154 Journal of Agricultural Research voi. v,no.4 



envelops theoretically the whole external surface of the solid particles 

 coated with colloids, or the mineral floccules and the organic particles; and 

 water also permeates their internal surface. The single solid mineral 

 grains, which may compose the compound particles, may be cemented 

 together in a way analogous to that found in a piece of sandstone, in 

 which case the water exists only in the interstices and not as a complete 

 film around each particle. Furthermore, whether the soil grains are 

 solid or spherical or compound and porous the water film is not uniform 

 in thickness over the entire inner surface of the soil mass, but thickens 

 more at the capillary angles between the particles. 



In view of these considerations, therefore, it was considered useless to 

 attempt to compute the thickness of the film, as many investigators have 

 done. Furthermore, in view of the nature of the soil particles, as dis- 

 cussed above, it does not appear strictly proper to define the capillary 

 water in the soil as a thin film overspreading the particles and thickened 

 into a waistlike form at their points of contact. Hence, a new definition 

 of capillary water is needed. 



If we are to accept the theory which has been used to explain the 

 foregoing phenomena of thermal translocation of water, that the soil pos- 

 sesses a very great attraction for water, that this attractive force is differ- 

 ent for various soils, that it decreases with a rise in moisture content, and 

 that it is completely satisfied at a considerably high moisture content, 

 then our present views concerning the movement of capillary water in 

 moist soils need modification. The present theory regarding the capil- 

 lary movement of water consists of an analogy from the rise of water 

 in capillary tubes. The interstitial spaces of a soil mass are considered 

 as forming channels analogous to capillary tubes and are often desig- 

 nated as bundles of capillary spaces. The capillary water is believed 

 to exist as surface films around the particles and as capillary films in 

 the capillary spaces between the particles, and its movement is said 

 to depend entirely upon the curvature of the capillary films. When 

 a dry soil, for instance, is well moistened and brought to equilibrium, 

 the water films are thick and the curvature of the capillary films small, 

 and there will be no further capillary attraction of water if this soil 

 is brought in contact with water. If this soil is allowed to dry at the 

 top, the surface films become thinner and the force of the capillary 

 films increases in direct ratio with their degree of cur\'ature; hence, 

 there will be a pull of water from the thicker surface films and less 

 curved capillary films below toward the surface. 



It is obvious that with this theory of capillary movement of water 

 the whole cause of the capillary movement of water in a moist soil is 

 attributed to the curvature of the capillary films between the particles, 

 and the moist soil is considered as being passive, inactive, and exerting 

 no influence whatever upon the movement of water. Indeed, Briggs 



