TEMPERATURE OF SURFACE SOIL 



159 



cooling of the soil in winter. Boussingault placed a ther- 

 mometer upon the soil beneath a layer of snow 4 inches 

 thick ; another thermometer lay on the top of the snow freely 

 exposed to radiation ; a third thermometer was suspended in 

 the air, 39 feet above the ground. The readings of these 

 thermometers during three days of clear weather were as 

 follows. The degrees are centigrade. 



TABLE XXVII 



TEMPERATURES BENEATH AND ON THE SURFACE OF SNOW 

 (BOXJSSINGAULT) 



Thus the temperatures of the surface of the ground under 

 the snow were on February 12 and 13, 6-2-85 C. (u-i5 F.) 

 higher after the night's radiation than those shown by the 

 thermometer freely exposed to the sky. 



The shading of a soil by vegetation has a considerable 

 influence in diminishing the extremes of temperature. Crops 

 covering the ground with an abundant foliage will have a 

 distinct effect in this direction. 



The soil of a forest, shaded by trees, and further protected 

 by a thick layer of forest litter, affords an extreme example 

 of the exclusion of solar radiation. According to Ebermayer 

 (Lehre der Waldstreu, 188), the mean temperature of the soil 



