if we are perceiving under absolutely ideal conditions, all that is guaranteed is

that the ratio of density and rarity is represented, with a quite different manner of existence, in

the medium, and from this weak effect in the medium this ratio is once more represented, with an

entirely different manner of existence, in the sensitive soul. Sensations of shape, size, texture,

and number generally correspond to the things themselves, but these common sensibles do not

propagate their own species and therefore, according to Zabarella (and, it seems, Fabricius), their

veridicality is not grounded by the fundamental assumption that species, if unmolested, represent

their causes faithfully.98

Gal and Chen-Morris write that “most historians of optics have failed to notice the

essential difference between light and visual rays in the perspectivist tradition.”99 Just after this

they censure many historians who conflate “light” and “visual species.” However, the latter is

decidedly not the same thing as a visual ray, as Gal and Chen-Morris would have it; a visual ray

was a mathematical abstraction used for a geometrical analysis of vision, while a visual species

329

98 This idea that premodern people were somehow intimately and unproblematically connected to nature through the teleology of the senses is most forcefully and influentially put forth by E. A. Burtt, The Metaphysical Foundations of Modern Science, Revised Edition (Anchor, 1954). For before the seventeenth-century, “The world of nature existed that it might be known and enjoyed by man.” p. 20. This is connected to “the teleological position of Platonic and Aristotelian philosophy and expressed with meticulous precision in the scholastic dictum that the cause must adequate to the effect ‘either formally or eminently’ [...] When worked out in detail this means an essentially religious picture of the world...” p. 308. The wedge that separates us moderns from this picture of the world is the mathematization of nature, the mechanization of physics (and a metaphysics subservient to both), and especially the primary and secondary quality distinction, which is the distinction between “that in the world which is absolute, objective, immutable, and mathematical; and that which is relative, subjective, fluctuating, and sensible.” p. 83. Galileo’s introduction of the distinction in The Assayer “is a fundamental step toward that banishing of man from the great world of nature and his treatment as an effect of what happens in the latter...” p. 89.99 Gal and Chen-Morris, Baroque Optics, 23.

is the form or similitude of the object of vision present in a transparent medium. Again, the

object of vision was usually just color, but sometimes light and color. As we have seen (§§ 2.7–

2.8), lumen was considered to be the species of lux, and so it is no conflation to identify “light”

and “visual species.” (Although, if a modern scholar does identify light and visual species, they

should distinguish between lux and lumen and ask if, for the historical actor being examined, lux

is a proper sensible.) After quoting A. Mark Smith’s accurate assessment that “Alhacen and his

medieval Latin followers were far more concerned with making sense of sight than with

understanding light”100 they write:

But even Smith does not relate this difference to Kepler’s change of the role of light in optics (or to his interest in artificial observations). According to Alhacen, Smith claims, “we see things by means of the luminous color they radiate to the eye.” This is true, however, only for luminous objects, namely, when the “forms” carried from the object to the eye are properly of the light of the object itself: “sight does not occur unless something of the visible object comes from the object.” This “something” cannot be light, unless the visible object itself is luminous. It has to be an entity that is both indubitably authentic to the object and immediately transparent to the intellect: a “form.” [...] Light is not the agent of vision in Alhacen’s optics; not even the vision of light.101

This is a particularly instructive case of misunderstanding scholastic (including perspectivist)

concepts, one which however is not uncommon. Importantly, Gal and Chen-Morris also perform

a common move and jump from Alhacen directly to Kepler, as if the long proces of influence,

appropriation, and at times rejection of Ibn al-Haytham’s works and notions up to Kepler was

inconsequential. Surely, jumping six-hundred years from one great figure to the next cannot tell

us much about the causes of historical change. I am unsure of what they take “form” to mean

here, but most of Kepler’s contemporaries would have understood the “forms” of the objects of

330

100 A. Mark Smith, “What Is the History of Medieval Optics Really About?,” Proceedings of the American Philosophical Society 148, no. 2 (June 2004): 181.101 Gal and Chen-Morris, Baroque Optics, 23.

vision to be just some ratio of the color contraries bright/white to dark/black — again, most

scholastics in the sixteenth and early seventeenth century did not believe that species of the

substantial forms of things were either propagated or capable of being directly perceived.

According to Zabarella, who was not atypical in his distinctions here, the forms that we perceive

are forms of color; they exist materially in a body (color considered absolutely), they exist in the

medium (their visible species), and they exist in the sensitive soul (as sensations). The mode of

existence in all three is different, but what they have in common, assuming ideal viewing

conditions, is that they are all characterized by the same ratio of light and dark — i.e., the same

form. But we do not see the form of color itself, much less the form of a substance; rather we see

a color that has a form. In the act of sensation (again, for Zabarella at least, but many others as

well) the agent that causes this sensation is color that has been activated by lumen. Actually, the

agent is twofold for Zabarella and Fabricius: first, illuminated color (or light tinged with color

for Fabricius) at the surface of a body is the agent that causes color, along with all its attendant

modes such as shape, relative size, texture, etc, to show up in the eye and be present to the visual

faculty; second, the faculty of vision is the agent of sensation itself by making a judgment of this

image, and this latter act takes an image with a tenuous material existence in the crystalline

humor and, based upon it, creates a sensation in the sensitive soul.

One key issue, present in many histories of vision that deal with Kepler, is a failure to

give a historically relevant contrast to the Paralipomena, and this inevitably causes a

misunderstanding of the text. Thus Gal and Chen-Morris write: “Produced by light, images are

mere causal effects; stains of light that happened to bounce off an object and fall on a screen; no

331

forms or visual rays are involved.”102 Images, they say, are other than “mere causal effects” for

Alhacen and scholastic philosophers because of the “intentionality and teleology of vision.” But,

again making a common mistake, they appear to be conflating the intentionality of species of

light and color with the intentionality of “mental objects.” However, many scholastic authors

made sure to distinguish between the intentionality of visible species and the intentionality of

mental objects.103 Furthermore, we have seen that according to Fabricius species of light exist

independently of any observer, they travel rectilinearly from every point in a self-luminous or

illuminated surface, and only the bits that “happen” to end up entering the pupil are resolved into

a perception of the bodies they originated from. Fabricius was also far from the only one holding

such a view. Kepler himself writes the following about light: “What wonder, then, if that

principle of all adornment in the world, which the divine Moses introduced immediately on the

first day into barely created matter, as a sort of instrument of the Creator, for giving form and

growth to everything...” etc. Clearly Kepler understands light according to a strong, external

teleological framework, and this Neoplatonic Christian understanding of light is present

throughout his work. Because they don’t specify what they mean by “teleology” here Gal and

Chen-Morris don’t, in fact, tell us how Kepler is fundamentally different from his

contemporaries.

The consequences of this supposed lack of teleology in Kepler’s theory of vision are

many, they claim. “Visual errors are of course nothing new, but Kepler’s is a new concept of

error. In the Aristotelian paradigm, errors are created by the intervention of the human

332

102 Ibid., 24.103 A good treatment of this in late scholasticism is Alison Simmons, “Explaining Sense Perception: A Scholastic Challenge,” Philosophical Studies: An International Journal for Philosophy in the Analytic Tradition 73, no. 2/3 (March 1, 1994), especially 91–103.

imagination; the visual data are indubitable.”104 The first clause should read “may be created” in

order to be accurate. The second clause is entirely mistaken, as I just have shown. “For Pecham

and the tradition he represents, ‘the arrangement of the species [is] exactly as the objects [are

arranged] outside.’”105 Here they quote David C. Lindberg’s translation of Pecham’s Perspectiva,

though the italics are theirs.106 This is supposed to be in contrast with Kepler, for whom there is

always some small fuzziness in the resolution of picturae on the retina; this fuzziness is due to

the finite size of the pupil, which acts as the aperture in the camera obscura that is the eye.

Pecham’s original Latin (here from the 1592 Cologne edition) reads “Visionem fieri per hoc,

quod in glaciali est ordinatio speciei, sicut rei exterius.”107 Thus Gal and Chen-Morris are

hanging quite a bit on Pecham’s “sicut.” In fact, “exactly” seems to be a slightly misleading

translation by Lindberg. “Sicut” is better rendered by “just as” or “in the same way.” Pecham is

certainly not claiming here that vision is indubitable, and he is not grounding a belief in the

incapacity of the senses to err in some kind of teleology. Pecham is just saying that, at least for

distinct vision made according to the central visual cone, there isn’t a confusion of color in the

crystalline, and that an image appears on the crystalline that corresponds to the arrangement of

things outside. Just five propositions later Pecham speaks of the reception of oblique rays into

the eye, and these result peripheral vision, which is indeed indistinct; the role of these oblique

rays in Perspectivist works are often neglected by historians, and these rays certainly don’t create

an image of things “exactly” as they are outside.

333

104 Gal and Chen-Morris, Baroque Optics, 25105 Ibid., 25.106 John Peckham, John Pecham and the Science of Optics: Perspectiva Communis, ed. David C. Lindberg (University of Wisconsin Press, 1970), 121.107 John Peckham, Perspectivae Communis Libris Tres (Cologne: In officina Berkmannica, sumptibus Arnoldi Mylii, 1592), 14v, proposition 37.

It seems that, on Gal and Chen-Morris’s account of vision prior to Kepler, the visual

process was necessarily free from error. It consisted of “self-authenticating re-presentations of

objects,” and all errors in perception are the fault of the imagination. For Kepler, in contrast, “the

visual process furnishes the intellect with effects that have no inherent relation to their cause”.108

For support they cite the following from book 5 of his Paralipomena:

How this image or picture is joined together with the visual spirits that reside in the retina and in the nerve, and whether it is arraigned within by the spirits into the caverns of the cerebrum to the tribunal of the soul or of the visual faculty; whether the visual faculty, like a magistrate, given by the soul, descending from the headquarters of the cerebrum outside to the visual nerve itself and the retina, as to lower courts, might go forth to meet this image — this, I say, I leave to the natural philosophers to argue about.109

This passage is often cited to show that, for Kepler, it was a mystery as to how the intellect meets

the challenge of transforming picturae into sensations. For Gal and Chen-Morris, it marks “the

optical paradox: the naturalization of the eye estranges the observer, and a deeper understanding

of optics turns vision into a mystery.”110 A far more natural reading of this passage in the context

of the beginning of the seventeenth century is that Kepler is referencing a commonly disputed

question about how the visual faculty functions. On the one hand stand the perspectivists such as

Alhazen, Witelo, and Pecham, for whom the visual sensitivity actively intervenes in the

refraction the image at the vitreous so that it is sent, upright, through the optical foramen;

afterwords this image is carefully guided by the visual faculty through the twisting path of the

optical nerve until it reaches the common sense. (Perhaps there are others who hold a version of

this while denying the presence of the optical foramen, but I am not aware of them.) Others, such

334

108 Gal and Chen-Morris, Baroque Optics, 25.109 Ibid., 26. Quotation from Kepler, Optics, 180. Original at Kepler, Paralipomena, 167.110 Gal and Chen-Morris, Baroque Optics, 26.

as Zabarella and Fabricius, have the visual faculty act directly on the image that has shown up

and become fixed in the crystalline; it makes a judgment about this image in the eye due to the

connection between the aranea, retina, optical nerve, and ultimately the brain. For the

perspectivists and others who hold a somewhat more passive account of the visual faculty, the

visual image is arraigned, ushered back, and set before a tribunal; for Zabarella, Fabricius, and

many others, the visual image is perceived by a magistrate sent out to judge things for himself.

Kepler simply doesn’t care to argue.

This analysis of Kepler’s Paralipomena sets the stage for their later arguments, and I will

just briefly touch on their analysis of Descartes and the rainbow because it likewise reflects

misapprehensions among scholars. They contrast Descartes with Aristotle, and say that “color

makes sense to Aristotle only on the surfaces or ‘boundaries’ of solid bodies. The rainbow,

therefore, can neither be a property of the transparent air, nor can it be a property of light,

because light is not a body and has no boundaries”.111 Regardless of whether their analysis of

Aristotle is correct here, it is mistaken to determine what was novel in the seventeenth century by

comparing Descartes to Aristotle himself, rather than contemporary Aristotelians. They do briefly

mention Grosseteste from the thirteenth century, Themo Judei and Nicole Oresme from the

fourteenth century, Alessandro Piccolomini from the mid-sixteenth century, and finally Orazio

Grassi from the seventeenth. Citing Oresme’s account of light, they write:

For all these commentators, however, the relations between light as mathematically analyzable radiation and light as the enabler of vision — the transparency of the medium — remained completely mysterious: “lumen is ... the quality of the diaphanous medium through which illumination is made.” 112

335

111 Ibid., Baroque Optics, 35.112 Ibid., Baroque Optics, 37. The quote is from Nicole Oresme, Nicolai Oresme. Expositio Et Quaestiones in Aristotelis de Anima: Edition, Etude Critique (Louvain-la-Neuve: Peeters, 1995),

They may have picked a tricky passage in Oresme, and indeed deciphering the relationship

between light, transparency, color, and mathematical optics in some authors is no easy task, but

this hardly makes all discussion of the relationship between rays and light mysterious.113

Zabarella and Fabricius, not to mention Aguilonius and Scheiner, seemed to be able to integrate

light as mathematically analyzable and light as the enabler of vison within an Aristotelian

framework. Gal and Chen-Morris also cite a famous passage by Descartes concerning colors:

I cannot accept the distinction the Philosophers make between true colours and others which are only false or apparent. For because the entire true nature of colours consists only in their appearance, it seems to me to be a contradiction to say both that they are false and that they appear.114

Descartes’s French here has “fausses” for false, and thus Descartes is almost certainly attacking

the distinction between real and apparent colors as presented by the Jesuits, from whom he

received his education. Descartes’s argument would hardly seem formidable to Zabarella, who

might ask: what is the disposition in matter that reliably causes such appearances to arise, if not

color? Furthermore, Zabarella might add that apparent colors are not, contra Descartes,

themselves false, but merely situations in which a judgment can be false. Gal and Chen-Morris

interpret this passage as follows: “It is only in reference to an intelligent observer that colors,

images, and other optical phenomena can be either true or false. Otherwise, they are simply

causal effects. Yet if optics no longer studies epistemic processes but merely the transportation of

light and its effects, it has no place for such an observer.”115 As we have seen, Zabarella and

336

113 For one attempt to resolve such mysteries, see Tawrin Baker, “Color, Cosmos, Oculus: Vision, Color and the Eye in Jacopo Zabarella and Hieronymus Fabricius ab Aquapendente” (PhD dissertation, Indiana University, 2014).114 Gal and Chen-Morris, Baroque Optics, 42. Quotation from René Descartes, Descartes: The World and Other Writings, ed. Stephen Gaukroger (Cambridge University Press, 1998), 91.115 Gal and Chen-Morris, Baroque Optics, 42.

Fabricius would agree with the first two sentences (provided “intelligent” is replaced with

“sensitive”). As for the last sentence, I fail to see why one can’t study both — and indeed

Zabarella, Fabricius, Kepler, and Descartes are all concerned with light and its effects as well as

the observer. Traditionally, however, optics just meant how vision takes place, so naturally vision

itself was at the center of the treatise. This changed in the seventeenth century, to be sure, and the

observer did seem to disappear from works titled “optics.” Nevertheless, there were many

popular treatises on burning mirrors in the Middle Ages and Renaissance that applied a

geometrical analyses of rays to light without reference to an observer. Furthermore, even after

this seventeenth-century shift in the scope of treatises with the label “optics,” works on vision,

primarily written by physicians who were interested in understanding the role of the eye and the

physiology of vision with respect to the observer, continued apace. They aren’t, however, well

studied at this point. Although most such treatises failed to contain important new mathematical

theorems or proofs, physicians nevertheless relied upon a mathematical analysis of light and

color in order to understand how vision works. This tradition, rather than the tradition

exemplified by Isaac Barrow’s Lectiones opticae, leads to Hermann von Helmholtz’s Treatise on

Physiological Optics, an extraordinarily important work in the history of science. This work

begins with a somewhat traditional structure: the anatomy of the eye, followed by physiological

optics that includes a meticulous account of the dioptrics of the eye, and so on.116 Gal and Chen-

Morris point to important changes to the scope of various genres of scientific writing. Rather

than a case of the disappearance of the observer in optics tout court, I suggest that optics

337

116 Printed together as Hermann von Helmholtz, Handbuch der physiologischen Optik (Voss, 1910). The first volume was published in 1876 in Leipzig.

bifurcated in the seventeenth century: what was once treated by a single author in a single work

became separate subjects treated by authors in different disciplines.

Gal and Chen-Morris point to Descartes’s famous image of a man looking at the pictures

cast upon the retina of an ox. They write:

The observer has disappeared from optics, but not the eye. Detached from the viewer, it is now reabsorbed into the mechanistic account and the empirical inquiry. But it is no longer the end of the visual process, merely an arbitrary point of reference, an unprivileged station in the natural process; “the eye of a newly deceased man, or, for want of this, of an ox or some other large animal” tells us as much about its operations as a living human eye could. This is already a clear rejection of Aristotle’s position that the eye must be a part of the visual process in order to be an eye.117

Why, then, doesn’t the observer disappear with Zabarella and Fabricius, for whom a dead eye

tells us as much about its operations as a living one as Descartes’s dead eye does? Indeed, they

appear to be the first to give a theory of vision in which it is unambiguously the case that the

visual faculty does not affect the propagation of rays within the eye. Why doesn’t the observer

disappear with Scheiner an Plempius, who performed these observations of the retinal image as

well but appropriated the results within an Aristotelian theory of vision? Surely, even Descartes

— who denied the existence of souls in animals — would agree that the eye of a dead ox does not

“see” in the same way as one connected to a living ox, nor that a detached eye is all that needs to

be investigated in order to understand vision in brute animals. Gal and Chen-Morris do not give

us any clear reason why Descartes’s experiment or the conclusions he draws from them differs

from the Aristotelians I have mentioned, at least with respect to the “disappearance of the

observer.”

338

117 Gal and Chen-Morris, Baroque Optics, 49.

§ 5.5: Conclusion

My analysis strongly suggests that the retinal theory of vision presented no insurmountable

problems for its adoption within some forms of Aristotelianism. Kepler’s idiosyncratic physics

and metaphysics of light, as well as certain ad-hoc assumptions about the anatomy of the eye and

how the reddish or bluish color of the retina is perfectly suited to project picturae upon, would

have suggested a host of problems to his contemporaries. Kepler’s work was revolutionary in

many senses, most of which have been thoroughly treated by scholars already and which I have

thus largely avoided. Although his Paralipomena certainly contributed to the mathematization of

nature in some sense, his scheme for vision wasn’t always interpreted as mathematizing nature in

the strong sense: as we saw with Scheiner and Plempius, one could certainly adopt Kepler’s

mathematical optics without believing that light and color were essentially mathematical.

Furthermore, as we have seen, the retinal theory of vision was not necessarily better suited to a

mechanical or corpuscular account of light and color than any of the scholastic Aristotelianisms

present at the beginning of the seventeenth-century. Historically, after Kepler the retinal theory of

vision was first adopted as an Aristotelian theory of vison. To understand the rise and eventual

dominance of the mechanical conception of light, color, and sensation we must look elsewhere.

339

Conclusion

For the causes and essences of color are as disputed, and obscure to the intellect, as they are themselves manifest to sight.1

§ 6.1: Summary

The general neglect of the history of color prior to Newton is a notable lacuna in the history of

science. More specifically, the lack of good analyses of physical color theory before the

seventeenth century has produced much confusion in the history of vision. Its neglect is

surprising. Color, according to Aristotle, is what we see, and the many and varied Aristotelian

accounts of vision that dominated natural philosophy in the late Middle Ages and Renaissance

addressed and debated vigorously the issue of what color was in itself, what species of color are,

and how these relate to visual sensation. As we have seen, major shifts in terminology compared

to today frustrates the task of analyzing scholastic theories of color, and the quite foreign, at least

to modern sensibilities, approach to color within this framework makes presenting a history of

physical color no easy task. I have only addressed one strand in the natural philosophy tradition.

Other strands, most importantly the color theory that takes the De coloribus account for granted

and ties color to the elements, accounts by Jesuit mathematicians and philosophers, the color

theory (or theories) of physicians, and further analyses of color within the alchemical

tradition are all needed.

The failure to properly integrate the histories of natural philosophy, medicine, and

mathematics has resulted in some significant distortion and omissions in the current

340

1 “Sunt enim causae, atque essentiae tam controversae, atque obscurae intellectui, quàm sunt ipsi visui manifesti.” Julius Caesar Scaliger, Exotericarum exercitationum liber quintus decimus, de subtilitate, ad Hieronymum Cardanum (ex officina typographica Michaelis Vascosani, 1557), 434v. Exercit. 325.

historiography of visual theory. By examining the visual theory of Zabarella and Fabricius in

detail — figures who were greatly attuned to all three traditions themselves — I hope to have

given a clearer and more detailed account of the concerns, problems, and developments related to

vision in the early modern period. Previous scholars looking at either Zabarella or Fabricius from

the separate points of view of the history of medicine, the history of science, or the history of

philosophy have not given their works on vision a proper assessment. This dissertation has tried

to bridge this gap between current disciplines within history, at least to some degree.

The achievements of Zabarella and Fabricius were several. Zabarella tackled vision from

within natural philosophy, which for him included an account of the nature and origin of color,

transparency, light, and visual sensation. Before him, discussions of color were often dispersed

across a number of different commentaries. Using the genre of the natural philosophy textbook,

which rose in prominence throughout the sixteenth and seventeenth centuries, Zabarella was able

to consolidate the scattered accounts of a huge number of past authors and come up with perhaps

the most complete and consistent account of color in the scholastic tradition. He endorses what I

have called the condensation theory of the origin of color. He was a natural philosopher at the

most prestigious medical school in Europe, and his engagement with medicine and, especially,

anatomy is a striking feature of his work. He uses up-to-date anatomical evidence of the eye to

adjudicate between past philosophers on the nature of light and color, to attack Galen on how

vision works, and to formulate (together with Fabricius, I argue) a new theory of vision.

Fabricius was a physician and anatomist writing in a new genre, that of philosophical

anatomy. His De visione incorporates, for the first time since antiquity, the concerns of the

anatomist, the natural philosopher, and the mathematician, but he does so in a far more thorough

manner than his model, Galen. Indeed, his treatment of vision was explicitly undertaken to

341

surpass that famous ancient follower of Aristotle. Although Fabricius can’t be considered a

mathematician himself, his researches were in part intended to provid the mathematician with

accurate models of the eye, complete with determinations of the shapes, sizes, centers of

curvature, and relative optical densities of the main humors and tunics responsible for the

refraction of rays within the eye. His, and to a lesser extent Zabarella’s, insistence that the eye of

the mathematician, the eye of the natural philosopher, and the eye of the physician were all one

and the same, and that this eye can only be revealed through a meticulous and skillful dissection

of the eye along with a careful assessment of every sensible characteristic of every part within,

marks a major turning point in the history of vision. It also has important ramifications for the

understanding of some important changes to science in the seventeenth century.

Their shared theory of vision was notable for the lack of interference by the sensitive

soul. Insofar as the refraction of rays was concerned, the eye was a dead eye, and thus dissection

yielded up the secrets of both its action and the purpose of its various parts — that is, the final

cause or the for-the-sake-of account of the parts. This theory of vision also strikingly placed a

burning lens in the eye, an instance of an artificial instrument being used to understand a natural

part. This burning lens was needed to ensure that what one sees is not marred by the reflection of

light at the retina, and thus to avoid the subsequent problem that we would always see the

interior of our eyes overlaid upon the images coming from outside. According to them, the

crystalline humor strongly refracts light into a point within the capacious vitreous humor,

causing the light to collide, dissipate, and disappear, but the burning action of this lens has no

purchase due to the watery complexion of the vitreous humor and the rest of the parts of the eye.

In accounting for how vision works, they say, Galen and every other writer since has failed both

342

to observe the eye carefully enough and to account in sufficient detail for the purpose of every

sensible quality of every part of the eye. Nature does nothing in vain, after all.

Through Fabricius’s student Johannes Jessenius, this theory of vision, and especially the

characterization of the size, shape, and relative densities of the parts of the eye, influenced

Kepler. The standard story has it that developments in sixteenth-century anatomy did not

contribute in a major way to Kepler’s theory of vision, but this is false. The visual theory of

Zabarella and Fabricius was also taken up by Aguilonius, whose mammoth work in mathematical

optics played a major role in Jesuit mathematical education and visual understanding, at the very

least. Fabricius’s approach to the problem of vision — hunting all things through dissection — was

mirrored by Christoph Scheiner in his Oculus, one of the first works to endorse a retinal theory of

vision after Kepler. The other major work to endorse the retinal theory before Descartes’s

Dioptrique of 1637 was Plempius’s Opthalmographia of 1632. Plempius analyzes and rejects the

characteristic feature of Zabarella’s and Fabricius’s theory, the presence of a burning lens that

causes light to self-annihilate in the vitreous. Nevertheless, Plempius’s treatise was a hybrid

anatomical-medical-philosophical work, and his approach overall to the problem of vision was

consonant with Fabricius’s. In contrast Kepler, while taking his anatomical information from the

best sources he could find, did not feel compelled to perform or witness dissections himself. His

approach to the problem of vision in some ways follows that of the mathematical perspectivists:

one first arrives at a mathematical solution to the problem of visual rays and image formation,

and afterwards constructs an eye that achieves this goal.

In the first part of the seventeenth century Kepler’s theory of vision was slow to take

hold, and indeed Scheiner and Plempius, the first figures to endorse the retinal theory, did so

without also adopting Kepler’s metaphysics of light or his characterization of how this

343

essentially mathematical, two-dimensional entity that is light interacts at the two-dimensional,

opaque wall of the retina. That Kepler’s version of the retinal theory did not have notable

adherents: he asked his readers to abandon too much of what they understood about light, color,

transparent bodies, and sensation. Furthermore, apart from the persuasive power of his

mathematical demonstrations, the physical and metaphysical foundation for his arguments would

have left much to be desired by his contemporaries. It is perhaps no accident, then, that the

retinal theory of vision gained its first adherents and was presented to a wide audience only after

it was appropriated and made serviceable within the more or less Aristotelian theories of vision

of Scheiner and Plempius. However, this dissertation has only scratched the surface of the

reception of the retinal theory of vision in the seventeenth century, and much more work needs to

be done to understand it fully.

Nevertheless, while Aristotelian retinal theory of vision seems to have been short lived, it

marks the end of a very long history of what I call the property of species-fixing. This property

came about due to Ibn al-Haytham’s reversal of Ptolemy’s visual cone. Ibn al-Haytham took

Ptolemy as his model, but he reversed Ptolemy’s Stoic-influenced extramission theory of vision

and appropriated aspects of it into his Aristotelian-influenced intromission theory of vision. In

making this reversal Ibn al-Haytham also took the properties that Ptolemy believed visible

objects must possess in order to be seen and applied those properties to the thing we see with.

For Ptolemy, to see a body it must be both illuminated and have a certain amount of density so

that the visual rays encounter some resistance and don’t penetrate completely through without

effect. For Ibn al-Haytham, the crystalline humor must have a certain degree of density so that

the forms of light and color are delayed and fixed there rather than passing completely through

without effect. This description of the crystalline humor as delaying and fixing the species of

344

light and color was central to the theories of vision in the perspectivist tradition. It also became,

for Zabarella and Fabricius, the essential material property of their theory of vision. A faculty of

vision in a living eye was of course needed, but without this species-fixing property to the

crystalline humor vision would not be possible, and in a sense all other observable parts and

properties of the eye are there to aid and facilitate the action of the species-fixing crystalline

humor. Notably, they both claim that this property is visible upon dissection, and in my own

anatomical recreations of some of their dissections and experiments, including the replication of

the temperature at which these dissections would typically take place in an anatomical theater in

the winter months, I have found that the crystalline humor does indeed show up as somewhat

dense, thickened, with parts that are a translucent white. In Scheiner and Plempius this species-

fixing property was attributed to the retina: it had some transparency, but also some density to it

in order to both admit as well as capture and fix the species of light and color within its

substance. The changing conditions of ocular dissection — notably, that Scheiner and Plempius

didn’t perform or witness their dissections of the eye at a public anatomical demonstration during

the winter — meant that they did not see this cloudiness of the crystalline humor. Thus they

described a completely transparent crystalline humor that refracts light and color without

interfering with it, which is the ideal situation for a retinal theory of vision. Finally, with

Descartes’s retinal theory of vision all of this anatomical detail and philosophical subtlety

becomes moot: the shapes, sizes, and refractive powers of the humors are all that is needed to

understand the mechanical interaction of impulses of light with our retinas.

§ 6.2: Color and Cosmos Revisited

345

I touched upon the rejection of scholastic color theory, Zabarella’s in particular, by corpuscular

and mechanical philosophers at the end of Chapter 2. However a few more remarks are

necessary, given that the adoption of the retinal theory of vision and the ascent of a mechanical

or corpuscular theory of light and color were, at least initially, separate affairs. Precisely how the

two are related throughout the seventeenth century — and they certainly are — is a complex topic

that is beyond the scope of this dissertation. The retinal theory per se does not appear to have

been a driving force behind the mechanization of nature or the mathematization of nature. On the

other hand, the demise of the condensation theory of the origin of color, which was perhaps the

dominant color theory in the sixteenth century, seems to be connected to the demise of the

Aristotelian cosmos. As we saw, the explicit reason for the adoption of the condensation theory

of the origin of color by Averroës, Zabarella, as well as many others is the need to account for the

visible difference in the heavens given that the celestial body is composed of single,

homogeneous, incorruptible substance. In the seventeenth century the main scholastic option

which did not invoke an Aristotelian cosmology was an account in which color is tied both to the

elements or the elemental qualities themselves and the substantial forms of things, and account

that the Jesuits seemed to have favored. Thus, it is worth examining the many Jesuit accounts of

color after the discoveries of Galileo, in particular. Along with this, it appears that the Jesuit

account of the real-apparent color distinction was the distinction refuted by Descartes, Boyle,

and other mechanical philosophers.

The mechanical account of the origin of color invariably took color in a body to be its

surface texture, and they almost always used the common examples of blowing bubbles and

grinding glass to refute scholastic theories of color — in particular the condensation theory of

346

color held by Zabarella and his followers. Yet Zabarella and other scholastics certainly had the

resources within their elaborate philosophical framework to answer the challenge of these

novatores, and indeed the prime examples used by corpuscular philosophers were well known to

them, being present in both Aristotle and Avicenna, among others. If we look to Robert Boyle we

can see the seventeenth-century pattern exemplified: the belief that color is modified light, that

what we call the color of bodies is just a texture, that there can be no distinction between color

arising from the juxtaposition of minute parts and the true, homogeneous color of a body, and

that there is no distinction between real and apparent colors. We can as well notice in Boyle a

curious inversion of the place given to the heavens and our connection to it. In his Experiments

Touching Colors, the literary experientia of bubbles and glass powder have made the transition

from a refutation of scholastic accounts of color to a starting point for an experimental history of

colors. After mentioning these two (it turns out) millennia-old examples, he then provides a

dynamic demonstration of the phenomena by which transparent substances give rise to white

ones, what Francis Bacon called a migratory instance.2 It is also a clear example of the

epistemological tactic identified by modern historians and philosophers of science as transdiction

or transduction — that is, the transference of macroscopic processes to the microscopic realm as a

means of explanation. Boyle describes mixing water and oil of turpentine in a glass. Individually

they are colorless. Agitating them, however, splits the oil into globules, and sufficient agitation

decreases the size of the oil drops until a whiteness akin to milk arises. Upon letting this liquid

rest for a time the tiny globules combine, the whiteness fades, and the transparency returns by

degrees. As the globules merge and grow into a size visible to the eye, the fact that each globule

347

2 Boyle’s dynamic experiments are easily seen as an elaboration and improvement of the examples of foam and ground glass producing whiteness that Bacon himself categorized as migratory instances in his Novum Organum, although first produced in his Valerius Terminus years earlier. Francis Bacon, Oxford Francis Bacon, vol. XI (London: Oxford University Press, 1996), 277.

behaves as a tiny mirror is revealed, and thus, for Boyle, it is proved experimentally that

whiteness is generated when two transparent bodies are intermixed such that a multitude of tiny

specula appear. Prefacing this experiment Boyle writes:

And here let me observe a thing that seems much to countenance the Notion I have been recommending: namely, that whereas divers parts of the Sky, and especially the Milky way, do to the naked Eye appear White, (as the name it self imports) yet the Galaxie look'd upon through the Telescope, does not shew White, but appears to be made up of a Vast multitude of Little Starrs; so that a Multitude of Lucid Bodies, if they be so Small that they cannot Singly or apart be discern'd by the Eye, and if they be sufficiently Thick set by one another, may by their confus'd beams appear to the Eye One White Body. And why is it not possible, that the like may be done, when a Multitude of Bright and Little Corpuscles being crowded together, are made to send together Vivid beams to the Eye, though they Shine but as the Planets by a Borrow'd Light?3

Those who held the condensation theory of color took for granted the incorruptibility of the

heavens and hung their theory of color and vision upon, what seemed to them, one of the most

lofty and secure branches in the tree of knowledge. Boyle reversed this picture. Instead of

fashioning an explanation of terrestrial color after an account of why certain parts of the heavens

are visible, Boyle reproduced the Milky Way in a glass.

348

3 Robert Boyle, Experiments and Considerations Touching Colors First Occasionally Written, Among Some Other Essays to a Friend, and Now Suffer’d to Come Abroad as the Beginning of an Experimental History of Colors. (London: Printed for Henry Herringman, 1664), 109-110

Appendix 1: Glossary

Albus – While also meaning white, albus can refer to something that is bright, transparent, or untainted with color. Use depends on author and context.

Density (Densitas)– Most of the time synonymous with thickness, crassness, corporeality, solidity, and intimately related to opacity in the sense below. Along with rarity this was usually considered to be the most fundamental of the second qualities, that is, the qualities apart from hot, cold, wet, and dry that are the consequence of those qualities (or perhaps consequent upon the elemental bodies themselves). For most of the authors looked at, densitas is probably best rendered as thickness. However, the precise meaning of thickness depends on the author, and this term changed radically with shifting conceptions of matter, space (particularly, whether void space was allowed), gravity, mechanics, and so on. Before the seventeenth century, this density or thickness usually accounted for the degree of refraction in a body, whether it was bright or dark, and whether it was colored or not (and perhaps what color it was). Transparent bodies were supposed to lack density, while elemental earth was supposed to be supremely dense.

Opaque (Opacus) – Throughout most of its history, the Latin term opacus meant shady or dark, and is probably best translated by the English work “murky” as in “a murky wood.” I primarily use the English term opaque and the Latin opacus in this sense, and not in the modern sense of blocking the direct passage of light. Lewis and Short give the following for opacus:

I. In the shade, shaded, shady; Transf. 1. Darkened as if by shades, dark, obscure (i.e., the earth, in the lower regions). 2. Bushy, thick (barba in Cat. 37) II. That gives or casts a shade, shady.”1

Lidell and Scott’s entry for the Greek word παχύς, from which opacus is derived, has: 1. thick, stout, Hom., Hes.:— later, stout, fat, Ar. 2. of things, thick, massive, Hom., Ar.:—adv. -έως, roughly, of stating or

arguing, Arist.; παχύτερον or -έρως, Plat.3. of liquids, thick, curdled, clotted, Il., Hdt.2

Only once we reach the seventeenth century is the modern sense represented in dictionaries. Thus Goclenius, in his 1613 Lexicon Philosophicum, gives:

349

1 Charlton Lewis et al., A Latin Dictionary (Oxford: Clarendon Press, 1933).2 Henry George Liddell, and Robert Scott, An Intermediate Greek-English Lexicon (New York: Harper and Brothers, 1896).

http://www.perseus.tufts.edu/hopper/morph?l=e%2Fws&la=greek&can=e%2Fws0&prior=pa%5Egh=nai

http://www.perseus.tufts.edu/hopper/morph?l=e%2Fws&la=greek&can=e%2Fws0&prior=pa%5Egh=nai

http://www.perseus.tufts.edu/hopper/morph?l=paxu%2Fteron&la=greek&can=paxu%2Fteron0&prior=e/ws

http://www.perseus.tufts.edu/hopper/morph?l=paxu%2Fteron&la=greek&can=paxu%2Fteron0&prior=e/ws

http://www.perseus.tufts.edu/hopper/morph?l=e%2Frws&la=greek&can=e%2Frws0&prior=paxu/teron

http://www.perseus.tufts.edu/hopper/morph?l=e%2Frws&la=greek&can=e%2Frws0&prior=paxu/teron

Opacum opponitur Transparenti. Estque quod radios non transmittit, qualis est terra. Scal.ex.80.s.1.sic. Est opacum, quod in umbra est, aut umbra ipsa apud Ciceronem, & illud, quod radios non transmittit.3

Rarity (Raritas) – Usually synonymous with subtlety, tenuity, thinness, and connected with some senses of spirituality (e.g., spirit of wine or alcohol, animal spirits). Along with density this was usually considered to be the most fundamental of the second qualities, that is, the qualities apart from hot, cold, wet, and dry that are the consequence of those qualities (or perhaps consequent upon the elemental bodies themselves). Intimately related to transparency. Aether, fire, air, and water were all thought to be rare (here listed in descending order of their degree of rarity).

Species Fixing – I use this to refer to the very specific properties that the crystalline humor, and later the retina, were though to possess in order for light and color to “show up” in the humor (or tunic) rather than pass through without effect. These properties arise from the precise level of condensation present in the humor or tunic.

Translucent – Literally, “allowing the passage of light.” Prior to the seventeenth century, at least, “translucent” did NOT have its current meaning, i.e., “Allowing the passage of light, yet diffusing it so as not to render bodies lying beyond clearly visible; semi-transparent.”4 Synonymous with diaphanous. An author may use translucent or transparent in order to emphasize whether light is being discussed or else sight.

Transparent – Literally, “allowing the passage of sight.” Synonymous with perspicuous.

350

3 Rudolph Goclenius, Lexicon Philosophicum (Becker, 1613).4 "translucent, adj.". OED Online. September 2014. Oxford University Press. http://www.oed.com/view/Entry/204868?redirectedFrom=translucent (accessed November 15, 2014).

Appendix 2: Translation Of Chapter 1 of Zabarella’s De visu1

IACOBI ZABARELLAEPATAVINI

DE VISV LIBRI DVO.Liber Primus.

The manner and division of what is to be said. Chapter I.

That vision is the most noble of all the senses, it is enough that everyone seems to agree that it is the most useful of all for grasping knowledge (scientia), and that it is likewise the most similar to the mind: because not only is [knowledge] able to be gathered from its operations, but also from it [knowledge is] most easily resolved. Regarding this [similarity] we are not in the habit to say the mind hears, or smells,

or tastes; nor are ears, or noses, or tongues ever attributed [to the mind] through transference (translatio); yet we say “the eyes of the mind” (oculi mentis) and “to inspect” (inspicere) on account of a similarity of action, and we are accustomed to say “to look at the mind” (videre mentem). Nature has also assigned to this sense the most beautiful instrument of the most skillfully wrought construction, and placed it in the highest part of the body from which it is able to lead the whole body to safety, and to better see into the distance. Moreover, there was great disagreement and celebrated controversy among the greatest of the philosophers — notably Aristotle, Plato, and Galen — who advanced thoroughly contradictory opinions concerning the action of this [sense]. Therefore we will presently speak about this faculty of the soul, whose worth is seen to be above all the rest, with zeal and industry; and we will relate its nature, and its manner of action will be most diligently scrutinized; and we will strive to show to all men those [opinions] which are stated by Aristotle both in De anima as well in the Parva naturalia. However, we divide our whole disputation into two parts: in one of which we will thus attempt to deliver Aristotle’s clear opinion on vision, so that it is understood as correctly as is possible; in the other however we will consider the opinion of Plato, which Galen has earnestly defended, and we will compare it with the thought of Aristotle, and the truth of Aristotle’s opinion will be demonstrated, and we will strive to vindicate it from the objections of Galen. However, concerning Aristotle’s thoughts (sententia) themselves that are to be shown, we will preserve this order: namely, since he himself judged that vision is made through [1] the action of the object [2] in the organ of vision [3] through a transparent medium, we will treat all these one by one, and we will resolve every one of the difficulties that arise, so that in the end we will understand, according to Aristotle, how vision takes place from the conjunction of those three. Therefore first the object, which is color, will be treated according to the instruction (praeceptio) of Aristotle, understanding the nature and generation of it, in order to better recognize why, and in what way the medium and the sensitive organ is affected by color.

Vision is similar to the intellect

351

1 Zabarella, Giacomo, De rebus naturalibus libri XXX (Venice: Paulus Meiettus, 1590), 600.

Appendix 3: Zabarella On the Nature and Generation of Color

352

Visibility• Defined in De anima• Visibility is a per se accident (in secundo modo dicendi per se) of a colored body; analogous to laugher in humans• It is a power to affect the visual faculty; i.e., it is relational• The surface of the body is generates these species• An illuminated surface, an illuminated medium, and a functioning eye are necessary for this power to exist in actuality

Absolute Color• Defined (with respect to sight) in De sensu• Exists in actuality both in the depths of a body and in the dark

Real Color Apparent Color• Mixture of visual species in the medium• Vision is not deceived (the appearances are not false) because these colors are truly received in the eye and have a definite cause• However, the faculty of judgment can be deceived about what the cause of our perception is• Sun at sunset appears red not because the sun itself is red, but due to the mixture of its white species with the dark, earthy fumes in the atmosphere

Arising in the Heavens• Formed without admixture of another body• The perspicuous is crowded together• This is not the same condensation that occurs, e.g., by squeezing a sponge.• The celestial substance is made dense, delimited, and able to terminate vision• The nature of the celestial body does not change due to this condensation• Celestial color is nothing but a shining white, which is called lux•Greater density results in more shining white• We gather that the moon is the least dense planet, because it is the most perspicuous and has the least innate lux

Arising in the Elements• The admixture of a dark body (admistio opaci) causes the perspicuous body to be crowded together (qua perspicuity, and not resulting in, e.g., increased specific gravity)• Fire, air, and water are perspicuous to varying degrees• Earth is entirely dark (opacus) because it lacks all perspicuity, i.e., it does not admit lumen at all• As various mixtures are made, so various colors are generated

Imperfect Mixture (Juxtaposition)• Combination without true (Aristotelian) mixture• Natures of the elements are preserved• Condensation of water or air gives rise to whiteness• However, unlike with the aether, some other dense material, i.e., one containing earth, must be commixed for this to take place• Condensation of fire gives rise to a shining white, or lux (though some earthy material needed for condensation to take place)• Flame is the exemplar for color by juxtaposition

Perfect (True) Mixture• Natures of the ingredients are changed (mutantur) into the nature of the mixt• Fire no longer shines because the being (esse) of the fire has ended• This mixt attains color, not splendor• Nevertheless, if the mixt is composed of much fire and little earth, some light can remain; this explains luminescent bodies such as cats’ eyes, fungi, rotting fish scales, etc.

x

354

Bibliography

Primary Sources

Aguilón, François de. Francisci Agvilonii e Societate Iesv opticorvm libri sex philosophis juxtà ac mathematicis utiles. Ex officina Plantiniana, 1613.

Alberti, Leon Battista. La pittura. Gabriel Giolito de Ferrari, 1547.

Albertus Magnus, Opera omnia. Edited by Petrus Jammy, 21 vols. Lyon: C. Prost, 1651.

———. Opera omnia. Edited by Augusti Borgnet, 38 vols. Paris: Vivès, 1890.

———. Philosophiae naturalis isagoge, Venice, 1514.

Alhazen and Witelo. Opticae thesaurus. Edited by Friedrich Risner. Basel, 1572.

Aristotle, and Averroës. Aristotelis de coelo; de generatione et corruptione; meteorologicorum; de plantis libri cum Averroës Cordubensis in variis eosdem comentariis. Vol. 5. Opera Omnia. Venice: Giunta, 1562.

Averroës. Libellus de substantia orbis ... expositus per Ioannem Baptistam Confalonerium. Eiusdem Io. Baptiste Confalonerii opuscula. Venice: in aedibus Francisci Bindoni & Maphei Pasini: sumptibus ac impensis Bernardini Benalii ac sociorum, 1525.

Averroës, and Marco Antonio Zimara. Averrois Cordubensis Sermo de substantia orbis: destructio destructionum philosophiae Algazelis; De animae beatudine, seu epistola de intellectu. M. Antonij Zimarae in sermonem de substantia orbis contradictionum solutiones. Venice: Giunta, 1562.

Avicena. Liber Canonis: De medicinis cordialibus  ; et Cantica. Edited by Benedetto Rinio. Basel: per Ioannes Heruagios, 1556.

Avicenna. Liber Quartus Naturalium: De Actionibus Et Passionibus Qualitatum Primarum. Brill, 1989.

Boyle, Robert. Experiments and Considerations Touching Colours First Occasionally Written, among Some Other Essays to a Friend, and Now Suffer’d to Come Abroad as the Beginning of an Experimental History of Colours. London: Printed for Henry Herringman, 1664.

Capodivacca, Girolamo. De methodo anatomica liber. Venice: apud Io. Baptistam Ciottum Senensem, 1593.

355

Carpi, Jacopo Berengario da, and Mondino. Carpi Commentaria cum additionibus super anatomia mundini vna cum textu eiusdem in pristinum et verum nitorem redacto. Bologna: Impressum per Hieronymum de Benedictis, 1521.

———. Isagoge breves perlucide ac uberime in anatomiam humani corporis, Bologna, 1520.

Casserius, Julius. Pentaestheseion, Hoc Est de Quinque Sensibus Liber. Venice, Apud Nicolaum Misserinum, 1609.

———. Tabulae anatomicae LXXIIX. Venice: Deuchinus, 1627.

Colombo, Realdo. De re anatomica libri XV. Venice: ex typographia Nicolai Builacquae, 1559.

Conimbricenses, and Aristotle. Commentarii Collegii Conimbricensis Societatis Iesu, in tres libros de anima Aristotelis Stagiritae. Cologne: Zetznerus, 1603.

Covarrubias, Franciscus Valles de. Controversiarum medicarum et philosophicarum libri decem. Frankfurt: Andreas Wechelus, 1582.

Descartes, René. Discours de la methode pour bien conduire sa raison, & chercher la verite dans les sciences. Plus la dioptrique. Les meteores. Et la geometrie. Qui sont des essais de cete methode. Leiden: Ian Maire, 1637.

Diels, Hermann, and Walther Kranz. Die Fragmente der Vorsokratiker, griechisch und deutsch. 3 vols. 7th ed. Berlin: Weidmann, 1954.

Fabricius ab Aquapendente, Hieronymus (Girolamo Fabrizi d’ Acquapendente). De visione, voce, auditu. Venice: per Franciscum Bolzettam, 1600.

———. De venarvm ostiolis. Padua: ex typographia Laurentij Pasquati, 1603.

———. Il grande teatro dei corpi: le pitture anatomiche di Girolamo Fabrici d’Acquapendente. Torino: UTET, 2011.

———. Opera omnia anatomica & physiologica: hactenus variis locis ac formis edita  : nunc verò certo ordine digesta, & in unum volumen redacta. sumptibus Johannis Friderici Gleditschii. Lugduni Batavorum, Apud J. van Kerckhem, 1738.

———. Pentateuchos Chirurgicum. Frankfurt, 1592.

Fallopio, Gabriele. Andreae Vesalii anatomicarum Gabrielis Falloppii observationum examen. Venice: apud Franciscis de Franciscis, 1564.

———. Observationes anatomicae. Paris: Bernard Turrisan, 1562.

356

Favaro, Antonio. Atti della Nazione Germanica artisti nello Studio di Padova. 2 vols. Venice, 1911.

Galenus, Claudius. Galeni Opera ex octaua Iuntarum editione. Quae, quid superioribus praestet, pagina versa ostendit. Ad amplissimum Venetorum medicorum Collegium: Galeni librorum septima classis curatiuam methodum tum diffuse tum breuiter descriptam, ... tractatum continet. Venice: Giunta, 1609.

Goclenius, Rudolph. Lexicon philosophicum. Frankfurt: Becker, 1613.

Gozzi, Niccolò Vito di. Commentaria in sermonem Aver.[roes] de substantia orbis et in propositiones de causis. Venice: Giunta, 1580.

Helmholtz, Hermann Ludwig Ferdinand von. Handbuch der physiologischen Optik. Hamburg: Voss, 1910.

———. Handbuch der physiologischen Optik. Allgemeine Encyclopädie der Physik, 9 vols. Leipzig: L. Voss, 1867.

Israeli, Ishaq ibn Sulaiman, and Constantino Africano. Omnia opera Ysaac in hoc volumine contenta... Lyon: in officina Ioannis de Platea, 1515.

Janduno, Johannes de, and Averroës. In libros Aristotelis De Coelo & Mundo quaestiones subtilissimae; quibus nuper consulto adiecimus Averrois sermonem de substantia orbis. apud Hieronymum Scotum, 1552.

Jessenius, Johannes. Iohannis Jessenii a Iessen, Anatomiae, Pragae, anno M.D.C. abs se solenniter administratae historia: accessit eiusdem de ossibus tractatus. Wittebergae: Excudebat Laurentius Seuberlich, impensis Samuelis Selfisch, 1601.

Kepler, Johannes. Ad Vitellionem paralipomena, quibus astronomiae pars optica traditur  ; potibimùm de artificiosa observatione et aestimatione diametrorum deliquiorumque Solis & Lunae. Cum exemplis insignium eclipsium. Habes hoc libro, lector, inter alia multa nova, Tractatum luculentum de modo visionis, et humorum oculi usu, contra opticos et anatomicos, authore Ioanne Keplero. Francofurti: apud Claudium Marnium & haeredes Ioannis Aubrii, 1604.

———. Dioptrice seu Demonstratio eorum quae visui & visibilibus propter conspicilla non ita pridem inventa accidunt: Praemissae Epistolae Galilaei de iis, quae post editionem Nuncii siderii ope Perspicilli, nova & admiranda in coelo deprehensa sunt. Item Examen praefationis Ioannis Penae Galli in Optica Euclidis, de usu Optices in philosophia. Augustae Vindelicorum: Typis Davidis Franci, 1611.

357

Magirus, Johann. Physica peripatetica ex Aristotele, eiusque interpretibus collecta, et in sex libros distincta: in usum Academiae Marpurgensis Studio & opera Johannis Magiri Doctoris Medici & Physiologiae. Frankfurt: Palthenius, 1597.

Massa, Nicolo. Liber introductorius anatomiae siue dissectionis corporis humani. Venice: in edibus Francisci Bindoni, ac Maphei Pasini, socios, 1536.

Nifo, Agostino. Commentationes in librum Averrois de substantia orbis, Venice:1508.

———. Commentationes in librum Averrois de substantia orbis quibus adjectus est locupletissimus index... Omnia multo quam antea emendatiora ac restituta non pauca. Venice: apud H. Scotum D. Amadei, 1546.

Oresme, Nicole. Nicolai Oresme. Expositio Et Quaestiones in Aristotelis de Anima: Edition, Etude Critique. Louvain-la-Neuve: Peeters, 1995.

Peckham, John. Ioannis Archiepiscopi Cantvariensis, Perspectivae commvnis libri tres: iam postremò correcti ac figuris illustrati. Cologne: Apud Haerades Arnoldi Birckmanni, 1580.

———. Perspectiua Joannis pisani anglici viri religiosi vulgo cõmunis appellata rationes visus in radiationibus ac lineis visualib[us]. atq[ue] speculares formas imagĩes ... Jn florentissimo gymnasio Liptzensi emendatum atq[ue] in figuris ... rectificata. Martinus Herbipolensis, 1504.

———. Perspectiva communis. Venice: per Jo. Baptistam Sessam., 1504.

———. Perspectiva communis. Edited by George Hartman. Nurenburg: apud Iohan. Petreium, 1542.

———. Perspectivae communis libris tres. Cologne: In officina Berkmannica, sumptibus Arnoldi Mylii, 1592.

Philoponus, John. On Aristotle’s “On the Soul 2.1-6.” Ancient Commentators on Aristotle. Ithaca, N.Y.: Cornell University Press, 2005.

———. On Aristotle’s “On the Soul 2.7-12.” Translated by William Charlton. Ancient Commentators on Aristotle. Ithaca, N.Y.: Cornell University Press, 2005.

Platter, Felix. De corporis humani structura et vsu. Basel: ex Officina Frobeniana, per Ambrosium Frob., 1583.

Plempius, Vopiscus Fortunatus. Ophthalmographia, sive Tractatio de oculi fabrica, actione, & usu praeter vulgatas hactenus philosophorum ac medicorum opiniones. Amseterdam: sumptibus Henrici Laurentii, 1632.

358

Porta, Giambattista della. De refractione optices parte: libri novem. Naples: Apud Io. Iacobum Carlinum & Antonium Pacem, 1593.

Priestley, Joseph. The History and Present State of Discoveries Relating to Vision, Light, and Colours, by Joseph Priestley. London: J. Johnson, 1772.

Theophilus, Protospatharius. De corporis humani fabrica libri V. Venice, 1537.

Ptolemy. L’Optique de Claude Ptolémée dans la version latine d’après l’arabe de l’émir Eugène de Sicile. Edited by Albert Lejeune. Université de Louvain. Recueil de travaux d’histoire et de philologie, 4. sér, fasc. 8. Louvain: Bibliothèque de l’Université, Bureaux du recueil, 1956.

Riccobonius, Antonius. In Obitu Iacobi Zabarellae Patavini Antonii Riccoboni Oratio. Padua: Apud Paulum Meiettum, 1590.

Santorio, Santorio. Methodi vitandorum errorum omnium qui in arte medica contingunt libri quindecim. Venice: Apud Franciscum Barilettum, 1603.

Scaliger, Julius Caesar. Exotericarum exercitationum liber quintus decimus, de subtilitate, ad Hieronymum Cardanum. ex officina typographica Michaelis Vascosani, 1557.

Scheiner, Christoph. Oculus, hoc est, fundamentum opticum, Oeniponti: apud Danlielem Agricolam, 1619.

———. Rosa Vrsina sive Sol ex admirando Facularum et Macularum suarum Phoenomeno varius. Bracciani: apud Andream Phaeum, 1626–1630.

Thienaeus, Cajetanus, Johannes van Gent, and Aristoteles. Super libros de anima. Questiones de sensu agente: de sensibilibus communibus: ac de intellectu. De substantia orbis Joannis de Gandavo cum questionibus ejusdem. Venice: per Gregorius de Gregoriis, 1505.

Tomasini, Giacomo Filippo. Gymnasium Patavinum Iacobi Philippi Tomasini episcopi Aemoniensis libris v. Udine: Nicolaus Schirattus, 1654.

———. Illustrium virorum elogia iconibus exornata. Padua: apud Donatum Pasquardum & socium, 1630.

Thuilius, Ioannes. Funus perillustris, & Excellentissimi Viri, D. Hieronymi Fabricii Ab Aquapendente Medicinae Doctoris, Equitis D. Marci, & in celeberrimo Gymnasio Patavino. Padua: Typis Petri Pauli Tozzii, 1619.

Valverde, Juan. Anatomia del corpo humano. Rome: per Ant. Salamanca et Antonio Lafrerj, 1559.

359

———. Historia de la composicion del cuerpo humano. Rome: impressa por Antonio Salamanca y Antonio Lafrerij, 1556.

Vesalius, Andreas. De Humani Corporis Fabrica Libri VII. Basel: Johannes Oporinus, 1543.

———. De humani corporis fabrica libri septem. Basel: Johannes Oporinus, 1555.

Zabarella, Jacopo. Commentarii Jac. Zabarellae Patavini, In III. Aristot. libros de anima. Frankfurt: Zetznerus, 1606.

———. De naturalis scientiae constitutione: (sive Comment. in Aristotelis lib. phys. auscultationis), Venice: apud Paulum Meietum, 1586.

———. De rebus naturalibus libri XXX, quibus quaestiones, quae ab Aristotelis interpretibus hodie tractari solent, accurate discutiuntur. Venice: apud Paulum Meietum, 1590.

———. De rebus naturalibus libri xxx. Frankfurt: Lazari Zetneri, 1607. Reprinted Frankfurt: Minerva, 1966.———. Opera logica. Venice: apud Meietum, 1578..

Zerbi, Gabriele. Opus preclarum anathomie totius corporis humani et singulorum membrorum illius. Venice: Bonetus, 1533.

Primary Sources in Translation

Alberti, Leon Battista. Leon Battista Alberti: On Painting: A New Translation and Critical Edition. Translated by Rocco Sinisgalli. Cambridge University Press, 2011.

Alexander of Aphrodisias. On Aristotle’s “On Sense Perception.” Translated by Alan Towey. Ithaca, NY: Cornell University Press, 2000.

———. On the Soul: Part I: Soul as Form of the Body, Parts of the Soul, Nourishment, and Perception. Translated by Victor Caston. London: Bloomsbury Academic, 2012.

———. Supplement to “On the Soul.” Translated by R. W. Sharples. Ithaca, NY: Cornell University Press, 2004.

Alhacen, and A. Mark Smith. “Alhacen on Refraction: A Critical Edition, with English Translation and Commentary, of Book 7 of Alhacen’s ‘De Aspectibus,’ the Medieval Latin Version of Ibn Al-Haytham’s ‘Kitāb Al-Manāzir.’ Volume One. Introduction and Latin Text.” Transactions of the American Philosophical Society, New Series, 100, no. 3 (January 1, 2010): i – 212.

360

———. “Alhacen on Refraction: A Critical Edition, with English Translation and Commentary, of Book 7 of Alhacen’s ‘De Aspectibus,’ the Medieval Latin Version of Ibn Al-Haytham’s ‘Kitāb Al-Manāzir.’ Volume Two. English Translation.” Transactions of the American Philosophical Society, New Series, 100, no. 3 (January 1, 2010): 213–550.

———. “Alhacen on the Principles of Reflection: A Critical Edition, with English Translation and Commentary, of Books 4 and 5 of Alhacen’s ‘De Aspectibus’, the Medieval Latin Version of Ibn Al-Haytham’s ‘Kitāb Al-Manāẓir’. Volume One: Introduction and Latin Text.” Transactions of the American Philosophical Society 96, no. 2 (January 1, 2006): i – 288.

———. “Alhacen on the Principles of Reflection: A Critical Edition, with English Translation and Commentary, of Books 4 and 5 of Alhacen’s ‘De Aspectibus’, the Medieval Latin Version of Ibn Al-Haytham’s ‘Kitāb Al-Manāẓir’. Volume Two: English Translation.” Transactions of the American Philosophical Society 96, no. 3 (January 1, 2006): 289–697.

———. “Alhacen’s Theory of Visual Perception: A Critical Edition, with English Translation and Commentary, of the First Three Books of Alhacen’s ‘De Aspectibus’, the Medieval Latin Version of Ibn Al-Haytham’s ‘Kitāb Al-Manāẓir’: Volume One.” Transactions of the American Philosophical Society 91, no. 4 (January 1, 2001): i – 337.

———. “Alhacen’s Theory of Visual Perception: A Critical Edition, with English Translation and Commentary, of the First Three Books of Alhacen’s ‘De Aspectibus’, the Medieval Latin Version of Ibn Al-Haytham’s ‘Kitāb Al-Manāẓir’: Volume Two.” Transactions of the American Philosophical Society 91, no. 5 (January 1, 2001): 339–819.

Al-Haytham, Ibn, and A. I. Sabra. Optics of Ibn Al-Haytham. 2 vols. London: The Warburg Institute, University of London, 1989.

Aristotle. Aristotle on Coming-to-Be and Passing-Away (De Generatione Et Corruptione): A Revised Text with Introduction and Commentary by Harold H. Joachim. Edited by Harold Henry Joachim. Oxford: The Clarendon Press, 1922.

———. Meteorologica. Translated by H. D. P. Lee. The Loeb Classical Library. Cambridge, MA: Harvard University Press, 1952.

———. On the Soul, Parva Naturalia, On Breath. Translated by W.S. Hett. The Loeb Classical Library. Cambridge, MA: Harvard University Press, 1975.

———. Physics. Books I-IV. Translated by Philip H Wicksteed and Francis Macdonald Cornford. Cambridge, Mass.: Harvard University Press, 1957.

———. Physics. Books V-VIII. Translated by Philip H Wicksteed and Francis Macdonald Cornford. Cambridge, Mass.: Harvard University Press, 1934.

361

———. Problems Books 1-19. Translated by Robert Mayhew. The Loeb Classical Library. Cambridge, MA: Harvard University Press, 2011.

———. Problems: Books XXII-XXXVIII; Rhetorica Ad Alexandrum. Translated by W.S. Hett and Harris Rackham. The Loeb Classical Library. Cambridge, MA: Harvard University Press, 1937.

———. The Complete Works of Aristotle: The Revised Oxford Translation. Edited by Jonathan Barnes. 2 vols. Princeton University Press, 1984.

———. The Organon. Translated by Harold Percy Cooke and Hugh Tredennick. The Loeb Classical Library. Cambridge, MA: Harvard University Press, 1938.

Averroës. Long Commentary on the De Anima of Aristotle. Translated by Richard C. Taylor. Yale University Press, 2009.

———. Middle Commentary on Aristotle’s De Anima: A Critical Edition of the Arabic Text. Translated by Alfred L. Ivry. Brigham Young University Press, 2002.

Averroës, and Arthur Hyman. Averroës on the Substance of the Celestial Sphere: Critical Edition of the Hebrew Text with English Translation and Commentary. Medieval Academy of America, 1986.

Bacon, Francis. The Instauratio Magna. Part 2, Novum Organum and Associated Texts. Edited by Graham Rees and Maria Wakely. Vol. XI. The Oxford Francis Bacon. New York: Oxford University Press, 2004.

———. The Works of Francis Bacon. Edited by James Spedding, Robert Leslie Ellis, and Douglas Denon Heath. Boston: Brown and Taggart, 1860.

Bacon, Roger, and David C Lindberg. Roger Bacon’s Philosophy of Nature: A Critical Edition, with English Translation, Introduction, and Notes, of De Multiplicatione Specierum and De Speculis Comburentibus. New York: Oxford University Press, 1983.

———. The Opus Majus of Roger Bacon. Translated by Robert Belle Burke. Vol. 1. Bristol: Thoemmes Press, 2000.

———. The Opus Majus of Roger Bacon. Translated by Robert Belle Burke. Vol. 2. Bristol: Thoemmes Press, 2000.

Carpi, Jacopo Berengario da. A Short Introduction to Anatomy: (Isagogae Breves). Chicago: University of Chicago Press, 1959.

362

Corner, George W. Anatomical Texts of the Earlier Middle Ages: A Study in the Transmission of Culture. Washington: Carnegie Institution of Washington, 1927.

Descartes, René. Descartes: The World and Other Writings. Edited by Stephen Gaukroger. Cambridge: Cambridge University Press, 1998.

———. Discourse on Method, Optics, Geometry, and Meteorology. Translated by Paul J. Olscamp. Indianapolis, IN: The Bobbs-Merrill Company, 1965.

Euclid. “The Optics of Euclid.” Translated by Harry Edwin Burton. Journal of the Optical Society of America 35, no. 5 (1945): 357–72.

Fabricius ab Aquapendente, Hieronymus (Girolamo Fabrizi d’ Acquapendente). Die Abhandlung über das Sehen von Hieronymus Fabricius ab Aquapendente (1537-1619): Übersetzung von “De actione oculorum” mit Kommentar. Zurich: Juris Druck + Verlag, 1984.

———. Die Augenanatomie des Fabricius ab Aquapendente (1537-1619): Übersetzung von“Oculi dissecti historia” mit Kommentar. Translated by Walter Birchler. Zurich: Juris Druck + Verlag, 1979.

———. De venarum ostiolis, 1603, of Hieronymus Fabricius of Aquapendente, 1533?-1619. Translated by K. J. Franklin. Springfield, Ill: Charles C. Thomas, 1933.

———. Die spezielle Physiologie des Auges von Hieronymus Fabricius ab Aquapendente (1533-1619): Übersetzung ausgewählter Kapitel des 3. Buches von “De visione” mit Kommentar. Translated by Jeannette Scharpf-Paravicini. Zurich: Juris Druck + Verlag, 1991.

Fabricius ab Aquapendente, Hieronymus, and Howard Bernhardt Adelmann. The Embryological Treatises of Hieronymus Fabricius of Aquadenpente. Ithaca, NY: Cornell University Press, 1967.

Galen. Galen on Anatomical Procedures: The Later Books. Edited by M. C. Lyons and B. Towers. Translated by Wynfrid Laurence Henry Duckworth. Cambridge University Press, 2010.

———. Galen on the Usefulness of the Parts of the Body. De Usu Partium. Translated by Margaret Tallmadge. Ithaca, NY: Cornell University Press, 1968.

———. On the Doctrines of Hippocrates and Plato (De placitis Hippocratis et Platonis). Translated by Phillip De Lacy. Corpus medicorum Graecorum, V 4,1,2. 3 vols. Berlin: Akademie-Verlag, 1978–1984.

363

Harvey, William. Anatomical Exercitations Concerning the Generation of Living Creatures to Which Are Added Particular Discourses of Births and of Conceptions, &c. / by William Harvey ... London: Printed by James Young, 1653.

Heseler, Baldasar, and Ruben Eriksson. Andreas Vesalius’ First Public Anatomy at Bologna: 1540. Uppsala: Almqvist & Wiksell, 1959.

Kepler, Johannes. Optics: Paralipomena to Witelo & Optical Part of Astronomy. Edited by William H. Donahue. Santa Fe, N.M.: Green Lion Press, 2000.

Kirk, G. S., and J. E. Raven. The Presocratic Philosophers; a Critical History with a Selection of Texts. Cambridge: Cambridge University Press, 1957.

Long, A. A., and D. N. Sedley. The Hellenistic Philosophers, Vol. I. Cambridge: Cambridge University Press, 1987.

Maurolico, Francesco, and Henry Crew. The Photismi de Lumine of Maurolycus: A Chapter in Late Medieval Optics. New York: Macmillan Publishing Company, 1940.

Peckham, John. John Pecham and the Science of Optics: Perspectiva Communis. Edited by David C. Lindberg. Madison: University of Wisconsin Press, 1970.

Plato. Plato: Complete Works. Edited by John M. Cooper. Indianapolis: Hackett Publishing Company, 1997.

———. Timaeus. Translated by Francis Macdonald Cornford. New York: Macmillan Publishing Company, 1959.

Plotinus. Ennead IV. Translated by A. H. Armstrong. Rev. Loeb Classical Library. Cambridge, MA: Harvard University Press, 1984.

Porphyry. On Aristotle’s Categories. Ancient Commentators on Aristotle. Ithaca, N.Y: Cornell University Press, 1992.

Priscian, and Simplicius. On Theophrastus on Sense-Perception with Simplicius On Aristotle’s On the Soul 2.5-12. Translated by Pamela M. Huby and Carlos G. Steel. Ithaca, NY: Cornell University Press, 1997.

Pseudo-Avicenna, and Oliver Gutman. Liber Celi Et Mundi: Introduction and Critical Edition. Leiden: Brill, 2003

Ptolemy. Ptolemy’s Almagest. Translated by J. G. Toomer. Princeton, N.J.: Princeton University Press, 1998.

364

Ptolemy, and A. Mark Smith. “Ptolemy’s Theory of Visual Perception: An English Translation of the ‘Optics’ with Introduction and Commentary.” Transactions of the American Philosophical Society 86, no. 2 (January 1, 1996): iii – 300.

Rashed, Roshdi. “Le ‘Discours de la lumière’ d’Ibn al-Haytham.” Revue d’histoire des sciences 21 (1968): 198–224.

Simplicius. On Aristole Physics 3. London: Duckworth, 2002.

———. On Aristotle’s “Categories 7-8.” The Ancient Commentators on Aristotle. Ithaca, N.Y: Cornell University Press, 2002.

———. On Aristotle’s “Physics 8.6-10.” The Ancient Commentators on Aristotle. Ithaca, N.Y: Cornell University Press, 2001.

———. Simplicius: On Aristotle On the Heavens 2.1-9. Translated by Ian Mueller. London: Bloomsbury Academic, 2014.

Vesalius, Andreas. The Fabric of the Human Body: An Annotated Translation of the 1543 and 1555 Editions of “De Humani Corporis Fabrica Libri Septem.” 2 vols. Basel: S Karger Ag, 2013.

Witelo. Witelonis Perspectivae Liber Secundus et Liber Tertius. Edited by Sabetai Unguru. Studia Copernicana, XXVIII. Wrocław: Ossolineum, 1991.

Secondary Sources

Adamson, Peter. Al-Kindī. New York: Oxford University Press, 2007.

———. “Vision, Light and Color in Al-Kindi, Ptolemy and the Ancient Commentators.” Arabic Sciences and Philosophy 16, no. 02 (2006): 207–36.

Albert, Daniel M., and Diane D. Edwards, eds. The History of Ophthalmology. Boston: Blackwell Science, 1996.

Avotins, Ivars. “Alexander of Aphrodisias on Vision in the Atomists.” The Classical Quarterly, New Series, 30, no. 2 (January 1, 1980): 429–54.

Belloni, Luigi. “The Repetition of Experiments and Observations: Its Value in Studying the History of Medicine (and Science).” Journal of the History of Medicine and Allied Sciences XXV, no. 2 (1970): 158–67.

365

Bonati, Maurizio Rippa, and José Pardo Tomás. Il teatro dei corpi: le pitture colorate d’anatomia di Girolamo Fabrici d’Acquapendente. Mediamed, 2004.

Boudon-Millot, Véronique. “Vision and Vision Disorders. Galen’s Physiology of Sight.” In Blood, Sweat and Tears - The Changing Concepts of Physiology from Antiquity into Early Modern Europe, edited by Claus Zittel, Manfred Horstmanshoff, and Helen King, 549–67. Brill Academic Publishers, 2012.

Bouillon, Dominiqe, ed. “Un discours inédit de Iacopo Zabarella préliminaire à l’exposition de la ‘Physique’ d’Aristote (Padoue 1568).” In Atti e memorie dell’Accademia galileiana di scienze lettere ed arti in Padova, cx/1:119–27. l’Accademia, 1998.

Broackes, Justin. “Aristotle, Objectivity, and Perception.” In Oxford Studies in Ancient Philosophy, 17:57–113. Oxford: Oxford University Press, 1999.

Burnyeat, Myles. “Aristote voit du rouge et entend un ‘do’: combien se passe-t-il de choses? Remarques sur ‘De anima’ II, 7-8.” Revue Philosophique de la France et de l’Étranger 183, no. 2 (April 1, 1993): 263–80.

———. “‘De Anima’ II 5.” Phronesis 47, no. 1 (January 1, 2002): 28–90.

Burtt, E. A. The Metaphysical Foundations of Modern Science. Revised Edition. Anchor, 1954.

Bylebyl, Jerome. “The School of Padua: Humanistic Medicine in the Sixteenth Century.” In Health, Medicine, and Mortality in the Sixteenth Century, edited by Charles Webster, 335–70. CUP Archive, 1979.

Cabot, Florence, Alain Saad, Colm McAlinden, Nour Maya Haddad, Alice Grise-Dulac, and Damien Gatinel. “Objective Assessment of Crystalline Lens Opacity Level by Measuring Ocular Light Scattering with a Double-Pass System.” American Journal of Ophthalmology 155, no. 4 (April 2013): 629–35, 635.e1–2.

Cassirer, Ernst. Das Erkenntnisproblem in der Philosophie und Wissenschaft der neuren Zeit. Vol. 1. Berlin, 1906.

Castiglioni, Arturo. A History of Medicine. A. A. Knopf, 1958.

Chen-Morris, Raz, and Sabetai Unguru. “Kepler’s Critique of the Medieval Perspectivist Tradition.” In Optics and Astronomy: Proceedings of the XXth International Congress of History of Science, edited by Gérard Simon and Suzanne Débarbat, XII:83–92. Brepolis, 2001.

Chevalley, Catherine. “L’optique des Jésuites et celle des médecins: A propos de deux ouvrages récents.” Revue d’histoire des sciences 40, no. 3/4 (July 1, 1987): 377–82.

366

Clulee, Nicholas H. “Astrology, Magic, and Optics: Facets of John Dee’s Early Natural Philosophy.” Renaissance Quarterly 30, no. 4 (December 1, 1977): 632–80.

Crombie, A. C. “Expectation, Modelling, and Assent in the History of Optics: Part I. Alhazen and the Medieval Tradition.” Studies in the History and Philosophy of Science 21, no. 4 (1990): 605–32.

———. “Expectation, Modelling, and Assent in the History of Optics: Part II. Kepler and Descartes.” Studies in History and Philosophy of Science 22, no. 1 (1991): 89–115.

———. “The Mechanistic Hypothesis and the Scientific Study of Visioin.” In Science, Optics, and Music in Medieval and Early Modern Thought, 175–284. London, 1990.

———. A. C. Styles of Scientific Thinking in the European Tradition: The History of Argument and Explanation Especially in the Mathematical and Biomedical Sciences and Arts. 3 vols. London: Duckworth, 1994.

Cunningham, Andrew. “Fabricius and the ‘Aristotle Project’ in Anatomical Teaching and Research at Padua.” In The Medical Renaissance of the Sixteenth Century, edited by Andrew Wear, Roger Kenneth French, and Iain M. Lonie, 195–222. Cambridge University Press, 1985.

———. The Anatomical Renaissance: The Resurrection of the Anatomical Projects of the Ancients. Scolar Press, 1997.

Dal Pra, Mario. “Una oratio programmatica di Giacomo Zabarella.” Rivista critica di storia della filosofia 21 (1966): 286–90.

De Angelis, Simone. “From Text to the Body: Commentaries on De Anima, Anatomical Practice and Authority around 1600.” In Scholarly Knowledge: Textbooks in Early Modern Europe, 205–28. Librairie Droz, 2008.

Dear, Peter. “Jesuit Mathematical Science and the Reconstitution of Experience in the Early Seventeenth Century.” Studies in History and Philosophy of Science Part A 18, no. 2 (June 1987): 133–75.

———. “The Meanings of Experience.” In The Cambridge History of Science: Early Modern Period, edited by Lorraine Daston and Katherine Park, 3:106–31. Cambridge, 2006.

Delaye, M, J I Clark, and G B Benedek. “Identification of the Scattering Elements Responsible for Lens Opacification in Cold Cataracts.” Biophysical Journal 37, no. 3 (March 1982): 647–56.

367

De Nil, Erwin, and Mark De Mey. “Hieronymus Fabricius d’Aquapendente: De Visione, Ending of the Perspectivist Tradition.” In Optics and Astronomy: Proceedings of the XXth International Congress of History of Science, 51–65. Brepols, 2001.

Dhanani, Alnoor. The Physical Theory of Kalām: Atoms, Space, and Void in Basrian Muʻtazilī Cosmology. Islamic Philosophy, Theology, and Science, v. 14. Leiden  ; New York: E.J. Brill, 1994.

Distelzweig, Peter. “Descartes’s Teleomechanics in Medical Context: Approaches to Integrating Mechanics and Teleology in Hieronymus Fabricius Ab Aquapendente, William Harvey, and René Descartes.” PhD Dissertation, University of Pittsburgh, 2013.

———. “Fabricius’s Galeno-Aristotelian Teleomechanics of Muscle.” In The Life Sciences in Early Modern Philosophy, edited by Ohad Nachtomy and Justin E. H. Smith, 232. New York: Oxford University Press, 2014.

Drew, Philip L. “Some Notes on Zabarella’s and Cremonini’s Interpretation of Aristotle’s Philosophy of Nature.” In Aristotelismo Veneto E Scienza Moderna, 2:647–59. Pado, 1983.

Dua, Harminder S., Lana A. Faraj, Dalia G. Said, Trevor Gray, and James Lowe. “Human Corneal Anatomy Redefined: A Novel Pre-Descemet’s Layer (Dua’s Layer).” Ophthalmology 120, no. 9 (September 2013): 1778–85.

Duhem, Pierre. Medieval Cosmology: Theories of Infinity, Place, Time, Void, and the Plurality of Worlds. University of Chicago Press, 1987.

Dupré, Sven. “Ausonio’s Mirrors and Galileo’s Lenses: The Telescope and Sixteenth-Century Practical Optical Knowledge.” Galilaeana 2 (2005): 145–80.

———. “Images In The Air: Optical Games, Magic And Imagination.” In Spirits Unseen: The Representation of Subtle Bodies in Early Modern European Culture, edited by C. Göttler and W. Neuber, 71–92. Brill Academic Publishers, 2007.

———. “Kepler’s Optics Without Hypotheses.” Synthese 185, no. 3 (2012): 501–25.

———. Renaissance Optics: Instruments, Practical Knowledge and the Appropriation of Theory. Max-Planck-Inst. für Wissenschaftsgeschichte, 2003.

Durling, Richard J. “A Chronological Census of Renaissance Editions and Translations of Galen.” Journal of the Warburg and Courtauld Institutes 24, no. 3/4 (July 1, 1961): 230–305.

———. “Girolamo Mercuriale’s De Modo Studendi.” Osiris, 2nd Series, 6 (January 1, 1990): 181–95.

368

Eastwood, Bruce S. “Alhazen, Leonardo, and Late-Medieval Speculation on the Inversion of Images in the Eye.” Annals of Science 43, no. 5 (September 1986): 413.

———. “Averroes’ View of the Retina—A Reappraisal.” Journal of the History of Medicine and Allied Sciences XXIV, no. 1 (1969): 77–82. doi:10.1093/jhmas/XXIV.1.77.

———. “The Elements of Vision: The Micro-Cosmology of Galenic Visual Theory according to Ḥunayn Ibn Isḥāq.” Transactions of the American Philosophical Society 72, no. 5 (January 1, 1982): 1–59. doi:10.2307/1006450.

Edgerton, Samuel Y. “Alberti’s Colour Theory: A Medieval Bottle without Renaissance Wine.” Journal of the Warburg and Courtauld Institutes 32 (1969): 109–34.

Edwards, William F. “The Logic of Iacopo Zabarella.” PhD Dissertation, Columbia University, 1960.

Ekholm, Karin. “Fabricius’s and Harvey’s Representations of Animal Generation.” Annals of Science 67, no. 3 (2010): 329–52.

Eyjólfur Kjalar Emilsson. Plotinus on Sense-Perception: A Philosophical Study. Cambridge [Cambridgeshire]  ; New York: Cambridge University Press, 1988.

Favaro, Giuseppe. “Contributi alla biografia di Girolamo Fabrici d’Acquapendente.” In Memorie e documenti per la storia della Università di Padova, Vol. 1. Padova, 1922.

———. “L’insegnamento anatomico di Girolamo Fabrici d’Acquapendente.” In Monografie storiche sullo studio di Padova, contributo del R. Instituto Veneto di Scienze, Lettere ed Arti alla celebrazione del VII centenario della Università di Padova. Venice, 1922.

Fazzo, Silvia, and Hillary Wiesner. “Alexander of Aphrodisias in the Kindi Circle and in Al-Kindi’s Cosmology.” Arabic Sciences and Philosophy 3 (1993): 119–53.

Feeser, Andrea, Maureen Daly Goggin, and Beth Fowkes Tobin. The Materiality of Color: The Production, Circulation, and Application of Dyes and Pigments, 1400-1800. Ashgate Publishing, Ltd., 2012.

Feingold, M. The New Science and Jesuit Science. Springer Science & Business Media, 2003.

Forcellini, E, G Furlanetto, F Corradini, and J Perin. Lexicon Totius Latinitatis. Patavi, 1940.

Fortuna, Stefania. “The Latin Editions of Galen’s Opera Omnia (1490-1625) and Their Prefaces.” Early Science and Medicine 17, no. 4 (January 1, 2012): 391–412.

Frangenberg, Thomas. “Perspectivist Aristotelianism: Three Case-Studies of Cinquecento Visual Theory.” Journal of the Warburg and Courtauld Institutes 54 (1991): 137–58.

369

Gage, John. Color and Culture: Practice and Meaning from Antiquity to Abstraction. Boston: Little, Brown and Company, 1993.

———. Color and Meaning: Art, Science, and Symbolism. University of California Press, 2000.

Gal, Ofer, and Raz Chen-Morris. “Baroque Optics and the Disappearance of the Observer: From Kepler’s Optics to Descartes’ Doubt.” Journal of the History of Ideas 71, no. 2 (April 1, 2010): 191–217.

———. Baroque Science. University of Chicago Press, 2013.

Gätje, Helmut. “Zur Farbenlehre in der muslimischen Philosophie.” Der Islam; Zeitschrift für Geschichte und Kultur des Islamischen Orients 43 (January 1, 1967): 280–301.

Gilbert, Neal Ward. “Galileo and the School of Padua.” Journal of the History of Philosophy 1, no. 2 (1963): 223–31.

Glasner, Ruth. Averroës’ Physics: A Turning Point in Medieval Natural Philosophy. Oxford University Press US, 2009.

———. “Ibn Rushd’s Theory of Minima Naturalia.” Arabic Sciences and Philosophy 11, no. 01 (2001): 9–26.

Gotthelf, Allan, and James G. Lennox, eds. Philosophical Issues in Aristotle’s Biology. Cambridge  ; New York: Cambridge University Press, 1987.

Goulet-Aouad. “Alexandros d’Aphrodisias.” In Dictionnaire Des Philosophes Antiques, I:125–39, 1989.

Grafton, Anthony. “The Availability of Ancient Works.” In The Cambridge History of Renaissance Philosophy, edited by C. B. Schmitt, Quentin Skinner, Eckhard Kessler, and Jill Kraye, 763–91. Cambridge: Cambridge University Press, 1988. Grant, Edward. Much Ado About Nothing: Theories of Space and Vacuum from the Middle Ages to the Scientific Revolution. Cambridge University Press, 1981.

Grant, Edward. Much Ado About Nothing: Theories of Space and Vacuum from the Middle Ages to the Scientific Revolution. Cambridge University Press, 1981.

———. Planets, Stars, and Orbs: The Medieval Cosmos, 1200-1687. Cambridge University Press, 1996.

Grendler, Paul F. The Universities of the Italian Renaissance. JHU Press, 2004.

Groot, Jean Christensen de. “Philoponus on ‘De Anima’ II.5, ‘Physics’ III.3, and the Propagation of Light.” Phronesis 28, no. 2 (1983): 177–96.

370

Groot, Jean De. Aristotle and Philoponus on Light. Garland Pub., 1991.

Guerlac, Henry. “Can There Be Colors in the Dark? Physical Color Theory before Newton.” Journal of the History of Ideas 47, no. 1 (January 1, 1986): 3–20.

Gutman, Oliver. “On the Fringes of the Corpus Aristotelicum: The Pseudo-Avicenna ‘Liber Celi et Mundi.’” Early Science and Medicine 2, no. 2 (January 1, 1997): 109–28.

Harvey, Edmund Newton. A History of Luminescence from the Earliest Times until 1900. American Philosophical Society, 1957.

Hatcher, Elizabeth R. “The Moon and Parchment: Paradiso II, 73-78.” Dante Studies, with the Annual Report of the Dante Society, no. 89 (January 1, 1971): 55–60.

Hirschberg, J. The History of Ophthalmology. Bonn: J. P. Wayenborgh, 1982.

Homans, Isaac Smith. A Cyclopedia of Commerce and Commercial Navigation. Harper, 1858.

Jardine, Nicholas. “Galileo’s Road to Truth and the Demonstrative Regress.” Studies in History and Philosophy of Science Part A 7, no. 4 (1976): 277–318.

———. “Keeping Order in the School of Padua: Jacopo Zabarella and Francesco Piccolomini on the Offices of Philosophy.” In Method and Order in Renaissance Philosophy of Nature, edited by Di Liscia, Kessler, and Methuen, 183–209. Ashgate, 1997.

———. The Birth of History and Philosophy of Science: Kepler’s A Defence of Tycho against Ursus, with Essays on Its Provenance and Significance. 1st pbk. ed. with corrections. Cambridge [Cambridgeshire]  ; New York: Cambridge University Press, 1988.

Kachlik, David, David Vichnar, Vladimir Musil, Dana Kachlikova, Kristian Szabo, and Josef Stingl. “A Biographical Sketch of Johannes Jessenius: 410th Anniversary of His Prague Dissection.” Clinical Anatomy 25, no. 2 (March 1, 2012): 149–54.

Kemp, Martin. The Science of Art: Optical Themes in Western Art from Brunelleschi to Seurat. Yale University Press, 1990.

King, Peter. “Rethinking Representation in the Middle Ages: A Vade-Mecum to Medieval Theories of Mental Representation.” In Representation and Objects of Thought in Medieval Philosophy, edited by Henrik Lagerlund, 81–100. Ashgate, 2007.

Kirchner, Eric, and Mohammad Bagheri. “Color Theory in Medieval Islamic Lapidaries: Nıshābūrı, Tūsı and Kāshānı.” Centaurus 55, no. 1 (2013): 1–19.

Klestinec, Cynthia. “A History of Anatomy Theaters in Sixteenth-Century Padua.” Journal of the History of Medicine and Allied Sciences 59, no. 3 (2004): 375–412.

371

———. “Civility, Comportment, and the Anatomy Theater: Girolamo Fabrici and His Medical Students in Renaissance Padua.” Renaissance Quarterly 60, no. 2 (2007): 434–63.

———. “Juan Valverde de (H)Amusco and Print Culture.” In Zergliedungeren: Anatomie Und Wahrnehmung in Der Frühen Neuzeit, edited by Albert Schirrmeister, 78–96. Zeitsprünge: Forschungen Zur Frühen Neuzeit. Frankfurt: Vittorio Klostermann, 2005.

———. Theaters of Anatomy: Students, Teachers, and Traditions of Dissection in Renaissance Venice. Johns Hopkins University Press, 2011.

Koelbing, Huldrych M. “Anatomie de l’œil et perception visuelle, de Vésale à Kepler.” In Le corps à la renaissance. Actes du XXXe Colloque de Tours 1987, 389–98. Paris, 1990.

———. Averroës’ Concepts of Ocular Function: Another View. Schullian, 1972.

Kuhn, Heinrich C. “Chartaceous Presence, Material Impact: Works by Paduan Aristotelians in German Libraries (A Bibliometric Study).” In La Presenza dell’Aristotelismo Padovano Nella Filosofia Della Prima Modernità, edited by Gregorio Piaia, 83–122. Editrice Antenore, 2002.

Kusukawa, Sachiko. “Meditations of Zabarella in Northern Europe: The Preface of Johann Ludwig Hawenreuter.” In La Presenza dell’Aristotelismo Padovano Nella Filosofia Della Prima Modernità, edited by Gregorio Piaia, 199–214. Roma-Padova, 2002.

———. “Nature’s Regularity in Some Protestant Natural Philosophy Textbooks 1530-1630.” In Natural Law and Laws of Nature in Early Modern Europe, edited by Lorraine Daston and Michael Stolleis, 105–22. Ashgate Publishing, Ltd., 2008.

Laird, Walter Roy. “The ‘Scientiae Mediae’ in Medieval Commentaries on Aristotle’s ‘Posterior Analytics.’” PhD Dissertation, University of Toronto (Canada), 1983.

———. “The Scope of Renaissance Mechanics.” Osiris, 2nd Series, 2 (January 1, 1986): 43–68.

Lefèvre, Wolfgang. “The Optical Camera Obscura I: A Short Exposition.” In Inside the Camera Obscura - Optics and Art Under the Spell of the Projected Image, edited by Wolfgang Lefèvre, 5–12. Berlin: Max Planck Institute for the History of Science, 2007.

Lehn, Waldemar H, and Siebren van der Werf. “Atmospheric Refraction: A History.” Applied Optics 44, no. 27 (September 20, 2005): 5624–36.

Lennox, James G. Aristotle’s Philosophy of Biology: Studies in the Origins of Life Science. Cambridge Studies in Philosophy and Biology. Cambridge, UK  ; New York: Cambridge University Press, 2001.

372

Lewis, Charlton, Charles Short, EA Andrews, and W Freund. A Latin Dictionary. Oxford: Clarendon Press, 1933.

Lindberg, David C. “Did Averroës Discover Retinal Sensitivity?” Bulletin of the History of Medicine 49, no. 2 (Summer 1975).

———. “The Cause of Refraction in Medieval Optics.” The British Journal for the History of Science 4, no. 1 (June 1, 1968): 23–38.

———. “The Genesis of Kepler’s Theory of Light: Light Metaphysics from Plotinus to Kepler.” Osiris 2 (January 1, 1986): 4–42.

———. Theories of Vision from Al-Kindi to Kepler. Chicago: University of Chicago Press, 1976.

Lines, David A. “Natural Philosophy in Renaissance Italy: The University of Bologna and the Beginnings of Specialization.” Early Science and Medicine 6, no. 4 (January 1, 2001): 267–323.

———. University Natural Philosophy in Renaissance Italy: The Decline of Aristotelianism?. Brill, 2002.

Lohr, Charles H. “Renaissance Latin Aristotle Commentaries: Authors L-M.” Renaissance Quarterly 31, no. 4 (1978): 532–603.

———. “Renaissance Latin Aristotle Commentaries: Authors Pi-Sm.” Renaissance Quarterly 33, no. 4 (Winter 1980): 623–734.

———. “Renaissance Latin Aristotle Commentaries: Authors So–Z.” Renaissance Quarterly 35, no. 2 (July 1, 1982): 164–256.

———. “The Sixteenth-Century Transformation of the Aristotelian Natural Philosophy.” In Aristotelismus Und Renaissance, 89–100. Harrassowitz, 1988.

Loose, Patrice Koelsch. Roger Bacon on Perception: A Reconstruction and Critical Analysis of the Theory of Visual Perception Expounded in the Opus Majus, 1979.

Maclean, Ian. Logic, Signs and Nature in the Renaissance: The Case of Learned Medicine. Cambridge University Press, 2007.

Maclean, Ian. “Meditations of Zabarella in Northern Germany, 1586-1623.” In La Presenza dell’Aristotelismo Padovano Nella Filosofia Della Prima Modernità, edited by Gregorio Piaia, 173–98. Roma-Padova, 2002.

Magee, Joseph M. “Sense Organs and the Activity of Sensation in Aristotle.” Phronesis 45, no. 4 (November 1, 2000): 306–30.

373

Martin, Craig. “Rethinking Renaissance Averroism.” Intellectual History Review 17, no. 1 (2007): 3–28.

———. Subverting Aristotle: Religion, History, and Philosophy in Early Modern Science. JHU Press, 2014.

Mellerio, J. “Light Absorption and Scatter in the Human Lens.” Vision Research 11, no. 2 (February 1971): 129–41.

Meyerhof, Max. “New Light on Hunain Ibn Ishaq and His Period.” Isis 8, no. 4 (October 1, 1926): 685–724.

Mikkeli, Heikki. An Aristotelian Response to Renaissance Humanism: Jacopo Zabarella on the Nature of Arts and Sciences. SHS, 1992.

———. “Giacomo Zabarella.” In The Stanford Encyclopedia of Philosophy, edited by Edward N. Zalta, Winter 2012., 2012. http://plato.stanford.edu/archives/win2012/entries/zabarella/.

———. “The Foundation of an Autonomous Natural Philosophy: Zabarella on the Classification of Arts and Sciences.” In Method and Order in Renaissance Philosophy of Nature, 211–28. Ashgate, 1997.

———. “Zabarella, Jacopo (Giacomo).” In Complete Dictionary of Scientific Biography, 25:387–90. Detroit: Charles Scribner’s Sons, 2008.

Muccilo, Maria. “Da Monte, Giovanni Battista, Dettò Montano.” In Dizionario Biographico Degli Italiani, 32:365–67, 1986.

———. “Fabrici d’Acquapendente, Girolamo.” In Dizionario Biographico Degli Italiani, Vol. 43, 1993.

Murdoch, John E. “The Medieval and Renaissance Tradition of Minima Naturalia.” In Late Medieval And Early Modern Corpuscular Matter Theories, edited by Christoph H. Lüthy, John E. Murdoch, and William R. Newman, 91–131. BRILL, 2001.

Nakajima, Hideto. “Two Kinds of Modification Theory of Light: Some New Observations on the Newton-Hooke Controversy of 1672 Concerning the Nature of Light.” Annals of Science 41, no. 3 (1984): 261–78.

Newman, William R. Atoms and Alchemy: Chymistry and the Experimental Origins of the Scientific Revolution. University of Chicago Press, 2006.

Nutton, Vivian. “Vesalius Revised. His Annotations to the 1555 Fabrica.” Medical History 56, no. 4 (October 2012): 415–43.

374

Omar, Saleh Beshara. Ibn Al-Haytham’s Optics: A Study of the Origins of Experimental Science. Studies in Islamic Philosophy and Science. Minneapolis: Bibliotheca Islamica, 1977.

Palmieri, Paolo. “Science and Authority in Giacomo Zabarella.” History of Science 14 (2007): 404–27.

Panofsky, Erwin. Die Perspektive Als “Symbolische Form.,” 1927.

———. Perspective As Symbolic Form. Zone Books, 1997.

Pantin, Isabelle. “Simulachrum, Species, Forma, Imago: What Was Transported by Light into the Camera Obscura? Divergent Conceptions of Realism Revealed by Lexical Ambiguities at the Beginning of the Seventeenth Century.” Early Science and Medicine 13, no. 3 (January 1, 2008): 245–69.

Perler, Dominik. Ancient and Medieval Theories of Intentionality. BRILL, 2001.

Petersen, P. Geschichte der Aristotelischen Phiosophie im Protestantischen Deuchland. Leipzig, 1921.

Pick, Friedel. Joh. Jessenius de Magna Jessen, Arzt und Rektor in Wittenberg und Prag hingerichtet am 21. Juni 1621. Ein Lebensbild aus der Zeit des 30jährigen Krieges. Vol. 15. Studien zur Geschichte der Medizin. Leipzig: Ambrosius Bbarth, 1926.

Pollack, Tamara. “Light and Mirror in Dante’s ‘Paradiso’: Faith and Contemplation in the Lunar Heaven and the Primo Mobile.” PhD Dissertation, Indiana University, 2008.

Pomata, Gianna. “Praxix Historialis: The Uses of Historia in Early Modern Medicine.” In Historia: Empiricism and Erudition in Early Modern Europe, edited by Gianna Pomata and Nancy G. Siraisi, 105–46. Cambridge (Mass.); London: MIT Press, 2005.

Poppi, Antonino. La dottrina della scienza in Giacomo Zabarella. Antenore, 1972.

———. “Zabarella, or Aristotelianism as a Rigorous Science.” In The Impact of Aristotelianism on Modern Philosophy, edited by Riccardo Pozzo, 35–63. Studies in Philosophy and the History of Philosophy 39. Washington, D.C.: The Catholic University of America Press, 2004.

Randall, John Herman. “The Development of Scientific Method in the School of Padua.” Journal of the History of Ideas 1, no. 2 (April 1, 1940): 177–206.

———. The School of Padua and the Emergence of Modern Science. Editrice Antenore, 1961.

Rāzī, Abū Bakr Muḥammad ibn Zakarīyā, ’Ali Ibn Al-’Abbās, and ’Ali Ibn Sīnā. Trois traités d’anatomie arabes. Translated by P. De Koning. Brill, 1903.

375

Reif, Mary. “Natural Philosophy in Some Early Seventeenth Century Scholastic Textbooks.” PhD Dissertation, Saint Louis University, 1962.

Rosenthal, F. “Al-Kindi and Ptolemy’.” Studi Orientalistici In Onore Di Giorgio Levi Della Vida 2 (1956): 436–56.

Sabra, A. I. Theories of Light, from Descartes to Newton. CUP Archive, 1981.

Sambursky, S. “Philoponus’ Interpretation of Aristotle’s Theory of Light.” Osiris 13 (January 1, 1958): 114–26.

San Juan, Rose Marie. “Restoration and Translation in Juan de Valverde’s Historia de La Composition Del Cuerpo Humano.” In The Virtual Tourist in Renaissance Rome: Printing and Collecting the Speculum Romanae Magnificentiae, edited by Rebecca Zorach. Chicago: University of Chicago Library, 2008.

Schmitt, Charles B. “Aristotelianism in the Venetio and the Origins of Modern Science: Some Considerations on the Problem of Continuity.” In Aristotelismo Veneto E Scienza Moderna, 1:104–23. Padova, 1983.

———. Aristotle and the Renaissance. Published for Oberlin College by Harvard University Press, 1983.

———. “Experience and Experiment: A Comparison of Zabarella’s View With Galileo’s in De Motu.” Studies in the Renaissance 16 (January 1, 1969): 80–138.

———. “The Rise of the Philosophical Textbook.” In The Cambridge History of Renaissance Philosophy, edited by C. B. Schmitt, Quentin Skinner, Eckhard Kessler, and Jill Kraye, 792–804. Cambridge: Cambridge University Press, 1988.

———. “Zabarella.” In Dictionary of Scientific Biography, edited by Charles Coulston Gillespie, 14:580–82. New York, 1970.

Schullian, Dorothy M. “Averroës’ Concepts of Ocular Function—Another View.” Journal of the History of Medicine and Allied Sciences XXVII, no. 2 (1972): 207–13.

Shapiro, Alan E. “Artists’ Colors and Newton’s Colors.” Isis 85, no. 4 (December 1, 1994): 600–630.

———. “Images: Real and Virtual, Projected and Perceived, from Kepler to Dechales.” Early Science and Medicine 13, no. 3 (2008): 270–312.

———. “Kinematic Optics: A Study of the Wave Theory of Light in the Seventeenth Century.” Archive for History of Exact Sciences 11, no. 2/3 (December 31, 1973): 134–266.

376

———. “The Evolving Structure of Newton’s Theory of White Light and Color.” Isis 71, no. 2 (June 1, 1980): 211–35.

Shotwell, Allen. “The Revival of Anatomical Practices and Techniques in the Renaissance.” PhD Dissertation, Indiana University, Bloomington, 2013.

———. “The Revival of Vivisection in the Sixteenth Century.” Journal of the History of Biology 46, no. 2 (July 1, 2013): 171–97.

Siegel, Rudolph E. Galen on Sense Perception: His Doctrines, Observations and Experiments on Vision, Hearing, Smell, Taste, Touch and Pain, and Their Historical Sources. Karger, 1970.

Simmons, Alison. “Explaining Sense Perception: A Scholastic Challenge.” Philosophical Studies: An International Journal for Philosophy in the Analytic Tradition 73, no. 2/3 (March 1, 1994): 257–75.

———. “Making Sense: The Problem of Phenomenal Qualities in Late Scholastic Aristotelianism and Descartes.” PhD Dissertation, Graduate School of Arts and Sciences, University of Pennsylvania, 1994.

Siraisi, Nancy G. Avicenna in Renaissance Italy: The Canon and Medical Teaching in Italian Universities after 1500. Princeton University Press, 1987.

———. “Historia, Actio, Utilitas: Fabrici E Le Scienze Della Vita Nel Cinquecento.” In Il Teatro Dei Corpi: Le Pitture Colorate D’anatomia Di Girolamo Fabrici d’Acquapendente, edited by Maurizio Rippa Bonati and Jose Pardo-Tomas, 63–73. Milano: Mediamed, 2004.

———. “Vesalius and Human Diversity in De Humani Corporis Fabrica.” Journal of the Warburg and Courtauld Institutes 57 (January 1, 1994): 60–88.

———. “Vesalius and the Reading of Galen’s Teleology.” Renaissance Quarterly 50, no. 1 (April 1, 1997): 1–37.

Skulsky, Harold. “Paduan Epistemology and the Doctrine of the One Mind.” Journal of the History of Philosophy 6, no. 4 (1968): 341–61.

Smith, A. Mark. “Getting the Big Picture in Perspectivist Optics.” Isis 72, no. 4 (Dezember 1981): 568–89.

———. “Le De aspectibus d’Alhazen  : Révolutionnaire ou réformiste  ?” Revue d’histoire des sciences Tome 60, no. 1 (August 1, 2007): 65–82.

377

———. “Ptolemy, Alhacen, and Ibn Mu’adh and the Problem of Atmospheric Refraction.” Centaurus 45, no. 1–4 (2003): 100–115.

———. “Reflections on the Hockney-Falco Thesis: Optical Theory and Artistic Practice in the Fifteenth and Sixteenth Centuries.” Early Science and Medicine 10, no. 2 (2005): 163–86.

———. “The Psychology of Visual Perception in Ptolemy’s Optics.” Isis 79, no. 2 (June 1988): 188–207.

———. “What Is the History of Medieval Optics Really About?” Proceedings of the American Philosophical Society 148, no. 2 (June 2004): 180–94.

Soler, Jorge Leoncio. “The Psychology of Iacopo Zabarella (1533 - 1589).” PhD Dissertation, State University of New York at Buffalo, 1971.

Sorabji, Richard. “Aristotle, Mathematics, and Colour.” The Classical Quarterly 22, no. 2 (November 1, 1972): 293–308.

———. “Aristotle on Colour, Light and Imperceptibles.” Bulletin of the Institute of Classical Studies 47, no. 1 (2004): 129–40.

———. “Aristotle on Demarcating the Five Senses.” The Philosophical Review 80, no. 1 (January 1, 1971): 55–79.

———. “Aristotle on Sensory Processes: A Reply to Myles Burnyeat.” In Ancient and Medieval Theories of Intentionality, edited by Dominik Perler, 49–61. Leiden, 2001.

———. “"From Aristotle to Brentano: The Development of the Concept of Intentionality.” In Aristotle and the Later Tradition, edited by Henry Blumenthal and Henry Robinson, supplementary volume:236–37. Oxford Studies in Ancient Philosophy. Oxford: Clarendon Press, 1991.

———. “John Philoponus.” In Philoponus and the Rejection of Aristotelian Science, 1–40. London: Duckworth, 1987.

South, James B. “Zabarella and the Intentionality of Sensation.” Rivista Di Storia Della Filosofia, January 1, 2002.

———. “Zabarella, Prime Matter, and the Theory of Regressus.” Graduate Faculty Philosophy Journal xxvi (2005): 79–98.

Spies, Otto. “Al-Kindi’s Treatise on the Cause of the Blue Colour of the Sky.” Journal of the Bombay Branch of the Royal Asiatic Society, no. 13 (1937): 7–19.

378

Spruit, Leen. Species Intelligibilis: From Perception to Knowledge. Volume 1: Classical Roots and Medieval Discussions. BRILL, 1994.

———. Species Intelligibilis: From Perception to Knowledge. Volume 2: Renaissance Controversies, Later Scholasticism, and the Eliminatinon of the Intelligible Species in Modern Philosophy. BRILL, 1995.

Staden, Heinrich Von. “Anatomy as Rhetoric: Galen on Dissection and Persuasion.” Journal of the History of Medicine and Allied Sciences 50, no. 1 (January 1, 1995): 47–66.

Straker, Stephen. “Kepler’s Optics: A Study in the Development of Seventeenth-Century Natural Philosophy.” PhD Dissertation, Indiana University, 1970.

———. “Kepler, Tycho, and the ‘Optical Part of Astronomy’: The Genesis of Kepler’s Theory of Pinhole Images.” Archive for History of Exact Sciences 24, no. 4 (January 1, 1981): 267–93.

Tachau, Katherine H. Vision and Certitude in the Age of Ockham. Brill Archive, 1988.

Taylor, C.C. W. The Atomists, Leucippus and Democritus: Fragments  : A Text and Translation with a Commentary. University of Toronto Press, 1999.

Thornton, Joy Allen. “Renaissance Color Theory and Some Paintings by Veronese.” PhD Dissertation, University of Pittsburgh, 1979.

Tweedale, Martin M. “Comments on ‘Explaining Sense Perception: A Scholastic Challenge’ by Alison J. Simmons.” Philosophical Studies: An International Journal for Philosophy in the Analytic Tradition 73, no. 2/3 (March 1, 1994): 277–81.

Vanagt, Katrien. “Early Modern Medical Thinking on Vision and the Camera Obscura. V.F. Plempius’ Ophthalmographia.” In Blood, Sweat and Tears - The Changing Concepts of Physiology from Antiquity into Early Modern Europe, edited by Claus Zittel, Manfred Horstmanshoff, and Helen King, 569–293. Brill Academic Publishers, 2012.

Villemaire, Diane Elizabeth Davis. E.A. Burtt, Historian and Philosopher. Springer, 2002.

Von Fritz, Kurt. “Democritus’ Theory of Vision.” In Science, Medicine, and History: Essays on the Evolution of Scientific Thought and Medical Practice, Written in Honour of Charles Singer, edited by E. A. Underwood, 83–99. London, 1953.

Von Staden, H. “Teleology and Mechanism: Aristotelian Biology and Early Hellenistic Medicine.” In Aristotelische Biologie, edited by W Kullmann and S Föllinger, 183–208. Franz Steiner, 1997.

379

Wear, Andrew. “Medicine in Early Modern Europe, 1500–1700.” In The Western Medicial Tradition: 800 B.C. – 1800 A.D., 215–340. Cambridge University Press, 1995.

World Meteorological Organization, and National Climatic Data Center (U.S.). 1961-1990 Global Climate Normals. Version 1.0. Asheville, NC: The Center  : NCDC Climate Services Branch, 1998.

Ziggelaar, August. François de Aguilón, S.J. (1567-1617), Scientist and Architect. Institutum Historicum S.I., 1983.

380

Tawrin Baker 1230 Boulevard Unit A

Athens, GA 30601

T 812 343-9391

[email protected]

E D U C AT I O N

November 2014 Indiana University, Bloomington Ph.D., History and Philosophy of Science Title of Dissertation: “Color, Cosmos, Oculus: Vision, Color, and the Eye in Jacopo Zabarella and Hieronymus Fabricius ab Aquapendente.”

May 2000 SUNY Binghamton B.S., Physics Minor in computer science

E D I T E D B O O K S

Early Modern Colour Worlds. Edited by Tawrin Baker, Sven Dupré, Sachiko Kusukawa, and Karin Leonhard. (To be published in 2015 as a double issue of Early Science and Medicine and simultaneously as a hardbound volume through Brill.)

A RT I C L E S A N D B O O K C H A P T E R S

“Sixteenth-Century Ocular Anatomy and the Anatomical Theater.” In Renaissance Cultures of Optics and Practices of Perspective. Edited by Sven Dupré and Jeanne Peiffer. Forthcoming.

“Colour and Contingency in Robert Boyle’s Works.” In Early Modern Colour Worlds. Edited by Tawrin Baker, Sven Dupré, Sachiko Kusukawa, and Karin Leonhard. (To be published in 2015 as a double issue of Early Science and Medicine and simultaneously as a hardbound volume through Brill.)

“Why All This Jelly? Jacopo Zabarella and Hieronymus Fabricius ab Aquapendente on the Usefulness of the Vitreous Humor.” In Early Modern Medicine and Natural Philosophy. Edited by Peter Distelzweig, Benjamin Goldberg, and Evan Ragland. Springer, forthcoming.

“Colour in Three Seventeenth-Century Natural Philosophy Textbooks.” In Colour Histories: Colour in the 17th and 18th centuries; Connexions between Science, Arts, and Technology. Edited by Friedrich Steinle and Magdalena Bushart. Walter de Gruyter, forthcoming.

P R E S E N TAT I O N S

7 November 2014, Session Organizer for “Replicating Early Modern Materials, Observations, and Experiments,” History of Science Society Annual Meeting, Chicago, Illinois.

7 November 2014, “Performing Early Modern Dissections and Experiments on the Eye,” History of Science Society Annual Meeting, Chicago, Illinois.

March 2014, “Colour and Contingency in Robert Boyle’s Works,” Early Modern Colour Practices Workshop II, Berlin, Germany.

26 September 2013, “The Most Godlike of the Instruments: Recreating Early Modern Ocular Dissections and Experiments,” Western Michigan University Medical Humanities Conference, Kalamazoo, Michigan, USA.

20 September 2013, Invited Paper, “Thickening the Celestial Aether versus Blowing Bubbles and Grinding Glass: The Shift from Aristotelian to Corpuscular Theories of the Origin of Colour,” Early Modern Colour Practices Workshop I, Berlin, Germany.

7 April 2013, “Sensation, Subjectivity, and Objectivity in the Early Modern Period: Historical and Historiographical Concerns,” 56th Meeting of the Midwest Junto for the History of Science, Notre Dame, Indiana, USA.

2–4 November 2012, “Why All This Jelly? Jacopo Zabarella, Hieronymus Fabricius ab Aquapendente, and Julius Casserius on the Usefulness of the Vitreous Humor,” Conference on Early Modern Medicine and Natural Philosophy, Pittsburgh, Pennsylvania, USA.

11–14 July 2012, “Cosmology and the Crystalline Humor: Color Theory in Natural Philosophy and Anatomy in Late Sixteenth-Century Padua,” HSS/BSHS/CSHPS 3-Society Meeting, Philadelphia, Pennsylvania, USA.

28–30 June 2012, “Colour in Seventeenth Century Natural Philosophy Textbooks,” Colour in the 17th and 18th Centuries: Connexions Between Science, Arts, and Technology, Technische Universität, Berlin, Germany.

9 December 2011, “Paduan Chiasmata: Color, Vision, and the Eye in Late Sixteenth-Century Natural Philosophy and Anatomy at the University of Padua,” Renaissance Studies Roundtable, Bloomington, Indiana, USA.

4–7 November, 2010, “Fixed Colors in the Works of Francis Bacon: A Reappraisal,” History of Science Society Annual Meeting, Montreal, Quebec, Canada.

FELLOWSHIPS AND AWARDS

June 2014–August 2014, Predoctoral Research Fellow Max Planck Institute for the History of Science, Berlin, working with the research group “Modern Geometry and the Concept of Space” led by Vincenzo de Risi.

2014, Victor E. Thoren Graduate Student Research Fellowship, History and Philosophy of Science Department, Indiana University.

2012–2013, Indiana University College of Arts and Sciences Dissertation Year Research Fellowship.

2012, Gladys Krieble Delmas Foundation Grant for Independent Research on Venetian History and Culture.

2012, Richard S. Westfall Fellowship for Graduate Student Research Travel.

January 2012–May 2012, Predoctoral Research Fellow, Max Planck Institute for the History of Science, Berlin, working with the research group “Art and Knowledge in Pre-Modern Europe” led by Sven Dupré.

T E A C H I N G

Fall 2010–Spring 2011Instructor, Indiana University, BloomingtonCourse: Science Revolutions: Plato to Nato

Fall 2011 Assistant Instructor, Indiana University, BloomingtonCourse: The Evolution of the Modern University

R E S E A R C H E X P E R I E N C E

Fall 2008–Spring 2010; Summer 2011, 2012, 2013 Research Assistant for William R. Newman, Indiana University, BloomingtonEditorial Assistant, Transcriber, Encoder for The Chymistry of Isaac Newton (www.chymistry.org)

June 1999–August 1999 REU (Research Experiences for Undergraduates) in physics, Georgia Institute of TechnologyWorked under Professor Sa De Melo on a novel two-particle problem in theoretical physics

Color Cosmos Oculus: Vision, Color, and the Eye in Jacopo Zabarella and Hieronymus Fabricius ab...

Documents

Transcript of Color Cosmos Oculus: Vision, Color, and the Eye in Jacopo Zabarella and Hieronymus Fabricius ab...