CHAPTER XI 



WATER IN THE SOIL 



100. How the Water Exists in the Soil. From our ex- 

 periments, we have noticed that the water in the soil 

 may be classed as: 



(a) Free, or gravitational water, the water which flows 

 under the influence of gravity and percolates down- 

 ward. When the water collects below, we call it bottom, 

 or ground, water, and the surface layer is called the 

 water table. (See Figs. 36 and 41.) 



(b) Capillary water is held in the capillary spaces or 

 pores of the soil and is not influenced by gravity, but 

 moves upward, or in any direction where the soil is 

 becoming drier. It is held in 



the soil by the same force 

 which causes the whole of a 

 rag to become wet when one 

 end is placed in water, or 

 which causes oil to rise in the 

 wick of a lamp. The amount 

 of capillary water, that is, 

 the water which the soil may 

 retain against the influence 

 of gravity, depends on the 

 size and form of the soil 

 particles, and several other 

 conditions. Where there is 

 only capillary water in the Fig - 39 - Dia s ram to illustrate how 



. . the soil particles are covered by 



SOll, there IS, Of COUrse, SOme capillary water. After Cameron. 



(67) 



