28 LAND DRAINAGE 



are always symmetrical, and are always exercising a 

 compressing stress as they do in the dew-drop. 



43. Direction of capillary movement. If, therefore, 

 capillary water is removed at some point in or on a soil 

 mass, this compressing stress causes the remaining water 

 to readjust itself so that the proportions of the thickness 

 of water layer and the symmetry of the surfaces are the 

 same as before the water was disturbed. (See Fig. 7.) 

 In this readjustment of capillary water, the movement 

 is along the surfaces of the soil particles and is always 

 toward the point where the water has been removed, 

 regardless of direction. If water is added at any point, 

 a readjustment will take place and the movement will 

 be away from that point, and out through the mass. 



44. Hygroscopic movements. These movements of 

 water are called thermal movements, because heat is 

 the chief factor involved in them. They take place from 

 the surface of the soil particles into the surrounding air, 

 or from the surrounding air to the surface of the soil 

 particle. 



