12 



CONTENTS 



CHAPTER PAG8 



XXVII. REFRACTION , . 252 



XXVIII. PHOTOGRAPHY AND THE CHEMICAL ACTION OF LIGHT . 262 



XXIX. COLOR 271 



XXX. ARTIFICIAL LIGHTING 275 



XXXI. SOUND 281 



XXXII. How MACHINES LIGHTEN LABOR 289 



XXXIII. THE POWER BEHIND THE ENGINE 311 



XXXIV. PUMPS, AND THEIR VALUE TO MAN 319 



XXXV. THE WATER PROBLEM OF A LARGE CITY .... 334 



XXXVI. WATER MAKES A GARDEN OF THE DESERT . . . 347 



XXXVII. THE WORK OF RUNNING WATER 357 



XXXVIII. AIR . ... 377 



XXXIX. THE WORK OF THE ATMOSPHERE 388 



XL. CLIMATE 393 



XLI. MOUNTAINS, EARTHQUAKES, VOLCANOES, GEYSERS . . 405 



XLII. THE ROCKS AND BUILDING STONES OF THE EARTH . .417 



XLIII. PLANTS AND THEIR RELATION TO MAN .... 423 



XLIV. THE ANIMALS OF THE EARTH . 460 



