THE; SOIL AND WATER 131 



into each other. One side of the tube was made of glass so that 

 the contents might be observed. The bottom tube was closed at 

 its lower end with muslin and the tubes filled with air-dry soil, 

 stirred in with a wire and made firm by a slight tapping on the 

 table. In experiments with a sandy soil, an alluvial soil, a silty 

 soil, and an adobe soil, water rose rapidly in the two coarser soils, 

 reaching 8 to 9 inches in the first hour, while the water in the 

 stiff soil rose only i to 2 inches. The water rose rapidly in the 

 sand, but only reached a final height of i6*/2 inches. The other 

 three soils, in 125 or 195 days, reached nearly the same height, 

 but the alluvial soil, composed mostly of fine sand and silt, carried 

 the water up most rapidly. This experiment is an instructive 

 illustration of the difference in the capillary powers of soils. 



Water thus tends to distribute itself in the soil, through 

 capillary passages or by the slower processes of surface distribu- 

 tion. When these operations are assisted by gravitation, as when 

 rain falls, the water moves rapidly. When the movement of 

 water is opposed by gravitation, as when a soil dries at the sur- 

 face and is wet below, the movement is retarded by the increasing 

 height of the column of water lifted, until finally it entirely 

 ceases. 



Capillary action has some effect in raising water from the 

 water table in a few instances when the water table is less than 

 about four feet from the surface. One great function of capillary 

 action and surface tension is to distribute water to the roots. 

 When water is withdrawn at one place by the roots, it disturbs the 

 equilibrium and causes a flow of water from points of least 

 resistance. 



Flowing Moisture. Water present in excess of the hygroscopic 

 moisture held by capillary action, may be termed flowing water. 

 It will pass downward through the soil at a rate depending upon 

 the permeability of the soil. 



The quantity of water in a saturated soil depends entirely upon 

 the air space in the soil. The soil is saturated when all the air 

 space is filled with water. The air space can be calculated from 

 the real and the apparent specific gravity of the soil. 



