10 
SOILS AND ALKALI. 
ous—and we know that these forms are the direct result 
of temperature. The changing of water from the solid to 
the liquid or gaseous form, is performed at the expense of 
heat; the more water evaporated from the soil, the more 
heat must be extracted from the soil for the evaporation. 
Therefore, the more water contained in the soil, the lower 
must be its temperature, because of the greater evapora¬ 
tion and consequent exhaustion of heat. The experi¬ 
ments of Liebenberg, Pattner, Schubler and Dickenson 
have practically settled all the questions of soil tempera¬ 
tures. The radiation of heat from the soil, and the con¬ 
sequent cooling propensity of the latter, are directly pro¬ 
portional to the absorptive power of the soil. Two soils 
of like absorptive power towards heat possess equal 
radiating power. But it does not follow that soils most 
rapidly warmed are likewise most rapidly cooled again ; 
because the sun’s rays are of two kinds, illuminating rays 
and heating rays, and substances absorbing or radiating 
one kind of ray mav be inactive toward the other. 
In a general way, it can be said the greater the heat¬ 
ing capacity and conductivity of a soil, the more readily 
and rapidly does it give off its heat and become cooled, 
clav being the most slowlv affected and sand the most 
readily influenced. There are many modifying circum¬ 
stances, as the properties of the atmosphere and protec¬ 
tive covering of various kinds—snow, vegetation and the 
clouds. In this connection, the explanation of the forma¬ 
tion of dew upon the plants has been radically changed. 
The old theory presupposed the coldness of the soil and 
the warmth of the atmosphere. Now, the facts in the 
case show that the soil at the place dew is deposited is 
generally warmer than the surrounding vapor-containing 
atmosphere. The temperature of the soil is modi fled by 
many circumstances, as the vegetation, condition of the 
atmosphere, clear or cloudy, the angle of contact between 
the sun’s rays and the soil surface. Even the electrical 
condition of the soil must not be overlooked, for Fischer 
