Oct. 25, 1915 
Temperature and Capillary Moisture in Soils 
155 
and Tapham (2), in trying to explain the differences in capillary action 
in dry and moist soils, make the following statement: 
In a moist soil, however, we have quite another condition. A film of the liquid 
covers all the surfaces of the soil grains. Since this film, once established, is main¬ 
tained in a saturated atmosphere, it follows that the solid air and solid liquid surface 
forces no longer play any part in the capillary movement, which is produced entirely 
by the air liquid surface force and is opposed only by the weight of the liquid column. 
In view of this general belief, Briggs, as well as other investigators, 
has tried to alter the properties of the soil water by increasing its surface 
tension, etc., with the object in view of increasing its capillary action. 
If it were true that as long as a thin film of water is maintained in a 
damp or slightly moist soil the soil material itself exerts no longer any 
influence upon the movement of capillary water, then the preceding the¬ 
ory might be true. But we have seen in postulate 1 (p. 148) that the 
soils, and especially those rich in colloidal material, possess a very great 
attractive power for water, that this attractive power is satisfied only at 
a considerably high moisture content, that as long as it is not satisfied 
the soils will continue to take up water, and that they hold the water 
with a force of great magnitude. In view of the considerations presented 
in this postulate, and in view of the fact that the preceding thermal move¬ 
ment of water appears to be controlled by the attractive forces of the 
soil for water, it seems wrong to consider the soil material in moist con¬ 
dition as a static, passive, inactive, and irresponsive skeleton upon 
which the liquid plays its r 61 e. The solid material in moist condition 
short of saturation is dynamic and not static in respect to moisture 
movement. Hence, the capillary movement of water should not be 
attributed entirely to the forces exerted by the curvature of the capil¬ 
lary films, but also to the forces exerted by the unsatisfied attractive 
power of the soil for water. When a moist soil, therefore, begins to lose 
water at the surface, two effects are produced: (1) The attractive forces 
of the soil for water are increased and (2) the curvature of the capillary 
films is increased. Both of these effects exert a pull on the moist soil 
below and tend to draw water to the surface. As to which one of these 
two forces exerts the greatest pull it is impossible to say, because there 
is no way of measuring them. It is certain, however, that the force 
resulting from the attractive power of the soil for water must be very 
considerable, and probably it is the predominant of the two. 
It might be argued that the preceding phenomena of thermal trans¬ 
location of water could be explained entirely by the film theory without 
having to resort to the conception of the attractive forces of the soil. 
Such contention, however, can not be maintained, first, because it can 
not be conceived that the tension of the capillary films is operative and 
effective at such high moisture contents employed and, second, because 
the fact remains, nevertheless, that the soil exerts a pull owing to its 
