and their Connexion with Volcanos. 69 



In short, the only known process, by which we can account 

 for so constant a supply of azotic gas, as we find to be disen- 

 gaged from the interior of the earth through the medium of 

 thermal waters, seems to be that of a combustion, which, how- 

 ever excited, is in part at least maintained by atmospheric air. 

 I humbly conceive, therefore, that this one phenomenon is suf- 

 ficient to confer on the chemical theory of voleanos a decided 

 advantage o\er the mechanical one; the characteristic of which, 

 in all its modifications, is to reject entirely the theory of combus- 

 tion of any kind constituting a part of the operations. 



Neither is the opinion, that volcanic action arises from the ac- 

 cess of water to the unoxidized nucleus of the globe, at all in- 

 consistent with the above position, for the combustion, excited in 

 the preceding manner, may very well be imagined to have been 

 kept up by the oxygen of the atmospheric air, which would ne- 

 cessarily find its way, wherever a partial vacuum had been occa- 

 sioned by the condensation of a portion of the steam, which, 

 would, in the first instance, at once produce and occupy the ca- 

 vities immediately surrounding the focus of the action *. 



On any hypothesis, indeed, it seems perfectly unnecessary 

 to imagine, that water has been the sole agent in maintaining the 

 fires it may have excited ; and a little consideration may easily 

 convince us, that such cannot be the case. 



Monsieur Neckar of Geneva, well known for his various pa- 

 pers on geology, and especially on that department of it which 

 has reference to the question here discussed, has taken the 

 trouble to calculate, that if the above supposition were correct, a 

 single eruption, such, for instance, as that which took place from 

 Etna in 1669, would have produced an expenditure of water, 

 and an evolution of hydrogen, so enormous in quantity as to 

 have affected materially the general economy of nature, and a 

 repetition of them such as to have caused even a sensible dimi- 

 nution in the depth of the Mediterranean. As the calculation 



• That atmospheric air does actually make its way into the recesses of a 

 volcano, seems to follow from the observations on Vesuvius, stated in a late 

 number of the Hoyal Institution Journal, by Dr Donati, who mentions his 

 having heard, during the continuance of an eruption, the air rushing ia 

 through the various spiracles of that volcano, with a loud and almost musical 

 sound. 



