244 M. Arago on Artesian Wells 



waters of the two fountains gradually fell, without, however, 

 surpassing in this descent their usual limit. 



At the time of a thaw, which had been preceded by a great 

 fall of snow, M. Desguirandes, the Mayor of Choques, was 

 alarmed by an extraordinary noise. He immediately descended 

 to his garden, and saw, with astonishment, the projecting foun- 

 tain elevating itself to three times its usual height. This lasted 

 only for five or six hours. This fact, for the knowledge of 

 which I am indebted to M. le chef de bataillon du genie Ber- 

 gere, it appears to me, may be considered as a proof that the 

 ascent of the water in these wells is truly the consequence of 

 a hydrostatic pressure. At the moment of the above occurrence, 

 the thaw must have been the means of filling, throughout all 

 their extent, the subterranean fissures which were situated higher 

 than the town of Choques, which usually, and even during the 

 time of rain, were either not quite full of water, or only con- 

 tained interrupted patches of it. Every one knows, that a very 

 small stream, even a capillary one, is sufficient to produce the 

 strongest pressure in an indefinite liquid mass. 



There is in Rochelle, at the distance of 215 feet from the 

 shore of the sea, a well, in which the sheet of water reached, un- 

 fortunately does not project a stream above the surface of the 

 ground. The surface of the water is 21 feet below ground. 

 The total depth of this well is nearly 584 feet. For four years 

 the level of this liquid column, of the length of 563 feet, did 

 not vary in any sensible degree. But in 1833, some attempts 

 having been made to increase the depth of the well, its waters 

 were observed to undergo the most extraordinary oscillatory 

 movements. 



On the 1st of September a fall of 147 feet took place. 



On the 2d there was a fall of 156 feet. 



On the 2d of October the water was at its former level. 



On the 3d there was a fresh fall. 



On the 4th the fall amounted to 30 feet. 



From the 5th to the 14th there was a rise of 9 feet. 



