There is an explanation of this presence of water and various gases in the masses of molten rock-materials within the earth's crust which at once suggests itself, and which was formerly very generally accepted. Volcanoes, as we have seen, are usually situated near coast-lines, and if we imagine fissures to be produced by which sea-water finds access to masses of incandescent rock-materials, then we can regard volcanic outbursts as resulting from this meeting of water with rock-masses in a highly healed condition. This supposition has been thought to receive much support from the fact that many of the gases evolved from volcanic vents are such as would be produced by the decomposition of substances present in sea-water. But it frequently happens that an explanation which at first sight appears to be very simple and obvious, turns out on more critical examination to be quite the reverse, and this is the case with the supposed origination of volcanic outbursts by the access of sea-water to incandescent rock-material by means of earth-fissures. It is difficult to understand how, by such means, that wonderfully intimate union between the liquefied rock and the water, evolved in such quantities during volcanic outbursts, could be brought about; and moreover, we can scarcely regard the production of fissures in the earth's crust as being at the same time both the cause and the effect of this influx of water to the deep-seated rock-masses at a high temperature. [Sidenote: ABSORPTION OF GASES BY LIQUIDS AND SOLIDS.] During recent years the attention of both geologists and physicists has been directed to a remarkable property exhibited by many liquids and solids, as supplying a possible explanation of the phenomena of volcanic action. The property to which we refer is that whereby some liquid and solid substances are able to absorb many times their volume of certain gases--which gases under different conditions may be given off again from the liquids or solids. This power of absorption is a very remarkable one; it is not attended with chemical combination, but the amount of condensation which gases must undergo within the solid or liquid substances is sometimes enormous. Water may be made to absorb more than 1,000 times its volume of ammonia, and more than 500 times its volume of hydrochloric acid. Alcohol may absorb more than 300 times its volume of sulphurous acid. Charcoal may absorb 100 times its volume of ammonia, 85 times its volume of hydrochloric acid, 65 times its volume of sulphuretted hydrogen, 55 times its volume of sulphurous acid, and 35 times its volume of carbonic acid. Platinum-black absorbs many times its volume of oxygen and other gases. This power of absorption of gases varies in different solids and liquids according to the conditions to which they are subjected. Dr. Henry showed it to be a general law in liquids that, as the pressure is augmented, the weight of the gas absorbed is proportionately increased.