86 Sir H. Davy on the Phenomena of Volcanoes, 



of the atmosphere ; it was not possible, consequently, that they 

 should be found at the surface of the globe, but probable that 

 they might exist in the interior : and allowing this hypothesis, 

 it became easy to account for volcanic fires, *by exposure of 

 the metals of earths and alkalies to air and water ; and to ex- 

 plain, not only the formation of lavas, but likewise that of ba- 

 salts and many other crystalline rocks, from the slow cooling 

 of the products of combustion or oxidation of the newly-dis- 

 covered substances. 



I developed this opinion in a paper on the decomposition 

 of the earths, published in 1808; and since 1812 I have en- 

 deavoured to gain evidence respecting it by examining volcanic 

 phenomena of ancient and recent occurrence in various parts 

 of Europe. 



In this communication I shall have the honour of laying 

 before the Royal Society some results of my inquiries. If they 

 do not solve the problem respecting the cause of volcanic fires, 

 they will, I trust, be found to offer some elucidations of t}ie 

 subject, and may serve as the foundation of future labours. 



The active volcano on which I have made my observations 

 is Vesuvius ; and there probably does not exist another so ad- 

 mirably fitted for the purpose: its vicinity to a great city; the 

 facility with which it may be ascended in every season of the 

 year; and the nature of its activity, — all offer peculiar advan- 

 tages to the philosophic inquirer. 



I had made several observations on Vesuvius in the springs 

 of 1814 and 1815, which I shall refer to on a future occasion 

 in these pages ; but it was in December 1819, and January and 

 February 1820, that the volcano offered the most favourable 

 opportunity for investigation. On my arrival at Naples, De- 

 cember 4, 1 found that there had been a small eruption a few 

 days before, and that a stream of lava was flowing with con- 

 siderable activity from an aperture in the mountain a little be- 

 low the crater. On the 5th I ascended the mountain, and ex- 

 amined the crater and the stream of lava. The crater emitted 

 so large a quantity of smoke, with muriatic and sulphurous 

 acid fumes, that it was impossible to approach it except in the 

 direction of the wind ; and it threw up every two or three mi- 

 nutes showers of red hot stones. The lava was flowing from 

 an aperture about one hundred yards below it, being appa- 

 rently forced out by elastic fluids with a noise like that made by 

 the steam disengaged from a pressure engine; it rose, perfectly 

 fluid, forming a stream of from five to six feet in diameter, and 

 immediately fell, as a cataract, into a chasm about forty feet 

 below, where it was lost under a kind of bridge formed of 

 cooled lava ; but it re-appeared sixty or seventy yards further 



down. 



