170 THE PRINCIPLES OF SOIL MANAGEMENT 



no movement. For the pull at any one point is balanced 

 by the pulls from every other point, due to the surface 

 curvature of the film and to the weight of the liquid. 

 In the bottom of the column, where the weight of the 

 water acts in conjunction with the curvature of the film, 

 the curvature is less than at the top of the column, 

 where the only effective pull is due to the curvature of 

 the water surfaces. This may be illustrated by the fol- 

 lowing diagram. (Fig. 52.) 



P represents soil particles carrying their maximum 

 film of water, and therefore in equilibrium at every 

 point, so that no movement may take place. The force 

 or pull exerted by the film at the different points is 

 represented by the arrows at A, B, C, D, E, etc., the 

 length of the arrow being proportional to the pull exerted 

 by the film, and in the same direction, or toward the 

 center of curvature of the surface. The difference 

 in the pull, and therefore the length of the arrows at 

 the top and bottom, is compensated by the weight of 

 the water at the bottom. If water is now taken from the 

 film into the rootlet at R, the curvature of the film at 

 that point will be increased. Therefore it will exert a 

 greater pull than the curvatures in the other spaces, 

 and water will be moved to R along the lines U, to 

 replace that taken in by the root. So that the new 

 adjustment would be represented by the dotted lines 

 which show the new curvature assumed at each point, 

 when equilibrium is reestablished, and the water comes 

 to rest. If water continues to be lost to the root, or by 

 evaporation from the soil at R, the movement of water 

 to that point will be continuous as long as movement is 



