Bodies muft have much lefs Motion than an equal Mafs of little ones, fince they may always by that Suppofition communicate their own Motion, but cannot always receive any from the lefTer, Thus this Suppofition being not contrary to all that Monfieur des Cartes had laid down in his Prin- ciples, from the beginning, to the Eftablifrimeht of his Rules of Motion, and according very well with theConfequence of thefe fame Principles, he thought the Rules of Motion, which he believ'd he had demonitrated in their Caufe, were fufficiently confirm'd by their Effects.
I agree with Monfieur des Cartes in the Bottom of the Thing, that great Bodies communicate "their Motion much eafier than the lefTer h and that therefore his firft Element is more agitated than the fecond, and the fecond than the third •, but the Caufe is manifeft without recourfe to his Sup- pofition. Little and fluid Bodies, as Water, Air, tftc. can but communicate to any great ones art uniform Motion, which is common to all their Parts. The Water of a River can only communi- cate to a Boat a defcending Motion, which is common to all the little Parts the Water is compo- led of-, each of which Particles, befides its common Motion, has infinite others, which are par- ticular. Which Reafon makes it evident that a Boat, for inltance, cannot have fo much Motion as an equal Volume of Water, fince the Boat can only receive from the Water a direcl Motion, and common to all the Parts of it. If twenty Parts of a fluid Body drive againft any other Body on one fide whilft there are as many urging it on the other, it remains immoveable; and all the Par- ticks of the furrounding Fluid it fwims in, rebound without lofing any thing of their Motion. Therefore grols Bodies, whofe Parts are united one to the other, can receive only a circular and uniform Motion from the Vortex of the encompafling fubtile Matter.
This Reafon feems fufficient to give us to underftand why grofs Bodies are not fo much agita- ted as little ones ^ and that it is not neceffary to the explaining thefe things, to fuppole any Force in Reft to refill Motion. The Certainty of Monfieur des Cartes's Philofophical Principles cannot therefore be of Ufe in proving or defending his Rules of Motion. And we have Reafon to be- lieve that if Monfieur des Cartes himfelf had, without PrepoiTeflion, examin'd his Principles afrefh, at the fame time weighing fuch Reafons as I have alledg'd, he would not have believ'd the Effe£ts of Nature had corroborated his Rules; nor have fallen into a Contradiction, in attributing the Hardnefs of hard Bodies only to the Reft of their Parts, and their Elafticity to the Effort of the fubtile Matter.
I now come to give the Rules of the Communication of Motion in a Vacuum, which follow up- on what I have before eftablifh'd concerning the Nature of Reft. Bodies being not hard in a Va- cuum, fince they are only fo by the preffiire of the fubtile Matter that furrounds them, if two Bo- dies meet together, they would flatten without rebounding: We muft therefore fuppofe them hard by their own Nature, and not by the preffure of the fubtile Matter, to give thefe Rules.
Reft having no Force to refill Motion, and many Bodies being to be confider'd but as one at the Inftant of their Collifion, 'tis plain they ought not to rebound, lave when they are equal in their Bulk and Swiftnefs, or that their Swiftnefs compenfates for the Want of Bulk, or their Bulk the Want of Swiftnefs. And 'tis eafie from hence to conclude, that they ought in all other Cafes fo to communicate their Motion, as afterwards to proceed along together, with an equal Pace. * General * Wherefore, to know what ought to happen in all the different Suppofitions of the Magnitude Ruiesof the and Celerity of Colliding Bodies, we need only add together all the Degrees of Motion of two or Commiu- more5 which ought to be confider'd but as one in the Moment of their Concourfe, and afterwards Motions! divide the Summ of the whole Motion proportionably to the Bulk of each refpeftive Body, f Semjes Hence I conclude, that of the t feven Rules of Motion, Monfieur des Cartes has given, the cartes's three firft are good.
f uIe5'nthe That the Fourth is falfe, and that B ought to communicate its Motion to C, in proportion to of hisPrfn- ^e bignefs of the fame C, and after go along in Company; fo as if Cbe double to £, and B have cipks. three Degrees of Motion, it muft give away two of them: For I have fufficiently prov'd, that Monfieur des Cartes ought not to have fuppos'd in Reft, a Force to refill Motion. That the Fifth is true.
That the Sixth is falfe, and that B ought to communicate half of its Motion to C. And that the Seventh is falfe, and that B ought ever to communicate its Motion to C, in propor- tion to the Magnitude and Motion of both B and C But that if, according to the Suppofition, C be double to j9, and have three Degrees of Motion, whilft C has but two, they muft proceed together in Company, Cand B being but one Body at the time of their Collifion -, and therefore we muft add together the Degrees of Swiftnefs, which are five, and afterwards divide them in proportion to their bignefs, and fo diftribute i » to B, and 34 to C, which is double to B. But thefe Rules, though certain, from what I have laid, are yet contrary to Experience, fince we are not in a Vacuum.
■ The chief of thole Experiences, which are contrary to what I have faid about the Rules of Mo- tion, is, the conftant rebounding of hard Bodies, when they meet, one one way, and another an- other; or at leaft, their not going in Company after their Encounter.
In Anfwer to which, we muft call to mind what we have formerly faid of the Caufe of Elaftici- ty •, namely, That there is a Matter, of a ftrangely-violent Motion, which continually paffes into the Parts of hard Bodies, and makes them fo by its compreffing both their outward and inward Parts: For it will be eafie from hence to fee, that at the time of Percuffion two encountring Bo- dies drive and turn off the Current of this Matter from the places neareft to the ftricken h which Matter refitting with great Violence, repclls the two Bodies, which llrike againft each other, and rdtores its Paflagc, which the Percuffion had ftopp'd up.
That Chap. IX. The Search after Truth* cjl That which more clearly ftill proves my Opinion is this, That if two Bowls of Lead, or of any other lels Elaitick Matter, meet, they rebound not after their Collifion, but proceed almolt ac- cording to the Rules before eftablifh'd, which they keep to fo much more exactly as they are Lis ipringing. Bodies therefore rebound after their Percuffion, becaufe they are hard ^ that is, as I have explained, becaufe there is an extremely agitated Matter, which compreffes them, and which paifing through their Pores with an extreme Violence, repel the Bodies which ftfike againft them. But it ought to be fuppos'd that the Percutient Bodies break not thofe which they da(h againit by a Motion over-powering the Refiftance the little Parts of the fubtile Matter are capable of making 5 as when we discharge a Musket againft a piece of Wood.
'Tis true, the i'ubtile Matter compreiTes loft Bodies, and paffes with a rapid Courfe through their Pores, no lefs than through thofe of hard • and yet thefe foft Bodies have no Elafticity: The Rea- fon whereof is this \ that the Matter palling through foft Bodies, can with a great deal of Eafe open it lelf new Pallages, by reafon of the Minutenefs of the Parts compofing them, or of fome other particular Configuration, proper for that Effetf; which hard Bodies will not admit, by rea- fon of the Largenefs and Situation of their Parts, which are contrary to the fame.
Thus when a hard Body ftrikes another that is foft, it alters all the Roads the fubtile Matter us'd to pals through, which is commonly vifible ^ as in a Musket-Bullet, which flattens when it is frnit- ten. But when a hard Body ftrikes againft another like it, it either makes none, or very few new Paths; and the fubtile Matter in its Pores is oblig'd to return upon the fame Ground, Or elfe mull repel the Body which blocks up its little Avenues. • Let A be a hard Body, B a foft one, C the Chanel of the fubtile Matter -, I fay, that if A ftrike B in the Point <r, the Chanel Cc is (hut up, and the fubtile Mat- ter finds out new Ways in the foft Body ■ and fo ha- ving an open Road, it repels not the ftriking Body, but the Body ftricken changes its Figure, and batters it felf a little: And it mult be fuppos'd, that in the leaft Body there are infinite PafTages like Cc. But if the Bodies A and a are both of them hard, the Paf- iage Cc is ftraiten'd, and the fubtile Matter included in it continuing its Motion in a Right Line, for want of new Paths, repels the Body ftriking it fo much more violently as it finds greater Difficulty in making a new Way i or elfe the Parts of the Body A break, and fe- /^ ^\^ \ ^ parate from one another, and are reduc'd to-Duft, or Pieces.
Laftly, It feems evident, that every mov'd Body, continually endeavouring to tend in a Right Line, and declining from it as little as is pOflible when it meets Refiftance, ought never to rebound, fince by that Motion it extremely deviates from a Right. 5Tis necelTary therefore, either that Bodies fhould grow flat, or that the ftronger fhould conquer the weaker, and make it bear it company: But becaufe Bodies are fpringing, and hard, they cannot go in company, fince if A pufhes #, a repels A; and fo they mult recede from one another.
Notwithstanding, if two Bodies were in a Vacuum, though never fb hard, they would go in company, becaufe having no Body to furround them, they could have no Elaftick Force, the Striker making no Refiftance to the Striking; but Air, Gravitation, &c. refilling the great Motion which the ftriking Body gives the ftricken, the ftricken refills the ftriking, and hinders it from follow- ing: For Experience teaches, us, that Air and Gravity refill Motion •, and that this Refiftance is fo much greater, as the Motion is more violent. 'Tis eafie to difcover from what I have been fay- ing, how it comes to pafs, that in the Percuffion of different Bodies, encompafs'd with Air or Water, CV. fometimes the Smiting rebounds, fometimes communicates all its Motion, and re- mains as it were unmoveable; and fometimes it follows the Smitten, but always with lefs De- grees of Swiftnels, if one or' other of them he not perfectly foft: For all this depends on the Pro- portion that is found between the Magnitude, the Hardnefs, and the Weight of one and the other, fuppofing them mov'd with an equal Swiftnels: If they are very hard, the Smiting rebounds more, becaufe the Elaterium is ftronger. If the Smiting is very little, the Smitten very large and weighty, the Smiting rebounds ftill much, becaufe of the Weight and the great Mais of Air furround- ing the Smitten, which withftands the Motion. Laft of all. If the Force of the Hardnefs is, as it were, abated by the little Volume of Air anfwering the Littlenefs of the ftricken Body, or the contrary h it may happen that the Smiting may remain as immoveable after the Percuffion. We need therefore but compare the Hardnefs of percutient Bodies, and the Air, which the Percuis'd ought to agitate anew at the time of Percuffion, whereby to move, to give a pretty exact- Con- jecture concerning what muft happen in the Percuffion of different Bodies. I ftill fuppofe an equal Swiftnefs ill the ftriking, for the Air more refills a great Motion than a little one •, and there is as much Motion in a Body twice as little, as in another, when proceeding twice as fall as that other. Thus the Smitten being driven as fall again, may be confider'd as having a Volume of Air twice as big, to repel, in order to its moving.
But it ought itill to be obferv'd, that at the Moment of one Body's ftriking another, the Parts of this fame Body have two contrary Motions j for thofe on the Fore-fide have a backward Ten- dency, $6 F. Malebranche Concerning dency by reafoli of the Collifion, when at the fame time thofe behind tend forwards on the Ac- count of the firft Motion 5 and 'tis that Counter-motion which flattens foft Bodies, and is the Caule that fome hard Bodies break in pieces •, but when Bodies are very hard, this Counter-iiroke, which vibrates fome of the Parts, and makes a fort of Trepidation in them, as appears from the Sound they give, always produces fome Changes in the Communication of Motion, which are very difficult to be known, for many Reafons; and 'tis, in my Mind, to little purpofe to examine them in particular.
Would a Man meditate on all thefe things, I believe he would eafily anfwer fome Difficulties which might ftill be rais'd upon the Subjeft -, but if I thought that what I have faid were infuffl- eient to f hew that Rcfl has no Force to refill Motion, and that the Rules of the Communication of Motions, given by Monfieur dcs Cartes are in part falfe, I would here make Out that it is impof fible by his Suppoiition to move our felves in the Air: And that which makes the Circulation of Motion in Fluid Bodies poflible, without recurring to a Vacuum, is, that the firft Element eafily divides it felf in feveral different manners, the Repofe of its Parts having no Force to refill Motion.
The CONCLUSION of the Three laft BOOKS.
I Have, if I miftake not, fufficiently fhewn in the Fourth and Fifth Booh, that Men's natural In- clinations and Pailions frequently occafion their falling into Errour:, becaufe they induce them more to a precipitate Judgment, than a careful Examination of Things. . I have fhewn in the Fourth 'Book, that our Inclination for Good in general, is the Caufe of the Reftlefnefs of the Will; that this Reftlefnefs of the Will puts the Mind in continual Agitation -, and that a Mind continually agitated, is utterly unfit for the Discovery of any the leaft intricate and hidden Truths: That the Love of new and extraordinary Things frequently prepoiTeffes us in their behalf. ^ and that whatever bears the Character of Infinite, is capable of confounding out Ima- gination, and mifleading us. I have explain'd how our Inclination for Greatnefs, Elevation and Independency infenfibly engage us in a falfly-pretended Learning, or in the Study of all vain and ulelefs Sciences, which flatter the fecret Pride of our Heart; becaufe this is what recommends us to the Admiration of the Vulgar. I have fhewn, that the Inclination for Pleafures conftantly throws off the View of the Mind from the Confideration of abftra&ed Truths, which are the molt fimple and exuberant-, and permits it not to confider any thing, with a competent Attention and Impartiality, to judge well of it: That Pleafures Wing the Modes of our Souls Exiftence, they neceflarily divide the Capacity of the Mind -, and that a Mind thus divided, cannot fully compre- hend a Subject of any great Extent. Laft of all, I have made appear, that the Relation and Natu- ral Union we have to all thofe with whom we live and converie, is the Occafion of many Errours we fall into, and of our communicating them to others, as others communicate to us the fame they were engaged in.
In the Fifth, where I have endeavour'd to give fome Idea of our Paflions, I have, I think, made it fufficiently evident, that they were ordain'd to unite us to all things fenfible •, and to give us, as we are among them, a due and necelTary Difpofition for their Prefervation and our own: That as our Senfes unite us to our Body, and expand our Soul into all the compofing Parts of it; fo our Commotions carry us, as it were, out of our felves, and diffufe us upon all things round about us: That, Laft/y, they inceffantly reprefent things, not as they are in themfelves, whereby we may form true Judgments; but according to the Relation they have to us, whereby to form Judg- ments ufeful to the Prefervation of our Being, and of thofe to whom we are either naturally or voluntarily united.
After having attempted the Difcovery of Errours in their Caufes, and the Deliverance of the Mind from the Prejudices it is fubjeft to, I thought it was time at laft to prepare it for the Search of Truth. Wherefore, in the Sixth Book, I have explain'd the Means which I thought moft na- tural for the increafing the Attention, and enlarging the Capacity of the Mind, by fhewing the life that might be made of its Senfes, its Fajfons, and Imagination, to the giving it all the Force and Penetration it is capable of After which, I have eftablifh'd certain Rules, which muft of ne- ceffity be obferv'd for the Difcovery of any Truth whatever: I have explain'd them by many Ex- amples, that I might make them more fenfible; and have chofen thole which I thought molt ufe- ful, or that included more fecund and general Truths; that they might be read with greater Ap- plication, and be made more fenfible and familiar.
Poflibly it may be acknowledg'd, by this Ejfay of Method which I have given, how necelTary it is to reafon only about clear and evident Ideas, and in which we are inwardly convine'd that all Nations do a"gree •, and never to proceed to Compound Things, till having fufficiently examin'd the Simple, whereon they depend.
And if it be confider'd that Arijlotle and his Followers have not obferv'd the Rules I have ex- plain'd, as we ought to be affur'd by the Reafons I have alledg'd, and by the Correfpondence that may be had with the moft zealous Defenders of that Philofopner, it may be we fhall deipife his Do'f trine, in fpight of all the Impreflions which petfuade fuch as give way to be amuz'd by Words they do not underftand.
Bui The Search after Truth. <pj But if we take notice of the manner of Monfieur des Cartes's Philofophizing, we cannot doubt of the Solidity of his Philofophy: For I have fufficiently fhewn that he reafons but upon diftincl and evident Ideas; beginning with molt Simple Things, and afterwards palling on to the more Compound, which depend on them. Thole who mall read the Works of that Learned Man, will have plenary Conviction of what I fay of him, provided they read them with all the Application that is necelfary to underftand them: And they will feel a Secret Joy, for being born in an Age and Country lb fortunate, as to free them from the Trouble of Seeking a Matter to teach therh Truth, among the paft Ages of the Heathens ^ and in the Extremities of the Earth, among Bar- barians and Strangers.
But as we ought not to be very follicitous to know the Opinions of Men, even though we were otherwile afliir'd they had found out Truth; fo I mould be very forry if the Efteem I manifeft for Monfieur des Cartes lhould prepoiTefs any Man in his behalf, and make him lit down latisfy'd with reading and retaining his Opinions, without caring to be enlightened with the Light of Truth. This would be preferring Man before GOD, and confulting him in God's Steady and acquiefcing in the obfeure Anfwers of a Philofopher, which do not enlighten us, to avoid the Trouble of In- terrogating by our Meditation Him who anfwers and enlightens us both together.
'Tis a mean and unworthy thing to become the Partizan of any Seel:, and to look upon the Au- thors of it as infallible. And thus Monfieur des Cartes, chufing rather to make Men Difciples of Truth, than Opinionated Followers of his Sentiments, exprefsly forewarns them. Not to take any thing he ivrites upon Tritji, and to embrace nothing but what the Force and Evidence of Reafon Jhould con f rain them to believe. Fie delires not, like fome Philofophers, to be credited upon his Word: He ever remembers that he is a Man j and that diffeminating his Light but by Reflexion, he ought to direct: the Minds of thofe who would be illuminated by him, towards Him alone who can make them more perfect by the Gift of Underltanding.
The principal Advantage that can be made of Application to Study, is, the rendring the Mind more accurate, more illuminated, more penetrating, and fit for the DiScovery of all the Truths we defire to know. But fuch as read the Philofophers, with Defign of remembring their Opinions, and factoring them to others, approach not Him who is the Lite and Nourishment of the Soul: Their Mind grows blind and enervate, by their Commerce with fuch as can neither Strengthen nor enlighten them: They are fwell'd up with a fpurious fort of Learning, the Weight whereof over- whelms, and the Glittering blinds them; and fancying to themfelves they are hugely learn'd when their Heads are cramm'd with the Opinions of the Antients, they forget that they become their Difciples who, St. Paul fays, became Fools by ufurping the Name of Wife. Dicentes fe efe Sa- pientes, fiulti fatli funt.
The Method I have given will, if I miftake not, be highly advantageous to thofe who defire to make ufe of their Reafon, or to receive of God the Anfwers he gives all thofe who can faithful- ■ ly confult Him r For I think I have faid what is chiefly requir'd to corroborate and conduct the Attention of the Mind ^ which is, the natural Prayer we make to the true Matter of all Men, in order to be instructed.
But becaufe this Natural Way of Searching out Truth is very painful, and commonly impracti- cable, except in the Refolution of Quettions of little Ufe, the Knowledge whereof commonly more gratifies our Pride, than perfects our Underltanding ^ I think it my Duty to fay, (that I may profitably conclude this Work,) that the molt expeditious and certain Method of difcovering Truth, and uniting our felves to God in the purelt and perfecteft manner poffible, is, to live as becomes true Chnfians h to follow exactly the Precepts of Eternal Truth, which unites it felf with us, only to re-unite us with it: 'Tis to liften rather to the Dictates of our Faith, than Reafon; and to tend to God, not fo much by our natural Forces, which, fince the Sin, are altogether languid and in- active •, as by the Affiitance of Faith, by which alone God purposes to lead us into that immenie Light of Truth which will diffolve and diffipate all our Darknefs: For, in brief, 'tis much better, as good Men, to fpend fome Years in Ignorance of certain Things, and find our felves enlighten'd in a Moment, for ever •, than by Natural Means, and abundance of Trouble and Application, pur= chafe a very imperfect Science, that Shall leave us in Darknefs to all Eternity.
The PREFACE: Wherein is (hewn what pjould be our Opinion of the federal Judgments com- monly pafs'd on Books, that encounter Prejudices.
WHen a B 0 OK is firft to appear in the World, one knows not whom to confult to learn its Deltiny: The Stars prefide not over its Nativity, their Influences have no Operation on it; and the molt confident Aftrologers dare not foretell the diverfe Risks of Fortune it muft run: Truth not being of this World, Celeftial Bodies have no power over her; and whereas (he is of a moft fpiritual Nature, the feveral Pofitions or Combinations of Matter can contribute noth'ng ei- ther to her Eftablifhment or Ruine. Befides, the Judgments of Men are fo different in refpe£t of the fame things, that we can never more hazardoufly and imprudently play the "Prophet, than in pre- faging the happy or unfortunate Succefs of a BOOK. So that every Man who ventures to be an Au- thor, at the fame time throws himfelf at the Reader's Mercy, to make him or eft eem him what he pleales: But of all Authors, thofe who encounter Prejudices ought moft infallibly to reckon upon their Condemnation; their Works fit too uneafie on moft Mens Minds, and if they eicape the Pafc fions of their Enemies, they are obliged to the almighty Force of Truth for their Protection.
:Tis a common Mifcarriage with all Mankind, to be too precipitate in judging; for all Men are obnoxious to Errour, and only obnoxious upon this account: But all hafty and raffi Judgments are ever confonant to Prejudices •, and therefore Authors who oppugn them, cannot poffibly eicape 8ente?ice from all their Judges, who appeal to Ancient Opinions, as the Laws whereby they ought to pronounce. For indeed moft Readers are both Judge and Party, in refpeft of thefe Authors. Their Judges they are, that Quality is inconteftable; but they are a Party likewife, being difturb'd by thefe Authors in the poiTeffion of their ancient Prejudices, for which they have the plea of Pre- fcription, and to which they have been accuftom'd many Years.
I confefs there's Abundance of Equity, Sincerity, and good Senfe in a great many Readers; and that they fometimes are Judges rational enough to fuperfede common Opinions, as not being the infallible Rule's of Truth. Many there are who retire into themfelves, and confult that Inward Truth, which ought to be their Rule to judge of all things; but very Few that confult it upon all Occafions, and IS! one at all who do it with all that Faithfulnefs and Attention, that is necenary to judge infallibly at all times. And thus, though we might fuppofe there were nothing blameable in a Treatife, which yet it would be Vanity to pretend to, I am perfuaded it would be impoff.ble to find one fingle Man to approve it in every refpe£t; efpecially if his Prejudices were attacked by it; fince it is not naturally poiTible, that a Judge conftantly provok'd, affronted and outraged by a Party, fhould do him entire Juftice; or that he fhould give himfelf the trouble of a ftrenuous Ap- plication to thofe Reafons, which at firft fight appear to him as extravagant Paradoxes, or ridicu- lous Parologifms.
But though a Man be pleafed with many things in a BOOK, if he fortunes to meet with fome that are offenfive, he (hall feldom be wanting to /peak ill of it, but moft commonly forgetfull to give it any good Charathr. Self love has a thoufand Motives to induce us to condemn what we diilike; andReafon in.this Inftance fully juftifies thefe Motives: fince Men fanfie they condemn Errours, and defend Truth, when they defend their Prejudices, and cenfure thofe that affault them. So that the moft equitable Judges of Books that fight againft Prejudices, pafs commonly fuch a general Sentenfe as is no way favourable on their behalf. Perhaps they will fay, there is fomething good in fuch a Work, and that the Author juftly oppofes certain Prejudices; but yet they fliall be lure to condemn him 5 and as his Judges give an authoritative and grave decifion upon the point, main- taining that he carries things too far on fuch or fuch an occafion. For when an Author is ruining Prejudices which the Reader is not prepoffefs'd with, whatever he (hall fay will feem reafonable enough: But the fame Author ever itretches things too fir, when he engages the Prejudices where- with the Reader is too deeply ting'd.