Volcanos and Earthqiiahcs. 37 



rocks,* are so raised ; it is yet a question whether its expan- 

 sive force could be sufficiently raised by heat ? Parrot-f- 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. But from more recent inquiries on 

 the elastic force of aqueous vapour, this calculation must un- 

 dergo considerable corrections. The formula of Mayer, as al- 

 tered according to the last results of the experiments at Vknna% 

 corresponds the most nearly with the elastic force of steam as 

 actually observed, so that it may be considered as the most cor- 

 rect determination of its elasticity at higher temperatures. If 

 we wish to find the pressure of the steam in Paris inches of a 

 column of mercury from this formula, we shall have 



log ^= 2.8316686 + log (213 ^t)— ^^^ 



in which t is the temperature in degrees of Reaumur = _ p « 



tery vapours 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 

 Ti'ncr'iffe emitted pure water only. Voy. de La Peyrouse, t. iii, p. 2. Hoffmann, 

 in liis letter to Von Buch on the geognostical structure of the Llpari Islandy, 

 in Poggondoi*ff's Annal. vol. xxvi, p. 9 and 45, and in several places in his ac- 

 count of the volcanic island which rose in the Dledlternmcan Sea, vol. xxiv, 

 p. 65. According to Monticelli and Covelli, tlie smoke which rises from the 

 lava-streams consist almost exclusively of aqueous vapour. Loco cit. p. 27, 

 05, and 83. Numerous fumaroles (exhalations of aqueous vapour) rise on 

 tlie island of hchia out of the cracks in the lava. Forbes in Edinb. 

 Journ. of Science, N. S. iv, p. 326. Reinwardt, Verhaudlingen van liet 

 liataviaasch genootsthap van Kunsten en Wetonschapen, negende deel, 

 l>atavia 1823, p. 1. Ordinaire mentions, in his "Histoire Naturelle dcs Vol- 

 cms," a mass of melting iron having been cast to a height of 150 feet, out 

 of a blast furnace, by some w^ater having accidentally got into it. See D'Au- 

 1)uisson, Traite de Geognosie, v. i, p. 215. 



* 'J'he water contained in basalt speaks in favour of this opinion. See 

 Klaprotli's Beitriigo, &c., vol. iii, p. 249, and Kennedy in Appendix to the 

 same, p. 255. On melting basalt, and introducing a gun-barrel into the cru- 

 cible, I observed a considerable evolution of aqueous vapour. 



t Grundriss der Physik der Erde imd Geologic. Riga u. Leipzig, 1815, 

 p. 264. 



t Arzberger in the Jalirbiichem des Polytechnischen Instituts, vol. i 

 ]). 144. 



§ On steam and steam-engines in the Abhandluugen der Kunigl. tcch- 

 nischen Deputation fiir Gewerbe, part i, p. 344. 



