In regard to the _effects_ of gravity, he pretends not to differ from the generally received opinion of the age; but the _application_ of them, as to the inner parts of insulated bodies, has enabled him to _improve_ in a knowledge of the formation of planets; and finally led him to form a correct idea of what _constitutes_ gravity.

The author of the new theory entertains a belief that the principles of planetary orbicular forms, developed by him, extend as well to the molecules of the most subtile fluids, as to the innumerable stars or suns of the universe, and all their planetary trains: he contends that though he may not have discovered any new principles in physics, yet that he has made interesting advances in a knowledge of the application of what was heretofore known.

Symmes's Theory of Concentric Spheres — Part 12

According to him, the planet which has been designated the Earth, is composed of at least five hollow concentric spheres, with spaces between each, an atmosphere surrounding each; and habitable as well upon the concave as the convex surface. Each of these spheres are widely open at their poles. The north polar opening of the sphere we inhabit, is believed to be about four thousand miles in diameter, and the southern above six thousand.[1] The planes of these polar openings are inclined to the plane of the ecliptic at an angle of about twenty degrees; so that the real axis of the earth, being perpendicular to the plane of the equator, will form an angle of twelve degrees with a line passing through the sphere at right angles with the plane of the polar openings; consequently the verge of the polar openings must approach several degrees nearer to the equator on one side than on the other. The highest north point, or where the distance is greatest from the equator to the verge of the opening in the northern hemisphere, will be found either in the northern sea, near the coast of Lapland, on a meridian passing through Spitsbergen, in about latitude sixty-eight degrees, or somewhat more eastwardly in Lapland; and the verge would become _apparent_, to the navigator proceeding north, in about latitude ninety degrees.

Symmes's Theory of Concentric Spheres — Part 12

The lowermost point, or the place where the distance is least from the equator to the verge of the northern polar opening, will be found in the Pacific ocean, about latitude fifty degrees, near the north-west coast of America, on or near a meridian running through the mouth of Cook's river, being in about one hundred and sixty degrees west longitude, the real verge being in about latitude fifty degrees and becoming apparent to a person travelling northward at right angles with the magnetic equator, at the distance of about twelve hundred miles further. The verge varies progressively from the lowest to the highest point, crossing the north-west coast of America between latitude fifty-two and fifty-four, thence across the continent of North America, passing through Hudson's Bay and Greenland, near cape Farewell; thence by mount Hecla to the highest point; thence tending gradually more to the south, across the northern parts of Asia, at or near the volcanoes of Kamtschatka, and along the extinguished volcanoes of the Fox Islands, to the lowermost point again, near the northwest coast.

Symmes's Theory of Concentric Spheres — Part 12