HYGROSCOPIC WATER 57 



the results due to rapid changes of temperature. The same 

 class of results is shown, but much less frequently, by the 

 drain-gauges filled with loam at Rothamsted. The persistent 

 wetness of land in February is doubtless connected with the 

 frequent condensation of moisture upon the cold soil. 



Besides the deposition of water upon the surface from the 

 atmosphere, there may be deposition on the surface from 

 vapour rising from the subsoil. This will happen chiefly in 

 the case of well-drained soils, made up of coarse particles, 

 in which a free movement of gases can take place. Move- 

 ments of the soil air will be determined by variations in its 

 temperature and pressure, but the condensation of water- 

 vapour at the surface will of course only happen when the 

 surface is colder than the subsoil. When this is the case a 

 veritable distillation may occur. 



An action of this kind may possibly explain in part the 

 maintenance of the moist condition of the surface soil during 

 a nearly rainless winter, which is observed in the case of the 

 early market-garden lands of Florida. These soils consist of 

 coarse sand, and hold on an average only 3 per cent, of water, 

 yet early vegetables are successfully grown on them without 

 irrigation during the winter months. The water level is 15-20 ft. 

 below the surface (Soils of Florida, Soils Bull. 13, p. 9). 



Hygroscopic Water. Quite apart from the power of a cold 

 body to condense water from a moist atmosphere is the power 

 which bodies possess in a varying degree of condensing water 

 on their surface even when at the temperature of the atmo- 

 sphere, and even when the air around them is not saturated 

 with water. Every body in a moist atmosphere has a moist 

 surface, the thickness of the covering film of water depending 

 on the temperature, and on the degree of saturation of the 



