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BOOK been of a great and searching wit, well skilled in geo" metry, to which he endeavoured to reduce natural phi
losophy, (although he failed in his attempt :) that he had a faculty of expressing his mind clearly in few words, above any either ancient or modern writer). Therefore it will be necessary to consider what Des Cartes yields, that we may not mistake or misrepresent his design.
1. He grants that God did at first create matter, which was capable of rest or motion.
2. That matter, left to itself, would be without any motion; and therefore the first motion was from God.
3. That God, by his ordinary providence, doth preserve as much motion in the world as was given at first.
4. That we have no reason to suppose any other alteration in the ordinary course of things, according to the laws of motion, than what we are certain of by experience or revelation.
And now the main point is, whether matter, being thus put into motion, can produce the phenomena of the world, without any farther interposition of Providence, than only to preserve the motion of matter? For which we must consider, that he doth not give a satisfactory account, 1, of the nature and laws of motion, nor, 2, of the phenomena of the universe.
As to the former, I shall inquire into his notion of motion, and then of the laws of it.
1. He asserts that motion, according to his principart. ii. ples, is barely a mode of matter, without any inward 1. 25.
principle of motion. For motion, he saith, is the change of the situation of bodies with respect to one another, or a removing a body from the vicinity of some bodies to the neighbourhood of others; and he places it in such a translation, on purpose that it may
be understood to be only a mode of the matter moved, CHAP. as figure is of a thing figured. But it is not so easy to understand that motion, which imports an action should be only a mode of the matter moved, as it is that figure belongs only to the thing figured. For it is not possible for the figure to be any where else but in that body which hath it; but it is possible to apprehend motion to come either from an external agent or an internal principle; and so it is not a mere mode of the thing moved. But when the whole weight is laid upon the nature of motion in this case, some greater evidence ought to have been given how motion, being once given to matter as a mode of it, must always continue, when the resistance of bodies doth certainly weaken it so as to need a new force to repair it. For either all motion of matter must be by a violent impulse, without regard to the different force or magnitude of things, (which is to overthrow the due laws of motion,) or else there must be a proportion in the force of the mover to the resistance of the body moved : and if there be a regard to that proportion, (or else the smallest body might move the greatest,) then there must be a resistance in that body which is moved: but every resistance gives a check to the motion of that body which moved it, and every check lessens the impulse; and so from a gradual resistance there must come a gradual decay, till at last all motion must cease; as it is in all machines whose motion depends upon external force. Des Cartes, indeed, saith, That whatever motion is lost by one body, is communicated to the next, and so the first motion is still preserved. But it is hardly possible to make it appear that motion is not so much weakened by resistance, but that it can preserve itself in a degree of motion proportionable to that which is not communicated to another. For the frequency of impulse
BOOK lessens the power of reflection, and it appears in light,
- and sounds, and other things, that whatever is reflected
grows weaker. So that resistance must gradually
weaken motion. And in the motion of projected bodies, Id. part. ii. Des Cartes himself grants, That the motion continues n. 38.
till it be hindered by the resistance it meets with ; and he saith, It is manifest that the motion is retarded by the air, and other ambient fluids, and so it cannot continue long. But is that an argument that bodies do continue motion till they be hindered, and that motion is only a mode of the body moved? Whatever mode it is, it comes from the force of the immediate agent, and not from the motion at first given to matter; and here we see the resistance it meets with soon gives a stop to it. Therefore it seems unconceivable that all the motion in the world, considering the continual resistance
of bodies, should be the same mode of matter which H. Mori was at first given to it. And as to his definition of Enchiride motion, some have undertaken to demonstrate it to be par. i. c. 7. false, by shewing how one body may come nearer to
another, without changing the situation of the parts next adjoining to it; and that there is no such reciprocal motion as he asserts, although there be a reciprocal
change of situation, which is unavoidable. But Mons. Rohault, Rohault saith, That motion is to be taken with respect Tr. Phys.
i. to the next, and not to any remote bodies. However Regis Ré. Mons. Regis thought fit to quit that definition of Des ponse aux Reflexions Cartes for another, which Du Hamel saith is not at all Critiques de M. Du Ha- better; but he thought it necessary to take in the effi
cient cause of motion, which makes it not to be a mere mode of the matter moved. And but for the authority of mathematicians and philosophers, it would be thought ridiculous for a thing not to be said to be moved, because it doth not change the situation as to the next bodies about it; as that the kernel of a nut is not
c. 10. .
moved, because it is thrown with the shell upon it; or CHAP. that the wine is not moved in a ship at sea, because it keeps within the vessel. So, if the earth be carried about with the force of the vortex wherein it is, it is as certainly moved as a pendulum is with the motion of the ship, although it hath a proper motion of its own. But Des Cartes undertakes to give an account of the Des Cartes
Prin.par. ii. proportion of the increase and lessening of motion, upon n. 45, &c. the meeting of two hard bodies, and he lays down seven rules to determine it ; but it falls out very unhappily, that six of them are denied to be true, and that the first doth not answer the end it was brought for. This was a bold charge on so great a mathematician; but all that Regis saith in answer to it is, That he did not Réponse,
&c. part. ii. undertake to defend all Des Cartes's rules of motion, ch. Pas because they did not appear to him exact enough. But if the particular rules of motion be no better fixed nor understood, how come they to be so certain that the same quantity of motion is still preserved in the world ? For that Des Cartes hath recourse to the im-Cart. Prin. mutable will of God, which hath determined it. No n. 36. doubt if God hath determined it, so it must be. But from whence comes Des Cartes to know this to be the immutable will of God? What antecedent reason is there to satisfy any man's mind that God, by his immutable will, must keep up the same proportion of motion in the world ? Why may not God alter or suspend the laws of motion, as to the parts of matter, in what way or manner he thinks good ? What repugnancy is there to the Divine nature in so doing? So that these arguments à priori (as they call them) have no kind of evidence as to such matters, which may be or not be, as God pleases. Besides, what necessity was there that motion must be only a mode of matter; and that
BOOK mode to be preserved by such laws of motion, which
- are so very uncertain ? A very skilful and ingenious Mr. Boyle of the high philosopher of our own saith, That this rule, which he Veneration saith is the most useful of all Des Cartes's, is very tellect owes metaphysical, and not very cogent to him. And he to God, sect. 20. doth not see how it can be demonstrated; and he ques
tions whether it be agreeable to experience. And he was a person very favourable to Des Cartes, as far as he could, as appears on all occasions in his writings ;
but here we see he gives up his fundamental rule. Du Réponse Hamel saith, The argument from God's immutability aux Reflexions, is of no force, because it holds not as to extrinsical par. ii. C. 13. actions. Regis, to defend this, runs into that absurdity
to make God a necessary agent, because God's will and his essence are the same; which overthrows all religion
in the consequence of it. Prin. part. But Des Cartes himself excepts such mutations as ii. n. 36.
are made in matter, by evident experience or Divine revelation. What is the meaning of this ? Can that be an immutable will of God which is contradicted by evident experience and Divine revelation ? Or were these words only put in to avoid censure? As the world was said to be indefinite, lest he should be charged with making the world infinite; and the definition of motion was altered, to avoid Galileo's fate. But there is no dissembling in this matter: if it be contradicted by evident experience, it can be no fixed and immutable rule; if it can be altered in case of miracles, the argument from God's immutability signifies nothing. For, if it be no repugnancy to the Divine nature to alter or suspend the laws of motion as he sees cause, then we can have no assurance as to God's will, any farther than himself hath declared it; and consequently they must prove that God hath manifested this to be his will. But, saith Rohault, it is unbecoming philosophers on