1887.] NEW YORK ACADEMY OF SCIElSrCES. 8^ 



of the large cities of this country are supplied with water that i& 

 really wholesome or good. 



There is some excuse for this state of things in the fact that 

 resort to the water of rivers and streams is generally had under 

 pressure of danger from polluted wells or from failure of previous 

 sources; and when the new system is decided upon, there is rarely 

 time enough for a thorough inquiry into the character of the 

 water to be taken. 



It is characteristic of sanitary progress, however, that the ten- 

 dency towards chemical investigation at the outset in such cases 

 is a growing one. 



The driven well, especially in its later development as the 

 gang-well system, seems to offer a cheap and speedy way of sup- 

 plying water in any desired quantity to a community. It has 

 obvious advantages over an aqueduct or pipe-line bringing water 

 from a distance. But there is a chemical question yet to be con- 

 sidered in regard to it. Unless the surface waters of the district 

 in which wells are to be sunk are themselves unobjectionable, 

 the method has little to recommend it to permanent application. 

 The action of powerful pumps which draw from a limited area 

 such enormous volumes of water as the system must supply will 

 result eventually in drawing in all water, surface as well as sub- 

 terranean, which the vicinity will yield. The increased depth of 

 these wells as compared with surface wells is really very slight, 

 when we consider the greatly increased draughts which are made 

 upon them. It has been shown that there are considerable varia- 

 tions in the level of the subterranean waters, during the action 

 of the pumps in a gang-well system, even at a distance from 

 the pipes. Such changes of level must be proportionally greater 

 near the wells. What is to prevent the gravitation of surface 

 water to fill the vacuum thus created ? 



The compact beds of clay so often appealed to to shut out all 

 surface water are a fallacious dependence, unless they are abso- 

 lutely watei'-tight over great areas and under enormous pressure. 

 It is too much to expect that a layer of clay sufficiently thick or 

 impervious to water will always be found or that prospectors 

 will go sufficiently far afield to secure for their wells a region of 

 which the surface is above suspicion. The danger to be feared 



