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XXV. Some Remarks in reply to Dr. Daubeny's Note on the Air disengaged from the 

 Sea over the Site of the recent Volcano in the Mediterranean. By John Davy, 

 M.D. F.R.S. Assistant Inspector of Army Hospitals. 



Received May 19, — Read May 29, 1834. 



In the second part of the last volume of the Philosophical Transactions, at the re- 

 quest of the Council of the Royal Society, Dr. Daubeny has stated his objections to 

 the explanation which I have proposed of the origin of the air disengaged over the 

 sunken remains of the volcano of 1831, as described in my last paper on the subject*. 



I am induced to reply to these objections on the ground that they do not appear to 

 me well founded, nor compatible with the facts which I have brought forward. 



In the paper alluded to, after having noticed the composition of the air, which I 

 had found to consist of about 80 per cent, azote and 10 oxygen, I remarked that two 

 views might be taken of its origin ; one, that it was of volcanic source ; the other, that 

 it was derived from the sea water, and merely disengaged by the heat of the volcano. 



The first view, that which Dr. Daubeny advocates, I could not adopt, as it appeared 

 to me least probable. The minuteness of the quantity of air observed in its ascent by 

 Captain Swinburne, rising " in small silver threads of bubbles," (this is his expres- 

 sion,) seemed very unfavourable to the idea of a deep volcanic source ; and the ad- 

 mixture of oxygen with the azote seemed to me to demonstrate that its source could 

 not be deep. For the sake of argument, let us suppose, with Dr. Daubeny, that the 

 volcano had a submarine communication either with Malta, more than 100 miles 

 distant, or with the nearest parts of Sicily, at least 20 miles distant. Supposing it 

 possible that air could penetrate so far, taking the shortest distance of 20 miles, it 

 appears incredible that it should not be deprived of its oxygen in its passage, espe- 

 cially considering the nature of the matter thrown up by the volcano, containing 

 elements possessing an attraction for oxygen. Whether the whole intermediate tract is 

 imagined to be similarly composed, or only the volcanic region, seems immaterial, as a 

 few feet thickness of such material may be supposed sufficient to deprive of its oxygen 

 a very large quantity of atmospheric air. Had the volcano been supplied with atmo- 

 spheric air through channels of communication with the land, some indications of 

 such a supply, it might be expected, would have been witnessed during the period of 

 its active eruption. But, as I have stated in my former paper, no indications of the 

 kind occurred : the iron contained in the ejected ashes was generally in the state of 

 protoxide, and the cinders generally contained traces of sulphur, and the gaseous 

 products appeared to be very inconsiderable, and such as might be fairly attributed 



* Philosophical Transactions, 1833, Part I. 

 4 B 2 



