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Introduction to the Study of Science 



waters and they support entirely the old religious belief. There 

 is some unusual potency in the waters, which destroys cholera 

 germs within five hours or less, and other disease-causing 

 bacteria still more quickly. It is a curious fact that water from 

 wells in the vicinity of the Ganges River is fairly teeming with 

 cholera germs, and must be purified before using. Boiling the 

 water from the Jumna destroys the properties which make it 

 safe ; cholera germs and other kinds of bacteria flourish in 

 boiled Jumna River water. What gives the waters of these 

 rivers their germicidal properties is not known. 



76. Deep wells. Another source of supply of considerable 

 importance and usually above suspicion of contamination is the 

 deep well. Such a well is from several hundred to several thou- 

 sand feet deep. The wells of Leipzig (5735 feet) and Berlin 

 (4194 feet), Germany, and those at Pittsburgh, St. Louis, and 

 Galveston, U. S. A., may be mentioned because of their depth 

 and free flow of water. 



Artesian wells. The well passes through the local or first 

 water table (Fig. 58) and through a layer or layers of earth 



WATER LEVEL OF IMPERMEABLE LAYERS 



FIG. 58. Ideal representation of conditions of artesian well ; the ground 

 water level and contour of surface ; river and surface well. 



that are not permeable to water, into a layer of sandstone or 

 other porous material which bears water. The water is thus 

 supplied by a table that runs to a distant place of higher eleva- 

 tion than the well. The higher altitude, together with a large 



