te —— Ss 
~ 
Natural History of Volcanos and Earthquakes. 233 
merits our 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 probability, that the 
interior of the earth possesses a very high temperature, 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 
'n the atmosphere, and falls in heavy showers, as was the case 
after the memorable eruption of Vesuvius, which destroyed Torre 
del Greeo in 1794. Among the elastic fluids evolved. from vol- 
fanos, besides aqueous vapor, we frequently find sulphuretted hy- 
Sen gas, as, for example, from those at the equator ; and from 
“8, 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. : 
the oxidation of the earthy and alkaline metals were to take 
at the expense of water, enormous quantities of hydrogen 
es See, among others, Monticelli and Covelli, der Vesuv. Deutsch bearbeitet von 
Sgerath and Pauls. Elberfeld, 1824, p. 157. Ee as 
*e von Buch’s geognostiche Beobachtungen, tom. i. 152. ere is, ho 
ret, still another cause which occasions these heavy showers, as we shall shew 
afterwards, : ; 
Nol. xxxv1, No. 2—April-July, 1839. vi 
