a Periodical Spring on the Jura. 309 



as the syphon carries off, the action of the syphon experiences 

 no interruption, and the spring becomes continuous in place of 

 intermittent. 



In the hypothesis of the presence of a syphon, an increase of 

 water in the reservoir must necessarily increase the continuance 

 of the flow and diminish the intermittence, even at length en- 

 tirely destroy it. But, according to this hypothesis, the period 

 of the rising and falling can never diminish in equal proportion ; 

 yet this we found to be the case in the Fontaine de Ronde. 

 Its rise generally continues three minutes, and it occupies the 

 same period for its fall. But on one day I observed that the 

 rise occupied only two minutes, and that the fall took the same 

 time. The period of the spring which, as already mentioned, 

 is six minutes, was on this day only four minutes. This pe- 

 riod of four minutes I obtained for a whole hour, during which 

 I observed the spring. This observation convinced me that the 

 periodic swelling or rise of the Fontaine Ronde could not be pro- 

 duced by a syphon : it must result from some other cause, as 

 appears from the following observations. 



During the swelling of this spring, a great quantity of car- 

 bonic acid rises from the bottom, and the water, owing to the 

 numerous air bubbles that pass through it, appears to be in a 

 state of ebullition. We might suppose that these air bubbles 

 originate from the atmospherical air which had interposed itself 

 among the uncovered gravel during the time of low water, and 

 which was not entirely driven out of the intervening spaces at the 

 moment of rising, but which afterwards, when the gravel bottom 

 was entirely covered, escaped in bubbles through the water. To 

 a belief in this conjecture we might feel supported by the circum- 

 stance of the number of the air bubbles being much increased 

 when we stir the bottom with a stick. But when, with the view 

 of ascertaining how far this opinion was founded, I collected a 

 quantity of this gas and mixed it with lime-water, I found that it 

 became clouded. The gas, therefore, was carbonic acid ; and that 

 ii contained no hydrogen gas was proved by the gas not inflaming. 

 It is evident, therefore, that the rising of the spring is accompanied 

 by an evolution of carbonic acid. This gas, which I conceive to 

 be formed in the interior of the earth, reaches the subterraneous 

 canals of the springs only periodically, because it is only perio- 

 dically forced out, whilst the spring flows constantly. In fact, 



