Philof. Prop. 20.

the Nearnefs it felf, or that of the Cubes, or Biquadrates, &c. of that Nearness or Distance. Yet would any other Proportion have been exceeding inconvenient for this System. For if it had been as the Nearness it felf, we have no regular Curve Line, in which the Eccentrical Planets or Comets could then revolve: If in a Triplicate such Bodies must ever have defcended, or afcended in Spiral Lines, till they fell into the See Math. Sun, or fome Fixed Star, and perished therein. And if the Proportion had been still greater, the Effect would have been quicker also.

Demonstration of the Fourth Part; that this
Gravity is the same in all Places, and at all
Times, and with regard to all Bodies whatso-

ever.

This is plain from Fact and Observation; for (1.) Heavy Bodies fall as fast in one Country as in another; and Gravity affects the Planets and Comets in its proper Proportion, equally in all the Parts of the Universe where Planets or Comets go, i. e. in all the immenfe Regions of it every Way.

(2.) The Planets and Comers, guided by this Law, have invariably preserv'd their Motions, Orbits, Periods, and Influences, fince the first Ages of Aftronomy and Chronology: And,

(3.) This Gravity does still, upon Tryal, equally affect Fluids and Solids; Bodies in Motion and at Rest; Great and Small; and this through the whole Universe alfo, fo far as we can examine it,

Demons Demonstration of the Fifth Part; that this Gravity is an entirely immechanical Power, and beyond the Abilities of all material Agents whatsoever.

(1.) This Power acts upon the very inward substantial Parts of Bodies, as well as the outward and visible; and is proportionable not to See Math. the Surface but to the solid Content, or Quan- Philof. tity of Matter contained in them: Whereas, Prop. 82. all Mechanical Causes are meerly superficial, and act by External Contact on the External Surface only.

Philof.

(2.) This Power acts upon Bodies equally, when they are in the most violent Motion, and when they are at Rest; as the Celerity of Descending Bodies with us; and the Celerity of See Math. the Comets in the Heavens, Geometrically computed, do particularly shew. Now this is ab- Prop. 3. folutely impoffible; that any Mechanical Preffure, or Impulse from a Body, let its Motion be never so swift, or its Pressure never so strong, should equally accelerate another Body, when at Rest, and when in Motion; it being a known See Math. Law of Mechanism, that a Body in Motion Philof. impels another at Rest with its whole Force; Law of ; Motion6, but one in Motion, with only the Excess of its own Velocity above the others; as is most obvious alfo on the leaft Reflexion.

(3.) By this Power Bodies act upon other Bodies at a Distance, nay at all Distances whatfoever; that is, they act where they are not : Which is not only impoffible for Bodies Mecha

nically

4

nically to do, but indeed is impossible for all Beings whatfoever to do, either Mechanically or Immechanically, it being just as good Sense to say, an Agent can act when he is not in Being, as where he is not present. Whence, by the way, as we shall fee hereafter, it will appear, that this Power of Gravity is not only Immechanical, or does not arife from Corporeal Contract or Impulse, but is not, strictly speaking, any Power belonging to Body or Matter at all; tho' for ease of Conception and Calculation we usually so speak; but is a Power of a superior Agent, ever moving all Bodies after such a manner, as if every Body did Attract, and were Attracted by every other Body in the Universe, and no otherwife.

N. B. Altho' I here do only insist in particular on the wonderful Power of Gravity, which is the general or universal Power of the entire System; and which is the best known, the most eafily proved, and is indeed the most evidently Immechanical; yet do not I exclude those other Noble and Immechanical Powers of Refraction in pellucid Bodies; of mutual Repulse in the Particles of the Air, which render it Elastical; of the Cohesion of Parts in con sistent Bodies, and of another Kind of AttraEtion in homogenial, and of Repulse in heterogeneous Fluids, &c. on which the particular Phænomena of Nature do now appear to depend; but shall upon Occasion make use of them sometimes in what follows,

PROP.

1

PROP. IV.

The Orbits, Revolutions, Distances, Diameters, Quantities of Matter, Densities, Gravity on the Surfaces, Revolutions about their Axes, Quantities of Light and Heat, above set down, concerning the Sun and Planets, both primary and secondary, with those of the Comets also, are True and Certain. With an Account of the Ways whereby we discover all those Particulars.

Demonstration of the several Particulars.

Martis.

(1.) That the Orbits of all the primary Planets are, as above stated, Elliptical, was first difcovered, and prov'd with the utmost Labour and Industry, from Tycho's Observations, by the famous Kepler; particularly as to the Planet De MotiMars; and is now discover'd by the great Ex- bus Stella actness of all the Planets Places, and apparent Diameters, when calculated in such Orbits, and compared with the best Observations. Nor was the old Hypothesis of the Eccentrick Cireu- See Fig. IV. lar Orbits, other than an Approximation to the true System; especially when the Aftronomers came to observe, that their Circular Eccentricity would not agree to Observation, without its Bisection, as it was call'd; i. e. without supposing the Point of even equable Motion to be as far beyond, as the Eccentrical Point was on this fide the Center of the Circle, which was almost the fame Thing with owning such Orbits to be Elliptical, and having the Sun in the Infe

rior, and the Point of even Motion in or very near the fuperior Focus; which is the State of those Orbits in our present Astronomy. And the Cafe will be the fame as to the Orbits of the Secondary Ones about their Primaries, where ever their Eccentricity can be discover'd. Nor is the State of the Comets to be excepted from this Rule: For tho' We now generally use Pa

rabolick instead of Elliptick Orbits in the ComSee Math. Philof. of putation of the Comets Motions, yet is this Comets, only for that small part of their Course which Pag. 381, we can fee, and for the ease of Calculation;

&c.

while we are fatisfy'd from their Appearances, that they really move in very Oblong Ellipfes, (or such as approach to Parabola's,) about the Sun in their lower Foci, as do the Planets; that accordingly they have their proper Periods, in which they revolve quite round, and return to the Sun again; four of which Periods are now discover'd; and that if we compute them in Ellipses, instead of Parabola's, where-ever the Species of those Ellipses are known, we should find our Calculations still more exactly to agree with our Obfervations, as is already the Cafe as to

the Comet 168.

(2.) The Revolutions of the primary Planets about the Sun, and of the Secondary Ones about their Primaries are above by me thus stated.

Merd