We cannot follow Mr. Fisher in "passing over the proofs of the existence of water in the crystals of volcanic rocks and in the materials of deep-seated dykes"; because the presence of water in these crystals when examined in a laboratory is no proof that water was present in them when they were liquid, and before they put on the form of crystals. There is no analogy between them and General Wade's read. Any crystals that a man can pick up anywhere, even from the mouth of a volcano, are quite capable of absorbing vapour of water from the atmosphere before he can carry them to his laboratory. All matter is supposed to be pervaded, more or less, by the ether, and there is always an open road for it, i.e. the vapour of water to enter by. Nature dives more rapidly into a piece of rock than a man can walk or drive down from the summit of a volcano, so that getting water out of it when he is in his laboratory, is no proof that the water was there when the piece of rock was at the bottom, not the mouth, of the volcano. The minute so-called water-vesicles in granite have only served the purpose of a snare to facilitate his deceiving himself, by the help of Mr. Clifton Ward, to further his speculations. For we think it would have been far more natural for him to have supposed that these vesicles were originally filled with the all-pervading ether. Or, are we to prohibit the ether from being present anywhere, except where it suits us? Even the dimensions given to the vesicles of a thousand millions of them being contained in a cubic inch makes us at once think of something more ethereal than water. And the whole object of Mr. Fisher's argument is to show how the depth of the ocean may be increased by water expelled from such magmas.
A hollow planet, with compressed gases in the centre, raises the idea of the possibility of explosion. It would have furnished Olbers, or any follower of his, with the bursting force to shatter into fragments the planet, out of which he supposed the asteroids to have been made. It need not cause any alarm with respect to the earth, whose shell is very much thicker than that of the exploded planet, seeing that its whole mass has been estimated not to have exceeded one-fourth of that of the earth (see Table I.). The 5000 atmospheres of pressure we have spoken of could have no such effect on so thick a shell as the earth's; and we cannot increase the number without diminishing its average density, as we have shown. When we see Mars blown up, whose diameter, and consequent thickness of shell, are not much more than half those of the earth, we may begin to think of getting out of the way.