Watei' Suppli/. 270 



rather landspring, supplies of water are olten undervalued, and 

 great expense is incurred in sinking to deeper sources. 



Artesian Wells. 



Dr. Buckland, in his ' Bridgewater Treatise,' defines artesian 

 wells as " pei'petually flowing fountains, obtained by boring a 

 small hole through strata that are destitute of water into lower 

 strata loaded with subterranean sheets of this important fluid, 

 which ascends by hydrostatic pressure through pipes let down to 

 conduct it to the surface." As there are very many cases in which 

 the water does not attain the surface of the ground, the name 

 artesiod has been applied to such, because they do not present 

 all the conditions in the above definition ; besides which, their 

 construction so far differs, that a shaft, as of an ordinary well, 

 must be sunk below the level attained by the water, from which 

 it must be raised by artificial means. All the deep wells in 

 London are of this character. 



There is a very common impression that water may be ob- 

 tained in any locality by boring, if it be carried to a sufficient 

 depth. Immense sums of money have been thrown away in such 

 attempts, and in other cases the quality of the water when 

 obtained renders it unfit for use. These wells should never be sunk 

 without a knowledge of the local geological conditions on Avhich 

 their success depends. The most experienced geologists may be 

 deceived by anomalous conditions of the substrata, which cannot 

 be foreseen. It may be useful to mention some localities and 

 strata where boring for water is most likely to succeed or to fail. 



It has been ascertained that water naturally rises in these wells 

 to the mean level between the highest source of supply and the 

 ultimate natural outfall. This is exemplified in the London and 

 Paris basins ; the one outfall being the River Thames below 

 London, the other the sea at or about Havre. Under Lcmdon 

 the level has been depressed to the amount of 60 feet ; at Pai'is 

 the famous artesian fountain of Grenelle has been slightly aflected 

 by the newly-bored well at Pass}'. In illustration of the former, 

 a section, B, is given of the ascertained height to which water rises 

 in artesian or artesiod wells on a certain line in the London basin, 

 which, with certain modifications, will show the way in' which 

 water will rise in other localities ; though, for all ordinary prac- 

 tical purposes, the best guide will be the known height to which 

 water will rise in such wells where the experiment has been made. 

 In the absence of such a guide, this may be calculated on the 

 principle illustrated by the section. The water will be found to 

 rise to the surface wherever the level of the surface falls below 

 the angle described by the subterranean water-level. This, not- 

 withstanding the unnatural depression caused by London pumping, 



