230 M. Arago on Artesian Wells 



at different elevations, may have very different powers of as- 

 cendino- ; and also how the same water should here be projected 

 to a great height, and should there rise no higher than the sur- 

 face of the soil. Simple inequalities of the level would clearly 

 appear to be the cause, and a sufficient as well as natural cause, 

 of all these apparent anomalies. 



The explanation which we have thus furnished of the ascen- 

 sion of water in wells is so natural, that it was the first which 

 offered itself to the intelligence of those who directed their at- 

 tention to the subject. As early as 1671, J. D. Cassini re- 

 marked, " These waters (those of the artesian well of Modena) 

 come perhaps by subterranean channels from the height of 

 Mount Apennine, which is not more than ten miles distant from 

 this spot." At the present time, however, confidence in this 

 view seems to be somewhat shaken : let us now inquire if on 

 any sufficient grounds. 



As is well known, there exist in Iceland certain springs cal- 

 led geysers, which project into the air, and even to considerable 

 heights, columns, sometimes of hot water, and sometimes only 

 of steam. The cause of this curious phenomenon has been sup- 

 posed to exist in the elastic force of the steam ; and it must be 

 allowed that the supposition is in perfect harmony with all 

 the facts which have been stated by those who have described 

 them. But does it follow, that because in Iceland, that is to 

 say, in the neighbourhood of many active volcanoes, steam fre- 

 quently produces a jet d'eau, we are thence necessarily to con- 

 clude, that in countries which are not volcanic, the projecting 

 fountains also depend on the action of vapour, and that com- 

 pressed air is the only assignable cause. This seems to be any 

 thino- rather than a necessary conclusion. But besides, it has 

 been observed concerning these geysers that they are intermit- 

 tent, and that a long cessation occurs between two consecutive 

 eruptions. But the very reverse of this is the case with the 

 fountains, which flow with a uniform stream for days and months, 

 and sometimes for vhole years. All comparison, therefore, of 

 phenomena so entirely unUke, seems most gratuitous and in- 

 judicious. 



Compressed air which is shut up in a subterranean cavity, 

 has not the power of propeUing water along the ascending pipe 



