B. TERRESTRIAL PHYSICS AND METEOROLOGY. 63 



B. TERRESTRIAL PHYSICS AND METEOROLOGY. 



ON THE EVAPORATION OF WATER FROM HARD AND BROKEN 



SOILS. 



In the course of an extended investigation by Schleh into 

 the relation between water and plants, he shows that in re- 

 spect to soils that are either matted down hard or well broken 

 up, the former elevates by capillarity the water quicker and 

 higher than the latter. If, then, layers of disintegrated soil 

 are placed above masses of solid earth, the elevation of the 

 water to the upper surface from the latter stratum is checked 

 as soon as it comes to the loose soil. As the capillary power 

 to elevate is diminished, so also is evaporation checked by 

 the broken character of the soil; so that, as a general result 

 of his investigation, a soil pressed hard together loses by far 

 more water under the daily influence of the sun and the 

 winds than a soil similarly circumstanced, but in which the 

 upper surface is well broken up. The experiments of Schleh 

 therefore give exact results, entirely confirmatory of the gen- 

 eral practice of agriculturists. 19 C, VIII., 136. 



ON THE CONDUCTIVITY OF VARIOUS KINDS OF SOIL FOR HEAT. 



A. von Littrow, as the result of investigation into the con- 

 ductivity for heat of various kinds of earth, concludes that 

 the principal influence upon the conductivity of dry soils is 

 exerted by their mechanical constitution, the conductivity 

 being determined by the quality, as recognized by the 

 microscope, of those portions of the soil that can be washed 

 away. As the fineness of the grains of the soil increases 

 the conductivity diminishes. Organic substances diminish 

 the conductivity, and the influence of chemical constitu- 

 tion disappears in comparison with the mechanical features. 

 Wet soils conduct the heat better than dry ones; in the 

 pores of such soil water, which is a good conductor, has re- 

 placed the air, which is a poor conductor. With some ex- 

 ceptions, damp soils conduct heat even better than water 

 does. Consequently in general the materials composing the 

 soils must, of themselves, conduct heat better than water. 



