THE 



PHILOSOPHICAL MAGAZINE 

 AND JOURNAL. 



3P' AUGUST 1823. 



XYL Rejections on Volcanos. By M. Gay-Lussac. Read 

 before the Royal Academy of Sciences at Paris, May 19, 1823 *i 



"DEFORE I offer to the public the following observations 

 on volcanos, a subject which has so long presented a 

 wide field for hypothesis and conjecture, I ought to premise 

 that I am not in possession of all the knowledge necessary for 

 its full discussion, and that I shall only take a brief and par- 

 tial view of it, confining myself to certain questions upon 

 which chemistry may throw some light, and which do not ab- 

 solutely demand an acquaintance with geology. The subject 

 is however one of considerable difficulty, and one which gives 

 me a claim on the indulgence of my readers. 



Two hypotheses may be formed as to the cause which pro- 

 duces volcanic phaenomena. According to one of these, the 

 earth remains in a state of incandescence at a certain depth 

 below the surface (a supposition strongly favoured by the ob- 

 servations which have been recently made on the progressive 

 increase of temperature in mines) ; and this heat is the chief 

 agent in volcanic phasnomena. According to the second hy- 

 pothesis, the principal cause of these phaenomena is a very strong 

 and as yet unneutralized affinity existing between certain sub- 

 stances, and capable of being called into action by fortuitous 

 contact, producing a degree of heat sufficient to fuse the lavas 

 and to raise them to the surface of the earth by means of the 

 pressure of elastic fluids. 



According to either of these hypotheses, it is absolutely ne- 

 cessary that the volcanic furnaces should be fed by substances 

 originally foreign to them, and which have been some how or 

 other introduced into them. 



In fact, at those remote epochs which witnessed the great 

 catastrophes of our globe, — epochs at which the temperature of 

 the earth must have been higher than it now is, the melted 

 substances which it contained consequently more liquid, the 

 resistance of its surface less, and the pressure exercised by 

 elastic fluids greater, — all that could be produced was pro- 



* Ann. de Chimie et de Pht/s. toni. xxii. p. 415, 

 Vol, 62. No. 304. ^w^. 1823, L duced; 



