ThMd'- ■ 1 ne ^r^-' t"ne mo^- univerfaU and fometimes the fafeft way we have, whereby to judge of the ums where- diftance of Objects, is the Angle made by the Rays of our Eyes, whereof the Object is the Verti- by we bww cal Point, that is, the Object is the Point, where the two Rays meet. When this Angle is very the Diftan- large, the Object appears near at hand, on the contrary when it is very acute, we fee the Object ces of ob- a great way off! ' And the change which happens in the fituation of our Eyes, according to the ^exminei. changes of this Angle, is the means the Soul imploys to judge concerning the Diftance or Nigh- nefs of Objects. For juft as a Blind Man having two ftrait Sticks in his hands,the length whereof he did not know, may by a kind of Natural Geometry give a tolerable conjecture concerning the di- ftance of any Body, in touching it with the end of his two Sticks, by reafon of the Difpofition and 77*? soul rjiftance he finds his hands in, with refpect to one another •, fo it may be faid that the Soul judges mike11 "all of the Diftance of an Object by the Difpofition of her Eyes, which is different according as the thofe judg- Angle, whereby fhe fees, is great or little, that is, as the Object is nearer or farther off!
menu I A Man would eafily be convinc'd oiwhat I fay, if he would be at the trouble of making a very attribute ea£e Experiment-: As, let him hang a Ring at the end of a thread, fo plac'd that the hoop being Wefc'hii- turn'd directly towards him, The aperture of it may not appear; or if he pleafe let him drive a turd judg- Stick in the ground, and t3ke another in his hand, that is curv'd at the end •, let him retreat three mems are or four fteps from the Ring or the Stick, and mutting one Eye with one hand, let him try to hit nothing the aperture of the Ring, or with the bent end of the Stick in his hand to touch the other acrofs, thus and at an neiSnt that is much upon a level with the Eye:, and he will be furpriz'd to find himfelf in- lonhfpeak capable of doing it at an hundred tryals, though nothing in the world feems ealier: Nay, though thus, the he ftiould lay afide the Stick, and only endeavour to direct his finger crofs-ways into the concavibetter to ty of the Ring, he would find it difficult enough to be done, though he flood very near it. explain gut it ought to be well obferv'd that I have faid, A Man mould endeavour to hit the aperture t mgs. Qjf tne Ring, or to touch the Stick crofs-wife, and not by way of a Right Line from our Eye to the Ring j for fo indeed there would be no difficulty at all: fo far from it, that it would be much eafier to effect it, with one Eye fhut, than with both of them open, fince that would be a Rule to direct him.
Now it may be faid, that the Difficulty, which is found, when a Man tries to direct the end of the Stick through the Ring crofs-wife, with only one Eye open, proceeds from this, namely, that one Eye being fhut, the Angle I have mention'd is unknown. For to, know the Magnitude of an Angle, it is not enough to know the length of its Bafe, and the Bignefs of the Angle made by one of its Sides upon the Bafe j for this is known in the foregoing Experiment: But it is yet farther ne- ceffary to know the other Angle, which is made by the other Side upon the Bafe, or the length of one o{t\\t Sides. Which cannot be exactly known without opening the other Eye. And thus the Soul cannot make ufe of her Natural Geometry to judge of the Diftance of the Ring.
The Difpofition then of the Eyes, which accompanies the Angle made of the Vifnal Rays which cut each other and centre in the Object, is one of the beft and molt univerfal means the Soul im- ploys whereby to judge of the Diftance of things. If then that Angle receives no fenfible Alterati- on, upon a little removal of the Object, whether it approaches nearer us, or recedes from us, it will thence follow, that it is a fallacious means, and unferviceable to the Soul whereby to judge of the true diftance of that Object.
Now 'tis plain that this Angle is notably chang'd, when an Object at about a foot diftance from our Sight is tranflated four foot off: but if it be only tranflated from four to eight, the Altera- tion is muck lefs difcernible-, if from eight to twelve, lefs yet: if from a thoufand to an hundred thoufand, hardly at all: Laftly, in carrying the Object farther on, even to the imaginary fpaces, the change of the Angle grows imperceptible, and is quite loft. So that were there a conlidera- ble fpace betwixt A and C, the Soul could not by that means know whether the Object were near B or D.
This is the Reafon why we fee the Sun and Moon, as if they were involv'd in Clouds, tho' they are vaftly diftant from them-, and that we naturally think all the Stars rang'd in an equal diftance from us j that we imagine the Comets are fixt, and almoft motionlefs, at the end of their courfe. We imagine too that Comets are entirely diflipated in fome Months time, becaufe they, recede from us in almoft a right Line, or a Line direct from our Eyes; and are going to lofe themfelves in the vaft fpaces, from whence they return not till after many Years, or even many Ages.
The Chap. IX. The Search after Truth. 23 The fecond Medium the Soul imploys to judge concerning the Diflance of Objeds, confiftsin ^e/econtl a Difpofition of the Eyes, different from that I have been fpeaking of. In order to explain it, we Jg™ muft know it is abfolutely necefTary that the figure of the Eye be different, according to the diffe- iudge 0f rent Diftance of Objedswhich we fee: For when a Man fees an Objed near him, there is a necef- the Di- fitv of his Eyes being longer, than if the Object were farther off: Becaufe to the end the Rays Jiang of of this Objed may be colleded in the Optick Nerve, which is necefTary to its being feen, the di- obPeSi ftance between this Nerve and the Cryftalline ought to be greater. • • >.
It is true, If the Cryftalline became more convex when the Object were near, that would effeft the fame thing as the Elongation of the Eye. But 'tis not credible that the Cryftalline can eafily change its convexity; and on the other fide, we have a moft evident Experiment for the E- lon^ation of the Eye: For Anatomy informs us, there are Mufcles that furround the middle of the^Eye; and we are fenfible of the Effort thefe Mufcles make to Comprefs it, and lengthen it, when we have a mind to fee any thing very near...But it is not at all necefTary, we mould know here, by what way this is done;, it isenough that there happens a Change in the Eye, whether it proceeds from the Preffure of the Mufcles, that furround it \ or whether the little Nerves, which anfwer to the Ciliary Ligaments which hold the Cryftalline, fufpended betwixt the other Humours of the Eye, become relax'd, to augment the convexity of the Cryftalline -, or intenfe, to diminifh it.
For this Change which happens, whatever it be, is only to collect, and unite the Rays of Ob- jects, with an exad juftnefs, upon the Optick Nerve. But it is certain that when the Object, is five hundred Paces, or ten thoufand Leagues diftant, we behold it with the fame Difpofition of Eyes, without any fenfible Change in the Mufcles which furround the Eye, or in the Nerves which anfwer to the Ciliary Ligaments of the Cryftalline: And the Rays of Objeds are very exadly collected upon the Retina, or the Optick Nerve. Thus the Soul judges, that Objects at ten thoufand or an hundred thoufand Leagues diftance, are no more than five or fix hundred Paces off; when fhe judges of their Diftance, Only by the Difpofition of the Eyes, which I have been fpeaking of. _ However, it is certain this Medium is of ufe to the Soul, when the Object, is nigh at hand. If, for inftance, an Object is only at half a foot Diftance, we difcern its-Diftance well enough, through the Difpofition of the Mufcles which conftringe our Eyes, in order to make them fome- what longer: And this Difpofition is moreover painful. If the Object, be remov'd two foot, we can ftill difcern the Diftance, becaufe the Difpofition of the Mufcles is fomewhat fenfible Hill, although no longer painful. But if the Objed be remov'd ftill fome feet farther, this Difpofition of our Mufcles, grows fo imperceptible* that it is altogether ufelefs to us in judging of the Di- ftance of the Object..
Thefe then are two Means the Soul makes ufe of, to judge of the Diftance of the Objed, which are altogether ufelefs, when the Objed is remote to five or fix hundred Paces, and which are ne- ver infallible, though the Object, be much nearer.
The third Medium confifts in the Greatnefs of the Image painted on the fund of the Eye, and The third, that makes the Reprefentation of the Objeds which we fee. 'Tis confefs'd that this Image Medium grows lefs in proportion as the Object, is remov'd to a greater Diftance, but this Diminution whereby to grows fo much lefs difcernable, as the Object, which changes itsDifta nee is more remote. For when ^C^«f of an Object, is at a confiderable Diftance, as of five or fiix hundred Paces, under or over in Pro- obietts. portion to its Bignefs, there happens very confiderable Changes in its remotenefs, without any confiderable Changes occafion'd in the Image which reprefents it, as is eafie to be demon- ftrated. Thus the third Medium has the fame defed as the other two, of which we have been fpeaking.
It is farther to be obferv'd, That the Soul does not judge thofe Objeds the remoteft, that have the leaft Images painted on the Retina. When I fee, for inftance, a Man and a Tree at an hun- dred Paces diftance, or fuppofe many Stars in the Heaven, I do not judge the Man to be more remote than the Tree, and the Little Stars farther diftant than the Greater* though the Images of the Man, and the little Stars, that are pidur'd on the Retina, are lefs than the Images of the Tree and the Greater Stars. Befides it is neceflary to know the greatnefs of an Objed, to be able to judge nearly of its Diftance, and becaufe I know an Houfe is bigger than a Man, tho' the Image of the Houfe be bigger than that of a Man, I do not however judge the Houfe neareft upon that account. And fb it is in refped of the Stars * Our Eyes reprefent them to us equally remote, though it is very reafbnableto believe fome of them at a far greater diftance than others. Thus there are infinite Objeds, the Diftance whereof we cannot know, fince there are infinite Objeds with whofe Magnitude we are unacquainted.
We judge farther of the remotenefs of an Objed by the Force wherewith it ads upon our Eyes, ^ cmrt^ becaufe a remote Objed ads more languifhing and weakly than another * and again, by the Di- and fifth fiintlnefs and Cleamefs of the Image, which is form'd in the Eye * becaufe when an Objed is re- Mediums, mote, the Pupil of the Eye mult needs be more open and Capacious, and ConfeqUently the Rays muft be colleded fomewhat confufedly. 'Tis for this reafon that obfeurer Objeds, and fuch as we fee confufedly, appear remote * and on the contrary, that luminous Bodies, and fuch as we fee diftindly, feem near. It is plain enough, that thefe laft Means are too fallible whereby to judge with any kind of Certainty concerning the diftance of Objeds: and I fhall not any longer infift upon them, but come to the laft of all, as being that which helps the Imagination moft, and in- clines the Soul more eafily to judge that Objeds are very remote, The Tkefixtb The fixth then and the Principal Medium of all, confifts in this, vil. that the Eye exhibits not wit T- to the Soij* a ^n^e °^Je<^ i"eParate from others, but gives her View at once of all thofe which lye Judge "of" betwixt us and the Principal Obje<3 of our a&ual Confederation.
the m- When for inftance, we behold a Steeple at a confiderable Diftance, we ufually fee a great many fiance of interjacent Lands and Houfes at the fame time: and becaufe we judge of the Remotenefs of thefe objeSs Lands, and Houfes, and in the mean time fee the Steeple beyond them, we judge likewife that it is not only more remote, but a great deal larger and taller, than if we faw it all alone: Not-, withftanding the Image which is proje&ed in the Fund of the Eye, is always of an equal Bignefs whether there are Lands and Houfes lying betwixt us and it, or whether there are none, pro- vided we fee it from a^ place equally Diftant, which is fuppos'd. Thus we judge of the Big- nefs of Obje&s, according as we believe them remote from us, and the Bodies which we fee betwixt us and the Objects, aftift the Imagination mightily in judging of their Remotenefs: juft as we* judge of the Extent of our Duration, or of the time that has pafs'd fince we have done any Action by the confus'd Remembrance of the things we have done, or of the Thou°hts we have had fucceflively fince that Attion. For they -are all thefe Thoughts and A&ions that* 'have fucceeded one another, which are afliftant to the Mind in judging of the length of any Time Or of any part of our Duration i Or rather the confus'd Remembrance of all thefe fucceffive Thoughts, is the fame thing as the judgment of our Duration; as the confus'd View of Lands betwixt us and a Steeple, is the fame thing as the judgment concerning the Remotenefs of the Steeple.
Hence it is eafy to affign the true Reafon of the Moon's appearing larger at her Rifing, than when confiderably elevated above the Horizon. For at her Rifing fhe appears many Leagues di- ftant, and even beyond the fenfible Horizon, or the Lands which terminate our Sight. Where- as we judge her but at half a Leagues Diftance, or feven or eight times higher than our Houfes when fhe is afcended above our Horizon. Thus we judge her far greater when fhe is near the Horizon, than when at a great diftance from it; becaufe we judge her to be far more remote from us, when fhe rifes, than when mounted very high above our Horizon.
I confefs a great part of the Philofophers attribute what I have been faying to the Vapours arifing from the Earth. I agree with them in this, that the Rays of Objefts being refra&ed by the Vapours, are a reafon of the Objefts feeming larger. I know there are more Vapours betwixt us and the Moon when rifing, than when fhe is elevated a good height j and confequently fhe ought to appear fomewhat larger than fhe would feem, if fhe were always equally remote. But yet it cannct be faid, that this Refradtion of the Lunary Rays is the caufe of thofe apparent Changes of her Magnitude: For that Refraction is no Impediment why the Image delineated in the Fund of the Eyes when we fee the xMoon rifing, may not be lefs than that which ihe pro- jects, when fhe hath been a long time rifen.
The Aftronomers who meafure the Diameters of the Planets, obferve that the Diameter of the Moon is magnify'd in proportion to her Diftance from the Horizon, and confequently in Pro- portion to her Appearing lefler to us: thus the Diameter of the Image which is painted in the Fund of our Eyes, it at that time leaftwhen we fee the Moon biggeft: Indeed, the Moon when fhe rifes,. is remoter from us by a Semidiameter of the Earth, than when fhe is perpendicular- ly over our Heads, and 'tis upon that account her Diameter grows greater in her Afcent above the Horizon, becaufe then fhe's approaching neareft us.
The reafon then that we fee her Greater when fhe rifes, is not the Refradtion of her Rays meeting' with the Vapours which proceed from the Earth, fince the Image which is at that time form'd from thofe Rays, is leffer; but 'tis the Natural Judgment we make of her Remotenefs, otcafion'd by her appearing beyond thofe Lands which we fee at a vaft Diftance from us, as has been before explain'd; and I am amaz'd to find Philofophers aflerting that the reafon of this Appearance, and Delufion of our Sences, is harder to be difcover'd than the greateft Equations of Algebra.
This Medium whereby we judge of the Remotenefs of any Objedt, by knowing the Diftance of the things betwixt us and it, is often of confiderable ufe, when the other means I have fpoke of, are wholly infignificant: for by this laft Medium, we can judge that certain objedts are ma- ny Leagues diftant which we cannot do by any of the other. And yet if we ftridtly furvey it, it will be found in feveral tilings deficient, • For, firft, we can only make ufe of it, about things upon the Earth, fince "it can be but very rarely, and then very unprofitably imploy'd upon thofe in the Air, or in the Heavens. Se- condly, it cannot be made ufe of on the Earth, but about things a few Leagues diftant. In the third place, we ought to be certain that there are neither Mountains^ nor Valleys, nor any thing of the like nature betwixt us and the Object, that hinders us from applying the afore-faid Me- dium. Laftly, lam perfwaded there is no body but has made fufficient Tryals upon the Sub- ject, to be convinc'd, that it is a thing extreamly difficult to judge with any certainty of the Re- motenefs of Objedts by a fenfible View of the things lying betwixt us and them: and we per- haps have dwelt two long upon it.
Thefe then are all the Means we have to judge of the Diftance of Objedts \ in which, fince we have found confiderable Imperfedtions we cannot but conclude, that the Judgments that are grounded upon them, muft needs be very Precarious and Uncertain.
Hence it is,eafy to manifeft the truth of the Propofitions I have advane'd. The Objedt C was fuppos'd confiderably remote from A: Therefore in many Inftances it may be advane'd on to- wards Chap. X. The Search after Truth. 25 wards D, or may have approach'd towards B, and no one Can difcover it, becaufe there is no infallible Means whereby to judge of its Diftance. Nay, it may recede towards D when it is thought to approach towards B; becaufe the Image of the Objed is fometimes augmented, and inlarged upon the Retina; whether it be becaufe the Air betwixt the Objed and the Eye occa- sions a greaterRefradion at one time than at another \ whether it proceeds from fome little Trem- lings, which happen in the Optick Nerve; or laftly, that the Impreflion, which is caus'd by an unexad Union of the Rays upon the Retina, is diffus'd and communicated to the parts, which ought to receive no Agitation from it; which may proceed from any different caufes. Thus the Image of the fame Objeds, being larger on thefe occafions, gives the Soulreafon to believe the Objed approaches nearer. The like may be faid of the other Propofitions.
Before I conclude this Chapter, I would have it obferv'd, That it is of great concern to us, in order to the Prefer vation of our Life, to have a nicer Knowledge of the Motion or Reft of Bodies, in Proportion to their Nighnefs to us: and that it is a thing ufelefs and iniignificant, to know exadly the truth of thefe things, when happening in places very remote. For this evi- dently (hews that what I have generally advanc'd concerning all the Sences, how they never Dif- cover things to us as they are abfolutely, and in their own Nature •, but only in Relation to the Pre- fervation of our Body, is found exadly True in this particular: fince we know the Motion or Refts of Objeds proportionably better, as they approach nearer to us, and are incapable of judging of them by the Sences, when they are fo remote as to feem to have no Relation at all, or very little to our Body: as, for inftance, when they are five or fix hundred Paces diftant, if they be of a Moderate Bignefs^ or even Nearer than this, when they are Leflerj or fome- what farther off, when they are proportionably Greater.
Of our Errors about fenjlble Qualities. I. The Diftin&ionofthe Soul and Bo- dy. II. An Explication of the Organs of the Senfes. III. To what part of the Body the Soul is immediately united. IV. An Inftance to explain the Ejfecl which Obje&s have upon our Bodies. V. What it is they produce in the Soul) and the Reafons why the Soul perceives not the Motions of the Fi- bres of the Body. VI. Four things which are generally confounded in every Sen fat ion.
WE have feen in the fore-going Chapters that the judgments we form upon the Tefti- mony of our Eyes, concerning Extenfion, Figure, and Motion, are never exadly true. And yet it muft not be allow'd that they are altogether falfe j they contain fb much Truth at leaft as this amounts to, that there are Extenfion, Figures, and Motions, whatever they be, which are extrinfical, or without our felves.
I confefs we often fee things that have no Exiftence, nor ever had, and it ought not to be concluded that a thing is Adually without us, from our Seeing it without us. There is no necef- lary Connexion between the Prefence of an Idea to the Mind of a Man, and the Exiftence of the Thing reprefented by the Idea. Which is manifeft enough from the Confideration of what happens to Men in a Dream or a Delirium: And yet we may fafely affirm, that ordinarily, Ex- tenfion, Figures, and Motions, are without us when we fee them fo. * Thefe things are not *Seetkeil- in the Imagination only, but are Real. And we are not deceiv'd in believing them to have luftmims. a Real Exiftence, and wholly independent on our Mind •, tho' it be a very hard thing to prove it.
It is certain then that the Judgments we form concerning the Extenfion, the Figures, and Mo- tions of Bodies, contain fome Truth: But 'tis another cafe in point of thofe Judgments we make concerning Light, Colours, Tafts, Smells, and all other Senfible Qualities: For Truth has no- thing to do with them, as fhall be made manifeft, in the remainder of this Firft Book.
We make not here any Diftindion between Light and Colours, becaufe we fuppofe them to have no great Difference; and that they cannot be feparately Explain'd. We fhall likewife be oblig'd to fpeak of other Senfible Qualities in general, at the fame time we fhall treat of thefe Two in particular, becaufe they may be accounted for upon the fame Principles. The things which follow demand the greateft Attention imaginable, as being of the higheft Impor- tance, and very different, as to their Ufefulnefs, from thofe of the foregoing Difcourfe.
We inftantly fuppofe a Man to have made fome Refledions upon two * Idea's which he, finds in his Soul: one that reprefents the Body, and the other which reprefents the Mind; iie Di- and that he is able eafily to diftinguifh them by the pofitive Attributes they contain: In a word,fimdioKof that he is very well fatisfi'd, that Extenfion is a different thing from Thought. Or we will fup- <*e soul pofe he has read and meditated on fome places of St. Auftin, as the 1 oth Chapter of the 1 oth Book, Tifffl the Name of Idea here whatever is the Immediate Objett of the Mini% H Concerning 26 F. Malebranche Concerning Book I.
Concerning the Trinity, the 4th and 1 4th Chapters of his Book concerning The Quantity J>f the Soul, at leaft Mr. Des-Canesh Meditations, efpecially that Part which treats of the Diftin&ion of the Soul and Body: or laftly Mr. Cordemofs fixth Diflertation, concerning the Difference of the Soul and Body.
"!*•. We fuppofe farther, that he is acquainted with the An at omy of the Organs of the Senfes j and *}**$* 'knows that they confift of little Threads or Fibres, which derive their Origine from the middle liecrSs ot* the Brain: tlwt they are difPers'd trough all the Members wherein there is Senfation, and of the sen- being continued without any Interruption, are terminated upon the External parts of the Body, Jei. that whilft a Man is awake and in health, one of the Extremities cannot be mov'd but the other will, be mov'd in the fame time, 'becaufe they are always fomewhat Intenfe and upon the ftretch: the fame thing which happens to a Cord that is intenfe, one part whereof cannot be mov'd, but the other mult receive fome Vibration.
'Tis farther neceflary to know that thefe little Threads or Fibres may be mov'd by two feve- ral ways, either by that end that is external to the Brain, or by the end which terminates in the Brain. If thefe Fibres are externally agitated byObje&s acting on them, and this Agi- tation be not communicated fo far as the Brain, as it happens in Sleep, the Soul receives no frefli Senfation from them at that time: But if thefe Fibres are moved in the Brain by the courfe of the Animal Spirits, or by any other caufe, the Soul has a Perception of fomething: though the Parts of thefe Fibres which are without the Brain, and aredifpers'd throughout all the Parts of the Body, are quiet and undifturb'd •, as it happens when a Man's afleep. IIT. it will not be amifs to obferve here, by the way, that Experience certifies us, it is not impof- ihe soul ^je tQ feel pajn -m t-hofg parts of our Body, which have been intirely cut off: Becaufe the Fi- tieh "^K.Dres or" the Brain, which correfpond to them, being Vibrated in the fame manner, as if thofe ted to that Parts were actually wounded, the Soul feels in thofe Imaginary Parts, a mofl real Pain. For all pan of the thefe things are a palpable Demonftration, that the Soul immediately refides in that Part of the Brain Brain in which all the Organs of the Senfes terminate and centre: I mean that in this Part fhe mZVtf receives the Senfation of all the Changes, that there occur, in reference to the Objects that have the" organs caus'd them, or have us'd to caufe them: and fhe has no Perception of any thing happening of the sen- in any other Part, but by the Intervention of the Fibres which terminate therein. This being f:s centre, j^ down and well underltood, it will be no hard thing to difcoverhow Senfation is effected, which is neceflary to be explain'd by fome particular Inftance. IV. When a Man thrufts the Point of a Needle into his hand, this Point moves and feparates the if" In\ Fibres of the Flefh. Thefe Fibres are extended from that Place to the Brain and whilft he is explain ° awake, they are fo Intenfe, that they can receive no Concuffion or Vibration, but it is Cpra- the effect municated to thofe in the Brain: It follows then that the Extremities of the Fibres in the which ob- grain mult be in like manner mov'd. If the motion of the Fibres of the Hand is Moderate, )ecls have t^t Q^ ^ piDres 0f the Brain will be fo too: and if this Motion is violent enough to break B^odielT fomething in the Hand, it will be more forcible and violent in the Brain.