242 M. Arago on Artesian Wells 



sively in the circular space between these two tubes, that the 

 water of the reservoir 170 feet down can ascend. Once more, a 

 third tube, considerably larger than the second, and including 

 it, descends to the depth of one of these absorbing beds of which 

 we have spoken so much. The circular space which is included 

 between the middle and the exterior tube sends up no water : on 

 the contrary, its sole use is, during the winter, to return into 

 the bowels of the earth the superabounding waters of the two 

 other pipes, which, were they to overflow into the street, would 

 become a sheet of ice. In this case, the water which is reab- 

 sorbed being pure, there can be no objection to its descent, as 

 there was at the works of Villetaneuse and Bondy, viz. the ap- 

 prehension that the waters of the neighbouring wells might be 

 injured by impure infiltration. 



Concerning some anomalies which have been observed in the Sinking 

 and in the Play of certain Fountains. 



At Biingel, in the valley of Ternoise, of three bores which 

 were undertaken in 1820, the first turned out a beautiful pro- 

 jecting fountain ; whilst the other two, on the contrary, have 

 not furnished a drop of water, though all the three are very near 

 each other. 



The districts of Lillers, of St Pol, and St Venant, present ir- 

 regularities of precisely the same kind. 



At Bethune, a bore, after having pierced seventy feet of 

 alluvial soil, and thirty feet of limestone, conducted to the 

 surface a beautiful limpid jet d'eau. In the garden of the con- 

 tiguous property, a similar operation of boring has not produced 

 a single streamlet of water, even though the chalk has been pe- 

 netrated more than 100 feet. 



But these facts, which might be multiplied to infinity, cannot 

 with propriety be considered as remarkable. Let it be remem- 

 bered that these subterranean waters do not form sheets of a 

 great extent, or more properly speaking, do not form sheets at 

 all, except at the surface of separation of two distinct mineral 

 beds; that, on the contrary, in the thickness of those of the 

 beds which are least compact, as, for example, in chalk, the 

 water neither exists in any certain defined limits, nor circu- 

 lates except in trenches, betwixt which are found masses of 



