Natural History of Volcanos and Earthquakes. 243 



ejection of lavas, red hot masses, and clouds of steam, just as 

 Spallanzani,* Scrope,f and Hoffmann, J observed on Stromboli. 



We have now to examine the circumstances under which wa- 

 ter might find its way to the origin of volcanic action. The diffi- 

 culties which present themselves when we suppose a direct com- 

 munication between the sea and the seat of the volcanos, have 

 already been discussed by Gay-Lussac. We shall make an at- 

 tempt to solve these difficalties. 



If we imagine the sea to have free access by means of fissures 

 to the seat of the volcanos, the depth of which, according to the 

 above calculation, may be taken at from 113505 to 126829 feet, 

 the elastic force of steam at that depth, where ^=^2282° F., will 

 be =5310 atmospheres. But the hydrostatic pressure of these 

 columns of water is only from 3547 to 3963 atmospheres. The 

 expansive force of steam at that depth in which the temperature 

 is 2282° F. is, therefore, greater than the hydrostatic pressure 

 opposed to it, so that the latter cannot resist it. But since, as 

 the temperature decreases, this expansive power diminishes more 

 rapidly than the hydrostatic pressure, there must be a certain 

 depth and a corresponding temperature in which they will be in 

 equilibrium. For a constant increase of temperature of 1° F. in 

 51 feet, this point will be at the depth of 88044 feet below the 

 surface of the sea, where the temperature is 1754°. 5 F. ;<§> for, 

 according to the above formula, if t be taken equal to 1754°. 5, 



* Voyag. t. ii, p. 21. 



t Considerations on Volcanos, &c., p. 54. A phenomenon observed by Scrope 

 during the night in the crater of Stromboli distinctly shows, that, by the force of 

 aqueous vapor alone, the column of lava is raised. The lava once suddenly dis- 

 appeared in the depth of the crater; on the contrary, innumerable little columns of 

 steam appeared at the edges of the mouth of the crater, which arose with a hissing 

 noise. This lasted for some minutes, when the melted mass rose again from be- 

 neath, and the phenomena pursued again its ordinary course. Spallanzani re- 

 marks very justly with a view to this, that the compressed vapors prevented from 

 being discharged by the sinking lava which had become tenacious on the surface, 

 will navy escape laterally through the fissures in the walls of the edge of the cra- 

 ter, and in this case the lava cannot be elevated by them. It is not until the lava 

 has been sufficiently heated and become again liquid, that the vapor can rise again 

 with the lava, and that the phenomenon can be re-established. 



i Loco cit. p. 9. — D. Curbeto also observed that a dense smoke always followed 

 the streams of lava which were ejected on the 7th June, 1731, Von Buch in the 

 Abhandl. d. Berliner Acad, of 1818-1819, p. 77. 



§ To simplify the calculation, I have supposed the mean temperature of the 

 surface = 32° F. 



