INFLUENCE OF WATER ON SOIL TEMPERATURE 175 



from a cubic foot of wet clay would lower the temperature 

 of the clay io-3 F. The loss of heat is nearly the same 

 at whatever temperature the evaporation takes place. The 

 cooling influence of. water is so great as to override the 

 influence of other conditions tending to warmth ; thus 

 Schiibler found that dry soils, coloured white, exposed to 

 the sun, became about 6 warmer than a wet, dark coloured, 

 humus soil, equally exposed to sunshine. The coldness of 

 a soil in summer time is generally in proportion to- the 

 amount of water which it permanently retains ; it is only 

 during the severer months of winter that a wet soil is 

 superior in temperature to a dry one. 



With these facts before us it is easy to understand why 

 a stiff clay or an undrained meadow are said to be cold 

 soils ; while a soil of open texture, and well-drained, is said 

 to be warm. Both soils may receive the same heat from 

 the sun ; but, in consequence of the properties of water 

 just mentioned, the temperature of the wet soil is always, 

 save in the depth of winter, below that of the dry one. The 

 coldest soil will be one having a permanently saturated sub- 

 soil, from which the surface soil is continually replenished with 

 water. The first step towards the amelioration of cold, wet 

 land, will be the removal of the excess of water by draining. 



Land in which there is a free percolation of water enjoys 

 generally a special rise in temperature from spring rains. 

 In spring time the rain is frequently warmer than the soil, 

 and if the rain can penetrate the soil it becomes an effective 

 agent for warming it. One pound of rain water at 60 F. 

 would be able, from its high specific heat, to raise the tempera- 

 'ture of 10 Ib. of dry sand from 45 to 50. 



King's observations in Wisconsin supply some illustrations 



