GIFT OF 
 
 Al 
 
AIRPLANES IN ACTION. 
 
GENERAL SCIENCE 
 
 A BOOK OF PROJECTS 
 
 BY 
 
 EDGAR A. BEDFORD, Sc.D. 
 
 HEAD OF THE DEPARTMENTS OF BIOLOGY AND GENERAL SCIENCE 
 DE WITT CLINTON HIGH SCHOOL, NEW YORK CITY 
 
 LECTURER ON METHODS IN TEACHING GENERAL SCIENCE 
 DEPARTMENT OF PEDAGOGY, NEW YORK UNIVERSITY 
 
 ALLYN AND BACON 
 
 BOSTON NEW YORK CHICAGO 
 
 ATLANTA SAN FRANCISCO 
 
COPYRIGHT, 1921 
 BT EDGAR A. BEDFORD. 
 
 

 PREFACE 
 
 THE material of General Science is organized according to 
 the project-problem plan. The class projects are broken 
 up into problems, in the solution of which the pupils are 
 led to form hypotheses from their observations, to check 
 and modify these hypotheses by further observations, and 
 finally to come to a conclusion which is of value in the 
 development of the project. 
 
 The following aims have been kept in mind : 
 
 First : to encourage the spirit of inquiry, and to cultivate 
 the attitude of independent judgment, of opemninded- 
 ness, and of reliance upon facts. 
 
 Second: to put the pupils in possession of certain funda- 
 mental truths which give an explanation of many 
 everyday activities. 
 
 Third: to lead pupils to a broad view of the forces that 
 affect their surroundings, rather than a detailed study 
 of some one section of their environment. The pupils 
 of this early adolescent period are interested in big 
 units and a broad outlook, rather than in minute 
 details. 
 
 The material has been selected from that part of the 
 environment which is related to the practical interests of 
 the pupils. No material has been included merely because 
 it helps in developing some scientific generalization. The 
 needs of the ordinarily well-educated citizen, rather than the 
 
 45^963 
 
iv PREFACE 
 
 needs of the scientist, have influenced the choice of topics. 
 Preference has been given to topics which lead to the 
 understanding of phenomena of large economic importance. 
 
 The environment has been considered as a whole, not as 
 made up of divisions which can be classified as physics, 
 chemistry, biology, astronomy, and physiography. In 
 working out a problem for the solution of the project, use 
 is made of any necessary facts, regardless of whether they 
 belong to this or that special division of science. 
 
 By means of a large number of suggested individual 
 projects, the teacher is enabled to adapt the course to his 
 special school. Pupils are encouraged to work out the 
 projects that are of the most interest to them. Not all 
 that are listed are to be required of any one student. Some 
 are so simple that any one can perform them easily, while a 
 few appeal only to those who have a decided mechanical 
 bent. 
 
 The text carries out the spirit of the recommendations 
 as to general science of the Commission on the Reorgani- 
 zation of Science in the Secondary Schools It is adapted 
 for use in the junior high school, or in the first year of the 
 high school. 
 
 The author wishes to express his appreciation to many 
 friends and fellow teachers whose assistance has contributed 
 much in the preparation of this book. Mr. Harry G. 
 Barber, Department of Biology, and Mr. Thomas Curry, 
 Chairman of the Department of Physics, in the De Witt 
 Clinton High School New York City, have read much of 
 the manuscript and have made helpful suggestions and 
 criticisms. The following teachers of general science in 
 the New York City schools, acting with the author in 
 planning a syllabus in general science, have given much 
 valuable advice: Mr. Maurice W. Kearney, Bay Ridge 
 
PREFACE v 
 
 High School; Dr. Elsie M. Kupfer, Wadleigh High School; 
 Miss Mary Morris, Newtown High School; Miss Ethel 
 Schwarz, Speyer Experimental Junior High School; Miss 
 Emily Topp, Julia Richman High School ; and Dr. George 
 C, Wood, Commercial High School. 
 
 Mr. George K. Gombarts, Head of Art Department, and 
 Mr. John W. Tietz of Department of Biology, De Witt 
 Clinton High School, have given valuable advice concerning 
 illustrations and have furnished original drawings and 
 photographs. 
 
 Dr. Charles F. Brooks of the Weather Bureau, Dr. L. O. 
 Howard, Chief of the Bureau of Entomology, and Mr. W. 
 B. Greeley, Chief of Forest Service, have been generous in 
 opening the resources of their departments. 
 
 Superintendent Clarence E. Meleney, Superintendent John 
 L. Tildsley, and Dr. Francis H. J. Paul, Principal of De Witt 
 Clinton High School, by their broadness of view and edu- 
 cational vision, have been sources of stimulation in the 
 development of the course represented in the book. 
 
 To his wife, Leila Hoge Bedford, the author desires 
 especially to express his indebtedness for her intelligent 
 and painstaking assistance. 
 
 E. A. B. 
 
TABLE OF CONTENTS 
 
 Suggested individual projects, reports, and references are not listed here, but 
 may be found at the end of most projects. 
 
 UNIT I 
 RELATION OF AIR TO EVERYDAY -ACTIVITIES 
 
 PAGE 
 
 PROJECT I. IMPORTANCE OF THE WEIGHT OF AIR . . 1 
 
 Problem 1. How an airplane remains in the air .1 
 
 2. Has air weight? ... . . . 4 
 
 3. Does air press upon things ? . . . .5 
 
 4. How air pressure may be measured . .6 
 
 5. Why water is not used in making barometers 7 
 
 6. How an aviator knows how high he is . . 9 
 
 7. Why air pressure does not prevent us from 
 
 lifting objects .'.-. . . . .9 
 
 8. Why a balloon or dirigible remains in the air 10 
 PROJECT II. How WE USE COMPRESSED AIR . . . .17 
 
 Problem 1. How air pressure is used in building founda- 
 tions and subways . . .17 
 
 2. How compressed air is used in automobile 
 
 tires . . . .... . . .19 
 
 3. How the tire pump works . . . .20 
 
 4. How a force pump sends a steady stream of 
 
 water .... . 22 
 
 PROJECT III. VENTILATION . . .25 
 
 Problem 1. Why rooms should be ventilated . . .25 
 
 2. How air in a room may be set in motion . 27 
 
 3. How convection currents may be used in 
 
 ventilating a room ' v . . 29 
 
 PROJECT IV. WINDS . '. . . . . . -31 
 
 Problem 1. How sea breezes are caused . .31 
 
 2. Why our winds vary in direction and velocity 33 
 
 3. What are hurricanes ? . . . .38 
 
 4. How the weather bureau is able to predict 
 
 the weather . ... .42 
 
 vii 
 
v iii TABLE OF CONTENTS 
 
 PAGE 
 
 J. How WE HEAR 44 
 
 Problem 1. What sound is . . . . .44 
 
 2. How a phonograph reproduces sound . . 47 
 
 3. How the ear is fitted to receive sounds . 50 
 
 PROJECT VI. IMPORTANCE TO Us OF OXIDATION (BURNING) 54 
 
 Problem 1. What burning is ; . . . . .54 
 
 2. How the power of an automobile is produced 57 
 
 3. How a match is lighted . . . .58 
 
 4. What causes iron to rust . . \- .,. . 60 
 
 5. Why coal is burned . . . . .63 
 
 6. How available energy is supplied to the 
 
 human body . . . . .65 
 
 7. Do plants breathe? .. .' . . .67 
 
 8. How animals take in oxygen and give off 
 
 carbon dioxide . -.'" .69 
 
 PROJECT VII. PREVENTION OF DESTRUCTIVE BURNING OR 
 
 OXIDATION . - . . . . .74 
 Problem 1. How destructive oxidation may be prevented 
 
 by excluding the air . . . . .75 
 
 2. How destructive oxidation may be prevented 
 
 by reducing the temperature below the 
 kindling point . " '. . . ; I . . . 77 
 
 3. How destructive oxidation may be prevented 
 
 by removal of fuel material . . . 77 
 
 PROJECT VIII. IMPORTANCE TO Us OF THE OTHER GASES OF 
 
 THE AIR . ' .- r " V '"" I 80 
 Problem 1. Does air contain any gas besides oxygen? . 80 
 
 2. How much of the air is oxygen? . . .80 
 
 3. Importance of nitrogen in the air . . . 81 
 
 4. Importance of carbon dioxide of the air . 82 
 
 PROJECT IX. To KEEP FOODS FROM SPOILING . . .92 
 Problem 1. What causes foods to spoil or decay? . . 92 
 
 2. Where bacteria are found . . . .93 
 
 3. Size, shape, and method of multiplication of 
 
 bacteria 95 
 
 4. What conditions are favorable and what un- 
 
 favorable for growth of bacteria and 
 molds? 96 
 
TABLE OF CONTENTS ix 
 
 PAGE 
 
 Problem 5. Use of cold in the home in checking the 
 
 growth of bacteria . . . .97 
 
 6. Use of cold in storage warehouses . . 100 
 
 7. Use made of heat in food preservation . 103 
 
 8. Use made of other methods of food preser- 
 
 vation 104 
 
 PROJECT X. To PROTECT OURSELVES AGAINST HARMFUL 
 
 MICROORGANISMS 108 
 
 Problem 1. How bacteria and other microorganisms 
 
 affect the health . . . . .108 
 
 2. How disease germs may pass from one per- 
 
 son to another . . . . . Ill 
 
 3. How the body fights disease . . .113 
 
 4. How the body acquires special power to 
 
 fight disease 115 
 
 5. Use of disinfectants and antiseptics . .119 
 
 PROJECT XI. To FIND OUT How SOME BACTERIA AND 
 
 MOLDS ARE USEFUL . . . .122 
 Problem 1. Are bacteria of decay of any value ? . . 122 
 
 2. How bacteria on the roots of some plants 
 
 may enrich the soil . ... 123 
 
 3. How bacteria are useful in other ways . 125 
 
 UNIT II 
 RELATION OF WATER TO EVERYDAY ACTIVITIES 
 
 PROJECT XII. MOISTURE IN THE AIR AND ITS IMPORTANCE 
 
 TO Us . . ., ..;: .... 127 
 
 Problem 1. How dew is caused 127 
 
 2. How fogs and clouds are produced . . 131 
 
 3. How rain, snow, and hail are formed . .132 
 
 4. Reasons for unequal distribution of rainfall 134 
 
 5. How water is supplied to dry areas . . 136 
 
 6. How moisture gets into the air . . . 138 
 
 7. How the amount of moisture in the air 
 
 affects our comfort V . . . 142 
 
 PROJECT XIII. THE RELATION OF PLANTS TO MOISTURE . 144 
 Problem 1. Do plants give off moisture? . v < , -* ; 144 
 
X TABLE OF CONTENTS 
 
 PAGE 
 
 Problem 2. The amount of water given off by plants . 145 
 
 3. How the root system of a plant is fitted to 
 
 find water . . . ;. . ' . . 145 
 
 4. How roots are especially fitted to take in 
 
 moisture . . : .... . . 146 
 
 5. How root hairs take in water . . . 148 
 
 6. How water passes out of the leaves . . 149 
 
 PROJECT XIV. WATER POWER . . ... .152 
 
 Problem 1. What is the source of energy of water power ? 153 
 2. Source of the power of hydraulic pressure . 157 
 
 PROJECT XV. To UNDERSTAND How COMMUNITIES OBTAIN 
 
 A GOOD SUPPLY OF WATER . . . 160 
 Problem 1. Why a wooded mountainous region is se- 
 lected to furnish water . .161 
 
 2. How the water is protected . . . 164 
 
 3. How other cities obtain a supply of water . 166 
 
 4. How the water system within the house 
 
 should be cared for . . . . 168 
 
 PROJECT XVI. To UNDERSTAND THE DISPOSAL OF SEWAGE 
 
 OF .HOMES AND COMMUNITIES . . : . 171 
 Problem 1. Care of waste water pipes . . . . 171 
 
 2. Sewage disposal in villages and isolated 
 
 houses . . . ..': .- - 171 
 
 3. Sewage disposal in cities . : . . . 172 
 
 PROJECT XVII. WATER AS "A MEANS OF TRANSPORTATION 175 
 Problem 1. How New York harbor originated . .175 
 
 2. Effect of the forests of the Adirondacks upon 
 
 New York harbor and the navigability 
 
 of the Hudson River . . . .178 
 
 3. Importance of internal waterways . .182 
 
 4. How ocean transportation depends upon 
 
 science 186 
 
 UNIT III 
 
 THE RELATION TO US OF SUN, MOON, AND STARS 
 PROJECT XVIII. To UNDERSTAND THE CAUSE OF TIDES . 191 
 
 Problem 1. What causes the water to rise 
 
 192 
 
TABLE OF CONTENTS 
 
 XI 
 
 PAGE 
 
 Problem 2. Why there are two high tides a day . .195 
 
 3. Why high tide is a little later every day . 196 
 
 4. Why the moon does not fall to the earth . 197 
 
 5. Why, at times, there are especially high tides 199 
 
 6. Why sometimes only a portion of the moon 
 
 is visible to us . . . .201 
 
 PROJECT XIX. How TO KNOW SOME OF THE FIXED STARS 205 
 Problem 1. How to recognize the constellations around 
 
 the north pole ..... 205 
 2. How to recognize the constellations seen only 
 
 hi winter ... . . . 207 
 
 PROJECT XX. TIME AND SEASONS . . . . . . 211 
 
 Problem 1. Why we have winter and summer . .211 
 
 2. Why July and August are the hottest months 
 
 and January the coldest month . . 213 
 
 3. How time is calculated .... 214 
 
 4. How places on the earth's surface are 
 
 indicated 217 
 
 UNIT IV 
 WORK AND ENERGY 
 
 PROJECT XXI. THE SUN AS A SOURCE OF ENERGY . . 219 
 Problem 1. How the sun's energy is used in making 
 
 pictures 221 
 
 2. Other chemical changes produced by the 
 
 sun's energy 223 
 
 3. How direct use may be made of the sun's 
 
 energy 223 
 
 4. How the energy of the sun is maintained . 225 
 
 PROJECT XXII. MACHINES .228 
 
 Problem 1. What is meant by work and force . . 228 
 
 2. How work and force are measured . . 229 
 
 3. Reasons for using machines . . . 230 
 
 4. How the lever is used in doing work . .231 
 
 5. How wheels are used in doing work . . 233 
 
 6. Why pulleys are used . . , . . 235 
 
 7. How inclined, planes are used in doing work 238 
 
 8. Why machines are not 100 per cent efficient 241 
 
Xll TABLE OF CONTENTS 
 
 PAGE 
 
 9. How friction may be reduced . ' . , . 242 
 
 10. Is friction ever useful . . . . . . 243 
 
 11. Causes of inefficiency of engines . 245 
 
 12. The working of the gas engine . , Y . 246 
 
 PROJECT XXIII. ELECTRICITY AND MODERN LIFE . . 252 
 
 Problem 1. How the electric bell rings . . -.'>;. . 253 
 
 2. How magnets are used . ' . y .' J . 255 
 
 3. How chemical energy may be changed into 
 
 electrical energy 257 
 
 4. How electricity is measured : volts, amperes, 
 
 kilowatts . . ' v . . . 259 
 
 5. Use of induction coil in wireless telegraphy 
 
 and in the production of spark in gaso- 
 line engine . . ; . . . 261 
 
 6. How mechanical energy is changed into elec- 
 
 trical energy by the dynamo . . 262 
 
 7. How electrical energy is changed into me- 
 
 chanical energy by the electric motor . 265 
 
 8. How electroplating and electrotyping are 
 
 done -. 266 
 
 9. How heat is produced by electricity . . 267 
 
 10. How electric lights are produced . . 268 
 
 11. How the " storage battery" is used y . 271 
 
 12. How lightning is produced . \ > ; , . 273 
 
 PROJECT XXIV. RELATION OF LIGHT TO OUR ABILITY TO 
 
 SEE THINGS 276 
 
 Problem 1. How objects are visible .... 276 
 
 2. Cost of artificial lighting of rooms . . 278 
 
 3. Why shades and reflectors are used . . 282 
 
 4. How the color of the wall affects the lighting 
 
 of a room 285 
 
 5. Why objects have different colors . . 286 
 
 6. What is the cause of the colors of sunset and 
 
 sunrise and of the blueness of the sky ? 287 
 
 7. Why eyeglasses are used by some persons . 288 
 
 8. Advantage of having two eyes . . . 293 
 
 9. How eyes may be injured . . . . 293 
 
 10. How a lens makes objects appear larger . 294 
 
 11. How motion pictures are produced . . 295 
 
TABLE OF CONTENTS xiii 
 
 Problem 12. How light effects may guide us in the selec- 
 tion of clothing . . . ' . . 297 
 PROJECT XXV. IMPORTANCE OF HEAT TO Us . . . . 300 
 Problem 1. How a thermos bottle keeps hot liquids hot 
 
 and cold liquids cold .... 300 
 
 2. How food may be cooked in a fire less cooker 30 1 
 
 3. What substances are good and what are 
 
 poor conductors of heat . . . 302 
 
 4. How houses are heated 304 
 
 UNIT V 
 
 RELATION OF SOIL AND PLANT LIFE TO EVERYDAY 
 ACTIVITIES 
 
 PROJECT XXVI. How SOIL Is MADE . . . . 308 
 
 Problem 1. Of what is soil composed ? .... 309 
 
 2. Evidence that soil is now being formed . 310 
 
 3. How soil has been produced by weathering 311 
 
 4. How soil has been produced by water and 
 
 wind erosion .. .... 313 
 
 5. How most of the soil of northern United 
 
 States has been produced . . 314 
 
 6. How soil has been produced by decay of 
 
 organic matter . . . .318 
 
 PROJECT XXVII. RELATION OF SOIL TO PLANTS . 321 
 
 Problem 1. How the water-holding power of the soil 
 
 may be increased ' ; ' 321 
 
 2. What plants take from the soil . 
 
 3. How nitrogen may be given to the soil . 324 
 
 4. How potassium and phosphorus are supplied 
 
 to the soil . 325 
 
 5. How plants remove needed materials from 
 
 the soil ... -326 
 
 6. What plants do with material taken from 
 
 the soil . . -327 
 
 PROJECT XXVIII. How PLANTS AND ANIMALS MAKE USE 
 OF THE FOOD MANUFACTURED BY 
 PLANTS . - 329 
 
XIV 
 
 TABLE OF CONTENTS 
 
 PAGE 
 
 Problem 1. Why must plants and animals have food? . 329 
 
 2. What foods are good for fuel, and what ones 
 
 for growth and repair .... 330 
 
 3. How the fuel value of foods is measured . 333 
 
 4. What is the proper amount of food ? Table 
 
 of 100 Calorie Portions . . . .336 
 
 5. What considerations should govern the plan- 
 
 ning of our diet ? . . . . . 342 
 
 6. Why must foods be digested? . . . 343 
 
 7. How can we prove that nutrients are 
 
 digested? 345 
 
 8. Where is food of the human body digested? 346 
 
 PROJECT XXIX. How PLANTS PRODUCE SEED . v- . 349 
 
 Problem 1. Why plants produce seed .... 349 
 
 2. What are the parts of a seed? . . . 349 
 
 3. Where seeds are produced . . . . 352 
 
 4. Do ovules always develop into seeds ? . - 353 
 
 5. How the pollen grain influences the develop- 
 
 ment of the ovule into the seed . . 354 
 
 6. Does it make any difference whether the 
 
 pollen comes from the same flower or 
 
 a different one? . ^ . . . 355 
 
 7. How self-pollination is prevented . . 356 
 
 8. How pollen is carried from one flower to 
 
 another '* . . . . . 357 
 PROJECT XXX. How BETTER PLANTS AND ANIMALS ARE 
 
 PRODUCED . . : : .,. , : . . 362 
 Problem 1. Have we evidence of improvement of plants 
 
 and animals during past generations ? 362 
 
 2. How plants and animals may be improved 
 
 by selection . . . *-"' . 363 
 
 3. How more rapid improvement may be 
 
 brought about . . . . . 364 
 
 PROJECT XXXI. INSECT ENEMIES OF PLANTS . . . 369 
 
 Problem 1. How insects are injurious to plants . * . 369 
 
 2. How injurious insects may be destroyed . 372 
 
 3. How the number of injurious insects is 
 
 reduced by natural means . . . 375 
 
 APPENDIX * . . 381 
 
LIST OF ILLUSTRATIONS 
 
 FIGURE PAQE 
 
 Airplanes in Action . . ^>u, - -. . Frontispiece 
 
 1. Sectional View of an Airplane . . r, 2 
 
 2. Airplane in Air . . . y , . . . 3 
 
 3. United States Airplane . . .* :>\^ -4 
 
 4. Weighing Basket Ball Inflated with Air . .5 
 
 5. Weighing Basket Ball after Air Has Been Exhausted . 5 
 
 6. Simple Barometer . . ...,. :,,..-. 6 
 
 7. Mercurial Barometer . , ..;,,.; -.:.: . . . 7 
 
 8. Aneroid Barometer . . .. . -.,. . . 8 
 
 9. Diagram of an Aneroid Barometer 9 
 
 10. Inverting a Glass Filled with Water . . . .10 
 
 11. French War Balloon ;..,.,... . ... 10 
 
 12. Making Hydrogen ... . ,. 
 
 13. Drawing Up Ink into a Medicine Dropper > . 11 
 
 14. Pouring Liquid from a Small Opening in a Can . . 12 
 
 15. Relative Size of Chest Cavity during Inspiration and 
 
 Expiration ., . . . .12 
 
 16. Non-skid Automobile Tire . . * , .... . .-.;-'. 
 
 17. Sole of Basket Ball Slipper ; .. -.; ; : 13 
 
 18. Suction Pump . . . . ..-. . . 14 
 
 19. Siphoning Liquid from a Barrel . ; . T-\4^ 14 
 
 20. An Inverted Drinking Glass Pushed Down into Water . 17 
 
 21. Caisson . . . ". | . . . . : ; ^;:- . 18 
 
 22. Bicycle Pump .... , ; . ,. . ^| . 21 
 
 23. Force Pump . . . , . .', ''.'.. / . . .. . 21 
 
 24. Compressed Air Drills . ..... . ,. : . - 22 
 
 25. Riveting Hammer /. . . -.. * . . 23 
 
 26. Electric Fan -:'. .. . ' . . .... , . -i '.. 27 
 
 27. Heating Air in a Flask . . ,,.., U .. . 28 
 
 28. Currents of Air in a Refrigerator . . . ,* , = . 28 
 
 29. Ventilation by Window . . . . - , , . .. . 29 
 
 30. Fireplace 30 
 
 31. Summer Monsoon . . . . , . \ ' V . 32 
 
 xv 
 
xvi LIST OF ILLUSTRATIONS 
 
 FIGUKE PAGE 
 
 32. Winter Monsoon . ' . . .. . . . . 32 
 
 33. The World's Winds . . A .. /,,. . . . .33 
 
 34. Progress of a Storm Center . .- 33 
 
 35. Weather Map . . . . . .... 34 
 
 36. Weather Map of the Following Day . . . .35 
 
 37. Usual Paths of " Highs" and " Lows" .... 36 
 
 38. Tornado . . .37 
 
 39. Results of a Severe Windstorm . . ... 38 
 
 40. Path of a Hurricane . , . .' . . . . 39 
 
 41. Cumulus Clouds . . "' ;; : , : . -' ; . .. . . 40 
 
 42. Thunderstorm . ; . 41 
 
 43. Touching the Surface of Water with a Tuning Fork. . 45 
 
 44. One of the Earliest Talking Machines . . ; .46 
 
 45. Phonograph .-* . . 47 
 
 46. Micro-photograph of Portion of a Record . . . 48 
 
 47. Phonograph Record . . . ' v . ."' . 49 
 
 48. Telephone Transmitter < . . -. . . ! . 50 
 
 49. Human Ear . ' . . . . '.''. :> - . . .51 
 
 50. Oil Fire . . . ^ . ; .' ' ,'. ;; .54 
 
 51. Lighted Candle under Inverted Glass Jar . . . 55 
 52a. Bunsen Burner ; . .. ; ;.. . . . . . 56 
 
 526. Gas Stove Burner . . . . . . . 56 
 
 53. Movements of Piston of Gas Engine . . . ' . 57 
 
 54. AMatch. . '' ; v ' . . . . . . . 58 
 
 55. Rusting of Iron . ..... .... 60 
 
 56. Sectional View of a Hotbed . . , ". . . 61 
 
 57. Factory Wrecked by a Dust Explosion . . . .62 
 
 58. Available Coal Supply . . . . * . . .63 
 
 59. Coal Fields of the United States -. . r ... 64 
 
 60. Fuel Value of Some Common Foods .' -. " . . 66 
 
 61. Flooded Region . . ; . ; . . .68 
 
 62. Organs of an Earthworm . . . . '.' . .69 
 
 63. Stages in the Life History of a Beetle .... 71 
 
 64. Breathing Organs of a Fish 72 
 
 65. Results of a Forest Fire 74 
 
 66. Fire Extinguisher 76 
 
 67. Fighting a Fire with Water . . . . ; . . 77 
 
 68. A Forest Fire Fighter .... .78 
 
 69. Forest Ranger on Lookout for Signs of Forest Fires . 79 
 
 70. Preparation of Oxygen . ./ . V- - &1 
 
LIST OF ILLUSTRATIONS xvii 
 
 FIGURE PAGE 
 
 71. Potato Plant ; '. 1. 83 
 
 72. Coal Bed . . : . < . . i ; V ' . ^. 86 
 
 73. Heating Value of Some Common Fuels < . -,i f , 87 
 
 74. Oil Wells in Oklahoma . ' ;r ^- ".-.-,- '. .! 88 
 
 75. A Balanced Aquarium . . . ' .', 7 89 
 
 76. Relation of Plants and Animals in a Balanced Aquarium 90 
 
 77. Colonies of Bacteria and Mold ... . . 94 
 
 78. The Four Types of Bacteria . . ' . . . . 95 
 
 79. Wall of a Refrigerator . . ... . .98 
 
 80. Currents of Air in a Refrigerator . . . . .98 
 
 81. Iceless Refrigerator . . . . . . . 99 
 
 82. Framework of an Iceless Refrigerator . ; . .100 
 
 83. Ice Plant ; . 101 
 
 84. Storage of Butter in a Refrigerating Plant . .. . .102 
 
 85. Dead Chestnut Trees . . . ^/.' . . . 109 
 
 86. A Fresh Air Camp in California . .115 
 
 87. Results of Use of Diphtheria Antitoxin ''. 118 
 
 88. Danger of Delay in Using Antitoxin . . .119 
 
 89. Roots of a Bean Plant . .... . 124 
 
 90. Altocumulus Clouds . . V 129 
 
 91. Undulated Alto-cumulus Clouds . . . . ' i 130 
 
 92. Cumulus Clouds over Pacific Ocean .. . v ": 131 
 
 93. Rain Gauge . . ftSj 
 
 94. Snowflakes . 
 
 95. Heavy Fall of Snow in a Pine Forest . 
 
 96. Average Rainfall of the United States . . .35 
 
 97. Landscape in an Almost Rainless District in Arizona . 136 
 
 98. Arizona Desert before Irrigation . . 137 
 
 99. Arizona Desert after Irrigation .> * 137 
 
 100. Roosevelt Dam, Arizona . * .,-. 
 
 101. Map Showing Location of Irrigation Projects . . 139 
 
 102. Russian Salt Fields . . V . .' . 141 
 
 103. Wet and Dry Bulb Thermometer . 
 
 104. Transpiration . . . '.' 
 
 105. Upturned Sugar Maple . U . . . 146 
 
 106. Young White Cedars . v ' ; . - . 147 
 
 107. Germinating Wheat Showing Root Hairs . . -148 
 
 108. Root Hairs . . . . . . ; ; ' . 148 
 
 109. A Living Tree with a Hollow Trunk . 
 
 110. Lower Epidermis of a Leaf . ., 150 
 
xviii LIST OF ILLUSTRATIONS 
 
 FIGURE PAGE 
 
 111. Train Drawn by an Electric Locomotive -, , >;.', : . 152 
 
 112. Waterfall, McKenzie River, Oregon ./ . ;, . 153 
 
 113. Diagram of a Power House . . . . . . . 154 
 
 114. Electric High Tension Transmission Line -....-' ; -. J- . 156 
 
 115. Water Power Station .... .157 
 
 116. Illustrating Hydraulic Pressure . . , ... . 157 
 
 117. Hydraulic Press . ... . . . . . 158 
 
 118. Source of Water Supply of New York City . .;'., . 161 
 
 119. Kensico Dam -'1J. . 162 
 
 120. Height to Which New York Water Will Rise . . . 162 
 
 121. Forest Floor. . . . . ...-,.... : 163 
 
 122. A Stream in the Catskill Mountains ... . . 164 
 
 123. Aerators . . . . . , . : .'< . 165 
 
 124. Diagram of a City Water Supply System . \ ... 166 
 
 125. Reservoir and Dam . . . . ...;. ' . .167 
 
 126. Limestone Cave . ..;..-. .,. . . 168 
 
 127. Water Closet Tank . . . . '. . ...; . 169 
 
 128. Trap of Waste Water Pipe . ... s .;-..- . ' . 171 
 
 129. SepticTank. . . .'.-,./ . . .- . 172 
 
 130. Map of New York Harbor . . : . -^ . . 176 
 
 131. Coast of Eastern United States . : . . .- . 177 
 
 132. Outline of South America ."->. . . . . 178 
 
 133. Outline Map of England -. . ..,..':, . 179 
 
 134. Stratified Rocks . ,. . . . .-.-.. . 180 
 
 135. Erosion by Small Stream ., *. . . . , . 181 
 
 136. Flood in Wabash River, Indiana . ... . .182 
 
 137. Use of River for Transportation of Logs . . .183 
 
 138. Use of Internal Waterways to Transport Farm Products 184 
 
 139. Possibilities of Development of Internal Waterways . 185 
 
 140. United States Warship Passing through Panama Canal 187 
 
 141. Minot's Ledge Lighthouse . . . ,-. . . 188 
 
 142. High Tide in a Harbor in Nova Scotia . . . .192 
 
 143. Low Tide in the Same Harbor . . . . .192 
 
 144. Plumb Line 194 
 
 145. Stable, Unstable, and Neutral Equilibrium . . . 195 
 
 146. Relation of Moon to the Tides . ' . . . .195 
 
 147. Action of Water and Mercury in Rotating Glass Globe 198 
 
 148. The Two Positions of the Moon When High Tide Is 
 
 Higher than Usual 200 
 
 149. The Two Positions of the Moon When High Tide Is 
 
 Not as High as Usual . . . ; . . . 200 
 
LIST OF ILLUSTRATIONS s xix 
 
 150. Phases of the Moon . . -. . . '.-'< . 201 
 
 151. A Total Eclipse of the Sun . . . . . . 202 
 
 152. Diagram of Our Solar System . . . . . 203 
 
 153. Constellations around the North Star .... 206 
 
 154. Evening Sky Map for January, 1921 . . . .208 
 
 155. Heat from Sun, Summer and Winter . . . .212 
 
 156. Path of Earth around the Sun . . . . . 212 
 
 157. Annual Temperature Curves 213 
 
 158. Lines of Latitude and Longitude 215 
 
 159. Standard Time Belts J 216 
 
 160. Windmill 220 
 
 161. A Negative '. . .221 
 
 162. Print Made from Negative . -:* . . . .222 
 
 163. Cold Frame . . . . ; .... 224 
 
 164. Solar Engine ... . . . .224 
 
 165. Spring Balance 229 
 
 166. Claw Hammer 230 
 
 167. Crowbar . 231 
 
 168. Tongs 232 
 
 169. Scissors v 232 
 
 170. Nutcracker . 
 
 171. Arm as a Lever . 233 
 
 172. Well Windlass 234 
 
 173. Part of a Derrick 235 
 
 174. Placing Heavy Pipe in Position 236 
 
 175. Pulleys 237 
 
 176. Block and Tackle 238 
 
 177. Road near Colorado Springs, Colorado . . . 239 
 
 178. Raising a Weight by Use of Inclined Plane . . . 239 
 
 179. Wedge . . . . . . : . . w . 240 
 
 180. Screw .240 
 
 181. Demonstration that Screw Is an Inclined Plane . . 240 
 
 182. Jackscrew . . . . v . . . . 240 
 
 183. " Skidding "Logs on Snow . . . . " ^ . 242 
 
 184 a. Roller Bearings . ..... . . . . 243 
 
 1846. Ball Bearings . . . . '.- . . . .243 
 
 185(o,6,c,d). Knots .245 
 
 186. Movements of Piston in a Four-cycle Engine s . . 246 
 
 187. Sectional View of an Automobile 248 
 
 188. Grand Central Terminal, New York City, before Elec- 
 
 trification . .252 
 
XX LIST OF ILLUSTRATIONS 
 
 FIGURE PAGE 
 
 189. Grand Central Terminal, New York City, after Elec- 
 
 trification ... . . . . . 253 
 
 190. Direction of Current through an Electric Bell . . 254 
 
 191. A Simple Electromagnet . :>.,- . r ; , . 255 
 
 192. Dynamo Attached to an Ambulance . , . . 255 
 
 193. Arrangement of Iron Filings between Poles of a Magnet 256 
 
 194. Magnetic Needle . . . ... . . 257 
 
 195. First of All Electric Batteries Prepared by Volta, A. D. 
 
 1800 . . .- i '. 257 
 
 196. Gravity Cell -,'.. . ' . . ; . , . - ; . 258 
 
 197. Daniel Cell. ... .... . . . . 259 
 
 198. Dry Cell . . . . . . . v .. ^ . 259 
 
 199. Structure of an Induction Coil . . . . - . 261 
 
 200. U. S. Army Wireless Operators Receiving Messages from 
 
 an Airplane, Tours, France . . . . 262 
 
 201. A Simple Dynamo . . ; ... . . 263 
 
 202. Principle of Dynamo . . , . .- a.v ; " . 263 
 
 203. A Simple Commutator 264 
 
 204. Use of Electric Motor in Running Sewing Machine . 264 
 
 205. Expc i imc nt 1 Illustration of Principle of the Motor . 265 
 
 206. Si'ver Plating .... .' . . '. ,. ',", . 266 
 
 207. An Electrotype . . ... . . .- '. . 267 
 
 208. E'ectric Flatiron . .... '.- - ' ' 268 
 
 209. Carbon Filament Lamp . . -. . , . 269 
 
 210. Tungsten Filament Lamp . /. . .. . 269 
 
 211. Amount of Light Given by Different Incandescent 
 
 Lamps . . .. . . ; ... i . 269 
 
 212. Fuse . . , .' . 270 
 
 213. Position of Carbons in an Arc Light . . . -:-.. 270 
 
 214. Storage Battery Dissected to Show Construction . 272 
 
 215. Reflection of Light from a Polished and a Mirrored 
 
 Surface . : ,, . . . . . ; . :. 276 
 
 216. Reflection of Light from a Smooth Surface . . . 277 
 
 217. Heliograph . ... . . .278 
 
 218. Reflection of light from a Slightly Rough and a Rough 
 
 Surface 279 
 
 219. Relation of Intensity of lUumination to Distance from 
 
 Source of Light o, - . 279 
 
 220. Photometer . 280 
 
 221. Gas Meter Reading 5700 Feet . . . ./ . 281 
 
LIST OF ILLUSTRATIONS XXI 
 
 FIGURE PAGE! 
 
 222. Gas Meter Reading 68700 Feet '-.' : i" ^ .^ ;' .281 
 
 223. Face of a Kilowatt Hour Meter . -';. : , ; ~ 4^ . 282 
 
 224. Relative Costs of Different Lights . . . .282 
 
 225. Comparative Amounts of Light Given by an Open Gas 
 
 Flame and a Gas Mantle . . . . .282 
 
 226. Cost Per Hour of Different Gas Lights . . .283 
 
 227. Shaded Light . . . .'.'-. . .283 
 
 228. Lamp Showing Effect of Use of Shade . 283 
 
 229. Reflection of Light by a Polished Metal Reflector . 284 
 
 230. Reflection and Transmission of Light . . 284 
 
 231. Breaking Up of Light in Passing through a Prism . 287 
 
 232. Rays of Light Passing into the Eye . .289 
 
 233. A Diagram Showing How a Light Ray May Be Bent . 290 
 
 234. Bending of Rays of Light by Grooved Glass . . 290 
 
 235. Change of Focus of Eye . y. .291 
 
 236. Farsightedness and Its Correction . 292 
 
 237. Nearsightedness and Its Correction . . . . . 292 
 
 238. Magnifying Glass 295 
 
 239. A Moving Picture Film ..... 296 
 
 240. Lines Which Deceive the Eye . . . .297 
 
 241. Thermos Bottle 300 
 
 242. Fireless Cooker . 301 
 
 243. House Heated by Hot Air 304 
 
 244. House Heated by Hot Water . . . . .305 
 
 245. Circulation of Water, in the Radiator and around the 
 
 Cylinders of an Automobile 306 
 
 246. Relative Size of Soil Particles . '.. . ' . . . 309 
 
 247. Disintegration of Rock 310 
 
 248. Rugged Mountains Showing the Effect of Weathering . 311 
 
 249. Weathered Rock at Base of a Cliff . ;", . . 312 
 
 250. Rock Being Split by the Growth of a Tree . f . ; . 313 
 
 251. Beech Tree Growing on Rocks . . . . . 314 
 
 252. Water Erosion . . . . v: . . v . 315 
 
 253. Soil Deposited by a Glacier . . . H . - ,- . 315 
 
 254. Rock Showing Glacial Scratches . . i - : ' . . 316 
 
 255. Extent of Ice Sheet during Glacial Period . v . 317 
 
 256. A Glacier 'V , : V . 318 
 
 257. Front of a Glacier, Mt. Rainier National Park . . 319 
 
 258. Formation of Humus . ' . .... .319 
 
 259. Vacant Lot Garden . . . V .322 
 
xxii tIST OF ILLUSTRATIONS 
 
 FIGURE PAGE 
 
 260. Absorption of Water by Soils . . K .. .... . 323 
 
 261. Lumbermen at Work .... ,. . . . 330 
 
 262. Composition of Bread and Cereal Foods . . .332 
 
 263. Composition of Some Common Vegetables . . . 333 
 
 264. Composition of Fish and Oysters . . ,., . . . 334 
 
 265. Composition of Eggs and Cheese .... . 335 
 
 266. Composition of Various Grains Used for Food . . 336 
 
 267. Cross and Longitudinal Sections of a Young Root . 344 
 
 268. Food Canal (Alimentary Canal) of Man . .... .346 
 
 269. Organs of Circulation of Man ,. . . . - . ; . 347 
 
 270. Seeds of Bean and Pea . . . . _ ; .. . . 350 
 
 271. Sprouting Corn Grain . . r . v . 351 
 
 272. Pear, from Bud to Fruit and Seed . . . . 352 
 
 273. Growth of Pollen Tubes Down through the Style . 354 
 
 274. Pollen Tube Entering Ovule . . ... 355 
 
 275. Pistillate Flowers of Corn . . . .. . ... . 356 
 
 276. Corn Tassel Made Up of Staminate Flowers . . 357 
 
 277. Staminate Flowers of Chestnut . ... . 358 
 
 278. Flowers of Oak ... . . . .- ." . 358 
 
 279. Flowers of Horsechestnut . . . . .. , . 359 
 
 280. Cherry Blossoms . . . '...- ... . 360 
 
 281. Variation . . . ... . .< . . ; , . 364 
 
 282. Tongue Grafting . . . , . ,. (j . ft .* ,,> . 365 
 
 283. Cleft Grafting . . -, ,, . ; : . '.... : . --*... . 366 
 
 284. Budding, a Form of Grafting Vv .- ,\- ,- . 366 
 
 285. Life History of Gypsy Moth . . .- . . 369 
 
 286. Potato Beetle . . .'',. .-. . ; . . . . 370 
 
 287. Peach -Tree Borer . . ..; ... .370 
 
 288. Group of Dying Locust Trees . . .: . .371 
 
 289. Worm in Apple, Larva of Codling Moth . . .371 
 
 290. Scale Insects on a Fern Leaf . . . . ;< . . 372 
 
 291. Tent Caterpillars . . ^: v . .> > .-.' . 373 
 
 292. A Modern Spraying Outfit . .. v . . . . 374 
 
 293. A Beneficial Beetle . =.;..,;, . . .375 
 
 294. Ladybird Beetle 376 
 
 295. Ladybird Beetle Feeding on Scale Insects . . .377 
 
 296. Toads Eating Caterpillars 378 
 
ACKNOWLEDGMENTS OF 
 ILLUSTRATIONS 
 
 Chicago, Milwaukee, and St. Paul R. R., No. 113. 
 
 Columbia 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, 111, 115, 188, 189, 204. 
 Grand Trunk R. R., No. 256. 
 Harvey Conard, Hollis, New York, No. 239. 
 John Reiss, New York City, No. 21. 
 Leon Barritt, Brooklyn, New York, No. 154. 
 New York Board of Health, No. 87, 88. 
 New York Zoological Society, No. 475. 
 National Lamp Works, General Electric Company, No. 215, 216, 
 
 217, 218, 227, 228, 229, 230, 234. 
 Packard Motor Company, No. 1, 187. 
 Pacific Northwest Tourist Association, No. 257. 
 Pennsylvania Lines, No. 136. 
 
 Signal Corps, American Expeditionary Force, No. 11, 192, 200. 
 Thomas Edison, Inc., No. 46, 47. 
 U. S. Bureau of Chemistry, No. 57, 67. 
 U. S. Bureau of Entomology, No. 63, 287, 288, 293, 295, 296. 
 U. S. Bureau of Standards, No. 219, 221, 222, 223, 224, 225, 226. 
 U. S. Dept. of Agriculture, No. 81, 82, 84, 263, 264, 265, 266, 267. 
 U. S. Geological Survey, No. 50, 58, 59, 72, 74. 
 U. S. Naval Observatory, No. 151. 
 U. S. Reclamation Service, No. 98, 99, 100, 101, 114. 
 U. S. Weather Bureau, No. 6, 8, 34, 35, 36, 37, 38, 41, 90, 91, 93, 
 
 94, 103. 
 
 U. S. Navy, No. 42. 
 
 Wcston Electrical Instrument Company, No. 193, 195, 201, 205. 
 
 xxiii 
 
GENERAL SCIENCE 
 
 UNIT I 
 
 RELATION OF AIR TO EVERYDAY ACTIVITIES 
 
 PROJECT I 
 IMPORTANCE OF THE WEIGHT OF AIR 
 
 FOR many centuries men who experimented with the prob- 
 lem of keeping a body heavier than air moving through it 
 as a bird flies were the objects of ridicule and derision. Only 
 so short a time ago as 1905, the first successful flying machine 
 was invented by Wilbur and Orville Wright of Dayton, 
 Ohio. 
 
 Now, after invaluable service in the Great War, the air- 
 plane in a highly perfected stage has crossed the Atlantic 
 Ocean. It has crossed our continent, a distance of 3000 
 miles, in 25 hours of actual flying time. One of man's 
 greatest ambitions has become a reality, and without doubt 
 the future holds further achievement in the development of 
 the airplane as wonderful as that of the last few years. 
 
 Problem 1. How an airplane remains in the air. The 
 study of the kite may help us to understand the airplane. 
 Is it possible to fly a kite on a day when there is no wind? 
 In starting to fly a kite, does a boy run with or against the 
 wind? Is running necessary to start the kite on a day 
 when a strong wind is blowing ? What happens if the string 
 
 1 
 
IMPORTANCE OF THE WEIGHT OF AIR 
 
 breaks? What is the purpose of the tail of the kite? As 
 a result of a consideration of these questions, it will be un- 
 derstood that a plane or flat surface, if held at the proper 
 angle, is kept up by the force exerted by the air in motion. 
 That air in motion has great force, is well known to us. 
 The destruction caused by a severe wind is sufficient proof 
 
 FIGURE 2. AIRPLANE IN AIR. 
 
 of this. We are also familiar with the fact that even when 
 there is no movement of the air, the same force is exerted if 
 an object is passing rapidly through the air. A ride on the 
 front seat of a street car or in a rapidly moving automobile 
 convinces us of the force which may be considered to be 
 exerted either by the moving body or by the air. 
 
 The airplane with its light, high power engine is able 
 by means of its propellers to attain great speed through the 
 
GENERAL SCIENCE 
 
 air. The planes may be so controlled that they present the 
 proper angle to the air. . The same force is exerted if the 
 machine is moving 75 miles per hour, as if the machine were 
 
 FIGURE 3. UNITED STATES AIRPLANE. 
 
 Photographed on the flying field at Tours, France. Explain the appear- 
 ance of the propeller and the dust cloud behind and to the left of the 
 machine. Note the slant of the planes. 
 
 stationary and the air were moving 75 miles per hour. It 
 will thus be seen that the airplane remains in the air for the 
 same reason that a kite remains in the air. 1 
 
 Problem 2. Has air weight? As the propeller of the 
 airplane drives the machine through the air very much as 
 the propeller of a boat drives it through the water, air 
 seems to be a substance, just as water is. If this is true, 
 it should have weight. Weight is the measure of the pull 
 of the earth (gravity) upon particles composing various 
 
 1 Many pupils will want to make model airplanes. At the end of 
 the chapter references are given which will provide directions as to the 
 details of their construction. 
 
IMPORTANCE OF THE WEIGHT OF AIR 
 
 materials. The weight of a book is the measure of 
 the pull of the earth upon the book. If we drop it, it falls 
 or is pulled toward the 
 center of the earth. How 
 may we discover that air 
 has weight ? The follow- 
 ing experiment has been 
 tried many times. 
 
 FIGURE 4. 
 
 Experiment. Weigh care- 
 fully a strong flask ; then by 
 means of an air pump remove 
 the air from it and weigh it 
 again. What is the result? 
 That air has weight, may 
 also be shown by blowing up 
 
 a basket ball or football until it is full and then weighing it (Figure 4), 
 and after allowing the air to escape, weighing it again (Figure 5). 
 
 Careful weighing has shown that one cubic foot of dry air 
 at sea level and at the freezing temperature (of water) weighs 
 
 about one thirteenth of 
 a pound. Calculate ap- 
 proximately the weight 
 of the air in the school- 
 room ; in your bedroom, 
 etc. 
 
 Problem 3. Does air 
 press upon things? If 
 air has weight, it should 
 exert pressure upon 
 
 everything; because the atmosphere extends many miles 
 
 above the earth's surface. 
 
 FIGURE 5. 
 
6 
 
 GENERAL SCIENCE 
 
 Experiment. Into a tin can which has a small opening, put a few 
 spoonfuls of water. Heat the can until sufficient steam is formed to 
 drive out the air. Plug the opening in the can with an airtight stopper. 
 
 As the can cools, the steam changes back 
 to water and the space within the can 
 contains neither steam nor air and is 
 called a vacuum. 
 
 What happens to the can ? Explain. 
 Use a wide-mouthed bottle instead of 
 the can and in place of the stopper tie 
 a piece of paper or still better a piece of 
 sheet rubber over the opening. Result ? 
 Conclusion ? 
 
 Problem 4. How air pressure 
 may be measured. The amount 
 of this pressure, which of course 
 will also be the measure of the 
 weight of the air over a certain 
 space, may be found by repeating 
 the experiment of Torricelli, a 
 pupil of Galileo, made in 1643. 
 This was the first measurement 
 made of air pressure. 
 
 Experiment. Fill with mercury a 
 glass tube about three feet long and 
 closed at one end. Closing the open end 
 with the finger to prevent the escape of 
 the mercury, invert the tube and place 
 the open end below the surface of mer- 
 cury in a dish. Now withdraw the finger 
 and note the result (Figure 6). What 
 keeps the mercury in the tube above 
 the level of the mercury in the dish? 
 
 If the tube has a cross section of one square inch, the 
 weight of the mercury held above the level of the mercury 
 
 FIGURE 6. SIMPLE BAROME- 
 TER. 
 
 Why must one end of the 
 tube be closed? Where does 
 the air press ? Why does the 
 mercury not reach the top of 
 the tube ? Scale is in inches. 
 
IMPORTANCE OF THE WEIGHT OF AIR 
 
 in the dish will be about fifteen pounds. 
 Therefore it may be stated that air exerts a 
 pressure of about fifteen pounds per square 
 inch. 
 
 The apparatus used in this experiment con- 
 stitutes the essentials of a mercury barometer 
 (Figure 7). Since weather changes are ac- 
 companied and frequently preceded by changes 
 in air pressure, the practical value of the 
 barometer may be understood. 
 
 Problem 5. Why water is not used in mak- 
 ing barometers. From the last experiment 
 we learn that the pressure of the air will hold 
 up a column of mercury about 30 inches in 
 height. Would a longer or shorter column of 
 a lighter liquid be held up? Explain. Evi- 
 dently, therefore, in selecting a liquid to be 
 used in a barometer, its weight must be con- 
 sidered. 
 
 Experiment. Into each of two beaker glasses put 
 respectively equal volumes of mercury and water. 
 Lift the glasses. Which is the heavier? Put the 
 beaker glasses containing the mercury and water on 
 the opposite pans of a balance and by the use of 
 weights find out how much heavier one substance is 
 than the other. What is the Jesuit ? 
 
 FIGURE 7. MERCURIAL BAROMETER. 
 
 The height of the mercury column is measured in 
 centimeters, c, surface of mercury upon which air is pressing, a, screw 
 by which the mercury in the mercury cup is adjusted so that the surface (c) 
 is at the zero point of the barometer tube, d, thermometer, e, screw for 
 adjustment of a scale (vernier) by which the height of the mercury may be 
 read more accurately. /, scale at top of mercury column. 
 
8 
 
 GENERAL SCIENCE 
 
 If mercury is thirteen and one-half times heavier than 
 water calculate the height of a column of water that may be 
 held up by the pressure of the air. Such a barometer was con- 
 structed by Otto von Guericke, the inventor of the air pump. 
 
 FIGURE 8. ANEROID BAROMETER. 
 
 The upper portion of the tube to the extent of about six feet 
 was of glass. Floating on the top of the liquid, the inventor 
 had introduced a small figure of a man which with the rising 
 of the column in fair weather presented itself to view ; but 
 with the approach of foul weather retreated out of sight. 
 
IMPORTANCE OF THE WEIGHT OF AIR 
 
 9 
 
 Ptin&r 
 
 C/ia/f\ 
 
 Problem 6. How an aviator knows how high he is. 
 If a barometer is carried up a mountain the mercury column 
 drops about 0.1 of an inch for every 90 feet of elevation. 
 Explain why this is so. Explain how an aviator is able to 
 determine his height above the earth. Why is a mercury 
 barometer unfitted for use in an airplane ? 
 
 Can you suggest a method of making a barometer which 
 will not have the objectional features of the mercury barom- 
 eter? Reference to the experiment in Problem 3 may help 
 you. Suppose some of the 
 air is removed from a me- 
 tallic box, having sides 
 that go in or out as the 
 pressure on it changes. 
 What will happen to the 
 sides when this box is 
 carried up in an airplane ? 
 When it is carried back 
 to the earth again ? 
 
 The aneroid barometer 
 is made according to this plan. In its simplest form it is a 
 metal box from which a large part of the air has been re- 
 moved. The cover will bend slightly with changes of pressure 
 of the atmosphere. By a series of levers the extent of 
 movements of the cover of the box is multiplied and repre- 
 sented by a pointer on a dial. 
 
 Problem 7. Why air pressure does not prevent us from 
 lifting objects. Calculate the weight of air resting on a 
 book six by ten inches. You know, however, that the book 
 can be lifted as though there were no weight on it. The follow- 
 ing experiment may help you to understand how this can be. 
 
 Vacuum bop 
 
 FIGURE 9. DIAGRAM OF AN ANEROID 
 BAROMETER. 
 
10 
 
 GENERAL SCIENCE 
 
 Experiment. Completely fill a glass with water and cover the top 
 of it with a piece of cardboard, making certain that the cardboard is 
 everywhere in close contact with the edge of 
 the glass. Invert the glass (Figure 10). What 
 happens ? Why ? Hold the glass in different 
 positions. Result ? Conclusion ? 
 
 FIGURE 10. 
 
 Problem 8. Why a balloon or a 
 dirigible remains in the air. Why do 
 you think that the explanation given 
 for the airplane remaining in the air will 
 not account for the buoyancy of a bal- 
 loon? Since we have learned that air 
 
 has weight we may compare the floating of objects in air 
 
 with the floating of objects in water. You know from 
 
 experience that objects like 
 
 iron and stones, that are 
 
 heavier than water, will sink 
 
 while cork and wood, which 
 
 are lighter than water, will 
 
 float. 
 
 The same is true of things 
 
 in the air. Cork and wood 
 
 and most things we know of 
 
 are heavier than air and will 
 
 not float in it. A balloon, 
 
 however, is lighter than air 
 
 and therefore will float in it. 
 
 We know that air pressure 
 is exerted in all directions. 
 The air under the balloon, 
 therefore, is pushing it up- 
 ward and the air above it, 
 
 t 
 
 FIGURE 11. FRENCH WAR BALLOON. 
 
 It is making an ascent at St. Nazaire, 
 France. 
 
IMPORTANCE OF THE WEIGHT OF AIR 11 
 
 is pushing it downward. If the balloon weighs the same as 
 air it will not be pushed either upward or downward. If, 
 
 FIGURE 12. 
 
 however, the balloon weighs more than an equal volume of 
 air, will the downward or upward pressure be greater? 
 Explain. If the balloon weighs less than the air that it 
 
 FIGURE 13. 
 
 displaces, which pressure will be the greater? Explain. 
 Explain why a balloon does not continue to go up until it 
 reaches the top of the atmosphere. 
 
12 
 
 GENERAL SCIENCE 
 
 Balloons and dirigibles must be filled with a gas much 
 lighter than air. Hydrogen gas, which is about 14| times 
 lighter than air, has been the gas generally used. The use 
 
 FIGURE 14. 
 Note that the can at the right has two holes in its top. 
 
 of hydrogen for filling balloons may be shown by making 
 soap bubbles with it. 
 
 Experiment. Make hydrogen by setting up the apparatus shown 
 in Figure 12 and pouring hydrochloric acid through the tube with the 
 enlarged top (thistle tube) over the pieces of zinc in the flask. By 
 means of a rubber tube attach the stem of 
 a clay pipe to the tube which carries the gas 
 from the flask. Dip the bowl of the pipe 
 into soapsuds. Shake off the bubbles into 
 the air as they are formed and note their 
 behavior. Touch a bubble with a match 
 and observe what happens. 
 
 A new gas (helium) which is found 
 in considerable quantities mixed with 
 the gas of some natural gas wells is 
 now being used. It is somewhat 
 heavier than hydrogen although much 
 FIGURE 15. RELATIVE lighter than air. The great advantage 
 ^ its use is that it will not burn, 
 EXPIRATION. whereas hydrogen does. 
 
IMPORTANCE OF THE WEIGHT OF AIR 
 
 13 
 
 EXERCISES 
 Explain tile following : 
 
 (1) How ink may be drawn up 
 into a medicine dropper such as is used 
 in filling a fountain pen (Figure 13). 
 
 (2) How lemonade may be sucked 
 through a straw. 
 
 (3) Why olive oil or any other liquid 
 can readily be poured from a small open- 
 ing in a can if there is another opening 
 above the liquid, but will not flow 
 evenly if this opening is closed (Fig- 
 ure 14). 
 
 (4) Why a fountain pen frequently 
 leaks when it is nearly empty. 
 
 (5) Why the raising of the ribs 
 and lowering of the diaphragm of the 
 body causes air to flow into the lungs 
 (Figure 15). 
 
 (6) Why two pieces of wet glass 
 stick .together. 
 
 (7) The action of non-skid auto- 
 mobile tires (Figure 16). 
 
 (8) Theabil- 
 
 FIGURE 17. SOLE OF 
 BASKET BALL SLIPPER. 
 
 FIGURE 16. NON-SKID AUTO- 
 ity of basketball MOBILE TlRE ' 
 
 players to keep from slipping on the smooth floor 
 of a gymnasium (Figure 17). 
 
 (9) Action of the ordinary suction pump 
 (Figure 18). How high will such a pump lift 
 water ? 
 
 (10) How air pressure may help in removing 
 liquids from casks or large bottles (siphoning). 
 (Figure 19.) 
 
 (11) Action of a vacuum cleaner. Why is 
 its use advisable? 
 
 (12) Why one's hat is apt to be carried off as 
 a swiftly moving train passes. 
 
14 GENERAL SCIENCE 
 
 (13) The action of a self-filling fountain pen. 
 
 (14) Difficulty of drinking from a small-mouthed bottje. 
 
 FIGURE 18. SUCTION PUMP. 
 
 V, V valves ; P, piston ; 5, pump stem ; W, water of well. What 
 causes V to open as piston moves upward ? What will be the position 
 of valves as piston is pushed downwards ? 
 
 (15) Sucking of blood by a mosquito." 
 
 (16) Noise caused by removing a thimble from a wet finger. 
 
 FIGURE 19. SIPHONING LIQUID FROM A BARREL. 
 
 The tube fits loosely in the opening at the top of the barrel. Why is this 
 necessary ? Why cannot this barrel be completely emptied by the tube as it 
 is ? How can this tube be changed so that the barrel may be emptied with it ? 
 
 (17) Difficulty of pouring a liquid through a funnel which fits tightly 
 into the mouth of a jug or bottle. How may the liquid be made to flow 
 rapidly ? 
 
 (18) Why the body is not crushed by the pressure of the air. 
 
WEIGHT OF AIR 15 
 
 SUGGESTED INDIVIDUAL PROJECTS 1 
 
 1. Make a kite and demonstrate by diagrams how it is able to fly. 
 
 2. Make an air-glider and explain how it acts. 
 
 3. Make a model airplane that will fly and demonstrate its action 
 to the class. 
 
 4. Construct a homemade mercury barometer and record for a 
 period of time the changes in air pressure. At the same time make a 
 record of the condition of the weather and determine if there seems to 
 be any connection between 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 lighter 
 than carbon dioxide gas. 
 
 7. Construct an apparatus to illustrate the expansion and con- 
 traction of the lungs in breathing. 
 
 8. Demonstrate the structure and action of a self-filling fountain 
 pen. 
 
 9. Demonstrate the structure and action of a vacuum cleaner. 
 10. Construct a siphon and demonstrate its use. Discuss various 
 
 applications that may be made of the siphon. 
 
 REPORTS 
 
 1. First successful attempts to cross the Atlantic Ocean in an air- 
 plane. 
 
 2. Early attempts to develop the airplane. 
 
 3. The use of the airplane in the Great War. 
 
 4. Commercial possibilities of the airplane. 
 
 REFERENCES FOR PROJECT I 
 
 1. Aircraft Today, Chas. Turner. J. B. Lippincott Co. 
 
 2. How to Fly, F. A. Collins. D. Appleton & Co. 
 
 3. The Air Men, F. A. Collins. Century Co. 
 
 1 As explained in the Preface, not all the Individual Projects are to be 
 required of every student. Some are for girls, some for boys ; some for 
 city pupils, some for country students ; some are so simple that nearly 
 anyone can perform them easily, while some, like Project 3 above, will 
 appeal only to those who have a decided mechanical talent. 
 
16 GENERAL SCIENCE 
 
 4. Boys' Book of Airships, H. Delacombe. Frederick A. Stokes Co. 
 
 5. How It Flies, Richard Ferris. Thomas Nelson & Sons. 
 
 6. The Story of the Airplane, C. Graham-White. Small, Maynard 
 &Co. 
 
 7. Boys' Book of Model Airplanes, Vols. I and II, F. A. 'Collins. 
 Century Co. 
 
 8. Aviation Book, Curtis. F. A. Stokes. 
 
 9. Harper's Book on Aircraft, Verrill. Harper & Bros. 
 
 10. Boys' Book of Inventions, Baker. Doubleday, Page & Co. 
 
 11. Flying Machines, etc., The American Boy's Handy Book, Beard. 
 Charles Scribner's Sons. 
 
 12. War Kites, Field and Forest Handy Book, Beard. Charles 
 Scribner's Sons. 
 
 13. Handicraft for Handy Boys, Hall. Lothrop, Lee & Shepard. 
 
 14. Historic Inventions, Holland. Geo. W. Jacobs 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. Sully & 
 Kleinteich. 
 
 18. Careers of Danger and Daring, Cleveland Moffet. Century Co. 
 (Divers, Balloonists, Bridge Builders, etc.) 
 
 19. The Barometer as the Footrule of the Air. Taylor Instrument 
 Co., Rochester, N. Y., 10 cents. 
 
 20. The Thermometer and Its Family Tree. Taylor Instrument 
 Co., 10 cents. 
 
 21. The Story of Great Inventions. Harper & Bros. 
 
 22. Modern Triumphs, E. M. Tappan, Editor. Houghton Mifflin 
 Co. 
 
 23. Harper's Machinery Book for Boys. Harper & Bros. 
 
PROJECT II 
 HOW WE USE COMPRESSED AIR 
 
 THE fact that we not only make use of air pressure 
 but also of compressed air is familiar to us all. Automo- 
 biles weighing several thousands of pounds are held up by 
 compressed air. The construction of bridge foundations 
 and tunnels under the beds of rivers is made possible by 
 it. Moving trains weighing hundreds of tons may be 
 quickly brought to a stop by the air brake. Drills, rivet- 
 ing machines, and many other appliances are operated by 
 compressed air. How such a substance as air can do all 
 these things opens up for us many problems. 
 
 Problem 1. How air pressure is used in building founda- 
 tions and subways. What is an air bubble? Can air and 
 water occupy the same space at the same time? 
 
 Experiment. To find out if air and water can occupy the same 
 space at the same time, push down into a vessel of water an inverted 
 drinking glass (Figure 20). What is the result? It is evident that 
 the pressure of the air within the glass is 
 sufficient to prevent the entrance of the 
 water into the glass. 
 
 This pressure is equal to the 
 weight of the column of water 
 
 above the level of the water which 
 
 . . . . . i,i_ FIGURE 20. 
 
 is inside or the glass plus tne 
 
 ordinary atmospheric pressure (how much?) on the sur- 
 face of the water. As the glass is pushed downward will 
 
 17 
 
18 
 
 GENERAL SCIENCE 
 
 any change occur in the amoun^ of pressure exerted by the 
 contained air? At what depth in the water will the air 
 exert a pressure equal to two atmospheres? At this point 
 the volume of the air will be one half of its original volume, 
 illustrating a law of every true gas, that the volume varies 
 
 5TCAM BABGE fOU 
 
 I HOSTING. FUPNISMING 
 COMPPE5SEDAIB, &, 
 ELECTBIUTY 
 
 FIGURE 21. CAISSON. 
 
 If the pressure of the air in the caisson is about 30 pounds per square 
 inch, how far from the surface of the water is the bottom of the excavation ? 
 What would happen if the doors at the top should be left open ? Why ? 
 
 inversely as the pressure exerted upon it. This law is known 
 as Boyle's law. 
 
 Caissons used in building foundations under water are 
 large metal cylinders open at the bottom, into which air 
 is pumped until it exerts sufficient pressure to prevent the 
 entrance of water (Figure 21). Air under pressure was used 
 
HOW WE USE COMPRESSED AIR 19 
 
 to keep out the water during the construction of the tunnels 
 under the East and North rivers at New York City. 
 
 Great care must be taken by men passing from the com- 
 pressed air chambers to the outer air. If this is done too 
 quickly, gases which are dissolved in the blood form small 
 bubbles which prevent the blood from passing through 
 capillaries (very small blood vessels), causing an acute 
 disease, the " bends." To prevent this, a man instead of 
 passing directly into the outer air goes through several 
 rooms of graduated pressures, remaining in each room a 
 sufficient length of time to permit the body to accommodate 
 itself to the changed pressure. 
 
 Problem 2. How compressed air is used in automobile 
 tires. We all know that bicycle tires and most automo- 
 bile tires are filled with air. At first thought it seems strange 
 that a substance like air can hold up the great weight of a 
 heavy automobile. Naturally we ask how this air is dif- 
 ferent from the air around us. 
 
 What happens if a nail punctures the tire? Sometimes 
 when the outer covering of the tire becomes badly worn a 
 " blow-out " occurs with a noise like an explosion, tearing a 
 hole in the tire. What does this indicate to you concern- 
 ing the condition of the air within the tire ? 
 
 It is evident that the compressed air in the tire is able to 
 hold up the weight of the automobile amounting to several 
 thousand pounds, just as the compressed air in the diving 
 bell resists the pressure of the water. 
 
 If you have ever ridden in a solid-tired automobile 
 and then in one having pneumatic or air-filled tires, you 
 have noticed that in the latter case the jars caused by 
 the roughness of the road were not felt as much. This 
 
20 GENERAL SCIENCE 
 
 observation shows that the compressed air in the tire acts 
 like a spring. The following simple experiment will show 
 this effect of compressed air. 
 
 Experiment. Bounce together on the floor a new, perfect tennis 
 ball and a tennis ball in which a small hole has been made by a pin or 
 nail. Result? In the same way compare the bouncing of a basket 
 ball which is just sufficiently filled with air to cause it to keep its shape 
 with the bouncing of a similar ball into which a large amount of air has 
 been pumped. 
 
 From the observations you have made you will conclude 
 that the compressed air in the automobile tire is able to sup- 
 port a great weight and gives springiness (elasticity) to the 
 tire. Many tire-filling compounds have been tried but none 
 has been successful because nothing has been found that 
 will give the springiness possessed by compressed air. 
 
 It is evident that in the construction of an automobile tire, 
 first, the tire must be air-tight to prevent the escape of the 
 air and, second, it must be of sufficient strength to resist the 
 pressure of the imprisoned air. An examination of an auto- 
 mobile tire will show how these two* requirements are met. 
 The inner tube made of elastic rubber is air-tight. The air 
 is pumped in through a metal tube in which is a valve that 
 will allow air to be pushed in but prevents its escape. 
 
 The outer tire or shoe is not necessarily air-tight but pro- 
 vides the strength to resist the outward pressure of the con- 
 fined air. It is very strongly made of a combination of 
 cotton fabric or cord and rubber. In bicycle tires where the 
 weight supported is not so great, frequently only one tube 
 is used. What two properties must this tube possess? 
 
 Air is forced into the tire by an air pump. 
 
 Problem 3. How the tire pump works. If you have 
 ever pumped up an automobile tire, did you find it more 
 
HOW WE USE COMPRESSED AIR 
 
 21 
 
 FIGURE 22. 
 BICYCLE 
 PUMP. 
 
 difficult to work the pump when the tire was 
 nearly empty or when it was nearly filled ? In 
 the tire pump which you used, was the push or 
 the pull upon the handle the harder? Does a 
 tire pump ever "get out-of-fix " or fail to 
 work? 
 
 Keeping these points in mind let us examine 
 the diagram of an air pump (Figure 22). As 
 the handle is pulled out, what happens to the 
 air? Why? As the handle is pushed down, 
 what happens to the air ? Why does it not go 
 out through the same place through which it 
 came in ? Why is it more difficult to push the 
 handle down than to pull it up? Why is it 
 more difficult to push the handle down as you 
 continue to pump air into the tire ? 
 
 The tire pump is a very simple air compressor, 
 
 but air . compressors for air brakes, 
 pneumatic drills, sand blasts, and for 
 pumping air into tunnels where work is 
 done under compressed air are built on 
 the same principle. 
 
 Suppose the valve through which the 
 air enters the pump should be reversed, 
 what would happen should the nozzle be 
 attached to a basket ball and the pump 
 used? This is the principle of the ex- 
 haust air pump, by which air is pumped 
 out of a closed vessel. Do you think that 
 all of the air could be removed from a 
 vessel with such a pump ? In answering 
 this, keep in mind that however little air 
 
 FIGURE 23. FORCE 
 
 PUMP. 
 
 p, piston ; c, cylin- 
 der ; v, valve ; D, dome 
 containing air ; d, de- 
 livery pipe ; 5, pump 
 stock. 
 
22 
 
 GENERAL SCIENCE 
 
 is in a space, it will be distributed equally, filling all the 
 space. 
 
 Problem 4. How a force pump sends a steady stream of 
 water. The tire pump is really an air force pump ; a 
 water force pump could be made on the same plan. Would 
 
 FIGURE 24. COMPRESSED AIR DRILLS. 
 Use of compressed air drills in excavating a tunnel through solid rock. 
 
 such a water force pump send a steady stream of water? 
 Such pumps are valuable in pumping water to a tank on the 
 top of a house or into a standpipe. Why cannot an ordinary 
 pump be used for this purpose ? 
 
 Some force pumps can send a steady stream of water. It 
 will be noticed that pumps of this kind have connected with 
 
HOW WE USE COMPRESSED AIR 
 
 23 
 
 them an iron dome. An examination of the accompanying 
 diagram will help us to understand how this is possible 
 (Figure 23). 
 
 Explain what happens when the piston (p) is pulled up. 
 When it is pushed down, what two courses will the water 
 take ? What will happen to the air that is in the iron dome ? 
 What will this compressed air do to the water when the 
 piston starts upward and the water is no longer being forced 
 
 FIGURE 25. RIVETING HAMMER. 
 A, air pipe ; B, trigger for controlling the air; C, the hammer. 
 
 into the dome? What kind of a stream will such a pump 
 send out ? The power of compressed air to throw a stream 
 of water is illustrated by the following experiment. 
 
 Experiment. Half fill a flask with water. Stopper it with a one- 
 hole stopper through which passes a tube extending down below the 
 surface of the water. Blow through the tube. What effect will this 
 have upon the air within the flask ? After the air has "been considerably 
 compressed, stop blowing into the tube and observe what happens. 
 
 Some other important uses of compressed air are : 
 Pneumatic tubes for the transmission of mail, and of cash 
 
24 GENERAL SCIENCE 
 
 and parcels in stores; air brakes; pneumatic drills and 
 riveters ; and the sand blast used in cleaning the fronts of 
 stone buildings. Can you suggest any other applications ? 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Construct a pump that will send a steady stream of water. 
 
 2. Demonstrate the working of air brakes. 
 
 3. Demonstrate the structure and the action of pneumatic drills. 
 
 4. Demonstrate the structure and the method of working of the 
 sand blast used in cleaning the outside of brick and stone buildings 
 
 REPORT 
 
 Use of compressed air in building bridge foundations and in the 
 construction of subways. 
 
PROJECT III 
 VENTILATION 
 
 do you understand by ventilation? We hear a 
 great deal about the importance of ventilation, so that we 
 naturally ask ourselves, why ventilation is so necessary and 
 how rooms may be ventilated. 
 
 Problem 1. Why rooms should be ventilated. Think 
 of how you have felt in rooms that were not ventilated and 
 in rooms that were ventilated. Did the fact that the room 
 was empty or full of people seem to make any difference? 
 What effect do people have on the air of the room? Your 
 first answer to this will be that even if pure air is breathed 
 in, impure or bad air is being breathed out. What, then, 
 will be one reason for the ventilation of a room ? 
 
 Another effect of a crowd of people on the air of a room is 
 noticed when you step from the fresh air into a poorly 
 ventilated room full of people. Unpleasant odors are 
 noticed. These are given off by the mouths, bodies, and 
 clothing of the persons in the room. Experiments have 
 shown that these odors are not only annoying but have a 
 bad effect on the appetite. What, therefore, is a second 
 reason for the ventilation of rooms in which there are many 
 people ? 
 
 Another reason for ventilation may be made clear by an 
 experience common to us all. How do you feel on a hot 
 sultry day in summer? Do you feel different when a 
 breeze begins to blow? What is the effect of riding in 
 
 25 
 
26 GENERAL SCIENCE 
 
 an open trolley car or in an automobile on such a summer 
 day? 
 
 The following experiment may help us to understand the 
 reason for this change in feeling. 
 
 Experiment. Put a drop of ether on the back of the hand. What 
 happens to the ether ? How does the spot, where the ether was, feel ? 
 
 Put a drop of water on the other hand. After it has been- there a 
 few moments, fan the hand. Do you notice any difference in tempera- 
 ture? The changing of the ether and water into a vapor or gas that 
 is invisible is called evaporation. What do you conclude is the effect 
 of evaporation upon temperature ? 
 
 Heat is being continually made in the body. How do you 
 suppose the body loses most of its extra heat in warm rooms 
 and in summer time? 
 
 Evaporation of water goes on much more slowly if there 
 is already a large amount of water vapor in the air. This 
 fact is made clear to you by the rapidity of the drying of 
 clothes on a damp day and on a dry day. In which case 
 does the drying go on more rapidly ? 
 
 Experiment. Wet two small pieces of cloth ; hang one in a dry 
 battery jar and the other in a battery jar in which there is a small 
 amount of water. Which piece of cloth dries the sooner ? Conclusion ? 
 
 It is estimated that each person gives off from his mouth 
 and skin about three pints of water daily and about as much 
 heat as is produced by a candle flame. Of course, if exercise 
 is being carried on, both more moisture and more heat are 
 given off. What, therefore, will be the condition of a poorly 
 ventilated room in which there are a number of persons? 
 
 It is an accepted fact that the dullness and drowsiness 
 felt in such a room are due chiefly to the heat and moisture. 
 Experiments have shown that men do 15 per cent less work 
 at a temperature of 75 degrees F. and 37 per cent less work 
 
VENTILATION 
 
 27 
 
 at 86 degrees F. than at 68 degrees F. In warm rooms the 
 blood comes to the surface of the body. Why ? What effect 
 will this have upon the amount of blood that goes to the 
 brain? What will be the result? In the same way, the 
 blood vessels in the nostrils become congested, making 
 an ideal condition for the growth of germs. As a result, 
 people who live in overheated rooms usually have colds. 
 The proper temperature for a room is 68 to 70 degrees F. 
 
 Although a poorly 
 ventilated room contain- 
 ing many people is likely 
 to have too much mois- 
 ture in the air, there is 
 danger in the winter of 
 having too little moisture 
 in the air; this is espe- 
 cially true in apartments 
 occupied by only a few 
 people. It is advisable 
 under these circum- 
 stances to keep on the 
 radiator or stove a basin 
 of water which will sup- . FlGURE 2 6. ELECTRIC FAN. 
 
 ply moisture to the air 
 
 by its evaporation. Hot air furnaces have a special water 
 
 basin which should be kept filled if the occupants of the 
 
 house are to enjoy the maximum of comfort and well-being. 
 
 Briefly summarize the reasons for ventilating a room. 
 
 Problem 2. How air in a room may be set in motion. 
 One method of keeping the air of a room in motion is by the 
 use of fans (Figure 26). Explain why, in summer, one feels 
 
28 
 
 GENERAL SCIENCE 
 
 so very much better in an office, room, or subway car in which 
 an electric fan is in motion. Recall how quickly one feels the 
 change when the fan is shut off. Why is ventilation of a room 
 entirely by an electric 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 question 
 then is, how may a circulation of the air be 
 caused, when fans are not used. The follow- 
 ing experiments may help us to answer this 
 FIGURE 27. question. 
 
 Experiment. Put a lighted candle in the bottom of an uncovered 
 battery jar. Light a stick of Chinese punk or incense and hold it 
 near the top of the jar. What 
 happens ? What do you think may 
 be the cause of this ? 
 
 Experiment. To find out the 
 effect of heat on the weight of air, 
 place a lighted Bunsen burner near 
 one of the scale pans of a sensitive 
 balance. Result ? Conclusion ? 
 The reason for this is made clear 
 by the following experiment. 
 
 Experiment. To find out how 
 heating air makes it lighter, pass a 
 glass tube through the stopper of a 
 flask. Take care that the stopper 
 is air-tight. Invert the flask, plac- 
 ing the outer end of the glass tube 
 under water. Gently heat the flask 
 (Figure 27). Result? Conclusion? 
 
 FIGURE 28. CURRENTS OF AIR IN 
 A REFRIGERATOR. 
 
 The currents of air caused by heat are called convection 
 currents. These currents of air are well illustrated by move- 
 ments of air in a refrigerator (Figure 28). 
 
VENTILATION 
 
 29 
 
 Problem 3. How convection currents may be used in 
 ventilating a room. Windows are very frequently de- 
 pended upon 'for ventilation. 
 
 Experiment. To find out the best arrangement of windows for 
 good ventilation of a room, take a wooden soap box or a starch box. 
 Across the front of the box place a piece of glass 
 so that it may act as a sliding door. In each end 
 of the box bore four holes so arranged as to repre- 
 sent the upper and lower parts of windows. 
 Provide corks for these openings. Place inside of 
 the box one or more candles. Light the candles. 
 Allow all the lower holes to remain open. Note 
 the result. Try various combinations. What is 
 your conclusion as to the best way to ventilate a 
 room by means of windows ? 
 
 If the air outside is cooler than the air 
 inside the room, and the window is open at 
 both top and bottom, where does the air 
 enter and where does it leave (Figure 29) ? 
 Explain. 
 
 A draft or a direct current of air striking 
 against the body is apt to induce a cold 
 since that portion of the body is cooled 
 so completely that the blood coming there 
 is forced into some other part, causing a 
 congestion which affords a favorable condi- 
 tion for the growth of bacteria or germs 
 that cause colds. 
 
 With a window open at the top and bottom, would the 
 greater danger of draft be from the top ? Suggest means of 
 protecting persons from a draft in a room ventilated in 
 this way. 
 
 Explain how a stove or fireplace will help in the ventilation 
 
 FIGURE 29. VENTI- 
 LATION BY WINDOW. 
 
 Window open at 
 both top and bot- 
 tom. 
 
30 
 
 GENERAL SCIENCE 
 
 of a room (Figure 30). Make a diagram 
 of a room containing a fireplace and indi- 
 cate by arrows the direction of the air in 
 the room. 
 
 How are your rooms at home ventilated 
 in summer ? In winter ? Make diagrams 
 of the summer and winter ventilation of 
 one room. 
 
 Modern office buildings, and sometimes 
 schools, are heated and ventilated by air 
 being forced into them by fans through 
 large pipes. If the air comes in heated, 
 ought the inlet to be at the top or bottom 
 of the room? Where ought the outlet 
 to be? 
 
 Experiments and observations have 
 shown that the health is much better if sleeping rooms are 
 well ventilated and kept at a relatively low temperature, 
 provided that the body is not in a draft and is properly 
 protected to prevent its becoming chilled. 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Carry out a series of experiments to show the direction of air 
 currents in a room. Show results in a diagrammatic drawing of the 
 room. Do this for different rooms of your house. 
 
 2. Carry out a plan to prevent a draft in a room ventilated by 
 windows. 
 
 FIGURE 30. FIRE- 
 PLACE. 
 
 What causes the air 
 to 'go up the flue? 
 
PROJECT IV 
 WINDS 
 
 SINCE winds are movements of air, you would naturally 
 suspect that they may be caused in the same way as the air 
 currents of ventilation. In considering the cause of winds 
 you will at once think of different kinds of winds, such as 
 sea breezes, gentle breezes that seem to come from any direc- 
 tion, violent gales, trade winds, hurricanes and tornadoes. 
 Does it seem probable that all these winds are caused by 
 the unequal heating of the air? 
 
 Problem 1. How sea breezes are caused. Anyone 
 living within a few miles of the sea coast is familiar with the 
 breeze that springs up on hot days in summer. Since this 
 wind occurs only on hot days and dies down toward evening, 
 being replaced frequently during the night by a breeze from 
 the land to the ocean, you will suspect that in some way it is 
 concerned with heat. 
 
 If this wind is caused in the same way that air currents of 
 ventilation are produced, there must be an unequal heating 
 of the land and water. Do you think that the ocean and 
 the land receive different amounts of heat from the sun? 
 The problem to be solved, therefore, is, how the unequal 
 heating can be accounted for. 
 
 Experiment. Put into different drinking glasses or beaker glasses 
 equal quantities of -water and earth. Put them into an oven for about 
 twenty minutes. On removal put into each beaker glass a thermometer. 
 
 31 
 
32 
 
 GENERAL SCIENCE 
 
 Note the temperature when first removed from the oven and at inter- 
 vals of ten or fifteen minutes. Result ? Conclusion ? 
 Explain 'now the cause of sea breezes. 
 
 The seasonal or monsoon winds of India are accounted for 
 in a similar manner. During the summer the land becomes 
 highly heated and winds blow from the Indian ocean to 
 
 
 FIGURE 31. SUMMER MONSOON. FIGURE 32. WINTER MONSOON. 
 
 the land, while in winter the water is warmer than the land 
 and the direction of the wind is reversed. 
 
 Considering the fact that land becomes warmed more 
 rapidly and cools more rapidly than 'water, explain the 
 following : 
 
 1. Why New York City has a later spring than places in 
 Ohio and Indiana which are no farther north or south. 
 
 2. Why the region along Lake Ontario is better for raising 
 fruit than places much farther south. 
 
 On the diagram representing the world's winds note the 
 direction of the trade winds. Why do they blow toward the 
 equator ? The fact that they blow from the southeast and 
 northeast rather than directly from the north and south 
 is due to the rotation of the earth. In the northern hem- 
 isphere the winds are deflected to the right and in the 
 southern, to the left. 
 
WINDS 
 
 33 
 
 Problem 2. Why our winds vary in direction and velocity. 
 Note the direction of the winds in your locality for a few 
 days. Do they 
 always come from 
 the same direc- 
 tion ? Do they 
 always seem to 
 come from a cooler 
 to a warmer place ? 
 Do you think that 
 they are caused in 
 the same way as 
 sea breezes? 
 
 Reference again 
 to the diagram of 
 world's winds may 
 help us. In what 
 general direction 
 
 \ \ 
 V>e4ta/F 
 
 FIGURE 33. THE WORLD'S WINDS. 
 
 are the winds of the part of the world in which we 
 live? These winds are called the prevailing westerlies. 
 
 Because of inequalities 
 of heating and irregulari- 
 ties of surface, low pres- 
 sure areas develop in this 
 general current (the pre- 
 vailing westerlies) . As 
 the air rushes in toward 
 a low pressure area a 
 
 whirlpool is formed such 
 FIGURE 34. PROGRESS OF A STORM as you may see as tne 
 
 CENTER. ' V j 
 
 Note the rate of speed of this storm Water 1S dramed fr m ^ 
 center. bath tub, or in the dust 
 
36 
 
 GENERAL SCIENCE 
 
 whirls which occur in the road in summer. The low pressure 
 which started the dust whirl is formed by the excessive 
 heating of a small area of the road. 
 
 These low pressure areas which develop in the prevailing 
 westerlies travel with the westerlies in a general direction 
 from west to east (Figures 34 and 37). 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 drained 
 from a bath tub. These great whirls of air, which are con- 
 tinually passing across the country, are called cyclones; and 
 most of our winds are portions of these. The cyclones, 
 of course, are separated by areas of high pressure (Figures 
 35 and 36). 
 
 Directly in the center of a low pressure area, in what 
 direction do the currents of air flow? What is the direction 
 of these currents in the center of a high pressure area? 
 
WINDS 37 
 
 Which is warmer, an area of low pressure 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 sometimes 
 wrongly called cyclones. They are usually not more than 
 40 to 500 yards in width. In tornadoes the air is rushing 
 spirally upward at a rate of 100 to 400 miles per hour. Di- 
 rectly in the center of the tornado there is a very much 
 
 Photograph by F. Cundill. 
 
 FIGURE 38. TORNADO. 
 This tornado was seen near Isabel, South Dakota, June 25, 1914. 
 
 lessened air pressure. The condensation of moisture within 
 this area of lessened pressure and the presence of dirt carried 
 up by the air cause the funnel shaped cloud which is char- 
 acteristic of this kind of storm (Figure 38). 
 
 But a cyclone is an entirely different kind of storm. 
 Compare a tornado and a cyclone as to size. Tornadoes 
 usually occur in the southeastern part of a cyclone and 
 move toward the northeast, which is the direction of the 
 
38 
 
 GENERAL SCIENCE 
 
 prevailing wind in that part of a cyclone. They travel at 
 the rate of 20 to 50 miles an hour. 
 
 Tornadoes are very destructive, frequently destroying 
 everything in their paths (Figure 39). Trees may be 
 completely demolished ; large stones and even locomotives 
 have been known to be carried a considerable distance; 
 straws have been driven into wood as though they were 
 
 FIGURE 39. RESULTS OF A SEVERE WINDSTORM. 
 
 nails, and many other astounding results have been known 
 to occur. Frequently the walls of buildings near which the 
 center of the storm passes fall outward as though from 
 an explosion. Explain this. Waterspouts are whirlwinds 
 over the ocean. 
 
 Problem 3. What are hurricanes? Hurricanes are 
 similar to cyclones but are usually of less extent and more 
 violent. They form over the ocean. The ones that affect 
 us originate near the West Indies and move toward the 
 
WINDS 
 
 39 
 
 80 
 
 3V* 
 
 FIGURE 40. PATH OF A HURRICANE. 
 
 northwest until the coast of the United States is reached. 
 They then move toward the north and northeast, paral- 
 lel with the coast, finally passing eastward out into the 
 
40 
 
 GENERAL SCIENCE 
 
 Atlantic Ocean (Figure 40). Occasionally, one of these 
 hurricanes passes into the Gulf of Mexico. Galveston, 
 Texas, was nearly destroyed in 1900 by the waves pro- 
 duced by such a hurricane. Similar storms in the Pacific 
 and Indian oceans are called typhoons. 
 
 Thunderstorms frequently develop at the close of a hot, 
 sultry day. They are caused by the rising of hot, moist 
 
 FIGURE 41. CUMULUS CLOUDS. 
 
 Photograph by McAdie. 
 
 air. The moisture of the air condenses into dome-shaped, 
 white clouds known as cumulm clouds (Figure 41). The 
 downpour of water is accompanied or preceded by a set- 
 tling downward of the cooler air which pushes out from 
 all sides of the storm area, forming the strong wind of the 
 approaching thunderstorm. After the thunderstorm has 
 passed, the temperature is usually cooler, largely because of 
 this settling of the cooler air from above. 
 
WINDS 
 
 41 
 
 Thunderstorms usually occur in the southeastern portion 
 of a low pressure area, and move in an easterly direction at 
 the rate of 20 to 50 miles an hour. The storm is preceded 
 as it travels by a sheet of clouds advancing at a rather high 
 elevation. As the storm draws near, there appears the 
 black mass of the main storm cloud. Soon the dense cur- 
 tain of rain may be seen pouring from its base (Figure 
 
 FIGURE 42. THUNDERSTORM. 
 
 Photographed by Lieutenant W. F. Reed, Jr., U. S. N. R. F., near Pensa- 
 cola, Florida, August, 26, 1918. (Published by permission of the Navy 
 Department.) ., '& 
 
 42). Along the front of the rain there is often a low cloud, 
 ragged and torn by the wind. 
 
 A short time after the rain ceases, sometimes even before, 
 the sky may begin to clear ; and the sun shining on the de- 
 parting rain curtain gives us one of the most beautiful and 
 wonderful spectacles of Nature, the rainbow. Then the storm 
 cloud, illumined by the sun, may be seen passing eastward. 
 
42 GENERAL SCIENCE 
 
 Problem 4. How the weather bureau is able to predict 
 the weather. Examine weather maps. Note the direc- 
 tion of winds, temperature, raininess or cloudiness, and low 
 and high pressure areas. Suggest a basis for the weather 
 predictions issued by the U. S. Weather Bureau. 
 
 Explain how a barometer enables one to forecast the 
 weather for a short time in advance. 
 
 What two factors are important in determining the veloc- 
 ity of a 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 relation between a cold wave and a 
 high pressure area. 
 
 The United States Weather Bureau has nearly 200 ob- 
 servation stations throughout the United States and Canada, 
 at which simultaneous records of barometric pressure, tem- 
 perature, direction and velocity of the wind, the rain or 
 snowfall and cloudiness, are made. These observations 
 are telegraphed to Washington and from there the collected 
 information is sent to the various stations where weather 
 maps showing the weather conditions in all parts of the 
 country are made. The forecasters study these maps and 
 are able to forecast the probable weather conditions for the 
 next 24 or 48 hours (Figures 35 and 36). 
 
 By means of telegraph, telephone, wireless, and mail or by 
 means of flags or steam whistles the daily forecasts -reach 
 every part of the country in a surprisingly short time. 
 
 Special warnings of frost and the approach of a cold wave 
 are sent to farming, gardening, and fruit districts and to 
 railroads and to shippers of vegetables and livestock. Warn- 
 ings of gales along coasts and on the Great Lakes are sent to 
 shipping offices and to vessels. 
 
WINDS 43 
 
 SUGGESTED INDIVIDUAL TOPICS 
 
 1. Keep a daily record of temperature, air pressure, direction, and 
 approximate velocity of the wind, cloudiness, and rain- or snowfall. 
 In connection with these observations study the maps of the United 
 States Weather Bureau. 
 
 2. Make a toy windmill and use it in running a simple machine. 
 
 REPORTS 
 
 1. The work of the United States Weather Bureau. 
 
 2. An account of the hurricane that caused so much damage to 
 Galveston, Texas. 
 
 3. An account of a tornado. 
 
 REFERENCES FOR PROJECT IV 
 
 1. Weather and Weather Instruments, P. R. Jameson. Taylor 
 Instrument Company, Rochester, N. Y., 50 cents. 
 
 2. Practical Hints for Amateur Weather Forecasters, P. R. Jame- 
 son. Taylor Instrument Company, 10 cents. 
 
 3. Instructions for Volunteer Observers. U. S. Weather Bureau, 
 Washington. 
 
 4. Practical Exercises in Elementary Meteorology, Ward. Ginn & 
 Co. 
 
 6. About the Weather, Mark W. Harrington. D. Appleton & Co. 
 
 7. The Weather and Climate of Chicago, Cox and Armington, 
 University of Chicago Press. 
 
 8. The Wonder Book of the Atmosphere, E. J . Houston. Frederick 
 A. Stokes Co. 
 
 9. Our Own Weather, Martin. Harper & Bros. 
 
 10. Reading the Weather,- T. M. Longstreth. Outing Publishing 
 Co. 
 
^ ' PROJECT V 
 
 HOW WE HEAR 
 
 THINK a moment of what you would miss and how you 
 would be handicapped if you were unable to hear. Make a 
 list of ten examples in which inability to hear would affect 
 you. 
 
 In considering how we hear, there are several things which 
 are at once evident ; first, there is always a sound of some 
 kind ; second, the sound may be reproduced or heard at some 
 distance from the place where it was originally produced; 
 third, we have a special organ, the ear, which receives the 
 sound. In working out this project, therefore, it will be 
 necessary to know just what sound is, how sound may 
 travel and be reproduced and how the human ear is fitted 
 to receive sounds. 
 
 Problem 1. What sound is. Think of the different 
 ways in which sound is produced. How is a drum made to 
 give out sound ? What is the effect of putting the hand on 
 the head of the drum while it is sounding? A violin or 
 banjo gives out sound when a string is pulled to one side and 
 then released. If the string is looked at carefully, it will 
 be seen to be vibrating. What happens the moment you 
 stop these vibrations by touching the string ? 
 
 Experiment. Touch the surface of water in a glass with the tips 
 of a tuning fork which is sounding (Figure 43). Result? Conclusion? 
 
 An examination of all bodies giving out sound will lead 
 us to the conclusion that sound always originates as a vi- 
 
 44 
 
HOW WE HEAR 
 
 45 
 
 bration. The vibrating bodies cause air waves very much 
 as the vibrating tuning fork produced waves in the water 
 in the glass. 
 
 Experiment. Blow diagonally into a small bottle or test tube. 
 Use tubes and bottles of various sizes. Result? In this experiment 
 air waves are produced directly. 
 
 It is in this way that sound is produced in such instru- 
 ments as the organ, flute, cornet, and trombone. The sound 
 here is produced by the vibration of columns of air. 
 
 In what three ways do sounds differ? Naturally we 
 wonder, what are the causes of 
 these differences. 
 
 Experiment. Compare the sound 
 (note) given by a violin or other stringed 
 instrument when the strings are stretched 
 very tightly and when the strings are 
 stretched less tightly. By holding the 
 finger on the string permit only a portion 
 of it to vibrate. Result ? Set into vibra- 
 tion one of the very slender strings of a 
 violin or guitar and one of the thicker 
 ones. Even though they are of the same 
 length and of the same tension or tight- 
 ness, what is the result? FIGURE 43. 
 
 A careful examination will show that in every case where 
 the tone or pitch was high, the vibrations were more rapid 
 than when a lower pitch was produced. You will also re- 
 call that blowing into very small bottles gave a much 
 higher pitch than blowing into larger ones. This was be- 
 cause the air vibrations produced in the smaller bottles were 
 more rapid. 
 
 If you look at the arrangement of strings of a piano, you 
 will find that they are not all of the same length ; the ones 
 
46 
 
 GENERAL SCIENCE 
 
 which give out the low tones being long and thick, and those 
 which produce the high tones, short and thin. 
 
 The human voice illustrates this very well. Children have 
 high-pitched voices, but boys' voices usually become deeper 
 or lower-pitched when they are about fourteen years old. 
 This is because the voice box, or " Adam's apple," of the 
 boy becomes considerably larger at this time, and the vocal 
 cords become longer and larger, and therefore vibrate more 
 
 slowly, producing a lower 
 tone. The voice box of 
 a girl does not usually 
 grow much larger as she 
 gets older, and conse- 
 quently the voice of a 
 woman remains high- 
 pitched. 
 
 If you are beating a 
 drum and wish to make 
 a louder sound, what do 
 you do? If some one is 
 sleeping and you do not 
 wish to disturb him, how 
 do you walk across the 
 floor? 
 
 The loudness of sound is caused by the width of the vi- 
 bration. Compare the sound given by the string of a violin 
 when it is set into gentle vibrations with the sound produced 
 when the vibrations are greater. It will be noticed that the 
 tone or pitch remains the same, but that there is a great 
 difference in loudness or volume. 
 
 The quality of the sound is due largely to secondary vi- 
 brations (overtones) which* vary with the character of the 
 
 FIGURE 44. ONE OF THE EARLIEST 
 TALKING MACHINES. 
 
HOW WE HEAR 
 
 47 
 
 sounding bodies. Hence, sounds of the same pitch and 
 loudness produced by piano, violin, guitar, or organ, have 
 distinctive qualities. This is, of course, the main reason 
 for having many kinds of instruments in an orchestra. 
 
 Briefly summarize your conclusions as to what sound is 
 and the cause of differences in pitch, loudness, and quality 
 of sounds. 
 
 
 FIGURE 45. PHONOGRAPH. 
 
 Note the sound box, to which is attached a needle which runs in the groove 
 
 of the record. 
 
 Problem 2. How a phonograph reproduces sound. 
 To understand how the voice of Caruso, the music of the 
 violin of Mischa Elman or of a wonderful church choir may 
 be reproduced in our own home by the phonograph, it will 
 be necessary to consider how the record is made. 
 
 The essential part of a phonograph is the sound box with 
 
48 
 
 GENERAL SCIENCE 
 
 its diaphragm which is similar to the head of a drum 
 (Figure 45). To the center of the diaphragm is attached a 
 rod which transmits to a needle any movement of the drum 
 head or diaphragm. Every vibration of the vocal cords of 
 the singer or of the strings of the violin produces in some 
 
 FIGURE 46. MICRO- PHOTOGRAPH OF PORTION OF A RECORD. 
 
 way a similar vibration of the diaphragm which transmits 
 the vibration to the needle which in turn leaves a record on 
 a revolving wax plate upon which it rests (Figure 46). 
 Copies of the wax plates made of hard material are the 
 records which we buy (Figure 47). How the vibrations 
 
HOW WE HEAR 
 
 49 
 
 of the diaphragm, located many feet from the source of 
 the sound, are caused is a problem to be solved. Evidently 
 there is nothing but air to carry the vibrations. 
 
 FIGURE 47. PHONOGRAPH RECORD. 
 An original wax impression of a phonograph record. 
 
 Experiment : Does air conduct sound ? Through the stopper of 
 a wide-mouthed bottle pass two wires connected with several dry cells 
 and a key for closing the circuit. (Care should be taken to make the 
 stopper air-tight.) Attach the ends of the wires to the binding posts 
 of an electric bell. Place the bell in the bottle, insert the cork, and 
 close the circuit. Can you hear the ringing of the bell ? Now put a 
 small amount of water in the bottle and heat it until the steam drives 
 
50 
 
 GENERAL SCIENCE 
 
 out the air, put the stopper into the bottle and, after the bottle has 
 cooled, again close the circuit. Do you hear the ringing as before? 
 Allow air to enter the bottle gradually. As it does so, do you notice 
 any difference in the sound of the bell ? Conclusion ? 
 
 As the finished record revolves under the needle, all the 
 movements of the original needle are reproduced and corre- 
 sponding vibrations are set up in the diaphragm of the sound 
 box. These in turn cause air waves 
 like the original ones and we may 
 enjoy wonderful musical treats which 
 in most cases would otherwise be 
 unattainable. 
 
 In the telephone the air waves pro- 
 duced by the voice cause vibrations 
 of the diaphragm in the telephone 
 transmitter (Figure 48) . By means of 
 an electro-magnet, concerning which 
 we shall learn more later, electric 
 currents varying according to the 
 
 phragm, held around its vibrations of the diaphragm are trans- 
 edge by a soft rubber ring ; . , , , , , 
 A and B. parallel carbon mitted along the telephone wire. 
 plates, separated by carbon These currents cause the diaphragm 
 in the telephone receiver to vibrate in 
 
 the same way as the one in the transmitter, and air waves 
 are set up corresponding to the air waves produced by the 
 voice of the person speaking into the telephone miles away. 
 
 Problem 3. How the ear is fitted to receive sounds. 
 The way in which the ear is able to receive sound waves 
 may be understood by a study of the diagram showing the 
 arrangement of the parts of the ear. The external portion, 
 which is roughly funnel-shaped, leads into a tube about an 
 
 FIGURE 48. TELEPHONE 
 TRANSMITTER. 
 
 M, mouthpiece ; F and 
 C, front and back of metal 
 case ; D. aluminum dia- 
 
HOW WE HEAR 51 
 
 inch in length at the end of which is the ear drum. Beyond 
 the ear drum is the middle ear which connects with the throat 
 by the Eustachian (u-sta/ 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 the other with 
 the membrane of the inner ear. In the inner ear, which is 
 
 FIGURE 49. HUMAN EAR. 
 
 1, external ear ; 2, hairs at entrance of auditory canal ; 3, auditory canal ; 
 4, semicircular canal, a portion of internal ear ; 5, auditory nerve leading 
 to the brain ; 6, ear drum, from which a chain of bones extends to the 
 inner ear ; 9, Eustachian tube, connecting the middle ear with the throat. 
 
 filled with liquid, are many minute projections of a large 
 nerve, the auditory nerve, which extends to the brain. 
 
 Your knowledge of the way in which sound waves act 
 will enable you to explain what goes on in the ear when air 
 waves reach it (Figure 49). What is the advantage of 
 the expanded outer portion of the ear? What effect will 
 
52 GENERAL SCIENCE 
 
 the air waves have upon the ear drum ? What is the pur- 
 pose of the chain of bones in the middle ear? What will 
 happen to the liquid in the inner ear as a result of the 
 movement of the chain of bones? The small nerve fila- 
 ments are affected by the motion of the liquid surrounding 
 them, and a message is carried to the brain by the auditory 
 nerve. Thus we have the sensation of hearing. 
 
 The purpose of the Eustachian tube is to equalize the 
 pressure of the air on the two sides of the ear drum so that 
 it will vibrate freely. Sometimes in yawning you will 
 notice that for a moment you cannot hear distinctly and that 
 you have a peculiar ringing in the ears. This is because 
 the tubes have become temporarily closed. The same con- 
 dition may arise for a longer time as a result of a cold. 
 
 The peculiar feeling in the ears experienced in going up or 
 down in an elevator in a high building or through a tunnel, 
 is due to the fact that the pressure of the air on one side 
 of the ear drum is greater than that on the other. Open- 
 ing the mouth or swallowing will relieve the pressure. 
 Why? Artillerymen are apt to have their ear drums 
 broken at the time of firing their guns unless they open 
 their mouths. Explain. 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1.- Demonstrate the structure and the method of production of 
 sound by one of the following musical instruments : violin, guitar, 
 banjo, cornet, flute, drum, piano, organ, etc. 
 
 2. The dictograph. 
 
 3. How the player-piano works. 
 
 4. Construct a telephone to be used between two rooms of the school 
 building. 
 
 5. Construct a speaking tube between two classrooms. 
 
 6. Construct the model of a human ear. 
 
HOW WE HEAR 53 
 
 REPORTS 
 
 1. The history of the development of certain musical instruments. 
 
 2. Discovery and development of the talking machine. 
 
 3* Different kinds of organs of hearing possessed by animals. 
 4. The Maxim " silencer " for firearms. 
 
PROJECT VI 
 
 IMPORTANCE TO US OF OXIDATION (BURNING) 
 
 WE realize that burning is of great importance to us 
 when we consider that it furnishes us with heat, light, and 
 power. When properly controlled, it is one of our most use- 
 ful servants; but when 
 it is uncontrolled, it be- 
 comes one of our most 
 destructive enemies. 
 
 Problem 1. What 
 burning is. We build 
 a bonfire or a fire .in a 
 stove for the heat it pro- 
 duces. Fires on hilltops 
 have been used from the 
 earliest times as night 
 signals. What, therefore, 
 may we say, is produced 
 by burning? 
 
 If the draft of the 
 stove or furnace is good, 
 the fire burns brightly; 
 
 FIGURE 50. OIL FIRE. 
 Burning of a 55,000 barrel oil tank. 
 
 if ashes are permitted to collect below the firebox, the fire is 
 likely to go out. What seems to be necessary for burning ? 
 Think of other examples of burning that are familiar to 
 you. Does air always seem to be necessary? Is heat or 
 
 54 
 
IMPORTANCE TO US OF OXIDATION (BURNING) 55 
 
 light produced in every case? The following experiment 
 will show that some of the air 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 51). After the candle 
 stops burning, the water rises in the jar to take the place of the air 
 that was used up. The part of the air that is used 
 in burning is called oxygen, and the uniting of the 
 oxygen with the substance which is being burned 
 (fuel) is called oxidation. 
 
 Experiment. To find out if -any new substance 
 is produced in burning, burn a piece of charcoal 
 (carbon) over the mouth of a test tube containing 
 lime water. Shake the lime water. What is the 
 result ? This milky appearance in the lime water is the test for a gas 
 called carbon dioxide. 
 
 It is evident, therefore, that in the burning of carbon the 
 carbon disappears and there is produced a new substance 
 called carbon dioxide, a gas made by the combination of 
 carbon with the oxygen of the air. Experiments have been 
 performed which show that the weight of the carbon dioxide 
 formed is exactly equal to the weight of the carbon which was 
 burned plus the weight of the oxygen used. This combina- 
 tion of carbon and oxygen is accompanied by heat and light. 
 
 A change in which a new kind of substance is formed is 
 called a chemical change. 
 
 Carbon and oxygen are simple substances which by no 
 method yet discovered have been separated into anything 
 else. Carbon dioxide, on the other hand, may be shown to 
 be composed of carbon and oxygen combined in a definite 
 proportion. Carbon dioxide is a gas that will prevent 
 burning and is therefore an entirely different substance 
 from its constituents, namely, carbon which is a solid and 
 oxygen which is necessary for burning. 
 
56 
 
 GENERAL SCIENCE 
 
 Substances, like carbon and oxygen, which cannot be 
 
 separated into two or more substances are called elements. 
 
 Some of the common elements are nitrogen, hydrogen, sul- 
 phur, phosphorus, iron, copper, 
 sodium, potassium, chlorine, and 
 silicon. 
 
 Substances like carbon dioxide 
 are called compounds. Water is 
 a compound composed of the two 
 elements, hydrogen and oxygen. 
 Starch is a compound of carbon, 
 hydrogen, and oxygen. Lime- 
 stone is a compound containing 
 the elements, calcium, carbon, 
 and oxygen. Almost all sub- 
 stances we know of are compounds 
 of two or more of about a dozen 
 elements. Altogether about 80 
 elements have been discovered, 
 
 but many of these occur in very small quantities or are not 
 
 found in common compounds. 
 
 Explain : (1) The failure of a furnace to burn if ashes are 
 
 FIGURE 52 a. BUNSEN BURNER. 
 
 FIGURE 52 b. GAS STOVE BURNER. 
 
 A, gas inlet ; B, air chamber ; F, air inlet ; G, tube containing mixture 
 of gas and air ; C, outlet of gas mixture. 
 
IMPORTANCE TO US OF OXIDATION (BURNING) 57 
 
 not removed ; (2) The failure of a wood fire to burn if wood 
 is not arranged loosely; (3) The reason for the holes at 
 the base of a lamp or of a Bunsen burner (Figure 52 a) ; 
 (4) Why firemen have more difficulty in checking a big fire 
 when wind is blowing hard; (5) Construction of a gas 
 stove burner (Figure 52 b). 
 
 Problem 2. How the power of an automobile is produced. 
 
 We all know that gasoline is burned to give the engines 
 of automobiles and motor boats their power. That there 
 
 Admhalor 
 
 Compression Stroke 
 
 Power Stroke 
 ^ Spar 
 
 Exhaust Stroke 
 
 3412 
 
 FIGURE 53. MOVEMENTS OF PISTON OF GAS ENGINE. 
 
 Diagram showing how the explosion of a mixture of air and gasoline vapor 
 produces movement in the gasoline engine. 
 
 is power developed in the burning of gasoline may be 
 illustrated by a very simple experiment. 
 
 Experiment. Make a hole in the side of a coffee pot or a can with 
 hinged lid, a short distance from the bottom. Into the can pour a 
 
58 GENERAL SCIENCE 
 
 few drops of high grade gasoline and close the lid. Put a burning 
 match or taper through the opening at the side. An explosion will 
 occur which lifts the lid. 
 
 In the gas engine, a mixture of gasoline vapor and air 
 compressed in the cylinder is exploded by a spark from the 
 spark plug and the piston is thrown back with great force 
 (Figure 53). By means of a crank shaft and the gears this 
 power is made to turn the rear wheels of the automobile 
 or the screw of the motor boat. 
 
 Explain : (1) The striking back of a Bunsen burner (Fig- 
 ure 52 a) ; (2) The popping of a gas grate or gas stove when 
 lighted (Figure 52 b). 
 
 .Problem 3. How a match is lighted. Explain what 
 you usually do to light a match. Can you light a match 
 without rubbing it over a somewhat rough surface? What 
 do you think was the reason for rubbing the match over a 
 rough surface? 
 
 Can you light a piece of wood in the same way that the 
 match was lighted ? 
 
 Compare the head of the match with the wooden stick as 
 to the ease of starting it to burn. What then is the reason 
 
 for the head of the match 
 (Figure 54) ? 
 
 -CHICTLY OXIDIZING MATERIAL 
 
 starts to burn at a much 
 
 lower temperature than wood, it is said to have a lower 
 kindling temperature. How would you define kindling 
 temperature ? 
 
 The head of the ordinary parlor or friction match is 
 usually a mixture of (1) phosphorus and a substance which 
 readily gives out oxygen, (2) some ground glass to increase 
 
IMPORTANCE TO US OF OXIDATION (BURNING) 59 
 
 friction, (3) glue, and (4) coloring matter. The stick is 
 dipped into paraffin before the head is put on. 
 
 You can now give the steps in the lighting of a match. 
 What does the rubbing or scratching of it on a rough surface 
 do? What is the effect of the burning of the phosphorus 
 upon the paraffin ? What is the effect of the burning of the 
 paraffin upon the wood of the match stick? The flame is 
 caused by the burning of the gases which are given off when 
 the wood is highly heated. 
 
 Since ordinary friction matches are a great source of 
 danger from fire, efforts have been made to produce a match 
 that is less dangerous. One method has been to coat the 
 sides of the head with a substance that has a relatively 
 high kindling temperature. The " birds-eye " matches are of 
 this type. To lessen the danger from fire, the " safety " 
 match also has been invented. You are all familiar with 
 the matches which will not usually light unless scratched upon 
 a special striking surface. The heads of these matches con- 
 tain a substance which gives out oxygen when heated but 
 contains no phosphorus, the phosphorus mixture being in the 
 striking surface on the side of the box. 
 
 You will notice that some match sticks do not continue 
 to burn until the entire stick has burned up. This is be- 
 cause the sticks have been soaked in a liquid that hinders 
 burning. Explain the great value of this. 
 
 Formerly the manufacture of matches was a very dan- 
 gerous occupation as the white or yellow phosphorus used 
 poisoned the workers, especially affecting the jaw bones. 
 The use of this form of phosphorus has now been prohibited 
 in practically all civilized countries, and either red phos- 
 phorus or a compound of phosphorus and sulphur, both non- 
 poisonous, is used in production of matches, 
 
60 
 
 GENERAL SCIENCE 
 
 Explain : (1) The lighting of a gas jet ; (2) the starting 
 and continued burning of a coal fire ; (3) The difficulty of 
 lighting a match when the wind is blowing. 
 
 Problem 4. What causes iron to rust. This question 
 may be answered by performing the following experiment. 
 
 Experiment. Put into a test tube a small quantity of iron filings 
 and a few drops of water. Move the test tube around until the moist 
 
 iron filings form a layer sticking to the 
 inside of the tube. Place the test 
 tube, mouth down, in a glass of water. 
 Note how much of the tube is filled 
 with air. Examine again on the follow- 
 ing day. 
 
 Experiment. Test the air that 
 remains in the test tube for the pres- 
 ence of oxygen. This may be done as 
 follows : Keeping a finger over the 
 bottom of the test tube turn it so that 
 the mouth is up. Insert into the air in 
 the test tube a lighted splinter or taper. 
 Does the taper continue to burn? 
 What does this prove? What, there- 
 fore, do you think happens in the rust- 
 ing of iron ? 
 
 FIGURE 55. -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 to note that moisture also is necessary for 
 the rusting, so that this process of oxidation is not quite 
 so simple as some of the other cases which have been 
 mentioned. 
 
 In addition to the rusting of iron there are many other 
 common happenings which are the result of slow oxidation. 
 
IMPORTANCE TO US OF OXIDATION (BURNING) 61 
 
 Rub a match over the hand in the dark. What do you ob- 
 serve ? If paint containing linseed oil is allowed to stand a 
 short time, a tough skin is formed on its surface. This is 
 caused by slow oxidation of the oil in the paint. The same 
 thing happens when the paint is spread upon a surface. The 
 " drying " of such paint is due to oxidation, and not to real 
 drying. 
 
 Oily rags which have been thrown together in a heap some- 
 times catch fire. What is the explanation of this fact? 
 
 FIGURE 56. SECTIONAL VIEW OF A HOTBED. 
 
 The oil slowly oxidizes and the heat which is produced grad- 
 ually increases until the temperature has been raised to the 
 kindling point. The whole mass will then break into flames. 
 This is called spontaneous combustion. Why does oily 
 clothing not catch fire spontaneously if hanging? 
 
 It is not an uncommon occurrence in the country for a 
 barn filled with slightly damp hay to catch fire. In this 
 case the production of heat is probably hastened by the 
 action of small living plants, called bacteria, which are present 
 on the stems of the grass or come from the air. The hay 
 does not give off the heat readily, and finally, as in the case of 
 
62 
 
 GENERAL SCIENCE 
 
 the oily rags, sufficient heat accumulates until the kindling 
 point is reached. 
 
 The heat produced in a hotbed is formed in the same way 
 as the heat was produced in the hay barn, but it does not 
 reach the point where the oxidation becomes rapid enough 
 to give off light. A hotbed is made of decomposing organic 
 matter, usually a mixture of straw and horse manure. 
 
 FIGURE 57. FACTORY WRECKED BY A DUST EXPLOSION. 
 
 This is covered with a layer of soil. The bed is inclosed with 
 frames of glass or cheesecloth to prevent the escape of the 
 heat produced (Figure 56). The hotbed is used for forcing 
 the early growth of plants. 
 
 Explosions occur in poorly ventilated coal bunkers and 
 flour warehouses (Figure 57). How can you account for 
 this? Why is the fineness of the dust particles a factor? 
 Why is an explosion not apt to occur unless the ventilation 
 is poor? 
 
IMPORTANCE TO US OF OXIDATION (BURNING) 63 
 
 Problem 5. Why coal is burned. Enormous quantities 
 of coal are used every year. A coal famine is a very serious 
 matter. During the winter of 1917-18 many cities suffered 
 from shortage of coal. In many cases theaters, schools, 
 and libraries were closed; and factories were shut down, 
 throwing thousands of people out of employment. Trans- 
 portation facilities were interrupted; the use of lights was 
 very much restricted, resulting 
 in much inconvenience and loss. 
 
 In your own home or apart- 
 ment building, coal is burned for 
 production of heat. But in many 
 cases, the production of heat is 
 not the final result desired. In 
 the steam engine, the heat pro- 
 duced by the burning of the coal 
 is used to change water into 
 steam which gives the engine the 
 power to do many things. What 
 
 B, the exhaustion to close of 
 1911; C, production in 1911. 
 
 FIGURE 58. AVAILABLE COAL 
 SUPPLY. 
 
 A, dimensions 10 miles along 
 each edge, represents the total 
 are some ot the things which coal resources of United States ? 
 
 steam engines can do? Most 
 electric power houses have great 
 steam engines which are used for the generation of electricity. 
 Therefore, from what source may electrical power be ob- 
 tained ? What are some of the things that electricity can do ? 
 To what power, therefore, may all these things be traced ? 
 
 It will thus be seen that heat, light, electrical and mechan- 
 ical power may be changed one into another. They are 
 different forms of energy. Energy may be defined as the 
 capacity for doing work. 
 
 Suggest specific examples which are known to you of the 
 change of one form of energy into another. 
 
64 
 
 GENERAL SCIENCE 
 
 v^ 
 
 
 
IMPORTANCE TO US OF OXIDATION (BURNING) 65 
 
 What is your conclusion as to why coal is burned ? Name 
 other substances which are burned for this purpose. These 
 various substances are called fuels. What is your, definition 
 of a fuel? 
 
 Problem 6. How available energy is supplied to the 
 human body. How can the energy in our bodies and in 
 the bodies of animals be explained? Every movement of 
 our body demands muscular energy. If your body weighs 
 one hundred pounds, every time you take a step you must 
 lift one hundred pounds. Energy is needed even iPor the 
 beating of the heart, for the digestion of food, and for the 
 other involuntary activities of the body. 
 
 If you will think of all the activities of the body at work 
 and play during the day, you may realize to some extent the 
 need of the body for energy. In addition to this energy, 
 the temperature must be kept at about 98.6 degrees Fahren- 
 heit, winter and summer, day and night, in spite of the con- 
 stant losses of heat from the body. 
 
 Judging from the way that energy is made available in 
 engines and machines, what do you suspect to be the source 
 of the energy of the human body? The correctness of 
 your answer can be tested. If it is correct, oxygen must 
 be taken into the body, a constant supply of fuel must be 
 furnished, and carbon dioxide must be given off. 
 
 Evidently the air which we breathe in must furnish the 
 oxygen. Does the air breathed out contain an increased 
 amount of carbon dioxide? This may be found out by the 
 following experiment. 
 
 Experiment. Put some lime water into a test tube and breathe 
 into it through a glass tube. What is the result ? You will remember 
 that a milky appearance indicates the presence of carbon dioxide. 
 Conclusion ? 
 
66 
 
 GENERAL SCIENCE 
 
 Careful analysis shows that expired air (air breathed out) 
 contains about 25 per cent less oxygen than inspired air 
 (air breathed in), with a correspond- 
 ing increase of carbon dioxide. 
 
 What constitutes the fuel in the body f 
 It is the food. Just as you may 
 obtain heat and light and power to 
 run engines by the burning of oil, so in 
 the body the fat, a form of oil, is 
 burned to produce heat energy and 
 muscular energy. Light is not pro- 
 duced, since the process goes on too 
 slowly. Likewise, other food materials 
 are burned in the body to produce 
 energy (Figure 60). An ounce of fat 
 or starch burned inside of the body 
 will furnish the same number of heat 
 or energy units as if it were burned 
 outside of the body. 
 
 Sum up now your conclusions as to 
 how energy is made available in the 
 human body. Compare this process 
 FIGURE 60. -FUEL VALUE in the human body with what goes 
 OF SOME COMMON FOODS, on in the fire box of a furnace or 
 
 A calorie is the amount engine, 
 of heat necessary to raise TTT1 , i T_ j j 
 
 the temperature of i kilo- Why does a man working hard need 
 gram of water 1 centi- more food than one who is not per- 
 forming hard muscular work? 
 
 Why do we eat more food in the winter than in the summer ? 
 
 By carefully taking temperatures, it has been shown that 
 the energy is set free in the part of the body that is active ; 
 chiefly of course in the muscles. 
 
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IMPORTANCE TO US OF OXIDATION (BURNING) 67 
 
 Why do the muscles of the body which are used most not 
 become overheated? The circulating blood, is constantly 
 receiving heat from the more active parts of the body, and 
 is giving it to those parts which are less active. As a result, 
 the temperature of the body is equalized. Since the heat 
 energy and muscular energy are made available in the various 
 parts of the body, three other uses of the circulating blood 
 are indicated. What are they? 
 
 Problem 7. Do plants breathe? If they do, then there 
 must be some proof that three different things occur. What 
 are they? 
 
 To find out if plants use oxygen and give out carbon 
 dioxide perform the following experiment. 
 
 Experiment. Into each of two flasks put an equal number of 
 peas that have been soaked in water. Cork one flask so that no air 
 can pass into it or out of it. Allow the other flask to remain open. 
 Place the flasks side by side so that they will have the same conditions 
 of light and heat. At the end of a week observe the contents of the 
 flasks. 
 
 What has happened ? What does this prove ? A blazing 
 splinter passed into the open flask continues to burn. What 
 happens when it is passed into the flask which has been kept 
 closed ? What does this prove ? If the air in each flask is 
 tested for the presence of carbon dioxide, it will be found 
 that the closed flask contains a considerable amount of 
 carbon dioxide while the other does not contain an appre- 
 ciable quantity. What does this prove? What is your 
 general conclusion as to the use of oxygen by sprouting 
 seeds ? 
 
 If oxidation goes on in sprouting seeds we should expect 
 that heat and energy of movement would result. 
 
68 
 
 GENERAL SCIENCE 
 
 Experiment. Into a flask put an inch or more of pea seeds which 
 have been killed by being heated for a short time in an oven. Into 
 another flask put an equal amount of living pea seeds. Put into each 
 flask the same amount of moisture. Place a thermometer in each flask, 
 covering the mercury bulb with the peas. Permit free access of air. 
 From time to time note whether the thermometers register a difference 
 in temperature. 
 
 It will be found that heat is generated by the sprouting 
 pea seeds. What observations have you made that will 
 
 FIGURE 61. FLOODED REGION. 
 Trees killed by having their roots drowned. 
 
 show that sprouting seeds are able to lift a weight or in 
 other ways exert mechanical energy ? 
 
 Seedlings take in the oxygen of the air and give off carbon 
 dioxide through any part of their surfaces. In fully grown 
 plants this occurs chiefly through the young roots and leaves. 
 In a region flooded for a considerable time, the trees will 
 
IMPORTANCE TO US OF OXIDATION (BURNING) 69 
 
 die, chiefly because their roots have been unable to get 
 oxygen from the air (Figure 61). They have been drowned. 
 
 Problem 8. How animals take in oxygen and give off 
 carbon dioxide. Animals have various ways of taking 
 in oxygen and giving off carbon dioxide. 
 
 (a) Very simple animals. Earthworms and other 
 simple animals have no lungs. How then do you suppose 
 they can take in oxygen? Plants, we already know, breathe 
 
 Pharynx Muscles 
 Brain ^_A-^~^-^-^-_ ^__ Stomach- Intestine 
 
 Oesophagus .Bloodvessels 
 
 FIGURE 62. ORGANS OF AN EARTHWORM. 
 
 Many small blood vessels (not represented in the figure) pass from near the 
 surface of the body into the large vessels, which are also near the surface. 
 
 through thin moist membranes. Possibly this is true of the 
 earthworm. If so, the earthworm must have a thin moist 
 skin. Examine an earthworm to see if this is the case. 
 An earthworm dies as soon as its skin becomes dry. Fre- 
 quently after a rain, many earthworms come to the surface 
 because their burrows have become filled with water. Early 
 in the morning they may be seen crawling on the sidewalk, 
 but it will be noticed that they die as soon as the sun has 
 dried their bodies. 
 
 If an earthworm breathes through its skin, what should 
 be directly below the thin moist membrane of the skin? 
 
70 GENERAL SCIENCE 
 
 Sum up your conclusions as to how the earthworm takes 
 oxygen into its body and gives out the carbon dioxide. 
 
 (6) Insects cannot breathe through the skin. Why not? 
 If a grasshopper is watched, it will be noticed that the 
 hinder portion of the body (abdomen), which is made up of 
 rings, expands and contracts in a way similar to the expansion 
 and contraction of our own chests during breathing. These 
 movements of the grasshopper are breathing movements. 
 
 The air containing oxygen goes into the body with each 
 expansion, and the air containing carbon dioxide passes 
 out at each contraction. Where does the air go in? If 
 you look very carefully along each side of the body you will 
 see a number of small holes, one in each of the divisions of 
 the abdomen. There are also two pairs of holes in the thorax, 
 the part of the body to which the legs and wings are attached. 
 Connected with these openings are small branching tubes 
 which carry air to all parts of the body. , 
 
 These breathing pores can usually be seen very distinctly 
 on the sides of a beetle larva (Figure 63) or of a caterpillar, 
 which you know, of course, is the young of a moth or 
 butterfly. The young or larva of the mosquito which lives 
 in water has only one breathing pore, which is located at 
 the tail end of the body. In order to get air, it must come 
 to the surface hanging head .downward. 
 
 Mosquitoes, therefore, may be destroyed by pouring 
 oil on ponds in which they live. The oil spreads over the 
 surface of the water, forming a thin layer through which 
 air will not pass. Thus the mosquito larvae are unable to 
 obtain air when they come to the surface, and suffocate. 
 
 (c) Fish breathe by means of gills which are located under 
 flaps just back of the head. If you examine a fish which 
 has been sent from the market with the head still attached, 
 
IMPORTANCE TO US OF OXIDATION (BURNING) 71 
 
 you will see under these flaps (opercula) four bony arches 
 on each side. Between these arches are slits opening into 
 the back of the mouth. Each arch has upon its outer edge 
 a large number of small, reddish, threadlike structures, 
 (gill-filaments) which project backward from the arch. 
 The inner side of each arch has on it a number of hard, 
 pointed structures (gill-rakers) (Figure 64). 
 
 if^ 
 
 FIGURE 63. STAGES IN THE LIFE HISTORY OF A BEETLE. 
 Note the breathing pores on the side of the larva (the worm-like stage). 
 
 Observe a fish in an aquarium. Do you notice any move- 
 ments which are probably connected with breathing ? Water 
 passes into the mouth of the fish and out through the gill 
 slits at the side of the head. Suggest a use for the gill 
 rakers. The heart is located on the under side of the fish, 
 in the space between the back parts of the gills. It pumps 
 the blood forward through a vessel which has four branches 
 on each side, one to each gill arch. These vessels in turn 
 send off very small vessels into the gill filaments. 
 
 What do you suppose the blood in these vessels receives ? 
 
72 
 
 GENERAL SCIENCE 
 
 What does it give off? The blood from the gill filaments 
 passes into vessels which carry it to the upper part of the 
 gill arches and from there it passes to all parts of the body, 
 finally returning to the heart loaded with carbon dioxide and 
 without its oxygen. What has become of the oxygen? 
 What is the source of the carbon dioxide ? 
 
 .Gill Filaments. 
 
 Gill Rakers 
 
 Gill of tile Fish 
 
 Gfil of White Fish 
 
 FIGURE 64. BREATHING ORGANS OF FISH. 
 
 (d) Higher animals. Most animals that live in the air, 
 except insects, breathe by means of lungs which are really 
 thin-walled bags connected with the outside air through 
 the nostrils. The walls of the lungs contain many small 
 blood vessels (capillaries). The blood in these takes in 
 oxygen and gives off carbon dioxide. 
 
IMPORTANCE TO US OF OXIDATION (BURNING) 73 
 
 INDIVIDUAL PROJECTS 
 
 1. Production of pure oxygen and comparison of the burning of 
 substances in air and in oxygen. 
 
 2. Making a safety match. 
 
 3. Demonstration of how the explosion of gasoline causes the gas 
 engine to work. 
 
 4. Demonstration of how air and gas are mixed in a gas stove. 
 
 5. Construction and use of a hotbed. 
 
 6. Making gas from coal and wood. 
 
 7. Collection of various kinds of coal. Source and special use of 
 each kind. 
 
 8. Dissection of the blood system and breathing system of a fish. 
 
 REPORTS 
 
 1. History of the discovery of oxygen. 
 
 2. The coal regions of the United States, methods 01 mining, and 
 approximate number of years our supply will last. 
 
 3. Formation of coal. 
 
 4. Different ways in which animals breathe. 
 
 REFERENCES FOR PROJECT VI 
 
 1. Book of Wonders, Bodmer, R. (Fire.) 
 
 2. Chemical History of a Candle, M. Faraday. Harper & Bros. 
 
 3. Fuels of the Household, Marian White. Whitcomb & Barrows, 
 Boston. 
 
 4. Sweden and Safety Matches, N. B. Allen. Ginn & Co. 
 
 5. Diggers in the Earth, E. M. Tappan. Houghton Mifflin Co. 
 (Coal mining.) 
 
 6. Earth and Sky Every Child Should Know, J. E. Rogers. 
 Doubleday, Page & Co. 
 
 7. The United States, J. O. Winston. D. C. Heath. (Coal.) 
 
 8. The Story of Oil, W. S. Tower. D. Appleton & Co. 
 
 9. Field and Forest Handy Book, Beard. Scribners. (Camp cook- 
 ing and stoves.) 
 
 10. American Inventions and Inventors, Mowry, Silver* Burdett 
 & Co. (Fire, Fuel, Matches.) 
 
PROJECT VII 
 
 PREVENTION OF DESTRUCTIVE BURNING OR 
 OXIDATION 
 
 WE have seen that oxidation is very valuable in giving us 
 usable energy. Can you name examples of oxidation or 
 burning which 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 vegetable 
 matter (humus) of the soil has been burned away. 
 
 about burning, we should be able to suggest means by 
 which destructive oxidation may be prevented. 
 
 What two conditions are always necessary for oxidation? 
 Suggest another which is usually necessary. It is clear that 
 if any one of the necessary conditions is removed, then 
 
 74 
 
PREVENTION OF DESTRUCTIVE BURNING OR OXIDATION 75 
 
 burning or oxidation must stop. Our problem then is simply 
 to discover methods by which these conditions necessary 
 for oxidation may be prevented. 
 
 Problem 1. How destructive oxidation may be pre- 
 vented by excluding the air. (a) Coating iron with a sub- 
 stance which does not rust. What are some of the ways 
 in which air may be kept from substances which are apt 
 to undergo harmful oxidation? How are iron fire escapes 
 kept from rusting? Give other examples of the use of this 
 means. 
 
 Is a tin pan made entirely of tin? Give proof for your 
 answer. Tinware is made of thin sheets of iron which, 
 after having been thoroughly cleaned, are dipped into melted 
 tin. Iron also may be prevented from rusting by covering 
 it with a layer of zinc, applied in the same way. This is 
 called galvanized iron and is very generally used for pails, 
 water troughs, and similar articles. It is not used for cook- 
 ing utensils, as zinc may form poisonous compounds. 
 
 How is the iron hot water boiler in the kitchen prevented 
 from rusting ? It is usually painted with a volatile substance 
 (a substance which evaporates quickly) in which there is 
 powdered aluminum, a metal which is not affected by the air. 
 The volatile liquid disappears, leaving on the boiler a thin 
 layer of powdered aluminum which not only gives the boiler 
 a pleasing appearance but also prevents it from rusting. 
 
 Iron may also be prevented from rusting by covering it 
 with a layer of nickel, which is put on by the use of elec- 
 tricity (nickel plating). 
 
 The iron of stove pipes and locomotive boilers is usually 
 protected from rusting by a coating which is produced by 
 passing over the hot iron a mixture of highly heated steam 
 
76 
 
 GENERAL SCIENCE 
 
 and carbon dioxide. This coating is an oxide of iron, dif- 
 ferent from the ordinary oxide of iron, and it protects the 
 iron from further oxidation. Iron, coated in this way, is 
 called Russia iron. 
 
 (b) How do .fire extinguishers work f A fire is put out by 
 surrounding the burning material with a gas which will 
 
 not burn. What happens 
 then to the fire? Some 
 fire extinguishers contain 
 a liquid, carbon tetrachlo-. 
 ride, which becomes a non- 
 inflammable gas when it 
 is squirted on the fire. 
 In the fire extinguishers 
 which are inverted just 
 before being used, sul- 
 phuric acid falls into a 
 solution of soda (Figure 
 66). The action of the 
 acid upon the soda pro- 
 duces a large quantity of 
 
 carbon dioxide which forces out the mixture of water and 
 
 carbon dioxide. What effect will this have when played 
 
 upon the burning objects? 
 
 Explain the reason for keeping pails of sand in various 
 
 parts of a garage. Why is water not used for the purpose? 
 
 Will water mix with gasoline? 
 
 (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 to start to run if his clothing 
 is on fire ? W T hy ? Why are burning draperies pulled down 
 and stamped upon? 
 
 FIGURE 66. FIRE EXTINGUISHER. 
 
PREVENTION OF DESTRUCTIVE BURNING OR OXIDATION 77 
 
 Problem 2. How destructive oxidation may be pre- 
 vented by reducing the temperature below the kindling 
 point. Throwing water on a fire, you all know, is the 
 usual way of putting it out. Why do you suppose it is so 
 effective? Do you think that the amount thrown by the 
 firemen upon a big fire 
 will prevent the air get- 
 ting to the fire? Why, 
 then, is water so valu- 
 able for putting out a 
 fire? Reference to your 
 study of ventilation will 
 help to answer this ques- 
 tion. What was the 
 effect of evaporation of 
 moisture on the skin? 
 What becomes of the 
 water that is thrown on 
 the fire? What effect 
 will this have upon the 
 temperature ? A wet 
 
 piece of wood does not FIGURE 67.- FIGHTING A FIRE WITH WATER. 
 burn readily because the 
 
 heat applied is used in evaporating the water instead of 
 raising the wood to its kindling temperature. 
 
 Sum up your conclusions as to the importance of water 
 in lowering the temperature of a burning substance below 
 the kindling temperature. Do not forget that the water and 
 steam produced are also useful in preventing the access of air. 
 
 Problem 3. How destructive oxidation may be pre- 
 vented by removal of fuel material. No fire can start or 
 
78 
 
 GENERAL SCIENCE 
 
 continue to burn unless there is a supply of fuel material ; 
 hence, the inspectors of the fire department prohibit the 
 collection of rubbish in basements and area ways. Every 
 year forest fires destroy property worth hundreds of thou- 
 sands of dollars .and cause the death of many people. Prob- 
 ably the most common cause of these fires is the careless- 
 ness of campers in failing to put out their camp fires. Very 
 
 FIGURE 68. A FOREST FIRE FIGHTER. 
 
 strict regulations concerning the use of fire are enforced 
 to prevent the starting of forest fires. To limit the spread 
 of a fire if once started in a forest reservation, there are 
 fire lanes which are kept cleared of underbrush. Why do 
 the fire lanes stop the fire ? 
 
 Ground fires which creep along the ground, depending for 
 fuel upon the underbrush and vegetable matter accumu- 
 
PREVENTION OF DESTRUCTIVE BURNING OR OXIDATION 79 
 
 lated during many years, are frequently stopped by plowing 
 up a strip of land in the path of the fire. What is the 
 advantage of this? 
 
 During severe fires in cities 
 which threaten to destroy 
 property in great areas, build- 
 ings are often deliberately de- 
 stroyed by dynamite. What 
 is the reason for this ? Where 
 there are buildings in solid 
 blocks, fireproof walls are con- 
 structed at intervals which 
 are known as fire walls. 
 
 W T hat is meant by fireproof 
 construction of buildings ? 
 In what respect is your school 
 building of fireproof construc- 
 tion? In other buildings 
 with which you are familiar, 
 what means have been taken 
 to make them fireproof? 
 What substances may be used 
 in fireproof construction? 
 
 INDIVIDUAL PROJECTS 
 
 1. Make and demonstrate a 
 fire extinguisher. 
 
 2. Collection and demonstra- 
 tion of fireproofing materials. 
 
 REPORTS 
 
 1. Fighting a forest fire. 
 
 2. Fireproof construction of 
 buildings. 
 
 FIGURE 69. FOREST RANGER ON 
 LOOKOUT FOR SIGNS OF FOREST 
 FIRES. 
 
 If signs of fire are discovered, the 
 ranger telephones to the fire station 
 nearest the fire, indicating by refer- 
 ence to the forest map the exact 
 location of the observed smoke. 
 
PROJECT VIII 
 
 IMPORTANCE TO US OF THE OTHER GASES OF 
 THE AIR 
 
 WE have seen that the oxygen of the air is of very great 
 importance to us. Mention several ways in which it is of 
 great value and several in which it is harmful. The ques- 
 tion naturally arises, are there other gases in the air and if 
 so, of what importance are they to us. The first problem 
 therefore is : 
 
 Problem 1. Does air contain any gas besides oxygen ? 
 
 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 the conclusion? 
 
 (3) Expose a vessel of limewater to the air. Note that a scum 
 appears on the surface. This is an indication of the presence of carbon 
 dioxide. 
 
 Problem 2. How much of the air is oxygen ? Can 
 
 you suggest a method by -which this may be found out? 
 
 Experiment. On a metal disk on a flat piece of cork, place a bit 
 of yellow phosphorus. Place the cork - on water and invert over it 
 a glass cylinder. Examine after two days. Result? Conclusion? 
 
 Quantitative experiments have shown that air has the 
 following composition : 
 Oxygen, 20+ per cent. 
 
 Nitrogen, including several inert gases, 79+ per cent. 
 Carbon dioxide, .03 to .04 of 1 per cent. 
 
 80 
 
IMPORTANCE TO US OF THE OTHER GASES OF THE AIR 81 
 
 Problem 3. Importance of nitrogen in the air. 
 
 Experiment. Manufacture some oxygen. This can be done by 
 heating a mixture of potassium chlorate with manganese dioxide in 
 a flask. The gas can be collected in a bottle in the manner shown in 
 the diagram (Figure 70). Burn various substances as wood splinters, 
 a candle, some sulphur, and an iron wire in bottles of pure oxygen. 
 
 D 
 
 FIGURE 70. PREPARATION OF OXYGEN. 
 
 A, bunsen burner; B, tube containing potassium chlorate and manganese 
 dioxide ; C, vessel containing water ; D, D, bottles for collecting gas. 
 
 Pass oxygen into a bottle until it is one fifth filled. Fill the remainder 
 with nitrogen, which may be made by heating together in a flask the 
 two chemicals, ammonium chloride and sodium nitrate. Try to burn 
 in this mixture of oxygen and nitrogen a splinter of wood, a candle, some 
 sulphur, and an iron wire. Do these substances burn the same as when 
 burned in the pure oxygen? 
 
 What would happen if the air contained a much larger 
 percentage of oxygen? What do you consider to be the 
 value of nitrogen in the air? Nitrogen is a very inactive 
 substance. It is due to this property that nitrogen is an 
 
82 GENERAL SCIENCE 
 
 important element in explosives. Explain. Under certain 
 conditions some of the nitrogen of the air may be used in 
 the growth of plants or may be made into substances from 
 which explosives may be manufactured. These cases will 
 be considered later. x 
 
 Problem 4. Importance of carbon dioxide of the air. 
 We found that certain animals in breathing give carbon 
 dioxide to the air. Also that it is added to the air in the 
 burning of a candle. In the same way it is given off in the 
 burning of coal, wood, oil, etc. As a result what do you 
 think should happen to the amount of carbon dioxide in the 
 air? But an examination of the air year after year indi- 
 cates that there is no increase in the amount of this gas. 
 What do you conclude from this? 
 
 Another interesting fact gained from the examination 
 of the air is that the oxygen of the air does not decrease in 
 quantity. In the solution of our problem, therefore, a num- 
 ber of smaller problems must be solved. The first of these 
 will be indicated by a fact that is familiar to you. W r hat 
 is the appearance of partially burned plant material ? What 
 does this indicate ? Since plants can grow in soil which con- 
 tains no carbon, what will you suspect is the source of the 
 carbon ? 
 
 Sub-problem I. Proof that carbon compounds are made 
 in leaves of plants. One of the most common plant sub- 
 stances containing carbon is starch. There is no starch in 
 the soil or in the air, therefore it evidently must be made 
 within the 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 AIR 83 
 
 oring matter, by soaking the leaf in alcohol, and then adding iodine, 
 which gives a blue color if starch is present. What is the result? 
 After this leaf has been removed, set the entire plant in the sunlight, 
 first placing upon several leaves pieces of black cloth or thin strips of 
 cork which completely exclude 
 the light from the portions of 
 the leaves covered. After a 
 few hours, remove and test 
 several leaves for the presence 
 of starch. What is the result ? 
 What two things are proved 
 by this experiment ? 
 
 Sub-problem II. What 
 raw materials are used by 
 leaves in making starch? 
 Analysis shows that 
 starch is made of the 
 following fundamental 
 substances or elements : 
 Carbon, 6 parts; hydro- 
 gen, 10 parts; oxygen, 5 
 parts. This is conven- 
 iently written, C 6 Hi O5. 
 Water, which is made of 
 two parts of hydrogen and 
 one part of oxygen (H 2 O), 
 
 
 FIGURE 71. POTATO PLANT. 
 
 and carbon dioxide, com- A plant in which a large amount of starch 
 
 is stored in an underground stem. , 
 posed of one part of carbon 
 
 and two parts of oxygen (CO 2 ), both of which are accessible 
 to the leaf, 'contain the elements necessajy for the formation 
 of starch. I( they were combined, the result might be repre- 
 sented as follows: Carbon dioxide (CO 2 )+ Water (H 2 O) = 
 Starch (CcHioOs). It will be noted that to get sufficient 
 
84 GENERAL SCIENCE 
 
 carbon for the starch, it is necessary that six parts of carbon 
 dioxide enter into the combination; and to provide the 
 proper proportion of hydrogen, five parts of water must 
 combine with the carbon dioxide. The action may then be 
 represented as follows: Six parts of carbon dioxide might 
 combine with five parts of water to form one part of starch 
 or 
 
 6C0 2 +5H 2 0=C 6 H 10 5 
 
 But if six parts of CO 2 unite with five parts of H 2 O to form 
 starch (CeHioC^), it will be noticed there is an excess of 
 oxygen, so that the action will finally be represented as 
 follows : 
 
 6 CO 2 +5 H 2 O = C 6 H 10 O 5 +6 O 2 
 
 If in the leaf, therefore, carbon dioxide and water actually 
 do unite in forming starch, oxygen should be given off. Does 
 this occur ? 
 
 Sub-problem III. Do plants give off oxygen in making 
 starch ? 
 
 Experiment. Place some aquarjum plants under a funnel in a jar 
 of water. Over the neck of the funnel put an inverted test tube filled 
 with water. Place the jar in the sunlight. What do you observe ? 
 
 Remove the test tube without allowing any of the contained gas to 
 escape, and pass into the mouth of the test tube a glowing ember. 
 What happens ? What does this prove ? 
 
 The work that the green leaf does with the assistance 
 of sunlight in combining carbon dioxide and water into 
 starch is called photosynthesis (from two Greek words : 
 photo, light, and synthesis, putting together). . . 
 
 Sub-problem IV. Proof that plants use carbon dioxide 
 in making starch. The fact that oxygen is given off by 
 plants is an indication that carbon dioxide and water are 
 
IMPORTANCE TO US OF THE OTHER GASES OF THE AIR 85 
 
 used by the plant in making starch. It can easily be proved 
 by the following experiment that carbon dioxide is used by 
 plants during the process of starch-making. 
 
 Experiment. Pass into a jar sufficient carbon dioxide to replace the 
 air almost entirely. Put into the jar a green plant which has been kept 
 in the dark for twenty-four hours. Pass a lighted taper into the jar. 
 What is the result? Also pass into the jar a glass rod from which is 
 hanging a drop of Jimewater. What is the result? Cover the jar 
 tightly and place it where it will be exposed to sunlight. After several 
 days again test the contained air with the limewater and the lighted 
 taper. Results ? Conclusions ? 
 
 Sub-problem V. Amount of carbon dioxide removed from 
 the air in making starch and wood. The woody sub- 
 stance of plants (cellulose) is also made of carbon, hydro- 
 gen, and oxygen in the same proportion as in starch. Wood, 
 therefore, represents a certain amount of carbon dioxide 
 takerf'out of the air and combined with water. It has been 
 calculated that for every pound of starch or cellulose (wood 
 manufactured by a plant) 1.6 pounds of carbon dioxide are 
 needed. From an acre of ground several tons of dry hay may 
 be obtained. A large proportion of the dry hay is cellulose, 
 or material of a similar composition. Considering this 
 fact, calculate approximately how much carbon dioxide 
 will have been taken from the air by a ten-acre field of hay 
 during one season. 
 
 The coal which we burn has had a similar origin. It was 
 formed from many generations of plants which formed layer 
 after layer of vegetable matter. This was partially oxidized 
 and then was covered by sediment which finally became 
 formed into rock. Soft or bituminous coal clearly shows 
 the layers of vegetable matter of which it is composed. 
 
 Soft or bituminous coal occurs in great beds usually more 
 
86 GENERAL SCIENCE 
 
 or less horizontal (Figure 72). Anthracite or hard coal 
 is found in portions of the country where the strata or 
 layers of the rock have been very much crumpled. This 
 crumpling process has evidently been accompanied by a 
 high temperature which has driven from the accumulated 
 vegetable matter many compounds, leaving almost pure 
 carbon. 
 
 Just as we have found that the starch is made by plants, 
 only under the action of the energy of sunlight, so likewise 
 
 FIGURE 72. COAL BED. 
 Horizontal bed of coal exposed along a river bed in Wyoming. 
 
 in the cases of wood and coal the energy of the sun has been 
 necessary. What, therefore, may be considered to be the 
 final source of the energy given out in the process of the 
 burning of wood or coal ? The amount of heat procured by 
 burning a piece of coal may be considered to be a measure 
 of the amount of the sun's energy necessary to separate the 
 carbon from the oxygen of carbon dioxide in the process of 
 photosynthesis (Figure 73). 
 
IMPORTANCE TO US OF THE OTHER GASES OF THE AIR 87 
 
 We are now able to understand why the relative quan- 
 tities of oxygen and carbon dioxide in the air remain the 
 same year after year. 
 
 BITUMINOUS ANTHRACITE 
 
 COAL COAL 
 
 5 t CALORIES 
 PER GRAM 
 
 8009 
 
 7000 
 
 4090 
 
 10 
 
 5000 
 
 4000 
 
 3000 
 
 2000 
 
 1000 
 
 FIGURE 73. HEATING VALUE OF SOME COMMON FUELS. 
 Note the relative amounts of carbon (C) in the various fuels. What 
 is the source of this carbon ? What is the source of the hydrogen (H) ? 
 The calories given here are small calories. The amount of heat necessary 
 to raise the temperature of one gram of water 1 C- is one calorie. Fuel 
 value of foods is usually given in large calories, 1000 times greater than 
 small calories. 
 
88 
 
 GENERAL SCIENCE 
 
 What are the chief ways in which oxygen is removed from 
 the air? 
 
 How is it restored to the air? 
 
 How do you suppose the composition of the air before the 
 carboniferous period (the period when most coal was formed) 
 differed from the composition of the air now ? 
 
 FIGURE 74. OIL WELLS IN OKLAHOMA. 
 
 These wells tap oil deposit 2000 to 3000 feet below the surface. Since 
 petroleum has evidently been formed from plant and animal material, what 
 is the source of its energy ? 
 
 Almost all plants are green. Is there any connection 
 between the possession of this green coloring matter 
 (chlorophyll) and the ability to make starch ? 
 
 Sub-problem VI. Is the green coloring matter (chlo- 
 rophyll) necessary for making starch. Place a plant 
 whose leaves have white streaks or spots (Tradescantia is a 
 good plant to use) in the sunlight for several hours. Test 
 
IMPORTANCE TO US OF THE OTHER GASES OF THE AIR 89 
 
 the leaves for starch. Result? Conclusion? Experiments 
 might, also be performed which show that it is only the 
 living leaf that will manufacture starch. 
 
 Sub-problem VII. How fish live in a balanced aquarium. 
 Fish and other animals may be kept for long periods of 
 time without being fed if they are in aquaria containing 
 green plants. In such 
 aquaria the green 
 plants do not decrease 
 in quantity. These 
 aquaria are known as 
 balanced aquaria 
 (Figure 75). 
 
 (a) Breathing. 
 From what you have 
 already learned, ex- 
 plain how the fish get 
 a supply of oxygen. 
 What do you sup- 
 pose becomes of the 
 carbon dioxide pro- 
 duced ? 
 
 (b) Food Supply. In a balanced aquarium, what do the 
 fish eat? A fish or any other living thing needs food not 
 only to furnish fuel which may be oxidized to set energy 
 free, but it must also have food to replace the waste which 
 is occurring in the different parts of the body, and for growth 
 if there is any growth going on. 
 
 Foods, therefore, may be divided into energy-producing 
 food* and tissue-forming foods. The tissue-forming por- 
 tion of foods is made up of complex substances called pro- 
 
 Courttsy of New Yorl Zoological SoctetU. 
 
 FIGURE 75. A BALANCED AQUARIUM. 
 
90 
 
 GENERAL SCIENCE 
 
 teins and certain mineral salts. The proteins, when oxidized, 
 will produce energy, but the chief energy-producing portions 
 of food are carbohydrates (starch and sugar) and fats. 
 
 FIGURE 76. RELATION OF PLANT AND ANIMAL IN A BALANCED AQUARIUM. 
 
 Since fish of the balanced aquarium maintain their size 
 and are active, what must be obtained from the plants? 
 
 Since the plants do not decrease in quantity, what must 
 they be able to do? 
 
IMPORTANCE TO US OF THE OTHER GASES OF THE AIR 91 
 
 We already have learned from what they make carbo- 
 hydrates. Explain. Carbohydrates in turn are some- 
 times changed by the activity of the living matter into fat. 
 For the manufacture of proteins, the plant must not only 
 have carbon, hydrogen, and oxygen, which may be obtained 
 from the carbon dioxide and water, but must also have 
 nitrogen and other elements. The wastes of the fish con- 
 tain all these needed elements. 
 
 In swimming about, the fish are contfnually exerting 
 energy. What is the final source of this energy? 
 
 The relation of the plants and animals in the balanced 
 aquarium is represented in the diagram (Figure 76) on the 
 preceding page. 
 
 What do you think would happen to animals, including 
 man, if there should be no more green plants ? Explain. 
 
 Summarize in a sentence or two the importance to us of 
 the carbon dioxide of the air. 
 
 INDIVIDUAL PROJECTS 
 
 1. Rapidity of starch manufacture in a leaf. 
 
 2. Keeping a balanced aquarium. 
 
 REPORT 
 The world's food supply. 
 
 REFERENCES FOR PROJECT VIII 
 
 1. The Fresh Water Aquarium and Its Inhabitants, Eggeling and 
 Ehrenberg. Henry Holt & Co. 
 
 2. Life in Ponds and Streams, W. Furneaux. Longmans, Green 
 &Co. 
 
 3. The American Boys' Handy Book, Beard. (Fresh water and 
 Marine Aquaria.) 
 
PROJECT IX 
 TO KEEP FOODS FROM SPOILING 
 
 You know that many foods if left in the air spoil or decay. 
 Name some fogds which you know will spoil if left exposed 
 to the air. Since foods must be transported long distances 
 and frequently must be kept many months before being used, 
 the problem of preserving foods is of the very greatest 
 importance. Without the means of preserving food from 
 decay our present civilization could not have arisen, 
 i Think for a moment of the possibility of the existence of 
 great cities, like New York, Chicago, or of great manu- 
 facturing centers, if ways of keeping foods from spoiling had 
 not been discovered. Could the United States have sent 
 her great army of 2,000,000 men to Europe, if there had 
 been no means of preserving foods for many months and 
 even years? In considering how foods may be kept from 
 spoiling, naturally the first problem is : 
 
 Problem 1. What causes foods to spoil or decay? 
 Is it the oxygen of the air acting upon the food which causes 
 the change, a process of slow oxidation such as we have 
 observed in a number of cases? The question can be 
 answered by performing -the following experiment. 
 
 Experiment. To find out what causes foods to spoil when left 
 exposed to the air, pour some beef tea made of beef extract and a 
 small amount of peptone (digested protein) into two test tubes. Boil 
 the beef tea in each test tube for an equal length of time. Stopper one 
 with cotton. Allow the other to remain open. Place the tubes side 
 by side in the room. (Experiments have proved that air will pass 
 
 92 
 
. TO KEEP FOODS FROM SPOILING 93 
 
 through a cotton stopper but that particles floating in the air are 
 caught by the cotton.) 
 
 After a few days observe the contents of the tubes. What 
 differences in appearance are noticeable? Smell the con- 
 tents of each tube. What is your conclusion? Is oxygen 
 alone able to cause substances to decay? If a drop of the 
 beef tea from the unstoppered tube is examined with a 
 high power microscope, a very large number of exceedingly 
 small objects will be seen. Some are spherical and some 
 are rod-shaped. 
 
 If even the smallest possible amount of the spoiled beef tea 
 is added to the unspoiled, stoppered tea, the latter also be- 
 comes spoiled in a few days. Another examination of the 
 tea with the microscope will show that there has been an 
 enormous increase in the number of the spherical and rod- 
 shaped bodies. The fact that they have increased in number 
 is an indication that they are living bodies. These small, 
 living bodies are. called bacteria. 
 
 It seems evident that the spoiling of the beef tea was 
 associated with the development of bacteria within it. 
 Many experiments have shown that the decay of plant and 
 animal (organic) matter is always brought about by bacteria 
 or their close relatives, the molds. 
 
 Problem 2. Where bacteria are found. By the follow- 
 ing experiments information may be obtained concerning 
 the distribution of bacteria. 
 
 As in these experiments it is important to keep separate the 
 descendants of different bacteria, a solid or semi-solid food 
 material must be used. The food mixtures which we 
 prepare to obtain a growth of bacteria, are called culture 
 media. In the previous experiment the beef tea was a 
 
GENERAL SCIENCE 
 
 liquid culture medium. A solid culture medium is made by 
 adding to beef tea some agar-agar, a vegetable gelatine ob- 
 tained from certain kinds of sea weeds. (Details of prepa- 
 ration are given in the appendix.) Into Petri dishes (flat 
 dishes especially designed for study of bacteria) which have 
 been highly heated to kill any living organisms present, pour 
 some of this melted agar medium. Cover the dishes imme- 
 diately. In a short time the culture medium will become 
 jellylike and ready for use. 
 
 Experiment. Expose open dishes in several of the following 
 places for five minutes, then close and label : a classroom, a corridor 
 before the passing of classes, a corridor during passing of classes, a win- 
 dow sill outside of room, street, subway, park, etc. 
 
 Experiment. By means of a needle, which has been heated (ster- 
 ilized) to kill organisms upon it, put into dishes small amounts of 
 material which you wish to test for the presence of microorganisms; 
 e.g. dust from floor, saliva, dirt from under finger nails, milk, soil, etc. 
 
 Experiment. Test various other substances, e.g. pupil's finger, 
 breath, paper and silver money, drinking water, the edge of drinking 
 
 cup, blade of a knife, pencil 
 point, etc. Take care in 
 every case that you prevent 
 the entrance of any other 
 material. 
 
 Describe the results of 
 these experiments. The 
 spots which you see are 
 colonies of bacteria or 
 mold (Figure 77). Are 
 there indications of the 
 presence of more than one kind of microorganisms? Do 
 you see any mold colonies? They are fluffy or hairy in 
 appearance instead of waxy like the bacteria colonies. Does 
 
 FIGURE 77. COLONIES OF BACTERIA AND 
 MOLD. 
 
 The agar culture med um in these d'shes 
 was exposed to the air for about 5 minutes. 
 
TO KEEP FOODS FROM SPOILING 
 
 95 
 
 there seem to be any connection between the presence of 
 dust and the abundance of microorganisms? 
 
 Problem 3. Size, shape, and method of multiplication of 
 bacteria. Could you see the bacteria upon the agar plate 
 when the plate was first exposed to the air? What does 
 this indicate as to the size of the bacteria? You will find 
 that they can be seen only with rather a high power of a 
 compound microscope. \j 
 
 They are the smallest and simplest plant life known. 
 The average rod-shaped bacterium measures about r^io~o of 
 
 From, Household Bacteriology by Buchanan. 
 FIGURE 78. THE FOUR TYPES OF BACTERIA. 
 A, cocci; B, bacilli; C, spirilla; D, branched filamentous organism. 
 
 an inch in length and about 50000 of an inch in diameter. 
 Some are larger and many are much smaller, some being 
 so small that they are invisible under the highest power 
 lenses, but known to be present because of the effect which 
 they produce in the substance in which they are living. A 
 calculation of the number in a cubic inch of average sized 
 bacteria will give you some idea of the extreme smallness 
 of these plants. 
 
 If you are fortunate enough to have a compound micro- 
 scope for the use of your class you may observe the 
 shape of the bacteria. If no microscope is available, examine 
 
96 GENERAL SCIENCE 
 
 the drawings representing the different shapes. It will be 
 noted that there are three principal forms of bacteria; 
 spherical or ball-shaped (coccus), rod-shaped (bacillus), 
 and spiral-shaped (spirillum) (Figure 78). 
 
 They multiply by dividing into two. These in turn, after 
 growing to full size, will again divide. If conditions are 
 favorable, bacteria may grow to full size and divide again in 
 thirty minutes. It has been estimated that if bacterial 
 multiplication went on unchecked and the division of each 
 bacterium took place as often as once an hour, the descend- 
 ants of each individual would in two days number 281,500,- 
 000,000. Actually, such unchecked multiplication never 
 occurs except for a very short period, as conditions develop 
 which interfere with further growth. 
 
 Not all microorganisms are bacteria. Yeasts and molds 
 are rather closely related to the bacteria. There are also 
 animals (protozoa) of approximately as simple structure as 
 the bacteria. Some of these, because of the harm that they 
 do, are of very great interest to us. 
 
 Since these extremely small living things cause our food to 
 decay, it is important that we know the conditions which 
 are favorable and conditions which are unfavorable for their 
 growth, hence our next problem is : 
 
 Problem 4. What conditions are favorable and what un- 
 favorable for growth of bacteria and molds ? This problem 
 can best be solved by a number of experiments. 
 
 Experiment. Take a number of test tubes, and into each pour 
 about an inch of the beef tea culture medium to which has been added 
 some material known to contain bacteria. 
 
 1. Stopper two tubes with cotton. Put one in a warm place, near 
 a radiator or stove and the other in a cold place, as in the ice box. 
 
TO KEEP FOODS FROM SPOILING 97 
 
 2. Take two test tubes. Boil the contents of one. Stopper both 
 tubes with cotton and keep both under the same conditions. 
 
 3. Into one of three test tubes put all the salt that will dissolve in 
 the beef tea. Into the second put one half the quantity of salt placed 
 in the first. Put nothing in the third. 
 
 4. Into one of three test tubes put an amount of sugar equal to the 
 amount of beef tea. Into the second put one half this amount of sugar. 
 Put nothing in the third. 
 
 After a few days, examine the various test tubes for bacteria. What 
 is the apparent effect on bacteria of (1) warmth, (2) boiling, (3) salt, 
 (4) sugar? 
 
 Experiment, Expose to the air for ten minutes several Petri 
 dishes containing agar culture medium. Paste over the covers black 
 paper from which have been cut large letters for purposes of iden- 
 tification. Put the dishes where they will be exposed to sunlight. 
 Examine after several weeks. Record the result. 
 
 Experiment. Expose to the air a Petri dish which has been kept 
 until the culture medium has become dry. 
 
 The facts which we have learned from these experiments f 
 have many applications both in our home life and commer- 
 cially. Some of these which most concern us in our every- 
 day life should be considered. 
 
 Problem 5. Use of cold in the home in checking the 
 growth of bacteria. . (a) You at once think of the ice chest 
 or refrigerator. Let us see if we can understand how the 
 refrigerator is so effective in preserving our milk, meats, and 
 vegetables. First, why is ice used in a refrigerator? You 
 will at once say, because it is cold; but you know that a 
 block of wood or stone or iron which might be just as cold 
 is never used in place of ice. The reason for this use of ice 
 may be illustrated by the following experiment. 
 
 Experiment. Nearly fill two beaker glasses with water of the same 
 temperature. Note the temperature. Place in one of the glasses 
 a piece of ice and in the other a stone of equal size which has been kept 
 
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 the tem- 
 perature from time to time. Result? What effect does the melting 
 
 of ice have upon the heat 
 of the surrounding water? 
 Is this not what you would 
 expect? The removal of 
 heat from water causes it 
 to change into ice, so heat 
 must be used up to change 
 the ice back into water. 
 Do you think that! your re 
 frigerator will be made colder 
 by covering the ice with 
 pads to keep it from melt- 
 ing? 
 
 s 07 id y 
 Courtesy of McCray Refrigerator Co. 
 
 FIGURE 79. WALL OF A REFRIGERATOR. 
 
 An ice chest or refrigerator is essentially a box whose walls 
 are so constructed that they are poor conductors of heat 
 (Figure 79). This is usually accomplished by having in the 
 wall an air space which is packed 
 with charcoal or some other poor 
 conductor. The ice in a refrigera- 
 tor should be placed near the 
 top. The melting of the ice cools 
 the air in contact with it. The 
 cold air falls. (Why?) In so 
 doing it forces the warm air to 
 the top where it in turn is cooled 
 and replaces the air which has 
 been warmed by coming in con- 
 tact with the food. The effective- 
 ness of the refrigerator depends 
 upon the circulation of air within 
 it; and accordingly care should 
 
 FIGURE 80. CURRENTS OF AIR 
 IN A REFRIGERATOR. 
 
TO KEEP FOODS FROM SPOILING 99 
 
 be taken that the free passage of air is not obstructed in 
 any way (Figure 80). 
 
 The ice chest is simply a means of checking the develop- 
 ment of bacteria but by no means does it stop their growth. 
 In a large ice chest, food may be preserved for a considerable 
 length of time but it 
 finally will decay. In 
 small ones, food may be 
 kept for only a few days. 
 All refrigerators should 
 be frequently cleaned, as 
 dirt and particles of fo6"d 
 furnish a place for the 
 growth of bacteria, and 
 after a time render the 
 refrigerator unfit for use. 
 
 Various methods have 
 been used in homes where 
 ice cannot be obtained to 
 provide a low tempera- 
 ture for the protection 
 of food against the ac- 
 tion of bacteria. Cool 
 cellars, cold running 
 water, spring houses, and FlGURE 81 1CELESS 
 suspension in deep wells are means frequently employed. 
 An iceless refrigerator (Figure 81) may be made as follows : 
 
 Cover a frame of wood with cloth such as duck (Figure 
 82). Sew a number of lamp wicks to the edge of the cloth 
 and allow the other end of the wicks to extend into a vessel 
 of water on top of the frame. The water soaks into the 
 cloth through the wicks. As heat is used up in evaporation 
 
100 
 
 GENERAL SCIENCE 
 
 of water, the temperature within the refrigerator is lowered 
 to 50-56 degrees F. The efficiency of this refrigerator is, 
 increased if it is kept where there is a current of air. Why ? 
 
 In tropical countries, 
 drinking water is kept 
 in porous earthenware 
 jars. Why? 
 
 Problem 6. Use of 
 cold in storage ware- 
 houses. In cold-storage 
 plants low, constant tem- 
 peratures are maintained. 
 Definite temperatures are 
 kept in different rooms, 
 as not all foods are best 
 preserved at the same 
 temperature. Fruits are 
 stored at a little above 
 freezing; fresh meat, at 
 about 25 degrees F. ; 
 poultry, at about 15 de- 
 grees F. ; fish, at about 
 degrees F. 
 
 The question arises, 
 How are these steady low 
 temperatures produced,? As ice is not used, a review of the 
 principle of the iceless refrigerator may help us. (Explain 
 the production of low temperature in the iceless refrigerator.) 
 Cold-storage plants generally use ammonia which has 
 been changed into a liquid from a gas by pressure. When 
 the pressure is released the ammonia returns to its gaseous 
 
 FIGURE 82. FRAMEWORK OF AN ICELESS 
 REFRIGERATOR. 
 
TO KEEP FOODS FROM 
 
 105 
 
 state, taking heat from everything arcuftd -it : 
 
 The effect of rapid evaporation (changing a liquid into a 
 
 gas) may be illustrated by the following experiment. 
 
 Experiment. Place some chloroform or ether in a thin watch 
 crystal. Place the crystal upon a drop of water. Through a tube blow 
 a current of air upon the chloroform or ether. As soon as it all has 
 evaporated, notice the condition of the water. Result? Conclusion? 
 
 Cold Water 
 
 
 Co Sewer 
 
 -Regulating Valve- 
 
 FIGURE 83. ICE PLANT. 
 
 Ammonia which has been made liquid passes slowly through the regulating 
 valve into pipes in which the pressure is very low. The ammonia quickly 
 changes into a gas, absorbing heat in doing so from everything around it. 
 The ammonia gas is removed by the pump at the left of the figure and is 
 changed again by pressure and the spray of cold water into liquid ammonia. 
 
 The development of cold storage has been of great advan- 
 tage both to producers and to consumers. Consider the 
 condition which existed before the use of cold storage in 
 the peach region of Michigan for example. Thousands of 
 bushels of peaches ripened in a few weeks, with the result 
 that the Chicago markets were swamped. Prices went 
 down to almost nothing ; but even then enormous quantities 
 rotted. Sometimes the money received for the peaches 
 was not sufficient to pay the transportation and brokerage 
 
102 
 
 GENERAL SCIENCE 
 
 , ,aq.d ;the fruit growers received nothing for their 
 year's work. Did the people of Chicago profit by this 
 condition? It is true that for a short time peaches could 
 be bought for a very low price; the peach season was, 
 however, made extremely short. 
 
 Since great storage plants have been built, conditions 
 have changed entirely. Now, only enough fruit is put 
 
 FIGURE 84. STORAGE OF BUTTER IN A REFRIGERATING PLANT. 
 
 upon the market to supply the normal demands; the 
 surplus is put into cold storage warehouses to be taken 
 out and sold as the supply direct from the orchards de- 
 creases. The producer now receives a fair return for his 
 labor and investment. The consumer has a lengthened 
 peach season and there is a minimum of waste. 
 
 It is now possible to have fresh at any season of the year 
 the perishable foods produced at almost any other season. 
 
TO KEEP FOODS FROM SPOILING 103 
 
 Without cold storage the supply of such foods as butter and 
 eggs and some other foods would be so limited at certain 
 times of the year that they could be used only by the wealth- 
 iest people (Figure 84). 
 
 By means of cold-storage cars and ships, perishable foods 
 may be transported almost any distance. American fresh 
 meat is sold in the markets of London and Paris. Argentine 
 beef is put on sale in American cities. Fruits of California 
 and the southern states are delivered with little or no loss 
 of flavor to every city in the country. 
 
 Problem 7. Use made of heat in food preservation. 
 A visit to a grocery store and observation of the rows of 
 canned vegetables, fruits, and meats are sufficient to indicate 
 the great use made of this method of preserving food. It is 
 one of the chief agencies by which a regular and varied food 
 supply is made possible. Without the modern methods of 
 food preservation, cities such as New York, Philadelphia, 
 and Chicago could not exist. 
 
 Experiment. Open a can of meat of some kind, permit some of the 
 contents to be exposed to the air for a day. Put portions of the meat 
 into two test tubes. Place one test tube in boiling water for an hour. 
 Stopper both test tubes with corks, dipping the stoppered ends into 
 melted paraffin to make them air-tight. Put the test tubes aside in 
 a warm place for a few days. Result ? Conclusion ? 
 
 Pasteurization of Milk. As diseases may be transmitted 
 by milk, the problem of destroying bacteria contained by 
 it is of great importance. Tuberculosis, typhoid fever, 
 scarlet fever, diphtheria, and very probably dysentery, 
 are diseases spread by milk. The problem is rendered more 
 difficult by the fact that boiling affects milk injuriously to 
 some exterit, causing it to become less digestible. It has 
 been found that by heating milk to a temperature of 142 
 
104 GENERAL SCIENCE 
 
 to 145 degrees F. for at least thirty minutes, the pathogenic 
 (disease-producing) germs will be killed without injuring the 
 digestible qualities of the milk. This process is known as 
 pasteurization. Hospital records show, however, that it is 
 advisable to give orange juice to children whose diet is 
 almost exclusively pasteurized milk. Otherwise, rickets (a 
 disease of the bones) or another disease known as scurvy 
 may develop. 
 
 Problem 8. Use made of other methods of food pres- 
 ervation. What methods for preserving food in addition 
 to use of cold and extreme heat can you think of? 
 
 The use of sugar to preserve food may be shown by the 
 following experiment. 
 
 Experiment. Put some pieces of fruit into a test tube and cover 
 loosely to prevent drying. Cover some similar pieces of fruit with 
 melted sugar. Slightly heat the mixture of sugar and fruit, put into 
 test tube and cover in the same way as the other tube was covered. 
 Put both tubes aside in a warm place. Result ? Conclusion ? 
 
 Jellies and marmalades are examples of the use of sugar 
 as a food preservative. From one of our experiments, what 
 was your opinion as to the amount of sugar that should be 
 used? If a smaller percentage is used, yeast will cause 
 fermentation with resulting bubbles of gas and an odor of 
 alcohol. Before canning became common, this method of 
 preservation was much more used than at present. The 
 large percentage of sugar causes some modification in the 
 flavor of the food, and makes the material more of a sweet- 
 meat than a fruit food. Condensed milk, which has come 
 into such general use, remains unspoiled for a considerable 
 time after the can has been opened because there has been 
 added to it 30 to 40 per cent of sugar. 
 
TO KEEP FOODS FROM SPOILING . 105 
 
 The use of salt as a food preservative is also very 
 common. 
 
 Experiment. Put small pieces of fresh fish into two test tubes. 
 Cover the fish in one tube with brine (a saturated mixture of salt and 
 water). Put aside in a warm place. Result? Conclusion? 
 
 Although salt preserves food from decay, the flavor 
 of the material is considerably changed and it is usually 
 less easily digested than when fresh. In many cases it 
 is wise to soak the salty food in water before it is 
 prepared for the table. Meats and fish are frequently pre- 
 served in brine. Eggs are also sometimes preserved in the 
 same way. Salted butter can be kept fresh and of good 
 flavor much longer than unsalted butter. Salt is used in 
 connection with other methods of preservation such as 
 drying and smoking. 
 
 Use of vinegar and spices. Name foods that you know 
 are preserved in vinegar. Sauerkraut is cabbage which 
 has produced in itself, by the process of fermentation, an acid 
 similar to that of vinegar, which protects it from further 
 decomposition. Most of the spices used in the home have 
 some antiseptic properties. Mince-meat is a good example 
 of the ability of spices to prevent decay. In the same way, 
 the spices in sausages not only give a desirable flavor but 
 also prevent rapid spoiling. Spices, however, are only 
 mildly antiseptic and are consequently of little value in 
 this respect except when used in cold weather. 
 
 Drying and smoking are other methods of. preserving foods. 
 
 Experiment. Put some raisins which have been soaked in water 
 for a day into a test tube. Into another test tube put some unsoaked 
 raisins. Put aside in a warm place. Result? Conclusion? 
 
 Next to canning, drying is the most important method 
 of preserving food. Compare flour which has been kept 
 
106 GENERAL SCIENCE 
 
 dry with some which 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 the 
 same kinds of seeds that have been soaked and permitted to 
 remain moist. What is an advantage of hard-tack and 
 crackers over bread? When fruits are completely dried, 
 their flavor is largely lost. Those which contain a large 
 percentage of sugar, such as grapes, prunes, peaches, figs, 
 dates, currants, etc., may be preserved by the removal of 
 only a limited portion of their water by drying. Why? 
 
 Meats are preserved on an immense scale by a combination 
 of salting, drying, and smoking. Give examples. Milk is 
 dried and put upon the market as a powder. When dis- 
 solved in water it has a flavor slightly different from that 
 of fresh milk, but none of its nutritive properties has been 
 lost. It possesses the advantages of occupying little space 
 in transportation, and of being able to be kept indefinitely 
 without decaying, souring, or molding. Evaporated milk has 
 had a portion of its water removed, thus greatly reducing its 
 bulk. 
 
 Briefly sum up the main points you have learned as to 
 how to keep foods from spoiling, and why these methods are 
 successful. 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Examination of bacteria with a microscope. Make drawings. 
 
 2. -Making of agar culture medium. 
 
 3. Can a dozen jars of vegetables or fruit. 
 
 4. Construct a homemade device for pasteurizing milk T 
 
 5. Make six glasses of jelly. 
 
 6. Construct an apparatus for dehydration of vegetables. Dehy- 
 drate some vegetables 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. Ginn 
 &Co. 
 
 2. Household Bacteriology, E. D. Buchanan. 
 
 3. Milk and Its Products, H. H. Wing. Macmillan Company. 
 
 4. An Iceless Refrigerator. Food Thrift Series No. 4, U. S. Depart- 
 ment of Agriculture. 
 
 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 Vegetables in the Home. 
 
 6. Circulars, U. S. Departm't of Agriculture, Canning, Evaporating. 
 7' Cold Pack Canning. International Harvester Company, Chicago. 
 
PROJECT X 
 
 TO PROTECT OURSELVES AGAINST HARMFUL 
 MICROORGANISMS 
 
 MICROORGANISMS can do many things beside causing foods 
 to decay. Some do very valuable work; so valuable in 
 fact, that without their aid life would cease to exist upon the 
 earth. Qn the other hand, some, such as the disease- 
 producing (pathogenic) forms, are extremely harmful, 
 causing the premature death of many persons. 
 
 Fortunately the large majority of microorganisms are 
 not pathogenic. If this were not true, we might well be 
 appalled at the results of our experiments as to the dis- 
 tribution of bacteria. Most of the bacteria discovered in 
 those experiments are capable of producing decay only, but 
 it must not be forgotten that the objects and substances 
 examined, while they are often carriers of non-pathogenic 
 bacteria alone, still may frequently be carriers of disease- 
 producing ones. . 
 
 In considering how to protect ourselves from harmful 
 microorg nisms, we must consider how they affect us, how 
 the microorganisms (germs) may be carried from one 
 person to another, how the body naturally fights the germs, 
 how the body may be given special power to fight them, and 
 finally how certain substances called disinfectants and 
 antiseptics may be used to destroy germs. 
 
 Problem I. How bacteria and other microorganisms 
 affect the health. What frequently happens when you get a 
 
 108 
 
TO PROTECT OURSELVES AGAINST MICROORGANISMS 109 
 
 splinter in your finger? It has been found that if the splin- 
 ter was free from bacteria no irritation resulted. What 
 is your conclusion ? The red, swollen, and painful condition 
 (inflammation) is now known to be due to poisons or toxins 
 which are produced by certain bacteria which were on the 
 splinter. 
 
 Usually after a short time the inflammation vanishes, 
 and a small amount of pus appears which should be removed 
 
 FIGURE 85. DEAD CHESTNUT TREES. 
 
 These trees along a road in New York State were killed by the chestnut 
 bark disease. 
 
 with a needle which has been passed through a flame and 
 the broken place in the skin washed with an antiseptic, 
 a substance that kills or checks the growth of bacteria. 
 The pus is produced by the action of white blood corpuscles 
 which have attacked and destroyed the bacteria. Some- 
 times, however, the bacteria are not destroyed and the in- 
 
110 GENERAL SCIENCE 
 
 flammation may spread and possibly finally develop into 
 blood poisoning. 
 
 The inflammation of pimples and boils is also caused by 
 bacteria, and the pus is formed in the same way. 
 
 You have all noticed that if one member of a family 
 gets, a cold frequently the other members also contract it. 
 Microscopic examinations have shown that bacteria of 
 certain kinds are always associated with colds. It is very 
 evident that this inflammation, as in other cases of in- 
 flammation, is due to the production of poisons or toxins 
 by the bacteria. 
 
 In the case of colds a congestion of blood in some organ 
 as in the lining of the nose, throat, or intestine offers a 
 favorable condition for the development of bacteria. Pre- 
 vention of unusual chilling of any part of the body will 
 assist in the avoidance of colds, as congestion of blood will 
 then be prevented. It is especially important to avoid 
 chilling the body when one is fatigued or tired, as then there 
 is greater susceptibility to disease. Regular and sufficient 
 muscular exercise, avoidance of overeating, and good 
 habits of sleep and rest are other conditions that enable 
 the body to resist the bacteria which cause colds. 
 
 Microscopic examination has shown that the decay of 
 teeth and diseased conditions of the tonsils are due to the 
 growth of bacteria. The seriousness of the growth of 
 bacteria in decayed teeth and in the tonsils is only beginning 
 to be realized. The bacteria or the poisons produced by 
 them may be carried by the circulatory system to other 
 organs and there cause serious diseases. Certain forms of 
 rheumatism, mental diseases, digestive troubles, etc., are 
 cured by getting rid of these breeding places for bacteria. 
 The teeth are also liable to a disease known as Riggs' disease, 
 
TO PROTECT OURSELVES AGAINST MICROORGANISMS 111 
 
 or pyorrhea, which consists in the formation of an abscess or 
 pus cavity between the roots and the jaw bone, causing the 
 teeth to loosen and in some cases to fall out. This disease 
 is not caused by bacteria, which are microscopic plants, 
 but by simple animals called amoeba. 
 
 With very few exceptions diseases are produced by 
 microorganisms, chiefly bacteria. Since the micn> 
 organisms (germs) which cause these diseases may be trans- 
 ferred in various ways from one person to another, the 
 diseases are called communicable. The better known 
 diseases of this kind are : tuberculosis, typhoid fever, 
 influenza, diphtheria, scarlet fever, measles, chicken-pox, 
 summer complaint of children, dysentery, smallpox, lock- 
 jaw, mumps, Asiatic cholera, infantile paralysis, malaria, 
 yellow fever, etc. In a few of the diseases mentioned 
 above, the germ which is believed to cause the disease has 
 not been seen with the microscope, but the way in which 
 those diseases develop and are transmitted indicates that 
 they are caused by living germs. 
 
 Problem 2. How disease germs may pass from one 
 person to another. Naturally in considering this problem 
 for any disease, we must consider how the germs le ve the 
 body of the person having the disease and how they may get 
 into the body of the well person. Germs usually leave the 
 body in the fine particles of moisture given out in sneezing 
 or coughing or in the sputum or other excretions of the 
 body, and occasionally by blood sucked up by insects. 
 Suggest ways by which disease germs may gain entrance to 
 the body. 
 
 The problem will be considered from the standpoint of a 
 few of the most common diseases. 
 
112 GENERAL SCIENCE 
 
 Tuberculosis or consumption. The most usual form of 
 this disease is tuberculosis of the lungs. How do you think 
 the germs may reach the outside of the body? A well 
 person may contract the disease by breathing in the germs 
 or in some way getting them into his mouth. Make a list 
 of the ways in which the germs of this disease might pass 
 from a sick person to a well person. 
 
 It has been found that the principal ways in which the 
 germs of this disease are carried from one person to another 
 are : (1) by personal contact of sick with well person, 
 especially by kissing; (2) by objects handled or put into 
 the mouth, as by food, forks, drinking cups, pencils, or 
 towels;* (3) by fine droplets given off in coughing or while 
 talking, (this is probably one of the most common 
 methods) ; (4) by dust containing dried sputum ; (5) by 
 milk or meat of tuberculous animals. 
 
 Typhoid fever. In a person sick with this disease the 
 germs are developing in the walls of the intestine. How 
 do you think the germs escape from the body? How do 
 you think that they may ever reach the intestine of a well 
 person to begin growing there to produce the poisons of the 
 disease ? 
 
 Typhoid fever germs are taken into the body with food 
 and drink. It hardly seems possible that anyone should ever 
 contract typhoid fever when we realize that the germs leave 
 the diseased person in the excretions of the body. However, 
 food and drink may become polluted in a number of ways. 
 Water may become contaminated by sewage; milk, by the 
 unclean hands of milkers ; oysters or clams, by growing near 
 the outlet of sewers ; vegetables, by manure ; fruits and ber- 
 ries, by filthy hands ; foods of all kinds, by flies which have 
 been crawling over the excretions of a typhoid patient. 
 
TO PROTECT OURSELVES AGAINST MICROORGANISMS 113 
 
 Suggest means to be taken to prevent the spread of 
 typhoid germs. 
 
 Unfortunately, persons who are immune to the disease 
 may yet have the germs produced in their bodies, and be 
 unconscious sources of infection. Thus we sometimes read 
 of such carriers of germs as " Typhoid Mary " of New York 
 City who, though perfectly well themselves, are a greater men- 
 ace to the public than persons who are ill with the disease. 
 
 Other diseases may be transmitted in some of the ways 
 in which tuberculosis and typhoid fever are transmitted, 
 while some are carried by somewhat different methods. 
 Diphtheria is a disease of the throat. Suggest how it might 
 be transmitted, and how its spread may be prevented. The 
 germ that is supposed to cause influenza is found in the 
 secretions of the mouth and nose of patients. Suggest 
 means by which it may be spread. 
 
 Tetanus or lockjaw is produced by germs which are 
 common in soil. They will not develop in man unless 
 injected into- the body along with considerable dirt in a 
 wound that closes up and prevents the access of 'air. Wounds 
 caused by rusty nails and toy pistol explosions are especially 
 favorable for the development of tetanus. How should a 
 wound of this kind be treated to prevent the development of 
 tetanus ? 
 
 The germs of pneumonia are present in the lungs and air 
 passages. Suggest possible means of infection. Malaria 
 germs are carried from one person to another by a certain 
 kind of mosquito which lives near swamps and flies only at 
 night. How can one protect himself from this disease? 
 
 Problem 3. How the body fights disease. Considering 
 the ease with which disease germs may enter the body, it 
 
114 GENERAL SCIENCE 
 
 may seem strange that a person is not constantly ill with 
 some disease. We know, however, that not every person 
 exposed to infection contracts the disease. There are a 
 number of reasons for this. 
 
 What is the effect of the unbroken skin? What happens 
 to large amounts of dirt and dust of the air which is breathed 
 in through the nose ? What is the appearance of the mucus 
 which is blown out of the nose after you have been working 
 in a very dusty place ? Not only does the mucus catch some 
 of the germs that are breathed in and permit their removal 
 but it has been found that it possesses some power to kill 
 the germs. Suggest one reason for breathing through the 
 nose rather than through the mouth. 
 
 Even though these outer defenses of the body are passed, 
 the germs are not permitted to develop unchecked. The 
 body offers a certain resistance to the attacks, partially by 
 means of the white blood corpuscles which engulf the bac- 
 teria, and partially by the resistant power of the blood and 
 living parts of the body, a power which is not so easily under- 
 stood. 
 
 This power of resistance is affected by a number of things. 
 The fact that certain diseases occur only in childhood 
 indicates that age is one of the factors concerned. A poor 
 diet, excessive fatigue, extremes of heat and cold, lack of 
 sleep, lack of fresh air, and weakness from other diseases 
 are conditions which lessen the power of the body to resist 
 disease. In general, any condition which increases the 
 health of the body increases its power to resist disease. 
 Because of this fact, 'outdoor life, deep breathing, moderate 
 exercise taken regularly, a proper amount of sleep, and good 
 food are not only the preventives of disease but in some 
 cases constitute a cure by giving the body a chance to 
 
TO PROTECT OURSELVES AGAINST MICROORGANISMS 115 
 
 fight off the enemy that has already gained a foothold 
 (Figure 86). 
 
 Problem 4. How the body acquires special power to 
 fight disease. You already have some information that 
 proves to you that special ability to fight disease may be 
 acquired by the body. A child has, had whooping cough, 
 or mumps, or measles. Does this have any effect upon his 
 
 FIGURE 86. A FRESH AIR CAMP IN CALIFORNIA. 
 
 chance of taking the disease again? What, therefore, is 
 your conclusion as to the effect of having had a disease upon 
 the ability of the body to fight that disease ? 
 
 Based upon this fact, it has been discovered that the body 
 may be made immune to certain diseases or protected against 
 them. You know of a number of such cases. Why is 
 smallpox not the common disease it was several hundred 
 years ago ? How are the soldiers protected against typhoid 
 
116 GENERAL SCIENCE 
 
 fever? Why is diphtheria not the dreaded disease it was 
 twenty-five years ago? 
 
 The most striking cases of acquired immunity are for 
 smallpox, typhoid fever, diphtheria, hydrophobia or rabies, 
 and anthrax, a disease of animals. ^ Efforts are being made 
 to develop acquired immunity from other diseases, and 
 considerable success has been obtained in the treatment of 
 tetanus or lockjaw, boils and carbuncles, meningitis and 
 plague. 
 
 (a) Vaccination against smallpox. Over a hundred 
 years ago, Edward Jenner, an English physician, observed 
 that dairymaids were not subject to smallpox, which at that 
 time was a very common disease. His experiments based 
 on this observation have led to the practice of vaccination to 
 develop immunity from smallpox. Cattle may have a disease 
 known as cowpox, during which small sores appear on the 
 animals. These sores contain the germs of the disease. 
 Jenner found that by scratching the arm of a person and 
 rubbing into the slight wound some material from these 
 sores on cattle, a mild disease, cowpox, was developed in 
 the person thus vaccinated. During the process of the 
 disease, something, evidently developed in the blood which 
 protected the person from smallpox. 
 
 Since vaccination has been practiced, smallpox, previously 
 one of the most common diseases, has become a very rare 
 one, developing only when vaccination is neglected. Stricter 
 regulations by boards of health, especially in regard to isola- 
 tion of patients, has helped materially in bringing about this 
 result. Formerly, when not so great care was taken as now 
 to insure the purity of the vaccine, infection occasionally 
 occurred from other germs introduced into the wound. This 
 has now been obviated, and anyone who objects to vaccina- 
 
TO PROTECT OURSELVES AGAINST MICROORGANISMS 117 
 
 tion is unwilling to perform his part as a good citizen to 
 maintain the health of the community. 
 
 (b) Vaccination against typhoid fever. Vaccination in 
 this case is performed by injecting into the body a large 
 number of dead typhoid fever bacteria. Usually three 
 injections are given at intervals of several days. Typhoid 
 fever up to recent times has been the special scourge of 
 army camps. The value of anti-typhoid vaccination may 
 be appreciated if we compare the prevalence of the disease 
 in the army before and after vaccination was practiced. 
 
 In the Franco-Prussian War, 60 per cent of the total 
 German mortality was due to this disease. In the Spanish- 
 American War the army of the United States consisting of 
 107,973 men had 20,738 cases of typhoid fever and 1580 
 deaths from the disease. During the summer of 1911, after 
 the adoption of anti-typhoid vaccination by our govern- 
 ment, an army division of over 12,000 men was encamped 
 at San Antonio, Texas, for about four months. Among these 
 men only one case of typhoid fever developed and that was 
 of a soldier who had not completed the necessary inocula- 
 tion. In the armies of the Great War, typhoid fever was 
 an almost unknown disease. 
 
 (c) Immunity from diphtheria. The antitoxin which has 
 curative as well as immunizing power against diphtheria is 
 made in the following manner. The bacteria are permitted 
 to develop in a culture medium until a considerable quantity 
 of toxin, or the poison produced by the germ, is present. 
 After all the living germs have been killed, a small amount 
 of the toxin is injected into a healthy horse. The toxin 
 evidently stimulates the blood of the horse to manufacture 
 something called antitoxin which counteracts the poison 
 so that the later injection of toxin may be greater in amount 
 
118 
 
 GENERAL SCIENCE 
 
 without injury to the horse. This process is continued 
 until the amount of toxin injected into the horse is several 
 hundred times as much as would have killed it at the begin- 
 ning. 
 
 A certain amount of the blood which contains great quan- 
 tities of antitoxin is now removed from a large vein in the 
 neck of the horse. (All this is done without pain or injury 
 to the animal.) The serum which separates from the 
 blood when it clots contains the antitoxin. This serum 
 
 s 
 
 55 
 
 IllltlilllltttltltlUmimt 
 
 I 
 
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 \ 
 
 m 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 i 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 ^ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 V 
 
 
 ^ 
 
 
 
 
 \ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 -.- 
 ^ 
 
 
 ^ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 ^ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 9 
 
 
 
 
 
 \ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 V 
 
 
 
 
 
 
 
 
 
 
 
 
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 _ !l 
 
 FIGURE 87. RESULTS OF USE OF DIPHTHERIA ANTITOXIN. 
 
 Chart showing death rate per 10,000 from diphtheria before and after 
 
 the introduction of antitoxin. 
 
 is tested for the amount of antitoxin it contains, is sterilized, 
 and put into vials ready for use by physicians. 
 
 The accompanying chart shows the effect of the use of 
 antitoxin upon the death rate from diphtheria in New York 
 City (Figure 87). 
 
 Antitoxin is of greater use as a curative than as an 
 immunizing agent. Persons who have been exposed to 
 diphtheria will be protected only from two to six weeks, but 
 this is usually long enough to protect the members of a 
 family in which there is a case of the disease. As a cure for 
 diphtheria, it is most important that the antitoxin be given 
 
TO PROTECT OURSELVES AGAINST MICROORGANISMS 119 
 
 at a very early stage of the disease. The importance of 
 this is shown by Figure 88. 
 
 (d) Pasteur treatment for hydrophobia or rabies. This 
 disease especially affects the nervous system. Pasteur, a 
 noted French scientist, found that while the spinal cord of 
 a rabbit having the disease contains a large amount of the 
 poison of the disease, the virulence or power of the poison 
 decreases if the spinal cord is removed from the rabbit and 
 allowed to dry. As the disease does not 
 develop for some time after a person is 
 bitten by a mad dog, there is sufficient 
 time for treatment. The treatment con- 
 sists in the injection of material from a 
 rabbit's spinal cord which has been per- 
 mitted to dry until the poison has almost 
 entirely disappeared. This is followed 
 by injections, more and more virulent, FIGURE 38. DAN- 
 of spinal cord material for a period of ER OF A DELAY IN 
 
 r USING ANTITOXIN. 
 
 about three weeks. In thousands of Numbers at the i e ft 
 cases which have been treated by this indicate the percent- 
 method there has been a mortality of 
 less than one per cent. Just as in the 
 case of the use of antitoxin for treatment of diphtheria, 
 this treatment should be begun at the earliest possible time 
 after infection has occurred. 
 
 age of the cases that 
 result in death. 
 
 Problem 5. Use of disinfectants and antiseptics. 
 
 Certain substances are used to prevent the growth of bac- 
 teria. Make a list of substances that you know are used 
 for this purpose. 
 
 The way in which they affect the growth of bacteria may 
 be found out by the following experiment. 
 
120 GENERAL SCIENCE 
 
 Experiment. Into each of several test tubes pour about 10 cc. 
 of unsterilized beef tea culture medium. 
 
 To one add 3 cc. of carbolic acid 5 % solution. 
 
 To another add 3 cc. saturated solution of boracic (boric) acid. 
 
 To another add 3 cc. 1-1000 solution of mercury bichloride. 
 
 To another add 3 cc. hydrogen peroxide. 
 
 To another add 3 cc. tincture of iodine. 
 
 To another add 3 cc. formaldehyde, 4%. 
 
 To the others add 3 cc. different disinfectants. 
 
 To one add nothing. 
 
 After four or five days examine all the test tubes and record the 
 results. 
 
 A distinction is usually made between antiseptics and dis- 
 infectants. An antiseptic is a substance that will check or 
 retard the growth of bacteria, but does not destroy them. A 
 disinfectant, or germicide, is a substance that kills bacteria. 
 Some substances may be classed under both heads ; a strong 
 solution of it acting as a disinfectant, a weak solution act- 
 ing only as an antiseptic. Salt, sugar, spices, and vinegar 
 may be considered antiseptics that are harmless when taken 
 into the body with food. With the exception of the use of 
 one tenth of one per cent of benzoate of soda, other antisep- 
 tics are not permitted to be used for the preservation of food. 
 
 The more important germicides are tincture of iodine; 
 carbolic acid (5 to 10 per cent solution) ; mercury bichloride 
 (1 part to 1000 or 1500 parts of water) ; chloride of lime, and 
 formaldehyde. 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 is frequently used as 
 an eye or mouth wash. Hydrogen dioxide (peroxide), when 
 it has not been allowed to remain exposed to the air, will 
 destroy germs. It has the advantage of being non-poisonous, 
 
TO PROTECT OURSELVES AGAINST MICROORGANISMS 121 
 
 but it has the disadvantage of losing its value if kept in a 
 bottle which is not well corked. 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Proof that flies may cany bacteria. 
 
 2. Demonstration of the comparative value of the use of a feather 
 duster and an oiled cloth in dusting, and of a broom and a vacuum 
 cleaner in sweeping. 
 
 REPORTS 
 
 1. Work of boards of health. 
 
 2. Dangers from decayed teeth. 
 
 3. Transmission of various diseases. - \ 
 
 4. Difference between the ordinary mosquito and the malaria- 
 carrying mosquito. 
 
 5. Description of operations that have been carried on to get rid 
 of malaria-carrying mosquitoes. 
 
 6. Description of experiments to prove that malaria is carried by 
 mosquitoes. 
 
 7. Account of experiments to prove that yellow fever is carried by 
 mosquitoes. 
 
 8. The fight against tuberculosis. 
 
 9. The history of the discovery of vaccination against smallpox. 
 
 10. Discovery and value of diphtheria antitoxin. 
 
 11. Vaccination against typhoid fever and its importance. 
 
 12. Pasteur and his discovery of the treatment for hydrophobia. 
 
 13. Transmission and seriousness of hook-worm disease. 
 
 REFERENCES FOR PROJECT X 
 
 1. Primer of Sanitation, John W. Ritchie. World Book Company. 
 
 2. Preventable Diseases, Woods Hutchinson. Houghton Mifflin 
 Company. 
 
 3. How to Live, Fisher and Fisk. Funk and Wagnalls. 
 
 4. Town and City, Frances Gulick Jewett. Ginn & Co. 
 
 5. A Home-made Fly Trap, International Harvester Company, 
 Chicago. 
 
 6. The Human 'Mechanism, Hough and Sedgwick. Ginn & Co. 
 
 7. House Flies, Farmers' Bulletins 459 and 851. U. S. Department 
 of Agriculture. 
 
PROJECT XI 
 
 TO FIND OUT HOW SOME BACTERIA AND MOLDS 
 ARE USEFUL 
 
 WE have found that bacteria and molds are a great 
 nuisance, bringing about a waste of food material and lead- 
 ing us into the expenditure of time and money to prevent 
 their ravages. We have found also that almost all diseases 
 are caused by them. Just think of how conditions would 
 be changed if there were no such little plants. Foods 
 would not spoil, and diseases like tuberculosis, typhoid 
 fever, influenza, etc., would be unknown. It would seem, 
 therefore, that the world might be a better place in which 
 to live if bacteria and molds ceased to exist. But before 
 we come to this conclusion it will be well for us to consider 
 if there is any evidence that bacteria and molds are of 
 value. 
 
 Problem 1. Are bacteria of decay of any value? A 
 consideration of the following facts may help us to solve 
 this problem. Just as plants take carbon dioxide from the 
 air and build it up into starch, so they also take simple sub- 
 stances from the soil and build them up into complete plant 
 materials. This means the removal from the soil every 
 year by plants of an immense amount of these simple sub- 
 stances needed by plants. Since the amount of these sub- 
 stances is limited, what must happen soon unless in some 
 way they are returned to the soil ? 
 
 This return is brought about by the action of bacteria in 
 causing complex plant and animal materials (organic mat- 
 
 122 
 
HOW SOME BACTERIA AND MOLDS ARE USEFUL 123 
 
 ter) to decay. By decay the organic matter is changed 
 back into the simple substances which plants use in growth. 
 Thus it may be understood that the same matter may many 
 times alternately be built up into plant and animal ma- 
 terial and again be reduced to a simple condition. 
 
 This building up and tearing down may be illustrated 
 very simply by considering the use of building blocks by a 
 child. Suppose a child has two hundred blocks, and builds 
 them up into a house, then tears it down and builds another 
 structure. This he may do time after time, using the "same 
 blocks over and over again in perhaps a different construc- 
 tion each time. Plants build up. Bacteria of decay tear 
 down. Just as the child builds up and tears down his block 
 houses many times, so these processes of building up by 
 plants and tearing down by bacteria will go on as long as 
 life exists upon the earth. What then do you think would 
 be the condition of the earth in a few years if there were 
 no bacteria and molds to do this tearing down ? 
 
 Problem 2. How bacteria on the roots of some plants 
 may enrich the soil. Farmers have known for a long time 
 that a crop of clover will improve the soil. But the reason 
 for this has been known for only relatively a few years. It 
 was found that in some fields clover plants did not have 
 the power to improve the soil. A comparison of the plants 
 showed that those which possessed this power all had little 
 enlargements (called nodules) on their roots (Figure 89). 
 
 It was found also that if some of the soil from the field 
 containing nodule-bearing clover plants was scattered over 
 the other field, the clover plants in this field also de- 
 veloped nodules on their roots and gained the power 
 to improve the soil. An examination of these nodules led 
 
124 
 
 GENERAL SCIENCE 
 
 to the discovery that they contained bacteria. It was 
 found then that the soil could be inoculated with a culture 
 of these bacteria either by mixing it with the clover seed 
 before it was planted or by adding it directly to the soil. 
 It has been found that the bacteria in these nodules 
 
 have the power 
 of changing the 
 nitrogen- of the 
 air, which cannot 
 be used directly 
 by plants, into a 
 form which may 
 be built up into 
 the living matter 
 of the plant. All 
 of the plants of 
 the clover family 
 (legumes) may 
 have these nod- 
 ules containing 
 nitrogen-fixing 
 bacteria. Some 
 of the principal 
 members of the 
 family are peas, 
 beans, vetches, 
 and alfalfa. If 
 the soil does not 
 
 FIGURE 89. ROOTS OF A BEAN PLANT. 
 
 The enlargements are nodules containing nitrogen- 
 fixing bacteria. 
 
 contain the proper kind of bacteria, the nodules will not be 
 formed and these plants will not be able to add to the 
 fertility of the soil. 
 There are other bacteria in the soil, not associated di- 
 
HOW SOME BACTERIA AND MOLDS ARE USEFUL 125 
 
 rectly with plants as these nodule-inhabiting bacteria are, 
 and these other bacteria have the power, under certain favor- 
 able conditions, of making the nitrogen of the air usable by 
 plants. 
 
 Problem 3. How bacteria are useful in other ways. 
 Butter made from sweet cream lacks the pleasant taste of 
 sour cream butter. This is because in the ripening of cream 
 bacteria have been growing in it, and these produce the 
 flavor which we enjoy in butter. That the especial bacteria 
 which produce the desirable taste may be present, the cream 
 may be inoculated with a pure culture or a starter, such as a 
 small quantity of cream known to have developed the de- 
 sired flavor. Frequently the desirable kinds of bacteria be- 
 come domesticated in a dairy and good butter is produced 
 without any effort on the part of the butter maker to bring 
 about their introduction. 
 
 Likewise the flavor .of cheese is produced by bacteria or 
 molds, the different flavors being produced by different 
 kinds of organisms. The ripening of cheese is a much more 
 complicated process than the ripening of butter, since it 
 depends upon the successive activity of different groups 
 of bacteria or molds as well as upon the presence at the right 
 time of suitable aroma-producing species. The holes in 
 certain cheeses are produced by gas formed as a result of the 
 action of particular bacteria. 
 
 The action of bacteria is important in the tanning of 
 skins for the production of leather; in the curing of to- 
 bacco ; in the process of obtaining linen fiber from flax ; and 
 in the manufacture of vinegar. The " mother " of vinegar 
 with which most of us are familiar is made up of a great 
 mass of bacteria which have the power to change the alco- 
 
126 GENERAL SCIENCE 
 
 hol of the wine or cider into the vinegar acid (acetic acid). 
 The action of these vinegar-forming bacteria is hastened 
 by free access of air, so that barrels containing cider to be 
 changed into vinegar should be only partially filled and an 
 opening should be left in the top of the barrel to admit air. 
 The formation of vinegar may be hastened by permitting 
 the cider to trickle through casks filled with shavings im- 
 pregnated with old vinegar. Why ? 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Grow clover seed in soil which has been baked and moistened with 
 boiled water, 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-fixing 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 immediately occur to us: how 
 dew, fogs, clouds, and rain are caused ; why some parts of 
 the earth receive a much larger rainfall than other parts; 
 how water may be supplied to regions of very little rainfall ; 
 how moisture gets into the air, and the effect of moisture in 
 the air (humidity) upon our comfort. 
 
 Problem 1. How dew is caused. We all have had 
 the experience of getting our feet wet by walking in the 
 grass early on a summer morning. This moisture upon 
 the grass is called dew. What are some of the things 
 that you know about dew? Was it on the grass during 
 the day before ? About what time did it begin to appear 
 in the evening? Have you ever seen it on anything except 
 grass? Does it seem to form to the same extent on all 
 objects ? If possible give examples. Does dew form on ob- 
 jects in the house ? On the porch ? Is there approximately 
 the same amount of dew every morning? Does wind 
 seem to make any difference ? Does it make any difference 
 whether the night is clear or cloudy? Have you ever no- 
 ticed moisture similar to dew on water pipes or on a glass 
 filled with cold water ? 
 
 127 
 
128 GENERAL SCIENCE 
 
 The questions above are for the purpose of bringing to 
 "attention the facts that you know about dew. Do not 
 guess at the answers, as that would destroy the value of the 
 questions. 
 
 Several simple experiments will enable us tc understand 
 something about how dew is formed, and under what con- 
 ditions. 
 
 Experiment. Take two large test tubes or drinking glasses. Into 
 one of these pour some ice water; into the other pour water at the 
 room temperature. Set side by side and note results. 
 
 Experiment. Into one of two wide-mouthed jars pour a small 
 quantity of water. Place the two jars on a radiator or heat slightly with 
 a Bunsen burner. Suspend for a few minutes in each jar a test tube 
 containing ice water. Note results. 
 
 After considering these two experiments, what do you 
 conclude are the two conditions necessary for the forma- 
 tion of a film of water like dew upon objects ? 
 
 Experiment. Pour a few drops -of water into a test tube. Heat the 
 test tube until the water disappears. Now partially immerse the test 
 tube in a jar of ice water. What is the result ? What do you conclude 
 to be the relation between the temperature of the air and its ability to 
 hold water in the form of vapor, or gas ? 
 
 The temperature at which moisture in the air changes 
 from an invisible vapor to visible drops of water, is called 
 the dew point. Is the dew point temperature always the 
 same? Why? Why is it possible to "see your breath " 
 on a cold day ? 
 
 We are now able to arrive at the explanation of the con- 
 ditions under which dew is formed. 
 
 (a) Objects on the earth cool off after the sun sets. What 
 effect does this have upon the surrounding air ? What may 
 result? 
 
MOISTURE IN THE AIR AND ITS IMPORTANCE TO US 129 
 
 (6) Some objects give off their heat more readily than 
 others, as for example, a hatchet left outdoors during the 
 night may have a very large amount of dew on the metal 
 part, and but little on the wooden handle. Suggest other 
 examples that you have observed. 
 
 (c) Clouds act like a blanket over the earth, preventing 
 
 Photographed ty A. J. Weed. 
 
 FIGURE 90. ALTO-CUMULUS CLOUDS. 
 
 the heat from escaping. What effect will this have on the 
 formation of dew ? 
 
 (d) The layer of air next to the cool object is cooled down 
 to its dew point. Why will wind prevent the formation of 
 dew? 
 
 (e) Since the dew point is affected by the amount of 
 moisture in the air, what is the effect of dry weather on the 
 formation of dew? 
 
130 
 
 GENERAL SCIENCE 
 
 (/) What is the result when the dew point is at the tem- 
 perature of freezing or below? 
 
 Explain the following : 
 
 (1) The appearance of steam from an exhaust pipe or a 
 steam whistle, and its appearance when it is a little farther 
 away from the vent. Where does it go? Hold a Bunsen 
 
 FIGURE 91. 
 
 Photographed by A.J. Henry. 
 UNDULATED ALTO-CUMULUS CLOUDS. 
 
 burner or a candle near the " visible steam " escaping from 
 a vessel, such as a tea-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 by 
 placing canvas or sheets of paper over them. 
 
 (4) Why the fruit grower sometimes makes a smudge 
 (smoke) in the orchard when frost threatens. 
 
 (5) Why gardens in the valleys are more likely to be 
 
MOISTURE IN THE AIR AND ITS IMPORTANCE TO US 131 
 
 affected by early frosts in the autumn than gardens on hill- 
 sides. 
 
 (6) Why the 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. 
 
 Problem 2. How fogs and clouds are produced. 
 
 (1) Explain the formation of the 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 the sun begins to shine ? 
 
 (2) Fogs are common on the Banks of Newfoundland 
 and the coast of Maine whenever the wind is from the 
 south. Farther south, as far as Cape Hatteras, fogs are 
 apt to occur when the wind is from the east. Why ? (Re- 
 
132 
 
 GENERAL SCIENCE 
 
 view your geography as to the relative locations of the 
 
 Gulf Stream and the Labrador Current.) 
 
 (3) Suggest an explanation of the great fogs which are so 
 
 common in the British Isles. (Note that bodies of land 
 
 cool more rapidly than large bodies of water.) At what 
 
 time of the year do you 
 think fogs would be most 
 common in England? In 
 all cases the presence in the 
 air of small particles of dust 
 encourages the formation 
 of fog. Why? This, no 
 doubt, has considerable 
 effect in intensifying fogs 
 over cities such as London. 
 Clouds are made up of a 
 collection of small particles 
 of water, floating some dis- 
 tance above the earth. 
 Suggest how the great 
 masses of clouds with hori- 
 zontal bases, 
 
 FIGURE 93. RAIN GAUGE. 
 
 The area of the top of the outer 
 cylinder (a) is exactly ten times as 
 great as that of the inner cylinder (b) ; 
 c, receiver. 
 
 seen on a 
 
 summer day, have been 
 formed (Figure 92). Re- 
 fer back to your study of 
 weather and explain why clouds are present in a low pres- 
 sure area and not present in a high pressure area. 
 
 Problem 3. How rain, snow, and hail are formed. In 
 a cloud or a fog the water particles are so small that they 
 will remain suspended in the air for a long time. The small 
 globules of water in a cloud are either prevented from fall- 
 
MOISTURE IN THE AIR AND ITS IMPORTANCE TO US 133 
 
 ing below the base of the cloud by upward currents of air, 
 or by passing into a part of the air where the conditions of 
 temperature and moisture are such that the globules . of 
 water will be changed back into invisible water vapor. 
 
 As the amount of water, however, in a cloud increases by 
 the changing of a greater quantity. of vapor into globules 
 of water (condensation), the small globules combine to form 
 
 FIGURE 94. SNOWFLAKES (enlarged many times). 
 
 drops of water which fall to the earth as rain. The change 
 from small globules to large drops 'may be illustrated by 
 the following experiment : 
 
 Experiment. Cover with a metal lid a large beaker glass containing 
 about an inch of water. Gradually heat the beaker glass with a Bunsen 
 burner. Note results. 
 
 If the temperature of the air at the time of condensation 
 is below the freezing point, the moisture crystallizes into 
 snowflakes (Figure 94). If raindrops are frozen into little 
 
134 GENERAL SCIENCE 
 
 balls in their passage through the air, they become hail- 
 stones. Hail is usually formed in summer, and is probably 
 caused by currents of air carrying the raindrops to such a 
 height that they are frozen and sometimes have formed on 
 them a layer of snow. Split hailstones will frequently show 
 several layers of ice and snow, indicating that they have 
 been carried up a number of times before finally falling 
 to the earth. 
 
 FIGURE 95. HEAVY FALL OF SNOW IN A PINE FOREST. 
 
 Problem 4. Reasons for unequal distribution of rainfall. 
 A study of the average annual rainfall map of the United 
 States (Figure 96) shows that the distribution of rainfall is 
 very unequal, varying from 80 to 100 inches per year in a 
 narrow strip along the ocean in Washington and Oregon to 
 less than 5 inches per year in portions of Nevada, southern 
 California, and Arizona (Figure 97). 
 
MOISTURE IN THE AIR AND ITS IMPORTANCE TO US 135 
 
136 
 
 GENERAL SCIENCE 
 
 With maps before you of the topography of the country 
 and the prevailing winds, explain the following : 
 
 (1) The great rainfall of the northwest coast of the 
 United States. What is the prevailing wind? (Air cools 
 as it rises along the side of a mountain.) Why is this 
 
 rainfall belt so narrow ? 
 
 (2) The small rainfall of 
 the great region just east of 
 this coast area. 
 
 (3) The sources of rainfall 
 of the Mississippi Valley and 
 region east of it to the At- 
 lantic Coast. 
 
 (4) In middle and south- 
 ern California, the prevailing 
 wind from December to May 
 is from the ocean, while dur- 
 ing the remainder of the year 
 it is from the land toward the 
 ocean. Explain the dry and 
 rainy seasons of this region. 
 
 FIGURE 97. LANDSCAPE IN AN AL- 
 MOST RAINLESS DISTRICT IN ARIZONA. 
 
 Problem 5. How water is supplied to dry areas. 
 Portions of the country, which were unfit for agriculture 
 because of too little rainfall, have been changed into good 
 farming regions by irrigation (Figures 98 and 99) ; water 
 from the mountains being collected in large reservoirs and 
 carried by flumes, pipes, or cemented ditches, for great 
 distances, to where the water is needed (Figure 100). 
 
 The accompanying map shows the location of districts 
 irrigated as a result of the work of the United States Rec- 
 lamation Service (Figure 101). 
 
MOISTURE IN THE AIR AND ITS IMPORTANCE TO US 137 
 
 FIGURE 98. ARIZONA DESERT BEFORE IRRIGATION. 
 
 FIGURE 99. ARIZONA DESERT AFTER IRRIGATION, 
 
138 
 
 GENERAL SCIENCE 
 
 Problem 6. How moisture gets into the air. Evap- 
 oration. It is evident that there must be considerable 
 water in the air, in the form of invisible vapor. It has 
 been estimated that if all the moisture in the 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 collection of water for irrigation. 
 
 very common observations will indicate to us how this 
 water gets into the air. 
 
 (1) What happens to wet clothes hung in the air? 
 
 (2) On what kind of days do they dry best ? 
 
 (3) Do they dry better during day or night ? 
 
 (4) What becomes of the rain puddles that are formed 
 on the streets? Does the temperature seem to make any 
 difference ? 
 
MOISTURE IN THE AIR AND ITS IMPORTANCE TO US 139 
 
 (5) What happens to a shallow pan of water left stand- 
 ing for a number of days ? 
 
 FIGURE 101. MAP SHOWING LOCATION OF IRRIGATION PROJECTS. 
 
 (6) What must be added to a balanced aquarium from 
 time to time ? 
 
 (7) Will frozen clothes, hanging on a line, dry ? 
 
140 GENERAL SCIENCE 
 
 (8) What happens to water that falls on soil, as in a 
 cultivated garden or field? 
 
 (9) After a number of dry days, compare the moisture of 
 soil under a board or stone with that of the surrounding 
 soil. During very dry weather in summer, almost the only 
 place one can find earthworms is under boards, logs, or 
 stones. How do you explain this ? 
 
 (10) When barrels are left empty they often fall to pieces. 
 Why? 
 
 (11) In dry weather, farmers sometimes pour water 
 around the rims of the wheels of their wagons. Why ? 
 
 (12) How do leaves appear after having been removed 
 from a plant ? 
 
 From these observations we must conclude that objects 
 containing water give it off to the air. The changing of the 
 water into a vapor is called evaporation, the reverse of con- 
 densation which we considered in the formation of dew, 
 clouds, and rain. From your observations, state the condi- 
 tions which you think would affect the rapidity of evapora- 
 tion. Not only are objects on the land giving off water in 
 the form of vapor, but also the surfaces of all bodies of 
 water, rivers, lakes, and oceans. This water, in an invisi- 
 ble form as vapor, is changed back into visible forms as 
 dew, clouds, rain, and snow. 
 
 When water evaporates, substances dissolved in the 
 water remain behind. This may be illustrated by allow- 
 ing a vessel of water in which has been dissolved some soda 
 or salt to stand exposed to the air until the water has 
 evaporated. Water in streams flowing to the ocean con- 
 tains some soluble mineral material taken from the earth, 
 through which the water has trickled. What happens to 
 this mineral material when the water evaporates (Fig- 
 
MOISTURE IN THE AIR AND ITS IMPORTANCE TO US 141 
 
 FIGURE 102. RUSSIAN SALT FIELDS. 
 Salt is left after evaporation of water. 
 
 ure 102) ? State in your own language, what you consider 
 to be the cause of the saltness of the ocean. Endeavor to 
 find out why the Great Salt Lake contains salt water, and 
 the Great Lakes, fresh water. 
 
142 GENERAL SCIENCE 
 
 Problem 7. How the amount of moisture in the air 
 affects our comfort. The effect of the amount of moisture 
 in the air (humidity) upon our bodily comfort has been dis- 
 cussed under ventilation. It is the relative humidity rather 
 than the actual humidity that affects us. The relative 
 humidity is the ratio of the amount of water in the air to 
 the amount which it can hold at a given 
 temperature. A relative humidity of 50 % 
 means that the air contains one half of 
 the amount of moisture that it can hold 
 at that temperature. 
 
 You will recall that damp days either 
 in summer or winter are more uncom- 
 fortable than dry days of the same 
 temperature. To understand this, we 
 must consider how heat is lost from the 
 body in winter and summer. What is 
 the chief means 'of loss of heat from the 
 body in winter? Explain the feeling of 
 chill experienced on a damp day in winter, 
 keeping in mind that moist air is a better 
 conductor of heat than dry air. What 
 is the principal way in which heat is lost 
 FIGURE 103. WET from the body in summer ? Explain now 
 AND DRY BULB THER- why we are more oppressed by the heat 
 
 MOMETER. on a damp day 
 
 The relative humidity of the air may be found by using 
 the wet and dry bulb thermometer or psychrometer (Fig- 
 ure 103). This consists of two thermometers, one of which 
 has a piece of wet muslin around its bulb. These are rapidly 
 whirled in the air. Observations of the readings of the ther- 
 mometers immediately after the muslin has become dry will 
 
MOISTURE IN THE AIR AND ITS IMPORTANCE TO US 143 
 
 show considerable difference. Explain. Tables have been 
 prepared which give the relative humidity of the air corre- 
 sponding to the difference between the dry bulb and the wet 
 bulb thermometers at the different degrees of temperature. 
 
 Another instrument for measuring the relative humidity 
 of the air is the hair hygrometer. The human hair, when 
 the oil has been removed, lengthens with dampness and 
 shortens with drying. A hair prepared in this way is at- 
 tached to a pointer which is moved across a dial as the hair 
 changes in length. 
 
 Use is made of the fact that paper or cloth impregnated 
 with certain chemicals will change color as the relative 
 humidity becomes greater or less. A paper flower, for 
 example, which has been soaked in a solution of cobalt 
 chloride and gelatine, will be violet in color when the rela- 
 tive humidity is high and blue when the air is dry. 
 
 REPORTS 
 
 1. How railroads fight snow. 
 
 2. Origin of borax and other salt deposits in the West. 
 
 3. The salt supply of the United States. 
 
 REFERENCES FOR PROJECT XII 
 
 1. Measurements for the Household, Bureau of Standards, Washing- 
 ton, D. C. 
 
 2. Humidity ; Its Effect on Our Health and Comfort, P. R. Jameson. 
 Taylor Instrument Company, Rochester, N. Y. 10 cents. 
 
 3. The Mountains of Cloudland 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 is a close relationship between 
 plants and moisture. How they give off water ; how much 
 they give off ; and how the water is obtained are problems 
 to be solved. 
 
 Problem 1. Do plants give off moisture ? Under 
 ordinary circumstances plants do not seem to give off water 
 
 to the air, as the leaves remain 
 fresh day after day. What hap- 
 pens, however, to leaves and 
 flowers when they have been 
 broken from the plant? What 
 does this seem to indicate ? How 
 may these leaves and flowers be 
 kept from wilting? The follow- 
 ing experiment will enable us to 
 find out if growing plants give 
 off water. 
 
 FIGURE 104. TRANSPIRATION. Experiment. Completely cover the 
 
 What is the source of the water P ot . of an active1 ^ & * g eranium 
 
 within the bell jar ? or similar plant with rubber tissue or 
 
 waxed paper, leaving only the stem 
 
 and leaves of the plant exposed. Cover the plant with a dry bell 
 jar. After a few hours observe and draw conclusions (Figure 104). 
 
 This process of giving off water by a plant is called tran- 
 spiration. 
 
 144 
 
THE RELATION OF PLANTS TO MOISTURE 145 
 
 Problem 2. The amount of water given off by plants. 
 
 Experiment. Cover the pot of an actively growing geranium or 
 similar plant with rubber tissue or waxed paper as in the preceding 
 experiment. Weigh the plant and its pot. After the plant has stood 
 in a warm room or outside the window if the day is warm, weigh again. 
 Result. Roughly estimate the area of the leaves and calculate the loss 
 of water per square inch or square foot. 
 
 Most persons are surprised when they realize the amount 
 of water that is given off by plants. It has been calcu- 
 lated that an oak tree may give off from its leaves in the 
 five months from June to October about 125 tons of water ; 
 and that a grass plot 50 by 150 feet may, under favorable 
 conditions, give off by transpiration a ton of water in a 
 day. A single corn plant was found to give off 31 pounds of 
 water during its growth. It will thus be seen that the miles 
 and miles of vegetation are continually giving back to the 
 air the water which has been deposited on the earth in the 
 form of rain. 
 
 Problem 3. How the root system of a plant -is fitted to 
 find water. We all know that plants obtain water from 
 the soil by means of their roots. Examine the roots of a 
 plant and notice how they are fitted to reach many parts of 
 the soil (Figures 105 and 106). There is a very close re- 
 lationship between the development of the root system and 
 the water supply. 
 
 Experiment. Across the middle of a cigar box fasten an incomplete 
 partition, not quite reaching the bottom of the box. In each com- 
 partment of the box, plant soaked pea seeds in moistened sawdust. 
 Keep both sides watered until the seedlings have begun to form well- 
 developed root systems. Then cease to water one side but continue 
 to water the other side generously. At the end of two weeks carefully 
 remove the sawdust and note the condition and arrangement of the, 
 roots. Conclusion ? 
 
146 
 
 GENERAL SCIENCE 
 
 In trees growing under normal conditions the roots ex- 
 tend out to a point directly under the outer ends of the 
 branches. Why? Alfalfa plants growing in dry regions 
 may have roots extending to a depth of 10 or 12 feet. Why ? 
 The mesquite plant living in the dry regions of the south- 
 western part of the United States and Mexico, although 
 only a low shrub, may send its roots to a depth of 60 feet in 
 
 I 
 
 FIGURE 105. UPTURNED SUGAR MAPLE. 
 Note the very large number of small roots. 
 
 search of water. Why does a lawn which has been sprinkled 
 for a short time every day look worse after being neglected 
 for a few dry weeks in August than the neighboring lawn 
 which has not received the same care? Give one reason 
 why weeds in a garden are harmful. 
 
 Problem 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 to prevent injury to the roots, a 
 plant is apt to wither and be checked in its growth when 
 transplanted (planted again after having been removed 
 from soil in which it has been growing). This might lead 
 us to suspect that there are special structures on the roots 
 which are injured in 
 the process of trans- 
 planting. 
 
 Growing roots in 
 such a way that they 
 can be examined 
 without being dis- 
 turbed may help us 
 to find out if roots 
 possess any special 
 structures. 
 
 Experiment. Place 
 some radish seeds or 
 other small seeds be- 
 tween a moist blotter 
 and the bottom of a Petri 
 dish or the inside of a test 
 tube. Keep in a warm 
 place and examine after 
 three or four days. 
 What do you find? 
 
 FIGURE 106. YOUNG WHITE CEDARS. 
 
 The small hairlike structures which you see on the young 
 root are called root hairs (Figure 107). Their structure, as 
 you will see from the diagram (Figure 108), is very simple. 
 Each hair consists of a delicate wall inclosing a thin layer of 
 the living matter of the plant and some watery material 
 called celLsap. It will be noticed that the root hair is 
 
148 
 
 GENERAL SCIENCE 
 
 only the extension of one of the little boxes containing living 
 matter (cells) of which the young root is composed. Of 
 
 what advantage are 
 these root hairs ? 
 
 Problem 5. How 
 root hairs take in 
 water. The way in 
 which root hairs take 
 in water is illustrated 
 by the following ex- 
 periment. 
 
 Experiment. Care- 
 fully chip off about one 
 half of a square inch of 
 the shell from the blunt 
 end of a fresh egg, taking 
 care not to injure the 
 membrane lying under the shell. Support the egg at the top of a glass 
 containing water so that the exposed membrane is immersed in the 
 water. Puncture the shell and membrane at the other end of the egg 
 and by means of a needle mix the white and yolk of the egg. Into this 
 end of the egg fasten a glass tube with sealing wax, clamp the tube to 
 an iron support and set aside 
 for a few hours. What has 
 happened ? Explain how this 
 illustrates the work of the 
 rot hair. Epidermal 
 
 Liquids separated by 
 a plant or an animal 
 membrane tend to mix 
 with each other, but in this case the contents of the egg, 
 like those of the root hair, are unable to pass through a 
 membrane, so the flow of liquid is all in one direction. At 
 
 FIGURE 107. GERMINATING WHEAT SHOWING 
 ROOT HAIRS. 
 
 Nucleus 
 
 FIGURE 108. ROOT HAIRS (enlarged). 
 
THE RELATION OF PLANTS TO MOISTURE 
 
 149 
 
 the same time that water passes into the root hair, raw 
 food material needed by the plant also passes in. The part 
 of the stem through which the liquids pass upward may be 
 seen by cutting across a 
 living twig, the base of 
 which has been kept in 
 red ink for several days. 
 
 Problem 6. How 
 water passes out of the 
 leaves. Does water 
 pass out equally well 
 from all parts of the leaf ? 
 This question may be 
 answered by the follow- 
 ing experiment : 
 
 Experiment. Remove 
 several leaves from a plant. 
 Cover the upper surface of 
 some of the leaves and the 
 lower surfaces of others with 
 a thin layer of vaseline. Ex- 
 amine after several hours. 
 Which leaves have withered 
 most ? Conclusion ? 
 
 Has the lower surface 
 of the leaf any openings 
 by which moisture es- 
 capes? To answer this 
 question examine a bit 
 of the membrane or epidermis stripped from the lower sur- 
 face of a leaf (Figure 110). 
 
 The kidney-shaped cells (guard cells) on each side of the 
 
 FIGURE 109. A LIVING TREE WITH A 
 HOLLOW TRUNK. 
 
 What does this indicate as to the part of 
 the stem through which liquids pass ? 
 
150 
 
 GENERAL SCIENCE 
 
 openings (stomates) absorb, in moist weather, moisture from 
 the air and swell up like the inner tube of an automobile 
 
 tire when filled with air, mak- 
 ing the opening or stomate 
 large. In dry weather they 
 lose their moisture, collapse, 
 and make the stomate smaller. 
 Of what advantage is this to 
 the plant? Plants that live 
 in dry regions possess various 
 devices for the prevention of 
 
 FIGURE 110. LOWER EPIDERMIS 
 OF A LEAF (highly magnified). 
 
 excessive transpiration, such as hairy, or thick-skinned 
 leaves, or the reduction of leaf surface. 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Find out approximately how much water may be given to the air 
 by a certain tree during one hour on a warm day in summer. 
 
 2. Find out the amount of water given to the air by a geranium plant 
 in 24 hours. 
 
 3. Endeavor to find out the total extent of the r'oot system of some 
 plant. 
 
 4. Construct an apparatus to illustrate the action of the stomates. 
 
 REPORTS 
 
 1. Comparison of the kinds of plants in arid regions and those in well 
 watered regions. 
 
 2. Importance of irrigation in the. United States. 
 
 3. Dry farming in the Western States. 
 
 4. The salt supply of the United States. 
 
 REFERENCES FOR PROJECT XIII 
 
 1. Agriculture on Government Reclamation Projects, Scofield and 
 Fairell. U. S. Department of Agriculture Year Book, 1916. 
 
 2. Irrigation an,d Drainage, F. H. Wing. Macmillan Company. 
 
THE RELATION OF PLANTS TO MOISTURE 151 
 
 3. A Primer of Forestry, Gifford Pinchot. Government Printing 
 Office, Washington, D. C. 
 
 4. First Book of Forestry, F. Roth. Ginn & Co. 
 
 5. Irrigation, Farmers' Bulletin 864. U. 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 States 
 were fully used, it would be sufficient to run all the machines 
 of our factories, to propel all railroad trains, street cars, and 
 automobiles, and to furnish light and heat for the many 
 
 FIGURE 111. TRAIN DRAWN BY AN ELECTRIC LOCOMOTIVE. 
 The power of this electric locomotive is derived from water power. 
 
 purposes for which they are used (Figure 111). At present 
 only a small part of this power is being used, but the possi- 
 bilities for the future are great (Figure 112). The ques- 
 tions that arise in our minds naturally are: What is the 
 source of the energy or power of water power and where 
 
 152 
 
WATER POWER 153 
 
 and how can water power be best developed. Another 
 problem somewhat associated in our minds with water 
 power is the advantage gained by the use of hydraulic 
 pressure. 
 
 Problem 1. What is the source of energy of water power ? 
 What is the source of this energy which may be used in 
 running water wheels or turbines, whose energy in turn may 
 
 FIGURE 112. WATERFALL, MCKENZIE RIVER, OREGON. 
 Sufficient unused power to light a city. 
 
 be transformed into heat, light, electrical and mechanical 
 energy (Figure 113)? We know that falling bodies exert 
 energy, but no more than is put into them in raising them to 
 the point from which they fall. The pile driver exerts en- 
 ergy in driving piles into the earth, but an engine must be 
 used to pull the weight up to the place from which it is 
 dropped. 
 
 In country houses, running water is frequently supplied 
 
154 
 
 GENERAL SCIENCE 
 
 from an elevated tank. The energy possessed by the run- 
 ning water may be demonstrated by permitting it to run 
 a water motor, which in turn may run a sewing machine, 
 a churn, or a washing machine. Energy, however, usually 
 supplied by a windmill or the burning of fuel in an engine 
 must be used to pump the water into the tank. Thus the 
 
 POWER HOUSE 
 
 FIGURE 113. DIAGRAM OF A POWER HOUSE. 
 
 Water passing through A turns the water wheel B. At D the energy of 
 motion is changed by a dynamo into electrical energy. 
 
 energy set free by the windmill or by the burning of the fuel 
 is transformed into the energy possessed by the water because 
 of its position. We can understand now,, that energy, or the 
 power of doing work, exhibited by water in rivers and streams 
 on their way to the ocean, must have been given to it in some 
 way. The following suggestions may lead you to an under- 
 standing of the source of the energy- of water power : 
 
WATER POWER 155 
 
 (a) What was the original location of the water concerned ? 
 (6) What is happening to water on the surface of oceans 
 and lakes? 
 
 (c) What is the relation of evaporation to heat? 
 
 (d) What is the source of the heat used up in changing the 
 water into invisible water vapor, a gas ? 
 
 (e) Just as steam, which is invisible water vapor, possesses 
 energy, so this water vapor which results from the ordinary 
 evaporation of water by the sun's rays has been given the 
 energy which was used in changing the water into vapor. 
 
 (/) Because of the energy which it possesses, the water 
 rapor is able to overcome the force of gravity (the force 
 which draws things to the earth) and to move away from the 
 surface. It is assisted in its movement by the currents of 
 air and winds, which you will recall, are caused by the heat 
 of the sun. 
 
 (g) When condensed into drops of water, the energy which 
 the vapor possessed as a gas is changed largely into energy 
 of position which is changed into the energy of water power, 
 as the water travels in streams toward the ocean again. 
 
 In your own language, explain how water power depends 
 upon the energy of the sun. 
 
 The energy of the water power developed at Niagara Falls, 
 from the Mississippi River at Keokuk, Iowa, and in the 
 streams which flow from the higher regions of the Appala- 
 chian Mountains, upper portions of the Great Lakes region, 
 and the Rocky and Sierra Mountains, can be changed into 
 electrical energy and be transmitted many miles to cities 
 where it may be used to run mills and trains, and to furnish 
 light and heat (Figure 114). 
 
 In order to make use of the water power of a river in which 
 there are no falls but only a gradual slope of the river bed, 
 
156. 
 
 GENERAL SCIENCE 
 
 dams are built which raise the surface to a higher level. 
 (Figure 115). By this means artificial falls are produced 
 which may represent the natural fall of the river for several 
 
 HI 
 
 FIGURE 114. ELECTRIC HIGH TENSION TRANSMISSION LINE. 
 
 By these wires electric power developed by a waterfall in the mountains is 
 
 carried to cities many miles away. 
 
 miles above the location of the mill or factory which is run 
 by its power. Thus we may understand how water power 
 can be developed from any stream in which there is an ap- 
 
WATER POWER . 157 
 
 preciable current. Even in parts of the country which are 
 relatively level, the mill dams from which power is de- 
 veloped to run flour or saw mills are common. With the 
 
 FIGURE 115. WATER POWER. STATION. 
 
 great demand for electricity there is need for the larger de- 
 velopment of this source of power. 
 
 Problem 2. Source of the power of hydraulic pressure. 
 Hydraulic pressure which is used in barbers' chairs, in some 
 kinds of elevators, and in various mechanical 
 operations to produce great pressure, may be 
 considered a form of water power. The follow- 
 ing experiment may help us to understand how 
 the great power of hydraulic pressure is ob- 
 tained. 
 
 Experiment. Fill a bottle with water. Into the 
 mouth of the bottle fit a perforated stopper which must 
 be wired in or fastened by the device represented 
 in the figure. Fit tightly into the opening in the FIGURE 116. 
 
158 
 
 GENERAL SCIENCE 
 
 stopper a metal rod (Figure 116). Push down on the metal rod. 
 What happens? 
 
 It is evident from this experiment that the force exerted on 
 the inner surface of the bottle is many times the force exerted 
 on the metal rod. This and other experiments show that 
 the pressure on liquid, as water, inclosed in a vessel is trans- 
 mitted undiminished in every direction and acts with equal 
 force on all surfaces of equal area. This is known as Pascal's 
 
 principle since it was first an- 
 nounced by Pascal, a Frenchman, 
 in 1653. How the great force 
 exerted by the hydraulic press is 
 gained may be understood by study- 
 ing the accompanying diagram 
 which shows how a 1 -pound weight 
 may balance a pressure of 100 
 pounds. In commercial hydraulic 
 presses, oil is generally used in- 
 stead of water. 
 
 By pushing down the small pis- 
 ton, a small amount of oil is forced 
 into the space below the large pis- 
 ton. The force exerted upon the large piston is as many 
 times greater than the force exerted upon the small one as 
 the surface of the large piston is greater than the surface of 
 the small one. A valve prevents the oil from passing out 
 of the cylinder below the large piston. 
 
 Because of the great force exerted by the hydraulic 
 press it is used in lifting heavy weights and in operations 
 where great pressure is needed. Heavy machinery and 
 crucibles filled with molten metal may be lifted with ease. 
 Baling of cotton and paper, punching holes in steel plates, 
 
 FIGURE 117. HYDRAULIC 
 PRESS. 
 
 A , large cylinder ; B, small 
 cylinder ; C, connecting tube ; 
 P, large piston; p, small 
 piston ; D, reservoir for liquid. 
 
WATER POWER 159 
 
 making pressed steel and forcing lead through a die in the 
 manufacture of lead pipe are some of the uses made of the 
 enormous force exerted by the hydraulic press. 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Construct a water wheel which when operated by water from 
 a faucet will run a simple machine. 
 
 2. Demonstration of the structure and action of a water motor. 
 
 3. Make a small hydraulic press. 
 
 4. Construct a map of the United States, and indicate in red the 
 places where water power is utilized, and in blue other places where 
 you think it might be used to advantage. 
 
 REPORTS 
 
 1. Utilization of the water power of Niagara 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. (Power 
 from Niagara Falls.) 
 
 2. Harper's Machinery Book for Boys, Adams. Harper & Bros. 
 (Water-Power. ) 
 
 3. Practical Things with Simple Tools, Goldsmith. Sully & Klein- 
 teich. (Making of Water Wheels.) 
 
 4. All about Engineering, Knox. Funk & Wagnalls. (Niagara 
 etc.) 
 
PROJECT XV 
 
 TO UNDERSTAND HOW COMMUNITIES OBTAIN A 
 GOOD SUPPLY OF WATER 
 
 Water Supply of New York City. The average daily 
 consumption of water in New York City during the year 
 1917 was almost 600,000,000 gallons or 80,000,000 cubic 
 feet. Naturally the question arises how such an enormous 
 quantity of water can be supplied. Cities like Chicago, 
 Cleveland, or Buffalo may get their supply from the great 
 fresh-water lakes near which they are located. New York, 
 however, is shut off from such a supply. When a small 
 city, it depended largely upon wells ; but as the population 
 increased, such a supply became both inadequate and un- 
 safe because of the danger of pollution. Beginning in 1842, 
 water of the Croton watershed, an area of 375 square miles, 
 about 22 miles north of the city, was collected in a number 
 of reservoirs and lakes, and carried to the city by the Croton 
 aqueduct. 
 
 With the enormous growth of population, even this great 
 supply was found to be insufficient ; and the city has ob- 
 tained control of a large area of land in the Catskill Moun- 
 tains, extending between 75 and 125 miles from New York. 
 With the expenditure of about $200,000,000 there has been 
 developed a water supply system which for many years to 
 come will be able to furnish the city with the enormous 
 quantity which it needs (Figure 118). 
 
 160 
 
HOW COMMUNITIES OBTAIN A GOOD WATER SUPPLY 161 
 
 Problem 1. Why a wooded mountainous region is 
 selected to furnish water. You will notice that a wooded 
 mountainous region has been selected as the water supply 
 area. If the popu- 
 lation of the city 
 should increase to 
 such an extent that 
 the Croton and the 
 Catskill regions would 
 not furnish a suffi- 
 cient supply of water, 
 there is still the great 
 Adirondack supply to 
 be tapped. The ad- 
 vantages of selecting 
 such a region may be 
 understood from a 
 consideration of the 
 following questions: 
 
 (a) From what di- 
 rection do the moist 
 winds of the eastern 
 part of New York 
 State come? 
 
 (b) What is the 
 effect of the moun- 
 
 these 
 
 FIGURE 118. SOURCE OF WATER SUPPLY OF 
 NEW YORK CITY. 
 
 tains upon 
 winds ? 
 
 (c) Compare the agriculture of the mountains and the 
 level country. How does this affect (a) the cost of acquiring 
 the land, (b) the removal from cultivation of crop-producing 
 land, and (c) danger from pollution? 
 
162 
 
 GENERAL SCIENCE 
 
 FIGURE 1 19. KENSICO DAM. 
 
 This is one of the greatest masonry structures in the world. It rises 307 
 feet above the rock foundation upon which it rests. . Its thickness at its 
 b,ase is 233 feet. 
 
 (d) Of what importance is the elevation of the source of 
 supply to the water pressure in the pipes in the city? The 
 
 
 FIGURE 120. HEIGHT TO WHICH NEW YORK WATER WILL RISE WITHOUT 
 BEING PUMPED. 
 
HOW COMMUNITIES OBTAIN A GOOD WATER SUPPLY 163 
 
 water surface of the chief reservoir (Ashokan) of the Catskill 
 system is 590 feet above sea level. Because water seeks its 
 level, there is sufficient pressure to raise it to all floors of 
 buildings of reasonable height, about 260 feet, without 
 the use of pumps (Figure 120). It is estimated that this 
 has saved an expense of $2,000,000 per year since the use of 
 the Catskill supply began. 
 
 (e) Does the fact that the mountains are covered with 
 forests make any difference? The floor of the forest, made 
 
 URE 121. FOREST FLOOR. 
 
 up largely of decayed leaves and interlacing roots, acts as 
 a great sponge (Figure 121). What effect will this have at 
 seasons of heavy rainfall ? On the other hand, during dry 
 weather the water which has been absorbed by the forest bed 
 is gradually being given off, usually in the form of springs, 
 
164 GENERAL SCIENCE 
 
 to the small streams which carry it into the collecting 
 reservoirs (Figure 122). 
 
 Problem 2. How the water is protected. The facts 
 (1) that the people of New York City drink water drawn 
 directly from the mains, and (2) that for many years there 
 have been no epidemics caused by polluted water, lead us 
 to wonder what precautions are taken to keep the supply 
 
 FIGURE 122. A STREAM IN THE CATSKILL MOUNTAINS. 
 
 This is one of the feeders of the Ashokan reservoir of the New York City 
 Water Supply. 
 
 pure, when we remember 1;hat the drinking of unboiled water 
 from a stream is often very dangerous, and that the reser- 
 voirs are supplied largely by small streams. 
 
 We have already found that water in mountains is less apt 
 to contain disease germs. Explain again the reason for this. 
 A number of special precautions, however, have been taken 
 to insure the purity of the water. 
 
HOW COMMUNITIES OBTAIN A GOOD WATER SUPPLY 165 
 
 (a) In order to keep settlements at a reasonable distance 
 from the shores of the Ashokan reservoir, the city has taken 
 enough land to afford a marginal strip of at least 1000 feet 
 wide around the shore. Explain the advantage of this. 
 
 (6) The reservoirs act as great settling tanks. Particles 
 of dirt which have been carried into the reservoirs sink to 
 the bottom, carrying with them the bacteria which may be 
 
 FIGURE 123. AERATORS. 
 
 Aeration of water before it passes into the great pipe that carries it to 
 the City. 
 
 attached to them. Experiments have shown that prac- 
 tically no pathogenic bacteria will long survive under these 
 conditions. Exposure of the water in the storage reservoirs 
 to sunlight and air also assists in the destruction of any 
 injurious germs that may be present. 
 
 (c) At the Ashokan and Kensico reservoirs aerators have 
 been built (Figure 123). These consist of large numbers of 
 nozzles through which jets of water are thrown into the air 
 
166 
 
 GENERAL SCIENCE 
 
 as in a fountain. Not only do the oxygen of the air and 
 the sunlight help to destroy bacteria, but unpleasant tastes 
 and odors are removed and the water made much more 
 palatable. The effect of aeration of water upon its palata- 
 bility may be tested by first drinking some boiled water, 
 and then drinking some which has been poured several times 
 in a thin stream from one vessel to another. 
 
 (d) In addition to what may be called the natural agencies 
 at work to make the water pure, chlorine gas (a very powerful 
 sterilizing agent) is introduced into it just below the Kensico 
 reservoir, if the bacteriological 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 prevention. 
 
 indicates the need for this treatment. The gas is wholly 
 neutralized or dissipated before the water reaches the dis- 
 tribution pipes of the city. 
 
 Problem 3. How other cities obtain a supply of water. 
 Every large city has special problems to work out in con- 
 nection with its water supply system. Many depend upon 
 the collected rainfall from an area more or less controlled 
 by the city, as New York does. Some depend partly upon 
 artesian wells, which tap layers of porous rock that come to 
 the surface sometimes hundreds of miles away and absorb 
 much of the -rainfall of that region. Others depend directly 
 
HOW COMMUNITIES OBTAIN A GOOD WATER SUPPLY 167 
 
 upon river water which is purified by chlorination and the 
 passage through great filters which remove much of the 
 suspended matter. Still others may obtain water directly 
 from large bodies of fresh water as do the cities on the Great 
 Lakes. 
 
 Make a list of the uses of water in your community. 
 What do you know concerning its water supply? 
 
 FIGURE 125. RESERVOIR AND DAM. 
 A part of the water supply system of Denver, Colorado. 
 
 Pupils should work out carefully the water supply of their 
 own community, finding out the source of the water, means 
 taken to protect its purity, and how it is carried to the 
 consumer. 
 
 Rural water supply. Villages and individual homes in 
 the country frequently depend upon relatively shallow wells, 
 the water of which is of course supplied by that portion 
 of the rainfall which has soaked into the earth. Great care 
 
168 
 
 GENERAL SCIENCE 
 
 should be taken as to the location of such wells, and their 
 protection from surface water. 
 
 In many cases, deeper wells which penetrate layers of clay 
 or even rock are depended upon. The water of such wells 
 frequently has minerals dissolved in it. Why? The 
 water from wells in a limestone region will not form a lather 
 with soap and is called " hard." Thie is due to the power of 
 
 water to dissolve lime- 
 stone. Illustration of 
 this may be seen in 
 any cemetery where 
 there are old marble 
 tombstones. What is 
 the condition of the 
 inscriptions on the 
 stones? In some 
 parts of the country, 
 especially in Ken- 
 tucky, Virginia, and 
 Indiana, underground 
 waters have dissolved 
 away the rock to such 
 an extent that large 
 caves have been 
 formed (Figure 126). 
 Notable among these are Mammoth Cave of Kentucky and 
 Luray Cave of Virginia. A tea-kettle in which " hard " 
 water is used becomes incrusted on the inside with a 
 grayish deposit which is really limestone. 
 
 Problem 4. How the water system within the house 
 should be cared for. The water pipes in our homes are, 
 
 FIGURE 126. LIMESTONE CAVE. 
 
 Dissolved out by water. The projections 
 from the roof were formed by deposits of 
 particles of limestone from water trickling into 
 the cave. 
 
HOW COMMUNITIES OBTAIN A GOOD WATER SUPPLY 1(39 
 
 of course, direct continuations of the main pipes. What 
 causes the water to flow out when we open a tap ? Providing 
 that there are no leaks, we need give the pipes very little 
 attention. For convenience in repairing the pipes and 
 faucets, there should be various places where the water may 
 be shut off, and outlets by which the pipes may be emptied. 
 In your own home locate these places. 
 
 Probably no part of the water system causes so much 
 annoyance as the tank of the water closet. The work- 
 ing of one kind in general use 
 is illustrated by the diagram 
 (Figure 127). From the dia- 
 gram explain how it works. 
 Examine the way the tank in 
 the water closet in your home 
 is emptied and filled. 
 
 In winter there is danger of 
 the water freezing in the pipes; 
 and as water expands in freez- 
 ing, the pipes often burst. This 
 
 FIGURE 127. WATER CLOSET 
 
 TANK. 
 
 How does the water pass out ot 
 the tank ? Notice the relation ox 
 
 may usually be prevented by J^JS *** 
 
 allowing the water to drip from 
 
 the faucets on a cold night. Moving water does not freeze 
 so rapidly as quiet water, as you know from observing 
 the differing rapidity with which ponds and streams freeze. 
 If a house is to be left vacant during the winter, the water 
 should be drained from the pipes, and if there are portions 
 from which the water cannot be removed in this way, a 
 plumber should be engaged to " blow out " the pipes by 
 forcing air through them. 
 
170 GENERAL SCIENCE 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Construct a model of the water system of your community. 
 
 2. Determine the source of water of any springs in your vicinity. 
 
 3. Make a plan of water pipes in your house. Explain the advan- 
 tage of this arrangement. In what way could the arrangement have 
 been improved ? Explain. 
 
 4. Demonstrate the structure of a faucet. Show how it may get 
 out of order and what may be done to correct the trouble. 
 
 5. Study out the mechanism in the tank of the toilet in your home. 
 Where is it apt to get out of order, and how may this condition be 
 corrected? 
 
 REPORTS 
 
 1. Describe the methods used by a number of large cities to obtain 
 a good water supply. 
 
 2. Tell how the American army was supplied with pure water in 
 
 France; 
 
 \ , 
 
 REFERENCES FOR PROJECT XV 
 
 1. Home Water Works, C. J. Lynde. Sturgis. 
 
 2. Water Works in 38 Cities in Iowa, John H. Dunlap. Univer- 
 sity Extension Division, University of Iowa, Iowa City, Iowa, 5 cents. 
 
 3. Low Cost Farm Water Works, Conference for Education in the 
 South. 508 McLachlen Building, Washington, D. C. 
 
 4. Drinking Water and Ice Supplies and Their Relations to Health 
 and Disease, T. M. Prudden. Putnam. 
 
PROJECT XVI 
 
 TO UNDERSTAND THE DISPOSAL OF SEWAGE OF 
 HOMES AND COMMUNITIES 
 
 THE problem of getting rid of the waste of the home and 
 of the community is almost, if not equally, as important as 
 obtaining a good water supply. As in the case of the water 
 supply its importance increases as cities increase in size. 
 
 Problem 1. Care of waste water pipes. With regard 
 to the waste water pipes which are 
 connected with the sewers, we are 
 chiefly concerned with the traps, the 
 usual form of which is represented in 
 the diagram (Figure 128). Explain 
 the need of a trap. What is apt to 
 happen to a trap if considerable solid 
 material is allowed to enter the waste 
 pipe from the kitchen sink? This 
 may be largely prevented if a sink 
 strainer is used. Sometimes the grease 
 from dishwater will collect in this 
 waste pipe. This may be avoided 
 
 by occasionally running through the pipe hot water con- 
 taining lye. No trouble is likely to occur in the waste pipe 
 of the water closet, providing that pieces of newspaper 
 and matches are not thrown into it. 
 
 Problem 2. Sewage disposal in villages and isolated 
 houses. If we live in a city in which there is a well- 
 
 171 
 
 FIGURE 128. TRAP OF 
 WASTE WATER PIPE. 
 
172 
 
 GENERAL SCIENCE 
 
 developed system of sewers there is really no concern for the 
 individual home, other than to make sure that there is a 
 proper connection with the sewer. In the home or school 
 not connected with a sewer, the septic tank system is the most 
 satisfactory. This consists essentially of two or sometimes 
 three concrete underground tanks. 
 
 FIGURE 129. SEPTIC TANK. 
 
 By the overflow pipe 4 the waste, liquified by action of bacteria, passes 
 into C, from which it is siphoned into D, flowing out from there by the 
 outlet pipe. 
 
 In the first tank, solids are acted upon by bacteria and 
 liquified. By an overflow pipe this liquid passes into the 
 second tank, from which it may be removed through the 
 top ; or, in the country, it may be conducted away by a series 
 of drains and permitted to escape into the surrounding soil 
 where it is soon completely decomposed by the soil bacteria. 
 Any method of disposal of waste from the toilet in which the 
 material is open to visits of flies, or in which it is permitted 
 to become mixed with the soil before it has been acted upon 
 for a long time by bacteria, is bad, as it may mean exposure 
 to typhoid fever and hookworm disease. 
 
 Problem 3. Sewage disposal in cities. The too common 
 method has been the easiest ; that of discharging sewage into 
 
TO UNDERSTAND THE DISPOSAL OF SEWAGE 173 
 
 streams, lakes, or oceans. In th cases of cities like New 
 York, located on the ocean, this method has not been so 
 serious as in that of cities on lakes and rivers. Previous to 
 1900 the sewage of Chicago was emptied into Lake Michigan, 
 from which body of water the city also obtained its drinking 
 water. The average annual death rate from typhoid fever 
 for the ten years preceding 1900 was 66.8 per 100,000. In 
 that year the drainage canal was completed by which the 
 Chicago River, which emptied into Lake Michigan, was 
 connected with the Illinois River, which empties into the 
 Mississippi River. So the lake water which now flows 
 toward the Gulf of Mexico carries away with it the sewage 
 of Chicago, leaving the lake uncontaminated. 
 
 In the ten years following the opening of the canal, the 
 annual death rate from typhoid fever fell to 22.3 per 100,000. 
 It was found that pathogenic bacteria in the Chicago sewage 
 had disappeared long before the water had reached the 
 Mississippi River. The chief influences that bring about 
 such a condition are sedimentation, activity of other micro- 
 organisms, light, temperature, and lack of food supply. 
 
 Many cities use a method somewhat similar to the septic 
 tank system on a large scale. The ideal plan would be 
 such treatment of sewage that the products could be safely 
 used as a fertilizer to enable the land to produce better 
 crops. A moment's thought will cause you to realize what 
 an enormous amount of material, which should be returned 
 to the soil, passes to the ocean every day in the sewage 
 from New York City alone. 
 
 Each pupil should find out the method of sewage disposal 
 practiced by his community and determine the points in 
 which the system is a good one and points in which it is 
 deficient. 
 
174 GENERAL SCIENCE 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Make a plan of the sewage system of your home. Point out the 
 advantage of the arrangement. In what way do you think the arrange- 
 ment might have been improved? Explain. 
 
 2. Clean out the various traps in the waste water system. 
 
 REPORTS 
 
 1. The transmission and the seriousness of the hookworm diseasec 
 
 2. Sewage disposal of a large city. 
 
 3. Sewage disposal on a farm. 
 
PROJECT xvn 
 
 WATER AS A MEANS OF TRANSPORTATION 
 
 IN addition to the value of water in the air, as rainfall ; 
 in furnishing power, from waterfalls ; for various industrial 
 purposes; and for drinking and household uses, it also 
 furnishes one of the chief means of transportation. The 
 location of cities and the development of nations have been 
 determined by opportunities for utilizing water trans- 
 portation. The development of New York into one of the 
 largest cities of the world has been greatly influenced by the 
 fact that it possesses a harbor which is almost unrivaled. 
 In the same way, Boston, Philadelphia, and Baltimore 
 on the Atlantic Coast ; St. Louis and New Orleans on the 
 Mississippi; Chicago, Buffalo, Cleveland, Detroit, and 
 Duluth on the Great Lakes ; and San Francisco, Portland, 
 and Seattle on the Pacific Coast, owe much to the advantages 
 which they offer to water transportation. Africa has few 
 harbors, Europe has many. Explain how this fact may have 
 led to the more rapid development oPcivilization in Europe. 
 
 Since harbors to such a great extent determine the im- 
 portance of a country, we naturally ask how a good harbor 
 such as that of New York has been formed. 
 
 Problem 1. How the New York harbor originated. 
 
 -Examine the outline map of the harbor (Figure 130). 
 
 Examine also the coast of North America from Chesapeake 
 
 Bay northward (Figure 131). Compare this coast line with 
 
 175 
 
176 
 
 GENERAL SCIENCE 
 
 the western coast line of South America (Figure 132). 
 There is evidence that the western coast line of South 
 America is rising. 
 
 MAD OF 
 NEW-YOBIK1TY 
 
 A * 
 
 FIGURE 130. MAP OF NEW YORK HARBOR. 
 
 Another fact to be noticed is that the Hudson River is 
 very deep, permitting very large vessels to pass up its 
 
WATER AS A MEANS OF TRANSPORTATION 
 
 177 
 
 waters a considerable distance. Those of you who are ac- 
 quainted with the river know that the tide extends 166 
 miles up the river to Troy above Albany. 
 
 How can we explain the shape and depth of the harbor, the 
 depth of the river, and the fact that the surface of the water 
 of the river is at sea level for over one hundred and fifty 
 miles above its 
 mouth ? 
 
 Since the smooth 
 coast line of west- 
 ern South America 
 is known to be due 
 to an elevation of 
 the land, we might 
 suspect that the 
 very irregular coast 
 line of eastern 
 North America is 
 due to a sinking 
 of the land. If 
 this is true will that 
 account for the con- 
 ditions of the New 
 
 FIGURE 131. COAST OF EASTERN UNITED STATES. 
 
 The heavy black line marks the distance the 
 tide extends up the rivers. 
 
 York harbor? 
 
 All evidence 
 seems to point to 
 
 the fact that New York harbor originated as did a great 
 many good harbors by a sinking of the coast (Figure 133). 
 This, of course, occurred many thousands of years ago in 
 what we call prehistoric times. 
 
 From what we learn by studying the earth's crust we 
 know that although we may think of the earth a the symbol 
 
178 
 
 GENERAL SCIENCE 
 
 of solidity, portions of the earth's surface have at times 
 been raised and at other times depressed. The stratified 
 sandstone, limestone, and slaty rocks found over a great 
 part of the country are evidences of the elevation of these 
 
 portions of the con- 
 tinent, as these rocks 
 are formed only at the 
 bottom of the ocean 
 (Figure 134). 
 
 Problem 2. Effect 
 of the forests of the 
 Adirondacks upon 
 New York harbor and 
 the navigability of the 
 Hudson River. In 
 order that a harbor 
 may be of the great- 
 est value, a certain 
 amount of dredging 
 must be done to keep 
 the channels free of 
 sand and mud. The 
 origin of this material 
 will be understood by 
 anyone who has no- 
 ticed the appearance 
 of the water in a small 
 
 stream after a rainstorm. If this small stream empties 
 into a large body of water, it will be noticed that the mud 
 and sand, which is being carried, is dropped. 
 
 Streams everywhere are wearing away the land and 
 carrying it to the ocean. This is the cause of much of the 
 
 FIGURE 132. OUTLINE OF SOUTH AMERICA. 
 
WATER AS A MEANS OF TRANSPORTATION 
 
 179 
 
 irregularity of the land surface. Each little stream forms a 
 ravine or valley of its own, carrying away the particles of 
 earth and rock which have been loosened by changes of 
 temperature, by the freezing of water in crevices, or by the 
 action of the oxygen 
 or carbonic acid of the 
 air. The action of 
 these agencies is 
 known as weathering. 
 These particles, car- 
 ried along by the 
 swiftly moving water, 
 help to wear away 
 the bed of the stream ; 
 this is known as 
 erosion (Figure 135). 
 Thus we see that the 
 land is gradually being 
 carried to the ocean, 
 where it is dropped as 
 soon as the velocity of 
 the water is checked 
 by coming in contact 
 with the greater body 
 of water. Nearly all 
 the streams that form 
 the Hudson River 
 begin in the Adirondack Mountains, about 3000 feet above 
 sea level. What must be true of the velocity of the water 
 of these streams? As the rainfall in the Adirondacks is 
 not evenly distributed throughout the year, what would 
 you expect to be the condition of the streams during the 
 
 FIGURE 133. OUTLINE MAP OF ENGLAND. 
 
 Note the fine harbors at the mouth of the 
 rivers. These were produced by a sinking of 
 the coast many thousands of years ago. 
 
180 GENERAL SCIENCE 
 
 season of great rainfall and at the time of the melting of 
 the snow? What would you expect to be the result when 
 this water meets the sluggish current of the tidal portion 
 of the Hudson, and when the tidal current from the river 
 meets the water of the harbor? 
 
 FIGURE 134. STRATIFIED ROCKS. 
 
 You will be surprised to learn that the streams are not 
 nearly so flooded, and that there is not so much sediment 
 deposited as you would imagine. Our consideration of the 
 effect of forests upon water-supply areas gives us the key 
 to the explanation. The Adirondack Mountains are heavily 
 forested. What effect does this have upon the volume of 
 water in its streams ? What also will be the effect, upon the 
 power of the streams to accomplish erosion and to carry 
 mud, sand, and rocks? What do you think would be the 
 
WATER AS A MEANS OF TRANSPORTATION 181 
 
 result of cutting the forests from this mountainous region 
 as affecting the navigability of the Hudson River and New 
 York harbor? 
 
 In parts of the country from which the forests have been 
 removed, great floods occur in the rainy periods of the year, 
 while at other times the navigable streams become too 
 
 FIGURE 135. EROSION BY SMALL STREAM. 
 
 After heavy rains and after melting of snow this stream becomes a 
 
 torrent. The forests on the mountains in the background have been 
 
 burned away. 
 
 shallow to permit the passage of boats. Their navigability 
 can be maintained throughout the year only by the expendi- 
 ture of large amounts of money for the purpose of dredging 
 the channels and of building dikes and dams. 
 
 These conditions are especially true of the Ohio River and 
 its tributaries. A large part of the drainage area, which was 
 at one time densely wooded, has developed into a rich agri- 
 cultural region necessitating the removal of most of the 
 forests. As a result, during the summer there is almost no 
 
182 
 
 GENERAL SCIENCE 
 
 water except in the larger streams, while in the spring they 
 overflow their banks, causing much damage to property and 
 often loss of lives (Figure 136). 
 
 Problem 3. Importance of internal waterways. For the 
 transportation of articles of commerce in which speed is 
 riot a prime requisite, internal waterways might well be 
 
 FIGURE 136. FLOOD IN WABASH RIVER, 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 the smaller ex- 
 pense (Figure 137). This would also relieve the railroads 
 so that their facilities might be used more completely in the 
 transportation of passengers, mails, foodstuffs, and articles 
 that demand quick delivery (Figure 138). Congestion of 
 railroad traffic has been one of the causes of the high cost of 
 living. In the great development of railroads during the 
 past fifty years, the development of transportation by water 
 has been neglected to a large extent. An illustration of the 
 
WATER AS A MEANS OF TRANSPORTATION 183 
 
 great importance of river navigation is seen in the carrying 
 of coal and iron from Pittsburgh down the Ohio and Mis- 
 sissippi rivers. 
 
 River traffic has been supplemented by the construction of 
 canals. Many of these have fallen into disuse during the 
 period of development of railroads, but recently steps have 
 been taken to put some of them into a usable condition. 
 
 FIGURE 137. USE OF RIVER FOR TRANSPORTATION OF LOGS. 
 
 The first half of the nineteenth century in the United 
 States might almost have been called the era of canal 
 building. Some of the canals were short ones around falls 
 in otherwise navigable rivers. Many were of interest 
 because they cut across watersheds and connected distinct 
 drainage systems, frequently at the portages used by the 
 Indians and early settlers. If railroads had not developed 
 as they did, we should have had a very complete system of 
 internal waterways. 
 
184 GENERAL SCIENCE 
 
 The most important of these was the Erie Canal, completed 
 in 1825 from Buffalo to Albany, a distance of 352 miles, 
 connecting the Great Lakes with the Hudson River. 
 Pennsylvania and Maryland attempted to connect their 
 tide- water rivers with the Ohio River ; Virginia endeavored 
 to connect Chesapeake Bay with the Ohio River; in New 
 Jersey the Morris Canal was built connecting New York 
 City with the Delaware River; Ohio and Indiana built 
 canals from the Great Lakes to tributaries of the Ohio 
 
 FIGURE 138. USE OF INTERNAL WATERWAYS TO TRANSPORT FARM 
 
 PRODUCTS. 
 
 River, and in Illinois a canal was constructed connecting 
 Lake Michigan with the Mississippi system. 
 
 The " Soo " canal at Sault Ste. Marie, between Lake 
 Superior and Lake Huron, and the Welland ship canal, 
 between Lake Erie and Lake Ontario in Canadian territory, 
 afford a continuous passage from all parts of the Great 
 Lakes to the Atlantic Ocean by way of the St. Lawrence 
 River. The route is of especial interest to us now because 
 in the Great War many of the large lake vessels were brought 
 to the Atlantic to be used to carry troops and supplies to 
 
WATER AS A MEANS OF TRANSPORTATION 
 
 185 
 
 8 
 
186 GENERAL SCIENCE 
 
 Europe. This route has put great areas of our country into 
 direct water connection with the markets of the world. 
 
 Problem 4. How ocean transportation depends upon 
 science. Ocean, transportation follows regular routes 
 which are determined to some extent by available harbors, 
 prevailing winds, ocean currents, the probability of the 
 presence of icebergs, and fogs. In a number of cases 
 routes have been shortened by the construction of canals; 
 the two most important ones are the Suez Canal through the 
 Isthmus between Asia and Africa, connecting the Medi- 
 terranean Ocean and the Red Sea, and the Panama Canal 
 through the isthmus between North and South America, 
 connecting the Atlantic and Pacific oceans. Along our 
 eastern coast, the Cape Cod Canal shortens very materially 
 the coastwise route between New York and Boston. The 
 Suez Canal, opened in 1869, has saved, in going from the 
 North Atlantic to India and the Far East, the long trip 
 around the southern end of Africa. 
 
 The building of the Panama Canal, opened in 1914, was 
 the greatest engineering project of the world. Its influence 
 upon the world's commerce is bound to be very great. 
 It shortens the water route from New York to San Francisco 
 by almost 8000 miles ; from New York to Hawaii by about 
 6000 miles; from New York to Callao by about 6000 miles; 
 from New York to Sydney, Australia, by about 4000 miles 
 (Figure 140). 
 
 The building of this canal was not only an engineering 
 triumph for the United States, but one equally great in the 
 field of sanitation. American physicians, by their work in 
 the canal zone, not only made possible the building of 
 the canal but they demonstrated that tropical diseases are 
 capable of human control. 
 
WATER AS A MEANS OF TRANSPORTATION 
 
 187 
 
 FIGURE 140. UNITED STATES WAR SHIP PASSING THROUGH PANAMA 
 
 CANAL. 
 
 The sanitary work was under the control of Dr. William 
 C. Gorgas, who built upon the work of the United States 
 yellow fever commission in Cuba, consisting of Drs. Reed, 
 Carroll, Lazear, and Agrimonte, who had proved at the cost 
 
188 
 
 GENERAL SCIENCE 
 
 of the life of Dr. Lazear that the only way that yellow fever 
 can be transmitted is by the bite of a certain kind of mos- 
 quito. Dr. Gorgas, 
 who had already 
 freed Havana and 
 Cuba of the yellow 
 fever plague, was ap- 
 pointed by President 
 Roosevelt to con- 
 tinue the work which 
 made possible the 
 building of the canal. 
 The French had been 
 defeated by the mos- 
 quitoes years before 
 in their attempt to 
 build the canal with- 
 out even having 
 known that these 
 insects were their 
 enemies. 
 
 That harbors are 
 necessary for the best 
 development of a 
 country is realized 
 in comparing the 
 coast line of Africa 
 with its few harbors 
 to that of Europe 
 with its many fine 
 
 ones. Countries are ready to go to war to get an outlet 
 to the sea. Because of the importance of ocean commerce, 
 
 FIGURE 141. MINOT'S LEDGE LIGHTHOUSE. 
 
 This lighthouse is located on a reef near 
 
 Boston Harbor. 
 
WATER AS A MEANS OF TRANSPORTATION 189 
 
 nations have cooperated to encourage it in every way possible. 
 The oceans and especially the waters near shores, where 
 most danger lies, have been carefully charted; lines of 
 magnetic force determined and charted; prevailing winds 
 studied; great breakwaters constructed; harbor channels 
 kept dredged; lighthouses, buoys, and foghorns placed as 
 guides (Figure 141) ; life-saving stations located at inter- 
 vals along the coasts ; vessels and shipping offices furnished 
 every day with weather forecasts and special warnings on 
 the occasion of storms. 
 
 Since wireless telegraphy has come into use, a vessel may 
 be at all times in touch with land stations and other ships, 
 so that the danger of serious results from a breakdown, fire, 
 or wreck at sea is very much minimized. 
 
 In addition to contributing largely to bringing about 
 the conditions just mentioned, science is being called on for 
 help in building larger, faster, and more seaworthy ships. 
 In our own country the demand of the war for more ships 
 has stimulated shipbuilding to such an extent that the 
 United States is destined to become a leading ship-owning 
 country. The ability of the captain to sail his vessel and 
 bring it into port depends upon his scientific training and the 
 scientific instruments which his ship carries. Without the 
 mariner's compass, the sextant, the chronometer, together 
 with his charts and nautical almanac, all the results of 
 highly specialized science work, his ship would be an aim- 
 less wanderer. 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Make a collection of rocks from your vicinity accompanied by a 
 story of the geological history of that part of the country. 
 
 2. Construct a model to illustrate erosion and deposit of earth and 
 sand. 
 
190 GENERAL SCIENCE 
 
 
 
 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 the work being done by the government to keep 
 rivers and harbors navigable. 
 
 3. The story of the Erie Canal. 
 
 4. History of the building of the Panama Canal. 
 
 5. Means taken to 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, the Canal, etc.) Browne. Mac- 
 millan Company. 
 
 3. Historic Inventions, Holland. Geo. W. Jacobs Company, Phila- 
 delphia. (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 TIDES 
 
 ALTHOUGH so far away, the sun and moon exert a 
 powerful influence upon everything that happens on the 
 earth. This influence has been mentioned in considering 
 the source of energy of food, coal, and wood, and the energy 
 of water power. 
 
 Then too, the sun, moon, and stars, although so distant, 
 have always been of the greatest interest to the inhabitants 
 of the earth. The earliest speculations concerning things 
 of Nature have been concerned with these heavenly bodies. 
 We know now that much that was fanciful and erroneous 
 crept into their ideas of these bodies ; but we, just as our 
 distant ancestors were, are interested in the wonders of the 
 heavens. We, however, are not satisfied with fanciful imagi- 
 nation but want to know the truth 
 
 In our study we shall begin with one of the very evident 
 ways in which the earth is affected by the nearest of these 
 heavenly bodies, the moon. A study of the tides may 
 give us some hints as to the relationship between the earth 
 and other heavenly bodies and of the relation of these to 
 one another. 
 
 If you live near the seashore or have ever visited it you 
 know something about tides. Let us first get together our 
 
 191 
 
192 
 
 GENERAL SCIENCE 
 
 FIGURE 142. HIGH TIDE IN A HARBOR IN 
 NOVA SCOTIA. 
 
 observations con- 
 cerning tides. How 
 many tides a day? 
 Does high tide oc- 
 cur at the same 
 time every day ? 
 If not, does it oc- 
 cur earlier or later 
 each day ? How 
 much higher is the 
 water at high tide 
 than at low tide 
 (Figures 142 and 
 143) ? Are there 
 any times when the 
 
 tide is especially high ? To find out the cause of tides it is 
 
 evident that we must be able to solve the following problems : 
 What causes the 
 
 rising of the water. 
 Why the water 
 
 comes up twice a 
 
 day. 
 
 Why high tide is 
 
 a little later each 
 
 day. 
 
 Why, at times, 
 
 there are especially 
 
 high tides. 
 Problem 1. What 
 
 causes the water to 
 
 rise. From the 
 
 FIGURE 143. Low TIDE IN THE SAME HARBOR. 
 
 fact that the highest tides occur at the time of the 
 
TO UNDERSTAND THE CAUSE OF TIDES 193 
 
 full moon and the new moon, what will you suspect ? But 
 since the moon is about 240,000 miles from the earth, at first 
 thought it seems hardly possible that it can exert a power 
 sufficient to pull up such an enormous amount of water. 
 This problem remained unsolved until Sir Isaac Newton, 
 in the seventeenth century, showed that the force which 
 causes an object to fall to the earth is the same force which 
 causes this tidal wave approximately every twelve hours 
 and twenty-five minutes. 
 
 In order to understand the cause of tides it is necessary for 
 us to consider this force. The essentials of Newton's dis- 
 covery are, that every particle of matter has an attraction 
 for every other particle of matter; and that the strength 
 of this attraction is directly proportional to the mass or 
 amount of material and inversely proportional to the square 
 of the distance between their centers. This means that if 
 the moon were twice as large, it would pull upon the earth 
 with twice the force it does now and that if it were twice 
 as far from the earth as now it would pull upon the earth 
 with a force only one fourth as great as at present. 
 
 In accordance with this law of gravitation, there is a pull 
 between the center of the earth and every object we know. 
 The measure of this pull constitutes the weight of a body. 
 The reason that the earth does not seem to be pulled toward 
 the ball that is dropping may be understood from the fol- 
 lowing experiment. 
 
 Experiment. Connect two marbles, A and B, of equal size, by a 
 rubber band. Draw the marbles apart and allow the elasticity of the 
 band to pull them together. Compare the amount of movement of 
 each marble. Now connect a very small marble with a very large one 
 by a rubber band. As before, compare the amount of movement of 
 each when they are pulled together by the elastic. If there is ten 
 
194 GENERAL SCIENCE 
 
 times as much material in the large marble as in the small one, the 
 large marble will move one tenth as far as the small one. Explain, 
 then, why the ball falls to the earth, and why the earth does not seem 
 to rise to the ball. 
 
 This force acts in solid bodies, through the center of mass 
 of the body. It is because of this that a mason's plumb 
 line points to the middle of the earth (Figure 
 144). In objects on the surface of the earth, this 
 center of mass or center of gravity, as it is called, 
 is the point of a body at which its weight may 
 be counteracted by a single upward, vertical force. 
 The location of the center of gravity is easily 
 found. Suppose the center of gravity of a piece 
 of cardboard is to be found. Suspend the card- 
 board by a thread. Draw a line on it continuous 
 with the line of the supporting thread. Now sus- 
 pend the cardboard in the same way from another 
 point of attachment. The point of intersection 
 of the two lines will be the location of the center 
 of gravity. Explain. 
 
 The fact that the center of gravity of a body 
 tends to get as near the center of the earth as pos- 
 sible is illustrated by the tipping over of bodies. 
 FIGURE 144. Why does a flat stone on the ground show no 
 PLUMB LINE, tendency to tip, while the same stone standing 
 on its edge tips over very easily? A body is said to be 
 in stable equilibrium when it cannot be tipped without 
 raising its center of gravity ; a body is in unstable equilibrium 
 when it cannot be tipped without lowering its center of 
 gravity (Figure 145). 
 
 Let us now go back to the tides and endeavor to under- 
 stand how this force of gravitation causes them. The moon 
 
TO UNDERSTAND THE CAUSE OF TIDES 
 
 195 
 
 attracts the solid earth as if the entire mass of the earth 
 
 were concentrated at its center. The water of the ocean, 
 
 however, is 4000 miles 
 
 from the center of the 
 
 earth. What, therefore, 
 
 is the relative pull of 
 
 the moon upon the solid 
 
 earth, and upon the ocean 
 
 on the side nearest the 
 
 moon? (Figure 146). 
 
 rjM.- .a. e xil FIGURE 145. 
 
 This is the cause of the ^ stable equihbrium . B> unstable 
 
 tide On the side of the equilibrium. C, neutral equilibrium. 
 
 earth nearest the moon. 
 
 Problem 2. Why there are two high tides a day. You 
 already know from your study of geography that the earth 
 rotates once in twenty-four hours. Therefore, how many 
 
 Low WATER. 
 
 THE MOON. 
 
 Low WATBTR. 
 
 FIGURE 146. RELATION OF MOON TO THE TIDES. 
 
 times a day is the moon directly opposite any part of the 
 earth? It can be easily understood, then, how a wave of 
 water will travel around the earth. In what direction will 
 it travel? Explain. (Note: Does the moon rise in the 
 east or the west?) According to this, how many tides a 
 day will there be? But, in reality, how many are there 
 (Figure 146) ? 
 
196 GENERAL SCIENCE 
 
 From the fact that high tides are about twelve hours 
 apart when there is high tide on any part of the earth, at 
 what other part of the earth is the other high tide? Our 
 problem then is, how is this second high tide, on the side of 
 the earth away from the moon, caused. 
 
 Recall the way in which gravitation acts upon the solid 
 earth and upon the water of the ocean. How much farther 
 away from the moon is the water on the opposite side of the 
 earth than the center of gravity of the solid earth? Upon 
 which, therefore, will the pull be greater? It can be under- 
 stood now how there is a tendency for the solid earth to be 
 pulled away from the water and as a result the water will 
 flow in, causing an elevation of the water, thus producing a 
 tidal wave on the side of the earth away from the moon. 
 In what direction will this tidal wave travel and at what 
 rate compared with the tidal wave directly under the moon ? 
 There is also another force which helps produce this tidal 
 wave on the side of the earth away from the moon, which 
 can be understood a little later. 
 
 Problem 3. Why high tide is a little later every day. 
 From our discussion, what would you conclude should be 
 the time between two high tides ? If, then, high tide occurs 
 at 12 o'clock on one day, at what time should there be high 
 tide on the following day? Is this actually what occurs? 
 Some of you have gone to the ocean bathing beaches. On 
 your visits there did you find that high tide always occurred 
 at the same time of day ? 
 
 Observation will show you that high tide is about fifty 
 minutes later every day. Our problem then is to under- 
 stand the reason for this seeming discrepancy. 
 
 In our discussion of the cause of tides we considered that 
 . the earth rotated once in twenty-four hours. If the moon 
 
TO UNDERSTAND THE CAUSE OF TIDES 197 
 
 kept in the same relative position with reference to the 
 earth, how often would a certain point on the earth's sur- 
 face be directly opposite the moon? Since, however, it 
 takes twenty-four hours and fifty minutes for any spot 
 which is directly opposite the moon to be again opposite 
 the moon, what will be your conclusion as to the movement 
 of the moon ? Can you determine whether the moon moves 
 around the earth in the same direction as the earth rotates 
 or in the opposite direction ? 
 
 Astronomers, scientists who study the movements of the 
 heavenly bodies, have shown that the conclusion we have 
 reached that the moon revolves around the earth in the 
 same direction in which the earth rotates is true. They 
 tell us that the moon revolves completely around the earth 
 in twenty-eight days. We can now consider the problem 
 which arose in discussing gravitation. 
 
 Problem 4. Why the moon does not fall to the earth. 
 You have probably wondered why, if the earth and moon 
 are pulling each other, they do not come together just as 
 we found that the rubber band pulled the two marbles to- 
 gether. In order to understand this, we must know that the 
 moon revolves around the earth once in twenty-eight days. 
 This is the explanation of the fact that the moon rises about 
 one hour later every night. If the moon occupied con- 
 tinuously the same relative position to the earth, it would 
 rise at the same time every night. What would be the time 
 between high tides ? What is the time between high or low 
 tides? 
 
 The way in which the revolution of the moon around the 
 earth prevents it from falling to the earth is illustrated by 
 many very common happenings. What happens when you 
 swing in a vertical circle a pail containing water? What 
 
198 GENERAL SCIENCE 
 
 happens to the water on a grindstone, when it is turned 
 rapidly? What happens to an automobile if it attempts 
 to turn a corner too rapidly? What is the advantage of 
 having a circular running track " banked " ? Wet clothes 
 are dried by putting them into a large, perforated, metal 
 cylinder and rotating the cylinder rapidly. If you are 
 familiar with milk separators, explain how the milk is 
 separated from the cream (Figure 147). 
 
 All of these observations, showing that rotating bodies 
 tend to fly away from the center around which the body is 
 
 .' - .- , : FIGURE 147. 
 
 Why do the mercury and water not remain at the bottom 
 of the glass globe? 
 
 turning, are illustrations of the fact, that bodies in motion 
 tend to 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, except in 
 so far as it is compelled by force to change that state." Give 
 other illustrations of the law. 
 
 For every body turning around a center there must be two 
 
TO UNDERSTAND THE CAUSE OF TIDES 199 
 
 forces ; one drawing it toward the center, called the centrip- 
 etal force (center-seeking force) ; and one drawing it away 
 from the center, called the centrifugal force. The moon 
 revolves around the earth once in every twenty-eight days. 
 As the moon is 240,000 miles from the earth, you can easily 
 calculate its velocity. Because of this motion what does the 
 moon tend to do? What prevents it? In your own lan- 
 guage explain why the moon is not drawn to the earth or 
 does not fly off into space. 
 
 You will recall that in discussing the cause of the tide 
 on the side of the earth away from the moon reference was 
 made to another force in addition to- the difference of the 
 pull of gravitation upon the solid earth and the liquid ocean. 
 This force we can now understand. The moon and earth 
 are held together by the force of gravitation very much as a 
 large man and a small boy might hold themselves together 
 by locking their hands together. 
 
 If, while holding hands in this way, the man should 
 swing the boy around, not only would the boy tend to 
 swing in as large a circle as possible, but the coat tails of the 
 man also would tend to fly out because of the centrifugal 
 force. In the same way the water on the side of the earth 
 away from the moon tends to heap up because of this centrif- 
 ugal force. 
 
 There remains yet one problem concerning tides which 
 we decided needed solution : Why, at times, there are es- 
 pecially high tides. 
 
 Problem 5. Why, at times, there are especially high 
 tides. Usually about twice a month the tides are es- 
 pecially high. During the winter of 1919-1920 such a tide 
 accompanied by a wind from the ocean flooded Coney 
 Island and Rockaway Beach near New York, wrecking 
 
200 
 
 GENERAL SCIENCE 
 
 many buildings. At the same time a large part of the 
 water front of New York City was covered with water. 
 
 FULL MOON. 
 
 > 
 
 FIGURE 148. THE Two POSITIONS OF THE MOON WHEN HIGH TIDE 
 Is HIGHER THAN USUAL. 
 
 This occurred at the time of the full moon. At every full 
 moon and new moon the tide' is especially high. On the 
 other hand, . when 
 
 *( ) FIRST QUARTER the moon is at first 
 
 MOON. 
 
 Y 
 
 ; 
 
 NEAP-TIDE. 
 
 and third quarters, 
 the high tides are 
 especially low. 
 
 The accompanying 
 diagrams (Figures 
 148 and 149) show 
 the relative positions 
 of the earth, moon, 
 and sun at these 
 times. From exam- 
 ination of these 
 diagrams explain the 
 cause of the espe- 
 cially high tides at 
 certain times. 
 
 Evidently the 
 theory that the tides are caused by the force of gravitation, 
 studied by Sir Isaac Newton, can be accepted, as it 
 offers a satisfactory explanation of the cause of tides and 
 
 NEAP-TIDB. 
 
 MOON.f J THIRD QUARTER. '" 
 
 FIGURE 149. THE Two POSITIONS OF THE 
 MOON WHEN HIGH TIDE Is NOT AS HIGH AS 
 USUAL. 
 
TO UNDERSTAND THE CAUSE OF TIDES 
 
 201 
 
 is in harmony with all the facts that we have observed 
 concerning them. 
 
 In mid-ocean the tide cannot be observed, but it is very 
 noticeable when it strikes against the land. Sometimes be- 
 cause of the charac- 
 ter of the coast line 
 the tides rise to a 
 great height, as in 
 the Bay of Fundy, 
 Nova Scotia, where 
 they are more than 
 sixty feet high. Some 
 shallow harbors can 
 be entered or left 
 only at high tide. 
 
 Do tides possess 
 energy? Can you 
 suggest a way by 
 which this energy 
 might be utilized? 
 
 The information 
 which we have 
 learned concerning 
 the movement of 
 the moon around 
 the earth may help 
 us to solve another 
 problem. 
 
 Problem 6. Why sometimes only a portion of the moon 
 is visible to us. At first sight this seems a difficult prob- 
 lem, but answering the following questions may help us. 
 
 1. Is the moon cold, or hot like the sun? 
 
 FIGURE 150. PHASES OF THE MOON. 
 
 The outside circle of positions of the moon 
 shows the part lighted by the sun. The inner 
 positions indicate how the moon appears to 
 us in its different positions. 
 
202 
 
 GENERAL SCIENCE 
 
 2. What is the source of the 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 the moon to go around the 
 earth? 
 
 5. About how often do we have a full moon? 
 
 An examination of the 
 following diagram, in con- 
 nection with the answers 
 to the questions above, 
 will make clear to you why, 
 at times, the moon appears 
 like a ball, while at other 
 times it appears as a cres- 
 cent. Even when the moon 
 appears only as a crescent 
 we can sometimes dimly 
 see the remaining portion 
 of its surface. This is be- 
 cause of reflection of light from the surface of the earth. 
 
 The following lines will enable you to know whether the 
 crescent you see in the sky is an old or new moon : 
 " Oh, Lady Moon, your horns point toward the east. Shine ; 
 
 be increased ! 
 
 Oh, Lady Moon, your horns point toward the west. Wane ; 
 be at rest ! " 
 
 Occasionally an eclipse of the sun occurs. If we look at 
 the sun at such a time through a piece of smoked glass, it 
 will be noticed that a rounded black notch or patch appears 
 on the edge of the sun. This black patch travels across the 
 surface of the sun. If the eclipse is a total one, it obscures 
 for a short time the entire face of the sun (Figure 151) ; if, 
 
 FIGURE 151. A TOTAL ECLIPSE OF 
 THE SUN. 
 
TO UNDERSTAND THE CAUSE OF TIDES 
 
 203 
 
 as is usual, the eclipse is only partial, only a segment of it is 
 obscured. 
 
 Considering the relative location of the bodies of the 
 solar system, what do you believe causes an eclipse of the 
 sun? There may also be an eclipse of the moon. Sug- 
 gest how this may occur. Draw diagrams showing the 
 relation of the moon, 
 earth, and sun in both 
 kinds of eclipse. The 
 accuracy with which the 
 time of an eclipse may be 
 foretold years in advance 
 of the event is an indi- 
 cation of how thoroughly 
 the laws of motions of 
 the members of the solar 
 system are understood. 
 
 Solar system. The 
 same two forces which 
 hold the moon in its path keep the earth and other planets 
 in their orbits or paths around the sun. In the order of 
 their distance from the sun the planets 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 brightest 
 object in the sky. At times it is the evening star, and at 
 other times the morning star. 
 
 Mars, which sometimes appears as a reddish star in the 
 sky, has been a favorite object for study with the telescope 
 because of its nearness and especially because in many re- 
 spects it resembles the earth, leading observers to think that 
 possibly life similar to that on the earth may exist there. 
 
 FIGURE 152. 
 
 DIAGRAM OF OUR SOLAR 
 SYSTEM. 
 
204 GENERAL SCIENCE 
 
 The thinness of the atmosphere and the small amount of 
 water present on Mars render this belief rather improbable. 
 The sun with the planets revolving around it is called the 
 solar system. The sun is a light-giving body; the planets 
 and their moons only reflect the light of the sun. 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Make a model to scale showing the relative size of the moon 
 and the earth, and the distance of the moon from the earth. 
 
 2. Make a diagram showing the location of the moon in the sky at 
 a certain hour on six successive nights. Show also the appearance of 
 the moon each night. Explain your observations. 
 
 3. Work out a plan of the solar system, representing to scale the 
 relative distances and sizes of the sun and the planets. 
 
 4. Make a model of sun, earth, and moon to show the cause of 
 eclipses, phases of the moon, and seasons. 
 
 REPORTS 
 
 1. Use of the energy of tides. 
 
 2. How the sun, moon, and planets have come into existence. 
 
 3. Discussion of the probability of life similar to that on this earth 
 existing on other planets. 
 
 REFERENCES FOR PROJECT XVIII 
 
 1. The Moon, G. P. Serviss. D. Appleton & Co. 
 
 2. The Ways of the Planets, M. E. Marten. Harper & Bros. 
 
 3. Giant Sun and His Family, Proctor. Silver, Burdett & Co. 
 
PROJECT XIX 
 HOW TO KNOW SOME OF THE FIXED STARS 
 
 THE thousands of stars which we see in the heavens are 
 light-giving bodies, and correspond to our sun. Many or 
 all of them may be the centers of solar systems. These 
 stars have a fixed position with reference to one another 
 and are accordingly called fixed stars. From the earliest 
 times the stars have been grouped and named according to 
 objects to which they seemed to bear a fanciful resemblance. 
 The ability to recognize a few of the more easily located 
 groups or " constellations " adds much to our enjoyment of a 
 starry night 
 
 Problem 1. How to recognize the constellations around 
 the north pole. The easiest way to begin the study of the 
 constellations is to locate the Great Dipper, which is known 
 by almost everyone (Figure 153). While the Great Dipper 
 is always in the northern part of the sky, it does not appear 
 at all times in the same position, as the stars seem to re- 
 volve around a fixed point in the sky. The bright star 
 located at this point is called the Pole or North Star. 
 Explain why these terms are appropriate. 
 
 The Pole Star can be located by looking along a line which 
 is a continuation of the line connecting the two stars form- 
 ing the front of the bowl of the Great Dipper. These stars 
 are called the Pointers. The Pole Star is along the line a dis- 
 tance of about five times the distance between the Pointers, 
 or about twenty-five degrees, since the distance between the 
 
 205 
 
206 
 
 GENERAL SCIENCE 
 
 Pointers is approximately five degrees. It will be well to 
 keep these figures in mind, as they will serve as standards 
 for measuring distances between stars. 
 
 The Pole Star is part of a constellation called the Little 
 Dipper. It also has seven stars, the number that you have 
 
 seen in the Great 
 Dipper. The out- 
 line of the Little 
 Dipper, however, 
 is not so distinct 
 as that of its big 
 namesake. The 
 Pole Star is at 
 the end of the 
 handle of the 
 Little Dipper. 
 The bowl is com- 
 posed of a clus- 
 ter of four stars, 
 the two of the 
 outer rim being 
 the brightest, lo- 
 cated about fifteen degrees from the Pole Star and facing 
 the open bowl of the Great Dipper. If you have found 
 the stars of the bowl, the other two stars of the handle 
 may be easily located between the bowl and the Pole Star. 
 It will be noticed that the end of the handle of the Little 
 Dipper is bent in a different direction from that of . the 
 handle of the Great Dipper. 
 
 The ancients imagined the stars of the Great Dipper to 
 represent the form of a great bear, and this constellation 
 was accordingly called Ursa Major or the Great Bear. 
 
 FIGURE 153. CONSTELLATIONS AROUND THE 
 NORTH STAR. 
 
HOW TO KNOW SOME OF THE FIXED STARS 207 
 
 Likewise the Little Dipper was called Ursa Minor or the 
 Little Bear. The ability to see a small star in the handle 
 of the Great Dipper is frequently used as a test for good 
 sight. Look at the second star counting from the end of 
 the handle. This is called Mizar. Directly above it at 
 a distance of about one degree is the faint star Alcor. The 
 Arabs call these two stars " the horse and the rider. " 
 
 The constellation Cassiopeia's Chan* is located about the 
 same distance from the Pole Star as the Great Dipper, but on 
 the opposite side. It is very easily recognized because its 
 five bright stars form a W-shaped figure. 
 
 Auriga, or the Charioteer, contains one of the brightest 
 stars, Capella, in the northern part of the heavens. Ca- 
 pella is about forty-five degrees from the Pole Star ; that is, 
 almost twice as far away as the Great Dipper or Cassiopeia's 
 Chair, and on a line drawn at right angles to a line connect- 
 ing the Pointers with the Pole Star. Another way to find 
 Capella is to follow a line drawn from the star at the bottom 
 of the Great Dipper that is nearest to the handle, and pass- 
 ing halfway between the Pointers. At a distance of about 
 fifty degrees along this line, Capella will be seen as a very 
 bright star. Capella with the four other brightest stars 
 of the constellation form a pentagon or five-sided figure. 
 
 The brightest stars of the constellation Perseus lie in 
 an arc extending from Capella to Cassiopeia's Chair. You 
 will be able to see along this arc six or seven stars that be- 
 long to the constellation. 
 
 Other rather conspicuous constellations which may be 
 seen within a radius of about forty or forty-five degrees 
 of the Pole Star are the Dragon, and Cepheus. 
 
 Problem 2. How to recognize the constellations seen 
 only in winter. Stars farther away from the pole can be 
 
208 
 
 GENERAL SCIENCE 
 
 seen only at certain times of the year. The best-known 
 of the winter constellations, located on a line passing almost 
 directly overhead from east to west, is Orion, the Hunter. 
 It is easily recognized by the three stars forming the belt. 
 
 FACE SOUTH ANL 
 HOLD THE MAP OVER 
 YOUR HEAD-THE 
 
 NORTH; AND YOU WILL SEE 
 
 BfAWMBF 
 
 IN THE HEAVENS 
 
 THE ARROW THROUGH 
 THE TWO STARS IN THE 
 BOWL OF THE BIG DIPPED 
 INTS TO THE NORTH STAR- 
 THE STAR AT THE END OF THE 
 HANDLE OF THE, LITTLE DIPPER. 
 
 FIGURE 154. EVENING SKY MAP FOR JANUARY, 1921. 
 
 Except for the planets the sky is always the same as above in Jan- 
 uary. Note the planets on the ecliptic : Mars the farthest to the west, 
 with Venus near it, and Neptune in the east. 
 
 Several small stars, extending at almost right angles, con- 
 stitute the sword hanging from his belt (Figure 154). 
 A very bright, reddish star, Betelgeuse, 1 marks the right 
 
 1 The diameter of Betelgeuse was recently measured for the first 
 time with an instrument devised by Professor Albert A. Michelson of 
 the University of Chicago. The star was found to be about 27,000,000 
 times larger than our sun. 
 
HOW TO KNOW SOME OF THE FIXED STARS 209 
 
 shoulder, while another bright star, Rigel, white instead of 
 reddish, is located in the left foot of the great hunter. After 
 you have located these stars, you will be able to make out 
 the stars which represent the lion's skin which hangs from 
 his left arm, and the stars of the right arm and of the club. 
 
 Facing Orion, and between him and the Pole Star, is the 
 constellation Taurus, or the Bull. The face of the Bull 
 is represented by several, stars arranged in the form of a V. 
 The bright red star, Aldebaran, at the top of the left branch 
 of the V is the eye of the Bull. 
 
 The constellation called the Pleiades, or Seven Sisters, 
 is in the shoulder of the Bull. The stars of this constella- 
 tion, six of which can easily be seen, are very close together 
 and arranged in the form of a very small dipper. 
 
 Farther south in the winter sky may be seen the constella- 
 tions whose brightest stars, Sirius and Procyon, are called 
 the hunting dogs of Orion. Sirius, the brightest of the 
 fixed stars, seems to follow at the heels of Orion and may 
 easily be located by following a line passing from the eye of 
 the Bull, Aldebaran, through the belt of Orion and beyond 
 about twenty degrees. Procyon, Sirius, and Betelgeuse 
 make a triangle, each side of which is about twenty de- 
 grees. 
 
 If you have located the constellations which have been 
 named in the preceding pages, you will be able with the 
 help of the many excellent books about the stars, to locate 
 other constellations, especially the most conspicuous ones 
 of the spring and summer skies; the Lion and the Twins 
 seen in the spring, and the Virgin, the Herdsman, the North- 
 ern Crown, and the Scorpion in the summer. 
 
210 GENERAL SCIENCE 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Identify at least eight constellations. 
 
 2. Work out the method of reading star maps. Collect and mount 
 star maps for every month. 
 
 REPORT 
 Origin of the names of some of the constellations. 
 
 REFERENCES FOR PROJECT XIX 
 
 1. A Beginner's Star Book, Kelvin McKready. G. P. Putnam's 
 Sons. 
 
 2. The Barritt-Serviss Star and Planet Finder, Leon Barritt, 367 
 Fulton St., Brooklyn, N. Y. 
 
 4. Astronomy with the Naked Eye, G. P. Serviss. Appleton 
 &Co. 
 
 5. Star Lore of All Ages, W. T. Olcutt. G. P. Putnam. 
 
 6. Earth and Sky Every Child Should Know, J. E. Rogers. Double- 
 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 difference 
 between winter and summer must be in some way associated 
 with some difference in relation between the sun and the 
 earth. Likewise our calculation of time must be based on 
 the relation between the earth and the sun. Every morn- 
 ing we see the sun rise in the east and at the end of the day 
 set again in the west. 
 
 Problem 1. Why we have winter and summer. There 
 are several facts with which we are familiar that will help us 
 to understand the cause of the seasons. What is the com- 
 parative length of day and night during winter and summer? 
 What is the relative height of the sun above the horizon 
 at midday in winter and in summer? Evidently the sun 
 shines more directly upon our part of the earth in summer 
 than 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 right angles to an imaginary line 
 running from the earth to the sun, what part of the earth 
 would always receive the most direct rays of the sun? But 
 since during the summer the portion of the earth north of the 
 equator receives the most direct rays of the sun, and during 
 the winter the same region receives fewer direct rays of the 
 sun, what is your conclusion in regard to the direction of 
 the earth's axis? (Figure 155.) 
 
 211 
 
212 
 
 GENERAL SCIENCE 
 
 Since on our longest day in summer the direct rays of 
 the sun strike a point 23^ degrees north of the equator 
 and on the shortest day of our winter strike a point 23J de- 
 grees south of the equator, we know that the axis of the 
 
 * 
 
 MAACH ruumtw 
 
 FIGURE 155. HEAT FROM SUN, SUMMER AND WINTER. 
 
 earth is inclined 23^ degrees to the imaginary line running 
 from the earth to the sun. 
 
 A careful study of Figure 156 will make clear how the 
 revolution of the earth and the inclination of its axis cause 
 the seasons. 
 
 1. At what times in 
 the year are the days and 
 nights equal in length? 
 These times are called the 
 vernal or spring equinox, 
 and the autumnal or fall 
 equinox. 
 
 2. On June 22, 1919, 
 at New York City, the 
 sun rose at 4 : 28 A.M. and 
 
 set at 7 : 35 P.M. What was the length of the period of 
 daylight? What was the length of the daylight period 
 within the arctic circle (23^ degrees from the north pole) 
 on this date ? 
 
 3. In your own language discuss the changes in the length 
 
 SPTtMBER I 
 
 FIGURE 156. PATH OF EARTH AROUND 
 THE SUN. 
 
TIME AND SEASONS 
 
 213 
 
 of day and night starting with June 22, as the earth revolves 
 around the sun. 
 
 Problem 2. Why July and August are the hottest months 
 and January the coldest month. According to the amount 
 of heat received from the sun, what days of the year would 
 you expect to be the hottest? Which is the chief source of 
 heat of the air, the direct rays of the sun, or the heat given 
 
 TEMP 
 
 MO" 
 
 -20' 
 
 -40' 
 
 -60' 
 
 Jan. 
 
 Feb. 
 
 Mar 
 
 dpr. 
 
 May Jutie Ju/y 
 
 5ept 
 
 Oct. 
 
 Nov. 
 
 Dec. 
 
 TEMP. 
 FAHFb 
 
 +80 
 +60 
 
 +2* 
 
 0' 
 
 FIGURE 157. ANNUAL TEMPERATURE CURVES. 
 
 Average annual temperature curves of two inland places and two 
 places located near the ocean. Compare the maximum average summer 
 
 temperatures. 
 
 out by the land and water of the earth's surface? (Of 
 course, they too have received their heat from the sun.) 
 What becomes of a large amount of the heat which comes 
 from the sun during the latter half of June? What finally 
 becomes of much of thi^ heat ? 
 
214 GENERAL SCIENCE 
 
 It takes a considerable time to heat the land and water, 
 and on the other hand they cool off gradually. Explain 
 why January is colder than the latter half of December. 
 You have already learned that bodies of land cool more 
 rapidly than bodies of water. Explain, therefore, why coast 
 cities have a later spring and winter than inland cities 
 (Figure 157). 
 
 Why is the strip of land about ten miles wide along Lake 
 Ontario the best peach-producing region of New York ? 
 
 Problem 3. How time is calculated. Some of us must 
 have been surprised when we received news of the signing 
 of the Peace Treaty before the time scheduled for the event 
 to occur in Paris. Then we were told that the time at Paris 
 was five hours faster than our own time; that when it is 
 noon at Paris, our 7 o'clock morning whistles are blowing; 
 and when we stop work for luncheon, the people of Paris 
 and London are ready to quit work for the day, as it is 5 P.M. 
 with them. 
 
 The general difference in time between different places 
 may easily be understood when we consider that one com- 
 plete rotation of the earth makes one day of 24 hours, and 
 that noon by sun time at any place is the time when the 
 sun is directly over a north and south line running through 
 that place. In what direction does the earth rotate? 
 In which city, New York or San Francisco, will 12 noon 
 of a certain day first occur ? 
 
 For convenience in comparing times and for the pur- 
 pose of locating places on the earth's surface, imaginary 
 lines (meridians) are supposed to be drawn around the earth 
 from pole to pole (Figure 158). There are 360 of these 
 equally distant from one another. Why 360 ? The distance 
 between these lines is called a degree of longitude. Is a de- 
 
TIME AND SEASONS 
 
 215 
 
 gree of longitude always of the same length in miles? At 
 the equator a degree of longitude measures about 69 miles. 
 How much does a degree of longitude measure in miles at 
 the poles? Usually the meridian passing through Green- 
 wich, England, is called zero, and longitude is stated as east 
 or west of Greenwich. 
 
 Since the earth rotates on its axis once in 24 hours, how 
 many degrees of longitude will pass 
 under the sun in an hour ? Thus, 
 for every 15 of longitude, the 
 sun time of two places differs one 
 hour. If our clocks were set 
 strictly by sun time, what would 
 be true of the clock time of every 
 place east and west of a given 
 place? In what way would this 
 be inconvenient? 
 
 To prevent the trouble and 
 annoyance arising from such a 
 
 condition, the United States Government in 1883, at the 
 suggestion of the American Railway Association, adopted 
 standard time. By this arrangement the time of the 
 following meridians, 75th, 90th, 105th, and 120th, were 
 taken as standards of time called Eastern, Central, Moun- 
 tain, and Pacific Time. The area of the country to which 
 the time was assigned extended approximately 1\ degrees 
 on each side of the standard meridian; the exact division 
 being determined largely by the location of important cities 
 (Figure 159). As a result, in going from New York to 
 Chicago, we need to change our watches only once. Should 
 the hands of the watch be advanced or turned back ? How 
 much? 
 
 FIGURE 158. LINES OF LATI- 
 TUDE AND LONGITUDE. 
 
216 
 
 GENERAL SCIENCE 
 
 Daylight saving. On. March 19, 1918, President Wil- 
 son approved a bill passed by Congress, by which the stand- 
 ard time throughout the United States was advanced one 
 hour for the period beginning at 2 A.M. on the last Sunday in 
 March and ending at 2 A.M. on the last Sunday in October. 
 Suggest advantages of this bill to the various classes of 
 people of your community. Does it seem to work a hard- 
 ship to any? During the summer of 1919, because of ob- 
 
 FIGURE 159. STANDARD TIME BELTS. 
 
 jection to the daylight-saving plan by various interests 
 of the country, Congress repealed the bill. 
 
 The movement originated in England in 1907. It was 
 not until 1916, however, that definite action was taken, when 
 within three months daylight saving was adopted in Eng- 
 land, France, Italy, Norway, Sweden, Denmark, Switzer- 
 land, Spain, Portugal, Holland, Germany, Austria, and Tur- 
 key. Practically no confusion resulted; everything went 
 on as before, people doing exactly the same things at the 
 
TIME AND SEASONS 217 
 
 same time by the clock, but in reality the whole routine of 
 life had been brought one hour nearer sunrise. The scheme 
 had brought about in the simplest way a vital change affect- 
 ing millions. A simple " twist of the wrist " had given these 
 nations their " place in the sun." Friends of the movement 
 in America claim that the annual conservation of coal in the 
 United States would amount to no less a sum than $40,000,- 
 000 per season. 
 
 Problem 4. How places on the earth's surface are in- 
 dicated. A ship having become disabled at sea needs 
 help. It has a wireless outfit for calling assistance, but 
 how is it to indicate its position to the rescuing ship ? Winds 
 and currents may have carried it far out of its course. Evi- 
 dently it is impossible to give its location by stating its 
 position in miles from certain points. The officer in charge, 
 by noting the difference between his sun time and the time 
 registered by his chronometer (a very accurate clock) giv- 
 ing the time at Greenwich, is able to determine his position 
 in degrees of longitude, east or west of Greenwich. Vessels 
 within reach of wireless stations receive daily the correct 
 Greenwich time. This is more satisfactory than depend- 
 ence on chronometers. Why? The north and south posi- 
 tion is determined, by comparing the height above the 
 horizon of a known fixed star as it crosses the meridian, 
 with tables in his nautical almanac giving the height of 
 this star above the horizon at different distances from the 
 equator. 
 
 For example, where would the Pole Star appear to you if 
 you were at the North Pole? Where would it appear to 
 you if you were at the Equator? If you should travel 
 from the Equator to the North Pole how would the posi- 
 tion of the Pole Star seem to change? 
 
218 GENERAL SCIENCE 
 
 The distance from the equator is measured by degrees of 
 latitude. The equator is zero, and the poles 90. Thus any 
 place on the earth's surface may be accurately determined 
 by giving its latitude and longitude. 
 
 The navigating officer of a ship with these means of de- 
 termining his position, by consulting his charts and by the 
 use of the compass is able to direct his course with sur- 
 prising accuracy. 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Chart the position of the sun above the horizon at a certain hour 
 every day for a month. Interpret the results. 
 
 2. At a certain hour one day each week determine the amount of 
 earth surface covered by a column of sunlight whose cross section is 
 one square foot. 
 
 REPORTS 
 
 1. Make, a chart showing the relative length of day and night 
 throughout the year. Accompany this by a diagram showing the cause 
 of the differences in the length of day and night. 
 
 2. Make a chart showing the standard time belts. 
 
 3. Give method of determining latitude and longitude of a place. 
 
UNIT IV 
 
 WORK AND ENERGY 
 
 PROJECT XXI 
 THE SUN AS A SOURCE OF ENERGY 
 
 THE question of energy and the work it makes possible 
 has been an important part of almost every project and 
 problem we have considered. It seems wise, however, to 
 get together the knowledge we have already gained con- 
 cerning work and energy and especially to take up the ques- 
 tion of how man makes use of energy to contribute to his 
 own comfort and to carry on the work of the world As 
 the sun has been frequently mentioned as the great source 
 of energy, our first project may well be the sun. 
 
 You will recall that we came to the conclusion that the 
 energy of water power and of food and fuel could be traced 
 back to the sun. Explain, therefore : 
 
 (a) The relation of the sun's energy to water power. 
 Into what other forms may the mechanical energy of water 
 power be transformed? (6) How the energy of the human 
 body may be traced back to the sun. (c) How the energy 
 obtained from the burning of coal and wood is really energy 
 derived from the sun. 
 
 There is reason to believe that petroleum from which 
 gasoline, kerosene, paraffin, and similar compounds are ob- 
 tained, and natural gas, which in many parts of the coun- 
 
 219 
 
220 
 
 GENERAL SCIENCE 
 
 try is used for fuel and lighting purposes, have been formed 
 as a result of decomposition of animal and plant deposits. 
 What, therefore, is the source of energy exerted by the 
 engine of the automobile and airplane ? 
 What do you consider to be the source of the energy of 
 
 FIGURE 160. WINDMILL. 
 
 The machine at the left is one of the earliest reapers for the cutting of 
 
 grain. 
 
 alcohol which may become the great fuel of the future if the 
 supply of petroleum becomes exhausted. Alcohol is made 
 by the action of yeast upon sugar. 
 
 The energy of winds also may be referred back to the sun's 
 energy. Wind is not only used to propel ships but also 
 to run windmills which are used especially for pumping 
 water and grinding grain (Figure 160). The windmills of 
 Holland are of considerable historic interest, but American 
 
THE SUN AS A SOURCE OF ENERGY 221 
 
 manufacturers are producing more efficient windmills than 
 those of Europe. In some agricultural districts the wind- 
 mill is very generally used for pumping water, although in 
 recent years it is being replaced to a great extent by the 
 gasoline engine. Suggest reasons for this. 
 
 Problem 1. How the sun's energy is used in making 
 pictures. You "know that the light strikes the film or 
 
 FIGURE 161. A NEGATIVE. 
 
 plate which is coated with gelatine containing a substance 
 that is sensitive to light. When the film is put into a solu- 
 tion known as a developer, a black precipitate made up of 
 minute particles of silver is produced wherever the light has 
 struck the film. It is now washed in " hypo " (a solution 
 of sodium thiosulphate) which dissolves out the sensitive 
 compound which has not been touched by the rays of light. 
 The film, on which the dark parts of the object repre- 
 sented are light and the light parts dark, is now called a 
 negative (Figure 161). This may be placed over paper 
 
222 
 
 GENERAL SCIENCE 
 
 coated with a sensitive substance similar to that on the 
 film, arid exposed to light. The print which is produced 
 has the light and dark places arranged just as they are in 
 the object (Figure 162). Explain why this is true. Light 
 other than direct sunlight may be used, but sunlight is much 
 more active. 
 
 FIGURE 162. : PRINT MADE FROM THE NEGATIVE ON PAGE 221. 
 
 Blue prints. Blue prints, which you have seen con- 
 tractors and builders consulting, are copies of architects' 
 drawings made in the following way. The drawing made in 
 opaque ink upon transparent linen paper is placed over a 
 sheet of paper which is coated with an almost colorless sub- 
 stance that becomes blue when exposed to the light. The 
 print is then washed in water and the positions of the opaque 
 ink lines appear white while all the remaining portion of the 
 paper is blue. 
 
 You will recall from your study of oxidation that a change 
 in which a new kind of a substance is produced is called a 
 
THE SUN AS A SOURCE OF ENERGY 223 
 
 Chemical change. It is evident, therefore, that the changes 
 produced by the sunlight in making pictures and blue prints 
 are chemical changes. 
 
 Problem 2. Other chemical changes produced by the 
 sun's energy. The power of the sun's rays to produce 
 what we call chemical changes, illustrated in the making of 
 starch in plants and in the making of pictures, is also shown 
 by some rather common phenomena, (a) Fading of colors. 
 (1) What is the appearance of portions of wall paper which 
 have been covered by pictures as compared with the re- 
 maining part of the wall ? (2) What is the appearance of 
 your straw hat after it has been worn in the sunlight for 
 several weeks? (3) Give other examples of changes of this 
 kind which you have noticed. 
 
 (b) Action upon living animals and plants. (1) What 
 is the effect of the sun upon the skin ? Will light of a gas or 
 electric lamp, or heat of a stove or furnace, produce the same 
 changes? (2) What is the effect of exposing to the sunlight 
 parts of a plant that have been kept in darkness, as a potato 
 or a stalk of bleached celery ? (3) What is the effect of sun- 
 light upon bacteria ? This is the result of a chemical change 
 in the living matter. 
 
 Problem 3. How direct use may be made of the sun's 
 energy. (a) Cold frame and sun parlor. A large part 
 of the sun's energy is turned into heat when it strikes 
 the earth. Much of this energy radiates back into space, 
 and while it is considered that no energy can be destroyed, 
 yet so far as its utility to us on the earth is concerned, it is 
 lost. The effect of clouds in preventing the direct escape of 
 this energy into space has been touched upon elsewhere. 
 
 The cold frame and sun parlor are other examples of the 
 capture of this energy (Figure 163). In both of these cases 
 
224 
 
 GENERAL SCIENCE 
 
 rays of the sun, in the form of light, pass through the glass ; 
 
 but the heat into which it is changed does not pass through 
 
 the glass easily, and as a result 
 the space inclosed in the glass 
 becomes considerably warmer than 
 
 FIGURE 163.-^- COLD FRAME. - , ., ,. 
 
 the outside air. 
 
 (b) Solar engines. We sometimes wonder what the 
 world will do for its supply of usable energy after the coal 
 and oil deposits have been exhausted. Here we have sug- 
 gested one possible solution. If the energy which is radiating 
 into space could be caught and used, all demands of energy 
 for light, heat, and power would be met. The amount of 
 this energy is enormous; it has been calculated that the 
 amount of energy of 
 the sun's rays falling 
 upon the deck of a 
 ship when the sun 
 is directly overhead, 
 if turned into work 
 without loss, would 
 be sufficient to drive 
 the vessel at a fair 
 rate of speed. 
 
 Efforts have been 
 made to develop a 
 solar engine by which 
 this energy which now 
 is lost to us might be FlGURE 164. SOLAR ENGINE. 
 
 applied to practical uses. In California, by means of great 
 reflectors, the sun's rays were thrown upon the surface of a 
 boiler composed of a coil of blackened copper tubing (Figure 
 164). Sufficient heat was developed to run an engine which 
 
THE SUN AS A SOURCE OF ENERGY 225 
 
 pumped water for irrigation purposes. The cost of the 
 power, however, because of expense of construction and 
 repairs, was much greater than if an ordinary engine had 
 been used. 
 
 Other plants have been constructed in which the sun's 
 rays were permitted to fall upon a series of shallow trays 
 whose sides and bottoms were made of a substance which is 
 a poor conductor of heat. The trays were covered with a 
 double layer of glass which acted in the same way as the 
 glass cover of a cold frame or sun parlor. Explain. A thin 
 layer of water which flowed through the trays absorbed the 
 heat. 
 
 The most successful plants for the direct use of solar energy 
 have been constructed in northern Africa. Suggest a reason 
 for this. Unfortunately, however, regions of this kind are 
 not apt to become centers of industry. Why? This objec- 
 tion is now overcome to a great extent by the development 
 of methods of transmission of electric power. 
 
 Problem 4. How the energy of the sun is maintained. 
 From what has been said in this chapter, what is your con- 
 clusion as to the source of all heat, light, and activity upon 
 the earth ? If the sun should become cold, do you think that 
 the earth would continue to revolve around it, and rotate 
 upon its own axis? Would the moon revolve around the 
 earth? Would there be any seasons? Explain your 
 answers. 
 
 This sun to which we owe so much has a diameter a hun- 
 dred times greater than that of the earth, but it is located 
 92,000,000 miles from us. Evidently the earth receives an 
 extremely small amount of the total energy sent out by the 
 sun. This amount has been calculated to be about 1 part 
 in 2,000,000,000. Although the amount of energy that is 
 
226 GENERAL SCIENCE 
 
 being given off is almost beyond our imagination, yet there 
 seems to be no lessening of it. Scientists believe that the 
 undiminished supply is maintained by the heat and light 
 which are produced as the particles that make up the sun, 
 which is less solid than the earth, are drawn toward its center 
 by the force of gravitation; the energy of gravitation being 
 changed into radiant energy. 
 
 Therefore, it is believed that at present the radiant energy 
 produced by contraction is equal to the amount of energy 
 continually being given off by the sun. Of course, this can- 
 not keep on forever, and in some future period, perhaps 
 millions of years from now, the loss of energy from the sun 
 will exceed the supply resulting from contraction, and the 
 sun with its planets will gradually become dark and cold. 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Make a collection of articles showing the effect of the sun in 
 causing colors to fade. Do any colors seem to be especially resistant 
 to the action of the sun ? 
 
 2. Demonstrate the process of making a photographic negative. 
 
 3. Demonstrate the process of making photographic prints. 
 
 4. Draw plans for something that you want to make, and make blue 
 print 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 in 
 different directions. 
 
 REPORTS 
 
 1. Write a brief history of the development of photography. 
 
 2. Describe efforts that have been made to make direct use of the 
 energy of the sun by means of solar engines. 
 
THE SUN AS A SOURCE OF ENERGY 227 
 
 REFERENCES FOR PROJECT XXI 
 
 1. How to Make Good Pictures, Eastman Kodak Co. Rochester, 
 New York. 
 
 2. Something to Do, Boys, E. A. Foster. W. A. Wilde & Co. 
 
 3. Harper's Machinery Book for Boys, Adams. Harper & Bros. 
 (Sun-power.) 
 
 4. All About Engineering, Knox. Funk & Wagnalls. (Power and 
 Its Source.) 
 
 5. Boy's Book of Inventions, Doubleday, Page & Co. (Harnessing 
 the Sun.) 
 
PROJECT XXII 
 MACHINES 
 
 DURING the earliest periods of which we have any record, 
 the earth was receiving just as much energy from the sun 
 as at present. Little use, however, was made of this energy 
 as compared with the present times. As man discovered 
 the use of tools and then machines, civilization advanced. 
 This is now an age of machinery. How man has multi- 
 plied his ablities by the use of machines is the project we 
 have for solution. 
 
 Before we can understand how machines have enabled 
 man to do much more than he could with his unaided hand, 
 the meaning of several terms which have been used inci- 
 dentally a number of times must be clearly understood. 
 
 Problem 1. What is meant by work and force. We 
 have already defined energy as the power to do work, but just 
 what do we mean by doing work? A man who digs a ditch 
 or shovels coal is doing work. Steam which moves a piston, 
 which in turn operates a pump, which lifts water to a tank 
 on the roof, does work. This water in turn, we know, as it 
 descends may operate a motor which will run a sewing ma- 
 chine or a churn, or may generate electricity which may 
 run a motor, or be changed into heat to be used again in boil- 
 ing water to produce steam. In raising the water, work is 
 being done ; also in the movement of the parts of the sew- 
 ing machine or churn or dynamo, work is being done. 
 
 The essential of all these examples of work is that there is 
 
 228 
 
MACHINES 229 
 
 the movement of a material thing through space against some 
 resistance. What is the resistance that is overcome in 
 lifting the water to the roof? In the sewing machine it is 
 the inertia (the tending of a body to remain in the condi- 
 tion in which it is), the friction of the parts of the machine, 
 and the friction of the needle as it passes through the cloth. 
 In the same way, the electricity in moving the parts of the 
 motor against resistance is doing work. 
 
 A boy who lifts a ten-pound weight from the floor to a 
 table is doing work. If the boy holds the weight he is doing 
 no work, although the muscles of his arms may become very 
 tired. He is, however, exerting sufficient force to resist the 
 force of gravity upon the ten-pound body. Since the body 
 is neither raised nor lowered, the force he is ex- 
 erting must be equal to the amount of the pull 
 of gravity upon it. 
 
 Problem 2. How work and force are meas- 
 ured. We measure forces in terms of pounds 
 or grams of force. The weight of a body is the 
 measure of the force of gravity upon it. Force, 
 however, may be exerted in many directions. 
 An easy method of measuring a force is by the 
 use of a spring balance (Figure 165). Work 
 considers the distance through which the force FIGURE 165. 
 
 is acting. This may be well illustrated in the ~T SPRING 
 . BALANCE. 
 
 following way. 
 
 Experiment. Attach a spring balance to a weight ; pull on the 
 balance until the weight moves, noting the number of pounds of force 
 represented by the pointer. Suppose the pointer registers one pound 
 of force; now pull the weight along one foot. The amount of work 
 which is done is called one foot-pound. If the weight is moved two 
 feet, two foot-pounds of work are performed. If the force necessary 
 
230 GENERAL SCIENCE 
 
 to move a larger weight is two pounds, then the amount of work done 
 in moving it one foot is two foot-pounds. 
 
 Time is not a factor in considering work done. Whether 
 it takes one minute or a year to move an object a certain 
 distance against a uniform resistance, the amount of work 
 done is the same. You know that whether a man takes an 
 hour or two days to shovel a ton of coal from one place to 
 another, the work done is the same. 
 
 The rate of work is measured in the terms of horse power. 
 This unit was chosen and named by James Watt who did so 
 much for the development of the steam engine. A horse 
 power was supposed to be the rate at which an average 
 horse works. A machine of one horse power is able to do 
 33,000 foot-pounds of work per minute or 550 foot-pounds 
 per second. 
 
 Problem 3. Reasons for using machines. A device 
 by which forces are advantageously applied to accomplish 
 work desired is called a machine. Name the machines 
 with which you are most familiar, and state the purpose of 
 each. Explain, as far as possible, how the invention of these 
 machines has resulted in the accomplishment of a greater 
 amount of, or more satisfactory, work. The chief advantages 
 gained in the use of machines may be made clear by a few 
 simple examples. 
 
 (a) What is the advantage of a claw 
 hammer in pulling out a nail (Figure 166) ? 
 Can you exert sufficient force with the 
 fingers to pull the nail ? . Give other exam- 
 ples showing that by use of a machine 
 greater force may be exerted at a parti- 
 cular point. 
 (6) What are the advantages gained in the use of a sew- 
 
MACHINES 231 
 
 ing machine? Why does a country doctor use an auto- 
 mobile instead of a horse and buggy as formerly? Give 
 other examples showing how speed is gained by the use of 
 machines. 
 
 (c) What is the advantage of using a single fixed pulley, 
 as in raising a flag to the top of a flagpole? Give other 
 examples in which an advantage is gained by changing the 
 direction of the force. 
 
 Complex machines. Most machines, such as a sewing 
 machine, typewriter, clock, automobile, or threshing ma- 
 chine, are so complex that, at first sight, to gain an under- 
 standing 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 which 
 can easily be understood. These simple machines are the 
 lever, the wheel and axle, the pulley, the inclined plane, 
 the wedge, and the screw. 
 
 Problem 4. How the lever is used in doing work. 
 1. Let us suppose that a heavy rock must be lifted, and we 
 find that we are unable to do it by hand. By the use of a 
 strong beam or a crowbar (a strong 
 steel bar) in the way indicated in the 
 diagram, the lifting is accomplished 
 
 j.i_ TXJ.I J'/T? ij_ /TV -tr-r\ FIGURE 167. CROWBAR. 
 
 with little difficulty (Figure 167). 
 
 The bar constitutes a lever; the point on which it rests 
 is the fulcrum, and the portions of the bar on either side 
 of the fulcrum are the arms. The amount of force that 
 must be applied may be determined by the following ex- 
 periment. 
 
 Experiment. Use a yard or meter stick as the lever ; use a 10- 
 pound weight, placing the lever on the fulcrum in such a way that 
 one arm is ten times as long as the other. Place small weights on the 
 
232 GENERAL SCIENCE 
 
 end of the long arm until the lever balances on the fulcrum and the 
 weight is lifted from the table. What weights have you placed on the 
 long arm ? Vary the experiment by putting the fulcrum at different 
 places, thus changing the relative length of the arms. 
 
 It will be noted that the force needed to lift the weight 
 is inversely proportional to the length of the arms. There- 
 fore 
 
 effort X its arm = weight or resistance X its arm. 
 
 The slight variations from this are due to the weight of 
 the lever, and the small amount of friction between the 
 lever and fulcrum. Measure the distance 
 through which each arm moves. What are 
 your conclusions? Compare the amount of 
 work done at the end of each 
 arm. 
 
 This experiment is duplicated 
 in the action of the seesaw which 
 most of you have tried. What is FIGURE 169. 
 the position of a heavy boy and SCISSORS. 
 FIGURE "TeS. ^hat ^ a n S n ^ boy? Compare Why is the cord 
 
 -TONGS. ' the distances through which each not cut b ^ th f end of 
 
 . the scissors ? 
 
 Why such a moves. Give all the uses you 
 
 long handle? ^ ^ ^^ Q{ ^ kind (p j g- 
 
 ures 168 and 169). These are called levers of the first class. 
 2. Considering the wheelbarrow as a lever, where is the 
 fulcrum, the resistance or weight, and the effort or power? 
 Why is it easier to lift a bag of flour in a wheelbarrow than 
 directly by hand ? Would making the handles longer cause 
 it to be harder or easier to lift the load ? Why are the handles 
 not made longer ? Give other examples of levers with the 
 same relative arrangement of fulcrum, resistance or weight, 
 and the effort or power (Figure 170). In these levers 
 
MACHINES 233 
 
 compare the length of the power arm and the entire lever. 
 These are called levers of the second class. 
 
 3. Considering a pitchfork or a fishing pole as a lever, 
 where is the fulcrum, the resistance or 
 
 weight, and effort or power? What is 
 the advantage in using such a lever? 
 
 In using a pole 10 feet long, about how FlGURE 170 -- 
 
 NUTCRACKER. 
 
 much force must be used to land a fish 
 
 weighing 5 pounds? What are the advantages and dis- 
 advantages of using a very long handled pitchfork? Give 
 other examples of levers of this kind. They are called levers 
 of the third class. 
 
 4. Explain how the bones of the human body act as levers 
 during walking, running, lifting, and throwing (Figure 171). 
 To which class of levers do they belong ? 
 
 Problem 5. How wheels are used in doing work. 
 Wheels are so commonly used in machines that when most 
 
 of us think of machines and 
 machinery, we also think of 
 wheels. Like the lever, they 
 may be used to gain force at 
 the expense of distance or 
 FIGURE 171. ARM AS A LEVER, speed, or may be used to ob- 
 
 Estimate force necessary to lift a tain speed or distance at the 
 
 10-pound weight. . 
 
 expense of force, or may be 
 
 used to change the direction of the action of a force as in 
 the beveled cogwheels used in transmitting the power of the 
 crank shaft to the inner axle which turns the wheels of an 
 automobile. 
 
 1. The windlass. One of the most easily understood 
 examples of the action of the wheel and axle is the case of 
 the windlass which is used to draw water from a well, raise 
 
234 GENERAL SCIENCE 
 
 the anchor of a ship, or move buildings (Figure 172). Most 
 of us have seen the delivery man on a coal wagon raising 
 the bed of the wagon containing several tons of coal by 
 turning a crank at the side of it. It 
 does not seem difficult, although he is 
 raising a weight many times greater 
 than he would be able to lift unaided. 
 The reason for the use of the crank, 
 which is really only a spoke of a large 
 wheel, may be understood by considering 
 it as a lever. 
 
 FIGURE 172. WELL Comparing this with a lever, what may 
 
 WINDLASS. , . . & . 
 
 be considered to be the fulcrum, what 
 the power arm, and what the weight or resistance arm? 
 Explain the advantage in the use of the windlass, and its 
 modifications in pulling or lifting heavy weights. Explain 
 the ease with which the grains of coffee are crushed by 
 the hand coffee grinder, and with which meat is chopped by 
 the kitchen meat chopper. 
 
 2. Cogwheels and wheels moved by belts. In machines 
 much use is made of cogwheels. With these, as with 
 other simple machines, power may be gained at the ex- 
 pense of speed, or speed may be gained at the expense of 
 power. The high and low speeds of the automobile illus- 
 trate this fact very well. Along the level road the car runs 
 in high gear ; but as soon as it begins to climb a steep hill, 
 the driver, by means of a lever at his side, shifts the gears 
 so that a different cogwheel (a smaller one) engages the 
 crank shaft. The machine now has greater power, but less 
 speed. Most automobiles have three speeds ; first, second, 
 and third, and the force exerted by the machine is in inverse 
 ratio to the speed. 
 
MACHINES 235 
 
 With an apparatus such as shown in the diagram (Figure 
 173), state how much force must be applied on the crank 
 to exert a pull of 2000 pounds. 
 
 In bicycles and in some motor trucks, a chain is used to 
 transfer the power exerted by the pedals upon the sprocket 
 wheel to the axle of the rear 
 drive wheel. In this case as in 
 cases of cogwheels that are in 
 contact or mesh directly, the 
 greater the size of the sprocket 
 wheel, the greater the speed 
 the machine possesses, with, 
 however, correspondingly less 
 power to climb hills. 
 
 Belts are very commonly 
 used in factories to convey FIGURE 1 73. PART OF A DERRICK. 
 power to machines. By a Combination of wheel and axle 
 graduated series of wheels, the 
 
 speed and the force exerted by the machine may be regu- 
 lated. A very simple example is seen in the foot power 
 sewing machine. The heavy rim of the small wheel, be- 
 cause of its inertia (the tendency of a body to remain in 
 the condition of rest or motion in which it is), makes the 
 running of the machine much more even, just as does the 
 flywheel on an automobile. 
 
 Why is the belt wheel on an engine that runs a thresh- 
 ing machine large, while the belt wheel of the threshing 
 machine itself is small? Belts are able to move the wheels 
 because of friction between the belt and the wheel. 
 
 Problem 6. Why pulleys are used. We can raise a 
 window fitted with weights any distance and it stays there. 
 The pulley reduces the friction. If the cord supporting 
 
236 
 
 GENERAL SCIENCE 
 
 FIGURE 174. PLACING HEAVY PIPE IN POSITION. 
 Use of block and tackle in putting in place heavy steel pipe, in con- 
 struction of an aqueduct. The portion of the aqueduct shown here 
 constitutes a siphon by which water is carried over the hill in the 
 background. 
 
 the weight ran through the opening in the window casing, 
 without the pulley, would the window move so easily, and 
 what would be the condition of the rope and the edge of the 
 
MACHINES 
 
 237 
 
 opening in a short time? Frequently, clothes lines extend 
 from windows of an apartment building to a pole or to the 
 opposite side of a courtyard. Explain how the clothes 
 may be hung on the line for its whole length though it is far 
 above the ground. What is the advantage of using a pulley 
 in this case? Explain the importance of a pulley in rais- 
 ing a flag to the top of a pole. If a pulley were not used, 
 how could the flag be placed in position? In these cases 
 where a single fixed pulley is used, is there any gain in force 
 applied or distance covered ? 
 
 Use of pulleys in hoisting heavy objects. We have 
 all seen pianos being raised to the upper windows of build- 
 ings. It seems rather easy, one man being able to raise one, 
 although we know that lifting a piano is difficult even for 
 several men, without some kind of apparatus. In the 
 same way, heavy blocks of stone or steel girders are lifted 
 into place during the construction of a building (Figure 
 174). Observation will show that pulleys are used, usually 
 in the form of what is known as a block 
 and tackle. The value of the pulley can 
 be understood by an examination of the 
 diagrams and by a few experiments. 
 
 Experiments. (a) In both A and B (Figure 
 175) if the weight is 10 pounds, what does the 
 spring balance register? To raise the weight 6 
 inches, how far must the cord to which the spring 
 balance is attached be pulled? In this respect 
 compare work done by pulley with work done 
 by lever, and by wheel and axle. What is the A. 
 purpose of using the fixed pulley? FIGURE 175. 
 
 (6) In the block and tackle represented in Figure 176, how many 
 sets of pulleys are there? How much force must be exerted in using 
 this machine to lift a weight of 300 pounds if the weight of the pulley 
 
238 
 
 GENERAL SCIENCE 
 
 itself is ignored ? How far will the rope have to be pulled to lift the 
 weight 10 feet? In lifting heavy weights, the power rope is usually 
 connected with a wheel and axle. Explain 
 the reason for this. Where have you seen sets 
 of pulleys such as this used ? 
 
 Problem 7. How inclined 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 very 
 steep one? In parks which have hills, 
 how are the paths laid out? In going up 
 mountains, railroads take a very winding 
 or zigzag course instead of going directly 
 up. Wagon and automobile roads are 
 built in the same way where a consider- 
 able elevation is to be reached (Figure 
 177). An automobile which fails to go to 
 the top of a hill at high gear, if the road 
 is one fourth of a mile. long, will go up 
 FIGURE 176. easily at this gear if the road is several 
 
 BLOCK AND TACKLE. ,. , T ,. i_ M 
 
 times longer. In pushing a heavily 
 
 loaded wheelbarrow into a door which is a foot above 
 the ground, is it better to use a board 2 feet long 
 or one 3 feet long, reaching from the doorsill to the ground ? 
 
 What conclusion do you draw from these points to which 
 your attention has been drawn, and from other similar 
 cases which you have observed? Evidently in these cases 
 as in the use of the lever, the windlass, and the pulley, in 
 doing a specified amount of work, the greater the distance 
 through which the force or effort works, the less is the re- 
 quired effort. 
 
 The following experiment will show the relation of effort 
 
MACHINES 
 
 239 
 
 FIGURE 177. ROAD NEAR COLORADO SPRINGS, COLORADO. 
 
 Note the grade necessary if the road ran directly to the point where 
 
 it disappears. 
 
 to length of the plane in raising a weight by the use of the 
 inclined plane. 
 
 Experiment. Take a smooth board 4 feet long ; raise one end of 
 the board 1 foot from the ground (Figure 178). Into a toy wagon 
 put weights until the wagon 
 and its contents weigh 8 pounds ; 
 attach a spring balance to the 
 front of the wagon and by 
 means of it pull the wagon up 
 the incline, taking care to keep 
 the spring balance parallel with 
 the board. What does the 
 spring balance register? (The 
 spring balance will register 
 somewhat too high because of the friction between the wheels and 
 the board.) 
 
 Change the raised end of the board to 2 feet above the ground, and 
 then to 4 feet, making note of the force necessary to pull the weight 
 
 FIGURE 178. 
 
240 
 
 GENERAL SCIENCE 
 
 up the different inclines. Draw your conclusion as to the advantage 
 of the use of the inclined plane. 
 
 Wedges (Figure 179), chisels, knives, and common pins 
 are all really inclined planes. One of the most interesting 
 of modified inclined planes is the screw (Figure 180), 
 which has many uses with which you are familiar. All 
 screws are inclined planes, as may be shown by the fol- 
 lowing experiment. 
 
 FIGURE 179. WEDGE. 
 Is a thick or a thin wedge easier to 
 
 FIGURE 180. SCREW. 
 How much is head of screw 
 lowered in complete 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, begin- 
 ning with the short side parallel with the 
 pencil (Figure 181). What is the ap- 
 pearance of the paper after it is wound 
 around the pencil ? 
 
 You will now 
 understand how a 
 
 FIGURE 181. DEMONSTRATION jackscrew (Figure 
 
 THAT SCREW Is AN INCLINED 10r>x . , 
 
 PLANE 182) is of assistance 
 
 in raising a build- 
 ing or a heavy weight, or how greater pres- 
 sure may be brought to bear by the use 
 of a screw clamp, by the nut on a bolt, 
 or by presses of various kinds in 'which FIGURE 182. JACK- 
 screws are used. The efficiency of the SCREW. 
 
MACHINES 241 
 
 screw as a machine is usually increased by the use of a 
 lever. 
 
 Examine various complex machines and determine in what 
 way these simple machines are combined, and the special 
 advantages of the use of each. \ 
 
 Problem 8. Why machines are not 100 per cent efficient. 
 Ideally, what should be the amount of work obtained from 
 a machine as compared with the amount of work put in? 
 For example, with a block and tackle such as represented 
 in the figure on page 238, how many pounds should you be 
 able to lift by an exertion of a force of 50 pounds? 
 Actually, however, you will be able to lift not more than 
 60 or 75 per cent of this amount. 
 
 In the same way you will find that the work obtained 
 by the use of the inclined plane, cogwheels, etc., is not 
 equal to the amount of work expended. This is due to the 
 fact that there is a certain amount of resistance when one 
 surface slides or rolls over another. This resistance, which 
 is called friction, results because the surfaces are not abso- 
 lutely smooth. Examination with the microscope will show 
 that even the smoothest appearing surface has many small 
 irregularities. Naturally, therefore, when two surfaces 
 rub together, what will happen? 
 
 The efficiency of a machine is the ratio of the work done 
 or energy given out to the work or energy put into it. For 
 example, if in the block and tackle which we have con- 
 sidered before, we pull the power rope 6 feet with a force of 
 50 pounds and are able to lift a maximum weight of 200 
 pounds 1 foot, then the efficiency of the machine may be 
 stated as follows : 
 
 v ffi work done (200X1) 200 2 
 
 Efficlency ~ work put in (50X6) = 300" 3 
 
242 
 
 GENERAL SCIENCE 
 
 After using the pulleys it will be found that they are 
 slightly warmer. What, therefore, has become of energy 
 that does not appear as useful work ? 
 
 Problem 9. How friction may be reduced. 
 
 Experiment. By means of a spring balance, pull an iron block 
 up an inclined plane. Note the pounds of force necessary. Now 
 put grease or heavy oil on the plane and on the lower side of the block. 
 Note again the force necessary to pull the block up the plane. Con- 
 clusion? 
 
 Give examples of the use of oil or grease in machines with 
 which you are familiar. Explain why failure to oil the 
 working parts of a machine will cause them to wear out 
 
 FIGURE 183. "SKIDDING" LOGS ON SNOW. 
 Why cannot this be done if there is no snow ? 
 
 more rapidly; why screws may be screwed into wood more 
 easily if soap is rubbed on them; why failure of the oil 
 supply of an automobile engine causes the engine to become 
 
MACHINES 
 
 243 
 
 overheated; why the wheel on a wagon or automobile will 
 sometimes refuse to turn if it has not been properly oiled. 
 (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 the force re- 
 quired. Now put rollers under the box and again pull it up the same 
 incline. Note the force required. 
 
 Can you skate faster with roller skates fitted with ball 
 
 bearings or with those which have plain bearings ? Is it easier 
 
 to slide a barrel along 
 
 on its end or to roll it? 
 
 All automobile and bicy- 
 cle wheels have roller 
 
 (Figure 184 a) or ball 
 
 (Figure 1846) bearings. 
 
 What is your conclusion 
 
 concerning the friction 
 
 between surfaces in 
 
 Which one rolls Upon FlcuRE ^ROLLER BEAHNOS. 
 
 the other as compared with the friction between surfaces 
 
 that slide upon one another ? Name all the cases you know 
 where the efficiency of machines is in- 
 creased by the substitution of rolling 
 friction for sliding friction. 
 
 Bearings are usually made of differ- 
 ent material from that of the axles that 
 rest upon them. This is done because 
 
 FIGURE 184 b. BALL generally the friction between two sur- 
 faces of different material is less than 
 
 that between surfaces of the same material. 
 
 Problem 10. Is friction ever useful? Since we have 
 
 seen how friction lessens the efficiencv of machines which we 
 
244 GENERAL SCIENCE 
 
 use in accomplishing work, we are likely to conclude that 
 friction is one of our greatest enemies, and that our every- 
 day work and the work of the world would be done much 
 better if all friction were eliminated. Let us see if this 
 conclusion is a correct one. 
 
 Let us suppose that instead of raising a piano to a high 
 window, we are lowering it from that position ; what effect 
 will friction have? What would happen to an automobile 
 going down a mountain side, if the brakes should fail to 
 work? What would happen to an automobile in the traffic 
 of a city, if it had no brakes? It is as important to have the 
 brakes in good working order as to have the engine working 
 well. Brakes do their work by increasing friction. 
 
 A train of cars weighs many hundreds of tons. Because 
 of inertia, a large amount of force is necessary to start it. 
 The energy is supplied by the burning of the coal or oil within 
 the engine, but the energy or force is applied between the 
 drive wheels and the track. If the track should be greased, 
 what would happen? How is friction concerned with the 
 starting of the train ? 
 
 Again, after the train is in motion, inertia tends to keep 
 it in motion : on a level track the engine only needing to 
 furnish sufficient force to overcome the friction between the 
 wheels and the track. If the train is going forty miles an 
 hour, it will be seen that the force necessary to overcome 
 its inertia will be very great. How is this force applied to 
 bring it to a stop? Why is there provision for sprinkling 
 sand on the rails? Why is an automobile apt to skid on 
 a wet or oily pavement? 
 
 Compare walking on an icy pavement with walking on 
 a pavement having no ice. Would you be able to walk if 
 there were no friction between your feet and the pave- 
 
MACHINES 
 
 245 
 
 ment? Why do baseball players wear spikes on their shoes? 
 
 In bringing a vessel alongside a dock, a rope is thrown 
 
 out and wound several times around a strong post (Figure 
 
 FIGURE 185. 
 
 a. TIMBER b. SQUARE OR REEF 
 
 c. Two HALF 
 
 d. BLACKWALL 
 
 HITCH. KNOT. 
 
 HITCHES. 
 
 HITCH. 
 
 The commonest 
 
 Useful because 
 
 Used to secure a 
 
 knot for tying two 
 
 they are easily 
 
 rope to a hook. 
 
 ropes together. Fre- 
 
 made and will 
 
 
 quently used in first 
 
 not slip under 
 
 
 aid bandaging; 
 
 any strain. 
 
 
 Neverslips or jams; 
 
 
 
 easy to untie. 
 
 
 
 185 a, b, c, d). .Suppose the rope and post are so slippery 
 that there is no friction, what will happen? What keeps 
 any knot from slipping? What causes threads in cloth to 
 remain in place ? 
 
 Lumber is fastened together by nails and screws; what 
 prevents them from dropping out? Endeavor to consider 
 the condition of things if friction did not exist. 
 
 Problem 11. Causes of inefficiency of engines. In 
 engines in which the burning of fuel is the source of energy, 
 there are other losses in addition to that due to friction. 
 Suggest some of the ways in which energy in the form of 
 
246 
 
 GENERAL SCIENCE 
 
 heat is lost from a steam engine; also the gasoline engine. 
 It has been estimated that in the steam engine about 95 per 
 cent of the energy of the coal is lost, and that the efficiency of 
 the engine is only about 5 per cent. In the gasoline engine, 
 since no heat escapes in the ashes and smoke and less surface 
 is exposed to be cooled, the loss is considerably less and the 
 efficiency of the engine may be as high as 30 or 35 per cent. 
 In the oxidation of fuel in the muscles of the human body, 
 only about 25 per cent of the energy is transformed into 
 
 working energy ; 75 per cent of it 
 taking the form of heat. Explain 
 why we become so heated while 
 exercising. Suggest how shivering, 
 when we are cold, may be of value 
 to the body. 
 
 Problem 12. The working of 
 the gas engine. The gas engine 
 has become of great importance 
 not only because of its economy 
 of fuel, but also because of its ease 
 of operation and lightness. Its 
 combination of great power with 
 
 light weight has made possible the 
 
 FIGURE 186. MOVEMENTS OF 
 PISTON IN A FOUR-CYCLE EN- marvelous development of the air- 
 
 GINE - plane and automobile. You will 
 
 be interested in looking into the working of the gasoline 
 engine as shown in the motor of an automobile. 
 
 The successive positions of the piston may be seen from 
 the examination of the accompanying diagrams. 
 
 First or suction stroke. The mixture of air and gasoline 
 passes into the cylinder. Note that the gasoline is not a 
 liquid but a gas, having become vaporized in the carburetor. 
 
MACHINES 247 
 
 Second or compression stroke. The mixture of air and 
 gas is compressed. 
 
 Third or power stroke. At the end of the compression 
 stroke, the air and gas mixture is exploded by the spark that 
 passes between the two wires, and the piston is forced down- 
 ward. 
 
 Fourth or exhaust stroke. The piston passes back into 
 the cylinder, forcing out the gases which remain after the 
 explosion. The piston is now in position for the beginning 
 of the suction stroke again. Note the position of the intake 
 and exhaust valves at each stroke. 
 
 Of the four strokes of the piston, how many are power 
 strokes ? 
 
 As four strokes are necessary to complete the cycle (circle), 
 an engine of this kind is known as a four-stroke cycle engine. 
 
 The power developed by the explosion in the cylinder is 
 applied to moving the automobile by having the piston rods 
 connected with the crank shaft, which is made to rotate by 
 the up-and-down stroke of the piston rod. By a series of 
 cogs called gears, the power is applied to the rear axle, caus- 
 ing the wheels to turn. 
 
 Need for a flywheel What causes the engine to run 
 between the times of the power strokes? A one-cylinder 
 engine would not run if a heavy flywheel were not at- 
 tached to a continuation of the crank shaft. The power 
 stroke sets in motion the flywheel which by its rotation 
 carries the crank shaft around until the piston is in position 
 for the next power stroke. 
 
 Advantage of a number of cylinders. The first automo- 
 biles made were equipped with one-cylinder gasoline engines, 
 but now they are fitted with engines having a number of 
 cylinders; four, six, eight, twelve, and in airplane engines 
 
248 
 
 GENERAL SCIENCE 
 
MACHINES 249 
 
 an even larger number. By the use of a number of cylinders, 
 the power is more continuously applied, withjthe result that 
 the engine runs much more steadily. 
 
 Explain how a four-cylinder, four-cycle engine would have 
 four times as many power strokes as a one-cylinder engine. 
 
 How the spark is furnished. When an engine is started, 
 the spark is usually furnished by an electric current generated 
 by a battery. However, after the engine has started, it 
 generates its own electricity by means of a magneto. This 
 explains how an automobile may be started without the 
 use of batteries by allowing it to coast downhill or by turn- 
 ing the crank rod a number of times, sometimes called 
 " spinning on the magneto." It is evident that the mag- 
 neto must be equipped with an apparatus for timing the 
 spark, for if the explosion occurs a fraction of a second too 
 soon or too late, the results will be unsatisfactory. 
 
 Explain why the engine must be started by hand (by 
 cranking) or by a self-starting apparatus. 
 
 Cooling the engine. As the cylinders become very hot 
 during the explosions, they must be cooled. This is usually 
 done by surrounding the cylinders with a space filled with 
 water. The water circulates through the radiator where 
 it is cooled by air drawn through the meshes of the radiator 
 by a fan. Some automobiles are cooled by air without the 
 assistance of water. 
 
 As all parts must slide easily in order to avoid loss of 
 power and overheating by friction, there must be a sys- 
 tem by which the engine automatically oils itself. 
 
250 GENERAL SCIENCE 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Plan and carry out a series of demonstrations to illustrate the 
 various uses of levers. 
 
 2. Construct a windlass and demonstrate its use to the class. 
 
 3. Construct a set of cogwheels by which power is gained at the 
 expense of speed. 
 
 .4. Construct a set of cogwheels by which speed is gained at the 
 expense of power. 
 
 5. Demonstrate the use of cogs in several machines. Calculate 
 the kind and amount of advantage gained. 
 
 6. Construct a toy machine in which belts are used. 
 
 7. Construct several sets of pulleys and demonstrate their use. 
 
 8. Construct an inclined plane and show its value. 
 
 9. Work o'ut the different kinds of simple machines used in the 
 construction of the sewing machine or other machines familiar to you. 
 
 10. Work out the efficiency of a number of machines. 
 
 11. Demonstrate the various kinds of knots described in the Manual 
 of the Boy Scouts of America. 
 
 12. Make a simple cylinder with piston to illustrate the action of 
 the piston of an automobile cylinder. 
 
 REPORTS 
 
 1. How things that were done by hand a hundred years ago are 
 now performed by machines. 
 
 2. How the power developed by the automobile engine is trans- 
 mitted to the drive wheels. 
 
 REFERENCES FOR PROJECT XXII 
 
 1. Great Inventors and Their Inventions, Bachman. American 
 Book Company. 
 
 2. Harper's Machinery Book for Boys, Adams. Harper & Bros. 
 
 3. Mechanics of Sewing Machines. Singer Sewing Machine Com- 
 pany. 
 
 4. Stories of Useful Inventions, S. E. Forman. Century Company. 
 
 5. The Story of Agriculture in the United States, Sanford. D. C. 
 Heath & Co. 
 
MACHINES 251 
 
 6. The Story of Iron and Steel, Smith. D. Appleton & Co. 
 
 7. The Romance of Modern Mechanism, Williams. J. B. Lippin- 
 cott Company. 
 
 8. Stories of Inventors, Doubleday. Doubleday, Page & Co. 
 (Automobiles.) 
 
 9. The Romance of Modern Locomotion, Williams. J. B. Lip- 
 pincott Company. 
 
 10. Historic Inventions, Holland. Geo. W. Jacobs, Philadelphia. 
 
 11. The Boy Mechanics. Chicago Popular Mechanics Company. 
 
PROJECT XXIII 
 ELECTRICITY AND MODERN LIFE 
 
 IF a man who lived a century ago should visit us, he would 
 be much surprised at the many changes which have occurred 
 since his tune. Especially would he be amazed at those 
 inventions which depend upon electrical energy. Elec- 
 tricity was being studied by some of the scientists of his 
 time, but probably none of them had the faintest idea of the 
 practical importance that it would have. 
 
 FIGURE 188. GRAND CENTRAL TERMINAL, NEW YORK CITY, BEFORE 
 ELECTRIFICATION. 
 
 The first electric motor, a very inefficient one, was con- 
 structed in 1838, and it was not until 1871 that really efficient 
 motors and dynamos were used. Electric lighting on a 
 commercial scale was used for the first time in Paris and 
 London in 1877. Think of the many things which this 
 visitor from a previous century would see for the first time. 
 Make a list of the appliances of present day life which make 
 use of electrical energy. 
 
 252 
 
ELECTRICITY AND MODERN LIFE 253 
 
 Problem 1. How the electric bell rings. One of the 
 best methods of beginning the study of the way in which we 
 make use of electrical energy is by an examination of the 
 electric bell, which not only is familiar to us all, but il- 
 lustrates many rather simple things concerning electricity 
 which have very wide application. You already know a 
 number of facts about the bell and the conditions necessary 
 for its working. 
 
 FIGURE 189. GRAND CENTRAL TERMINAL, NEW YORK CITY, AFTER 
 ELECTRIFICATION. 
 
 How is the bell connected with the place from which it 
 may be rung, for example, the front door? How many 
 wires run to the bell ? Are the metal wires bare or covered ? 
 Are the wires covered where they are fastened to the bell? 
 Of what metal are the wires made ? To ring the bell, what 
 must you do to the push button ? This brings together the 
 ends of the two wires so that there is a continuous metal 
 circuit beginning at one side of the bell and ending at the 
 other. 
 
 Will the bell ring if the wire is broken at any place? 
 Most of you know that the wires are usually connected with 
 one or more batteries which in some way generate electricity, 
 and that the batteries must occasionally be renewed or re- 
 placed by fresh ones. If you have removed the small metal 
 
254 
 
 GENERAL SCIENCE 
 
 covering just above or below the bell itself, you have noticed 
 two small spools of wire lying side by side. Each is made 
 of a rod of iron, around which is wound some covered copper 
 wire. 
 
 When the current from the batteries passes through 
 this copper wire, it magnetizes (makes a magnet of) the 
 rod of iron. One end of the wire is 
 connected with one of the binding 
 posts. At one end of the spools or 
 coils is an iron bar called an arma- 
 ture held in position by a spring, 
 so that when the circuit is open 
 (that is, when the push button is 
 not pressed down bringing the two 
 ends of the wire into contact) it does 
 not quite touch the iron centers of 
 the spools. 
 
 From the diagram (Figure 190) 
 note the course taken by the current 
 of electricity in passing from the wire 
 connected with one binding post to 
 the wire connected with the other. Note also that the 
 clapper is connected with the armature. When the circuit 
 is closed, it will be seen that the coils are magnetized and 
 the armature is drawn toward the coils, causing the clapper 
 to. strike the bell. 
 
 The pulling of the armature toward the coils breaks the 
 circuit. Immediately the coils lose their power to at- 
 tract the armature, which springs back and closes the cir- 
 cuit. Again the coils are able to attract the armature, and 
 the clapper strikes the bell. This breaking and making 
 of the circuit continues as long as pressure is maintained 
 on the push button. 
 
 FIGURE 190. DIREC- 
 TION OF CURRENT TH-ROUGH 
 AN ELECTRIC BELL. 
 
ELECTRICITY AND MODERN LIFE 
 
 255 
 
 Problem 2. How magnets are used. The current of 
 electricity passing through the coil of wire gives the iron 
 rod around which it is wound the power of a magnet. This 
 kind of magnet is tem- 
 porary, possessing its 
 power only when the 
 current of electricity is 
 passing through the 
 wires. For this reason 
 it is called an electro- 
 magnet (Figure 191). 
 Electromagnets are used FlGURE ' 
 
 in many electrical devices (Figure 192) ; among which are 
 telephone, telegraph, and wireless apparatus, ignition sys- 
 
 FIGURE 192. DYNAMO ATTACHED TO AN AMBULANCE. 
 
 The current generated by the dynamo produces an electro-magnet 
 
 which is used to remove pieces of metal from eyes. 
 
256 
 
 GENERAL SCIENCE 
 
 tern of automobiles, and in electric motors and dynamos. 
 Large electro-magnets attached to cranes are used to 
 
 
 ^v^jHMSli 
 
 FIGURE 193. ARRANGEMENT OF IRON FILINGS BETWEEN POLES OF A MAGNET. 
 
 lift masses of iron which may be dropped at the desired 
 spot by simply breaking the circuit. 
 
 The action of permanent magnets may be observed by 
 experimenting with a common horseshoe or bar magnet. 
 
 Experiment. Place the magnet under a piece of paper over which 
 iron filings have been scattered. Gently tap the paper and observe 
 the position taken by the filings (Figure 193). 
 
 Experiment. Rub a needle along the magnet and move it near 
 some fine iron filings. What has happened to the needle? Suspend 
 the needle horizontally by an untwisted silk thread. Move one end 
 (pole) of the magnet near one end of the needle. Reverse the magnet 
 and approach the same end of the needle with the other pole of the 
 magnet. What is the result ? Allow the needle to remain suspended 
 
ELECTRICITY AND MODERN LIFE 
 
 257 
 
 undisturbed. What position does it take ? The earth itself is a great 
 magnet ; one magnetic pole being near the geographic north pole, and 
 the other near the geographic south pole. A magnetic needle, therefore, 
 which swings freely will take an ap- 
 proximate north and south position 
 (Figure 194). What practical use is 
 made of this fact? The use of the 
 compass has had a great influence 
 upon the development of navigation, - 
 
 Problem 3. How chemical |j| 
 energy may be changed into 
 electrical energy. The elec- 
 trical energy which caused 
 
 ,i . . . ,, , FIGURE 194. MAGNETIC NEEDLE. 
 
 the ringing of the bell was 
 
 generated in a battery cell by a chemical action. The 
 
 FIGURE 195. FIRST OF ALL ELECTRIC BATTERIES PREPARED BY VOLTA, 
 
 A.D. 1800. 
 
 At the right is the famous Voltaic pile, consisting of a series of alternate 
 disks of zinc and copper separated by moistened felt. At the left each 
 cell consists of a plate of copper and one of zinc immersed in brine. 
 
 simplest form of a cell of this kind, called the voltaic cell, 
 was invented in 1800 by Alessandro Volta, a professor in 
 
258 GENERAL SCIENCE 
 
 an Italian University (Figure 195). You can easily make 
 a cell of this kind. 
 
 Experiment. In a jar containing dilute sulphuric acid place two 
 metal plates ; one of zinc and the other of copper. If each plate (called 
 an electrode) is connected by means of a wire with the binding posts of 
 an electric bell, the bell will ring. After a few minutes the bell ceases 
 to ring although the circuit has not been broken. 
 
 An examination of the copper plate will show that it is 
 covered with bubbles of a gas, so that the acid is not able to 
 touch it. The battery is now said to be polarized. If the 
 bubbles are rubbed off, the bell will again begin to ring. 
 Various methods have been used to 
 prevent this polarization. One method 
 is illustrated by the gravity cells. In 
 this cell, the copper is placed at the 
 bottom of the jar in a solution of 
 copper sulphate, (blue vitriol) ; and 
 the zinc near the top in weak sul- 
 phuric acid. The blue vitriol solu- 
 tion is heavier than the acid, and 
 remains at the bottom; hence the 
 FlGURE CEuT 01 ^ 1 ^ Imme ' gravity cell (Figure 196). 
 
 A solution^! zinc sul- The blue vitrio1 Or CO PP 6r suI P hate 
 
 phate. B, solution of solution prevents the gas (hydrogen) 
 ' from Caching the copper plate, but 
 it causes copper to separate from 
 the solution and be deposited on the copper plate as a 
 bright layer. 
 
 In the Daniell cell, the zinc and sulphuric acid are in a 
 porous cup which is placed in a jar containing the copper 
 and blue vitriol solution (Figure 197). In another form of 
 cell, one electrode is carbon and the other zinc, and the 
 
ELECTRICITY AND MODERN LIFE 
 
 259 
 
 FIGURE 197. DANIELL 
 CELL. 
 
 liquid in which they are immersed is a strong solution of 
 
 sal ammoniac (ammonium chloride). 
 
 The dry cell, which for most pur- 
 poses is more convenient than any 
 
 other, is like the last cell mentioned, 
 
 except that, instead of a jar, a cup or 
 
 cylinder made of zinc is used as the 
 
 container, and this forms one electrode 
 
 (Figure 198). Then instead of sal 
 
 ammoniac solution being used, a moist 
 
 paste saturated with sal ammoniac and 
 
 usually containing manganese dioxide 
 
 to prevent polarization, is packed be- 
 tween the carbon and this zinc outer 
 
 wall. 
 Problem 4. How electricity is measured : volts, amperes, 
 
 kilowatts. In all the cells discussed, you have noticed that 
 
 there has been greater chemical action at the zinc electrode 
 
 than at the other. This gives rise 
 to what may be called an electri- 
 cal pressure or electromotive force 
 (E. M. F.) and causes a current 
 somewhat as differences in water 
 pressure will produce a current. 
 This current passes from the zinc 
 to the other electrode within the 
 cell, and from the carbon to the 
 zinc electrode through the wire 
 circuit. 
 
 The unit of electromotive force 
 is called the volt. It is approxi- 
 FIGURE 198. DRY CELL, mately the electromotive force of 
 
260 GENERAL SCIENCE 
 
 the simple voltaic cell. By connecting the several cells in 
 series, that is, by connecting the carbon of one cell with 
 the zinc electrode of the next one, etc., the voltage or elec- 
 tromotive force of the battery of cells will be equal to the 
 sum of the electromotive forces of the individual cells. 
 The electrical pressure is measured by an instrument called 
 the voltmeter. 
 
 The pressure in a water pipe may be very great, but yet 
 there may be very little, if any, flow of water because 
 the faucet opening is quite small. On the other hand, the 
 pressure may be relatively low with a large flow, providing 
 there is nothing to obstruct the current. In the same way, 
 the amount of electricity that passes through a wire de- 
 pends 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 electricity, who worked during the 
 early part of the nineteenth century. 
 
 The unit of current is called an ampere, in honor of another 
 great scientist who was contemporary with Volta and Ohm. 
 The relation of current, electromotive force, and resistance 
 to flow is expressed in Ohm's law : 
 
 electromotive force Volts ~, 
 
 Current = : or Amperes = or Ohms = 
 
 resistance Ohms 
 
 Volts 
 
 Amperes 
 
 The instrument used to measure the current is called an 
 ammeter. A rheostat is a device by which the amount of 
 resistance may be controlled. Just as the amount of work 
 done by water power depends upon the pressure and the 
 amount of water, so the work done by an electric current 
 may be determined by multiplying the voltage (pressure) 
 by the amperage (amount of electricity). 
 
ELECTRICITY AND MODERN LIFE 
 
 261 
 
 The unit of work,' called a watt in honor of James Watt, 
 is the work done by one ampere having the voltage of 1. 
 Since this is such a small unit, the kilowatt, which is equal 
 to 1000 watts, is more often used. Electrical energy is 
 charged for by the kilowatt hour, which is the energy fur- 
 nished by a current providing in one hour one kilowatt of 
 work. A kilowatt hour is equal to about Ij horsepower 
 (hours), and in New York City costs from 4| to 7 cents. 
 
 FIGURE 199. STRUCTURE OF AN INDUCTION COIL. 
 P, P, primary wire connected with battery. 5, S, ends of sec- 
 ondary coil between which sparks leap. F, iron block which is 
 pulled back when iron core is magnetized, thus breaking the cir- 
 cuit. The iron core is then demagnetized and the spring h pulls 
 back the iron block F closing the circuit again. Note that there 
 are more turns of the secondary than of the primary. 
 
 Problem 5. Use of induction coil in wireless telegraphy 
 and in the production of spark in gasoline engine. By 
 means of a spark coil, a sufficiently high voltage is produced 
 to cause the current to leap across an air space, forming a 
 spark. It consists of a central iron core, surrounded by a 
 coil of heavy wire called the primary, and by a second outside 
 coil, the secondary (Figure 199). The primary is connected 
 with a few cells of a battery, and with an interrupter as in 
 the case of the electric bell. 
 
262 
 
 GENERAL SCIENCE 
 
 It is by the use of the induction coil that the sparks are 
 produced which explode the gasoline vapor in the cylinders 
 of a gasoline engine, and which send out the electric waves 
 of the wireless telegraph. An Induction coil is also an 
 essential part of the transmitting apparatus of a long dis- 
 tance telephone. 
 
 In the wireless telegraph, the electric waves act upon the 
 antenna, which is made of a number of parallel wires sus- 
 pended on insulating supports from a mast or tower, and con- 
 nected by a single wire with a rod on one side of the spark 
 
 FIGURE 200. U. S. ARMY WIRELESS OPERATORS RECEIVING MESSAGES 
 FROM AN AIRPLANE, TOURS, FRANCE. 
 
 gap. Electric waves pass out into surrounding space from 
 the antenna and cause similar electric waves in the antenna 
 of the receiving station, which by means of pieces of ap- 
 paratus called crystal detectors or audion detectors, are 
 made susceptible of being detected by a telephone receiver. 
 
 Problem 6. How mechanical energy is changed into 
 electrical energy by the dynamo. In our discussion of 
 
ELECTRICITY AND MODERN LIFE 
 
 263 
 
 oxidation of fuel, the use of water power, etc., we under- 
 stood that heat energy and mechanical energy may be trans- 
 formed into electrical energy. This is done by the dynamo, 
 a machine complicated in 
 appearance, which, how- 
 ever, in its simplest form 
 is not difficult to under- 
 stand. 
 
 You will it call that in 
 
 the electric bell a current FiouRE.20i.-A SIMPLE DYNAMO 
 of electricity passing N, north pole of a permanent magnet. 
 through the coil of wire, 5 ' south P le of a P erm *nent magnet. 
 
 . . , G, point of contact of brushes for carrying 
 
 wound around a piece of curren t into outside circuit. 
 iron, caused the iron to 
 
 become a magnet. In generating a current of electricity 
 by a dynamo, the reverse occurs. If a coil of wire is 
 rotated continuously between the poles of a strong mag- 
 net, an electric current is produced in the coil of wire 
 (Figure 201). The effect of a magnet in producing an 
 
 electric current in a 
 coil of wire may be 
 shown by the follow- 
 ing experiment- 
 Experiment. Move a 
 magnet in and out of a 
 coil of wire, the ends of 
 which are attached to a 
 FIGURE 202. PRINCIPLE OF DYNAMO. 
 
 Current produced by thrusting magnet into a 
 coil of wire. 
 
 galvanometer (an instru- 
 ment for detecting cur- 
 rents of electricity (Figure 
 202) . It will be noted that 
 
 trie current is produced only when the magnet is in motion, and that 
 the direction of the current is in one direction when the magnet is 
 pushed into the coil, and in the opposite direction when it is pulled out. 
 
264 
 
 GENERAL SCIENCE 
 
 The essential parts of a dynamo are (1) a rotary coil 
 (armature), (2) a stationary magnet (field magnet), and 
 (3) a sliding contact device for carrying the current from 
 the armature to the external circuit. The efficiency of the 
 
 dynamo is increased by the 
 use of electro-magnets as field 
 magnets. Large dynamos 
 may develop electrical power 
 equal to 8000 or 10,000 
 horse power. For some pur- 
 poses an alternating current 
 
 FIGURE 203. A SIMPLE COM- 
 MUTATOR. 
 
 a and b, two halves of a split tube is satisfactory, but for other 
 connected with the two ends of the 
 coil of the armature. + and , 
 two brushes connected with the ex- 
 ternal circuit L, L. S, shaft upon 
 which a and b are mounted. 
 
 purposes 
 rent in 
 
 a continuous cur- 
 one direction is 
 necessary. By means of an 
 attachment called a commu- 
 tator (Figure 203), the alternating current of the dynamo 
 may be changed to a direct current. 
 
 FIGURE 204. USE OF ELECTRIC MOTOR IN RUNNING SEWING MACHINE. 
 
ELECTRICITY AND MODERN LIFE 
 
 265 
 
 Problem 7. How electrical energy is changed into me- 
 chanical energy by the electric motor. A motor (Figure 
 204) by which the electrical energy developed by the dy- 
 namo is changed back into mechanical energy is really the 
 reverse of a dynamo ; a current passes both into the field 
 magnets and the armature, resulting in a rotation of the 
 armature, which by means of belts, etc., may set machinery 
 in motion. The principle of the motor may be illustrated 
 in the following way. 
 
 Experiment. Suspend a loop or a coil of wire between the poles 
 of a magnet. It will hang in any position in which it is placed. If 
 now a current of electricity is passed through it, the coil, as in the 
 case of the electric bell coil, becomes a magnet and takes a definite 
 position with reference to the field magnets. If the current is re- 
 versed, the coil swings around 180. 
 
 FIGURE 205. EXPERIMENTAL ILLUSTRATION OF PRINCIPLE OF THE MOTOR. 
 
 The dotted line represents the position of the wire as current passes 
 through it. 
 
 Figure 205 represents the influence of a magnet upon a 
 wire through which a current of electricity is passing. 
 It can easily be understood how the armature will con- 
 
266 
 
 GENERAL SCIENCE 
 
 tinue its rotation, if the current is reversed at proper in- 
 tervals of time. 
 
 Problem 8. How electroplating and electrotyping are 
 done. It will be recalled that in the gravity cell, in which 
 there was a solution of copper sulphate, a layer of copper 
 was deposited on the copper electrode. By this process 
 the electrode was really copper-plated. Copper-plate some 
 object such as a piece of tin or nickel as follows. 
 
 Experiment. Suspend in a jar of copper sulphate the object to 
 be plated, and a piece of copper; connect the former with the nega- 
 tive and the latter with the positive terminal (pole) of a battery. 
 
 Silver, gold, or nickel plating may be done in a similar 
 way. Name various objects which have been plated with a 
 
 metal. In each case, state the 
 reason for doing so. 
 
 Electrotyping. This power of 
 the electric current to cause a 
 layer of metal to be formed on 
 an object is made use of in 
 printing. This book and nearly 
 all others are printed from elec- 
 
 FIGURE 206. SILVER PLATING, trotype plates. The type is set 
 .solution of up and a mold of it is taken in 
 wax. The type may now be 
 taken down and used again. The 
 mold is coated with graphite (a form of carbon) to make 
 it a conductor, and is immersed in a bath of copper sul- 
 phate, in which is suspended a piece of pure copper. 
 
 A current of electricity is now sent through the liquid 
 from the copper to the graphite-covered wax plate and in this 
 way a layer of copper is deposited on the wax plate. The 
 
 a, bar of silver, 
 a silver compound, c, objects 
 to be plated. 
 
ELECTRICITY AND MODERN LIFE 
 
 267 
 
 wax is replaced then by metal to give strength to the mold. 
 This electrotype plate, which is an exact reproduction of the 
 original page of type, may be conveniently used to print 
 thousands of copies, whereas the type is awkward to handle 
 and soon wears down. 
 
 In the printing of 
 newspapers a much 
 quicker method is 
 necessary. A ma- 
 chine called the lino- 
 type is used. The 
 operator, by manip- 
 ulating the keys of 
 a keyboard very 
 much as in using the 
 typewriter, sets the 
 type. The type is 
 then pressed against 
 melted metal, and an 
 imprint made which 
 is used in printing 
 the paper. 
 
 The electric current 
 may also be used in 
 refining metals ; those 
 
 refined in this way FIGURE 207. -AN ELECTROTYPE. 
 
 being the purest ob- Photograph of the plate from which a page 
 tainable. of a book is printed. 
 
 Problem 9. How heat is produced by electricity. 
 Name various household appliances in which heat is pro- 
 duced by an electric current. The way in which this is 
 done is illustrated as follows. 
 
268 
 
 GENERAL SCIENCE 
 
 Experiment. Make a circuit of several electric cells and a copper 
 wire of the thickness generally used in making connections. Now 
 replace a small portion of the copper wire with fine iron or German 
 silver wire wound around the bulb of a thermometer. What is the 
 result ? 
 
 The resistance of small wires to the current of electricity 
 is much greater than the resistance of large wires, and the 
 electrical energy is changed into heat energy. This is 
 
 similar to the way that 
 mechanical energy when 
 resisted by friction is 
 changed into heat energy. 
 All the electric appliances 
 you have named, such as 
 flatirons, toasters, curling- 
 iron heaters, electric chaf- 
 ing dishes, electric stoves, 
 foot warmers, car heaters, 
 bacteriological incubators 
 and sterilizers, are heated 
 in this way (Figure 208). 
 
 Industrially, the changing of electrical energy into heat 
 energy has made possible many important processes. An 
 intense heat (about 3000 C.) is developed in the electric 
 furnace, due to resistance offered to the passage of the cur- 
 rent. Some of the uses to which the electric furnace has 
 been put, because of the intense heat generated, are the pro- 
 duction of carborundum, the most important abrasive used ; 
 artificial graphite, used in the manufacture of electrodes 
 and lubricants ; and smelting, the refining of metals. 
 
 Problem 10. How electric lights are produced. Ob- 
 servation of an incandescent electric light lamp will show 
 
 FIGURE 208. ELECTRIC FLATIRON. 
 
 E, wires offering great resistance to 
 electric current. A, wooden handle. 
 
ELECTRICITY AND MODERN LIFE 
 
 269 
 
 that there is within the bulb a very slender filament, which 
 becomes white-hot when the current is turned on. Evi- 
 dently the condition here is similar to 
 that which we observed in obtaining 
 heat from the electric current. Would 
 you consider the resistance to the cur- 
 rent to be greater or less in the lamp 
 than in the wire of a heating device? 
 The wires in an electric stove would meltj 
 or become oxidized if raised to such a FIGURE 209. CARBON 
 high temperature. What, therefore, do FlLAMENT LAMP - 
 you consider must have been the great problem in 
 the development of the incandescent lamp? 
 The bulb contains no air. What is the 
 advantage of this ? Very few substances 
 have been found capable of carrying the 
 current and yet able to remain in a solid 
 form at the temperature necessary for the 
 production of light. For many years spe- 
 cially treated carbon filaments were used (Fig- 
 FIGURE 210. ure 209). More recently, metallic filaments 
 have very largely replaced the carbon ones; 
 the most satisfactory filament being made 
 of tungsten (Figure 210). It uses only about one third as 
 much .electricity as the 
 carbon to produce the 
 same amount of light 
 (Figure 211). 
 
 The name which has FIGURE 211. AMOUNT OF LIGHT GIVEN 
 . , j BY DIFFERENT INCANDESCENT LAMPS. 
 
 been the most closely 
 
 . i |T . The length of the arrows represents the 
 
 associated With the im- intensit y O f light given off in different 
 provement of the incan- directions. 
 
 TUNGSTEN FILA- 
 MENT LAMP. 
 
 Gem lamp 
 
 Tungsten Lamp 
 
 Carbon Lamp 
 
270 GENERAL SCIENCE 
 
 descent lamp, as well as with almost every improvement 
 in the application of electricity, is Thomas A. Edison. 
 
 The voltage of the electricity in the main distributing 
 wires is very high. You will find, however, that the electric 
 light bulbs in your house are probably labeled 110 volts. 
 A current of much higher voltage is dangerous to human 
 life. You have probably noticed on some electric light poles 
 iron boxes from which wires pass to the neighboring houses. 
 These boxes are called transformers, and in them the voltage 
 is changed from 1100 or 2200 volts to 110 volts. Some- 
 times transformers are used in the house to still further re- 
 duce the voltage of a current used for ringing electric bells, 
 running electric toys, etc. 
 
 To prevent danger from fire, the wires 
 used in a house must be of sufficiently large 
 size to carry the current without being ap- 
 preciably heated, and they must be inclosed 
 FIGURE 212. in metal conduits or tubes in walls and par- 
 
 FusE> titions.. 
 
 An amount of electricity which might prove harmful is pre- 
 vented from passing into a wire by means of fuses (Figure 
 212), which are pieces of metal 
 of a low melting point inserted 
 in the circuit. When the cur- 
 rent becomes too strong the 
 fuse melts and automatically 
 breaks the circuit. Wires must 
 all be carefully . insulated ; that 
 is, covered with a material 
 which will not conduct an elec- 
 tric current. FIGURE 2 13 POSITION OF CAR- 
 The arc light, which is of very SONS IN AN ARC LIGHT. 
 
ELECTRICITY AND MODERN LIFE 271 
 
 high candle-power, may be understood from a demonstration 
 of the lamps of a projection lantern. It will be noted that 
 there are two carbons (Figure 213), which are first brought 
 into contact to complete the circuit. When they are pulled 
 apart, the circuit is not broken but the current continues 
 to flow across the space, producing the arc. The (+) 
 carbon becomes hollowed out, and the ( ) carbon be- 
 comes pointed, apparently by the addition of particles 
 of carbon to it. It seems quite clear that particles of 
 carbon jump across the gap between the two carbons. 
 
 Problem 11. How the " storage battery " is used. 
 Storage batteries have come into common use. Most of 
 you will know of some instances of their use. Find out 
 as many examples as you can of the use of storage bat- 
 teries. The following experiment will help you to under- 
 stand a storage battery. 
 
 Experiment. Suspend two pieces of lead in a very dilute (1-40) so- 
 lution of sulphuric acid in a battery jar. Connect the lead plates with 
 a battery of three or more dry cells. Do you notice signs of any ac- 
 tivity in the battery jar ? After allowing current to pass through the 
 lead plates for about five minutes, disconnect the dry cells. 
 
 Connect the wires attached to the lead plates to an electric bell. 
 Result? 
 
 From the facts that one of the plates became brown and 
 gas is given off from the plates during the process of charg- 
 ing, what kind of a change do you think is taking place? 
 The electric current in passing through the lead plates and the 
 sulphuric acid causes changes somewhat like the ones we 
 observed in electroplating. The effect is to make these 
 plates unlike each other in a way similar to that in which 
 the zinc plate is unlike the copper plate in the simple voltaic 
 cell. When the two changed lead plates are connected 
 
272 
 
 GENERAL SCIENCE 
 
 with an electric bell, the bell rings, showing that the chemi- 
 cal energy which has been derived from electrical energy 
 has now been changed back again into electrical energy. 
 
 About 75 per cent of the electrical energy passed into 
 a storage cell may be recovered again as electrical energy. 
 
 FILLING PLUG 
 , VALVE : 
 
 ELECTROLYTE: 
 
 C E LL Co N N tQTO R 
 
 SCALING NUT 
 POST GASKET 
 NEGATIVE POST 
 NEGATIVE STRAP 
 
 WOOD SEPARATOR 
 
 POSITIVE PLATE 
 
 NEGATIVE Pi-ATE 
 RuBBERiJAR 
 
 WOOD CASE 
 
 FIGURE 214. STORAGE BATTERY DISSECTED TO SHOW CONSTRUCTION. 
 
 Heat developed during the process of charging and dis- 
 charging the cell accounts for the loss. 
 
 Lighter storage cells have nickel and iron plates, but the 
 principle of their action is the same. Electrical energy is 
 changed into chemical energy which is changed in turn again 
 into electrical energy when the cell is discharged. Com- 
 mercial storage cells are made of a large number of plates 
 
ELECTRICITY AND MODERN LIFE 273 
 
 (Figure 214). All the negative plates are connected with 
 one wire and all the positive plates with another wire. 
 While the voltage remains the same, with the increased 
 surface of plates the amperage is increased. 
 
 Problem 12. How lightning is produced. Lightning 
 is an instantaneous discharge of electricity of high voltage 
 between a cloud and some object on the earth or between 
 two clouds. If on a cold day you scuffle over the carpet and 
 then hold your knuckle to the gas fixture or even to the 
 cheek of another person, a spark will be produced. Because 
 of friction between your feet and the carpet, electricity 
 called static electricity has been generated. Since cold, 
 dry air is a poor conductor, the electricity remains upon 
 your body. When, however, your hand is brought so near 
 the gas fixture that the voltage of the electricity is sufficient 
 to cause it to leap through the dry air, the spark results. 
 
 In the formation of a storm cloud, large quantities of 
 static electricity are generated and condensed on the drops 
 of moisture. When the voltage becomes sufficiently great, 
 the electricity is discharged to the earth or to a neighboring 
 cloud. Benjamin Franklin's experiment in which he drew 
 lightning from the clouds is a very interesting one. He 
 flew a kite into the thunderclouds, using a string which was 
 a fair conductor of electricity, to which .was attached at its 
 lower end a metal key. Near the lower end of this string 
 was a silk cord (a very poor conductor) which he held in his 
 hand. Sparks passed between the key and the ground. 
 
 The crackling of the fur of a cat when stroked, and of 
 hair when combed with a rubber comb, especially on a 
 clear cold day; and the tendency of tissue paper, when 
 rubbed, to stick to the wall, are common examples of the 
 manifestations of static electricity resulting from friction. 
 
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 
 number of objects. 
 
 4. Endeavor to 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 ah electric motor. 
 
 9. Construct a simple electric heater. 
 
 10. Calculate the cost per hour of the different electric lights in 
 your home or in your father's store. 
 
 REPORTS 
 
 1. The story of the discovery and development of the electric 
 light. 
 
 2. Give a sketch of the life of Thomas A. Edison. 
 
 3. Benjamin Franklin and electricity. 
 
 4. The making of electroplates from which books are printed. 
 
 5. 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, Editor. 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, Double- 
 day, Page & Co. 
 
ELECTRICITY AND MODERN LIFE 275 
 
 8. The Story of Great Inventions, E. E. Burns. Harper & Bros. 
 (Electric Furnace.) 
 
 9. The Book of Wireless, A. F. Collins. D. Appleton & Co. (Tele- 
 graph, Telephone.) 
 
 10. Book of Electricity, A. F. Collins. D. Appleton & Co. 
 
 11. Harper's Everyday Electricity, Shafer. Harper & Bros. 
 
 12. Wonders of Science, Houghton Mifflin Company. (The Mak- 
 ing of a Book.) 
 
 13. Great Inventions and Discoveries, Piercy. Chas. E. Merrill 
 Company. (Telegraph.) 
 
 14. Stories of Inventors, Doubleday. Doubleday, Page & Co. 
 (Telephone.) 
 
 15. The Boy's Life of Edison, Meadowcraft. Harper & Bros. 
 
 16. Boy's Book of Inventions. Doubleday, Page & Co. (Elec- 
 tric Furnace, Electric Light, etc.) 
 
 17. The Wireless Man, Collins. Century Company, Philadelphia. 
 
 18. Historic Inventions, Holland. Geo. W. Jacobs, Phila. (Bell, 
 Edison, Marconi.) 
 
 19. American Inventions and Inventors, Mowry. Silver, Burdett 
 & Co. (Telegraph, Telephone, etc.) 
 
 20. Things a Boy Should Know about Electricity. T. M. St. 
 John, New York. 
 
PROJECT XXIV 
 RELATION OF LIGHT TO OUR ABILITY TO SEE THINGS 
 
 WE have already considered the great source of our light 
 and the ways in which we produce light. Briefly review 
 this. We also understand the importance of light as energy, 
 and its relation to other forms of energy. Briefly review 
 your knowledge of this. In this chapter we shall be con- 
 cerned chiefly with the relation of light to our ability to see 
 things. 
 
 Problem 1. How objects are visible. Our common 
 experiences prove to us without further experiment that 
 light must be present in order to see objects. Recall ex- 
 periences which prove this. It is easy to understand how an 
 object which produces light is visible, but how are objects 
 like books, chairs, etc., visible? When light strikes an 
 object, a book for example, some or all of the rays of light 
 are reflected. 
 
 a B 
 
 FIGURE 215. REFLECTION OF LIGHT FROM A POLISHED AND A MIRRORED 
 
 SURFACE. 
 
 Arrows represent the relative intensity of the rays of light. 
 276 
 
RELATION OF LIGHT TO OUR ABILITY TO SEE 277 
 
 If the surface of the book were perfectly smooth (Fig- 
 ures 215 and 216), the rays would all be reflected in the 
 same direction, and no rays would reach our eyes unless 
 we were in a certain location (Figure 217). The cover of 
 the book, however, is not so smooth as it appears to be, 
 
 FIGURE 216. REFLECTION OF LIGHT FROM A SMOOTH SURFACE. 
 
 and consequently the light rays striking these inequalities 
 are reflected in every direction (Figure 218) in straight lines, 
 so that rays will reach our eyes regardless of our position, 
 providing there is nothing between us and the object to 
 intercept the rays. 
 
 The effect of the inequalities may be understood by throw- 
 ing several tennis balls together upon an irregular surface 
 and noting the directions in which they bounce. The rays 
 of light which pass into the eye from an object form an 
 
278 
 
 GENERAL SCIENCE 
 
 image or picture on the sensitive inner coat of the eye, the 
 retina, just as such an image or picture is formed on the 
 sensitive plate or film of a camera. In some way which we 
 do not thoroughly understand, nerve fibers carry to the 
 brain information of impressions made by the light on the 
 nerve endings, and we become conscious of the size, color, 
 and shape of the object. 
 
 How do you account for the fact that a room may be light 
 although the sun does not shine directly into it ? 
 
 Problem 2. Cost of artificial lighting of rooms. Name 
 
 FIGURE 217. HELIOGRAPH. 
 
 By means of a mirror light of the sun is reflected to a place many miles 
 distant. Dots and dashes of the telegraph code are produced by a shutter 
 operated by the sender of the message. 
 
 the various methods of producing light for the illumination 
 of rooms when sunlight is not available. We are especially 
 concerned with the comparative costs of these different 
 kinds of lights. To determine this, we must be able to 
 measure the intensity of a light. To do this we must know 
 
RELATION OF LIGHT TO OUR ABILITY TO SEE 279 
 
 FIGURE 218. REFLECTION OF LIGHT FROM A SLIGHTLY ROUGH AND 
 
 A ROUGH SURFACE. 
 
 /' 
 
 how the intensity of a light decreases as the distance from 
 the light increases. This may be found out by the follow- 
 ing experiment. 
 
 Experiment. Darken a room except for one small source of light. 
 Arrange pieces of opaque cardboard respectively 1, 2, and 3 inches 
 square, on supports so that they can be moved away from or toward 
 
 FIGURE 219. RELATION OF INTENSITY OF ILLUMINATION TO DISTANCE FROM 
 SOURCE OF LIGHT. 
 
 Compare the area of B and C with area of A. What is the intensity of 
 light upon one of the squares of C as compared with intensity upon A~> 
 
 the source of light. Place the 1-inch screen one foot from the light 
 and place the second screen so that the shadow cast by the first just 
 covers it, 
 
 In the same way place the third screen so that it is just covered by 
 the shadow. Measure the distances between the first and second and 
 the second and third screens. What is the relation of these distances 
 
280 GENERAL SCIENCE 
 
 to the distance between the source of light and the first screen (Figure 
 219)? 
 
 If the first screen is removed it is evident that the light striking the 
 second screen is the same that illuminated the first screen. But what 
 is the area of the second screen as compared with the first? What, 
 therefore, will be the intensity or brightness of the light on the second 
 screen as compared with the intensity on the first screen ? 
 
 In the same way compare the intensity of the light upon the third 
 screen with that on the first screen. What conclusion can you draw 
 now concerning the decrease of brightness or intensity of light as the 
 distance from the source of light increases? 
 
 Your conclusion may be stated in the following terms : 
 The intensity of light is inversely proportional to the square 
 of the distance from the light-giving body. 
 
 This experiment may be modified by substituting for the 
 first screen a larger screen in which is cut an opening one 
 inch square. In this modification of the experiment the 
 light-giving body should be surrounded by an opaque screen 
 in which a small pinhole has been made so that the light 
 comes from a point. Unless the opening is very small the 
 result will not be satisfactory. 
 
 The principle which we have discovered in the preced- 
 ing experiment may be used hi the following way to com- 
 pare the relative light-giving power of two lights. 
 
 FIGURE 220. PHOTOMETER. 
 
 An apparatus used to measure the comparative light-giving power 
 of two lights. 
 
 Experiment. Place the lights to be tested several feet apart on a 
 table in a room which is otherwise dark. Slide an upright piece of 
 
RELATION OF LIGHT TO OUR ABILITY TO SEE 281 
 
 FEE? 
 
 opaque cardboard along between the lights until no shadow is cast on 
 either side of the cardboard (Figure 220). This means, of course, that 
 there is an equal illumination of each side of the cardboard. Since 
 the intensity of light is inversely proportional to the square of the 
 distance from the light-giving body, the relative power of the two 
 lights may be calculated. If, for example, it is found that one of the 
 lights (a) is 4 times as far from the cardboard as the other (6), then 
 a:6::4 2 :l 2 , or as 16:1. 
 
 The standard of measurement of the light-giving power 
 of a light is called a candle power. This was originally the 
 light given by a candle 
 made according to cer- 
 tain specifications. At 
 the present time the 
 value of the candle 
 power in the United 
 States is established by 
 a set of standard in- 
 candescent lamps main- 
 tained in the Bureau of Standards in Washington. Most 
 incandescent lamps have the candle power etched upon 
 them. It can be seen that if the candle power of one light 
 
 is known the candle 
 power of another lamp 
 may be determined by 
 the experiment above. 
 
 Knowing the light- 
 giving power of two 
 
 lamps, it is possible by 
 FIGURE 222. GAS METER READING ~ ,f , ' . 
 
 68700 FEET. finding how rapidly the 
 
 oil or gas (Figures 221 
 
 and 222) is consumed or the number of kilowatt hours 
 (Figure 223) of electricity used, and the price charged, to 
 
 FIGURE 221. GAS METER READING 
 5700 FEET. 
 
 
 E.J&J .l| 
 
GENERAL SCIENCE 
 
 estimate the cost per candle power of various kinds of 
 lights. The following table (Figure 224) has been worked 
 out, showing the relative 
 cost of producing a cer- 
 tain amount of light. 
 
 Costs have been based KILOWATT HOURS 
 
 on the following prices: FIGURE 223. FACE OF A KILOWATT HOUR 
 Candles, 12 cents per 
 
 pound; kerosene, 15 cents per gallon; gas, $1.00 per 
 1000 feet; and electricity,. 10 cents per kilowatt hour. 
 
 Problem 3. Why 
 shades and reflec- 
 tors are used. - 
 The effectiveness of 
 the lighting of a room 
 may be increased 
 by the proper use of 
 shades and reflectors. 
 In lighting a room 
 several things must 
 be kept in mind : 
 that strong direct 
 rays of light are injurious to the eyes; that in some 
 
 Inverted Manila Open Flame Upright Manffe 
 
 Candles 
 
 Kerosene Ffame 
 
 Cos Open Ftame 
 Gas Mantle 
 Carbon Electric 
 'Gem" Elecfr/c 
 Tungsten > 
 
 5 10 IS 20 25 30 3S * 
 
 Cost of IOOO candle-hours in cents 
 FIGURE 224. RELATIVE COSTS OF DIFFERENT 
 LIGHTS. 
 
 FIGURE 225. COMPARATIVE AMOUNTS OF LIGHT GIVEN BY AN OPEN 
 GAS FLAME AND A GAS MANTLE. 
 
RELATION OF LIGHT TO OUR ABILITY TO SEE 283 
 
 1 1 NUMERALS REFER TO COST PER HOUR IN MILLS (TENTHS OF A CENT). 
 
 cases a general il- 
 
 lumination of the 
 room is desired ; and 
 that in other cases 
 certain parts or ob- 
 jects in the room 
 should be more bril- 
 liantly lighted. 
 
 Give examples 
 showing when a 
 general illumination 
 is desired ; when 
 special parts of the 
 room should be bet- 
 ter lighted. All 
 these aims are ac- 
 complished by means 
 of the use of shades 
 and reflectors. Can you recall any room that has seemed 
 
 ft* 
 
 Regular Upright Mantle 
 
 Junior Upright Mantle 
 
 (Fish Toll) Burner Turned Do** 
 
 Mantle Pilot 
 
 FIGURE 226. COST PER HOUR OF DIFFERENT 
 GAS LIGHTS. 
 
 FIGURE 227. 
 
 FIGURE 228. 
 
 Figures 237 nd 228 shew how small an amount of light passes upward 
 when lights are shaded. 
 
284 
 
 GENERAL SCIENCE 
 
 to be satisfactorily 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 the terms, direct and indirect lighting, 
 used. In direct lighting, the rays are reflected in one general 
 
 FfGURE 230. 
 
 A, reflection and transmission of light by opal glass. B, reflection of 
 light by enameled steel. 
 
 direction by the use of an opaque reflector Figures 229 and 
 230 B) . Individual reading lamps are usually of this type. 
 
RELATION OF LIGHT TO OUR ABILITY TO SEE 285 
 
 By the use of translucent shades which permit some of the 
 rays to pass through, we have what might be called semi- 
 direct lighting (Figures 227 and 230-4). Many halls and 
 meeting rooms, where a general distribution of light is 
 desired, have opaque or partially opaque bowl reflectors 
 by which the rays of light are directed to the white ceiling 
 which in turn reflects them downward throughout the room. 
 If translucent shades are used, considerable light also 
 passes directly outward and downward from the lamp. 
 
 Problem 4. How the color of the wall affects the light- 
 ing of a room. We 'can best understand the relation of 
 th'e color of the wall to the lighting of the room by perform- 
 ing a simple experiment. 
 
 Experiment. Obtain or make a pasteboard cylindrical box from 
 four to six inches in diameter and a foot or more in depth. Paste a 
 picture or some printed matter in the bottom. Loosely roll a piece of 
 white paper, slip it into the box as a lining, and look at the picture or 
 printed matter. Remove the white paper and insert a roll of colored 
 paper. Do this successively with wall paper of various colors. What 
 is the effect upon the illumination of the interior of the box ? 
 
 Make a list of the wall papers in the order of their value 
 for use in rooms that are likely to be dark. Make a list 
 of wall papers in order of their value for use in rooms that 
 are likely to be too light. Compare dirty with clean wall 
 paper and glazed with unglazed paper with respect to their 
 relation to illumination. 
 
 You have seen that the color of the walls makes a great 
 difference in the lighting of a room. Dark-colored walls 
 absorb more light, and hence reflect less than light- 
 colored walls. Pure white walls reflect about 80 per cent 
 of the light that strikes them ; while dark green, maroon, 
 chocolate brown, or dark blue walls do not reflect more 
 
286 GENERAL SCIENCE 
 
 than about 5 per cent of the light striking them. Smooth 
 walls reflect more light than those which are rough. Dirt 
 upon the walls reduces their power of reflection. 
 
 Problem 5. Why objects have different colors. If we 
 see the various things around us by reflected light, is it not 
 rather surprising that they should have different colors? 
 The light which comes from one book affects the nerve 
 endings in the eye in such a way that it carries a message to 
 the brain which gives us a sensation of red ; the light from a 
 book beside it may give us the sensation of green. The 
 light striking the books must be the same, for if we put the 
 red book where the green one was, it still continues to be 
 red. Apparently, therefore, the object from which light 
 is reflected causes a change which gives rise to the color. 
 
 Another illustration of the production of color by light 
 is the color seen at sunset and sunrise. What colors have 
 you seen on these occasions ? Have you ever seen the colors 
 in water spray when looked at from certain positions, or 
 colors along the edge of broken glass? What are the colors 
 of the rainbow ? 
 
 These observations all indicate that ordinary light, which 
 we call white light, may be broken up into various colors. 
 The truth of this may be shown by the following experi- 
 ment. 
 
 1 Experiment. Darken the room. Place a glass prism in such a 
 position that a beam of sunlight admitted through a small opening 
 will pass through it (Figure 231). What do you observe on the oppo- 
 site wall? 
 
 This experiment shows that white light is really a com- 
 bination of the colors that are seen in the rainbow. We 
 are now ready to understand why not all objects are white. 
 When light strikes the wall, for example, a portion of it is 
 
RELATION OF LIGHT TO OUR ABILITY TO SEE 287 
 
 absorbed, and a portion of it is reflected. You have noticed 
 that some walls reflect more light than others. The cover 
 of a green book reflects only that part of the white light 
 which gives us the sensation of green; a red book, on the 
 other hand, absorbs all the light except the part which gives 
 us the sensation of red. 
 
 \ 
 
 FIGURE 231. BREAKING UP OF LIGHT IN PASSING THROUGH A PRISM. 
 
 The white paper of this page reflects almost all of the light 
 which strikes it, but the black letters absorb practically 
 all the light which strikes them. A piece of red glass allows 
 only red rays to pass through ; all of the others being ab- 
 sorbed or in some cases partially reflected. 
 
 Since the absorbed light is changed into heat, explain 
 why light-colored clothing is more comfortable in the summer 
 and in the tropics, and dark-colored clothing is preferred 
 for winter wear. Explain why the colors of objects may 
 not be the same in artificial light as in sunlight. This can 
 be shown in an extreme form by comparing the colors of a 
 number of pieces of paper or cloth when observed first by 
 sunlight, and then by a candle in which is held a glass rod 
 which has been dipped in common salt solution. 
 
 Problem 6. What is the cause of the colors of sunset 
 
288 GENERAL SCIENCE 
 
 and sunrise and of the blueness of the sky? What are the 
 chief colors of sunset and sunrise? In the experiment, 
 in which by means of the prism you broke up white light into 
 the different colors, which colors were bent least, and which 
 most, from the original path of the light ray? The at- 
 mosphere, with its particles of moisture and dust, has some 
 power of separating the colors which make white light. 
 Explain now why the reds and oranges are seen at sunset 
 and sunrise. Why are they not seen at midday ? 
 
 Keeping in mind again the rays that are bent most by 
 the prism, and the fact that the atmosphere has some power 
 to separate the rays which compose sunlight, how do you 
 account for the blueness of the sky? This can be illus- 
 trated to some extent by putting a few drops of milk into a 
 jar of water and looking through the jar at a light. Ex- 
 plain why the sunsets are apt to be most brilliant in late 
 summer and fall. During the great forest fires in the 
 northern United States and in Canada, the sun appeared 
 orange or even red in color. Explain. 
 
 Problem 7. Why eyeglasses are used by some persons. 
 You all know people who without glasses must hold a 
 book very close to the eyes in reading. These nearsighted 
 persons have trouble in seeing distinctly anything which is 
 more than a few feet from them. On the other hand, you 
 may have friends who are farsighted ; who can read signs 
 at a greater distance than you can, but who have trouble 
 in reading a book or newspaper held at the ordinary read- 
 ing distance from the eye. Nearly all persons, as they grow 
 older, become farsighted ; and you will notice that many 
 begin to wear glasses at about the age of forty or even 
 much younger. 
 
 By the use of glasses both the nearsighted and the far- 
 
RELATION OF LIGHT TO OUR ABILITY TO SEE 289 
 
 sighted are enabled to see as well as those who are not 
 troubled by these eye defects. To understand how glasses 
 are able to bring about this change, it is necessary to know 
 how the rays of light act in entering the eye. 
 
 Sub-problem 1. How a picture or image is formed in the 
 eye. The following diagram (Figure 232) represents the con- 
 
 ch 
 
 ch 
 
 FIGURE 232. RAYS OF LIGHT PASSING INTO THE EYE. 
 /, 2, extreme points of the object. /', 2', focus of rays upon sensitive 
 layer of eye (retina), c, cornea. /', iris, ch, choroid (colored coat of 
 eyeball). /, crystalline lens, o.n, optic nerve, passing from eye to brain. 
 
 dition in the normal eye. It will be noticed that the rays of 
 light are bent as they strike the curved surface of the cornea, 
 and again as they pass through the crystalline lens, finally 
 coming to a focus on the nervous layer, the retina, lining the 
 back of the eye cavity. This is the same process that takes 
 place in a camera when the rays of light coming from an 
 object are bent by the lens of the camera and focused on the 
 sensitive film or plate. 
 
 Sub-problem 2. How light is bent in passing from one 
 substance into another. The ability of a lens to bend the 
 rays of light is very well illustrated by a burning glass, with 
 which the parallel rays of the sun may be focused on one point, 
 producing enough heat there to burn a piece of paper. 
 
290 
 
 GENERAL SCIENCE 
 
 The effect of a lens upon a ray of light may be understood 
 from the following diagram (Figure 233). 
 
 Light may be considered to be made of a column of trans- 
 verse vibrations. These 
 are slowed as they pass 
 into a denser substance like 
 glass. You can easily un- 
 derstand how the column 
 will be bent if the glass 
 is entered at an angle. In 
 
 FIGURE 233. A DIAGRAM SHOWING HOW 
 A LIGHT RAY MAY BE BENT. 
 
 the same way, as the ray 
 of light passes from the 
 glass into the air again, it 
 will be bent. This bending 
 of the rays of light (Fig- 
 ure 234), in passing from 
 one substance into another, 
 called refraction, explains 
 the fact that a stick, projecting at an angle from the water, 
 appears to be bent at the point where it leaves the water. 
 
 Sub-problem 3. How the eye is able to focus on near and 
 distant objects. You will 
 wonder how we can focus 
 the eye upon a distant ob- 
 ject, and then without any 
 appreciable effort, focus it 
 upon something near. The 
 power of accommodation 
 
 may be illustrated , as FlGURE 234. -BENDING OF RAYS OF LIGHT 
 follows. BY GROOVED GLASS. 
 
 Experiment. Hold a pencil before your eyes and read the label 
 on it. How does a picture on the opposite side of the room appear? 
 Still keeping the pencil in the same position, look at the picture. How 
 does the pencil appear now ? 
 
RELATION OF LIGHT TO OUR ABILITY TO SEE 291 
 
 In a camera, such a change in focus is brought about by 
 moving the lens closer to or farther from the sensitive film. 
 In the case of the eye, it is of course impossible -to change the 
 distance between the lens and the sensitive inner coat of the 
 eye, the retina. The same result, however, is accomplished 
 by changing the shape of the lens. This is done by muscles 
 which are connected with a tough membrane or ligament in- 
 closing the lens. The muscle by its contraction flattens the 
 lens, with the following result. 
 
 When near objects are to be looked at, the muscles relax 
 
 FIGURE 235. CHANGE OF Focus OF EYE. 
 
 Upper figure, eye focused on a near object. Lower figure, eye focused 
 on a. distant object. 
 
 and the lens, because of its elasticity, becomes more convex 
 and the object is focused upon the retina (Figure 235). 
 
 Sub-problem 4. Cause and correction of farsightedness 
 and nearsightedness. As a person becomes older, the lens 
 loses its elasticity and it becomes impossible for him to see 
 near objects distinctly, although his power of seeing things at 
 
292 GENERAL SCIENCE 
 
 some distance remains unimpaired. You can easily see how 
 the use of slightly convex glasses will do the work that the 
 flat lens of his eye will not do, enabling him to see, for exam- 
 ple, the print of a book as 
 well as before the lens began 
 
 Farsightedness, not the 
 FIGURE 236. FARSIGHTEDNESS AND ITS result of age, is usually due 
 CORRECTION. to the fact that the eye- 
 
 L, lens. /= focus. ball is too short. An exam- 
 
 ination of the diagram (Figure 236) will show that a distinct 
 image of near objects cannot be formed on the retina. This 
 condition can be corrected by the use of convex glasses. 
 Explain. 
 
 Nearsightedness, on the other hand, is usually caused by the 
 eyeball being too long. In this case the image of an object 
 held at the normal reading distance, or at any distance farther 
 away, is formed in front 
 of instead of on the retina. 
 This condition can be cor- 
 rected by the use of. con- 
 cave eyeglasses (Figure 23 7). 
 Explain. FIGURE 237. NEARSIGHTEDNESS AND ITS 
 
 CORRECTION. 
 Sub-problem 5. What 
 
 is astigmatism and how is it corrected ? Many persons 
 who are neither farsighted nor nearsighted must wear glasses 
 or suffer from headaches. This is caused by a defect of the 
 eye called astigmatism, which results from the unequal curva- 
 ture of the cornea (the front of the eyeball). What effect 
 will this have upon the bending of the different rays of light 
 that enter the eye? The glasses for these eyes are curved 
 in such a way that the defects of the cornea are counter- 
 acted. If - glasses are not worn, the ciliary muscle in its 
 effort to bring about a condition which will result in a clearer 
 image is overworked and eyestrain and headache result. 
 
RELATION OF LIGHT TO OUR ABILITY TO SEE 293 
 
 If you are troubled with eyestrain or headache after 
 using the eyes for some time, have your eyes examined at 
 once by a competent oculist or optometrist. Eyestrain 
 results in both discomfort and lessened efficiency. Fre- 
 quently headaches, nervousness, and other troubles are 
 relieved as by magic when eyestrain has been removed 
 by the use of proper glasses. 
 
 Problem 8. Advantage of having two eyes. 
 
 Experiment. Close one eye and attempt to put the cap on a 
 fountain pen held at arm's length. With one eye still closed, attempt 
 to put a pencil into a hole which it just fits. Try the same things with 
 both eyes open. Hold a book several feet in front of you, with its 
 edge toward you. Look at it first with both eyes open, then alter- 
 nately with one eye closed and then the other. What are the results ? 
 
 Evidently each eye forms an image of an object viewed 
 from a slightly different angle. The effect of this is to 
 give us a sense of the thickness of objects, and also of their 
 distance from us. The brain is able to interpret the angle 
 formed by the rays of light coming from the object to the 
 eyes, and consequently we are conscious that one object is 
 farther from us than another. Pictures viewed with an 
 instrument called the stereoscope give an impression of 
 depth and distance such as an ordinary photograph fails to 
 give. The two pictures which are mounted together have 
 been taken with a double camera, the lenses of which are 
 the same distance apart as the human eyes. 
 
 Problem 9. How eyes may be injured. It must be 
 remembered that although the eyes are in perfect condi- 
 tion they may be .abused, and eyestrain with its accom- 
 panying troubles will result. Too .continuous focusing 
 upon close work tires the eye. Occasionally looking away 
 at some distant object for a few moments rests the eye to a 
 surprising degree. : 
 
294 GENERAL SCIENCE 
 
 Reading by a dim light causes overwork of the muscles 
 of the iris in their effort to enlarge the pupil to admit all the 
 light possible. The image is indistinct on the retina, caus- 
 ing one to hold the page closer to the eye, throwing an ex- 
 cessive amount of work upon the ciliary muscle. One is 
 very apt to abuse the eye by reading in the evening as the 
 light is fading; the eye gradually accommodating itself 
 to the lessening light until a condition of excessive strain is 
 reached. 
 
 Too strong a light is almost as bad. The muscles of 
 the iris make a brave effort to narrow the pupil as much as 
 possible to shut out the excessive light which is tiring the 
 nerve endings of the retina. 
 
 A flickering or changing in the intensity of the light com- 
 ing to the eye causes constant changes in the eye. From 
 this point of view discuss the best kind of light to 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 printed in fine type or 
 on glossy paper is highly objectionable; especially is small 
 type objectionable in books used by young persons. 
 
 Serious eye diseases have been contracted by those who 
 have rubbed their eyes with their fingers after having been 
 holding to a strap in a street car or after having touched 
 door knobs or railings which have been handled by many 
 persons. Explain. 
 
 Problem 10. How a lens makes objects appear larger. 
 The action of a reading glass or a .simple lens is illus- 
 trated by the following figure. 
 
 It will be noticed that the rays of light come to the eye 
 at the same angle as though they came from a much larger 
 
RELATION OF LIGHT TO OUR ABILITY TO SEE 295 
 
 object, and the brain thus interprets the image formed on 
 the retina. 
 
 In the case of the compound microscope, the rays of 
 light before reaching the eye become crossed, and also enter 
 the eye at a much wider angle ; hence, the object is highly 
 magnified .and appears upside down. All instruments such 
 
 FIGURE 238. MAGNIFYING GLASS. 
 
 as the telescope, opera glasses, and projection lanterns, 
 which are used to give us a magnified appearance of an ob- 
 ject, depend on lenses which cause the light coming from that 
 object to enter the eye at a much wider angle than if the 
 light came directly from it. The brain, in every case, in- 
 terprets the image on the retina as though these wide- 
 angled rays were coming directly from the object. 
 
 Problem 11. How motion pictures are produced. The 
 moving picture machine which has come to play such an 
 important part in our lives in giving us recreation and in- 
 struction is really a projection lantern in which the pictures 
 to be projected are very small, and developed on a roll of 
 transparent celluloid or a similar substance. 
 
 The pictures were taken 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 differing slightly from the succeeding one, 
 
296 
 
 GENERAL SCIENCE 
 
 FIGURE 239. A MOVING PICTURE FILM. 
 
RELATION OF LIGHT TO OUR ABILITY TO SEE 297 
 
 as the movement progresses. By a mechanism similar to 
 that used in taking them, the successive pictures are thrown 
 upon the screen. However, we do not see them as separate 
 pictures, but as one, in which the motions of the original 
 subject are reproduced. 
 
 The way in which a succession of pictures appears as one 
 continuous picture is well illustrated by the appearance of 
 the spokes of the wheels of a rapidly moving automobile. 
 Do you see each individual spoke? A lantern swung 
 rapidly in a circle is seen as a circle of light. It is evident 
 that the image of an object does not disappear immediately 
 upon the disappearance of the object. 
 
 Problem 12. How light effects may guide us in the 
 selection of clothing. It is not only by the use of lenses 
 that our sense of sight may be deceived. Have you ever 
 noticed that one's feet look larger when white shoes are worn, 
 that stout people look stouter when dressed in white, and 
 that a house once white, which has been painted a dark 
 color, appears to have become smaller in size? 
 
 FIGURE 240. 
 
 The three systems of lines are equally distant from one another at 
 all points. Do they appear so ? 
 
 Certain arrangements of lines also deceive us. A stout 
 person appears stouter when he wears clothes which have 
 horizontal stripes, and a thin person appears thinner when 
 
298 GENERAL SCIENCE 
 
 he wears clothes which have vertical stripes. The way in 
 which lines deceive us is illustrated by the preceding figure. 
 Endeavor to explain the following : 
 
 1. Why ground glass or glass with an irregular surface 
 is used in office partitions. 
 
 2. Why concave mirrors are used behind headlights of 
 locomotives, trolley cars,, etc. 
 
 3. Why undimmed automobile headlights are not usually 
 permitted. 
 
 4. Why corrugated glass is used in automobile head- 
 lights. 
 
 5. Why a piece of glass will cast a shadow. 
 
 6. The presence of a wavy appearance over a hot radia- 
 tor or stove, or over a dry road on a hot day. 
 
 7. Why colored glasses are frequently worn at the 
 seashore and by motorists. 
 
 8. Why it is more difficult to see objects when you 
 first go out at night than later. 
 
 9. Why it is difficult to see when you enter a brilliantly 
 lighted room after having been in the dark. 
 
 10. Why the inside of a camera is painted black. 
 
 11. Why a cake of ice is transparent, and a block of 
 snow is not. 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Determine the relative candle power of the lights in your home 
 and the cost per candle power. 
 
 2. Experiments to show the effect of color of walls upon the illumi- 
 nation of a room. (Suggestion. Use long narrow boxes with dif- 
 ferently colored walls.) 
 
 3. Experiments to show that sunlight may be broken up into rays of 
 light of various colors, and that rays of light of various colors may be 
 combined to form white light. 
 
RELATION OF LIGHT TO OUR ABILITY TO SEE 299 
 
 4. Demonstration of the power of cloth of different colors to absorb 
 light, and change it into heat. 
 
 5. Experiments to show the action of convex lenses in correction 
 of farsightedness. 
 
 6. Demonstration of how objects are made to appear larger by the 
 use of a lens or reading glass. 
 
 7. Demonstration of the focusing of a camera. 
 
 8. Demonstration of a motion picture machine. 
 
 9. Demonstration of how we may be deceived as to the size and 
 shape of objects by the arrangement of black and white portions. 
 
 REPORTS 
 
 1. Various ways in which eyes may be injured, and care that must 
 be taken for their protection. 
 
 2. The lighting of factories or office buildings. 
 
 REFERENCES FOR PROJECT XXIV 
 
 1. Stories of Inventors, Doubleday. Doubleday, Page & Co. 
 (How Moving Pictures Came to Be.) 
 
 2. Wonders of Science. Houghton Mifflin Company. (Making 
 Moving Pictures.) 
 
 3. The American Boys' Handy Book, Beard. Scribners. (Tele- 
 scopes.) 
 
 4. Historic Inventions, Holland. Geo. W. Jacobs, Philadelphia. 
 (Galileo and the Telescope.) 
 
 5. American Inventions and Inventors, Mo wry. Silver, Burdett 
 & Co. (Torches, Candles, Kerosene, Gas, Electric Lights.) 
 
PROJECT XXV 
 
 IMPORTANCE OF HEAT TO US 
 
 THE production of heat and its relation to other forms 
 of energy have already been considered. Briefly review 
 your knowledge of these matters. Some of the ways in which 
 problems of heat affect our everyday life have been dis- 
 cussed, but there still remain some cases which need further 
 attention. 
 
 Problem 1. How a thermos bottle keeps hot liquids hot 
 and cold liquids cold. 
 
 Experiment. Fill one of two thermos bottles with hot water ; 
 fill the other with cold water. Set them side by side together with two 
 ordinary bottles filled respectively with hot and cold water. Examine 
 after two or three hours. Results ? Conclusion ? 
 
 An explanation of the structure of 
 the thermos bottle (Figure 241) will 
 help us to understand its ability to keep 
 hot things hot and cold things cold. 
 
 The space between the two bottles is 
 a vacuum ; the air having been pumped 
 from it during the process of manu- 
 facture of the bottle. Evidently this 
 vacuum in some way prevents the cool- 
 ing or warming of the contents. We 
 
 FIGURE 241 THER can understand tnis better if we realize 
 MOS BOTTLE. that coldness is only a lack of heat, 
 
 300 
 
 Shook AbBotbei 
 Heavy Glaai 
 
IMPORTANCE OF HEAT TO US 
 
 301 
 
 and that a body cools because heat escapes from it. It 
 becomes warm because heat is absorbed. What is your 
 conclusion as to the ability of heat to pass through a 
 vacuum? A vacuum is called a poor conductor of heat. 
 The polished inner surface of the thermos bottle also helps 
 in preventing a loss of heat, since heat will not pass as 
 readily from a highly polished surface as from a dull sur- 
 face. 
 
 Problem 2. How food may be cooked in a fireless cooker. 
 Food which has already been heated to the boiling point 
 when placed in a fireless cooker 
 continues to cook although 
 no additional heat is applied. 
 State some of the advan- 
 tages of such an apparatus. 
 It consists of two boxes of 
 wood or metal, one inside 
 of the other, separated by 
 an air space filled with excel- 
 sior, sawdust, newspapers, 
 hay, or glass wool which pre- 
 vents the circulation of air (Figure 242). What are your 
 conclusions concerning the power of still air and the sub- 
 stances mentioned to conduct heat ? 
 
 Refrigerator walls are similar in their construction to the 
 walls of a fireless cooker. The space between the walls is 
 usually filled with charcoal. 
 
 What is the chief use of clothing in winter? What kind 
 is usually worn then? Explain why loosely woven, woolen 
 clothing is warmer than that which is tightly woven ? Why 
 are fur coats so warm ? In the summer linen is the coolest 
 material to wear, but any thin, tightly woven, light-colored 
 clothing is comfortable. Explain. 
 
 FIGURE 242. FIRELESS COOKER. 
 
302 GENERAL SCIENCE 
 
 Problem 3. What substances are good and what are 
 poor conductors of heat. 
 
 Experiment. Place in a cup of hot water a silver spoon and a tin 
 or plated spoon. After a few minutes touch the handle of each. Re- 
 sult ? Conclusion ? 
 
 Experiment. Fill a test tube with water in which has been placed 
 a piece of ice weighted by having wire wrapped around it. Heat the 
 test tube near the top. Result? Conclusion? 
 
 Recall your experiences on a cold morning of stepping 
 on a bare wood floor ; on a carpet ; on paper ; or on a tile or 
 stone floor. What are your conclusions as to the power of 
 these different substances to conduct heat ? 
 
 These observations are sufficient to show you that sub- 
 stances differ very much in their power of conducting heat. 
 The metals may all be classed as good conductors. They 
 may be ranked in the following order : 
 
 1. Silver 6. Tin 
 
 2. Copper 7. Iron 
 
 3. Aluminum 8. German Silver 
 
 4. Brass 9. Mercury 
 
 5. Zinc 
 
 Substances which are medium conductors of heat are : 
 
 1. Rock 5. Glass 
 
 2. Ice 6. Water 
 
 3. Porcelain 7. Plaster 
 
 4. Tiling 
 
 Poor conductors of heat are : 
 
 1. Wood 5. Wool 
 
 2. Asbestos 6. Feathers 
 
 3. Paper 7. Air 
 
 4. Cork 
 
IMPORTANCE OF HEAT TO US 303 
 
 Explain the following : 
 
 1. Why birds ruffle up their feathers on a cold day. 
 
 2. Why a light-weight feather or down coverlet keeps 
 one so warm. 
 
 3. Why heat pipes in basements are frequently covered 
 with asbestos, and mats of this material are used under 
 hot dishes at the table. 
 
 4. Why asbestos is fastened to the wall behind a stove. 
 
 5. Why newspapers folded under the coat will protect 
 one from becoming chilled on a very cold day. 
 
 6. Why the thermos bottle is stoppered with cork. 
 
 7. Why the water in deep holes in a lake remains cold 
 during the hottest part of summer. 
 
 8. Why iron is better than brick or porcelain for stoves. 
 
 9. Why bakers' ovens are sometimes inclosed in brick. 
 
 10. Why tea-kettles frequently have wooden handles. 
 
 11. Why oven door handles are usually made of coiled 
 wire. 
 
 12. Why dead air spaces are left between the walls of a 
 building. 
 
 13. Why building paper is placed in the wall of a wooden 
 house. 
 
 14. Why the outer vessel of an ice cream freezer is made 
 of wood. 
 
 15. Why farmers who plant wheat in the fall of the year 
 are glad to have much snow in winter. 
 
 16. Why the ticket choppers at the elevated and sub- 
 way stations keep a wooden box beneath their feet in cold 
 weather. 
 
 17. Why ice is packed in sawdust. 
 
 18. Why on a very cold morning outdoors the fingers 
 will freeze to the metal head of an ax but not to the wooden 
 handle. 
 
304 
 
 GENERAL SCIENCE 
 
 19. Why iron is a good material for steam or hot water 
 radiators. 
 
 20. Why a loosely fitting overcoat is warmer than one 
 which fits tightly. 
 
 Problem 4. How houses are heated. Houses may be 
 heated by stoves or fireplaces which are located in all or 
 several rooms. Most modern houses, however, are heated 
 by furnaces, located in the basement. What are the ad- 
 vantages of this? Are there any disadvantages? The heat 
 produced by oxidation of fuel in the furnace is distributed 
 to the various parts of the house by hot air pipes or by 
 pipes carrying steam or hot water. 
 
 Electrical companies are now producing heaters in which 
 electrical energy is changed into heat energy. These are 
 especially valuable when only a small amount of heat is 
 needed as in spring and fall. How are trolley cars heated ? 
 
 Sub-problem 1. How 
 houses are heated by hot 
 air. A hot air furnace 
 (Figure 243) is essentially 
 a large stove around which 
 is a metal jacket through 
 which the air passes to be 
 heated. What causes the 
 air to pass through the 
 pipes into the rooms above? 
 What should be the size 
 of the intake pipes as com- 
 pared with the size of the 
 
 FIGURE 243. -HOUSE HEATED BY HOT AIR. Pi? 68 carrying air from 
 
 the furnace? In order 
 
 that a fresh supply of air may enter a room, there must be 
 an opportunity for the air already there to escape. How 
 
IMPORTANCE OF HEAT TO US 
 
 305 
 
 may this be provided for? Hot air furnaces sometimes fail 
 to heat satisfactorily the rooms of a house on the side 
 against which a strong wind is blowing. What is the ex- 
 planation of this fact ? 
 
 Some hot air furnaces not 
 only have an intake pipe 
 which receives air directly from 
 outside, but also a pipe which 
 carries air from the first floor 
 back to be heated again. Do 
 you think such an arrangement 
 is good or bad ? Explain your 
 answer. 
 
 Do you think that hot air 
 heating would be a good method 
 of heating large apartment 
 houses? Why? 
 
 The extreme heat of the 
 firebox may cause a warping 
 and cracking of the iron plates 
 of its walls. Explain why gas 
 from the burning coal some- 
 times comes up through the 
 hot air pipes. This is not 
 usually the case when the 
 damper in the flue is so ar- 
 ranged that the draft is not 
 interfered with. Explain. 
 
 Sub-problem 2. How houses 
 are heated by hot water (Figure 244) . What causes 
 the water to rise? (Water expands when heated.) Why 
 is it necessary to have the tank in the attic? Must the 
 pipes be full of water? Why? What precautions must be 
 taken if the house is left unoccupied in the winter? The 
 radiator (R), just as a stove, heats a room in two ways; by 
 
 FIGURE 244. HOUSE HEATED BY 
 HOT WATER. 
 
 In what direction is water moving 
 in pipe ? in 0? Why is the tank 
 B in the attic necessary ? 
 
306 GENERAL SCIENCE 
 
 radiation, the giving out of heat directly, and by setting up 
 air currents as was discussed in the study of ventilation. 
 
 Sub-problem 3. How houses are heated by steam. In 
 a steam heating plant, steam instead of water passes through 
 the pipe into the radiator. This steam in the radiator con- 
 
 I 
 
 FIGURE 245. CIRCULATION OF WATER, IN THE RADIATOR AND AROUND 
 THE CYLINDERS OF AN AUTOMOBILE. 
 
 The reasons for the circulation of water here are the same as in the 
 pipes and boiler of a hot water heating plant. 
 
 denses into water. How does this fact affect the heating of the 
 room ? Should the boiler of a steam heating plant be filled with 
 water? Why? Explain the need for the safety valve of the 
 boiler. Explain why on days when only a small amount of heat 
 is needed in the house, steam heat is not so satisfactory as 
 either hot air or hot water heat. Explain why rooms heated 
 
IMPORTANCE OF HEAT TO US 307 
 
 by steam cool off much more rapidly after the fire is shut down 
 at night than rooms heated by hot water. 
 
 Explain why in all furnaces the opening of the door below 
 the firebox makes the fire burn better, and why the opening 
 of the coal door checks the fire. 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Make a fireless cooker. 
 
 2. Find out the value of different kinds of clothing in preventing 
 the escape of heat from the body. (Suggestion. Cover bottles con- 
 taining hot water with various combinations of cloth, and observe how 
 soon the water becomes cool.) 
 
 3. Determine by experiments the power of different substances to 
 conduct heat. 
 
 4. Study the plan of the heating system of your house and make a 
 diagram of it. Explain the reason for the arrangement and the use of 
 various devices. 
 
 REPORTS 
 
 Describe the methods of heating houses in different countries, 
 including the kinds of fuel 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 Its Family Tree. Taylor Instrument 
 Company, Rochester, N. Y. l(ty. 
 
 4. Chemistry of Common Things, Brownlee, Fuller, and others. 
 Allyn and Bacon 
 
UNIT V 
 
 RELATION OF SOIL AND PLANT LIFE TO EVERYDAY 
 ACTIVITIES 
 
 PROJECT XXVI 
 HOW SOIL IS MADE 
 
 WE have already seen how plant life is essential to animal 
 life upon the earth. Without plant life therefore, there could 
 be no human life upon the earth. Explain. In this unit 
 we shall consider projects and problems concerned with the 
 production of plants. 
 
 The working out of these projects and the solution of the 
 problems that arise will in many cases help us to solve impor- 
 tant problems of animal and human life. 
 
 Since the growth of plants is dependent on soil it is evident 
 that we must consider the projects how soil is formed and 
 how it is related to plants. Other projects will naturally 
 be how plants and animals make use of the manufactured 
 food in their growth, how plants produce seed, how better 
 plants and animals are produced, and how plants are pro- 
 tected from harmful insects. 
 
 It is known that, if we go back far enough in the world's 
 history, there was once a time when there was no soil. The 
 wnole surface of the earth was rock, just as we find the 
 earth's crust if we dig down through the soil. An examina- 
 tion of soil may give us some hints which will help us to 
 understand how it has been formed. 
 
 308 
 
HOW SOIL IS MADE 309 
 
 Problem 1. Of what is soil composed? Examine a 
 handful of dry soil. Do you find any particles of sand in it ? 
 What is sand? Examine a very small amount of it with a 
 magnifying glass or microscope. What do you find ? Some- 
 times soils have so many small pieces of rock that they are 
 called gravelly soils or sandy soils. What do you suspect 
 is the origin of the sand or gravel ? What is the color of 
 soil? Where have you ever seen soil that is very dark in 
 color? Can you suggest a possible explanation for this 
 color ? 
 
 Experiment. Heat some soil from a flower pot in a crucible or in 
 a test tube if you have no crucible. What change in color appears 
 first? Of what does the odor that is given off remind you? What 
 change in color occurs after continued heating? The material which 
 remains after continued burning is called mineral matter. From your 
 observations what do you consider to be the composition of the soil, 
 and from what do you think it has been formed? 
 
 FIGURE 246. RELATIVE SIZE OF SOIL PARTICLES (all highly magnified). 
 From left to right : clay, silt, sand, gravel. 
 
 Plants cannot grow unless air and water are present in the 
 soil. A good soil, therefore, consists of decomposed rock 
 material, 60 to 05 per cent of its weight, together with 
 
310 GENERAL SCIENCE 
 
 humus, bacteria, air, and moisture. The materials which 
 make up soils may be classed as follows (Figure 246) : 
 
 (a) Humus, or vegetable mold. 
 
 (b) Clay, made up of finely powdered rock. The particles 
 are less than one ten-thousandth of an inch in diameter. When 
 dry, clay is powdery ; when wet, it is sticky. 
 
 (c) Silt, consisting of particles somewhat coarser than clay. 
 When moist it becomes a soft mud and usually crumbles when 
 it 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. DISINTEGRATION OF ROCK. 
 Limestone ledge breaking up and forming soil. 
 
 sand, silt, and humus. Since moisture is so necessary to 
 plants, the power of a soil to take up and hold water is a 
 very important characteristic of it. 
 
 Problem 2. Evidence that soil is now being formed. 
 Apparently a portion of the soil has been formed from rock. 
 
HOW SOIL IS MADE 
 
 311 
 
 If this is so, then there should be indications that such a 
 change is going on at the present time. An examination 
 of the side of a railroad cut will usually show gradations 
 from solid rock, through partially disintegrated rock, to 
 well-formed soil. The accompanying picture (Figure 247) 
 
 shows rocks of various . , 
 
 sizes which have been 
 broken off from the 
 great mass of rock. Old 
 marble gravestones with 
 their rounded edges and 
 more or less indistinct 
 lettering are indications 
 that rock may be worn 
 away. These evidences 
 coupled with the fact 
 that pebbles and small 
 fragments of rocks are 
 found in soils indicate 
 that the process of soil 
 making is still going on. 
 
 Problem 3. How soil 
 has been produced by 
 weathering. Some of 
 the agencies that change 
 rock into soil can easily 
 be understood. Break a 
 rock, and compare the 
 
 broken surface with the surface of the rock which has 
 been exposed to the weather. What is your conclusion ? 
 
 The oxygen of the air may act upon some of the minerals 
 of the rocks causing a change which results in their crumbling. 
 
 FIGURE 248. RUGGED MOUNTAINS SHOW- 
 ING THE EFFECT OF WEATHERING. 
 
312 
 
 GENERAL SCIENCE 
 
 This is similar to the action of oxygen in causing the rusting 
 of iron. Carbon dioxide dissolved in water is one of the 
 most efficient agents in the breaking down of rocks. It is 
 the action of carbon dioxide in water which has produced 
 the great caves such as Luray Cave in Virginia, Mammoth 
 Cave in Kentucky, and Wyandotte Cave in Indiana, as well 
 as hundreds of smaller ones in various parts of the country 
 where limestone is the common rock. This action can be 
 shown by passing carbon dioxide through water containing 
 a small amount of finely powdered marble. 
 
 What do you think 
 
 might be the effect upon 
 some rock of alternate 
 heating and cooling 
 caused by the tem- 
 perature changes of day 
 and night? 
 
 Experiment. Heat a glass 
 tube and plunge it into cold 
 water. What happens? The 
 cracking of the rocks by 
 this means exposes more sur- 
 face for the action of the 
 weather. 
 
 What will happen in 
 cold weather to the water 
 which is in the crevices 
 of the rock? What ef- 
 fect will this have upon the rock? This can be illustrated 
 by exposing to a freezing temperature a tightly stoppered 
 test tube filled with water. The force due to the expan- 
 sion of water when it changes into ice causes the bursting 
 
 FIGURE 249. WEATHERED ROCK AT BASE 
 OF A CLIFF. 
 
HOW SOIL IS MADE 
 
 313 
 
 of water pipes and the ruin of automobile radiators, if 
 cars are permitted to remain in unheated garages in very 
 cold weather without removal of the water. (This latter 
 may be prevented by adding to the water in the radiator 
 some substance, alcohol 
 for example, which has 
 a lower freezing point.) 
 
 The great masses of 
 broken rock at the foot 
 of cliffs (Figure 249), as 
 at the base of the Pali- 
 sades along the Hudson 
 River, are caused very 
 largely by the final 
 breaking off of pieces 
 of rock by the expan- 
 sion of freezing water 
 which has gotten into 
 the crevices formed by 
 temperature changes. 
 Roots of trees growing 
 in the crevices of rocks 
 also assist in the further 
 splitting of the rocks 
 (Figures 250 and 251). 
 
 Problem 4. How soil 
 has been produced by 
 water and wind ero- 
 sion. Water erosion. The fragments of rock, pro- 
 duced by the processes mentioned above, are carried 
 along by the swiftly moving water of rivulets and streams. 
 What will be the effect upon the bottom of such streams? 
 
314 
 
 GENERAL SCIENCE 
 
 What will be the effect upon the fragments themselves? 
 What is the shape of pebbles and rocks found in a stream ? 
 Why? Explain how the valleys of streams have been cut 
 down through the rock. This action of water carrying 
 fragments of rock is called erosion (Figure 252). It is ex- 
 actly similar to the way 
 in which a grindstone is 
 able to sharpen tools; 
 both the grindstone and 
 the metal of the tool are 
 worn away. As the 
 streams become less swift 
 much of the material is 
 deposited, so that soil is 
 constantly being eroded 
 from the more elevated 
 regions and deposited in 
 the lowlands. 
 
 Wind erosion. In 
 some parts of the world 
 considerable erosion is 
 done by wind carrying 
 
 FIGURE 251. BEECH TREE GROWING ON 
 ROCKS. 
 
 The roots penetrate into crevices and by their 
 growth split the rocks. 
 
 sand in the same way 
 
 that a sand blast is used in etching glass or in cleaning the 
 surface of a stone building. Wind, however, as an agent 
 in the formation of soil is of very little importance in com- 
 parison with those already mentioned. 
 
 Problem 5. How most of the soil of northern United 
 States has been produced. In the northern part of our 
 country, pebbles and rocks of all sizes, unlike the solid rock 
 bed of that region, are frequently found imbedded in the soil 
 (Figure 253). Evidently the soil and rocks of those regions 
 
HOW SOIL IS MADE 315 
 
 have not been carried there by water, since the rocks are 
 scattered indiscriminately in the fine soil (clay). Explain 
 
 FIGURE 252. WATER EROSION. 
 
 Gravel and rock have been eroded from the higher land and carried 
 down by water. 
 
 FIGURE 253. SOIL DEPOSITED BY A GLACIER. 
 Note the irregularly shaped boulders. 
 
316 
 
 GENERAL SCIENCE 
 
 the reason for this conclusion. On examination many of 
 the rocks are found to have scratches on them (Figure 254). 
 Also if the soil is removed, the surface of the country rock 
 will be found to have deep parallel scratches and grooves. 
 
 Many thousands of years ago, a great sheet of ice, called a 
 glacier, covered the northern part of the United States (Fig- 
 ure 255). As it moved southward, its immense weight broke 
 off fragments of rock which rubbed along the bottom of the 
 glacier and ground up the rocky bed into a finely powdered 
 
 FIGURE 254. ROCK SHOWING GLACIAL SCRATCHES. 
 
 soil (clay) leaving great scratches and grooves. The clay 
 and the boulders, or rocks, became thoroughly mixed in 
 the ice. As the glacier reached its southern extent, it 
 melted and the material in it was deposited there as a 
 series of ridges of hills called a terminal moraine (Figure 
 257). 
 
 As the glacial period gradually passed, the glacier was 
 unable to push farther south and as a result a series of these 
 moraines have been formed. When the entire ice sheet 
 
HOW SOIL IS MADE 
 
 317 
 
 melted, the rock and soil carried by it was left wherever it 
 happened to be. As some parts of the glacier carried a large 
 quantity of material and other parts only a small amount, 
 
 FIGURE 255. EXTENT of ICE SHEET DURING GLACIAL PERIOD. 
 
 a layer of rock and soil of unequal thickness was deposited 
 over all the northern parts of the country. The depressions 
 became filled with water and thus the large number of the 
 lakes of these northern states is accounted for. , 
 
318 GENERAL SCIENCE 
 
 Problem 6. How soil has been produced by decay of 
 organic matter. Plants gain a foothold in the soil formed 
 by the decomposition of rock material and, by their own 
 decay and that of animals which live upon them, add to 
 the soil that part of it which causes it to blacken when 
 
 FIGURE 256. A GLACIER. 
 Glacier flowing down side of Mt. Robson, British Columbia. 
 
 burned. This organic part of the soil, or humus (Figure 
 258), is of special importance in giving it the proper texture 
 and increased power of holding water. It is also the prin- 
 cipal source of nitrogen which is so necessary for plant 
 growth. If you will recall your study of bacteria, you will 
 remember that they are necessary in soils in order to decom- 
 pose the vegetable and animal matter so that this material 
 may be used again in the growth of plants. 
 
FIGURE 257. FRONT OF A GLACIER, Mr. RAINIER NATIONAL PARK. 
 
 Notice the broken rock which was carried down and deposited when the 
 
 glacier extended somewhat farther into the valley. 
 
 FIGURE 258. FORMATION OF HUMUS. 
 
 Vertical section showing forest floor, humus, soil, and roots. 
 319 
 
320 GENERAL SCIENCE 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Collect and put into test tubes specimens of different kinds 
 of soils, including rock and vegetable material which has partially 
 changed into soil. 
 
 REPORTS 
 
 1. Evidences in the United States of the glacial periociu 
 
 2. Description of a glacier. . 
 
 3. Character of the soil in different parts of your state. 
 
 REFERENCES FOR PROJECT XXVI 
 
 1. Glaciers of North America, J. C. Russell. Ginn & Co. 
 
 2. Soils ; Their Properties and Management, T. L. Lyon. Mac- 
 millan Company. 
 
 3. Agronomy, Clute. Ginn & Co. 
 
 4. Story of Agriculture in the United States, A. H. Sanford. 
 D. C. Heath & Co. 
 
 5*. Essentials of Agriculture, H. W. Waters. Ginn & Co. 
 
 6. The Land We Live In, O. W. Price. Small, Maynard& Co. 
 
 7. Earth and Sky Every Child Should Know, J. E. Rogers. 
 Doubleday, Page & Co. 
 
 8. The United States, J. O. Winston. D. C. Heath & Co. 
 (The Great Glacier and Its Effect.) 
 
 9. Wonders of Science. Houghton Mifflin Company. 
 
 10. Farm Science, W. J. Spellman. World Book Company. 
 
 11. Elementary Agriculture, James S. Grim. Allyn and Bacon. 
 
PROJECT XXVII 
 RELATION OF SOIL TO PLANTS 
 
 SINCE the amount of moisture in the soil has a great effect 
 upon the growth of plants one important problem is : how 
 the water-holding power of the soil may be increased. As 
 the project is further analyzed it will be seen that other 
 problems will be those concerned with what plants take 
 from the soil, how these substances may be returned to the 
 soil, how materials are taken from the soil and what the 
 plant does with this material. 
 
 Problem 1. How the water-holding power of the soil 
 may be increased. We all know from observation that 
 the growth of plants depends upon their being able to 
 get sufficient water from the soil. How does grass appear 
 during a prolonged dry period in summer? How may 
 lawns and parks be kept green during such a time? We 
 may water a small garden by the use of a hose, but such 
 a means of supplying water to a large field is impossible. 
 Therefore, any method by which the water-holding power 
 of soil may be improved is very important. 
 
 The water which is taken from the soil by plants may 
 have two sources. It may be from water which has recently 
 fallen as rain or it may be from water which has come up 
 through the soil from below. A hole dug in the soil during 
 dry weather will show that the upper part of the soil is dry 
 and that the lower part is moist. If you lift either a board 
 or a stone which has been undisturbed for a considerable 
 time, what is the condition of the soil beneath it ? What is 
 
 321 
 
322 
 
 GENERAL SCIENCE 
 
 the condition of the soil under a layer of leaves or straw 
 which has been lying in one place for a long time? 
 
 During dry weather lay a board on freshly cultivated 
 earth in the garden, and in a few days compare the appear- 
 ance of the surrounding soil with that under the board. 
 All of these observations indicate that the water which is 
 coming from below is escaping by evaporation at the surface 
 and that the loss may be prevented by a covering of some 
 kind. Sometimes such a covering is provided by a layer 
 
 FIGURE 259. VACANT LOT GARDEN. 
 Give two seasons for hoeing a garden. 
 
 of leaves called a leaf mulch. But usually such a method 
 cannot be employed very extensively. It has been found 
 that hoeing (Figure 259) or " cultivating " by making a 
 mulch of dry soil prevents to a great extent this escape 
 of water at the surface. This is because the small capil- 
 lary spaces through which the water has been coming from 
 
RELATION OF SOIL TO PLANTS 
 
 323 
 
 below are broken up. One of the reasons, therefore, for fre- 
 quent hoeing of a garden or cultivating of a field of corn is 
 to prevent the loss of moisture from the surface of the soil. 
 The power of different kinds of soils to absorb water from 
 below may be illustrated by the following experiment. 
 
 Experiment. Over the bottom of 
 each of four or five glass tubes having 
 a diameter of one or two inches, tie 
 a piece of cheesecloth (Figure 260). 
 Fill the different tubes with the fol- 
 lowing kinds of soil : coarse sand, fine 
 sand, loam, and clay. Place the bot- 
 toms of the tubes in a vessel of water, 
 and support them so that they will 
 
 a a a D 
 
 FIGURE 260. ABSORPTION OF 
 WATER BY SOILS. 
 
 stand upright. After a day examine From left to right : loam, clay, 
 
 the tubes and draw conclusions. 
 
 fine sand, coarse sand. 
 
 The finer the soil the smaller are the openings through 
 which the water passes. How does this experiment help 
 you to explain the effectiveness of the loose soil mulch? 
 How does it explain the fact that seeds will grow better if 
 the earth is pushed down firmly around them ? 
 
 The power of soils to hold the rain which falls upon them 
 is shown by the following experiment. 
 
 Experiment. Into four funnels in each of which has been placed 
 filter paper, put equal amounts of different soils : coarse sand, fine sand, 
 loam, and clay. Pour into the funnels equal amounts of water. Catch 
 the water that runs through in measuring glasses. After pouring the 
 water through several times, note the amount of water that runs 
 through each and draw your conclusions as to the conditions which 
 make soils good holders of water. Suggest how the ability of the soil 
 of a garden to hold moisture may be increased. 
 
 Problem 2. What plants take from the soil. Chemical 
 analysis of plants and experiments in their culture indicate 
 
324 GENERAL SCIENCE 
 
 that the following ten elements are necessary for their 
 growth: Carbon, hydrogen, oxygen, nitrogen, potassium, 
 magnesium, calcium, iron, sulphur, and phosphorus. In our 
 study of the making of starch and wood by plants, we have 
 already discovered from what source the plant gets its 
 carbon, hydrogen, and oxygen. Review and explain. All 
 the other elements must come from the soil. 
 
 Fortunately, the soil usually contains all of these with the 
 exception of three, in such quantities that there is not much 
 danger of them being exhausted. The three which are 
 likely to be lacking are nitrogen, potassium, and phosphorus. 
 These frequently have to be added to the soil in some way. 
 
 Problem 3. How nitrogen may be given to the soil. 
 Nitrogen is found largely in the organic part of the soil, and 
 Konsequently the addition of plant and animal material 
 will increase the stock of nitrogen. One form of organic 
 matter put upon the soil is horse manure. In some parts 
 of the country, fish which are useless for food are spread over 
 the fields. It is said that the early American explorers 
 found that the Indians placed a fish in each hill of corn. 
 
 Waste from slaughter houses; guano, the excrement of 
 countless generations of sea birds ; cottonseed meal ; linseed 
 meal, etc., are useful sources of nitrogen. The nitrogen in 
 none of these plant or animal substances can be used by the 
 growing plant until the bacteria in the soil cause them to 
 decay. 
 
 Nitrate of soda, of which there are great deposits in the 
 rainless regions of Chili, and sulphate of ammonia, which is 
 a by-product of the manufacture of gas, are other valuable 
 sources of nitrogen. 
 
 It has been known for a very long time that a crop of clove* 
 seems to enrich the soil. As a result of this knowledge, 
 
RELATION OF SOIL TO PLANTS 325 
 
 most farmers after using a field for various crops for several 
 years plant clover in it. In order to understand this, we 
 must first know that the nitrogen of the air cannot be used 
 directly by plants. Plants may fail to grow because of 
 nitrogen starvation, although the crevices in the soil around 
 their roots and the space around their leaves are filled with 
 air, four fifths of which is nitrogen. Clover and related 
 plants, such as peas, beans, alfalfa, etc., have small enlarge- 
 ments on their roots which are not possessed by /others. 
 These enlargements contain a certain kind of bacteria 
 which have the power to convert some of the ni- 
 trogen of the air into a form which can be used by the 
 plant. 
 
 Several methods have been discovered by which the 
 nitrogen of the air has been made to combine with some other 
 substance, forming a compound which may be used for plant 
 growth. The need for nitrogen compounds during the war, 
 chiefly for making explosives, has caused large factories to be 
 built for the production of nitrogen compounds. Now that 
 the need for explosives has largely disappeared, the prod- 
 ucts of these factories may be used to supply nitrogen com- 
 pounds needed for the growth of plants. 
 
 Problem 4. How potassium and phosphorus are supplied 
 to the soil. Both of these elements are found in the mineral 
 part of soil. They are usually in an insoluble form which 
 cannot be taken up by plants. The action of weather and 
 of the acids produced by decay of vegetable and animal 
 matter in the soil change the insoluble potassium and phos- 
 phorus compounds into soluble 'substances which can be 
 taken up by plants. 
 
 Decaying animal and plant matter not only helps to make 
 the potassium and phosphorus compounds already in the 
 
326 GENERAL SCIENCE 
 
 mineral part of the soil usable, but as they themselves 
 contain compounds of these two elements their addition 
 increases the supply. Wood ashes spread upon the soil 
 improve the growth of plants largely because of the great 
 amount of potassium which they contain. 
 
 The chief source, however, of potassium fertilizers has 
 been the great deposits of Stassfurt, Germany. During 
 the war the United States together with all other countries 
 faced a potassium famine which threatened to lessen crop 
 production. At the time the war ended, methods for obtain- 
 ing potassium from rocks holding it in an unusable form 
 were being perfected. It had also been found that consider- 
 able quantities could be obtained from kelp or seaweed, which 
 is very abundant on some parts of the Pacific coast. So, if 
 the war had continued, we could have had a supply of potas- 
 sium to meet all our needs. 
 
 One of the sources of phosphorus fertilizers is organic 
 matter such as slaughter house waste and fish scraps ; bone 
 meal is especially valuable since a large part of the mineral 
 material of bones consists of a compound of phosphorus. 
 Other important sources of phosphorus fertilizers are phos- 
 phate rocks, and slag from steel mills. The phosphate rock 
 is found in many of the southern and western states. The 
 slag is obtained in the process of removing phosphorus from 
 iron in the making of steel. 
 
 Problem 5. How plants remove needed materials from 
 the soil. Review what we have already learned concerning 
 how the roots of plants are fitted to take in water. Since 
 the dissolved mineral substances in the soil are taken in with 
 the water, the adaptations of the roots for taking in water 
 are also adaptations for taking in the needed mineral sub- 
 stances. 
 
RELATION OF SOIL TO PLANTS 327 
 
 
 
 If the ashes of different kinds of plants growing side by 
 side are analyzed by a chemist, it is found that the various 
 mineral substances are not present in the same relative 
 amounts. For example, clover will contain many times as 
 much lime or calcium as wheat ; while wheat, on the other 
 hand, may contain as much as ten or fifteen times as much 
 silica as clover. Apparently, the plant is able to select the 
 materials which it needs. This is known as selective absorp- 
 tion. The explanation seems to be that if the living matter 
 of the plant does not take a certain kind of mineral sub- 
 stance out of the water which has passed into the plant 
 through the wall of the root hair, then the sap or water in 
 the root hair becomes saturated with that special kind of 
 mineral substance and no more will pass through the wall 
 of the root hair. If, however, the plant uses a particular 
 mineral substance, then it is constantly being taken out of 
 the sap and more comes through the wall of the root hair 
 to replace that which has been taken out by the living 
 matter. 
 
 Clover, for example, in its growth is continually building 
 lime material into plant substance; and as a result, more 
 lime comes through the membrane of the root hair. Wheat 
 does not use nearly so much lime; and accordingly, very 
 little need come through the root hair to replace the amount 
 taken out by the living matter of the plant. 
 
 Problem 6. What plants do with material taken from the 
 soil. You have already learned how in the green leaves 
 of the plant the carbon dioxide of the air and the water from 
 the soil are made into starch. As a result of the action of 
 the living material of the plant, the starch may be made 
 into cell walls, and into fat or oil. There are always asso- 
 ciated with, the living matter of the plant more complex 
 
328 m GENERAL SCIENCE 
 
 substances called proteins. These contain not only carbon, 
 hydrogen, and oxygen as starch does, but also nitrogen, 
 phosphorus, iron, etc., which have been taken from the soil. 
 The proteins are necessary for the growth of new living 
 matter. 
 
 Some of the elements, in addition to being necessary con- 
 stituents of living matter and of the food materials formed 
 in plants, have special duties to perform. Some seem to 
 neutralize acids formed in the plant; others are necessary 
 constituents of the coloring matter of plants; while still 
 others give firmness to the woody substance of the plant. 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Use different kinds of fertilizer in your garden and record the 
 results. 
 
 2. Experiments to show the water-retaining power of different kinds 
 of soil. 
 
 REPORTS 
 
 1. Obtaining potassium from seaweed. 
 
 2. Records of the amount of various mineral materials taken 
 from soil by some of the standard crops. 
 
 REFERENCES FOR PROJECT XXVII 
 
 1. Soils; Their Properties and Management, T. L. Lyon. Mac- 
 millan Company. ^ 
 
 2. Agronomy, Clute. Ginn & Co. 
 
 3. Story of Agriculture in the United States, A. H. Sanford. 
 D. C. Heath & Co. 
 
 4. Essentials of Agriculture, H. W. Waters. Ginn & Co. 
 
 5. The Land We Live In, O. W. Price. Small, Maynard & Co. 
 
 6. Earth and Sky Every Child Should Know, J. E. Rogers. Double- 
 day, Page & Co. 
 
 7. Farm Science, W. J. Spellman. World Book Company. 
 
 8. Elementary Agriculture, J. S. Grim. Allyn and Bacon. 
 
PROJECT XXVIII 
 
 HOW PLANTS AND ANIMALS MAKE USE OF THE 
 FOOD MANUFACTURED BY PLANTS 
 
 Problem 1. Why must plants and animals have food? 
 Compare the growth of a bean or pea seedling, from which the 
 seed leaves have been removed, with the growth of one from 
 which they have not been removed. What is the result? 
 Since the food for the growing seedling is stored up in the 
 seed leaves, what is your conclusion? 
 
 Your observations are sufficient without any experiments 
 to prove to you that animals also must have food. The 
 question is : Why is food so necessary ? 
 
 We know that animals and plants exert energy. Plants 
 are able to push their roots through the soil and against the 
 force of gravity Give examples of this. Likewise, animals 
 have the power of movement, produce heat, and are able to 
 do work. Knowing that animals and plants breathe in 
 oxygen and breathe out carbon dioxide, and that food must 
 be taken in, what is your conclusion as to what happens to 
 some of the food in the body? One use of food, therefore, 
 is to act as a fuel which when burned furnishes heat, and 
 power to do work. 
 
 Another use of food is evident to you; you weigh more 
 this year than you did last year; you say that you have 
 grown ; your bones have become longer and thicker ; muscles 
 are larger ; heart is a little bigger, etc. Where did the addi- 
 tional material come from? What, then, will you conclude 
 
 329 
 
330 
 
 GENERAL SCIENCE 
 
 is another reason why plants and animals, and we, ourselves, 
 must take in food ? 
 
 In the work of the body there is a certain amount of 
 wearing away of its parts. This wear evidently must be 
 made good by food being built up into the muscles, nerves, 
 
 and other parts of the 
 body. State, now, the 
 three uses made of food 
 by plants, animals, and 
 the human body. 
 
 Our next question 
 naturally will be : What 
 foods are good for each 
 of these purposes ? 
 
 Problem 2. What 
 foods are good for fuel, 
 and what ones for growth 
 and repair ? Consider- 
 ation of the kinds of 
 food that are eaten 
 under certain conditions 
 may help us to solve 
 this problem. People 
 living in the Arctic re- 
 gions must have food 
 which will produce a great deal of heat. You all 
 know that fat forms the greater part of their diet. What 
 will be your conclusion, therefore, as to the value of fat in 
 the food ? Consider your own diet in regard to the use of 
 fat. Do you eat a greater quantity in winter or in summer ? 
 The hard work of lumbermen in the northern woods is done 
 chiefly in winter (Figure 261). They need food which will 
 
 FIGURE 261. LUMBERMEN AT WORK. 
 
 Why do these men need a large amount 
 
 of energy-producing food ? 
 
USE OF THE FOOD MANUFACTURED BY PLANTS 331 
 
 give them heat, and the power to do hard work. They eat 
 much fat meat, as you would expect, but they also eat a great 
 amount of molasses, large quantities of potatoes, and other 
 starchy foods. This is an indication of the value of foods 
 which contain starch and sugar. 
 
 These observations concerning the use of fats, starch, and 
 sugar are in harmony with experiments which have been 
 made as to the value of different food substances. Starches 
 and Ugar, which together are called carbohydrates, and fats 
 because they are common to so many foods, are called food 
 principles or nutrients. 
 
 We have already decided that foods, in addition to furnish- 
 ing energy, are also necessary for growth and repair. For 
 this purpose it has been found that there must be present 
 a food principle or nutrient called protein, and certain 
 mineral substances. These contain elements which are not 
 present in fats and carbohydrates but which are necessary 
 for the building of different parts of the body. 
 
 For example, living matter contains nitrogen; and as 
 protein is the only nutrient which contains nitrogen, it is 
 necessary for growth and repair of living matter. Foods 
 containing a large percentage of protein are lean meat, fish, 
 eggs, milk, cheese, beans, and peas, and to a lesser extent 
 cereals (oats, wheat, barley, and rye). 
 
 Mineral matters are not only necessary for the making of 
 new living matter and for the formation of the bones of the 
 body, but their presence is necessary for the action of nerves 
 and muscles, and for the passing of liquids through the walls 
 of the small blood vessels and through other membranes. 
 Iron has a special duty in forming the coloring matter of the 
 red blood corpuscles. Mineral materials are very widely 
 distributed among foods. Most natural foods contain 
 
332 
 
 GENERAL SCIENCE 
 
 considerable mineral matter, so that usually the ordinary 
 diet contains a sufficient amount. Milk, eggs, lean meat, 
 leafy vegetables, fruits, and flour made from the whole grain 
 
 flnnmn ^M mm ^^ MM\ F Ue ivaiu 9 
 
 Protein Fat Carbohydrate* Ash Water Biooo Carrie* 
 
 WHITE BREAD WHOLE WHEAT BREAD 
 
 iter:35.3 Water;38.4 
 
 rotein:9.2 Protein:9.7 
 
 FUEL VALUE: 
 
 Carbo- Carbo- 
 
 tes:53.1 hydrates: 49.7 
 
 OAT 
 BREAKFAST FOOD 
 
 121 5 CALORIES ' Water: 84.5 
 
 PER POUND 
 
 Protei 
 
 TOASTED BREAD 
 
 Ash: 0.7 
 
 FUEL VALUE: 
 
 1140 CALORIES 
 PER POUND 
 
 Fat: 0.5 
 
 rbohydrates:11.5 
 
 CORN BREAD 
 
 FUEL VALUE: 
 
 ater: 24.0 
 otein:11.5 Protein77.9 
 
 Carbo- Carl 
 
 hydrates: 61. 2 hydrates:46.3 
 
 MACARONI 
 
 COOKED 
 
 FUEL VALUE: 
 
 Carbo- 
 hydrates: 15.8 
 
 FuEL 
 VALUE: 
 
 41 5 CALORIES 
 PER POUNO 
 
 FIGURE 262. COMPOSITION OF BREAD AND CEREAL FOODS. 
 
 are especially rich in mineral matter and very nutritious. 
 
 Recent experiments have shown that unless .certain 
 
 chemical substances (vitamines) which are found especially 
 
USE OF THE FOOD MANUFACTURED BY PLANTS 333 
 
 in green vegetables and milk are present, normal growth 
 does not occur. Therefore, it is very important to include 
 these in the diet. 
 
 onnn 
 
 Protein Fat Carbohydrate! 
 
 Ah 
 
 Water 
 
 I Fuel Value, 
 ^Sq.ln.Equals 
 1000 Calories 
 
 ONION 
 
 WaU 
 Prote'u 
 
 Carbohydrates: 9.9- 
 ater:83.0 FUEL VALUE: 
 
 225 CALORIES 
 Protein:!. 6 I I PER POUND 
 
 Fat:0.5 
 Carbohydrates: 13.5 
 
 il.4 
 
 PARSNIP 
 
 POTATO 
 
 Protein:2.2 
 
 Water.94.5 
 
 Carbohydrates: 18.4 ^Water:78.3 
 
 FUEL VALUE: Protein 
 
 Carbohydrates: 3. 
 
 385 CALORIES PER POUND 
 
 Ash:1.0 
 
 FIGURE 263. COMPOSITION OF SOME COMMON VEGETABLES. 
 
 Name ten foods that are good for supplying energy. 
 Name five foods that are good for growth and repair. 
 Problem 3. How the fuel value of foods is measured. 
 
334 
 
 GENERAL SCIENCE 
 
 Foods burned outside of the body furnish the same amount 
 of energy as if they were burned within the body. The fuel 
 
 Protein 
 
 COD 
 
 Lean Fish 
 
 Fat Carbohydrates Ash 
 
 Water 
 
 Fuel Value 
 iSq. In. Equals 
 1000 Calorie* 
 
 FUEL VALUE: 
 .Water:82.6 
 
 325 CALORIES 
 PER POUND 
 P rote in,:] 5. 8 
 
 Wat 
 
 Carbohydrates: 3. 
 SMOKED HERRING 
 
 ate r: 34.6 
 rotein:36..4 
 
 FtTEL VALUE: 
 
 1355 CALORIES 
 
 PER POUND 
 
 Ash:T3. 
 
 410 CALORIES 
 PER POUND 
 
 Protein 21.5 
 
 645 CALORIES 
 PER POUND 
 
 FIGURE 264. COMPOSITION OF FISH AND OYSTERS. 
 
 value of carbohydrate, fat, and protein is therefore obtained 
 by burning known amounts of these nutrients in an instru- 
 ment called a calorimeter, so constructed that all the heat 
 produced is used to heat a measured amount of water. The 
 
USE OF THE FOOD MANUFACTURED BY PLANTS ' 335 
 
 amount of heat necessary to warm a kilogram of water 
 one degree Centigrade, is taken as the unit. This unit is 
 
 mmnnn 
 
 Protein Fat Carbohydrates 
 
 WHOLE EGG 
 
 Ash 
 
 I Fuel Value 
 
 Water Sq.ln.Equali 
 
 Water i 000 Calories 
 
 EGG 
 
 WHITE AND YOLK 
 
 Protein 
 
 14. 
 Fat: 10.5 
 
 Ash:1. 
 FUEL VALUE OF 
 
 WHOLE EGG: 
 
 FUEL VALUE OF YOLK: 
 
 700 .CALORIES 
 PER POUND 
 
 CREAM CHEESE 
 
 Water: 34.: 
 
 1608 CALORIES 
 PER POUND 
 
 /Pr;otein:13.0 
 
 Fat: 0.2 
 Ash:0.6 
 
 FUEL VALUE OF WHITE: 
 
 c 
 
 265 CALORIES 
 PER POUND 
 
 COTTAGE CHEESE 
 
 lte in:25.9 Wate !: :72 - 
 
 rbo- 
 ydrates: 2.4 
 
 in:20.9 
 
 Carbo 
 hydrates: 4.3 
 
 FuELVALUE: 
 1950 CALORIES PER POUMO 
 
 510 CALORIES PER POUKD 
 
 FIGURE 265. COMPOSITION OF EGGS AND CHEESE. 
 
 called a calorie. A pound of pure starch, sugar, or protein 
 will yield when burned about 1850 calories, and a pound of 
 pure fat about 4220 calories. 
 
 It can be seen that if the amount of these nutrients in a 
 
336 
 
 GENERAL SCIENCE 
 
 food are known, it is very easy to calculate the fuel value 
 of the food. The following table, compiled by Dr. Irving 
 
 Protein Fat Carbohydrates Ash 
 
 CORN 
 
 Water: 10.8 
 
 rotein:10.0 
 
 Water 
 
 Water :1 0.6 
 Protein- 12.2 
 
 I Fuel Value 
 ft Sq.ln. Equals 
 1000 Calories 
 
 WHEAT 
 
 at: 1.7 
 
 FUEL VALUE; 
 
 BUCKWHEAT 
 
 1800 CALORIES Protein: 10. 
 PER POUND f 
 
 Carbohydrates: 73.7 
 
 Water:12.6 | 75 CALORIES 
 Fat: 2. 2 PER POUND 
 
 FufLVALUE: 
 
 OAT . RICE 
 
 Water: 11.0 1600 CALORIES Water:12.0- 
 Fat:5.0-~$r-Protein:11.8 ' ERPOUNO Protein:' 
 
 m Carbo- RYE 
 
 Fat:' 
 
 at:2.0 
 
 Ash:1.0 
 
 FUEL VALUE; 
 
 HH hydrates: 73.9 \i^Ash:1.9 
 1720 CALORIES FUEL VALUE; 
 
 PER POUND 
 
 1720 CALORIES 
 PER POUND 
 
 (750 CALORIES 
 PER POUND 
 
 FIGURE 266. COMPOSITION OF VARIOUS GRAINS USED FOR FOOD. 
 
 Fisher of Yale, gives the amount of each of a number of 
 common foods which will furnish 100 calories. 
 
 Problem 4. What is the proper amount of food ? We 
 know from experience that the amount of food needed is 
 
USE OF THE FOOD MANUFACTURED BY PLANTS 337 
 
 not the same for all persons, and not even the same for one 
 person under all circumstances. Fortunately, if we are in 
 good health the appetite is a fair guide, although if it is 
 disregarded and abused it soon becomes unreliable. Eating 
 between meals, eating highly flavored food, etc., destroys 
 the keenness of the appetite and either undereating or 
 overeating may result. It is necessary, therefore, to know 
 what the body needs under certain conditions so that the 
 appetite may not lead us astray. 
 
 Your own experiences will indicate to you some of the 
 conditions that determine the amount of food needed by 
 the body as indicated by the appetite. Do you eat more 
 food when you have been spending the day reading or when 
 you have been playing outdoors or doing some active work? 
 Why do you think this should be true? Do you eat more 
 food in summer or in winter? Explain the reason for this. 
 In both of these cases should the increase be in energy- 
 producing food or in food used for growth and repair? 
 Suggest how you think the diet should be modified at such 
 times ? 
 
 Experiments have shown that there is no need for any 
 increase of protein, or building material, in the diet at times 
 when the body is exerting more energy than us.ual, but that 
 the increase in the amount of food should be by additions of 
 fats or carbohydrates. 
 
 Growing children, of course, should have a slightly higher 
 percentage of protein in their food than adults. Explain. 
 This is well illustrated by the fact that milk, which should 
 always be an important part of the food of children and 
 which in the earliest years constitutes either all or a very 
 large part of their diet, has a higher percentage of protein 
 than is demanded by people who are no longer growing. 
 
338 
 
 GENERAL SCIENCE 
 
 TABLE OF 100-CALORIE PORTIONS 1 
 
 EDIBLE PORTIONS 
 
 APPROXIMATE MEASXTRE 
 OF IOO-CALORIE 
 PORTION 
 
 WEIGHT 
 IN OUNCES 
 OF IOO- 
 CALORIE 
 PORTION 
 
 CALORIES 
 DERIVED 
 
 FROM 
 
 PROTEIN 
 
 Almonds ... 
 
 15 average 
 
 0.5 
 
 12.6 
 
 
 2 medium 
 
 5.6 
 
 2.5 
 
 Apricots, fresh . . . 
 
 2 large 
 
 6.1 
 
 7.7 
 
 Asparagus, cooked . . 
 
 2 servings 
 
 7.5 
 
 17.9 
 
 Bacon, smoked (un- 
 
 
 
 
 
 1 thin slice, small 
 
 0.6 
 
 6.7 
 
 
 Ilarce 
 
 3.6 
 
 5.3 
 
 Beans, baked, canned 
 
 MOAjf^ 
 
 1 small serving ( cup- 
 
 
 
 
 ful) 
 
 ^2.8 
 
 21.5 
 
 string, canned . . 
 
 5 servings 
 
 17.2 
 
 21.5 
 
 lima, canned . . . 
 
 1 large saucedish 
 
 4.6 
 
 20.8 
 
 Beef, corned .... 
 
 
 1.2 
 
 21.2 
 
 dried, salted and 
 
 
 
 
 smoked .... 
 
 4 large slices 
 
 2.0 
 
 67.2 
 
 porterhouse steak . 
 
 1 small steak 
 
 1.3 
 
 32.4 
 
 ribs, lean . . ... 
 
 1 average serving 
 
 1.9 
 
 42.3 
 
 ribs, fat .... 
 
 
 0.9 
 
 15.6 
 
 round, free from vis- 
 
 
 
 
 ible fat .... 
 
 1 generous serving 
 
 3.1 
 
 80.7 
 
 rump, lean . . 
 
 
 1.7 
 
 41.0 
 
 rump, fat . . . . 
 
 
 0.9 
 
 17.5 
 
 sirloin steak . . 
 
 1 average serving 
 
 1.4 
 
 31.0 
 
 Beets, cooked . . . 
 
 3 servings 
 
 8.9 
 
 23.2 
 
 Brazil nuts . . . ; . . 
 
 3 average size 
 
 0.5 
 
 10.2 
 
 Bread, graham . . . 
 
 1 thick slice 
 
 1.3 
 
 13.5 
 
 toasted .... 
 
 2 medium slices 
 
 
 
 
 (baker's) 
 
 1.2 
 
 15.2 
 
 white homemade 
 
 1 medium slice 
 
 1.3 
 
 13.8 
 
 average .... 
 
 1 thick slice 
 
 1.3 
 
 14.0 
 
 whole wheat . . . 
 
 1 thick slice 
 
 1.4 
 
 15.9 
 
 Buckwheat flour . 
 
 i cupful 
 
 1.0 
 
 7.4 
 
 1 The Approximate Measure of 100-Calorie portions is based in part upon 
 "Table of 100 Food Units," compiled by Dr. Irving Fisher. The Weight 
 in Ounces of 100-Calorie Portions and Calories derived from Protein are 
 based upon data found on page 319 of " Chemistry of Food and Nutrition," 
 by Henry C. Sherman, 
 
USE OF THE FOOD MANUFACTURED BY PLANTS 339 
 
 EDIBLE PORTIONS 
 
 APPROXIMATE MEASURE 
 OF 100-CALORIE 
 PORTION 
 
 WEIGHT 
 
 IN OUNCES 
 
 OF 100- 
 CALORIE 
 
 PORTION 
 
 CALORIES 
 DERIVED 
 
 FROM 
 
 PROTEIN 
 
 Butter . . . . . 
 
 1 tablespoon (ordinary 
 
 
 
 Buttermilk . . . . 
 
 pat) 
 It cupfuls (1 glasses) 
 2 servings 
 
 0.5 
 9.9 
 11.2 
 
 0.5 
 33.6 
 20.3 
 
 Calf s-foot jelly ... 
 Carrots, fresh . . . 
 Cauliflower 1 . . . 
 Celery * 
 
 2 medium 
 
 4.1 
 7.8 
 11.6 
 19 1 
 
 19.8 
 9.7 
 23.6 
 23 8 
 
 Celery soup, canned . 
 Cheese, American pale l 
 American red x . 
 ' Cheddar 1 . . . ,~ 
 Cottage .... 
 Neufchatel . . . 
 
 Roquefort 1 . . ; 
 
 2 servings 
 H cubic inches 
 H cubic inches 
 li cubic inches 
 4 cubic inches (^ cupful) 
 H cubic inches (i cup- 
 ful) (^ small pack- 
 age) 
 
 li cubic inches 
 
 6.6 
 0.8 
 0.8 
 0.8 
 3.2 
 
 1.1 
 1.0 
 0.8 
 
 15.7 
 26.5 
 26.0 
 24.4 
 76.1 
 
 23.2 
 25.3 
 25.4 
 
 Chicken, broilers . 
 Chocolate .... 
 
 1 large serving 
 " generous half" square 
 2^ tablespoonfuls 
 
 3.3 
 0.6 
 07 
 
 79.1 
 8.3 
 17.3 
 
 Cod, salt . . ... ; 
 Corn, green 1 . . ,. 
 Corn meal . . . ; 4 .. 
 Crackers, graham . . 
 soda . . . . . 
 
 1 side dish 
 2 tablespoonfuls 
 3 crackers 
 3 crackers 
 
 3.4 
 3.6 
 .1.0 
 0.9 
 0.9 
 
 97.5 
 11.4 
 10.3 
 9.6 
 9.4 
 
 
 3 crackers 
 
 0.9 
 
 10.3 
 
 Cranberries x . . . 
 Cream . . . . . 
 
 1 cupful (cooked) 
 
 ij CUpful 
 
 7.5 
 1.8 
 
 3.4 
 5.0 
 
 Cucumbers . . . . 
 Dates, dried . . . 
 Doughnuts . . . 
 Eggs, uncooked . .. 
 Farina . . . . . 
 
 2 large 
 4 medium 
 doughnut 
 1 medium or 2 small 
 
 20.3 
 1.0 
 0.8 
 2.4 
 1.0 
 
 18.4 
 2.4 
 6.2 
 36.4 
 12.3 
 
 Figs, dried .... 
 Flour, rye .... 
 wheat, entire 
 wheat, graham . 
 wheat, average high 
 and medium . . 
 
 1 large 
 i? cupful 
 i cupful 
 i cupful 
 
 \ cupful 
 
 1.1 
 
 1.0 
 1.0 
 1.0 
 
 1.0 
 
 5.5 
 
 7.9 
 15.5 
 14.9 
 
 12.8 
 
 1 As purchased. 
 
340 
 
 GENERAL SCIENCE 
 
 EDIBLE PORTIONS 
 
 APPROXIMATE MEASURE 
 OF 100-CALORIE 
 PORTION 
 
 WEIGHT 
 IN OUNCES 
 OF 100- 
 CALORIE 
 PORTION 
 
 CALORIES 
 DERIVED 
 
 FROM 
 
 PROTEIN 
 
 
 4 tablespoonfuls 
 
 1.0 
 
 98:7 
 
 
 1 large bunch 
 
 3.7 
 
 5.4 
 
 Haddock 
 
 
 4.9 
 
 96.3 
 
 Halibut steaks . . . 
 Ham, fresh, lean . 
 fresh, medium . . 
 smoked, lean . . 
 Herring, whole . 
 Hominy, uncooked 
 Lamb, chops, broiled 
 leg, roast . 
 Lard, refined . . . 
 Lemons 
 
 1 average serving 
 1 average serving 
 
 i cupful 
 1 small chop 
 1 average serving 
 .1 tablespoonful (scant) 
 3 medium 
 
 2.9 
 1.5 
 1.1 
 1.3 
 
 2.5 
 1.0 
 1.0 
 1.8 
 0.4 
 80 
 
 61.8 
 44.0 
 19.0 
 30.1 
 54.6 
 9.3 
 24.3 
 41.0 
 
 (-) 
 9.0 
 
 Lettuce . . . 
 
 50 large leaves 
 
 20.4 
 
 25.2 
 
 Liver, veal, uncooked 
 Macaroni, uncooked . 
 Macaroons .... 
 Mackerel, uncooked . 
 salt .... 
 
 2 small servings 
 i cupful (4 sticks) 
 2 
 1 large serving 
 
 2.9 
 1.0 
 0.8 
 2.5 
 1 2 
 
 61.6 
 15.0 
 6.2 
 53.9 
 29.5 
 
 Marmalade, orange . 
 Milk, condensed, 
 sweetened . . . 
 skimmed .... 
 whole . . . . 
 
 Molasses, cane . . . 
 Muskmelons . . . 
 Mutton, leg . . . . 
 Oatmeal, uncooked 
 Olives, green . . . 
 Onions, fresh . . . 
 Oranges . 
 
 1 tablespoonful 
 
 ITS cupfuls 
 li cupfuls (scant) 
 f- cupful (generous half 
 glass) 
 i cupful 
 average serving 
 1 average serving 
 i cupful 
 7 to 10 
 2 medium 
 1 very large 
 
 1.0 
 
 1.1 
 9.6 
 
 5.1~ 
 1.2 
 8.9 
 1.8 
 0.9 
 1.2 
 7.3 
 6 9 
 
 0.7 
 
 10.9 
 37.1 
 
 19.1 
 3.4 
 6.0 
 41.2 
 16.1 
 1.5 
 13.2 
 
 fi 9 
 
 Oysters, canned . . 
 Parsnips 
 Pea soup, canned . . 
 Peaches, canned . . 
 fresh . . . . 
 
 5 oysters 
 1 large 
 
 1 large serving 
 4 medium 
 
 4.9 
 5.4 
 6.9 
 7.5 
 
 85 
 
 48.6 
 9.9 
 
 28.2 
 6.0 
 
 A Q 
 
 
 10 to 12 (double kernels) 
 
 06 
 
 18 6 
 
 Peas, canned . . . 
 Peas, dried, uncooked 
 
 2 servings 
 2 tablespoonfuls 
 
 6.3 
 1.0 
 
 25.9 
 27.6 
 
 As purchased. 
 
USE OF THE FOOD MANUFACTURED BY PLANTS 341 
 
 EDIBLE PORTIONS 
 
 APPROXIMATE MEASURE 
 OF IOO-CALORIE 
 PORTION 
 
 WEIGHT 
 IN OUNCES 
 OF IOO- 
 CALORIE 
 PORTION 
 
 CALORIES 
 DERIVED 
 
 FROM 
 
 PROTEIN 
 
 Peas, green .... 
 Pies, apple .... 
 custard . . ... 
 
 1 generous serving 
 i piece 
 | piece 
 ^ piece 
 
 3.5 
 1.3 
 2.0 
 1.4 
 
 28.0 
 4.6 
 9.4 
 56 
 
 
 \ piece 
 
 1.2 
 
 8.1 
 
 squash .... 
 Pineapples, fresh . . 
 canned .... 
 Pork, chops, medium 
 fat, salt l . . . . . 
 Potatoes, white, 
 uncooked . . . 
 sweet, uncooked 
 Prunes, dried . . . 
 Raisins ... 
 
 piece 
 5 slices 
 1 small serving 
 1 very small serving 
 
 1 medium 
 medium 
 3 large 
 ^ cupful (packed solid) 
 
 2.0 
 8.2 
 2.3 
 1.1 
 0.5 
 
 4.2 
 2.9 
 1.2 
 i o 
 
 9.9 
 3.7 
 1.0 
 19.9 
 1.0 
 
 10.6 
 5.8 
 2.8 
 
 Q 
 
 Rhubarb, uncooked . 
 Rice, uncooked . . 
 Salmon, whole . . . 
 Shad, whole . . . 
 Shredded wheat . . 
 Spinach, fresh 1 . . . 
 
 Succotash, canned 
 
 3% cupfuls (scant) 
 2 tablespoonfuls 
 1 small serving 
 1 average serving 
 1 biscuit 
 3 ordinary servings 
 (after cooking) 
 1 average serving 
 13 lumps, 5 teaspoonfuls 
 granulated 
 
 15.3 
 1.0 
 1.7 
 2.2 
 1.0 
 
 14,7 
 3.6 
 
 0.9 
 
 10.4 
 9.3 
 43.1 
 45.9 
 11.3 
 
 35.0 
 14.7 
 
 (-) 
 
 Tomatoes, fresh . . 
 canned . . . .'' 
 Turkey 
 
 6 teaspoonfuls pow- 
 dered sugar 
 4 average servings 
 If cupfuls 
 1 serving 
 
 15.5 
 15.6 
 1.2 
 
 15.8 
 21.3 
 
 28.7 
 
 
 2 large servings (2 tur- 
 
 
 
 Veal, cutlet . . . > 
 fore quarter . . . 
 . hind quarter . . . 
 Vegetable soup, canned 
 Walnuts, California . 
 Wheat, cracked ... 
 Whitefish . . . '4 . 
 Zwieback .... 
 
 nips) 
 
 4 whole nuts 
 1 thick slice 
 
 9.0 
 2.3 
 2.3 
 2.3 
 
 25.9 
 0.5 
 1.0 
 2.4 
 0.8 
 
 13.3 
 53.6 
 52.8 
 53.0 
 85.3 
 10.3 
 12.4 
 61.4 
 9.4 
 
 As purchased, 
 
342 GENERAL SCIENCE 
 
 Another condition which will affect the amount of food 
 needed is the size of the body. Other conditions being the 
 same, a small person needs somewhat less food than a larger 
 person. It has been calculated that the number of calories 
 which should be supplied by the food when light work is 
 being done may be determined by multiplying the weight of 
 the body by 16.1. Thus a person weighing 160 pounds will 
 need sufficient food to furnish 2576 calories. Of course, if 
 more active muscular work is being performed, food pro- 
 ducing a greater number of calories is needed. A man doing 
 moderately active work needs about 3000 calories; a farmer 
 during the busy season, as much as 4000 calories; and 
 lumbermen, from 5000 to 9000 calories. 
 
 The proper amount of protein in the diet has been a much 
 discussed question. This is of great importance, since an 
 excess of protein in the diet is harmful to the body. The 
 tendency of the American people is to eat rather more protein 
 than is absolutely necessary, and therefore in most cases the 
 diet would be improved by cutting down the foods rich in 
 protein; for example, meats. About two and one half 
 ounces or from 70 to 80 grams of protein a day seem to be 
 sufficient, according to experiments. It will be found, how- 
 ever, that our actual diet is. likely to have nearly three and 
 one half or four ounces or about 100 grams of protein. 
 
 Problem 5. What considerations should govern the plan- 
 ning of our diet? It is evident that our diet must have the 
 proper fuel value, and contain the proper amount of protein. 
 Since there is usually too much protein in an unrestricted 
 diet, large amounts of lean meats and other foods containing 
 a high percentage of protein should be avoided. It would 
 be well to calculate by the use of the 100-calorie portion 
 tables given the calorie value of your food for a day. If more 
 
USE OF THE FOOD MANUFACTURED BY PLANTS 343 
 
 than 15 per cent of the calories are from protein, then your 
 diet is too rich in that. An excess of fat or carbohydrate 
 in the diet is apt to cause an increase of weight due to the 
 storing up of excess fuel in the form of fat. 
 
 A diet which contains the proper amount of protein, car- 
 bohydrate, and fat may, however, be a very unsatisfactory 
 one. There must be included in it foods which will supply 
 the minerals needed by the body, and those minute sub- 
 stances sometimes called mtamines, without which normal 
 growth and repair does not occur. Vegetables, whole grain 
 bread and cereals, fruits, and milk are especially valuable 
 for their minerals. Milk and leafy vegetables such as lettuce 
 and spinach are indispensable in the diet. Fruits and coarse 
 elements in the food such as the bran or outer coat of wheat 
 exert a beneficial effect upon the digestive organs. 
 
 A good diet, therefore, will be one which supplies the 
 proper amount of the three nutrients, and includes milk, 
 leafy vegetables, some fruit and coarse food such as whole 
 wheat bread, and is so varied as not to become monotonous. 
 It is presumed, also, that those parts of the food which are 
 cooked have been made both more digestible and more 
 appetizing, and that there has been no waste of their elements. 
 
 Problem 6. Why must foods be digested ? Consider 
 the condition in the corn seedling. Where is the food stored ? 
 Where is growth going on, and where is energy being exerted ? 
 The food then must be able to travel from the seed to the 
 growing point. But the young stem and root, just as we 
 saw in the older root and in the leaves, are made up of little 
 box-like structures (Figure 267) (cells) so that the food in 
 reaching the point where it is needed must pass through 
 hundreds of the thin walls of these cells. The question now 
 is, is the stored-up food in condition to pass through these 
 
344 
 
 GENERAL SCIENCE 
 
 membranous walls? The following experiment will enable 
 you to answer this question. 
 
 Experiment.- Break off the bottom of a test tube so that it forms 
 a tube open at both ends. Over one end of it tie a piece of parch- 
 ment paper or a piece of the dried bladder of a pig or other animal. 
 Place the tube with the parchment end down in a vessel of water in 
 which has been stirred some starch. After about an hour test the 
 water which has come into the tube through the parchment for the 
 presence of starch. This test is made by adding to the water an 
 iodine solution which turns it blue if starch is present. What is the 
 result ? What is your conclusion ? 
 
 The parchment or mem- 
 brane represents the cell walls 
 through which the food must 
 pass. Evidently the starch 
 must be changed into something 
 else or it can be of no value 
 to the plant. Since we know 
 that it disappears from the 
 seed and that energy is exerted 
 at the growing point, then we 
 know that it is changed into 
 something which will pass 
 through the walls. 
 
 The protein and the fat stored 
 in the seed are also unable to 
 pass through membranes and 
 they too must be changed. The 
 process by which all of these 
 foods are changed is called diges- 
 tion. Our own foods must be 
 changed in the same way ; starch, 
 protein, and fats are unable to 
 
 FIGURE 267. CROSS AND LON- 
 GITUDINAL SECTIONS OF A YOUNG 
 ROOT. 
 
 Note that the entire root is 
 made up of small divisions 
 (cells), every one of which is 
 surrounded by athin membrane. 
 
USE OF THE FOOD MANUFACTURED BY PLANTS 345 
 
 
 
 get into our blood until they are changed into something 
 which is able to pass through membranes. 
 
 Problem 7. How can we prove that nutrients are 
 digested ? We have already seen that starch cannot pass 
 through a membrane and that it must be changed into some- 
 thing that will. Since sugar is very similar to starch in its 
 chemical composition, we may suspect that starch may be 
 changed into sugar during digestion. But is sugar able to 
 pass through a membrane ? 
 
 This may be determined by trying the same experiment as 
 before, except that a solution of grape sugar should be sub- 
 stituted for the mixture of starch and water. The water 
 passing through the membrane may be tested for grape sugar 
 by heating some of it to which has been added a few drops of 
 Fehling's solution. The presence of grape sugar is indicated 
 by a reddish orange or brick red color. What is the result 
 in this case ? What is your conclusion ? 
 
 Grind up an unsprouted corn grain, mix it with a little water, and 
 test for grape sugar. Result? Do the same with sprouting corn 
 grain. Result ? Conclusion ? 
 
 Chew up a piece of cracker which has been shown by a test to con- 
 tain no grape sugar. After it has been thoroughly chewed and mixed 
 with saliva, test again for grape sugar. Result ? Conclusion ? 
 
 There is evidently something in the sprouting corn grain 
 and in the saliva which has the power to change starch into 
 sugar. A substance of this kind, which by its presence is 
 able to cause other substances to change chemically, remain- 
 ing unchanged itself, is called an enzyme. In the corn grain 
 the enzyme becomes active only when the proper conditions 
 of temperature and moisture are present. There are also 
 enzymes that act upon proteins, and others that act upon 
 fats. 
 
346 
 
 GENERAL SCIENCE 
 
 tongue 
 
 pancreas 
 
 Problem 8. Where is food of the human body digested? 
 We know that food taken into the mouth passes down 
 tnrough the gullet into the stomach, where it remains for 
 several .hours, and then passes into the small intestine, and 
 on into the large intestine. This entire tube extending from 
 the mouth to the end of the rectum, the last division of the 
 
 large intestine, is called the 
 alimentary canal. The food is 
 forced along through this tube 
 by means of muscles in its 
 walls. 
 
 After the food has been broken 
 up by the teeth and mixed with 
 saliva which acts to some extent 
 upon the starch, it is worked 
 upon by enzymes of the gastric 
 juice of the stomach which act 
 chiefly upon the protein food, 
 and by a number of enzymes 
 from the pancreatic juice and 
 intestinal juice which act upon 
 all of the different nutrients. 
 The bile, a juice manufactured 
 by the liver, is of special use in digesting fat. As the food 
 is digested, it is absorbed through the walls of the alimentary 
 canal. Most of the absorption occurs in the small 
 intestine. 
 
 The material which reaches the large intestine is principally 
 food which could not be digested and hence could not be ab- 
 sorbed. If this refuse material remains too long in the 
 large intestine, which is the condition in constipation, bacteria 
 act upon it and produce soluble poisons which are absorbed 
 
 eppndi 
 
 FIGURE 268. FOOD CANAL 
 (ALIMENTARY CANAL) OF MAN. 
 
USE OF THE FOOD MANUFACTURED BY PLANTS 347 
 
 into the blood through 
 the walls of the large 
 intestine and give rise 
 to headaches, an in- 
 ability to do our best 
 mental and physical 
 work, and make the 
 body, less able to resist 
 disease. 
 
 By the circulatory 
 system of the blood 
 (Figure 269) the di- 
 gested food is carried 
 to various parts of the 
 body, where it is used 
 for growth and repair 
 and as a fuel for the 
 production of energy, 
 or the excess of fuel 
 food is stored up in 
 the form of fat. 
 
 The wastes which 
 are produced in the 
 different parts of the 
 body as a result of oxi- 
 dation and the activity 
 of the living matter, 
 are, in time, carried 
 away by the circula- 
 tory system to the 
 kidneys, lungs, and skin, by which they are taken out of 
 the blood. 
 
 FIGURE 269. ORGANS OF CIRCULATION 
 OF MAN. 
 
348 GENERAL SCIENCE 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. By weighing the food used each day for a week and calculating 
 from tables showing percentage of nutrients in different foods, determine 
 the amount of each nutrient eaten by you during the week. How does 
 the result compare with the standard of Atwater or Chittenden ? 
 
 2. Plan a bill of fare for your family for a week. Estimate the 
 amount of nutrients and the cost. Suggest how the diet of your family 
 might be improved without any great increase in cost. 
 
 3. Perform experiments to show that the gastric juice will digest 
 protein. 
 
 4. Dissect the heart of a sheep. Explain its action in causing a 
 circulation of the blood. 
 
 REPORTS 
 
 1. The value of milk as a food. 
 
 2. The use of fruit and fresh vegetables as foods. 
 
 3. Causes and prevention of indigestion. 
 
 4. Causes and prevention of constipation. 
 
 REFERENCES FOR PROJECT XXVIII 
 
 1. Feeding the Family, Mary S. Rose. Macmillan Company. 
 
 2. The Story of Sugar, G. T. Surface. D. Appleton & Co. 
 
 3. Food and Household Management, Kinne and Cooley. Mac- 
 millan Company. 
 
 4. How to Live, Fisher and Fisk. Funk & Wagnalls. 
 
 5. All About Milk. Metropolitan Life Insurance Company. 
 (Free.) 
 
 6. The Body at Work, Jewett. Ginn & Co. 
 
 7. Town and City, Jewett. Ginn & Co. 
 
 8. The Story of Bread. International Harvester Company, Chi- 
 cago, Illinois. 
 
 9. Economy in the Buying and Preparation of Meats, E. L. Wright. 
 Wilson & Co. 
 
 10. American Inventions and Inventors, Mowry. Silver, Burdett 
 & Co. (Foods cultivated and uncultivated.) 
 
PROJECT XXIX 
 HOW PLANTS PRODUCE SEED 
 
 Problem 1. Why plants produce seeds ? Make a list of 
 the plants you know which produce seeds. In making this 
 list, include grains and nuts as seeds. What is your conclu- 
 sion concerning the number of plants which produce seeds? 
 If a seed is placed in the soil with the proper conditions of 
 moisture and temperature, what finally develops from it? 
 If a farmer wishes new wheat or grass or bean plants, what 
 
 does he do ? 
 i 
 
 If you have a garden, after the soil has been prepared you 
 plant seeds in it which either you or the seedsman have 
 obtained from plants grown the previous year. Weeds may 
 die as winter comes, but before this happens they have pro- 
 duced large numbers of seeds which fall to the ground and 
 remain there until the following spring. Considering these 
 and other observations which you have made, what is your 
 answer to the question, why do plants produce seeds? 
 Why do you suppose plants produce so many seeds? 
 
 Problem 2. What are the parts of a seed ? Soak a num- 
 ber of rather large seeds as peas, beans, or corn. Examine 
 a bean seed. It will be noticed that there is a scar on one 
 edge. To understand the cause of this scar, open a bean pod 
 and note how the seeds are attached. While the seed is 
 growing, what do you suppose passes through the little stalk 
 by which the seed is attached to the side of the pod ? The 
 
 349 
 
350 
 
 GENERAL SCIENCE 
 
 point of attachment of this little stalk to the side of the pod 
 is called the placenta. What materials pass through the 
 placenta ? 
 
 Remove the seed coat and find two large structures that 
 make up almost the whole bulk of the seed (Figure 270). 
 
 These are called seed 
 leaves, and it will be 
 noted that they are 
 attached to a little 
 stalk, the pointed end 
 of which will later de- 
 velop into the root of 
 the growing bean plant. 
 At the other end of 
 the little stalk, and just 
 beyond where the big 
 seed leaves are at- 
 tached, you will see 
 two little plume-like 
 structures which at 
 first look like the parts 
 of a fish's tail, but on 
 closer examination 
 prove to be small leaves. These leaves, with the very 
 small stalk to which they are attached, will develop into 
 the stem and leaves of the plant. 
 
 Altogether the bean seed is made up of a little plant called 
 an embryo, of which two leaves are filled to such an extent 
 with food material that they have become so thickened that 
 they no longer look like leaves. These constitute the seed 
 leaves. Compare the embryo making up the seed of the bean 
 with a bean seedling. Pick out the corresponding parts. 
 
 FIGURE 270. SEEPS OF BEAN AND PEA. 
 
 A and C, little stem, lower end of which 
 will develop into -the first roots. B, plu- 
 mule, a bud which will develop into the 
 stem and leaves of plant. A, B and the 
 two large seed leaves constitute the em- 
 bryo. D, scar, the place of attachment 
 of the little stalk within the bean pod. E, 
 micropyle, a small opening. 
 
HOW PLANTS PRODUCE SEED 
 
 351 
 
 Plumule 
 
 *- Root 
 
 Examine a soaked pea seed and endeavor to find the same 
 parts that you found in the bean seed. In the same way 
 compare the embryo of the pea seed with a pea seedling 
 and note the corresponding parts. 
 
 A corn seed may be best studied if it is examined together 
 with one which has begun to sprout (Figure 271). The part 
 which corresponds to the root end of the little stem can 
 easily be seen, as in whatever position 
 the corn grain is kept this root end 
 begins to grow downward. The other 
 end, which begins to push upward to 
 form the main part of the plant, is 
 pointed and made up of tightly 
 twisted leaves in much the same 
 way that you can furl up a piece of 
 paper leaving a sharp point at one 
 end. 
 
 The seed leaf (there is only one) 
 is not at all leaf-like in appear- 
 ance but is embedded in stored food material which in 
 the corn seed is outside of the embryo. The relation of 
 the seed leaf to the stored food material can best be seen by 
 cutting lengthwise and cross sections of soaked corn grains, 
 and dipping the cut surfaces in an iodine solution. The 
 stored food material, since it contains a very large amount 
 of starch, becomes colored a very dark blue ; while the parts 
 of the embryo are colored very slightly. 
 
 It will thus be seen that the corn seed, although apparently 
 so unlike the bean or pea seeds, also contains an embryo, or 
 undeveloped plant, which consists of a seed leaf attached to 
 a stalk, one end of which will develop into the roots, and the 
 other end into the stem and leaves of the plant. 
 
 FIGURE 271. SPROUT- 
 ING CORN GRAIN. 
 
352 GENERAL SCIENCE 
 
 Examination of other seeds will show the same thing, so 
 that we may conclude that the seed of a plant always contains 
 an embryo or baby plant with considerable stored-up food 
 which may either be in the seed leaves or outside of the 
 embryo. 
 
 Problem 3. Where seeds are produced. It is a com- 
 mon observation that seeds are produced in some way by 
 
 FIGURE 272. PEAR, FROM BUD TO FRUIT AND SEED. 
 
 the flowers of a plant. It will be well for us, therefore, to 
 examine a flower. An examination of a typical flower, such 
 as a pear blossom or bean or pea blossom, will lead us to 
 find the following parts (Figure 272) : 
 
 The outermost parts are green leaf-like structures called 
 sepals. Together they make a cup-shaped formation around 
 the base of the flower called the calyx. Just inside of these 
 are the colored parts of the flower called the petals. The 
 
HOW PLANTS PRODUCE SEED 353 
 
 petals together constitute the corolla. Next there are a 
 number of little stalks with knobs on their tops. These are 
 the stamens, the stalks being called filaments, and the knobs 
 at the top, anthers. The anthers are little box-like structures 
 containing a powdery substance called pollen. 
 
 The center of the flower is occupied by the pistil, of which 
 there are usually three divisions : an enlarged part at. the 
 base called the ovary, one or more little stalks running up 
 from this called styles, and at the top of the styles enlarge- 
 ments usually slightly rough and moist called stigmas. If 
 the ovary is cut through, there will be found in it small seed- 
 like structures which are called ovules. Very evidently, 
 these are the parts of the flower which will develop into 
 seeds. 
 
 Problem 4. Do ovules always develop mto seeds? 
 Apparently, ovules do not necessarily develop into seeds. 
 It will be found by an examination of a number of pea or 
 bean pods that occasionally an ovule has not developed 
 into a seed. An account of some experiments which have 
 been performed many times will help us to understand why 
 ovules do not always develop into seeds. Stamens were 
 carefully removed from a flower before any pollen had 
 escaped from the anthers. The flower was then covered with 
 a fine netting or a paper bag. None of the ovules developed 
 into seeds. 
 
 This would indicate that the pollen is necessary for the 
 production of the seeds. This conclusion may be confirmed 
 as follows : A flower was treated as the one described above ; 
 but in this case some pollen from another flower of the same 
 kind was placed upon the stigmas of the flower from which 
 the stamens had been removed. The ovules all developed 
 into seeds. What conclusion will you draw from this result? 
 
354 
 
 GENERAL SCIENCE 
 
 Stigma 
 
 Pollen. 
 Grain 
 
 Tube 
 
 Nucleus 
 
 Loose Tissue 
 of Style 
 
 Problem 5. How the pollen grain influences the de- 
 velopment of the ovule into the seed. It has been found 
 that each pollen grain resting upon the surface of the stigma 
 grows out into a tube which pushes its way down through 
 the style until it reaches the ovary (Figure 273). The pollen 
 
 tube now grows through a small 
 opening (micropyle) on the side of 
 the ovule (Figure 274). Some of 
 the living material (sperm cell) 
 of the pollen grain, containing a 
 denser portion, the nucleus, passes 
 down through the tube. 
 
 After the tube has penetrated 
 into the ovule through the micro- 
 pyle, the end of the tube disap- 
 pears and the nucleus of the pollen 
 (sperm cell nucleus) combines with 
 the nucleus of a little bit of living 
 matter in the ovule called the egg cell. The egg cell, which 
 is now composed of living material from the pollen grain 
 in addition to its own original living material, grows and 
 divides into two, then four, eight, and finally thousands 
 of little masses of living matter (cells) which arrange 
 themselves to form the parts of the embryo or baby plant. 
 
 The egg cell, which is composed of living material from 
 these two sources, is called a fertilized egg cell ; and the 
 union of the sperm cell nucleus with the egg cell nucleus is 
 called the process of fertilization. Unless this process of 
 fertilization occurs, the egg cell will not grow and divide, 
 but will finally wither and die. 
 
 In all living things except the very lowest animals and 
 plants, this general process of the union of two masses of 
 
 FIGURE 273. GROWTH 
 OF POLLEN TUBES DOWN 
 THROUGH THE STYLE. 
 
HOW PLANTS PRODUCE SEED 
 
 355 
 
 living matter precedes the development of an egg into a new 
 plant or animal. 
 
 Problem 6. Does it make any difference whether the 
 pollen comes from the same flower or a different one ? 
 It is clear that if seeds 
 are produced by a plant 
 the pollen must in some 
 way pass from the 
 anther to the stigma. 
 This would seem very 
 easy, as the flowers of 
 most plants have both 
 stamens and pistils. 
 Experiments, however, 
 by the great English 
 scientist, Charles Dar- 
 win, have shown that 
 in many plants cross- 
 pollination (transfer of 
 pollen from an anther 
 of one flower to the 
 stigma of another flower 
 
 of the same kind) gave C oat of ovule ; D, inner coat of ovule ; 
 much more satisfactory E > embryo sac ; F, sperm cell nucleus ; 
 
 G, egg cell nucleus. 
 
 results than if the pol- 
 len that fell upon the stigma came from the anther of the 
 same flower (self-pollination). He found in some cases of 
 self-pollination that a smaller number of seeds were pro- 
 duced ; that the seeds were frequently smaller and that 
 poorer plants * developed from the seeds. Naturally the 
 question arises as to how self-pollination is prevented, and 
 how cross-pollination is encouraged. 
 
 FIGURE 274. POLLEN TUBE ENTERING 
 
 OVULE. 
 A, pollen tube ; B, micropyle ; C, outer 
 
356 
 
 GENERAL SCIENCE 
 
 Problem 7. How self-pollination is prevented. Some 
 plants, like the willow and the cottonwood or poplar, have 
 flowers containing only stamens on one plant and flowers 
 having only pistils on another plant. In these cases self-pol- 
 lination is impossible. Other plants, among which are corn 
 (Figures 275 and 276) and many of our common trees as ash, 
 chestnut (Figure 277), oak (Figure 278), maple, hickory, 
 
 pines, etc,, have stamens 
 and pistils in different 
 flowers but on the same 
 plant. 
 
 In corn, for example, 
 the tassel (Figure 276) 
 at the top of the corn 
 plant is a collection of 
 staminate flowers'; while 
 the silks (Figure 275) of 
 the ear of corn, down 
 along the stalk, are 
 stigmas and styles, and 
 the corn grains are ovaries 
 of the pistillate flowers. 
 Even in this kind of 
 plants better results 
 
 occur when the pollen is carried from the anthers of another 
 plant. A solitary cornstalk usually has on it very poorly 
 developed ears of corn. 
 
 In many plants the stamens ripen and the pollen escapes 
 from the anthers before the stigmas in the same flower are 
 ready to receive it. In some plants the reverse is true, the 
 stigma being ready to receive pollen before the pollen in that 
 plant is mature. 
 
 FIGURE 275. PISTILLATE FLOWERS OF 
 CORN. 
 
 Each silk (style and stigma) is at- 
 tached at its base to the young corn 
 grain (ovary). 
 
HOW PLANTS PRODUCE SEED 
 
 357 
 
 Experiments have shown that in some flowers if the pollen 
 from the same flower and pollen from a different flower of 
 the same kind are placed side by side upon the stigma, the 
 pollen tube of the pollen of the other flower will grow more 
 rapidly than the tube of the pollen of the same flower. 
 
 Problem 8. How pollen 
 is carried from one flower 
 to another. If a branch of 
 a pine or oak tree or a piece 
 of ragweed or a corn tassel 
 is shaken slightly at the time 
 the pollen is ripe, the pollen, 
 in the form of a light, dry dust, 
 will fall out in great quanti- 
 ties. How do you suppose 
 pollen of these flowers may 
 be carried from one flower 
 to another? Explain the 
 reason for the enormous 
 quantity of pollen produced. 
 The stigmas of flowers pol- 
 linated in this way are fre- 
 quently very much enlarged 
 and branched so as to expose 
 a large surface. What is the 
 advantage of this? These 
 flowers that are pollinated by the wind do not correspond 
 in their appearance to our idea of flowers. They are usually 
 greenish and inconspicuous with no odor or bright colors. 
 
 Many flowers have pollen which is not so dry and light as 
 that of the flowers we have been considering. They evi- 
 dently cannot have pollen carried to any extent by the wind. 
 
 FIGURE 276 CORN TASSEL MADE 
 UP OF STAMINATE FLOWERS. 
 
358 
 
 GENERAL SCIENCE 
 
 These are our familiar 
 flowers (Figures 279 and 
 280), of various colors 
 and frequently having 
 more or less odor. You 
 will recall that you have 
 often seen insects, es- 
 pecially bees and but- 
 terflies, visiting them. 
 The insects are seeking 
 the sweet material, nec- 
 tar, which is down in 
 the interior of the flowers. 
 By pulling out the little 
 flowers from a head of 
 red clover, and touching 
 their bases with the 
 tongue, you can taste 
 the nectar. Examination of the head of a butterfly and 
 
 FIGURE 277. STAMINATE FLOWERS OF 
 CHESTNUT. 
 
 FIGURE 278. FLOWERS OF OAK. 
 
HOW PLANTS PRODUCE SEED 359 
 
 the legs and body of a bee will show you that they are cov- 
 ered with hairs. Explain now how you believe these flowers 
 are pollinated. 
 
 The irregular shapes of flowers are in general associated 
 with making more certain that the proper kinds of insects 
 
 FIGURE 279. FLOWERS OF HORSECHESTNUT. 
 
 will visit them ; and the stamens and pistils are so arranged 
 that the insect is quite certain to rub against them to receive 
 pollen from one flower, and then to rub the pollen off on the 
 stigma of the next flower visited. 
 
360 
 
 GENERAL SCIENCE 
 
 Some flowers have their pollen carried by water ; and in 
 some cases humming birds act as the carriers ; but the great 
 majority of flowers are pollinated either by wind or by in- 
 sects. Insect-pollinated flowers have much less pollen than 
 wind-pollinated flowers. Explain. 
 
 FIGURE 280. CHERRY BLOSSOMS. 
 
 Suggest any advantage of the grouping into clusters of these small 
 white flowers. 
 
 Nearly all of the flowers that bloom at night are white 
 or yellow. What reason can you give for this? Flowers 
 have various means of excluding small crawling insects like 
 ants. Of what advantage is this to the plant ? 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Make a collection of seeds and give a brief statement of the eco- 
 nomic value of each seed. 
 
 2. Germinate ten different seeds. Make sketches of several stages 
 of the development of each. 
 
HOW PLANTS PRODUCE SEED 361 
 
 3. Examine ten different flowers. Make sketches of the essential 
 organs of each. 
 
 4. Cross-pollinate a number of flowers of a plant. 
 
 5. Grow pollen tubes from the pollen of several kinds of flowers in 
 sugar solutions of different densities. 
 
 6. Observe a bed of flowers for a considerable time to find out the 
 kinds and numbers of insects that visit the flowers. Catch some of the 
 insects and examine them to find whether they are carrying pollen and 
 how well fitted they are for this purpose. Also determine whether the 
 flowers are fitted in any special way to profit by the visits of the insects. 
 
 7. Make a collection of the flowers of a number of common trees. 
 
 8. Collect frogs' eggs and describe the changes which they undergo 
 when kept in an aquarium. 
 
 REPORTS 
 
 1. Describe the methods of cross-pollination. 
 
 2. Describe special devices in several flowers to prevent self-pollina- 
 tion and to bring about cross-pollination. 
 
 REFERENCES FOR PROJECT XXIX 
 
 1. Farmers' Bulletin 154, The Home Fruit Garden; 218, The School 
 Garden ; 255, The Home Vegetable Garden ; 408, School Exercises in 
 Plant Production. 
 
 2. The Home Vegetable Garden, Adolph Kruhm. Orange Judd 
 Company. 
 
 3. Outline Studies on School Garden, Home Garden, and Vegetable 
 and Growing Projects, Kern. Division of Agricultural Education, 
 University of California. 
 
 4. Wild Flowers Every Child Should Know, Stack. Doubleday, 
 Page & Co. 
 
PROJECT XXX 
 
 HOW BETTER PLANTS AND ANIMALS ARE 
 PRODUCED 
 
 Problem 1. Have we evidence of improvement of plants 
 and animals during past generations ? Of course we mean 
 by improvement, making these plants and animals better 
 fitted to meet our needs. The history of some of our domes- 
 ticated animals and plants runs back to the point where 
 our knowledge of the history of man begins, so that it is 
 impossible to trace them directly from their wild ancestors. 
 They may, however, be compared in some cases with wild 
 plants and animals which apparently are similar to these 
 unknown ancestors. Wheat, oats, rye, barley, etc., have 
 evidently been derived from wild grasses, from which they 
 now differ chiefly in the amount of food material stored in 
 the grain or seed. 
 
 Chickens have changed much from the Asiatic bird which 
 is thought to be most nearly like the one from which they 
 have descended. Dogs have become quite unlike their wild 
 ancestors, apparently wolves and coyotes or the close rela- 
 tives of these. Turkeys, which have become domesticated 
 in relatively recent times, have already begun to be changed 
 in some respects from the wild turkeys which were found in 
 the American woods by the early settlers. 
 
 The most striking effect of the influence of domestication 
 in causing improvement in plants is shown by those plants 
 which are native to America and whose whole histories are 
 
 362 
 
HOW BETTER PLANTS AND ANIMALS ARE PRODUCED 363 
 
 known. The Indian corn, which explorers found the Ameri- 
 can Indians cultivating in a very crude way, would hardly 
 be recognized as being related to the large-grained, full- 
 eared corn whose crop in 1920 was worth over $4,000,000,000. 
 
 The potatoes found by these early explorers were about 
 the size of marbles. During the few hundreds of years since 
 they have been cultivated by civilized man, both quality 
 and size have been greatly improved. In 1920 the average 
 yield per acre was over 100 bushels; some areas yielding 
 300 to 400 bushels per acre. 
 
 Not only has there been an improvement under domesti- 
 cation of the plants and animals mentioned above, but the 
 same is true to a greater or less extent of all plants and 
 animals for which we have use. The question that arises 
 in our minds is, how has this improvement been brought 
 about, and how may we continue the process ? . 
 
 Problem 2. How plants and animals may be improved 
 by selection. From the very earliest times selection has 
 been a factor in producing better animals and plants. Se- 
 lection has depended upon two facts with which we are all 
 familiar : first, that no two plants or animals are exactly 
 alike; and second, that a plant or animal tends to be like 
 its parents. In a classroom, for example, there are no two 
 pupils exactly alike. This is also true if we consider all the 
 people in the whole world. Likewise, you will find that no 
 two bean or wheat plants or apple trees or horses are exactly 
 alike (Figure 281). This we call variation. 
 
 On the other hand, each pupil in the class resembles his 
 parents or grandparents in many respects. It may be in 
 the shape of the nose or face, coloring, tone of voice, size, 
 mental traits, etc. The same is true of every plant and 
 animal. Chickens never come from duck eggs, or chestnuts 
 
364 
 
 GENERAL SCIENCE 
 
 from cherry trees. Every plant or animal resembles its 
 parents in hundreds of ways. This law of resemblance is 
 called heredity; and we say that a person inherits a good dis- 
 position, black eyes, etc., from his antecedents. The farmer, 
 who each year selects the best corn or wheat grains for seed, 
 
 FIGURE 281. VARIATION. 
 
 Variation in the size and shape of timothy heads in the same kind 
 of- timothy. 
 
 will keep his crops up to the highest grade. He may select 
 for any special characteristic; size of ear, rapid growth, 
 large or small amount of starch, protein, or oil. 
 
 Problem 3. How more rapid improvement may be 
 brought about. Greater variation may be brought about 
 by pollinating flowers by hand. By this means also, a 
 variety of plant or fruit possessing certain desirable char- 
 acteristics may be obtained rather quickly. For example, 
 
HOW BETTER ANIMALS AND PLANTS ARE PRODUCED 365 
 
 edible oranges cannot be produced in a region where frosts 
 are likely to occur. There is, however, a species of orange 
 tree having a bitter, uneatable 
 fruit which is very hardy and 
 will grow much farther north 
 than the sweet orange. 
 
 In 1896 and 1897, plant 
 breeders of the United States 
 Department of Agriculture at- 
 tempted to produce an edible 
 orange which would grow much 
 farther north. This was done in 
 the following way. Pollen from 
 the flowers of the bitter orange 
 was placed on the stigmas of 
 flowers of the sweet orange and 
 vice versa. This was done for 
 thousands of flowers, and is called 
 hybridizing. 
 
 There was great variation in 
 the plants that developed from 
 the seeds of these flowers. The 
 young plants were grown where 
 they would be exposed to con- 
 siderable cold. Many of them 
 could not withstand the low temperature and died. Others 
 which showed good healthy growth in spite of the cold 
 were grafted l upon orange trees. Out of the thousands 
 
 1 That is, the end of the branch of an orange tree was cut off and in 
 a slit cut in the end of it was placed a one-year-old seedling plant (the 
 graft) . The important thing about this is that the fruit borne on the 
 grafted part is the same as though the twig had grown from its own 
 roots. 
 
 FIGURE 282. TONGUE 
 GRAFTING. 
 
 In all forms of plant graft- 
 ing, it is essential that the 
 actively growing layer 
 (cambium) situated be- 
 tween the bark and the 
 wood of the graft be held 
 in contact with the cam- 
 bium layer of the plant to 
 which the graft is attached. 
 
366 
 
 GENERAL SCIENCE 
 
 of grafts made, only 
 three produced fruit 
 that was of value. The 
 flavor of these was good 
 and they possessed the 
 advantage of being able 
 to live two to four hun- 
 dred miles north of 
 where the ordinary 
 sweet orange was able 
 to exist. These varie- 
 ties were propagated in 
 
 FIGURE 283. CLEFT GRAFTING. turn by further graft- 
 
 ing. 
 
 In plants that can be propagated by cuttings, as roses, 
 carnations, geraniums, etc. ; by roots, rootstocks, or tubers, 
 
 FIGURE 284. BUDDING, A FORM OF GRAFTING. 
 The four successive steps are shown left to right. 
 
HOW BETTER ANIMALS AND PLANTS ARE PRODUCED 367 ' 
 
 as potatoes, gladioli, etc. ; or by grafting, as fruit trees, 
 favorable variations obtained by hybridizing may be readily 
 retained. In plants, however, that are propagated only by 
 seed, as cotton, corn, wheat, most vegetables, etc., a process 
 of rigorous selection must follow. After four to six genera- 
 tions the plants will " come true to seed " fairly well, but 
 the process of selection must continue every year or the 
 desirable characteristics will disappear. 
 
 Very striking results have been obtained by plant and 
 animal breeders through the use of selection and hybridiz- 
 ing. Luther Burbank especially has developed some very 
 interesting plants, such as the white blackberry and spine- 
 less cactus. 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. From a corn or wheat crop, etc., make a selection of seed to bring 
 about an improvement along some definite line in future crops. 
 
 2. Graft the twig of one kind of apple tree upon the limb of 
 another. 
 
 3. Propagate a number of different kinds of plants by cuttings. 
 
 REPORTS 
 
 1. Improvement of the corn crop. 
 
 2. Improvement of the wheat crop. 
 
 3. Reports on various achievements of Luther Burbank. 
 
 4. The work of the U. S. Bureau of Agriculture in developing new 
 species of animals and plants. 
 
 5. Give a brief account of the work of Charles Darwin. 
 
 6. Give a brief account of the work of Gregor Mendel. 
 
 REFERENCES FOR PROJECT xxx 
 
 1. New Creations in Plant Life : Life and Work of Luther Burbank, 
 W. S. Harwood. Grosset & Dunlap, 1907. 
 
368 GENERAL SCIENCE 
 
 2. Evolution of Our Native Fruits, L. H. Bailey. Macmillan 
 Company. 
 
 3. The Story of a Grain of Wheat, W. C. Edgar. D. Appleton & Co. 
 
 4. Corn Plants, Their Uses and Ways of Life, F. L. Sargent. Hough- 
 ton Mifflin Company. 
 
 5. Plant Production, Moore and Halligan. American Book Company. 
 
PROJECT XXXI 
 
 INSECT ENEMIES OF PLANTS 
 
 Problem 1. How insects are injurious to plants. 
 
 Most of you know some of the ways in which insects are 
 
 injurious to plants. 
 You have seen rose 
 bushes, currant bushes, 
 or even whole trees 
 stripped of their leaves 
 by little worm-like ani- 
 mals (Figures 285 and 
 291). If you have had 
 a garden or have been 
 in the country in sum- 
 mer you have seen 
 potato bugs, or more 
 accurately, potato 
 beetles (Figure 286). 
 
 You may have seen 
 a little heap of sawdust 
 at the foot of a plum, 
 
 GYPSY 
 
 FIGURE 285. LIFE HISTORY OF 
 MOTH. 
 
 One of the insects most injurious to 
 foliage of shade and forest trees. Common 
 in the New England States. 
 
 peach or cherry tree 
 which led you to find a 
 grub, a worm-like animal, eating a tunnel in the wood under 
 the bark (Figure 287), which if not detected would have killed 
 the tree (Figure 288). You may have seen lumber which has 
 been meide useless by wormholes made by grubs, a young 
 
370 
 
 GENERAL SCIENCE 
 
 stage of beetles ; or you have had the leaves of plants in your 
 flower or vegetable garden eaten by grasshoppers. If you 
 have been in an orchard which has not been well cared for, 
 you have found that practically every apple was " wormy " 
 (Figure 289). The "worm" is 
 the young stage of a small moth 
 which flies at night. 
 
 FIGURE 286. POTATO BEETLE. 
 
 FIGURE 287. PEACH-TREE 
 BORER. 
 
 These are only a few of the enormous number of ways in 
 which insects harm crops, fruit, and forests by eating them. 
 Give other examples seen by you. 
 
 Another group of injurious insects is represented by the 
 plant lice which you sometimes see on house plants. They 
 do much damage to plants in general. And there are the 
 scale insects (Figure 290) which at various times have 
 ruined all of the fruit trees in certain parts of the country. 
 
INSECT ENEMIES OF PLANTS 
 
 371 
 
 FIGURE 288. GROUP OF DYING LOCUST TREES. 
 Effect of borers and leaf -miners. 
 
 The squash bug is another example of this group of in- 
 sects which does harm by sucking out the juices of 
 
 
 FIGURE 289. WORM IN APPLE, LARVA OF CODLING MOTH. 
 
372 
 
 GENERAL SCIENCE 
 
 plants. The bedbug, of unsavory reputation, is a close 
 relative. 
 
 It has been estimated by the Chief of the Bureau of Ento- 
 mology of the United States Department of Agriculture 
 that the damage done in one year in this country by insects 
 is as follows: Farm crops cereals, $430,000,000; hay, 
 $116,000,000; cotton, $141,000,000; tobacco, $17,000,000; 
 
 FIGURE 290. SCALE INSECTS ON A FERN LEAF. 
 
 vegetables, $200,000,000; sugar, $8,000,000; fruits, $141,- 
 000,000 ; other crops about $55,000,000 ; making a total of 
 over $1,100,000,000 damage done to farm crops. 
 
 In addition, forests and forest products are estimated to 
 have suffered a damage of $100,000,000 ; products in storage, 
 $100,000,000; insect-borne diseases of man have caused a 
 loss of $150,000,000 ; domestic animals have been damaged 
 to the extent of $100,000,000 ; making a grand total of more 
 than $1,500,000,000. 
 
 The question is, how can this great loss be lessened? 
 
 Problem 2. How injurious insects may be destroyed. 
 
INSECT ENEMIES OF PLANTS 
 
 373 
 
 What do you think would be the best method of destroying 
 insects that eat the leaves of plants? The usual way is to 
 spray the tree (Figure 292) with a poisonous mixture. Paris 
 green mixed with lime and water is frequently used. Ar- 
 
 FIGURE 291. TENT CATERPILLARS. 
 Nest and larvae of apple tree tent caterpillar in wild cherry tree. 
 
 senate of lead is less apt to injure the leaves and is replacing 
 Paris green to a great extent. To prevent apples from be- 
 coming wormy, it is necessary to spray the tree just as the 
 petals fall from the blossom and while the calyx is still open. 
 This is because the moth lays eggs in the blossom and the 
 
374 
 
 GENERAL SCIENCE 
 
 poison must get into the cup formed by the calyx before 
 the little larva, or " worm," has a chance to eat its way 
 into the fruit. 
 
 Of course insects that live by sucking juices from plants 
 
 FIGURE 292. A MODERN SPRAYING OUTFIT. 
 
 are not affected by poisonous sprays. They are usually 
 killed by being suffocated in some way. Dry insect powder 
 may be sprayed over the plant by bellows. This clogs up 
 the breathing holes along the body of the insect. A spray 
 
INSECT ENEMIES OF PLANTS 
 
 375 
 
 made of kerosene, soap, and water, another made of whale 
 oil soap, and still another made by pouring hot water over 
 tobacco stems, have been found to be effective in killing these 
 sucking insects. In greenhouses and cold frames which 
 can be tightly closed, tobacco smoke is valuable for killing 
 plant lice. 
 
 FIGURE 293. A BENEFICIAL BEETLE. 
 Caterpillar of gypsy moth attacked by Calosoma beetle. 
 
 Problem 3. How the number of injurious insects is 
 reduced by natural means. Man's fight against injurious 
 insects might be a losing one if he were not assisted by the 
 many animals that prey upon insects. The big dragon 
 flies which you see soaring in the air, reminding you of minia- 
 ture airplanes, are on the lookout for flying insects, of which 
 they devour an enormous number. The immature stage 
 (larva) of the dragon fly, living in ponds, have also as their 
 one occupation the destruction of the young stages of other 
 insects. 
 
 Ladybird beetles (Figure 294), commonly called " lady- 
 bugs/' those small round beetles which most of us know, 
 are very helpful in keeping down the increase of plant lice 
 and scales (Figure 295). A number of years ago a species of 
 the ladybird beetle saved the orange industry of California. 
 
376 
 
 GENERAL SCIENCE 
 
 The orange groves- were threatened with destruction by a 
 scale insect introduced from Australia. As its spread could 
 not be stopped by the ordinary methods of fighting insects, 
 an expert in the study of insects was sent to Australia to 
 find if the scale had any natural enemy. It was found that 
 a certain kind of ladybird beetle fed upon them and thus 
 
 FIGURE 294. LADYBIRD BEETLE. 
 
 kept them in check. Beetles were brought back to Cali- 
 fornia, where they succeeded in saving this very important 
 industry. 
 
 In gathering cocoons of moths, it will be frequently found 
 that the interior is filled with a large number of small larvae or 
 their cast-off skins. The reason for this is that an insect 
 called an ichneumon fly, a relative of the wasps, punctured 
 the skin of the moth larva and deposited a number of eggs. 
 These eggs developed into small larvae which finally com- 
 pletely devoured the body of their host. From these larvae 
 adult ichneumon flies develop which in turn are ready to 
 attack other caterpillars which are injurious to vegetation. 
 It is thought that parasitic insects like the ichneumon flies 
 
INSECT ENEMIES OF PLANTS 
 
 377 
 
 do more to keep in check the increase of injurious insects 
 than all our artificial methods. 
 
 Epidemics among insects caused by molds or bacteria 
 sometimes also destroy enormous numbers of them. 
 
 It very frequently happens that the year in which some 
 
 
 FIGURE 295. LADYBIRD BEETLE FEEDING ON SCALE INSECTS. 
 Note that both larvae and adults feed on scale insects. 
 
 insect has been a pest is followed by one in which there are 
 very few of that kind of insect. Can you suggest a reason 
 for this? 
 
 Many species of birds live entirely on insects and others 
 
378 GENERAL SCIENCE 
 
 during a portion of the year subsist chiefly on insects. Many 
 birds that are not primarily insect feeders supply a diet of 
 insects for their young. Students of the subject estimate 
 
 FIGURE 296. TOADS EATING CATERPILLARS. 
 
 that birds, by destroying harmful insects, each year save 
 crops worth many millions of dollars. 
 
 Toads, snakes, and bats are other animals that deserve 
 protection from man because of their value in destroying 
 injurious insects. 
 
 SUGGESTED INDIVIDUAL PROJECTS 
 
 1. Make a collection showing the various ways in which insects 
 injure plants. 
 
 2. Make a collection of injurious insects and give a brief account of 
 the harm done by each kind. 
 
 3. Protect the fruit of an apple tree from injury by the codling moth. 
 
 4. Make life history cases of a number of injurious insects. 
 
 REPORTS 
 
 1. The work of the U. S. Bureau of Agriculture in helping the farmer 
 in his fight against insects. 
 
 2. An account of the introduction of the gypsy moth, of the harm 
 done by it, and of the efforts made to check it. 
 
 3. An account of the life history ; of harm done by them ; methods 
 used to tight them : potato beetle, cotton boll weevil, codling moth, 
 
INSECT ENEMIES OF PLANTS 379 
 
 Hessian fly, San Jose scale, chinch bug, grasshopper, brown-tailed moth, 
 army worm, etc. 
 
 4. Work of birds in destroying harmful insects. 
 
 REFERENCES FOR PROJECT XXXI 
 
 1. Insects Injurious to the Household and Annoying to Man, G. W. 
 Herrick. Macmillan Company. 
 
 2. Insect Pests of Farm, Garden, and Orchard, E. D. Sanderson. 
 John Wiley & Co. 
 
 3. Farmers' Bulletins. 
 
 4. Farm Friends and Farm Foes, C. M. Weed. Ginn & Co. 
 
 5. Birds of Village and Field, F. I. Merriam. Houghton Mifflin 
 Company. 
 
 6. Book of Birds, Vols. I and II, Miller. Houghton Mifflin Company. 
 
 GENERAL REFERENCE BOOKS 
 
 Child's Book of Knowledge, Grolier Co., New York. 
 
 The Book of Wonders, Presbrey Syndicate, New York. 
 
 Wonders of Science, E. M. Tappan, editor. Houghton Mifflin 
 Company. 
 
 The Story-Book of Science, Fabre. Century Company. 
 
 Modern Triumphs, E. M. Tappan, editor. Houghton Mifflin 
 Company. 
 
 Wonders of Physical Science, E. E. Fournier. Macmillan Company. 
 
 Field and Forest Handbook, D. C. Beard. Scribners. 
 
 Romance of Modern Inventions, A. Williams. J. B. Lippincott 
 Company. 
 
 Stories of Useful Inventions, S. C. Forman. Century Company. 
 
 Stories of Great Inventions, E. E. Burns. Harper & Bros. 
 
 Makers of Many Things, E. M. Tappan. Houghton Mifflin 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 & Co. 
 
 Scientific American Boy at School, Bond. Munn & Co. 
 
 Harper's Outdoor Book for Boys. Harper & Bros. 
 
380 GENERAL SCIENCE 
 
 Everyday Physics, Packard. Ginn & Co. 
 
 The Wonders of Modern Mechanism, C. H. Cochrane. J. . Lippin- 
 cott Company. 
 
 The Land We Live In, O. W. Price. Small, Maynard & Co. 
 
 Uncle Sam's Business, C. Mariott. Harper & Bros. 
 
 Commercial and Industrial Geography, Heller and Bishop. Ginn 
 &Co. 
 
 With Men Who Do Things, Bond. Munn & Co. 
 
 Pioneers of Science in America, W. J. Youmans. D. Appleton & Co. 
 
 Famous Men of Science, S. K. Bolton. T. Y. Crowell & Co., New 
 York. 
 
 How It Works, A. Williams. Thos. Nelson & Sons. 
 
 Romance of Modern Engineering, A. Williams. Seeley Service 
 Company. London. 
 
 Great American Industries, W. F. Rocheleau. A. Flanagan Company, 
 Chicago. 
 
 A Source Book of Biological Nature Study, Downing. University of 
 Chicago Press. 
 
 Chemistry of the Home, Weed. American Book Company. 
 
 Chemistry of Common Things, Brownlee, etc. Allyn and Bacon. 
 
 Boys' Book of Chemistry, Clark. E. P. Dutton & Co. 
 
 Farm Science, W. J. Spellman. World Book Company. 
 
 Commercial Raw Materials, Chas. R. Toothaker. Ginn & Co. 
 
 Scientific American Reference Book, Hopkins and Bond. Munn 
 &Co. 
 
 Measurements for the Household. Bureau of Standards, Washing- 
 ton, D. C. 
 
 World Almanac. New York World. 
 
 Official Handbook, Boy Scouts of America. Doubleday, Page & Co. 
 
 Occupations, E. B. Gowin and A. W. Wheatley. Ginn & Co. 
 
 The Story of Iron and Steel, J. R. Smith. D. Appleton & Co. 
 
 The Story of the Submarine, Bishop. Century Company. 
 
 Practical Physics, Carhart and Chute. Allyn and Bacon. 
 
APPENDIX 
 
 I. AVERAGE RISE AND FALL OF TIDE 
 
 PLACES 
 
 Feet 
 
 Inch. 
 
 PLACES 
 
 Feet 
 
 Inch. 
 
 Baltimore, Md. ... 
 Boston Mass 
 
 1 
 
 9 
 
 * 2 
 
 7 
 
 Old Point Comf t, Va. 
 Balboa Panama 
 
 2 
 12 
 
 6 
 
 Q 
 
 Charleston, S. C. . . . 
 Colon, Panama . . . 
 Eastport, Me 
 Galveston, Tex. . . . 
 Key West, Fla. . . . 
 Mobile, Ala 
 
 5 
 
 
 18 
 1 
 1 
 1 
 
 2 
 11 
 2 
 
 
 
 2 
 6 
 
 Philadelphia, Pa. . . 
 Portland, Me 
 San Diego, Cal. . . . 
 Sandy Hook, N. J. . . 
 San Francisco, Cal. . 
 Savannah, Ga 
 
 5 
 8 
 3 
 4 
 3 
 6 
 
 4 
 11 
 11 
 8 
 11 
 6 
 
 New London, Ct. . . 
 New Orleans, La. . . 
 
 2 
 None 
 
 6 
 None 
 
 Seattle, Wash 
 Tampa Fla 
 
 11 
 
 2 
 
 4 
 
 2 
 
 Newport R I . . 
 
 3 
 
 6 
 
 Washington D C 
 
 2 
 
 11 
 
 New York, N.Y. . . 
 
 4 
 
 5 
 
 
 
 
 II. 
 
 Highest tide at Eastport, Maine, 218 inches. Lowest tide in 
 United States at Galveston, Texas, 12 inches. 
 
 SPECIFIC GRAVITY OF SOME COMMON SUBSTANCES 
 LIQUIDS 
 
 Water 100 
 
 Sea Water 103 
 
 Dead Sea . . . 124 
 
 Alcohol 84 
 
 Turpentine 99 
 
 Milk. . 103 
 
 SOLIDS 
 
 Cork 24 
 
 Poplar Wood 38 
 
 Maple Wood 75 
 
 Ice 92 
 
 Butter 94 
 
 Coal 130 
 
 Marble 270 
 
 Glass 289 
 
 The weight of a cubic foot of distilled water at a temperature of 
 60 F. is 1000 ounces avoirdupois, therefore the weight (in ounces, 
 avoirdupois) of a cubic foot of any of the substances in the table above 
 is found by multiplying the specific gravities by 10. 
 
 381 
 
 Granite 278 
 
 Steel 783 
 
 Copper 895 
 
 Silver 1.047 
 
 Lead 1.135 
 
 Gold 1.926 
 
 Platinum . 2.150 
 
382 GENERAL SCIENCE 
 
 III. COMPARATIVE SCALES OF THERMOMETERS 
 
 Centi- 
 
 j 
 
 Fahren- 
 
 
 Centi- 
 
 Fahren- 
 
 
 grade, 
 100 
 
 heit, 212 
 
 WATER BOILS 
 AT SEA- 
 
 grade, 
 100 
 
 heit, 212 
 
 
 95 
 
 203 
 
 LEVEL 
 
 20 
 
 68 
 
 
 90 
 
 194 
 
 
 15.3 
 
 60 
 
 Temperate 
 
 85 
 
 185 
 
 
 12.8 
 
 55 
 
 
 78.9 
 
 174 
 
 
 10 
 
 50 
 
 
 75 
 
 167 
 
 Alcohol Boils 
 
 7.2 
 
 45 
 
 
 70 
 
 158 
 
 
 5 
 
 41 
 
 
 65 
 
 149 
 
 
 1.7 
 
 35 
 
 
 60 
 
 140 
 
 
 
 
 32 
 
 WATER 
 
 55 
 
 131 
 
 
 1.1 
 
 30 
 
 FREEZES 
 
 52.8 
 
 127 
 
 Tallow Melts 
 
 5 
 
 23 
 
 
 50 
 
 122 
 
 
 6.7 
 
 20 
 
 
 45 
 
 113 
 
 
 10 
 
 14 
 
 
 42.2 
 
 108 
 
 
 12.2 
 
 10 
 
 
 40 
 
 104 
 
 
 15 
 
 5 
 
 
 36.7 
 
 98 
 
 Blood Heat 
 
 17.8 
 
 
 
 ZERO FAHR. 
 
 35 
 
 95 
 
 
 20 
 
 4 
 
 
 32.2 
 
 90 
 
 
 25 
 
 13 
 
 
 30 
 
 86 
 
 
 30 
 
 22 
 
 
 26.7 
 
 80 
 
 
 35 
 
 31 
 
 
 25 
 
 77 
 
 
 40 
 
 40 
 
 
 IV. COMPARISON OF SOME COMMON UNITS OF 
 MEASUREMENT 
 
 1 inch equals 2.54 centimeters 
 
 1 centimeter " .3937 inches 
 
 1 foot " .3048 meters . 
 
 1 meter " 3.28083 feet 
 
 1 yard " .9144 meters 
 
 1 meter " 1.0936 yards 
 
 1 mile " 1.60935 kilometers 
 
 1 kilometer " .62137 miles 
 
APPENDIX 
 
 liter equals 1.0567 quarts liquid 
 quart (liq.) " .9463 liters 
 quart (dry) " 1.1012 liters 
 liter " .9081 quarts dry 
 gallon " 3.78543 liters 
 1 liter " .26417 gallons 
 
 1 ounce (av.) " 
 1 gram 
 1 pound " 
 1 kilo 
 
 28.35 grams 
 .035 ounces (av.) 
 .45359 kilos 
 2.2046 pounds 
 
 1 gallon of water 
 1 gallon 
 1 cubic foot 
 1 gallon 
 1 cubic foot of water (4 C.) 
 
 weighs 8.345 pounds , 
 equals .13368 cubic feet 
 " 7.48052 gallons 
 " 231. cubic inches 
 weighs 62.425 pounds 
 
 383 
 
 1 ton anthracite coal occupies 40-43 cubic feet 
 1 ton bituminous coal " 40-48 cubic feet 
 
 V. PREPARATION OF AGAR CULTURE MEDIUM 
 
 Place 500 grams, about one pound, of finely chopped lean beef in 
 1000 cc. of distilled water and keep in an ice box overnight. Strain 
 and squeeze out the juice. Boil the juice for half an hour to coagulate 
 the albumins. Filter and add sufficient distilled water to bring the 
 amount up to 1000 cc. 
 
 The use of 3 grams of a standard meat extract, such as Liebig's, to 
 1000 cc. of water may be used instead of the fresh meat. 
 
 Ten grams of peptone should be carefully stirred in and dissolved by 
 boiling. 
 
 Add sufficient sodium hydroxide to make the reaction of the broth 
 neutral or slightly alkaline to litmus. 
 
 Chop into fine pieces 15 grams of pure thread agar. Dissolve the 
 chopped agar in a small quantity of boiling water. Add this to the 
 hot broth. Filter the broth containing the agar through a filter made 
 of cheese-cloth, enclosing a layer of absorbent cotton. Filtration will 
 be facilitated by first wetting the filter and funnel with boiling water. 
 Sterilize in an autoclave and pour into sterilized Petri dishes. 
 
384 GENERAL SCIENCE 
 
 VI. CLASSIFICATION OF ROCKS AND DIVISIONS OF 
 GEOLOGIC TIME 
 
 (Prepared by the U. S. Geological Survey) 
 
 The rocks composing the earth's crust are grouped by geologists into 
 three great classes, igneous, sedimentary, and metamorphic. The 
 igneous rocks have solidified from a molten state. Those that have 
 solidified beneath the surface are known as intrusive rocks. Those that 
 have flowed out over the surface are known as effusive rocks, extrusive 
 rocks, or lavas. The term volcanic rock includes not only lavas but 
 bombs, pumice, tuff, volcanic ash and other fragmental materials thrown 
 out from volcanoes. Sedimentary rocks are formed by the 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 the remains or products of animals 
 or plants (certain limestones and coal) ; of the product -of chemical 
 action or of evaporation (salt, gypsum, etc.) ; or of mixtures of these 
 materials. A characteristic feature of sedimentary deposits is a layered 
 structure known as bedding or stratification. Metamorphic rocks are 
 derivatives of igneous or sedimentary rocks produced through mechani- 
 cal or chemical activities in the earth's crust. The unaltered sedi- 
 mentary rocks are commonly stratified, and it is from their order of 
 succession and that of their contained fossils that the fundamental 
 data of historical geology have been deduced. 
 
APPENDIX 
 
 385 
 
 ERA 
 
 PERIOD 
 
 EPOCH 
 
 CHARACTERISTIC LIFE 
 
 Cenozoic 
 (Recent Life) 
 
 Quaternary 
 
 Recent Pleisto- 
 cene (Great 
 Ice Age ) 
 
 " Age of man." Animals 
 and plants of modern 
 types. 
 
 Tertiary 
 
 Pliocene 
 Miocene 
 Oligocene 
 Eocene 
 
 " Age of mammals." Pos- 
 sible first appearance of 
 man. . Rise and develop- 
 ment of highest orders 
 of plants. 
 
 Mesozoic 
 (Intermediate 
 Life) 
 
 Cretaceous 
 
 Upper 
 Lower 
 
 "Age of reptiles." Rise 
 and culmination of huge 
 land reptiles (dinosaurs) . 
 First appearance of birds 
 and mammals ; palms 
 and hardwood trees. 
 
 Jurassic 
 
 
 Triassic 
 
 
 Paleozoic 
 (Old Life) 
 
 Carbonifer- 
 ous 
 
 Permian 
 Pennsylvanian 
 Mississippian 
 
 "Age of amphibians." 
 Dominance of tree ferns 
 and huge mosses. Primi- 
 tive flowering plants and 
 earliest cone-bearing 
 trees. Beginnings of 
 backboned land animals . 
 Insects. 
 
 Devonian 
 
 
 "Age of fishes." Shell- 
 fish (mollusks) also 
 abundant. Rise of am- 
 phibians and land plants . 
 
 Silurian 
 
 
 Shell-forming sea animals 
 dominant. Rise of fishes 
 and of reef - building 
 corals. 
 
 Ordovician 
 
 
 Shell-formingseaanimals. 
 Culmination of the bug- 
 like marine crustaceans 
 known as trilobites. 
 First trace of insect life. 
 
 Cambrian 
 
 
 Trilobites, brachiopods 
 and other sea shells. 
 Seaweeds (algse) abun- 
 dant. No trace of land 
 animals. 
 
 Proterozoic 
 (Primordial 
 Life) 
 
 Algonkian 
 
 
 First life that has left dis- 
 tinct record. Crusta- 
 ceans, brachiopods and 
 seaweeds. 
 
 Archean 
 
 Crystalline 
 Rocks 
 
 No fossils found. 
 
386 
 
 GENERAL SCIENCE 
 
 The first striking fact in the geological history of climate is that the 
 present climate of the world has been maintained since the date of the 
 earliest, unaltered, sedimentary deposits. The oldest sandstones of the 
 Scotch Highlands and the English Longmynds show that in pre-Cam- 
 brian times the winds had the same strength, the raindrops were of the 
 same size, and they fell with the same force as at the present day. 
 The evidence of paleontology proves that the climatic zones of the earth 
 have been concentric with the poles as far back as its records go ; the 
 salts deposited by the evaporation of early Paleozoic lagoons show that 
 the oldest seas contained the same materials in solution as the modern 
 oceans; and glaciations have recurred in Arctic and, under special 
 geographical conditions, also in temperate regions at various periods 
 throughout geological time. The mean climate of the world has been 
 fairly constant, though there have been local variations which have led 
 to the development of glaciers in regions now ice free, at various points 
 'in the geological scale. That there has been no progressive chilling of 
 the earth since the date of the oldest known sedimentary rocks is shown 
 by their lithological characters and by the recurrence of glacial deposits, 
 some of which were laid down at low levels at intervals throughout 
 geological time. 
 
 VII. SOLAR SYSTEM 
 
 
 
 
 GRAVITY 
 
 
 
 
 
 AT SUR- 
 
 TIME OF REVO- 
 
 
 DISTANCE FROM SUN 
 
 RADIUS 
 
 FACE. 
 
 LUTION AROUND 
 
 
 
 
 EARTH 
 
 SUN 
 
 
 
 
 = 1 
 
 
 Mercury 
 
 35,960,500 miles 
 
 1504 miles 
 
 .38 
 
 88 days 
 
 Venus 
 
 67,195,600 " 
 
 3787 " 
 
 .89 
 
 225 " 
 
 Earth 
 
 92,897,400 " 
 
 3958 " 
 
 1.00 
 
 365^ " 
 
 Mars 
 
 141,546,600 " 
 
 2107 " 
 
 .38 
 
 687 " 
 
 Jupiter 
 
 483,327,000 " 
 
 43,341 " 
 
 2.66 
 
 4332 i '~ 
 
 Saturn 
 
 886,134,000 " 
 
 36,166 " 
 
 1.14 
 
 10,759 *' 
 
 Uranus 
 
 1,782,792,000 " 
 
 15,439 " 
 
 .96 
 
 30,688 " 
 
 Neptune 
 
 2,793,487,000 " 
 
 16,465 " 
 
 .98 
 
 60,178 " 
 
 Sun 
 
 
 432,196 " 
 
 27.98 
 
 
 Moon : Diameter, 2160 miles; average distance from Earth, 238,862 
 miles; time of revolution around the Earth, 27.32 days; force of 
 gravity at surface of Moon, one-sixth of the force of gravity at 
 surface of Earth. 
 
APPENDIX 387 
 
 VIII. BIRD COUNT IN THE UNITED STATES 
 
 (By E. W. Nelson, Chief of the Bureau of Biological Survey, United 
 States Department of Agriculture) 
 
 Early in the summer of 1914 the Biological Survey of the United 
 States Department of Agriculture took initial steps toward a count of 
 the birds of the United States for the purpose of ascertaining approxi- 
 mately the number and relative abundance of the different species. 
 This preliminary count proved to be so satisfactory that the Survey 
 repeated it on a larger scale in 1915, and extended it over a still greater 
 area in 1916 and 1917. The results obtained in 1914 have been sur- 
 prisingly corroborated by those of succeeding year , and the work gives 
 promise of producing, after a series of years, results that, in view of the 
 recognized value of birds to agriculture, cannot fail to be of great value. 
 It has been ascertained through these counts that birds in the agricul- 
 tural- districts in the Northeastern United States average slightly more 
 than a pair to the acre, though in parts of the arid West and oh the 
 treeless plains this number dwindles to an average of half a pair, or 
 even less, to the acre. 
 
 By far the most abundant birds in the United States are the robin 
 and the English sparrow, but several others are common enough to 
 make their total numbers run well into the millions. The counts so far 
 show that the most abundant bird on farms in the Northeastern States 
 is the robin ; next to this is the English sparrow, and following these 
 are the catbird, brown thrasher, house wren, kingbird, and bluebird, 
 in the order named. The densest bird population anywhere recorded 
 is near Washington, D. C., where a careful count showed, in 1915, one 
 hundred and thirty -five pairs of forty species on five acres. Two city 
 blocks, well furnished with trees, in the city of Aiken, S. C., harbored 
 sixty-five pairs on ten acres. These high figures show the important 
 results which will follow from careful protection and encouragement of 
 birds. 
 
INDEX 
 
 References are to pages 
 
 Accommodation of eye . . 290-291 
 
 Acetic acid 126 
 
 Adir ndack Mountains, relation 
 
 to Hudson River . . . 178-182 
 
 Aeration of water 165-166 
 
 Agar 94 
 
 Agriculture, affected by irrigation 136 
 Agrimonte, Dr., member of Yel- 
 low Fever Commission . .187 
 
 Air, composition 80 
 
 compressed 17-24 
 
 conductor of sound 49 
 
 effect of heating 28 
 
 force in motion 2 
 
 heating by hot air ... 304-305 
 inspired and expired . . . 65-66 
 
 pressure 5, 6, 7,9 
 
 relation of moisture to com- 
 fort 142-143 
 
 weight 4, 5 
 
 Airplane 1-4 
 
 Alcohol, changed into acetic acid 
 
 by bacteria 125 
 
 Aldebaran, a fixed star .... 209 
 
 Alimentary canal 346 
 
 Ammeter 260 
 
 Amoeba, causfe of disease of teeth 111 
 
 Ampere 260 
 
 Antenna, of wireless telegraphy . 262 
 
 Anthers 353 
 
 Antiseptics 108,120 
 
 use of 119-121 
 
 Antitoxin, preparation of diph- 
 theria 117-118 
 
 importance of early use . 118-119 
 Appetite, as a guide in eating . 337 
 
 Apple worm 370-371, 373 
 
 Aquarium, balanced .... 89-91 
 
 Arc light 270-271 
 
 Armature, of dynamo 264 
 
 of electric bell 254 
 
 of motor . 265 
 
 Arms, of a lever 231 
 
 Arsenate of lead, as an insecti- 
 cide 373 
 
 Artesian wells 166 
 
 Astigmatism 292-293 
 
 Audion detectors, wireless . . 262 
 
 Auriga, a constellation .... 207 
 
 Automobile, engine .... 246-249 
 
 gears for high and low speed . 234 
 
 source of power 57-58 
 
 Automobile tires .... 13, 19, 20 
 Autumnal equinox 212 
 
 Bacteria 61, 93 
 
 action of, on sewage 172 
 
 cause of decay of food. . . 92-93 
 conditions favorable for 
 
 growth 96-97 
 
 destruction of, in rivers . . .173 
 in water supply reservoirs . 1 65 
 growth affected by disin- 
 fectants and antiseptics 1 1 9- 1 20 
 importance in causing de- 
 cay 125-126 
 
 important in production of 
 leather, curing tobacco, 
 preparing linen, and in mak- 
 ing vinegar 125-126 
 
 necessary in soil 318 
 
 nitrogen-fixing 123-124 
 
 producing flavor of butter . . 125 
 
 of cheese 125 
 
 where found 93-94 
 
 Balanced aquarium 89-90 
 
 Ball bearings, use in preventing 
 
 friction 243 
 
 Balloon 10 
 
 Barometer, aneroid 8-9 
 
 mercury 6-7 
 
 Bats', value in destroying insects . 378 
 
 Battery, storage 271-273 
 
 Bee, adaptation for pollination . 359 
 
INDEX 
 
 References are to pages 
 
 Beetle, lady bird .... 375-376 
 
 Bell, electric 253-254 
 
 Belts, use in machinery .... 235 
 
 Bends 19 
 
 Benzoate of soda, use as an anti- 
 septic . 120 
 
 Betelgeuse, a fixed star .... 209 
 Bicycle, application of power to 
 
 drive wheel 235 
 
 Big Dipper 205 
 
 Bile .346 
 
 Binding posts, of electrical ap- 
 paratus 254 
 
 Birds, value in destroying insects 378 
 
 Block and tackle 237 
 
 Blood corpuscles, white . . 109,114 
 
 Blood poisoning 110 
 
 Blood system 347 
 
 Blueprints 222-223 
 
 Blue vitriol 258 
 
 Blueness of sky 288 
 
 Boils 110 
 
 Bone meal, use as a fertilizer . 326 
 Bones of body as levers .... 233 
 
 Boyle's law 18 
 
 Brain, interpretations of light 
 
 impressions 295 
 
 Brakes, use in overcoming inertia 244 
 Bread, composition of .... 332 
 Breathing, of animals .... 69-72 
 
 of human body 67 
 
 of plants 67-69 
 
 reason for breathing through 
 
 nose 114. 
 
 Breathing movements .... 12 
 
 Bull, a constellation 209 
 
 Bunsen burner 56 
 
 Buoyancy 10-11 
 
 Burbank, Luther, 367 
 
 Burning ; 54-56 
 
 destruction 74-79 
 
 Butter, flavor improved by 
 
 growth of bacteria . . . .125 
 Butterfly, adaptation for pol- 
 lination 358-359 
 
 Caisson 18 
 
 Calorie 335 
 
 Calorimeter 334 
 
 Calyx 352 
 
 Camera, similarity to eye . . . 289 
 
 focusing 291 
 
 Canal, alimentary 346 
 
 Canals, importance in navi- 
 gation 183-186 
 
 Candle power, measurement of . 281 
 
 Capella, a fixed star 207 
 
 Capillaries 72 
 
 Carbohydrates, importance as 
 
 food 331 
 
 manufacture of 82-85 
 
 Carbon dioxide ....... 55 
 
 action on rocks 312 
 
 amount removed from air by 
 
 plants 85-87 
 
 percentage in air 80 
 
 proof of use in starch- 
 making 84-85 
 
 Carboniferous period 88 
 
 Carburetor 246 
 
 Carrol, Dr., member of Yellow 
 
 Fever Commission . . . .187 
 Cassiopeia's Chair, a constel- 
 lation : . . . 207 
 
 Catskill Mountains, as a source of 
 
 water supply 161 
 
 Caves, formation in limestone 
 
 regions 168 
 
 produced by action of carbon 
 
 dioxide in water 312 
 
 Cell, dry .259 
 
 gravity 258 
 
 storage 271-272 
 
 Cells, plant 148 
 
 Cell-sap 147 
 
 Centrifugal force, examples 
 
 of 197-198 
 
 Cepheus, a constellation . 206, 207 
 Chain drive, bicycles and motor 
 
 trucks 235 
 
 Charioteer, a constellation . . . 207 
 Cheese, flavor produced by bac- 
 teria and molds 125 
 
 Chemical change, oxidation . . 55 
 in electric cells ....... 258 
 
 in making picture, caused 
 
 by energy of sun. . . 221-223 
 of storage cell .... 271-272 
 
 Chemical elements 56 
 
 in soil 324 
 
 necessary for growth of plants 324 
 
INDEX 
 
 References are to pages 
 
 Chicago drainage canal . . . .173 
 Chisel, as an inclined plane . . 240 
 Chlorine gas, use in sterilizing 
 
 water 166 
 
 Chlorophyll, necessary for 
 
 starch-making 88-89 
 
 Chronometer, use in determining 
 
 longitude 217 
 
 Ciliary muscle 292 
 
 Circulation of blood, need for . 67 
 
 Circulatory system 347 
 
 Clay, as a constituent of soil 309-310 
 Clothing, for winter and summer 301 
 
 light effects of 297 
 
 Clouds 
 
 formation of ...... 131132 
 
 Clover, effect upon soil of ... 123 
 Coal, bituminous and anthra- 
 cite 85-86 
 
 burning of 63-64 
 
 origin 85-86 
 
 Coal famine, results of .... 63 
 
 Coffee grinder 234 
 
 Cogwheels 234-235 
 
 Coils, electric, of electric bell . . 254 
 Cold, extremes of heat and cold in 
 lessening resistance to dis- 
 ease 114 
 
 Cold frame 223-224 
 
 Colds, caused by bacteria ... 110 
 Cold-storage cars and ships, im- 
 portance of 103 
 
 Cold-storage plants .... 100-103 
 
 Color, explanation of ... 286-287 
 
 importance of color of flowers 358 
 
 of clothing 297 
 
 of sunset and sunrise .... 288 
 relation of wall-color to 
 
 lighting 285-286 
 
 Communicable diseases .... Ill 
 Commutator, effect on alternating 
 
 current 264 
 
 Compounds, chemical 56 
 
 Concave lens, for correction of 
 
 near-sightedness 292 
 
 Constellations 205 
 
 Constipation 346-347 
 
 Consumption (tuberculosis), 
 
 transmission of 112 
 
 Convection currents, of air . 28-29 
 , of water 306-307 
 
 Convex lens, for correction of 
 
 far-sightedness 292 
 
 Cooking appliances, electric . . 268 
 
 Copper-plating 266 
 
 Corn, primitive . 362 
 
 Cornea of eye 289 
 
 Corolla . . 353 
 
 Cotton seed meal, use as fer- 
 tilizer 324 
 
 Cowpox 116 
 
 Crankshaft 247 
 
 Cross-pollination 355 
 
 Crow bar 231 
 
 Crystal detectors, wireless . . 262 
 
 Culture media 93 
 
 Cyclones . 36 
 
 Dams, use in developing 
 
 water power .... 153-157 
 
 Daniell cell 258-259 
 
 Darwin, Charles 355 
 
 Day-light saving 216 
 
 Decay, cause of 92-93 
 
 importance of 122-123 
 
 Detectors, wireless 262 
 
 Developer, in photography . . 221 
 Dew, formation of .... 127-128 
 
 Dew point 128 
 
 Diet, amount of food in . . 336-342 
 good, as protection against 
 
 disease 114 
 
 importance of green vege- 
 tables and milk in . . 332-333 
 of mineral matter in. . 331-332 
 
 of lumbermen 330 
 
 planning of 342-343 
 
 value of fat in 330-331 
 
 value of starch and sugar in . . 331 
 use of orange juice in . . . .104 
 
 Digestion 343-344 
 
 in human body ...... 346 
 
 of starch 345 
 
 Diphtheria, transmission of. . . 113 
 Direct lighting .....;.. 284 
 
 Dirigible 10 
 
 Diseases, carried by milk . . . 103 
 
 communicable .111 
 
 natural protection against . 114 
 
 of eyes . 294 
 
 Disinfectants 108, 120 
 
 use of 119-121 
 
INDEX 
 
 References are to pages 
 
 Domestication of plants and 
 
 animals 362-363 
 
 Draft, of furnace 307 
 
 Dragon, a constellation .... 207 
 Dragon fly ......... 375 
 
 Dry cell . . 259 
 
 Drying, as a means of food 
 
 preservation .... 105-106 
 
 Dust, carrier of bacteria .... 94 
 
 effect upon sunset colors . . 288 
 
 Dynamo 262-264 
 
 Ear, human 50-52 
 
 Earthworm, breathing of ... 69 
 
 Eclipses 202-203 
 
 Edison, Thomas A 270 
 
 Efficiency of machines .... 241 
 
 of engines 245-246 
 
 of storage cell 272 
 
 Egg cell 354-355 
 
 Electric cells 257-259 
 
 in series 260 
 
 Electric current, alternating and 
 
 direct 264 
 
 generated by cells . . . 257-259 
 by dynamo 262-264 
 
 in electroplating and elec- 
 trotyping 266-267 
 
 used to produce heat . . 267-268 
 
 use in refining metals .... 267 
 
 Electric furnace 268 
 
 Electric heating and cooking 
 
 appliances 268 
 
 Electric lights '. 268-271 
 
 Electric transformer 270 
 
 Electrical pressure ...:.. 259 
 Electricity, early use of .... 252 
 
 relation of water power to 153-157 
 
 static . . . . : 273 
 
 Electro-magnet 255-256 
 
 use in dynamo 264 
 
 Electromotive force 259 
 
 Electroplating 266 
 
 Electrotyping "... 267 
 
 Elements, chemical 56 
 
 Embryo 350 
 
 Energy 63 
 
 available in human body . . 67 
 
 Engines, gas 246-249 
 
 four-stroke cycle 247 
 
 solar . . 224-225 
 
 Engines Continuued 
 
 inefficiency of 225 
 
 Enzyme 345 
 
 Equilibrium, stable and unstable 194 
 Equinox, vernal, autumnal . . 212 
 
 Erosion, stream 179 
 
 wind 314 
 
 Eustachian tube 51-52 
 
 Evaporation . . . . 26, 77 
 
 in cold-storage plants . 100-101 
 in iceless refrigerator . . 99-100 
 Expansion tank, hot water heat- 
 ing system . . ' 305 
 
 Eye, abuse of ...... 293-294 
 
 advantage of two eyes .... 293 
 
 care of 293-294 
 
 normal 289 
 
 Eye strain 293 
 
 Eyeglasses, use of .... 291-293 
 
 Fading of colors 223 
 
 Far-sightedness 288 
 
 cause and correction of . 291-292 
 
 Fat, use in food 330 
 
 Fatigue, excessive, lessening re- 
 sistance to disease . . . .114 
 Fermentation, by yeast . . . . 104 
 
 in sauerkraut 105 
 
 Fertilization, of egg cell . . 354-355 
 Fertilizer, nitrate of soda as . . 324 
 
 organic matter as 324 
 
 sewage used as ....... 173 
 
 sulphate of ammonia as . . 324 
 Field magnet, of dynamo . . . 264 
 
 of motor 265 
 
 Filaments 353 
 
 Filaments, of electric light bulbs 269 
 
 Film, photographic 221 
 
 Fire extinguisher 76 
 
 Fire lanes 78 
 
 Fire walls 79 
 
 Fireless cooker 301 
 
 Fireproof construction .... 79 
 
 Fish, breathing of 71-72 
 
 in balanced aquarium . . . 89-91 
 
 use as fertilizer 324 
 
 Fishing pole, as a lever .... 233 
 
 Flame 59 
 
 Flies, relation to typhoid 
 
 fever 112, 172 
 
 Floods, prevented by forests 181-182 
 
INDEX 
 
 References are to pages 
 
 Flower, purpose of 352 
 
 structure of 352-353 
 
 Fly wheel, advantage of . . . .- 247 
 
 Focus, of camera . 291 
 
 of eye 290-291 
 
 Fog, formation of .... 131-132 
 Food, composition 
 
 of 332-336, 338-341 
 
 energy and tissue forming . 89-91 
 foods, rich in jiitrogen . . .331 
 for growth and repair . . 330-331 
 
 preservation 92-106 
 
 rich in mineral matter . . .331 
 storage in seeds .... 350-351 
 
 value as fuel 66 
 
 Food principles 331 
 
 Force 228 
 
 measurement of .... 229-230 
 Forest fires, effect upon color of 
 
 sunset 288 
 
 Forests, injured by insects. . . 372 
 
 relation to floods 181 
 
 relation to navigability of 
 
 rivers and harbors . . 178-180 
 relation to water supply . . .163 
 
 Fountain pen 13 
 
 Franklin, Benjamin 273 
 
 Freezing of water in breaking 
 
 rock 312-313 
 
 Friction, cause of 241 
 
 reduction of 242-243 
 
 value of 243-245 
 
 Friction matches 58-59 
 
 Fuel, denned 65 
 
 Fuel value of foods, measure- 
 ment of 334-336 
 
 Fulcrum, of a lever 231 
 
 Furnace, electric 268 
 
 hot air 304-305 
 
 Fuses, electric . 270 
 
 Galvanized iron 75 
 
 Gastric juice ......... 346 
 
 Gears, automobile 247 
 
 Germicides 120 
 
 Germs 108 
 
 Gills, offish 72 
 
 Glacial lakes 317 
 
 Glacial scratches 316 
 
 Glacier 316-319 
 
 Gorgas, Dr. William C., com- 
 bating yellow fever 
 
 and malaria 187-188 
 
 Grafting . 365-360 
 
 Grasses, ancestors of grain 
 
 plants 262 
 
 Gravel, as a constituent of 
 
 soil 309-310 
 
 Gravitation, law of 193 
 
 Gravity, center of 194 
 
 Gravity cell 258 
 
 Grease, use to prevent fric- 
 tion 242-243 
 
 Great Bear, a constellation . . 206 
 Great Dipper, a constellation . 205 
 Grindstone, use in sharpening 
 
 tools 314 
 
 Guano, use as fertilizer .... 324 
 Guard cells, action of, in con- 
 trolling transpiration ... 149 
 
 Hail, formation of 134 
 
 Harbors, caused by sunken 
 
 coast 175-178 
 
 importance of 175 
 
 Hard water 168 
 
 Headache, caused by eye strain 293 
 Health increases resistance to 
 
 disease . 114 
 
 Hearing 50-52 
 
 Heat, absorption by land and 
 
 water 31-32 
 
 conductors of 303-304 
 
 effect on rocks . 312 
 
 extremes of heat and cold 
 in lessening resistance to 
 
 disease 114 
 
 from electric current . . 267-268 
 
 from oxidation 54 
 
 passage through glass .... 224 
 
 value in food preservation 103-104 
 
 Heating appliances, electric . . 268 
 
 of houses 304-307 
 
 Helium 12 
 
 Heredity 363-364 
 
 Horse power 230 
 
 Hotbed 61-62 
 
 Hot air, heating by .... 304-305 
 Hudson River, a submerged 
 
 river valley 175-177 
 
INDEX 
 
 References are to pages 
 
 Humidity, determination of 142-143 
 
 relative 142 
 
 Humus 310,318 
 
 importance in soil 318 
 
 Hurricanes 38-40 
 
 Hybridizing .......... 365 
 
 Hydraulic pressure, source 
 
 of power of 157-158 
 
 uses of 158-159 
 
 Hydrogen .!...- . . 12 
 
 Hydrophobia, Pasteur treatment 
 
 for 119 
 
 Hygrometer, to determine 
 
 humidity .-..,, . . . 142-143 
 Hypo 221 
 
 Ice, use in refrigerator . . . 
 Iceless refrigerator . . 
 Ichneumon fly . ... . ..' 
 
 Illumination of a room . . 
 Immunity, acquired . 
 
 to diphtheria 
 
 Improvement of plants and 
 animals . . . . ; . 
 Inclined planes, use of, ex- 
 amples of 
 
 Indirect lighting . . . . 
 Induction coil, use and struc- 
 ture 
 
 Inertia, defined 
 
 relation to centrifugal 
 force ........ 
 
 Inflammation 
 
 Insecticides 
 
 Insects, adaptation for polli- 
 nation 
 
 breathing of 
 
 carriers of disease . . . 
 
 destruction of harmful . 
 
 injurious to plants . . . 
 
 yearly damage by ... 
 
 Intestine 
 
 Iron, galvanized 
 
 Irrigation 
 
 97-99 
 .99-100 
 . . 376 
 278-286 
 115-119 
 117-118 
 
 362-367 
 
 238-240 
 
 . 284 
 
 261-262 
 . 235 
 
 197-199 
 . . 108 
 373-375 
 
 357-359 
 . 70-71 
 112-113 
 373-378 
 269-372 
 . . 372 
 346-347 
 . . 75 
 . 136 
 
 Jackscrew, use in doing work . 24Q 
 Jenner, Edward llg 
 
 Kerosene emulsion, as an in- 
 secticide 375 
 
 Kilowatt 261 
 
 Kilowatt hour . .261 
 
 Kindling temperature ..... 58 
 
 Kite 1-2 
 
 Knife, as an inclined plane . . 240 
 Knots, importance of friction in 245 
 
 Ladybird beetle 375-376 
 
 Lakes, glacial 317 
 
 Latitude 218 
 
 Lazear, Dr., martyr in fight 
 
 against yellow f^ver .... 188 
 
 Leaf, work of 82-89 
 
 Leaf mulch 322 
 
 Legumes, effect upon soil of . . 124 
 Lens, use as magnifying glass 289-290 
 Lenses, for correction of defec- 
 tive vision 292 
 
 Lever, use in doing work . 231-233 
 Light, broken up by prism . . . 287 
 
 intensity 279-280 
 
 reflected and diffused . . 276-277 
 
 refraction of 289-290 
 
 result of oxidation 55 
 
 Lighting of rooms, cost . . 278-282 
 
 direct and indirect 284 
 
 from sunlight 276-278 
 
 Lightning 273 
 
 Limestone composition .... 56 
 Little Bear, a constellation . . 207 
 Little Dipper, a constellation . . 206 
 
 Longitude 214 
 
 Low pressure areas 33-36 
 
 Lumber, injured by insects . . 369 
 
 Lungs 72 
 
 Luray Cave, formation of ... 312 
 
 Machines, efficiency of . . 241-243 
 
 reasons for use 228 
 
 Magneto 249 
 
 Magnetic needle 256-257 
 
 Magnets, electro- and per- 
 manent 255-256 
 
 of dynamo 263-264 
 
 Malaria, transmission of ... 113 
 Mammoth Cave, formation of . 312 
 Manure, use as fertilizer . . . 324 
 Mars, possibility of life upon 203-204 
 Match, lighting of ...... 58-60 
 
 Meat chopper 234 
 
 Medicine dropper 11 
 
 Micro-organisms 94, 108 
 
 Micropyle 354-355 
 
INDEX 
 
 References are to pages 
 
 Microscope, principle of . . 294-295 
 
 Milk, condensed 104 
 
 evaporated 106 
 
 importance in die^t 343 
 
 pasteurization of .... 103-104 
 powdered . 106 
 
 Mineral matters, importance of, 
 
 in foods 331 
 
 Mizar, a fixed star 207 
 
 Moisture of air, relation to 
 
 comfort 142-143 
 
 Moisture, given off by plants . 145 
 taken up by roots of plants 145-146 
 
 Mold, cause of decay of food . . 93 
 conditions favorable for 
 
 growth 96-97 
 
 importance in ripening cheese 125 
 
 Monsoon 32 
 
 Moon, eclipse of 203 
 
 phases 201-202 
 
 relation to tides .... 192-195 
 revolution around earth . . . 197 
 
 Mosquitoes, breathing of ... 70 
 
 carriers of malaria 113 
 
 carriers of yellow fever ... 188 
 
 "Mother" of vinegar 125 
 
 Motion pictures 295-297 
 
 Motor, electric 265-266 
 
 gasoline 246-249 
 
 Mountains, as a source of water 
 
 supply 161 
 
 Mucus, importance in keeping 
 germs out of throat and 
 lungs 114 
 
 Mulch, importance in holding 
 
 water in soil 322 
 
 Near-sightedness 288 
 
 cause and correction of . 291-292 
 
 Nectar 358 
 
 Negative, in photography . . . 221 
 
 Nerve, optic 278 
 
 endings in eye . . .". : . . 278 
 
 New York City, water supply of 160 
 Newton, Sir Isaac, first law of 
 
 motion . : 198 
 
 law of gravitation 193 
 
 Niagara Falls, a source of water 
 
 power 155 
 
 Nitrate of soda, use as fertilizer 324 
 
 Nitrogen, fixation of 325 
 
 foods containing much . . .331 
 importance in the air . . . 81-82 
 necessity of, for making pro- 
 tein 328 
 
 source of, for plants . . . 324-325 
 Nitrogen-fixing bacteria . . 123-124 
 Nodules, on roots of plants of 
 
 clover family 124 
 
 North Star 205-206 
 
 value in determining lati- 
 tude . . 217-218 
 
 Nucleus 354 
 
 Nutrients 331 
 
 Ocean, cause of saltiness . . . 141 
 
 Oculist 293 
 
 Ohm 260 
 
 Ohm, Georg 260 
 
 Oil, origin of, in plants .... 327 
 use to prevent friction . . 242-243 
 
 Opera glasses 295 
 
 Optometrist 293 
 
 Organic matter, a source of 
 
 nitrogen 324 
 
 a source of potassium and 
 
 phosphorus 325-326 
 
 importance of decay of . 122-123 
 Orion, a constellation . . . 208-209 
 
 Osmosis 148 
 
 Ovules 353 
 
 Oxidation 55 
 
 in human body 65-67 
 
 in plants 67-69 
 
 slow 60-62 
 
 Oxygen 55 
 
 given off by plants 84 
 
 percentage in air 80 
 
 test for 84 
 
 Panama Canal, importance in 
 
 ocean transportation ... 186 
 Paris green, as an insecticide . 373 
 Pascal's principle, in relation to 
 
 hydraulic pressure .... 158 
 Pasteur treatment for rabies . 119 
 Pasteurization of milk . . 103-104 
 Perseus, a constellation .... 207 
 
 Petals 352 
 
 Petri dish 94 
 
 Phonograph 47-49 
 
INDEX 
 
 References are to pages 
 
 Phosphate rock, use as fertilizer 326 
 Phosphorus . . . . . . . . 59 
 
 in soil 324 
 
 source of, as fertilizer . 325-326 
 
 Photography 221-222 
 
 Photosynthesis, denned .... 84 
 
 Pimples 110 
 
 Pin, as an inclined plane . . . 240 
 
 Pistil 353 
 
 Pistillate flowers ...... 356 
 
 Pitchfork, as a lever 233 
 
 Placenta 350 
 
 Planets . 203-204 
 
 Plants, breathing of .... 67-68 
 
 importance in a balanced 
 
 aquarium 89-91 
 
 Pleiades, a constellation . . . 209 
 
 Pneumatic drill 23 
 
 Pneumatic tubes 23 
 
 Pneumonia, transmission of . . 113 
 Polarization of electric cell . . . 258 
 Pole Star 205-206 
 
 value in determining lati- 
 tude 217-218 
 
 Pollen 353 
 
 Pollen grain 354 
 
 Pollen tube 354 
 
 Pollination 355 
 
 insect 357-359 
 
 wind 357 
 
 Potassium 56 
 
 in fertilizers 325-326 
 
 in soil . 324 
 
 sources of 326 
 
 Potatoes, primitive condition . 363 
 Power, of automobile . . . 57-58 
 Prevailing westerlies . . . . . 36 
 Prints, in photography .... 222 
 
 blue 222 
 
 Proeyon, a fixed star 209 
 
 Projection lantern, use of lens in 295 
 Propagation of plants, by seeds . 349 
 
 vegetative 365-367 
 
 Proteins ....... 89-90,328 
 
 in diet 337 
 
 Protozoa 96 
 
 Psychrometer, in determination 
 
 of relative humidity ... 142 
 
 Pulleys, uses of 235-237 
 
 Pump, exhaust air 21 
 
 force . . 22-23 
 
 Pump Continued 
 
 suction 14 
 
 tire 21-22 
 
 Pus 109-110 
 
 Push button, of electric bell . . 253 
 Pyorrhea Ill 
 
 Rabies (hydrophobia), Pasteur 
 
 treatment for 119 
 
 Radiation, of heat 306 
 
 Radiator, automobile . . . 249, 306 
 injured by freezing . . . 312-313 
 of heating plant .... 305-306 
 
 Rain 40-41 
 
 formation of 132-133 
 
 Rainbow 41 
 
 Rainfall, distribution of . . 134-135 
 Record of phonograph . . . 48-49 
 Reed, Dr=, member of Yellow 
 
 Fever Commission .... 187 
 
 Reflectors, use 282-285 
 
 Refraction of light .... 289-290 
 
 Refrigerator 97-100 
 
 walls of 301 
 
 Reservoirs, importance in 
 
 water supply system . 165, 167 
 Resistance, natural, of body 
 
 against disease . . . . . .114 
 
 Retina of eye . 291 
 
 Rickets 104 
 
 Rigel, a fixed star 209 
 
 Riggs' disease of teeth . . . .110 
 Rocks, disintegration of, in 
 
 formation of soil 311 
 
 phosphate 326 
 
 stratified 178,180 
 
 Roller bearings, use in preventing 
 
 friction 243 
 
 Roots, extent of 145-146 
 
 selective absorption by ... .327 
 special structures for taking in 
 
 moisture 147 
 
 splitting rocks 313 
 
 Root hairs, importance in taking 
 
 in moisture ....... 148 
 
 selective absorption by ... 327 
 
 structure 148 
 
 Rotation of earth, effect on 
 
 winds 32-33 
 
 Rusting of iron . 60 
 
 prevention of 75-76 
 
INDEX 
 
 References are to pages 
 
 Safety matches 59 
 
 Safety valve, of steam boiler . . 306 
 
 Saliva 346 
 
 Salt, use in food preservation . 105 
 Sand, as a constituent of soil 309-310 
 
 Sand blast, action of 314 
 
 Sauerkraut 105 
 
 Screw, an inclined plane . . . 240 
 
 Sea breeze 31 
 
 Seasons, cause of .... 211-212 
 Seaweed, as a source of potas- 
 sium 326 
 
 Seed leaves 350 
 
 Seedlings, growth of ..... 350 
 
 Seeds, formation of 354 
 
 structure of 349-352 
 
 See-saw 232 
 
 Selection, in improvement of 
 
 animals and plants . . 363-364 
 Selective absorption ..... 327 
 
 Self-pollination 355 
 
 prevention of 356-357 
 
 Sepals 352 
 
 Septic tank for disposal of sew- 
 age 172 
 
 Seven Sisters, a constellation . 209 
 Sewage, disposal of .... 172-173 
 
 use as fertilizer 173 
 
 Shades, use 282-285 
 
 Silt, as a constituent of soil . . .310 
 
 Siphon 14 
 
 Sirius, a fixed star 209 
 
 Skin, unbroken, protection 
 
 against germs 114 
 
 Sky, blueness of 288 
 
 Slag, use as fertilizer 326 
 
 Slaughter house waste, use 
 
 as fertilizer 324, 326 
 
 Sleep, lack of, in lessening re- 
 sistance to disease . . . .114 
 Smallpox, vaccination against . 116 
 Snakes, value in destroying in- 
 sects 378 
 
 Snow, formation of .... 132-133 
 Soil, composition of .... 309-310 
 
 glacial 314-317 
 
 importance of bacteria in 
 returning organic matter 
 
 to 122-123 
 
 importance of legumes in 
 
 improving 123-124 
 
 Soil Continued 
 
 produced by decay of organic 
 matter 318 
 
 produced by erosion . . 313-314 
 
 produced by weathering . 311-313 
 
 water-holding power of . 321-323 
 
 Solar engines 224 
 
 Solar system . 203 
 
 Sound 44-47 
 
 Sound box of phonograph . . 47-48 
 
 Sperm cell 354 
 
 Spices, use in food preservation . 105 
 Spontaneous combustion ... 61 
 Spraying to kill insects . . 373-374 
 Sprocket wheel, bicycle .... 235 
 Staminate flowers .... 356-357 
 
 Standard time 215 
 
 Starch, composition of . . . 56,83 
 
 digestion of 345 
 
 test for starch in leaf . . . 82-83 
 Starch making, proof of, in 
 
 leaf 82-83 
 
 raw materials .:.... 83-84 
 Stars, fixed . . .' 209 
 
 value in determining latitude . 217 
 
 Static electricity 273 
 
 Steam heat 304-305 
 
 Stereoscope 293 
 
 Stigma 353 
 
 Stomates, action of, in control- 
 line; transpiration .... 150 
 
 Stratified rocks 178, 180 
 
 Stripes, effect of, in clothing . . 297 
 Suez canal, importance in ocean 
 
 transportation 186 
 
 Sugar, use in food preservation . 104 
 Sulphate of ammonia, use as fer- 
 tilizer 324 
 
 Sun, eclipse 202 
 
 maintenance of energy of 225-226 
 
 source of energy of coal and 
 
 wood 86 
 
 source of energy of gasoline . 219 
 
 source of energy of water 
 
 power 153-155 
 
 source of energy of winds . . 220 
 
 use of sunlight in making 
 
 pictures 221-223 
 
 Sunlight, use in making 
 
 pictures 221-223 
 
 Sun parlor 223 
 
10 
 
 INDEX 
 
 Sunrise and sunset, color of . . 288 
 Sun time . 214-215 
 
 Taurus, a constellation .... 209 
 Teeth, dangers from decay 
 
 of 110-111 
 
 Telegraphy, wireless . . . 261-262 
 
 Telephone 50 
 
 Telescope, use of lens in ... 295 
 Temperature, in cold storage 
 
 plant 100 
 
 relation to formation of dew 128 
 Terminal moraine, of 
 
 glacier . . . ' . . 316-317, 319 
 Tetanus, transmission of ... 113 
 Thermometer, wet and dry bulb 142 
 
 Thermos bottle 300-301 
 
 Thunderstorm 40,41 
 
 Tides, cause 192 
 
 Time, calculation of ... 214-215 
 
 sun 215 
 
 Toads, value in destroying in- 
 sects .... 378 
 
 Tobacco, as an insecticide . . . 375 
 Tonsils, danger from in- 
 flammation of .... 110-111 
 
 Tornadoes 37 
 
 Torricelli 6 
 
 Toxin 109 
 
 of diphtheria .117 
 
 Trade winds 32 
 
 Transformer, electric 270 
 
 Transpiration 144 
 
 amount of 145 
 
 control of 145-14G 
 
 Transportation, water . . . 175-189 
 Traps of waste water pipes . .171 
 Tuberculosis, transmission of .112 
 Tungsten, use in electric light 
 
 bulbs . . 269 
 
 Typhoid fever, relation to water 
 
 supply 173 
 
 transmission of 112 
 
 vaccination against 117 
 
 "Typhoid Mary" ....... 113 
 
 Typhoons 40 
 
 Ursa Major, a constellation . . 206 
 Ursa Minor, a constellation . . 207 
 
 Vaccination, against smallpox . 116 
 against typhoid fever .... 117 
 
 Vacuum . 6 
 
 of thermos bottle .... 300-301 
 
 Valleys, origin of .314 
 
 Valve, safety, of steam boiler . 306 
 
 Variation 363 
 
 Ventilation, methods of ... 27-30 
 
 need for 25-27 
 
 Vernal equinox 212 
 
 Vinegar, manufacture of .... 125 
 
 use in food preservation . . . 105 
 Vitamines, necessity of , in diet . 343 
 
 Vocal cords 46 
 
 Volt 259 
 
 Volta, Alessandro 257 
 
 Voltage, of electric light wires . 270 
 
 Voltaic cell 257 
 
 Voltmeter 260 
 
 Von Guericke, Otto 8 
 
 Wall color, relation to light- 
 ing ...' 285-286 
 
 Walking, importance of friction 
 
 in 244 
 
 Water, composition 82 
 
 effect of heat on .... 305-306 
 
 erosion by 313-314 
 
 expansion in freezing . . 169, 312 
 
 hard 168 
 
 heating by hot water . . 305-306 
 use in righting fire 77 
 
 Water pipes 168-169 
 
 waste 171 
 
 Water power, relation to other 
 
 sources of power 154 
 
 source of energy 1 . . . . 153-155 
 
 Water supply, of New York 
 
 City 160-166 
 
 Water ways, internal, im- 
 portance of 182-185 
 
 Watt 261 
 
 Watt, James 230, 261 
 
 Weather Bureau 42 
 
 Weathering, defined 179 
 
 production of soil by . . 311-313 
 
 Wedge, an inclined plane . . . 240 
 
 Wells 166-168 
 
 Westerlies, prevailing .... 36 
 
 Wheel and axle, as a simple 
 
 machine 233-235 
 
 Wheelbarrow . . 232 
 
INDEX 
 
 11 
 
 References are to pages 
 
 White blood corpuscles . . 109, 114 
 Windlass, use in doing work 233-234 
 
 Windmills 220-221 
 
 Winds, cyclones 36 
 
 erosion by 314 
 
 prevailing westerlies . . . 33, 36 
 
 sea breeze 31 
 
 tornadoes 37 
 
 trade 32 
 
 Winds Continued 
 
 use of energy of .... 220-221 
 
 Wireless telegraphy 262 
 
 Work, defined 228 
 
 measurement of .... 229-230 
 Wyandotte Cave, formation of . 312 
 
 Yeast 
 
 cause of fermentation 
 
 96 
 104 
 
YB 35750 
 
 UNIVERSITY OF CALIFORNIA LIBRARY