That is, one Pound with us weighs on the Sun's Surface 24 Pounds, and fo of the reft.

Thefe Numbers are easily deriv'd from fome of those that go before. For fince we have already obtain'd those that exprefs the Gravitation towards thefe Heavenly Bodies, at equal distances from their refpective Centers; and fince we have also already obtain'd their true Diameters; and thence know their true Semi-diameters; and fince we know withal, that the Power at different diftances is ever at the Squares of those distances reciprocally: It cannot be difficult thence to compute the quantity of this Power at the particular diftances of every ones Semi-diameter; which is the fame with the Weight of equal Bodies on their respective Surfaces.

Thus for Example: The quantity of Matter in the Earth is to that in the Moon as 39 to 1, and in the fame proportion do all Bodies gravitate to them at equal Diftances from their respective Centers. But fince the Force of Gravitation diminishes, as the Square of the distance increases, and the distance of the Earth's Surface from its Center is to that of the Moon's from its Center, as 365 to 100, whofe Squares are as 13 to 1, this greater diftance diminishes the former Excefs of Proportion, and reduces it to that of 39% to 133, or, as in the Table, to that

2

of

of 100 to 34. And the Cafe is the fame in the reft.

(8.) The Diurnal Revolutions of the Sun and Planets about their own Axis, with refpect to the Fixed Stars, have been already stated thus:

The way by which thefe Diurnal Revolutions are difcovered in the Sun, Jupiter, Mars, and Venus, is obvious; I mean the Obfervations by Telescopes of certain Spots in their Surfaces, and the Noting how long it is e'er thofe Spots come round again. The Earth's Period is known from the apparent Motion of the Fixed Stars from any Meridian to the fame again; which is a Periodical Revolution, or Day. The Moon's diurnal Period is known from the Periodical Month, which is exactly equal thereto; otherwife the fame fide of the Moon would not be always turned to our Earth, as it certainly is; and that to fuch a degree of Nicety, that the Menftrual and Diurnal Motions of the Moon have not in the leaft gain'd nor loft upon each other from the earliest Times of Obfervation: which is a thing exceeding remarkable, and what will be taken particular Notice of hereafter.

Corollary. By comparing this and the fourth Table together, we learn the true Horary Diur

nal

nal Velocity of the Equatorial Parts of the feveral Planets: which therefore are as follows.

(9.) The Quantity of Light and Heat deriv'd from the Sun to every Primary Planet of this Syftem, and to each of the four Comets, when at their mean distance, has been already fet down, according to the Numbers following.

Thefe Numbers are easily found; being as the Squares of the Planets diftances from the Sun reciprocally.

(10.) The Eccentricities of the Orbits of the feveral Planets, and of the 4 Comets, are thus fet down already; fuppofing each of their middle Distances to be represented by 1000.

In

N. B. The Eccentricities of the Orbits of the four Comets, are nearly equal to their middle Distances themselves; which are already fet down, p. 51. prius.

Thefe Eccentricities are known, as to the Planets, by the Difference of their Apparent Diameters, and of their Real Distances, reciprocally proportional to them in the Aphelia and Perihelia of the Planets; the half of which Difference is equal to this Eccentricity. But in the Comets, whofe fartheft Diftance is invifible, 'tis known by the mere Subtraction of their nearest from their mean Distance; and noting the Difference: this Difference is the Eccentricity it felf.

The Times in which the feveral Primary Planets would fall to the Sun, and the Secondaries to their Primaries, if their Projectile Velocities were ftopp'd, and they were permitted to fall directly to thofe Centers, by the Power of Gravity, are by me elsewhere thus ftated.

A Stone would fall to the Earth's Center, if there were a hollow Paffage, in 21'. 9′′.

The Way of discovering thefe Numbers is this: It has been demonftrated in the Place already referr'd to, that half the Period of every Planet, when it is diminished in the Sefquialteral Proportion of the Number 1 to the Number 2,

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or