CONTENTS ix 



PAGK 



CHAPTER XI. . MECHANICAL USES OF WATER AND AIR . 128 

 Questions for Discussion. Water transferred by the siphon. The 

 lift pump. Why the water rises in the pump. Transmission of 

 pressure in liquids. The principle of the hydraulic press. Dams. 

 Buoyancy. Floating objects. Submarines and balloons. Densities. 



CHAPTER XII. CLIMATIC INFLUENCES OF BODIES OF 



WATER 141 



Questions for Discussion. Water and temperature. Lake and sea 

 breezes. Cause of the lake and sea breezes. Causes of unequal 

 heating of land and water. Cooling of land and water. Extent 

 of influence of water. Causes of difference between east and west 

 shores. Some effects of lake climate. 



CHAPTER XIII. WATER AND COMMERCE .152 



Questions for Discussion. Commercial importance of waterways. 

 Water transportation on the Great Lakes. Origin of lake cities : 

 Chicago as a type. Extension and improvement of waterways. 

 Railroads. Harbors, lights, buoys, and life-saving stations. 



CHAPTER XIV. WATER SUPPLY AND SEWAGE DISPOSAL lf0 

 Questions for Discussion. Sources of water supply. Importance of 

 pure water. Impurities in water. Sources of bacteria in lakes and 

 rivers. Methods of securing pure water. Proper handling of water 

 in the house. Sewage disposal. A sanitary canal. Sewage treat- 

 ment. Rural water supplies. Disposal of wastes in rural districts. 



PART III. WORK, ENERGY, AND ELECTRICITY 



CHAPTER XV. COMMON TYPES OF WORK 173 



Questions for Discussion. About work in general. Different 

 methods of working. A problem in work. Decreasing friction 

 by the use of rollers. Some facts about pulleys. Mechanical 

 advantage of pulleys. Work and pulley systems. Work defined. 

 Measurement of work. Calculation of work in pulley systems. 

 Efficiency. 



CHAPTER XVI. MECHANICAL ENERGY AND HEAT .... 183 

 Questions for Discussion. Capacity for doing work. Kinds of 

 energy. Measurement of energy. Work against friction produces 

 heat. Energy transformed into heat. Work done by heat. The 

 engine. Transformations of energy. Loss of energy. The source 

 of energy. Amount of energy frdm the sun. Energy and work in 

 living things. 



CHAPTER XVII. HEAT AND LIGHT FROM ELECTRIC 



CURRENTS 195 



Questions for Discussion. Light and heat. The use of fuses for 

 safety. How electric circuits are opened and closed. The dry cell 



