Gay Lussac on Volcanoes. 131 



pothesis. According- to ihe other, their principal cause'is a very 

 energetic, and as yet unsaturated, affinity between substances, which 

 a fortuitous contact would permit them to obey ; whence would 

 result a heat adequate to melt the lavas, and to elevate them, by 

 the pressure of elastic fluids, to the surface of the earth*. 



On consulting- analogy, the substances capable of penetrating 

 into the volcanic fires in masses sufficient to feed them, are air or 

 water, or both together. M. Gay Lussac shews satisfactorily 

 enough, that the instrumentality of air need not be taken into ac- 

 count. That water penetrates into the fires of volcanoes cannot 

 be called in question. There is no great eruption, which is not 

 followed with an enormous quantity of aqueous vapours, which 

 condensing afterwards, by cold, on the summits of the volcanic 

 mountains, fall back again in abundant rains, accompanied with 

 frightful thunders, as was witnessed in the famous eruption of 

 Vesuvius in 1794, which destroyed Torre del Greco. There have 

 also been observed in the daily ejections of volcanoes, aqueous 

 vapours, and muriatic acid gas, whose formation it is hardly 

 possible to conceive in the interior of volcanoes, without the 

 concurrence of water. 



Admitting that water may be one of the principal agents of vol- 

 canoes, it remains for us to examine the part which it probably 

 plays. On the second hypothesis, it is necessary for the water 

 to meet in the interior of the earth substances to which it has an 

 affinity, sufficiently powerful for its decomposition, and for giving 

 rise to a considerable disengagement of heat. 



Now the lavas vomited by volcanoes, being essentially com- 

 posed of silica, alumina, lime, soda, and oxide of iron, all oxidized 

 bodies, and having no longer an action on water, it is not in this 

 state, that they must have originally existed in the volcanoes; and 

 from what is now known of their true nature, since the beautiful 

 discoveries of Sir H. Davy, they should exist there, if not wholly, 

 at least in part, in the metallic state. In this case it can without 

 difficulty be conceived, that by their contact with water, they may 

 be decomposed, be changed into lavas, and produce sufficient 

 heat, to explain the greater part of volcanic phenomena. One of 

 the consequences, and perhaps the most important, would be the 

 disengagement, through the crater of the volcano, of an enormous 

 quantity of hydrogen, either free or combined with some other 

 principle, if it be really water which maintains by its oxygen, 

 the volcanic fires. It does not, however, appear that the disen- 

 gagement of hydrogen is very frequent in volcanoes. Although 

 during his residence at Naples, in 1805, with his friends, MM. 

 Alexandre de Humboldt, and Leopold de Buch, M. Gay Lussac 



* Thia idea is due to Sir H. Davy. It was a natural inference from his dis- 

 covery of the metallic bases of alknlis aud earths. — Editor. 

 K 2 



