the earth does not change its form in obedience to the attraction of the sun and moon, are based on a misconception, and that a molten globe with a thin crust would attain to such a state of equilibrium in this respect as not to be distinguishable from a solid planet. This view has been maintained by the French physicist, Delaunay, and for some time it made geologists suppose that, after all, the earth's crust may be very thin. Sir William Thomson, however, and Archdeacon Pratt, have ably maintained the previous opinion, based on Hopkins' calculations; and it is now believed that we may rest upon this as representing the most probable condition of the interior of the earth at present. Another fact bearing on this point is the form of the earth, which is now actually a spheroid of rotation; that is, of such a shape as would result from the action of gravity and centrifugal force in the motion of a huge liquid drop rotating in the manner in which the earth rotates. Of course it may be said that the earth may have been made in that shape to fit it for its rotation; but science prefers to suppose that the form is the result of the forces acting on it. This consideration would of course corroborate the deductions from that just mentioned. Again, if we examine a map showing the distribution of volcanoes upon the earth, and trace these along the volcanic belt of Western America and Eastern Asia, and in the Pacific Islands, and in the isolated volcanic regions in other parts of the world; and if we add to these the multitude of volcanoes now extinct, we shall be convinced that the sources of internal heat, of which these are the vents, must be present almost everywhere under the earth's crust. Lastly, if we consider the elevations and depressions which large portions of the crust of the earth have undergone in geological time, and the actual crumpling and folding of the crust visible in great mountain chains, we arrive at a similar conclusion, and also become convinced that the crust has been not too thick to admit of extensive fractures, flexures, and foldings. There are, however, it must be admitted, theories of volcanic action, strongly supported by the chemical nature of the materials ejected by modern volcanoes, which would refer all their phenomena to the softening, under the continued influence of heat and water, of materials within the crust of the earth rather then under it.[A] Still, the phenomena of volcanic action, and of elevation and subsidence, would, under any explanation, suppose intense heat, and therefore probably an original incandescent condition. [A] Dr. T. Sterry Hunt, in Silliman'a Journal, 1870.