The eruption from the crater increased with so much violence that we proceeded to make our experiments and observations as speedily as possible. A little above the source of the lava I found a chimney of about four feet in height,from which proceeded smoke, and sometimes stones. I approached and gathered some pure sulphur, which had formed itself upon the edges of the mouth of this chimney, the smell of which was so powerful that I was forced to hold my breath all the while I remained there. I seized an opportunity to gain a momentary view down this aperture, and perceived nothing but the glare of the red-hot lava that glare beneath it. We then returned to examine the lava at its source. Sir W. Hamilton had conceived that no stones thrown upon a current of lava would make any impression. We were soon convinced of the contrary. Light bodies of five, ten, and fifteen pounds weight, made little or no impression even at the source; but bodies of sixty, seventy, and eighty pounds were seen to form a kind of bed on the surface of the lava, and float away with it. A stone of three hundredweight, that had been thrown out by the crater, lay near the source of the current of lava. I raised it upon one end, and then let it fall in upon the liquid lava, when it gradually sunk beneath the surface and disappeared. If I wished to describe the manner in which it acted upon the lava, I should say it was like a loaf of bread thrown into a bowl of very thick honey, which gradually involves itself in the heavy liquid which surrounds it, and then slowly sinks to the bottom. The lava itself' had a glutinous appearance, and although it resisted the most violent impression, seemed as if it might easily be stirred with a common walking stick. A small distance from its source, as it flows on, it acquires a darker tint upon its surface, is less easily acted upon, and as the stream gets wider, the surface having lost its state of perfect solution, grows harder and harder, and cracks into innumerable fragments of very porous matter, to Which they give the name of scori , and the appearance of which has led many to suppose that it proceeded thus from the mountain; itself being composed of materials less soluble than the rest of the lava, lighter, and of course liable to float continually on the surface. There is, however, no truth in this. All lava at its first exit from its native volcano flows out in a liquid state, and all equally in fusion. The appearance of the scori is to be attributed only to the action of the external air, and not to any difference of the materials which compose it, since any lava whatever, separated from its channel and exposed to the action of the external air, immediately cracks, becomes porous, and alters its form. As we proceeded downward this became more and more evident, and the same lava, which at its original source flowed in perfect solution, undivided, and free from encumbrances of any kind, a little farther down had its surface loaded with scori in such a manner, that upon its arrival at the bottom of the mountain the whole current resembled nothing so much as a heap of unconnected cinders from an iron-foundry.

Aug. 22, 1793. There was to-day a most singular appearance in the mountain. On opening the shutters to "view it, I perceived the crater to be in great agitation, puff after puff impelling each other with the greatest violence. I could perceive thousands of stones and scori thrown into the air, and falling in all directions. The clouds from the crater were as white as the purest snow; on a sudden, as I was looking at these, a column of smoke rushed impetuously out of another mouth behind the crater, as black as the deepest ink; and rising in curling volumes to a vast magnitude, formed a pillar perfectly unconnected with the smoke from the crater, and presented a striking contrast by opposing its jet black to the snowy whiteness of the other. These appearances continued at intervals the whole day. Sometimes the two columns of different colours rose together, as if emulating each other, and striving which should rise the highest or display the greatest magnitude, but never mixing or interfering with each other.

" Aug. 30.-The lava, which was last night so great, this evening suddenly stopped; hardly a trace of it was visible. But the crater displayed such girandoles of fire, such beautiful columns of light red flame, as I think I never saw before. Millions of red-hot stones were shot into the air, full half the height of the cone itself, and then bending, fell all round in a fine arch. As soon as I got home I fixed the telescope. Sometimes, in the middle of the clear flame, another and another still more bright and glorious displayed itself, breaking on the eye like the full sun, so that the interior was always the most luminous. The interior and bright attendants upon the principal column seemed to be lava in perfect fusion, which boiled and bubbled up above the crater's edge; and sometimes falling over it, I could perceive splash upon the cone, and take its course gently down the side of the mountain. Sometimes, and more usually, it fell again into the crater. I write this with the burning mountain now before my eyes. All the top of the cone is covered with red-hot stones and lava. The flame of the crater continues without intervals of darkness, as usual. It is always in flame, or rather the clouds of smoke, tinged with the boiling matter within, are like burnished gold, and as bright as fire.

"Sept. 5. Vesuvius continues to throw most superbly; the lava flows again. At sunset he showed that Tyrian hue which he assumes sometimes, and which has a glow beyond description. I had undressed myself and was prepared to get into bed, when a violent shock from the mountain agitated the door of my room, so as to startle me not a little. I went into my sitting-room, and, upon opening the window toward the mountain, I perceived all the cop of the cone covered with red-hot matter. At the same time such a roaring was heard as made me expect something more than common. In an instant a column of lucid fire shot up into the air, and after ascending above half the height of the cone itself, fell in a glorious parabolic girandole, and covered near half the cone with fire. This was followed, after an interval of about thirty seconds, by a shock which agitated the doors and windows, and indeed the whole house in a most violent manner. Immediately after this shock the sound of the explosion reached us louder than the greatest cannon, or the most terrible thunder, attended with a noise like the trampling of horses' feet, which, of course, was nothing More than the noise occasioned by the falling of so many enormous stones among the hard lava. The shock of this explosion was so violent that it disturbed many things I had left on my table, such as brushes for painting, &c. I dressed myself again, and remained in the balcony above an hour, during which time I had the pleasure of beholding Vesuvius in his terrific grandeur, and more awfully sublime than I had ever before seen him. The consul, Sir James Douglas, has just been observing to me that be never saw the mountain so agitated since the great eruption of 1779."

Between the end of the 18th century and the year 1822, the crater of Vesuvius had been gradually filled by the boiling up of lava and the crumbling down of the upper part of the cone. In place, therefore, of a regular cavity, was a rough and rocky surface covered with blocks of lava and scori . But this state of things was totally changed by the eruption of October, 1822, when the whole accumulated mass within the crater, together with a large part of the cone itself, was blown out, so as to leave an irregular gulf about three miles in circumference, when measured along the winding edge of its margin, but somewhat less than three-quarters of a mile in its largest diameter. The depth has been variously estimated, from 2000 feet to less than half that quantity. More than eight hundred feet of the cone were carried away during the eruption, so that the mountain was reduced in height from about 4200 to 3400 feet.

Vesuvius now consists of a double mountain, upon an extended base, from thirty to forty miles in circumference. Upon this stands the long ridge of Somma, so often mentioned, bending in the form of a crescent, with its convex side presented to the N.E., its points to the S.W. The western horn is separated by a deep valley from a lower mountain, called Cantaroni, which, inclining to the south, meets the lower projection, or terrace, called La Pedamentina. This is again separated by an excavated valley from the eastern horn of Somma. Between Somma and Vesuvius is the deep valley, called Atrio de' Cavalli, the Hall of Horses, and in the centre of the amphitheatre rises the cone Of Vesuvius itself, dark, sterile, and desolate; to the eye, a mass of loose scori and ashes, without order or coherence. This however on inspection is proved not to be the case. It consists of alternate layers of sand or ashes, scori , and lava, inclining outwards at an angle of from 45 to 30 with the axis of the cone. The strata of course are partial and irregular in extent and thickness, as circumstances have determined the fall of the ejected matter or the flow of the lava; but the irregularities of these numerous beds compensate for each other, and the general effect, on viewing the interior of the crater, is one of considerable order and regularity. Even the loose substances, falling together half melted, and continually acted on by the hot vapours which steam upwards in all parts of the cone, soon acquire a considerable degree of coherence; and the solidity of the whole is mainly assisted by dykes of solid lava, injected into the cracks of the mountain when the molten liquid has boiled up to its summit.