vi CONTENTS 



CHAPTER 'AGE 



XIX. SOME EFFECTS OF HEAT 141 



XX. THE ATMOSPHERE 147 



XXI. AIR AND WATER COMPARED. ATOMS AND ELE- 

 MENTS 155 



XXII. HEAT AND THE ATMOSPHERE 162 



XXIII. THE SEASONS AND THE SOLAR SYSTEM . . 169 



XXIV. WINDS AND WEATHER 178 



XXV. ECONOMIC IMPORTANCE OF WINDS, RAINS, 



CYCLONES, CLOUDS, TORNADOES . . . 189 



XXVI. HEATING AND VENTILATION 199 



XXVII. COMBUSTION 209 



XXVIII. LIGHT, COLOR, AND SOUND 216 



XXLX. SOME EFFECTS OF LIGHT. PHOTOGRAPHY. 



PHOTOSYNTHESIS 225 



XXX. FOOD. THE NUTRITIVE CYCLE . . . . 232 



XXXI. PLANT LIFE 242 



XXXII. THE STORY OF SEEDS 247 



XXXIII. PLANT GROUPS 257 



XXXIV. RELATIONS BETWEEN PLANTS AND THEIR 



SURROUNDINGS 265 



XXXV. ANIMALS. VERTEBRATES 270 



XXXVI. INSECTS 2?6 



285 



