172 THE PRINCIPLES OF SOIL MANAGEMENT 



Theoretically, therefore, there is no limit to which 

 this adjustment might take place in the horizontal plane. 

 Water might be moved in from a distance of one inch 

 or one rod. Vertically, however, there would be a limit 

 to the height to which water could be lifted, because 

 of the limit to the pull of the surfaces in plane 1. 



The larger the number of curves, the greater the total 

 pull per unit area, and consequently the higher could 

 water be lifted just as there is a definite limit to which 

 water will rise in glass tubes of different sizes. It is 

 therefore possible to keep trimming off the upper end 

 of a column of soil, whose lower end dips in water, until 

 the maximum height through which water may be lifted 

 and lost by evaporation, or otherwise, is determined. 

 This is the maximum capillary efficiency of the soil, or 

 the maximum height to which it could deliver water. 



According to the above propositions, the movement 

 of water would go on freely and uniformly until the mini- 

 mum thinness of film was reached. This free movement 

 is modified, however, by another condition. Water, 

 in moving from any point, as C to R, must pass through 

 the thin part of the film between the points of contact, 

 and where it comes in close contact with the soil sub- 

 stance. In this, friction is developed, and the thinner 

 the film, and the closer it is drawn about the particle, 

 the greater does this friction become until it all but stops 

 movement. 



For a period, when the film is thick, the movement 

 is relatively free; but, after the water comes within the 

 range of great attraction of the particle, the friction 

 increases rapidly, and therefore the movement of water 



