CONTENTS 



PAGE 



UNIT I. THE OCEAN OF AIR IN WHICH WE LIVE 1 



Topic 1. What We Know About Air 1 



Topic 2. Some Devices which Use the Pres- 

 sure of Air 7 



Topic 3. Man's Use of Compressed Air .... 12 



Topic 4. The Relation of Air to Sound 16 



Topic 5. Air and Living Things 21 



UNIT II. THE WEATHER AND CLIMATE ABOUT Us 28 



Topic 1. How Moisture Gets into the Air . . 29 



Topic 2. When Moisture Comes out of the Air 33 



Topic 3. Winds and Weather 37 



Topic 4. How the Weather Man Predicts the 



Weather 



42 



Topic 5. Interesting Weather Happenings and 

 Their Causes 47 



Topic 6. The Climates of the World 



50 



UNIT III. THE RELATION OF THE WATER SUPPLY 



TO THE WELFARE OF THE COMMUNITY .... 57 



Topic 1. Methods of Purifying Water 57 



Topic 2. How Communities Obtain Pure 



Water 62 



Topic 3. Using Water in the Home and Com- 

 munity 71 



UNIT IV. OUR FOOD SUPPLY 76 



Topic 1. Man's Need of Food 76 



Topic 2. Importance of a Balanced Diet .... 80 



Topic 3. Preparing and Preserving Food ... 86 



Topic 4. How the Human Body Uses Food 92 



UNIT V. How WE LIGHT OUR HOMES 98 



Topic 1. The History of Lighting 98 



Topic 2. Some Important Things About Light 103 



Topic 3. Proper Lighting in the Home 107 



Topic 4. Devices which Use Light Ill 



UNIT VI. RELATION OF HEAT TO HEALTH AND 



COMFORT 1 19 



Topic 1. How Heat is Produced 119 



Topic 2. How Heat and Temperature are 



Measured 126 



Topic 3. Devices Used for Heating 129 



Topic 4. How Fire is Controlled and Pre- 

 vented 137 



Topic 5. Protecting Our Bodies with Cloth- 

 ing 141 



PAGE 



UNIT VII. USING MACHINES TO HARNESS ENERGY 146 



Topic 1. Some Forces and Motions in Daily 



Life 146 



Topic 2. The Machines We Use in Everyday 



Life 155 



Topic 3. Harnessing the Energy about Us . . 162 



UNIT VIII. THE RELATION OF OUR EARTH TO 



OTHER HEAVENLY BODIES 170 



Topic 1. Learning About the Stars 170 



Topic 2. The Sun and His Family 179 



Topic 3. Our Earth, a Planet 186 



UNIT IX. ROCKS AND SOILS OF THE EARTH 195 



Topic 1. How Rocks Were Formed 1% 



Topic 2. The Wearing Away of the Earth's 



Surface 201 



Topic 3. The Importance of Soil 207 



UNIT X. LIFE ON THE EARTH 215 



Topic 1. Our Smallest Living Things 215 



Topic 2. Other Enemies of Man 221 



Topic 3. The Origin and Development of Liv- 

 ing Things 228 



Topic 4. Improvement of Living Things .... 232 



UNIT XI. ELECTRICITY AND How WE USE IT .... 239 



Topic 1. Some Ways of Securing Electrical 



Energy 239 



Topic 2. Securing Electrical Energy from 



Magnets and Electromagnets 245 



Topic 3. How Electricity Is Generated 248 



Topic 4. Using Electricity About the Home 253 



Topic 5. How Electricity Is Measured 258 



UNIT XII. How MAN COMMUNICATES 264 



Topic 1. Early Forms of Communication . . . 264 



Topic 2. Communication by Telegraph 266 



Topic 3. The Telephone in Communication . . 272 



Topic 4. Telegraphing Without Wires 277 



Topic 5. Communication by Radio 282 



UNIT XIII. TRAVEL AND TRANSPORTATION ..".... 291 



Topic 1. Transportation on Land 291 



Topic 2. Travel on Water 302 



Topic 3. Travel in the Air 308 



INDEX . 317 



