Prince

Ca ano, a member of our Royal Society, produced an instance of the violent heat of the lava which i ued from Vesuvius to that learned body, which seems more to the purpose than that of the academicians: the torrent of lava alluded to approached a convent of Carmelites; every combustible article was immediately consumed, even before the ma came into contact with it; M. Bottis seems to have been one of the first maturalists, who observed rapidity with -which the. fire of\Vesuvius causes fusion; that gentleman mentions, in his description of the eruption of July 1779, that he saw a small hill, composed of porous iava and scorie, inclosing an inconsiderable gulph, that produced a noise like that of-oil or fat, in the act of boiling or simmering over a fire; this appear a nee induced him to examine it, when he found it contained matter in fusion, which immediately heated red hot, and then melted fragments of java or scori# thrown into it. As Spallanzani acknowledges that his efforts to melt similar substances required half an hour, we must admit, that this is another proof of the superior heat of volcanic fires. A still further evidence of their extreme heat is, the great length of time which lavas retain it. In the year 1737, some labourers were employed to remove the lava which had cro ed a road, and although a month had elapsed from the period of the eruption, they were compelled to desist, as the heat softened their tools beyond the po ibility of using them. Sir William Hamilton also found it very great, and dropping some pieces of wood into the fi ures of a ma , situated four miles from the volcano, they immediately took fire; but Spallanzani illustrated this fact more decidedly, by pa ing a body of lava near the upper crater of Atna, visibly red hot, even in full day-light, which had flowed from the mountain eleven months before. It is supposed that the voleanic fires of Iceland are very active and powerful, which is inferred from the incompetency of the blow-pipe to fuse the gla i uing from them. Vallisneri, scribing a new volcanic island, which rose from the sea in the year 1707, near San to rine, a erts, that the sea in its vicinity became so violently heated, that vast numbers of fish perished, and were actually boiled; and it is well known that the same cause melted the pitch in the seams of ships’ bottoms, and occasioned their leaking: _ this modern fact is corroborated on the authority of Strabo, who declares, that the sea was observed to boil for four days between Thera and The ras i a. The complete fluidity of lava is another convincing proof of the exce ive heat prevailing in the centre of volcanos. M. Bottis produces two instances, derived from Vesuvius in 1771 and 1776, which demonstrate that this fiery ma a umes a state of liquidity almost equal to water: the profe or mentions four hills to have arisen suddenly in the first case near the aperture ‘whence the lava proceeded, and from three of those in the shape of cones, i ued streams of the melted matter, exactly resembling fountains of water. During the eruption of the latter year, fresh lava, rushing from the crater, fell upon that — of 1771, and rebounding from it into the air, there congealed in various figures capriciously ~_ ramified, and terminating in thin sharp points like needles. A circumstance observed by sir William Hamilton, count de Wilzek, card mal Herzan, and the archduke Maximilian of Aus~ tri a, in the year 1775, seems to establish the fact, that the fluidity of the lava has been such in times,-as to separate into portions, which being thrown up from the crater, fell again near it in a state so soft, that a guide who a isted in conducting these illustrious visitors, perceiving a fragment, pa ed a stick through it, and presented it thus to the prince, who ordered both ‘to be deposited in his private museum; this, however, seldom occurs, at least the indefatigable Spallanzani never discovered these fragments flattened or indented, as if they had fallen on some hard substance when in the consistence of paste. With respect to the rapidity of its motion, this must greatly depend upon the quantity ejected, as well as the intensity of its heat: when an opportunity happens for attentive observation, the lava has been known to rise suddenly to the summit of the crater, and as suddenly overflowing its boundaries, rush down in various rivulets of fire; indeed Bottis compares it to ‘¢ a liquor which boils in a ve el, and rises and overflows the edges of that ve el from the violence of the heat.” The lava from Vesuvius, i uing in 1751, flowed over the space of twenty-eight palms in one minute; in 1754, it proceeded in two branch at the rate of thirty feet in forty-five seconds, and afterwards uniting, at thirty-three feet in fifty seconds: to these facts may be added the testimony of sir William Hamilton, who thought its velocity in 1765, equal to that of the Severn, at the pa age near Bristol. It may, however, be nece ary to observe, that the fluidity of the matter does not always alone occasion its motion, which may be accelerated by a great descent, © or the violent pre ure of fresh Java constantly i uing from the source, particularly as lavas are known to harden when actually moving, so as to produce a sound when struck, and to bear stones thrown on their surface; but to place this fact — el beyond a doubt, sir William Hamilton informs _ us, that himself and others, following the exam-_ ple of Mr. Jamineau, British consul at Naples, actually cro ed a moving ma above fifty feet in breadth; yet even thus circumstanced, those — dreadful rivers of fire have been known to reach ~ the sea eighteen, twenty, and even thirty miles — from their commencement. The arguments used to establish an idea that fires excited and maintained by human means exceed those of volcanic origin in force lie in a very small compa indeed; they are derived — from observing, that some furnaces “ vitrify lavas more decidedly than volcanos, and melt schorls which remain perfect in the former.” Dolomieu _ places this supposition in a clear point of view, in a memoir published by him of basaltes. “ I shall again repeat,” observes this celebrated French naturalist, “* what: cannot be teo frequently inculcated, that lavas not vitrifications; their fluidity is similar to that of metals reduced to fusion; it does not change the order and manner of being, of the constituent parts of the lava. When they cease flow, they resume, like metals, the grain, texture, and all the characters of their primitive base; effects which we cannot produce upon stones in our furnaces, since we know not how to soften them by fire, without changing the manner in which they are aggregated. The fire of volcanos has not that intensity ‘which is supposed, and produces its effects rather by the extension and duration of its action than by its activity.” Arguing upon these various facts, and remarks of his own, leading to the same point, Spallanzani candidly acknowledges, that he had been more than once inclined to believe, that our fires po e ed more energy than those of volcanos; a number of experiments, however, induced him to say that ‘ these facts prove, first, that it is not always true that volcanic fires are insufficient for the fusion of schorls; secondly, by the vitrification of the garnets, they confitm the powerful activity of those fires; thirdly, that those fires operate in ‘@ manner in some measure unknown to us; since, at the same time that they vitrify the garnets, they leave the base in which they are included in a state perfectly recognizable, notwithstanding that the former are refractory to the fire of the furnace, while the latter is easily fusible.”. It has been a generally received a ertion, that volcanos emit flame during eruption, and that flowing lavas are attended by the same accompaniment of fire; this supposition is erroneous, as may be proved by referring to the works of Serao, father Torre, Bottis, and sir William Hamilton, all of whom will be found to have omitted the observation of flames. The first expre ly says of, the lavas of Vesuvius, “ that when seen by night, at any distance, they emit a light, not shining, like a bright flame, but of a dead kind, like that of red-hot substances which burn without flame;” and the last mentions, that he has “ observed upon mount Vesuvius, that soon after a Java has borne down and burned a tree, a bright flame i ues from its surface; otherwise I have never seen any flame attending an eruption:”’ adding, that the light reflected on the smoke, as it riseS from the crater, by the raging of the fire in the gulph beneath, is frequently mistaken for flame. Spallanzani confirms the opinion of these accurate observers, and declares he never saw flame in, or proceeding from, any of the craters he examined. Faujas thought it not improbable that fire ‘united with water may produce some of those combinations of which we know not the origin; he says on this subject, “I almost incline to be of opinion, that the aqueous fluid, raised to a degree of ebullition and incandescence, of which our feeble furnaces can give us no idea, sometimes concurs with the inactive and concentrated fire which exists in the immense volcanic caverns, and that from this concurrence results a multitude of combinations hitherto unknown.to us, which take effect on the stones and earths that remain perhaps whole ages in these burning gu!phs, where the fire, intent to destroy, has ‘for. its adversary the water, which ince antly creates and opposes to it all the forms and modifications of which the matter is susceptible.” It will now be nece ary to mention some of the effects of ga in the operations of these fierce internal fires! it is well known that their violent