Natural History of Volcanos and Barthinkss. 241 
_ Ifwe suppose steam to be the power by which the lavas are 
raised from this enormous depth, and by which the volcanic 
bombs, rapilli, and ashes are thrown up, and according to all ob- 
servations hitherto made, water in its elastic state seems to be the 
only means by which the lavas* and other volcanic rocks,+ are so 
taised ; it is yet a question whether its expansive force could be 
sufficiently raised by heat? Parrott reckons that the temperature 
of lava, at the moment of its ejection, is five times as great as 
Would be necessary to raise it 48000 feet by the elastic force of 
steam, supposing the steam to be formed in the presence of water. 
it from more recent inquiries on the elastic force of aqueous 
Vapor, this calculation must undergo considerable corrections. 
The formula of Mayer, as altered according to the last results of 
the experiments at Vienna§ corresponds the most nearly with the 
elastic force of steam as actually observed, so that it may be con- 
sidered as the most correct determination of its elasticity at higher 
‘emperatures. If we wish to find the pressure of the steam in 
Boece ey 
the increase of temperature follows an arithmetical progression as far as these 
depths. With this exception, we can hardly hope ever to b quainted wi 
the true progression of the increase of the temperature to the interior. Therefore 
all such calculations, as the former, can but give approximations to the truth. 
Von Humboldt’s Reise, t. i, p. 186. A short time before the great eruption of 
the interior of the crater did not redden litmus. Many other naturalists have 
also found that the outlets of smoke of the Peak of Teneriffe emitted pure wa- 
Tonly. Voy. de La Peyrouse, t. iii, p. 2. H ann, in his letter to Von Buch 
7” the geognostical structure of the Lipari Islands, in Poggendortf’s Annal. vol. 
oat P-/ and 45, and in several places in his account of the voleanic island which 
rose the Mediterrunean. Sea, vol. xxiv, p- 65. According to Monticelli and Co- 
Velli, the smoke which rises from the lava-streams consist almost exclusively of 
aqueous vapor. Loco cit. p. 27, 65. and 83. Numerous fumaroles (exbalations of 
“queous vapor) rise on the island of Ischia out of the cracks in the lava. Forbes, 
‘a Edinb. Journ. of Science, N. 8. iv, p. 326. Reinwardt, Verhandlingen van het 
4, Pp. 215, 
; The water contained in basalt speaks in favor of this opinion. See Klaproth’s 
an . ge, &e., vol. iii, p. 249, and Kennedy in Appendix to the same, p. 255. 
elting basalt, and introducing a gun-barrel into the crucible, I observed a consid- 
erable evolutio por. 
ndriss der Physik der Erde und Geologie. Riga u. Leipzig, 1815, p. 264. 
§ Arzherger in the Jahrbiichern des Polytechnischen Instituts, vol. i, p 
ol. xxxvi, No. 1.—April—July, 1839. 3 
