£23 



CAPACITY OF SOILS FOR HEAT. 



ascribes a greater power to the gases compressed or condensed 

 within the interstices of the soil. But the action of the air upon ihe 

 roots of vegetables is readily conceivable in soils of a h)ose nature, 

 especially if ihcy have been sufficiently worked, without the necessity 

 of having recourse to such an explanation. 



Capacity of soUs for heat. The quantity of heat which a soil will 

 receive, retain, or throw off in a given time, depends upon the con- 

 ducting power which it possesses. M. Schiibler endeavored to 

 measure this power comparatively by measuring the rates of cooling. 

 In a vessel of the capacity of 595 cubic centimetres, or 234.2 cubic 

 inches, filled with the substance to be tried, a thermometer was 

 placed, with its bulb in the centre. The temperature having been 

 brought up to 62.5° C, (144.5° Fahr.,) the time was noted which 

 each substance required to fall to 21.2° C, or about 70° Fahr., the 

 temperature of the surrounding air being 16.2° C, or about 61' Fahr. 



The general observations which these experiments suggest, are 

 that, for equal volumes, calcareous or silicious sand possesses greater 

 powers of retaining heat than any of the other substances tried. 

 This fact explains the high temperature and the dryness which 

 sandy soils maintain even during the night in summer. Humus is 

 obviously the substance which possesses the highest conducting 

 powers. 



Degrees in which soils become heated under exposure to the sun. 

 There is no one who has not had occasion to observe the high tem- 

 perature which bodies acquire when exposed to the rays of the 

 bright sun. There are some, such as dry sand, slates, and certain 

 colored rocks, which become burning hot. It is by the heat of the 

 sun that the soil, before it is shaded by the leaves and stems of plants, 

 rises in temperature, and throws off the excess of moisture which it 

 had imbibed in the winter. Agriculturists all know how different 

 the degree in which this heating takes place, even in soils that are 

 close to one another. A light-colored, moist, clayey soil will heat 

 giucb less thaa a dajk-colored, calcareous, or sandy soil. The dif 



