ing the phænomena, and let him him have all the honour of it. But never let it be a pretence for saddling us with occult powers in solid matters; if his followers make that use of it, they will gain no credit to their master in the end; and hitherto they have gained but little to themselves by it, as it must have appeared from what hath been said in all which, I hope there hath been on my part no mixture of envy or prejudice, unless matters of fact, and plain argumenta-' tion, are so to be interpreted.

We are to conclude, then, that the attraction of gravity, understood as an universal property of matter, is void of all geometrical evidence. If Sir Isaac Newton hath left. this affair undecided, no other geometrician, of this age or the next, is like to supply his defects; and yet every smatterer almost in natural philosophy is persuaded he can make it out against all opposition. The ground and reason of which mistake I apprehend to be this: that many of our geometricians, ambitious of dictating to us about the causes and first springs of nature, while their art can reach only to the measure of some of its effects, have not been careful to distinguish how far a mathematical conclusion will ex

tend,

tend, and how far not. Hypothetical forces, or real ones, as it was observed above, will equally afford matter for an astronomer to work upon *. *. For example, if the moon, as she moves in her orbit, is imagined to be influenced by forces acting in lines which tend toward the centres of the earth and sun, then the different inclinations of her orbit to the ecliptic, the irregular motion of her nodes, her retardation about the quadratures, her acceleration about the conjunctions, &c. may follow by the rules of geometry. Upon these principles, Sir Isaac Newton is universally allowed to have accounted for the lunar irregularities with great sagacity; and, as an astronomer, to have left that matter in a much better state than he found it, though it is not yet perfected. But what these forces are in special, and in what manner they act; whether as an active immaterial virtue, exerted through a void space, from the centres of the earth and sun, or as a pressure of some etherial medium acting in lines toward those centres, none of his reasonings have determined

* Neque necesse putant, ut hypotheses istæ veræ sint,

imo ne verisimiles quidem, sed sufficit hoc unum, ut calcu

lum observationibus congruentem exhibeant. Horrace. Op. Post. 179.

mined for us. So far from it, that we find his Principia inclining to one side, and his Physical Queries to the other. And I may appeal to the judgment of any ingenuous man, sufficiently versed in mathematical studies, whether the phænomena above mentioned may not arise from a pressure behind, as well as from an attraction before; and whether Sir Isaac's geometrical reasoning will not be as conclusive in the one case as in the other? How comes it then to have been published to the world, that “one spe"cies of attraction hath been undeniably

proved to be diffused through the whole "planetary system?" This having been no more proved by any of his arguments, than that one species of impulse or pressure is diffused through the whole planetary system; and for the truth of this, I may refer to the definition, where the terms attraction and impulse are taken indifferently, and are to be so taken throughout the whole book, otherwise this can answer no purpose as a definition. That some force prevails, and im such particular directions, is capable of demonstration; but the reasoning and observation, which only prove the existence of some force in general, will never demonstrate

in

that

that of attraction to be the force in particular so that nothing farther need be said

in this way.

ment.

Let us now go on to experi

CHAP. V.

The Attraction of Gravity, understood as an universal Property or Quality in the Parts of Matter, is not agreeable to Experiment and Observation.

N that phat is called the attractive force

experience has hitherto shewn us,

of the sun and planets, is answerable to their quantities of solid matter. Their bulk, as computed from their respective distances and apparent diameters, is far from yielding a proportion of gravity so uniform as might have been expected. Gravity toward the earth proves to be much greater, in proportion to the bulk of the earth, than gravity toward the sun, or any of the primary planets. This seems to be a great difficulty in the hypothesis of gravity. But how easily is it reconciled, if we are allowed to alter the density

of

of the heavenly bodies, and by this means bring their quantities of matter to an agreement with the hypothesis! The fiat of a favourite philosopher can so reduce the density of the solid matter in the body of the sun, that the density of the earth shall be four times greater, and then the attractive. power of the sun shall exactly answer to his quantity of solid matter; and the same liberty must be taken with the other great bodies of the solar system. Their density must be accommodated to their attractive powers: then, if their attractive powers be taken for granted, their densities will pass for a discovery. Thus great men amuse themselves and the world by arguing in a circle, or proving the truth of a proposition by the conclusions they have drawn from it: for, unless you admit of this density, which, arbitrarily, and without any observations to support it, is accommodated to the hypothesis of gravity; that hypothesis will labour under a disagreement with observation.

That there may be some shew of experience, however, in all this, it is intimated, that the sun must needs be rarer than the earth, because of the immense heat of his

body.