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The following are Dr. Antisels views respecting the cause of volcanoes, which we promised to present three weeks ago but which we have not been able to do before now. After referring in advance to the internal heat of the earth, the lecturer observed that volcanoes were nothing more nor less than so many vents through which the contents of the interior ol the earth were passed to the outside. There are about 270 of these vents active, though all of them are not in operation at the same time. One hundred and sixteen of them are on this Continent. Some ninety of them are in the Pacific, and the remainder are scattered over Europe and the islands of the Indian Seas, Sumatra, Java, &c, and along the islands of the Chinese coast. Volcanoes, in fact, are scattered all over the globe from the furthest north to the extreme south.— Those within the tropics, however, outnumber the others. There are about twenty volcanoes in action every year, so we have 250 of them quiescent—their action appears reciprocal, as one became silent another comes into operation. The lecturer pointed out upon diagrams the general features of the volcanic system, and went on to speak of the enormous amount of matter upheaved from the bosom of the earth by the force of volcanic action. Thus, in the eruption of Etna, 1659, the quantity of lava thrown out was twelve times the mass ol the entire mountain itself. Vesuvius in 1780 emitted a stream of lava nine miles in length ; and in 1805 a stream some three miles long and forty feet deep. In the year 69 an eruption of the same mountain utterly overwhelmed the cities of Hercu-laneum and Pompeii, as most know. These eruptions from time to time made in the appearance and configuration of the surface or the earth vast changes, as might naturally be expected. Dr. A. then went into a minute detail of the peculiarities of phenomena attending eruptions, and described in a graphic manner the terrific sublimity ot the celebrated volcano of Kiranca, in the Island of Owy-hee, and touched upon, in this part of his lecture, the difference which the Vesuvius of the present day presents when compared with that of the time of Strabo. This part of the subject was very intelligibly illustrated by several spirited diagrams. With regard to the source of the heat which occasioned the throwing out of such vast quantities of matter trona volcanoes, there were many hypotheses advanced; but only two of them were tenable. The idea advanced by Sir Humphrey Davy was that the centre of the earth was composed of metals in a pure state, which, when coming in contact with water, evolved an expansive gas, and so produced earthquakes and volcanoes. The mere probable theory, observed Dr. A., was this:—Our earth derived its heat from the action of the suns rays upon it only. The action of the suns rays was to produce an electrical current. When this current passed along a body that conducted well, no result was observable, but if we placed at the end ot the wire a nonconductor—a charcoal point for instance—intense heat was the result. Tlie suns rays then passing through the atmosphere produced electrical currents which passing into the earth ignited the interior like the charcoal point. This he considered the most reasonable mode ot accounting for the discharge of igneous masses through volcanoes. Were the earth heated interiorily by artificial means— as suggested by Davy—it might readily be supposed it would soon cool, seeing that its interior was exposed in 270 places, or the masses within would be consumed like coal by the ordinary mode of combustion. Though much destruction of life and property and many lesser evils resulted from the development of volcanic phenomena, yet they were not unattended by many advantages. Were it not for earthquakes, the land would not rise above the level of the sea. If it were otherwise we would have no dry land distinctively—no hills, consequently no rains, no rivers—of course no navigation, and i everything ultimate would be reduced to one great horizontal surtace—in fine, chaos would be once more produced. Volcanic eruptions in themselves were beneficial. They throw within the reach of the hand of man copper, and silver, and platinum. Note for instance the vast quantities of copper found in the volcanic basalt on the shores of Lake Superior. Our porphyry, marbles, and finer descriptions of stone were all the result of volcanic action, and he need not add, that to the same origin we owed the exposure of that most valuable and deservedly prized of minerals—coal.
