134 now CROPS FEED. 



have least effect on lipfht-colored soils. (See the table on 

 p. 196.) 



The Rapidity of Change of Temperature independently 

 of color or moisture has been determined on a number of 

 soils by Schiibler. A given volume of dry soil was heat- 

 ed to 145°, a thermometer was placed in it, and the tim3 

 •Avas observed whicli it required to cool down to 70°, the 

 temperature of the atmosphere being 61°. The subjoined 

 table gives his results. In one column are stated the 

 times of cooling, in another the relative j^ower of retaining 

 heat or capacity for heat, that of lime sand being assumed 

 as 100. 



Lime sand 3 hours 30 min 



Quartz suud 3 



Potter's clny 2 



Gypsum 3 



Clay loam 2 



Cliy plow land 2 



Heavy clay 2 



Pure iiniy clay .' 2 



Garden earth 2 



Fine carb. lime 2 



Humus 1 



Magnesia 1 



It is seen that the sandy soils cool most slowly, then 

 follow clays and hea^-y soils, and lastly comes humus. 



The order of cooling above given is in all respects 

 identical with that of Avarming, provided the circumstances 

 are alike. In other Avords these soils, containing no moist- 

 ure, or but little, and exposed to heat of low intensity, 

 Avould be raised through a given range of temperature i:i 

 the same relative times that they fall tli rough a given 

 number of degrees. 



It is to be particularly noticed that dark humus and white 

 magnesia are very closely alike in their rate of cooling, 

 and cool rapidly ; Avhile Avhite Ihne sand stands at the op- 

 posite extreme, requiring twice as long to cool to the same 

 extent. These facts strikingly illustrate the great differv 



