ARTICLE LXXV.

PHILOSOPHICAL

LETTERS

written by Mr. LEIBNITZ and Mr. HARTSOEKER.

T

HE following Letters have been published by the Authors of the Memoirs of Trevoux. Thofe Gen." tlemen have prefixed to them a fhort Preamble, which I fhall infert here.

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"M. Leibnitz, being defired by Mr. Hartfoeker to give him his Opinion about the Conjectures Phyfiques, "published by the latter, fent fome Objections to "M. Hartfoeker, which have been anfwered by that "Philofopher in his Eclairciffemens *, without naming M. Leibnitz. That Difpute, far from ending with the Impreffion of the Eclairciffemens, is grown warmer. M. Leibnitz found himself infen"fibly engaged to attack the Principles of his Ad"verfary's Syftem, viz. The perfect Liquidity of one "of his Elements, and the Indivifibility of the o"ther. He maintained against him, That Atoms are 66 no lefs impoffible than a perfect Liquid; and that "the Cohesion of the Parts of a Body, wherein its Hardness confifts, is occafioned by the Conformity " of

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* I have published an Account of that Book.

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"of the Motions working upon those Parts. Mr. Leibnitz believes, that when those confpiring Mo"tions are difturbed by fome Accident, the Parts lofe "their Union, and the body becomes liquid. M. Hartfoeker knew not at firft what M. Leibnitz meant. The Dispute wen: thus far, when M. Leibnitz fent the firft of the following Letters to Father Desboffes a Jefuit at Cologne, and defired him to get it delivered to M. Hartfoeker. Father Desboffes, "who now teaches Divinity at Paderborn, has been a long time an intimate Friend of the Famous "M. Leibnitz. His great Learning and Penetration, "and his eminent Virtue have occafioned a strict "Friendship between them, notwithstanding their being of different Religions. Father Desboffes pro"pofed to his Illuftrious Friend to publish his DiIpute with M. Hartfoeker. The latter has given us "leave to do it; and we think we have done a good Service to thofe, who love to dive into the "Bottom of the Principles of Natural Philosophy."

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I. . . .

A Letter of M. LEIBNITZ to M. HARTSOEKER.

You

OU fpeak, Sir, as if you knew not what I mean by confpiring Motions; and you ask, Whether what I call fo, be not the fame thing with Reft? I answer, It is not. For Reft does not tend to make or preferve the Cohesion of the Parts that are at Reft; and tho' two Bodies remain one by another, they make no Effort to continue to remain together, whether they touch one another, or not: But when there is a confpiring Motion in their Parts, which is difturbed by a Separation, fome Strength is requifite to overcome that Obitacle. Nor is it neceffary, that in the confpiring Motions the Parts fhould not change

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change their Distance. They may very well change it, provided that fpontaneous Change be quite añother thing than a violent Change, which would oc cafion a Separation, and difturb thofe Motions: And the Parts of Bodies refift a Separation, not because they have a Tendency to be divided; for in fuch a Cafe they would refift ftill, if they were altogether at Reft, which is contrary to what I maintain; but because they have a confiderable Motion, which must be disturbed by a Separation. If thofe Parts tend to a Separation of themselves, they help any one who would feparate them; but when they do not help him, it does not follow that they make an Oppofition, and fome pofitive Caufe is requifite for that.

I own that fome Force is requifite to expel a Body from its Place, or to make it go fafter than it would do of itself; but if the Body D tends to drive

the Body C from its Place, the Refiftance of the Body C, which leffens the Swiftnefs of the Body D, has nothing in it; from whence it may be inferred that the Body B, tho' nothing tends to drive it out, ought to accompany the Body C; whether the Interval between B and C be great or fmall, or none at all. We must therefore fuppofe, in order to produce that Union between B and C, or their going along together, fome other Reasons than Reft, or the Situation of the one by the other; but be caufe it ought to proceed from the Mechanifm, I can find it no where but in the confpiring Motion,

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common to fome Parts of the Bodies B and C, which conveys fome Parts from the one into the other by a kind of Circulation, and which must be difturbed by the Separation of the Bodies.

To fay, that the confpiring Motions are a Fiction, is the fame as to fay, that every Motion is a Fiction. For, Sir, how will you make a Motion, unless there be fome Relation among the Motions of the Parts? The very Nature of Fluids in Agitation leads them to thofe Motions, that are most fitting. You fay, your Atoms have no Parts; and you think it ftrange that I fhould fuppofe one may conceive that an Atom A has two Parts B and C. But are you not obliged to own, that one may conceive that an Atom D goes against the Atom Á, without going directly against the Part B; and in fuch a manner that it would carry C along with it, and leave B, if A was not an Atom, or a folid Body? There is therefore fome Reason to affirm, that the pretended Atom is not without Parts. You must affign the Causes of its Atomity, if I may fo fpeak, that is, why D cannot carry C along with it, without carrying B at the fame time; and you must find a strong Glue to make one of those Parts ftick to the other, if you are not willing to have recourfe to the conSpiring Motion.

If you alledge only the Will of God for it, you have recourse to a Miracle, and even to a perpetual Miracle; for the Will of God works through a Mi racle, whenever we are not able to account for that Will and its Effects from the Nature of the Objects. For Example; if any one fhould fay, It is God's Will that a Planet fhould move round in its Orb, without any other Caufe of its Motion; I maintain, that it would be a perpetual Miracle: For by the Nature of Things, the Planet going round tends to remove from its Orb through the Tangent, if no. thing hinders it; and God muft continually prevent it, if no natural Caufe does it. The fame ought to Gg 4

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be laid of your Atoms; for the Body C will be naturally carried away by the Body D, and the Body B will not follow, if nothing hinders fuch a Separati on; and if you look out for the Reason of it in the Will of God, you must suppose a Miracle.

It may be faid in a very good Senfe, That every Thing is a continued Miracle, that is, Worthy of Admiration: But it feems to me that the Example of a Planet, which goes round, and preferves its Mo tion in its Orb without any other Help but that of God, being compared with a Planet kept in its Orb by the Matter, which conftantly drives it towards the Sun, plainly fhews what Difference there is between natural and rational Miracles, and thofe that are properly fo called, or Supernatural; or rather between a reasonable Explication, and a Fiction invented to fupport an ill-grounded Opinion. Such is the Method of thɔse who say, after Mr. de Roberval's Ariftarchus, that all Bodies attract one another by a Law of Nature, which God made in the Beginning of Things. For alledging nothing ele to obtain fuch an Effect, and admitting nothing that was made by God, whereby it may appear how he attains to that End, they have recourte to a Mirace, that is, to a supernatural thing, which continues for ever, when the Queftion is to find out a ną, tural Caufe.

You are in the right, Sir, when you fay, We ought frequently to acknowledge our Ignorance, and that it is a wiser Method than to run into Nonsense, by pretending to account for those things, which we do not understand. But, to own that we know not the Causes of some Effects, is a different thing from affirming, that there are fome things, of which no Reason can be given; which is contrary to the first Principles of Reasoning: Tis just as if some Body had denied the Axiom, which Archimedes made ufe of in his Book de Equiponderantibus, viz. That a Ba lance, when every Thing is equal on both Sides,

remains