Oct. 25. 191S Temperature and Capillary Moisture in Soils 155 



and Lapham (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 capillar^' movement, which is produced entirely 

 by the air liquid surface force and is opposed only by the weight of the liquid column. 



In vievi^ 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 i (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 role. 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: (i) 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 



