The researches of the last few years have, however, as it appears to me, rendered any theory that demands as its postulates a _very thin crust_, and a universal liquid nucleus beneath it, absolutely untenable. Without attaching any importance to the arguments of Mr. Hopkins, based upon precession and nutation, it appears to me, on various other grounds, some of which have been urged by Sir William Thompson, that the earth's solid crust is not a thin one, at least not thin enough to render it conceivable that water can ever gain admission to a fluid nucleus, if any such still exist, situated at so great a depth; and without such access we can have no Volcano. It is not necessary to go to the extent of a crust of 800 or 1,000 miles thick: with one of half the minor thickness, I believe it may be proved, on various grounds, hydraulic amongst others, that neither water could reach the nucleus, nor the liquid matter of the nucleus reach the surface. Mr. Hopkins having proved to his own satisfaction an enormous thickness for the crust, and seeing clearly the difficulties that this involved to the generally accepted volcanic theory, and having no other to substitute for it, fell back upon that most vague and weak notion of the existence of isolated lakes of liquid rock, existing at comparatively small depths beneath the earth's surface within the solid and relatively cold crust, each supplying its own Volcano, or more than one, with ready-made lava. What is to produce these lakes of fused matter in the midst of similar solidified matter? what is perpetually to maintain their fluidity in the midst of solid matter continually cooling? what has given them their local position? why near or less near the surface? what should have arranged them in directions stretching in some cases nearly from Pole to Pole? Surely this creation of imaginary lakes, merely because it happens to fit the vacant chink that seems needed to wedge up a falling theory, is an instance of that abuse of hypothesis against which Newton so vehemently declaims--"_Hypotheses non fingo._"