Oct. 25, 1915 
Temperature and Capillary Moisture in Soils 
169 
This excessively greater temperature of the dry mulch diminishes the 
adhesive and absorptive forces of the dry soil, so that its capacity 
and intensity to withdraw water from the moist soil below are either 
entirely prohibited or greatly reduced. The result is that the water is 
saved from direct evaporation. On the other hand, during the night 
the soil temperature reverses itself and becomes lowest at the surface and 
increases with the depth, but the difference between the mulch and moist 
soil is generally not as great during night as during the sun insolation. 
Since the attractive and adhesive force of the dry soil and the surface ten¬ 
sion of the soil water are increased by the low temperature, the tendency 
of the soil moisture is to move upward very energetically. To what 
extent this movement occurs can not be stated with certainty, because 
the moisture not very fat below the mulch is held with a great force and 
is given up with great reluctancy unless moisture moves from a farther 
depth below, satisfies the absorptive power, and thickens the surface and 
capillary films. 
Furthermore, the amount of water moved will depend upon the 
temperature gradient—that is, upon the range of temperature between 
the surface and lower depths. As already stated, this temperature 
gradient at night is most marked during the summer and fall and is 
smallest during the spring. Any water, however, that the mulch pulls 
up during the night is certain of being evaporated during the day. May 
it not be, then, that an appreciable amount of water is lost from the soil 
in this manner? 
Temperature not only tends to conserve moisture in the soil after the 
mulch is formed but also aids and hastens the formation of this mulch. 
It has been seen that as the temperature of the moist soil at the upper 
depth increases, the surface tension of the soil water and the adhesive 
and absorptive forces of the soil decrease. The upward pulling force, 
therefore, is diminished, and the water is not brought up with sufficient 
rapidity to keep the upper layers moist, so that a mulch is formed at 
the top. The diminution of the surface tension of the soil water at or 
near the surface is very large during the sun insolation and far greater 
than the increase during the night, because during the sun insolation the 
soil absorbs heat from the sun very rapidly, and since the soil is a poor 
conductor of heat the heat is allowed to accumulate at the surface and 
raise its temperature far above that of the next layers. 
The foregoing considerations have been deduced from the experi¬ 
mental data and from the laws of kinetic energy of matter, surface 
tension of liquids, etc., in their relation to temperature. It is now of 
great importance as well as of high interest to know whether these 
deductions can be verified experimentally. The type of experiment 
which the writer probably would have performed to test out whether or 
not the temperature does tend to conserve moisture in the soil has 
