.' Royal Society. 373 



the protection of the conductor, she must inevitably have been de- 

 stroyed by the second tremendous explosion, which, thus guarded, 

 she sustained without the slightest injury. The author remarks 

 that copper is a better material for such a conductor than iron, from 

 its being less liable either to fusion or corrosion: and also that a 

 rod is, from its continuity, a better form of conductor than a chain. 

 In the case of ships, however, the greater convenience of a chain, 

 arising from its flexibility, will generally insure it the preference. 

 The author recommends, that, instead of carrying the conductor 

 through the decks to the keel, as suggested by Mr. Harris, the 

 lower end of the chain should be kept at a distance from the sides 

 of the ship, by means of a light outrigger, or spar, as was done in 

 the New York. 



March 20. — Read a paper On the Phenomena of Volcanoes ; by 

 Sir H. Davy, Bart. F.R.S. 



In a paper on the decomposition of the earths, published in the 

 Phil. Trans, for 1812, the author offered it as a conjecture, that the 

 metals of the alkalies and earths might exist in the interior of the 

 globe ; and on being exposed to the action of air and water, give 

 rise to volcanic fires, and to the production of lavas, by the slow 

 cooling of which basaltic and other crystalline rocks might subse- 

 quently be formed. Vesuvius, from local circumstances, presents 

 peculiar advantages for investigating the truth of this hypothesis ; 

 and of these the author availed himself during his residence at 

 Naples, in the months of December 1819, and of January and Fe- 

 bruary 1820. A small eruption had taken place a few days before 

 he visited the mountain, and a stream of lava was then flowing with 

 considerable activity from an aperture in the mountain a little below 

 the crater, which was throwing up showers of red-hot stones every 

 two or three minutes. On its issuing from the mountain, it was 

 perfectly fluid, and nearly white hot : its surface appeared to be in 

 violent agitation from the bursting of numerous bubbles, which 

 emitted clouds of white smoke. There was no appearance of vivid 

 ignition in the lava when it was raised and poured out by an iron 

 ladle. A portion was thrown into a glass bottle, which was then 

 closed with a ground stopper, and, on examining the air in the 

 bottle some time afterwards, it was found not to have lost any of 

 its oxygen. Nitre thrown upon the surface of the lava did not 

 produce such an increase of ignition as would have attended the 

 presence of combustible matter. The gas disengaged from the lava 

 proved on examination, to be common air. 



When the white vapours were condensed on a cold tin plate, the 

 deposit was found to consist of very pure common salt ; and the 

 vapours themselves contained nine per cent of oxygen, the rest 

 being azote, without any notable proportion of carbonic acid or 

 sulphureous acid gases ; although the fumes of the latter of these 

 gases were exceedingly pungent in the smoke from the crater of 

 the volcano. On another occasion, the author examined the saline 

 incrustations in the rocks near the ancient bocca of Vesuvius ; and 

 found them to consist principally of common salt, with some chlo- 

 ride of iron, a little sulphate of soda, and a still smaller quantity of 



sulphate 



