SUNSHINE AND SOIL TEMPERATURE 



455 



considerably greater than in the air above, and this 

 excess extends to a depth of nearly one foot. At greater 

 depths in the soil, the range in temperature is less than 

 in the air and much less than at the surface, and the 

 waves of temperature change fall successively behind 



SEPT. OCT- 



TIME IN MONTHS 



Fig. 123. Curves showing the mean monthly range in temperature of (he 

 air, and of the soil at different depths, as given in Table LXIX. Note the in- 

 fluence of the rate of heat conduction, as shown by the curves. 



those of the atmosphere. These variations are asso- 

 ciated directly with the amount and intensity of the 

 sunshine. 



325. The specific gravity and specific heat. The 

 first of these directly affects the temperature to only a 

 small degree. The larger the mass, the more heat required 

 to change its temperature. Hence, the more dense the 

 soil, the more heat absorbed in each layer. 



The specific heat 'of the soil has a considerable in- 

 fluence on its temperature and, because of its marked 



