EXPERIMENT STATION BULLETINS. 549 



and the heavy soils the least; next day the air temperature rises con- 

 siderably and the temperature of the soils rises according to their 

 specific keat: the light soils attain the highest temperature as in the 

 spring, and the heavier seals the lowest; another day follows with very 

 low temperature whereupuu all the soils lose heat again in the same 

 order as above: the sand and gravel as usual lose more than the other 

 soils, but they attained a higher temperature during the day time and 

 consequently have more apparent heat to lose. These alternate cold and 

 warm days with the downward trend of air temperature tend to keep 

 the lighter soils as warm as the heavier soils. 



If the air temperature would continue to drop very rapidly without 

 any warm days intervening, then the light soils would cool or freeze 

 most rapidly and would continue to have a much lower temperature. 

 This is well illustrated whenever a severe cold weather sets in as on 

 January 8, 1911, when the coldest day of the year occurred and the 

 soil temperature dropped very low. On this date the light soils cooled 

 the most and the heavy soils the least. It is in such occasions or cir- 

 cumstances as these that high moisture content becomes an advantage 

 and renders highly practical benefits. 



The next most interesting fact that the foregoing tables and charts 

 show is the same magnitude of temperature in the upper 6 inches of all 

 the different types of soil at all times except during thawing. Here 

 again it is the common belief that the light soils, for the same reason 

 that they warm up the fastest in the spring and cool most rapidly in 

 the fall, have the highest temperature during the summer months and 

 lowest during the winter months. The data, as already stated, show 

 most decidedly that the average temperatures of all the soils in the 

 upper 6-inch layer are practically the same, varying, as a monthly aver- 

 age, only about 1° F. from May through summer and fall till freezing 

 time, and this slight variation being in favor of the peat during July, 

 August, and September. The variation is greater than 1° on certain 

 individual days but this is largely due to rapid changes in the air tem- 

 perature and to some other temporary factors. The 12 and 18-inch 

 depths of all the soils have also practically the same temperature 

 throughout the year except during thawing. 



Theoretically, that is what should be expected if heat conductivity 

 had no very marked influence, and if all the other conditions, evapora- 

 tion, color and radiation, were about equal. The color was eliminated 

 by covering all the soils by the same kind of soil ; there was probably 

 not a very great difference in evaporation. If these two iactors were 

 about equal for all soils then they all received about the same amount 

 of warmth during the sun insolation. Their temperature, howe\'er, rose 

 to different degrees on account of their different specific heats. The 

 light soils having the smallest heat capacity under the field conditions 

 attained the highest temperature during the day and the heavier soils 

 the lowest. During the night they all cooled and since the previous 

 study on radiation shows that all soils in well-moistened condition 

 radiate equally well and since all these soils were covered with the same 

 kind of soil and since it is conceived that radiation takes place at the 

 surface, then all the soils lost about the same amount of heat, but 

 received different degrees of lowering of temperature on account of 



