own part, I adhere only to the matter of fact; and that I know will bear me out against all the metaphysical subtilties in the world. But if the reader should be distressed with any doubts in this matter, only let him remember that matter acts upon matter, not by an essential but a mechanical power, i. e. by its motion: for, in the natural, as in the moral world, we hold that there is no power but of God. If this distinction be attended to, all that has been so industriously written in defence of immaterial impulses in a metaphysical way, by the author of the Enquiry into the nature of the human soul, falls to the ground without any particular confutation.

CHAP. III.

An Answer to a physical Objection from Sir ISAAC NEWTON.

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Meet with a third objection, which may be properly termed a physical one, and deserves a particular consideration. “I have explained (says Sir Isaac Newton in

the

the Scholium generale at the conclusion of his Principia) "the phænomena of the heavens "and sea by the force of gravity-which

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acts, not proportionably to the surfaces of "the particles it acts upon, as mechanical causes use to do, but in proportion to the "quantity of solid matter." The same thing is somewhat differently expressed by Dr. Clarke, in his notes on Rohault's physics. "There are innumerable phænomena of nature, and especially that principle of gravitation in all matter, which cannot possibly arise from the impulse of bodies; "for all impulse is in proportion to the "surfaces; but gravity is always answerable "to the quantity of solid matter; therefore gravity must be attributed to some cause "which can penetrate the inmost substance "of solid matter." P. I. c. 11, & 15.

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A person who is tolerably conversant with the writings of Sir Isaac, would naturally apprehend that this assertion of Dr. Clarke is not consistent with them. He has plainly declared, that "what he calls attraction

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may possibly arise from impulse." Dr. Clarke on the other hand affirms, that the same attraction of gravity cannot arise from impulse, though Sir Isaac, whose philosophy

he was defending, has granted the possibility of such a thing. There must either be a flat contradiction between them, or some distinction is wanted with regard to the word impulse, for the clearing up of this difficulty. The secret then lies here: the impulse which Dr. Clarke denies, is corporeal impulse, and should arise from the action of some impelling matter; whereas that which Sir Isaac Newton allows, is incorporeal, if his commentator, Dr. Clarke, who must be supposed to have known his mind, has not misunderstood him; for thus he has expounded the passage-fieri sane potest ut ea efficiatur impulsu (non utique corporeo*) "It may be, "that this (attraction) is the effect of im"pulse, but this impulse is not corporeal."

The consequence which every intelligent reader will draw from this doctrine of incorporeal impulses, gave Mr. Leibnitz and others occasion to charge the Newtonian hypothesis with the impiety of making God the soul of the world, as the heathens of old did. But this matter is not now before me: Our business at present is to consider the force of this objection so far only as it is physical. It is in fact no more than this-mechanical

* Ubi fupra.

causes

causes use to act in proportion to the surfaces; but the cause of gravity acts in proportion to the quantity of solid matter; therefore that cause cannot be mechanical,

Thus much is certain, that every mechanical cause, which is not subtile enough to penetrate the contexture of a solid body, will be stopt at the surface; and the action or force of such a cause will be proportionable to the surface. If there were in nature. No other mechanical causes but such as act upon the surface, and it could be fairly made out, this objection would be unanswerable. It ought to have been proved, that there really are no other; at least it should have been attempted: yet, as far as I can find, it hath not; and I think it never will be, for the two following reasons.

First, because there may be in some cases. an impelling matter, which is too subtile for the observation of our bodily senses: and to conclude that there can be no material agency, where it does not discover itself to the organs of the body, is rather too hasty. If the parts of man's body were of the substance of iron, and put together in the same manner, he would probably feel the cause of magnetism, as plainly as he now perceives

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the heat of the sun's rays, or the blowing of

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the wind against his face: but then it would be of small use to lose the motion of the joints, and receive a polar direction in the body, merely for the satisfaction of feeling that the cause of magnetism is material and mechanical; which perhaps may be discovered, to as much satisfaction, by a more advantageous method.

My second reason for believing that we are to expect no proof of this negative, comes a little closer to the point; and it is this, that the opposite affirmative is evident from a great variety of experiments; there being in nature such mechanical causes as are able to penetrate the solid bulk of bodies, and whose action extends to every single particle of which they are composed. The rays of light can pass as easily through the solid substance of glass, if not more so, than through the open air and it is plain, their effect on bodies is not regulated by the exterior surfaces, because an hollow bubble of glass hath the same exterior surface, whether it be empty, or filled with water; yet the light is well known to take a different course through it in these two cases. If a leaf of gold be held up between the eye and the

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sun's