An essay on comets, their nature, the laws of their motions, the cause and…

There is a Species of Heavenly Bodies, called COMETS, which revolve about the Sun; in very Oblong Elliptic Orbits, approaching to Parabolic Curves. The Times of their Periodical Revolutions are very long, since in three or four Thousand Years, we have not positively determined the Returns of above one or two; however, its certain, that like our Planets, they do move in a recurring Orbit, that the Sun is in one of the Foci of this Orbit, that by a Ray from the Sun, they describe equal ⟨p. 5⟩Area's in equal Times, that the same Law of Gravitation obtains in them, which does in the Planets; that their Periodical Times are certain and invariable, and that their Motions are regular, only their Course in their Orbits is not determined one way, but in differently some of 'em move one way, others another: They are also about the same Bulk with the Planets, generally speaking; and like them are compact solid Bodies, but surrounded with a vastly large thin Fluid, intermixed with several grosser Particles, and composing an irregular unequally disposed and uncertainly agitated Mass; which is called its Atmosphere, whose Diameter, is ten or fifteen Times as long as that of its Body. Besides which, it has a long lucid Train, which is raised in its Approach to the Sun, by the Heat thereof, and extends sometimes to four hundred Thousand Miles above its Body. It is always opposite to the Sun, because it is the thinner part of its Atmosphere, extremely rarefied by his Rays; and so rare that the Stars may be seen through it. This Tail accompanies it through its Course overall the Planetary Regions, increasing in its Approach to the Sun, and lessening in its Recess. These Comets sometimes come so near the Sun, as to be heated to such a Degree that they cannot become cool again, in many Thousands of Years. This with its violent Motion in a Curve, which comes near to a straight Line, after it has passed its Perihelium, and the irregular Disposition of the confused Mass of its Atmosphere, makes it an unfit Habitation for Animals, that are not in a State of Punishment, so far as we can conceive of the Nature of Animals. And therefore some have thought it designed, to supply the Expense of Fluids in the Sun and the Planets. But as I have before hinted, this does not seem so very probable, because Nature always supplies constant and regular Expenses after a constant and regular Manner.

There is a Species of Heavenly Bodies, call'd COMETS, which revolve about the Sun; in very Oblong Elliptick Orbits, approaching to Parabolick Curves. The Times of their Periodical Revolutions are very long, since in three or four Thousand Years, we have not positively determin'd the Returns of above one or two; however, its certain, that like our Planets, they do move in a recurring Orbit, that the Sun is in one of the Foci of this Orbit, that by a Ray from the Sun, they describe equal