The crater he found to be of a circular form, with edges composed of a chaos of sand, scoria, and lava; and he imagined the circumference to be about three hun dred and forty feet. Similar to all other craters, that of Stromboli assumes the shape of a truncated inverted cone, the sides of which, from east to south, were gently inclined, but the remainder very steep. Many parts of this internal de scent appeared to be incrusted with yellow substances, which he supposed to be the muriate of ammonia (sal ammoniac) or sulphur.
Fluid lava, resembling melted brass, red-hot, and liquid, filled the crater to a certain height, and this matter appeared to be influenced by two distinct impelling ' powers, the one whirling and agitated, and the other upwards ; at times it rose rapid ly, and when the surface had reached within thirty feet of the edges of the cra ter, an explosion took place like a short clap of thunder, and -at the same instant a portion of the lava. was hurled with in conceivable swiftness into the air, which was as instantaneously separated into nu. merous fragments, and those were accom panied by a copious discharge of sand, ashes and smoke. Immediately before the eruption occurred, the lava appear ed inflated, and large bubbles, some se veral feet in diameter, rose and burst, the detonation followed, and the lava sunk, till a repetition of this operation was com menced; during the rising, a sound issu ed from the crater like that produced by a liquid boiling violently in a cauldron. Many of the eruptions were so inconside.
• rahle, that their effect could not be visible at a small distance from the mountain ; in - those the fragments constantly fell back into the guiph,. with a sound, on their collision wall the great mass of natter, similar to that produced by water when forcibly struck with flat staves : in the greater explosions, many of the pieces t e turned into the crater, some falling on the sides and rolling dos but many descend ed a precipice, formed by one side of the mountain, to the sea.
The pieces of scoriaceous lava as they moved in the air, retained their red.hot ap pearance, though the sun shone clear; many of them came in contact during their progress, and, according to the degree of heat they possessed, they adhered or were broken. The smoke seemed to be foieign to the lava, as none attended the frag ments thrown into the air, and that which escaped passed through fissures, and at the moment the lava burst. According to Spallanzani's conjectures, the crater may be about twenty-five or thirty feet in depth, when the lava is raised to its great. est height, and upon its subsiding, forty or fifty. There are no visible marks of its ever having overflowed so as to de scend like those of /Etna and Vesuvius.
" Though the ejections of the larger and heavier stones have- short intermix. sions, those of the lesser and lighter have scarcely any. Did not the eye perceive how those showers of stones originate, it would be supposed that they fell /'runt the sky : the noise of the more violent erup. tions, resembling that of thunder, and the darkness occasioned by the mounting cloud of smoke, present the image of a tempest.
• While this naturalist was employed in intense observation, the eruption suddenly ceased, the lava sunk to a greater depth than usual, and remained thus depressed ; the fierce light subsided, and at the same instant the various streams of smoke, is. suing before silently from the apertures west of the crater, began to rush forth with a loud hissing noise, and the aper tures to shine with a bright colour of fire. " I know nothing," says Spallanzani, " to which the sound produced by the issuing of these fumes can be more properly com pared than the blowing of large bellows in. to a furnace by which metals are melted ; such as I have seen at Zalatna, in Transyl. vania, and Schemnitz and Kremnitz, in Hungary, except that those volcanic bel lows roared a hundred times louder, and almost deafened the ear." We cannot conclude this article more properly than by giving an account of the crater of 'Etna, as it was examined by the above author, to which he ascended with equal danger and difficulty, and where he was compelled to sit nearly two hours ere he could commence his observations : he then says, " I viewed with astonishment the configuration of the borders, the in ternal sides, the form of the immense ca vern, its bottom, an aperture which ap peared in it, the melted matter which boil ed within, and the smoke which ascended from it. The whole of this stupendous scene was distinctly displayed before me; and I shall now proceed to give some de scription of it, though it will only be possi ble to present the reader with a very feeble image, as the sight alone can enable him to form ideas at all adequate to objects so grand and astonishing. The upper edges
of the crater, to judge by the eye, are about a mile and a half in circuit, and form an oval, the longest diameter of which extends from east to west. As the are in several places broken, and Cr' mbled away in large fragments, they 'appear as it were indented, and these in dentations are a kind of enormous steps, formed of projecting lavas and scoriae. The internal sides of the cavern, or crater, are inclined in different angles in different places: " on the west the inclination is gentle ; on the north the steepness increa ses ; and from this point to the south east the descent becomes more sudden, till, where the observer stood, they were al most perpendicular. The funnel,shape, however, still prevails, as in every other instance, and the surface was extremely rugged, and strewed with concretions of an orange colour, which proved to be the mu riate of ammonia ; and it is very probable that the numerous stripes of yellow on the nearly horizontal plain at the bottom may be the same substance. " In this plain, from the place where I stood, a cir cular aperture was visible, apparently about five poles in diameter, from which issued the larger column of smoke, which I had seen before I arrived at the summit /Etna. 1 shall not mention several streams of smoke which arose like thin clouds from the same bottom, and differ ent places in the sides. The principal column, which, at its origin, might be about twenty feet in diameter, ascended ra pidly in a perpendicular direction while it was within the crater; but when it had ri sen above the edges inclined towards the west from the action of a light wind ; and when it had risen higher, dilated into an extended but thin volume. This smoke was white, and being impelled to the side opposite to that on which 1 was, did not prevent my seeing within the aperture ; in which, I can affirm, I very distinctly per:. ceived a liquid ignited matter, which c.m tinually undulated, boiled,- and rose and fell, without spreading over the bottom. This certainly was the melted lava, which had arisen to that aperture from the bottom of the Xtnean gulph." Being favourably situated for observing the effects of external violence on the li quid matter within the aperture, the abbe rolled large fragments of lava down the side, which, entering the' opening, pro duced a sound resembling the sudden immersion of a heavy substance in a thick tenaceous paste. In performing this ex periment, the effect was multiplied by the stones loosening others in their pas sage, some of which fell on the plane ; those rebounding, even when very large, caused a sound extremely different from the others that struck the liquid lava : this circumstance proves, that, though the bottom may be a comparatively thin covering of the gulph, it is capable of great resistance. 'We shall proceed with a short notice of in the moon. As the moon has on its surface , mountains and valleys in common with the earth, some modern astronomers have discovered a still great er similarity, vi:. that some of these are really volcanoes, emitting fire as those on earth do. An appearance of this kind was discovered some years ago by Don Ulloa in an eclipse of the sun. It was a small bright spot, like a star, near the margin of the moon, and which he at that time supposed to have been a hole, with the sun's light shining through it. .Suc ceeding observations, however, have in duced astronomers to attribute appear ances of this kind to the eruption of vol canic fire ; and Dr. Herschel has particu larly observed several eruptions of the lunar volcanoes, the last of which he gives an account of in the Philosophical Trans actions for 1787. "April 19, 10" 36.., sidereal time. I perceive (says lie) three volcanoes in different places of the dark part of the new moon. Two of them are either already nearly extinct, or other wise in a state of going to break out ; which perhaps may be decided next lunation. The third shows an actual eruption of fire or luminous matter. I measured the distance of the crater from the northern limb of the moon, and found it 3' 57.3": its light is much brighter than the nucleus of the comet which M. Mechain discovered at Paris the 10th of this month.