The British Society for the History of Science

The Origins of the FitzGerald ContractionAuthor(s): Bruce J. HuntSource: The British Journal for the History of Science, Vol. 21, No. 1 (Mar., 1988), pp. 67-76Published by: Cambridge University Press on behalf of The British Society for the Historyof ScienceStable URL: http://www.jstor.org/stable/4026862Accessed: 11/01/2010 15:39

Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available athttp://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unlessyou have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and youmay use content in the JSTOR archive only for your personal, non-commercial use.

Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained athttp://www.jstor.org/action/showPublisher?publisherCode=cup.

Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printedpage of such transmission.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact support@jstor.org.

Cambridge University Press and The British Society for the History of Science are collaborating with JSTOR todigitize, preserve and extend access to The British Journal for the History of Science.

http://www.jstor.org

BJHS, 1988, 21, 67-76

The Origins of the FitzGerald Contraction

BRUCE J. HUNT-

The FitzGerald-Lorentz contraction hypothesis has become well known in connection with Einstein's theory of relativity, and its role in the origin of that theory has been the subject of considerable study. But the origins of the contraction idea itself, and particularly of G. F. FitzGerald's first statement of it in 1889, have attracted much less attention and are surrounded by several misconceptions.' The hypothesis has usually been depicted as a rather wild idea put forward without any real theoretical justification simply to explain away the troublesome null result of Michelson and Morley's 1887 ether drift experiment. In the words of Gerald Holton, 'it has traditionally been called the very paradigm of an ad boc hypothesis'.' H. A. Lorentz, who hit upon the contraction idea independently in 1892, has been credited with giving it some justification in terms of his electron theory, but little or none of this credit has been extended to FitzGerald. s His statement of the contraction hypothesis has usually been viewed, in the words of his friend R. T. Glazebrook, as nothing more than 'the brilliant baseless guess of an Irish genius'.4

Closer examination of the events leading up to FitzGerald's formulation of the contraction hypothesis reveals, however, that it had a considerably stronger theoretical foundation than has generally been recognized. Rather than being just an isolated inspiration, it was a natural outgrowth of the work on electromagnetic theory that FitzGerald and his Maxwellian colleagues had been pursuing since the early 1880s. In particular, it appears that FitzGerald drew on Oliver Heaviside's discovery in December 1888 that the electromagnetic field around a moving charge would shrink slightly along its line of motion-by just the amount, in fact, that was later required by relativity theory. By combining Heaviside's formula with what he already believed about the electro- magnetic nature of intermolecular forces, FitzGerald would have been able to predict the contraction effect had he never heard of the Michelson-Morley experiment.

1 A.M. Bork, 'The "FitzGerald" contraction', Isis, (1966), 57, pp. 199-207, remains the chief source, but it contains serious oversights and must be supplemented by S.G. Brush, 'Note on the history of the FitzGerald- Lorentz contraction', Isis, (1967), 58, pp. 230-232.

2 G. Holton, 'Einstein, Michelson, and the "crucial" experiment', in: Thematic Origins of Scientific Thought: Kepler to Einstein, Cambridge, Mass., 1973, p. 311. For a typical popular treatment of the origins of the contraction hypothesis, see R.W. Clark, Einstein: The Life and Times, New York, 1971, pp. 110-111.

3 E.Zahar, 'Why did Einstein's research programme supersede Lorentz's?' British Journal for the Philosophy of Science, (1973), 24, pp. 95-123, 223-262, argues that the contraction hypothesis should not be considered ad hoc, but focuses on Lorentz and says almost nothing about FitzGerald.

4 R.T. Glazebrook, 'H.A. Lorentz', Nature, (25 Feb. 1925), 121, pp. 287-288.

* Department of History, University of Texas, Austin, TX 78712, U.S.A.

68 Bruce J. Hunt

The moving charge

The FitzGerald contraction hypothesis had its beginnings at the September 1888 Bath meeting of the British Association for the Advancement of Science in a debate over what FitzGerald called the 'murder of 4i.i 'd' was Maxwell's symbol for the electric potential; in his Treatise on Electricity and Magnetism he had made it a fundamental quantity and, following older theories, had assumed that it propagated instantaneously. In the 1880s, however, studies of telegraphic signalling and then Heinrich Hertz's dramatic discovery of electromagnetic waves (first announced in Britain by FitzGerald at the Bath meeting), focused new attention on propagation phenomena and engendered doubts about Maxwell's use of the potentials. Some of the younger Maxwellians, led by FitzGerald and Heaviside, began to advocate a new interpretation in which the potentials were given a decidedly subsidiary role and the emphasis was instead put on the electric and magnetic forces, which had a more direct physical significance and were known to propagate at the speed of light. At the Bath meeting, Sir William Thomson (later Lord Kelvin) put up a spirited defence of the older view, parrying FitzGerald's arguments against the primacy of the potentials and contending that tP might well be propagated instantaneously. Although the issue was not fully resolved at Bath, the debate, together with the interest aroused by Hertz's work, greatly sharpened thinking about electromagnetic propagation.

FitzGerald's friend Oliver Lodge took an active part in the debate at Bath and later wrote an account of it for the Electrician, a London electrical trade journal. There it came to the attention of Heaviside, a former telegraph engineer and self-taught mathematician who had made himself one of the leading students of Maxwellian theory. In 1885, he had recast Maxwell's theory into the four 'Maxwell's equations' now in general use, in which the electric and magnetic forces E and H play the leading roles and the potentials are treated as purely derivative quantities. Late in October 1888, he threw his weight behind the 'murder of if' in a note to the Philosophical Magazine, 'On the metaphysical nature of the propagation of the potentials', in which he argued that since E and H give the most direct representation of the physical state of the field, particularly its energy, only these forces should be regarded as being propagated.6 The potentials were merely mathematical fictions, Heaviside said, and the question of their rate of propagation was 'metaphysical'-it could not, even in principle, be decided by experiment. He had the editor of the Philosophical Magazine forward the note to Kelvin, one of the journal's advisory editors and the man Heaviside most wanted to impress with his views on the primacy of E and H.7 Kelvin replied that he did not agree that the rate of propagation of electric potential was 'a merely metaphysical question' and suggested that it could in principle be determined experimentally by moving a charged body back and forth and testing to see whether sensitive electrometers at different distances from it were affected simultaneously or only after a time-lag.8

5 O.J. Lodge, 'Sketch of the electrical papers in Section A at the recent Bath Meeting of the British Association', Electrician, (21 Sept. 1888), 21, pp. 622-625.

6 0. Heaviside, 'On the metaphysical nature of the propagation of the potentials', Phil. Mag. (Jan. 1889), 27, pp. 47-50, reprinted in Heaviside, Electrical Papers, 2 vols, London, 1892, 2, p. 483.

7 Notebook 3a, entries 159 and 164, Heaviside Collection, Institution of Electrical Engineers, London. 8 Kelvin to Heaviside, 2 November 1888, Heaviside Collection, op. cit. (7); part published in Heaviside,

1892, op. cit. (6), Electrical Papers, 2, p. 490.

The FitzGerald Contraction 69

Kelvin's letter had important consequences, for it turned the debate over the propa- gation of potential into one about the state of the electromagnetic field around a moving charge. This problem had never before been fully solved; earlier theorists had treated only the slow motion of charges, for which it could be safely assumed that the electrostatic field was simply carried along unchanged-that is, that the potential adjusted itself instan- taneously. Kelvin had in effect challenged Heaviside to find what, on Max- wellian principles, the electromagnetic field would be around a charge moving at any speed. Heaviside's answer to this challenge was to play a key role in the genesis of FitzGerald's contraction hypothesis.

Heaviside's first reaction to Kelvin's letter was more mundane: he saw it as ammunition in his campaign for recognition. Heaviside's work on telegraphic propagation had landed him in a dispute with officials of the government telegraph department and had contributed to the abrupt cancellation in October 1887 of his long-running series of articles on electromagnetic theory in the Electrician.9 Heaviside was anxious that the series be renewed, in part because he had no other job and needed the ?40 a year he got for the articles. He was spurred even more, however, by his desire to avenge the wound to his considerable pride and to win back a public forum from which to demonstrate the errors of his opponents and the superiority of his own version of electromagnetic theory. It was with this in mind that in November 1888 he asked Kelvin for permission to publish his letter in the Electrician, along with Heaviside's reply. He wanted to use Kelvin's name as bait; as he said in a postscript to his request, 'I may mention as a private reason for wishing to publish it that it may lead the Ed. to see his way to resume my Articles on Propagation, so you might be doing me a great service'.10 Kelvin's reputation was enormous; anything from his pen would be snapped up by the editors of the Electrician. Heaviside hoped they would be led to swallow his own work as well. Kelvin gave his permission, but Heaviside's strategy was only partially successful: the Electrician published his letter and shortly thereafter two others on the same subject, but it did not resume his regular series until 1891."

Kelvin's challenge led Heaviside back to a question he had first attacked as long ago as 1880-1881; indeed, his research notebooks show him to have been perhaps the first person ever to treat the moving charge problem comprehensively on the basis of Maxwell's theory.' 1 He had then derived such important results as the force on a charge moving in a magnetic field, F= qvxB, later well known as the 'Lorentz force'. At that time, however, Heaviside was still using Maxwell's scalar and vector potentials and his derivations were long and cumbersome. He did not then publish his findings, many of which were independently derived and first published by J. J. Thomson in April 1881." V

9 See B. Hunt, "'Practice versus theory": the British electrical debate, 1888-1891', Isis, (1983), 74, pp. 341-355.

10 Heaviside to Kelvin (draft), 5 November 1888, Heaviside Collection, op. cit. (7). 11 Kelvin to Heaviside, 6 November 1888, Heaviside Collection, op. cit. (7); Heaviside, 1892, op. cit. (6),

Electrical Papers, 2, pp. 490-496. 12 Notebook 7, Heaviside Collection, op. cit. (7), marked 'Done 1880-1'. 13 J.J. Thomson, 'On the electric and magnetic effects produced by the motion of electrified bodies', Phil.

Mag. (April 1881), 11, pp. 229-249.

70 Bruce J. Hunt

Thomson's paper contained several important results and was later cited as a precursor of electron theory, but it was seriously flawed. Thomson had fallen into contradictions by tracing all of the electromagnetic effects of a moving charge to the displacement currents set up in the surrounding space, and mistakes in his use of the vector potential led him to erroneous values for the energy of and forces on a moving charge-he gave the 'Lorentz force', for example, as half its true value.'4 FitzGerald had followed this work closely and corrected the first of Thomson's errors in a note presented to the Royal Dublin Society in November 1881. He pointed out explicitly that in Maxwell's theory a moving charge must itself be regarded as what he called a 'convection current', a point he followed up a few months later in an important paper, 'On electro- magnetic effects due to the motion of the Earth'.') Heaviside finally published his own correction of Thomson's value for the energy of a moving charge in 1885, but it was buried at the end of one of his Electrician articles and attracted no attention; Thomson repeated his uncorrected values as late as 1888.16

To this point, Thomson, FitzGerald and Heaviside had treated only the slow motion of charges. They had ignored self-induction, by which the motion of the electric field around a charge induces a magentic field whose motion in turn induces an additional electric field, and so on. They had taken into account only the first term of the resulting infinite series-a legitimate procedure so long as the speed of the charge was a small fraction of that of light, but one that tacitly assumed that the field adjusted instan- taneously to the motion. Kelvin's challenge to Heaviside on precisely this point in November 1888 drove him to attack the problem again without this simplifying assumption.

Heaviside knew by general reasoning that the electric and magnetic fields around a moving charge would tend to bunch up around the middle, but at first he was able to derive only a complicated infinite series of harmonics to describe this effect. To his own surprise, however, he found early in December that this series could be reduced to a fairly simple formula that was exact for any speed up to that of light. He immediately sent a letter off to the Electrician, where the formula first appeared in print on 7 December 1888."7

14 Ibid., p. 241; cf. E.T.Whittaker, History of Theories of the Aether and Electricity, 2 vols, New York, 1951, 1, pp. 306-310. The sequence of Maxwellian treatments of charge convection is discussed very fully in J.Z. Buchwald, From Maxwell to Microphysics: Aspects of Electromagnetic Theory in the Last Quarter of the Nineteenth Century, Chicago, 1985, pp. 269-277.

15 G.F.FitzGerald, 'Note on Mr J.J. Thomson's investigation of the electro-magnetic action of a moving electrified sphere', Scientific Proceedings of the RoyalDublin Society, (Nov. 1881), 3, pp. 250-254, reprinted in G.F. FitzGerald, Scientific Writings of the late George Francis FitzGerald (ed. J. Larmor), Dublin, 1902, pp. 102- 107; G.F. FitzGerald, 'On electromagnetic effects due to the motion of the Earth', Scientific Transactions of the Royal Dublin Society, (May 1882), 1, pp. 319-324, reprinted in FitzGerald, op. cit., Scientific Writings, pp. 111-118.

16 Heaviside, 1892, op. cit. (6), Electrical Papers, 1, p. 446,2, pp 505-507; J.J. Thomson, Applications of Dynamics to Physics and Chemistry, London, 1888, pp. 32-35.

17 Heaviside, 'The electro-magnetic effects of a moving charge', Electrician, (7 Dec. 1888), 22, pp. 147-148, reprinted in Heaviside, 1892, op. cit. (6), Electrical Papers, 2, pp. 494-496.

The FitzGerald Contraction 71

Heaviside found that

E q (1 - v2/c2) r2 (1 -v2/c2 sin2 0)3/2

directed radially outward, and

H = Ev sinO,

in circles centred around the line of motion, where q is the charge, v its velocity through the ether, c the speed of light, r the distance from the charge to a point, and 0 the angle to the line of motion. Note especially the (1 - v2/c2) factor and the way the field lines bunch up around the 'equator' (if we picture the charge moving along its polar axis) as the speed increases (Fig. 1). This compressed field is in fact the same as the FitzGerald-Lorentz

q IV2/C2 Radial field of a charge at rest r (I - v2/c2 sin e)3/2

H =Evsine

q = charge v = velocity of charge c = velocity of light r = distance from charge e = angle with line of motion

q

r~~~~~~~~~~~~~~~ 8~~~~~~~~~~~~~~~~

q

Contracted field of a charge in motion, showing the new surface of equilibrium

Figure 1. Radial field of a charge at rest (above); contracted field of a charge in motion, showing the new surface of equilibrium.

72 Bruce J. Hunt

contraction of the electrostatic field of a charge at rest, in exact accordance with Einstein's theory of relativity. The surface of electrical equilibrium, called a 'Heaviside ellipsoid', is an oblate spheroid contracted along the line of motion by a factor of 1V-tv2/, although it was not until 1892 that this last fact was fully clarified by Heaviside's friend G. F. C. Searle.18 All of this follows directly from Maxwell's equations and shows quite clearly that 'relativistic' effects were already implicit in Maxwell's theory.

Heaviside was proud of his formula; it was simple and clear enough, he said, 'to take a place in text-books'. He made it the basis of an important paper he sent to the Philosophical Magazine late in December 1888 and made a point of drawing attention to it in letters to FitzGerald, Kelvin, Hertz and J. J. Thomson.'9

It was at about this time and on these issues that Heaviside first began to correspond with FitzGerald-a development of great importance for the origin of the FitzGerald contraction and for the evolution of the Maxwellian group. Heaviside saw FitzGerald's work on convection currents mentioned in the Electrician in November 1888 and wrote to him for details. FitzGerald replied late in December and sent copies of several of his papers."' Heaviside took special note of FitzGerald's remark in his 1881 paper on convection currents that it would be 'most interesting' to have a solution to the moving charge problem that was valid for any speed, and at the end of January he wrote to draw FitzGerald's attention to the solution he had recently published in the Electrician. FitzGerald replied that he was 'very glad to hear that you have solved completely the problem of the moving sphere' and remarked that, as the formula suggested, the velocity of light might be a physical limit to speed.2 He also mentioned the possible application of Heaviside's work to 'a theory of the forces between molecules', indicating that FitzGerald already thought that intermolecular forces might be essentially electromagnetic. Indeed, since he believed that all physical forces, as well as matter itself, arose from the various motions of a single ether, FitzGerald regarded Heaviside's formula for how electro- magnetic forces varied with velocity as a valuable guide to how other forces were likely to be affected by motion through the medium.22

18 Heaviside, 1892, op. cit. (6), Electrical Papers, 2, p. 514n; cf. Searle to Heaviside, 19 August, 24

September 1892, Heaviside Collection, op. cit. (7) and G.F.C. Searle, 'Problems in electrical convection', Phil.

Trans. (1896), 187A, pp. 675-713. That the contraction of the field implies a contraction of matter was by no

means clear at first; although FitzGerald took this step quite readily, most other physicists did not accept it until

after the advent of electron theory. 19 Heaviside, 1892, op. cit. (6), Electrical Papers, 2, p. 495; Heaviside, 'On the electromagnetic effects due

to the motion of electrification through a dielectric', Phil. Mag. (April 1889), 27, pp. 324-339, reprinted in

Heaviside, 1892, op. cit. (6), Electrical Papers, 2, pp. 504-518; Heaviside to FitzGerald, 30 January 1889,

FitzGerald Collection, Royal Dublin Society; Heaviside to Kelvin, 27 February 1889, Kelvin Collection,

University Library, Cambridge; Heaviside to Hertz, 1 April 1889, Hertz Collection, Deutsches Museum,

Munich; Thomson to Heaviside, 7 April 1889 and 26 May 1889, Heaviside Collection, op. cit. (7).

20 S.P. Thompson, 'Electrical theory', Electrician, (16 Nov. 1888), 22, pp.54-55; FitzGerald to Heaviside,

27 December 1888, Heaviside Collection, op. cit. (7). 21 Heavisideto FitzGerald, 30January 1889, FitzGerald Collection, op. cit. (19); FitzGerald to Heaviside,

4 February 1889, Heaviside Collection, op. cit. (7). 22 On FitzGerald's commitment to the ether as the ultimate basis of all physical phenomena, see G.F.

FitzGerald, 'On a model illustrating some properties of the ether', Scientific Proceedings of the Royal Dublin

Society, (Jan. 1885), 4, pp. 407-419, reprinted in FitzGerald, 1902, op. cit. (15), Scientific Writings, pp.

142-156, especially pp. 154-155; on his attempts to extend theories of the motion of the ether to explain

molecular and chemical forces, see G.F. FitzGerald, 'Helmholtz Memorial Lecture', Journal of the Chemical

Society, (Jan. 1896), 69, pp. 885-912, reprinted in FitzGerald, 1902, op. cit. (15), Scientific Writings, pp.

340-377.

The FitzGerald Contraction 73

It was on 8 February 1889, just a few days after writing to Heaviside, that FitzGerald first visited him in London. Their main topic of conversation seems to have been Hertz's work on electromagnetic waves, but they apparently discussed the moving charge problem as well.'3 Their correspondence lapsed for a time after that, but Heaviside made a point of sending FitzGerald a copy of one of his papers on moving charges in the summer of 1889 and the subject came up repeatedly in their letters in the 1890s.24 In any case, it is clear that by early 1889, FitzGerald knew that Heaviside had shown that Maxwell's theory implied that the electromagnetic field around a moving charge would be compressed by an amount dependent on v2/c2.

Lodge and the Michelson-Morley experiment

The scene now shifts to Liverpool, the home of FitzGerald's good friend Oliver Lodge. Early in 1889 and for several years thereafter, much of Lodge's attention was directed towards problems of motion through the ether; in particular, those problems raised by the Michelson-Morley experiment.25 There was abundant evidence, drawn from the analysis of stellar aberration and other phenomena, that the ether of space was stationary and that the Earth moved freely through it. Yet Michelson and Morley's experiment had shown no sign of this motion. It seemed, as Heaviside later said, to confront the accepted laws of physical optics, and so of electromagnetism, with a 'flat contradiction.26 FitzGerald, too, had been puzzled by the problem and had spoken on the Michelson- Morley experiment three times at meetings of the Royal Dublin Society in 1888.27

Sometime in the spring of 1889, probably late in March or in April, FitzGerald paid one of his periodic visits to Lodge in Liverpool. It was while they were sitting in Lodge's study at 21 Waverley Road, discussing the Michelson-Morley experiment and the difficulty of reconciling it with the evidence for a stationary free ether, that, as Lodge later recalled, 'the brilliant suggestion ... flashed on' FitzGerald that the motion of bodies through the ether might cause them to change in size by just the amount needed to account for Michelson and Morley's null result.28 Lodge gave at least four accounts of the occasion, ranging from a single sentence in an obituary of FitzGerald which he wrote in

23 Heaviside to Hertz, 13 July 1889, Hertz Collection, op. cit. (19). See also Heaviside to Lodge, 4 August 1902, Lodge Collection, University College London, for evidence that FitzGerald raised the moving charge problem on his visit to Heaviside in 1889.

24 There is a proof copy of O. Heaviside, 'The electromagnetic effects of a moving charge-III', Electrician, (6 Sept. 1889), 23, pp. 458-459, reprinted in Heaviside, 1892, op. cit. (6), Electrical Papers, 2, pp. 496-499, dated 25 August and corrected in Heaviside's hand, in the FitzGerald Collection, op. cit. (19).

25 O.J. Lodge, 'Modern views of electricity', Nature, (31 Jan. 1889), 39, p. 321; see also B. Hunt, 'Experimenting on the ether: Oliver J. Lodge and the great whirling machine', Historical Studies in the Physical Sciences, (1 986), 16, pp. 1 1-134.

26 Heaviside to Lodge, 13 November 1893, Lodge Collection, op. cit. (23). 27 G.F. FitzGerald, 'Michelson and Morley on the relative motion of the Earth and the luminiferous aether'

(Royal Dublin Society, 18 Jan., 14 Feb. and 18 April 1888), listed (title only ) in Yearbook of Scientific and Learned Societies, London, 1889.

28 O.J. Lodge, 'G.F. FitzGerald', Proceedings of the Royal Society, (1905), 75, pp. 152-160, reprinted in FitzGerald, 1902, op. cit. (15), Scientific Writings, pp. xxxii-xxxix, on p. xxxiv.

74 Bruce J. Hunt

1901, to a full page in his 193 1 autobiography, complete with verbatim quotes.29 As these accounts grow more elaborate, they become less reliable, and it is sometimes difficult to disentangle FitzGerald's ideas from Lodge's later additions. In particular, in his later accounts, Lodge said that FitzGerald had suggested that a moving body does not simply contract along its line of motion but expands laterally as well, so that its volume remains constant. :' FitzGerald himself, however, always spoke only of a change in the length of a moving body and there is no reason to think that the idea that flashed on him in Lodge's study involved anything other than a simple contraction.

The actual course of FitzGerald's thinking is, of course, inaccessible to us, but it should be stressed that he had the prerequisites for a plausible contraction hypothesis well in mind before his talk with Lodge about the Michelson-Morley experiment precipitated its statement. Although in 1889 he did not yet have a developed electron theory of matter, FitzGerald already thought it likely that intermolecular forces were electromagnetic; in any case, he was sure that they depended on the ether just as electromagnetic forces did and so would presumably be affected by motion in much the same way. Most impor- tantly, he had fresh in his mind Heaviside's formula giving just the f fv2/c effect needed to account for Michelson and Morley's result. In early 1889, FitzGerald had reason to think that bodies should change in size when they move through the ether- given what he knew about how electromagnetic forces change with velocity and what he believed about the nature of intermolecular forces, he could in principle have predicted Michelson and Morley's result, had the experiment not yet been done. Indeed, he apparently told Lodge when the idea first occurred to him-certainly he repeated the remark later-that the contraction ought to occur and 'that Michelson's experiment proves, and is one of the only ways of proving, that the length of a body depends on how it is moving through the ether'.:" Lorentz, who followed a similar train of reasoning in 1892, apparently felt much the same way. In 1915, he wrote to Einstein that 'one arrives at this [contraction] hypothesis if one extends to other forces what one can already say about the influence of translation on electrostatic forces. If I had stressed this more, then the hypothesis would have given much less of an impression of having been invented ad hoc' 3X}

FitzGerald usually aired his new ideas at the Royal Dublin Society; it was there, for instance, that he had first published his work on moving charges in the early 1880s. But one of his efforts to reform the Society led early in 1889 to a confrontation in which his faction was defeated. He resigned as honorary vice-president in February 1889 and had nothing more to do with the Society for nearly ten years.:': With his usual outlet thus

29 Ibid.; O.J. Lodge, The Ether of Space, London, 1909, pp. 65-66; O.J. Lodge, 'Continuity' (Presidential Address), British Association Report, (1913), pp. 3-42, on pp. 25-26; O.J. Lodge, Past Years, London, 1931, pp. 204-205.

30 See Bork, op. cit. (1), p. 206, with the relevant passages from Lodge's 1913 and 1931 accounts (op. cit., 29).

31 FitzGerald to Lorentz, 14 November 1894, quoted in Brush, op. cit. (1), p.231; cf. Lodge, 1931, op. cit. (29), Past Years, p. 205.

32 Lorentz to Einstein, January 1915 (draft), in A. Pais, Subtle is the Lord: The Science and the Life of Albert Einstein, Oxford, 1982, p. 167.

33 See C. Mollan, 'Science and its industrial applications', in The Royal Dublin Society, 1731-1981 (ed. J. Meenan and D. Clarke), Dublin, 1981, pp. 210-21 1.

The FitzGerald Contraction 75

blocked, FitzGerald had to look for another forum in which to announce his contraction hypothesis. He chose the New York journal Science, apparently because Michelson and Morley were Americans. In a brief letter sent on 2 May and published two weeks later, he wrote that almost the only way to reconcile their results with the abundant evidence for a stationary ether was by the hypothesis that:

... the length of material bodies changes, according as they are moving through the ether or across it, by an amount depending on the square of the ratio of their velocities to that of light. We know that electric forces are affected by the motion of the electrified bodies relative to the ether, and it seems a not improbable assumption that the molecular forces are affected by the motion and that the size of bodies alters consequently.34

FitzGerald clearly tied the contraction hypothesis to the known way electromagnetic forces were altered by motion, but the letter was brief and elementary and he did not cite Heaviside's actual formula.

Science was not an especially prominent journal in those days and it was a poor place for FitzGerald to try to publicize his contraction idea. He rarely saw the journal himself and in fact never saw his own letter in print, nor is there any evidence that anyone else of interest saw it at the time-indeed, it remained almost wholly unknown until Stephen Brush unearthed it in 1967.35 The letter was so obscure that it was overlooked when FitzGerald's collected Scientific Writings were published posthum- ously in 1902-a particular irony since the editor was Joseph Larmor, FitzGerald's close friend and a great proponent of the contraction hypothesis and of FitzGerald's claim to credit for it.36

Once he had sent his letter off to Science, FitzGerald did little more to publicize his hypothesis; he often did not follow up his ideas very thoroughly, a failing he ascribed to laziness. 7 He mentioned the contraction idea in his lectures at Trinity College, Dublin and to some of his scientific friends, including R. T. Glazebrook and J. J. Thomson, and unsuccessfully urged his former student Thomas Preston to include it in his 1890 text- book Theory of Light.:18 FitzGerald eventually persuaded Lodge to mention it in a paper on ether and matter that appeared in Nature in June 1892-the first published reference to the contraction hypothesis since FitzGerald's own letter to Science three years before. This was followed in 1893 by a somewhat fuller (though still very brief) discussion in Lodge's major Royal Society paper on 'Aberration problems'.:"'

34 G.F. FitzGerald, 'The ether and the Earth's atmosphere', Science, (17 May 1889), 13, p. 390. 35 Brush, op cit. (1); FitzGerald's Science paper was, however, listed in the Royal Society Catalogue of

Scientific Papers, Cambridge, 1916, 15, p.2. 36 On Larmor's advocacy of credit for FitzGerald, see Larmor to Lodge, 24 October 1901, Lodge

Collection, op. cit. (23). 37 FitzGerald may also have been put off from following up his initial insight by confusion about the

directional variation of the forces between charges moving together, the intricacies of which were not cleared up until 1892 and were not well known for several years after that; see Searle and Heaviside (note 18), and FitzGerald to Larmor, 30 March and 4 April 1895, Larmor Collection, Royal Society, London.

38 FitzGerald to Lorentz, 14 November 1894, in Brush, op. cit. (1). The contraction is not mentioned in the first edition of Preston's Light (London, 1890), but it appears in the second (1895) and later editions of this widely used text. See also Glazebrook, op. cit. (4), describing a visit from FitzGerald to Cambridge, apparently in June 1893.

76 Bruce J. Hunt

It was via the latter paper that FitzGerald's hypothesis came to the attention of Lorentz in Holland. Lorentz had hit upon the same idea independently late in 1892 and went on to develop it comprehensively in conjunction with his electron theory. He wrote to FitzGerald in November 1894 to ask if he had ever published anything on the subject. FitzGerald replied that he recalled writing the letter to Science but doubted that it had ever been published. He was glad to hear that Lorentz was working on the problem and seemed content to leave its further development to others.4' Lorentz inserted a footnote in his major work on electron theory, his Versuch of 1895, mentioning that FitzGerald had also proposed the contraction hypothesis, and it is largely because of this reference that

'4' the effect has become known as the 'FitzGerald-Lorentz contraction'. FitzGerald continued to have some involvement with the contraction hypothesis in

the 1890s through his advice to Frederick Trouton on an electrostatic test for motion through the ether and his collaboration with Larmor on the electron theory of matter.42 By 1900, mainly through the parallel efforts of Lorentz and Larmor, the contraction idea had passed into general circulation among electromagnetic theorists. It came into much greater prominence after 1905, of course, in connection with Einstein's theory of relativity, though with a fundamentally new interpretation.

In a letter written to Lodge shortly before FitzGerald's death in February 1901, Heaviside referred to him as 'our friend of brilliant ideas', and it was as a source of ideas, some of them indeed brilliant, that FitzGerald made his greatest contributions to science.43 It is perhaps appropriate that his scientific fame, such as it is, rests today largely on the credit he is given for an idea he initially tossed off in conversation. But to the extent that the contraction hypothesis is seen as simply a bright idea, a 'brilliant baseless guess', FitzGerald's fame is precarious and perhaps misplaced. It is only when the contraction idea is set in its proper context that the real significance of FitzGerald's contribution can be appreciated, and that it can be recognized as a product of a long-continued and co-operative effort to explore the implications of Maxwell's theory in which FitzGerald and the other Maxwellians, particularly Heaviside and Lodge, worked closely together.

39 O.J. Lodge, 'On the present state of our knowledge of the connection between ether and matter: an historical summary', Nature, (16 June 1892), 46, pp. 164-165; O.J. Lodge, 'Aberration problems', Phil. Trans. (1893), 184A, pp. 727- 804, on pp. 749-750.

40 Lorentz's letter of 10 November 1894 and FitzGerald's reply of 14 November are reproduced in Brush, op. cit. (1).

41 H.A. Lorentz, Versuch einer Theorie der Electrischen uind Optischen Erscheinungen in Bewegten Korpern, Leiden, 1895, p. 122n. The relevant part is reprinted in H.A. Lorentz et al., The Principle of Relativity, London, 1952, pp. 3-7.

42 F.T. Trouton, 'The results of an electrical experiment, involving the relative motion of the Earth and the ether, suggested by the late Professor FitzGerald', in FitzGerald, 1902, op. cit. (15), Scientific Writings, pp. 557-565

43 Heaviside to lodge, 19 January 1901, Lodge Collection, op. cit. (23).