494 NOTES ON THE SOIL. 



of the soil as the evaporation of water from its surface. 

 "When a pint of water evaporates from a cubic foot of soil, 

 it carries with it heat enough to lower the temperature of 

 the soil considerably if sandy soil about 20 C., if clay-loam 

 about 15 C. To dry saturated sandy soil till it contains 

 half its maximum amount of water requires the evaporation 

 of about 9 Ibs. to the square foot when the drying extends to 

 the depth of a foot ; the similar drying of clay -loam requires 

 ihe evaporation of about 12 Ibs. of water. It is largely owing 

 to the latent heat of vaporisation of water and to the low 

 specific heat of soil that a wet soil is cooler than the same soil 

 when dry. 



When soil is rolled, its texture is made firmer, and it con- 

 ducts heat better, so that the surface layers become warmer ; 

 the temperature at a depth of 2 ins.may be about 5 C., at 4 ins. 

 about 3 C., higher than in entirely similar and adjacent but 

 not rolled soil. 



