88 THE TEXTURE OF THE SOIL [chap. hi. 



the early spring, and can be set down to the conden- 

 sation of dews by the thoroughly chilled ground from 

 a warm and moist atmosphere. Warington has sug- 

 gested that the persistent wetness of the soil in February 

 must be attributed to this cause. In a coarse-grained 

 soil mostly filled with air, the cooling of the surface that 

 comes by radiation at night may result in an upward 

 distillation of water from the wetter and warmer subsoil. 

 Hilgard has suggested this explanation to account for 

 the capacity of some Californian soils to maintain a 

 crop during a rainless winter, when the soil itself shows 

 only 3 per cent or so of water. 



A. Mitscherlich has made a number of determina- 

 tions of the heat that is evolved on moistening dry soil 

 (benetzungs-warme), due to the condensation of the 

 hygroscopic water on the surface of the soil particles, 

 and regards the figure thus obtained as of great 

 significance in judging of the physical properties of a 

 soil, since it provides a measure of the total surface of 

 all the particles composing the soil. He obtained results 

 of the following order, in calories evolved per gram of 

 soil — sand ooi, calcium carbonate 0-38, sandy soil 0-79, 

 sandy loam 2-37, strong clay 14-98, peat 22-66. Un- 

 fortunately the determination is by no means an easy 

 one to make, and no sufficient number of results have 

 been obtained for soils of known behaviour in the field 

 to enable one to form a judgment of the value of the 

 method. 



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