more remarkable in fome of the other Globes. Thus particularly in the Sun, whose Ambit is 2582873 miles, and whirls round once in about 257 days, doth confequently revolve at the rate of 4262 miles an hour (3), above four times as faft as the Earth; which in a little time would endanger its diffipation, without fuch a provifion as Gravity is.

But what is this to the Centrifugal force of Jupiter? whofe Bulk far exceeds our terraqueous Ball, and whofe Rotation is performed in lefs than half the time. But from a computation of particulars we shall better eftimate the Matter. The Diameter

(3)The Sun's Diameter being 822148 miles. the numbers here affigned will naturally follow.

As to the Sun's Gravity or Attractive Power it is (by the calculation of my Friend, the acute and learned Dr. Halley to the Sun's Centrifugal Force, as 47000 to i: The method for finding which fee in Note 5.

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of

of Jupiter being 120653 miles, its Circumference is 379045 miles: which revolving round in less than Ten hours,is at the rate of 38159 (4) miles an hour under its Equator. And if the Density of every Planet be proportional to its Distance from the Sun, as is now with great reason imagined, that is, if thofe Planets nearest the Sun, as Mercury and Venus, are proportionably denfer than those more remote, as Jupiter and Saturn; then is the Globe of Jupiter of a laxer texture than ours is, and in fo much the greater danger therefore of being

(4) Jupiter's Ambit being 379045 miles,and his Revolution 9 h. 56′ or 596 minutes; the Revolution in an hour is by the Logarithms

thus.

379045 miles

5.5786912

:: 60 minutes

1.7781513

7.3568425

38159 miles

4.5815962

whirl'd

whirl'd to pieces by fo rapid a motion as that Planet manifeftly hath, were not its parts kept clofe together and fedate by fuch a Band as Gravity (5) is.

(5) The Proportion of Jupiter's or any other Planet's, or the Sun's Gravity to their Centrifugal force may be computed from the most fagacious Sir Newton's Princip. L. 3 Prop. 8 & 19. But the before commended Savilian Profeffor fuggefted to me this eafier and quicker Rule, for fuch Planets as have Satellites, viz The Proportion of the Centrifugal to the Centripetal force, or Gravity of any Planet at its Surface,is compounded of the Ratio which the Cube of the Semidiameter of the Planet hath to the Cube of the Distance of any of its Satellites from the Center of that Planet; and the Ratio which the Square of the Satellites Periodick time bath to the Square of the Periodick Time of the Planet's Revolution. Thus for inftance, the diftance of Jupiter's Outermoft Satellite being 253 Semidiameters of Jupiter, and it's Period 16 days, 16 hours, 32 minutes or 24022 minutes, and Jupiter's Revolution 596 minutes; we fhall find the Gravity in Jupiter's Surface to be to his Gentrifugal Force in his Equator, as 1 to 9.96.

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CHAP. III.

Of the Power and Usefulness of Gravity to retain the Planets in their Orbits.

Or a Conclufion of this fixth Book, I fhall take notice of one more remarkable benefit of Gravity, which is grounded upon the fuppofition of the truth of the Newtonian Philofophy; which hath so good Grounds, and great Reafon, I might fay Demonftrations, on it's fide, particularly in this matter, that admitting of it here, we fhall difcover a another admirable work of the Creation, and that is, the preventing the Evagation of the Planets, and the accurate Retaining them within the due Bounds of their Orbits. That this is done by Gravity, and that Gravity

Gravity and Motion folve, in the most compleat manner, all the Phænomena of the Planetary Motions both Primary and Secondary, is abundantly made out by the wonderful Sagacity of the great Sir Ifaac Newton; as may be seen in his Principia.

But before I come to the particular agency of Gravity, it will be neceffary to premise fomething concerning its Nature, and fome of its Properties, viz. That Gravity is not terminated at the Surface, but reaches to the very Center, and is extended to immenfe diftances all round the Centers of all the Globes: By which means the celeftial Bodies are enabled to have Systems of leffer Globes revolving about them. For had the force of Gravity determined at, or near the Surface (as it might have done, if intended only for the Confervation of the Globes) in this cafe, all the Bodies that were put