1st. As to the first objection, I would enquire, has it yet been ascertained with mathematical certainty, in what exact proportion one particle of matter attracts another? And may there not be some law of nature with which we are not yet well acquainted? All the experiments, hitherto made on the attractive power of gravity, were made on the principle, and under the belief, that the earth is a solid globe; and consequently the deductions were drawn accordingly. Suppose the attraction of gravitation, inherent in matter, to be so much increased, that a hollow sphere would possess the same attractive power, as if it were a solid globe, would not all the results and consequences be exactly the same? This being the case,――and I know no reason why we should conclude differently,――the whole force of the objection appears to fall to the ground. According to Newton's principle of gravity, the matter of the sphere would attract all particles of matter placed on the surface, as well upon the concave as convex, in nearly equal proportions; and the centrifugal force, which, on the outer side of the sphere, tends to throw bodies off, on the concave side, would have an opposite effect. Hence, a person standing, or trees growing, on the interior surface, would be in no more danger of being precipitated to the next sphere, between them and the centre, than those on the outer part of the sphere, when they should be _turned_ (what is familiarly called) _down_. The experiments made on the density of the globe, by observations with the plum-line, at the foot of a mountain, are very ingenious; but they must be subject to great uncertainty. The true deviation of the plum-line, the exact quantity of matter in the mountain, or, indeed, the quantity of matter between the plummet and the centre of gravity, are points difficult, if not impossible, to be ascertained with mathematical precision. If the attraction of the sun is just sufficient to keep the earth in its orbit, what can give the tendency to retain Jupiter and Saturn in theirs, each of which, if solid, contains such a vast quantity more than the earth, and removed to so great a distance from the sun, that his influence upon either must be greatly lessened by both? 2d. As to the objections that a hollow sphere of the dimension of the earth cannot exist in nature, I can discover no sound reason to warrant such a conclusion. Many hollow cylinders and spherical figures, we know do exist on the surface of the earth; and notwithstanding their own gravity, which the different parts exert on each other, as well as the gravity of the earth, they retain their shape and position; and had the matter in the earth originally been thrown by a centrifugal force into the form of a hollow sphere, or had the first creating power originally given it that shape,――I can discover no good reason for a change; neither should I entertain any apprehensions of the particles of matter coalescing at the centre.