8O FARM DEVELOPMENT 



out by the air, if left in a dry room, so that only hygro- 

 scopic moisture remains. If the pot is again placed in 

 an oven which is kept at or above the boiling point of 

 water, the soil will be again reduced to the water-free 

 state, as in Figure 28. 



Figure 29 illustrates the fact that the capillary force 

 carries water in all directions in the soil. A funnel tube 

 is used to carry water slowly to the center of the mass 

 of earth made air-dry, as in Figure 28. The particles 

 immediately surrounding the point of 

 the tube are saturated with the water. 

 This water clings to the surfaces of the 

 particles and spreads out in thin films 

 8 over surrounding particles. The attrac- 

 28. Pot of soil tion of the neighboring soil particles 



from which the capillary 



moisture has been dried causes these films to stream outward 



out by exnosmg it for 



fouo e wed eeks by "severni toward drier particles where the capil- 

 ovfn &$$ hot To lary forces are less satisfied. Thus the 

 "and "thS^driviS moisture moves upward and side wise 



it out leave the soil dry .< 1*1 



of water, water free, nearly as rapidly as downward, in which 



"dry substance," as ,. . . . , t 



ttMblaiSi* soii F S' e nrat direction gravitation helps to move it, 

 placed in the air. while slightly retarding the flow over 

 surfaces in other directions, especially its upward move- 

 ment. 



The soil acts like a sponge. In regions of light rainfall 

 most soils, instead of having this underground supply of 

 water stored up to be given out gradually, are generally 

 not very moist at a depth of several feet. The rain which 

 falls upon the soil, in part runs off over the surface, es- 

 pecially if it be hard or if the land be hilly. That which 

 is drawn in by the capillary force or sinks in by gravita- 

 tion, is taken up and held as capillary water, or is added 

 to the ground water. A light rain is carried downward a 

 short distance only, while a heavier rain will go corre- 

 spondingly deeper. Continuous rainfall for a number of 

 hours is necessary, to penetrate to the depth of several 



