Oct. 25, 1915 
Temperature and Capillary Moisture in Soils 
161 
in the fall, when the trend of the air temperature is downward and the 
surface soil temperature continually falls. At this time the variation in 
temperature between the surface and 6 inches of the mineral soils may 
be as high as 8° C. 
The truth of the matter, however, seems to be that instead of vapor 
rising from the warmer soil below to the colder soil at the surface, vapor 
enters the soil from the atmosphere. This is a natural conclusion from 
the law enunciated that during the day air is exhaled from the soil and 
during the night air is inhaled from the atmosphere. The amount of 
moisture that will thus enter the soil will depend upon the quantity of 
air inhaled and upon its absolute humidity, but, as calculations show, 
it is extremely small. The water may be abstracted by the dry 
soil at the surface as the air is drawn in or it may enter unaffected. 
Thus, it is possible that the moisture lost by the soil during the day by 
the expulsion of its moist air is partly, if not wholly, regained at night. 
What is, then, the source of the water of the dew? The greatest part 
of it comes from the lower layer of the atmosphere itself by condensation. 
Some of it comes from the leaves of trees and plants; and a certain 
amount comes from the soil by capillary and thermal capillary action, 
as set forth previously. 
According to the foregoing consideration, therefore, the notion that 
“ dew is formed from the vapor rising from the warmer soil into a colder 
atmosphere” is wrong, and those who proposed and adhere to this theory 
seem to be laboring under a misapprehension of facts. 
MOVEMENT OF MOISTURE FROM A MOIST AND WARM COLUMN TO A 
DRY AND COLD COLUMN OF SOIL AND FROM A MOIST AND COLD 
COLUMN TO A DRY AND WARM COLUMN OF SOIL 
The soil moisture under field conditions exists during the warm period 
of the year nearly always in a gradient form. During a long drought even 
the upper surface dries out, either of its own accord or induced by 
artificial means. This layer of dry soil formed at the surface is known 
as mulch. To this mulch is ascribed the important function of conserv¬ 
ing the moisture in the soil by its ability to reduce evaporation of water 
at the surface. It accomplishes this conservation of moisture, it is 
claimed, by producing a change or break in the capillary connections 
between itself and the moist soil below. 
Since, on account of the kinetic energy, the absorptive and adhesive 
forces of the solid substance decrease with a rise in temperature, the 
interesting question arose whether the dry mulch with an excessively 
high temperature would absorb moisture from a moist soil with low tem¬ 
perature, even when the capillary connections were ideal. The desire 
to secure information upon this important and exceedingly interesting 
point led to the execution of the following experiments: Brass tubes, as 
described in the preceding sections, were filled with soil, one half with 
