50 DOMESTIC WATER SUPPLIES FOR THE FARM 



become through their experience in locating wells better observers 

 of the occurrence and movements of ground water than the aver- 

 age person. 



It is to be noted that notwithstanding the pretensions of 

 divining-rod men, especially the inventors of the more complicated 

 appliances, they have not been able to prove their claims to the 

 satisfaction of the government, and all applications for patents 

 are denied by the Patent Office. 



Basis of Scientific Location of Underground Waters. - - The 

 only scientific basis at present known for locating underground 

 supplies is a knowledge of the laws of occurrence and movements 

 of the ground-water body, for on these factors depend the quantity, 

 quality and safety of the supply. The occurrence and quality 

 of the water in rocks of different kinds has been already discussed 

 in Chapter VI. It remains to consider briefly the nature of the 

 movements of the ground-water body. 



The Water-table. Proceeding downward from the surface in 

 porous or semi-porous materials, such as those in which most 

 open wells are located, a level is soon reached below which the 

 ground is saturated with water (at least down to the first im- 

 pervious stratum). This water-body, or ground water as it is 

 called, has a definite upper surface, known as the water-table. 

 This is not, like its surface counterpart, a level surface, but slopes 

 gently in various directions, conforming with the broader surface 

 irregularities. 



While the water-table is typically developed only in the 

 porous soils and rocks, it commonly exists, even in the dense 

 rocks like granite, as a more or less definite, though irregular, 

 surface, since the joints and other planes which subdivide the 

 rock usually communicate with one another so that the water 

 level stands at a fairly uniform height. 



The surface of the water-table, though conforming in a general 

 way with the surface contour, is almost always comparatively 

 flat, its slope being only a fraction of that of the overlying surface. 

 This is brought out by Figure 25, which shows the water-table 



