Oct. 25, 1915 
Temperature and Capillary Moisture in Soils 
171 
of water from the former. This explanation is correct, of course, in so 
far as it represents the result of the mulch, but how this mulch was 
formed and how it was capable of accomplishing this result he fails to 
explain correctly. In the opinion of the writer the above results offer 
an excellent proof that temperature aids and hastens the formation of a 
mulch, and tends to conserve the soil moisture in the manner previously 
set forth. 
This is a remarkable paradox indeed that a temperature which causes 
the loss of water should also cause its conservation. 
SUMMARY 
The main and most important facts presented in the foregoing series 
of studies may be summarized as follows: 
(1) When one half of a column of soil of uniform moisture content is 
maintained at 20° and 40° and the other half at o° C. for eight hours the 
percentage of water moved from the warm to the cold soil increased in 
all the different types of soil with a rise in moisture content until a certain 
water content was reached, and then it began to decrease again with 
further increase in moisture content. The results then plot into a para¬ 
bola. The percentage of moisture at which the maximum thermal trans¬ 
location of water occurred is different for the diverse classes of soil, but 
the percentage of the maximum thermal translocation of water is about 
the same for all classes of soil for any one of the temperature amplitudes. 
The percentage of moisture at which this maximum thermal transloca¬ 
tion occurred is designated as the “thermal critical moisture content.” 
These results are contrary to what might be expected from the laws 
of surface tension and viscosity. They have led to the conclusion that 
the capillary movement of water in moist soils is not controlled entirely 
by the curvature of the capillary films, as is generally believed, but also 
by the unsatisfied attractive forces of the soil for water. 
(2) When a moist column of soil was kept at 20° and 40° and a dry 
column of soil at o° C. for eight hours and the two columns were sepa¬ 
rated by an air space, the percentage of moisture distilled over from the 
moist and warm column to the dry and cold column of soil was very 
insignificant for both amplitudes of temperature and was about the same 
for all moisture contents. 
These results lead to the conclusion (a) that the amount of water lost 
from the soil by water vapor is very small; (b) that there is no rising of 
vapor during the night from the warmer soil below to the cold soil above; 
and (c) that the water of the dew is not derived from the soil vapor, as 
is commonly believed. 
(3) When a moist column of soil was in contact with a dry column of 
soil and the former was kept at 20° and 40° and the latter at o° C. for 
eight hours the amount of moisture moved from the moist and warm soil 
