In Rees' Cyclopedia, under the article 'ring,' is the following sentence; by which it appears that Kepler first suggested the earth to be composed of concentric crusts. "Kepler, in his Epitom. Astron. Copern. (as after him Dr. Halley, in his enquiry into the causes of the variation of the needle, Phil. Trans. No. 195.) supposes our earth may be composed of several _crusts_ or _shells_, one within another, and concentric to each other. If this be the case, it is possible the ring of Saturn may be the fragment or remaining ruin of his former exterior shell, the rest of which is broken or fallen down upon the body of the planet." [46] Maclaurin, in his fourteenth chapter of the second volume on Fluxions, investigates the theory of Dr. Halley at considerable length; and in conclusion, appears to consider the existence of a hollow globe as very possible. CHAPTER IX. _A few brief suggestions, relative to the description, tonnage, and number of vessels, necessary to be equipped for a voyage of discovery to the interior regions of the earth; the number of men necessary to be employed on board, articles necessary for the outfit, and the probable expense attending the same; also, as to the route most proper to be pursued to accomplish the object of the expedition._ Captain Symmes, in his first circular, published at St. Louis, on the 10th day of April, 1818, asks an outfit of one hundred brave companions, well equipped, to set out from Siberia in autumn, with rein-deer and sleighs, to pass over the ice of the frozen sea. On being furnished with an outfit of this description, he engages to explore the concave regions, and discover a warm, or at least a temperate country, of fertile soil, well stocked with animals and vegetables, if not men, on reaching about sixty-nine miles beyond latitude eighty-two degrees. The route, intended to be pursued by Captain Symmes, appears to be that of the rein-deer, and the time of setting out, the same season of the year, in which (according to Professor Adams) the rein-deer migrate from that coast north. In this route it would be necessary to cross the verge, or region of most intense cold, with the greatest possible expedition, so as to reach an inner temperate climate, in the shortest time. The concave regions could be partially explored during the winter; and the party return in the spring, and at the same time of the rein-deer, to the mouth of the river Lena.