Without

entering into an examination of the difference of opinion existing between these philosophers, we shall give an extract from the works of Spallarzani, that fully illustrates this part of our subject; ‘* I shall,” he observes, “ now proceed to enquire what part this aériform vapour acts in the eruptions of volcanos. Where it exists in the depths of a volcanic crater, abundantly mixed with a liquid Java violently urged by sub« terrane an conflagrations, IT 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 le scale. [ placed on a gla 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 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 gla es and volcanic enamels, as also with a variety of cellular lavas, and always with the same succe .” aio 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 pa age, produce loud noises resembling thunder, and Jocal tremblings of the surrounding earth, besides forcing its way upwards through 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 matra es he used broke without noise, and without ejecting or scattering the substance, and particularly, as the escape of ga es has been frequently ascertained by the hi ing sounds attending eruptions; unfortunately, though those vapours offer themselves to examination, it would be impo ible 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 eruptions, by rushing at uncertain intervals, and from unknown causes, through the caverns of the earth, upon the eyer-enduring fires there existing; and this supposition is supported by the fact which has been repeatedly observed of the sudden retiring 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 vehement 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 dimensious had ' been ordered to be cast, at Modena, and preparations of the usual description were made under 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 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 volcauo, 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 ve el, on the introduction of water into a cavity made in it.” From what has been already said, a tolerable conception may be furmed 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 caunot help condemning him for the exercise of very daring temerity. The visit we allude to was made in 1788, when the appearauce 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 beight 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 crae ter, 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 hi ing noise; the fragments of lava were actually fluid during their progre , which was evident from their globular shape, and becoming hard before they fell upon the sides of the mountain, that form is preserved. “ 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 po ible 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 voleano, 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 yery short intervals between the eruptions. my great satisfaction, my expectations were completely fulfilled; I could here look down into the very bowels of the volcano, and truth and nature stood as it were unveiled before me.” Thus situated in probable safety, the intrepid Spallanzani saw the following wonders, The crater he found to be of a circular form, with edges composed of a chaos of sand, scoriz, and lava; and he imagined the circumference to be about three hundred and forty feet. Similar to all other craters, that of Stromboli a umes 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 descent appeared to be incrusted with yellow substances, which he supposed to be the muriat of ammonia (sal ammoniac) or sulphur, The pieces of scoriaceous lava, as they moved in the air, retained their red-hot appearance, though the sun shone clear; many of them came in contact during their progr , and, according to the degree of heat they po e ed, they adhered, or were broken. The smoke seemed. to be foreign to the lava, as none attended the fragments thrown in to the air, and that which escaped pa ed through fi ures, and at the Moment the lava burst. According to Spallan- Zani’s conjectures, crater may be. about twenty-five or thirty feet in depth, when the Java is raised to its greatest height, and upon its subsiding, forty or fifty, There are no visible marks of its ever having overflowed so as to descend like those of Zitna and Vesuvius. Though the ejections of the larger and heavier stones have short intermi ions, those of the le er. and lighter have scarcely any. Did not the eye perceive how those showers of stones originate, it would be supposed that they fell from the sky: the noise of the more violent eruptions, resembling that of thunder, and the darkne occasioned by the mounting cloud of smoke, pre- - sent the image of a tempest,” 175 176 177 178 179