Natural Hisio)y of Volcanos and Earthquakes. 233 



merits onr attention in preference to any other process. He him- 

 self, however, observes, that the observations in mines and in hot 

 springs seem to indicate, with some degree of probabihty, that the 

 interior of the earth possesses a very high temperatm'e, and that, 

 if the earth's nucleus be supposed in a state of fusion, the expla- 

 nation of volcanic phenomena is simpler than according to his 

 own theory. 



Gay-Lussac very justly remarks, that it is impossible to con- 

 ceive the admission of atmospheric air into the focus of volcanos, 

 as there must be a force within them acting outwards, by which 

 the liquid lava, a substance about three times as heavy as water, 

 is raised to a height of above 3000 feet, as at Vesuvius, and more 

 than 9000 feet in many other volcanos. A pressure of 3000 feet 

 of lava, equal to that of a column of water of 9000 feet high, or 

 to about 300 atmospheres, necessarily prevents the entrance of air 

 into the interior of the volcanos ; and as this pressure continues 

 for many years, during which time the phenomena by no means 

 abate in activity, it is impossible that air should in any way con- 

 tribute to it. 



The presence of water in volcanos during the various stages of 

 their activity is, on the 'other hand, a circumstance repeatedly 

 witnessed by all observers.* Even the smoking during their in- 

 tervals of repose is, for the most part, nothing but a disengage- 

 ment of aqueous vapor. Violent eruptions are not unfrequently 

 followed by such enormous quantities of steam, that it condenses 

 in the atmosphere, and falls in heavy showers, as was the case 

 after the memorable eruption of Vesuvius, which destroyed Torre 

 del Greco in 1794.f Among the elastic fluids evolved from vol- 

 canos, besides aqueous vapor, we frequently find sulphuretted hy- 

 drogen gas, as, for example, from those at the equator ; and from 

 others, as Vesuvius, muriatic acid gas. But the formation of 

 these gases in the interior of volcanos cannot be conceived with- 

 out the presence of water. 



If the oxidation of the earthy and alkaline metals were to take 

 place at the expense of water, enormous quantities of hydrogen 



* See, among others, Montieelli and Covelli, der Vesuv. Deutsch bearbeitet von 

 Noggerath and Pauls. Elberfeld, 1824, p. 157. 



t See von Buch's geognostiche Beobaclitungen, torn. ii. 152. There is, how- 

 ever, still another cause, which occasions these heavy showers, as we shall shew 

 afterwards. 



Vol. XXXVI, No. 2.— April-July, 1839. 30 



