562 ARTESIAN WELLS. 
titute of water, into lower strata loaded with sub- 
terraneous sheets of this important fluid, which 
ascends by hydrostatic pressure, through pipes 
let down to conduct it to the surface. The name 
is derived from Artois (the ancient Artesium,) 
where the practice of making such wells has for 
a long time extensively prevailed.* 
* The manner of action of an Artesian Well is explained by 
the Section PI. 69. Fig. 3, copied from M. Hericart de Thury's 
representation of a double Fountain at St. Ouen, which brings 
up water, from two water-bearing strata at different levels below 
the surface. In this double fountain, the ascending forces of 
the water in the two strata A and B are different; the water 
from the lowest stratum B rising to the highest level h' ; that 
from the upper stratum A rising only to a . The water from 
both strata is thus brought to the surface by one Bore Hole of 
sufficient size to contain a double pipe, viz. a smaller pipe in- 
cluded within a larger one, with an interval between them for 
the passage of water ; thus, the smaller pipe h brings up the 
water of the lower stratum B,to the highest level of the fountain 
h'\ whilst the larger pipe a brings up the water from stratum A 
to the lower level a'\ both these streams are employed to supply 
the Canal-basin at St. Ouen, above the level of the Seine. 
Should the lower stratum B contain pure water, and that in the 
upper stratum A be tainted, the pure water might by this appa- 
ratus be brought to the surface through the impure, without 
contact or contamination. 
In common cases of Artesian wells, where a single pipe alone 
is used, if the boring penetrates a bed containing impure water ; 
it is continued deeper until it arrives at another stratum contain- 
ing pure water; the bottom of the pipe being plunged into this 
pure water, it ascends within it, and is conducted to the surface 
through whatever impurities may exist in the superior strata. 
The impure water, through which the boring may pass in its de- 
scent, being excluded by the pipe from mixing with the pure 
water ascending from below. 
