viii ELEMENTS OF GENERAL SCIENCE 



PAOK 



CHAPTER XVI. WORK 170 



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. Calcula- 

 tion of work in pulley systems. Efficiency. Summary. 



CHAPTER XVII. MECHANICAL ENERGY AND HEAT .... 180 

 Capacity for doing work. Examples of bodies possessing energy. 

 Kinds of energy. Measurement of energy. Work against friction 

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

 The steam engine. Transformations of energy. Loss of energy. 

 The source of energy. Amount of energy from the sun. Energy 

 and work in living things. 



PART IV. THE EARTH'S CRUST 



CHAPTER XVIII. NATURAL FORCES UPON THE SURFACE 

 OF THE EARTH 191 



The surface of the earth. The surface and water. Work by freez- 

 ing water. Other changes due to water. Glaciers and the earth's 

 crust. Effect of plants and animals. The soil and its significance. 



CHAPTER XIX. PHYSICAL STRUCTURE OF THE SOIL ... 200 

 Kinds of soil. The structure of the soil. Size of soil particles. 

 Plants and animals as soil formers. Raw materials for plant food. 



CHAPTER XX. SOIL WATER, DRAINAGE, AND IRRIGATION 205 

 Amount of water in the soil. Soil water and soil temperature. 

 Amount of water used by crops. Soil water as affected by tillage. 

 Natural drainage of the soil water. Artifipial drainage of soil 

 water. Irrigation. Source of water for irrigation. Dry farming. 

 Reclamation of swamp lands. 



CHAPTER XXI. EROSION AND SEDIMENTATION 215 



Removal of the soil : erosion. Loss from water erosion. Vegeta- 

 tion and erosion. Deposit of soil from erosion. Erosion by wind. 



CHAPTER XXII. LIFE IN THE SOIL 224 



Living things in the soil. Interrelationship of living things in the 

 soil. Bacteria of the soil. Soils and man. 



