76 ELEMENTS OF AGRICULTURE 



world. In the second chapter the influence of the 

 evaporation of surface moisture on the earth's tempera- 

 ture is discussed. This action may be compared to the 

 evaporation of perspiration from the human body. The 

 temperature of the human body is prevented from be- 

 coming too high by the evaporation of moisture given 

 off through the skin. So it is with the surface of the 

 earth, which may be called the skin; when it becomes 

 too warm moisture is given off and its evaporation cools 

 the soil. In very wet soils moisture is continually 

 evaporating, and in consequence such soils are usually 

 cold. In dry soils, on the other hand, there is but little 

 evaporation, and the soil through the sun's heat be- 

 comes warm. As a rule, the dryer the soil the greater 

 the amount of heat absorbed. When no moisture is 

 found the soil is turned into a desert. 



The color of soils also influences the temperature. 

 It is a well-known fact that dark clothes are warmer 

 than white. So it is with soils — a dark soil is warmer 

 than a light one. 



The composition of soils also has an effect on the 

 amount of heat absorbed. As a rule, sandy soils are 

 warmer than clay soils. 



The fineness of the soil particles has also a marked 

 influence on its temperature. Coarse, rocky soils suffer 

 from extremes of temperature. In fine, well-cultivated 

 soils the temperature is almost uniform. 



Questions 



1. Soils that have been moved from their place of forma- 

 tion are called what? 2. Soils that remain where they are 

 formed are called what? 3. By what means are soils usually 



