THE TEMPERATURE OP THE SOIL 



31 



The temperature of a soil depends secondly upon the 

 amount of moisture in it. 



The temperature of a soil depends thirdly upon its 

 color. 



20. How the Air Space in a Soil affects its Tempera- 

 ture. — The greater the amount of air space, the warmer 

 the soil. Air is warmer than the earth in the spring. 

 Therefore when either air or rain water, which is warmed 

 in passing through the air, enters the soil in the spring, 

 the temperature of the land is raised. 



We have already in Exercises 10 and 11 determined the 

 amount of air space in certain soils. Let us now see what 

 influence this has upon the temperature. We remember 

 from Exercise 1 that while sand is made up of coarse 

 particles, clay consists of particles so small and fine that 

 it becomes pasty when wet. 



EXERCISE 12 



Object. — To determine how the size of particles, and 

 consequently of the air space in a soil, influences its tem- 

 perature. 



Procedure. — Fill two cans, one with clay, the other 

 with sand. Plunge the bulb of a thermometer into each 

 soil, about one inch below the surface. Moisten each 

 soil and place the cans in the sunlight. Copy the follow- 

 ing table into your notebook and complete it by recording 

 the temperatures every hour. 



