thought to have been original, and are certainly not so, if their strata correspond with those of the Montagno Nuovo. I should be glad to know whether you think this project of mine will be useful; and, if you do, the result of my observations may be the subject of another letter.

I cannot have a greater pleasure than to employ my leisure hours in what may be of some little use to mankind; and my lot has carried me into a country, which affords an ample field for observation. Upon the whole, if I was to establish a system, it would be, that mountains are produced by volcanoes, and not volcanoes by mountains.

I fear I have tired you: but the subject of volcanoes is so favourite a one with me, that it has led me on I know not how: I shall only add, that Vesuvius is quiet at present, though very hot at top, where there is a deposition of boiling sulphur. The lava that run in the Fossa Grande during the last eruption, and is at least 200 feet thick, is not yet cool; a stick, put into its crevices, takes fire immediately. On the sides of the crevices are fine crystalline salts: as they are the pure salts, which exhale from the lava that has no communication with the interior of the mountain, they may perhaps indicate the composition of the lava.

[Phil. Trans. 1769.]

SECTION IV.

Eruption of Vesuvius in 1799, as described in a Letter from SIR WILLIAM HAMILTON, K. B. F. R. S. to JOSEPH BANKS, ESQ. F. R.S.

SIR,

NAPLES, October 1, 1779.

THE late eruption of Mount Vesuvius was of so singular a nature, so very violent and alarming, that it necessarily attracted the attention of every one, not only in its immediate neighbourhood, but for many miles around; and, consequently, several slight descriptions of it have been already handed about, and some (as I am informed) more accurate and circumstantial are preparing for the press*.

The inhabitants of this great city in general give so little attention to Mount Vesuvius, though in full view of the greatest part of it, that I am well convinced many of its eruptions pass totally unnoticed by at least two-thirds of them.

That on which the Abbot Bottis is actually employed, by command of his Sicilian Majesty, will undoubtedly be executed with the same accuracy, truth, and precision, as have rendered that author's former publications upon the subject of Mount Vesuvius so universally and deservedly esteemed.

Such a publication, executed with magnificence in the royal printing office, may, perhaps, render every other account of the late eruption superfluous: nevertheless, I should think myself in some degree guilty of a neglect towards the Royal Society, who have done so much honour to my former communications, if I did not, through the respectable channel of its worthy president, and my good friend, simply relate to them such remarkable circumstances as attended the late tremendous explosions of Mount Vesuvius, and as either came immediately under my own inspection, or have been related to me by such good authority as cannot be called in question.

Since the great eruption of 1767, of which I had the honour of giving a particular account to the Royal Society, Vesuvius has never been free from smoke, nor ever many months without throwing up red-hot scoriæ, which, increasing to a certain degree, were usually followed by a current of liquid lava; and, except in the eruption of 1777, those lavas broke out nearly from the same spot, and ran much in the same direction, as that of the famous eruption of 1767.

No less than nine such eruptions are recorded here since the great one above-mentioned, and some of them were considerable. I never failed visiting those lavas whilst they were in full force, and as constantly examined them and the crater of the volcano after the ceasing of each eruption.

It would be but a repetition of what has been described in my former letters on this subject, were I to relate my remarks on those different expeditions. The lavas, when they either boiled over the crater, or broke out from the conical parts of the volcano, con

The last visit to the crater of Vesuvius, which was in the month of May, 1799, was my fifty-eighth, and to be sure I have been four times as often on parts of the mountain, without climbing to its summit, and after all am not ashamed to own, that I comprehend very little of the wonders I have seen in this great laboratory of nature; yet there have been naturalists of such a wonderful penetrating genius, as to have thought themselves sufficiently qualified to account for every hidden phenomenon of Vesuvius, after having, literally speaking, given the volcano un coup d'œil.

stantly formed channels as regular as if they had been cut by art down the steep part of the mountain, and, whilst in a state of perfect fusion, continued their course in those channels, which were sometimes full to the brim, and at other times more or less so, according to the quantity of matter in motion.

These channels, upon examination after an eruption, I have found to be in general from two to five or six feet wide, and seven or eight feet deep. They were often hid from the sight by a quantity of scoria that had formed a crust over them, and the lava baving been conveyed in a covered way for some yards, came out fresh again into an open channel. After an eruption I have walked in some of those subterraneous or covered galleries which were exceedingly curious, the sides, top, and bottom, being worn perfectly smooth and even in most parts by the violence of the currents of the red-hot lavas, which they had conveyed for many weeks successively; in others, the lava had incrusted the sides of those channels with some very extraordinary scoriæ : beautifully ramified with white salts,* in the form of dropping stalactites, were also attached to many parts of the ceiling of those galleries. It is imagined here, that the salts of Vesuvius are chiefly ammoniac, though often tinged with green, deep, or pale yellow, by the vapour of various minerals.

In the month of May last, there was a considerable eruption of Mount Vesuvius, when I passed a night on the mountain in the company of one of my countrymen,, as eager as myself in the pursuit of this branch of natural history t.

We saw the operation of the lava, in the channels as abovementioned, in the greatest perfection; but it was, indeed, owing to our perseverance, and some degree of resolution. After the lava bad quitted its regular channels, it spread itself in the valley, and, being loaded with scoria, ran gently on, like a river that had been frozen, and had masses of ice floating on it: the wind changing. when we were close to this gentle stream of lava, which might be about fifty or sixty feet in breadth, incommoded us so much with its heat and smoke, that we must have returned without having satisfied

I sent a large specimen of this curious volcanic production to the BritishMuseum last year.

+ Mr. Bowdler, of Bath.

our curiosity, had not our guide proposed the expedient of walking across it, which, to our astonishment, he instantly put in execution, and with so little difficulty, that we followed him without hesitation, having felt no other inconveniency than what proceeded from the violence of the heat on our legs and feet; the crust of the lava was so tough, besides being loaded with cinders and scoriæ, that our weight made not the least impression on it, and its motion was so slow, that we were not in any danger of losing our balance and falling on it however, this experiment should not be tried except in cases of real necessity; and I mention it with no other view than to point out a possibility of escaping, should any one hereafter, upon such an expedition as ours, have the misfortune to be inclosed between two currents of lava.

Having thus got rid of the troublesome heat and smoke, we coasted the river of lava and its channels up to its very source, within a quarter of a mile of the crater. The liquid and red-hot matter bubbled up violently, with a hissing and crackling noise, like that which attends the playing off of an artificial firework; and, by the continual splashing up of the vitrified matter, a kind of arch or dome was formed over the crevice from which the lava issued. It was cracked in many parts, and appeared red-hot within, like an heated oven this hollowed hillock might be about fifteen feet high, and the lava that ran from under it was received into a regular channel, raised upon a sort of wall of scoria and cinders, almost perpendicularly, of about the height of eight or ten feet, resembling much an ancient aqueduct.

We then went up to the crater of the volcano, in which we found, as usual, a little mountain throwing scoria and red-hot matter with loud explosions; but the smoke and smell of sulphur was so intolerable, that we were under the necessity of quitting that curious spot with the utmost precipitation.

In another of my excursions to Mount Vesuvius last year, I picked up some fragments of large and regular crystals of close-grained lava or basalt, the diameter of which, when the prisms were complete, may have been eight or nine inches. As Vesuvius does not exhibit any lavas regularly crystallized, and forming what are vul garly called Giants Causeways (except a lava that ran into the sea

Bartolomeo, the Cyclops of Vesuvius, who has attended me on all my expeditions to the mountain, and who is an excellent guide. 2 A

VOL. I.

near Torre del Greco in 1631, and which in a small degree has sueir an appearance), this discovery gave me the greatest pleasure".

After this slight sketch of the most remarkable events on Vesuvius since the year 1767, which I flatter myself will not be unacceptable, as it may serve to connect what I am going to relate with what has already been communicated to the Society in my former letters on the same subject, I come to the account of the late eruption, which affords indeed ample matter for curious speculation.

As many poetical descriptions of this eruption will not be wanting, I shall confine mine to simple matter of fact in plain prose, and endeavour to convey to you, Sir, as clearly and as distinctly as I am able, what I saw myself, and the impression it made upon me at the time, without aiming in the least at a flowery style.

The usual symptoms of an approaching eruption, such as rumbling noises and explosions within the bowels of the volcano, a quantity of smoke issuing with force from its crater, accompanied at times with an emission of red-hot scoria and ashes, were manifest, more or less, during the whole month of July; and towards the end of the month, those symptoms were increased to such a degree as to exhibit in the night-time the most beautiful fire-works that can be imagined.

These kinds of throws of red-hot scorie and other volcanic matter, which at night are so bright and luminous, appear in broad daylight like so many black spots in the midst of the white smoke; and it is this circumstance that occasions thé vulgar and false supposition, that volcanoes burn much more violently at night than in the day-time.

On Thursday, the 5th of August last, about two o'clock in the afternoon, I perceived from my villa at Pausilipo in the bay of Naples, from whence I have a full view of Vesuvius (which is just

* As the fragments of basalt columns, which I found on the cone of Vesuvius, had been evidently thrown out of its crater, may not lava be more subject to crystallize within the bowels of a volcano than after its emission, and hav ing been exposed to the open air? And may not many of the Giants' Causeways, already discovered, be the nuclei of volcanic mountains, whose lighter and less solid parts may have been worn away by the hand of time? Mr. Faujais de St. Fond, in his curious book lately published, and intitled, “Recherches sur les Volcains eteints du Vivarais et du Velay," gives (p. 286) an example of basalt columns, that are placed deep within the crater of an extinguished volcano.