GENERAL

A BOOK OF

EDGAR A. BEDFORD,SC .D.

HEAD OF THE DEPARTMENTS OF B IOLOGY AND GENERAL SCIENCE

DE WITT CL INTON HIGH SCHOOL , NEW YORK CITYLECTURER ON M ETH ODS IN TEACH ING GENERAL SCIENCE

DEPARTMENT OF PEDAGOGY, NEW YORK UNIVERSITY

ALLYN A N D BACON

BOSTON NEW YORK CHICAGO

ATLANTA SAN FRANCISCO

SC ENC

PROJECTS

COPYRIGHT, 1921

BY EDGAR BEDFORD.

PREFACE

THE mat erial of General Science is organized according tot he project-problem plan. The class projects are brokenup into problems, in t he solution of which t he pupils are

led t o form hypotheses from the ir observations, to checkand modify these hypotheses by further observations

, and

finally t o come t o a conclusion which is of value in the

deve lopment of t he project .The following aims have been kept in mind

First : to encourage the Spir it of inquiry, and t o cultivate

t he attitude of independent judgment, of openmindedness, and of re liance upon facts.

Second : t o put the pupils in possession of certain fundamental truths which give an explanation of manyeverydayactivities.

Tbird t o lead pupils to a broad V iew of the forces thataffect the ir surroundings, rather than a detai led studyof some one section of the ir environment . The pupilsof this ear ly adolescent per iod are interested in bigunits and a broad outlook, rather than in minutedetails.

The mater ial has been selected from that part of the

environment wh ich is re lated t o the practical interests of

the pupils. No mater ial has been included mere ly becauseit he lps in deve loping some scientific general ization. The

needs of t he ordinari ly we ll-educated citizen, rather than the

iv PREFACE

needs of the scientist, have influenced the choice of topics.

Preference has been given t o topics which lead t o t he

understanding of phenomena of large economic importance .

The environment has been considered as a whole , not asmade up of divisions which can be classified as physics,chemistry, biology, astronomy , and physiography . In

working out a problem for t he solution of t he project, useis made of any necessary facts, regardless of whether theybe long t o this or that special division of science .

By means of a large number of suggested individualprojects, t he teacher i s enabled t o adapt the course t o hisspecial school . Pupils are encouraged to work out t he

projects that are of the most interest t o them . Not all

that are l isted are t o be required of any one student . Someare so simple that any one can perform them easily, while a

few appeal only to those who have a decided mechanicalbent .The text carries out t he spir it of the recommendations

as t o general science of t h e Commission on the Reorgani

zat ion of Science in t he Secondary Schools It is adaptedfor use in the junior h igh school , or in the first year of t he

high school .The author wishe s to express his appreciation to many

fr iends and fe l low teacher s whose assistance has contr ibutedmuch in the preparation of th i s book . Mr . Harry G.

Barber , Department of Biology, and Mr . Thomas Curry,Chairman of t he Department of Physics, in the De WittCl inton High School New York City, have read much of

t he manuscr ipt and have made helpful suggestions and

criticisms. The following teachers of general science inthe New York City schools, acting with the author inplanning a syllabus in general science , have given muchvaluable advice : Mr . Maur ice W. Kearney, Bay Ridge

PREFACE

High School ; Dr . E lsie M . Kupfer , Wadle igh High School ;Miss Mary Morr is, Newtown High School ; Miss EthelSchwarz , Speyer Exper imental Junior High School ; MissEmily Topp, Julia Richman High School ; and Dr . GeorgeC. Wood, Commercial High School .Mr . George K . Gombart s, Head ofArt Department, and

Mr . John W. Tietz of Department of Biology, De WittCl inton High School, have given valuable advice concerningillustrations and have furnished or iginal drawings and

photographs .Dr . Charles F. Brooks of t he Weather Bureau, Dr . L . O.

Howard, Chief of the Bureau of Entomology, and Mr . W.

B . Greeley, Chief of Forest Service , have been generous inopening the resource s of the ir departments .Super intendent Clarence E .Me leney, Super intendent John

L . Tildsley, andDr . Francis H. J . Paul , Principal ofDeWittClinton High School, by the ir broadness of V iew and edu

cat ional vision, have been sources of stimulation in t he

deve lopment of the course represented in t he book .

To h is wife , Le i la Hoge Bedford, t he author desiresespecially t o express h is indebtedness for her intell igentand painstaking assistance .

E . A. B .

TABLE OF CONTENTS

Sugg ested individua l proj ec ts , r epor ts , and r eferen ces a r e not listed h er e , bu t

may be found a t th e end of most pr oj ec ts .

UNIT I

RELATION OF AIR TO EVERYDAY A CTIVITIES

PAGE

PROJECT I . IMPORTANCE OF THE WE IGHT OF AIR

Prob lem 1 . How an airplane remains in th e air

Has air weight ?Does air press upon things ?How air pressure may b e measured

Why water is not used in making b arometersHow an aviator knows h ow high h e isWhy air pressure does not prevent us from

lifting ob jects8 . Why a b alloon or dirigib le remains in th e air

PROJE CT II . How WE USE COMPRE SSED AIR

Prob lem 1 . How air pressure is used in building foundations and subways

2 . How compressed air is used in automob ile

tires3 . How th e tire pump works4 . How a force pump sends a st eady stream of

waterPROJECT III . VENTILATION

Prob lem 1 . Why rooms shouldb e ventilated2 . How air in a room may b e set in motion3 . How convection currents may b e used In

ventilating a room

WINDS

1 . How sea b reezes are caused .

2 Why our winds vary in direction and velocity3 . What are hurr icanes ?4 . How t h e weather bureau Is ab le t o predict

th e weatherv ii

viii TABLE OF CONTENTS

PROJECTV. How WE HEAR

Prob lem 1 . What sound is2 . How . a phonograph reproduces sound3 . How t he ear is fitted t o receive sounds

PROJECT VI . IMPORTANCE To Us OF OXIDATION (BURN ING)Prob lem 1 .

-What burning isHow t h e power of an automob ile is produced

3 . How a match is lightedWhat causes iron t o rustWhy coal is burnedHow availab le energy is supplied tOthe

human bodyDo plants b reathe ?How animals take in ox ygen and give off

carb on dioxide

PROJECT VII . PREVENTION OF DESTRUCTIVE BURNING OR

OXIDATION

Prob lem 1 . How destructive oxidation may b e preventedby excluding the air

2 . How destructive oxidation may b e preventedby reducing the temperature b elow t hekindling point

3 . How destructive oxidation may be preventedby removal of fuel material

PROJECT VIII . IMPORTANCE To Us OF THE OTHER GASES OF

THE AIR

Prob lem 1 . Does air contain any gas besides oxygen ?2 . How much of the air is oxygen ?3 . Importance ofnitrogen in t h e air

4 . Importance of carb on dioxide of th e air

PROJECT IX. To KEEP FOODS FROM SPOILING

Prob lem 1 . What causes foods to spoil or decay ?2 . Where b acteria are found3 . Size , shape , and method ofmultiplication of

bacteria4 . What conditions are favorab le and what un

favorab le for growth of bacteria and

molds?

PAGE

TABLE OF CON TENTS 1x

Prob lem 5. Use of cold in the home in checking thegrowt h of b acteria

6. Use of cold in storage warehouses7. Use made of heat in food preservation8 Use made of other methods of food preser

PROJECT X . To PROTE CT OURSELVES AGAINST HARMFULMICRO

'

ORGAN ISMS

Prob lem 1 . How bacteria and other microorganisms

affect the health2 . How disease germs may pass from one per

son to another3 . How the b ody fights disease4 . How t he body acquires special power t o

fight disease5 . Use of disinfectants and antiseptics

PROJECT XI . To FIND OUT How SOME BACTERIA AND

MOLDS AR E USEFUL

Prob lem 1 . Are b acteria ofdecay of any value ?2 . How b acteria on t h e roots of some plants

may enrich the soil3 . How b acteria are useful in other ways

UNIT II

RELATION OF WATER TO EVERYDAY ACTIVITIES

PROJECT IGI . MOISTUR E IN THE AIR AND ITS IMPORTANCE

To Us 127

How dew is caused 127

How fogs and clouds are produced 131

How rain, snow, andhail are formed 132

Reasons for unequal distribution of rainfall 134

How water is supplied t o dry areas 136

How moisture gets into t he air 138

How th e amount of moisture in the air

affects our comfort 142

PROJECT XIII . THE RELATION OF PLANTS To MOISTURE 144

Prob lem 1 . Do plants give offmoisture ? 144

X TABLE OF CONTENTS

PAGE

Prob lem 2 . The amount ofwater given off by plants3 . How th e root system of a plant is fitted to

find water4 . How roots are especially fitted t o take in

moisture5 . How root hairs take in water6. How water passes out of t he leaves

PROJECT XIV. WATER POWER

Prob lem 1 . What is th e source ofenergy ofwater power ?2 . Source of th e power ofhydraulic pressure

PROJECT XV. To UNDERSTAND How COMMUN ITIE S OBTAINA GOOD SUPPLY OF WATER

Prob lem 1 . Why a wooded mountainous region is se

lect ed t o furnish water2 . HOW the water is protected3 . How other c ities obtain a supply ofwater4 . How the water system within th e house

should b e cared for

PROJECT XVI . To UNDERsTAND THE DISPOSAL OF SEWAGE

OF ,HOME S AND COMMUN ITIES

Prob lem 1 . Care ofwaste water pipes2 . Sewage disposal in Villages and isolated

houses3 . Sewage dISposal in cities

PROJECT XVII . WATER As‘

A MEANS OF TRANSPORTATION

Prob lem 1 . HowNew York harbor originated2 . Effect of the forests of the Adirondacks upon

New York harb or and the navigab ilityof the Hudson River

3 . Importance of internal waterways4 . How ocean transportation depends upon

science

UNIT III

THE RELATION TO US OF SUN ,MOON , AND STARS

PROJECT XVIII . To UNDERSTAND THE CAUSE OF TIDEs 191

Prob lem 1 What causes the water t o rise 192

Problem 2.

3 .

4 .

5 .

6

PROJECT XIX.

Prob lem 1 .

2 .

TABLE OF CONTENTS

Why there are two high tides a dayWhy high tide is a little later every dayWhy t he moon does not fall t o th e earthWhy , at times, there are especially high tidesWhy sometimes only a portion of th e moon

is Visib le t o usHow To KNOW SOME OF THE FIXED STARS

How t o recognize t he constellations around

the north poleHOW t o recognize t h e constellations seen only

in Winter

PROJECT XX. TIME AND SEASONS

Prob lem 1 .

2 .

3 .

4 .

Why we have Winter and summerWhy July andAugust are th e hottest months

and January th e coldest month .

How time is calculatedHow places on the earth’s surface are

indicated

UNIT IV

WORK AND ENERGY

PROJECT XXI . THE SUN As A SOURCE or ENERGY

Problem 1 .

2 .

3.

4.

PROJECT XXII .

Prob lem 1 .

N

g

v

e

ws

8 .

How t he sun’s energy is used in making

picturesOther chemical changes produced by the

sun’

s energyHOW direct use may b e made of the sun

’

s

energyHow th e energy of the sun ismaintainedMACHINES .

What Is meant by work and force

HOW work and force are measured

Reasons for using machinesHow t h e lever is used in doing workHOW Wheels are used in doing workWhy pulleys are used

How inclined.planes are used In doing workWhy machines are not 100 per cent efficient

x i

TABLE OF CONTENTS

PAGE

9 . How friction may b e reduced

10 . Is friction ever useful11 . Causes of inefficiency of engines12 . Th e working of the gas engine

PROJECT XXIII . ELECTR ICITY AND MODERN LIFE

Prob lem 1 . How th e electric b ell rings2 . How magnets are used

3 . How chemical energy may b e changedintoe lectrical energy

How electricity ismeasured : volts, amperes,kilowatts

5 . Use of induction coil in wireless telegraphyand in th e production of spark in gasoline engine

6. Howmechanical energy is changed into elect rical energy by th e dynamo

7. How electrical energy is changed into me

chanical energy by th e electric motor8 . How electroplating and electrotyping are

done

9 . How heat is produced by electricity10 . How electric lights are produced11 . How t h e storage b attery is used

12 . How lightning is produced

PROJECT XXIV. RELATION OF LIGHT To OUR AB ILITY To

SEE THINGS

Prob lem 1 . How ob jects are visib leCost of artificial lighting of rooms

3 . Why shades and reflectors are used4 . How th e color ofth e wall affects th e lighting

of a room5 . Why ob jects have different colors6 . What Is t he cause of t he colors ofsunset and

sunrise and of th e b lueness of th e sky ?

7 . Why eyeglasses are used by some persons

8 . Advantage of having two eyes

9 . How eyes may b e injured10. How a lens makes ob jects appear larger11 . How motion pictures are produced

TABLE OF CONTENTS xiii

PAGE

Prob lem 12 . HOW light effects may guide us in th e se lection of clothing

PROJECT XXV. IMPORTANCE OF HEAT To Us

Prob lem 1 . How a thermos bottle keeps hot liquids hotand cold liquids cold

HOW food may b e cooked In a fire less cooker

What substances are good and What are

poor conductors of heatHOW houses are heated

'

UNIT V

RELATION OF SOIL AND PLANT LIFE TO EVERYDAY

ACTIVITIES

PROJECT XXVI . How SOIL IS MADE 308

Prob lem 1 . OfWhat Is soil composed ? . 309

2 . Evidence that soil 18 now b eing formed 3 10

3 . HOW soil has b een produced by weathering 3 11

4 . How soil h as b een produced by water and

Wind erosion5 . How most of t h e soil of northern United

States has b een produced6 . HOW soil h as been produced by decay of

organic matter

PROJECT XXVII . RELATION OF SOIL To PLANTS

Prob lem 1 . HOW th e water—holding power of t he soilmay b e increased

2 . What plants take from t he Soil3 . How nitrogen may b e given t o t he soil4 How potassium and phosphorus are supplied

t o th e soil5 . HOW plants remove needed materials from

th e soil6 . What plants do with material taken from

th e soil

PROJECT XXVIII . How PLANTS AND AN IMALS MAKE USE

OF THE FOOD MANUFACTURED BY

PLANTS

Xiv

Prob lem 1 .

2 .

3 .

4 .

5 .

6 .

7 .

8 .

PROJECT XXIX .

Prob lem 1 .

P‘

P

WN

95

7 .

8 .

PROJECT XXX .

Prob lem 1 .

2 .

3 .

PROJECT XXXI .

Prob lem 1 .

2 .

3 .

APPENDIX

TABLE OF CONTENTS

Why must plants and animals have food ?What foods are good for fuel

, andwhat onesfor growth and repair

HOW th e fuel value of foods is measuredWhat is t he proper amount of food ? Tab le

of 100 Calorie PortionsWhat considerations should govern the plan

ning of our diet ? .

Why must foods b e digested ?How can we prove that nutrients are

digested ?Where Is food of the human body digested ?HOW PLANTS PRODUCE SEED

Why plants produce seed

What are t he parts of a seed ?

Wh ere seeds are producedDo ovules always deve lop into seeds ?

HOW t he pollen grain influences t he development of the ovule into the seed

Does it make any difference Whether thepollen comes from t he same flower or

a different one ?HOW self~pollinat ion is preventedHow pollen is carried from one flower t o

anotherHOW BETTER PLANTS AND AN IMALS ARE

PRODUCED

Have we ev idence of improvement ofplantsand animals during past generations ?

HOW plants and animals may b e improvedby selection

How more rapid improvement may b e

b rought aboutINSECT ENEMIEs OF PLANTS

How insects are injurious t o plantsHow injurious insects may be destroyedHow t he numb er of injurious insects is

reduced by natural means

PAGE

LIST OF ILLUSTRATIONS

FIGUREAirplanes in ActionSectional View of an AirplaneAirplane in AirUnited States AirplaneWeighing Basket Ball Inflated with AirWe ighing Basket Ball after Air Has Been ExhaustedSimple BarometerMercurial BarometerAneroid BarometerDiagram of an Aneroid BarometerInverting a Glass Filled with WaterFrench War BalloonMaking HydrogenDrawing Up Ink into a Medicine DropperPouring Liquid from a Small Opening in a Can

Relative Size of Chest Cavity during Inspiration and

ExpirationNon-skid Automob ile TireSole of Basket Ball SlipperSuction PumpSiphoning Liquid from aBarrelAn Inverted Drinking Glass Pushed

.

Down intOWaterCaissonBicycle PumpForce PumpCompressed AifDrillsRiveting HammerElectric FanHeating Air InaFlaSkCurrents OfAir In a RefrigeratorVentilation byWindowFireplaceSummer Monsoon

x vi LIST OF ILLUSTRATIONS

FIGURE32 . Winter Monsoon

33 . The World’

sWinds34 . Progress of a Storm Center35. Weather Map

36. Weather Mapof th e Following Day37. Usual Paths of “ Highs”and

“ Lows38 . Tornado

39 . Results of a SevereWindstorm40. Path of a Hurricane41 . Cumulus Clouds42 . Thunderstorm43 . Touching the Surface ofWater with a Tuning Fork .

44 . One of the Earliest Talking Machines45. Phonograph46. Micro-photograph ofPortion of a Record

47 . Phonograph Record48. Telephone Transmitter49 . Human Ear

50 . Oil Fire51 . Lighted Candle under InvertedGlass Jar52a . Bunsen Burner52b . Gas Stove Burner53 . Movements ofP iston ofGas Engine54 . A Match55 . Rusting of Iron56 . Sectional View of aHotbed57 . FactoryWrecked by a Dust Explosion58 . Availab le Coal Supply59 . Coal Fields of the United States60 . Fuel Value ofSome Common Foods61 . Flooded Region62 . Organs of an Earthworm .

63 . Stages In the Life History of a Beetle64 . Breathing Organs of a Fish65 . Results of a Forest Fire66. Fire Extinguisher67. Fighting a Fire withWater68 . A Forest Fire Fighter69 . Forest Ranger on Lookout for Signs ofForestFires70. Preparation ofOxygen

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Xv l l l LIST OF ILLUSTRATIONS

FIGURE111 . Train Drawn by an Electric Locomotive112 . Waterfall , McKenzie R iver , Oregon113 . Diagram of a Power House1 14 . Electric High Tension Transmission Line115 . Water Power Station116 . Illustrating Hydraulic Pressure117 . Hydraulic Press

118 . Source ofWater Supply ofNew YorkCity .

1 19 . Kensico Dam120. Height t oWhich NewYorkWater Will R ise121 . Forest Floor .

122 . A Stream in the Catskill Mountains123 . Aerators124 . Diagram of a CityWater Supply System125 . Reservoir and Dam126 . Limestone Cave127 . Water Closet Tank128 . Trap ofWaste Water Pipe129 . Septic Tank .

130 . Map ofNew York Harb or

131 . Coast of Eastern United States132 . Outline ofSouth America133 . Outline Map ofEngland134 . Stratified Rocks135 . Erosion by Small Stream136 . Flood inWab ash River , Indiana137 . Use ofRiver for Transportation ofLogs138 . Use of Int ernalWaterways t o Transport Farm Products139 . Possib ilities OfDevelopment of InternalWaterways140 . United StatesWarship Passing through Panama Canal141 . Minot’s Ledge Lighthouse142 . High Tide ina Harb or in Nova Scotia .

143 . LOW Tide in the Same Harb or

144 . Plumb Line145 . Stab le , Unstab le , andNeutral Equilib rium146 . Relation ofMoon t o the Tides147 . Action ofWater and Mercury In RotatingGlassGlob e148 . The Two Positions of t he Moon When High Tide Is

Higher than Usual149 . The Two Positions of t he Moon When High Tide Is

Not as High as Usual

LIST OF ILLUSTRATIONS

FIGURE150 . Phases of the Moon

151 . A Total Eclipse Of the Sun152 . Diagram OfOur Solar System153 . Constellations around th e North Star154 . Evening Sky Map for January, 1921155. Heat from Sun, Summer andWinter156 . Path ofEarth around t he Sun

157 . Annual Temperature Curves158 : Lines ofLatitude and Longitude159 . Standard Time Belts160 . Windmill161 . A Negative162 . Print Made from Negative163 . Cold Frame164 . Solar Engine

165. Spring Balance166. Claw Hammer167 . Crowbar168 . Tongs

169 . Scissors

170 . Nutcracker171 . Arm as a Lever172 . WellWindlass173 . Part of a Derrick174 . Placing Heavy P ipe in Position175. Pulleys176 . Block and Tackle

177 . Road near Colorado Springs, Colorado178 Raising aWeight by Use of Inc lined P lane179 . Wedge

180 . Screw181 . Demonstration that Screw Is an Inclined P lane182 . Jackscrew183 . Skidding Logs on Snow184 a . Roller Bearings

Ball Bear ings185 (a ,

b,c,

.d) Knots186 . Movements of P iston in a Four cycle Engine187 . Sectional View of an Automob ile .

188. Grand Central Terminal , New York City, b eforeElect rificat ion

xix

PAGE

XX

FIGURE

LIST OF ILLUSTRATION S

Grand Central Termmal, New York City,after Elec

t rificat ion

Direction Of Current through an Electric BellA Simple E lectromagnetDynamo Attached t o an Ambulance

Ar rangement of Iron Filings b etween Poles ofaMagnetMagnetic NeedleFirst of All Electric Batteries Prepared by Volta, A . D .

1800

Grav ity CellDaniel CellDry Cell

Structure Ofan Induction COilU . S . ArmyWire less OperatorsRece lv ingMessages from

an Airplane , Tours, FranceA Simple Dynamo

Pr inciple ofDynamo

A Simple Commutator .

Use ofElectric Motor In Running Sew mgMachineE x przimcnt l Illustration ofPrinciple of t he MotorSilver PlatingAn E lect rotypeE

’

ect ric FlatironCarbon Filament LampTungsten Filament LampAmount Of Light Given by Different Incandescent

LampsFuse

Position ofCarbons m an Arc LightStorage Battery Dissected t o Show ConstructionReflection of Light from a Polished and a Mirrored

Surface

Reflection ofLight from a SmoothSurfaceHeliographReflection ofI ight from a SlightlyRough and aRough

Surface

Relation of Intensity Of I iluminat ion t o Distance fromSource ofLight

PhotometerGasMeter Reading 5700 Feet

PAGE

LIST OF ILL USTRATIONS

FIGURE222 . GasMeter Reading 68700 Feet223 . Face of a Kilowatt Hour Meter224 . Relative Costs ofDifferent Lights225. Comparative Amounts of Light Given by an OpenGas

Flam e and a Gas Mantle226 . Cost Per Hour ofDifferent Gas Lights227 . Shaded Light228 . Lamp Showing Effect ofUse ofShade229 . Reflection ofLight by a PolishedMetal Reflector230. Reflection and Transmission ofLight231 . Breaking Up of Light In Passing through a Prism232 . Rays of Light Passing into t h e Eye233 . A Diagram Showing How a Light Ray May Be Bent

Bending ofRays of Light by Grooved Glass235 . Change of Focus ofEye

236 . Farsightedness and It s Correction237 . Nears1gh t edness and Its Correction238 . Magnify ing Glass239 . A Moving Picture Film240 . LinesWhich De ceive the Eye24 1 . Thermos Bottle242 . Fireless Cooker243 . House Heated by Hot Air

244 . House Heated by Hot Water245 . Circulation ofWater , in t he Radiator and around t he

Cylinders of an Automob ile246 . Relative Size of Soil Particles247 . Disintegration Of Rock

248 . Rugged Mountains Showing th e Effect ofWeathering .

249 . Weathered Rock at Base of a Cl iff250 . Rock Being Split by th e Growth of a Tree

251 . Beech Tree Growing on Rocks252 . Water Erosion253 . Soil Deposited by a Glacier

Rock Showing Glacial Scratches255 . Extent of Ice Sheet dur ing Glacial Period256 . A Glacier257 . Front of a Glacier

,Mt . Rainier National Park258 . Formation ofHumus259 . Vacant Lot Garden

xxii LIST OF ILLUSTRATIONS

FIGUREAbsorption ofWater by SoilsLumbermen at Work

Composition of Bread and Cereal FoodsComposition OfSome Common Vegetab lesComposition of Fish and Oysters .

Composition of Eggs and Cheese .

Composition ofVarious Grains Used for FoOdCross and Longitudinal Sections of a Young RootFood Canal (Al imentary Canal) ofMan

Organs ofCirculation ofMan

Seeds of Bean and Pea

Sprouting Corn GrainPear, from Bud t o Fruit and SeedGrowth ofPol len Tub es Down through the StylePollen Tub e Enter ing OvuleP istillate Flowers OfCornCorn Tassel Made Up ofStaminate FlowersStaminate Flowers ofChestnutFlowers OfOakFlowers ofHorsech estnut

Cherry B lossomsVariationTongue GraftingCleft GraftingBudding

, a Form OfGraftingLife History ofGypsy MothPotato BeetlePeach -Tree BorerGroup ofDying Locust TreesWorm In Apple , Larva ofCodling MothScale Insects on a Fern Leaf

Tent CaterpillarsA Modern Spraying OutfitA Beneficial Beet leLadyb ird Beet leLadyb ird Beetle Feeding on Scale InsectsToads Eating Caterpillars

ACKNOWLEDGMENTS OFILLUSTRATIONS

Chicago, Milwaukee , and St . Paul R . R ., NO . 113 .

Columb ia Graphophone Company, No . 44, 45 .

Ford Motor Company, No . 214,245 .

Forest Service , U . S . Dept . Agriculture , NO . 39 , 61, 65, 68, 69 , 85,

86, 92, 95, 97, 105, 106, 109 , 112, 121, 125, 134, 135, 137, 177,183, 248, 250, 251, 252, 253 .

General Electric Company, NO . 26,11 1

, 115, 188, 189 , 204 .

Grand Trunk R . R .

,No . 256 .

Harvey Conard, Hollis, New York, NO . 239 .

John Reiss, New York City, NO . 2 1 .

Leon Barritt, Brooklyn,N ew York

,No . 154 .

New York Board ofHealth , No . 87 , 88 .

New York Zoological Society, NO . 475 .

National Lamp Works, General Electric Company, No . 215, 216,2 17 , 218, 227, 228 , 229 , 230, 234 .

Packard Motor Company, No . 1,187 .

Pacific Northwest Tourist Association, NO . 257 .

Pennsylvania Lines, NO . 136.

Signal Corps, Am erican Expeditionary Force, No . 1 ] , 192, 200 .

Thomas Edison,Ino.

,No .

S . Bureau ofChemistry, No . 57, 67 .

S . Bureau ofEntomology, No . 63, 287, 288, 293 , 295, 296.

S . Bureau OfStandards, NO . 219 , 221, 222, 223 , 224, 225, 226 .

S . Dept . of Agriculture , NO . 81, 82, 84 , 263 , 264, 265, 266, 267 .

S . Geological Survey, NO . 50 , 58, 59 , 72, 74 .

S . Naval Ob servatory, No . 151 .

. .S Re clamation Service ,U . S . Weathe r Bureau, NO . 6, 8, 34, 35, 36, 37 , 38, 41, 90, 9 1, 93,

U . S . Navy ,No . 42 .

Weston E lectrical Instrument Company, NO . 193, 195, 201, 205 .

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IMPORTANCE OF THE WEIGHT OF A IR 3

breaks ? What is t he purpose of t he tail of t he kite ? As

a'

result of a consideration of these questions, it will b e underst ood that a plane or flat surface , if he ld at t he properangle , is kept up by the force exerted by t he air in motion .

That air in motion has great force , is well known t o us .The destruction caused by a severe Wind is sufficient proof

FxcURE 2 .— AIRPLANE IN AIR .

of this . We are also familiar with t he fact that even whenthere is no movement of the air , t he same force is exerted ifan object is passing rapidly through the air . A r ide on the

front seat of a street car or in a rapidly moving automobile

convinces us Of t he force which may be considered t o be

exerted e ither by the moving body or by the air .

The airplane with it s l ight , high power engine is ab le

by means of its prope llers to attain great speed through the

4 GENERAL SCIENCE

air . The planes may b e so controlled that they present theproper angle t o t h e air .

.The same force is exerted if t he

machine i s moving 75 miles per hour , as if t he machine were

FIGURE 3 .—UNITED STATES AIRPLANE.

Photograph ed on th e flying fie ld at Tours , France . Explain the appear

anc e of- .the prope lle r and the dust c loud b eh ind and to the left of the

mach ine . Note th e slant of th e planes .

stationary and t he air were moving 75 miles per hoUr . It

will thus b e Seen that t he airplane remains in t he air for t he

same reason that a kite remains in t he air .

1

P rob lem 2 . Has air we ight ? As t he prope ller of t heairplane dr ives t he machine through t he air very much as

t he prope ller of a boat dr ives it through t he water , air

seems t o be a substance , just as water is. If this is true ,it should have we ight . Weight is the measure of the pullof the earth (gravity) upon particles composing var ious

1 Many pupils will want t o make model airplanes. At t h e end of

t he chapter references are givenwhich will provide directions as to thedetails of their construction.

IMPORTANCE OF THE WE I GHT OF A IR

mater ials . The we ight Of a book is the measure of

t he pull of t he earth upon the book . If we drop it, it falls

or 1s pulled toward the

center Oft he earth . How

may we discover that airhaswe ight ? The following exper iment has beentr ied many times.

Experiment —Weigh carefully a strong flask ; then bymeans ofan air pump removethe air from it and weigh itagain. What is the result ?That air has weight, may

also b e shown by b lowing up

FIGURE 4.

a b asket b all or football until it is full and then weighing it (Figureand after allowing the air t o escape , weighing it again (Figure

Careful we ighing has shown that one cubic foot ofdry an

at sea leve l and at the freezing temperature (ofwater) weighs

FIGURE 5.

about one thirteenth of

a pound. Calculate ap

proximately the we ightOf the air in t he schoolroom ; in your bedroom ,

et c .

Prob lem 3 . Does air

press upon th ings ?— If

air has we ight, it should

exe r t p r e ssu r e up on

everyt hing ; because the atmosphere extends many miles

above t he earth ’s surface .

6 GENERAL SCIENCE

Ex perimm t . Into a t in can which has a small opening, put a fewspoonfuls ofwater . Heat t he can until sufficient steam is formed to

drive out the air . Plug t he opening in the canwith an airtight stopper .

FIGURE 6 . S IMPLE BAROMBTER.

Why must one end of the

tub e b e c losed Where doesth e air press Why does th emercury not reach the top of

the tub e Scale is in inches .

As the can cools, t he steam changes backt o water and the space within the can

contains neither steam nor air and is

called a vacuum.

What happens t o t he can ? Explain.

Use awide-mouthed b ottle instead of

the can and in place of t he stopper t iea piece of paper or st ill b etter a piece of

sheet rubb er over t he Opening. Result ?Conclusion

Prob lem 4 . How air pressure

may b e measured . The amountof this pressure , which of cour sew ill also b e t he measure of the

we ight of the air over a certainspace , may b e found by repeatingthe exper iment of Torr ice ll i , a

pupil of Galileo, made in 1643 .

This was t he first measurementmade of air pressure .

Experiment . Fill with mercury a

glass tub e about three feet long and

closed at one end . Closing the open end

with the finger t o prevent t he escape of

the mercury ,invert t he tub e and place

the Open end b elow t he surface ofmer

cury in a dish . Now withdraw the fingerand note t he result (Fi gure Whatkeeps t he mercury in the tub e ab ovethe level of the mercury in the dish ?

If t he tube has a cross section of one square inch , t hewe ight of t he mercury held above the level of the mercury

IMPORTANCE OF THE WE IGHT OF A IR 7

In t he dish will b e about fifteen pounds .Therefore it may b e stated that air exerts apressure of about fifteen pounds per squareinch .

The apparatus used in this exper iment const itut es t he essentials of a Mercury barometer

(Figure Since weather changes are ac

companied and frequently preceded by change sin air pressure , t h e practical value of the

barometer may

,

b e understood .

Prob lem 5 . WhyWater is not used in making barometers . From the last exper imentWe learn that t he pressure of t he air will holdup a column Of mercury about 30 inches inhe ight . Would a longer or shorter column of

a lighter l iquid be he ld up ? Explain . Ev i

dent ly, therefore , in se lecting a liquid t o be

used in a barometer, it s we ight must be con

sidered.

Experiment . Into each of two b eaker glasses put

respectively equal volumes of mercury and water .

Lift t he glasses. Which is t he heavier ? Put the

b eaker glasses containing t he mercury and water on

t he opposite pans of a balance and by t he use of

weights find out how much heavier one sub stance isthan t he other . What is t he r esult

FIGURE 7.—MERCUR1AL BAROMETER .

Th e h e igh t of the mercury c olumn is m easured in

c entime ters. c , surface of me rcury upon wh ich air is pressing. a. screw

by wh ich th e mercury in th e mercury cup is adjusted so that the surfac e (c)is at th e ze ro point of the barome ter tub e . d, the rmom e ter. e , sc rew for

adjustment of a scale (vernie r) by wh ich the he igh t of th e me rcury may b e

read more accurate ly . f, scale at top ofme rcury c olumn .

8 GENERAL SCI ENCE

If mercury is thirteen and one-half times heavier thanwater calculate t he he ight of a column ofwater that may b e

he ld up by t he pressur e oft he air . Such a barometer was constructed by Otto vonGuer icke , the inventor Of the air pump

FIGURE 8 .

— ANEROID BAROMETER.

The upper portion of t he tube t o t he extent of about six feetwas of glass. Floating on t he t op of t he l iquid, t he inventor

had introduced a small figure of a man which with t he r isingof t he column in fair weather presented itself t o view ; butwith the approach Of foul weather retreated out Of sight .

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10 GENERAL SCIENCE

Experiment. Completely fill a glass with water and cover t he t opof it with a piece of cardb oard, making certain that t he cardboard is

FIGURE 10 .

everywhere in close contact with t he edge of

t he glass. Invert t he glass (Figure Whathappens ? Why ? Hold t he glass in differentpositions. Result ? Conclusion ?

Prob lem 8 . Why a bal loon or a

dir igib le remains in the air .

— Why doyou think that t he explanation givenfor t he airplane remaining in t he air willnot account for t he buoyancy of a bal

loon ? Since we have learned that airhas We ight we may compare t he floating of objects in air

With t he floating Of objects in water .

exper ience that objects l ikeiron and stones, that are

heavier than water , will sinkwhile cork and wood, wh ichare lighter than water , willfloat . .

The same i s’

true of thingsin the air . Cork and Wood

and most things we know of

are heavier than air and wil lnot float in it . A balloon,

however , is lighter than air

and therefore will float in it .We know that air pressurei s exerted in all directions .

The air under t he balloonther e fore , is pushing it up

ward and the air above it,

You know from

FIGURE 11.—FRENCH WAR BALLOON.

It is making an ascent at S t . Nazaire .

France.

IMPORTANCE OF THE WE IGHT OF A I R 1 1

is pushing it downward. If the balloon We ighs t he same as

air it w il l not be pushed e ither upward or downward. If,

FIGURE 12 .

however , t he balloon we ighs more than an equal volume of

air , will the downward or upward pressure be greater ?Explain. If the balloon we ighs less than t he air that it

FIGURE 13 .

displaces, which pressure will be the greater ? Explain.

Explain why a balloon does not continue t o go up until itreaches t he top of t he atmosphere .

12 GENERAL SCIENCE

Balloons and dir igibles must be filled with a gas muchl ighter than air . Hydrogen gas, which is about 145 timeslighter than air, has been t he gas generally used . The use

FIGURE 14 .

Note that the can at the righ t has two holes in its top.

of hydrogen for filling balloons may be shown by makingsoap bubbles with it .

Experiment .—Make hydrogen by setting up t he apparatus shownin Figure 12 and pouring hydrochloric acid through t h e tub e with t h eenlarged t op (thistle tube ) over t he pieces of zinc in th e flask. By

means of a rubb er tub e attach the stem of

a clay pipe t o the tub e which carries the gas

from t he flask. Dip t he bowl of t he pipeinto soapsuds. Shake ofl t he bubb les intot he air as they are formed and note theirb ehavior . Touch a bubb le with a matchand ob serve what happens.

FIGURE 15 .—RELATIVE

S IZE QF CHEST CAVITY '

DURING INSPIRATION AND

EXPIRATION.

A new gas (he lium) wh ich is foundin considerable quantities mixed witht he gas of some natural gas wells is

now be ing used. It is somewhatheavier than hydrogen although muchlighter than air . The great advantage

of it s use i s that it will not burn,

Whereas hydrogen does .

IMP ORTANCE OF THE WE IGHT OF A IR 13

EXERCISE S

Explain the following

(1) How ink may be drawn up

into a medicine dropper such as is used

in filling a fountain pen (Figure(2) How lemonade may be sucked

through a straw.

(3 ) Why olive oil or any other li Iid

can readily b epouredfrom a small opening in a can if there is another openingabove t he liquid, b ut will not flow

evenly if this opening is closed (Figure

(4) Why a fountain pen frequentlyleakswhen it is nearly empty.

(5) Why the raising of the ribsand lowering of the diaphragm of the

body causes air t o flow into th e lungs(Figure

(6) Why two pieces of wet glassstick t ogether .

(7) The action of non-skid automobile tires (Figure

(8) The abil

ity ofbasketballFIGURE 16.

—NON-S I<ID AUTO

MOBILE TIRE.

players t o keep from Slipping on t he smooth floorof a gymnasium (Figure(9 ) Action of the ordinary suction pump

(Figure How high will such a pump liftwater(10) How air pressure may help in removing

liquids from casks or large bottles (siphoning) .(Figure(11 ) Action of a vacuum cleaner . Why is

it s use advisable ?FIGURE 17.

—SoLg op (12 ) Why one’

s hat is apt t o b e carried Off asBASKET BALL S LIPPER. a swiftly moving t rain passes.

14 GENERAL SCI EN CE

(13 ) The ac tion of a self-filling fount ain pen .

(14 ) Difficulty of drinking from a small-m outhed b ottle .

FIGURE 18.— SUCTION PUMP .

V. V’ valves ; P , piston ; S , pump s tem ; W: wate r of w e ll. Whatcauses V to open as pis ton moves upward ? What w ill b e th e position

ofvalves as piston is pushed dow nwards

(15) Sucking of b lood by a mosquito .

‘

(16) Noise'

caused by removing a thimb le from a we t finger.

FIGURE l 9 .—S IPHONING LIQUID FROM A BARREL .

The tub e fits loose ly in the Opening at the top of the barre l. Why is th isne c essary Why cannot th is b arre l be comple te ly empt ied by the tub e as it

is How can this tub e b e changed so that the barre lmay be emptiedw ith it

(17) Difficulty ofpouring a liquid through a funnel which fit s tightlyinto t he mouth ofa jug or bottle . How may t he liquid be made t o flow

rapidly(18) Why t he body is not crushed by the pressure of t he air.

WE IGHT OF A IR 15

SUGGE STED INDIVIDUAL PROJECTS 1

1 . Make a kite and demonstrate by diagrams how it is ab le t o fly.

2 . Make an air-glider and explain how it acts.

3 . Make a model airplane that will fly and demonstrate it s actiont o the class.

4 . Construct a homemade mercury barometer and record for a

period of time t he changes in air pressure . At the same time make a

record of t he condition of the weather and determine if there seems t o

b e any connection b etween changes in air pressure and the weather .

5. Construct and demonstrate a suction pump.

6 . Demonstrate that air is heavier than hydrogen gas and is lighterthan carbon dioxide gas.

7. Construct an apparatus to illustrate the expansion and con

traction of the lungs in b reathing.

8 Demonstrate the structure and action of a self-filling fountain

9 . Demonstrate the structure and action of a vacuum cleaner.

10. Construct a siphon and demonstrate it s use . Discuss variousapplicat ions that may b e made of t h e siphon.

REPORTS

First successful attempts t o cross the Atlantic Ocean in an

Early attempts t o develop t he airplane .

The use of t he airplane in t he GreatWar.

4 . Commercial possib ilities of t he airplane .

REFERENCES FOR PROJECT I

1 . Aircraft Today, Chas. Turner . J. B . Lippincott Co.

2 . How t o Fly, F. A. Collins. D. Appleton C0 .

3 . The Air Men, F. A. Collins. Century Co .

1 AS explained in t he Preface , not all t he Individual Projects are to berequired of every student. Some are for girls, some for b oys ; some for

city pupils, some for country students ; some are so simple that nearlyanyone can perform them easily ,

wh ile some , like Proje ct 3 above , willappeal only t o those who h ave a de cided mechanical talent.

16 GENERAL SCIENCE

4 . Boys’ Book ofAirships,H.Delacomb e . FrederickA . StokesCO.

5 . How I t Flies, Richard Ferris. Thomas Nelson Sons.

6. The Story of the Airplane , C. Graham-White . Small,Maynard

85 Co.

7 . Boys’ Book ofModel Airplanes, Vols. I and II, F. A.

‘Collins.

Century Co .

8 . Aviation Book,Curtis. F. A . Stokes.

9 . Harper’

s Book on Air craft, Verrill. Harper 85 B ros.

10. Boys’ Book Of Inventions, Baker . Doub leday, Page 85 Co.

1 1 . FlyingMachines, e t c . , The American Boy’

sHandy Book, Beard.

Charles Scribner ’s Sons.

12 . War Kites, Field and Forest Handy Book, Beard. CharlesScribner

’

s Sons .

13 . Handicraft for Handy Boys, Hall . Lothrop, Le e Shepard.

14 . Historic Inventions, Holland. Geo . W. Jacob s Company.

15 . Harper’

s Outdoor Book for Boys. Harper Bros.

16 . The Outdoor Handy Book,Beard. Charles Scribner

’

s Sons.

17. Practical Things with Simple Tools, M. Goldsmith. SullyKleint eich .

18. Careers ofDanger andDaring, ClevelandMoffet. Century Co.

(Divers, Balloonists, Bridge Builders, et c . )19 . The Barometer as the Footrule of the Air . Taylor Instrument

Co. , Rochester , N . Y. ,10 cents.

20. The Thermometer and It s Family D ee . Taylor InstrumentCo .

,10 cents.

2 1 . The Story ofGreat Inventions. Harper Bros.

22 . Modern Triumphs, E . M. Tappan, Editor . Houghton lVIifflin

23. Harper’

sMachinery Book forBoys. Harper Bros.

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18 GENERAL SCIENCE

any change occur in the amount of pressure ex ert ed by t hecontained air ? At what depth in t he water will t he air

exert a pressure equal t o two atmospheres ? At this pointthe volume of t he air will be one half of its or iginal volume ,illustrating a law of t rue gas, that t he volume var ies

DfDDOCK

FIGURE 2 1. CAISSON .

If the pressure of the air in the paisson is about 30 pounds pe r squareinch ,

h ow far from the surface of the water is the bot tom of th e excavat ionWhat w ould happen if the doors at th e top should b e left open Why

inverse ly as t he pressure exerted upon it . This law is knownas Boyle

’

s law .

Caissons used in building foundations under water are

large metal cylinders open at t he bottom , into which air

is,

pumped until it exerts sufficient pressure t o prevent t heentrance ofwater (Figure Air under pressure was used

HOW WE USE COMP RES SED AIR,19

to keep out the water dur ing t he construction of the tunne lsunder the East and North r ivers at New York City .

Great care must be taken by men passing from the com

pressed air chamber s t o t he outer air . If this is done t ooquickly, gases which are dissolved in t he blood form smallbubble s which prevent the blood from passing throughcapillar ies (very small blood vesse ls) , causing an acutedisease , the bends.

”To prevent th is

,a man instead of

passing directly into the outer air goes through severalrooms of graduated pressures

,remaining in each room a

sufficient length of time t o permit the body to accommodateitself t o t he changed pressure .

Prob lem 2 . How compressed air is used in automob iletires.

—We all know that bicycle tire s and most aut omo

bile tire s are filled with air . At first thought it seems strangethat a substance like air can hold up t he great we ight of aheavy automobile . Naturally we ask how this air is different from t he air around us .What happens if a nail punctures t he tire ? Sometimes

when t he outer cover ing of t he tire becomes badly worn a

blow-out occurs with a noise l ike an explosion, tear ing ahole in the tire . What does this indicate t o you concerning t he condition of t he air within the

.

tire ?It is evident t hat t he compressed air in t he tire is able t o

hold up t he we ight of the automobile amounting t o severalthousand pounds, just as the compressed air in the divingbell resists t he pressur e of t he water .

If you have ever r idden in a sol id-tired automobileand then in one hav ing “ pneumatic or air-filled tires, you

have noticed that in the latter case t he jars caused byt he roughness of t he road were not felt as much . This

20 GEN ERAL SCI EN CE

Observation shows that t he compressed air in the tire actslike a Spr ing . T he following simple exper iment will showthis effect of compressed air .

Experim ent . —Bounce together on the floor a new , perfect tennisball and a tennis b all in which a small hole has b een made by a pin or

nail. Result ? In the same way compare th e b ouncing of a b asketball which is just sufficiently filledwith air t o cause it t o keep it s Shapewith t he b ouncing of a similar b all into which a large amount of air hasb een pumped.

From t he observations you have made you will concludethat t he compressed air in t he automobile tire is able t o sup

port a great we ight and gives spr inginess (e lasticity) t o t hetire . Many tire-filling compounds have been tr ied but nonehas been successful because nothing has been found thatwill give t he spr inginess possessed by compressed air .

It is evident that in t he construction of an automobile tire,

first, t he tire must be air-tight t o prevent t he escape of t he

air and, second, it must be Of sufficient strength t o resist thepressure of t he impr isoned air . An examination ofan automobile tire wil l show how these two' requirements are met .

The inner tube made of e lastic rubber is air-tight . The air

i s pumped in through a metal tube in which is a valve thatwill a llow air t o be pushed in but prevents it s escape .

The outer tire or shoe is not necessar ily air-tigh t but provides t he strength t o resist t he outward pressure of t he con

fined air . It is very strongly mad e of a combination of

cotton fabr ic or cord and rubber . In bicycle tires where t hewe ight supported is not so great, frequently only one tube

is used . What two propert ies must this tube possess ?Air is forced into t he tire by an air pump .

Prob lem 3 . How th e t ire pump,

works. If you have

ever pumped up an automobile t ire , did you find it more

HOW WE USE COMPRE SSED AIR 2 1

difficult t o work the pump when t he tire was

near ly empty or when it was near ly filled ? In

t he tire pump which you used, was t he push or

t he pull upon t he handle t he harder ? Does a

tire pump ever get out -Of-fix or fail towork ?Keeping these points in mind let us examine

the diagram of an air pump (Figure AS

the h s pulled out , what happens to theair ? As the handle is pushed down,

what 8 t o t he air ? Why does it not goout thr ough the same place through wh ich itcame in ? Why is it more difficul t t o push thehandle down than to pull it up ? Why is itmore difficult t o push t he handle down as" youcontinue t o pump air into t he tire ?The tire pump is a very simpleair compressor ,

but air . compressors for air brakes,pneumatic dr ills, sand ."blasts, and for

pummng air into tunne ls where work isdone under compressed air are built on

the same pr inciple .

Suppose t he valve through which t heair enters t he pump shou ld be reversed,

what would happen Should t he nozzle beattached t o a basket ball and t he pumpused ? This is the pr inciple of the e x

PUMP.

haust air pump , by which air is pumped

p, piston ; C, cylinout ofa closed vesse l . Do you think that

der ; v , v alv e ; D, dom'

e all of t he air could be removed from a

c ontaining air ; d’ dc” vesse l with such a pump ? In answer inglive ry pipe ; 5 , pumpstock. this, keep In mind that however lIt t le air

FIGURE 23 . FORCE

22 GENERAL SCIENCE

Is In a space, it will be distributed equally, filling all thespace .

Prob lem 4 . How a force pump sends a steady stream of

water . The tire pump is really an air force pump ; a

water force pM p could be made on t he same plan. Would

FIGURE 24 .—COMPRESSED AIR DRILLS .

Use of compressed air drills in excavat ing a tunne l through solid rock.

such a water force pump send a steady stream of water ?Such pumps are valuable in pumping water t o a tank on

'

thet op of a house or into a standpipe . Why cannot an ordinarypump be used for this purpose?Some force pumps can send a steady stream ofwater . It

wil l be noticed that pumps of this kind have connected with

HOW WE USE COMPRESSED AIR

them an iron dome . An examination of t he accompanyingdiagram will he lp us t o understand how this is possible

(FigureExplain what happens when t he piston (p) is pulled up .

When it is pushed down, what two courses wil l t he watertake ? What will happen t o t he air that is in t he iron dome ?What will this compressed air do t o t he water when t he

piston starts upward and t he water is no longer be ing forced

FIGURE R IVETING HAMMER .

A , air pipe B , t rigge r for c ontrolling th e air ; C, th e hamm e r.

into t he dome ? What kind of a stream will such a pumpsend out ? The power of compressed air t o throw a streamof water is illustrated by t he following exper iment .

Experiment . Half fill a flask with water . Stopper it with a one

hole stopper thr ough which passes a tub e extending down b elow the

surface of the water . Blow through the tube . What effect will thishave upon the air within the flask ? After the air hasb een considerab ly

compressed, stop blowing into t he tube and ob serve what happens.

Some other important uses of compressed air are

Pneumatic tubes for t he transmission of mail , and of cash

24 GENERAL SCI ENCE

and parcels in stores ; air brakes ; pneumatic drills and

r iveters ; and t he sand blast used in cleaning t he fronts ofstone buildings . Can you suggest any other applications ?

SUGGESTED INDIVIDUAL PROJECTS

1 . Construct a pump that will send a steady stream ofwater .

2 . Demonstrate the working of air brakes.

3 . Demonstrate t he structure and t he action of pneumatic drills.

4 . Demonstrate t he structure and t he method of working of the

sand b last used in cleaning the outside of b rick and stone buildings

REPORT

Use of compressed air in building b ridge foundations and in t he

construction of subways.

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26 GENERAL SCI EN CE

an Open trolley car or in an automobile on such a summerday ?

The following exper iment may help us t o understand t hereason for this change in feeling .

Experiment . Put a drop of ether on t he back of t he hand. Whathappens t o t he ether ? How does t he spot, where t he ether was, feel ?Put a drop ofwater on t he other hand. After it has b een there a

few moments, fan the hand. Do you notice any difference in temperature ? The changing of t he ether and water into a vapor or gas thatis invisib le is called evaporation . What do you conclude is t he effectof evaporation upon temperatur e ?

Heat is be ing continually made in t he body . How do you

suppose t he body.

loses most of it s extra heat in warm roomsand in summer time ?Evaporation of water goe s on much more slowly if there

isalready a large amount of water vapor in t he air . Thisfact is made clear t o you by t he rapidity of t he drying of

clothe s on a damp day and on a dry day . In which casedoes t he drying go on more rapidly ?

Experiment . —We t two small pieces of cloth ; hang one In a dry

battery jar and t he other in a b attery jar in which there is a small

amount ofwater . Which piece of cloth dries t he sooner ? Conclusion ?

It is estimated that each per son gives off from his mouthand Skin about three pints ofwater daily and about as muchheat as is produced by a candle flame . Of course , if exerciseis being carr ied on,

both more moisture and more heat aregiven off. What, therefore , will be t he condition of a poorlyventilated room in which t here are a number of per sons ?

It is an accepted fact that t he dullness and drowsinessfe lt in such a room are due chiefly t o t he heat and moisture .

Exper iments have shown that mendo 15 per cent less workat a temperature of 75 degrees F. and 37 per cent less Work

VEN TILA TION 27

at 86 degrees F. than at 68 degree s F. In warm rooms t heblood comes t o t he surface of t he body. Why ? What effectwill this haVe upon the amount of blood that goes t o t hebrain ? What will be the result ? In t he same way , t he

blood vesse ls in t he nostr ils become conge sted,making

an ideal condition for t he growt h of germs. As a result,people who live In overheated rooms usually have colds.

The proper temperature for a room is 68 t o 70 degrees F.

Although a poorlyventilated room containing many people is like lyt o have t oo much moisture in t he air

,there is

danger in t he winter of

having t oo little moisturein t he air ; this is especially true in apartmentsoccupied by only a few

people . It is advisableunde r the se c i r cumstances t o keep on t he

radiator or stove a basinof water which will supply moisture t o the air

by its evaporation . Hot air furnaces have a special waterbasin which should be kept filled if t he occupants of t he

house are t o enjoy t he maximum of comfort and we ll-be ing .

Br iefly summar ize t he reasons for ventilating a room .

FIGURE 26 . ELECTRIC FAN .

Prob lem 2 . How air in a room may b e se t in motion .

One method of keeping t he air of a room in motion is by t he

use of fans (Figure Explainwhy, in summer,one fee l s

28 GENERAL SCIENCE

so verymuch better in an office, room,or subway car inwhich

an e lectr ic fan is in motion . Recall how quickly one fee ls t he

change when t he fan i s shut off. Why is ventilation ofa roomentire ly by an e lectr ic fan not a perfect method ?

What is not provided for by such ventilation ?We know, however , that most ventilating

systems do not depend on fans. The questiont hen is, how may ,

a circulation of t he air be

caused, when fans are not used. The.

following exper iments may help us t o answer this

FIGURE 27. question.

Experiment . Put a lighted candle in t he bottom of an uncoveredbattery jar . Light a stick of Chinese punk or incense and hold itnear t he t op of t he jar . Wh athappens ? What do you think may

b e t he cause of this ?Ex pefiment .—To find out t he

effect of heat on t he weight of air,place a lighted Bunsen b urner nearone of t he scale pans of a sensitivebalance . Result ConclusionThe reason for this ISmade clear

by t he following experiment.Experiment . - To find out how

heating air makes it lighter , pass a

glass tub e through t he stopper of a

flask . Take care that t he stopperis air-tight. Invert t he flask, placing th e outer end of t h e glass tub eunder water . Gent ly heat t he flask FIGURE 28.

—CURRENTS OF AIR IN

(Figure Result ? Conclusion ? A REFRIGERATOR

The currents of air caused by heat are called convection

currents . These currents ofair are we ll il lustrated by movements of air in a refr igerator (Figure

VEN TILATION 29

Prob lem 3 . How convection currents may b e used inventilating a room . Windows are very frequently de

pended upon°

for ventilation .

Experiment .—To find out t he b est arrangement of windows forgood ventilation of a room , t ake a wooden soap b ox or a starch box .

Across t he front of the b ox place a piece of glass

so that it may act as a sliding door . In each endof t he b ox b ore four holes so arranged as t o repre

sent the upper and lower parts of windows.

Provide corks for these openings. Place inside of

t he box one or more candles. Light t he candles.

Allow all t he lower holes t o remain open . Notet he result. ”

Try var ious comb inations. What isyour conclusion as t o t he b est way t o vent ilate a

room by means ofwindows ?

If t he air outside is cooler than t he air

inside t he room,and t he window is open at

both t op and bottom ,where does t he air

enter and where doe s it leave (FigureExplain .

A draft or a direct current ofair strikingagainst t he body is apt t o induce a coldsince that port ion of t he body is cooledso complete ly that t he blood coming thereis forced into some other part, causing a

congest ioni

wh ich affords a favorable condition for t he growth of bacter ia or germst hat cause colds.

INSIDE

UTBLDE

FIGURE 29 .—VENTI

LATION BYWINDOW.

Window open at

both top and bot

tom .

With a Window open at t he t op and bottom , would t he

greater danger of draft be from t he t op? Suggest means ofprotecting persons from a draft in a room ventilated in

this way .

Explain how a stove or fireplace will help in t he ventilation

30 GENERAL SCI ENCE

of a room (Figure Make a diagramof a room containing a fireplace and indicate by arrows t he directionof t he air in

t he room .

How are your rooms at home ventilatedin summer ? In w inter ? Make diagramsof the summer and winter ventilation of

one room.

Modern office buildings, and sometimesschools

,are heated and ventilated by air

being forced into them by fans throughlarge pipes . If the air comes in heated,

pwURg HRH ought t he inlet t o be at t he t op or bottomPLACE of t he room ? Where ought t he outlet

What causes the air t o be ?to

‘

go up the flueExperiments and observations have

shown that t he health i s much better if sleeping rooms arewe ll ventilated and kept at a re latively low temperature,provided that t he body is not in a draft and i s properlyprotected to prevent its becoming chilled .

SUGGESTED INDIVIDUAL PROJECTS

1 . Carry out a series of experiments t o show the direction of air

currents in a room . Show results in a diagrammatic drawing of t he

room . Do this for different rooms ofyour house .

2 . Carry out a plan t o prevent a draft in a room ventilated byWindows.

PROJECT IV

WINDS

SINCE winds are movements of air , you would naturallysuspect that they may b e caused in t he same way as the air

currents of venti lation. In consider ing t he cause of winds

you will at once think of different kinds of winds, such as

sea breezes, gentle breezes that seem t o come from any direc

tion,violent gales, trade winds, hurr icanes and tornadoes.

Does it seem probable that all these winds are caused bythe unequal heating of t he air ?

Prob lem 1 . How sea b ree zes are caused . Anyonel iving within a few miles of t he sea coast is familiar with t hebreeze that spr ings up on hot days in summer . Since thiswind occurs only on hot days and die s down toward evening,being replaced frequently dur ing t he night by a breeze fromt h e land t o t he ocean, you will suspect that in some way it isconcerned with heat .

If this wind is caused in t he same way that air currents ofventilation are produced

,there must b e an unequal heating

of t he land and water . Do you think that t he ocean and

t he land rece ive different amounts of heat from t he sun ?

The problem to b e solved, therefore , is, how the unequalheating can b e accounted for .

Experiment .

- Put into different dr inking glasses or b eaker glasses

equal quantities ofwater and earth. Put them into an oven for abouttwent y minutes. 0 11

'

removal put into each b eaker glass a thermometer .

3 1

32 GEN ERAL SCI ENCE

Note t he temperature when first removed from t he oven and at intervals of t en or fifteen minutes. Result ? Conclusion ?

Ex plain‘

now t he cause of sea b reezes.

The seasonal or monsoon winds of India are accounted forin a similar manner . Dur ing t he summer t he land becomeshighly heated and Winds blow from t he Indian ocean t o

FIGURE 3 l .—SUMMER MONSOON . FIGURE 32 .

—WINTER MONSOON .

t he land, while in winter t he water is warmer than t he landand t he direction of t he wind is reversed.

Consider ing t he fact that land becomes warmed morerapidly and cools more rapidly than

'

water , explain the

following :1 . Why New York City has a later spring than places in

Oh io and Indiana wh ich are no fart her north or south2 . Why the region along Lake Ontar io is better for raising

fruit than place s much farther south .

On the d iagram representing t he wor ld’s Winds note t he

direction of t he trade winds . Why do they blow toward t heequator ? The fact that they blow from the southeast and

northeast rather than directly from t he north and southis due t o the rotation of the earth . In t he northern hem

isphere t he winds are deflected t o t he r ight and in the

southern, t o t he left .

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36 GENERAL SCIENCE

whir ls which occur in t he road in summer . The low pressurewhich started t he dust whir l is formed by t he excessiveheating of a small area of t he road.

These low pressure areas which deve lop in t he prevailingwester l ies trave l with t he wester lies in a general directionfrom west t o east (Figures 34 and The air for hun

dreds of miles passes in toward a low pressure area,not

FIGURE 37.—USUAL PATHS OF

“ HIGHS AND“ Lows .

directly but in a spiral, just as water does when drainedfrom a bath t ub . These great whirls of air , which are con

t inually passing across t he country,are called cyclones ; and

most of our winds are portions of these . The cyclones,of course , are separated by areas of high pressure (Figures35

"

and

Directly int he cent er of a low pressure area, in whatdirection do t he currents of air flow ? What is the directionofthese currents in the center ofa high pressure area ?

37

Wh ich is warmer , an area of low pre ssure or an area‘

of

high pressure ? Low pressure areas are cloudy and rainy .

High pressure areas are clear .

Tornadoes are violent wind storms, and are sometime swrongly called cyclones. They are usually not more than

40 t o 500 yards in width . In tornadoes t he air is rushingspirally upward at a rate of 100 t o 400 miles per hour . Di

rect ly in.

t he center of t he tornado there is a very much

P hotograph by F . Cundill .

FIGURE 38. TORNADO .

Th is tornado was seen near Isab e l, S outh Dakota , june 25 , 19 14 .

lessened air pressure . The condensation ofmoisture withinthis area of lessened pressure and t he presence ofdirt carr iedUp by t he air cause t he funne l shaped cloud which is charact erist ic of this kind of storm (FigureBut a cyclone is an entire ly different kind of storm .

Compare a tornado and a cyclone as t o size . Tornadoes

usually occur in t he southeastern part of a cyclone and

move toward t he,

nort heast, which is t he direction of t he

38 GENERAL SCI EN CE

prevailing wind in that part of a cyclone . They trave l att he rate of20 t o 50 miles an hour .

Tornadoes are very destructive,frequently destroying

everything in their paths (Figure Trees may be

complete ly demolished ; large stone s and even locomotiveshave been known t o be carr ied a considerable distance ;straws have been dr iven into wood as though they were

FIGURE 39 .—RESULTS OF A S EVERE WINDSTORM .

nails, and many other astounding results have been known

t o occur . Frequently t he walls of buildings near which t he

center of t he storm passes fall outward as though froman explosion . Explain this. Waterspouts are whir lwinds

over the ocean .

Prob lem 3 . What are hurricanes ? Hurricanes'

are

similar t o cyclone s but are usually of less extent and more

V iolent . They form over t he ocean . The ones that affectus originate near the West Indies and move toward t he

WINDS 3 9

FIGURE 40 .

—PATH OF A HURRICANE.

northwest until t he coast of t he United States is reached.

They then move toward t he north and northeast , parallel with t he coast, finally passing eastward out into the

“

40 GENERAL SCI ENCE

Atlantic Ocean (Figure Occasionally, one of thesehurr icanes passes into t he Gulf of Mexico . Galveston

,

Texas, was near ly.

destroyed in 1900 by the wave s produced by such a hurr icane . Similar storms in the Pacificand Indian oceans are called typhoons.

Thunderstorms frequently deve lop at the close of a hot ,

sultry day . They are caused by the r ising of hot , moist

P hot ograph byM cAdte.

FIGURE . 4 1 CUMULUS CLOUDS .

air . The mo isture of t he air condenses into dome-shaped,white clouds known as cumulus clouds (Figure The

downpour of water is accompanied or preceded by a set

tling downward of t he cooler air which pushes out fromall Sides of the storm area, forming t he strong wind of t he

approaching thunderstorm . After the thunderstorm has

passed, t he temperature is usually cooler , large ly because of

this settling of t he cooler air from above .

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42 GENERAL SCI EN CE

Prob lem 4 . How th e weath er bureau is ab le to predictth e weath er . Examine weather maps. Note t he direc

tion of winds, temperature , raininess or cloudiness, and lowand high pressure areas. Suggest a basis for t he weather.

predictions issued by the U. S. Weather Bureau .

Explain how a barometer enables one to forecast theweather fora Short time in advance .

What two factor s are important in determining t he v eloc

ity ofa wind at any one point ?Explain how a hot wave may be caused by a cyclone .

Explain how a blizzard or norther may be caused by a

cyclone . Suggest the re lation between a cold wave and a

high pressure area.

The United States Weather Bureau has near ly 200 ob

servation stations throughout t he United State s and Canada,

at wh ich simultaneous records of barometr ic pressure , t em

perat ure , direction and ve locity of t he wind, t he rain or

snowfall and cloudiness, are made . These observationsare te legraphed t o Washington and from there t he collectedinformation is sent t o t he var ious st ations where weathermaps showing t he weather conditions in all parts of t he

country are madef The forecasters study these maps and

are able t o forecast t he probable weather conditions for t henext 24 or 48 hour s (Figures 35 and

By means of te legraph, te lephone , wire less, and mai l or bymeans of flags or steam wh istles t he daily forecasts r eachevery part of t he country in a surprisingly short time .

Spe cial warnings of frost and t he approach of a cold waveare sent t o farming, gardening, and fruit distr icts and t o

railroadsand t o shippers Ofvegetables and livestock . Warn

ings of gales along coasts and on t he Great Lakes are sent t o

shipping offices and t o vessels .

WINDS 43

SUGGESTED INDIVIDUAL TOPICS

1 . Keep a daily record of temperatur e , air pressure , direction, and

approximate velocity of t he wind, cloudiness, and rain or snowfall.In connection with these observations study t he maps of t he UnitedStatesWeather Bureau .

2 . Make a t oy windmill and use it in running a simple machine .

REPORTS

l . Th e work of t he United StatesWeather Bureau .

2 . An account of t he hurricane that caused so much damage toGalveston, Texas.

3 . An account of a tornado .

REFEREN CES FOR PROJECT IV

1 . Weather and Weather Instruments, P . R . Jameson. TaylorInstrument Company , Ro chester , N . Y.

,50 cents.

2 . Practical Hints for Amateur Weather Forecasters, P . R . Jame

son . Taylor Instrum ent Company ,10 cents.

3 . Instructions for Volunteer Ob servers. U. S . Weather Bureau,

Washington.

4 . Practical Exercises In Elementary Meteorology ,Ward. Ginn 85

6 . Ab out the Weather , MarkW. Harringt on . D. Appleton Co .

7 . The Weather and Climate of Chicago , Cox and Armington .

University of Chicago Press.

8 . TheWonder Book of t he Atmosphere , E . J. Houston. Frederick

A. Stokes Co .

9 . Our OwnWeather , Martin. Harper 85 Bros.

10 . Reading the Weather ; T. M. Longstreth. Outing Pub lishingCo .

PROJECT V

HOW WE HEAR

THINK a moment of what you‘

would miss and how you

would be handicapped if you were unable t o hear . Make a

l ist of t en example s In which inability t o hear would affect

you.

In consider ing how we hear , there are several things wh ichare at once evident ; fir st, there is always a sound of somekind second , the soundmay b e reproduced or heard at somedistance from t he place where it was or iginally produced ;third

,we have a Special organ , t he ear , which rece ives t he

sound. In working out this project , therefore , it will b enecessary t o know just what sound is

,how sound may

trave l and be reproduced and how t he human ear is fittedto rece ive sounds.

’ Prob lem 1 . What sound is. Think of the differentways in wh ich sound is produced. How is a drum made t ogive out sound ? What is t he effect of putting t he hand on

t he head of t he drum wh ile it . is sounding ? A violin or

banjo gives out sound when a str ing is pulled t o one side andthen re leased. If t he str ing 18 looked at carefully, it willb e seen t o b e vibrating . What happens t he moment youstop these vibrations by touching t he str ing ?

Experiment. —Touch t he surface ofwater in a glass with t he tipsof a tuning fork which is sounding (Figure Re sult ? Conclusion ?

An examination of all bodies giving out sound will leadus t o t he conclusion that sound always or iginates as a vi

44

HOW WE HEAR

bration . The vibrating bodies cause air waves very muchas t he vibrating tuning fork produced waves in t he waterin t he glass.

Ex periment. Blow diagonally into a small bottle or test tub e .

Use t ubes and bottles of various sizes. Result ? In this experimentair waves are produced directly .

It is in this way that sound is produced in such inst ruments as t he organ, flute , cornet, and trombone . The soundhere is produced by t he V ibration of column s of air .

In what three ways do sounds Naturally we

wonder , what are t he cause s of

these difference s .

Experiment . Compare t he sound

(note ) given by a V iolin or other stringedinstrument when t he str ings are stretchedvery tightly and when t he strings are

stretched less tightly . By holding the

finger on t he string permit only a portionof it t o vibrate . Result ? Set into vibration one of t he very slender strings of a

violin or guitar and one of t h e thickerones. Even though they are of t h e same

length and of t he same tension or tightness, what is the result“ ? FIGURE 43

A careful examination will Show that in every case where

the tone or pitch was high , t he vibrations were more rapidthan when a lower pitch was produced} You will a lso re

cal l that blowing into very small bottles gave a muchhigher pitch than blowing into larger ones. This was b ecause t he air V ibrations produced in t he smaller bottles weremore rapid.

If you look at t he arrangement of str ings of a piano , youwill find that they are not all oft he same length ; t he one s

46 GENERAL SCIEN CE

which give out the low tones be ing long and thick, and those'

which produce t he high tones, short and thin .

The human voice illustrates this very well . Children haveh igh-pitched voices, but boys

’ voices usually become deeperor lower-pitched when they are about fourteen years old.

This is because the voice box , or Adam ’s apple ,”

Of‘

t he

boy becomes considerably larger at this time , and t he vocalcords

,become longer and larger , and therefore V ibrate more

slowly, producing a lowertone . The voice box of

a gir l does not usuallygrow much larger as she

gets older , and conse

quently t he voice of a

woman remains highpitched .

If you are beating a

drum and wish to makea louder sound, what do

you do ? If some one is

sleeping and you do not

wish t o disturb him,how

do you walk across thefloor ?

The loudness of sound is caused by t he width of t he vibration . Compare the sound given by t he str ing of a violinwhen it is set into gentle V ibrations with t he sound producedwhent he vibrations are greater . It Will b e noticed that t hetone or pit ch remains t he same

,but that there is a great

difference in loudness or volume .

The qual ity of t he sound is due large ly to secondary vibrat ions (overt ones) which -vary with t he character of the

FIGURE 44 .—ONE OF THE EARLIEST

'

TALKING MACHINES .

HOW WE HEAR 47

sounding bodies. Hence , sounds of . t he same pitch -andloudness produced by piano, viol in, guitar , or organ

,have

distinctive qualities. This is, of course , t he main reason

for having many kinds of instruments in an orchestra .

Br iefly summar ize your conclusions as t o what sound isand the cause of differences in pitch, loudness, and qual ityof sounds .

FIGURE 45. PI-IONOGRAPH.

N ote th e sound b ox , to wh ich is at tached a ne edle wh ich runs in the grooveof the re c ord.

Prob lem 2 . How a phonograph reproduces sound.

To understand how t he vo ice of Caruso , t he music of t he

violin ofMischa Elman or of a wonderful church choir may

be reproduced in our own home by the phonograph , it willbe necessary to consider how. t he record is made .

The essential part of a phonograph is t he sound box with

48 GENERAL SCIEN CE

it s diaphragm which is Similar t o t he head of a drum

(Figure To t he center of t he diaphragm is attached a

rod which transmits t o a needle any movement of t he drumhead or diaphragm . Every vibration of t he vocal cords of

the singer or Of t he str ings of t he violin produces in . some

FIGURE 46.—MICRO-PHOTOGRAPH OF PORTION OF A RECORD.

way a similar vibration of t he diaphragm which transmitst he V ibration t o t he needle Which in turn leave s a record on

a revolvmg wax plate upon which it rests (FigureCopies of t he wax plates made of hard mater ial are t he

records which we buy (Figure How t he vibrations

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50 GEN ERAL SCI EN CE

out t he air , put t he stopper into t he bottle and, after t he bottle hascooled, again

.

close t he circuit. Do you hear t he ringing as before ?

Allow air t o enter t he bottle gradually . AS it does so, do you noticeany difference inthe sound of t he b ell ? Conclusion ?

As t he finished record revolves under t he needle , all th e

movements of t he or iginal needle are reproduced and corresponding vibrations are set up in t he diaphragm of t he sound

box . These in turn cause air waveslike the or iginal ones and we may

enjoy wonderful musical treats whichin most cases would otherwise beunattainable .

In t he te lephone the air waves produced by the vo ice cause vibrationsof t he diaphragm in the te lephone

FIGURE 48.—TELEPHONE transmitter (Figure By means of

TRANSMITTER an e lectro-magnet, concerning whichM' mouthpie ce ; F and we shall learn more later , e lectr ic

C, front and back ofm e tal

Case ; D. alum inum dip; current s v arying according to the

phragm , h e ld around itsVibrations Of t he diaphragm are trans

edge by a soft rubb er ring ;

A and 3 . paralle l carb on mit t ed along t he te lephone WIrc .

Plates- Separated by carb én These currents cause t he diaphragm1 0 o o ogran“ es

In t he te lephone recelv er t o Vibrate Int he same way as t he one in the transmitter, and air wavesare set up corresponding t o the air .wave s produced by thevo ice of th e person speaking into the te lephone miles away .

Prob lem 3 . How th e ear is fitted to receive sounds.

The way in which the ear is able t o rece ive sound wavesmay b e understood by a study of t he diagram showing thearrangement of the parts of the ear . The external portion,

wh ich i s rough ly funnel-shaped, leads into a tube about ‘an

HOW WE HEAR'

51

inch in lengt h at t he end ofwhich is t he ear drum . Beyondthe ear dr tim is the middle ear which connects with t he throatby the Eustac hian (fi-st a

’ki—an) tube . Across the cavity of

the middle ear extends a chain of very small bones, one end

of which is in contact with the ear drum , and t he other witht he membrane of t he inner ear . In t he inner ear , which is

FIGURE 49 . HUMAN EAR.

1 , external ear ; 2 , hairs at entrance of auditory canal ; 3 , auditory c anal ,

4 , sem ic ircular c anal, a port ion of internal ear ; 5 , auditory ne rv e leading

to the b rain ; 6 , ear drum , from wh ich a ch ain of bones extends to the

inne r ear ; 9 , Eustac h ian tub e , c onne c t ing th e m iddle e ar w ith th e th roat .

filled with liquid, are many minute projections of a largenerve , t he auditory nerve , which extends t o t he brain .

Your knowledge of the way in which sound waves act

will enable you t o explain what goe s on in t he ear when air

waves reach it (Figure What is t he advantage of

t he expanded outer port ion of the ear ? What effect will

52 GENERAL SCI ENCE

t he air waves have upon t he ear drum ? What is t he purpose of t he chain of bones in t he middle ear ? " What willhappen to t he liquid in the inner ear as a result of the

movement of t he chain of bones ? The smal l nerve filaments are affected by the motion of the l iquid surroundingt hem , and a message i s carr ied t o thebrain by t he auditorynerve . Thus we have t he sensation of hear ing .

The purpose of t he Eustachian tube is t o equalize t hepressure of t he air on t he two sides of t he ear drum so thatit will vibrate freely . Sometimes in yawning you willnotice that for a moment you cannot hear distinctly and that

you have a pec‘uliar r inging in t he ears . This is becauset he tubes have become temporar ily closed. The same con

dition may ar ise for a longer time as a result of a cold'

The peculiar fee ling In the ears exper ienced In going up ordown In an e levator In a high building or through a tunnel,is due t o t he fact that t he pressure of the air on one sideof t he ear drum is greater than that on t he other . Opening t he mouth or swallowing will relieve t he pressure .

Why ? Artillerymen are apt t o have the ir ear drumsbroken at the time of fir ing their guns unless they opentheir mouths . Explain.

SUGGESTED INDIv AL PROJECTS

1 . Demonstrate t he structure and t he method of production of

sound by one of t he following musical instruments : violin, guitar,banjo, cornet, flute , drum , piano, organ, et c .

2 . The dictograph.

3 . How the player-piano works.

4 . Construct a telephone t o b e usedbetween two rooms of the schoolbuilding .

5 . Construct a speaking tub e b etween two classrooms.

6. Construct the model of a human ear .

H

HOW WE HEAR 53

REPORTS

Th e history of t he development of cert ain musical instruments.

Discovery and development of the talking machine .

Different kinds of organs'

ofhearing possessed by animals.

The Maxim silencer for firearms.

PROJECT VI

IMPORTANCE TO Us OF OXIDATION (BURNING)

WE real ize that burning is of great importance t o uswhen we consider that it furnishes us with heat, l ight, andpower . When properly controlled, it is one of our most use

ful servants ; but whenit is uncontrolled, it becomes one of our mostdestructive enemies .

P rob lem 1 . Wh atburning 15 .

—We builda bonfire or a fire ,

in a

stove for t he heat it produces. Fires on h illtopshave been used from the

earl iest times as nightsignals . What , therefore ,may we say, is producedby burning ?If t he draft of t he

stove or furnace is good,t he fire burns br ightly ;

if ashes are permitted t o collect be low t he firebox, t he fire islike ly t o go out . What seems t o b e necessary for burning ?Think of other examples of

.

burning that are familiar t o

you . Does air always seem to be necessary ? Is heat or

54

FIGURE 50 . OIL FIRE.

Burning of a barre l oil tank.

IMPORTANCE TO US OF OXIDATION (B URN ING) 55

l ight produced in every case ? The following ex perMent

wil l Show that some of t he a ir is used up in burning .

Experiment. Place a lighted candle on a cork floating in a pan of

water and invert a glass jar over it (Figure After t he candle

stops burning, t he water rises in the jar t o take t he place of t he air

that was used up. The part oft he air that is usedin burning is called ox ygen, and t he uniting of t he

oxygen with t he sub stance which is b eing burned(fuel) is called ox idation.

Experiment . To find out if any new sub stanceis produced

‘in burning, burn a piece of charcoal(carbon) over t he mouth of a test tub e containinglime water . Shake the lime water . What is t he FIGURE 5 1'

result ? Th is milky appearance in the lime water is the test for a gas

called carbon diox ide.

It is evident , therefore, t hat in t he burning of carbon t hecarbon disappears and there is produced a new substancecalled carbon dioxide, a gas made by t he combination of

carbon with t he oxygen of t he air . Exper iments have beenperformed which Show t hat t he we ight of t he carbon dioxideformed is exactly equal t o t he we ight oft he carbon which wasburned plus t he we ight of t he oxygen used . Th is combinat ion of carbon and oxygen i s accompanied by heat and l ight .A change in which a new kind of substance is formed is

cal led a chemical change.

Carbon and oxygen are simple substances which by no

method yet discovered have been separated into anythingelse . Carbon dioxide , on the ot her hand, may be Shown t obe composed of carbon and oxygen combined in a definiteproportion. Carbon dioxide is a gas that will preventburning and i s therefore an entirely different substancefrom its constituents, name ly, carbon wh ich is a solid and

oxygen which is necessary for burning .

56 GENERAL SCIENCE

Sub stances, like carbon and oxygen, wh ich cannot be

separated into two or more substances are called elements .

Some of the common elements are nitrogen, hydrogen, sul

FIGURE 52 a.—~BUNSEN BURNER.

phur , phosphorus, iron, copper ,sodium ,

potassium , chlor ine , and

silicon .

Substances like carbon dioxideare called compounds . Water i sa compound composed of t he two

e lements, hydrogen and oxygen.

Starch is a compound of carbon,hydrogen, and oxygen . Limestone is a compound ' containingt he elements, calcium ,

carbon,

and oxygen . Almost all substanceswe know oi are compoundsof two or more of about a dozene lements. Al together about 80e lements have been discovered,

but many of these occur in very smal l quantities or are not

found in common compounds .Ex plaln : (1) The failure of a furnace t o burn if ashes are

C

FIGURE 52 b .—GAS STOVE BURNER .

A , gas inlet ; B, air chamb er ; F, air inle t ; G, tub e c ontaining mixtureof gas and air ; C, out le t of gas mixture .

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58 GENERAL SCI ENCE

few drops of high grade gasoline and close the lid. .Put a burning

match or taper thr ough the opening at t he side . An ex plosion willoccur which lifts t he lid.

In t he gas engine , a mixtur e of gasoline Vapor and air

compressed in t he cylinder is exploded by a spark from t hespark plug and t he piston i s thrown back with great force

(Figure By means of a crank shaft and t he gears thispower is made t o turn t he rear wheels of t he automobileor t he screw of t he motor boat .Explain : (1) The str iking back of a Bunsen burner (Fig

ure 52 a) (2) The popping of a gas grate or gas stove whenlighted (Figure

.

52 b) .

.Prob lem 3 . How a match is lighted.

—Explain what

you usually do t o light a match . Can you light a matchwithout rubbing it over a somewhat rough surface ? Whatdo you think was the reason for rubbing t hematch over a

rough surface ?Can you light a piece of wood in t he same way that t he

match was lighted ?Compare t he head of the match with t he wooden stick as

t o t he ease of starting it t o burn . What then is t he reason

for the head of t he match

(FigureCHIEFLY LOW x mouuc MATERIAL

Since the head oft he matchFIGURE 54 .

—A MATCH.

starts t o burn at a muchlower temperature than wood , it is said t o have a lowerkindling temperature . How would you define kindlingtemperatureThe head of the ordinary parlor or fr iction match is

usually a'

mix t ure of (1) phosphorus and a substance whichreadi ly gives out oxygen, (2) some ground glass t o increase

CHIEF-“

LV OYlUIZIBGMATERIAL

IMPORTANCE TO US OF OXIDATION (B URN ING) 59

fr iction, (3) glue , and (4) color ing matter . The stick “

is

dipped into paraffin before t he head is put on .

You can now give t he steps in t he l ighting of a match .

What does t he rubbing or scratching of it on a rough surfacedo ? What is t he effect of t he burning of t he phosphorusupon t he paraffin ? What is t he effect of t he burning of theparaffin upon t he wood of t he match stick ? The flame iscaused by t he burning of t he gases which are given off when

the wood is highly heated .

Since ordinary fr iction matches are a great source of

danger from fire , effort s have been made t o produce a matchthat is less dangerous. One method has

"

been t o coat t hesides of t he head with a substance that has a re lative lyhigh kindling temperature . The birds-eye matches are of

this type . To lessen t he danger from fire , t he safety ”

match also has been invented. You are all familiar wi tht he matcheswhich will not usually ligh t unless scratched upona Special str iking sur face . The heads of these matches contain a substance which give s out oxygen when heated butcontains no phosphorus, t he phosphorus mixt ure be ing in t hestr iking surface on t he side of t he box .

You will notice that some match sticks do not continuet o burn until t he entire stick has burned up . This is because t he sticks have been soaked in a l iquid that h indersburning . Explain t he great value of this.

Former ly t he manufacture of matche s was a very dan

gerous occupation as t he white or ye llow phosphorus usedpoisoned t he workers, especially affecting t he jaw bones.

The use of this form of phosphorus has now been prohibitedin practically all civilized countr ies, and e ither red phos

phorus or a compound of phosphorus and sulphur , both nonpoisonous, is used in production ofmatches.

60 GENERAL SCIENCE

Explain : (l ) ~The lighting of a gas jet ; (2) the startingand continued b urning of a coal fire ; (3) The difficulty of

lighting a match when the wind is blowing .

Prob lem 4 . What causes iron to rust.—This questionmay be answered by performing the following exper iment .

Experiment . Put into a test tub e a small quantity of iron filingsand a few drops ofwater . Move the test tub e around until th e moist

iron filings form a layer sticking to'

the

inside of t he tub e . Place t he testtub e , mouth down, in a glass ofwater .

Note how much Of t he tub e is filledwith air . Examine again on t he following day .

Experiment. Test t he air thatremains in the test tub e for th e presence of oxygen. This may b e done as

follows : Keeping a finger over the

b ottom of t he test tub e turn it so thatthe mouth is up. Insert into t he air in

t he test tub e a lighted splinter or taper .

Does t he taper continue t o burn ?

What does this prove ? What, therefore , do you think happens in t he rusting of iron ?

Can you suggest a reason for

not noticing any heat or light ?It IS evident that some cases of oxidation are relatively slow.

It is interesting t o ‘

not e that moisture also is necessary fort he rusting, so that this process Of oxidation is not quiteso simple as some of the other cases which have beenmentioned .

In addition t o the rusting of iron there are many othercommon happenings which are t he result of slow oxidation.

FIGURE 55 .

—RusTINO OF IRON.

IMPORTANCE TO US OF OXIDATION (B URNING) 61

Rub a match over t he hand in t he dark . What do you Ob

serve ? If paint containing linseed oil is allowed t o stand a

short time , a tough skin is formed on its sur face . This is

caused by slow oxidation Of t he oil in the paint . The same

thing happens when t he paint is spread upon a sur face . The

drying of such paint is due to oxidat ion, and not to real

drying .

Oily rags which have been thr own together in a heap sometimes catch fir e . What is t he explanation of th is fact ?

FIGURE 56 .—SECTIONAI. VIEW OF A HOTBED.

The oil slowly oxidizes and t he heat which is produced gradually increases until t he temperatur e has been raised t o t hekindling point . The whole mass will then break into flames .This is called spontaneous combus tion. Why does oilyclothing not catch fir e spontaneously if hanging ?It is not an uncommon occurrence in t he country for a

barn filled with sl ightly damp hay t o catch fir e . In - thiscase t he production of heat is probably hastened by t heaction ofsmall l iving plants, called bacteria, which are presenton t he stems of t he grass or come from t he air . The hay

does not give offt he heat readily, and finally, as in the case of

62 GENERAL SCIENCE

t he Oily rags, sufficient heat accumulates unt il the kindlingpoint is reached.

The heat produced in a hotbed is formed in t he same wayas t he heat wasproduced in t he hay barn,

but it does notreach the point where the oxidation becomes rapid enought o give Off l ight . A hotbed is made ofdecomposing organicmatter , usually a mixt ure of straw and horse manure .

FIGURE 57 .—FACTORY WRECKED BY A DUST EXPLOS ION.

This is covered with a layer of so il . The b ed is inclosed withframes of glass or cheesecloth t o prevent t he escape of t he

heat produced (Figure The hotbed is used for forcingt he ear ly growt h of plants .Explosions occur in poorly ventilated coal bunkers and

flour warehouses (Figure How can you account for

this ? Why is t he fineness of t he dust particles a factor ?Why is an explosion not apt t o occur unless the ventilationis poor ?

IMPORTANCE TO US OF OXIDATI ON (B URN ING) 63

Prob lem 5 . Why coal is burned. Enormous quantitie s

Of coal are used every year . A coal famine is a very ser iousmatter . Dur ing t he winter of 19 17—18 many cities sufferedfrom shortage of coal . In many cases theaters, schools,and librar ies were closed ; and factor ies were shut down,

throwing thousands of people out Of employment . Trans

port at ion facilities were interrupted ; the use of l ights wasvery much restr icted,

resultingin much inconvenience and loss .In your '

own home or apartment building, coal is burned forproduction ofheat . But inmanycases, t he production of heat isnot t he final result desired . In

t he steam engine,t he heat pro

duced by t he burning of t he coalis used t o change water into FIGURE 58.

—AVAILABLE COALsteam which gives t he engine t he SUPPLY

power t o do many things. What A , dimensions 10 m iles alongeach edge , represents the total

are some Of t he things Wh ich coal resourc es OfUnited S tates

steam engines can do ? Most B , the exhaust ion to c lose of

e lectr ic power houses have greatC'produc t ion in 19 1 1 '

steam engineswhich are used for t he generation of electr icity .

Therefore , from what source may e lectr ical power b e Ob

tained ? What are some oft he things that e lectr icity can do ?To what power , therefore , may all these things b e traced ?It will thus b e seen t hat 'heat , light, e lectr ical and mechan

ical power may be changed one into another . They are

different forms Of energy . Energy may be defined as t he

capacity for doing work.

Suggest specific examples which are known t o you Of the

change of one form of energy into another .

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66 GENERAL SCIENCE

Careful analysis shows that expired air (air breathed Out )contains about 25 per cent less oxygen than inspired air

FIGURE 60 . FUEL VALUE

OF SOME COMMON Focus.

A calorie is th e amount

Of heat ne c essary to raise

the temperature Of 1 kilo

gram Oi water 1°

centi

grade .

(air breathed in) , with a corresponding increase of carbon dioxide .

What constitutes the fuel in the body ?—It is t he food . Just as you may

obtain heat and l ight and power t orun engines by t he burning Of Oil, so int he body t he fat , a form of oil, is

burned t o produce heat energy and

muscular energy . Light is not pro

duced, since the process goes on t oo

slowly . Likewise , other foodmater ialsare burned in t he body t o produceenergy (Figure An ounce of fat

or starch burned inside Of t he bodywill furnish t he same number of heator energy units as if it were burnedoutside of t he body .

Sum up now your conclusions as t o

how energy is made avai lable in t he

human body . Compare t his process

in the human body with what goeson in the fire box of a furnace or

engine .

Why does aman working hard needmore food than one who is not per

forming hard muscular work ?

Why dowe eat more food in thewinter than in the summerBy carefully taking temperatures, it has been shown that

the energy is set free in t he part of t he body that is active ;chiefly of course in t he muscles.

IMPORTANCE TO US OF OXIDATION (B URN ING) 67

Why do t he muscles of t he body Which are used most notbecome overheated ? The circulating blood, i s constantly

rece iving heat from t he more active parts Of t he body, and

is giving it to those parts which are less active . As a result,t he temperature of t he body is equalized . Since t he heatenergy andmuscular energy are made available in t he var iousparts of t he body, three other uses of the circulating bloodare indicated . What are they ?

Prob lem 7 . Do plants b reath e ? If t hey do, then t heremust be some proof that thr ee different things occur .

‘Whatare they ?TO find out if plants use oxygen . and give out carbon

dioxide perform the following exper iment .

Experiment. Into each of t wo flasks put an equal number of

peas that have b een soaked in water . Cork one flask so that no air

can pass into it or out of it. Allow the other flask t o remain Open .

Place t he flasks side by side so that they will have t he same conditionsof light and heat. At the end of a week observe t he content s of the

flasks.

What has happened ? What does this prove ? A'

b lazing

splinter passed into t he open flask continues t o burn . Whathappens when it i s passed into t he flask which has been keptclosed ? What does this prove ? If t he air in each flask istested for t he presence of carbon dioxide , it will be foundthat t he closed flask contains

.

a considerable amount of

carbon dioxide while the other does not contain an appre

ciab le quantity. What does this prove ? What is yourgeneral conclusion as t o t he use of oxygen by sproutingseeds ?If oxidation goes on in sprouting seeds we should expect

that heat and energy ofmovement would result .

68 GENERAL SCI ENCE

Ex periment . Into a flask put an inch or more of pea seeds whichhave b een killed .

‘

by being heated for a short time in an oven. Intoanother flask put an equal amount Of living pea seeds. Put into eachflask the same amount ofmoisture . Place a thermometer in each flask,covering t he mercury bulb with the peas. Permit free access of air :

From time t o time note whether t he thermometers register a differencein temperatur e .

It wi ll be ‘found that heat is generated by t he sprouting

pea seeds . What Observations have you made that will

FIGURE 6 1.—FLOODED REGION.

Trees killed by having their roots drowned.

show that sprouting seeds are able t o lift a we ight or

other ways exert mechanical energy ?

Seedlings t ake in the oxygen of the air and give Off carbon

dioxide through any part Of the ir surfaces . In fully grownplants thi s occurs chiefly through t he young roots and leaves .

In a region flooded for a considerable time, t he trees will

IMPORTANCE TO‘

US OF OXIDATION (B URN ING) 69

die, chiefly because the ir roots have been unable t o get

oxygen from t he air (Figure They have been drowned.

Prob lem 8 . How animals take in ox ygen and give ofi

carbon diox ide . Animals have various ways of takingin oxygen and giving Off carbon dioxide .

(a) Very simple animals. Earthworms'

and othersimme animals have no lungs . How then do you supposethey can t ake in oxygen ? Plants, we already know,

breathe

FIGURE 62 .—ORGANs OF AN EARTHWORM .

Many small b lood vesse ls (not represented in the figure ) pass from near the

surface of the body into the large vesse ls, wh ich are also near the surface .

through t hin moist membranes. Possiblythis is true of t he

earthworm . If so, t he eart hworm must have a thin moistskin. Examine an earthworm t o see if this is the case .

An eart hworm dies as soon as it s skin becomes dry . Ere

quently after a rain ,many earthworms come t o t he surface

because the ir burrows have become filled with water . Earlyin t he morning they may b e seen crawling on t he sidewalk,but it will be noticed that they die as soon as t he sun has

dr ied the ir bodies .If an earthworm breat hes

'

t hrough'

it s skin,what should

be directly below the thin moist membrane of t he skin ?

70 GENERAL SCIENCE

Sum up your conclusions as to how the eart hworm takesoxygen into its body and gives out the carbon dioxide .

(b) Insects cannot breathe through the skin. Why not ?

If a grasshopper is watched, it will be noticed that thehinder portion of the body (abdomen) , which is made up ofr ings, expands and contracts in a way similar t o t he expansionand contraction of our own chests dur ing breathing . Thesemovements of the grasshopper are breathing movements .The air containing oxygen goe s into t he body with each

expansion, and the air containing carbon dioxide passe sout at each contraction. Where doe s t he air go in ? If

you look very carefully along each side of t he body you wi llsee a number of small holes, one in each of t he divisions Of

t he abdomen . There are also two pairs ofhole s in t he thorax,t he part oft he body t o which t he legs and wings are attached.

Connected with these openings are smal l branching tube swhich carry air t o all parts of t he bodyThese breathing pores can usually b e seen very distinctly

on the side s of a beetle larva (Figure 63) or Of a caterpillar ,wh ich you know, of cour se , is t he young of a moth or

butterfly . The young or larva of t he mosquito which livesin water has only one breath ing pore , which is located at

the tail end of t he body . In order t o get air, it must comet o t he surface hanging head downward .

Mosquitoes, therefore , may be destroyed by pour ingoil on ponds in .which they live . The oil spreads over t hesurface of t he water

,forming a thin layer thr ough which

air wil l not pass . Thus t he mosquito lar vae are unable t oObtain air wh en t hey come t o t he surface , and suffocate .

(c) Fish breathe by means ofgills which are located underflaps just back of t he head . If you examine a fish whichhas been sent from t he market with t he head still attached,

IMPORTANCE TO US OF OXIDATION (B URN ING) 71

you will see under these flaps (Opercula) four bony archeson each side . Between these arche s are slits opening intot he back Of the mouth . Each arch has upon it s outer edgea large number of small, reddish, t hr eadlike st ruct ures,(gill-filament s) which project backward from the

The inner side of each arch has on it a number of hard,pointed structures (gill-rakers) (Figure

FIGURE 63 .— STAGES IN THE LIFE HISTORY OF A BEETLE.

Note the b reath ing pores on the side of the larva (the worm-like stage) .

Observe a fish in an aquar ium . DO you notice any movementswhich are probably connectedwith breathing ? Waterpasses into t he mouth of t he fish and out through t he gillslits at t he side of t he head . Suggest a use for t he gil lrakers . The heart is located on t he under side Of the fish ,

in t he space between t he back part s of t he gills. It pumpst he blood forward througha vesse l wh ich has four brancheson each side , one to each gil l arch . These vesse ls in t urnsend off very small vessels into t he gill filaments .What do you suppose the blood in these vessels rece ives ?

72 GENERAL SCIENCE

What does it give Off The blood from the gil l filament spasses into vesse ls which carry it t o t he upper part of thegill arches and from there it passes t o all part s of t he body,finally returning t o the heart loaded with carbon dioxide and

without its oxygen. What has become of t he oxygen ?What is t he source of‘

t he carbon dioxide ?

FIGURE 64 .

—BREATH ING ORGANS OF FISH .

(d) Higher animals . Most animals that live in the air ,

except insects, breathe by means of lungs which are reallythin~walled bags connected with the outside air throughthe nostr ils . The walls of the lungs contain many smal lblood vessel s (capillar ies) . The blood in these takes inoxygen and gives Off carbon , dioxide .

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PROJECT VII

PREVENTION OF DESTRUCTIVE BURNING OR

OXIDATION

WE have seen that oxidation is very valuable in giving ususable energy . Can you name examples of oxidation or

burning wh ich are harmful ? From what we have learned

FIGURE 65.—RESULTS OF A FOREST FIRE.

Not only have the trees been destroyed but almost all the vege tab lemat ter (humus) of the soil has b een burned away .

about burning, we should b e able t o suggest means bywh ich destructive oxidation may b e prevented.

What two conditions are always necessary for oxidation ?Suggest another which is usually necessary . It is clear thatif any one of the necessary conditions is removed, then

74

PREVEN TION OF DESTRUCTI VE B URNING OR OXIDATION 75

burning or oxidation must stop . Our problem then is simplyto discover methods by which these conditions nece ssaryfor oxidation may be prevented .

Prob lem 1 . How destructive ox idation?

may b e pre

vented by excluding th e air . (a) Coating iron with a substance which does not rust . What are some of t h e waysin which air may b e kept from substance s which are apt

to undergo harmful oxidation ? How are iron fire e scapeskept from rusting ? Give other example s of the use of th i smeans.

IS a t in pan made entire ly of t in ? Give proof for youranswer . Tinware is made of thin Sheets Of iron wh ich

,

after having been thoroughly cleaned, are dipped into me ltedt in . Iron also may b e prevented fromrusting by cover ingit with a layer of zinc, applied in t he same way . Th is i scalled galvanized iron and i s very generally used for pails,water troughs, and Similar article s . It is not used for cocking utensils, as zinc may form po isonous compounds .How i s the iron hot water bo iler in t he kitchen prevented

from rusting ? It is usually painted with a volatile substance

(a substance which evaporates quickly) in wh ich there i spowdered aluminum

,a metal which is not affected by t he air .

The volatile l iquid disappears; leaving on t he bo iler a thinlayer of powdered aluminum wh ich not only gives t he bo ilera pleasing appearance but also prevents it from rusting .

Iron may also b e prevented from rusting by cover ing itwith a layer of nickel , which is put on by the use of e lectricity (nicke l plating) .The iron of stove pipes and locomotive boilers is usually

protected from rusting by a coating which is produced bypassing over the hot iron a mixture Of h ighly heated steam

76 GENERAL SCIENCE

and carbon dioxide . This coating is an oxide of iron, different from t he ordinary oxide of iron,

and it protects t heiron from further oxidation. Iron, coated in this way ,

is

called Russia iron .

(b) How do .fire ex tinguishers work? A fire is put out bysurrounding the burning mater ial with a gas which will

not burn. What happensthen t o the fire ? Somefire extinguishers containa l iquid, carbon t et rachlor ide , which becomes a noninflammab le gas when itis squirted on the fire .

In the fire extinguisherswh ich are inverted justbefore be ing used, sul

phuric acid falls into a

solution of soda (FigureThe action of t he

acid upon the soda pro

duces a large quant ity _ of

carbon dioxide wh ich forces out t he mixture Of water and

carbon dioxide . What effect will th is have when playedupon t he burning objects ?

FIGURE 66. FIRE EXTINGUISHER .

Ex plain t he reason for keeping pails Of sand in var iousparts of a garage . Why is water not used for the purpose ?Will water mix with gasol ine ?(c) Smothering a fire .

-Explain why it is advisable to

roll a person whose clothing is on fire In a rug or blanket.Is it advisable for a person t o start t o run if his clothingis on fire ? Why ? Why are burning draper ies pul led downand stamped upon ?

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78 GENERAL SCIENCE

continue to burn unless there is a supply of fue l mater ial ;hence , the inspectors Of t he fire department prohib it t hecollection of rubbish in basements and area ways. Everyyear forest fires destroy property worth hundreds of thousands Ofdollar s .and cause the death ofmany people . Probably the most common cause Of these fires is t he care lessness of campers in fail ing t o put out their camp fires . Very

FIGURE 68 .— A FOREST FIRE FIGHTER.

str ict regulations concerning the use of fire are enforcedt o prevent t he starting Of forest fires . To l imit the spreadof a fire if once started in a forest reservation,

there are

fire lanes wh ich’

are kept cleared of underbrush . Why dothe fire lane s stop t he fire ?Ground fires which creep along the ground, depending for

fue l upon t he underbrush and vegetable matter accumu

PREVENTI ON OF DES TR UCTI VE B URN ING OR OXIDA TI ON 79

lated dur ing many years, are frequently stopped by plowingup a str ip of land in the path of the fire .

'

What is theadvantage Of this?Dur ing severe fires in citie s

which threaten to destroyproperty in great areas, buildings are Often de l iberate ly destroyed by dynamite . Whatis the reason for t his ? Wherethere are buildings in solidblocks, fireproof wallsare constructed at intervals whichare known asfire walls.

What ismeant by fireproofconstruction of buildings ?In what respect isyour schoolbuilding offireproof construotion ? In other buildingswith wh ich you are familiar

,

what means have been takento make them fireproof ?What sub stancesmay b e usedinfireproof construction ?

INDIVIDUAL PROJECTS1 . Make and demonstrate a

2 . Collection and demonstration offireproofing materials.

REPORTS

1 . Fighting a forest fire .

2 . Fireproof construction of

buildings.

FIGURE 69 .—FOREST RANGER ON

LOOKOUT FOR S IGNS OF FOREST

FIRES .

If signs of fire are discovered, theranger te lephones to the fire stat ion

nearest th e fire , indicating by refer

enc e to th e forest map the exac tlocat ion of th e Ob se rved smoke .

PROJECT VIII

IMPORTANCE TO US OF THE OTHER GASES OF

THE AIR

WE have seen that the ~

ox ygen of the air is of very greatimportance to us . Mention several ways in wh ich it is Of

great value and several in which it is harmful . The question naturally ar ises, are there other gases in the air and ifso, of what importance are they to us. The first problemtherefore i s

Prob lem 1 . Does air contain any gas b esides ox ygen ?

Experiments. (1) Burn a taper in air, and then in oxygen.

(2) Burn in oxygen a bundle of fine iron wire, dipped in sulphur.

What are the results ? What is t he conclusion ?

(3) Expose a vessel Of limewater t o t he,air. Note that a scum

appears on the surface. This is an indication Of the presence ofcarbon

dioxide.

Prob lem 2 . HOW much of th e air is ox ygen Can

you suggest a method by-which thi s may b e found out ?

Experiment . On a metal disk on a flat piece of cork, place a bit

of yellow phosphorus. Place t he cork o on water and invert over ita glass cylinder . Examine after two days. Result ? Conclusion ?

Quantitative exper iment s have shown that air has the

following composition :

Oxygen,20+ per cent .

Nitrogen,including several inert gases, 79+ per cent .

Carbon dioxide , .03 t o .04 of 1 per cent80

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82 GENERAL SCIENCE

important element in explosives. Explain. Under certainconditions some of t he nitrogen of the air may b e used inthe growth Of plants or may b e made into substances fromwhich explosive s may be manufactured. These cases willb e considered later .

Prob lem 4 . Importance of carb on diox ide of th e air .

We found that certain animals In breath ing give carbondioxide t o the air . Also that it is added t o t he air in t he

burning of a candle . In t he same way it is given off in the .

burning of coal , wood, oil,.

e t c . As a result what do you

think Should happen t o t he amount Of carbon dioxide in theair ? But an ex amination of t he air year after year indicate s that there is no increase in the amount of this gas.

What do you conclude from this?Another interesting fact gained from t he examination

of t he air i s that t he oxygen of t he air does not decrease inquantity . In t he solution of our problem , therefore , a numb er Of smaller problems must b e solved. Th e fir st of the sewill b e indicated by a fact that is familiar t o you . Whatis

’

the appearance ofpartial ly burned plant mater ial ? Whatdoes this indicate ? Since plants can grow in soil wh ich con

t ains‘

no carbon, what will you suspect is the source of the

carbon

Sub -prob lem I . Proof that carbon compounds are made

in leaves of plants. One of the most common plant substances containing carbon is starch . There is no starch int he soil or in the air , therefore it evidently must b e made

within t he plant .

Experiment .

—To prove that starch is manufactured in a leaf

place a geranium in a dark closet for twenty-four hours, then remove a

leaf and test for starch. This is done‘

by first removing the green col

IMPORTANCE To US OF THE OTHER GASES OF THE A IR 83

oring matter, by soaking the leaf in alcohol, and then adding iodine ,

which gives a b lue color if starch is present. What is t he result ?After this leaf has been removed,

set t he entire plant in t he sunlight,first placing upon several leaves pieces of b lack cloth or thin strips Ofcork which complete ly excludet he light from the portions of

t he leaves covered. After a

few hours, remove and testseveral leaves for the presenceof starch. What is the result ?What two things are provedby this experiment ?

Sub -prob lem II. Whatraw mater ials are used byleaves in making starch ?

—Analysi s Shows thatstarch is made Of the

fo l lowing fu'ndamenta lsubstance s or elementsCarbon, 6 parts ; hydro

gen, 10 parts ; oxygen, 5

parts. Th l S ls conv en

ient ly wr itten, C6H1 00 5 .

'

“later , which is made Of

two parts of hydrogen and

one part of oxygen FIGURE 7 1.

— POTATO PLANT.

and carbon dioxide , com_A plant In Wt h a large amount Of starch

is stored in an unde rground stem .

posed ofone part ofcarbonand two parts of oxygen both ofwhich are accessiblet o the leaf,

‘

cont ain t he e lements necessary for t he formationofstarch . Ifthey were combined, t he result might b e represented as follows : Carbon dioxide (C0 2)+VVat er (HgO)Starch (C6H1 00 5) . It will be noted that t o get sufficient

84 GENERAL SCIENCE

carbon for the starch , it is necessary that six part s of carbondioxide enter into t he combination ; and t o provide t he

proper proportion Of hydrogen, fiv e parts Of water mustcombine with t he carbon dioxide . The action may then b erepresented as follows : Six parts of carbon dioxide mightcombine with fiv e parts of water to form one part Of starchor

6 C0 2+5 H20 C6H100 5

But if six parts OfC0 2 unite with fiv e parts ofH20 t o formstarch (C6Hl oO5) , it will b e noticed there is an excess of

oxygen, so that t he action will'

finally b e represented as

followse co.+sH20 = C6H1 00 5+6 0 2

If in the leaf, therefore , carbon dioxide and water actuallydo unite in forming starch , oxygen should b e given Off. Does

this occur ?

Sub -prob lem III . Do plants give off ox ygen in making

starch

Experiment . Place some aquarium plants under a funnel in a jar

Ofwater . Over t he neck of t he funnel put an inverted test tub e filledWith water . Place the jar in t he sunlight. What do you observe ?Remove t he test tub e without allowing any of t he contained gas to

escape , and pass into t he mouth Of the test tube‘

a glowing emb er .

What happens ? What does this prove ?

The work that t he green leaf does with t he assistanceof sunl ight in combining carbon , dioxide and water intostarch is called photosynthesis (from two Greek words :

photo, light, and synthesis, putting together)

Sub -prob lem IV. Proof that plants use carb on diox ide

in making starch .

—The fact that oxygen is . given off byplants is an indication that carbon dioxide and water are

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86 GENER AL SCI ENCE

or less hor izontal (Figure Anthracite or hard coalis found in portions of t he country

'

where the strata or

lav ers o of t he rock have been very much crumpled. Thiscrumpling process has evidently been accompanied by a

high temperature which has dr iven from t he accumulatedvegetable matter many compounds, leaving almost purecarbon .

Just as we have found that the starch is made by plants,only under th e action Of t he energy of sunl ight, so l ikewise

FIGURE 72 .—COAL BED.

Horizontal b ed Of c oal exposed along a river b ed inWyoming.

in t he cases Ofwood and coal the energy of [ t he Sun has beennecessary. What, therefore , may be considered to b e t he

final source'

of the energy given out in t he process of t heburning Ofwood or coal ? The amount of heat procured byburning a piece of coal may b e considered t o b e a measureOf the amount of the sun’

s energy necessary t o separate t hecarbon from the oxygen of carbon dioxide in the process ofphotosynthesis (Figure

IMPORTANCE TO US OF THE OTHER GASES OF THE A IR 87

We are now able'

t o understand why the re lative quantities Of oxygen and carbon dioxide in the air remain the

same year after year .

BITUMINOUS ANTHRACITE

FIGURE 73 .—HEATING VALUE OF SOME COMMON FUELS .

Note th e re lat ive amounts of carb on (C) in the various fue ls. Whatis the source of th is carb on ? What is the source of the hydrogen (H) ?

The c alories given he re are small calories. The amount Of h eat necessary

to raise the temperature of one gram of wate r 1°C. is one calorie . Fue l

value Of foods is usually given‘

in large Calories , 1000 t imes greater than

small calories.

88 GENERAL SCIEN CE

What are the chief ways in which oxygen i s removed fromthe air ?

How is it restored t o t he air ?How do you suppose t he composition of the air before the

carboniferous per iod (the per iod when most coal was formed)differed from the

‘

composition of the air now ?

FIGURE 74.—OIL WELLS IN OKLAHOMA.

Th ese w e lls tap Oil deposit 2000 to 3000 fe e t b e low the surface . S ince

pe troleum has evident ly b een formed from plant and animal mate rial , what

is th e sourc e of its energy

Almost all plants are green . Is there any connectionbetween t he possession of this green color ing matter

(chlorophyll) and t he ability t o make starch ?

Sub -prob lem VI . Is th e. green coloring matter (ch lo

rOphyll) necessary for making starch .

—Place a plantwhose leaves have white streaks or spots (Tradescantia is a

good plant to use) in the sunl ight for several hours. Test

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90 GENERAL SCIENCE

teins and certain mineral salts . The prote ins, when oxidized,wil l produce energy, but t he chief energy-producing portionsof food are carbohydrates (starch and sugar) and fat s .

FIGURE 76.—RELATION OF PLANT AND ANIMAL IN A BALANCED AQUARIUM .

Since fish of the balanced aquar ium maintain their sizeand are active, what must b e obtained from the plant s ?Since the plants do

~

not decrease in quantity, what mustthey b e able to do ?

IMPORTANCE TO US OF THE OTHER GA SES OF THE A IR 9 1

We already have learned from what they make carbohydrates . Explain. Carbohydrates in turn are sometimes changed by t he activity of t he l iving matter into fat .

For the manufacture Of prote ins, t he plant must not onlyhave carbon, hydrogen, and oxygen, which may b e obtainedfrom the carbon dioxide and water , but must

.

alsO havenitrogen a nd other e lements . The wastes of the fish con

tain all these needed e lements.

In swimming about, the fish are continually exertingenergy. What is the final source of th i s energy ?The re lation of the plants and animals in the balanced

aquar ium is represented in the diagram (Figure 76) on t he

preceding page .

Wh at do you think would happen to animals, includingman, if there should be no more green plants? Explain.

Summar ize in a sentence or two t he importance t o us of

the carbon dioxide of t he air .

INDIVIDUAL PROJECTS

1 . Rapidity of starch manufacture in a leaf.

2 . Keeping a balanced aquarium .

The world’s food Supply .

REFERENCES FOR PROJECT VIII

1 . The Fresh Water Aquariumand I t s Inhab itants, Eggeling and

Ehrenb erg . Henry Holt 85 Co .

2 . Life in Ponds and Streams, W. Furneaux . Longmans, Green

CO .

PROJECT IX

TO KEEP FOODS FROM SPO ILING

YOU know that many foods if left in t he air spoil or decay .

Name some foods which you know will spoil if left exposedt o the air . Since foods must be transported long

.

distancesand frequently must be kept many months before be ing used,t he problem of preserving foods is of t he very greatestimportance . Without the means of preserving food fromdecay our present civil ization could not have ar isen.

i Think for a moment of t he possibil ity of t he existence of

great cities, l ike New York, Chicago, or of great manufact uring centers, if ways of keeping foods from Spoil ing hadno t been discovered. Could t he United States have senther great army of men t o Europe , if

'

there hadbeen no means of preserving foods for many months and

even years ? In consider ing how'

foods may b e kept from

spoil ing, naturally t he first problem is :

Prob lem 1 . Wh at causes foods to spoil or de cay ?Is it t he oxygen of the air acting upon t he food which causesthe change , a process of Slow oxidation such as we haveObserved in a number of cases ? The question can be

answered by performing t he following exper iment .

Experiment. TO find out what causes foods t o spoil when leftexposed t o t he air , pour some beef t ea made of b eef extract and a

small amount of peptone (digested protein) into two test tub es. Boil

the beef t ea in each test tub e for an equal length Of time . Stopper onewith cotton . Allow the other to remain open. Place the tubes side

by side in t he room. (Ex periments have proved that air will pass92

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94 GENERAL SCIENCE

liquid culture medium . A sol id culture medium 1s made by

adding t o beef t ea some agar-agar , a vegetable ge latine ob

tained from cert ain kinds of sea weeds . (Details Of prepa

ration are given in t he appendix .) Into Petr i dishes (flatdishes especially designed for study of bacter ia) which havebeen highly heated t o kill any l iving organisms present, poursome of this melted agar medium . Cover t he dishes immediat ely . In a short time t he culture medium will becomejellylike and ready for use .

Experiment . Expose open dishes in several of the followingplaces for fiv e minutes, then close and lab el : a classroom, a corridorbefore the passing of classes, a corridor during passing of classes, a Window Sill outside of room , street, subway, park, et c .

Experiment . - By means of a needle , which has been heated (sterilized) t o kill organisms upon it , put into dishes small amounts of

mat erial which you wish t o test for the presence of microorganisms ;

e.g. dust from floor, saliva, dirt from under finger nails, milk, soil, et c.

Experiment .—Test various other sub stances, e.g. pupil

’

s finger,b reath, paper and silver money, drinking water , the edge of drinking

cup, blade of a knife , pencilpoint, et c . Take care in

every case that you preventthe entrance of any other

Descr ibe t he results oft hese exper iments. The

FIGURE 77.-4- COLONIES OF BACTERIA AND

Spots.

Wt h,y0 11 are

MOLD colonies of bacteria or

The agar culture med um in th ese d’

shes mold (Figure Ar ewas exposed to th e air for ab out Sm inutes.

there 1nd1cat Ions of the

presence of more than one kind Of microorganisms ? DO

you see any mold colonies ? They are flufl’

y or hairy in

appearance instead Ofwaxy like t he bacter ia colonies. Doe s

TO KEEP FOODS FROM SPOIL ING 95

there seem t o be any“connection between t he presence of

dust and the abundance of microorganisms ?

Prob lem 3 . Size , Shape , andmeth od of multiplication of

bacteria. Could you see t he bacter ia upon t he agar platewhen t he plate was first exposed t o t he air ? What doesthis indicate as t o t he size of t he bacter ia ? You will findthat t hev can b e seen only with rather a high power of a

compound microscope .

They are t he smallest and simplest plant life known .

The average rod-shaped bacterium measures about 17m of

From.Househ old B act eriology b y B uch anan.

FIGURE 78.— THE FOUR TYPES OF BACTERIA .

A , c oc c i ; B , bac illi ; C, spirilla ; D, b ranch ed filamentous organism .

an Inch in length and about m of an inch in diameter .

Some are larger and many are much smal ler , some be ingso small that they are invisible under t he h ighest powerlenses, but known t o b e present because of t he effect whichthey produce in t he substance in which they are l iving . A

calculation of t he number in a cubic . inch of average sizedbacter ia will give you some idea of t he extreme smallnessof these plants.

If you are fortunate enough t o have a compound microscope for t he use of your class you may Observe t he

shape of t he bacter ia . Ifno microscope is '

available , examine

96 GENERAL SCI ENCE

the drawings representing t he different shape s . It will benoted that t here are three pr incipal forms Of bacteria ;Spher ical or ball-shaped (coccus) , rod-shaped (bacillus) ,and Spiral-shaped (spir illum) (FigureThey multiply by dividing into two . These in turn, aft er

growing t o ful l Size , will again divide . If conditions are

favorable , bacter ia may grow t o full Size and divide agam In

thirty minutes. It has been estimated that if bacter ialmul tiplication went on unchecked and th e division of eachbacter ium took place as often as once an hour

, the descendants Of each individual would in two days number

Actually,such unchecked multiplication never

occurs except for a very Short per iod, as conditions deve lopwhich interfere with furt her growth .

Not all microorganisms are bacter ia. Yeasts and moldsare rather close ly re lated t o ‘

t he bacter ia. There are alsoanimals (protozoa) of approximate ly as simple structure as

the bacter ia . Some of these , because Of t he harm that theydo

,are of very great interest t o us.

Since these ext reme ly small living things cause our food t odecay , it is Mport ant that we know t he conditions whichare favorable and conditions which are unfavorable for the irgrowth , hence our next problem 13 :

Prob lem 4 . Wh at conditions are favorab le and what nu

favorab le for growth ofb acteria and molds This problemcan b est b e solved by a number of exper iments .

Experiment . Take a numb er of test tub es, and into each pourab out an inch of t he b eef t ea culture medium t o which has b een added

some material known t o contain bacteria.

1 . Stopper two tub es with cotton . Put one in a warm place , neai'

a radiator or stove and t he other in a cold place, as in the ice box .

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98 GENERAL SCIENCE

on ice and has the same temperature . Place the two glasses side by

side and apply gradually an equal amount of heat. Note t he t em

perature from time t o time . Result ? What effect does the meltingof ice have upon the heatof the surroundingwater ?IS this not what you wouldexpect ? The removal of

heat from water causes it

t o change into ice , so heatmust be used up t o changet he ice back into water.

DO you think that}your re

frigerat orwill b e made colder

by covering t he ice withCourtesy ofM cCray R efrigerator Co. pads t o keep it from melt

FIGURE 79 .—WALL OF A REFRIGERATOR . ing ?

An ice chest or refrigei'at or is essentially a box whose wallsare so const ruct ed that they are poor conductors of heat

(Figure This is usually accomplished by having in t hewall an air Space which is packedwith charcoal or some other poorconductor . The Ice In a refr igerat or should be placed near t he

t op. The melt lng Of t he ice coolst he air in contact with it . The

cold air falls. (Why ?) In so

doing it?

forces t he warm air t o

t he t opwhere it in turn is cooledand replaces t he air which hasbeen warmed by coming in con

tact with t he food . The effectiveness of t he refr igerator dependsupon t he circulation of air within

FIGURE 80 .—CURRENTS OF A IR

it ; and accordingly care should IN A REFRIGERATOR.

TO KEEP FOODS FROM SPOILING 99

be t aken that the free passage of air is not Obstructed in

any way (FigureThe Ice chest 18 simply a means Of checking t he deve lopment Of bacter ia but by no means doe s it stop their growt h .

In a large ice chest, food may be preserved for a considerablelength of time but itfinally will decay . In

smal l ones, food may be

kept for only a few days.

All refr igerators should

be frequently cleaned, asdirt and part icles of foOd

furnish a place for t he

growth of bacter ia, and

after a time render t he

refr igerator unfit for use .

Var ious methods havebeen used in homeswhereice cannot be obtained t oprovide a low temperature for t he protectionof food against t he ac

tion Of bacter ia . Coolc e l lar s, co l d r unn ingwater , Spr ing houses, and

FIGURE 8 1.— icELEss REFRIGERATOR .

suspension in deep we lls are means frequently employed.

An ice less refr igerator (Figure 81) may be made as followsCover a frame of wood with cloth such as duck . (Figure

Sew a number?

of lamp wicks t o t he edge of t he clothand allow t he other end of t he wicks t o ext end into a vesse lof water on t op of t h e frame . The water soaks into t he

cloth through the wicks. AS heat is used up in evaporat ion

100 GENERAL SCI ENCE

the t emperature with in t he refr igerator is lowereddegrees F. The efficiency of this refr igerator is

,

if it is kept where there is a current of air . Why ?In tropical countr ies,dr inking water is keptin porous eart henwarejars . Why ?

Prob lem 6. Use of

cold in storage warehouses. In cold-storagepl’ants low, constant t em

peratures are maintained .

Definite temperatures arekept in different rooms,as not all foods are bestpreserved at t he sametemperature . Fruits arestored at a little abovefreezing ; fresh meat, at

about 25 degrees F. ;

poultry, at about 15 degrees F. ; fish , at about0 degrees F.

FIGURE 82 .— FRAMEWORK OF AN ICELESS The question arises

,

REFRIGERATOR.

How are these steady lowt emperatures produced? AS ice is not used, a review of the

pr inciple of t he iceless refr igerator may help us . (Explaint he production of low temperature in t he ice less refr igerator .)Cold-storage plants generally use ammonia which has

been changed into a l iquid from a gas by pressure . Whenthe pressure is re leased the aw onia returns to it s gaseous

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‘

i

5GENERAL SCI ENCE

theifruit growers rece ived nothing for t heirk i

year’

s work . Did t he people of Chicago profit by thiscondition ? It is true that for a short time peaches couldbe bought for a very low pr ice ; t he peach season was,

however, made extremely short .

Since great storage plants have been built, conditionshave changed entirely . Now, only enough fruit is put

FIGURE 84 .—STORAGE OF BUTTER IN A REFRIGERATING PLANT.

upon the market t o supply t he normal demands ; t he

surplus is put into cold storage warehouses t o be takenout and sold as t he supply direct from t he orchards decreases . The producer now rece ive s a fair return for hislabor and investment . The consumer has a lengthenedpeach season and there is a minimum ofwaste .

It is now possible t o have fresh at any season of t he yearthe per ishable foods produced at almost any other season.

TO KEEP FOODS FROM SPOILING 103

Wi thout cold storage the supply of such foods as butter and

eggs and some other foods Would be so limited at cert aintimes of t he year that they could be used only by t he wealth

iest people (FigureBy means of cold-storage cars and ships, per ishable foods

may be transported almost any distance . American freshmeat is sold in t he markets ofLondon and Par is. Argentinebeef is put on sale in Amer ican cities. Fruits of California

and t he southern states are de l ivered with little or no loss

of flavor t o every city in t he country .

Prob lem 7 . Use made of h eat in food preservation .

A visit t o a grocery store and observation of t he rows of

canned vegetables, fruits, and meats are sufficient t o indicatet he great use made Of this method of preserving food. It is

one of t he chief agencies by which a regular and var ied foodsupply is made possible . Without t he modern methods offood preservation, cities such as New York

,Philadelphia,

and Chicago could not exist .

Experiment . Open a can ofmeat of some kind, permit some of the

contents t o b e exposed t o the air for a day . Put portions of the meatinto two test tub es. Place one test tub e in b oiling water for an hour .

Stopper both test tub es with corks, dipping the stoppered ends intomelted paraffin t o make them air-tight. Put t he test tub es aside in

a warm place for a few days. Result ? Conclusion ?

Pasteurization of Milk. As diseases may b e transmittedby milk, t he problem of destroying bacter ia contained byit is of great importance . Tuberculosis, typhoid fever ,scarlet fever , diphther ia,

and very probably dysentery,are diseases spread by milk . The problem is rendered moredifficult by t he fact that boiling affects milk injur iously t osome extent , causing it t o become less digestible . It has

been found that by heating milk t o a temperature of 142

104 GENERAL SCIENCE

t o 145 degrees F. for at least t hirty’

minut es, the pathogenic

(disease-producing) germs will be killed without inj ur ing thedigestible qual ities of t he milk . This process is '

known as

pasteurization . Hospital records Show, however , that it isadvisable t o give orange juice t o ch ildren whose diet isalmost exclusive ly pasteur ized milk . Otherwise , r ickets (adisease of t h e bones) or another disease known as scurvymay develop .

Prob lem 8 . Use made of oth er methods of food pres

ervation. What methods for preserving food in additionto use of cold and extreme heat can you think of?

The use of sugar t o preserve food may be shown by thefollowing exper iment .

Experiment . Put some pieces of fruit into a test tube and coverloosely t o prevent drying . Cover some similar pieces of fruit withmelted sugar . Slightly heat the mixture of sugar and fruit, put intotest tube and cover in the same way as t he other tub e was covered.

Put both tubes aside in a warm place . Re sult ? Conclusion ?

Jell ies and marmalades are examples of t he use of sugaras a food preservative . From one of our ex per iments, whatwas your opinion as t o the amount of sugar that Should b eused ? If a smaller percentage is used, yeast will causefermentation with resulting bubbles of gas and an Odor of

alcohol . Before canning became common, this method of

preservation was much more used than at pre sent . The

large percentage of sugar cause s some modification in the

flavor of the food, and makes the mater ial more of a sweetmeat than a fruit food . Condensed milk, wh ich has comeinto such general use , remains unspoiled for a considerabletime after the can has been opened because there has beenadded to it 30 t o 40 per cent of sugar .

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106 GENERAL SCIENCE

dry with some wh ich has been kept slightly moist for a

week . In the same way compare bean and pea seeds and

grains of corn and wheat which have been kept dry with thesame kinds of seeds that have been soaked and permitted toremain mo ist . What is an advantage of hard-tack and

cracker s over bread ? When fru its are completely dr ied,the ir flavor i s large ly lost . Those which contain a largepercentage of sugar , such as grapes, prunes, peaches, figs,dates, currants, e t c . ,

may b e preserved by the removal ofonly a l imited portion of the ir water by drying . Why ?Meats are preserved on an immense scale by a combination

of salting, drying, and smoking . Give examples . Milk isdr ied and put upon t he market as a powder . Wh en dissolved in water it has a flavor slightly different from thatof fresh milk, but none of it s nutr itive properties has beenlost ; It possesses t he advantages of occupying little spacein transportation, and of be ing able t o be kept indefinitelywithout decaying, sour ing, or molding . Evaporated milk hashad a portion of its water removed, thus greatly reducing itsbulk.

B r iefly sum up the m ain points you have learned as t o

how t o keep foods from spoil ing, and why these methods aresuccessful .

SUGGESTED INDIVIDUAL PROJECTS

1 . Examination of bacteria with a microscope . Make drawings.

2 .

‘Making of agar culture medium .

3 . Can a dozen jars of vegetab les or fruit.4 . Construct a homemade device for pasteurizing milk.

5 . Make six glasses of jelly .

6. Construct an apparatus for dehydration of vegetab les. DebyQ

drate some vegetab les that are difficult to keep through the winter .

Cook and test.7. Construction of an iceless refrigerator .

TO KEEP FOODS FROM SPOILING 107

REFERENCES FOR PROJECT IX

1 . Bacteria, Yeasts and Molds in the Home , W. H. Conn. GinnCo.

2 . Household Bacteriology, E .,D. Buchanan.

3 . Milk and It s Products, H. H.Wing . Macmillan Company .

4 . An Iceless Refrigerator . FoodThrift SeriesNo. 4 , U. S. Department ofAgriculture .

5 . Farmers’ Bulletins, U. S . Department of Agriculture

375 . Care of Food in the Home .

521 . Canning Tomatoes at Home and in Club Work.

839 . Canning by the Cold-Pack Method.

841 . Drying Fruits and Vegetab les in th e Home .

6 . Circulars, U. S . Departm’

t ofAgriculture , Canning, Eyaporat ing.

7 ColdPackCanning. InternationalHarvester Company,Chicago .

PROJECT X

TO PROTECT OURSELVES AGAINST HARMFUL

MICRooRGANISMS

MICROORGANISMS can do many th ings beside causing foodsto decay . Some do very valuable work ; so valuable infact, that without their aid l ife would cease t o exist upon theearth . t he other hand, some , such as t he diseaseproducing (pat hogenic) forms, are extreme ly harmful

,

causing t he premature death ofmany persons.

Fortunate ly the large major ity of microorganisms are

not pathogenic . If this were not true , we might well b eappalled at t he results of our exper iments as t o the dis

t ribut ion of bacter ia . Most of t he bacter ia discovered inthose exper iments are capable of producing decay only,

'

but

it must not b e forgotten that th e objects and substancesexamined, while they are often carr iers of non-pathogenicbacter ia alone , still may frequently b e carr ier s of disease

producing ones .In consider ing how t o protect our se lves from harmful

microiirg nisms, we must consider how they affect us, howt he microorganisms (germs) may b e carr ied from one

person t o another , how the body naturally fights the germs,how t he body may b e given special power t o fight them , and

finally how certain substances called disinfectants and

antiseptics may b e used t o destroy germs .

Prob lem I . How b acteria and oth er microfirganisms

affect th e h ealth . What frequently happenswhen you get a108

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1 10 GENERAL SCIEN CE

fiammat ion may spread and possibly finally deve lop intoblood poisoning.

The inflammation of pimmes and bo ils is also caused bybacter ia

,and the pus is formed in t he same way .

You have all noticed that if one member of a familygets a cold frequently the other members also contract it .Microscopic examinations have shown that bacter ia of

certain kinds are always associated with colds. It is veryevident that this inflammation, as in other cases of in

flammat ion, is due t o the production of poisons or toxinsby t he bacter ia .

In the case of colds a congestion of blood in some organas in the l ining of t he nose , throat, or intestine offers a

favorable condition for t he deve lopment of bact er la . Pre

v ent ion of unusual chilling of any part of the body willassist in the avo idance of colds, as congestion of blood wil lthen b e prevented. It is

\

especially important t o avoidchilling the body when one is fatigued ortired, as then thereis greater susceptibility t o disease . Regular and sufficientmuscular exercise , avo idance of overeating, and goodhabits of Sleep and rest are other conditions that enablethe body t o re sist t he bacteria wh ich cause colds.

Microscopic examination has shown that t he decay of

teeth and diseased conditions of t he tonsils are due t o t he

growth of bacter ia . The ser iousness of the growth of

bacter iain decayed teeth and in the tonsils is only beginningt o b e real ized. The bacter ia or the poisons produced bythem may b e carr ied by t he circulatory system t o otherorgans and there cause ser ious diseases. Certain forms of

rheumatism ,mental diseases, digestive troubles, et c .

,are

cured by getting rid of these breeding places for bacter ia .

The teeth are also l iable t o a disease known asR iggs’ disease ,

To PROTECT OURSELVES AGA INST M I CROORGAN I SMS . 1 1 1

or pyorrhea, which consists in t he formation of an abscess or

pus cavity between the roots and the jaw bone , causing t heteeth t o loosen and in some cases t o fall out . This diseaseis not caused by bacter ia, which are microscopic plants ,but by simple animals called amoebae.

With very few exceptions diseases are produced bym1croorganisms, chiefly bacter ia . Since the microorganisms (germs) which cause these diseases may be transferred in var ious ways from one person t o another , thediseases are called communicable . The better knowndiseases of this kind are : tuberculosis, typho id fever ,influenza, diphther ia, scar let fever , measles, chicken-

pox ,

summer complaint of childr en,dysentery, smal lpox, lock

jaw , mumps, Asiatic cholera, infantile paralysis, malar ia,ye llow fever , e t c . In a few of t he diseases mentionedabove , t he germ wh ich is bel ieved t o cause t he disease hasnot been seen with t he microscope , but the way in whichthose diseases deve lop and are transmitted indicate s th atthey are caused by living germs .

Prob lem 2 . How disease germs may pass from one

person to anoth er . Naturally in consider ing thisproblemfor any disease , we must consider how the germs le v e the

body of the person having the disease and how they may get

into t he body of the well person. Germs usually leave thebody in the fine particle s ofmo isture given out in sneezingor coughing or in the sputum or other ex cre t lons of the

body, and occasionally by blood sucked up by insects .Suggest ways by which disease germs may gain entrance t othe body .

The problem will b e considered from the standpo int of afew of t he most common diseases.

GENERAL SCIEN CE

Tuberculosis or consumption . The most usual form of

th is disease is tuberculosis of t he lungs. How do you thinkth e germs may reach t he outside of t he body ? A wel lperson may contract the disease by breathing in t he germsor in some way getting them into h is mouth . Make a l istof t he ways in which the germs of this disease might passfrom a sick person t o a we ll person .

It has been found that the pr incipal ways in which thegerms of this disease are carried from one person t o anotherare : (l ) by personal contact

'

of sick with we ll person,

especially by kissing ; (2) by objects handled or put intot he mouth, as

.

by food, forks, dr inking cups, pencils, or

towel s ; (3) by fine droplets given off in coughing or whiletalking (this is probably one of the most commonmethods) ; (4 ) by dust conta ining dr ied Sputum (5) bymilk or meat of tuberculous animals .Typhoid fever . In a person sick with this disease the

germs are developing in the walls of t he intestine . How

do you think the germs escape from t he body ? How do

you th ink that they may ever reach the intestine of a we llperson tobegin growing there t o produce t he po isons of thedisease ?Typhoid fever germs are taken into th e body with food

and dr ink . It h ardly seems possible that anyone should evercont ract typho id fever when we real ize that t he germs leavet he diseased person in t he excretions of th e body . However ,food and dr ink may become polluted in a number of ways.

Water may become contaminated by sewage; milk, by t heunclean hands ofmilkers ; oysters or Clams, by growing nearthe outlet of sewer s ; vegetables, by manure ; fruits and berr ies, by filthy hands ; foods of all

‘kinds, by flies which havebeen crawling over the excretions of a typho id patient .

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1 14 GENERAL SCIENCE

may seem strange that a person is not constantly ill w ithsome disease . We know, however , that not every personexposed t o infection contracts t he disease . There are a

number of reasons for this.

What is the e ffect of t he unbroken skin ? What happenst o large amounts ofdirt and dust of t he air which is breathedin through t he nose ? What is t he appearance of t he mucuswhich is blown out of t he nose after you have been workingin a very dusty place ? Not only does t he mucus catch someof t he germs that are breathed in and permit the ir removalbut it has been found that it possesses some power t o killt he germs. Suggest one reason for breathing through t henose rather than through t he mouth .

Eventhough these outer defenses of t he body are passed,t he germs are not permitted t o deve lop unchecked. The

body offers a certain resistance t o t he attacks,partially by

means of t he white blood corpuscles which engulf t he bacter ia, and partially by t he resistant power of t he blood and

living parts of t he body, a power which is not so easily understood.

This power of resistance is affected by a number of things.

The fact that certain diseases occur only In childhoodindicates that age is one of t he factors concerned. A poordiet

, excessive fatigue,extremes of heat and cold, lack of

Sleep, lack of fresh air , and weakness from other diseasesare conditions which lessen t he power of t he body t o resistdisease . In general , any condition which increases t he

health of t he body increases it s power t o resist disease .

Because of this fact,‘

outdoor l ife , deep breathing, moderate

exercise taken regular ly, a proper amount of sleep , and good

food are not only t he preventives of disease but in some

cases constitute a cure by giving the body a chance to

TO PROTECT OURSELVES AGA IN ST M I CROORGAN I SM S 1 15

fight off t he enemy that has already ga ined a footho ld

(Figure

Prob lem 4 . How the body acquires special power to

figh t disease . You already have some information thatproves t o you that special ability t o fight disease may b e

acquired by the body . A child has,had whooping cough ,

or mumps, or measles. Does this have any effect upon his

FIGURE 86.—A FRES H AIR CAMP IN CALIFORNIA.

chance of taking t he disease again ? What, therefore , isyour conclusion as t o t he effect of having had a disease upont he ability of t he bOdy t o fight that disease ?Based upon this fact, it has been discovered that t he body

may b e made immune t o certain diseases or protected againstthem . You know of a number of such cases. Why issmal lpox not t he common disease it was several hundredyears ago ? How are t he soldiers protected against typho id

1 16 GENERAL SCI EN CE

fever ? Why i s diphther ia not the dreaded disease it wastwenty-fiv e years ago ?

The most str iking cases of acquired immunity are for

smallpox, typhoid fever , diphther ia, hydrophobia or rabies,

and anthrax, a disease of animals.

Efforts are be ing madet o deve lop acquired immunity from other diseases, and

considerable success has been obtained in t he treatment of

tetanus or lockjaw,boils and carbuncle s, meningitis and

plague .

(a) Vaccination against smallpox . Over a hundredyears ago, Edward Jenner , an English physician,

observedthat dairymaids

,were not subject t o smallpox, which at that

time was a very common disease . His experiments basedon this observation have led t o t he practice of vaccination t odeve lop immunity from smallpox . Cattle may have a diseaseknown as cowpox , during which small '

sores appear on t he

animals . The se sore s contain t he germs of t he disease .

Jenner found that by scratch ing t he arm of a' person and

rubbing into the Slight wound some mater ial1from these

sores on cattle , a mild disease, ,cowpox ,

"

was deve loped int he person thus vaccinated . Dur ing th e process

“of the

disease , something . evidently deve loped in the blood whichprotected t he person from smallpox .

Since vaccination has been practiced, smallpox, previouslyone of the most common diseases, has become a very rare

one , deve loping only when vaccination is neglected. Str icterregu lations by boards of health , especially in regard t o isolation of patients

,has he lped mater ially in br inging about this

result . Former ly, when not so great care was taken as now

t o insure t he pur ity of the vaccine , infection occasionallyoccurred from other germs introduced into t he wound . Thishas now been obviated, and anyone who objects t o vaccina

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1 18 GENERAL SCIEN CE

without injury t o t he horse . Th is process -is cont inueduntil t he amount of toxin injected into t he horse is severalhundred times as much as would have killed it at t he beginning .

A certain amount of the blood which contains great quantities of antit oxin i s now removed from a large ve in in t heneck of t he horse . (All this is done without pain or injuryt o t he animal .) The serum which separat es from t he

b lood serum

FIGURE 87.—RESULTS OF USE OF DIPHTHERIA Am'

rrox m.

Chart showing death rate per from diph th eria b efore and after

the introduc tion of ant itoxin.

is t est ed for t he amount of antitoxin it contains, is ster ilized,and put int o vial s ready for use by physicians .The accompanying chart shows t he effect of t he use of

antitoxin upon t he death rate from diphther ia in New YorkCity (FigureAntitoxin i s of greater use as a curative than as an

immunizing agent . Persons who have been exposed t o

diphther ia will be protected only from two t o six weeks, butthis is usually long enough t o protect t he member s of a

family in which there is a case of t he disease . AS a cure fordiphther ia, it is most import ant that the antitoxin be given

TO PROTECT OURSEL VES AGAIN ST M ICROoRGANI SMS 1 19

at a very early stage of t he disease . The importance of

this is Shown by Figure 88 .

(d) Pasteur treatment for hydrophobia or rabies.

—Thisdisease especially affects t he nervous syst em. Pasteur , a

noted French scientist, found that wh ile the spinal cord of

a rabbit having t he disease contains a large‘

amount of t hepoison of the disease , t he virulence or power of t he poisondecreases if the Spinal cord is removed from the rabbit andallowed t o dry . AS t he disease does notdevelop for some time after a per son isbitten by a mad dog, there is sufficienttime for treatment . The treatment consists in t he injection ofmater ial from a

rabbit ’s Spinal cord which has been permit t ed t o dry until t he poison has almostentire ly disappeared . Th is is followedby injections, more and more virulent, FIGURE 88.

—DANof spinal cord mater ial for a per iod of

GER 0 " DELAY 1“

US ING ANTITOXIN .

about three weeks . In thousands ofNumbe rs at th e left

cases Which have been t reated by this indicate the percent

method there has been a mortality ofage of the cases that

result In death .

less than one per cent . Just as in t he

case of t he use of antitoxin for treatment of diphther ia,this treatment should b e begun at t he ear liest possible timeafter infection has OCCUI I‘ed.

Prob lem 5 . Use of disinfectants and antiseptics.

Certain substances are used t o prevent t he growt h of bac

ter ia . Make a l ist of substances that you know are usedfor this purpose .

The way in which they affect t he growth of bact eria maybe found out by t he following experiment .

120 GENERAL SCIENCE

Experiment.—Into each of several test tubes pour about 10ofunsterilized beef t ea culture medium .

To one add 3 cc . of carb olic acid 5 solution.

To another add 3 cc . saturated solution of boracic (boric) acid.

To another add 3 cc . 1—1000 solution ofmercury b ichloride.

To another add 3 cc . hydrogen peroxide .

To another add 3 cc . tincture of iodine .

To another add 3 cc . formaldehyde ,To the others add 3 cc . different disinfectants.

To one add nothing .

After four or five days examine all t he test tubes and record the

results.

A distinction is usually made between antiseptics and disinfectants . An antiseptic is a substance that will check or

retard th e growt h ofbacter ia, but does not destroy them . A

di sinfectant, or germicide , is a substance that kills bacteria.

Some substance s may be classed under both heads ; a strongsolution of it acting as a disinfectant, a weak solution act

ing only as an antiseptic . Salt, sugar, spices, and vinegarmay be considered antiseptics that are harmless when takeninto t he body with food. With t he exception of the use of

one tenth of one per cent of benzoate of soda, other ant iseptics are not permitted t o be used for the preservation of food.

The more important germicides are tincture of iodine ;carbolic acid (5 t o 10 per cent solution) mercury bichlor ide

(1 part t o 1000 or 1500 parts ofwater) chlor ide of l ime , andformaldehyde . These are all highly poisonous when swal

lowed, and great care Should be taken that they are not

placed where they may accidentally be .used in this way .

Boracic acid is a mild antiseptic which i s frequently used asan eye or mouth wash . Hydrogen dioxide (peroxide) , whenit has not been allowed t o remain exposed t o t he air , wil ldestroy germs . It has the advantage ofbeing non-poisonous,

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PROJECT XI

TO FIND OUT HOW SOME BACTERIA AND MOLDS

ARE USEFUL

WE have found that bacter ia and molds are a greatnuisance , br inging about a waste of food mater ial and leading us into t he expenditure of time and money t o preventthe ir ravages . We have found also that almost all diseasesare caused by them . Just think of how conditions wouldb e changed if there were no such little plants . Foodswould not Spo’ il, and diseases l ike tuberculosis, typhoidfever , influenza, et c . , would b e unknown . It would seem ,

therefore , that t he wor ld might b e a better place in whicht o l ive if bacteria and molds ceased to exist . But beforewe come t o this conclusion it will be well for us t o considerif there i s any evidence that bacter ia and molds are of

value .

Prob lem 1 . Are bacteria of decay of any value ? A

consideration of the following facts may help us t o solve .

this problem . Just as plants take carbon dioxide from the

air and build it up into starch , so they also take simple substances from t he soil and build them up into complete plantmater ials . Th is means the removal from t he soil everyyear by plants of an immense amount of these simple sub

stances needed by plants. Since t he amount of these substances is limited, what must happen soon unless in someway they are returned t o t he soil ?Th is return is brought about by t he action of bacter ia incausing complex plant and animal mater ials (organic mat

122

HOW SOME BACTERIA AND MOLDS ARE USEFUL 123

ter) t o decay . By decay the organic matter is changedback into t he simple substances wh ich plants use in growth .

Thus it may b e understood that t he same matter may manytimes alternately b e built up into plant and animal ma

t erial and again be reduced t o a simple condition.

This building up and tear ing down may be illustratedvery Simply by consider ing t he use of building blocks by a

child. Suppose a child has two hundred blocks, and buildsthem up into a house , then tears it down and builds anotherstructure . Th is he may do time after time , using t he

‘

same

blocks over and over again in perhaps a different construotion each time . Plants build up . Bacter ia of decay teardown . Just as t he child builds up and tears down his blockhouses many times, so these processes of building up byplants and tear ing down by bacter ia will go on as long as

life exists upon t he earth . What then do you think wouldbe t he condition of t he earth in a few year s if there wereno bacter ia and molds t o do thi s tear ing down ?

Prob lem 2 . How bacteria onth e roots of some plantsmay enrich th e soil . Farmers have known for a long time

that a crop of clover will improve t he soil . But the reasonfor this has been known for only relative ly a few years . It

was found that in some fields clover plants did not havet he power t o improve t he soil . A compar ison of t he plantsshowed that those which possessed th is power all had l ittleenlargements (called nodules) on the ir roots (FigureIt was found also that if some of t he soil from t he fie ld

containing nodule—bear ing clover plants was scattered overthe other field, the clover plants in this fie ld also de

v eloped nodules on the ir roots and gained t he powerto , improve t he soil . An examination of these nodules led

124 GENERAL SCIENCE

to t he discovery that they contained bacteria. It was

found then that t he soil could‘

be inoculated with a cultureof these bacter ia e ither by mixing it with t he clover seed

before it was planted or by adding it directly t o t he soil .It has been found that t he bacter ia in these nodules

FIGURE 89 .—ROOTS OF A BEAN P LANT.

Th e enlargements are nodules containing nitrogen

fixing bac teria.

have t he powerof changing t he

nitrogen of t he

air ,which cannotb e used directlyby plants

,into a

form which may

b e built up intot he l iving matteroft he plant . All

of the plants of

t he clover family

(legumes) may

have these nod

ules containingn i trogen-fix ingbacter ia . Someof t he pr incipalmembers of t he

family are peas,beans,

l

v et ches,

and alfalfa . If

the soi l does notcontain t he proper kind of bacter ia, t he,

nodules will not b eformed and these plants will not b e able t o add t o t he

fertility of t he soil .There are other bacteria in t he soil , not associated di

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126 GENERAL SCIENCE

hol of t he wine or cider into t h e vinegar acid (acetic acid) .The . act ion of these vinegar-forming bacter ia is hastenedby free access of air , so that barre ls containing cider t o bechanged into vinegar Should b e only partially filled and an

opening Should be left in t he t op of t he barre l t o admit air .

The formation of vinegar may be hastened by permittingt he cider t o tr ickle through casks filled with Shavings im

pregnat ed with old vinegar . Why ?

SUGGESTED INDIVIDUAL PROJECTS

1 . Grow clover seed in soilwhich has been baked andmoistenedwithboiledwater , and in ordinary garden soil .2 . Collection of different roots showing nodules.

3 . Manufacture of vinegar from cider .

REPORTS

1 . Practical use made of nitrogen-fix ing bacteria.

2 . Importance of bacteria in manufacture of dairy products.

UNIT II

RELATION OF WATER TO EVERYDAY ACTIVITIES

PROJECT XII

MOISTURE IN THE AIR AND ITS IMPORTANCE

TO US

A NUMBER of problems immediate ly occur t o uS : how

dew ,fogs, clouds, and rain are caused ; why some part s of

t he earth rece ive a much larger rainfall than other part s ;how water may be Supplied t o regions of very little rainfall ;how moisture gets into t he air , and the effect ofmoisture int he air (humidity) upon our comfort .

Prob lem 1 . How dew is caused.

—We all have hadt he exper ience of getting our feet wet by walking in the

grass early on a summer morning . This moisture upont he grass is called dew . What are some of t he thingsthat you

‘know about dew ? Was it on t he grass dur ingt he day before ? About what time did it begin t o appearin t he evening ? Have you ever Seen it on anything exceptgrass ? Does it seem t o form t o t he same extent on all

objects ? If possible give examples. Does dew form on ob

ject s in t he house ? On t he porch ? IS there approximate lyt he same amount of dew every morning ? Does windseem t o make any difference ? Does it make any differencewhether t he night is clear or cloudy ? Have you ever no

ticed moisture similar t o dew on water pipes or on a glassfilled with cold water ?

1 28 GENERAL SCIENCE

The questions above are for , t he purpose of bringing t o‘

attention t he facts t hat you know about dew . Do not

guess at t he answers,as t hat would destroy t he value of the

questions .Several Simple experiments wil l enable us t o understand

someth ing about how dew is formed, and under what condit ions.

Experiment . Take two large test tubes or drinking glasses. Intoone of these pour some ice water ; into t he other pour water at t he

room temperature . Set Side by side and note results.

Experiment . Into one of two wide-mouthed jars pour a smallquantity ofwater . Place t he two jars on a radiator or heat slightlywitha Bunsen burner . Suspend for a few minutes in each jar a test tubecontaining ice water. Note results.

After consider ing these two exper iments, what do you

conclude are t he two conditions ne cessary for t he formation of a film ofwater l ike dew upon objects ?

Experiment. Pour a few dropso fwater into a test tube . Heat t hetest tube until the water disappears. Now partially immerse t he testtube in a jar of icewater . What is t he result ? What do you conclude

t o b e the relation between the temperature of the air and it s ability toholdwater in t he form ofvapor, or gas ?

The temperature at wh ich moisture in t he air changesfrom an invisible vapor t o visible drops of water , is calledt he dew point . IS t he dew point temperature always t hesame ? Why ? Why is it possible to

“

see your breathon a cold day ?We are now able to arrive at t he ex planation of the con

dit ions under wh ich dew is formed .

(a) Objects on t he earth cool offafter the sun set s . Whateffect doe s th i s have upon t he surrounding air ? What mayresult

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130 GENERAL SCI ENCE

(f) What is the result when the dew point is at t he t em

perat ure of freezing or be low ?’

Explain t he following

(1) The appearance of steam from an exhaust pipe or a

steam whistle , and it s appearance when it is a little fartheraway from t he vent . Where does it go ? Hold a Bunsen

P hotograph ed by A . J . Henry .

FIGURE 9 1. UNDULATED ALTO-CUMULUS CLOUDS .

burner or a candle near t he visible steam e scaping froma vessel , such as a t ea-kettle . Result ?

(2) The mist produced by blowing one’

s breath on a

mirror or window glass .

(3) Why growing plants may be protected from frost byplacing canvas or Sheets ofpaper o v er them .

(4) Why t he fruit grower sometimes makes a smudge

(smoke) in t he orchard when frost threatens.

(5) Why gardens in t he valleys are more likely t o be

MOI STURE IN THE A IR AND I TS IMPORTANCE TO US 13 1

affected by early frosts in t he autumn than gardens on hillsides.

(6) Why t he farmer is much more afraid of frost on a

clear night than on a cloudy one .

(7) Why he is more afraid of frost on a quiet night than

on a windy one .

Prob lem 2 . How fogs and clouds are produced.

(1) Explain t he formation of t he thin layer of mist which

FIGURE 92 .—CUMULUS CLOUDS OVER PACIFIC OCEAN .

Point Loma, San Diego , California, late afternoon.

is sometimes seen spread over a swamp or valley bottom .

Why does it disappear as soon as t he sun begins t o shine ?

(2) Fogs are common on t he Banks of Newfoundlandand t he coast of Maine whenever t h e wind is from t he

south . Farther south , as far as Cape Hatteras , fogs are

apt t o occur when t he wind is from t he east . Why ? (Re

132 GENERAL SCIENCE

V iew your geography as t o t he relative locations of t he

Gulf Stream and t he Labrador Current .)(3) Suggest an explanation of t he great fogs which are so

common in t he Br itish Isles . (Note that bodies,

of landcoOl more rapidly than large bodies of water .) At what

FIGURE 93 .—RAIN GAUGE.

The area of the tOp of the outer

time of t he year do you

think fogs would be mostcommon in England ? In

all cases t he presence in t heair ofsmall particles of dustencourages t he formationof fog . Why ? Th is, no

doubt, has considerableeffect in intensifying fogsover cities such as London .

Clouds are made up of a

collection of small particlesof water , floating some distance above t he earth .

Suggest how t he greatmasses of clouds with hor izont al bases, seen on a

cylinder (a) is exac t ly ten t imes as summer day. have beengreat as that of the inner cy linder (b )C, rec e iver .

formed (Figure Re

fer back t o your study o f

weather and explain why clouds are present in a low pressure area and not present in a high pressure area.

Prob lem 3 . How rain, snow , and hail are formed. In

a cloud or a fog t he water particles are so small that theywill remain suspended in t he air for a long time . The smal lglobules of water in a cloud are e ither prevent ed from fall

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134 GENERAL SCIENCE

balls in the ir passage through t he air , they become hailstones . Hail is usually formed in summer , and i s probablycaused by currents of air carrying t he raindrops t o such a

height that they are frozen and sometimes have formed on

them a layer of snow . Split hailstones will frequently Showseveral layers of ice and snow,

indicating that they havebeen carr ied up a number of times before finally fall ingt o t he earth .

FIGURE 95.—HEAVY FALL OF SNow IN A PINE FOREST.

Prob lem 4 . Reasons for unequal distribution of rainfall .

A study of t he average annual rainfall map of t he United

States (Figure 96) Shows that the distribution of rainfall isvery unequal , varying from 80 t o 100 inches per year in a

narrow strip along t he ocean inWashingt on and Oregon to

less than 5 inches per year in portions of Nevada, southern

Cali fornia, and Ar izona (Figure

36 GENERAL SCIEN CE

With maps before you of t he topography of t he country

and t he prevailing winds, explain t he following

(1) The great rainfall of t he northwest coast of t he

United States. What is t he prevailing wind ? (Air coolsas it r ises along t he side of a mountain .) Why is this

rainfal l belt so narrow ?

(2) The small rainfall of

t he great region just east ofthis coast area .

(3) Th e sources of rainfallof t he Mississippi Valley andregion east of it t o t he At

lantic Coast .

(4) In middle and southern Cal ifornia, t he prevailingwind from December t oMay

is from t he ocean, while during t he remainder of the yearit is from t he land tbward t he

FIGURE 97 .—LANDSCAPE IN AN AL

ocean. Ex plam t he drY and

MOST RAINLEss DISTRICT IN ARIZONA. raIny seasons of th Is reglon.

Prob lem 5 . How water is supplied to dry areas.

Portions of t he country , wh ich were unfit for agr icultur ebecause of t oo l ittle rainfall

,have been changed into good

farming regions by irr igation (Figures 98 and waterfrom t he mountains being collected in large reservoirs and .

carr ied by flumes, pipes, or cemented ditches, for greatdistances, t o where t he water is needed (FigureTh e accompanying map Shows th e location of districts

irr igated as a result of th e work of th e United States Reclamat ion Service (Figure

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138 GENERAL SCIENCE

Prob lem 6 . How moisture gets into th e air . Evaporation. It is evident that there must b e considerablewater in t he air , in t he form of invisible vapor . It has

been estimated that if all t he moisture in t he air were con

densed into water, it Would make a layer of about one

inch in depth over the entire surface of the earth . Some

FIGURE 100 —ROOSEVELT DAM , ARIZONA.

A large dam for collec tion ofwater for irrigat ion.

very common observations will indicate t o us how thiswater gets into t he air .

(1) What happens t o wet clothes hung in t he air ?

(2) On what kind of days do they dry best ?

(3) Do they dry better dur ing day or night ?

(4) What becomes of t he rain puddle s that are formedon t he streets ? Does t he temperature seem t o make any

difference ?

MOI STURE IN THE A IR AND ITS IMPORTANCE TO US 139

(5) What happens t o a Shallow pan of water left stand

ing for a number ofdays ?

FIGURE 10 1 .— MAI" SHOWING LOCATION OF IRRIGATION PROJECTS .

(6) What must b e added t o a balanced aquar ium fromtime t o time ?

(7) Will frozen clothes, hanging on a l ine , dry ?

140 GENERAL SCIENCE

(8) What happens t o water that falls on soil , as in a

cultivated. garden or fie ld ?

(9) After a number of dry days, compare t he moisture of

soil under a board or stone with that of t he surroundingsoil . Dur ing very dry weather in summer, almost t he onlyplace one can find earthworms is under boards, logs, or

stones . How do you explain this ?

(10) When barre ls are left empty they often fal l t o pieces .Why ?(11) In dry weather , farmers sometimes pour water

around t he r ims of t he whee ls of the ir wagons. Why ?

(12) How do leaves appear after having been removedfrom a plant ?From these observations we must conclude that objects

containing water give it off t o t he air . The changing of t hewater into a vapor i s called evaporation, t he reverse of con

densation which we considered in t he formation of dew ,

clouds, and rain. From your observations, state t he conditions which you think would affect the rapidity of evaporation . Not only are objects on t he land giving off water int he form of vapor , but also t he surfaces of all bodies of

water,

r ivers, lakes, and oceans. Thiswater , in an invisib le form as vapor , is changed back into visible forms as

dew , clouds, rain,and snow .

When water evaporates, substance s dissolved in the

water remain behind . Thi s may be illustrated by allowing a vesse l ofwater in wh ich has been dissolved some sodaor salt t o stand exposed t o the air unt il t he water hasevaporated. Water in streams flowing t o t he ocean con

tains some soluble mineral mater ial taken from t he earth,through wh ich t he water has tr ickled. What happens t oth is mineral mater ial when the w ater evaporates (Fig

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142 GENERAL SCIENCE

Prob lem 7 . How th e amount of moisture in th e air

afiects our comfort . The effect of t he amount ofmoisturein t he air (humidity) upon our bodily comfort has been discussed under ventilation . It is t he re lative humidity ratherthan t he actual humidity that affects us. The relative

humidity is t he ratio of t he amount of water in t he air t o

t he amount which it can hold at a giventemperature . A relative humidity of50%means that t he air contains one half oft he amount of moisture that it can holdat that temperature .

You will recal l that damp days e itherin summer or winter are more uncom

fort ab le than dry days of t he samet emperature . To understand this, we

must consider how heat is lost from t he

body in winter and summer . What ist he chief means

'

of loss of heat from t he

body in winter ? Explain t he feeling of

chill exper ienced on a damp day in winter ,keeping in mind that moist air is a betterconductor of heat than dry air . Whatis t he pr incipal way in which heat is lost

FIGURE 103 .

from t he body in summer ? Explain nowAND DRY BULB THER why we are more Oppres

‘sed by t he heatMOMETER '

on a damp day .

The re lative humidity of t he air may be found by usingt he wet and dry bulb thermometer or psychrometer (Figure This consists of two thermometers, one of wh ichhas a piece ofwet muslin around it s bulb . These are rapidlywhirled in t he air . Observations of t he readings of t he thermomet ers immediate ly after t he muslin has become dry wil l

MOISTURE IN THE AIR AND I TS IMPORTANCE TO US 143

Show considerable difference . Explain . Tables have beenprepared which give

.

t he relative humidity of t he air correSponding t o t he difference between th e dry bulb and the we t

bulb thermometers at the different degrees of temperature .

Another instrument for measur ing t he re lative humidityof t he air is t he hair hygrometer . The human hair , whenthe oil has been removed,

lengthens with dampness and

short ens with drying . A hair prepared in' this way i s att ached t o a pointer wh ich is moved across a dial as the hairchanges in length .

Use i s made of t he fact that paper or cloth impregnatedwith cert ain chemicals will change color as t he relativehumidity becomes greater or less . A paper flower , forexample, which has been soaked in a solution of cobaltchlor ide and gelatine , will b e violet in colpr when t he relat ive hum idity is h igh and blue when t he air i s dry .

REPORTS

1 . How railroads fight snow.

2 . Origin of borax and other salt deposits in t he West.3 . The salt supply of the United States.

REFERENCES FOR PROJECT XII

1 . Measur ements for the Household, Bur eau ofStandards,Washington, D. C.

2 . Hu'

midity ; ItsEffect onOur Health andComfort, P . R . Jameson.

Taylor Instrument Company , Rochester , N . Y. 10 cents.

3 . Th e Mountains ofCloudland and Rainfall, P . R . Jameson. Tay

lor Instrument Company , Rochester , N . Y . 10 cents.

4 . Water Wonders Every Child Should Know,Jean M . Thompson.

Doubleday, Page Co.

PROJECT XIII

THE RELATION OF PLANTS TO MOISTURE

WE all know that there i s a close relationship between

plants and moisture . How they give off water ; how mucht hey give off; and how the water i s obtained are problemsto be solved .

Prob lem 1 . Do plants give ofi moisture Under

ordinary circumstances plants do not seem t o giveoff watert o t he air , as t he leaves remainfresh day after day . What happens, however, t o leaves and

flowers when they have beenbroken from t he plant ? Whatdoes this seem t o indicate ? Howmay these leaves and flowers b ekept from wilting ? The following exper iment will enable us t ofind out if growing plants giveoff water

Experiment . Completely cover the

What is the source Of the water pot Of an actively growing geraniumwithin the b e ll jar ? or similar plant with rubb er tissue or

waxed paper, leaving only the stemand leaves of the plant exposed. Cover the plant with a dry belljar . After a few hours observe and draw conclusions (Figure

FIGURE 104 .—TRANS PIRATION .

Th is process of giving off water by a plant is called transpiration.

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146 GENERAL SCI ENCE

In t rees growing under normal conditions the roots ext end out t o a point directly under t he outer ends of t he

branche s . Why ? Alfalfa plants growmg In dry regionsmay have roots extending t o a depth of 10 or 12 feet . Why ?The mesquite plant living In t he dry regions of t he southwestern part of t he United States and Mexico, althoughonly a low shrub , may send it s roots t o a depth of 60 feet in

FIGURE 105.—UPTURNED SUGAR MAPLE.

Note th e very large numb er Of small roots.

search ofwater . Why does a lawn which has been spr inkledfor a short time every day look worse after being neglectedfor a few dry weeks in August than t he ne ighbor ing lawnwhich has not rece ived t he same care ? Give one reasonwhy weeds in a garden are harmful .

Prob lem 4 . How roots are especially fitted to take in

moisture . You have probably noticed that even though

THE RELATION OF PLANTS TO MOISTURE 147

the greatest care be taken t o prevent injury t o the roots, aplant is apt t o wither and be checked in its growth whentransplanted (planted again after having been removedfrom soil in which it has been growing) . Th i s might leadus t o suspect that there are special structures on t he rootswhich are injured int he process of transplanting .

Growing roots insuch a way that theycan b e examinedwithout be ing dis

t urbed may he lp ust o find out if rootspossess any specialstructures .

Ex periment . Place

some radish seeds or

other small seeds be

tween a moist blotterand the bottom ofa Petridish or the inside ofa testtub e . Keep in a warmplace and examine afterthr ee or four days.

What do you find ? FIGURE 106 .—YOUNG WH ITE CEDARS .

The small hairlike structures which you see on t he youngroot are called root hairs (Figure Their structure, as

you will see from the diagram (Figure is very Simple .

Each hair consists of a de licate wall inclosing a thin layer oft he l iving matter of t he plant and some watery mater ialcalled cell-sap. It will be noticed that t he root hair is

148 . GENERAL SCIENCE

only t he ext ension of one of t he l ittle boxes containing livingmatter (ce lls) of which t he young root is composed. Of

what advantage are

these root hairs ?

Experiment . Care

fully chip off about onehalf of a square inch of

the shell from the b luntend ofa fresh egg, takingcare not t o injure the

memb rane lying under the Shell. Support the egg at t he t op of a glass

containing water so that the ex posed membrane is immersed in th e

water . Puncture th e shell and memb rane at the other end of t he egg

and by means ofa needle mix the white and yolk of the egg. Into thisend of the egg fasten a glass tube with sealing wax , clamp t he tube toan iron support and set asidefor a few hours. What hashappened ? Explain how thisillustrates t he work of t h e

root hair .

FIGURE 107.—GERM INATING WHEAT S HOWING

ROOT HAIRS .

L iquids separated bya plant or an animalmembrane tend t o mixwith each other , but in this case t he contents of the egg,

like those of t he root hair , are unable t o pass through amembrane, so t he flow of l iquid is all in one direction. At

FIGURE 108.—ROOT HAIRS (enlarged) .

Prob lem 5 . How

root hairs take in

water . The way in

wh ich root hairs takeIn water is illustratedby t he following ex

periment .

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150 GENERAL SCIENCE

Openings (stomates) absorb , in moist weather , moist ure fromt he air and swe ll up like t he inner tube of an automobile

tire when fi lled with air , mak

ing t he opening or stomatelarge .

‘

In dry weather theylose the ir moisture , collapse ,and make t he stomate smaller .

Of what advantage is this t ot he plant ? Plants that live

FIGURE 1 10 .

—LoWER EPIDERMIS in dry regions possess var iousOF A LEAF (h igh ly magnified) ’ devices for t he prevention of

excessive transpiration, such as hairy , or thick-skinnedleaves, or t he redu

’

ction of leaf surface .

SUGGESTED INDIVIDUAL PROJECTS

1. Find out approx imately how much water may b e given t o the air

by a certain tree during one hour on awarm day in summer .

2 . Find out t he amount ofwater given t o t he air by a geranium plantin 24 hours.

3 . Endeavor t o find out t he total ext ent of t he r‘

oot system of some

plant.4 . Construct an apparatus t o illustrate t he action of t he stomates.

REPORTS

1 . Comparison of t he kinds ofplants in arid regions and those inwellwatered regions.

2 . Importance of irrigation in t he .United States.

3 . Dry farming in t he Western States.

4 . The salt supply of t he United States.

REFERENCES FOR PROJECT XIII

1 . Agriculture on Government Re clamation Projects, Scofield and

Farrell . U. S . Department ofAgriculture Year Book, 19 16.

2. Irrigation,andDrainage , F. H. Wing. Macmillan Company.

THE RELATION OF PLAN TS TO MOI STURE 151

3 . A Primer of Forestry, Gifford Pinchot. Government PrintingOffice , Washington, D. C.

4 . First Book ofForestry, F. Roth. Ginn C0 .

5 . Irr igation, Farmers’ Bulletin 864 . S . Department of Agri

culture , Washington, D . C.

6 . Dry Farming,‘Widtsoe . Macmillan Company.

PROJECT XIV

WATER POWER

IT is estimated that if the water power of the United Stateswere fully used, it would b e sufficient t o run all t he machinesof our factor ies, t o prope l all railroad trains, street cars, andautomobiles, and to furni sh l ight and heat for the many

FIGURE l l l . —TRAIN DRAWN BY AN ELECTRIC LOCOMOTIVE.

The power of this e lec tric locomotive is derived from water power .

purposes for which they are used (Figure At presentonly a small part of this power is be ing used , but the possib ilit ies for the future are great (Figure The questions that ar ise in our minds naturally are : What is t hesource of the energy or power of water power and where

152

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154 GENERAL SCIENCE

from an elevated tank . The energy possessed by the run

ning water may b e demonstrated by permitting it to run

a water motor , which in turn may run a sewing mach ine ,a churn, or a washing machine . Energy, however , usuallysupplied by a windmill or the burning of fuel in an enginemust b e used t o pump the water into the tank . Thus the

POW/ER HOUSE

7 A". OR

WASTC WATER

FIGURE 1 13 .—DIAGRAM OF A POWER HOUSE.

Water passing through A turns th e water whee l B. At D the energy Of

motion is changed by a dynamo into e lec trical energy.

energy set free by t he windmill or by t he burning of the fueli s transformed into t he energy possessed by t he water becauseof its position . We can understand now,

. that energy, or thepower ofdoing work , exhibited by water in r ivers and streamson the ir way to t he ocean, must have been given t o it in someway . The following suggestions may lead you t o an understanding of the sour ce of t he energy ofwater power

WATER POWER 155

(a) What was the or iginal location of the water concerned ?

(6) What is happening t o water on the surface of oceansand lakes ?

(c) What is the relation of evaporation t o heat ?

(d) What is t he source of t he heat used up in changing t hewater into invisible water vapor , a gas ?

(e) Just as steam, which is invisible water vapor , possessesenergy, so th i s water vapor which results from the ordinaryevaporation of water by t he sun’s rays has been given t he

energy which was used in changing t he water into vapor .

(f) Because of t he energy wh ich it possesses, the watervapor is able t o overcome t he force of gravity (t he forcewhich draws th ings t o t he earth) and to move away from t he

surface . It is assisted in it s movement by the currents ofair and winds, which you will recall, are caused by t he heatof the sun.

(g) When condensed into drops ofwater , the energy wh ichthe vapor possessed as a gas i s changed large ly into energyof "position which is changed into t he energy ofwater power ,as t he water travels in streams toward the ocean again.

In your own language, e xplain how water power dependsupon the energy of the sun.

The energy of the water power developed at N iagara Fall s,from the Missi ssippi R iver at Keokuk, Iowa, and in the

streams .yvhich flow from the h igher regions of the Appala

chian Mountains, upper portions of t he Great Lakes region,

and the Rocky and Sierra Mountains, can b e changed intoelectrical energy and b e transmitted many miles t o citieswhere it may b e used to run mills and trains, and to furnishl ight and heat (FigureIn order t o make use of t he water power of a r iver in which

there are no falls but only a gradual Slope of t he river bed,

156 GENERAL SCIENCE

dams are built which raise the surface to a higher level.

(Figure By this means artificial fal ls are producedwhich may represent the natural fall of the r iver for several

FIGURE 1 14 .—ELECTRIC HIGH TENS ION TRANSMISS ION LINE.

By these w ires e lec tric pow er deve loped by a waterfall in the mountains is

carried to c it ies many miles away .

miles above the location of the mill or factory which i s run

by its power . Thus we may understand how water power

can be developed from any stream in which there is an ap

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158 GENERAL SCIENCE

stopper a metal rod (Figure Push down on the metal rod.

What happens ?

It is evident from this exper iment that t he force exerted onthe inner surface of t he bottle is many time s t he force exertedon the metal rod. This and other exper iments Show thatthe pressure on l iquid, as water , inclosed in a vessel is transmit t ed undiminished in every direction and acts with equalforce onall sur faces ofequal area . This is known as Pascal

’

s

principle Since it was first,

an

nounced by Pascal, a Frenchman,

in 1653 . How t he great forceexerted by the hydraulic press isgainedmay b e understood by studying t he accompanying diagramwhich shows how a l igpound vfé gh tmay balance a pressure of 100

pounds . In commercial hydraulicFIGURE “

l

g — HYDRAULIC presses, oil is generally used inRES S .

stead ofwater .

A , large cy linder ; B , small

cylinder ; C, c onnec ting tub e ;By push lng down the smal l pIS

P , large Piston i.

P , Sn? “ t on, a small amount of oil i s forced

piston ; D, reservoir for liquid.

Into the space below the large piston. The force exerted upon the large piston i s as manytimes greater than t he force exerted upon t he smal l one as

t he surface of the large piston is greater than the surface of

t he smal l one. A valve prevents t he oil from passing out

of the cylinder below the large piston.

Because of t he great force exerted by t he hydraulicpress it is used in l ifting heavy we ights and in operationswhere great pressure is needed. Heavy machinery and

crucibles filled with molten metal may b e l ifted with ease .

Bal ing of cotton and paper , punching holes in steel plates,

WATER POWER 159

making pressed steel and forcing lead through a die in t he

manufacture of lead pipe are some of the uses made of the

enormous force exerted by t he hydraulic press .

SUGGESTED INDIVIDUAL PROJECTS

1 . Construct a water wheel which when operated by water froma faucet will run a Simple machine .

2 . Demonstration of t he structure and action of awater motor .

3 . Make a small hydr aulic press.

4 . Construct a map of t he United States, and indicate in red the

places where water power is utilized, and in b lue other places whereyou think it might b e used t o advantage .

REPORTS

1 . Utilization of t he water power ofN iagara Falls.

2 . Water power development in different parts of the United States.

REFERENCES FOR PROJECT XIV

1 . How It Is Done , A . Williams. Thos. Nelson Sons. (Powerfrom Niagara Falls.)

2 . Harper’

s Machinery Book for Boys, Adams. Harper Bros.

(Water—Power . )3 . Practical Thingswith Simple Tools, Goldsmith . Sully 85 Klein

teich . (lVIaking ofWater Wheels. )4 . All about Engineering, Knox . Funk Wagnalls. (N iagara

PROJECT XV

TO UNDERSTAND HOW COMMUNITIES OBTAIN A

GOOD SUPPLY OF WATER

Water Supply of New York City. The average dailyconsumption of water in New York City dur ing t he year .

19 17 was almost gal lons or cubicfeet . Naturally the question ar ises how such an enormousquantity of water can b e supplied. Cities like Chicago,Cleveland, or Buffalo may get the ir supply from the greatfresh-water lakes near wh ich they are located . New York,however , is shut off from such a supply . When a smal lcity

,it depended large ly upon wells ; but as the population

increased, such a supply became both inadequate and um

safe because of the danger of pollution . Beginning in 1842 ,water of t he Croton watershed, an area of 375 square miles,about 22 miles north of t he city, was collected in a numberof reservoirs and lakes, and carr ied t o t he city by the Crotonaqueduct .

With t he enormous growth of population, even th is greatsupply was found t o b e insufficient ; and t he City has ob

t ained control of a large area of land in t he Catskill Mountains, extending between 75 and 125 miles from New York .

With ‘the expenditure of about there has beendeveloped a water supply system which for many years tocome will b e able t o furnish the city with t he enormousquantity wh ich it needs (Figure

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162 GENERAL SCI ENCE

FIGURE 1 19 .—KENS ICO DAM.

This is one of the greatest masonry struc tures in the world. It rises 307

fee t.

above the rock foundat ion upon wh ich it rests.,lts th ickness at its

base is 233 feet.

(d) Of what importance is the elevation of the Source of

supply t o the water pressure in t he pipes in the city ? The

FIGURE 120 .—HEIGHT To WH ICH NEW YORK WATER WILL RISE WITHOUT

BEING PUMPED.

HOW COMM UN I TIES OB TAIN A GOOD WATER S UP PL Y 163

water surface of t he chief reservoir (Ashokan) of t he Catskillsystem is 590 feet above sea level . Because water seeks itslevel , there i s sufficient pressure t o raise it t o all floors of

buildings of reasonable he ight, about 260 feet, withoutt he use

.

of pumps (Figure It is estimated that thishas saved an expense of per year Since the use of

t he Catskill supply began.

(e) Does th e fact that t he mountains are covered withforests make any difference ? The floor of t he forest , made

FIGURE 12 1. FORES'

T FLOOR .

up largely of decayed leaves and interlacing roots, acts as

a great sponge (Figure What effect wil l this have at

seasons of heavy rainfall ? On t he other hand, dur ing dryweather t he water which has been absorbed by t he forest b edis gradual ly being given off, usually in the form of spr ings,

164 GENERAL SCIENCE

t o t he smal l streams which carry it into the collectingre servo ir s (Figure

Prob lem 2 . How th e water is protected. The facts

(1) that t he people of New York City drink water . drawndirectly from t he mains, and (2) that for many years therehave been no epidemics caused by polluted water , lead ust o wonder what precautions are taken t o keep t he supply

FIGURE 122 .— A STREAM IN THE CATSKILL MOUNTAINS .

Th is is one of the feeders of th e Ashokan reservoir of the New York CityWater Supply .

pure , when we remember that t hedr inking ofunboiled waterfrom a stream is often very dangerous, and that t he reservoirs are supplied large ly by small streams .We have already found that water inmountains is less apt

t o contain disease germs . Explain again t he reason for this .A number of special precautions, however , have been taken

to insure the purity of the water.

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166 GENERAL SCIENCE

as in a fountain . Not only do t he oxygen of the air and

t he sunl ight he lp to destroy bacter ia, but unpleasant tastesand odors are removed and the water made much morepalatable . Th e effect of aération of water upon it s palatab ility may b e tested by first dr inking some bo iled water,and then drinking some which has been poured severa l timesin a thin stream from one vessel t o another .

(d) In addition to what may b e called t he natural agenciesat work t o make t he water pure , chlor ine gas (a very powerfulster il izing agent) i s introduced into it just be low t he Kensico

reservo ir , if the bacter iological examination of the water

FIGURE 124 .—DIAGRAM OF A CITY WATER SUPPLY SYSTEM .

Note pumping station, stand pipe , water supply for‘

(

houses, fountain and

,fire prevent ion.

indicates the need for th is treatment . The gas is whollyneutral ized or dissipated before the water reaches t he dist ribut ion pipes of t he city .

Prob lem 3 . How oth er cities ob tain a supply ofwater .

Every large city has special problems to work out in con

nect ion with it s water supply system . Many depend upon

t he collected rainfall from . an area more or less controlled

by the city,as New York does . Some depend partly upon

artesian wells, wh ich t ap layers of porous rock that come t othe surface sometimes hundreds of miles away and absorbmuch of the r ainfall of that region. Others depend directly

HOW COMM UN ITIES OBTAIN A GOOD WATER S UP PL Y 167

upon r iver water which i s pur ified by chlor ination and t he

passage through great filter s wh ich remove much of the

suspended matter . Still others may obtain water directlyfrom large bodies of fresh water as do the cities on t he GreatLake s.Make a list of the uses of wat er in -your community .

What do you know concerning its water supply ?

FIGURE 125 .—RES ERVO IR AND DAM.

A part Of th e wate r supply system ofDenve r , Colorado.

Pupils should work out careful ly the water supply of the irown community, finding out th e sour ce of the water , meanstaken to protect its pur ity, and how it is carr ied t o t he

consumer .

Rural water supply. Villages and individual homes inthe country frequently depend upon relative ly Shallow well s,the water of wh ich is of course supplied by that portionof the rainfall wh ich has soaked into t he eart h. Great care

68 GENERAL SCIENCE

should b e taken as t o t he location of such we ll s, and theirprotection from surface water .

In many cases, deeper well s wh ich penetrate layers of clayor even rock are depended Upon . The water of such we llsfrequently has minerals dissolved in it . Why ? Th e

water from wells in a l imestone region will not form a latherwith soap and i s called hard.

”This is due t o the power of

water t o dissolve l imestone . Illustration of

t his may be seen in

any cemetery wheret here are old marblet ombstones . What isthe condition of t he

inscr iptions on t he

s tone s ? In som e

parts of t he country,especially in Ken

tucky, Virginia, and

Indiana, undergroundwaters have di ssolvedaway t he rock t o such

Dissolved out by wate r. The proj ec tionsXt t t h t 1

from th e roof w ere formed by deposits ofan 6 en 3 arge

partic les of limestone from water trickling into cav e s hav e b e enthe Cav e ’ formed (FigureNotable among these are Mammoth Cave of Kentucky and

Luray Cave of Virginia . A t ea-kettle in which “ hardwater is used becomes incrusted on the inside with a

grayish deposit which is really limestoiie .

FIGURE 126.—LIMESTONE CAVE.

Prob lem 4 . How th e water system w ith in the house

sh ould b e cared for . The water pipes in our homes are ,

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170 GENERAL SCIENCE

SUGGE STED INDIVIDUAL PROJECTS

1 . Construct a model of the water system of your community .

2 . Determine t he source ofwater of any springs in your vicinity .

3 . Make a plan ofwater pipes in your house . Explain t he advan

tage of this arrangement. In what way could the arrangement havebeen improved ? Explain .

4 . Demonstrate t he structure of a faucet. Show how it may get

out Of order andwhat may be done t o correct the troub le .

5 . Study out the mechanism in t he tank of t he t oilet in your home .

Where is it apt to get out of order, and how may this condition becorrected?

REPORTS

1. Describe t he methods used by a number of large cities to obtaina goodwater supply .

2 . Tell how t he American army was supplied with pure water inFrance.

REFERENCES FOR PROJECT XV

L Home Water Works, C. J . Lynde . Sturgis.

2 . Water Works in 38 Cities in Iowa, John H. Dunlap. University Ext ension Division, University of Iowa, Iowa City, Iowa, 5 cents.

3 . LOW Cost Farm Water Works, Conference for Education in t heSouth. 508 McLachlen Building, Washington, D. C.

4 . DrinkingWater and Ice Supplies and Their Re lations to Healthand Disease, T. M. Prudden. Putnam.

PROJECT XVI

TO UNDERSTAND THE DISPOSAL OF SEWAGE OF

HOMES AND COMMUNITIES

THE problem of getting rid of t he waste of t he home andof t he community is almost , if not equally, as important as

Obtaining a good water supply . As in t he case of t he watersupply it s importance increases as cities increase in size .

Prob lem 1 . Care of waste water pipes.

-With regardto t he waste water pipes which are

connected with t he sewers, we are

chiefly concernedwith t he traps, —t heusual form of which is represented inthe diagram (Figure Explainthe need of a trap . What is apt t o

happen t o a trap if considerable solidmater ial is allowed t o enter t he wastepipe from t he kitchen sink ? Th ismay be largely prevented if a sinkstrainer is used . Sometimes the greasefrom dishwater will collect in thiswaste pipe . Th i s may be avoidedby occasionally running through t he pipe hot water con

taining lye . No trouble is l ike ly t o occur in t he waste pipeof t he water closet, providing that piece s of newspaperand matches are not thrown into it .

Prob lem 2 . Sewage disposal in villages and isolatedhouses.

—If we l ive in a city in which there is a wel l171

FIGURE 128 .—TRAP OF

WASTE WATER P IPE.

172 GENERAL SCIENCE

developed syst em of sewers there is really no concern for theindividual home , other than t o make sure that there is a

proper connection with t he sewer . In t he home or schoolnot connected with a sewer , t he septic tank system is t he mostsatisfactory . This consists essentially of two or sometimesthr ee concrete underground tanks .

FIGURE 129 .—SEPTIC TANK .

By th e overflow pipe 4 th e waste , liquified by ac t ion of b ac te ria, passes

into 0 , from wh ich it is siphoned into 0 , flow ing out from there by the

out le t pipe .

In the first tank, sol ids are acted upon by bacter ia and

liquifled. By an overflow pipe th is l iquid passes into '

t he

second t ank, from which it may be removed thr ough t het op or , in t hecountry, it may be conducted away by a ser iesof drains and permitted t o escape into t he surrounding soilwhere it is soon complete ly decomposed by t he soil bacteria.

Any method ofdisposal ofwaste from t he toilet in wh ich t hemater ial is Open t o visits of flies , or in which it is permittedt o become mixedwith t he soil before it has been acted uponfor a long time by bacter ia, is bad, as it may mean exposuret o typhoid fever and hookworm disease .

Prob lem 3 . Sewage di sposal in c ities. The t oo commonmethod has been t he easiest ; that ofdischarging sewage into

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174 GENERAL SCIENCE

SUGGESTED INDIVIDUAL PROJECTS

1 . Make a plan of t he sewage system ofyour home . Point out t headvantage of t he arrangement. Inwhat way do you think t he arrangement might have been improved ? Explain.

2 . Clean out t he various traps in t he waste water system.

REPORTS

1 . The transmission and the seriousness of t he hookworm disease .

2 . Sewage disposal of a large city .

3 . Sewage disposal on a farm.

PROJECT XVII

WATER AS A MEANS OF TRANSPORTATION

IN addition t o the value of water in the air , as rainfall ;in furnishing power , from waterfalls ; for var ious industr ialpurposes ; and for dr inking and household uses, it alsofurnishes one of t he chief means of transportation . The

location of cities and t he deve lopment of nations have beendetermined by opportunities for utilizing water trans

portat ion . The development of New York into one of t he

largest cities of t he wor ld has been greatly influenced by t hefact that it possesses a harbor which is almost unrivaled.

In t he same way ,Boston,

Philade lphia, and Baltimoreon t he Atlantic Coast ; St . Louis and New Orleans on t heMississippi ; Chicago, Buffalo, Cleveland, Detroit , and

Duluth on t he Great Lakes ; and San Francisco,Portland ,

andSeattle on t he Pacific Coast, owe much t o t he advantageswhich they offer t o water transportation. Afr ica has few

harbors, Europe hasmany . Ex plain how th is fact may haveled t o t he more rapid development of‘civ ilizat ion in Europe .

Since harbors t o such a great ext ent determine t he importance of a country, we naturally ask how a good harborsuch as that ofNew York has been formed.

Prob lem 1 . HOW th e New York harbor originated.

-Examine t he but line map of the harbor (FigureExamine also t he coast ofNorth Amer ica from ChesapeakeBay northward (Figure Compare th is coast line with

175

176 GENERAL SCIENCE

t he western coast line of South Amer ica (FigureThere is evidence that the west ern coast line of SouthAmerica i s r ising.

FIGURE 130 .—MAP OF NEW YORK HARBOR.

Another fact.

t o b e noticed is that t he Hudson River isvery deep , permitting very large vessels t o pass up its

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178 GENERAL SCIENCE

of sol idity, portions of t he earth’s surface have at timesbeen raised and at other times depressed. The stratified

sandstone, limestone , and slaty rocks found over a great

part Of t he country are evidences of t he.

e levation of theseportions Of t he con

t inent , as these rocksare formed only at t hebottom of t he ocean

(FigureProb lem 2 . Efiect

of th e forests of th e

Adirondacks uponNew York harbor and

th e navigab ility of th e

Hudson River .

—Inorder that a harbormay b e of t he greatest value , a certainamount of dredgingmust be done t o keepthe channe ls free of

sand and mud . The

origin of this mater ialwill be understood byanyone who has no

ticed t he appearanceof the water in a smal l

stream after a rainstorm . If this smal l stream emptiesinto a large body ofwater , it will b e noticed that t he mudand sand

,wh ich i s be ing carr ied , is dropped .

Streams everywhere are wear ing away t he land and

carrying it to the ocean. This i s t he cause ofmuch of the

FIGURE 132 —OUTLINE OF SOUTH AMERICA .

WATER AS A MEANS OF TRANSPORTATION 179

irregularity of the land surface . Each l ittle stream forms aravine or valley of its own, carrying away t he particles ofearth and rock which have been loosened by changes oftemperature , by t he freezing

'

ofwater in crevices, or by the

action of t he oxygenor carbonic acid of t heair . The action of

these agencies 18

known as weathering.

These particles, carried along by the

swiftly-moving water,help t o wear awayt he b ed oft he stream ;thi s is known as

erosion (FigureThus we see that theland is graduallyb eingcarr ied t o t he ocean,

where it is dropped assoon as t he ve locity ofthe water is checkedby coming in contactWith t he greater body FIGURE 133 .

—OUTLINE MAP OF ENGLAND.

of water , Near ly all Note the fine harbors at the mouth of the

rivers. These were produced by a sinking of

Sal e St

a—6

51

31 3 that£0 11 11

the c oast many thousands ofyears ago.

e u SOIl lVOI‘

begin in the Adirondack Mountains, about 3000 feet abovesea level . What must be true of t he

‘ velocity of t he waterOf these streams ? As t he rainfall in t he Adirondacks isnot evenly distr ibuted throughout t he year , what would

you expect t o be the condition of t he streams dur ing t he

l i t/G”6“

180 GENERAL SCIENCE

season of great rainfal l and at t he time Of t he me lting of

t he snow ? What would you expect t o b e t he result whenth is water meets t he sluggish current of the tidal portionof the Hudson,

and when t he t idal current from the r ivermeets t he water of t he harbor ?

FIGURE 134 .—STRATIF'IED ROCKS .

You will be surpr i sed t o learn that t he streams are notnear ly so flooded, and that there is not so much sedimentdeposited as you would imagine . Our consideration of t he

effect of forests upon water-supply areas gives us t he keyt o t he explanation . The Adirondack Mountains are heavilyforested . What effect does thi s have upon t he volume of

water in its streams ? What also will be t he effect . upon t hepower of t he streams t o accomplish erosion and t o carrymud

, sand, and rocks ? What do you think would be the

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82 GENERAL SCIENCE

water except in the larger streams, while in t he spring t heyoverflow their banks, causing much damage t o property and

Often loss of l ives (FigureProb lem 3 . Importance of internal

'

waterways. For t he

transportation of articles of commerce in which speed is

not a pr ime requisite , internal waterways might we ll be

FIGURE 136 .—FLOOD IN WABASH R IVER , INDIANA.

This flood was due to the removal of forests from the region of the

head waters of the river.

used far more than at present because of t he smaller ex

pense (Figure Thi s would also rel ieve t he railroadsso that the ir facilities might be used more complete ly in t hetransportation of passengers, mails, foodstuffs , and articlest hat demand quick de l ivery (Figure Congestion of

railroad traffic has been one Of t he causes of t he high cost ofl iving . In t he great deve lopment of railroads dur ing t hepast fifty years, t he development of transportation by waterhas been neglected to a large ext ent . An illustration of the

WATER AS A MEANS OF TRANSPORTATION 183

great import ance of r iver navigation ls seen in t he carryingOf coal and iron from Pittsburgh down the Oh io and Mis

sissippi r ivers .R iver traffic has been supplemented by t he construction Of

canals. Many of these have fallen into disuse dur ing t heper iod of development of railroads, but recently steps havebeen taken t o put some of them into a usable condition.

FIGURE 137 .—USE OF R IVER FOR TRANSPORTATION OF Loos.

The first half of t he nineteenth century in the UnitedStates might almost have been called t he

'

era Of canalbuilding . Some of t he canals were short ones around fallsin otherwi se navigable r ivers . Many were of interestbecause they cut across watersheds and connected distinctdrainage systems

,frequently at the port ages used by t he

Indians and ear ly settlers . If railroads had not deve lopedas they did, we should have had a very complete system of

internal waterways.

184 GENERAL SCI ENCE

The most impor tant ofthese was t he Erie Canal, completedin 1825 from Buffalo t o Albany, a distance of 352 miles,connecting t he Great Lakes with t he Hudson R iver .

Pennsylvania and Maryland attempted t o connect theirt ideiwat er r ivers with t he Ohio River ; Virginia endeavoredto connect Chesapeake Bay with t he Oh io R iver ; in New

Jersey t he Morr is Canal was built connecting New YorkCity with t he Delaware R iver ; Ohio and Indianacanals from t he Great Lakes t o t r ibutar ies of t he Oh io

FIGURE 138.-USE OF INTERNAL WATERWAYS To TRANSPORT FARM

PRODUCTS .

River , and in Illinois a canal was constructed connectingLake Michigan with t he Mississippi system .

The Soo canal at Sault St e . Mar ie , between LakeSuper ior and Lake Huron, and t he We lland sh ip canal,between Lake Er ie and Lake Ontar io in Canadian terr itory,afford a continuous passage from all parts of t he Great

Lakes to the Atlantic Ocean by way of'

the St . LawrenceRiver . The route is of especial interest t o us now becausein t he GreatWar many of t he large lake vessels were broughtto th e Atlantic to be used to carry troops and supplies to

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186 GENERAL SCIENCE

Europe . This route has put great areas of our country intodirect water connection with t he markets of t he world .

Prob lem 4 . How ocean transportation depends upon

science . Ocean . transportation follows regular routeswhich are determined t o some extent by available harbors,prevail ing winds, ocean currents, t he probability of t he

presence of icebergs, and fogs . In a number of casesroutes have been shortened by the construction of canals ;the two most important ones are t he Suez Canal through theIsthmus between Asia and Afr ica, connecting the Mediterranean Ocean and the Red Sea, and the Panama Canalthrough the i sthmus between North and South Amer ica,connecting the Atlantic and Pacific oceans . .Along our

eastern coast, the Cape Cod Canal shortens very mater iallythe coastwise route between New York and Boston . The

Suez Canal, opened in 1869 , has saved, in going from t he

North Atlantic t o India and the Far East, t he long tr iparound the southern end ofAfr ica.

The building of the Panama Canal , opened in 1914 , wasthe greatest engineer ing project of the world . It s influenceupon the world’s commerce i s bound t o b e very great .It shortens the water route from New York t o San Franciscoby almost 8000 mile s ; from New York to Hawai i by about6000 miles ; from New York to Callao by about 6000 miles ;from New York to Sydney, Austral ia, by about 4000 miles

(FigureThe building of th is canal was not only an e ngineer ing

tr iumph for the United States, but one equal ly great in t hefield of sanitation. Amer ican physicians, by the ir work in

the canal zone, not only made possible the building of

t he canal but they demonstrated that tropical disease s arecapable of human control .

WATER AS A MEAN S OF TRANSPORTATION 187

FIGURE 140 .—UNITED STATES WAR S H IP PASS ING THROUGH PANAMA

CANAL .

The sanitary work was under the control ofDr . WilliamC. Gorgas, who built upon t he work of t he United State syellow fever commission in Cuba, consisting of Drs. Reed,Carrol l, Lazear , and Agrimonte , who hadproved at the cost

188 GENERAL SCIENCE

Of the l ife ofDr . Lazear that the only way that yellow fevercan be transmitted is by t he bite of a certain kind ofmos

FIGURE 14 1 .—MINOT

’S LEDGE LIGHTHOUSE.

This ligh thouse is located on a reef near

Boston Harb or.

quito. Dr . Gorgas,who had alreadyfreed Havana and

Cuba of the ye llowfever plague , was appointed by PresidentRooseve lt t o con

t inue the work whichmade possible t he

building of the canal .The French had beendefeated by t he mos

quitoes years beforein their attempt t obuild the canal without even havingknown that theseinsects were theirenem les.

That harbors are

necessary for the bestdeve lopment of a

country is real izedin compar ing the

coast line of Afr icawith it s few harborst o

,

that of Europewith its many fine

ones . Countr ies are ready t o go t o war t o get an outlett o t he sea. Because of the importance of ocean commerce,

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GENERAL SCIENCE

Q

3 . Construct a model canal lock by which boats in canals are passed

from one level to another.

REPORTS

1 . The general geological history of the North American continent.2 . A description of theWork b eing done by t he government t o keep

rivers and harbors navigable .

3 . The story of the Erie Canal.4 . History of the building of t he Panama Canal .

5 . Means taken t o prevent disease in the Panama Canal Zone .

REFERENCES FOR PROJECT XVII

1 . Panama and the Canal, Hall and Chester . Newson and Co . ,

New York.

2 . Peeps at Many Lands (Panama, t he Canal, et c .) Browne . Mac

millan Company .

3 . Historic Inventions, Holland. Geo .W. Jacobs Company, Philadelphia . (Fulton and the Steamboat. )4 . Book of the Ocean, Ingersoll. Century CO.

UNIT III

THE RELATION TO US OF SUN,MOON, AND STARS

PROJECT XVIII

TO UNDERSTAND THE CAUSE OF TID‘

ES

ALTHOUGH so far away, the:

sun and moon exert a

powerful influence upon everything that happens on t he

earth . Th is influence has been mentioned in consider ingt he source of energy of food, coal, and wood , and t he energyofwater power .

Then t oo, t he sun, moon, and stars, although so distant,have always been of t he greatest interest t o t he inhabitantsof the eart h . The earliest speculations concerning thingsofNature have been concerned with these heavenly bodies.

We know now that much that was fanciful and erroneouscrept into their ideas of these bodies ; but we , just as our

distant ancestors were , are interested in t he wonders of t he

heavens . We , however , are not satisfied with fanciful imagination but want t o know t he truthIn our study we shall begin with one of t he very evident

ways in which t he earth is affected by t he nearest of theseheavenly bodies , t he moon . A study of the tides may

give“

us some h ints as t o the relationship between the eart hand other heavenly bodies and of t he relation of these t oone another .

If you l ive near the seashore or have ever visited it youknow something about tides . Let us first get together our

19 1

192 GENERAL SCIENCE

observations con

cerning tides . HOWmany tides a day ?Does high tide oc

cur at t he sametime every day ?

If not , does it oc

cur earlier or latereach day ?

I

How

much h igher is t hewater at h igh tidethan at low tide

(Figures 142 and

FIGURE l42 .—HIGH TIDE IN A HARBOR IN Are

.

thereNOVA SCOTIA.

any t Imeswhen t hetide i s especially h igh ? To find out t he cause of tides it is

evident that we must be able t o solve t he following problems

What causes ther ising of t he water .

Why t he watercomes up twice a

day .

Why h igh tide isa little later eachday .

Why, at times,there are especiallyhigh tides .Prob lem 1 . What

causes th e water torise , Fr om t h e FIGURE 143 .

—Low TIDE IN THE SAME HARBOR .

fact that t he highest tides occur at the time of t he

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94 GENERAL SCIENCE

times as much material in the large marb le as in the small one, t he

large marb le will move one tenth as far as the small one . Explain,

then, Why t he ball falls t o the earth, and why t he earth does not seemt o rise t o the ball.

This force acts in sol id bodies, through t he center Ofmassof t he body . It is because of this that a mason’s plumb

line points t o t he middle of t he earth (Figure,

In objects on t he surface of t he earth , thiscenter of mass or center of gravity, as it is called,is t he point of a body at which it s we ight may

b e counteracted by a single upward, vertical force .

The location of t he center of gravity is easilyfound. Suppose the center of gravity of a pieceof cardboard is t o b e found. Suspend t he cardboard by a thread. Draw a line on it continuouswith t he l ine oft he supporting thread . Now suspend t he cardboard in t he same way from anotherpoint of attachment . The point Of intersectionof t he two lines will be the location of t he centerof gravity . Explain .

The fact that t he center of gravity of a bodytends t o get as near t he center of t he

'

earth aspossible is illustrated by t he tipping over of bodies .

FIGURE 144 ,Why does a flat stone on the ground Show no

PLUMB LINE tendency t o tip,while t he same stone standing

on its edge tips over very easily ? A body is said t o bein stable equilibrium when it cannot b e tipped withoutraising its center ofgravity ; a body is in unstable equilibriumwhen it cannot be tipped without lower ing it s center of

gravity (FigureLe t us now go back t o t he tides and endeavor t o understand how this force of gravitation causes them . The moon

TO UNDERSTAND THE CA USE OF TIDES

attracts t he solid earth as if t he entire mass of t he earthwere concentrated at it s center . The water of the ocean,

however , is 4000 milesfrom t he center of t he

earth . What, therefore ,is t he relative pull of

t he moon upon t he sol idearth , and upon t he oceanon the side nearest t hemoon ? (FigureThis is the cause of t he

FIR“ ? 145°

A . stab le equIlIb rIum . B , unstab le

tide on t he Side Of the equilib rium . C, neutral equilib rium .

earth nearest t he moon.

Prob lem 2 . Why‘

th ere are two h igh tides a day. You

already know from your study of geography that t he earthrotates once in twenty-four hours . Therefore, how many

Low WATER .

FIGURE 146 .—RELATION OF MOON TO THE TIDES .

t imes a day is t he moon directly opposite any part of t heeart h ? It can be easily understood

,then

,how a wave of

water will travel around t he earth . In what direction willit trave l ? Explain. (Note : Does t he moon r ise in t he

east or t he west ?) According t o this,how many tides a

day will there be ? But, in real ity, how many are there(Figure

From the fact that h igh tides are‘

about twelve hoursapart when there is high tide on any part of t he eart h, atwhat other part of t he earth is t he other high tide ? Our

problem then is, how is this second high tide , on the side of

t he earth away from t he moon, caused.

Recall t he way in which . gravitation act s upon t he sol id

eart h and upon t he water of t he ocean. How much fartheraway from t he moon is t he water on the Opposite side Of t heearth than t he center of gravity of t he solid earth ? Uponwhich

,therefore , will t he pull be greater ? It can be under

stood now how there is a tendency for t he solid earth t o be

pulled away from t he water and as a result t he water willflow in, causing ari e levation of t he water , thus producing atidal wave on t he side of t he earth away from t he moon .

In what direction will this t idal wave trave l and at whatrate compared with t he tidal wave directly under the moon ?There is also another force which helps produce this tidalwave on t he side of

.

t he earth away from t he moon, wh ichcan be understood a l ittle later .

Prob lem 3 . Why h igh tide is a litt le later every day.

From our discussion, what would you conclude should bet he time between two h igh tides ? If, then,

h igh tide occursat 12 O

’clock on one day, at what time should there be hightide on t he following day ? Is this actually what occurs?Some Of you have gone t o t he ocean bathing beaches . On

your visits there did you find that high tide always occurredat t he same time ofday ?

Observation will show you that high ,t ide is about fifty

minutes later every day . Our problem then is t o understand t he reason for th is seeming discrepancy .

In our discussion of the cause of tides we considered t hatt he earth rotated once in twenty-four hours. If t he moon

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198 GENERAL SCI ENCE

happens t o t he water on a gr indstone,when it is turned

rapidly ? What happens t o an automobile if it attemptst o turn a corner t oo rapidly ? What is t he advantage of

having a circular running track banked Wet clothesare dr ied by putting them into a large, perforated, metal

cylinder and rotating t he cylinder rapidly . If you are

familiar with milk separators, explain how t he milk is

separated from t he cream (FigureAll of these observations , showing that rotating bodies

tend t o fly away from the center around which t he body is

FIGURE 147.

Why do the mercury and water not remain at the b ot tom

of the glass glob e ?

turning , are illustrations of t he fact, that bodies in motiontend t o remain in motion in a straight line . They are

illustrations of a law stated by Sir Isaac Newton, known as

Newton’

s first law of motion :“Every body continues in its

state of rest or of uniform motion in a straight line, ex cept in

so far as it is compelled by force to change that state.

”Give

other illustrations of t he law .

For every body turning around a center there must be two

TO UNDERSTAND THE CAUSE OF TIDES 199

forces ; one drawing it t oward t he cent er, called the centrip

etal force (center-seeking force) and one drawing it awayfrom the center , called t he centrifugal force . The moonrevolves around t he eart h once in every twenty-e ight days .As t he moon is miles from t he earth , you can easilycalculate its velocity . Because of this motion what does t hemoon tend t o do ? What prevents it ? In your own lan

guage explain why t he moon is not drawn t o t he eart h or

does not fly off into space .

You will recal l that in discussing t he cause of t he tideon t he side of t he earth away from t he moon reference wasmade to another force in addition t o t he difference of t he

pull ofgravitation upon t he sol id eart h and t he l iquid ocean.

This force We can now understand. The moon and earthar e held together by t he force ofgravitation very much as a

large man and a Small boy might hold themselves togetherby locking the ir hands together .

If, while holding hands in th i s way , t he man should

swing t he boy around , not only would’

t he boy tend t o

swing in as large a circle as possible , but t he coat tails Of t heman also would tend t o fly out because of t he cent rifIIgal

force . In t he same way t he water on t he side of t he earthaway from the moon tends t o heap up because of th is cent rifugal force .

There remains yet one problem concerning tides wh ichwe decided needed solution : Why, at times, there are es

pecially high tides.

Prob lem 5 . Why, at times, th ere are especially high

tides. Usual ly about twice a month t he tides are es

pecially high . Dur ing t he winter of 1919—1920 such a tideaccompanied by a wind from t he

‘

Ocean flooded ConeyIsland and Rockaway Beach near New York, wrecking

200 GENERAL SCIENCE

many buildings . At t he same time a large part of t he

water front of New York City was covered with water .

FULL MOON.

FIGURE 148.—THE Two POS ITIONS OF THE MOON WHEN HIGH TIDE

Is HIGHER THAN USUAL.

This occur red at t he time of t he full moon. At every fullmoon and new moon the t ide

’

i s especially high . On t he

other hand, whenMOON. t he moon is at first

and third quarters,the high tides are

especially low .

The accompanyingdiagrams (Figures148 and 149) Showthe re lative positionsof t he earth , moon,

and sun at theset imes . From exam;

inat ion of thesediagrams explain t hecause of t he espe

FIGURE 149 .—THE Two POSITIONS OF THE cially high tides at

MOONWHEN HIGH TIDE Is NOT AS HIGH As,certain times .

USUAL.E v i d e n t l y the

theory that the tides are caused by t he force of gravitation,

studied by Sir Isaac Newton, can be accepted, as itoffers a satisfactory explanation of t he cause of tides and

THIRDQUARTER.

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202 GENERAL SCIENCE

2 . What is the source of t he light which comes to us from

the moon ?

3 . What motion has the moon in relation to the earth ?

4 . How long does it take t he moon t o go around the

earth ?5 . About how often do we have a full moon ?

An examination of the

following diagram,in con

nect ion with t he answersto t he questions above ,wi ll make clear t o you why,at times, t he moon appearsl ike a ball, while at othertimes it appears as a crescent . Even when t he moonappear s only as a crescentwe can sometimes dimlysee t he remaining portionof it s sur face . This is b e

cause of reflection of light from the surface of t he earth .

The following lines will enable you t o know whether thecrescent you -See in t he Sky i s an old or new moon

Oh , Lady Moon, your horns point toward t he east. Shine ;be increased 1

Oh , Lady Moon, your horns point toward the west. Wane ;

b e at rest "”

Occasionally an eclipse of the sun occur s . If we look at

the sun at such a time through a piece of smoked glass, itwill b e noticed that a rounded black notch or patch appearson the edge of the sun. Th i s black patch travel s across thesurface of t he sun . If the eclipse is a total one , it obscuresfor a short t ime the entire face of the sun (fi gure if

,

FIGURE 15 1.—A TOTAL ECLIPSE OP

THE SUN.

TO UNDERSTAND THE CA USE OF TIDES 3

as is usual, th e eclipse is only partial, only a segment ofit isobscured.

Consider ing the relative location of the bodies of the

solar system, what do you be lieve causes an eclipse of t he

sun ?‘

There may also b e an eclipse of t he moon. Sug

gest how this may occur . Draw diagrams showing the

relation of the moon,earth, and sun in bothkinds of eclipse . The

accuracy with which the

time ofan eclipse may b e

foretold years in advanceof the event is an indication Of how thoroughlythe laws of motions of

t he members of the solarsystem are understood.

Solar system. The

same two forces wh ichhold t he moon in its path keep the earth and other planetsin the ir orbits or paths around t he sun. In t he order of

the ir distance from t he sun t he planet s are Mercury,Venus, Earth, Mars, Jupiter , Saturn, Uranus, and Neptune

(Figure 152) To us, Venus is the most conspicuous of

these planets . Next to the sun and moon it is the brightestobject in the Sky . At times it is t he evening star , and at

other t imes the morning star .

Mars, wh ich sometimes appears as a reddish star in thesky, has been a favor ite object for study with the telescope

because of its nearness and especial ly because in many re

spect s it resembles t he earth , leading observers t o think thatpossibly life similar t o that on the eart h may exist there .

FIGURE 152 .—DIAGRAM OF OUR

SYSTEM .

204 GENERAL SCI ENCE

The th inness of the atmosphere and t he small amount of

water present onMars render this bel ief rather Improbable .

The sun with t he planets revolving“

around it is called th e

solar system. Th e sun is a l ight-giving body ; the planetsand the ir moons only reflect t he light of the sun.

SUGGESTED INDIVIDUAL PROJECTS

1. Make a model t o scale showing the relative size of the moon

and t he earth, and the distance of t he moon from t he earth.

2 . Make a diagram showing t he location of t he moon in the sky at

a certain hour on six successive nights. Show also t he appearance of

t he moon each night. Explain your observations.

3 . Work out a plan of t he solar system, representing t o scale t he

relative distances and sizes of t he sun and the planets.

4 . Make a model of sun, earth, and moon t o show t he cause of

eclipses, phases of t he moon, and seasons.

1. Use of t he energy of tides.

2. How the sun,moon, and planets have come into existence .

3 . Discussion of t he probability of life Sim ilar t o that on this earthexisting on other planets.

REFERENCES FOR PROJECT XVIII

l . The Moon, G. P . Serviss. D. Appleton CO .

2 . The Ways of t he Planets, M . E . Marten . Harper Bros.3 . Giant Sun andHis Family, Proctor . Silver, Burdett Co.

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206 GENERAL SCIENCE

Pointers is approximately fiv e degrees . It will be well t okeep these figures in mind, as they will serve as standardsfor measur ing distances between stars.

The Pole Star i s part of a constellation called t he LittleDipper . It also has seven stars, the number that you have

seen in t he GreatDipper . The out

l ine Oi t he LittleDipper , however ,i s not so distinctas that of it s bignamesake . The

Pole Star i s at

t he end of t he

handle of the

Little Dipper .

The bowl is composed of a clust er Of four stars,t he two of t he

outer rim beingt he br ightest, lo

cat ed about fifteen degrees from the Pole Star and facingt he open bowl of t he Great Dipper . If you have foundthe stars of t he bowl , t he other two stars of the handlemay b e easily located between the bowl and t he Pole Star .

It will b e noticed that the end of the handle of t he LittleDipper is bent in a different direction from that of thehandle of t he Great Dipper .

Th e ancients imagined the stars of the Great Dipper torepresent t he form of a great bear , and this conste llationwas accordingly called Ursa Major or the Great Bear .

FIGURE 153 .—CONSTELLATIONS AROUND

NORTH STAR.

HOW To KNOW SOME OF THE FIXED STARS 207

Likewise the Little Dipper was cal led Ursa Minor or t he

Little Bear . The abil ity t o see a smal l star in the handleof t he Great Dipper i s frequently used as a test for goodsight . Look at t he second star counting from t he end of

t he handle . This is called Mizar . Directly above it at

a distance of about one degree i s t he faint star Alcor . The

Arabs call these two stars t he horse and the r ider .

”

The conste llation Cassiope ia’s Chair i s located about thesame distance from the Pole Star as the GreatDipper , but onthe opposite side . It i s very easily recognized because itsfiv e br ight stars form aW-shaped figure .

Aur iga, or the Char ioteer , contains one of t he br ighteststars, Cape lla, in the northern part of t he heavens. Ca

pe lla i s about forty-fiv e degree s from t he Pole Star ; that is,almost twice as far away as t he Great Dipper or Cassiope ia’sChair , and on a l ine drawn at r ight angles t o a line connecting t he Pointer s with the Pole Star . Another way t o findCapella i s t o follow a l ine drawn from t he star at the bottomof the Great Dipper that is nearest t o t he handle , and passing halfway between t he Po inters. At a distance of aboutfifty degrees along this l ine , Cape lla will b e seen as a verybr ight star . Cape lla with t he four other br ightest starsof t he constellation form a pentagon or fiv e-sided figure .

The br ightest stars of the conste llation Perseus lie in

an arc extending from Cape lla t o Cassiope ia’

s Chair . You

will b e able to see along this arc six or seven stars that b elong t o the constellation .

Other,

rather conspicuous constellations which may b e

seen Within a radius of about forty or forty-fiv e degreesof t he Pole Star are the Dragon, and Cepheus .Prob lem 2 . How to recognize th e constellations seen

only in winter . Stars farther away from t he pole can be

208 GENERAL SCIENCE

seen only at cert ain t imes of t he year . The best-knownof the winter constel lations, located on a line passingfialmostdirectly overhead from east t o west, i s OrIon, t he Hunter .

It is easily recognized by _ _

the thr ee stars formIng

R ATTHEEN

HANDLEOFTHELITTLESOUTH

FIGURE 154 .—EVENING SKY MAP FOR JANUARY, 192 1.

Except for the plane ts the sky is always the same as above in January. Note the plane ts on the e c liptic : Mars the farth est to the west ,

w ith Venus near it , and Neptune in the east.

Several smal l stars, extending at almost r ight angles, const itut e the sword hanging from his belt (FigureA very br ight, reddish star, Betelgeuse ,

1 marks the r ight

1 The diameter of Betelgeuse was recently measured for the firsttime with an instrument devised b y Professor Alb ert A . Michelson of

t he University ofChicago . The star was found t o b e abouttimes larger than our sun.

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2 10 GENERAL SCIENCE

SUGGESTED INDIVIDUAL PROJECTS

1 . Identify at least eight constellations.

2 . Work out t he method of reading star maps. Collect andmountstar maps for every month.

REPORT

Origin of the names of some of the conste llations.

REFERENCES FOR PROJECT XIX

1 . A Beginner’

s Star Book, Kelvin McKready . G. P .

Sons.

2 . The Barritt-Serviss Star and Planet Finder, Leon Barritt, 367Fulton St . , Brooklyn, N . Y.

4 . Astronomy with t he Naked Eye , G. P . Serviss. AppletonCo.

5 . Star Lore ofAll Ages,W. T. Olcut t . G. P . Putnam .

6. Earth and Sky Every Child ShouldKnow, J . E . Rogers. Doub le

day, Page Co .

7 . The Children’

s Book of Stars, G. A. Milton. Adam and Chas.

Black,London .

8 . The Friendly Stars, M . E . Marten. Harper Bros.

9 . The Stars and Their Stories, Griffith. Henry Holt Co.

PROJECT XX

TIME AND SEASONS

SINCE light and heat come from the sun, the differencebetween winter and summer must b e in some way associatedwith some difference in relation between the sun and t he

earth . Likewise our calculation of time must b e based on

t he relation between the earth and the sun. Every morning we see t he sun r ise in the east and at the end of the . day

se t again in the west .Prob lem 1 . Why we have winter and summer . There

are several facts with which we are familiar that will help ust o understand t he cause of the seasons . What is the com

parat iv e length ofday and night dur ing winter and summer ?What is t he relative he ight of t he sun above the hor izonat midday in winter and in summer ? Evidently t he sun

shines more directly upon our part of t he earth in summerthan in winter .

We have already learned that the earth rotates (turns)upon its own axis, and revolves around the sun. If the

axis of the earth is at r ight angles t o an imaginary linerunning , from t he earth t o t he sun,

what part of t he earthwould always rece ive the most direct rays of the sun ? But

since dur ing the summer the portion of t he earth north of theequator rece ives t he most direct rays of t he sun,

and dur ingth e winter the same region rece ive s fewer direct rays of t hesun, what is your conclusion in regard t o t he direction of

t he earth ’s axis ? (Figure2 1 1

2 12 GENERAL SCIENCE

Since on our longest day in summer the direct rays ofthe sun strike a point 235 degrees north of the equatorand on t he shortest day of our winter str ike a point 23—5 de

grees south of t he equator, we know that the axis of the

P”

FIGURE 155.—HEAT FROM SUN , SUMMER AND WINTER.

earth i s inclined -5 degrees to the imaginary line runningfrom t he earth t o t he sun.

A careful study of Figure 156 will make clear how the

revolution of t he earth and the inclination of its axis causethe seasons .

1 . At what times in

the year are the days andnights equal in length ?The se times are c alled t hevernal or spring equinox ,

and the autumnal or fallequinox .

2 . On June 22 , 19 19,

FIGURE 156.—PATH OF EARTH AROUND at New York City, theTHE SU

'N'

sun rose at AM . and

set at P .M. What was the length of the per iod of

daylight ? What was the length of t he daylight per iodwithin t he arctic circle (235 degrees from the north pole)on this date ?3 . In your own language discuss the changes in t he length

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214 GENERAL SCIENCE

It takes a considerable time t o heat the . land and water,and on t he other hand they cool off gradually . Explainwhy January is colder than t he latter half of December .

You have already learned that bodies of land cool morerapidly than bodies ofwater . Explain, therefore , why coastcities have a later spr ing and winter than inland cities

(FigureWhy is t he str ip of land about t en miles wide along Lake

Ontar io the best peach-producing region ofNew York ?Prob lem 3 . How time i s calculated. Some of us must

have been surpr ised when we rece ived news of t he signingof t he Peace Treaty before t he time scheduled for t he eventt o occur in Par i s .‘ Then we were told that the time at Par i swas fiv e hours faster than our own time ; that when it isnoon at Par is, our 7 o

’clock morning whistles are blowing ;and when we stop work for luncheon, t he people of Par isand London are ready t o quit work for t he day, as it is 5 P .M.

with them .

The general difference in time between different placesmay easily b e under stood when we consider that one com

plet e rotation of the earth makes one day of 24 hours, andthat noon by sun t ime

’

at any place is t he time when the

sun is directly over a north and south line running throughthat place . In what direction does t he earth rotate ?In which city, New York or San Francisco, will 12 noon

of a certain day first occur ?For convenience in compar ing times and for the pur

pose Of locating place s on t he earth ’s surface , imaginarylines (mer idians) are supposed t o b e drawn around the earthfrom pole t o pole (Figure There are 360 of theseequally distant from one another . Why 360 ? Th e distancebetween these lines is called a degree of longitude . Is

'

a de

TIME AND SEASONS 215

gree of longitude always of t he same length in miles ? At

t he equator a degree of longitude measures about 69 miles.

How much does a degree of longitude measure ln m iles at

the poles ? Usually t he mer idian passing through Greenwich

, England, i s called zero,and longitude is stated as east

or west ofGreenwich .

Since the earth rotates on it s axis once in 24 hours, howmany degreesof longitude will passunder t he sun in an hour ? Thus,for every 15

°

of longitude , t he

sun time of two places differs onehour . If our clocks were set

str ictly by sun time , what wouldb e true of the clock time of everyplace east and west of a givenplace ? In what way would thisb e inconvenient ?

FIGURE 158 .

—Lmr—:s OF LATI

To prevent t he trouble and TUBE AND Loncnuos.

annoyance arising from such a

condition, the United States Government in 1883, at t hesuggestion of the American Railway Association,

adoptedstandard time . By this arrangement t he time of the

fo llowing mer idians, 75th , 90t h , 105th , and 120t h , weretaken as standards of time called Eastern, Central , Moun

tain, and Pacific Time . The area of t he country t o wh icht he time was assigned extended approximately 7 degreeson each side

i

of the standard mer idian ; t he exact divisionbeing determined largely by the location of important cities

(Figure As a result, in going from New York t o

Chicago , we need t o change our watches only once . Shouldt he hands of the watch be advanced or turned back? How

much ?

216 GENERAL SCIENCE

Daylight saving. On March 19 , 19 18, President Wilson approved a bill passed by Congre ss

,by wh ich the stand

ard time throughout t he United States was advanced one

hourfor the per iod beginning at 2 A .M. on the last Sunday inMarch and ending at 2 A .M . on t he last Sunday in October .

Sugge st advantages of th i s bill to t he various classes of

people of your community . Does it seem t o work a hardship to any ? Dur ing t he summer of 19 19 , because of ob

FIGURE 159 .—STANDARD TIME BELTS .

ject ion to the daylight-saving plan by var ious interestsof t he country, Congress repealed t he bill .The movement or iginated in England in 1907 . It was

not until 19 16, however , that definite action was taken, whenwithin three months daylight saving was adopted in England, France , Italy, Norway, Sweden, Denmark, Switzerland, Spain,

Portugal , Holland, Germany, Austr ia, and Turkey . Practically no confusion resulted ; everything wenton as before , people do ing exactly the same things at the

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218 GENERAL SCIENCE

The distance from the equator is measured by degrees oflatitude. The equator is zero, and the poles Thus anyplace on the earth’s surface may b e accurately determinedby giving its latitude and longitude .

Th e navigating officer of a sh ip with these means of det ermining his position, by consulting h i s charts and by t heuse of the compass is able to direct h i s course with sur

pr ising accuracy.

SUGGE STED INDIVIDUAL PROJECTS

1 . Chart t he position of t he sun above t he horizon at a certain hourevery day for a month. Interpret t he results.

2 . At a certain hour one day each week determine t he amount ofearth surface covered by a column of sunlight whose cross section isone square foot.

1 . Make,a chart showing t he relative length of day and night

throughout the year . Accompany this by a diagram showing t he causeof t he differences in the length of day and night.2 . Make a chart showing t he standard time b elts.

3 .

i

Give method ofdetermining latitude and longitude ofa place.

UNIT IV

WORK ANDENERGY

PROJECT XXI

THE SUN‘AS A SOURCE OF ENERGY

THE question of energy and the work it makes possiblehas been an important part of almost every project and

problem we have considered. It seems wise , however , to

get together t he knowledge we have a lready gained con

cerning work and energy and especial ly t o take up the question of how man makes use of energy t o cont ribut e

v

t o his

own comfort and t o carry on the work of t he wor ld As

the sun has been frequently mentioned as the great sourceof energy, our first project may wel l b e the sun.

You will recal l that we came to the conclusion that theenergy ofwater power and of food and fue l could b e tracedback t o t he sun . Explain

,therefore :

(a) The relation of t he sun’s energy t o water power .

Into what other forms may t he mechanical energy of waterpower b e transformed ? (b) How t he energy of t he humanbody may b e traced back t o th e sun. (0 ) How th e energyobtained from the burning of coal and wood is really energyder ived from t he sun .

There is reason t o bel ieve that petroleum from whichgasoline, kerosene , paraffin, and similar compounds are ob

tained, and natural gas, which in many parts of the coun219

220 GENERAL SCIENCE

t ry i s used for fuel and l ighting purposes, have been formedas a result of decomposition of animal and plant deposits .

What, therefore, is the source of energy ex erted by t he

engine of the automobile and airplane ?

What do you consider t o b e the source of the energy of

FIGURE 160 . WINDM ILL.

The machine at the left is one of the earliest reapers for the cut ting of

grain.

alcohol which may become t he great fue l of the future if the

supply of petroleum becomes exhausted. Alcohol is made

by the action ofyeast upon sugar .

The energy ofwinds also may b e referred back t o t he sun’

senergy . Wind i s not only used t o propel ships but also

to run windmills which are used especially for pumpingwater and gr inding grain (Figure The windmills of

Holland are of considerable hi stor ic interest, but Amer ican

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222 GENERAL SCIENCE

coated with a sensitive substance s imilar t o that on the

film , and exposed t o light . The pr int which is producedhas t he l ight and dark places arranged just as they are in

t he object (Figure Explain why this is true . Lightother than direct sunl ight may b e used, but sunl ight is muchmore active .

FIGURE 162 . PRINT MADE FROM THE NEGATIVE ON'

PAGE 22 1.

B lue prints. Blue pr ints, which you have seen con

tractors and bu ilders consulting, are copies of architects’

drawings made in the following way . The drawing made inopaque ink upon transparent linen paper is placed over a

sheet of paper which is coated with an almost color less substance that becomes blue when exposed t o t he light . The

pr int is then washed in water and the positions of t he opaqueink l ines appear white wh ile all the remaining portion of the

paper is blue .

You will recal l from your study ofoxidation that a changein which a new kind of a substance is produced i s called a

THE S UN AS A SOURCE OF ENERGY 223

chemical change . It is evident, therefore , that t he changesproduced by the sunl ight in making pictures and blue pr ints

are chemical changes.

Prob lem 2 . Oth er ch emical changes produced by the

sun ’

s energy— The power of t he sun’s rays t o produce

what we call chemical changes, illustrated in t hemaking ofstarch in plants and in t he making of pictures , is also shownby some rather common phenomena . (a) Fading ofcolors.

(1) What is t he appearance of portions ofwall paper whichhave been covered by pictures as compared with t he re

maining part of t h e wall ? (2) What is t he appearance of

your straw hat after it has been worn in t he sunl ight forseveral weeks? (3) Give other examples of change s of th i skind which you have noticed.

(b) Action upon living animals’

and plants. (1) Whatis t he effect of the sun upon t he skin ? Will l ight of a gas ore lectr ic lamp , or heat of a stove or furnace , produce t he samechanges? (2) What is the effect of exposing t o t he sunlightparts of a plant that have been kept in darkness, as a potatoor a stalk ofbleached celery ? (3) What is the effect of sunl ight upon bacter ia ? This is t he result ofa chemical changein t he l iving matter .

Prob lem 3 . How direct use may b e made of th e sun’

s

energy . (a) Cold frame and sun parlor .

— A large partof t he sun’

s energy is turned into heat when it str ikesthe earth . Much of this energy radiates back into space ,and while it is considered that no energy can b e destroyed,yet so far as it s utility t o us on t he earth is concerned, it i slost . The effect of clouds in preventing t he direct escape ofthis energy into space has been touched upon e lsewhere .

The cold frame and sun par lor are other examples of the

capture of th is energy (Figure In both of these cases

24 GENERAL SCIENCE

rays of the sun,in the form of l ight

,pass through the glass ;

but t he heat into which it is changed does not pass throught he glass easily, and as a resultthe space inclosed in t he glassbecomes considerably warmer thant he outside air .

(6) Solar engines. We sometime s wonder what the

world will do for its supply of usable energy after t he coaland oil deposits have been exhausted. Here we have suggested one possible solution . Ift he energyWhich is radiatinginto space could b e caught and

’

used, all demands of energyfor l ight, heat, and power would b e met . The amount ofthis energy is enormous it has been calculated that t heamount of energy of

the sun’s rays fall ingupon the deck of a

ship when t he sun

i s directly overhead,if turned into workwithout loss, wouldb e sufficient to drivet he vesse l at a fairrate of speed.

Efforts have beenmade t o develop a

solar engine by whichthis energywhichnowis lost t o us might be FIGURE —SOLAR ENGINE

applied t o practical uses. In Cal ifornia, by means of greatreflectors, t he sun

’

s rays were thrown upon t he surface of a

boiler composed of a co il of blackened copper tubing (FigureSufficient heat was developed t o run an engine which

FIGURE 163 .—COLD FRAME.

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226 GENERAL SCIENCE

be ing given off is almost beyond our imagination, yet thereseems t o b e no lessening of it . Scientists bel ieve that t heundiminished supply is maintained by t he heat and l ightwh ich are produced as t he particle s that make up t he sun,

which is less solid than t he earth, are drawn toward its centerby t he force of gravitation ; t he energy of gravitation beingchanged into radiant energy .

Therefore , it is bel ieved that at present t he radiant energyproduced by contraction i s equal t o t he '

amount of energycontinually be ing given off by t he sun. Of course , this cannot keep on forever , and in some future per iod,

perhapsmillions of years from now , t he loss of energy from t he sun

will exceed t he supply resulting from contraction, and t he

sun with its planets will gradually become dark and cold .

SUGGESTED INDIVIDUAL PROJECTS

1 . Make a collection of articles showing t he effect of the sun in

causing colors t o fade . Do any colors seem t o be especially resistantt o t he action of t he sun ?

2 . Demonstrate t he process ofmaking a photographic negative.

3 . Demonstrate t he process ofmaking photographic prints.

4 . Draw plans for something that youwant t o'

make , andmake b lueprint Copies of it.5 . Make a cold frame and use it in growing plants.

6 . Make a sailboat and demonstrate how the wind makes it go indifferent directions.

REPORTS

1 . Write a briefhistory ofthe development ofphotography.

2 . Describe efforts that have b een made t o make direct use of the

energy of t he sun by means of solar engines.

THE S UN AS A SOURCE OF ENERGY 227

REFERENCES FOR PROJECT XXI

1. How t o Make Good Pictures, Eastman Kodak Co. Rochester,New York.

2 . Something t o Do, Boys, E . A. Foster . W. A.Wilde 85 Co.

3 . Harper’

s Machinery Book for Boys, Adams. Harper 85 Bros.

(Sun-power . )

4 . All About Engineering, Knox . 85Wagnalls. (Power and

It s Source . )

5 . Boy’

s Book of Inventions, Doub leday, Page 85 C0 . (Harnessingt he Sun.)

PROJECT XXII

MACHINES

DURING t he earl iest per iods ofwhich we have any record,

t he earth was rece iving just as much energy from t he sun

as at present . Little use , however , was made of this energyas compared with t he present times . As

‘

man discoveredt he use of tools and then machines, civilization advanced.

This is now an age of machinery . How man has multiplied his ab lit ies by t he use of mach ines is the project wehave for solution.

Before we can understand how machines have enabledman t o do much more than he could with his unaided hand,

t he meaning of several terms which have been used incidentally a number of times must b e clearly understood.

Prob lem 1 . What is meant by work and force . We

have already defined energy as the power to do work, but justwhat do we mean by doing work? A man who digs a ditchor shove ls coal i s doing work . Steam wh ich moves a piston,

which in turn Operates a pump, wh ich lifts water t o a tankon t he roof

, does work. Th i s water in turn,we know, as it

descends may operate a motor wh ich will run a sewing ma

chine or a churn, or may generate electr icity which may

run a motor , or b e'

changed into heat t o be used again In boiling water t o produce steam . In raising

’

t he water , work isbe ing done ; also in t he movement of t he parts of t he sew

ing machine or churn or dynamo, work i s being done .

The e ssential of all these examples ofwork is that there is228

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230 GENERAL SCIENCE

t o move a larger weight is two pounds, then the amount ofwork donein moving it one foot is t wo foot-pounds.

Time i s not a factor in consider ing work done . Whetherit take s one minute or a year t o move an object a certaindistance against a uniform resistance , t he amount of workdone is the same . You know that whether a man takes anhour or two days t o shove l a t on of coal from one place t oanother , the work done is t he same .

The rate ofwork is meetsured in t he terms of horse power .

Th is unit was chosen and named by JamesWatt who did so

much for t he development of t he steam engine . A horsepower was supposed t o b e t he rate at which an averagehorse works . A machine of one horse power is able t o do

foot-pounds of work per minute or 550 foot-pounds

per second.

Prob lem 3 . Reasons for using mach ines. A deviceby which forces are advantageously applied t o accomplishwork desired i s called a machine. Name t he machineswith which you are most familiar , and state t he purpose of

each. Explain, as far as possible , how t he invention of thesemachines has resulted in t he accomplishment of a greateramount of, or more satisfactory, work . The chief advantagesgained in t he use ofmach ines may be made clear by a few

simple examples .

(a) What is the advantage of a clawhammer in pulling out a nail (FigureCan you exert sufficient force with t he

fingers t o pull t he nail ? Give other examples showing that by use of a machine

FIGURE 166 .

greater force may be exerted at a particular point .

(6) What are t he advantages gained In t he use of a sew

MACHINES 23 1

ing machine ? Why does a country doctor use an automobile instead of a horse and buggy as former ly? Giveother examples showing how speed is gained by t he use of

machines .

(c) What is the advantage of using a single fixed pulley ,as in raising a flag t o t he t op of a flagpole ? Give otherexamples in which an advantage is gained by changing t hedirection of t he force .

Complex machines. Most mach ines, such as a sewingmachine, typewr iter , clock, automobile , or thresh ing machine , are so complex that, at first sight, t o gain an understanding of their mechanism seems almost an endless task .

It will be found, however , that each of these machines is a

combination of a large number of simple machines whichcan easily be understood . These simple machines are t helever , t he wheel and axle, t he pulley, t he inclined plane,t he wedge , and t he screw.

Prob lem 4 . How th e lever is used in doing Work.

1 . Let us suppose that a heavy rock must b e lifted, and wefind that we are unable t o do it by hand . By t he use of a

strong beam or a crowbar (a st rongSt ee l bar) in the way indicated in thediagram , t he lift ing is accomplishedWith little difficult y (Figure

FIGURE 167 .—

,CROWBAR.

The bar const itmt es a lever ; t he point’

on which it restsis the fulcrum, and the portions of the bar on e ither side

of t he fulcrum are the arms. The amount of force thatmust be applied may be determined by t he following ex

Experiment .—Use a yard or meter stick as the lever ; use a 10

pound weight, placing t he lever on t he fulcrum in such a way thatone arm is t en times as long as t he other . Place small weights on the

232 GENERAL SCIENCE

end of t he long arm until the lever balances on t he fulcrum and t he

weight is lifted from t he tab le . What weights have you placed on t he

long arm ? Vary t he experiment by putting t he fulcrumat differentplaces, thus changing t he relative length of t he arms.

It will b e noted that t he force needed t o l ift t he we ightis inversely proportional t o t he length of t he arms . Therefore

effort Its arm weight or resistance X its arm .

The slight var iations fromth i s are due t o the we ight of

the lever , and t he smal l amount of fr iction between‘

t he

lever and fulcrum . Measure t he distancethrough wh ich each arm moves . What are

your conclusions ? Compare t he amount of

work done at t he end of eacharm .

Thi s exper iment is duplicatedin t he action of the seesaw wh ichmost ofyou have tr ied . What is FIGURE 169 .

t he position of a heavy boy and —SCISSORS .

FIGURE (68.

that of a light boy ? Compare Why is the ‘cord

—T0 NGs. t he distances through which each5

0

212233;end °f

Why S

'

uch a moves. Give all t he uses youcan of levers of this kind (Fig

ures 168 and These are called levers of the first class.

2 . Consider ing t he whee lbarrow as a lever , where is t hefulcrum ,

t he resistance or we ight, and t he effort or power ?

Why is it easier t o l ift a bag of flour in a wheelbarrow than

directly by hand ? Would making the handles longer causeit t o b e harder or easier t o l ift t he load ? Why are t he handlesnot made longer ? Give other examples of levers with t hesame relative arrangement of fulcrum , resistance or we ight,and t he effort or power (Figure In these levers

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34 GENERAL SCIENCE

t he anchor of a ship , or move buildings (Figure Most

of us have seen t he de l ivery man on a coal wagon raisingthe b ed of the wagon containing several tons of coal by

turning a crank at t he side of it . It

does not seem d ifficult, although he i sraising a we ight many times greaterthan he would be able t o

’

l ift unaided.

The reason for t he use of t he crank,

which is really only a spoke of a largewheel, may b e understood by consider ingit as a lever .

Compar ing this WIt h a lever , what may

b e Considered t o b e t he fulcrum , whatt he power arm ,

and what t he we ight or resistance arm ?

Explain t he advantage in t he use of t he Windlass , and itsmodifications In pulling or lift ing heavy we ights . Explaint he ease with which t he grains of coffee are crushed byth e hand coffee gr inder , and with which meat is chopped bythe kitchen meat chopper .

2 . Cogwheels and wheels moved by belts.

— In machinesmuch use is made of cogwhee ls . With these , as withother simple machines, power may be gained at t he ex

pense of speed, or speed may be gained at t he expense of

power . The h igh and low speeds of the automobile illus

trate this fact very we ll . Along t he level road the car runs

in high gear ; but as soon as it begins t o climb a steep hill,t he dr iver , by means of a lever at h is side , shifts t he gear s

so that a different cogwheel (a smaller one) engages t he

crank shaft . The machine now has greater power , but lessspeed. Most automobiles have three speeds ; first, second,and third, and the force exerted by the machine is in inverse

ratio t o t he speed .

FIGURE 172 . WELL

WINDLAss

MACHINES 35

With an apparatus such as shown in the diagram (Figurestate how much force

'

must be applied on t he crankt o exert a pull of 2000 pounds .In bicycles and in some motor trucks, a chain i s used t o

transfer t he power exerted by t he pedals upon t he sprocketwheel t o t he axle of t he rear

dr ive wheel . In this case as in

cases of cogwhee ls that are incontact or mesh directly, t hegreater t he size of t he sprocketwheel , t he

'

greater t he speedt he machine . possesses, with ,however , correspondingly lesspower '

to climb hills .Belts are very commonly

used in factor ies t o convey FIGURE3 173 .-PART OF A DERRICK.

pdwer t o machines . By 3 , Comb ination ofwhee l and ax le

graduated ser ies of wheels, t heand cogs

speed and t he force exerted by the machine may be regulated. A very simple example is seen in t he foot powersewing machine . The heavy rim of t he small whee l, because -of it s inertia (t he tendency of a body t o remaIn In

t he condition of rest or motionin wh ich it is) , makes t herunning of t he machine much more even,

just as does t heflywhee l on an automobile .

Why is t he belt whee l on an engine that runs a threshing machine large , while t he belt whee l of t he threshingmachine itse lf is smal l ? Belts are able t o move t he whee lsbecause of

’

fr iction between t he be lt and t he whee l .Prob lem

,6 . Why pulleys are used.

— We can raise a

window fitted with weights any distance and it stays there .

The pulley reduces t he fr iction. If t he cord support ing

236 GENERAL SCIENCE

FIGURE 174 .—PLACING HEAVY P IPE IN POS ITION.

Use of b lock and tackle in putting in place heavy stee l pipe , in con

struc tion of an aqueduc t . The port ion of the aqueduc t shown here

const itutes a siphon by which water is carried over the h ill in the

background.

the weight ran through t he opening in t he window casing,without t he pulley , would t he window move so easily, andwhat would be t he condition of t he rope and t he edge of t he

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238 GENERAL SCIENCE

itself is Ignored ? How far will the rope have t o be pulled t o lift t heweight 10 feet ? In lifting heavy weights, t he power rope is usually

connected with a wheel and axle . Explaint he reason for this. Where have you seen setsofpulleys such as this used ?

Prob lem 7 . How inc lined planes are

used in doing work —Which seems to

demand more effort ; walking to the top

of a hill up a gradual slope , or up a verysteep one ? In parks which have hills,how are the paths laid out ? In going upmountains, railr oads take a very windingCr zigzag course instead of go ing directlyup . Wagon and automobile roads are

built in t he same way where a considerable elevat ionz i s t o b e reached (Figure

An automobile which fails t o go t ot he t op of a h il l at high gear , if t he roadis one fourth of a mile . long , will go up

FIGURE 176~ easily at this gear if t he road is severalB LOCKANDTACKLE times longer . In pushing a heavilyloaded whee lbarrow into a door which i s a foot abovet he ground, i s it better t o use a board 2 feet longor one 3 feet long, reaching from t he doorsill t o t he ground ?What conclusion do you draw from these po ints t o which

your attention has been drawn, and from other similarcases which

'

you have observed ? Evidently in these casesas in the use of the lever , the Windlass, and the pulley, indoing a specified amount of work, t he greater the distancethrough wh ich the force or effort works, the less is t he re

quired effort .

The following exper iment will show the relation of effort

MACHINES 239

FIGURE 177 .—ROAD NEAR COLORADO S PRINGS , COLORADO.

Note the grade necessary if the road ran direc t ly to the point where

it disappears .

to length of t he plane in raising a we ight by t he use of t he

inclined plane .

Experiment. - Take a smooth board 4 feet long ; raise one end of

t he board 1 foot from t he ground (Figure Into a t oy wagonput weights until t he wagonand it s contentsweigh 8 pounds ;attach a spring balance t o t he

front of t he wagon and by

means of it pull the wagon up

t he incline , taking care t o keep

the spring balance parallel witht he board. What does t he

spring balance register ? (The

spring b alance will registersomewhat t oo high b ecause of the friction between t he wheels and

t he board. )Change t he raised end oft he b oard t o 2 feet above the ground,and

then t o 4 feet, making note of the force necessary t o pull t he weight

FIGURE 178.

240 GENERAL SCIENCE

up the different inclines. Draw your conclusion as t o the advantageof the use of the inclined plane .

Wedges (Figure ch isels, knives, and common pinsare

'

all really inclined planes . One of t he most interestingof modified inclined planes is t he screw (Figurewhich has many uses with wh ich you are familiar . All

screws are inclined planes, as may be shown by t he .fol

lowing exper iment .

FIGURE 180 . SCREW.

FIGURE 179 —WEDGE° How much is head of sc rew

Is a th ick or a th in wedge easier to lowered in comple te turn 5 ,

drive in ? pitch of screw .

Experiment . Cut a piece of paper into a right-angle triangle,with the shorter side of the triangle 2 inches and the longer one 8 inches.

Wind the paper around a pencil, b egin

ning with t he short side parallel with th epencil (Figure What is t he ap

pearance of t he paper after it is woundaround the pencil ?

You wil l now

under stand how a

FIGURE l8L - DEM0 N3TRATION jackscrew (FigureTHAT SCREW Is AN INCLINED

182) IS ofass1st ancePLANE.

in raising a building or a heavy weight, or how greater pressure may b e brought t o bear by t he use

of a screw clamp , by the nut on a bolt,or by presse s of var ious kinds in

'

wh ich FIGUR5 182 ,_ JACK.

screws are used . The efficiency of the SCREW

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242 GENERAL SCIENCE

After using the pulleys it will b e found that they are

slightly warmer . What, therefore , has become of energy

that doe s not appear as useful work ?Prob lem 9 . How fr iction may b e reduced.

Experiment . -By means of a spring balance , pull an iron b lockup an inclined plane . Note t he pounds of force necessary . Now

put grease or heavy oil on t he plane and on the lower side of the b lock .

Note again t he force necessary t o pull the b lock up the plane . Con

elusion ?

Give example s of the use of oil or grease in machines withwhich you are familiar . Explain why failure t o oil t he

working part s of a machine wil l cause them to wear out

FIGURE 183 .—“ S KIDDING Loos ON SNow.

Why cannot th is b e done if there is no snow ?

more -rapidly why screws may b e screwed into wood more

easily if soap is rubbed on them ; why failure of t he oil

supply of an automobile engine causes the engine to become

MACHINES 243

overheated ; why the wheel on a wagon or automobilewillsometimes refuse to turn i f it has not been proper ly o iled .

(Note that metal expands when heated.)

Experiment. By means of a spring balance pull a small box

filled with weights or sand up an inclined plane . Note t he force re

quired. Now -put rollers under t he box and again pull it up t he same

incline . Note t he force required.

Can you skate faster with roller skates fitted with ballbear ingsor with those which have plain bear ings ? Is it easiert o slide a barre l alongon it s end or t o roll it ?All automobile and b icycle whee ls have rol ler

(Figure 184 a) or bal l

(Figure 184 b) bear ings .What is your conclusionconcerning the fr ictionbetween surfaces in

which one rolls upont he other as compared with the fr iction between surfacesthat sl ide upon one another ? Name all t he cases you know

where t he efficiency of machines is increased by the substitution of rollingfriction for sl iding fr iction.

Bear ings are usually made of different mater ial from that of t he axles thatrest upon them . This is done because

17 10 0 13

251

54 b—BALL generally the fr iction between two sur

RINGS

faces of different mater ial is less thanthat between surfaces of t he same mater ial .Prob lem 10 . Is fr iction ever use ful ? — Since we haveseen how friction lessens t he efficiency ofmachines which we

FIGURE 184 a.—ROLLER BEARINGS .

244 GENERAL SCIENCE

use in accomplishing work, we are l ikely to conclude thatfr iction i s one of our greatest enemies, and that our everyday work and t he work of the world would b e done muchbetter if all fr iction were e l iminated . Let us see if th i sconclusion i s a correct one .

Let us suppose that instead of raising a piano t o a h ighwindow, we are lower ing it from that position ; what effectwill friction have ? What would happen t o an automobilegoing down a mountain Side , if the brakes should fail towork ? What would happen t o an automobile in the trafficofa city, if it had no brakes ? It i s as important to have thebrakes in good working order as t o have the engine workingwell . Brakes do the ir work by increasing fr iction.

A train of cars we ighs many hundreds of tons . Becauseof inertia, a large amount of force i s necessary t o start it .The energy is supplied by the burning of t he coal or oil with int he engine , but t he energy or force i s applied between t he

dr ive wheel s and t he track . If t he track should be greased,what would happen ? How i s fr ictionconcerned with the

starting of t he train ?Again, after the train is in motion, inertia tends to keep

it in motion : on a level track t he engine only needing tofurnish suflicient force to overcome t he fr iction between thewheels and t he track . If t he train is going forty miles an

hour , it will b e seen that t he force necessary to overcomeit s inertia will b e very great . How i s thi s force applied tobr ing it t o a stop ? Why is there provision for spr inklingsand on t he rail s ? Why is an automobile apt t o skid on

a wet or oily pavement ?Compare walking on an icy pavement with walking on

a pavement having no ice . Would you b e able t o walk ifthere were no fr iction between your feet and t he pave

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GENERAL SCIENCE

heat is lost from a steam engine ; also t he gasol ine engine .

It has’

been estimated that in t he steam engine about 95 percent of the energy of the coal is lost, and that t he

’

efficiency ofthe engine is only about 5 per cent . In t he gasol ine engine ,since no heat escapes in t he ashes and smoke and less surfaceis exposed t o b e cooled, t he loss is considerably less and theefficiency of t he engine may b e as high as 30 or 35 per cent .In t he oxidation of fue l in t he muscles oft he human body,

only about 25 per cent of the energy is transformed intoworking energy ; 75 per cent of ittaking t he form of heat . Explainwhy we become so heated whileexercising . Suggest how Sh iver ing,whSn we are cold, may b e of valuet o t he body .

Prob lem 12 . Th e working of

th e gas e ngine .

— The gas enginehas become of great importancenot only because of its economyof fuel , but also because of it s easeof operation and l ightness . It s

combination of great power with

FIGURE 186.—MOVEMENTS OF

l ight we ight has made possible t he

plsmN m A FOUR-CYCLE EN marve lous development of t he alr

GINE plane and automobile . You willb e interested in looking into the working of the gasolineengine as shown in t he motor of an automobile .

The successive positions of the pist on.may b e seen fromthe examination of t he accompanying diagrams.

First or suction stroke .

—The mixture of air and gasolinepasses into t he cylinder . Note that t he gasol ine is not a

l iquid but a gas, having become vapor ized in t he carburetor .

MACHINES 247

Second or compression stroke.

—The mix ture of air and

gas is compressed.

Third or power stroke. At the end of the compressionstroke , the air and gas mixture is exploded by t he spark thatpasses between the two wires, and the piston i s forced downward.

Fourth or ex haust stroke.

—The piston passes back intot he cylinder , forcing out the gases which remain after theexplosion. The piston i s now in position for t he beginningof the suction stroke again. Note the posit ion of the intakeand exhaust valves at each stroke .

Of the four strokes of t he piston, how many are power

strokes ?As four strokes are necessary to complet e the cycle (circle) ,

an engine of th i s kind is known as a four-stroke cycle engine .

The power deve loped by the explosion in t he cylinder i sapplied t o moving the automobile by having the piston rodsconnected with t he crank Shaft, wh ich i s made t o rotate byt he up

-and-down stroke of t he piston rod. By a ser ies ofcogs called gears, t he power is applied to the rear axle, causing t he wheels t o turn.

Need for a flywheel. What causes the engine to run

between the times of t he power strokes? A one-cylinderengine would not run if a heavy flywheel were not at

t ached t o a continuation of t he crank shaft . The powerstroke sets In motion t he flywhee l which by its rotationcarr ies t he crank shaft around until the piston i s in positionfor t he next power stroke .

Advantage of a number of cylinders. The first automobiles made were equipped with one-cylinder gasoline engines,but now they are fitted withf engines having a number of

cylinders ; four , six, e ight, twelve , and in‘

airplane engines

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250 GENERAL SCI ENCE

SUGGESTED INDIVIDUAL PROJECTS

1 . Plan and carry out a series of demonstrations t o illustrate thevarious uses of levers.

2 . Construct a Windlass and demonstrate it s'

use t o t he class.

3 . Construct a set of cogwhee ls by which power is gained at the

expense of speed.

4 . Construct a set of cogwheels by which speed is gained at t he

expense ofpower .

5 . Demonstrate t he use of cogs in several machines. Calculatet he kind and amount of advantage gained.

6 . Construct a t oy machine in which b elts are used.

7 . Construct several sets ofpulleys and demonstrate their use .

8 . Construct an inclined plane and Show it s value .

9 . Work out t he different kinds of simple machines used In t he

construction of the sewing mach ine or other machines familiar t o you.

10. Work out t he efficiency of a numb er ofmachines.

1 1 . Demonstrate t he various kinds ofknots describ ed in t he Manual

of the Boy Scouts of America .

12 . Make a Simple cylinder with piston t o illustrate t h e action of

t he piston of an automob ile cylinder .

REPORTS

1 . How things that were done by hand a hundred years ago are

now performed by machines.

2 . How t he power developed by t he automob ile engine is transmit t ed t o t he drive wheels.

REFERENCES FOR PROJECT XXII

1 . Great Inventors and Their Inventions, Bachfx1an . AmericanBook Company .

2 . Harper’

sMachinery Book for Boys, Adams. Harper 85 Bros.

3 . Mechanics of Sewing Machines. Singer Sewing Machine Company .

4 . St ories ofUseful Inventions, S . E . Forman . Century Company .

5 . The Story ofAgriculture in t he United States, Sanford. D. C.

Heath 85 Co.

MACHINES 251

6. The Story of Iron and Stee l, Smith. D. Appleton 85 Co .

7. The Romance ofModern Mechanism , Williams. J . B . Lippin

cott Company .

8 . Stories of Inventors, Doub leday, Page 85 Co.

(Automobiles )

9 . The Romance of Modern Locomotion, Williams. J. B . Lip

pincot t Company .

10. Historic Inventions, Holland. Geo . W. Jacob s, Philadelphia .

11 . The Boy Mechanics. Chicago Popular Mechanics Company .

PROJECT XXIII

ELECTRICITY AND MODERN LIFE

IF a man who l ived a century ago should V i sit us, he wouldb e much surpr ised at t he many changes wh ich have occurredsince h is time . . Especially would he be amazed at thoseinventions wh ich depend upon e lectrical energy . Elec

t ricity was be ing studied by some of t he scientists of h i stime , but probably.none of them had t he faintest idea of the

practical import ance that it would have .

FIGURE 188.—GRAND CENTRAL TERMINAL , NEW YORK CITY, BEFORE

ELECTRIFICATION.

Th e first e lectr ic motor , a very ineflicient one , was con

structed in 1838, and it was not until 1871 that really efficientmotors and dynamos were used . Electric lighting

,on a

commercial scale was used for the first time in Pari s andLondon in 1877 . Think of the many

'

things which thisvisitor from a previous century would see for t he first time .

Make a list of t he appliances of present day l ife which makeuse of electr ical energy.

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254 GENERAL SCIENCE

covering just above or below t he bell itself, you have noticedtwo small spools of wire lying Side by side . Each i s madeofa rod of iron, around wh ich i s wound some covered Copper

When t he current from t he batter ies passes throughth is copper wire , it magnetizes (makes a magnet of) the

rod of iron. One end of t he wire i sconnect ed with one . of t he binding

posts. At one end of th e spools or

coils i s an iron bar called an arma

turé he ld in position by a spr ing,so that when t he circuit IS open

(that is, when the push button i snot pressed down bringing t he two

ends of t he wire into contact ) it doesnot quite touch the iron centers of

the Spools .From the diagram (Figure 190)

FIGUREnote t he course taken by the current

TION OFCURRENTTH'

ROUGH

AN Er ecm c BELL .

of elect rICIty In passing from the WIre

connected with one binding post t ot he wire connected with t he other . Note also that t heclapper i s connected with the armature . When t he circuitis closed , it will b e seen that the coils are magnetized and

the armature is drawn toward the coils, causing t he clapperto

,str ike t he bell .The pulling of t he armature toward t he coils breaks the .

circuit . Immediately t he coils lose the ir,

power t o at

tract t he armature , which spr ings back and closes t he cir- x

cuit . Again t he coils are able t o attract t he armature , andthe clapper str ikes t he bell . This breaking and makingof t he circuit continues as long as pressure is maintainedon t he push button.

ELECTRICI TY AND MODERN L IFE‘

255

Prob lem 2 . How magnets are used. The current of

electr icity passing through t he coil of wire gives t he iron

rod around which it is wound the power of a magnet . Thiskind of magnet is t em

porary,possessing its

power only when the

current of e lectr icity ispassing through t he

wires . For this reason

it is cal led an electro

magnet (FigureElectromagnets are used FIGURE 19 1°

in many e lectr ical devices (Figure 192) among which are

telephone , te legraph , and wireless apparatus, ignition sys

A S IMPLE'

ELECTROMAGNET.

FIGURE 192 .—DYNAMO ATTACHED To AN AMBULANCE.

~ The current generated by th e dynamo produc es an e lec tro-magne t

wh ich is used to remove pieces ofmetal from eyes .

256 GENERAL SCIENCE

tem of automobiles, and in e lect ric motors and dynamos.

‘

Large electro-magnets at tached to cranes are used t o

FIGURE 193 .—ARRANGEMENT OP IRON FILINGS BETWEEN POLES OFAMAGNET.

lift masses of iron wh ich may be dropped at t he desiredspot by simply breaking t he circuit .The action of permanent magnets may b e observed by

exper imenting with a common horseshoe or bar magnet .

Experiment . Place t he magnet under a piece ofpaper over whichiron filings have b een scattered. Gently tap the paper and ob serveth e position taken by t he filings (FigureExperiment .

—Rub a needle along t he magnet and move it nearsome fine iron filings. What has happened t o t he needle ? Suspend

t he needle horizontally by an untwisted silk thread. Move one end

(pole ) of t he magnet near one end of t he needle . Reverse t he magnetand approach th e same end of the needle with th e other pole of the

magnet. What is t he result ? Allow the needle t o remain suspended

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258 GENERAL SCIENCE

an Ital ian University (Figure You can easily makea cell of this kind.

Experiment . In a jar containing dilute sulphuric acid place two

metal plates ; one of zinc and t he other of copper . If each plate (calledan electrode) is connected by means of a wire with t he b inding posts ofan electric b ell, the b ellwill ring . After a few minutes t he b ell ceasest o ring although the circuit has not b een b roken.

An examination of the copper plate will Show that it iscovered with bubbles of'a gas, so that t he acid is not able t otouch it . The battery is now said t o b e polarized. If t he

bubbles are rubbed off, t he be ll will again begin t o r ing .

Var ious‘

methods have been used t oprevent this polar ization .

‘

One methodis illustrated by t he gravity cells . In

t his cell , t he Copper is placed at t he

bottom of t he jar in a solution of

copper sulphate . (blue vitr iol) ; and

t he zinc near the t op in weak sul

phuric acid. The blue vitr iol solu

t ion is heavier than t he acid, and

remains at t he bottom ; hence t he

CELL.

name , gravity cell (Figure

A , solut ion of zinc sul_ The blue vitr iol or copper sulphate

phate 3 . solut ion:of solution prevents t he gas (hydrogen)

zfp

c

p

o

’

gpit’

o

phate ' Z’ zmc ' from reaching t he Copper plate, but

it causes copper t o separate from

t he solution and be deposited on t he Copper plate as a

br ight layer .

In t he Daniell cell, the zinc and sulphur ic acid are in a

porous cup which is placed in a jar containing t he Copper

and blue vitr iol solution (Figure In another form of

cell , one electrode is carbon and t he other zinc, and t he

FIGURE 196. GRAVITY

ELECTRICI TY AND MODERN L IFE 259

l iquid in which they are immersed is a strong solution of

sal ammoniac (ammonium chlor ide) .The dry cell, which for most pur

pose s is more convenient than any

other,is like t he last ce ll mentioned,

except that , instead of a jar , a cup orcylinder made of zinc is used as t he

container , and this forms one e lectrode

(Figure Then instead of sal

ammoniac solution be ing used, a moistpaste saturated with sal ammoniac andusually containing manganese dioxidet o prevent polar ization, is packed be

FIGURE l 97.—DANIELL

tween t he carbon and th1s z1nc out er CELL.

wall .Prob lem 4 . How e lectricity is measured : volts, amperes,

kilowatt s . In all t he ce lls discussed, you have not iced thatthere has been greater chemical action at t he zinc e lectrode

than at t he other . Th is gives r iset o what may be called an elect ri

cal pressure or electromotive force

(E . M . F.) and causes a currentsomewhat as differences in water

pressure wil l produce a current .This current passes from the zinct o t he other e lectrode withint hecell , and from t he carbon t o t he

zinc e lectrode thr ough t he wirecir cuit .

The unit of electromotive forceis called t he volt . It is approx i

FIGURE 198.—DRY CELL. mately t he electromotive force of

260 GENERAL SCI ENCE

the simple voltaic ce ll . By connecting t he several cells inseries that is, by connecting t he carbon of one ce l l witht he z1nc electrode of the next one

,et c .

, t he voltage or e lect romot iv e force of the bat t eryo f ce lls will be equal t o t he

sum of t he e lectromotive forces of t he individual ce lls .The e lectr ical pressure is measured by an instrument calledthe voltmeter .

The pressure in a water pipe may be very great, but yetthere may be very little , if any,

flow of water becauset he faucet opemng 1s quite small . On t he other hand, t hepressure may be re lative ly low with a large flow, providingthere is nothing t o obstruct t he current . In t he same way,

t he amount of e lectr icity that passe s through a wire depends upon the voltage or pressure , and upon the resistance .

The unit of resistance is called an ohm,in honor of Georg

Ohm , an investigator in e lectr icity, who’

worked dur ing t heearly part of t he nineteenth century .

The unit of current is called an ampere, in honor ofanothergreat scientist who was contemporary with Volta and Ohm .

The relation of current, e lectromotive force, and resistancet o flow is expressed in Ohm’s law :

1 t r t'

f rCurrent

e ec w e 0 ce

or Amperes or Ohmsres1st ance

VoltsM peres

The instrument used t o measure the current is called an

ammeter . A rheostat is a device by which t he amount of

resistance may be controlled. Just as t he amount of workdone by water power depends upon the pressure and t he

amount of water , so t he work done by an electr ic currentmay b e determined by multiplying t he voltage (pressure)by t he amperage (amount of electr icity) .

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262 GENERAL SCIENCE

It is by t he use of t he induction coil that the sparks areproduced wh ich explode t he gasol inevapor in t he cylinders

of a. gasoline engine , and which send out t he e lectr ic waves

of th e wireless telegraph . An induction coil is also an

essential part of t he transmitting apparatus of a long dis~

t ance telephone .

In t he wireless telegraph , t he e lectr ic wave s act upon t he

antenna, wh ich is made of a number of parallel wires suspended on insulating supports from a mast or tower , and con

nect ed by a single wire with a rod on one Side of t he spark

FIGURE 200 —U. S . ARMY WIRELESS OPERATORS RECEIVING MESSAGES

PROM AN AIRPLANE, TOURS , FRANCE.

gap. Electr ic waves pass out into surrounding space fromt he antenna and cause similar e lectr ic waves in the antennaof t he rece iving station, which by means of pieces of ap

paratus called crystal detectors or audion detectors, are

made susceptible ofbeing detected by a telephone rece iver .

Prob lem 6 . How mechanical energy is changed into

electrical energy by th e dynamo.

— In our discussion of

ELECTRI CITY AND MODERN LIFE 263

oxidation of fuel, t he use of water power , et c .

,we under

stood that heat energy and mechanical energy may b e transformed into e lectr ical energy . This is done by t he dynamo

,

a machine complicated inappearance , which, however

,in it s simplest form

is not diffi cult t o understand.

You will recall that inthe electr ic bell a current FIGURE

,20 1.

- A S IMPLE DYNAMOOf electr icity passing N, north pole of a permanent magne t .

through t he coil of wire , 5 , 5 0 9 th PO16 Of a pe rmanent magne t

G, pomt of contac t ofb rush es for carrymgwouhd around a Piece Of current into outside c ircuit .

iron, caused t he iron t o

become a magnet . In generating a current of electr icityby a dynamo , t he reverse occurs. If a coil of Wire is

rotated continuously be tween { t he poles of a strong mag

net , an e lectr ic current is produced in t he coi l of wire

(Figure The effect of a magnet in producing an

e lectr ic current in a

coil of wire may be

shown by t he following exper iment

Experiment. Move amagnet in and out of a

coil of wire , t he ends of

which are attached t o a

FIGURE 202 —PRINCIPLE OF DYNAMO. galvanometer (an instru

Current produc ed by i t‘

h rust ing magne t into ament for det ect lng CUI

coil of“

w ire . rents of electricity (Figure202 ) It will b e notedthat

t h e current is produced only when t he magnet is in motion, and thatthe direction of th e current is in one direction when t h e magnet ispushed into the coil , and in the opposite direction when it is pulled out .

264 GENERAL SCIENCE

The essential part s of a dynamo are (1) a rotary coil(armature) , (2) a stationary magnet (field magnet) , and

(3) a sliding contact device for carrying t he cur rent fromt he armature t o t he external circuit . The efficiency of the

dynamo is increased by t he

use of e lectro-magnets as field'

magnets. Large dynamosmay deve lop e lectr ical powerequal t o 8000 or

horse power . For some purF’GURE 203 "

—A S IMPLE COM"

poses an alternating currentMUTATOR.

a and b , two halves of a split tub e is satisfactory,but for other

c onnec ted WIth the two ends of the purposes a continuous cup0 0 11 of the armature . and

two b rush es c onnec ted w ith the ex Tent In one dlI‘eCt Il l S

te rnal Circuit L , L S , Shaft upon necessary . By means Of anwh ich a and b are mounted.

attachment called a commu

tator (Figure t he alternating current of t he dynamomay be changed t o a direct current .

FIGURE 204 .—US E OF ELECTRIC MOTOR IN RUNNING S EWING MACHINE.

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266 GENERAL SCIENCE

t inue its rotation, if t he current is reversed at proper int erv als of time .

Prob lem 8 . How e lectroplating and e lectrotyping are

done . It will be recalled that in t he gravity cell , in whichthere was a solution of Copper sulphate , a layer of copperwas deposited on t he copper e lectrode . By this processt he e lectrode was really Copper-plated. Copper-plate someobject such as a piece of t in or nickel as follows.

Experiment . - Suspend in a jar of copper sulphate t he ob ject t ob e plated, and a piece of copper ; connect t h e former with t he nega

t ive and the latter with t he positive terminal (pole ) ofa b attery .

Si lver , gold, or nicke l plating may be done in a similarway . Name var ious objects which have been plated with a

metal . In each case , state the

reason for doing so .

Electrotypfing. Th is power of

the e lectr ic cur rent t o cause a

layer of metal t o be formed on

an object is made use of in

pr inting . This book and nearlyall others are pr inted from elec

FIGURE 206 .—S ILVER PLATING.

t rotype plates . The type is set

a, b ar'

ot silver. solution Of up and a mold of it is taken ina silv er c ompound. C, Ob jec ts wax : The type may nOW

i

beto b e plated.

taken down and used again . The

mold is coated with graphite (a form of carbon) to makeit a conductor , and is immersed in a

’ bath of copper sulphate , in which is suspended a piece ofpure copper .

A current of e lectr icity is now sent through t he l iquidfrom t he copper t o t he graphite-coveredwax plate and in thisway a layer of Copper is deposited on the wax plate . The

ELECTRICITY AND MODERN LIFE 267

wax is replaced then by metal t o give strength t o the mold .

This e lectrotype plate , which is an exact reproduction of t he

or iginal page of type , may be conveniently used t o pr intthousands of copies, whereas the type is awkward t o handleand soon wears down .

In t he pr inting of

newspapers a muchquicker method is

necessary . A ma

chine called t he l inotype i s used . The

operator , by manipulat ing t he keys of

a keyboard verymuch as In us1ng t he

typewr iter , sets t he

type . The type isthen pressed againstme lted metal , and an

impr int made whichis used in pr intingthe paper .

The e lectr ic currentmay also be used inrefining metals thoserefined in this way FIGURE 207 .

—AN ELECTROTYPE.

be ing t he Purest Ob‘

Photograph Of th e plate from wh ich a page

tainable .

Of a b ook is printed.

Prob lem 9 . How h eat is produced by e lectri city.

Name var ious household appliances in which heat is produced by an e lectr ic current . The way in which this isdone is illustrated as follows.

268 GENERAL SCI ENCE

Experiment. Make a circuit of several electric cells and a copper

Wire of t he thickness generally used in making connections. Now

replace a small portion of t he copper wire with fine iron or German

silver wire wound around t he bulb of a thermometer . What is t heresult

The resistance of smal l wires t o the current of e lectr icityis much greater than t he resistance of large wires, and t heelectr ical energy is changed into heat energy . This is

similar t o t he way thatmechanical energy whenresisted by fr iction ischanged into heat energy .

All t he e lectr ic appliances

you have named, such as

fiat irons, toasters , curl ingiron heaters, e lectr ic chafing dishes, e lectr ic stoves,foot warmers, car heaters,bacter iological incubators

E , w ires Offering great resistance to

e lec t ric current . A , wooden handle .

and.

St er lhzers) are heatedin this way (Figure

Industr ially, t he changing of e lectr ical energy Into heatenergy has made possible many important processes. An

intense heat (about 30000

C.) is deve loped in t he electr icfurnace, due t o resistance offered t o t he passage of t he cur

rent . Some of t he uses t o which t he e lectr ic furnace hasbeen put , because of t he intense heat generated , are t he production of carborundum , t he most important abrasive usedart ificial graphite , used in t he manufacture of e lectrodesand lubr icants ; and smelting , t he refining ofmetals.

Prob lem 10 . How e lectric ligh ts are produced. Ob

servation of an incandescent e lectr ic light lamp will show

FIGURE 208 .- ELECTRIC FLATIRON.

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270 GENERAL SCI ENCE

descent lamp , as we l l as with almost every improvementin t he application of e lectr icity, is Thomas A . Edison .

Th e voltage of t he electr icity in the main distributingWires IS very high . You will find

,however , t hat

'

t he electr iclight bulbs in your house are probably labeled 110 volts .A current of much higher voltage is dangerous t o humanl ife . You have probably noticed on some e lectr ic light pole siron boxes from which wires pass t o t he neighbor ing houses.

These boxes are called transformers, and in them t he voltageis changed from 1100 or 2200 volts t o 1 10 volts. Sometimes transformers are used in t he house t o still further re

duce t he voltage of a current used for r inging e lectr ic b el ls,running electr ic toys, et c .

To prevent danger from fire , t he wiresused in a house must b e of sufficiently largesize t o carry t he current without being ap

preciab ly heated, and they must b e inclosed

FIGURE 2 12 . in metal conduits or tubes in walls and par

FUSEt it ions.

.

An amount ofe lectr icity which might prove harmful is pre

Vented from passing into a wire by means -of fuses (Figurewhich are pieces of metal

of a low me lting point inserted

in t he circuit . When t he cur

rent becomes t oo strong t he

fuse me lts and automaticallybreaks t he circuit . Wires mustall b e carefully . insulat ed ; that18 , covered with a mater ialwhich will not conduct an e lect rlc current

. 0

FIGURE 2 13—POS ITION OFCARThe are ttght, which is of very mm IN AN ARC LIGHT.

ELECTRICI TY AND MODERN LIFE 271

high candle-power , may be understood from a demonstration

of t he lamps of a projection lantern. It will b e noted thatthere are two carbons (Figure which are first brought

into contact t o complete t he circuit . When they are pulledapart

,t he circuit is not broken but t he current continues

t o flow across t he space , producing the are . The

carbon becomes hollowed out , and t he carbon be

comes pointed, apparently by t he addition of particlesof carbon t o it . It seems quite clear that particles of

carbon jump across t he gap between t he two carbons.

Prob lem 11 . How th e“

storage battery”is used.

Storage batter ies have come into common use . Most of

you wil l know of some instances of the ir use . Find out

as many examples as you can of t he use of storage batt eries. The following experiment will he lp you t o understand a storage battery .

Experim ent . Suspend two pieces of lead in a very dilute (1—40) solut ion of sulphur ic acid in a b att ery jar . Connect t he lead plateswitha b attery of three or more dry ,

cells. Do you notice signs of any ac

t iv ity in t he b attery jar ? After allowing current t o pass through t helead plat es for about fiv e minutes, disconnect t he dry cells.

Connect t he wires attached t o t he lead plates t o an electric bell .Result

From t he facts that one of the plates became brown and

gas is given off from t he plates dur ing t he process of_charg

ing , what kind of a change do you think is taking place ?The e lectr ic current in passing through the lead platesand thesulphur ic acid causes changes somewhat like the ones weobserved in e lect roplating . The effect is t o make theseplates unl ike each other in a way similar t o that in wh icht he zinc plate is unl ike t he Copper plate in the simple voltaiccell . When t he two changed lead plates are connected

272 GENERAL SCIENCE

with an electr ic bell , t he be ll r ings, showing that t he chemical energy which has been der ived from electr ical energyhas now been changed back again into e lectr ical energy .

About 75 per cent of t he electr ical energy passed intoa storage cell may be recovered again as e lectr ical energy .

FIGURE 214 .—STORAGE BATTERY DISSECTED TO SHOW CONSTRUCTION .

Heat deve loped dur ing the process of charging and dis

charging t he cel l accounts for t he loss.

Lighter storage ce lls have nickel and . iron plates, but thepr inciple of the ir action is t he same . Electr ical energy ischanged into chemical energy which is changed in turn againinto e lectr ical energy when t he cell is discharged. Com

mercial storage cells are made of a large number of plates

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274. GENERAL SCIENCE

SUGGESTED INDIVIDUAL PROJECTS

1 . Construct an electro—magnet.2 . Construct electric cells of various kinds.

3 . Construct a copper or nickel-plating apparatus and plate a.

numb er of ob jects.

4 . Endeavor t o rejuvenate a dry electric cell .5 . Use of ammeter

,and voltmeter in an automobile.

6 . Construct an induction coil .

7 . Make a model Showing how a dynamo works.

8 . Make a model Showing action of an electric motor.9 . Construct a Simple electric heater .

10 . Calculate t he cost per hour of t he different electric lights inyour home or in your father

’

s store .

REPORTS

The story of t he discovery and development of the electric

Give a sketch of t he life ofThomas A . Edison.

Benjamin Franklin and electricity .

The making of electroplates from which books are printed.

The printing of a newspaper .

REFERENCES FOR PROJECT XXIII

1 . Farmers’

Electrical Handbook. Western Electric Company,New York

,50 cents.

2 . The Compass, the Signpost of the World. P . R . Jameson.

Taylor Instrument Company , Rochester , N . Y.

3 . Benjamin Franklin, P . E . More . Houghton Mifflin Company .

4 . Great Inventors and Their Inventions. Bachman . American

Book Company . (Edison)5 . Modern Triumphs, E . M . Tappan, Edit or . Houghton Mifflin

Company . (Edison and Electric Light. )6 . Wonders of Science . Houghton Mifflin Company . (An Inter

view with Edison.)7 . Electricity and Its Everyday Uses, J . F. Woodhull. Doub le

day, Page Co.

ELECTRICITY AND MODERN LIFE 275

8 . The Story of Great Inventions, E . E . Burns. Harper 85 Bros.

(Electric Furnace . )

9 . The Book ofWireless, A. F. Collins. D. Appleton 85Co . (Tele

graph, Telephone . )10 . Book ofElectricity, A . F. Collins. D. Appleton 85 Co .

11 . Harper’

s Everyday Electricity, Shafer . Harper 85 Bros.

12 . Wonders of Science , Houghton Mifliin Company . (The Mak

ing Of a Book. )

13 . Great Inventions and Discoveries, Piercy . Chas. E . Merrill

Company . (Telegraph. )14 . Stories of Inventors, Doub leday. Doubleday, Page 85 Co .

(Telephone )15 . The Boy

’

s Life ofEdison, Meadowcraft . Harper 85 Bros.

16 . Boy’

s Book of Inventions. Doub leday, Page 85 Co . (Elec

tric Furnace , Electric Light, e t c . )17. The WirelessMan, Collins. Century Company ,

Philadelphia .

18 . Historic Inventions, Holland. Geo . W. Jacob s, Phila. (Bell,Edison,

”

Marconi.)

19 . American Inventions and Inventors, Mowry . Silver, Burdett86 Co . (Telegraph, Telephone , et c . )20. Things a Boy Should Know about Electricity. T. M. St .

John, New York.

PROJECT XXIV

RELATION OF LIGHTTO OUR ABILITYTO SEE THINGS

WE have already/

considered the great source of our l ightand the ways in which we produce l ight . Briefly reviewth is . We also understand t he importance

‘

of l ight as energy,and its relation t o other forms of energy . Br iefly reviewyour knowledge of this. In this chapter we shall be con

cerned ch iefly with the relation of light t o our ability t o see

th ings.

Prob lem 1 . How ob jects are visib le . Our commonexperiences prove t o us without further exper iment thatlight must b e present in order t o see objects . Recall ex

periences which prove th is. It i s easy t o understand how an

object wh ich produces light is visible , but how are objectslike books

,chairs

, et c .,visible ? When light str ikes an

object, a book for example , some or all of t he rays of lightare reflected .

A 5

FIGURE 2 15 .—REI=LECTION OF LIGHT FROM A POLISHED AND A MIRRORED

SURFACE.

Arrows represent the re lat ive intensity Of the rays of ligh t .

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278 GENERAL SCIENCE

image or pict ure on t he sensitive inner coat of t he eye , t he

retina, just as such an image or picture is formed on t he

sensitive plate or film of a camera . In some way which wedo not thoroughly understand, nerve fibers carry t o the

brain information of impressions made by t he light on t he

nerve endings, and7'

we become conscious of t he size , color ,and shape of the object .How do you account for t he fact that a room may be light

although t he sun does not shine directly into it ?Prob lem 2 . Cost of artificial lighting of rooms. Name

FIGURE 2 17. HELIOGRAPH .

By means of a m irror ligh t Of the sun is reflec ted to a place many miles

distant . Dots and dashes of the te legraph c ode are produced by a shut ter

operated by th e sende r of the m essage .

t he var ious methods of producing light fOr t he illuminationof rooms when sunlight is not available . We are especiallyconcerned with t he comparative

'

costs of these differentkinds of lights. To determine this, we must b e able t o

measure t he intensity of a light . To do this we must know

RELATION OF LIGHT TO OUR AB ILITY TO SEE 279

FIGURE 2 18 .- REFLECTION OF LIGHT FROM A SLIGHTLY ROUGH AND

A ROUGH SURFACE.

how t he intensity of a light decreases as t he distance from

the light increases . Th is may be found out by t he following experiment .

Experiment . Darken a room except for one small source of light.Arrange pieces of opaque cardboard respectively 1 , 2 , and 3 inchessquare , on supports so that they can be moved away from or toward

FIGURE 2 19 .—RELATION OF INTENS ITY OF ILLUMINATION TO DISTANCE FROM

SOURCE OF LIGHT.

Compare the area OfB and 0 w ith area OfA . What is the intensity Of

ligh t upon one Of th e squares of 0 as compared w ith intensity upon A ?

t he source of light. Place t he l -inch screen one foot from t he lightand place t he second screen so that t he shadow cast by t he first justcovers it .In the same way place t he third screen S0 that it is just covered by

t he shadow. Measure t he distances b etween t he fir st and second and

t he second and third screens. What is t he relation of these distances

280 GENERAL SCIENCE

t o the distance b etween the source of light and the first screen (Figure2 19)

If t he first screen is removed it is evident that the light striking t hesecond screen is t he same that illuminated t he fir st screen . But whatis t h e area of t he second screen as compared with t he first ? What,therefore , will b e t he intensity or b rightness of t he light on t he second

screen as compared with t he intensity on the first screen ?In the same way compare t he intensity of th e light upon the third

screen with that on t he first screen. What conclusion can you drawnow concerning t he decrease

‘

of b rightness or intensity of light as t hedistance from t he source of light increases ?

Your conclusion may b e stated in t he following terms '

The intensity of light is inversely proportional to the square

of the distance from the light-giving body.

This exper iment may b e modified by substituting for t hefirst screen a larger screen in which is cut an opening one

inch square . In this modification of t he exper iment t helight-giving body Should b e surrounded by an Opaque screenin which a small pinhole has been made so that t he lightcomes from a pomt . Unless t he opening is very small t heresult will not be satisfactory .

"The principle which we have discovered in t he preceding exper iment may be used in t he following way t o com

pare t he relative light-giving power of two l ights.

FIGURE 220 .—PHOTOMETER .

An apparatus used to measure the comparative ligh t-giving powerof two ligh ts.

Experiment . Place t he lights t o be tested several feet apart on a

table in a room which is otherwise dark. Slide an upright piece of

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282 GENERAL SCIENCE

estimate t he cost per candle power of var ious kinds of

lights. The following table (Figure 224) has been workedout , Showing t he relativecost of producing a cer

tain amount of”

fl ight .Costs have been based KM WATT HOURS

on t he following pr ices : FIGURE 223 .—FACE OF A KILOWATT HOUR

Candles, 12 cents perMETER'

pound ; kerosene , 15 cents per gallon ; gas, per

1000 feet ; and e lectr icity ,. 10 cents per kilowatt hour .

a nd)” Prob lem 3 . Whyshades and reflec

tors are used.

The effectiveness of

t he lighting ofa roommay b e increasedby t he proper use ofShades and reflectors .In lighting a room

5 3° 35 4° several things must5 IO 0 2 5

Cos/of /000 cand/c -bours in cenls

FIGURE 224 . RELATIVE COSTS OF DIFFERENT be kept In mind

6 0 5 Mont/e

O

LIGHTS " that strong direct

rays of light are injur ious t o t he eyes ; that in some

InvertedMant le OpenFlame UprightMantle

FIGURE 225 .—COMPARATIVE AMOUNTS OF LIGHT GIVEN BY AN OFEN

GAS FLAME AND A GAS MANTLE.

RELATION OF

cases a general illumination of t he

room is desired ; andthat in other casescertain parts or ob

ject s in t he roomShould be more brilliant ly lighted.

Give examplesShowing when a

general illuminationis desired ; whenSpecial parts of t he

room Should b e be tt er lighted. All

these aims are ac

complished by meansof t he use of shades

LIGHT TO OUR AB ILI TY TO SEE 283

m ean s u m To COST PER norm m wa s (TENTHS OF A CENT)

Max imum lo

“ e “ 6(FM/DTai/l fiat /let

5Inyer/edMani/o

as

Junior Upr ig /II Man/la

Q

(Fla/r 7b”) Burner fumed Dan

Mantle Pr/of

FIGURE 226 .—COST P ER HOUR OF DIFFERENT

GAS LIGHTS .

and reflectors . Can you recall any room that has seemed

FIGURE 227. FIGURE 2 8.

Figures 22? and 228 show how small an amount of ligh t passes upward

when ligh ts are shaded,

284 GENERAL SCIENCE

t o be satisfactor ily lighted in which there was not some

use made of shades or reflectors ?

FIGURE 229 .—REFLECTION OF LIGHT’ BY A POLISHED METAL REFLECTOR.

We sometimes hear t he terms, direct and indirect lighting,used. In direct lighting, t he rays are reflected in one general

6 / f

FIGURE 230.

A , reflec t ion and transmission Of ligh t by Opal glass. B , reflec tion of

ligh t by ename led stee l.

direction by t he use of an opaque reflector Figures 229 and

230B ) . Individual reading lamps are usually of this type .

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286 GENERAL SCIENCE

than about 5 per cent of t he light str iking them . Smoothwalls reflect more l ight than thosewhich are rough . Dirtupon t he walls reduces their power of reflection .

Prob lem 5 . Why ob jects have different colors. If we

see t he var ious things around us by reflected light, is it notrather surprising that they should have different colors ?The l ight which comes from one book affects t he nerveendings in t he eye in such a way that it carries a message t othe brain wh ich gives us a sensation of red ; t he l ight from a

book beside it may give us t he sensation of green . The

l ight str iking t he books must b e t he same , for if we put t hered book where t he green one was, it still continues t o bered. Apparently; therefore , t he object from which lightis reflected causes a change which gives r ise t o t he color .

Another illustration of t he production of color by lightis t he color seen at sunset and sunr ise . What colors have

you seen on these occasions ? Have you ever seen t he colorsin water Spray when looked at from certain positions, or

color s along t he edge of broken glass ? What are the colorsof t he rainbow ?These observations all indicate that ordinary light, wh ich

we call white l ight, may be broken up into var ious color s.The truth of this may be shown by t he following ex peri

ment .

Experiment . - Darken t he room . Place a glass prism in such a

position that a beam of sunlight admitted through a small opening

will pass through it (Figure What do you ob serve on t he oppo

site wall ?

Th i s exper iment Shows that wh ite l ight is really a com

b ination of t he colors that are seen in t he rainbow . We

are now ready t o understand why not all objects are white.

When l ight str ikes t he wall, for example , a portion of it ' is

RELATION OF LIGHT TO OUR AB ILITY TO SEE 287

absorbed, and a portion of it is reflected. You have noticedt hat some walls reflect more light than other s . The coverof a green book reflects only that part of t he white l ightwh ich give s us t he sensation of green ; a red book, on t he

other hand, absorbs all t he l ight except t he part wh ich givesus t he sensation of red.

FIGURE 23 1.—BREAKING UP OF LIGHT IN PAS S ING THROUGH A PRISM .

The white paper of th is page reflects almost all of t he lightwhich strike s it, but t he black letters absorb practicallyall t he l ight which str ikes them . A piece of red glass allowsonly red rays t o pass through ; all of t he others be ing ab

sorbed or in some cases partially reflected.

Since t he absorbed light is changed into heat , explainwhy light-coloredclothing ismore comfortable in t he summerand in t he tropics, and dark-colored Clothing is preferredfor winter wear . Explain why the colors of objects may

not b e t he same in artificial light as in sunlight . This can

be Shown in an extreme form by comparing t he colors of a

number of pieces of paper or cloth when observed first bysunl ight, and then by a candle in which is he ld a glass rodwhich has been dipped in common salt solut ion.

Prob lem 6. What is th e cause of th e colors of sunset

288 GENERAL SCIENCE

and sum'ise‘

and of th e b lueness of th e sky ?—What are the

chief colors of Sunset and sunr ise ? In t he exper iment ,in which by means of t he p

’

rism~

you broke upwhite l ight intot he different colors, which colors were bent least, and whichmost , from t he or iginal path of t he light ray ? The at

mosphere , with it s particles of moisture and dust,has some

power of separating t he colors which make white light .Explain now why t he reds and oranges are seen at sunsetand sunr ise . Why are they not seen at midday ?Keeping in mind again t he rays that are bent most by

t he prism , and t he fact that t he atmosphere has some powert o separate t he rays which compose sunl ight , how do you

account for t he bluene ss of t he sky ? This can b e illust rat ed t o some extent by putting a few drops ofmilk into a

jar of water and looking through t he jar at a light . Ex

plain why t he sunsets are apt t o b e most br ill iant in latesummer and fall . Dur ing t he great forest fires in t he

northern United States and in Canada, t he sun appearedorange or even red in color . Explain.

Prob lem 7 . Why eyeglasses are used by some persons.

- You all know people who without glasses must hold a

book very close t o t h e eyes in reading. These nearsightedpersons have trouble in see ing distinctly anything which ismore than a few feet from them . On t he Other hand, youmay have fr iends who are farsighted ; who can read Signsat a greater distance than you can,

but who have troublein reading a book or newspaper he ld at t he ordinary read

ing distance from t he eye . Nearly all persons, as they growolder , become farsighted and you will notice that manybegin t o wear glasses at about t he age of forty or even

much younger .

By t he use of glasses both t he nearsighted and t he far

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290 GENERAL SCI ENCE

The effect of a lens upon a ray of light may b e understoodfrom t he following diagram (FigureLight may b e considered t o

i

b e made of a column of transverse V ib rations. Theseare Slowed as they passinto a denser sub st ance likeglass. You can easily um

derst and how t he columnwill b e b ent if the glassis entered at an angle . In

t he same w ay , as t he ray

of light passes from the

glass into t h e air again, itwill b e b ent . This b endingof th e rays of light (Figur e in passing fromone sub stance into another ,called refraction,

e x plains

t he fact that a stick, projecting at an angle from the water ,appears t o b e bent at t he point where it leaves the water .

Sub -

prob lem 3 . How th e eye is ab le to focus on near and

distant ob j e cts. You willwonder how we can focust he eye upon a distant ob

jec t , and then without any

appreciab le effort, focus itupon something near . The

power of accommodationmay b e i llustrated as

FIGURE 234 .—.

BENDING OF RAYS OF LIGHT

follows. BY GROOVED GLAS S .

FIGURE 233 .— A DIAGRAM S HOWING HOW

A LIGHT RAY MAY BE BENT.

Experiment. Hold a pencil b efore your eyes and read the labe l

on it . How does a picture on th e opposite side of t he room appear ?

Still keeping t h e pencil in the same position,look at the picture . How

does th e pencil appear now ?

RELATION OF LIGHT TO OUR AB ILI TY TO SEE 29 1

In a camera, such a change in focus is brought about bymoving t he lens c loser t o or farther from the sensitive film .

In t he case of the eye , it is of course impossib le t o change thedistance between the lens and t he sensitive inner coat of theeye , t he retina . The same result, however , is accomplishedby changing t he Shape of the lens . This is done by musc leswhich are connected with a tough memb rane or ligament inclosing the lens . Th e musc le by its contraction flattens thelens, with the following result.Wh en near ob jects are t o be looked at , the muscles re lax

FIGURE 235 .

—CHANGE OF FOCUS OF EYE.

Upper figure , eye focused on a near Ob jec t . Lowe r figure , eye focused

on a distant Ob j ec t .

and t he lens, b e cause of it s e lasticity, b e comes more convexand the ob ject is focused upon the retina (FigureSub -prob lem 4 . Cause and corre ction of farsigh tedness

and nearsightedness.

— As a person becomes older , t he lensloses its e lasticity and it b ecomes impossib le for him t o see

near objects distinctly, although his power of see ing things at

292 GENERAL SCI ENCE

some distance remains unimpaired. You can easily see how

t he use of slightly convex glasses will do t he work that theflat lens of h is eye will not do, enab ling him t o see , for e x am

ple , t he pr int of a book as

well as before the lens begant o lose it s e lastic ity .

Farsightedness, not the

FIGURE 236 .—FARS IGHTEDNES S AND ITS result of age . is usually dueCORRECTlON t o t he fact that t he eye

L . lens F. focus ball is t oo short . An examinat ion of t he diagram (Figure 236) will Show that a distinctimage of near ob jects cannot b e formed on t he retina . Thiscondition can b e ocorreCt ed by the use

'

of convex glasses.

Explain .

Nearsigh t edness, on the other hand, is usually caused by the

eyeball b e ing t oo long . I n this case t he image of an ob jecthe ld at the normal reading distance

, or at any distance fartheraway,

is formed in frontof instead of on the retina .

This condition can b e cor

rect ed by t he use of. con

cave eyeglasses(FigureExplain.

FIGURE 237.—NEARS IGHTEDNESS AND ITS

Sub -prob lem 5 .

‘Wh atCORRECTION.

is astigmatism and h ow is it corrected ? — Many personswho are ne ither farsighted nor nearsighted must wear glassesor suffer from headaches. This is caused by a de fect of t heeye called astigmatism, \

wh ich results from the unequal curvature of the cornea (the front of the eyeball) . What effectwill this have upont h e bending of t he different rays of lightthat enter t he eye ? The glasses for these eyes are curvedin such a way that the defects of the cornea are counteracted. If-glasses are

‘

not worn, t he ciliary muscle in it s

e ffort t o b ring about a condition which will result in a c learerimage is overworked and eyestrain and headache result.

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294 GENERAL SCIENCE

Reading by a dim l ight causes overwork of t he musclesof t he ir is in the ir effort t o enlarge t he pupil t o admit all t helight possible . The image is indistinct on t he retina, causing one t o hold t he page closer t o t he eye , throwing an ex

cessiv e amount of work upon t he ciliary muscle . One is

very apt t o abuse t he eye by reading in t he evening as t he

light is fading; t he eye gradual ly accommodating itsel ft o t he lessening light until a condition of excessive strain isreached.

Too strong a light is almost as bad. Th e muscles of

t he ir is make a brave effort t o narrow t he pupil as much as

possible t o Shut out t he excessive light wh ich i s tir ing t henerve endings of t he retina .

A flicker ing or changing in t he intensity of t he l ight coming t o t he eye causes constant changes in t he eye . Fromthis point of view discuss t he best kind of light t o be used

in reading .

Reading on street cars and trains, especially at night ,often results in headache and eyestrain . Explain .

The reading of books and papers pr inted in fine type or

on glossy paper is highly objectionable ; especially is smal ltype objectionable in books used by young persons .Ser ious eye diseases have been contracted by those who

have rubbed the ir eyes with the ir fingers after haVIng beenholding t o a strap in a street car or after having touched

door knobs or railings which have been handled by manypersons. Explain.

Prob lem 10. How a lens makes ob jects appear larger .

—The action of a reading glass or a s imple lens is illust rat ed by t he following figure .

It will b e noticed that t he rays of light come t o t he eye

at t he same angle as though they came from a much larger

RELATION OF LIGHT TO OUR AB ILI TY TO SEE 295

object, and t he brain thus interprets t he image formed on

t he retina .

In t he case of t he compound microscope , t he rays of

light before reaching t he eye become crossed, and also enter

t he eye at a much wider angle ; hence , t he Object is highlymagnified and appears upside down . All instruments such

FIGURE 238.—MAGNIFYING GLAS S .

as the telescope , opera glasses, and projection lanterns,which are used t o give us a magnified appearance of an ob

ject , depend on lenses which cause t he light coming from thatobject t o enter t he eye at a. much wider angle than if t helight came directly from it . The brain, in every case , int erpret s t he image on t he retina as though these wideangled rays were coming directly from t he object .

Prob lem 1 1 . How mot ion pictures are produced.

— The

moving picture machine which has come t o play such an

important part in our l ives in giving us recreation and in

struction is really a projection lantern in which t he picturest o b e projected are very small , and deve loped on a roll oftransparent celluloid or a

‘

similar substance .

The pictures were t aken by a camera in which the photo

graphic film was drawn along by a revolving mechanism ,

thus getting a succession of exposures of moving objects,each exposure differ ing slightly from t he succeeding one ,

296 GENERAL SCIENCE

FIGURE 239 .

—A MOV ING P ICTURE FILM .

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298 GENERAL SCIENCE

he wears clothes wh ich have vert ical str ipes . The way in

which lines dece ive us is illustrated by t he preceding figure .

Endeavor t o explain t he following1 . Why ground glass or glass with an irregular surface

i s used in office partitions.

2 . Why concave mirrors are used behind headlights of

locomotives, trolley cars, e t c .

3 . Why undimmed automobile headlights are not usuallypermitted.

4 . Why corrugated glass i s used in automobile headl ights.

5 . Why a piece of glass will cast a Shadow6 . Th e presence of a wavy appearance over a hot radia

t or or stove , or over a dry road on a hot day .

7 . Why colored glasses are frequently worn at the

seashore and by motor ists.

8 . Why it is more difficult t o see Objects when you

first'

go out at night than later .

9 . Why it is diffi cult t o see when you enter a br illiantlylighted room after having been in the dark .

10 . Why t he inside of a camera is painted black .

1 1 . Why a cake of ice is transparent, and a block of

snow is not .

SUGGESTED INDIVIDUAL PROJECTS

1 . Determine th e relative candle power of t he lights in your home

and the cost per candle power .

2 . Experim ents t o Show the effect of color ofwalls upon t he illumination of a room . (Suggestion. Use long narrow boxes with different ly coloredwalls.)3 . Experiments t o Show that sunlight may b e broken up into rays of

light of various colors, and that rays of light of various colors may b e

comb ined to form white light.

RELATION OF LIGHT TO OUR AB ILI TY TO SEE 299

4 . Demonstration of t he power of cloth ofdifferent colors t o absorb

light, and change it into heat.5 . Experiments t o Show t he action of convex lenses in corr ection

of farsightedness.

6. Demonstration of how ob jects are made t o appear larger by t he

use of a lens or reading glass.

7 . Demonstrat ion of t he focusing of a camera.

8 . Demonstrat ion of a motion pictur e machine .

9 . Demonstration of how we may b e deceived as t o t he Size and

shape of ob jects by t he arrangement of black andwhite portions.

REPORTS

1 . Various ways in which eyes may b e injured, and care that mustbe taken for the ir protection .

2 . The lighting of factories or office buildings.

REFERENCES FOR PROJECT XXIV

1 . Stories of Inventors, Doub leday . Doub leday, Page 85 Co.

(How Moving Pictur es Came t o Be . )2 . Wonders of Science . Houghton Mitflin Company . (Making

Moving Pictures. )

3 . The American Boys’ Handy Book, Beard. Scribners. (Tele

Scopes. )4 . Historic Inventions, Holland. Geo . W. Jacob s, Philadelphia .

(Galileo and the Telescope . )5 . American Inventions and Inventors, Mowry . Silver , Burdett

8L Co . (Torches, Candles, Kerosene, Gas, Electric Lights.)

PROJECT XXV

IMPORTANCE OF HEAT T0 US

THE production of heat and its relation t o other formsof energy have already been considered. Br iefly reviewyour knowledge ofthese matters. Some oft he ways in whichproblems of heat affect our everyday life have been discussed, but there still remain some cases which need furtherattention .

Prob lem 1 . How a th ermos b ott le keeps h ot liquids h otand cold liquids cold.

Experiment . Fill one of two thermos bottles with hot water ;fill the other with coldwater . Set them side by side together with twoordinary bottles filled respectively With hot and cold water . Examineafter t wo or three hours. Results ? Conclusion ?

An explanation of t he structure of

t he thermos bottle (Figure 241 ) willhe lp us t o under stand it s ability t o keephot things hot and cold things cold.

The Space between t he two bottles is

W P ,

a vacuum ; t he air having been pumpedmu m sf‘f‘ from it dur ing t he process of manu

facture of t he bottle . Evidently this

vacuum in some way prevents t he cool

ing or warming of t he contents . We

Fcan understand this better if we realize

IGURE 24 1.—THER

MOS BOTTLE.that coldness is only a lack of heat,

300

Bu o of Case

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302 GENERAL SCI ENCE

Prob lem 3 . What sub stances are good and what are

poor conductors of h eat.

Experiment . Place in a cup of hot water a silver spoon and a t in

or plated spoon. After a few minutes touch the handle of each . Re

sult ? Conclusion ?Experiment. Fill a test tub e with water in which has b een placed

a piece of ice weighted by having wire wrapped around it . Heat t hetest tub e near t he t op. Result ? Conclusion ?

Recall your exper iences on a cold morning of steppingon a bare wood floor ; on a carpet ; on paper ; or on a tile or

stone floor . What are your conclusions as t o t he power of

these different substances t o conduct heat ?These observations are sufficient t o Show you that sub

stances differ very much in the ir power of conducting heat .The metals may all b e classed as good conductors. Theymay be ranked in t he following order

1 . Silver 6 . Tin

2 . Copper 7 . Iron

3 . Alum inum 8 . German Silver4 . Brass 9 . Mercury5 . Zinc

Substances which are medium conductors Of heat are

1 . Rock 5 . Glass2 . Ice 6 . Water3 . Porce lain 7 . P laster4 . Tiling

Poor conductors of heat are

1 . Wood

2 . Asb estos3 . Paper4 . Cork

IMPORTANCE OF HEAT TO US 303

Explain t he following1 . Why birds ruffle up the ir feathers on a cold day .

2 . Why a light-we ight feather or down cover let keeps

one so warm .

3 . Why heat pipes in basement s are frequently coveredwith asbestos, and mats of this mater ial are used underhot dishes at t he table .

4 . Why asbestos is fastened t o t he wal l behind a stove .

5. Why newspapers folded under t he coat will protectone from becoming chilled on a very cold day .

6 . Why t he thermos bottle is stoppered with cork .

7. Why t he water in deep holes in a lake remains colddur ing t he hottest part of summer .

8 . Why iron is better than br ick or porcelain for stoves.

9 . Why bakers’

ovens are sometimes inclosed in br ick .

10. Why t ea-kettles frequently have wooden handles.

11 . Why oven door handles are usually made of coiledwire .

12 . Why dead air Spaces are left between t he walls of a

building .

13 . Why building paper is placed in t he wall of a woodenhouse .

14 . Why the outer vesse l of an ice cream freezer is madeofwood.

15 . Why farmers who plant wheat in t he fall of t he yearare glad t o have much -

snow in winter .

16 . Why t he ticket choppers at t he e levated and sub

way stations keep a wooden box beneath the ir feet in coldweather .

17. Why ice is packed in sawdust.18. Why on a very cold morning outdoors the fingers

will freeze t o the metal head of an ax but not t o the woodenhandle .

I

304 GENERAL SCIENCE

19 . Why iron is a good mater ial for steam or hot wat erradiators .20 . Why a loosely fitting overcoat is warmer than one

wh ich fits tightly .

Prob lem 4 . How houses are h eated. Houses may be

heated by stoves or fireplaces which are located in all or

several rooms . Most modern houses, however , are heatedby furnaces, located in t he basement . What are t he ad

vantages of thi s ? Are there any disadvantages ? The heatproduced by oxidation of fuel in t he furnace is distr ibutedt o t he various parts of t he house by hot air pipe s or bypipes carrying steam or hot water .

Electrical companies are now producing heaters in whiche lectr ical energy is changed into heat energy . These are

especially valuable when only a small amount of heat isneeded as in spring and fal l . How are trolley cars heated ?

Sub -prob lem 1 . How

houses are h eated by h otair . A hot air furnace

(Figure 243) is essentiallya large stove aroundwhichis a metal jacket throughwhich the air passes t o b eheated. Wh at causes theair to pass through the

pipes into the rooms above ?What should be the sizeof the intake pipes as compared with the size of t h e

FIGURE 243 .—HOUSE HEATED BY HOT A IR.

pipes carrying air fromt h e furnace ? In order

that a fresh supply of air may enter a room , there must b ean opportunity for the air alr eady there t o escape . How

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306 GENERAL SCIENCE

radiation, the giving out of heat directly, and by setting up

air currents as was discussed in t he study of ventilation .

Sub -prob lem 3 . How h ouses are h eated by st eam .

—In

a steam heating plant, steam instead of water passes throughthe pipe into t he radiator . This steam in t he radiator con

FIGURE 245.—CIRCULATION . OF WATER , IN THE RADIATOR AND AROUND

THE CYLINDERS OF AN AUTOMOBILE.

The reasons for th e circulat ion ofwater here are the same as in the

pipes and b oile r of a hot wate r h eat ing plant .

denses into water . How does this fact affect t he heating of theroom ? Should the boiler of a steam heating plant b e filledwithwater ? Why ? Explain the need for t he safety valve of the

boiler . Explain why on days when only a small amount ofheatis needed in t he house , steam heat is not so satisfactory as

e ith er hot air or hot water heat . Explain why rooms heated

IMPORTANCE OF HEA T TO US 307

by steam cool offmuch more rapidly after the fire is shut downat night than rooms heated by hot water .

Explain why in all furnace s t he opening of t he door be low

t he firebox make s t he fire burn better, and why the opening

of the coal door checks t he fire .

SUGGESTED INDIVIDUAL PROJECTS

1. Make a fireless cooker.

2 . Find out the value of different kinds of clothing in preventingthe escape of heat from t he body. (Suggestion . Cover b ottles con

taining hot water with various comb inations of cloth, and ob serve howsoon the water b ecomes cool . )3 . Determine by experiments t he power of different sub stances t o

conduct heat.4 . Study t he plan of t he heating system of your house and make a

diagram of it. Explain the reason for the arrangement and t he use ofvarious devices.

REPORTS

Describe t he methods of heating houses in different countries,including the kindsoffuel used.

REFERENCES FOR PROJECT XXV

1 . The Fireless Cooker . Farmers’ Bulletin No. 771 U. S. Depart

ment of Agriculture .

2 . Shelter and Clothing, Kinne and Cooley . Macmillan Company .

3 . The Thermometer and It s Family Tree . Taylor InstrumentCompany , Rochester , N . Y. 1095.

4 . Chemistry of Common Things, Brownlee , Fuller, and others.

Allyn and Bacon

UNIT V

~

RELA-

TION OF SOIL AND PLANT LIFE TO EVERYDAY

ACTIVITIES

PROJECT XXVI

HOW SOIL IS MADE

WE have already seen how plant life is essential t o animallife upon t he earth . Without plant life therefore , there couldbe no human l ife upon t he earth . Explain. In this unitwe Shall consider projects and problems concerned with theproduction of plants .The working out of these projects and t he solution of the

problems that ar ise will in many cases help us t o solve impor-itant problems of animal and human life .

Since t he growth ofplants is dependent on soil it is evidentthat we must consider the projects how soil is formed and

how it is related t o plants . Other projects will naturallybe how plants and animals make use of the manufacturedfood in the ir growth , how plants produce seed, how betterplants and animals are produced, and how plants are pro

t ect ed from harmful insects .It is known

“

that , if we go back far enough in the wor ld’sh istory, there was once a time when there was no soil . The

whole surface of t he earth was rock, just as we find the

earth ’s crust if we dig down through t he soil . An examination of soil may give us some h ints wh ich will he lp us t ounderstand how it has been formed .

308

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3 10 GENERAL SCIENCE

humus, bacter ia, air ; and moisture . The mater ials whichmake up soi ls may be classed as follows (Figure 246)

(a) Humus, or vegetab le mold.

(b) Clay, made up of finely powdered rock . Th e partic lesare less than one t en-thousandth of aninch in diameter . Whendry, clay is powdery ; when we t , it is sticky.

(c) Silt, consisting of particlessomewhat coarser than c lay .

When moist it b ecomes a soft mud and usually crumb les whenit is dry .

(d) Sand, made of rock fragments.

(e) Gravel, composed of large pieces of rock fragments.

Ordinary soils.

are usually made up of a mixture of clay,

FIGURE 247.—DIS INTEGRATION OF ROCK.

Limestone ledge b reaking up and form ing soil.

sand, silt , and humus . Since moisture is so necessary t o

plants, the power of a soil t o take up and hold water is a

very important character istic of it .Prob lem 2 . Ev idence that soil -is now b e ing formed.

Apparently a portion of the soil has been formed from rock .

HOW SOIL I S MADE 1 1

If this is so, then there Should b e indications that such a

change is going on at t he present time . An examinationof t he side of a railroad cut will usually Show gradationsfrom solid rock, through partially disintegrated rock

, to

well-formed soil . The accompanying picture (Figure 247)shows rocks of var iousSizes which have beenbroken off from t he

great mass of rock . Old

marble gravestones withthe ir rounded edges andmore or less indistinctletter ing are indicationsthat rock may be wornaway . These evidencescoupled with the factthat pebbles and smallfragments of rocks are

found in soils indicatethat t he process of soilmaking is still go ing on .

Prob lem 3 . How soil.

has b een produced by

weath er ing — Some of

t he agencies that changerook into SOil can easily FIGURE 248 .

—RUGGED MOUNTAINS SHOW

b e understood. Break a, INC THE EFFECT OF WEATHERING.

rock, and compare the

broken surface with the surface of t he rock wh ich has

been exposed t o t he weather . What is your conclusion ?The oxygen of t he air may act upon some of t he minerals

of t he rocks causing a change which results in the ir crumbling .

3 12 GENERAL SCIEN CE

This is Similar t o t he action of oxygen in causing t he rustingof iron . Carbon dioxide dissolved in water is one of t he

most efficient agents in the breaking down of rocks. It is

t he action of carbon dioxide in water which has producedt he great caves such as Luray Cave in Virginia, MammothCave in Kentucky , andWyandotte Cave in Indiana, as wellas hundreds of smaller ones in var ious parts of t he countrywhere limestone is t he Commonrock . This action can be

shown by passing carbon dioxide through water containinga small amount of fine ly powdered marble .

What do you th inkmight be t he effect uponsome rock of alternateheating and cool ingcaused by t he t em

perature changes of day

and night ?

Experiment . Heataglasstub e and plunge it into cold

water . What happens ? The

cracking of t he rocks by

this means exposes more sur

face for t he action of t he

weather .

What will happen in

FIGURE 249 .—WEATHERED ROCK AT BASE CO’dWeather t o t he water

OF A CLIFF. which is in the crevicesof t he rock ? What ef

feet will this have upon t he rock ? Th is can be illustratedby exposing t o a freezing temperature a tightly stopperedtest tube filled with water . The force due t o t he ex pan

sion ofwater when it changes into ice causes the bursting

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3 14 GENERAL SCIENCE

What'

will be t he effect upon the fragments themselves ?What is t he shape of pebbles and rocks found in a stream ?Why ? Explain how t he valleys of stream s have been cutdown through t he rock . Th is action of water carryingfragments of rock is called erosion (Figure It is ex

act ly similar t o the wayin wh ich a gr indstone isable t o sharpen tools ;both t he gr indstone and

t he metal of t he tool .are

worn away . As t he

streams become less swiftmuch of t he mater ial i sdeposited, so that soil isconstantly being eroded

from t he more elevatedregions and deposited inthe lowlands .Wind erosion. In

FIGURE 251 .—BEECH TREE GROWING ON some parts Of the wor ld

ROCKS .

consIderable erosion ISThe rootspene trate Into c revices and by the ir

growth split th e rocks .done by Wind carryingsand in t he same way

that a sand blast is used in etching glass or in cleaning t hesur face of a stone building . Wind, however , as an agentin t he formation of soil is of very little importance in com

par ison with those already mentioned.

Prob lem 5 . How most of th e soil of northern United

Stat es has b een produced.

— In t he northern part of our

country, pebbles and rocks of all sizes, unlike t he solid rockb ed of that region

,are frequently found imbedded in t he soil

(Figure Evidently the soil and rocks of those regions

HOW SOIL I S MADE 3 15

have not been carr ied there by water , since t he rocks are

scattered indiscr iminate ly in t he fine soil (clay) . Explain

FIGURE 252 .—WATER EROS ION .

Grave l and rock have been e roded from the h ighe r land and carried

down by water.

FIGURE 253 .—SOIL DEPOS ITED BY A GLACIER.

Note the irregularly shaped b oulders.

31 6 GENERAL SCIENCE

t he reason for this conclusion. On examination many of

t he rocks are found t o have scratches on them (FigureAlso if t he soil is removed, t he surface of ’ the country rockwill be found t o have deep paralle l scratches and grooves.

Many thousands ofyears ago, a great sheet of ice , called a

glacier , covered t he northern part of t he United States (Figure As it moved southward, its immense we ight brokeoff fragments of rock wh ich rubbed along the bottom of t he

glacier and ground up t he rocky b ed into a finely powdered

FIGURE 254 .—ROCI< S HOWING GLACIAL SCRATCHES .

soil (clay) leaving great scratches and grooves. Th e clayand t h e boulders, or rocks, became thoroughly mixed int he ice . As t he glacier reached its southern extent , itmelted and t he mater ial in it was deposited there as a

ser ies of r idges of h ills cal led a terminal moraine (Figure

As the glacial per iod gradually passed, the glacier wasunable t o push farther south and as a result a ser ies of thesemoraines have been formed . When the entire ice sheet

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3 18 GENERAL SCIENCE

Prob lem 6 . How soil has b een produced by decay of

organic matt er . Plants gain a foothold in t he soil formedby t he decomposition of rock mater ial and, by the ir own

decay and that of animals which l ive upon them , add t o

t he soil that part of it wh ich causes it t o blacken when

FIGURE 256 .—A GLACIER.

Glacier flowing down side ofMt . Robson, B ritish Columb ia.

burned . Th is organic part of t he soil, or humus (Figureis of special importance in giving it t he proper texture

and increased power of holding water . It is also t he prin

cipal source of nitrogen which is‘

so necessary for plant

growth . If you will recall your study of bacter ia, you w illremember that t hev are necessary in soils in order t o decom

pose t he vegetable and animal matter so that this mater ial

may be used again in t he growth ofplants .

FIGURE 257 .—FRONT OF A GLACIER , MT. RAINIER NATIONAL PARK.

Not ice the broken rock wh ich was carried down and deposited when the

glac ier extended somewhat farther into th e valley .

FIGURE 258.—FORMATION OF HUMUs.

Vert ical sec tion show ing forest floor , humus. soil , and roots.

3 19

320 GENERAL SCI EN CE

SUGGE STED INDIVIDUAL PROJECTS

1 . Collect and put into test tub es specimens of different kindsof soils, including rock and vegetab le material which has partiallychanged into soil .

REPORTS

1 . Evidences in t he United States of t he glacial period.

2 . Description of a glacier . .

3 . Character of t he soil in different part s of your stat e .

REFERENCES FOR PROJECT XXVI

1 . Glaciers of.

North America, J . C . Russell . Ginn Co .

2 . Soils ; Their Properties and Management, T. L . Lyon. Mao

millan Company .

3 . Agronomy , Clute . Ginn Co .

4 . Story of Agricult ure in t he United States, A . H. Sanford.

D . C . Heath Co .

5 . Essentials ofAgriculture , H. W. Waters . Ginn Co .

6 . Th e LandWe Live In, 0 . W. Price . Small, Maynard Co .

7 . Earth and Sky Every Child Should Know, J . E . Rogers.

Doub leday , Page Co .

8 . Th e United States, J. O . Winston. D. C. Heath Co.

(The Great Glacier and It s Effect.)9 . Wonders of Science . Houghton Mitfiin Company .

10. Farm Science , W. J. Spe llman . World Book Company.

1 1 . Elementary Agriculture ; James S . Grim. Allyn and Bacon.

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22 GENERAL SCIENCE

t he condition of t he soil under a layer of leaves or strawwhich has been lying in one place for a long time ?Dur ing dry weather lay a board on freshly cultivated

earth in t he garden,and in a few days compare t he appear

ance of t he surrounding soil with that under t he board.

All of these observations indicate that t he water which iscoming from below is e scaping by evaporation at t he surfaceand that t he loss may be prevented by a cover ing of somekind . Sometimes such a covering IS provided by a layer

FIGURE 259 .—VACANT LOT GARDEN.

Give two re asons for hoe ing a garden.

of leaves called a leaf mulch. But usually such a methodcannot b e employed very ext ensive ly . It has been foundthat hoe ing (Figure 259 ) or

“ cultivating by making a

mulch of dry soil prevents t o a great extent this escapeof water at t he surface . This is because t he small capillary spaces through which the water has been coming from

RELATION OF SOIL TO PLANTS 323

below are broken up . One of t he reasons, therefore, for frequent hoe ing oi-a garden or cul tivating of a fie ld of corn is

to prevent the loss of mo isture from t he sur face of the soil .

The power of different kinds of soils t o absorb water frombe low may b e illustrated by t he following exper iment .

Experiment . Over t he bottom of

each of four or fiv e glass tub es havinga diameter of one or two inches, t iea piece of cheesecloth (Figure

Fill t he different tub es with t he fol

lowing kinds of soil : coarse sand, fine

sand, loam, and clay . Place t he bot

toms of t he tub es in a vessel of water, FIGURE 260 . ABSORPTION OF

and support them so that they will WATER BY S O ILS .

stand upright. After a day examine From left to righ t : loam , c lay ,

t he tub es and draw conclusions.fine sand, c oarse sand.

The finer the soi l t he Smal ler are the openings throughwhich the water passes. How does this exper iment he lp

you t o explain t he effectiveness of t he loose soil mulch ?How does it

'

ex plain t he fact that seeds will grow better ift he earth is pushed down firmly around t hem ?The power of soils t o hold t he rain which falls upon them

is shown by t he following exper iment .

Experiment. Into four funnels in each ofwhich has been placedfilter paper, put equal amounts ofdifferent soils : coarse sand, fine sand,loam ,

and clay . Pour into t he funnels equal amounts ofwater . Catcht he water that runs thr ough in measuring glasses. After pouring t hewater through several times, note t he amount of water that runs

through each and draw your conclusions as t o t he conditions whichmake soils good holders ofwater . Suggest how t he ab ility of t he soil

of a garden t o hold moisture may b e increased.

0 Prob lem 2 . What plants take from th e soil . Chemicalanalysis of plants and exper iments in the ir culture indicate

324 GENERAL SCIENCE

that t he following ten e lements are necessary for theirgrowth : Carbon, hydrogen, oxygen, nitrogen

,potassium

,

magnesium , calcium,iron, sulphur , and phosphorus . In our

study of t he making of starch and wood by plants, we havealready discovered from what source t he plant gets itscarbon,

hydrogen ,and oxygen. Review and explain. Al l

t he other e lements must come from t he soil .Fortunate ly, t he soil usually contains all of these with the

exception of three , in such quantities that there is not muchdanger Of them be ing exhausted. The three which are

l ike ly t o be lacking are nitrogen, potassium, and phosphorus .These frequently have t o be added t o t he soil in some way .

Prob lem 3 . How nitrogen may b e given to t h e soil .N itrogen is found largely in t he organic part of the soil, andIronsequent ly t he addition of plant and animal mater ialwil l increase t he stock of nitrogen. One form of organicmat t er

'

put upon t he soil is horse manure . In some partsof t he country, fish which are use less for food are spread overthe fields . It is said that t he ear ly Amer ican explorersfound that the Indians placed a fish in each hill of corn.

Waste from slaughter houses ; guano, t he excrement of

countless generations of sea b irds ; cottonseed meal ; l inseedmeal , et c .

, are useful sources of nitrogen . The nitrogen innone of these plant or animal substances can b e used by t he

growmg plant until t he bacter ia in t he soi l cause them t o

decay .

N itrate of soda , of wh ich there are great deposits in t herainless regions of Chili, and sulphate of ammonia, which isa by-product of t he manufacture of gas, are other valuablesources of nitrogen .

It has been known for a very long time that a crop ofcloverseems t o enr ich t he soil . As a result of t his knowledge,

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326 GENERAL SCIENCE

mineral part of t he’

soil usable , but as they themselvescontain compounds of these two e lements the ir additionincreases t he supply . Wood ashes spread upon the soilimprove t he growt h of plants largely because of t he greatamount ofpotassium which they contain .

The chief source , however , of potassium fertilizers hasbeen t he great deposits of Stassfurt

, Germany . Dur ingt he war t he United States together with all other countr iesfaced a potassium famine which threatened t o lessen cropproduction . At t he time t he war ended, methods for obtaining potassium from rocks holding it in an unusable formwere be ing perfected. It had also been found that considerable quantities could be obtained from ke lp or seaweed, wh ichis very abundant on some parts of t he Pacific coast . So, ift he war had continued, we could have had a supply ofpot as

sium t o meet all our needs.

One of t he sources of phosphorus fertil izer s is organicmatter such as slaughter house waste and fish scraps ; b one

meal is especially valuable since a large part of t he mineralmater ial of bones consists of a compound of phosphorus .Other important sources ofphosphorus fertilizers are phosphate rocks, and slag from stee l mills. The phosphate rockis found in many of t he southern and western states. The

slag is obtained in t he processof removing phosphorus fromiron in t he making of steel .Prob lem 5 . How plants remove needed materials from

th e soil .— Review what we have already learned concerninghow t he roots of plants are fitted t o take in water . Sincet he dissolved mineral substances in t he soi l are taken in withthe water , t he adaptations of t he roots for taking in waterare also adaptations for taking in the needed mineral substances.

RELATION OF SOIL TO PLAN TS 327

If the ashes of different kinds of plants growmg side byside are analyzed by a chemist, it is found that t he var iousmineral substance s are not present in t he . same re lative

amounts. For example , clover will contain many times as

much lime or calcium as wheat ; while wheat, on t he otherhand, may contain as much as t en or fifteen times as muchSilica as clover . Apparently, t he plant is able t o se lect t hemater ials which it needs. This is known as selective absorp

tion. The explanation seems t o b e that if t he l iving matterof the plant does not take a certain kind of mineral substance out of t he water which has passed into the plantthr ough t he wal l of t he root hair , then t he sap or water inthe root hair becomes saturated with that Special kind of

mineral substance and no more will pass through the wallof t he root hair .

’

If, however , the plant uses a particularmineral substance , then it is constantly be ing taken out of

t he sap and more comes through the wal l of the root hairt o replace that which has been taken out by the

'

l ivingmatter .

Clover , for example , in its growth i s continual ly buildinglime mater ial into plant substance ; and as a result, morel ime comes through t he membrane of t he root hair . Wheatdoes not use near ly so much lime °

and accordingly, verylittle need come through t he root hair t o replace the amounttaken out by t he l iving matter of the plant .Prob lem What plants do with material taken from th e

soil —You have already learned how in the green leavesof t he plant the carbon dioxide of the air and t he

'

Wat er fromt he so i l are made into starch . As a result of t he action of

the l iving mater ial of the plant, t h e starch may be madeinto ce ll walls, and into fat or oil. There are always associat ed with t he l iving matter of t he plant more complex

328 GENERAL SCIENCE

substances cal led proteins. These contain not only carbon,hydrogen, and oxygen as starch does, but also nitrogen,phosphorus, iron, et c . , which have been taken from the so il .The prote ins are necessary for the growth of new livingmatter .

Some of the e lements, in addition t o be ing necessary con

st ituent s of l iving matter and of t he food mater ials forme din plants, have Special duties t o perform . Some seem to

neutral ize acids formed in t he plant ; others are nece ssaryconstituents of t he color ing matter of plants ; while stillothers give firmness t o t he woody substance of t he plant .

SUGGESTED INDIVIDUAL PROJECTS

1. Use different kinds of fert ilizer in your garden and record the

results.

2 . Experiments t o show t he water-retainingpower ofdifferent kindsof soil.

REPORTS

1 . Obtaining potassium from seaweed.

2 . Records of t he amount of various mineralfrom soil by some of t he standard crops.

REFERENCES FOR PROJECT XXVII

l . Soils ; Their Propert ies and Management, T.

millan Company .

2 . Agronomy, Clute . Ginn 85 Co.

3 . Story of Agriculture in t he United State s, A. H. Sanford.

D. C. Heath Co .

4 . Essentials ofAgriculture , H. W. Waters. Ginn 85 Co.

5 . The LandWe Live In, 0 . W. Price . Small, Maynard C0 .

6. Earth and Sky Every Child ShouldKnow, J . E . Rogers. Double

day, Page 85 Co.

7 . Farm Science ,W. J . Spellman . World Book Company .

8 . Elementary Agriculture , J . S. Grim . Allyn and Bacon.

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30 GENERAL SCI ENCE

is another reason why plants and animals, and we , ourselves,must take in food ?In t he work of t he body there is a certain amount of

wear ing awav of it s parts. This wear evidently must bemade good by food be ing built

,

up into t he muscles , nerves,and other parts of t he

body . State , now, t he

three uses made of foodby plants, animals, and

t he human body .

Our next questionnaturally will b e : Whatfoods are good for eachof these purposes ?Prob lem 2 . What

foods are good for fuel,andwhat one s for growthand repair ? Consideration Of the kinds of

food that are eatenunder certain conditionsmay help us t o Solve

FIGURE 26 1.—LUMBERMEN AT WORK. th is problem . PeopleWhy do these men ne ed a large amount l iving in t he Arctic re

of energy-

producmg food? gions must have food

which will produce a great deal of heat . You all

know that fat forms t he greater part of the ir diet . Whatwill be your conclusion,

therefore , as t o t he value of fat in

t he food ? Consider your own diet in regard t o t he use of

fat . Do you eat a greater quantity in winter or in summer ?

The hard work of lumbermen in t he northern woods is donechiefly in winter (Figure They need food which will

USE OF THE FOOD MAN UFACTURED B Y PLAN TS

give them heat,and the power t o do hard work . They eat

much fat meat, asyou would expect, but they also eat a greatamount of molasses, large quantities of potatoes, and otherstarchy foods . This is an indication of t he value of foodswh ich contain starch and sugar .

These observations concerning t he use of fats, starch, andsugar are in harmony with exper iments wh ich have beenmade as t o t he value ofdifferent food substances. Starchesand sugar , which together are called carbohydrates, and fatsbecause they are common t o so many foods, are cal led food

principles or nutrients .

We have already decided that foods,in addition t o furnish

ing energy , are also necessary for growth and repair . For

this purpose it has been found that there must b e presenta food pr inciple or nutr ient called protein, and certainmineral substances . These conta in e lements wh ich are not

present in fats and carbohydrates but which are necessaryfor t he building ofdifferent parts of t he body .

For example , l iving matter contains nitrogen ; and as

prote in is t he onlv nutr ient wh ich contains nitrogen, it i snecessary for growth and repair of l iving matter . Foodscontaining a large percentage of prote in are lean meat, fish ,eggs, milk, cheese , beans, and peas, and t o a lesser extentcereals (oats,wheat, bar ley , and rye) .

Mineral matters are not only necessary for t he making ofnew l iving matter and for t he formation of t he bones of t hebody, but their presence is necessary for t he action ofnervesand muscles, and for t he passing of liquids through t he wallsof t he small blood vessels and through other membranes .Iron has a special duty in forming t he color ing matter of t hered blood corpuscles. Mineral mater ials are very widelydistr ibuted among foods . Most natural foods contain

332 GENERAL SCIENCE

considerable mineral matter , so that usually the ordinarydiet contains a sufficient amount. Milk, eggs, lean meat,leafy vegetables, fruits, and flour made from t he Whole grain

llIlllllIll m [HIHHIB 1Fuel Value

Prot ein Fat Carbohydrates Ash Wat er 3331

35321

33

WHITE BREAD WHOLEWHEAT BREAD

ates : 53 . l hydrates : 49 .7

furl. VALUE: o

BREAKFA ST FOOD“ m " L“

coox ro

1140 CALORIESranroom

Fat :

rbohydrates:

TOASTECORN BREAD

hydrates : hydrat es: 46 .3

Furl. VALUE: MA CARON IFUEL VALUE:

coox ro

1420cuomzs

Carbo FUEL.Ehydrates :

m us.

FIGURE 262 —COMPOS ITION OF BREAD AND CEREAL FOODS .

are especially r ich in mineral matter and very nutr itious.Recent exper iments have shown that unless

,certain

chemical substance s (vitamines) which are found especially

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334 GENERAL SCIENCE

Foods burned outsideof t he body furnish the same amountof energy as if they were burned within t he body . The fue l

.VFue l Value

Fat Carbohydrates Ash Water3

6

56161

352321.

SALT COD

FUEL VALUES.

4 l0 CALORIES

OYSTER

harbohydrat e s: 3 .

rotenn: 6 .2Fat F's

SMOKED HERRING

235 cALomEsran rousu

Prote in

FUEL mus:'

Fur-: L m us

1355 cALomEsPER rouno

FIGURE 264 .—COMPOS ITION OF FISH AND OYSTERS.

value of carbohydrate , fat , and prote in is therefore obtainedby burning known amounts of these nutr ients in an inst ru

ment called a calorimeter , so constructed that all t he heatproduced is used t o heat a measured amount ofwater . The

USE OF THE FOOD MAN UFACTURED B Y PLANTS 335

amount of heat necessary t o warm a kilogram of waterone degree Centigrade , is taken as t he unit . This unit is

Prot ein Fat1000

r

CaloriesWHOLE EGG

wum: ANDYOLK

r: 86 .2

n: l

at :

FULL VALUE orwnou: see Furl. VALUE or umt s

1608 cALomEsl’EB ronno

CREAM CHEESE COTTAGE CHEESE

Wat e

in: 259Water:

in:

sh :

FUEL wuu

momsm rouuo 510 CALORIES ranrouuo

FIGURE 265 .

—COMPOS ITION OF EGGS AND CHEESE.

called a calorie . A pound of pur e starch , sugar , or prote inwill yie ld when burned about 1850 calor ies, and a pound of

pure fat about 4220 calor ies.

It can be seen that if t he amount of these nutr ients in a

336 GENERAL SCIENCE

food are known, it is very easy t o calculate t he fuel valueof t he food. The following table , compiled by Dr . Irving

lllllllllll m m lllllllIlI]1J—‘uel Value

Protein Fat Carbohydrat es Ash Water

CORN

Wat e r : 10.

Ash '1 .5 ydrates: 73 .4 Carboh atesz73

FULL VALU£ :

BUCKWHEAT

1800 CALONES PfOt e lni lo. | 750 CALOMESPearouno

arPenrouuo

hydratesz73 sh :

Wate r: 1600 moms Wate r: 12.0

e in: 11 .8 m rouuoPro

RYE hydratesz77

Ash : 3 .0 Ash : l .0

FULL VALUEln: 12.2

FueL VALUE:

sh : 1.9

FIGURE 266 .—COMPOS ITTON OF VARIOUS GRAINS USED FOR FOOD.

Fisher of Yale, gives the amount of each of a number ofcommon foods wh ich will furnish 100 calor ies .Prob lem 4 . What is th e proper amount of food ? We

know from exper ience that the‘

amount of food needed is

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338 GENERAL SCIENCE

TABLE OF 100—CALOR IE PORTIONS 1

AP PROXIMA TE MEA SURE

EDIB LE PORTION S OF 100-CA LOR IE

PORTION

Almonds

Apples

Apricots, freshAsparagus, cooked

Bacon ,smoked (un

cooked) .

Bananas

Beans, b aked, canned

string , canned

lima, canned

Beef, corned .

dried, salted and

smoked . 4 large slices

porterhouse steak 1 small steakrib s

,lean 1 average serving

ribs, fat

round, free from VIS

ib le fat 1 generous servingrump,

lean

rump, fat

Sirloin steakBeets, cookedBrazil nutsB read, grahamtoasted

white homemade

averagewhole wheat

Buckwheat flour

1Th e Approximate Measure of 100-Calorie port ions is b ased in part upon

Tab le of\100 Food Unit s,

”compiled by Dr . Irv ing Fish er . Th e Weigh t

in Ounces of 100-Calorie Por t ions and Calories de rived from P rot ein are

b ased upon dat a found on page 3 19 of Ch emist ry of Food and Nu t rit ion ,

”

b y Henry C. Sherman .

15 average2 medium

2 large

2 servings

1 thin slice , small

1 large

1 small serving (Paupful )

5 servings1 large saucedish

1 average serving3 servings3 average size

1 thick Slice

2 mediurri slices

(b aker’

s)1 medium Slice

1 thick slice

1 thick slice

cupful

USE OF THE FOOD MAN UFACTURED B Y PLAN TS 339

EDIB LE PORTION S

Butter

ButtermilkCab b age .

Calf’

s-foot jellyCarrots, freshCaul iflower 1CeleryCelery soup, canned

Cheese , American pale1

American red 1

Cheddar 1CottageNeuichatel

Roquefort 1Swiss

Chicken,b roilers

ChocolateCocoa

Cod, saltCorn, green

1

Corn meal

Crackers, grahamsoda

waterCranb erries 1

Cream

Cucumb ers

Dates, dr iedDoughnutsEggs, uncooked

Farina

Figs, dried

Flour,rye

wheat, entirewheat, grahamwheat, average high

and medium

.CALOR IE SAP PROXIMATE MEA SURE IN OUN CE S

DER IVEDOF 100-GALORE OF 100 “ FR OM

PORTION CA LOR IEPROTE IN

PORTI ON

1 tab lespoon (ordinarypat )

1acupfuls (laglasses)2 servings

2 medium

2 servings171; cub ic incheslacub ic inchesIEcub ic inches4 cubic inches cupful)1% cub ic inches (3; cup

ful) (é small pack

age )

1 cub ic inches1 large servinggenerous half squaretab lespoonfuls

1 side dish2 tab lespoonfuls3 crackers

3 crackers

3 crackers

1 cupful (cooked)71

; cupful

2 large

4 medium

doughnut1—12 medium or 2 small

1 large

71

; cupful

cupful

4; cupful

i; cupful

1 A s purch ased .

340

EDIB LE PORTION S

GelatinGrapes

Haddock

Halibut steaksHam , fresh, leanfresh, medium

smoked, lean

Herring , wholeHominy ,

uncooked

Lamb , chops, b roiledleg , roast

Lard, refinedLemons

LettuceLiver , veal

,uncooked

Macaroni, uncooked

Macaroons

Mackerel, un cooked

saltMarmalade , orange

Milk, condensed,Sweetened

skimmed

Molasses, cane

Muskmelons

Mutton, legOatmeal , uncooked

Olives, greenOnions, freshOranges

Oysters, cannedParsnips .

Pea soup, canned

Peaches, cannedfresh

PeanutsPeas

, canned

Peas, dried, uncooked

GENERAL SCIENCE

WE IGHT

AP PROXIMATE M E A SURE IN OUN CE S

OF 100-CALOR IE OF 100

PORTION CAL OR IE

PORTION

4 tab lespoonfuls1 large bunch

1 average serving

1 average serving

CALOR IE S

DE R IVED

FR OMPROTE IN

Cupful

1 small chop1 average serving

. 1 tab lespoonful (scant)3 medium

50 large leaves2 small servingscupful (4 sticks)

2

1 large serving

1 tab lespoonful

1111; cupfuls

Cupfuls (scant)cupful (generous halfglass)

cupful

71

; average serving1 average servingcupful

7 t o 10

2 medium

1 very large5 oysters1 large

1 large serving4 medium

10 t o 12 (doub le kernels)2 servings2 tab lespoonfuls

1 A s purch ased .

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342 GENERAL SCIENCE

Another condition which will affect t he amount of foodneeded is t he Size of the body . Other conditions be ing t hesame , a small person needs somewhat less food than a largerperson . It has been calculated that the number of calor ieswhich should be supplied by t he food when light work isbe ing done may be determined by multiplying t he we ight oft he body by T hus a person we igh ing 160 pounds willneed sufficient food t o furnish 2576 calor ies . Of course, ifmore active muscular work is be ing performed, food producing a greater number of calor ies is needed. A man doingmoderately active work needs about 3000 calor ies ; a farmerdur ing t he busy ‘season, as much as 4000 calor ies ; and

lumbermen, from 5000 t o 9000 calor ies .The proper amount ofprote in in the diet has been a much

discussed'

quest ion . Th is is of great Importance , since an

excess of protein in t he diet is harmful t o the body . The

tendency of t he Amer ican people i s t o eat rather more prote inthan is absolutely necessary, and therefore in most cases t hediet would be improved by cutting down t he foods r ich inprote in ; for example , meats . About two and one halfounces or from 70 t o 80 grams of prote in a day seem t o be

sufficient, according t o exper iments . It will b e found, however , that our actual diet is. l ikely t o have near ly t hree and

one half or four ounces or about 100 grams ofprote in .

Prob lem 5 . What considerat ions should govern th e planning of our diet ? -It is evident that our d iet must have theproper fuel v ae , and contain t he proper amount ofprote in .

Since there is usually t oo much prote in in an unrestr icteddiet, large amounts of lean meats and other foods containinga high percentage of prote in should b e avoided. It wouldbe wel l t o calculate by t he use of t he 100-calor ie portion

t ables given the calor ie value ofyour food for a day . Ifmore

USE OF THE FOOD MAN UFACTURED B Y PLANTS 343

than 15 per cent of t he calor ies are from protein, then yourdiet is t oo r ich in that . An excess of fat or carbohydratein t he diet is apt t o cause an increase of we ight due t o thestor ing up of excess fue l in t he form offat .

A diet which contains t he proper amount ofprotein, car

bohydrat e , and fat may, however , be a very unsatisfactoryone . There must be included in it foods wh ich will supplyt he minerals needed by t he body, and those minute substances sometimes called Uitamines, without wh ich normalgrowth and repair does not occur . Vegetables, whole grainbread and cereals, fruits, and milk are especially valuablefor the ir minerals. Milk and leafy vegetables such as lettuceand spinach are indispensable in t he diet . Fruits and coarsee lements in t he food such as t he bran or outer coat ofwheatexert a beneficial effect upon t he digestive organs.

1 A good diet, therefore , will be one which supplies t heproper amount of t he three nutr ients, and includes milk

,

leafy vegetables, some fruit and coarse food such as wholeWheat bread, and is so var ied as not t o become monotonous .It is presumed, also, that those parts of t he food wh ich are

Cooked have been made both more digestible and more

appetizing, and that there has been no waste ofthe ir e lements .Prob lem 6 . Why must foods b e dige sted ? Consider

t he condition in t he corn seedling . Where i s t he food stored ?Where is growth going on, andwhere is energy be ing exerted ?The food then must b e able t o trave l from t he seed t o t he

growing point . But t he young stem and root,just as we

saw in t he older root and in t he leaves, are made up of l ittlebox -l ike structures (Figure 267) (ce lls) so that t he food inreach ing t he point ' where it is needed must pass throughhundreds of t he thin walls of these cells. The question now

is, is the stored-up food in condition t o pass through these

344 GENERAL SCIENCE

membranous walls ? The following exper iment will enable

you t o answer this question.

Experiment . —Break off the b ottom of a'

te st tube so that it formsa tube open at both ends. Over one end of

_it t ie a piece of parch

ment paper or a piece of t he dried b ladder of a pig or other animal .

Place t he tub e with t h e parchment end down in a vessel of water inwhich has been stirred some starch . After about an hour test thewat er which has come into th e tube t hrough t he parchm ent for thepresence of starch . This test is made by adding t o the water an

iodine solution which turns it b lue if starch is present. What is t heresult ? What is your conclusion ?

The parchment or mem

brane represents the cel l wallsthrough wh ich the food mustpass . Evidently t he starchmust b e changed into somethinge lse or it can b e of no valuet o the plant . Since we knowthat it disappears from the

seed and that energy is exertedat the growing point, then we

know that it is changed intosomething which will passthrough the walls .The prote in and t he fat stored

in the seed are also unable t o

pass through membranes and

they t oo must b e changed . TheFIGURE 267 . CROS S ANDLON

f hGITUDINAL S ECTIONS OF AYOUNG

process by Wt h an O t 6 86

ROOT foods are changed is cal led digesNote that th e entire root is tion , Our own foods must b e

made up of small divisions(Ce lls) , every one of wh ich is

changed In the same way starch,surroundedbyathinmembrane . prot e in, and fats are unable to

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346 GENERAL SCIENCE

Prob lem 8 . Wh ere is food of th e human b ody digested ?-We know that food taken into t he mouth passes downthrough t he gullet into t he stomach , where it remains forseveral hours, and then passes into t he small

“

intestine, and

on into t he large intestine . This entire tube ext ending fromt he mouth t o t he end of t he rectum, the last division of the

large intestine , is called t he

alimentary canal. The food isforced along through this tubeby means of muscles in its

ophsgus walls .After the food has been broken

up by t he teeth and mixed withsal iva which acts t o some extentupon t he starch , it is workedupon by enzymes of the gastricjuice of t he stomach which act

chiefly upon t he prote in food,

and by a number of enzymesfrom t he pancreatic juice and

2 8intestinal juice wh ich act upon

FIGURE 6 '_ FOOD CANAL

all of t he different nutr ients .(ALIMENTARY CANAL) OF MAN .

The.b ile , a juice manufactured

by t he l iver , is of special use in digesting fat . As t he foodis digested, it is absorbed through t he walls of t he alimentarycanal . Most

[

of t he absorption occur s in the smallintestine .

The mater ial wh ich reaches the large intestine is principallyfood which could not be digested and hence could not be ab

sorbed. If th is refuse mater ial remains t oo long in t he

large intestine , which is t he condition in constipation, bacter iaact upon it and produce soluble poisons which are absorbed

USE OF THE FOOD MAN UFACTURED B Y PLANTS 347

into t he blood throught he wal ls of t he largeintestine and give r iset o headaches, an in

ability to do our bestmental and physicalwork, and make t he

body , less able t o resistdisease .

By t he circulatorysystem of t he blood

(Figure 269) t he digested food is carr iedt o var ious parts of t he

body , where it is usedfor growth and repairand as a fuel for t he

production of energy ,or t he excess of fue lfood is stored up in

t he form of fat .

The wastes wh ichare produced In t he

different parts of t he

body as a result of ox idation and t he activityof t he l iving matter ,are , in time , carr iedaway by t he circula FIGURE 269 .

—ORC"INS OF CIRCULATION

OF AN .

tory system t o t he

kidneys, lungs, and Skin, by which they are taken out of

the blood .

GENERAL SCI ENCE

SUGGESTED INDIVIDUAL PROJECTS

1 . By weighing t he food Used each day for a week and calculatingfromtab les showing percentage ofnut rients in different foods, determinet he amount of each nutrient eaten by you during t he week. How does

the result compare with t he standard ofAtwater or Chittenden ?2 . Plan a b ill of fare for your family for a week. Estimate t he

amount ofnutrients and t he cost. Suggest how t he diet ofyour familymight b e improved without any great increase in cost.3 . Perform experiments t o Show that t he gastric juice will digest

protein .

4 . Dissect t he heart of a sheep. Explain it s action incirculation of the blood.

REPORTS

The value ofmilk as a food.

The use offruit and fresh vegetab les as foods.Causes and prevention of indigestion.

Causes and prevention of constipation.

REFERENCES FOR PROJECT XXVIII

1 . Feeding the Family, Mary S. Rose . Macmillan Company .

2 . The Story ofSugar, G. T. Surface . D. Appleton Co .

3 . Food and Household Management, Kinne and Cooley . Mac

millan Company .

4 . How t o Live , Fisher and Fisk.

’

Funk Wagnalls.

5 . All Ab out Milk. Metropolitan Life Insurance Company.

(Free )

6 . The Body at Work, Jewe t t . Ginn 81. Co .

7. Town and City, Jewet t . Ginn Co.

8 . The Story of Bread. International ‘Harvester Company, Chicago, Illinois.

9 . Economy in the Buying and Preparation ofMeats, E . L .Wright.Wilson 81. Co .

10. American Inventions and Inventors, Mowry. Silver, BurdettCo. (Foods cultivated and uncultivated.)

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350 GENERAL SCIENCE

point of attachment Of this l ittle stalk t o the Side of the pod

is called t he placenta . What materials pass through the

placentaRemove t he seed coat and find two large structures that

make up almost t he whole bulk of t he seed (Figure

These are called seed

leaves, and it will b e

noted that they are

attached t o a'

l ittlestalk, t he pointed end

of which will later de

v elop into the root of

t he growing bean plant .

At t he other end of

t he l ittle stalk, and justbeyond where the big

A and C, lit t le stem , low er end ofwh ichseed leaves at

w ill deve lop into t he first roots . B, plu t ached, you Will see

mule , a bud wh ich w ill deve lop into the

stem and leaves of plant . A , B and thetwo little plume like

two large seed leaves const itute th e em Structures Wh ich at

b ryo. D, scar , the place Of at tachment first 10 k l‘

kO l e

of th e lit t le stalk w ith in the bean pod. E ,

t he parts

micropyle , a small Opening.

Of a fiSh 5 tal l ; bu t on

c l o s e r e xam ina t i on

prove t o be smal l leaves . These leaves , with t he verysmall stalk t o which they are attached, will develop intot he stem and leaves of t he plant .

Altogether t he bean seed is made up ofa l ittle plant called.

an embryo, of which two leaves are filled t o such an ext entwith foodmater ial that they have become so thickened thatthey no longer look like leaves . These constitute t he seedleaves. Compare t he embryo making up th e seed of t he head

with a bean seedling . Pick out t he corresponding parts .

FIGURE 270.— SEEDS OF B EAN AND PEA.

HOW PLANTS PRODUCE SEED 351

Examine a soaked pea seed and endeavor t o find the sameparts that you found in the bean seed . In t he same waycompare t he embryo of t he pea seed with a pea seedlingand note t he corresponding parts .A corn seed may be best studied if it is examined together

with one wh ich has begun t o sprout (Figure Th e partwh ich corresponds t o the root end of the l ittle stem can

easily be seen, as in whatever positiont he corn grain is kept thisroot end

begins t o grow downward . The otherend

, which begins t o push upward t o

form the main part of the plant, is

pointed and made,up of tightly

twisted leaves ln much the sameway that you can fur l up a piece of

paper leaving a sharp point at one

end.

The seed leaf (there i s only one) FIGURE 27 1 —S PROUT

is not at all leaf-l ike in appearma CORN GRAIN '

ance but is embedded in stored food mater ial which 111

t he corn seed i s outside of the embryo. The relation of

t he seed leaf t o t he stored food mater ial can best be seen bycutting lengthwise and cross sections of soaked corn grains,and dipping t he cut surfaces in an iodine solution. The

stored food mater ial , since it contains a very large amountof starch , becomes colored a very dark blue ; wh ile t he

'

partsof t he embryo are colored very sl ightly .

It will thus b e seen that t he corn seed , although apparentlyso unl ike t he bean or pea seeds,

.

also contains an embryo, orundeveloped plant , which consists of a seed leaf attached t oa stalk, one end ofwhich will deve lop into t he roots, and theother end into the stem and leaves of t he plant.

352 GENERAL SCI ENCE

Examination of other seeds wil l show the same t hing, sothat we may conclude that t he seed ofa plant always containsan embryo or baby plant with considerable stored-lip foodwh ich may e ither be in the seed leave s or outside of the

embryo .

Prob lem 3 . Wh ere seeds are produced.

—It i s a com

mon observation that seeds are produced ,in some way by

FIGURE 272 —PEAR . FROM BUD ‘t o FRUIT AND S EED.

t he flowers of a plant . It will be wel l for us, therefore , t oexamine a flower . An examination of a typical flower , suchas a pear blossom or bean or pea blossom , wi ll lead us t ofind t he following parts (Figure 272)The outermost part s are green leaf-l ike structure s called

sepal3 . Together they make a cup-shaped formation aroundt he base of t he flower called t h e calyx . Just inside of t heseare t he colored part s of t he flower called t he petals. The

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354 GENERAL SCIENCE

Prob lem 5 . How th e pollen grain influences th e'

de

velopment of th e ovule into th e seed. It has been foundt hat each pollen grain resting upon t he surface of t he stigmagrows out into a tube wh ich pushes it s way down throught he style until it reaches t he ovary (Figure The pollen

tube now grows through a smallopening (micropyle) on t he side of

t he ovule (Figure Some of

t he l iving mater ial (sperm cell)of the pollen grain, containing a

denser portion, t he nucleus, passesdown through t he tube .

After t he tube has penetratedinto t he ovule through the micropyle , t he end of t he t ube disap

pIGURE 273 — 6 120 e pears and t he nucleus of the pollenOF

.POLLEN TUBFS DOWN (sperm ce ll nucleus) combines with

THROUGH THE STYLEt he nucleus of a l ittle bit of l iving

matter in the ovule called t he egg cell. The egg ce ll , whichi s now composed of l iving mater ial from the pollen grainin addition t o its own or iginal living mater ial, grows and

divides into two, then four, e ight, and finally t housands

of little masses of l iving matter (cells) which arrangethemselves t o form t he part s of the embryo or baby plant .The egg cell , wh ich is composed of l iving material from

t hese two sources, is called a fertilized egg ce ll ; and the

union of t he sperm cell nucleus with t he egg ce l l nucleus i scalled t he process of fertilization. Unless thi s process of

fert ilization occurs, t he egg cel l will not grow and divide,but will finally wither and die .

In all l iving th ings except the very lowest animals and

plant s, this general process of the union of two masses of

HOW PLAN TS PRODUCE SEED 355

living matter precede s t he deve lopment ofan egg into a newplant or animal .Prob lem

'

6 . Does it make any difference wheth er th epollen comes from th e same flower or a difi erent one ?

It is clear that if seedsare produced by a plantt he pollenmust in someway pass from t he

anther t o t he stigma .

This would seem veryeasy, as t he flowers ofmost plants have bothstamens and pistils .Exper iments, however,by the great Englishscientist, Charles Dar

win, have shown that

in many plants cross

pollination (t ransfer of

pollen from an antherof one flower to t he

stigmaofanother flowerof t he same kind) gavemuch more satisfactoryresults than if t he pol

FiGURE 2 74 .—P0 LLEN TUBE ENTERING

OVULE.

A , ,pollen tub e ; B , m ic ropy le ; C, outer

c oat of ovule ; D. inne r c oat of ovule ;E , emb ryo sac ; F, sperm c e ll nuc leus

G, egg c e ll nuc leus .

len that fe ll upon t he stigma came from . the anther of t he

same flower (self-pollination) : He found in some cases of

self-poll ination that a smaller number of seeds were produced ; that t he seeds were frequently smaller and thatpoorer plants ‘ deve loped from t he seeds. Naturally the

question ar ises as t o how se lf-poll ination is prevent ed, andhow cross-pollination is encouraged .

Prob lem 7 . How se lf-pollinat ion is prevent ed. Someplants, l ike t he willow and t he cottonwood or poplar , haveflowers containing only stamens on one plant and flowershaving only pistils on another plant . In these cases se lf-pollinat ion i s impossible . Other plants , among wh ich are corn

(Figures 275 and 276) andmany of our common trees as ash ,chestnut (Figure oak (Figure maple , h ickory,

pines, e t c . , have stamensand pistils in differentflowers but on t he sameplant .

In corn, for example,t he tassel (Figure 276)at t he t op of t he corn

plant is a collection of

staminate flowers wh ilet he silks (Figure of

the .ear of corn, downalong t he stalk, are

FIGURE - P ISTILLATE FLOWERS OF St lgma's and sty19 3 ; and

COR“ the corngrains are ovariesBach

‘silk (style and stigma) is at

of t he pistillate flowers .tached at its b ase to the young corn

grain (ovary ) , Even“

in t h is kind of

plants better resultsoccur when t he pollen i s carried from t he anthers ofanotherplant . A solitary cornstalk usually has on it very poor lydeveloped ears of corn.

.In many plants t he stamens r ipen and t he pollen escapesfrom t he anthers before t he stigmas in t he same flower are

ready t o rece ive it . In some plants t he rever se is true , t hestigma be ing ready t o receive pollen before the pollen in thatplant is mature.

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358 GENERAL SCI ENCE

FIGURE 277.—STAMINATE FLOWERS '

OF

CHESTNUT.

the nectar . Examination of the

FIGURE 278.—FLOWERs OF OAK.

These are our familiarflowers (Figures 279 and

of var ious colorsand frequently havingmore .or less odor . You

will recall that you haveoften seen insects, es

pecially bees and butt erflies, visiting them .

The insects are seekingt he sweet mater ial , nectar , which is down in

the inter ior oft he flowers .By pulling out t he l ittleflower s from a head of

red clover ,and touchingtheir bases with t he

tongue , you can tastehead of a butterfly and

HOW P LANTS PRODUCE SEED 359

the legs and b ody of a bee will show you that they are cov

ered with hairs. Ex plain now how you bel ieve these flowers

are pollinated .

The irregular shapes of flowers are in general"

associat ed

with making more cert ain t hat t he proper kinds of insects

FIGURE 279 .—FLOWERs OF HORSECHESTNUT.

will visit t hem ; and t he stamens and pistils are so arrangedt hat t he insect is quite certain t o rub against them t o rece ive

pollen from one flower , and then to rub the pollen offon the

stigma of the next flower visited.

360 GENERAL SCIENCE

Some flowers have the ir pollen carr ied by water ; and in

some cases humm ing birds act as t he carr iers ; but t he greatmajor ity of flowers are pollinated e ither by wind or by insects . Insect-pollinated flowers have much less pollen thanwind-poll inated flowers . Explain.

FIGURE 280 .—CHERRY BLOSSOMS .

Suggest any advantage of the grouping into c lusters of these small

wh ite flowers.

Nearly all of t he flowers that bloom at night are white

or yellow . What reason can you give for this ? Flowershave var ious means of excluding small crawling insect s like

ants . Ofwhat advantage is this t o t he plant ?

SUGGESTED INDIVIDUAL PROJECTS

1 . Make a collection of seeds and give a brief statement of the economic value of each seed.

2 . Germinate t en different seeds. Make sketches of sev eral stagesof the development of each.

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PROJECT XXX

HOW BETTER PLANTS AND ANIMALS ARE

PRODUCED

Prob lem 1 . Have we ev idence of improvement of plantsand animals during past generat ions Of course we meanby improvement, making these plants and animals betterfitted t o meet our

'

needs. The history of some ofour domest icat ed animals and plants runs back t o t he point whereour knowledge of t he history of man begins

, so that it i s“

impossible t o trace them directly from the ir wild ancestors.

They may ,however, b e compared in some cases with wild

plants and animals wh ich apparently are similar t o theseunknown ancestors . Wheat, oats, rye, barley, et c . , haveevidently been der ived from wi ld grasses, from which theynow differ ch iefly in t he amount of food mater ial stored int he grain or seed.

Ch ickens have changed much from t he Asiatic bird whichi s thought t o be most near ly like t he one from wh ich theyhave descended. Dogs have become quite unlike their wildancestors, apparently wolves and coyotes or t he close rela

t iv es of these . Turkeys , wh ich have become domesticatedin re lative ly recent times, have already begun t o be changedin some respects from t he wild turkeys wh ich were found inthe Amer ican woods by t he early settlers .The most str iking effect of t he influence of domestication

in causing improvement in plants is Shown by those plantswh ich are native t o Amer ica and whose whole h istor ies are

362

HOW B ETTER PLAN TS AND AN IMALS .ARE PRODUCED 363

known . The Indian corn ,wh ich explorers found t he Amer i

can Indians cultivating in a very crude way , would hardlyb e recognized as be ing related t o t he large-grained, fulleared corn whose crop in 1920 wasworth overThe potatoes found by these early explorer s were about

t he size ofmarbles. Dur ing t he few hundreds ofyears sincethey have been cultivated by civilized man, both qual ityand size have been greatly improved. In 1920 the averageyield per acre was over 100 bushe ls ; some areas yie lding300 t o 400 bushe ls peracre .

Not only .has there been an improvement under domest i

cation of t he plants and animals mentioned above , but t hesame is true t o a greater or less ext ent of all plants and

animals for wh ich we have use . The question that ar isesin our minds is, how has th is improvement been broughtabout, and how may we cont iniIe t he process?Prob lem 2 . How plants and animals may b e improved

by se lection. From t he very ear l iest times selection hasbeen a factor in producing better animals and plants . Se

lection has depended upon two facts with which we are all

famil iar : first, that no two plants or animals are exactlyalike ; and second, that a plant or animal tends t o be likeits parents . In a classroom , for ,

ex ample , there are no two

pupils exactly al ike . This is also true if we consider all t he

people in t he whole world . Likewise, you will find that notwo bean or wheat plants or apple trees or horses are exactlyalike (Figure Th is we call

.

variation.

On t he other hand , each pupil in t he class resembles hisparents or grandparents in many respects. It may be in

t he shape of t he nose or face , color ing, tone of voice , size ,mental traits, et c . The same is true of every plant and

animal . Ch ickens never come from duck eggs, or chestnuts

364 GENERAL SCIENCE

from cherry t rees . Every plant or animal resembles it s

parents‘

inh

hundreds of ways . Th is law of resemblance iscalled heredity; and we say that a person inherits a good disposition, black eyes, et c . , from his antecedents . The farmer ,who each year selects t he best corn or wheat grains for seed ,

FIGURE 28 1.—VARIATION .

Variation in the size and shape of timothy heads in the same kind

oi t imothy.

will keep his mom up t o t he highest grade . He may selectfor any special character istic ; size of ear , rapid growth,large or small amount of starch , prote in, or oil .

Prob lem 3 . How more rapid improvement may b e

b rough t about . Greater var iation may be brought aboutby pollinating flowers by hand. By this means also, a

variety of plant or fruit possessing cert ain desirable charact erist ics may be obtained rather quickly . For example ,

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366 GENERAL SCIENCE

FIGURE 283 .—CLEET GRAFTING.

of grafts made, only

three produced fruitthat was of v aliIe . The

flavor of these was goodand they possessed ‘ the

advantage of be ing ablet o l ive two t o four hundred miles north of

where t he ordinarysweet orange was ablet o exist . These var ieties were propagated inturn by further grafting .

In - plants that can b e propagated by cuttings, as roses,carnations, geraniums, et c . ; by roots, rootstocks, or tubers,

FIGURE 284 .—BUDDING, A FORM OF GRAETING.

The four succ essive steps are shown left to righ t .

HOW BE TTER AN IMALS AND PLANTS ARE PRODUCED 367'

as potatoes, gladiol i , et c . or by grafting, as fruit trees,

favorable var iations obtained by hybr idizing may b e readilyretained. In plants, however , that are propagated only byseed, as cotton, corn, wheat, most vegetables, et c .

,a process

of r igorous se lection must fol low . After four t o six generations the plants will come true t o seed fair ly we ll, butt he process of se lection must continue every year or the

desirable charact er istics will disappear .

Very str iking results have been obtained by plant and

animal breeder s through t he use of se lection and hyb ridiz

ing . Luther Burbank especially has developed some veryinteresting plants, such as the wh ite blackberry and Spineless cactus.

SUGGESTED INDIVIDUAL PROJECTS

1 . From a corn or wheat crop, et c . , make a selection of seed t o bring

about an improvement along some definite line in futur e crops.

2 . Graft the twig of one kind of apple tree upon t h e limb of

another .

3 . Propagate a numb er of different kinds ofplants by cuttings.

REPORTS

1 . Improvement of the corn crop.

2 . Improvement of th e wheat cr op.

3 . Reports on various achievements of Luther Burb ank.

4 . The work of t h e U. S. Bur eau of Agriculture in developing newspecies of animals and plants.

5 . Give a brief account of th e work ofCharlesDarwin.

6 . Give a brief account of t he work ofGregor Mendel .

REFERENCES FOR PROJECT xxx

1 . New Creations in Plant Life : Life andWork ofLuther Bur bank,

W. S . Harwood. Grosset Dunlap, 1907.

368 GENERAL SCIENCE

2 . Evolution of Fruits, L. H. Bailey. MacmillanCompany .

3 . The Story ofa Grain ofWheat,W. C. Edgar . D. Appleton Co .

4 . Corn Plants, Their Uses andWays ofLife, F. L . Sargent. Hought on lVIifflin Company.

5. PlantProduction,Moore andHalligan. Amer ican Book Company.

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370 GENERAL S CIENCE

stage ofbeetles ; or you have had t he leaves of plants in yourflower or vegetable garden eaten by grasshoppers. If you

have been in an orchard which has no t been we ll cared for ,you have found that practically every apple was wormy

(Figure The“ worm is

the young stage of a small mothwh ich fl ies at night .

FIGURE 286. POTATO BEETLE. FIGURE 287 . P EACH-TREEBORER .

These are only a few of t he enormous number of ways in

which insects harm crops, fruit, and forests by eating them .

Give other examples seen by you .

Another group of injur ious insects is represented by the

plant lice wh ich you sometime s see on house plants . Theydo much damage t o plants in general . And there are the

scale insects (Figure 290) wh ich at var ious times haveruined all of t he fruit t rees in cert ain part s of t he country .

IN SECT ENEM I ES OF PLANTS 371

FIGURE 288 .-GROUP OF DYING LOCUST TREES .

Effec t of borers and leaf-miners

The squash bug is another example of th is group of in

sects which does harm by sucking out t he juices of

FIGURE 289 .—WORM IN APPLE, LARVA OF CODLING MOTH .

372 GENERAL SCIENCE

plants . The bedbug, of unsavory reputation, is a closerelative .

It has been estimated by t he Ch ief of the Bureau ofEntomology of t he Un ited States Department of Agriculturethat the damage done in one year in this country by insectsis as follows : Farm crops cereals, hay ,

cotton, tobacco,

FIGURE 290 .—SCALE INSECTS ON A FERN LEAF.

vegetables, sugar , fruits, $141 ,other crops about making a total of

over damage done t o farm crops .In addition, forests and forest products are estimated to

have suffered a damage of products instorage ,insect-borne diseases of man have caused a

loss of 81 domestic animals have beendamagedt o t he extent of making a grand total ofmorethanThe question is, how can this great loss be lessened ?Prob lem 2 . HOW injurious insects may b e de stroyed.

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374 GENERAL SCIENCE

poison must get into t he cup formed by t he calyx beforet he l ittle larva, or worm,

”has a chance to eat its way

into t he fruit .Of course insects that live by sucking juices from plants

FIGURE 292 —A MODERN S PRAYING OUTFIT.

are not affected by poisonous sprays . They are usuallykilled by be ing suffocated in some way . Dry insect powdermay b e sprayed over the plant by bellows . This clogs upthe breath ing holes along the body of the insect. A spray

IN SECT ENEM IES OF PLANTS 375

made of kerosene , soap, and water , another made of whale

oil soap, and still another made by pour ing hot water overtobacco stems, have been found t o be effective in killing thesesucking insects. In greenhouses and cold frames which

can be tightly closed, tobacco smoke is valuable for

plant l ice .

FIGURE 293 .- A BENEFICIAL B EETLE.

Caterpillar of gypsy moth at tacked by Calosoma bee tle .

Prob lem 3 . How th e numb er of injur ious insects isreduced by natural means. Man

’

s fight against injur iousinsects might b e a losing one if he were not assisted by t hemany animals that prey upon insects. The big dragonfl ies which you see soar ing in t he air, reminding you ofminiature airplanes, are on t he lookout for flying insects, ofwhichthey devour an enormous number . The immature stage

(larva) of t he dragon fly ,

'

liv ing in ponds, have also as the irone occupation t he destruction of t he young stages of otherinsects.

Ladybird beetles (Figure commonly cal led “ ladybugs, those small round beetles which most of us know,

are very he lpful in keeping down t he increase of plant liceand scales (Figure A number ofyears ago a species oft he ladybird beetle saved the orange industry ofCalifornia.

3 76 GENERAL SCIENCE

The orange groves . were t hr eatened with destruction by a

scale insect introduced from Australia . AS it s Spread couldnot be stopped by t he ordinary methods of fighting insects,an expert in t he study of insects was sent t o Austral ia tofind if t he scale had any natural enemy . It was found thata certain kind of ladybird beetle fed upon them and thus

FIGURE 294 .—LADYBIRD BEETLE.

kept t hem in check . Beetles were brought back t o California, where they succeeded in saving th i s very import antindustry .

In gather ing cocoons ofmoths, it will be frequently foundt hat t he inter ior i s filled with a large number ofsmall larvae ort he ir cast-off skins. The reason for this i s that an insectcalled an ichneumon fly

,a re lative of the wasps, punctured

t he skin of the moth larva and deposited a number of eggs.

These eggs developed into small larvae which finally com

plet ely devoured t he body of the ir host . From these larvaeadult ichneumon fl ies deve lop which in turn are ready t oattack other caterpillars which are injurious t o vegetation.

It is thought that parasit ic insects like the ichneumon flies

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378 GENERAL SCIENCE

dur ing a portion of t he year subsist chieflyon insect s . Manybirds that are not pr imar i ly insect feeder s supply a diet ofinsects for the ir young . Students of t he subject estimate

0

FIGURE 296.—TOADS EATING CATERPILLARS .

that birds, by destroying harmful insects, each year savecrops worth many millions ofdollarsToads, snakes , and bats are other animals that de serveprotection from man because of the ir value in destroyinginjurious insects

SUGGESTED INDIVIDUAL PROJECTS

1 . Make a collection showing the various ways m which insectsinjure plants.

2 . Make a collection of injurious insects and give a brief account oft he harm done by each kind.

3 . Protect th e fruit of an apple tree from injury by th e codling moth.

4 . Make life history cases of a numb er of injurious insects.

REPORTS

1 . Th e work of th e U. S. Bur eau ofAgriculture in helping th e farmerin his fight against insects.

2 . An account of th e introduction of th e gypsy moth, of th e harmdone by it, and of the effortsmade t o check it .

3 . An account of the life history ; of harm done by them ; methodsused t o fight them : potato b eetle , cotton boll weevil, codling moth,

INSECT ENEM IES OF PLAN TS 379

Hessian fly, San José scale , chinch bug, grasshopper , b rown-tailedmoth,army wofm , e t c .

4 . Work of b irds in destroying harmful insects.

R EFERENCES FOR PROJECT XXXI

1 . Insects Injur ious t o the Household and Annoying t o Man, G. W.

Herrick. Macmillan Company .

2 . Insect Pests of Farm , Garden, and Or chard, E . D. Sanderson.

JohnWiley Co .

3 . Farmers’ Bulletins.

4 . Farm Fr iends and Farm Foes, C. M .Weed. Ginn 85 Co .

5 . Birds of Village and Field, F. I . Merriam . Houghton M fflin

Company .

6 . Book ofBirds, Vols. I and II ,Miller . HoughtonMitflin Company.

GENERAL REFERENCE BOOKS

Child’

s Book ofKnowledge , Grolier Co . , New York.

Th e Book ofWonders, Presb rey Syndicate, New York.

Wonders of Science , E . M . Tappan, editor . Houghton MifflinCompany .

The Story-Book ofScience , Fabr e . Century Company .

Modern Triumphs, E . M . Tappan, editor . Houghton Mifflin

Company .

Wonders ofPhysical Science , E . E . Fournier . Macmillan Company .

Field and Forest Handb ook, D. C. Beard. Scribners.

Romance of Modern Inventions, A . Williams. J . B . LippincottCompany .

Stories ofUseful Inventions, S. C. Forman . Century Company .

Stories of Great Inventions, E . E . Burns. Harper 85 BrOs.

Makers ofManyThings, E .M . Tappan . HoughtonMifflin Company.The Boys

’

Own Book of Great Inventions, F. L . Darrow. Mac

millan Company .

Handicraft for Handy Boys, Hall. Lothrop, Lee Co

The Boy Craftsman,Hall. Lothrop, Lee 86 Co.

Scientific American Boy at School, Bond. Munn Co .

Harper’

s Outdoor Book for Boys. Harper Bros.

380 GENERAL SCIENCE

Everyday Physics, Packard. Ginn 8LCo .

TheWonders ofModernMechanism, C. H. Cochrane . J . B. Lippincott Company .

The LandWe Live In, O. W. Price . Small, Maynard 85 Co.

Uncle Sam’

s Business, C. Mariott. Harper 85 Bros.

Commercial and Industrial Geography, Heller and Bishop. Ginn85 Co .

WithMenWhoDo Things, Bond. Munn 85 Co.

Pioneers ofScience in America,W. J . Youmans. D. Appleton 85 Co .

Famous Men of Science , S. K . Bolton. T. Y. Crowell 85 Co . , New

York.

How It Works, A . Williams. Thos. Nelson 85 Sons.

Romance of Modern Engineering, A . Williams. Seeley ServiceCompany . London .

0

GreatAmerican Industries,W. F. Rocheleau. A . Flanagan Company,

Chicago .

A Source Book of Biological Nature Study, Downing. University of

Chicago Press.

Chemistry of t he Home ,Weed. American Book Company .

Chemistry of Common Things, Brownlee , e t c . Allyn and Bacon.

Boys’ Book ofChemistry, Clark. E . P . Dutton 85 Co .

Farm Science ,W. J . Spellman. World Book Company .

Commercial Raw Materials, Chas. R . Toothaker . Ginn 85 Co .

Scientific American Reference Book, Hopkins and Bond. Munn

85 Co.

Measurements for the Household. Bureau of Standards, Washing

t on, D. C.

World Almanac . New YorkWorld.

Oflicial Handbook, Boy Scouts ofAmerica. Doub leday, Page 85 Co .

Occupations, E . B . Gowin and A . W. Wheatley . Ginn 85 Co .

The Story of Iron and Steel, J . R . Smith . D. Appleton 85 Co .

The Story of t he Submarine,Bishop. Century Company .

Practical Physics, Carhart and Chute . Allyn and Bacon.

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382 GENERAL SCIENCE

III . COMPARATIVE SCALES OF THERMOMETERS

Fahrenheit

,2 12

° WATER BOILSA T S E A

LEVEL

Temperate

Alcohol Boils

TallowMelts

B lood Heat ZERO FARR .

COMPARISON OF SOME COMMON UNITS

MEASUREMENT

equals centimeters3937 inches3048 meters

feet.9 144 meters

yards

kilometers.62 137 miles

APPENDIX 383

grams

035 ounces (av .)45359 kilos

pounds

1 gallon ofwater weighs pounds

1 gallon equals . 13368 cub ic feet1 cub ic foot gallons

1 gallon 23 1 . cub ic inches1 cub ic foot ofwater (4° C.) weighs pounds

1 t on anthracite coal occupies 40—43 cub ic feet

1 t on b ituminous coal 40—48 cub ic feet

V. PREPARATION OF AGAR CULTURE MEDIUM

Place 500 grams,ab out one pound, of finely chopped lean b eef in

1000 cc . of distilled water and keep in an ice b ox overnight . Strainand squeeze out t he juice . Boil t he juice for half an hour t o coagulatet he albumins. Filter and add sufficient distilled water t o b ring t heamount up t o 1000 cc .

The use of 3 grams of a standard meat extract, such as Lieb ig’s,to

1000 cc . ofwater may be used instead of t he fresh meat .

Ten grams ofpeptone should be carefully stirred in and dissolved byb oiling .

Add sufficient sodium hydroxide t o make t he reaction of t he b rothneutral or slightly alkaline t o litmus.

Chop into fine pieces 15 grams of pure thread agar . Dissolve t hechopped agar in a small quantity of b oiling water . Add this t o t hehot b roth. Filter t he b roth containing t he agar through a filter made

of cheese-cloth, enclosing a layer of ab sorb ent cotton . Filtration willb e facilitated by first wetting t h e filter and funnel with b oiling water .

~

Sterilize in an autoclave and pour into sterilized Petri dishes.

quart-s liquid9463 liters

liters9081 quarts dry

liters264 17 gallons

384 GENERAL SCIENCE

VI . CLASSIFICATION or ROCKS AND DIVISIONS or

GEOLOGIC TIME

(P repared by the U. S . Geological Survey)

The rocks composing t he earth’s crust are grouped by geologists intothree great classes

,igneous, sedimentary , and metamorphic . The

igneous rocks have solidified from a molten state . Those that havesolidified b eneath t he surface are known as intrusive rocks. Those thathave flowed out over t he surface are

,known as effusive rocks, extrusive

rocks, or lavas. The term volcanic rock includes not only lavas butb omb s, pumice , tuff, volcanic ash and otherfragmental materials thrownout from volcanoes. Sedimentary rocks are formed by t he accumula

tion of sediment in water (aqueous deposits or eolian deposits) . The

sediment may consist of rock fragments or particles of various sizes

(conglomerate sandstone , shale) of t he remains or products of animals

or plan ts (certain limestones and coal) ; of t he product o f chemicalaction or of evaporation (salt, gypsum , or of mixtures of thesematerials. A characteristic feature of sedimentary deposits is a layeredstructure known as b edding or stratification . Metamorphic rocks are

derivatives of igneous or sedimentary rocks produced through mechani

cal or chemical activities in t he earth ’s crust . Th e unaltered sedi

mentary rocks are commonly stratified, and it is from their order of

succession and that of their contained fossils that t he fundamentaldata of historical geolog

'

y have b een deduced.

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386 GENERAL _SCIENCE

The first striking fact in t he geological history of climate is that t hepresent climate of t he wor ld has b een maintained since t he date of t he

earliest, unal t ered, sedimentary deposits. Th e oldest sandstones of t heScotch Highlands and t he English

‘

Longmynds show that in pre-Camb rian times th e winds had t he same strength, t he raindr ops were of t h e

same size , and they fell with t he same force as at t he present day .

Th e evidence ofpaleontology proves that t he climatic zones of t he earthhave b een concentric with t he poles as far b ack as it s records go ; t he

salts deposited by t he evaporation of early Paleozoic lagoons show thatt he oldest seas Contained t he same materials in solution as t he modern

oceans ; and glaciations have recurred in Arctic and,under special

geographical conditions, also in temperate regions at various periodsthroughout geological time . The mean climate of t he world has b eenfairly constant, though there have b een local variations which have ledt o t h e development of glaciers in regions now ice free , at various pointsin t h e geological scale . That there has b een no progressive chilling of

t he earth since t he date of t he oldest known sedimentary rocks is shownby their lithological characters and b y t he recurrence of glacial deposits,some of which were laid down at low levels at intervals throughoutgeological time .

VII . SOLAR SYSTEM

GRAVITYAT SUR TIME OF REVO

DISTANCE FROM SUN RADIUS FACE . LUTION AROUND

EARTH SUN

1

miles

,000

Moon —Diameter , 2 160 miles ; average distance from Earth,miles ; time of revolution around t he E arth, days ; force of

gravity at surface of Moon, one-sixth of t he force of gravity at

surface of Earth .

APPENDIX 387

VI II . BIRD COUNT IN THE UNITED STATES

(By E . W. Nelson,Chief of the Bureau of Biological Survey, United

S tates Depar tment ofAgriculture)

Early in the summer of 19 14 t he Biological Survey of t he UnitedStates Department of Agriculture took initial steps toward a count oft he b irds of t he United States for t he purpose of ascertaining approx i

mately t he numb er and relative abundance of t h e different species.

This preliminary count proved t o b e so satisfactory that t he Surveyrepeated it on a larger scale in 19 15, and extended it over a still greaterarea in 19 16 and 19 17 . Th e results obtained in 19 14 have b een sur

prisingly corrob orated b y those of succeeding year and t he work givespromise ofproducing , after a series of years, results that, in view of t he

recognized value of b irds t o agriculture , cannot fail t o b e of great value .

I t has b een ascertained through these counts that b irds in t h e agricul

tural districts in t he Northeastern United States average slightly more

than a pair t o t he acre,though in parts of t he arid West and onthe

treeless plains this numb er dwindles t o an average of half a pair , oreven less, t o t h e acre .

By far t he most abundant b irds in t he United States are t he rob in

and the English sparrow,but several others are common enough t o

make their total numb ers run well into t he millions. The counts so farshow that t he most abundant b ird on farms in t h e Northeastern Statesis t he rob in next t o this is t he English sparrow,

and following theseare t he catb ird

, b rown thrasher , house wren ,kingb ird, and b lueb ird,

in t he order named . Th e densest b ird population anywhere recorded

is near Washington ,D . C .

,wh ere a careful count showed, in 19 15, one

hundred and thirty-fiv e pairs of forty species on fiv e acres . Two cityb locks, well furnished with trees, in t he city of Aiken , S . C .

,harb ored

sixty-fiv e pairs on t en acres. These high figures show th e importantresultswhich will follow from careful protection and encouragement ofb irds.

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INDEX

References are to pages

Bee tle , lady b ird 375—376B ell , elect ric 253—254B elt s, use in machinery 235

B ends 19

B enzoat e of soda, use as an ant i

sept ic . 120

B e t elgeuse , a fix ed st ar 209

Bicycle , applicat ion of pow er t o

drive wh eel 235

Big Dipper 205

Bile 346

Binding posts, of elect rical ap

paratus 254

Birds, value in destroying insec ts 378

Block and tackle 237

Blood corpuscles, wh it e 109 , 1 14

Blood poisoning 1 10

Blood syst em 347

Blue print s 222—223Blue vitriol 258

Blueness of sky 288

Boils 1 10

Bone meal , use as a fer t ilizer 326

Bones of b ody as levers . 233

Boyle’s law 18

Brain, int erpre t at ions Of ligh timpressions 295

Brakes, use in ov ercommg 1ner t ia 244

Bread, composit ion of 332

Breathing , of animals 69—72of human body . 67

of plant s 67—69reason for b reat h ing t hroughnose 1 14 .

Breathing movements 12

Bull , a const ellat ion 209l

Bunsen b urner 56

Buoyancy 10—1 1Burb ank , Luth er , 367

54- 56

dest ruct ion 74—79But t er , flavor improved b y

grow t h of b act eria 125

But t erfly , adapt at ion for pol

linat ion 358—359

18

335

334

352

Camera , similarity t o ey e

focusingCanal , aliment ary

Canals, impor t ance m n‘

av 1

gat ion 183—186Candle power , m easurement of 281Cape lla, a fixed st ar 207

Capillaries 72

Carb ohydrat es,food

manufac ture of

Carb on diox ide

ac t ion on rocks

amount removed from air by

Import ance as

plant s

percent age m an 80

proof of use in st ar ch

making 84—85Carb onife rous period 88

Carb uretor 246

Carrol , Dr . , m ember Of Yellow

Fever CommissionCassiopeia

’s Ch air , a const e l

lat ion

Cat skill Mountains, as a source of

wat er supply

Cave s, format ion in limestone

regions

produced by act ion of carbon

dioxide in wat erCell , dry

gravitystorage

Cells, plant

Cell-sapCentrifugal force , examples

of 197—198Ceph eus, a const ellat ion 206 , 207

Ch ain drive , b icy cles and mot or

t rucks

Ch ariot e er , a const ellat ion

Ch e ese , flavor produced b y b act eria and molds

Ch emical ch ange , ox idat ion

in elec t ric cells

in making picture , caused

b y energy of sun . 22 1—223of st orage cell 27 1—272

Ch emical elements 56

in soil 324

necessary fOr grow th ofplant s 324

INDEX 3

References are to pages

Ch icago drainage canal 173

Chisel , as an inclined plane

Chlorine gas, use in st erilizing

wat er 166

Chloroph yll , necessary for

st arch -making 88—89Chronome t er , use in de t erm ining

longitude 2 17

Ciliary muscle

Circulation of b lood, need for 67

Circulatory syst em

Clay, as a const ituen t ofsOil 309 3 10Clothing , for Wint er and summ er 301

ligh t effect s of 297

Clouds 40

form at ion of . 13 1—132Clover , effect upon soil of

Coal , b ituminous and anth ra

cit e 85—86burning of 63—64origin

Coal famine , result s of

Cofi e e grinder 234

Cogwh e els 234—2350 0 115 , ele ct r1c ofelect ric b ell 254

Cold , e x t rem es ofh eat and cold in

lessening resist ance t o dis~

ease 1 14

Cold frame 223- 224

Colds, caused b y b ac t eria 1 10

Cold-storage cars and ships, im

por t ance Of 103

Cold-storage plants 100—103Color , e x planat ion of 286—287import ance of color of flow ers 358

of clot h ing .

of sunse t and sunrise

relat ion of w all-color

ligh t ingCommunicab le diseases

Commutator , effec t on al t ernat ingcurrent 264

Compounds, ch em ical .

Concav e lens, for correct ion of

t o

285—286

near sigh t edness

Const ellations 205

Constipation 346—347Consumption (tub erculosis) ,

t ransmission of 1 12

Convection current s, of air 28—29(of wat er 306—307

Convex lens, for correc t ion Of

far-sigh t edness

Cooking appliance s, e lec t ric

Copper -platingCorn , primit iveCornea of eye

Corolla

Cott on se ed meal , use as fent ilize r

CowpoxCranksh aft

Cross-pollination

Crow b ar

Crystal de t e ctors, wir elessCulture media

Cyclones

Dams, use in deve lopingw at er pow er 153—157

Daniell cell 258—259Darw in , Ch arles 355

Day-ligh t saving 2 16

De cay, cause of 92—93impor t ance of 1 22- 123

De t ectors, wireless 262

Dev eloper , in phot ography 22 1

Dew , form at ion of 127—128Dew point . 128

Diet , amount of food m 336—342good, as prot ect ion against

disease

impor t ance of gr een vegot ab les and milk in 332—333ofmineral mat t er in . 33 1—332

oflum b erm en 330

planning of 342—343value offat in 330—33 1value of st arch and sugar in 33 1

use of orange juice in 104

Dige stion 343—344in human b ody 346

of st arch 345

Diph th eria, t ransm ission of 1 13

Dir e ct ligh ting 284

Dirigib le 10

Diseases, carried b y milk‘

103

communicab le

natural prot ec t ion against 1 14

of ey es

Disinfectant s

use of

INDEX

References are to pages

4

Domestication of plants and

animals 3 62—363Draft , of furnace 307

Dragon, a const ell at ion 207

Dragon fly 375

Dry cell 259

Drying , as a m eans of food

preserva t ion 105—106Dust , carrier of b ac t eria 94

effec t upon sunse t ~colors 288

Dynamo 2 62- 264

Ear , human 50—52Earthworm , b reat h ing of 69

Eclipses 202—203Edison , Th omas A . 270

Efficiency of mach in‘é s 24 1

of engines 245—24 6of storage cell 272

Egg cell 354—355Electric cells 257—259in series 260

Elect ric current , al t ernat ing and

direc t . 264

generat ed b y cells 257—259by dynamo 262—264

in elect roplat ing and e lec

t rot yping 266—267used t op roduce h eat 267—268use in refining m e t als 267

Electric furnace 268

Electric h eating and cookingappliances . 268

Electric ligh t s 268—271Electric transformer 270

Electrical pressur e 259

Electricit y, early use of 252

relat ion of wat er pow er t o 153—157st at ic 273

Electro-magnet 255—256use in dynamo 264

Electromotive force 259

Electroplating 2 66

Elect rotyping 267

Element s, ch emical 56

Emb ryo 350

Energy 63

availab le ln human b ody‘

67

Engines, gas . 246—249four -st roke cycle 24 7

"

solar'

224—225A

Engines Cont inuuedinefficiency of 225

Enzyme 345

Equilib rium , st ab le and unst able 194

Equinox, vernal , autumnal 2 12

Erosion , st ream 179

w ind 3 14

Eustachian tub e 5 1—52Evaporationin cold-storage plant s 100—101in iceless refrigerat or 9 9—100

Ex pansion tank , h ot w at er h eat

ing syst emEye , abuse of .

advant age of two ey es .

care of

normal

Eye strain .

Eyeglasses, use of 29 1—293

Fading of colors 223Far-sigh t edness 288

cause and corr ec t ion of 29 1—292Fat , use in food 330

Fatigue , e x cessive , lessening re

sist ance t o disease 1 14

Fermentation, by yeast 104

in sauerkraut 105

Fer tilization, of egg ce ll 354—355Fert ilizer , ni t rat e of soda as 324

organic m at t er as 324

sewag e used as 173

sulphat e of ammonia as 324

Fie ld magne t , of dynamo 264

ofmot or 265

Filament s 353Filaments, of ele c t ric ligh t bulb s 2 69Film , ph ot ographic 22 1

Fire ext inguish er 76Fire lanes 78Fire walls 79Fire less cooker 301Fireproof construction 79Fish , b reat h ing of 71—72in b alanced aquarium 89—9 1use as fert il izer 324

Fish ing pole , as a lever 233

Flame 59

Flies, relat ion t o t yph oidfever 1 12

,172

Floods, prevent ed by forest s 18 1 182

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INDEX

Refer ences are to pages

Humidit y, de t erminat ion of 142- 143

r elat ive 142

Humusimpor t ance in soil 3 18

Hurricanes 38—40Hyb ridizing 365

Hydraulic pre ssure , source

of pow er of 157—158uses of 158—159

HydrogenHydroph ob ia, Past eur t reatm ent

for 1 19

Hygrome t er , t o de termine

humidit y 142—143Hypo 22 1

Ice , use in refrigerator

Icele ss refrigerator 99—100Ichneumon fly 376

Illumination of a room 278 286

Immunity , acquir ed 1 15—1 19t o diph t h eria 1 17—1 18

Improv ement of plant s and

animals 3 62—367Inclined planes, use of, e x

amples of

Indirect ligh tingInduct ion coil , use and st rue

ture .

Inertia, definedrelat ion t o cent rifugalforce

Inflammation

Insecticides

Inse ct s, adapt at ion for polli 1

nat ion 357—359b reat h ing of 70—7 1

carriers of disease 1 12—1 13dest ruct ion of h armful . 3 73—378injurious t o plant s 269—372yearly damage by 372

Int estine 346—347Iron , galvanized 75

Irrigation 136

Jackscrew, use in doing work 240Jenner , Edward 1 16

Kerosene emulsion, as an in

se c t icide 375

Kilowatt 26 1

Kilowat t h our 2 61

Kindling t emperature 58

Kit e 1—2Knife , as an inclined plane 240

Knot s, impor t ance of fric t ion In 245

Ladyb ird b e e t le

Lake s , glacial

Lat itude

Lazear , Dr . , m ar t y r in figh tagainst y e llow fev er 188

Le af, work of 82—89Leaf mulch 322

Legum es , effec t upon soil of . . 124

Lens, use asmagnifying glass 289 290

Lenses, for corr ec t ion of defec

t iv e vision . 292

Lever , use in doing w ork 23 1—233Ligh t , b roken up by prism 287

intensity 279—280reflec t ed and diflused . 2 76—277refrac t ion of 289—290r esult Of o x idat ion 55

Ligh t ing of rooms , cost 278—282direc t and indirec t 284

from sunligh t 2 76—278Ligh tning 273

~

Lime stone composition 56

Litt le B ear , a const ellat ion 207

Lit t le Dipper , a const ellat ion 206

Longitude 2 14

Low pressure areas 3 3—36Lumb er , in jured b y insect s 369

Lu'

ngs 72

Luray Cave , form at ion of 3 12

Machines , efficiency of

reasons for use

Magne to

Magne tic ne edle

Magne t s, ele c t ro and per

m anent 255—256ofdynamo 263- 264

Malaria , t ransmission of 1 13

Mammoth Cave , form at ion of 3 12

Manure , use as fer t ilizer 324

Mars , possib ility oflife upon 203—204Mat ch , ligh t ing of 58—60M eat ch opper 234

Medicine dropper 1 1

Micro-organisms

Micropyle 354—355

References are to pages

Microscope , principle of 294—295Milk , condensed 104

evaporat ed 106

impor t ance in diet 343

past eurizat ion of 103—104

powdered 106

Mineral mat t e rs, impor t ance of,

in foods 33 1

Mizar , a fix ed st ar 207

Moisture of air , relat ion to

comfort 142—143Moisture , given off by plant s 145

t aken up by roo t s ofplant s 145—146

Mold, cause of decay of food 93

condit ions favorab le for

grow t h 96—97impor t ance in ripemn g ch eese 125

Monsoon 3 2

Moon , e clipse of 203

ph ases 201—202relat ion t o t ides 192—19 5revolut ion around ear t h 197

Mosquitoes, b reat hing of 70

carriers of malaria 1 13

carriers of y ellow fever 188“ Moth er

”of vinegar 125

Motion picture s 295—297Motor , elec t ric 265—266gasoline 246—249

Mountains, as a source of w at er

supply 16 1

Mucus , import ance in keeping

germs out of t hroat and

lungs 1 14

Mulch , impor tance in holdingw at er in soil 322

N ear sigh t edness . 288

cause and corr e ct ion of 29 1—29 2Ne ctar 3 58

Negative , inphot ography 22 1

N erv e , opt ic 278

endings in ey e 278

New York City , wat er supply of 160

Newt on , Sir Isaac , first law of

mot ion

law of gravit a t ionNiagara Falls, a source of w at er

power 155

Nitrat e of soda, use as fert ilizer 324

Nitrogen, fix at ion of 325

foods cont aining much 33 1

impor t ance in t h e air 8 1—82ne cessity of, for m aking pro

t ein 328

source of, for plant s . 324—325Nitrogen-fix ing b act eria 123—124Nodules, on root s of plant s of

clover familyNorth Star

value in de t ermming lat ltude

Nucleus

Nutrients

Ocean, cause of sal t iness

Oculist

OhmOhm , GeorgOil , origin of, in plant s

use t o prevent frict ionOpe ra glasses

Opt ome trist

Organic mat t er , a source of

ni t rogen

a source of pot assium and

phosph orus 325—326import ance of decay of 122—123

Orion , a const e llat ion 208—209Osmosis 148

Ovules 353

O x idation 55

in human body 65—67in plants 67—69slow 60—62

Oxygen 55

given off byplantspercent age in air

t est for

Panama Canal , import ance in

ocean t ransport at ion 186

Paris gre en, as an insec t icide 373

Pascal ’s principle , in relat ion t o

hydraulic pressure 158

Past eur treatment for rab ies 1 19

Past eurization ofmilk 103—104P erseus, a conste llat ion 207

P e tals 352

P e t ri dish 94

Ph onograph 47—4 9

8 INDEX

Ph osph at e rock , use as fert ilizer 326

Ph osph orus 59

in soil 324

source of, as fertilizer 325- 326

Photography . 22 1- 222

Ph otosynth esis, defined 84

Pimples . 1 10

Pin, as an inclined plane 240

353

Pist illat e flowers 356

Pit chfork , as a lever 233

Placenta . 350

P lane ts 203—204Plant s , b reat hing of 67—68impor t ance in a bal anced

aquarium 89—9 1Pleiades, a const ellat ion 209 ,

Pneumatic drill 23

Pneumatic tub es 23

Pneumonia, t ransm1ssmn of 1 13

Polarization of electri c cell . 258

Pole Star 205—206v alue in det ermining latit ude 2 17- 2 18

Pollen . 353

Poll en grain 354

Poll en tub e 354

Pollination 355

insec t 357—359wind 357

Potassium 56

in fer t ilizers 325—326in soil 3 24

sources of . 326

Potatoes, primit ive condit ion 363

Power , of automob ile 57—58Prevailing west erlies 3 6

Prints, in photography 222

b lue 222

Proeyon, a fix edstar 209

Proj ection lant ern , use oflens in 295

Propagation ofplants, by seeds 349

vege t at ive 3 65—3 67Prot eins 89—9 0 , 328

in die t 337

Protozoa 96

Psych rome ter , in det erm inat ion

of relat ive humidity 142

Pulleys, uses of 235—237Pump, exh aust air 2 1

22—23

Pump Cont inuedsuct ion

Pus

Push b utt on, of elect ric bellPyorrh ea

Rab ies (hydrophob ia) , Past eur

t reatment for

Radiation, of h eat

Radiator , aut omob il e

injured b y freezingof h eat ing plant

Rain

format ion of

Rainb ow

Rainfall , dist ributionof .

R ecord of ph onograph

Reed, Dr ., m ember of YellowFever Commission

Reflectors, useR efraction of ligh t

R efrigerator

wal ls of

R eservoirs, import ance in

wat er supply syst em 165 , 167

Resistance , natural , of body ,

against disease 1 14

R e tina of eye 29 1

Ricke ts 104

Rigel , a fixed star.

209

Riggs’ disease of t e e th 1 10

Rocks , disint egrat ion of, in

format ion Of soil 3 1 1

phosphate 326

st rat ified 178 , 180

Roller b earings, use In prevent ingfrict ion

Root s, ext ent ofselec t ive ab sorpt ion by .

special st ructures for t aking mmoistur e

split t ing rocks

Root h airs, impor t ance in t akingin moisture

selec t ive ab sorpt ion b yst ructure

Rotation of earth,winds

Rusting of non

prev ent ioh Of

effect on

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l O‘ INDEX

References are to pages

Sunrise and sunse t , color of 288

2 14—2 15

Taurus, a const ellat ion 209

Te e th , dangers from decayof 1 10—1 1 1

Telegraphy, wireless 26 1—262Te leph one 50

Te lescope , use of lens m 2 95

Tempe rature , in cold st orage

plant 100

rela t ion t o format ion of dew 128

Terminal moraine , of

g lacier 3 16—3 17 , 3 19Tetanus, t ransm i ssion of 1 13

Th ermome t er , w e t and dry bulb 142

Th ermos b ot tle 300—301Thunderstorm

Tides, cause 192

Time , calculat ion of 2 14—2 15sun 2 15

Toads, value in dest roy ing in

sect s 378

Tob acco, as an inse c t icide 375

Tonsils, danger from in

flammat ion of 1 10—1 1 1Tornadoes 37

Torrice lli 6

Toxin . 109

ofdiph t h eria . 1 17

Trade Winds 32

Transformer , elect ric 2 70

Transpiration 144

amoun t of 145

cont rol of 145- 146

Transport ation, w at er 175—189Traps of wast e wat er pipes 17 1

Tub erculosis, t ransm ission of 1 12

Tungst en, use in e lec t r ic ligh t

bulb s

Typh oid fever , relation t o wat ersupply 173

t ransmission of . 1 12

vaccinat ion against 1 17“ Typh oid Mary

” 1 13

Typh oons 40

Ursa Major , a const ellat ion 206

Ursa Minor , a const ellat ion 207

Vaccination, against smallpox ‘1 16

against t yph oid fever 1 17

Vacuum 6

of t h ermos b ot tle . 300—30 1Valleys, origin of . 3 14

Val v e , safe ty , of st eam boil er 306

Variation 363

Ventilation, me t hods of 27- 30

need for . 25—2 7Vernal equinox 2 12

Vinegar , m anufacture Of . 125

use in food preservat ion 105

Vitamines, necessit y of, in die t 343

Vocal cords 46

Volt 259

Volta, Al essandro 257

Voltage , of elect ric ligh t wi res 2 70

Voltaic cell 257

.Voltme t er 260

Von Guericke , O tt o 8

Wall color , relat ion t o ligh t

ing 285—286Walking , impor t ance of frict ion

In

Wat er , composit ion

effec t of h ea t on

erosion b y

e x pansion in freezing

h ard

h eat ing by hot wat eruse in figh t ing fireWat er pipes

w ast e

Wat er power , r elat ion toot h er

sour c es of pow er

source of energy .

Wat er supply, of N ew YorkCi ty 160- 166

Wat er ways, int ernal , im

port ance of

Watt , Jame s

Weath er Bureau

Weath ering , definedproduc t ion of soil byWedge , an inclined plane

Wells

West erlies, prevailingWh e e l and ax l e , as a simple

mach ine

Wh e elb arrow

INDEX

References are to pages

Wh it e b lood corpuscles 109 , 1 14

Windlass, use in doing work 233—234Windmills 220—22 1Winds, cy clones 36

erosion by 3 14

prevailing w est erlies 33 , 36

sea b reeze 3 1

tornadoes 37

t rade 32

1 1

Winds Cont inued

use of energy of 220—22 1Wir e less t elegraphy 262

Work , defined 228

m easurem ent of 229—230Wyandott e Cav e , format 1on of 3 12

Yeast

cause of fermentat ion