springs and Ai^tificial Fountains. 273 



the pressure would be resisted and would not be indicated by the 

 tube, but it would be changed into a force of cohesion. 



41. When the waters, whatever besides be their manner of ex- 

 tension, subterraneously, in descending from the superior regions 

 toward the inferior, either in veins, streams or torrents or in a level 

 sheet, happen to meet any outlet in the earth, (Plate I. and II.) they 

 enter it and are elevated to a height, equal to the level, or point of 

 departure, or in other words to a height, which balances the pressure, 

 which the water exerts against the sides of the channel which con- 

 tains it. 



42. Whence it follows, that to obtain a fountain, which shall 

 rise to the surface, it is necessary, 1st, to endeavor, according to the 

 nature of the earth, at a greater or less depth, to meet an effusion ot 

 water descending from superior basins, flowing in the bosom of the 

 earth, between compact and impermeable beds; 2d, give to this 

 water by the aid of a tube, formed by boring, the possibility of rising 

 to a height, proportioned to that of the level from whence it proceeds ; 

 and 3d, prevent by metallic tubes, forced down the shaft, the escape 

 of the ascending water through sand, crevices, or fissures of the earth, 

 traversed by the perforation made by the auger. 



43. And from whence it is perceived, that water can be made to 

 rise to the surface, by the aid of the auger, in almost every country 

 which presents in the structure of its formations, sheets of subterrane- 

 an water, between the alternate and continued superpositions of 

 permeable or impermeable beds, extending to the regions, or mount- 

 ains, which conceal the reservoirs of these sheets of water, and whose 

 basis or declivities are covered by these superpositions. 



44. But nevertheless it is possible, that a second shaft, bored a 

 litde distance from another, which affords water, would not yield any, 

 if this last was supplied by a subterranean current, instead of a sheet 

 of water, or if it was pierced upon the extremity of an elevated bed, 

 supported against a formation of a different nature. 



EXPLANATION OF PLATES I. AND II. 



Whatever be the origin of the water produced by a shaft made by 

 boring whether it proceed from a sheet of subterranean water (§37), 

 or results from a subterranean stream or current (§38), the ex- 

 planation can be sought in the theory of jets d'eau, or in that of the 

 syphon. 



Vol. XVIII.— No. 2. 35 



