Observations on Mount Vesuvius, Mount Etna, and Other Volcanos Part 7

[42] By having remarked, that all the implements of stone brought by Mess. Banks and Solander from the new-discovered islands in the South-Seas, are evidently of such a nature as are only produced by Volcanos; and as these gentlemen have a.s.sured me, that no other kind of stone is to be met with in the islands; I am induced to think, that these islands (at so great a distance from any continent) may have likewise been pushed up from the bottom of the sea by like explosions.

[43] Any one, the least conversant in Volcanos, must be struck with the numberless evident marks of them the whole road from the lake of Albano to Radicofani, between Naples and Florence; and yet, though this soil bears such fresh and undoubted marks of its origin, no history reaches the date of any one eruption in these parts.

[44] May not the air in countries replete with sulphur be more impregnated with electrical matter than the air of other soils? and may not the sort of lightning, which is mentioned by several ancient authors to have fallen in a serene day, and was considered as an omen, have proceeded from such a cause?

Horace says, Ode x.x.xiv.

"--Namque Diespeter "Igni corusco nubila dividens "Plerumque per purum tonantes "Egit equos volucremque currum."

"Non alias coelo ceciderunt plura sereno "Fulgura----"

Virgil. Georgic. i.

"Aut c.u.m terribili perculsus fulmine civis "Luce serenanti vitalia lumina liquit."

Cic. i. de Divin. n. 18.

"--Sabinos pet.i.t aliquanto tristior, quod sacrificanti hostia aufugerat: quodque tempestate serena tonuerat."

Sueton. _t.i.t._ cap. 10.

[45] This letter was not received by Dr. Maty in its present form: and is rather the substance of an explanatory catalogue, which was sent to that gentleman with sundry specimens of the different materials that compose the soil described in the preceding letter; which catalogue remains, with the specimens, in the Museum of the Royal Society, for the inspection, and, I flatter myself, the satisfaction, of the curious in natural history.

[46] See p. 103 of this collection.

[47] See Letter I. p. 18.

[48] Having heard the same remark with respect to the lava's of Vesuvius, I determined, during an eruption of that Volcano, to watch the progress of a current of lava, and I was soon enabled to comprehend this seeming phnomenon; though it is, I fear, very difficult to explain.

Certain it is, that the lava's, whilst in their most fluid state, follow always the law of other fluids; but when at a great distance from their source, and consequently inc.u.mbered with scori and cinders, the air likewise having rendered their outward coat tough, they will sometimes (as I have seen) be forced up a short ascent, the fresh matter pus.h.i.+ng forward that which went before it, and the exterior parts of the lava acting always as conductors (or pipes, if I may be allowed the expression), for the interior parts, that have retained their fluidity by not having been exposed to the air.

[49] The flames Lord Winchelsea mentions, were certainly produced by the lava having met with trees in the way; or perhaps his Lords.h.i.+p may have mistaken the white smoak which constantly rises from a lava (and in the night is tinged by the reflection of the red hot matter), for flame, of which indeed it has greatly the appearance at a distance. I have observed upon Mount Vesuvius, that, soon after a lava has borne down and burned a tree, a bright flame issues from its surface; otherwise I have never seen any flame attending an eruption.

THE END.