On Volcanos and Earthquahes. 25 



there meets with a fluid denser than itself; that either in the 

 open sea, or between the crevices of the rocks and ground 

 at that depth, is its inferior level ; that at the surface of the 

 earth, fresh water ascends higher than the superior level of 

 the sea, in proportion to its relative levity, and the depth at 

 which they come in contact. This is what we have particu- 

 larly tried to demonstrate in a former communication, (vol. 

 xiv. p. 174) ; that below four miles and seven-eighths is con- 

 densed air which supports the combustion of inflammable 

 bodies, and keeps in activity those subterranean fires, the im- 

 mediate cause of earthquakes and volcanos ; that it ceases to 

 be problematical how these fires under ground are not smoth- 

 ered for want of oxygen, and how those under the sea are 

 not extinguished by its water ; that we now may account for 

 volcanic islands suddenly rising or disappearing ; that it also 

 explains why earthquakes, without any outward explosion, 

 extend to a greater distance, and are more destructive, than 

 those breaking out in a volcanic eruption, &c. &c. 



But it is high time to close this article, not because the 

 subject is exhausted, for it seems to extend in proportion as 

 we proceed, but because the hmits granted to a pubhcation 

 are perhaps already outreached. We will hereafter present 

 our readers with some new considerations derived from the 

 same principle. 



Joseph Du Commun, 



West Point, April \Uh, 1828. 



Objections to the above Theory.^ 



1st. The experiments of Perkins! prove that air, and those 

 of Mr. Faraday,! that many gases, and from analogy, (ground- 

 ed on so many established cases,) we may infer that all 

 gases, under extreme compression, especially when aided by 

 cold, lose their elastic form, and become fluid. 



2d. This being the fact, all reasonings respecting the con- 

 dition of air under extreme pressure, must contemplate it as 

 a fluid — (truly such while the pressure exists) — and resuming 

 its elastic character, by diminution or removal of pressure. 



3d. Whether it would form a stratum, distinct from wa- 

 ter, must depend upon the existence or absence of affinity 



* Forwarded to the author in a letter from the Editor. 



t Jones' Mechanics' Mag. IV. 2. 1: Phil. Transac, London, 1823, 



Vol, XV,— No. L 4 



