Comets are supposed to to be solid opaque bodies of various magnitudes, with long transparent tails, resembling a pale flame, and issuing from the part of the comet farthest from the sun. They move round the sun in very elliptic orbits, and cross the orbits of the planets in all directions. From the curved direction of their paths, Newton concludes that when they disappear they go much beyond the orbit of Jupiter, and that in their Perihelion, they frequently descend within the orbits of Mars, and the inferior planets. He computed the heat of the comet which appeared in 1680, when nearest the sun, to be two thousand times hotter than red hot iron, and that it must retain its heat until it comes round again, even if its period should be more than twenty thousand years, and it is computed at only five hundred and seventy-five.

Mr. Whiston has conjectured that the deluge, of which in the sacred writings we have the only authentic record, but of which the annals of most nations have traditionary accounts, was produced by the near approach of a comet, whose atmosphere had been attracted by the earth; and he further surmises, that the final catastrophe foretold in the scriptures, may be produced by the approach of a comet prodigiously heated in its perihelion. We pretend not, however, on such subjects as these, to penetrate the secrets of Almighty wisdom, which can produce its own ends, by means of which we have no conception.

Such is the solar system, and the basis upon which it rests is, that the sun, and not the earth, is the centre of it; and that the earth is not fixed, but revolves round the sun like the other planets. That this system is true, and agreeable to the constitution of nature, is certain, from the observations which have been made by the greatest philosophers; aided by telescopes, and all the assistance of mathematical and physical knowledge. When the heavens are beheld from the surface of the earth, or even from its centre, the motions of the planets appear to be very unequal, and not to observe any regular course; and therefore we may certainly conclude, that the earth is not the centre of their motions. He, therefore, who would observe the real motions of the planets, must place himself in the centre of the sun, or not far distant from it, and then all the various phenomena would be perfectly regular, and exactly such as they would be if the earth was the centre, round which the sun and planets revolved.

Another proof of the motion of the earth, is drawn from physical causes. Sir Isaac Newton has proved, that all the planets gravitate to the sun; that is, are attracted by it; and that when two bodies gravitate to each other, without directly approaching to each other in right lines; they must both turn round their common centre of gravity. The sun and the earth therefore both turn round their common centre of gravity; but the sun is a body so much larger than the earth, viz. a million times, that the common centre of gravity of the earth and sun, must be within the body of the sun itself, and not far from its centre. The earth therefore turns round a point which is within the body of the sun, and therefore turns round the sun.