1 50 Journal of A gricultural Research voi. v. No. 4 
and cohesive forces, due entirely to temperature, between the warm 
and cold columns of soil are equal in amount, as in the soil with the 
lowest moisture content. Water, therefore, tends to move from the 
warm to the cold soil. Inasmuch as the attraction of the soil has been 
further satisfied and the water films further thickened, the pull of the 
cold soil, due only to the attractive forces of the soil for water, is decreased; 
on the other hand, the ease with which the warm soil gives up moisture 
is increased. The result is that even though the total effective pull 
(composed of the increased surface tension of water, the increased attrac¬ 
tive adhesive forces of soil for water, and the force of the curvature of the 
capillary films) of the cold soil with the high moisture content is less than 
that of the soil with low moisture content, the greater ease with which 
the warm soil with high water content parts with moisture enables the 
reduced effective pull to draw more water from the warm to the cold 
side. As the moisture content of the soil is continually increased, its 
attractive power is satisfied and the curvature of the capillary films 
decreased correspondingly. The total effective pull of the cold column 
of soil is continually decreased, but the ease with which the warm column 
of soil gives up moisture is also continually increased, so that the thermal 
translocation of water is constantly increased with rise in moisture 
content. 
Finally, a degree of moisture content is reached in which the effective 
pull of the cold column of soil is able to extract the greatest amount of 
water from the .warm column of soil. This degree of water content is 
the thermal critical moisture content. At this point the attractive 
power of the soil for water is considerably satisfied but is far from being 
entirely appeased; the total effective pull of the cold column of soil is 
also considerably less than that of the preceding columns of soil, but 
the warm column yields water to this pull with such ease that there 
occurs a maximum thermal water translocation. Inasmuch as the 
water-attractive power is different for the various kinds of soils, 
this thermal critical moisture content is of necessity also different. 
After this thermal critical moisture content is reached, the effective 
pull of the cold column of soil is further decreased with a continued 
increase of moisture content. And although the willingness of the 
warm column of soil to part more readily with moisture is also 
increased, yet the pull of the cold column of soil is not sufficiently 
strong to draw it; consequently the thermal movement of water 
commences to decrease and continues to diminish very regularly and 
gradually with a continued increase in moisture content. When the 
highest percentage of water is reached, the warm soil is very willing to 
part with a very large amount of water, but since the effective pull of the 
solid soil is reduced almost to a minimum, only a small amount of mois¬ 
ture is drawn from the former to the latter. 
The degree of moisture of the different soils could not be further in¬ 
creased, on account of the difficulty of sifting them, and consequently it 
