quently of that refiftance which has been afcribed to the visinertia. To fay then, that the vis inertiæ muft hold equally in the moft fubtile Æther as in the groffeft Matter, and that from the different Degrees of weight or refiftance, different quantities of Matter are contained in equal Spaces, is to beg the Question, that Gravity has no material Caufe. But it would be unfair, to demonstrate that it has none, merely by attributing to it fuch a property, as from its Nature and Office it cannot poflibly have.

65. "It is incumbent therefore on all thofe, who would build a Philosophy on the vis inertiæ, firft to fhew us what it is, and to prove by fome Experiment, that there really is fuch an original Principle in Matter, to be discovered apart, and independent of every other Principle at prefent established in Nature, before they can raise from it one fingle conjecture, much lefs a demonstration. I fay, of every other Principle; for a refiftance to Motion may be occafioned by more Principles than one. A Mass of Iron or Stone, firft examined with refpect to the Principle of Gravity, then to that of Cobefion, or the Application of its conftituent Parts to one another, will teach us, that the whole quantity may be put in Motion with refpect to the Earth's Center, much more eafily than half the quantity can be moved with respect to the other half: So that if the force with which fome folid Bodies cohere, were to take place in Matter, as univerfally as gravity now

does;

does; we might compute the vis inertia to be ten thousand times as great as it is, because we fhould oppofe the cohesion of Bodies, where we now oppofe their gravity.

66. "Were all Matter at reft, and the action of the Elements made to ceafe, fo that not a fingle particle of matter should have any determination to one fort of motion rather than to another, that would be the time to make an Experiment on the vis inertiae. But this Principle, fo far as it is fubjected to examination under the prefent economy of the world, is a thing unfixed and confequential, not uniform and independent, as the Mathematicians have fuppofed; whofe greatest misfortune it hath been, not to confider things as they are, but to feign an arbitrary and abftracted state of Matter, and thence to argue upon it in its dependent ftate; when they are really more different, than the ore of a metal depofited in the Earth, from the fame metal formed into the wheels of a Clock. And what is much more offenfive, the fame Philofophy which has given to Matter an indifference to motion by the vis inertia, has alfo given it an inclination to motion by the virtue of Attraction; both of them inherent (as fhall be hereafter fhewn) in the fame particles. The former of thefe does indeed feem oppofite to materialism; but the latter has fo ftrong a relifh of it, that a Friend to the Principles of Spinoza, hath blended them both together*. And even Dr. * See the Phyfical Paragraphs, in a Piece entitled, an Effay on Spirit. Q q Derbam,

Derham, an undisguised and well-defigning Author, has granted as much as Epicurus himself would have required of him. It was his opinion, that in the first production of Matter, the great Author of all Things INSPIRITED the materials of which the World confifts with fuch an active quality, as ferves to preferve the Globes entire, and enables them to revolve about their Centers*. If this Paffage does not allow to Matter, a power of directing itself, and conferving its own motions, I know not what to make of it. But it is no concern of mine, fo I return to the argument; leaving it to those who pretend to have renounced materalifm, to reconcile their own conjunct doctrines of inert Matter, and infpirited Materials!"

67. Now if all this be true, and Mr. Jones' Reafoning cannot fairly be set aside, the present Philofophy must be allow'd to reft on a very incomplete foundation, and, when strictly examin'd, will be found not as yet to have reach'd the fummit of perfection; and if so, will it not be the most egregious folly to neglect the cultivation of fo remarkable and furprising a Difcovery of a fubtile elastic Medium; a Medium which had been hitherto denied, and yet without which the operations of Nature cannot be fatisfactorily accounted for? If his affertions are false, how comes it to pass that they have never been anfwer'd and refuted in the fpace of four

* Aftro-theol. p. 148.

years,

years, nothwithstanding he seems earnestly to defire that his Reasonings may be examined? His words are "If there be a confiderable defect in any of my deductions, I fhall be very glad to be better informed; and perhaps fome of the followers of Sir Ifaac Newton may fhew fo much candour and humility toward a Man, who means well, as not to think him too infignificant to be taken notice of."

CHA P. V.

PART III.

SECTION 68.

The Doctrine of Refiftances confidered, and other Arguments for a Vacuum examined and refuted.

HE Quotations from Mr. Jones' ElT fay, contained in the foregoing Chapter, may fuffice to fhew, "That the

celebrated demonftration of a Vacuum has fet out wrong. It will, continues he, be ast easy to prove, even waving all that has been said on the vis inertia, that it has concluded wrong; if the relation between a moving Body and a refifting Medium be rightly understood."

69. When a Pendulum is made to fwing in Air, Water, or Mercury, the refiftance it meets with is greater, as the medium is denfer: And as a plenum of Æther, fuch as the mechanical Philofophy

lofophy requires, would be more denfe than any other Fluid*, its refiftance, they fay, must be greater: No Motion could poffibly continue in it. But then as motion is obferved to continue in the heavens, without any fenfible diminution, there can be no resistance in the heavenly Spaces, and confequently no matter of fufficient density to occafion it.

79. This was Sir Ifaac Newton's way of computing refiftances, and the use he made of them when computed. That we may fee whether this doctrine agrees with Experience, Let us fuppofe a Ship, with its Sails fpread, to be in motion before the Wind: Every Body must allow me, that if the Wind were to keep its direction, and the Ship to have an open fea, itwould go quite round the globe; and for the fame reafon that it makes one revolution, it would make another, and fo on ad infinitum. Are we to fay, that the Air, in which it moves, is an unrefifting Medium? We ought to fay this, if the demonftration abovementioned really is what it pretends to be. But the truth is, a Medium may, in its Nature, be a refifting one, and yet in fact give no fuch refiftance, as fhall be any impediment to a Body moving in it, For let any Perfon tell me, how much refift

Is not here a palpable mistake which ought to be clear'd up? Does not Sir Ifaac Newton affirm that Æther is exceedingly more rare than Air, and do not electrical Experiments prove it to be vaftly more fo? Why then is it here fuppofed more denfe than any other fluid?

ance