THE PROPERTIES OF SOIL 39 



vital importance to the life of plants, and 

 to the profitable cultivation of crops. If 

 certain definite weights of such substances 

 as iron, copper, and lead, are exposed to 

 the same amount of heat for definite periods 

 it will be found that the temperature of these 

 bodies varies considerably, showing either 

 that they have taken up varying quantities 

 of heat or that for the same amount of heat 

 their temperature has responded in varying 

 degree. The property of a body to absorb 

 heat is known as its capacity for heat, the 

 standard of measurement being the capacity 

 for heat, or the Specific Heat, of water. 

 Specific heat may be defined as the quantity 

 of heat which a definite weight of a sub- 

 stance requires in order that its temperature 

 may rise through one degree of temperature, 

 that of water being taken as unity. The im- 

 portant constituents of the soil show marked 

 variations as regards their capacity for heat, 

 and, according to the proportion in which the 

 constituents are present, soils may be warm 

 or cold. Of all the constituents of soil, 

 water is the one which requires most heat in 

 order that its temperature may rise through 

 a denmte number of degrees ; that is to say, 

 it stands at the top of the list as regards 

 specific heat. The specific heat of water 



