Oct. as, 1915 
Temperature and Capillary Moisture in Soils 
151 
can not be stated with certainty whether the thermal movement of water 
would become zero at a still higher moisture content. From the theo¬ 
retical point of view, however, it should not become zero, because the 
pull due to the surface tension of water alone is not affected by increase 
of moisture content, but remains constant. The portion of pulling force 
which is decreased constantly with a rise in moisture content is that 
pertaining to the attractive power of soil for water and to the curvature 
of the capillary film. At or near the point of saturation the pulling 
power due to these two factors is probably zero; at this point the soil 
may be considered to be passive. Any thermal movement of water that 
takes place at or near 
the point of satura¬ 
tion is to be attrib¬ 
uted to the surface 
tension of the soil wa¬ 
ter. If this assump¬ 
tion is correct and if 
the percentage of 
moisture moved at 
the highest moisture 
contents employed is 
to be considered as a 
measure of the 
amount of thermal 
translocation due to 
surface tension of wa¬ 
ter alone, it will be 
found that the quan¬ 
tity due to this force 
is very small indeed. 
As will be seen from the experimental data, the percentage of moisture 
moved at both amplitudes of temperature is reduced to an insignificant 
value at the highest moisture contents. 
The foregoing exposition as to the cause and mechanism of the phe¬ 
nomena of thermal water translocation will probably bd made clearer 
by figure 4. This diagrammatic representation, however, by no means 
pictures the real cause and mechanism absolutely and accurately, but 
it will serve, it is believed, to make clearer what has already been said. 
Let the abscissa represent the effective pull of the cold column of soil and 
the willingness of the warm column of soil to part with water at a different 
moisture content, and let the ordinates represent the different percentages 
of water contained by the soil. By plotting the effective pull and will¬ 
ingness against the moisture content it will be seen that the effective 
pull decreases and the willingness increases with a rise in moisture 
content. At the point where the two lines cross probably occurs the 
Fig. 4.—Diagram illustrating the cause and mechanism of moisture 
movement from a warm to a cold column of soil of uniform mois¬ 
ture content. 
