M. Gay-Lussac on Volcanos. 83 



served in the daily ejections of volcanos. It is scarcely pos- 

 sible to conceive the formation of these in the interior of vol- 

 canos without the agency of water. 



If we admit that water is one of the principal agents in 

 volcanos, we must proceed to examine the real means by 

 which it acts, upon either of the hypotheses we have just laid 

 down concerning the heat of volcanic furnaces. If we sup- 

 pose, according to the first hypothesis, that the earth continues 

 in a state of incandescence, at a certain depth below its sur- 

 face, it is impossible to conceive the existence of water at 

 that dei)th ; for the temperature of the earth having formerly 

 been of necessity higher, its fluidity greater, and the thickness 

 of its solid crust less than at the pi'esent time, the water must 

 necessarily have disengaged itself from its interior and have 

 risen to the surface. 



If we wish therefore to give any air of probability to this 

 hypothesis, and to mamtain the importance of water as a prin- 

 cipal agent in volcanos, we must assume that it penetrated 

 from the surface downwards to the incandescent strata of the 

 earth; but in order to come to this conclusion, we must 

 suppose that it had a free communication with those strata, that 

 it gradually acquired heat before it reached them, and that 

 the vapour it produced compressed by the weight of its whole 

 liquid column, obtained a sufficient elastic force to elevate the 

 lavas, to produce earthquakes, and to cause all the other 

 terrible phajnomena of volcanos. 



The difficulties obviously involved in these suppositions, and 

 to which many others might be added, render the hypothesis 

 that the heat of volcanos is to be attributed to the state of in- 

 candescence of the earth at a certain depth below the surface 

 perfectly inadmissible. I must further remark that this in- 

 candescence is itself quite hypothetical ; and that, notwith- 

 standing the observations on the increase of temperature in 

 mines, I regard it as extremely doubtful. 



Upon the second hypothesis which we laid down, that the 

 principal cause of volcanic phaenomena is a very strong and as 

 yet unneutralized affinity existing between certain substances, 

 and capable of being called into action by fortuitous contact, 

 it is necessary to suppose tliat the water meets, in the interior 

 of the earth, substances wiUi which it has an affinity so strong 

 as to effiict its decomposition and to disengage a considerable 

 quantity of heat. 



Now the lavas ejected by volcanos are essentially composed of 

 silica, alumina, lime, soda, and oxide of iron ;— bodies which, 

 being all oxides and incapable of acting upon water, cannot 

 be supposed lo have oiiginally existed in their present state ni 



'L 2 vokano5. 



