inclined to think, must have been attended with a corresponding depression of the earth's general surface, or of the part immediately in connection with the vent. But so far from finding depression the rule, we find that elevation of land precedes, accompanies, and succeeds volcanic action; and that, when depression does take place, it takes place slowly, and at a considerable distance of time. The phenomena suggests to us the idea, not of a fountain, but of the overboiling of some pot containing a dense material, when air separating the particles, gives the appearance of a vast increase in size and quantity. That the comparison between the lava stream and an overboiling pot is not simply a flight of fancy may readily be seen by any one who considers the phenomena presented by both. Let us fill a large pot, or a long tube, with rosin, or some other dense material capable of undergoing gaseous decomposition by heat; we will apply our heat suddenly; the result will be that a layer of the material is first melted, the upper portion of which imparts its heat to the cool part above, while the lower is converted into gaseous vapour, and thus being increased immensely and suddenly in size, drives up the whole mass and makes its escape. Here we have in petto the phenomenon of the earthquake which precedes for a long time the eruption. The same process continues until the whole mass is heated thoroughly, and in a state of ebullition. Gaseous products still continue to be formed, and explode when they reach the surface; others, retained by the cloggy matter, are diffused through the whole, making it porous as bread, a phenomenon repeated on a large scale by the rise of the coast of Misenum, prior to the eruption of Monte Nuova. As the heat continues or increases, ebullition goes on more furiously; the material is decomposed into its gaseous elements with greater intensity; they detonate more loudly as they are nearer the surface; the mass, swelled to greater dimensions by the increasing size of the bubbles enclosed within, and by the diminished pressure to which they are subjected, at length boils over, and continues to do so as long as there is material in the pot and heat in the fire. When we examine the rosin that has boiled over we find it equally porous with lava and pumice; and thus it is we see that the real is not equal to the apparent increase of bulk. By and by the fluid cools; the heated gases diminish in volume; the whole material contracts, and the substance remaining in the pot is seen diminished in size. This is nothing more than analogous to the depression of soil which takes place after the eruption of a volcano has passed, and the heated matter has had time to cool, which it does slowly. The chymical hypothesis having received this much negative evidence in its favour, let us examine into the positive evidences that support it. In so doing we must necessarily be brief, as it would be impossible in a short paper to treat the subject with the detail a strict proof demands. First, all the phenomena we have noticed, i. e. the expulsion of boiling water, of steam, of mud, of carbonic, muriatic, and sulphuric acids, the presence of electric sparks, all tend to show that volcanic eruptions are attended by occurrences on a large scale similar to those that take place in the laboratory during chymical decompositions on a small scale. Second, that the detonations which are incompatible with the idea of a flow through a vent of some central fluid fire are quite compatible with the hypothesis that they arise from the explosion of gases. Hydrogen and oxygen coming together and being ignited, will, by their explosive power, produce an earthquake shock; and, by their united product being water, there will be a reaction, and return to the original condition. In this we can see an explanation of the back-stroke of the earthquake wave. The development of carburetted hydrogen would have a similar result. The presence of water would increase the bulk of the material; but as the mass gets hotter, the water, which in the first instance probably began the chymical change, would be converted into steam, and its pressure gradually increasing would at last burst the boiler with a terrific explosion. As the steam gets free vent the explosion would cease, just as we find that it does. Again, we find evidence of the action being near the surface, and of its being greatly increased by rain. We find, from the accumulated observations of the past, that a drying up of the wells, i. e., a large absorption of water in the lower strata, is a common precursor of volcanic eruptions. We find that most active volcanoes are situated near large accumulations of water. We find that they all abound in sulphur and other elementary substances, which we know will unite together in the laboratory with the extrication of light, heat, and inflammable and explosive gas. We know that those unions are favoured by moisture. We know that the thermal springs in the volcanic districts contain commonly some of the combinations of sulphur. We have seen phenomena elsewhere of a similar nature to those we are seeking to explain. Thus, for example, on the west coast of Ireland, we read of a cliff having fallen which contained a large quantity of sulphuret of iron. This exposed a new surface to the waves; chymical action was set up; the rock shortly became red-hot, and as the waters of the Atlantic dashed against it, abundance of steam was generated, which produced a sound not unlike that of the explosion of cannons, or distant thunder. The self-ignition of coals containing pyrites, and the rapid heating of sulphur and iron, when both are in powder and in contact with each other and moist, have long been known. There being, then, all the ingredients present in volcanic regions necessary for chymical action, what is there to object against the theory? Nothing but the persistent nature of the operations in some parts, and its intermitting nature in others. To answer this, we can ouly point to many vast volcanoes, to show that the fires have burnt out entirely, and that there is reason to believe that others will do so too. One other objection may be started, viz. that the evidence of the telescope shows us that there are volcanoes of huge size in the moon; and as everything tends to prove that no water does or can exist in our satellite, it is reasonable to conclude that water has not the influence in producing volcanic action which we have given it credit for. This argument is one of considerable force, but is easily met by the assertion that there are not, and there is no proof that there ever were, volcanoes in the moon, and that what have been considered as hugh craters and burning mountains have no analogy with real ones on the earth. They have much more the character assumed by bubbles which have burst at the surface of a boiling mass, and have been instantly cooled. But as this has nothing to do with the subject of our paper, we must not continue the speculation. The chymical theory of the volcanic action certainly appears, at the present time, to explain the phenomena better than any other; and it is not without wonder that we contemplate the fact that such vast fires as have existed, and still smoulder extensively, have been kindled by the operation of water. The American who, when standing on the mountain, watching the eruption of liquid lava from Vesuvius, remarked that they had in their country a waterfall that would put out the fire in five minutes, evidently had no notion that those very fires had been produced by some internal cataract, deluging a bed of pyrites, or similar formation. The wonders of creation are infinite, and not the least of them is the that kindles the earth into a flame by the same element which man employs to destroy it when produced. power An animated discussion followed, in which the views of the President were strongly opposed by holders of the other theory. DONATIONS, FROM JUNE, 1856, TO JUNE, 1857. 1856, Oct. 20.-From the Society.-Notices of the Royal Astronomical Society, Vol. 16, No. 8, and Drawing of Saturn. From the Institution.-Notices of the Royal Institution of Great Britain, 1855-56, Part 6. From the Society.-Proceedings of the Linnean Society, 1856, Vol. 1, Part 2. From the Society.-Proceedings of the Royal Society From the Society.-Journal of Geological Society of From the Society.-Report of the Proceedings of the From the Society.-Report of the Leeds Philosophical From the Society.-Twenty-third Report of the Royal From the Society.-Transactions of the Historic Society From the Society.-Transactions of the Polytechnic From the Society.-Proceedings of the Philomathic October 29.-From the Author.-Liverpool, as it was during the Last Quarter of the Eighteenth Century, 1775 From the Society.-Notices of the Royal Astronomical 1856, Oct. 29. From the Society.-Proceedings of the Linnean Society, Vol. 1, Part 3. Nov. 17. From the Author.-Disorders of the Stomach. By James Turnbull, M.D. Dec. 1. From the Society. Journal of the Geological Society From the Society.-Memoirs of the Literary and From the Society.-Proceedings of the Belfast Natural From the Committee.-Eighth Annual Report, and From the Society. Journal of the Dublin Natural From the Society.-Notices of the Royal Astronomical 1857, Jan. 12.-From the same.-Ib. No. 2. From Dr. Hume.-Reports of the Royal Society of 26. From the Author.-Table Talk of Olden Times. By Feb. 9. From the Society.-Notices of the Royal Astronomical Society, Vol. 17, Part 3. From the Society.—Journal of the Dublin Geological Society, Vols. 1 (first part wanting), 2, 3, 4, and 5. 23. From the Society.-Proceedings of the Zoological April 20.-From the Society.-Notices of the Royal Astronomical From the Author.-Statistical Details respecting the From the Society.-Transactions of the Liverpool |