If we know that the Parts of the Air are in per- petual Agitation, as thofe of all fluid Bodies ufe to be, we fhall not doubt but they continually ftrike againft the Load-ftone c, which they fur- round •, but becaufe they ftrike it equally on all fides, they impel it one way no more than another, • as >^ Chap. VIII. The, Search after Truth. 8 as long as there is an equal Quantity of Air on all fides. It being fo, 'tis eafie to judge that the Magnet C hinders, left there fhould be as much Air towards a as towards /;, which cannot be done but by its difFufing fome other Corpufcles betwixt C and c, and therefore there exhale fuch Particles out of both Load-ftones, which filling up that Space, and carrying away the Air about a, make the Load-itone c lefs prefs'd on that fide than on the other; and it mult by cohfequence approach the Magnet C, fince all Bodies move towards the fide on which there is the leaft Pfeffure or Re- filtance..
But if in the Load-ftone c, about the Pole a, there were not many Pores fit to receive the fmall Particles ftreamtng out of the Pole B of the Magnet C, and too fmall to admit tliofe of the Air, 'tis plain that thole fmall Particles being more agitated than the Air, fince they are to chafe it from betwixt the Load-ftones, they would drive the Load-ftone c, and remove it from the Mag- net C: Therefore, fince the Load-ftone c approaches to, or removes from the Magnet C, accord- ing as they are oppos'd by different or the fame Poles, we muft needs infer that the Poles a and b of the Load-ftone c are full of different Pores; otherwife, the fmall Particles iffuirig out of the Magnet C could not have a free PafTage, without impelling the Load-ftone c at the fide a, nor would they repel it at the fide b. What I fay of one of thefe Load-ftones, muft be underftood of the other.
Tis plain that we always learn fomething by that Method of Arguing from clear Ideas, and un- deniable Principles: For we have difcover'd that the Aif which environs the Load-ftone c, was driven from thence by Corpufcles perpetually flowing out of the Pores of both Load-ftones; which Corpufcles find a free PafTage at one fide, but are fhut out at the other. If We defir'd nearly to diicover the Bignefs and Figure of the Pores of the Load-ftone through which thofe Particles pafs, we ought to make other Experiments; but that would lead us to Subjects which we intend not to treat of The Curious may confult des Cartels Principles of Philofopby: I only obferve, as an Anfiver to an Objection which will prefently be made againft this Hypothec's -, that is, Wby tbofe fmall Particles cannot re-enter tbrougb tbe Pores from whence they came? That befides that the Pores of the Load-ftones may be fuppos'd to be wrought like the Channelling of a Screw, which may pruduce the propos'd ErrecF; it may be faid likewife, that the fmall Branches, of which thofe Pores are made, bend one way to obey and yield to the Motion of the entring Particles; whereas they ftand on end, and fhut them out another way: So that we muft not be furprrz'd at tliis Difference betwixt the Pores of the Load-ftone, for it may be explain'd in feveral manners, and the only Difficulty confifts in chufing the beft.
If we had endeavour'd to refolve the fore-mention'd Queftion, beginning witli the Corpufcles that are fuppos'd to ftream out of the Magnet C, we mould have found the fame; and likewife difcover'd that Air is compos'd of an infinite Number of Parts that are in a perpetual Motion, with- out which it would be impoflible that the Load-ftone c could approach the Magnet C. I infill not 'on the Explication of this, becaufe there is no Difficulty in it. '..■'.
Here follows a Queftion more compound and complicate than the fore-going •, for the Solution of which, 'tis neceffary to make ufe of many Rules. 'Tis ask'd, Which may be tbe Natural and Mecbanical Caufe of tbe Motion of our Members.
The Idea of Natural Caufe is clear and diftincF when underftood, as I have explain'd it in the former Queftion: But the Words, Motion of our Members, are equivocal and confiis'd, becaufe there are feveral fuch Motions •, fome being Voluntary, others Natural, and others Convulfive. There are alfo different Members in the Humane Body -, and therefore, according to the firft Rule, I muft ask, Of which of thefe Motions the Caufe is requir'd from me? But if the Queftion be left undetermined, and to my Difcretion, I examine it after this manner.
I attentively confider the Properties of thofe Motions; and difcovering at firft that Voluntary Motions are fooner perform'd than Convulfive, I infer that their Caufe is different, and therefore that I may and muft examine the Queftion by Parts, for it feems to require a long Difcuflion.
I reftrain then my felf to confider only Voluntary Motions; and becaufe feveral of our Members are employ 'd about them, I content my fclf for the prefent with the Confidefation of the Arm. I obferve that it is compos'd of feVeral Mufcles, which are moft or all in Acfion when we raife fo'.nething from the Ground, or remove it from one place to the other: But I only infift upon one, being willing to fuppofe that the others are very near fafhion'd after the fame manner. I inform my felf of its Texture and Shape by fome Book of Anatomy, or rather by the fehfible Sight of its Fibres and Tendons, which I caufe to be differed in my prefence, by fome skilful Anatbmift, to whom I put all the Queries which, in the fequel, may exhibit to my Mind a Medium tdfind out what I feek for.
After fuch a ferious Confideration, I cannot doubt but the Principle of the Motion of my Arm depends on the Contraction of its Mufcles which compofe it. I am likewife content, left I fhould puzzle my felf with too many Difficulties, to fuppofe, according to the common Opinion, that this Contraction is perform'd by the Animal Spirits, which filling up the Ventricle of thofe Muf- cles, may caufe their Extremities to come nearer. Now the whole Queftion concerning Voluntary Motion is reduc'd to this Pointy Hozb tbe fmall Quantity of Animal Spirits which are contained in our Arm, may at tbe Command of tbe Will, fo fuddenly /well the MuJ "dies, di to afford afufficient Strength to lift up an Hundred Weight, or more.
Upon an attentive Reflexion thereupon, the firft Means that offers it felf to the Imagination, is commonly that of a quick and violent Fermentation, like to that of Gun-pOwder, or of fome • Liquors fill'd with Volatile Salt, when they are mix'd with others that are Acid, or full of a X fixed %i F. Malebranche Concerning BookVt' fixed Salt. A final! quantity of Gun-powder is able, when kindled, to raife not only an Hun- dred Weight, but even a Tower,, and a Mountain. Earthquakes, that overthrow Cities, and lhake whole Countries, proceed from Spirits kindling under the Ground, almoft as Gun-powde:, So that iuppofing in the Arm fuch a Caufe of the Fermentation and Dilatation of the Spirits, ir. may be look'd upon as the Principle of that Force, by which Men perform fo fudden and violent Motions.
But as we ought to miftruft thofe Means that are offefd to the Mind by the Senfes, and of which we have no clear and evident Knowledge, fo we mult not eafily admit this; for it is not fufficient to give an Account of the Strength and Quicknefs of our Motions, by a Comparifon:; For this is both a confused, and imperfeS Account h becaufe we are here to explain a volunta- ry Motion, and Fermentation is not fo. The Blood is exceedingly fermented in Fevers, and we cannot hinder it: The Spirits are infiam'd and agitated in the Brain, but we cannot rule their Agitation, nor leffen it by our Defire. When a Man moves the Arm feveral Ways, a Thouland Fermentations, great and fmall, fwift and flow, ought to begin, and (what is harder to ex- plain) to end likewife in a Moment, as often and as foon as it is defir'd, if this Hypothefis were true. Befides, Thofe Fermentations ought not to diflipate all their Matter, but need al- ways be ready to take Fire. When a Man has walk'd Twenty Miles, how many Thoufand times muff the Mufcles, employ'd in walking, have been fill'd and empty'd h and what a vaft quantity of Spirits would be requir'd, if Fermentation mould diffipate and deaden them fo often? And therefore this Suppofition is infuiflcient to explain fuch Motions of our Body as entirely depend upon our Will.
3Tis plain that the prefent Queftion may be reduc'd to this Problem of Mechanicks, To find out by Fneumatick Engines a Means to overcome fuch a Force of an Hundred Weight by another Force, though never fo fmall \ a* that of an Ounce Weight: And that the Application of that fmall Force may produce the defied Effetl, at the Difcretion of the Will. The Solution of that Problem is eafie, and the Demonftration of it clear.
It may be folv'd by a VeiTel which hath two Orifices, one of which is a little more than 1600 times larger than the other, in which the Pipes of two equal Bellows are inferted; and let a Force precifely 1600 times ftronger than the other be apply'd to the Bellows of the larger Mouth, for then the Force 1600 times weaker fhall overcome the ftronger. The Demonftration of which is clear in Mechanicks, fince the Forces are not exaftly in a reciprocal Proportion with their Mouths; and that the Relation of the weaker Force to the fmaller Mouth, is greater than the Relation of the ftronger Force to the larger Mouth.
But to folve this Problem by an Engine which fets better before the Eyes the Effecl of the Muf- cles, than the Former: We muft blow a little in a Foot-ball, and hinder the Air from going out with a Sucker; then put upon that Foot-ball, half full of Wind, a Stone of 5 or 600 weight -, or having fet it on a Table, lay on it a Board, and on that Board a huge Stone, or caufe a heavy Man to fit upon the Board, allowing him to hold by fomething, that he may fit the fafter upon the riling Foot-ball -, for if you blow again into it only with the Mouth, it will raife the Stone that compreffes it, or the Man that fits upon it. The Reafon of this is, that the Mouth of the Foot-ball is fo fmall, or at leaft muft be fuppos'd fo, in comparifon to the Capacioufnefs of the Foot-ball that withftands the Weight of the Stone, that by fuch means a very fmall, is able to over- come a very great Force.
If we alio confider that Breath alone is capable of violently driving a Leaden Ball through a long and ftrait Trunk, becaufe the Strength of the Breath is not diffipated, but continually re- newed, it will vifibly appear, that the neceffary Proportion betwixt the Mouth and the largenefs of the Foot-ball being fuppos'd, Breath alone may overcome a very confiderable Force.
If we therefore conceive that the whole Mufcles, or each of the Fibres of which they are made, have, as this Foot-ball, a competent Capacity to admit Animal Spirits, that the Pores through which thofe Spirits flow are yet proportionably ftraiter than the Neck of a Bladder, or the Aper- ture of the Foot-ball; that the Spirits are detain'd in, or driven through the Nerves, almoft as the Breath through a Trunk; that the Spirits are more agitated than the Air of the Lungs, and dri- ven with a greater Violence to the Mufcles than it is in a Bladder -y we fhall perceive that the Mo- tion of the Spirits which are difpers'd through the Mufcles, can conquer the Force of the heavieft Weight we carry ^ and that if we cannot move other more ponderous, this Want of Strength pro- ceeds not fo much from the Spirits, as from the Fibres and Membranes of which the Mufcles are compos'd, which would burtt fhould we make too great an Effort. Befides, If we obferve that, by the Laws of the Union betwixt Soul and Body, the Motion of thofe Spirits, as to their Deter- mination, depends on the Will of Man, we fhall fee that the Motion of the Ann muft needs be vo- luntary.
Tis true that we move our Arm fo readily, that it feems, at firft fight, incredible that the CourTe of the Spirits into the Mufcles fhould be fo fwift as to effecl; that Motion. But we ought to confider that thole Spirits are extremely agitated, always ready to pafs from one Mufcle into another; and that a fmall quantity of that Spirituous Liquor may fuificiently fwell them up, fo as to move them, or to lift up from the Ground fomething very light: For we cannot raife great Weights very readily, becaufe that Effort requires a great ftretching and fwelling of the Mufcles, which cannot be perfbrm'd by the Spirits that are in the neighbouring 01 Ant agon i ft Mufcles -, and therefore lotrie Time is requifd to call in more Spirits to their help, and in fuch a Quantity, as that they may be able to with Hand the Heavineis of the Weight, Thus we fee that thofe fchap. VIII. the Search after Truth. 83 thofe that are loadeii cannot run, and that a ponderous thing is not lifted up from the Ground fb readily as a Straw.
If we coniider that thofe that are of a fiery Temper, or heated with Wine, are quicker than §therss that amongft living Creatures, thofe whofe Spirirs are more agitated, as Birds, move fwifter than thofe in which Blood is colder, as it is in Frogs ^ and that in fome of them, as the Chamelion, theTortoife, and fome Infecls, the Spirits are fo little agitated, that their Mufcles are not fooner fill'd than a Foot-ball would be by the Brearh of a Man. AH thefe things being well ob- ferv'd, may probably make our Explication acceptable. • ^ But though that part of the Queftion propos'd which concerns Voluntary Motions be fufficient- ly refolv'd, yet we rauft not alTert that it is fully and perfectly, or that nothing elfe in our Body contributes to thofe Motions beiides what has been mention'd -, for moft probably there are a Thou- fan.l Springs that facilitate them, which will for ever be unknown, even to thofe who give a better Guels upon the Works of God.
The fecond Part of the Queftion to be examin'd concerns the Natural Motions, or thofe that have nothing extraordinary in them, as Convulfions have •, but are abfolutely neceiTary to the Pre- fervation of our Machine, and confequently altogether independent on our Will.
I firft confider with all the poffible Attention, what Motions have thofe Conditions, and whe- ther they are perfectly alike: And as I quickly perceive that they are for the moft part different from each orher, left I fliould perplex my felf with too many things, I fliall only infill upon the Motion of the Heart •, which, of all the inward Parts, is the belt known, and its Motions the raoit fenfible. Whilft I examine its Conftru&ion, I obferve two Things, amongft many others: Firft, That it is compos'd of Fibres, as the other Mufcles: And Secondly, That there are two re- markable Cavities in it: And therefore I judge that its Motion may be perform'd by means of the Animal Spirirs, fince ir is a Mufcle^ and that the Blood ferments and dilates in it, fince it has Cavities. The firft of thefe Judgments is founded upon what I have faid before: The fecond, upon the Heart's being much hotter than any other Parts of the Body ^ and that it difTufes Heat, together with Blood, into all our Members ^ and that thofe two Ventricles could neither be form'd, nor preferv'd, but by the Dilatation of the Blood: So that they are fubiervient to the Caufe that has produc'd them. I can then give a fufficient Reafon of the Motion of the Heart, by the Spirits that agitate, and the Blood that dilates it, during the Fermentation: For though the Caufe I alledge of its Motion fhould not be true, yet I plainly fee that it is fufficient to pro- duce it.
Tt may be, that the Principle of Fermentation or Dilatation of Liquors is not fo well known to all Readers, as that I may pretend to have explain'd an EfFeft:, by generally mewing that it pro- ceeds from Fermentation: But all particular Queftions are not to be refolv'd by afcending to the firft Caufe, though that may be done too, and a true Syftem on which all particular Effects depend, difcovef d, provided we only infift upon clear Ideas. But that Way of Philofophizing is neither the exaO:eft, nor yet the fhorteft.
To comprehend this, it muft be obferv'd that there are Queftions of two forts; in the firft, it is requir'd to difcover the Nature and Properties of fome Thing •, in the others, we only defire to know whether a Thing has fuch or fuch Properties j or if we know it has, we defire only to di£ cover what is the Caufe of them.
To folve the Queftions of the firft fort, we muft confider Things in their Birth and Original, and conceive that they are always produc'd by the moft fimple and natural Ways: But the Solu- tion of the others requires a very different Method, for they muft be refolv'd by Suppofitions •, and then we muft examine whether thofe Suppofitions induce into any Abfurdity, or whether they lead to any Truth plainly and clearly known.
For inftance, We defire to difcover the Properties of the Rou/et, or fome one of the Coniek Seffions: We muft confider thofe Lines in their Generation, and form them by the moft fimple and leaft perplexing Ways; for that is the belt and fhorteft Means to difcover their Nature and Properties. We eafily fee that the Subtendent of the Roulet is equal to the Circle whence it is form'd: And if we difcover not many of its Properties that way, 'tis becaufe the Circular Line that produces it is not fufficiently known. But as to Lines merely Mathematical, the Relations of which may be more clearly known, fuch as are Coniek Settions •, 'tis fufficient for the difcover- ing a vaft Number of their Properties, to confider them in their Generation: Only we muft ob- ferve, that as they may be produc'd by a Regular Motion feveral Ways, fb all forts of Generation are not equally proper to enlighten the Mind •, that the moft fimple are the belt ^ and that it of- ten happens, notwithftanding that fome particular Methods are fitter than others, to demonftrate fome particular Properties.
But when it is not requir'd to difcover in general the Properties of a Thing, but to know whe- ther fuch a Thing has fuch a Property ^ then we muft fuppole that it actually enjoys it, and care- fully examine the Confequences of that Suppofition, whether it induces into a manifeft Abfurdi- ty<, or leads to an undeniable Truth, that may ferve as a Means to find out what is fought for. That is the Method which Geometricians ufe to folve their Problems: They fuppofe what they feek, and examine what will follow of it •, they attentively confider the Relations that refult from the Suppofition •, they reprefent all thofe Relations that contain the Conditions of the Problem, by Equations, and then reduce thofe Equations, according to the ufual Rule's; fb that what is unknown, is found equal to one or feveral Things perfectly known, I fay ^. F. Malebranche Concerning Book VI.
I fay therefore, that when 'tis requir'd to difcover in general the Nature of Fire, and of the dif- ferent Fermentations, which are the moft univerfal Cauies of^iatural Effecfs, the fhorteft and ih- reft Way is to examine them in their Principle. We mull confider the Formation of the molt agi- tated Bodies, the Motion of which is diffus'd into thofe that ferment. We muft by clear Ideas, and by the moft fimple Ways, examine what Mot,ion may produce in Matter. And becaufe Fire and the various Fermentations are very general Things, and coniequently depending upon few Cauies, there will be no need of confidering very long what Matter is able to perform when ani- mated by Motion, to find out the Nature of Fermentation in its very Principle; and we fhall learn withall feveral ot^r Things, altogether requifite to the Knowledge of Phyficks: Whereas he that would in fuch a'Queftion argue from Sitppafitions, fo as to afcend to the firft Cauies, even to the Laws of Nature, by which all things are form'd, would make a great many of them that fhould prove falfe and unprofitable.
Fie might perhaps difcover that the Caufe of the Fermentation is the Motion of an invifible Matter, communicated to the agitated Parts of Matter: For 'tis fufficiently known, that Fire and the various Fermentations of Bodies, confift in their Agitation •, and that by the Laws of Nature, Bodies receive their immediate Motion only from their meeting with others that are more agita- ted: So that he might difcover that there is an invifible Matter, the Motion of which is commu- nicated to vifible Bodies by Fermentation. But 'tis morally impoffible that he mould ever, by his Siippofitions find out how all that is perform'd •, which however is not fo hard to do, when we examine the Formation of Elements, or of Bodies, of which there is a greater Number of the fame Nature ^, as is to be feen in Monfieur des Cartes's Syftem.
The Third Part of the Queftidn concerning Convulfive Motions, will not be very difficult to folve, if we fuppofe that there are in our Bodies Animal Spirits fufceptible of Fermentation • and withall, Humours fo piercing, as to infinuate themfelves into the Pores of the Nerves, through which the Spirits are diftus'd into the Mufcles; provided always that we pretend not to determine the true Texture and Difpofition of thofe invifible Parts that contribute to thefe Convulfions.
When we have feparated a Mufele from the reft of the Body, and hold it by the two Ends, we fenfibly. perceive that it endeavours to contract it felf when prick"d in the Middle. 'Tis likely that this depends on the Conftru&ion of the imperceptible Parts, of which it is made ^ which are as fo many Springs determin'd to fome certain Motions, by that of Compuncfion. But who can be fare he has found out the true Difpofition of the Parts employ'd in the Producfion of that Mo- tion ^ and who can give an uncontroverted Demonftration of it > Certainly that appears altogether impofhble, though perhaps by long thinking we might imagine fuch a Conftruclion of Mufcles, as would be fit to perform all the Motions we know them to be capable of ^ we muft not therefore pretend to determine the true Conftruftion of the Mufcles. However, becaufe it cannot be rea- fonably doubted, but that there are Spirits fufceptible of fome Fermentation, by the Mixture of a very fubtile heterogeneous Matter •, and that acriminious and pungent Humours may creep into the Nerves, that Hypothecs may be fuppos'd.
Now to proceed to the Solution of the Queftion propos'd: We muft firft examine how many forts of Convulfive Motions there are -, and becaufe their Number is indefinite, we muft infift on the Principal, the Caufes of which feem to be different: We muft confider in what Parts they are made, what Difeafes precede and follow them; whether they are attended with Pain, or free from it •, and above all, what are the Degrees of their Swiftnefs and Violence; for fome are ve- ry fwift and violent -, others are very fwift, but not violent •, a third fort are violent, and not fwift j and others again are free from both thefe Symptoms: Some finifh and begin afrefh perpetually, others keep the Parts rigid and unmoveable for fome time; and others deprive us of their life, and altogether deform them.
All this being well weigh'd, it will be no hard matter to explain in general, after what has been laid concerning Natural and Voluntary Motions, how the Convulfive are perform'd: For if we conceive that fome Matter, capable of fermenting the Spirits, mixes with thofe contain'd in a Mulcle, it muft needs fweli up, and produce in that part a Convulfive Motion.
If that Motion may eafily be refifted, 'tis a fign that the Nerves are not yet obftru£ted by any Humour, fince we may empty the Mufele of the Spirits that have enter'd into it, and determine them to fwell up the oppofite Mufele. But if we cannot do it, we muft conclude that pungent and piercing Humours have fome p^art atleaft in that Motion: Even it may often happen that thofe Humours are the only Caufe of Convulfions, fince they may determine the Courfe of the Spirits to fome certain Mufcles, by opening fome Paffages that convey them, and fhutting others: Be- fides, that they may contract the Tendons and Fibres, by penetrating their Pores.
When a very ponderous Weight hangs at the end of a Rope, it may confiderably be rais'd by only wetting that Cord; becaufe the Particles of Water penetrating as fo many little Wedges be- twixt the Threads of the Rope, fhorten it by dilating it: So the piercing and pungent Humours, infinuating into the Pores of the Nerves, contracf them, ftretch the Parts to which they are tied, and produce in the Body Convulfive Motions, that are extremely flow, violent and painful, and and often leave the Part fadly diftorted for a long time.
As to the Convulfive Motions that are very fwift, they are caus'd by the Spirits; but it is not neceftliry that thole Spirits fhould receive any Fermentation •, 'tis enough that the Conduits, through which they pals, be more open at one fide than at the other.
When Chap. IX. The Search after Truth. ' %* When all the Parts of the Body are in their natural Situation, the Animal Spirits diffufe them- felves equally and readily through them, according to the Neceffities of the Machine, and faith- fully perform the Orders of the Will. But when Humours difturb the Difpofition of the Brain alter or varioully move the Apertures of the Nerves, or penetrate into the Mufcles, they agitate Their Springs; and the Spirits diffuhng into thofe Parts after a new and unufual manner, produce extraordinary Motions, without the Confent of the Will.
However, we may often, by a ftrong Refiftance, hinder fome of thofe Motions, and infenfi- bly diminifh the Traces that produce them, even when the Habit is wholly form'd. Thofe that look carefully to themfelves, find little Difficulty in preventing Grimaces, unbecoming Geltures, and a fourifh Countenance, though their Body have a Difpofition to them j and may even con- quer them when itrengthen'd by Habit, but with a great deal more Difficulty • for fuch Difpofi- tions mould always be oppos'd in their Birth, and before the Spirits have traced out a Way not eafie to be ftopp'd up.
The Caufe of thofe Motions is often in the agitated Mufcle, and proceeds from fome pungent Humour, or fermenting Spirits; but we mull judge that it is in the Brain, efpecially when the Convulfions agitate not one or two parts of the Body, but moft or all; and withall, in ieveral Difeafes which alter the natural Conftitution of the Blood and Spirits.
'Tis true, that one Nerve often having different Branches, which difperfe through Parts of the Body very remote, as into the Face and Bowels, it fometimes happens that a Convulfion, the Caufe of which lies in a Part to which fome one of thofe Branches reforts, may have Communi- cation with thofe to which -other Branches reach, without proceeding from the Brain, and with- out a Corruption of the Spirits.
But when the Convulfive Motions are common to moft Parts of the Body, we muft needs fay, either that the Spirits ferment in a very extraordinary manner, or that the Order and Difpofition of the Parts of the Brain is difturb'd, or that it proceeds from both Caufes together. I (hall not irifift any longer upon this Queftion, becaufe it grows fo compound, and depending on fo many things, when we enter into Particulars, that it cannot eafily be made ferviceable to a clear Expli- cation of the Rules we have given.