depth, the other fifteen. They were shaped like an inverted cone, and the matter with which they were covered was similar to the rest of the surface, but they emitted neither smoke nor heat.

The ascent of our adventurers was accomplished with more difficulty, though perhaps with less danger, than the descent. It also occupied a greater space of time; for they could only ascend one at a time after considerable intervals, for fear of burying, under torrents of dust and volcanic matters, those who immediately succeeded.

Both the inside of the crater and the base of many volcanos consist of lava, either entire or decomposed nearly as low as the level of the sea; but they finally rest either on granite, as in Peru, or schistus, as the extinguished volcanos of Hesse and Bohemia, or on limestone, as those of Silesia, mount Vesuvius, &c. No ore is found in these mountains, except that of iron, of which lava contains from twenty to twenty-five parts in the hundred, and some detached fragments of the ores of copper, antimony, and arsenic. Vesuvius ejected, from the year 1779 to 1783 309,658,161, cubic feet of matter of different kinds; we must therefore conclude the seat of these fires to be several miles below the level of the sea; and as iron makes from one-fourth to one-fifth of these ejections, we may infer that the internal parts of the earth abound much in this metal.

One of the best, as well as of the most modern, writers upon this subject is the abbe Spallanzani. In the course of a variety of interesting enquiries upon the spot, he examined minutely into the nature of the gasses poured forth; and observed that the stony substances thrown forth are invariably, when completely heated by the subterraneous fire, rarified, inflated, and rendered cellular, by their elasticity, an effect which is observable in numbers of lavas, glasses, and enamels, ejected during eruptions: and he discovered, in addition, that their violence continually raised the liquified matter from the interior of the craters to their very borders, over which it flowed at each impulse.

He was, at the same time, equally attentive to the nature and force of the fire which acts in the bowels of volcanic mountains; and, in the course of his researches, discovered that the immense mountains of Vesuvius, Ætna, the Eolian Islands, and Ischia, are composed of rocks that have been liquified, and even vitrified, by the violence of the subterraneous conflagration. "What fire," he exclaims, "can we produce equivalent to these effects!" Humble, however, as all experiments appear with our limited means, this venerable philosopher justly thought imperfect knowledge of volcanos preferable to contented ignorance, and, undismayed by the magnitude of the object, proceeded to ascertain, as far as possible, what man is permitted to know on this terrific subject. "I have," he observes, "discovered, that the fire of the glass-furnace will completely refuse the vitrifications, enamels, pumices, scoriæ, and lavas, of these and other volcanic countries. The same will, in like manner, vitrify rocks congenerous to those from which these mountains have originated, by the means of subterranean conflagrations. A less intense fire, on the contrary, produces no such effect on any of these substances. Determined to exercise the most rigorous research, and to ascertain, with the greatest possible precision,the exact degree of heat

requisite to produce the above effects, he had recourse to the pyrometer of Wedgwood, which he compliments and praises by saying, nothing could be better adapted for his purpose.

The terrific appearance of a volcano in eruption is so appalling, so grand, and altogether so wonderful, that it is by no means astonishing the world should suppose the vast volumes of smoke, ignited matter, and stones, hurled into the air with inconceivable violence and rapidity, exciusive of the torrents of liquified substances wich roll down its sides in solemn and destructive majesty, were caused by more powerful fires than those man has been permitted to kindle; in saying the world, we wish to be understood as meaning those who have seen or read of eruptions without examining the subject further. Of natural philosophers, there were many who coincided with this general opinion; and others have maintained the direct contrary supposition, asserting that volcanic fires are extremely feeble in their operations: following the example of Spallanzani, we shall give the substance of the arguments of each, in order that the reader may draw his own conclusion. It is evident that we must have recourse to the same rule for ascertaining the intensity of volcanic fires which we make use of in measuring the effects of our fires when in activity on bodies immersed in them; and we have already mentioned, that Wedgwood's pyrometer answers for the purpose, as nearly as the nature of the pursuit will permit; but long before the invention of this instrument attempts were made to attain the object in question, particularly by the academicians of Naples, who at the time of the great eruption, in the year 1737, made an experiment on the lava near the Torre del Greco, in a valley where it had accumulated; and though it had ceased its motion several days, yet retained a beat equal to that of red-hot iron. They formed a piece of lead weighing two ounces, in a conical shape, which they placed on the red-hot surface of the lava; the metal became soft in two minutes and a half, and in one minute more it was completely melted: another piece of lead, in every respect exactly similar, was then deposited on a plate of red-hot iron rendered so by burning coals beneath it, when they found that it required six minutes and a half to soften, and seven and a half to liquify it. Water placed on the lava boiled furiously in three minutes, and on burning coals, one minute later. Judging from these facts, the academicians concluded that lava, though exposed to the external air for some days, and consequently far less intensely heated than when first issuing from the crater, was much more fiery in its nature than red hot iron or burning coals: but this conclusion is obviously incorrect; because the plate of iron, being surrounded by air, could not acquire all the heat which was applied to it; neither was it fair to rest an opinion of this description upon a result produced by a means so unequal, as a vast depth of ignited matter opposed to a thin plate of iron.

Prince Cassano, a member of our Royal Society, produced an instance of the violent heat of the lava which issued 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 mass came into contact with it;

and the heat was so excessive, that the glasses standing upon a table in the refectory were instantly reduced to shapeless pieces of that useful material: this circumstance produced an experiment, attended with the same consequences, which was the fastening of a fragment of glass to the end of a long stick, and holding it near the lava, when, at the close of four minutes, it became a mere paste. A fact of the same nature is mentioned by professor Bottis, in bis account of the eruption of Vesuvius, in the year 1667. Now, though this effect may be produced by suspending a piece of glass in the air of a glass furnace, it must be admitted, that this being in a state of full activity, and the heat excited to the utmost by every human means, is not a just comparison with a body of lava far removed from the spot where it acquired its heat, which must, without doubt, be at that spot ten times greater; hence it appears decidedly clear, that the internal fire of Vesuvius far exceeds that of our glass-furnaces.

M. Bottis seems to have been one of the first naturalists, who observed the 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 lava and scoriæ, 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 appearance induced him to examine it, when he found it contained matter in fusion, which immediately heated red hot, and then melted fragments of lava or scoria 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 crossed 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 possibility of using them. Sir William Hamilton also found it very great, and dropping some pieces of wood into the fissures of a mass, situated four miles from the volcano, they immediately took fire; but SpallanZani illustrated this fact more decidedly, by passing a body of lava near the upper crater of Ætna, visibly red hot, even in full day-light, which had flowed from the mountain eleven months before.

It is supposed that the volcanic fires of Iceland are very active and powerful, which is inferred from the incompetency of the blow-pipe to fuse the glass issuing from them. Vallisneri, describing a new volcanic island, which rose from the sea in the year 1707, near Santorine, asserts, 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 observ. ed to boil for four days between Thera and Therasia. The complete fluidity of lava is another convincing proof of the excessive heat prevailing in the centre of volcanos. M. Bottis produces two instances, derived from Vesuvius in 1771 and 1776, which demonstrate that this fiery mass assumes a state of liquidity almost equal to water: the professor 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, issued 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 nal Herzan, and the archduke Maximilian of Austria, 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 assisted in conducting these illustrious visitors, perceiving a fragment, passed 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 vessel, and rises and overflows the edges of that vessel from the violence of the heat." The lava from Vesuvius, issuing in 1751, flowed over the space of twenty-eight palms in one minute; in 1754, it proceeded in two branchat 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 passage near Bristol. It may, however, be necessary 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 pressure of fresh lava constantly issuing 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 beyond a doubt, sir William Hamilton informs us, that himself and others, following the example of Mr. Jamineau, British consul at Naples, actually crossed a moving mass 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 compass 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 too frequently inculcated, that lavas are 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 to 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 possessed 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 confirm the powerful activity of those fires; thirdly, that those fires operate in a 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 assertion, 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 expressly 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 issues 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 gulphs, where the fire, intent to destroy, has for its adversary the water, which incessantly creates and opposes to it all the forms and modifications of which the matter is susceptible."

It will now be necessary to mention some of the effects of gass in the operations of these fierce internal fires: it is well known that their violent efforts to reach the surface of the liquified masses contained in craters causes it to rise suddenly

from the bottom, completely filling their whole circumference, and at length forcing it over the sides in destructive streams, which overwhelm in their passage every object, either natural or artificial. Spallanzani made ten distinct experiments, in order to obtain some idea of the nature and effects of gass as exhibited by volcanos; for this purpose he made use of different lavas, enamels, and glasses, ejected from them, and the consequence was, a couviction that the bubbles and inflations of various dimensions, observable in these substances, are not produced by the action of any permanent gass, "but by that of an aeriform fluid, produced by the excessive attenuation of those same products in consequence of heat." Dr. Priestley made similar experiments, which differed in some degree from those related by the above celebrated Italian naturalist. The doctor fused 4 ounces of lava from Ireland in a sand-stone retort, and obtained twenty measures of air, half of which, at the commencement of the process, was carbonic acid gass, and the remainder, in purity 1.72, extinguished a candle; between the interstices of this lava was a sand, which the operator could not separate from it. Five ounces and a half of Vesuvian lava produced thirty measures of air, with a slight appearance of carbonic acid gass, the rest was azotic gass, from the degree 1.64 to 1.38, with respect to what came last. On cooling, the residue broke the retort by its excessive inflation.

Without entering into an examination of the difference of opinion existing between these philosophers, we shall give an extract from the works of Spallanzani, that fully illustrates this part of our subject; "I shall," he observes, " now proceed to enquire what part this aëriform vapour acts in the eruptions of volcanos. Where it exists in the depths of a volcanic crater, abundantly mixed with a liquid lava violently urged by subterranean conflagrations, I can easily conceive, that by its energetic force it may raise the lava to the top of the crater, and compel it to flow over the sides and form a current. Art can imitate this grand operation of nature on an infinitely less scale. I placed on a glass furnace a cylindrical crucible, one foot high, and two inches and a half in breadth, which I filled half full with one of those volcanic products which most inflate and boil in the fire. After some hours, I observed that the liquid matter began slowly to rise, and afterwards to rise higher, until it at last overflowed the edges of the crucible, forming small streams down its sides, which, when they reached the plane on which the crucible stood, gave origin to small currents, if that plane was at all inclined. When I put more of the same product into the crucible, the currents became larger. If the plane was then taken from the surface, and the small currents, thus produced, examined, they were found full of minute bubbles, as was likewise the matter which remained in the crucible. This curious experiment I made with several glasses and volcanic enamels, as also with a variety of cellular lavas, and always with the same suc'cess."

Judging from the result of the above trial, it cannot be doubted that a similar elastic vapour, collecting in vast quantities under the surface of the earth, must, upon meeting with resistance in its passage, produce loud noises resembling thunder, and local tremblings of the surrounding earth, besides forcing its way upwards throngh super-incumbent lava: other experiments, made

by Spallanzani, however, seem to prove that it must be another cause which expels the fiery matter with violence out of craters, as the matrasses he used broke without noise, and without ejecting or scattering the substance, and particularly, as the escape of gasses has been frequently ascertained by the hissing sounds attending eruptions; unfortunately, though those vapours offer themselves to examination, it would be impossible to collect any part of them without exposing the life of the experimentalist to almost certain destruction, we must therefore admit their existence, and conjecture must supply the

rest.

It will be recollected that all volcanos, at present in a state of activity, are surrounded by, or situated very near, the sea; hence it appears clear, that the agency of that body is extremely powerful in promoting the violence of their cruptions, by rushing at uncertain intervals, and from unknown causes, through the caverns of the earth, upon the ever-enduring fires there existing; and this supposition is supported by the fact which has been repeatedly observed of the sudden retir ing of the sea immediately preceding a violent explosion from a crater, the certain consequence of a rapid diminution of water on the shore. Little need be urged to prove the immediate and vebement separation that takes place upon the collision of fire and water, and of the force of steam thus produced; one instance, however, may be safely cited, which will place this supposed collision in a true light, and is extracted from the fourth volume of the Memoirs of the Academy at Bologna. A bell of enormous dimensions had been ordered to be cast, at Modena, and preparations of the usual description were made uuder a spacious portico. After the metal had been completely melted, it was led into the mould, situated at a small depth under the pavement, through a small channel; the burning fluid had no sooner entered the mould than a dreadful explosion took place, which resembled in every particular the horrid effects of springing a mine; a deep hole was sunk in the earth, the metal, the mould, and every material of the portico above it, were scattered in the air, and several persons were killed and severely wounded: if such were the immediate consequences of a trifling degree of moisture remaining in the sand which composed the mould, it may be naturally inferred, that a body of water, meeting with subterraneous fires, is capable of producing eruptions and earthquakes. It seems, however, extremely probable from experiments, that this effect principally arises from the insinuation of water under or below the surface of the sides of those fires, as it has been ascertained that water thrown upon fire evaporates without much violence, and yet if the vapour thus generated is confined by superincumbent earth, or rocks, its struggles for a vent must occasion the violent disruption of those parts; the event is different on pouring water on melted tin, which is the only metal that is separated by this means so as to render it a dangerous operation to the experimentalist,

Spallanzani concludes many curious and interesting observations derived from experience,by remarking, "from this series of experiments I think we are authorised to conclude, that when a quantity of water falls on the burning crater of a volcano, it has not the power of producing explosions; but that the latter on the contrary are very violent when the water penetrating below,

reaches the conflagration; when suddenly reduced to vapour by the heat, it finds no room for its dilatation; or when it insinuates itself laterally among the liquified matters; of which we have a satisfactory proof in the explosion of the lava violently forced from the containing vessel, on the introduction of water into a cavity made in it."

From what has been already said, a tolerable conception may be formed of the probable causes of volcanic eruptions. It now remains for us to add a concise narrative of their visible phenomena, and for this purpose we find ample materials furnished by Spallanzani, whose ascent of Stromboli deserves every praise for its courage, though we cannot help condemning him for the exercise of very daring temerity. The visit we allude to was made in 1788, when the appearance of the mountain was bifurcated, and the crater situated at some distance from the summits, from both of which the operations within it are distinctly visible, and from those the height of the ejections may be ascertained, with tolerable accuracy. During violent internal agitation the matter appears to ascend half a mile and more, but when the mountain is in actual eruption, the scattered fragments prove, that the impelling force is very greatly increased. After having attentively examined the crater from the summit above alluded to, Spallanzani approached the crater, where he found that the explosions succeeded each other so rapidly, that they might almost be said to occur without any intervals of quiet, but they varied in their force; the matter, in some instances, not rising more than fifty feet, and falling again into the crater, and in others it was elevated half a mile; the sounds, consequently, are proportionably loud, or the reverse, and resemble a hissing noise; the fragments of lava were actually fluid during their progress, which was evident from their globular shape, and becoming hard before they fell upon the sides of the mountain, that form is preserved.

The exbalations exhibited a thick cloud several miles in extent, which were strongly impregnated with sulphur; this cloud was impenetrable by the beams of the sun, and appeared very black in the mitist, but white on the edges, and was, in all probability, a mile in depth. The vapour thus floating from the mountain was derived from three distinct sources, though doubtlessly produced by the same cause in the first instance: when an ejection of lava took place, it was always accompanied by a cloud of grey smoke from the crater; to the west of that spot were a number of obscure apertures, each of which sent forth a volume of similar vapour, and to the east, a fast caveru emitted a column at least twelve feet in diameter, extremely black and dense.

"Not satisfied with the observations I had already made," observes Spallanzani," my curiosity impelled me to attempt further discoveries. From the pointed rock on which I stood, I could only see the edges of the inside of the crater, I considered, therefore, whether it might not be possible to obtain a sight of the lower parts likewise; and, looking round me, I perceived a small cavern hollowed in the rock, very near the gulph of the volcano, into which the rock above prevented the entrance of any burning stones, should they be thrown so far. It was likewise so elevated, that from it the crater was open to my view. I therefore hastened to take my station in this cavity, taking advantage of one of the very short intervals between the eruptions. To