Natural History of Volcanos and Earthquakes. 241 



If we 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,t are so 

 raised ; it is yet a question whether its expansive force could be 

 sufficiently raised by heat ? Parrot:j; reckons that the temperature 

 of lava, at the moment of its ejection, is five times as great as 

 would be necessary to raise it 48U00 feet by the elastic force of 

 steam, supposing the steam to be formed in the presence of water. 

 But 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 

 temperatures. If we wish to find the pressure of the steam in 



the increase of temperature follows an arithmetical progression as far as these 

 depths. With this exception, we can hardly hope ever to become acquainted with 

 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 

 Vesuvius, in the year 1805, he and Gay-Lussac observed that the watery vapors 

 in 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- 

 ter only. Voy. de La Pey rouse, t. iii, p. 2. Hoffmann, in his letter to Von Buch 

 on the geognostical structure of the Lipari Islands, in PoggendorfTs Annal. vol. 

 xxvi, p. 9 and 45, and in several places in his account of the volcanic island v^hich 

 rose in the Mediterranean 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 (exhalations of 

 aqueous vapor) rise on the island of Ischia out of the cracks in the lava. Forbes, 

 in Edinb. Journ. of Science, N. S. iv, p. 326. Reinwardt, Verhandlingen van het 

 Bataviaasch genootsthap van Kunsten en Wetenschapen, negende deel, Batavia, 

 1823, p. 1. Ordinaire mentions, in his " Histoire Naturelle des Volcans," a mass of 

 melting iron having been cast to a height of 150 feet, out of a blast furnace, by some 

 water having accidentally got into it. See D'Aubuisson, Traite de Geognosie, 

 V. i, p. 215. 



t The water contained in basalt speaks in favor of this opinion. See Klaproth's 

 Beilrage, &c., vol. iii, p. 249, and Kennedy in Appendix to the same, p. 255. On 

 melting basalt, and introducing a gun-barrel into the crucible, I observed a consid- 

 erable evolution of aqueous vapor. 



1^ Grundriss der Physik der Erde und Geologie. Riga u. Leipzig, ]815, p. 264. 



§ Arzberger in the Jahrbiichern des Polytechnischen Instituts, vol. i, p. 144. 



Vol. XXXVI, No. 1.— April-July, 1839. 31 



