and with another degree of velocity.

The

one excludes the other. In a word, a body cannot have a tendency to change its prefent ftate, and at the fame time a tendency not to change it, more than two contradictory propofitions can both be true: for these two are really fuch. This is a remarkable property of the refiftance of matter, That it is inconfiftent with any power or force in it; and should never be forgot by us. It infers many notable confequences, which it seems we are not fufficiently aware of at all times: and, among others, an utter impoffibility that matter can ever become, by any power, a living, self-moving fubftance; feeing, as will appear, matter must refift all change of its present state, as it is a folid substance. If this had been attended to, an infinity of doubting and difputing might have been faved to mankind.

XVI. This will change our phyficks a little, and establish a new Theory of matter. For it will follow that all gravity, attraction, elafticity, repulfion, or whatever other tendencies to motion are obferved in

matter, commonly called natural powers

of

matter,

matter, are not powers implanted in matter, or poffible to be made inherent in it; but (therefore) impulfe, or force impressed upon it ab extra. We are apt to think that it is a certain natural quality, or power, implanted in the matter of a stone, v. g. and inherent in it, that makes it tend to the earth (g) but, by what is faid in the laft

paragraph,

(g) Even fo great a man as Borelli feems to have been of this opinion. In the chapter de caufis & principiis motûs (the 2d of his book de vi percuffionis) he fays, Tandem fummâ contentione controvertitur, an aliqua corpora moveri poffunt à feipfis, vel potius quicquid movetur, à diftineto feparato que motore propelli debeat : & profectò, ut à poftremo exordiamur, evidentiffimum eft aliqua corpora à diftinéto, & externo motore impelli, fic ea omnia quæ vebuntur, percutiuntur, aut projiciuntur, manifeftiffimè ab externo impulfore promoventur; fed an reliqua omnia, quæ in mundo moventur, pariter ab extrinfeco principio, & caufa propellantur, boc profectò impoffibile & incredibile videtur, quandoquidem corpora gravia, & animalia per fe videntur moveri, fcilicet à caufa & principio intrinfeco, &c. What difference there is to be affigned between the moving principle in an animal, and in a heavy body defcending, we shall see below; only I think it was not right to conclude them under one head. The expreffion [ subftantia animaftica,] which farther on he says is both agent and patient, without a clear idea of it in the mind of the perfon that writes, and an explication of that idea, to communicate

C 4

as in

paragraph, it appears that it refifts this motion, as much as it would a motion in any other direction, with the fame velocity : or that matter is as much impelled in this case, any other, by fome cause or virtue, ab extra, i. e. by fomething not matter. The effect of gravity is not to deftroy the resistance of matter, or to make it unrefifting matter, but to overcome its refiftance to be moved in certain circumstances; where it ftill refifts as much every new change of ftate, as if its refiftance to the former had not been overcome. And this is the cafe in all force impreffed ab extra, by No 13. When the refiftance of the body A, to be moved with a celerity as a 1000 times C,

communicate it to the person that reads, is of no use in philofophy; or of bad use: but of such things Mr. Locke hath faid enough. No man can conceive that the fame thing fhould be both movens and motum. There is a plain contradiction in this affertion, eadémque fubftantia corporis gravis, migrat & defcendit, à feipfo impulfa. A moved refists motion; a mover overcomes that refiftance: these oppofites can never confift in the fame individual thing. If the diftinction of agent and patient is neceffary in projection, and percussion, and the effects of art, it is also neceffary in the works of nature. Two things, neceffarily two in the one cafe, cannot become one in the other.

is overcome, though it refifts no more to be carried on with that celerity, which is now to be confidered as its permanent state; yet it refifts as much to be out of this ftate, as it did formerly to be brought to it. And this is just the case in the descent of heavy bodies any velocity from the beginning of the fall would be a permanent state of the body, if new impulfes ab extra did not add ftill farther degrees of velocity. This truth is alfo plain from this confideration, that if a body moving more swiftly than another body moves by the force of gravity, attraction, elafticity, &c. overtakes it; the body fo overtaken will make resistance to the impulse of the overtaking body, even though the direction of their motions confpire. For inftance, if we call the celerity which a piece of wood hath acquired in falling down through a certain fpace, K ; and the celerity, with which a bullet leaves the muzzle of the gun, C; and then fup pose the bullet moving with the fum of these two celerities (C+K) to overtake the piece of wood in the end of that space; it is demonftrable that the bullet would pierce the wood, even though their motions were confpiring.

confpiring. For, the relative velocity of the ball and piece of wood being the fame, both when it is discharged against the piece of wood at rest, and when it overtakes it in its descent, the greatness of the stroke, and the effect of it will be the same; namely that the ball will pierce the wood. One may be also more familiarly certain of this, if he lets a ball drop out of his hand, and strikes it before it reach the ground; for he will feel it refift the ftroke very fenfibly. This lets us fee that matter refifts even the force of gravity, or any other acting in the fame direction, as was afferted N° 5. and confequently, by what was faid in N° 15. that the force of gravity (the fame is to be understood of elafticity, fuga, attraction,) is a force impreffed ab extra, and no conatus, or tendency belonging to matter, or inherent in it. But all this will still appear more evidently when we come to confider what moment (impetus, or force in a moving body) is for all moment proceeds from the refiftance in matter to change its state; and whatever matter hath force, or moment, in its motion, must be refifting matter. And confequently matter refifts to be moved by

the