648 



STATE BOARD OF AGRICULTURE. 



SECOND DAY 



This table bears out the foregoing explanation perfectly. It will be 

 seen that af the beginning of the experiment the temperature of the cul- 

 tivated sand did not rise as fast as that of the uncultivated. This was 

 due to the large amount of evaporation in the case of the cultivated 

 sand, partly on account of its greater area exposed and partly because 

 more heat was accumulating at the surface; and to a less amount of 

 evaporation and to a small quantity of heat accumulating at the sur- 

 face, in the case of the uncultivated sand. By 1.00 o'clock, however, the 

 temperature of the cultivated sand attained the same degree of magni- 

 tude as the other sand. From that time on the results were reversed, 

 the cultivated sand attained and continued to have a higher temperature 

 than the uncultivated. This is explained on the basis that as soon as 

 the mulch was formed on the surface of the cultivated sand the evapora- 

 tion was considerably cut down, while in the uncultivated sand it was 

 still large. The amount of heat that was expended in evaporating the 

 moisture of the uncultivated sand w'as apparently larger than that radi- 

 ated back to the air by the dry mulch of the cultivated sand. On the 

 second day the results were again reversed, the cultivated sand which 

 in the latter part of the previous day had the highest temperature of 

 the two sands, had now the lowest. This is again explained on the basis 

 of the moisture content and of the effect of the dry mulch. The uncul- 

 tivated sand lost most of its moisture in the previous day during the 

 time that its temperature remained below that of the cultivated, while 

 the latter lost less except at the beginning of the experiment. The result 

 was that the uncultivated sand was losing now a less amount of heat 

 by evaporation and consequenth^ utilizing more of the air temperature 

 for the raising of its own temperature, while the cultivated sand had 

 still some moisture below the dry mulch and on account of the slow but 

 continuous evaporation of this moisture, and also on account of the 

 large amount of heat received being radiated back to the atmosphere by 

 the dry mulch, this sand, therefore, was now utilizing a less amount of 

 heat for the raising of its own temperature, and consequently its tern- 



