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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..6833f05 --- /dev/null +++ b/.gitattributes @@ -0,0 +1,3 @@ +* text=auto +*.txt text +*.md text diff --git a/4722-h.zip b/4722-h.zip Binary files differnew file mode 100644 index 0000000..9699680 --- /dev/null +++ b/4722-h.zip diff --git a/4722-h/4722-h.htm b/4722-h/4722-h.htm new file mode 100644 index 0000000..9498fbd --- /dev/null +++ b/4722-h/4722-h.htm @@ -0,0 +1,3471 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<HTML> +<HEAD> + +<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> + +<TITLE> +The Project Gutenberg E-text of An Essay Towards a New Theory of Vision, +by George Berkeley +</TITLE> + +<STYLE TYPE="text/css"> +BODY { color: Black; + background: White; + margin-right: 10%; + margin-left: 10%; + font-family: "Times New Roman", serif; + text-align: justify } + +P {text-indent: 4% } + +P.noindent {text-indent: 0% } + +P.poem {text-indent: 0%; + margin-left: 10%; + font-size: small } + +P.letter {text-indent: 0%; + font-size: small ; + margin-left: 10% ; + margin-right: 10% } + +P.finis { font-size: larger ; + text-align: center ; + text-indent: 0% ; + margin-left: 0% ; + margin-right: 0% } + +</STYLE> + +</HEAD> + +<BODY> + + +<pre> + +The Project Gutenberg EBook of An Essay Towards a New Theory of Vision, by +George Berkeley + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: An Essay Towards a New Theory of Vision + +Author: George Berkeley + +Posting Date: June 29, 2009 [EBook #4722] +Release Date: December, 2003 +First Posted: March 7, 2002 + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK ESSAY--NEW THEORY OF VISION *** + + + + +Produced by Col Choat. HTML version by Al Haines. + + + + + +</pre> + + +<BR><BR> + +<H1 ALIGN="center"> +An Essay Towards<BR>a New Theory of Vision +</H1> + +<BR> + +<H3 ALIGN="center"> +by +</H3> + +<H2 ALIGN="center"> +George Berkeley (1685-1753) +</H2> + +<BR><BR><BR> + +<H2 ALIGN="center"> +CONTENTS +</H2> + +<BR> + +<H3> +Sect. +</h3> + +<PRE STYLE="font-family: Times New Roman, serif; font-size: small"> + 1 <A HREF="#sect001">Design</A> + 2 <A HREF="#sect002">Distance of itself invisible</A> + 3 <A HREF="#sect003">Remote distance perceived rather by experience than by sense</A> + 4 <A HREF="#sect004">Near distance thought to be perceived by the ANGLE of the OPTIC AXES</A> + 5 <A HREF="#sect005">Difference between this and the former manner of perceiving distance</A> + 6 <A HREF="#sect006">Also by diverging rays</A> + 7 <A HREF="#sect007">This depends not on experience</A> + 8 <A HREF="#sect008">These the common accounts, but not satisfactory</A> + 9 <A HREF="#sect009">Some IDEAS perceived by the mediation of others</A> + 10 <A HREF="#sect010">No IDEA which is not itself perceived, can be the means of perceiving another</A> + 11 <A HREF="#sect011">Distance perceived by means of some other IDEA</A> + 12 <A HREF="#sect012">Those lines and angles mentioned in optics, are not themselves perceived</A> + 13 <A HREF="#sect013">Hence the mind does not perceive distance by lines and angles</A> + 14 <A HREF="#sect014">Also because they have no real existence</A> + 15 <A HREF="#sect015">And because they are insufficient to explain the phenomena</A> + 16 <A HREF="#sect016">The IDEAS that suggest distance are, 1st, the sensation arising from the turn of the eyes</A> + 17 <A HREF="#sect017">Betwixt which and distance there is no necessary connection</A> + 18 <A HREF="#sect018">Scarce room for mistake in this matter</A> + 19 <A HREF="#sect019">No regard had to the angle of the OPTIC AXES</A> + 20 <A HREF="#sect020">Judgment of distance made with both eyes, the result of EXPERIENCE</A> + 21 <A HREF="#sect021">2ndly, Confusedness of appearance</A> + 22 <A HREF="#sect022">This the occasion of those judgments attributed to diverging rays</A> + 23 <A HREF="#sect023">Objection answered</A> + 24 <A HREF="#sect024">What deceives the writers of optics in this matter</A> + 25 <A HREF="#sect025">The cause why one IDEA may suggest another</A> + 26 <A HREF="#sect026">This applied to confusion and distance</A> + 27 <A HREF="#sect027">Thirrdly, the straining of the eye</A> + 28 <A HREF="#sect028">The occasions which suggest distance have in their own nature no relation to it</A> + 29 <A HREF="#sect029">A difficult case proposed by Dr. Barrow as repugnant to all the known theories</A> + 30 <A HREF="#sect030">This case contradicts a received principle in catoptrics</A> + 31 <A HREF="#sect031">It is shown to agree with the principles we have laid down</A> + 32 <A HREF="#sect032">This phenomenon illustrated</A> + 33 <A HREF="#sect033">It confirms the truth of the principle whereby it is explained</A> + 34 <A HREF="#sect034">Vision when distinct, and when confused</A> + 35 <A HREF="#sect035">The different effects of parallel diverging and converging rays</A> + 36 <A HREF="#sect036">How converging and diverging rays come to suggest the same distance</A> + 37 <A HREF="#sect037">A person extreme purblind would judge aright in the forementioned case</A> + 38 <A HREF="#sect038">Lines and angles, why useful in optics</A> + 39 <A HREF="#sect039">The not understanding this, a cause of mistake</A> + 40 <A HREF="#sect040">A query proposed, by Mr. Molyneux in his DIOPTRICS, considered</A> + 41 <A HREF="#sect041">One born blind would not at first have any IDEA of distance by sight</A> + 42 <A HREF="#sect042">This not agreeable to the common principles</A> + 43 <A HREF="#sect043">The proper objects of sight, not without the mind, nor the images of any thing without the mind</A> + 44 <A HREF="#sect044">This more fully explained</A> + 45 <A HREF="#sect045">In what sense we must be understood to see distance and external things</A> + 46 <A HREF="#sect046">Distance, and things placed at a distance, not otherwise perceived by the eye than by the ear</A> + 47 <A HREF="#sect047">The IDEAS of sight more apt to be confounded with the IDEAS of touch than those of hearing are</A> + 48 <A HREF="#sect048">How this comes to pass</A> + 49 <A HREF="#sect049">Strictly speaking, we never see and feel the same thing</A> + 50 <A HREF="#sect050">Objects of SIGHT twofold, mediate and immediate</A> + 51 <A HREF="#sect051">These hard to separate in our thoughts</A> + 52 <A HREF="#sect052">The received accounts of our perceiving magnitude by sight, false</A> + 53 <A HREF="#sect053">Magnitude perceived as immediately as distance</A> + 54 <A HREF="#sect054">Two kinds of sensible extension, neither of which is infinitely divisible</A> + 55 <A HREF="#sect055">The tangible magnitude of an OBJECT steady, the visible not</A> + 56 <A HREF="#sect056">By what means tangible magnitude is perceived by sight</A> + 57 <A HREF="#sect057">This further enlarged on</A> + 58 <A HREF="#sect058">No necessary connection between confusion or faintness of appearance, and small or great magnitude</A> + 59 <A HREF="#sect059">The tangible magnitude of an OBJECT more heeded than the visible, and why</A> + 60 <A HREF="#sect060">An instance of this</A> + 61 <A HREF="#sect061">Men do not measure by visible feet or inches</A> + 62 <A HREF="#sect062">No necessary connection between visible and tangible extension</A> + 63 <A HREF="#sect063">Greater visible magnitude might signify lesser tangible magnitude</A> + 64 <A HREF="#sect064">The judgments we make of magnitude depend altogether on experience</A> + 65 <A HREF="#sect065">Distance and magnitude seen as shame or anger</A> + 66 <A HREF="#sect066">But we are prone to think otherwise, and why</A> + 67 <A HREF="#sect067">The moon seems greater in the horizon than in the meridian</A> + 68 <A HREF="#sect068">The cause of this phenomenon assigned</A> + 69 <A HREF="#sect069">The horizontal moon, why greater at one time than another.</A> + 70 <A HREF="#sect070">The account we have given proved to be true</A> + 71 <A HREF="#sect071">And confirmed by the moon's appearing greater in a mist</A> + 72 <A HREF="#sect072">Objection answered</A> + 73 <A HREF="#sect073">The way wherein faintness suggests greater magnitude illustrated</A> + 74 <A HREF="#sect074">Appearance of the horizontal moon, why thought difficult to explain</A> + 75 <A HREF="#sect075">Attempts towards the solution of it made by several, but in vain</A> + 76 <A HREF="#sect076">The opinion of Dr. Wallis</A> + 77 <A HREF="#sect077">It is shown to be unsatisfactory</A> + 78 <A HREF="#sect078">How lines and angles may be of use in computing apparent magnitudes</A> + 79 <A HREF="#sect079">One born blind, being made to see, what judgment he would make of magnitude</A> + 80 <A HREF="#sect080">The MINIMUM VISIBLE the same to all creatures</A> + 81 <A HREF="#sect081">Objection answered</A> + 82 <A HREF="#sect082">The eye at all times perceives the same number of visible points</A> + 83 <A HREF="#sect083">Two imperfections in the VISIVE FACULTY</A> + 84 <A HREF="#sect084">Answering to which, we may conceive two perfections</A> + 85 <A HREF="#sect085">In neither of these two ways do microscopes improve the sight</A> + 86 <A HREF="#sect086">The case of microscopical eyes, considered</A> + 87 <A HREF="#sect087">The sight, admirably adapted to the ends of seeing</A> + 88 <A HREF="#sect088">Difficulty concerning erect vision</A> + 89 <A HREF="#sect089">The common way of explaining it</A> + 90 <A HREF="#sect090">The same shown to be false</A> + 91 <A HREF="#sect091">Not distinguishing between IDEAS of sight and touch, cause of mistake in this matter</A> + 92 <A HREF="#sect092">The case of one born blind, proper to be considered</A> + 93 <A HREF="#sect093">Such a one might by touch attain to have IDEAS of UPPER and LOWER</A> + 94 <A HREF="#sect094">Which modes of situation he would attribute only to things tangible</A> + 95 <A HREF="#sect095">He would not at first sight think anything he saw, high or low, erect or inverted</A> + 96 <A HREF="#sect096">This illustrated by an example</A> + 97 <A HREF="#sect097">By what means he would come to denominate visible OBJECTS, high or low, etc.</A> + 98 <A HREF="#sect098">Why he should think those OBJECTS highest, which are painted on the lowest part of his eye, and VICE VERSA</A> + 99 <A HREF="#sect099">How he would perceive by sight, the situation of external objects</A> + 100 <A HREF="#sect100">Our propension to think the contrary, no argument against what has been said</A> + 101 <A HREF="#sect101">Objection</A> + 102 <A HREF="#sect102">Answer</A> + 103 <A HREF="#sect103">An object could not be known at first sight by the colour</A> + 104 <A HREF="#sect104">Nor by the magnitude thereof</A> + 105 <A HREF="#sect105">Nor by the figure</A> + 106 <A HREF="#sect106">In the first act of vision, no tangible thing would be suggested by sight</A> + 107 <A HREF="#sect107">Difficulty proposed concerning number</A> + 108 <A HREF="#sect108">Number of things visible, would not at first sight suggest the like number of things tangible</A> + 109 <A HREF="#sect109">Number the creature of the mind</A> + 110 <A HREF="#sect110">One born blind would not at first sight number visible things as others do</A> + 111 <A HREF="#sect111">The situation of any object determined with respect only to objects of the same sense</A> + 112 <A HREF="#sect112">No distance, great or small, between a visible and tangible thing</A> + 113 <A HREF="#sect113">The not observing this, cause of difficulty in erect vision</A> + 114 <A HREF="#sect114">Which otherwise includes nothing unaccountable</A> + 115 <A HREF="#sect115">What is meant by the picture being inverted</A> + 116 <A HREF="#sect116">Cause of mistake in this matter</A> + 117 <A HREF="#sect117">Images in the eye, not pictures of external objects</A> + 118 <A HREF="#sect118">In what sense they are pictures</A> + 119 <A HREF="#sect119">In this affair we must carefully distinguish between ideas of sight and touch</A> + 120 <A HREF="#sect120">Difficult to explain by words the true Theory of Vision</A> + 121 <A HREF="#sect121">The question, whether there is any IDEA common to sight and touch, stated</A> + 122 <A HREF="#sect122">Abstract extension inquired into</A> + 123 <A HREF="#sect123">It is incomprehensible</A> + 124 <A HREF="#sect124">Abstract extension not the OBJECT of geometry</A> + 125 <A HREF="#sect125">The general IDEA of a triangle, considered</A> + 126 <A HREF="#sect126">Vacuum, or pure space, not common to sight and touch</A> + 127 <A HREF="#sect127">There is no idea, or kind of idea, common to both senses</A> + 128 <A HREF="#sect128">First argument in proof hereof</A> + 129 <A HREF="#sect129">Second argument</A> + 130 <A HREF="#sect130">Visible figure and extension, not distinct IDEAS from colour</A> + 131 <A HREF="#sect131">Third argument</A> + 132 <A HREF="#sect132">Confirmation drawn from Mr. Molyneux's problem of a sphere and a cube, published by Mr. Locke</A> + 133 <A HREF="#sect133">Which is falsely solved, if the common supposition be true</A> + 134 <A HREF="#sect134">More might be said in proof of our tenet, but this suffices</A> + 135 <A HREF="#sect135">Further reflection on the foregoing problem</A> + 136 <A HREF="#sect136">The same thing doth not affect both sight and touch</A> + 137 <A HREF="#sect137">The same idea of motion not common to sight and touch</A> + 138 <A HREF="#sect138">The way wherein we apprehend motion by sight, easily collected from what hath been said</A> + 139 <A HREF="#sect139">QU. How visible and tangible IDEAS came to have the same name if not of the same kind</A> + 140 <A HREF="#sect140">This accounted for without supposing them of the same kind</A> + 141 <A HREF="#sect141">OBJ. That a tangible square is liker to a visible square than to a visible circle</A> + 142 <A HREF="#sect142">ANS. That a visible square is fitter than a visible circle, to represent a tangible square</A> + 143 <A HREF="#sect143">But it doth not hence follow, that a visible square is like a tangible square</A> + 144 <A HREF="#sect144">Why we are more apt to confound visible with tangible IDEAS, than other signs with the things signified</A> + 145 <A HREF="#sect145">Several other reasons hereof, assigned</A> + 146 <A HREF="#sect146">Reluctancy in rejecting any opinion, no argument of its truth</A> + 147 <A HREF="#sect147">Proper objects of vision the language of nature</A> + 148 <A HREF="#sect148">In it there is much admirable, and deserving our attention</A> + 149 <A HREF="#sect149">Question proposed, concerning the object of geometry</A> + 150 <A HREF="#sect150">At first view we are apt to think visible extension the object of geometry</A> + 151 <A HREF="#sect151">Visible extension shown not to be the object of geometry</A> + 152 <A HREF="#sect152">Words may as well be thought the object of geometry, as visible extension</A> + 153 <A HREF="#sect153">It is proposed to inquire, what progress an intelligence that could see, but not feel, might make in geometry</A> + 154 <A HREF="#sect154">He cannot understand those parts which relate to solids, and their surfaces, and lines generated by their section</A> + 155 <A HREF="#sect155">Nor even the elements of plane geometry</A> + 156 <A HREF="#sect156">The proper objects of sight incapable of being managed as geometrical figures</A> + 157 <A HREF="#sect157">The opinion of those who hold plane figures to be the immediate objects of sight, considered</A> + 158 <A HREF="#sect158">Planes no more the immediate objects of sight, than solids</A> + 159 <A HREF="#sect159">Difficult to enter precisely into the thoughts of the above-mentioned intelligence</A> + 160 <A HREF="#sect160">The object of geometry, its not being sufficiently understood, cause of difficulty, and useless labour in that science</A> +</PRE> + +<BR><BR><BR> + +<H2 ALIGN="center"> +AN ESSAY TOWARDS A NEW THEORY OF VISION +</H2> + +<BR> + +<A NAME="sect001"></A> +<P CLASS="noindent"> +1. My design is to show the manner wherein we perceive by sight the +distance, magnitude, and situation of OBJECTS. Also to consider the +difference there is betwixt the IDEAS of sight and touch, and whether +there be any IDEA common to both senses. +</P> + +<A NAME="sect002"></A> +<P CLASS="noindent"> +2. It is, I think, agreed by all that DISTANCE, of itself and +immediately, cannot be seen. For DISTANCE being a Line directed end-wise +to the eye, it projects only one point in the fund of the eye, which +point remains invariably the same, whether the distance be longer or +shorter. +</P> + +<A NAME="sect003"></A> +<P CLASS="noindent"> +3. I find it also acknowledged that the estimate we make of the distance +of OBJECTS considerably remote is rather an act of judgment grounded on +EXPERIENCE than of SENSE. For example, when I perceive a great number of +intermediate OBJECTS, such as houses, fields, rivers, and the like, which +I have experienced to take up a considerable space, I thence form a +judgment or conclusion that the OBJECT I see beyond them is at a great +distance. Again, when an OBJECT appears faint and small, which at a near +distance I have experienced to make a vigorous and large appearance, I +instantly conclude it to be far off: And this, it is evident, is the +result of EXPERIENCE; without which, from the faintness and littleness I +should not have inferred anything concerning the distance of OBJECTS. +</P> + +<A NAME="sect004"></A> +<P CLASS="noindent"> +4. But when an OBJECT is placed at so near a distance as that the +interval between the eyes bears any sensible proportion to it, the +opinion of speculative men is that the two OPTIC AXES (the fancy that we +see only with one eye at once being exploded) concurring at the OBJECT do +there make an ANGLE, by means of which, according as it is greater or +lesser, the OBJECT is perceived to be nearer or farther off. +</P> + +<A NAME="sect005"></A> +<P CLASS="noindent"> +5. Betwixt which and the foregoing manner of estimating distance there is +this remarkable difference: that whereas there was no apparent, necessary +connection between small distance and a large and strong appearance, or +between great distance and a little and faint appearance, there appears a +very necessary connection between an obtuse angle and near distance, and +an acute angle and farther distance. It does not in the least depend upon +experience, but may be evidently known by anyone before he had +experienced it, that the nearer the concurrence of the OPTIC AXES, the +greater the ANGLE, and the remoter their concurrence is, the lesser will +be the ANGLE comprehended by them. +</P> + +<A NAME="sect006"></A> +<P CLASS="noindent"> +6. There is another way mentioned by optic writers, whereby they will +have us judge of those distances, in respect of which the breadth of the +PUPIL hath any sensible bigness: And that is the greater or lesser +divergency of the rays, which issuing from the visible point do fall on +the PUPIL, that point being judged nearest which is seen by most +diverging rays, and that remoter which is seen by less diverging rays: +and so on, the apparent distance still increasing, as the divergency of +the rays decreases, till at length it becomes infinite, when the rays +that fall on the PUPIL are to sense parallel. And after this manner it is +said we perceive distance when we look only with one eye. +</P> + +<A NAME="sect007"></A> +<P CLASS="noindent"> +7. In this case also it is plain we are not beholding to experience: it +being a certain, necessary truth that the nearer the direct rays falling +on the eye approach to a PARALLELISM, the farther off is the point of +their intersection, or the visible point from whence they flow. +</P> + +<A NAME="sect008"></A> +<P CLASS="noindent"> +8. I have here set down the common, current accounts that are given of +our perceiving near distances by sight, which, though they are +unquestionably received for true by MATHEMATICIANS, and accordingly made +use of by them in determining the apparent places of OBJECTS, do, +nevertheless seem to me very unsatisfactory: and that for these following +reasons:— +</P> + +<A NAME="sect009"></A> +<P CLASS="noindent"> +9. FIRST, It is evident that when the mind perceives any IDEA, not +immediately and of itself, it must be by the means of some other IDEA. +Thus, for instance, the passions which are in the mind of another are of +themselves to me invisible. I may nevertheless perceive them by sight, +though not immediately, yet by means of the colours they produce in the +countenance. We often see shame or fear in the looks of a man, by +perceiving the changes of his countenance to red or pale. +</P> + +<A NAME="sect010"></A> +<P CLASS="noindent"> +10. Moreover it is evident that no IDEA which is not itself perceived can +be the means of perceiving any other IDEA. If I do not perceive the +redness or paleness of a man's face themselves, it is impossible I should +perceive by them the passions which are in his mind. +</P> + +<A NAME="sect011"></A> +<P CLASS="noindent"> +11. Now from sect. 2 it is plain that distance is in its own nature +imperceptible, and yet it is perceived by sight. It remains, therefore, +that it be brought into view by means of some other IDEA that is itself +immediately perceived in the act of VISION. +</P> + +<A NAME="sect012"></A> +<P CLASS="noindent"> +12. But those LINES and ANGLES, by means whereof some MATHEMATICIANS +pretend to explain the perception of distance, are themselves not at all +perceived, nor are they in truth ever thought of by those unskilful in +optics. I appeal to anyone's experience whether upon sight of an OBJECT he +computes its distance by the bigness of the ANGLE made by the meeting of +the two OPTIC AXES? Or whether he ever thinks of the greater or lesser +divergency of the rays, which arrive from any point to his PUPIL? Everyone +is himself the best judge of what he perceives, and what not. In vain +shall all the MATHEMATICIANS in the world tell me, that I perceive certain +LINES and ANGLES which introduce into my mind the various IDEAS of +DISTANCE, so long as I myself am conscious of no such thing. +</P> + +<A NAME="sect013"></A> +<P CLASS="noindent"> +13. Since, therefore, those ANGLES and LINES are not themselves perceived +by sight, it follows from sect. 10 that the mind doth not by them judge +of the distance of OBJECTS. +</P> + +<A NAME="sect014"></A> +<P CLASS="noindent"> +14. Secondly, the truth of this assertion will be yet farther evident to +anyone that considers those LINES and ANGLES have no real existence in +nature, being only an HYPOTHESIS framed by the MATHEMATICIANS, and by them +introduced into OPTICS, that they might treat of that science in a +GEOMETRICAL way. +</P> + +<A NAME="sect015"></A> +<P CLASS="noindent"> +15. The third and last reason I shall give for rejecting that doctrine is, +that though we should grant the real existence of those OPTIC ANGLES, +etc., and that it was possible for the mind to perceive them, yet these +principles would not be found sufficient to explain the PHENOMENA of +DISTANCE, as shall be shown hereafter. +</P> + +<A NAME="sect016"></A> +<P CLASS="noindent"> +16. Now, it being already shown that distance is suggested to the mind by +the mediation of some other IDEA which is itself perceived in the act of +seeing, it remains that we inquire what IDEAS or SENSATIONS there be that +attend VISION, unto which we may suppose the IDEAS of distance are +connected, and by which they are introduced into the mind. And FIRST, it +is certain by experience that when we look at a near OBJECT with both +eyes, according as it approaches or recedes from us, we alter the +disposition of our eyes, by lessening or widening the interval between +the PUPILS. This disposition or turn of the eyes is attended with a +sensation, which seems to me to be that which in this case brings the +IDEA of greater or lesser distance into the mind. +</P> + +<A NAME="sect017"></A> +<P CLASS="noindent"> +17. Not that there is any natural or necessary connection between the +sensation we perceive by the turn of the eyes and greater or lesser +distance, but because the mind has by constant EXPERIENCE found the +different sensations corresponding to the different dispositions of the +eyes to be attended each with a different degree of distance in the +OBJECT: there has grown an habitual or customary connection between those +two sorts of IDEAS, so that the mind no sooner perceives the sensation +arising from the different turn it gives the eyes, In order to bring the +PUPILS nearer or farther asunder, but it withal perceives the different +IDEA of distance which was wont to be connected with that sensation; just +as upon hearing a certain sound, the IDEA is immediately suggested to the +understanding which custom had united with it. +</P> + +<A NAME="sect018"></A> +<P CLASS="noindent"> +18 Nor do I see how I can easily be mistaken in this matter. I know +evidently that distance is not perceived of itself. That by consequence +it must be perceived by means of some other IDEA which is immediately +perceived, and varies with the different degrees of distance. I know also +that the sensation arising from the turn of the eyes is of itself +immediately perceived, and various degrees thereof are connected with +different distances, which never fail to accompany them into my mind, +when I view an OBJECT distinctly with both eyes, whose distance is so +small that in respect of it the interval between the eyes has any +considerable magnitude. +</P> + +<A NAME="sect019"></A> +<P CLASS="noindent"> +19. I know it is a received opinion that by altering the disposition of +the eyes the mind perceives whether the angle of the OPTIC AXES is made +greater or lesser. And that accordingly by a kind of NATURAL +GEOMETRY it judges the point of their intersection to be nearer +or farther off. But that this is not true I am convinced by my own +experience, since I am not conscious that I make any such use of the +perception I have by the turn of my eyes. And for me to make those +judgments, and draw those conclusions from it, without knowing that I do +so, seems altogether incomprehensible. +</P> + +<A NAME="sect020"></A> +<P CLASS="noindent"> +20. From all which it follows that the judgment we make of the distance +of an OBJECT, viewed with both eyes, is entirely the RESULT OF +EXPERIENCE. If we had not constantly found certain sensations arising +from the various disposition of the eyes, attended with certain degrees +of distance, we should never make those sudden judgments from them +concerning the distance of OBJECTS; no more than we would pretend to +judge a man's thoughts by his pronouncing words we had never heard +before. +</P> + +<A NAME="sect021"></A> +<P CLASS="noindent"> +21. Secondly, an OBJECT placed at a certain distance from the eye, to +which the breadth of the PUPIL bears a considerable proportion, being +made to approach, is seen more confusedly: and the nearer it is brought +the more confused appearance it makes. And this being found constantly to +be so, there ariseth in the mind an habitual CONNECTION between the +several degrees of confusion and distance; the greater confusion still +implying the lesser distance, and the lesser confusion the greater +distance of the OBJECT. +</P> + +<A NAME="sect022"></A> +<P CLASS="noindent"> +22. This confused appearance of the OBJECT doth therefore seem to be the +MEDIUM whereby the mind judgeth of distance in those cases wherein the +most approved writers of optics will have it judge by the different +divergency with which the rays flowing from the radiating point fall on +the PUPIL. No man, I believe, will pretend to see or feel those imaginary +angles that the rays are supposed to form according to their various +inclinations on his eye. But he cannot choose seeing whether the OBJECT +appear more or less confused. It is therefore a manifest consequence from +what bath been demonstrated, that instead of the greater or lesser +divergency of the rays, the mind makes use of the greater or lesser +confusedness of the appearance, thereby to determine the apparent place +of an OBJECT. +</P> + +<A NAME="sect023"></A> +<P CLASS="noindent"> +23 Nor doth it avail to say there is not any necessary connection between +confused VISION and distance, great or small. For I ask any man what +necessary connection he sees between the redness of a blush and shame? And +yet no sooner shall he behold that colour to arise in the face of +another, but it brings into his and the IDEA of that passion which hath +been observed to accompany it. +</P> + +<A NAME="sect024"></A> +<P CLASS="noindent"> +24. What seems to have misled the writers of optics in this matter is +that they imagine men judge of distance as they do of a conclusion in +mathematics, betwixt which and the premises it is indeed absolutely +requisite there be an apparent, necessary connection: but it is far +otherwise in the sudden judgments men make of distance. We are not to +think that brutes and children, or even grown reasonable men, whenever +they perceive an OBJECT to approach, or depart from them, do it by virtue +of GEOMETRY and DEMONSTRATION. +</P> + +<A NAME="sect025"></A> +<P CLASS="noindent"> +25. That one IDEA may suggest another to the mind it will suffice that +they have been observed to go together, without any demonstration of the +necessity of their coexistence, or without so much as knowing what it is +that makes them so to coexist. Of this there are innumerable instances of +which no one can be ignorant. +</P> + +<A NAME="sect026"></A> +<P CLASS="noindent"> +26. Thus, greater confusion having been constantly attended with nearer +distance, no sooner is the former IDEA perceived, but it suggests the +latter to our thoughts. And if it had been the ordinary course of Nature +that the farther off an OBJECT were placed, the more confused it should +appear, it is certain the very same perception that now makes us think an +OBJECT approaches would then have made us to imagine it went farther off. +That perception, abstracting from CUSTOM and EXPERIENCE, being equally +fitted to produce the IDEA of great distance, or small distance, or no +distance at all. +</P> + +<A NAME="sect027"></A> +<P CLASS="noindent"> +27. Thirdly, an OBJECT being placed at the distance above specified, and +brought nearer to the eye, we may nevertheless prevent, at least for some +time, the appearances growing more confused, by straining the eye. In +which case that sensation supplies the place of confused VISION in aiding +the mind to judge of the distance of the OBJECT; it being esteemed so +much the nearer by how much the effort or straining of the eye in order +to distinct VISION is greater. +</P> + +<A NAME="sect028"></A> +<P CLASS="noindent"> +28. I have here set down those sensations or IDEAS that seem to be the +constant and general occasions of introducing into the mind the different +IDEAS of near distance. It is true in most cases that divers other +circumstances contribute to frame our IDEA of distance, to wit, the +particular number, size, kind, etc., of the things seen. Concerning +which, as well as all other the forementioned occasions which suggest +distance, I shall only observe they have none of them, in their own +nature, any relation or connection with it: nor is it possible they should +ever signify the various degrees thereof, otherwise than as by EXPERIENCE +they have been found to be connected with them. +</P> + +<A NAME="sect029"></A> +<P CLASS="noindent"> +29. I shall proceed upon these principles to account for a phenomenon +which has hitherto strangely puzzled the writers of optics, and is so far +from being accounted for by any of their THEORIES OF VISION that it is, +by their own confession, plainly repugnant to them; and of consequence, +if nothing else could be objected, were alone sufficient to bring their +credit in question. The whole difficulty I shall lay before you in the +words of the learned Dr. Barrow, with which he concludes his optic +lectures:— +</P> + +<P CLASS="noindent"> +'I have here delivered what my thoughts have suggested to me concerning +that part of optics which is more properly mathematical. As for the other +parts of that science (which being rather physical, do consequently +abound with plausible conjectures instead of certain principles), there +has in them scarce anything occurred to my observation different from what +has been already said by Kepler, Scheinerus, Descartes, and others. And +methinks, I had better say nothing at all, than repeat that which has +been so often said by others. I think it therefore high time to take my +leave of this subject: but before I quit it for good and all, the fair +and ingenuous dealing that I owe both to you and to truth obligeth me to +acquaint you with a certain untoward difficulty, which seems directly +opposite to the doctrine I have been hitherto inculcating, at least, +admits of no solution from it. In short it is this. Before the double +convex glass or concave speculum EBF, let the point A be placed at such a +distance that the rays proceeding from A, after refraction or reflection, +be brought to unite somewhere in the AxAB. And suppose the point of union +(i.e. the image of the point A, as hath been already set forth) to be Z; +between which and B, the vertex of the glass or speculum, conceive the +eye to be anywhere placed. The question now is, where the point A ought +to appear? Experience shows that it does not appear behind at the point +Z, and it were contrary to nature that it should, since all the +impression which affects the sense comes from towards A. But from our +tenets it should seem to follow that it would appear before the eye at a +vast distance off, so great as should in some sort surpass all sensible +distance. For since if we exclude all anticipations and prejudices, every +OBJECT appears by so much the farther off, by how much the rays it sends +to the eye are less diverging. And that OBJECT is thought to be most +remote from which parallel rays proceed unto the eye. Reason would make +one think that OBJECT should appear at yet a greater distance which is +seen by converging rays. Moreover it may in general be asked concerning +this case what it is that determines the apparent place of the point A, +and maketh it to appear after a constant manner sometimes nearer, at +other times farther off? To which doubt I see nothing that can be +answered agreeable to the principles we have laid down except only that +the point A ought always to appear extremely remote. But on the contrary +we are assured by experience that the point A appears variously distant, +according to the different situations of the eye between the points B and +Z. And that it doth never (if at all) seem farther off, than it would if +it were beheld by the naked eye, but on the contrary it doth sometimes +appear much nearer. Nay, it is even certain that by how much the rays +falling on the eye do more converge by so much the nearer doth the OBJECT +seem to approach. For the eye being placed close to the point B, the +OBJECT A appears nearly in its own natural place, if the point B is taken +in the glass, or at the same distance, if in the speculum. The eye being +brought back to O, the OBJECT seems to draw near: and being come to P it +beholds it still nearer. And so on little and little, till at length the +eye being placed somewhere, suppose at Q, the OBJECT appearing extremely +near, begins to vanish into mere confusion. All which doth seem repugnant +to our principles, at least not rightly to agree with them. Nor is our +tenet alone struck at by this experiment, but likewise all others that +ever came to my knowledge are, every whit as much, endangered by it. The +ancient one especially (which is most commonly received, and comes +nearest to mine) seems to be so effectually overthrown thereby that the +most learned Tacquet has been forced to reject that principle, as false +and uncertain, on which alone he had built almost his whole CATOPTRICS; +and consequently by taking away the foundation, hath himself pulled down +the superstructure he had raised on it. Which, nevertheless, I do not +believe he would have done had he but considered the whole matter more +thoroughly, and examined the difficulty to the bottom. But as for me, +neither this nor any other difficulty shall have so great an influence on +me as to make me renounce that which I know to be manifestly agreeable to +reason: especially when, as it here falls out, the difficulty is founded +in the peculiar nature of a certain odd and particular case. For in the +present case something peculiar lies hid, which being involved in the +subtilty of nature will, perhaps, hardly be discovered till such time as +the manner of vision is more perfectly made known. Concerning which, I +must own, I have hitherto been able to find out nothing that has the +least show of PROBABILITY, not to mention CERTAINTY. I shall, therefore, +leave this knot to be untied by you, wishing you may have better success +in it than I have had.' +</P> + +<A NAME="sect030"></A> +<P CLASS="noindent"> +30. The ancient and received principle, which Dr. Barrow here mentions as +the main foundation of Tacquet's CATOPTRICS, is that: 'every visible point +seen by reflection from a speculum shall appear placed at the intersection +of the reflected ray, and the perpendicular of incidence:' which +intersection in the present case, happening to be behind the eye, it +greatly shakes the authority of that principle, whereon the +aforementioned author proceeds throughout his whole CATOPTRICS in +determining the apparent place of OBJECTS seen by reflection from any kind +of speculum. +</P> + +<A NAME="sect031"></A> +<P CLASS="noindent"> +31. Let us now see how this phenomenon agrees with our tenets. The eye +the nearer it is placed to the point B in the foregoing figures, the more +distinct is the appearance of the OBJECT; but as it recedes to O the +appearance grows more confused; and at P it sees the OBJECT yet more +confused; and so on till the eye being brought back to Z sees the OBJECT +in the greatest confusion of all. Wherefore by sect. 21 the OBJECT should +seem to approach the eye gradually as it recedes from the point B, that +is, at O it should (in consequence of the principle I have laid down in +the aforesaid section) seem nearer than it did at B, and at P nearer than +at O, and at Q nearer than at P; and so on, till it quite vanishes at Z. +Which is the very matter of fact, as anyone that pleases may easily +satisfy himself by experiment. +</P> + +<A NAME="sect032"></A> +<P CLASS="noindent"> +32. This case is much the same as if we should suppose an Englishman to +meet a foreigner who used the same words with the English, but in a +direct contrary signification. The Englishman would not fail to make a +wrong judgment of the IDEAS annexed to those sounds in the mind of him +that used them. Just so, in the present case the OBJECT speaks (if I may +so say) with words that the eye is well acquainted with, that is, +confusions of appearance; but whereas heretofore the greater confusions +were always wont to signify nearer distances, they have in this case a +direct, contrary signification, being connected with the greater +distances. Whence it follows that the eye must unavoidably be mistaken, +since it will take the confusions in the sense it has been used to, which +is directly opposed to the true. +</P> + +<A NAME="sect033"></A> +<P CLASS="noindent"> +33. This phenomenon as it entirely subverts the opinion of those who will +have us judge of distance by lines and angles, on which supposition it is +altogether inexplicable, so it seems to me no small confirmation of the +truth of that principle whereby it is explained. But in order co a more +full explication of this point, and to show how far the hypothesis of the +mind's judging by the various divergency of rays may be of use in +determining the apparent place of an OBJECT, it will be necessary to +premise some few things, which are already well known to those who have +any skill in dioptrics. +</P> + +<A NAME="sect034"></A> +<P CLASS="noindent"> +34. FIRST, any radiating point is then distinctly seen when the rays +proceeding from it are, by the refractive power of the crystalline, +accurately reunited in the retina or fund of the eye: but if they are +reunited, either before they arrive at the retina, or after they have +passed it, then there is confused vision. +</P> + +<BR><BR> + +<A NAME="sect035"></A> +<P CLASS="noindent"> +35. SECONDLY, suppose in the adjacent figures NP represent an eye duly +framed and retaining its natural figure. In Fig. 1 the rays falling +nearly parallel on the eye, are by the crystalline AB refracted, so as +their focus or point of union F falls exactly on the retina: but if the +rays fall sensibly diverging on the eye, as in Fig. 2, then their focus +falls beyond the retina: or if the rays are made to converge by the lens +QS before they come at the eye, as in Fig. 3, their focus F will fall +before the retina. In which two last cases it is evident from the +foregoing section that the appearance of the point Z is confused. And by +how much the greater is the convergency, or divergency, of the rays +falling on the pupil, by so much the farther will the point of their +reunion be from the retina, either before or behind it, and consequently +the point Z will appear by so much the more confused. And this, by the +bye, may show us the difference between confused and faint vision. +Confused vision is when the rays proceedings from each distinct point of +the OBJECT are not accurately recollected in one corresponding point on +the retina, but take up some space thereon, so that rays from different +points become mixed and confused together. This is opposed to a distinct +vision, and attends near objects. Faint vision is when by reason of the +distance of the object or grossness of the interjacent medium few rays +arrive from the object to the eye. This is opposed to vigorous or clear +vision, and attends remote objects. But to return. +</P> + +<A NAME="sect036"></A> +<P CLASS="noindent"> +36. The eye, or (to speak truly) the mind, perceiving only the confusion +itself, without ever considering the cause from which it proceeds, doth +constantly annex the same degree of distance to the same degree of +confusion. Whether that confusion be occasioned by converging or by +diverging rays, it matters not. Whence it follows that the eye viewing +the object Z through the glass QS (which by refraction causeth the rays +ZQ, ZS, etc., to converge) should judge it to be at such a nearness at +which if it were placed it would radiate on the eye with rays diverging +to that degree as would produce the same confusion which is now produced +by converging rays, i.e. would cover a portion of the retina equal to DC +(VID. Fig. 3 supra). But then this must be understood (to use Dr. +Barrow's phrase) SECLUSIS PRAENOTIONIBUS ET PRAEJUDICIIS, in case we +abstract from all other circumstances of vision, such as the figure, +size, faintness, etc. of the visible objects; all which do ordinarily +concur to form our idea of distance, the mind having by frequent +experience observed their several sorts or degrees to be connected with +various distances. +</P> + +<A NAME="sect037"></A> +<P CLASS="noindent"> +37. It plainly follows from what hath been said that a person perfectly +purblind (i.e. that could not see an object distinctly but when placed +close to his eye) would not make the same wrong judgment that others do +in the forementioned case. For to him greater confusions constantly +suggesting greater distances, he must, as he recedes from the glass and +the object grows more confused, judge it to be at a farther distance, +contrary to what they do who have had the perception of the objects +growing more confused connected with the idea of approach. +</P> + +<A NAME="sect038"></A> +<P CLASS="noindent"> +38. Hence also it doth appear there may be good use of computation by +lines and angles in optics; not that the mind judgeth of distance +immediately by them, but because it judgeth by somewhat which is +connected with them, and to the determination whereof they may be +subservient. Thus the mind judging of the distance of an object by the +confusedness of its appearance, and this confusedness being greater or +lesser to the naked eye, according as the object is seen by rays more or +less diverging, it follows that a man may make use of the divergency of +the rays in computing the apparent distance, though not for its own sake, +yet on account of the confusion with which it is connected. But, so it +is, the confusion itself is entirely neglected by mathematicians as +having no necessary relation with distance, such as the greater or lesser +angles of divergency are conceived to have. And these (especially for +that they fall under mathematical computation) are alone regarded in +determining the apparent places of objects, as though they were the sole +and immediate cause of the judgments the mind makes of distance. Whereas, +in truth, they should not at all be regarded in themselves, or any +otherwise, than as they are supposed to be the cause of confused vision. +</P> + +<A NAME="sect039"></A> +<P CLASS="noindent"> +39. The not considering of this has been a fundamental and perplexing +oversight. For proof whereof we need go no farther than the case before +us. It having been observed that the most diverging rays brought into the +mind the idea of nearest distance, and that still, as the divergency +decreased, the distance increased: and it being thought the connexion +between the various degrees of divergency and distance was immediate; +this naturally leads one to conclude, from an ill-grounded analogy, that +converging rays shall make an object appear at an immense distance: and +that, as the convergency increases, the distance (if it were possible) +should do so likewise. That this was the cause of Dr. Barrow's mistake is +evident from his own words which we have quoted. Whereas had the learned +doctor observed that diverging and converging rays, how opposite soever +they may seem, do nevertheless agree in producing the same effect, to +wit, confusedness of vision, greater degrees whereof are produced +indifferently, either as the divergency or convergency and the rays +increaseth. And that it is by this effect, which is the same in both, +that either the divergency or convergency is perceived by the eye; I say, +had he but considered this, it is certain he would have made a quite +contrary judgment, and rightly concluded that those rays which fall on +the eye with greater degrees of convergency should make the object from +whence they proceed appear by so much the nearer. But it is plain it was +impossible for any man to attain to a right notion of this matter so long +as he had regard only to lines and angles, and did not apprehend the true +nature of vision, and how far it was of mathematical consideration. +</P> + +<A NAME="sect040"></A> +<P CLASS="noindent"> +40. Before we dismiss this subject, it is fit we take notice of a query +relating thereto, proposed by the ingenious Mr. Molyneux, is his TREATISE +OF DIOPTRICS,[Par. I. Prop. 31, Sect. 9.] where speaking of this +difficulty, he has these words: 'And so he (i.e. Dr. Barrow) leaves this +difficulty to the solution of others, which I (after so great an example) +shall do likewise; but with the resolution of the same admirable author of +not quitting the evident doarine which we have before laid down, for +determining the LOCUS OBJECTI, on account of being pressed by one +difficulty which seems inexplicable till a more intimate knowledge of the +visive faculty be obtained by mortals. In the meantime, I propose it to +the consideration of the ingenious, whether the LOCUS APPARENS of an +object placed as in this 9th section be not as much before the eye as the +distinct base is behind the eye!' To which query we may venture to answer +in the negative. For in the present case the rule for determining the +distance of the distinct base, or respective focus from the glass, is this: +as the difference between the distance of the object and focus is to the +focus or focal length, so the distance of the object from the glass is to +the distance of the respective focus or distinct base from the glass. +[Molyneux Dioptr., Par. I. Prop. 5.] Let us now suppose the object to be +placed at the distance of the focal length, and one half of the focal +length from the glass, and the eye close to the glass, hence it will follow +by the rule that the distance of the distinct base behind the eye is double +the true distance of the object before the eye. If therefore Mr. Molyneux's +conjecture held good, it would follow that the eye should see the object +twice as far off as it really is; and in other cases at three or four times +its due distance, or more. But this manifestly contradicts experience, the +object never appearing, at farthest, beyond its due distance. Whatever, +therefore, is built on this supposition (VID. COROL. I. PROP. 57, IBID.) +comes to the ground along with it. +</P> + +<A NAME="sect041"></A> +<P CLASS="noindent"> +41. From what hath been premised it is a manifest consequence that a man +born blind, being made to see, would, at first, have no idea of distance +by sight; the sun and stars, the remotest objects as well as the nearer, +would all seem to be in his eye, or rather in his mind. The objects +intromitted by sight would seem to him (as in truth they are) no other +than a new set of thoughts or sensations, each whereof is as near to him +as the perceptions of pain or pleasure, or the most inward passions of +his soul. For our judging objects provided by sight to be at any +distance, or without the mind, is (VID. sect. 28) entirely the effect of +experience, which one in those circumstances could not yet have attained +to. +</P> + +<A NAME="sect042"></A> +<P CLASS="noindent"> +42. It is indeed otherwise upon the common supposition that men judge of +distance by the angle of the optic axes, just as one in the dark, or a +blind-man by the angle comprehended by two sticks, one whereof he held in +each hand. For if this were true, it would follow that one blind from his +birth being made to see, should stand in need of no new experience in +order to perceive distance by sight. But that this is false has, I think, +been sufficiently demonstrated. +</P> + +<A NAME="sect043"></A> +<P CLASS="noindent"> +43. And perhaps upon a strict inquiry we shall not find that even those +who from their birth have grown up in a continued habit of seeing are +irrecoverably prejudiced on the other side, to wit, in thinking what they +see to be at a distance from them. For at this time it seems agreed on +all hands, by those who have had any thoughts of that matter, that +colours, which are the proper and immediate object of sight, are not +without the mind. But then it will be said, by sight we have also the +ideas of extension, and figure, and motion; all which may well be thought +without, and at some distance from the mind, though colour should not. In +answer to this I appeal to any man's experience, whether the visible +extension of any object doth not appear as near to him as the colour of +that object; nay, whether they do not both seem to be in the very same +place. Is not the extension we see coloured, and is it possible for us, +so much as in thought, to separate and abstract colour from extension? +Now, where the extension is there surely is the figure, and there the +motion too. I speak of those which are perceived by sight. +</P> + +<A NAME="sect044"></A> +<P CLASS="noindent"> +44. But for a fuller explication of this point, and to show that the +immediate objects of sight are not so much as the ideas or resemblances +of things placed at a distance, it is requisite that we look nearer into +the matter and carefully observe what is meant in common discourse, when +one says that which he sees is at a distance from him. Suppose, for +example, that looking at the moon I should say it were fifty or sixty +semidiameters of the earth distant from me. Let us see what moon this is +spoken of: it is plain it cannot be the visible moon, or anything like +the visible moon, or that which I see, which is only a round, luminous +plane of about thirty visible points in diameter. For in case I am +carried from the place where I stand directly towards the moon, it is +manifest the object varies, still as I go on; and by the time that I am +advanced fifty or sixty semidiameters of the earth, I shall be so far +from being near a small, round, luminous flat that I shall perceive +nothing like it; this object having long since disappeared, and if I +would recover it, it must be by going back to the earth from whence I set +out. Again, suppose I perceive by sight the faint and obscure idea of +something which I doubt whether it be a man, or a tree, or a tower, but +judge it to be at the distance of about a mile. It is plain I cannot mean +that what I see is a mile off, or that it is the image or likeness of +anything which is a mile off, since that every step I take towards it the +appearance alters, and from being obscure, small, and faint, grows clear, +large, and vigorous. And when I come to the mile's end, that which I saw +first is quite lost, neither do I find anything in the likeness of it. +</P> + +<A NAME="sect045"></A> +<P CLASS="noindent"> +45. In these and the like instances the truth of the matter stands thus: +having of a long time experienced certain ideas, perceivable by touch, as +distance, tangible figure, and solidity, to have been connected with +certain ideas of sight, I do upon perceiving these ideas of sight +forthwith conclude what tangible ideas are, by the wonted ordinary course +of Nature like to follow. Looking at an object I perceive a certain +visible figure and colour, with some degree of faintness and other +circumstances, which from what I have formerly observed, determine me to +think that if I advance forward so many paces or miles, I shall be +affected with such and such ideas of touch: so that in truth and +strictness of speech I neither see distance itself, nor anything that I +take to be at a distance. I say, neither distance nor things placed at a +distance are themselves, or their ideas, truly perceived by sight. This I +am persuaded of, as to what concerns myself: and I believe whoever will +look narrowly into his own thoughts and examine what he means by saying +he sees this or that thing at a distance, will agree with me that what he +sees only suggests to his understanding that after having passed a +certain distance, to be measured by the motion of his body, which is +perceivable by touch, he shall come to perceive such and such tangible +ideas which have been usually connected with such and such visible ideas. +But that one might be deceived by these suggestions of sense, and that +there is no necessary connexion between visible and tangible ideas +suggested by them, we need go no farther than the next looking-glass or +pictures to be convinced. Note that when I speak of tangible ideas, I +take the word idea for any the immediate object of sense or +understanding, in which large signification it is commonly used by the +moderns. +</P> + +<A NAME="sect046"></A> +<P CLASS="noindent"> +46. From what we have shown it is a manifest consequence that the ideas +of space, outness, and things placed at a distance are not, strictly +speaking, the object of sight; they are not otherwise perceived by the +eye than by the ear. Sitting in my study I hear a coach drive along the +street; I look through the casement and see it; I walk out and enter into +it; thus, common speech would incline one to think I heard, saw, and +touched the same thing, to wit, the coach. It is nevertheless certain, +the ideas intromitted by each sense are widely different and distinct +from each other; but having been observed constantly to go together, they +are spoken of as one and the same thing. By the variation of the noise I +perceive the different distances of the coach, and know that it +approaches before I look out. Thus by the ear I perceive distance, just +after the same manner as I do by the eye. +</P> + +<A NAME="sect047"></A> +<P CLASS="noindent"> +47. I do not nevertheless say I hear distance in like manner as I say +that I see it, the ideas perceived by hearing not being so apt to be +confounded with the ideas of touch as those of sight are. So likewise a +man is easily convinced that bodies and external things are not properly +the object of hearing; but only sounds, by the mediation whereof the idea +of this or that body or distance is suggested to his thoughts. But then +one is with more difficulty brought to discern the difference there is +betwixt the ideas of sight and touch: though it be certain a man no more +sees and feels the same thing than he hears and feels the same thing. +</P> + +<A NAME="sect048"></A> +<P CLASS="noindent"> +48. One reason of which seems to be this. It is thought a great absurdity +to imagine that one and the same thing should have any more than one +extension, and one figure. But the extension and figure of a body, being +let into the mind two ways, and that indifferently either by sight or +touch, it seems to follow that we see the same extension and the same +figure which we feel. +</P> + +<A NAME="sect049"></A> +<P CLASS="noindent"> +49. But if we take a close and accurate view of things, it must be +acknowledged that we never see and feel one and the same object. That +which is seen is one thing, and that which is felt is another. If the +visible figure and extension be not the same with the tangible figure and +extension, we are not to infer that one and the same thing has divers +extensions. The true consequence is that the objects of sight and touch +are two distinct things. It may perhaps require some thought rightly to +conceive this distinction. And the difficulty seems not a little +increased, because the combination of visible ideas hath constantly the +same name as the combination of tangible ideas wherewith it is connected: +which doth of necessity arise from the use and end of language. +</P> + +<A NAME="sect050"></A> +<P CLASS="noindent"> +50. In order therefore to treat accurately and unconfusedly of vision, we +must bear in mind that there are two sorts of objects apprehended by the +eye, the one primarily and immediately, the other secondarily and by +intervention of the former. Those of the first sort neither are, nor +appear to be, without the mind, or at any distance off; they may indeed +grow greater or smaller, more confused, or more clear, or more faint, but +they do not, cannot approach or recede from us. Whenever we say an object +is at a distance, whenever we say it draws near, or goes farther off, we +must always mean it of the latter sort, which properly belong to the +touch, and are not so truly perceived as suggested by the eye in like +manner as thoughts by the ear. +</P> + +<A NAME="sect051"></A> +<P CLASS="noindent"> +51. No sooner do we hear the words of a familiar language pronounced in +our ears, but the ideas corresponding thereto present themselves to our +minds: in the very same instant the sound and the meaning enter the +understanding: so closely are they united that it is not in our power to +keep out the one, except we exclude the other also. We even act in all +respects as if we heard the very thoughts themselves. So likewise the +secondary objects, or those which are only suggested by sight, do often +more strongly affect us, and are more regarded than the proper objects of +that sense; along with which they enter into the mind, and with which +they have a far more strict connexion, than ideas have with words. Hence +it is we find it so difficult to discriminate between the immediate and +mediate objects of sight, and are so prone to attribute to the former +what belongs only to the latter. They are, as it were, most closely +twisted, blended, and incorporated together. And the prejudice is +confirmed and riveted in our thoughts by a long tract of time, by the use +of language, and want of reflexion. However, I believe anyone that shall +attentively consider what we have already said, and shall say, upon this +subject before we have done (especially if he pursue it in his own +thoughts) may be able to deliver himself from that prejudice. Sure I am +it is worth some attention, to whoever would understand the true nature +of vision. +</P> + +<A NAME="sect052"></A> +<P CLASS="noindent"> +52. I have now done with distance, and proceed to show how it is that we +perceive by sight the magnitude of objects. It is the opinion of some +that we do it by angles, or by angles in conjunction with distance: but +neither angles nor distance being perceivable by sight, and the things we +see being in truth at no distance from us, it follows that as we have +shown lines and angles not to be the medium the mind makes use of in +apprehending the apparent place, so neither are they the medium whereby +it apprehends the apparent magnitude of objects. +</P> + +<A NAME="sect053"></A> +<P CLASS="noindent"> +53. It is well known that the same extension at a near distance shall +subtend a greater angle, and at a farther distance a lesser angle. And by +this principle (we are told) the mind estimates the magnitude of an +object, comparing the angle under which it is seen with its distance, and +thence inferring the magnitude thereof. What inclines men to this mistake +(beside the humour of making one see by geometry) is that the same +perceptions or ideas which suggest distance do also suggest magnitude. +But if we examine it we shall find they suggest the latter as immediately +as the former. I say, they do not first suggest distance, and then leave +it to the judgment to use that as a medium whereby to collect the +magnitude; but they have as close and immediate a connexion with the +magnitude as with the distance; and suggest magnitude as independently of +distance as they do distance independently of magnitude. All which will +be evident to whoever considers what hath been already said, and what +follows. +</P> + +<A NAME="sect054"></A> +<P CLASS="noindent"> +54. It hath been shown there are two sorts of objects apprehended by +sight; each whereof hath its distinct magnitude, or extension. The one, +properly tangible, i.e. to be perceived and measured by touch, and not +immediately falling under the sense of seeing: the other, properly and +immediately visible, by mediation of which the former is brought in view. +Each of these magnitudes are greater or lesser, according as they contain +in them more or fewer points, they being made up of points or minimums. +For, whatever may be said of extension in abstract, it is certain sensible +extension is not infinitely divisible. There is a MINIMUM TANGIBILE and a +MINIMUM VISIBILE, beyond which sense cannot perceive. This everyone's +experience will inform him. +</P> + +<A NAME="sect055"></A> +<P CLASS="noindent"> +55. The magnitude of the object which exists without the mind, and is at +a distance, continues always invariably the same: but the visible object +still changing as you approach to, or recede from, the tangible object, +it hath no fixed and determinate greatness. Whenever, therefore, we speak +of the magnitude of anything, for instance a tree or a house, we must +mean the tangible magnitude, otherwise there can be nothing steady and +free from ambiguity spoken of it. But though the tangible and visible +magnitude in truth belong to two distinct objects: I shall nevertheless +(especially since those objects are called by the same name, and are +observed to coexist), to avoid tediousness and singularity of speech, +sometimes speak of them as belonging to one and the same thing. +</P> + +<A NAME="sect056"></A> +<P CLASS="noindent"> +56. Now in order to discover by what means the magnitude of tangible +objects is perceived by sight. I need only reflect on what passes in my +own mind, and observe what those things be which introduce the ideas of +greater or lesser into my thoughts, when I look on any object. And these +I find to be, FIRST, the magnitude or extension of the visible object, +which being immediately perceived by sight, is connected with that other +which is tangible and placed at a distance. SECONDLY, the confusion or +distinctness. And thirdly, the vigorousness or faintness of the aforesaid +visible appearance. CETERIS PARIBUS, by how much the greater or lesser +the visible object is, by so much the greater or lesser do I conclude the +tangible object to be. But, be the idea immediately perceived by sight +never so large, yet if it be withal confused, I judge the magnitude of +the thing to be but small. If it be distinct and clear, I judge it +greater. And if it be faint, I apprehend it to be yet greater. What is +here meant by confusion and faintness hath been explained in sect. 35. +</P> + +<A NAME="sect057"></A> +<P CLASS="noindent"> +57. Moreover the judgments we make of greatness do, in like manner as +those of distance, depend on the disposition of the eye, also on the +figure, number, and situation of objects and other circumstances that +have been observed to attend great or small tangible magnitudes. Thus, +for instance, the very same quantity of visible extension, which in the +figure of a tower doth suggest the idea of great magnitude, shall in the +figure of a man suggest the idea of much smaller magnitude. That this is +owing to the experience we have had of the usual bigness of a tower and a +man no one, I suppose, need be told. +</P> + +<A NAME="sect058"></A> +<P CLASS="noindent"> +58. It is also evident that confusion or faintness have no more a +necessary connexion with little or great magnitude than they have with +little or great distance. As they suggest the latter, so they suggest the +former to our minds. And by consequence, if it were not for experience, +we should no more judge a faint or confused appearance to be connected +with great or little magnitude, than we should that it was connected with +great or little distance. +</P> + +<A NAME="sect059"></A> +<P CLASS="noindent"> +59. Nor will it be found that great or small visible magnitude hath any +necessary relation to great or small tangible magnitude: so that the one +may certainly be inferred from the other. But before we come to the proof +of this, it is fit we consider the difference there is betwixt the +extension and figure which is the proper object of touch, and that other +which is termed visible; and how the former is principally, though not +immediately taken notice of, when we look at any object. This has been +before mentioned, but we shall here inquire into the cause thereof. We +regard the objects that environ us in proportion as they are adapted to +benefit or injure our own bodies, and thereby produce in our minds the +sensation of pleasure or pain. Now bodies operating on our organs, by an +immediate application, and the hurt or advantage arising therefrom, +depending altogether on the tangible, and not at all on the visible, +qualities of any object: this is a plain reason why those should be +regarded by us much more than these: and for this end the visive sense +seems to have been bestowed on animals, to wit, that by the perception of +visible ideas (which in themselves are not capable of affecting or any +wise altering the frame of their bodies) they may be able to foresee +(from the experience they have had what tangible ideas are connected with +such and such visible ideas) and damage or benefit which is like to +ensue, upon the application of their own bodies to this or that body +which is at a distance. Which foresight, how necessary it is to the +preservation of an animal, everyone's experience can inform him. Hence it +is that when we look at an object, the tangible figure and extension +thereof are principally attended to; whilst there is small heed taken of +the visible figure and magnitude, which, though more immediately +perceived, do less concern us, and are not fitted to produce any +alteration in our bodies. +</P> + +<A NAME="sect060"></A> +<P CLASS="noindent"> +60. That the matter of fact is true will be evident to anyone who +considers that a man placed at ten foot distance is thought as great as +if he were placed at a distance only of five foot: which is true not with +relation to the visible, but tangible greatness of the object: the +visible magnitude being far greater at one station: than it is at the +other. +</P> + +<A NAME="sect061"></A> +<P CLASS="noindent"> +61. Inches, feet, etc., are settled stated lengths whereby we measure +objects and estimate their magnitude: we say, for example, an object +appears to be six inches or six foot long. Now, that this cannot be meant +of visible inches, etc., is evident, because a visible inch is itself no +constant, determinate magnitude, and cannot therefore serve to mark out +and determine the magnitude of any other thing. Take an inch marked upon +a ruler: view it, successively, at the distance of half a foot, a foot, a +foot and a half, etc., from the eye: at each of which, and at all the +intermediate distances, the inch shall have a different visible +extension, i.e. there shall be more or fewer points discerned in it. Now +I ask which of all these various extensions is that stated, determinate +one that is agreed on for a common measure of other magnitudes? No reason +can be assigned why we should pitch on one more than another: and except +there be some invariable, determinate extension fixed on to be marked to +the word inch, it is plain it can be used to little purpose; and to say a +thing contains this or that number of inches shall imply no more than +that it is extended, without bringing any particular idea of that +extension into the mind. Farther, an inch and a foot, from different +distances, shall both exhibit the same visible magnitude, and yet at the +same time you shall say that one seems several times greater than the +other. From all which it is manifest that the judgments we make of the +magnitude of objects by sight are altogether in reference to their +tangible extension. Whenever we say an object is great, or small, of this +or that determinate measure, I say it must be meant of the tangible, and +not the visible extension, which, though immediately perceived, is +nevertheless little taken notice of. +</P> + +<A NAME="sect062"></A> +<P CLASS="noindent"> +62. Now, that there is no necessary connexion between these two distinct +extensions is evident from hence: because our eyes might have been framed +in such a manner as to be able to see nothing but what were less than the +MINIMUM TANGIBILE. In which case it is not impossible we might have +perceived all the immediate objects of sight, the very same that we do +now: but unto those visible appearances there would not be connected +those different tangible magnitudes that are now. Which shows the +judgments we make of the magnitude of things placed at a distance from +the various greatness of the immediate objects of sight do not arise from +any essential or necessary but only a customary tie, which has been +observed between them. +</P> + +<A NAME="sect063"></A> +<P CLASS="noindent"> +63. Moreover, it is not only certain that any idea of sight might not +have been connected with this or that idea of touch, which we now observe +to accompany it: but also that the greater visible magnitudes might have +been connected with, and introduced into our minds lesser tangible +magnitudes and the lesser visible magnitudes greater tangible magnitudes. +Nay, that it actually is so we have daily experience; that object which +makes a strong and large appearance, not seeming near so great as +another, the visible magnitude whereof is much less, but more faint, and +the appearance upper, or which is the same thing painted lower on the +RETINA, which faintness and situation suggest both greater magnitude and +greater distance. +</P> + +<A NAME="sect064"></A> +<P CLASS="noindent"> +64. From which, and from sect. 57 and 58, it is manifest that as we do +not perceive the magnitudes of objects immediately by sight, so neither +do we perceive them by the mediation of anything which has a necessary +connexion with them. Those ideas that now suggest unto us the various +magnitudes of external objects before we touch them, might possibly have +suggested no such thing: or they might have signified them in a direct +contrary manner: so that the very same ideas, on the perception whereof +we judge an object to be small, might as well have served to make us +conclude it great. Those ideas being in their own nature equally fitted +to bring into our minds the idea of small or great, or no size at all of +outward objects; just as the words of any language are in their own +nature indifferent to signify this or that thing or nothing at all. +</P> + +<A NAME="sect065"></A> +<P CLASS="noindent"> +65. As we see distance, so we see magnitude. And we see both in the same +way that we see shame or anger in the looks of a man. Those passions are +themselves invisible, they are nevertheless let in by the eye along with +colours and alterations of countenance, which are the immediate object of +vision: and which signify them for no other reason than barely because +they have been observed to accompany them. Without which experience we +should no more have taken blushing for a sign of shame than of gladness. +</P> + +<A NAME="sect066"></A> +<P CLASS="noindent"> +66. We are nevertheless exceeding prone to imagine those things which are +perceived only by the mediation of others to be themselves the immediate +objects of sight; or, at least, to have in their own nature a fitness to +be suggested by them, before ever they had been experienced to coexist +with them. From which prejudice everyone, perhaps, will not find it easy +to emancipate himself, by any [but] the clearest convictions of reason. +And there are some grounds to think that if there was one only invariable +and universal languages in the world, and that men were born with the +faculty of speaking it, it would be the opinion of many that the ideas of +other men's minds were properly perceived by the ear, or had at least a +necessary and inseparable tie with the sounds that were affixed to them. +All which seems to arise from want of a due application of our discerning +faculty, thereby to discriminate between the ideas that are in our +understandings, and consider them apart from each other; which would +preserve us from confounding those that are different, and make us see +what ideas do, and what do not include or imply this or that other idea. +</P> + +<A NAME="sect067"></A> +<P CLASS="noindent"> +67. There is a celebrated phenomenon, the solution whereof I shall +attempt to give by the principles that have been laid down, in reference +to the manner wherein we apprehend by sight the magnitude of objects. The +apparent magnitude of the moon when placed in the horizon is much greater +than when it is in the meridian, though the angle under which the +diameter of the moon is seen be not observed greater in the former case +than in the latter: and the horizontal moon doth not constantly appear of +the same bigness, but at some times seemeth far greater than at others. +</P> + +<A NAME="sect068"></A> +<P CLASS="noindent"> +68. Now in order to explain the reason of the moon's appearing greater +than ordinary in the horizon, it must be observed that the particles +which compose our atmosphere intercept the rays of light proceeding from +any object to the eye; and by how much the greater is the portion of +atmosphere interjacent between the object and the eye, by so much the +more are the rays intercepted; and by consequence the appearance of the +object rendered more faint, every object appearing more vigorous or more +faint in proportion as it sendeth more or fewer rays into the eye. Now +between the eye and the moon, when situated in the horizon, there lies a +far greater quantity of atmosphere than there does when the moon is in +the meridian. Whence it comes to pass that the appearance of the +horizontal moon is fainter, and therefore by sect. 56 it should be +thought bigger in that situation than in the meridian, or in any other +elevation above the horizon. +</P> + +<A NAME="sect069"></A> +<P CLASS="noindent"> +69. Farther, the air being variously impregnated, sometimes more and +sometimes less, with vapours and exhalations fitted to retund and +intercept the rays of light, it follows that the appearance of the +horizontal moon hath not always an equal faintness, and by consequence +that luminary, though in the very same situation, is at one time judged +greater than at another. +</P> + +<A NAME="sect070"></A> +<P CLASS="noindent"> +70. That we have here given the true account of the phenomena of the +horizontal moon will, I suppose, be farther evident to anyone from the +following considerations. FIRST, it is plain that which in this case +suggests the idea of greater magnitude must be something which is itself +perceived; for that which is unperceived cannot suggest to our perception +any other thing. SECONDLY, it must be something that does not constantly +remain the same, but is subject to some change or variation, since the +appearance of the horizontal moon varies, being at one time greater than +at another. And yet, THIRDLY, it cannot be the visible figure or +magnitude, since that remains the same, or is rather lesser, by how much +the moon is nearer to the horizon. It remains therefore that the true +cause is that affection or alteration of the visible appearance which +proceeds from the greater paucity of rays arriving at the eye, and which +I term FAINTNESS: since this answers all the forementioned conditions, +and I am not conscious of any other perception that doth. +</P> + +<A NAME="sect071"></A> +<P CLASS="noindent"> +71. Add to this that in misty weather it is a common observation that the +appearance of the horizontal moon is far larger than usual, which greatly +conspires with and strengthens our opinion. Neither would it prove in the +least irreconcilable with what we have said, if the horizontal moon +should chance sometimes to seem enlarged beyond its usual extent, even in +more serene weather. For we must not only have regard to the mist which +happens to be in the place where we stand; we ought also to take into our +thoughts the whole sum of vapours and exhalations which lie betwixt the +eye and the moon: all which cooperating to render the appearance of the +moon more faint, and thereby increase its magnitude, it may chance to +appear greater than it usually does, even in the horizontal position, at +a time when, though there be no extraordinary fog or haziness, just in +the place where we stand, yet the air between the eye and the moon, taken +all together, may be loaded with a greater quantity of interspersed +vapours and exhalations than at other times. +</P> + +<A NAME="sect072"></A> +<P CLASS="noindent"> +72. It may be objected that in consequence of our principles the +interposition of a body in some degree opaque, which may intercept a +great part of the rays of light, should render the appearance of the moon +in the meridian as large as when it is viewed in the horizon. To which I +answer, it is not faintness anyhow applied that suggests greater +magnitude, there being no necessary but only an experimental connexion +between those two things. It follows that the faintness which enlarges +the appearance must be applied in such sort, and with such circumstances, +as have been observed to attend the vision of great magnitudes. When from +a distance we behold great objects, the particles of the intermediate air +and vapours, which are themselves unperceivable, do interrupt the rays of +light, and thereby render the appearance less strong and vivid: now, +faintness of appearance caused in this sort hath been experienced to +coexist with great magnitude. But when it is caused by the interposition +of an opaque sensible body, this circumstance alters the case, so that a +faint appearance this way caused doth not suggest greater magnitude, +because it hath not been experienced to coexist with it. +</P> + +<A NAME="sect073"></A> +<P CLASS="noindent"> +73. Faintness, as well as all other ideas or perceptions which suggest +magnitude or distance, doth it in the same way that words suggest the +notions to which they are annexed. Now, it is known a word pronounced +with certain circumstances, or in a certain context with other words, +hath not always the same import and signification that it hath when +pronounced in some other circumstances or different context of words. The +very same visible appearance as to faintness and all other respects, if +placed on high, shall not suggest the same magnitude that it would if it +were seen at an equal distance on a level with the eye. The reason +whereof is that we are rarely accustomed to view objects at a great +height; our concerns lie among things situated rather before than above +us, and accordingly our eyes are not placed on the top of our heads, but +in such a position as is most convenient for us to see distant objects +standing in our way. And this situation of them being a circumstance +which usually attends the vision of distant objects, we may from hence +account for (what is commonly observed) an object's appearing of +different magnitude, even with respect to its horizontal extension, on +the top of a steeple, for example, an hundred feet high to one standing +below, from what it would if placed at an hundred feet distance on a +level with his eye. For it hath been shown that the judgment we make on +the magnitude of a thing depends not on the visible appearance alone, but +also on divers other circumstances, any one of which being omitted or +varied may suffice to make some alteration in our judgment. Hence, the +circumstances of viewing a distant object in such a situation as is +usual, and suits with the ordinary posture of the head and eyes being +omitted, and instead thereof a different situation of the object, which +requires a different posture of the head taking place, it is not to be +wondered at if the magnitude be judged different: but it will be demanded +why an high object should constantly appear less than an equidistant low +object of the same dimensions, for so it is observed to be: it may indeed +be granted that the variation of some circumstances may vary the judgment +made on the magnitude of high objects, which we are less used to look at: +but it does not hence appear why they should be judged less rather than +greater? I answer that in case the magnitude of distant objects was +suggested by the extent of their visible appearance alone, and thought +proportional thereto, it is certain they would then be judged much less +than now they seem to be (VIDE sect. 79). But several circumstances +concurring to form the judgment we make on the magnitude of distant +objects, by means of which they appear far larger than others, whose +visible appearance hath an equal or even greater extension; it follows +that upon the change or omission of any of those circumstances which are +wont to attend the vision of distant objects, and so come to influence +the judgments made on their magnitude, they shall proportionably appear +less than otherwise they would. For any of those things that caused an +object to be thought greater than in proportion to its visible extension +being either omitted or applied without the usual circumstances, the +judgment depends more entirely on the visible extension, and consequently +the object must be judged less. Thus in the present case the situation of +the thing seen being different from what it usually is in those objects +we have occasion to view, and whose magnitude we observe, it follows that +the very same object, being an hundred feet high, should seem less than +if it was an hundred feet off on (or nearly on) a level with the eye. +What has been here set forth seems to me to have no small share in +contributing to magnify the appearance of the horizontal moon, and +deserves not to be passed over in the explication of it. +</P> + +<A NAME="sect074"></A> +<P CLASS="noindent"> +74. If we attentively consider the phenomenon before us, we shall find +the not discerning between the mediate and immediate objects of sight to +be the chief cause of the difficulty that occurs in the explication of +it. The magnitude of the visible moon, or that which is the proper and +immediate object of vision, is not greater when the moon is in the +horizon than when it is in the meridian. How comes it, therefore, to seem +greater in one situation than the other? What is it can put this cheat on +the understanding? It has no other perception of the moon than what it +gets by sight: and that which is seen is of the same extent, I say, the +visible appearance hath the same, or rather a less, magnitude when the +moon is viewed in the horizontal than when in the meridional position: +and yet it is esteemed greater in the former than in the latter. Herein +consists the difficulty, which doth vanish and admit of a most easy +solution, if we consider that as the visible moon is not greater in the +horizon than in the meridian, so neither is it thought to be so. It hath +been already shown that in any act of vision the visible object +absolutely, or in itself, is little taken notice of, the mind still +carrying its view from that to some tangible ideas which have been +observed to be connected with it, and by that means come to be suggested +by it. So that when a thing is said to appear great or small, or whatever +estimate be made of the magnitude of any thing, this is meant not of the +visible but of the tangible object. This duly considered, it will be no +hard matter to reconcile the seeming contradiction there is, that the +moon should appear of a different bigness, the visible magnitude thereof +remaining still the same. For by sect. 56 the very same visible +extension, with a different faintness, shall suggest a different tangible +extension. When therefore the horizontal moon is said to appear greater +than the meridional moon, this must be understood not of a greater +visible extension, but a of greater tangible or real extension, which by +reason of the more than ordinary faintness of the visible appearance, is +suggested to the mind along with it. +</P> + +<A NAME="sect075"></A> +<P CLASS="noindent"> +75. Many attempts have been made by learned men to account for this +appearance. Gassendus, Descartes, Hobbes, and several others have +employed their thoughts on that subject; but how fruitless and +unsatisfactory their endeavours have been is sufficiently shown in THE +TRANSACTIONS,[Phil. Trans. Num. 187. p. 314] where you may +see their several opinions at large set forth and confuted, not without +some surprize at the gross blunders that ingenious men have been forced +into by endeavouring to reconcile this appearance with the ordinary +Principles of optics. Since the writing of which there hath been published +in the TRANSACTIONS [Numb. 187. P. 323] another paper relating to the same +affair by the celebrated Dr. Wallis, wherein he attempts to account for +that phenomenon which, though it seems not to contain anything new or +different from what had been said before by others, I shall nevertheless +consider in this place. +</P> + +<A NAME="sect076"></A> +<P CLASS="noindent"> +76. His opinion, in short, is this; we judge not of the magnitude of an +object by the visual angle alone, but by the visual angle in conjunction +with the distance. Hence, though the angle remain the same, or even +become less, yet if withal the distance seem to have been increased, the +object shall appear greater. Now, one way whereby we estimate the +distance of anything is by the number and extent of the intermediate +objects: when therefore the moon is seen in the horizon, the variety of +fields, houses, etc., together with the large prospect of the wide +extended land or sea that lies between the eye and the utmost limb of the +horizon, suggest unto the mind the idea of greater distance, and +consequently magnify the appearance. And this, according to Dr. Wallis, +is the true account of the extraordinary largeness attributed by the mind +to the horizontal moon at a time when the angle subtended by its diameter +is not one jot greater than it used to be. +</P> + +<A NAME="sect077"></A> +<P CLASS="noindent"> +77. With reference to this opinion, not to repeat what hath been already +said concerning distance, I shall only observe, FIRST, that if the +prospect of interjacent objects be that which suggests the idea of +farther distance, and this idea of farther distance be the cause that +brings into the mind the idea of greater magnitude, it should hence +follow that if one looked at the horizontal moon from behind a wall, it +would appear no bigger than ordinary. For in that case the wall +interposing cuts off all that prospect of sea and land, etc. which might +otherwise increase the apparent distance, and thereby the apparent +magnitude of the moon. Nor will it suffice to say the memory doth even +then suggest all that extent of land, etc., which lies within the +horizon; which suggestion occasions a sudden judgment of sense that the +moon is farther off and larger than usual. For ask any man who, from such +a station beholding the horizontal moon, shall think her greater than +usual, whether he hath at that time in his mind any idea of the +intermediate objects, or long tract of land that lies between his eye and +the extreme edge of the horizon? And whether it be that idea which is the +cause of his making the aforementioned judgment? He will, I suppose, +reply in the negative, and declare the horizontal moon shall appear +greater than the meridional, though he never thinks of all or any of +those things that lie between him and it. SECONDLY, it seems impossible +by this hypothesis to account for the moon's appearing in the very same +situation at one time greater than at another; which nevertheless has +been shown to be very agreeable to the principles we have laid down, and +receives a most easy and natural explication from them. For the further +clearing' up of this point it is to be observed that what we immediately +and properly see are only lights and colours in sundry situations and +shades and degrees of faintness and clearness, confusion and +distinctness. All which visible objects are only in the mind, nor do they +suggest ought external, whether distance or magnitude, otherwise than by +habitual connexion as words do things. We are also to remark that, beside +the straining of the eyes, and beside the vivid and faint, the distinct +and confused appearances (which, bearing some proportion to lines and +angles, have been substituted instead of them in the foregoing part of +this treatise), there are other means which suggest both distance and +magnitude; particularly the situation of visible points of objects, as +upper or lower; the one suggesting a farther distance and greater +magnitude, the other a nearer distance and lesser magnitude: all which is +an effect only of custom and experience; there being really nothing +intermediate in the line of distance between the uppermost and lowermost, +which are both equidistant, or rather at no distance from the eye, as +there is also nothing in upper or lower, which by necessary connexion +should suggest greater or lesser magnitude. Now, as these customary, +experimental means of suggesting distance do likewise suggest magnitude, +so they suggest the one as immediately as the other. I say they do not +(VIDE sect. 53) first suggest distance, and then leave the mind from +thence to infer or compute magnitude, jut suggest magnitude as +immediately and directly as they suggest distance. +</P> + +<A NAME="sect078"></A> +<P CLASS="noindent"> +78. This phenomenon of the horizontal moon is a clear instance of the +insufficiency of lines and angles for explaining the way wherein the mind +perceives and estimates the magnitude of outward objects. There is +nevertheless a use of computation by them in order to determine the +apparent magnitude of things, so far as they have a connexion with, and +are proportional to, those other ideas or perceptions which are the true +and immediate occasions that suggest to the mind the apparent magnitude +of things. But this in general may, I think, be observed concerning +mathematical computation in optics: that it can never be very precise and +exact since the judgments we make of the magnitude of external things do +often depend on several circumstances, which are not proportionable to, +or capable of being defined by, lines and angles. +</P> + +<A NAME="sect079"></A> +<P CLASS="noindent"> +79. From what has been said we may safely deduce this consequence; to +wit, that a man born blind and made to see would, at first opening of his +eyes, make a very different judgment of the magnitude of objects +intromitted by them from what others do. He would not consider the ideas +of sight with reference to, or as having any connexion with, the ideas of +touch: his view of them being entirely terminated within themselves, he +can no otherwise judge them great or small than as they contain a greater +or lesser number of visible points. Now, it being certain that any +visible point can cover or exclude from view only one other visible +point, it follows that whatever object intercepts the view of another +hath an equal number of visible points with it; and consequently they +shall both be thought by him to have the same magnitude. Hence it is +evident one in those circumstances would judge his thumb, with which he +might hide a tower or hinder its being seen, equal to that tower, or his +hand, the interposition whereof might conceal experimental means the +firmament from his view, equal to the firmament: how great an inequality +soever there may in our apprehensions seem to be betwixt those two +things, because of the customary and close connexion that has grown up in +our minds between the objects of sight and touch; whereby the very +different and distinct ideas of those two senses are so blended and +confounded together as to be mistaken for one and the same thing; out of +which prejudice we cannot easily extricate ourselves. +</P> + +<A NAME="sect080"></A> +<P CLASS="noindent"> +80. For the better explaining the nature of vision, and setting the +manner wherein we perceive magnitudes in a due light, I shall proceed to +make some observations concerning matters relating thereto, whereof the +want of reflexion, and duly separating between tangible and visible +ideas, is apt to create in us mistaken and confused notions. And FIRST, I +shall observe that the MINIMUM VISIBILE is exactly equal in all beings +whatsoever that are endowed with the visive faculty. No exquisite +formation of the eye, no peculiar sharpness of sight, can make it less in +one creature than in another; for it not being distinguishable into +parts, nor in any wise a consisting of them, it must necessarily be the +same to all. For suppose it otherwise, and that the MINIMUM VISIBILE of a +mite, for instance, be less than the MINIMUM VISIBILE of a man: the +latter therefore may by detraction of some part be made equal to the +former: it doth therefore consist of parts, which is inconsistent with +the notion of a MINIMUM VISIBILE or point. +</P> + +<A NAME="sect081"></A> +<P CLASS="noindent"> +81. It will perhaps be objected that the MINIMUM VISIBILE of a man doth +really and in itself contain parts whereby it surpasses that of a mite, +though they are not perceivable by the man. To which I answer, the +MINIMUM VISIBILE having (in like manner as all other the proper and +immediate objects of sight) been shown not to have any existence without +the mind of him who sees it, it follows there cannot be any pan of it +that is not actually perceived, and therefore visible. Now for any object +to contain distinct visible parts, and at the same time to be a MINIMUM +VISIBILE, is a manifest contradiction. +</P> + +<A NAME="sect082"></A> +<P CLASS="noindent"> +82. Of these visible points we see at all times an equal number. It is +every whit as great when our view is contracted and bounded by near +objects as when it is extended to larger and remoter. For it being +impossible that one MINIMUM VISIBILE should obscure or keep out of sight +mote than one other, it is a plain consequence that when my view is on +all sides bounded by the walls of my study see just as many visible +points as I could, in case that by the removal of the study-walls and all +other obstructions, I had a full prospect of the circumjacent fields, +mountains, sea, and open firmament: for so long as I am shut up within +the walls, by their interposition every point of the external objects is +covered from my view: but each point that is seen being able to cover or +exclude from sight one only other corresponding point, it follows that +whilst my sight is confined to those narrow walls I see as many points, +or MINIMA VISIBILIA, as I should were those walls away, by looking on all +the external objects whose prospect is intercepted by them. Whenever +therefore we are said to have a greater prospect at one time than +another, this must be understood with relation, not to the proper and +immediate, but the secondary and mediate objects of vision, which, as +hath been shown, properly belong to the touch. +</P> + +<A NAME="sect083"></A> +<P CLASS="noindent"> +83. The visive faculty considered with reference to its immediate objects +may be found to labour of two defects. FIRST, in respect of the extent or +number of visible points that are at once perceivable by it, which is +narrow and limited to a certain degree. It can take in at one view but a +certain determinate number of MINIMA VISIBILIA, beyond which it cannot +extend its prospect. Secondly, our sight is defective in that its view is +not only narrow, but also for the most part confused: of those things +that we take in at one prospect we can see but a few at once clearly and +unconfusedly: and the more we fix our sight on any one object, by so much +the darker and more indistinct shall the rest appear. +</P> + +<A NAME="sect084"></A> +<P CLASS="noindent"> +84. Corresponding to these two defects of sight, we may imagine as many +perfections, to wit, 1ST, that of comprehending in one view a greater +number of visible points. 2DLY, of being able to view them all equally +and at once with the utmost clearness and distinction. That those +perfections are not actually in some intelligences of a different order +and capacity from ours it is impossible for us to know. +</P> + +<A NAME="sect085"></A> +<P CLASS="noindent"> +85. In neither of those two ways do microscopes contribute to the +improvement of sight; for when we look through a microscope we neither +see more visible points, nor are the collateral points more distinct than +when we look with the naked eye at objects placed in a due distance. A +microscope brings us, as it were, into a new world: it presents us with a +new scene of visible objects quite different from what we behold with the +naked eye. But herein consists the most remarkable difference, to wit, +that whereas the objects perceived by the eye alone have a certain +connexion with tangible objects, whereby we are taught to foresee what +will ensue upon the approach or application of distant objects to the +parts of our own body, which much conduceth to its preservation, there is +not the like connexion between things tangible and those visible objects +that are perceived by help of a fine microscope. +</P> + +<A NAME="sect086"></A> +<P CLASS="noindent"> +86. Hence it is evident that were our eyes turned into the nature of +microscopes, we should not be much benefited by the change; we should be +deprived of the forementioned advantage we at present receive by the +visive faculty, and have left us only the empty amusement of seeing, +without any other benefit arising from it. But in that case, it will +perhaps be said, our sight would be endued with a far greater sharpness +and penetration than it now hath. But it is certain from what we have +already shown that the MINIMUM VISIBILE is never greater or lesser, but +in all cases constantly the same: and in the case of microscopical eyes I +see only this difference, to wit, that upon the ceasing of a certain +observable connexion betwixt the divers perceptions of sight and touch, +which before enabled us to regulate our actions by the eye, it would now +be rendered utterly unserviceable to that purpose. +</P> + +<A NAME="sect087"></A> +<P CLASS="noindent"> +87. Upon the whole it seems that if we consider the use and end of sight, +together with the present state and circumstances of our being, we shall +not find any great cause to complain of any defect or imperfection in it, +or easily conceive how it could be mended. With such admirable wisdom is +that faculty contrived, both for the pleasure and convenience of life. +</P> + +<A NAME="sect088"></A> +<P CLASS="noindent"> +88. Having finished what I intended to say concerning the distance and +magnitude of objects, I come now to treat of the manner wherein the mind +perceives by sight their situation. Among the discoveries of the last +age, it is reputed none of the least that the manner of vision hath been +more clearly explained than ever it had been before. There is at this day +no one ignorant that the pictures of external objects are painted on the +RETINA, or fund of the eye: that we can see nothing which is not so +painted: and that, according as the picture is more distinct or confused, +so also is the perception we have of the object: but then in this +explication of vision there occurs one mighty difficulty. The objects are +painted in an inverted order on the bottom of the eye: the upper part of +any object being painted on the lower part of the eye, and the lower part +of the object on the upper part of the eye: and so also as to right and +left. Since therefore the pictures are thus inverted, it is demanded how +it comes to pass that we see the objects erect and in their natural +posture? +</P> + +<A NAME="sect089"></A> +<P CLASS="noindent"> +89. In answer to this difficulty we are told that the mind, perceiving an +impulse of a ray of light on the upper part of the eye, considers this +ray as coming in a direct line from the lower part of the object; and in +like manner tracing the ray that strikes on the lower part of the eye, it +is directed to the upper part of the object. Thus in the adjacent figure, +C, the lower point of the object ABC, is projected on C the upper part of +the eye. So likewise the highest point A is projected on A the lowest +part of the eye, which makes the representation CBA inverted: but the +mind considering the stroke that is made on C as coming in the straight +line CC from the lower end of the object; and the stroke or impulse on a +as coming in the line AA from the upper end of the object, is directed to +make a right judgment of the situation of the object ABC, notwithstanding +the picture of it is inverted. This is illustrated by conceiving a blind +man who, holding in his hands two sticks that cross each other, doth with +them touch the extremities of an object, placed in a perpendicular +situation. It is certain this man will judge that to be the upper part of +the object which he touches with the stick held in the undermost hand, +and that to be the lower part of the object which he touches with the +stick in his uppermost hand. This is the common explication of the erect +appearance of objects, which is generally received and acquiesced in, +being (as Mr. Molyneux tells us [Diopt. par. 2. c. 7. P. 289.]) 'allowed +by all men as satisfactory'. +</P> + +<A NAME="sect090"></A> +<P CLASS="noindent"> +90. But this account to me does not seem in any degree true. Did I +perceive those impulses, decussations, and directions of the rays of +light in like manner as hath been set forth, then indeed it would not be +altogether void of probability. And there might be some pretence for the +comparison of the blind man and his cross sticks. But the case is far +otherwise. I know very well that I perceive no such thing. And of +consequence I cannot thereby make an estimate of the situation of +objects. I appeal to anyone's experience, whether he be conscious to +himself that he thinks on the intersection made by the radious [SIC] +pencils, or pursues the impulses they give in right lines, whenever he +perceives by sight the position of any object? To me it seems evident +that crossing and tracing of the rays is never thought on by children, +idiots, or in truth by any other, save only those who have applied +themselves to the study of optics. And for the mind to judge of the +situation of objects by those things without perceiving them, or to +perceive them without knowing it, is equally beyond my comprehension. Add +to this that the explaining the manner of vision by the example of cross +sticks and hunting for the object along the axes of the radious pencils, +doth suppose the proper objects of sight to be perceived at a distance +from us, contrary to what hath been demonstrated. +</P> + +<A NAME="sect091"></A> +<P CLASS="noindent"> +91. It remains, therefore, that we look for some other explication of +this difficulty: and I believe it not impossible to find one, provided we +examine it to the bottom, and carefully distinguish between the ideas of +sight and touch; which cannot be too oft inculcated in treating of +vision: but more especially throughout the consideration of this affair +we ought to carry that distinction in our thoughts: for that from want of +a right understanding thereof the difficulty of explaining erect vision +seems chiefly to arise. +</P> + +<A NAME="sect092"></A> +<P CLASS="noindent"> +92. In order to disentangle our minds from whatever prejudices we may +entertain with relation to the subject in hand, nothing seems more +apposite than the taking into our thoughts the case of one born blind, +and afterwards, when grown up, made to see. And though, perhaps, it may +not be an easy task to divest ourselves entirely of the experience +received from sight, so as to be able to put our thoughts exactly in the +posture of such a one's, we must, nevertheless, as far as possible, +endeavour to frame true conceptions of what might reasonably be supposed +to pass in his mind. +</P> + +<A NAME="sect093"></A> +<P CLASS="noindent"> +93. It is certain that a man actually blind, and who had continued so +from his birth, would by the sense of feeling attain to have ideas of +upper and lower. By the motion of his hand he might discern the situation +of any tangible object placed within his FI reach. That part on which he +felt himself supported, or towards which he perceived his body to +gravitate, he would term lower, and the contrary to this upper; and +accordingly denominate whatsoever objects he touched. +</P> + +<A NAME="sect094"></A> +<P CLASS="noindent"> +94. But then, whatever judgments he makes concerning the situation of +objects are confined to those only that are perceivable by touch. All +those things that are intangible and of a spiritual nature, his thoughts +and desires, his passions, and in general all the modifications of the +soul, to these he would never apply the terms UPPER and LOWER, except +only in a metaphorical sense. He may, perhaps, by way of allusion, speak +of high or low thoughts: but those terms in their proper signification +would never be applied to anything that was not conceived to exist +without the mind. For a man born blind, and remaining in the same state, +could mean nothing else by the words HIGHER and LOWER than a greater or +lesser distance from the earth; which distance he would measure by the +motion or application of his hand or some other part of his body. It is +therefore evident that all those things which, in respect of each other, +would by him be thought higher or lower, must be such as were conceived +to exist without his mind, in the ambient space. +</P> + +<A NAME="sect095"></A> +<P CLASS="noindent"> +95. Whence it plainly follows that such a one, if we suppose him made to +see, would not at first sight think anything he saw was high or low, +erect or inverted; for it hath been already demonstrated in sect. 41 that +he would not think the things he perceived by sight to be at any distance +from him, or without his mind. The objects to which he had hitherto been +used to apply the terms UP and DOWN, HIGH and LOW, were such only as +affected or were some way perceived by his couch: but the proper objects +of vision make a new set of ideas, perfectly distinct and different from +the former, and which can in no sort make themselves perceived by touch. +There is, therefore, nothing at all that could induce him to think those +terms applicable to them: nor would he ever think it till such time as he +had observed their connexion with tangible objects, and the same +prejudice began to insinuate itself into his understanding, which from +their infancy had grown up in the understandings of other men. +</P> + +<A NAME="sect096"></A> +<P CLASS="noindent"> +96. To set this matter in a clearer light I shall make use of an example. +Suppose the above-mentioned blind person by his touch perceives a man to +stand erect. Let us inquire into the manner of this. By the application +of his hand to the several parts of a human body he had perceived +different tangible ideas, which being collected into sundry complex ones, +have distinct names annexed to them. Thus one combination of a certain +tangible figure, bulk, and consistency of parts is called the head, +another the hand, a third the foot, and so of the rest: all which complex +ideas could, in his understanding, be made up only of ideas perceivable +by touch. He had also by his touch obtained an idea of earth or ground, +towards which he perceives the parts of his body to have a natural +tendency. Now, by ERECT nothing more being meant than that perpendicular +position of a man wherein his feet are nearest to the earth, if the blind +person by moving his hand over the parts of the man who stands before him +perceives the tangible ideas that compose the head to be farthest from, +and those that compose the feet to be nearest to, that other combination +of tangible ideas which he calls earth, he will denominate that man +erect. But if we suppose him on a sudden to receive his sight, and that +he behold a man standing before him, it is evident in that case he would +neither judge the man he sees to be erect nor inverted; for he never +having known those terms applied to any other save tangible things, or +which existed in the space without him, and what he sees neither being +tangible nor perceived as existing without, he could not know that in +propriety of language they were applicable to it. +</P> + +<A NAME="sect097"></A> +<P CLASS="noindent"> +97. Afterwards, when upon turning his head or eyes up and down to the +right and left he shall observe the visible objects to change, and shall +also attain to know that they are called by the same names, and connected +with the objects perceived by touch; then indeed he will come to speak of +them and their situation, in the same terms that he has been used to +apply to tangible things; and those that he perceives by turning up his +eyes he will call upper, and those that by turning down his eyes he will +call lower. +</P> + +<A NAME="sect098"></A> +<P CLASS="noindent"> +98. And this seems to me the true reason why he should think those +objects uppermost that are painted on the lower part of his eye: for by +turning the eye up they shall be distinctly seen; as likewise those that +are painted on the highest part of the eye shall be distinctly seen by +turning the eye down, and are for that reason esteemed lowest; for we +have shown that to the immediate objects of sight considered in +themselves, he would not attribute the terms HIGH and LOW. It must +therefore be on account of some circumstances which are observed to +attend them: and these, it is plain, are the actions of turning the eye +up and down, which suggest a very obvious reason why the mind should +denominate the objects of sight accordingly high or low. And without this +motion of the eye, this turning it up and down in order to discern +different objects, doubtless ERECT, INVERSE, and other the like terms +relating to the position of tangible objects, would never have been +transferred, or in any degree apprehended to belong to the ideas of +sight: the mere act of seeing including nothing in it to that purpose; +whereas the different situations of the eye naturally direct the mind to +make a suitable judgment of the situation of objects intromitted by it. +</P> + +<A NAME="sect099"></A> +<P CLASS="noindent"> +99. Farther, when he has by experience learned the connexion there is +between the several ideas of sight and touch, he will be able, by the +perception he has of the situation of visible things in respect of one +another, to make a sudden and true estimate of the situation of outward, +tangible things corresponding to them. And thus it is he shall perceive +by sight the situation of external objects which do not properly fall +under that sense. +</P> + +<A NAME="sect100"></A> +<P CLASS="noindent"> +100. I know we are very prone to think that, if just made to see, we +should judge of the situation of visible things as we do now: but we are +also as prone to think that, at first sight, we should in the same way +apprehend the distance and magnitude of objects as we do now: which hath +been shown to be a false and groundless persuasion. And for the like +reasons the same censure may be passed on the positive assurance that +most men, before they have thought sufficiently of the matter, might have +of their being able to determine by the eye at first view, whether +objects were erect or inverse. +</P> + +<A NAME="sect101"></A> +<P CLASS="noindent"> +101. It will, perhaps, be objected co our opinion that a man, for +instance, being thought erect when his feet are next the earth, and +inverted when his head is next the earth, it doth hence follow that by +the mere act of vision, without any experience or altering the situation +of the eye, we should have determined whether he were erect or inverted: +for both the earth itself, and the limbs of the man who stands thereon, +being equally perceived by sight, one cannot choose seeing what part of +the man is nearest the earth, and what part farthest from it, i.e. +whether he be erect or inverted. +</P> + +<A NAME="sect102"></A> +<P CLASS="noindent"> +102. To which I answer, the ideas which constitute the tangible earth and +man are entirely different from those which constitute the visible earth +and man. Nor was it possible, by virtue of the visive faculty alone, +without superadding any experience of touch, or altering the position of +the eye, ever to have known, or so much as suspected, there had been any +relation or connexion between them. Hence a man at first view would not +denominate anything he saw earth, or head, or foot; and consequently he +could not tell by the mere act of vision whether the head or feet were +nearest the earth: nor, indeed, would we have thereby any thought of +earth or man, erect or inverse, at all: which will be made yet more +evident if we nicely observe, and make a particular comparison between, +the ideas of both senses. +</P> + +<A NAME="sect103"></A> +<P CLASS="noindent"> +103. That which I see is only variety of light and colours. That which I +feel is hard or soft, hot or cold, rough or smooth. What similitude, what +connexion have those ideas with these? Or how is it possible that anyone +should see reason to give one and the same name to combinations of ideas +so very different before he had experienced their coexistence? We do not +find there is any necessary connexion betwixt this or that tangible +quality and any colour whatsoever. And we may sometimes perceive colours +where there is nothing to be felt. All which doth make it manifest that +no man, at first receiving of his sight, would know there was any +agreement between this or that particular object of his sight and any +object of touch he had been already acquainted with: the colours, +therefore, of the head would to him no more suggest the idea of head than +they would the idea of foot. +</P> + +<A NAME="sect104"></A> +<P CLASS="noindent"> +104. Farther, we have at large shown (VID. sect. 63 and 64) there is no +discoverable necessary connexion between any given visible magnitude and +any one particular tangible magnitude; but that it is entirely the result +of custom and experience, and depends on foreign and accidental +circumstances that we can by the perception of visible extension inform +ourselves what may be the extension of any tangible object connected with +it. Hence it is certain that neither the visible magnitude of head or +foot would bring along with them into the mind, at first opening of the +eyes, the respective tangible magnitudes of those parts. +</P> + +<A NAME="sect105"></A> +<P CLASS="noindent"> +105. By the foregoing section it is plain the visible figure of any part +of the body hath no necessary connexion with the tangible figure thereof, +so as at first sight to suggest it to the mind. For figure is the +termination of magnitude; whence it follows that no visible magnitude +having in its own nature an aptness to suggest any one particular +tangible magnitude, so neither can any visible figure be inseparably +connected with its corresponding tangible figure: so as of itself and in +a way prior to experience, it might suggest it to the understanding. This +will be farther evident if we consider that what seems smooth and round +to the touch may to sight, if viewed through a microscope, seem quite +otherwise. +</P> + +<A NAME="sect106"></A> +<P CLASS="noindent"> +106. From all which laid together and duly considered, we may clearly +deduce this inference. In the first act of vision no idea entering by the +eye would have a perceivable connexion with the ideas to which the names +EARTH, MAN, HEAD, FOOT, etc., were annexed in the understanding of a +person blind from his birth; so as in any sort to introduce them into his +mind, or make themselves be called by the same names, and reputed the +same things with them, as afterwards they come to be. +</P> + +<A NAME="sect107"></A> +<P CLASS="noindent"> +107. There doth, nevertheless, remain one difficulty, which perhaps may +seem to press hard on our opinion, and deserve not to be passed over: for +though it be granted that neither the colour, size, nor figure of the +visible feet have any necessary connexion with the ideas that compose the +tangible feet, so as to bring them at first sight into my mind, or make +me in danger of confounding them before I had been used to, and for some +time experienced their connexion: yet thus much seems undeniable, namely, +that the number of the visible feet being the same with that of the +tangible feet, I may from hence without any experience of sight +reasonably conclude that they represent or are connected with the feet +rather than the head. I say, it seems the idea of two visible feet will +sooner suggest to the mind the idea of two tangible feet than of one +head; so that the blind man upon first reception of the visive faculty +might know which were the feet or two, and which the head or one. +</P> + +<A NAME="sect108"></A> +<P CLASS="noindent"> +108. In order to get clear of this seeming difficulty we need only +observe that diversity of visible objects doth not necessarily infer +diversity of tangible objects corresponding to them. A picture painted +with great variety of colours affects the touch in one uniform manner; it +is therefore evident that I do not by any necessary consecution, +independent of experience, judge of the number of things tangible from +the number of things visible. I should not, therefore, at first opening +my eyes conclude that because I see two I shall feel two. How, therefore, +can I, before experience teaches me, know that the visible legs, because +two, are connected with the tangible legs, or the visible head, because +one, is connected with the tangible head? The truth is, the things I see +are so very different and heterogeneous from the things I feel that the +perception of the one would never have suggested the other to my +thoughts, or enabled me to pass the least judgment thereon, until I had +experienced their connexion. +</P> + +<A NAME="sect109"></A> +<P CLASS="noindent"> +109. But for a fuller illustration of this matter it ought to be +considered that number (however some may reckon it amongst the primary +qualities) is nothing fixed and settled, really existing in things +themselves. It is entirely the creature of the mind, considering either +an idea by itself, or any combination of ideas to which it gives one +name, and so makes it pass for an unit. According as the mind variously +combines its ideas the unit varies: and as the unit, so the number, which +is only a collection of units, doth also vary. We call a window one, a +chimney one, and yet a house in which there are many windows and many +chimneys hath an equal right to be called one, and many houses go to the +making of the city. In these and the like, instances it is evident the +unit constantly relates to the particular draughts the mind makes of its +ideas, to which it affixes names, and wherein it includes more or less as +best suits its own ends and purposes. Whatever, therefore, the mind +considers as one, that is an unit. Every combination of ideas is +considered as one thing by the mind, and in token thereof is marked by +one name. Now, this naming and combining together of ideas is perfectly +arbitrary, and done by the mind in such sort as experience shows it to be +most convenient: without which our ideas had never been collected into +such sundry distinct combinations as they now are. +</P> + +<A NAME="sect110"></A> +<P CLASS="noindent"> +110. Hence it follows that a man born blind and afterwards, when grown +up, made to see, would not in the first act of vision parcel out the +ideas of sight into the same distinct collections that others do, who +have experienced which do regularly coexist and are proper to be bundled +up together under one name. He would not, for example, make into one +complex idea, and thereby esteem an unit, all those particular ideas +which constitute the visible head or foot. For there can be no reason +assigned why he should do so, barely upon his seeing a man stand upright +before him. There crowd into his mind the ideas which compose the visible +man, in company with all the other ideas of sight perceived at the same +time: but all these ideas offered at once to his view, he would not +distribute into sundry distinct combinations till such time as by +observing the motion of the parts of the man and other experiences he +comes to know which are to be separated and which to be collected +together. +</P> + +<A NAME="sect111"></A> +<P CLASS="noindent"> +111. From what hath been premised it is plain the objects of sight and +touch make, if I may so say, two sets of ideas which are widely different +from each other. To objects of either kind we indifferently attribute the +terms high and low, right and left, and suchlike, denoting the position +or situation of things: but then we must well observe that the position +of any object is determined with respect only to objects of the same +sense. We say any object of touch is high or low, according as it is more +or less distant from the tangible earth: and in like manner we denominate +any object of sight high or low in proportion as it is more or less +distant from the visible earth: but to define the situation of visible +things with relation to the distance they bear from any tangible thing, +or VICE VERSA, this were absurd and perfectly unintelligible. For all +visible things are equally in the mind, and take up no part of the +external space: and consequently are equidistant from any tangible thing +which exists without the mind. +</P> + +<A NAME="sect112"></A> +<P CLASS="noindent"> +112. Or rather, to speak truly, the proper objects of sight are at no +distance, neither near nor far, from any tangible thing. For if we +inquire narrowly into the matter we shall find that those things only are +compared together in respect of distance which exist after the same +manner, or appertain unto the same sense. For by the distance between any +two points nothing more is meant than the number of intermediate points: +if the given points are visible the distance between them is marked out +by the number of the interjacent visible points: if they are tangible, +the distance between them is a line consisting of tangible points; but if +they are one tangible and the other visible, the distance between them +doth neither consist of points perceivable by sight nor by touch, i.e. it +is utterly inconceivable. This, perhaps, will not find an easy admission +into all men's understanding: however, I should gladly be informed +whether it be not true by anyone who will be at the pains to reflect a +little and apply it home to his thoughts. +</P> + +<A NAME="sect113"></A> +<P CLASS="noindent"> +113. The not observing what has been delivered in the two last sections +seems to have occasioned no small part of the difficulty that occurs in +the business of erect appearances. The head, which is painted nearest the +earth, seems to be farthest from it: and on the other hand the feet, +which are painted farthest from the earth, are thought nearest to it. +Herein lies the difficulty, which vanishes if we express the thing more +clearly and free from ambiguity, thus: how comes it that to the eye the +visible head which is nearest the tangible earth seems farthest from the +earth, and the visible feet, which are farthest from the tangible earth +seem nearest the earth? The question being thus proposed, who sees not +the difficulty is founded on a supposition that the eye, or visive +faculty, or rather the soul by means thereof, should judge of the +situation of visible objects with reference to their distance from the +tangible earth? Whereas it is evident the tangible earth is not perceived +by sight: and it hath been shown in the two last preceding sections that +the location of visible objects is determined only by the distance they +bear from one another; and that it is nonsense to talk of distance, far +or near, between a visible and tangible thing. +</P> + +<A NAME="sect114"></A> +<P CLASS="noindent"> +114. If we confine our thoughts to the proper objects of sight, the whole +is plain and easy. The head is painted farthest from, and the feet +nearest to, the visible earth; and so they appear to be. What is there +strange or unaccountable in this? Let us suppose the pictures in the fund +of the eye to be the immediate objects of the sight. The consequence is +that things should appear in the same posture they are painted in; and is +it not so? The head which is seen seems farthest from the earth which is +seen; and the feet which are seen seem nearest to the earth, which is +seen; and just so they are painted. +</P> + +<A NAME="sect115"></A> +<P CLASS="noindent"> +115. But, say you, the picture of the man is inverted, and yet the +appearance is erect: I ask, what mean you by the picture of the man, or, +which is the same thing, the visible man's being inverted? You tell me it +is inverted, because the heels are uppermost and the head undermost? +Explain me this. You say that by the head's being undermost you mean that +it is nearest to the earth; and by the heels being uppermost that they +are farthest from the earth. I ask again what earth you mean? You cannot +mean the earth that is painted on the eye, or the visible earth: for the +picture of the head is farthest from the picture of the earth, and the +picture of the feet nearest to the picture of the earth; and accordingly +the visible head is farthest from the visible earth, and the visible feet +nearest to it. It remains, therefore, that you mean the tangible earth, +and so determine the situation of visible things with respect to tangible +things; contrary to what hath been demonstrated in sect. 111 and 112. The +two distinct provinces of sight and touch should be considered apart, and +as if their objects had no intercourse, no manner of relation one to +another, in point of distance or position. +</P> + +<A NAME="sect116"></A> +<P CLASS="noindent"> +116. Farther, what greatly contributes to make us mistake in this matter +is that when we think of the pictures in the fund of the eye, we imagine +ourselves looking on the fund of another's eye, or another looking on the +fund of our own eye, and beholding the pictures painted thereon. Suppose +two eyes A and B: A from some distance looking on the pictures in B sees +them inverted, and for that reason concludes they are inverted in B: but +this is wrong. There are projected in little on the bottom of A the +images of the pictures of, suppose, man, earth, etc., which are painted +on B. And besides these the eye B itself, and the objects which environ +it, together with another earth, are projected in a larger size on A. +Now, by the eye A these larger images are deemed the true objects, and +the lesser only pictures in miniature. And it is with respect to those +greater images that it determines the situation of the smaller images: so +that comparing the little man with the great earth, A judges him +inverted, or that the feet are farthest from and the head nearest to the +great earth. Whereas, if A compare the little man with the little earth, +then he will appear erect, i.e. his head shall seem farthest from, and +his feet nearest to, the little earth. But we must consider that B does +not see two earths as A does: it sees only what is represented by the +little pictures in A, and consequently shall judge the man erect. For, in +truth, the man in B is not inverted, for there the feet are next the +earth; but it is the representation of it in A which is inverted, for +there the head of the representation of the picture of the man in B is +next the earth, and the feet farthest from the earth, meaning the earth +which is without the representation of the pictures in B. For if you take +the little images of the pictures in B, and consider them by themselves, +and with respect only to one another, they are all erect and in their +natural posture. +</P> + +<A NAME="sect117"></A> +<P CLASS="noindent"> +117. Farther, there lies a mistake in our imagining that the pictures of +external objects are painted on the bottom of the eye. It hath been shown +there is no resemblance BETWEEN the ideas of sight and things tangible. +It hath likewise been demonstrated that the proper objects of sight do +not exist without the mind. Whence it clearly follows that the pictures +painted on the bottom of the eye are not the pictures of external +objects. Let anyone consult his own thoughts, and then say what affinity, +what likeness there is between that certain variety and disposition of +colours which constitute the visible man, or picture of a man, and that +other combination of far different ideas, sensible by touch, which +compose the tangible man. But if this be the case, how come they to be +accounted pictures or images, since that supposes them to copy or +represent some originals or other? +</P> + +<A NAME="sect118"></A> +<P CLASS="noindent"> +118. To which I answer: in the forementioned instance the eye A takes the +little images, included within the representation of the other eye B, to +be pictures or copies, whereof the archetypes are not things existing +without, but the larger pictures projected on its own fund: and which by +A are not thought pictures, but the originals, or true things themselves. +Though if we suppose a third eye C from a due distance to behold the fund +of A, then indeed the things projected thereon shall, to C, seem pictures +or images in the same sense that those projected on B do to A. +</P> + +<A NAME="sect119"></A> +<P CLASS="noindent"> +119. Rightly to conceive this point we must carefully distinguish between +the ideas of sight and touch, between the visible and tangible eye; for +certainly on the tangible eye nothing either is or seems to be painted. +Again, the visible eye, as well as all other visible objects, hath been +shown to exist only in the mind, which perceiving its own ideas, and +comparing them together, calls some PICTURES in respect of others. What +hath been said, being rightly comprehended and laid together, doth, I +think, afford a full and genuine explication of the erect appearance of +objects; which phenomenon, I must confess, I do not see how it can be +explained by any theories of vision hitherto made public. +</P> + +<A NAME="sect120"></A> +<P CLASS="noindent"> +120. In treating of these things the use of language is apt to occasion +some obscurity and confusion, and create in us wrong ideas; for language +being accommodated to the common notions and prejudices of men, it is +scarce possible to deliver the naked and precise truth without great +circumlocution, impropriety, and (to an unwary reader) seeming +contradictions; I do therefore once for all desire whoever shall think it +worth his while to understand what I have written concerning vision, that +he would not stick in this or that phrase, or manner of expression, but +candidly collect my meaning from the whole sum and tenor of my discourse, +and laying aside the words as much as possible, consider the bare notions +themselves, and then judge whether they are agreeable to truth and his +own experience, or no. +</P> + +<A NAME="sect121"></A> +<P CLASS="noindent"> +121. We have shown the way wherein the mind by mediation of visible ideas +doth perceive or apprehend the distance, magnitude and situation of +tangible objects. We come now to inquire more particularly concerning the +difference between the ideas of sight and touch, which are called by the +same names, and see whether there be any idea common to both senses. From +what we have at large set forth and demonstrated in the foregoing parts +of this treatise, it is plain there is no one selfsame numerical +extension perceived both by sight and touch; but that the particular +figures and extensions perceived by sight, however they may be called by +the same names and reputed the same things with those perceived by touch, +are nevertheless different, and have an existence distinct and separate +from them: so that the question is not now concerning the same numerical +ideas, but whether there be any one and the same sort of species of ideas +equally perceivable to both senses; or, in other words, whether +extension, figure, and motion perceived by sight are not specifically +distinct from extension, figure, and motion perceived by touch. +</P> + +<A NAME="sect122"></A> +<P CLASS="noindent"> +122. But before I come more particularly to discuss this matter, I find +it proper to consider extension in abstract: for of this there is much +talk, and I am apt to think that when men speak of extension as being an +idea common to two senses, it is with a secret supposition that we can +single out extension from all other tangible and visible qualities, and +form thereof an abstract idea, which idea they will have common both to +sight and touch. We are therefore to understand by extension in abstract +an idea of extension, for instance, a line or surface entirely stripped +of all other sensible qualities and circumstances that might determine it +to any particular existence; it is neither black nor white, nor red, nor +hath it any colour at all, or any tangible quality whatsoever and +consequently it is of no finite determinate magnitude: for that which +bounds or distinguishes one extension from another is some quality or +circumstance wherein they disagree. +</P> + +<A NAME="sect123"></A> +<P CLASS="noindent"> +123. Now I do not find that I can perceive, imagine, or any wise frame in +my mind such an abstract idea as is here spoken of. A line or surface +which is neither black, nor white, nor blue, nor yellow, etc., nor long, +nor short, nor rough, nor smooth, nor square, nor round, etc., is +perfectly incomprehensible. This I am sure of as to myself: how far the +faculties of other men may reach they best can tell. +</P> + +<A NAME="sect124"></A> +<P CLASS="noindent"> +124. It is commonly said that the object of geometry is abstract +extension: but geometry contemplates figures: now, figure is the +termination of magnitude: but we have shown that extension in abstract +hath no finite determinate magnitude. Whence it clearly follows that it +can have no figure, and consequently is not the object of geometry. It is +indeed a tenet as well of the modern as of the ancient philosophers that +all general truths are concerning universal abstract ideas; without +which, we are told, there could be no science, no demonstration of any +general proposition in geometry. But it were no hard matter, did I think +it necessary to my present purpose, to show that propositions and +demonstrations in geometry might be universal, though they who make them +never think of abstract general ideas of triangles or circles. +</P> + +<A NAME="sect125"></A> +<P CLASS="noindent"> +125. After reiterated endeavours to apprehend the general idea a +triangle, I have found it altogether incomprehensible. And surely if +anyone were able to introduce that idea into my mind, it must be the +author of the ESSAY CONCERNING HUMAN UNDERSTANDING; he who has so far +distinguished himself from the generality of writers by the clearness +and significancy of what he says. Let us therefore see how this +celebrated author describes the general or abstract idea of a triangle. +'It must be (says he) neither oblique nor rectangular, neither +equilateral, equicrural, nor scalenum; but all and none of these at once. +In effect, it is somewhat imperfect that cannot exist; an idea, wherein +some parts of several different and inconsistent ideas are put together' +ESSAY ON HUM. UNDERSTAND. B. iv. C. 7. S.9. This is the idea which he +thinks needful for the enlargement of knowledge, which is the subject of +mathematical demonstration, and without which we could never come to know +any general proposition concerning triangles. That author acknowledges it +doth 'require some pains and skill to form this general idea of a +triangle.' IBID. But had he called to mind what he says in another place, +to wit, 'That ideas of mixed modes wherein any inconsistent ideas are put +together cannot so much as exist in the mind, i.e. be conceived.' VID. B. +iii. C. 10. S. 33. IBID. I say, had this occurred to his thoughts, it is +not improbable he would have owned it above all the pains and skill he +was master of to form the above-mentioned idea of a triangle, which is +made up of manifest, staring contradictions. That a man who laid so great +a stress on clear and determinate ideas should nevertheless talk at this +rate seems very surprising. But the wonder will lessen if it be +considered that the source whence this opinion flows is the prolific womb +which has brought forth innumerable errors and difficulties in all parts +of philosophy and in all the sciences: but this matter, taken in its full +extent, were a subject too comprehensive to be insisted on in this place. +And so much for extension in abstract. +</P> + +<A NAME="sect126"></A> +<P CLASS="noindent"> +126. Some, perhaps, may think pure space, VACUUM, or trine dimension to +be equally the object of sight and touch: but though we have a very great +propension to think the ideas of outness and space to be the immediate +object of sight, yet, if I mistake not, in the foregoing parts of this +essay that hath been clearly demonstrated to be a mere delusion, arising +from the quick and sudden suggestion of fancy, which so closely connects +the idea of distance with those of sight, that we are apt to think it is +itself a proper and immediate object of that sense till reason corrects +the mistake. +</P> + +<A NAME="sect127"></A> +<P CLASS="noindent"> +127. It having been shown that there are no abstract ideas of figure, and +that it is impossible for us by any precision of thought to frame an idea +of extension separate from all other visible and tangible qualities which +shall be common both to sight and touch: the question now remaining is, +whether the particular extensions, figures, and motions perceived by +sight be of the same kind with the particular extensions, figures, and +motions perceived by touch? In answer to which I shall venture to lay +down the following proposition: THE EXTENSION, FIGURES, AND MOTIONS +PERCEIVED BY SIGHT ARE SPECIFICALLY DISTINCT FROM THE IDEAS OF TOUCH +CALLED BY THE SAME NAMES, NOR is THERE ANY SUCH THING as ONE IDEA OR KIND +OF IDEA COMMON TO BOTH SENSES. This proposition may without much +difficulty be collected from what hath been said in several places of +this essay. But because it seems so remote from, and contrary to, the +received notions and settled opinion of mankind, I shall attempt to +demonstrate it more particularly and at large by the following arguments. +</P> + +<A NAME="sect128"></A> +<P CLASS="noindent"> +128. When upon perception of an idea I range it under this or that sort, +it is because it is perceived after the same manner, or because it has a +likeness or conformity with, or affects me in the same way as, the ideas +of the sort I rank it under. In short, it must not be entirely new, but +have something in it old and already perceived by me. It must, I say, +have so much at least in common with the ideas I have before known and +named as to make me give it the same name with them. But it has been, if +I mistake not, clearly made out that a man born blind would not at first +reception of his sight think the things he saw were of the same nature +with the objects of touch, or had anything in common with them; but that +they were a new set of ideas, perceived in a new manner, and entirely +different from all he had ever perceived before: so that he would not +call them by the same name, nor repute them to be of the same sort with +anything he had hitherto known. +</P> + +<A NAME="sect129"></A> +<P CLASS="noindent"> +129. SECONDLY, light and colours are allowed by all to constitute a son +or species entirely different from the ideas of touch: nor will any man, +I presume, say they can make themselves perceived by that sense: but +there is no other immediate object of sight besides light and colours. It +is therefore a direct consequence that there is no idea common to both +senses. +</P> + +<A NAME="sect130"></A> +<P CLASS="noindent"> +130. It is a prevailing opinion, even amongst those who have thought and +writ most accurately concerning our ideas and the ways whereby they enter +into the understanding, that something more is perceived by sight than +barely light and colours with their variations. Mr. Locke termeth sight, +'The most comprehensive of all our senses, conveying to our minds the +ideas of light and colours, which are peculiar only to that sense; and +also the far different ideas of space, figure, and motion. ESSAY ON HUMAN +UNDERSTAND. B. ii. C. 9. S. 9. Space or distance, we have shown, is not +otherwise the object of sight than of hearing. VID. sect. 46. And as for +figure and extension, I leave it to anyone that shall calmly attend to +his own clear and distinct ideas to decide whether he had any idea +intromitted immediately and properly by sight save only light and +colours: or whether it De possible for him to frame in his mind a +distinct abstract idea of visible extension or figure exclusive of all +colour: and on the other hand, whether he can conceive colour without +visible extension? For my own part, I must confess I am not able to +attain so great a nicety of abstraction: in a strict sense, I see nothing +but light and colours, with their several shades and variations. He who +beside these doth also perceive by sight ideas far different and distinct +from them hath that faculty in a degree more perfect and comprehensive +than I can pretend to. It must be owned that by the mediation of light +and colours other far different ideas are suggested to my mind: but so +they are by hearing, which beside sounds which are peculiar to that +sense, doth by their mediation suggest not only space, figure, and +motion, but also all other ideas whatsoever that can be signified by +words. +</P> + +<A NAME="sect131"></A> +<P CLASS="noindent"> +131. THIRDLY, it is, I think, an axiom universally received that +quantities of the same kind may be added together and make one entire +sum. Mathematicians add lines together: but they do not add a line to a +solid, or conceive it as making one sum with a surface: these three kinds +of quantity being thought incapable of any such mutual addition, and +consequently of being compared together in the several ways of +proportion, are by then esteemed entirely disparate and heterogeneous. +Now let anyone try in his thoughts to add a visible line or surface to a +tangible line or surface, so as to conceive them making one continued sum +or whole. He that can do this may think them homogeneous: but he that +cannot, must by the foregoing axiom think them heterogeneous. A blue and +a red line I can conceive added together into one sum and making one +continued line: but to make in my thoughts one continued line of a +visible and tangible line added together is, I find, a task far more +difficult, and even insurmountable: and I leave it to the reflexion and +experience of every particular person to determine for himself. +</P> + +<A NAME="sect132"></A> +<P CLASS="noindent"> +132. A farther confirmation of our tenet may be drawn from the solution +of Mr. Molyneux's problem, published by Mr. Locke in his ESSAY: which I +shall set down as it there lies, together with Mr. Locke's opinion of it, +'"Suppose a man born blind, and now adult, and taught by his touch to +distinguish between a cube and a sphere of the same metal, and nighly +[SIC] of the same bigness, so as to tell, when he felt one and t'other, +which is the cube and which the sphere. Suppose then the cube and sphere +placed on a table, and the blind man to be made to see: QUAERE, whether +by his sight, before he touched them, he could now distinguish and tell +which is the globe, which the cube?" To which the acute and judicious +proposer answers: "Not. For though he has obtained the experience of how +a globe, how a cube, affects his touch, yet he has not yet attained the +experience that what affects his touch so or so must affect his sight so +or so: or that a protuberant angle in the cube that pressed his hand +unequally shall appear to his eye as it doth in the cube." I agree with +this thinking gentleman, whom I am proud to call my friend, in his answer +to this his problem; and am of opinion that the blind man at first sight +would not be able with certainty to say which was the globe, which the +cube, whilst he only saw them.' (ESSAY ON HUMAN UNDERSTANDING, B. ii. C. +9. S. 8.) +</P> + +<A NAME="sect133"></A> +<P CLASS="noindent"> +133. Now, if a square surface perceived by touch be of the same sort with +a square surface perceived by sight, it is certain the blind man here +mentioned might know a square surface as soon as he saw it: it is no more +but introducing into his mind by a new inlet an idea he has been already +well acquainted with. Since, therefore, he is supposed to have known by +his touch that a cube is a body terminated by square surfaces, and that a +sphere is not terminated by square surfaces: upon the supposition that a +visible and tangible square differ only IN NUMERO it follows that he +might know, by the unerring mark of the square surfaces, which was the +cube, and which not, while he only saw them. We must therefore allow +either that visible extension and figures are specifically distinct from +tangible extension and figures, or else that the solution of this problem +given by those two thoughtful and ingenious men is wrong. +</P> + +<A NAME="sect134"></A> +<P CLASS="noindent"> +134. Much more might be laid together in proof of the proposition I have +advanced: but what has been said is, if I mistake not, sufficient to +convince anyone that shall yield a reasonable attention: and as for those +that will not be at the pains of a little thought, no multiplication of +words will ever suffice to make them understand the truth, or rightly +conceive my meaning. +</P> + +<A NAME="sect135"></A> +<P CLASS="noindent"> +135. I cannot let go the above-mentioned problem without some reflexion +on it. It hath been evident that a man blind from his birth would not, at +first sight, denominate anything he saw by the names he had been used to +appropriate to ideas of touch, VID. sect. 106. Cube, sphere, table are +words he has known applied to things perceivable by touch, but to things +perfectly intangible he never knew them applied. Those words in their +wonted application always marked out to his mind bodies or solid things +which were perceived by the resistance they gave: but there is no +solidity, no resistance or protrusion, perceived by sight. In short, the +ideas of sight are all new perceptions, to which there be no names +annexed in his mind: he cannot therefore understand what is said to him +concerning them: and to ask of the two bodies he saw placed on the table, +which was the sphere, which the cube? were to him a question downright +bantering and unintelligible; nothing he sees being able to suggest to +his thoughts the idea of body, distance, or in general of anything he had +already known. +</P> + +<A NAME="sect136"></A> +<P CLASS="noindent"> +136. It is a mistake to think the same thing affects both sight and +touch. If the same angle or square which is the object of touch be also +the object of vision, what should hinder the blind man at first sight +from knowing it? For though the manner wherein it affects the sight be +different from that wherein it affected his touch, yet, there being +beside his manner or circumstance, which is new and unknown, the angle or +figure, which is old and known, he cannot choose but discern it. +</P> + +<A NAME="sect137"></A> +<P CLASS="noindent"> +137. Visible figure and extension having been demonstrated to be of a +nature entirely different and heterogeneous from tangible figure and +extension, it remains that we inquire concerning. Now that visible motion +is not of the same sort with tangible motion seems to need no farther +proof, it being an evident corollary from what we have shown concerning +the difference there is between visible and tangible extension: but for a +more full and express proof hereof we need only observe that one who had +not yet experienced vision would not at first sight know motion. Whence +it clearly follows that motion perceivable by sight is of a sort distinct +from motion perceivable by touch. The antecedent I prove thus: by touch +he could not perceive any motion but what was up or down, to the right or +left, nearer or farther from him; besides these and their several +varieties or complications, it is impossible he should have any idea of +motion. He would not therefore think anything to be motion, or give the +name motion to any idea which he could not range under some or other of +those particular kinds thereof. But from sect. 95 it is plain that by the +mere act of vision he could not know motion upwards or downwards, to the +right or left, or in any other possible direction. From which I conclude +he would not know motion at all at first sight. As for the idea of motion +in abstract, I shall not waste paper about it, but leave it to my reader +to make the best he can of it. To me it is perfectly unintelligible. +</P> + +<A NAME="sect138"></A> +<P CLASS="noindent"> +138. The consideration of motion may furnish a new field for inquiry: but +since the manner wherein the mind apprehends by sight the motion of +tangible objects, with the various degrees thereof, may be easily +collected from what hath been said concerning the manner wherein that +sense doth suggest their various distances, magnitudes, and situations, I +shall not enlarge any farther on this subject, but proceed to consider +what may be alleged, with greatest appearance of reason, against the +proposition we have shown to be true. For where there is so much +prejudice to be encountered, a bare and naked demonstration of the truth +will scarce suffice. We must also satisfy the scruples that men may raise +in favour of their preconceived notions, show whence the mistake arises, +how it came to spread, and carefully disclose and root out those false +persuasions that an early prejudice might have implanted in the mind. +</P> + +<A NAME="sect139"></A> +<P CLASS="noindent"> +139. FIRST, therefore, it will be demanded how visible extension and +figures come to be called by the same name with tangible extension and +figures, if they are not of the same kind with them? It must be something +more than humour or accident that could occasion a custom so constant and +universal as this, which has obtained in all ages and nations of the +world, and amongst all ranks of men, the learned as well as the +illiterate. +</P> + +<A NAME="sect140"></A> +<P CLASS="noindent"> +140. To which I answer, we can no more argue a visible and tangible +square to be of the same species from their being called by the same +name, than we can that a tangible square and the monosyllable consisting +of six letters whereby it is marked are of the same species because they +are both called by the same name. It is customary to call written words +and the things they signify by the same name: for words not being +regarded in their own nature, or otherwise than as they are marks of +things, it had been superfluous, and beside the design of language, to +have given them names distinct from those of the things marked by them. +The same reason holds here also. Visible figures are the marks of +tangible figures, and from sect. 59 it is plain that in themselves they +are little regarded, or upon any other score than for their connexion +with tangible figures, which by nature they are ordained to signify. And +because this language of nature doth not vary in different ages or +nations, hence it is that in all times and places visible figures are +called by the same names as the respective tangible figures suggested by +them, and not because they are alike or of the same sort with them. +</P> + +<A NAME="sect141"></A> +<P CLASS="noindent"> +141. But, say you, surely a tangible square is liker to a visible square +than to a visible circle: it has four angles and as many sides: so also +has the visible square: but the visible circle has no such thing, being +bounded by one uniform curve without right lines or angles, which makes +it unfit to represent the tangible square but very fit to represent the +tangible circle. Whence it clearly follows that visible figures are +patterns of, or of the same species with, the respective tangible figures +represented by them: that they are like unto them, and of their own +nature fitted to represent them, as being of the same sort: and that they +are in no respect arbitrary signs, as words. +</P> + +<A NAME="sect142"></A> +<P CLASS="noindent"> +142. I answer, it must be acknowledged the visible square is fitter than +the visible circle to represent the tangible square, but then it is not +because it is liker, or more of a species with it, but because the +visible square contains in it several distinct parts, whereby to mark the +several distinct corresponding parts of a tangible square, whereas the +visible circle doth not. The square perceived by touch hath four +distinct, equal sides, so also hath it four distinct equal angles. It is +therefore necessary that the visible figure which shall be most proper to +mark it contain four distinct equal parts corresponding to the four sides +of the tangible square, as likewise four other distinct and equal parts +whereby to denote the four equal angles of the tangible square. And +accordingly we see the visible figures contain in them distinct visible +parts, answering to the distinct tangible parts of the figures signified +or suggested by them. +</P> + +<A NAME="sect143"></A> +<P CLASS="noindent"> +143. But it will not hence follow that any visible figure is like unto, +or of the same species with, its corresponding tangible figure, unless it +be also shown that not only the number but also the kind of the parts be +the same in both. To illustrate this, I observe that visible figures +represent tangible figures much after the same manner that written words +do sounds. Now, in this respect words are not arbitrary, it not being +indifferent what written word stands for any sound: but it is requisite +that each word contain in it so many distinct characters as there are +variations in the sound it stands for. Thus the single letter A is proper +to mark one simple uniform sound; and the word ADULTERY is accommodated +to represent the sound annexed to it, in the formation whereof there +being eight different collisions or modifications of the air by the +organs of speech, each of which produces a difference of sound, it was +fit the word representing it should consist of as many distinct +characters, thereby to mark each particular difference or part of the +whole sound. And yet nobody, I presume, will say the single letter a, or +the word ADULTERY, are like unto, or of the same species with, the +respective sounds by them represented. It is indeed arbitrary that, in +general, letters of any language represent sounds at all: but when that +is once agreed, it is not arbitrary what combination of letters shall +represent this or that particular sound. I leave this with the reader to +pursue, and apply it in his own thoughts. +</P> + +<A NAME="sect144"></A> +<P CLASS="noindent"> +144. It must be confessed that we are not so apt to confound other signs +with the things signified, or to think them of the same species, as we +are visible and tangible ideas. But a little consideration will show us +how this may be without our supposing them of a like nature. These signs +are constant and universal, their connexion with tangible ideas has been +learnt at our first entrance into the world; and ever since, almost every +moment of our lives, it has been occurring to our thoughts, and fastening +and striking deeper on our minds. When we observe that signs are +variable, and of human institution; when we remember there was a time +they were not connected in our minds with those things they now so +readily suggest; but that their signification was learned by the slow +steps of experience: this preserves us from confounding them. But when we +find the same signs suggest the same things all over the world; when we +know they are not of human institution, and cannot remember that we ever +learned their signification, but think that at first sight they would +have suggested to us the same things they do now: all this persuades us +they are of the same species as the things respectively represented by +them, and that it is by a natural resemblance they suggest them to our +minds. +</P> + +<A NAME="sect145"></A> +<P CLASS="noindent"> +145. Add to this that whenever we make a nice survey of any object, +successively directing the optic axis to each point thereof, there are +certain lines and figures described by the motion of the head or eye, +which being in truth perceived by feeling, do nevertheless so mix +themselves, as it were, with the ideas of sight, that we can scarce think +but they appertain to that sense. Again, the ideas of sight enter into +the mind several at once, more distinct and unmingled than is usual in +the other senses beside the touch. Sounds, for example, perceived at the +same instant, are apt to coalesce, if I may so say, into one sound: but +we can perceive at the same time great variety of visible objects, very +separate and distinct from each other. Now tangible extension being made +up of several distinct coexistent parts, we may hence gather another +reason that may dispose us to imagine a likeness or an analogy between +the immediate objects of sight and touch. But nothing, certainly, doth +more contribute to blend and confound them together than the strict and +close connexion they have with each other. We cannot open our eyes but +the ideas of distance, bodies, and tangible figures are suggested by +them. So swift and sudden and unperceived is the transition from visible +to tangible ideas that we can scarce forbear thinking them equally the +immediate object of vision. +</P> + +<A NAME="sect146"></A> +<P CLASS="noindent"> +146. The prejudice which is grounded on these, and whatever other causes +may be assigned thereof, sticks so fast that it is impossible without +obstinate striving and labour of the mind to get entirely clear of it. +But then the reluctancy we find in rejecting any opinion can be no +argument of its truth to whoever considers what has been already shown +with regard to the prejudices we entertain concerning the distance, +magnitude, and situation of objects; prejudices so familiar to our minds, +so confirmed and inveterate, as they will hardly give way to the clearest +demonstration. +</P> + +<A NAME="sect147"></A> +<P CLASS="noindent"> +147. Upon the whole, I think we may fairly conclude that the proper +objects of vision constitute an universal language of the Author of +Nature, whereby we are instructed how to regulate our actions in order to +attain those things that are necessary to the preservation and well-being +of our bodies, as also to avoid whatever may be hurtful and destructive +of them. It is by their information that we are principally guided in all +the transactions and concerns of life. And the manner wherein they +signify and mark unto us the objects which are at a distance is the same +with that of languages and signs of human appointment, which do not +suggest the things signified by any likeness or identity of nature, but +only by an habitual connexion that experience has made us to observe +between them. +</P> + +<A NAME="sect148"></A> +<P CLASS="noindent"> +148. Suppose one who had always continued blind be told by his guide that +after he has advanced so many steps he shall come to the brink of a +precipice, or be stopped by a wall; must not this to him seem very +admirable and surprizing? He cannot conceive how it is possible for +mortals to frame such predictions as these, which to him would seem as +strange and unaccountable as prophesy doth to others. Even they who are +blessed with the visive faculty may (though familiarity make it less +observed) find therein sufficient cause of admiration. The wonderful art +and contrivance wherewith it is adjusted to those ends and purposes for +which it was apparently designed, the vast extent, number, and variety of +objects that are at once with so much ease and quickness and pleasure +suggested by it: all these afford subject for much and pleasing +speculation, and may, if anything, give us some glimmering analogous +prenotion of things which are placed beyond the certain discovery and +comprehension of our present state. +</P> + +<A NAME="sect149"></A> +<P CLASS="noindent"> +149. I do not design to trouble myself with drawing corollaries from the +doctrine I have hitherto laid down. If it bears the test others may, so +far as they shall think convenient, employ their thoughts in extending it +farther, and applying it to whatever purposes it may be subservient to: +only, I cannot forbear making some inquiry concerning the object of +geometry, which the subject we have been upon doth naturally lead one to. +We have shown there is no such idea as that of extension in abstract, and +that there are two kinds of sensible extension and figures which are +entirely distinct and heterogeneous from each other. Now, it is natural +to inquire which of these is the object of geometry. +</P> + +<A NAME="sect150"></A> +<P CLASS="noindent"> +150. Some things there are which at first sight incline one to think +geometry conversant about visible extension. The constant use of the +eyes, both in the practical and speculative parts of that science, doth +very much induce us thereto. It would, without doubt, seem odd to a +mathematician to go about to convince him the diagrams he saw upon paper +were not the figures, or even the likeness of the figures, which make the +subject of the demonstration. The contrary being held an unquestionable +truth, not only by mathematicians, but also by those who apply themselves +more particularly to the study of logic; I mean, who consider the nature +of science, certainty, and demonstration: it being by them assigned as +one reason of the extraordinary clearness and evidence of geometry that +in this science the reasonings are free from those inconveniences which +attend the use of arbitrary signs, the very ideas themselves being copied +out and exposed to view upon paper. But, by the bye, how well this agrees +with what they likewise assert of abstract ideas being the object of +geometrical demonstration I leave to be considered. +</P> + +<A NAME="sect151"></A> +<P CLASS="noindent"> +151. To come to a resolution in this point we need only observe what hath +been said in sect. 59, 60, 61, where it is shown that visible extensions +in themselves are little regarded, and have no settled determinable +greatness, and that men measure altogether, by the application of +tangible extension to tangible extension. All which makes it evident that +visible extension and figures are not the object of geometry. +</P> + +<A NAME="sect152"></A> +<P CLASS="noindent"> +152. It is therefore plain that visible figure are of the same use in +geometry that words are: and the one may as well be accounted the object +of that science as the other, neither of them being otherwise concerned +therein than as they represent or suggest to the mind the particular +tangible figures connected with them. There is indeed this difference +between the signification of tangible figures by visible figures, and of +ideas by words: that whereas the latter is variable and uncertain, +depending altogether on the arbitrary appointment of men, the former is +fixed and immutably the same in all times and places. A visible square, +for instance, suggests to the mind the same tangible figure in Europe +that it doth in America. Hence it is that the voice of the Author of' +Nature which speaks to our eyes, is not liable to that misinterpretation +and ambiguity that languages of human contrivance are unavoidably subject +to. +</P> + +<A NAME="sect153"></A> +<P CLASS="noindent"> +153. Though what has been said may suffice to show what ought to be +determined with relation to the object of geometry, I shall nevertheless, +for the fuller illustration thereof, consider the case of an +intelligence, or unbodied spirit, which is supposed to see perfectly +well, i.e. to have a clear perception of the proper and immediate objects +of sight, but to have no sense of touch. Whether there be any such being +in Nature or no is beside my purpose to inquire. It sufficeth that the +supposition contains no contradiction in it. Let us now examine what +proficiency such a one may be able to make in geometry. Which speculation +will lead us more clearly to see whether the ideas of sight can possibly +be the object of that science. +</P> + +<A NAME="sect154"></A> +<P CLASS="noindent"> +154. FIRST, then, it is certain the aforesaid intelligence could have no +idea of a solid, or quantity of three dimensions, which followeth from +its not having any idea of distance. We indeed are prone to think that we +have by sight the ideas of space and solids, which ariseth from our +imagining that we do, strictly speaking, see distance and some parts of +an object at a greater distance than others; which hath been demonstrated +to be the effect of the experience we have had, what ideas of touch are +connected with such and such ideas attending vision: but the intelligence +here spoken of is supposed to have no experience of touch. He would not, +therefore, judge as we do, nor have any idea of distance, outness, or +profundity, nor consequently of space or body, either immediately or by +suggestion. Whence it is plain he can have no notion of those parts of +geometry which relate to the mensuration of solids and their convex or +concave surfaces, and contemplate the properties of lines generated by +the section of a solid. The conceiving of any part whereof is beyond the +reach of his faculties. +</P> + +<A NAME="sect155"></A> +<P CLASS="noindent"> +155. Farther, he cannot comprehend the manner wherein geometers describe +a right line or circle; the rule and compass with their use being things +of which it is impossible he should have any notion: nor is it an easier +matter for him to conceive the placing of one plane or angle on another, +in order to prove their equality: since that supposeth some idea of +distance or external space. All which makes it evident our pure +intelligence could never attain to know so much as the first elements of +plane geometry. And perhaps upon a nice inquiry it will be found he +cannot even have an idea of plane figures any more than he can of solids; +since some idea of distance is necessary to form the idea of a +geometrical plane, as will appear to whoever shall reflect a little on +it. +</P> + +<A NAME="sect156"></A> +<P CLASS="noindent"> +156. All that is properly perceived by the visive faculty amounts to no +more than colours, with their variations and different proportions of +light and shade. But the perpetual mutability and fleetingness of those +immediate objects of sight render them incapable of being managed after +the manner of geometrical figures; nor is it in any degree useful that +they should. It is true there are divers of them perceived at once, and +more of some and less of others: but accurately to compute their +magnitude and assign precise determinate proportions between things so +variable and inconstant, if we suppose it possible to be done, must yet +be a very trifling and insignificant labour. +</P> + +<A NAME="sect157"></A> +<P CLASS="noindent"> +157. I must confess men are tempted to think that flat or plane figures +are immediate objects of sight, though they acknowledge solids are not. +And this opinion is grounded on what is observed in painting, wherein (it +seems) the ideas immediately imprinted on the mind are only of planes +variously coloured, which by a sudden act of the judgment are changed +into solids. But with a little attention we shall find the planes here +mentioned as the immediate objects of sight are not visible but tangible +planes. For when we say that pictures are planes, we mean thereby that +they appear to the touch smooth and uniform. But then this smoothness and +uniformity, or, in other words, this planeness of the picture, is not +perceived immediately by vision: for it appeareth to the eye various and +multiform. +</P> + +<A NAME="sect158"></A> +<P CLASS="noindent"> +158. From all which we may conclude that planes are no more the immediate +object of sight than solids. What we strictly see are not solids, nor yet +planes variously coloured: they are only diversity of colours. And some +of these suggest to the mind solids, and other plane figures, just as +they have been experienced to be connected with the one or the other: so +that we see planes in the same way that we see solids, both being equally +suggested by the immediate objects of sight, which accordingly are +themselves denominated planes and solids. But though they are called by +the same names with the things marked by them, they are nevertheless of a +nature entirely different, as hath been demonstrated. +</P> + +<A NAME="sect159"></A> +<P CLASS="noindent"> +159. What hath been said is, if I mistake not, sufficient to decide the +question we proposed to examine, concerning the ability of a pure spirit, +such as we have described, to know GEOMETRY. It is, indeed, no easy +matter for us to enter precisely into the thoughts of such an +intelligence, because we cannot without great pains cleverly separate and +disentangle in our thoughts the proper objects of sight from those of +touch which are connected with them. This, indeed, in a complete degree +seems scarce possible to be performed: which will not seem strange to us +if we consider how hard it is for anyone to hear the words of his native +language pronounced in his ears without understanding them. Though he +endeavour to disunite the meaning from the sound, it will nevertheless +intrude into his thoughts, and he shall find it extreme difficult, if not +impossible, to put himself exactly in the posture of a foreigner that +never learned the language, so as to be affected barely with the sounds +themselves, and not perceive the signification annexed to them. +</P> + +<A NAME="sect160"></A> +<P CLASS="noindent"> +160. By this time, I suppose, it is clear that neither abstract nor +visible extension makes the object of geometry; the not discerning of +which may perhaps have created some difficulty and useless labour in +mathematics. Sure I am, that somewhat relating thereto has occurred to my +thoughts, which, though after the most anxious and repeated examination I +am forced to think it true, doth, nevertheless, seem so far out of the +common road of geometry, that I know not whether it may not be thought +presumption, if I should make it public in an age, wherein that science +hath received such mighty improvements by new methods; great part whereof, +as well as of the ancient discoveries, may perhaps lose their reputation, +and much of that ardour with which men study the abstruse and fine +geometry be abated, if what to me, and those few to whom I have imparted +it, seems evidently true, should really prove to be so. +</P> + +<BR><BR><BR><BR> + + + + + + + + +<pre> + + + + + +End of the Project Gutenberg EBook of An Essay Towards a New Theory of Vision, by +George Berkeley + +*** END OF THIS PROJECT GUTENBERG EBOOK ESSAY--NEW THEORY OF VISION *** + +***** This file should be named 4722-h.htm or 4722-h.zip ***** +This and all associated files of various formats will be found in: + https://www.gutenberg.org/4/7/2/4722/ + +Produced by Col Choat. 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You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: An Essay Towards a New Theory of Vision + +Author: George Berkeley + +Posting Date: June 29, 2009 [EBook #4722] +Release Date: December, 2003 +First Posted: March 7, 2002 + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK ESSAY--NEW THEORY OF VISION *** + + + + +Produced by Col Choat. HTML version by Al Haines. + + + + + + + + + +An Essay Towards a New Theory of Vision + + +by + +George Berkeley (1685-1753) + + + +CONTENTS + + +Sect. + + 1 Design + 2 Distance of itself invisible + 3 Remote distance perceived rather by experience than by sense + 4 Near distance thought to be perceived by the ANGLE of the + OPTIC AXES + 5 Difference between this and the former manner of perceiving + distance + 6 Also by diverging rays + 7 This depends not on experience + 8 These the common accounts, but not satisfactory + 9 Some IDEAS perceived by the mediation of others + 10 No IDEA which is not itself perceived, can be the means of + perceiving another + 11 Distance perceived by means of some other IDEA + 12 Those lines and angles mentioned in optics, are not themselves + perceived + 13 Hence the mind does not perceive distance by lines and angles + 14 Also because they have no real existence + 15 And because they are insufficient to explain the phenomena + 16 The IDEAS that suggest distance are, 1st, the sensation arising + from the turn of the eyes + 17 Betwixt which and distance there is no necessary connection + 18 Scarce room for mistake in this matter + 19 No regard had to the angle of the OPTIC AXES + 20 Judgment of distance made with both eyes, the result of EXPERIENCE + 21 2ndly, Confusedness of appearance + 22 This the occasion of those judgments attributed to diverging rays + 23 Objection answered + 24 What deceives the writers of optics in this matter + 25 The cause why one IDEA may suggest another + 26 This applied to confusion and distance + 27 Thirrdly, the straining of the eye + 28 The occasions which suggest distance have in their own nature + no relation to it + 29 A difficult case proposed by Dr. Barrow as repugnant to + all the known theories + 30 This case contradicts a received principle in catoptrics + 31 It is shown to agree with the principles we have laid down + 32 This phenomenon illustrated + 33 It confirms the truth of the principle whereby it is explained + 34 Vision when distinct, and when confused + 35 The different effects of parallel diverging and converging rays + 36 How converging and diverging rays come to suggest the same + distance + 37 A person extreme purblind would judge aright in the + forementioned case + 38 Lines and angles, why useful in optics + 39 The not understanding this, a cause of mistake + 40 A query proposed, by Mr. Molyneux in his DIOPTRICS, considered + 41 One born blind would not at first have any IDEA of distance by + sight + 42 This not agreeable to the common principles + 43 The proper objects of sight, not without the mind, nor the images + of any thing without the mind + 44 This more fully explained + 45 In what sense we must be understood to see distance + and external things + 46 Distance, and things placed at a distance, not otherwise perceived + by the eye than by the ear + 47 The IDEAS of sight more apt to be confounded with the IDEAS + of touch than those of hearing are + 48 How this comes to pass + 49 Strictly speaking, we never see and feel the same thing + 50 Objects of SIGHT twofold, mediate and immediate + 51 These hard to separate in our thoughts + 52 The received accounts of our perceiving magnitude by sight, false + 53 Magnitude perceived as immediately as distance + 54 Two kinds of sensible extension, neither of which is + infinitely divisible + 55 The tangible magnitude of an OBJECT steady, the visible not + 56 By what means tangible magnitude is perceived by sight + 57 This further enlarged on + 58 No necessary connection between confusion or faintness + of appearance, and small or great magnitude + 59 The tangible magnitude of an OBJECT more heeded than the visible, + and why + 60 An instance of this + 61 Men do not measure by visible feet or inches + 62 No necessary connection between visible and tangible extension + 63 Greater visible magnitude might signify lesser tangible magnitude + 64 The judgments we make of magnitude depend altogether on experience + 65 Distance and magnitude seen as shame or anger + 66 But we are prone to think otherwise, and why + 67 The moon seems greater in the horizon than in the meridian + 68 The cause of this phenomenon assigned + 69 The horizontal moon, why greater at one time than another. + 70 The account we have given proved to be true + 71 And confirmed by the moon's appearing greater in a mist + 72 Objection answered + 73 The way wherein faintness suggests greater magnitude illustrated + 74 Appearance of the horizontal moon, why thought difficult to + explain + 75 Attempts towards the solution of it made by several, but in vain + 76 The opinion of Dr. Wallis + 77 It is shown to be unsatisfactory + 78 How lines and angles may be of use in computing apparent + magnitudes + 79 One born blind, being made to see, what judgment he would make + of magnitude + 80 The MINIMUM VISIBLE the same to all creatures + 81 Objection answered + 82 The eye at all times perceives the same number of visible points + 83 Two imperfections in the VISIVE FACULTY + 84 Answering to which, we may conceive two perfections + 85 In neither of these two ways do microscopes improve the sight + 86 The case of microscopical eyes, considered + 87 The sight, admirably adapted to the ends of seeing + 88 Difficulty concerning erect vision + 89 The common way of explaining it + 90 The same shown to be false + 91 Not distinguishing between IDEAS of sight and touch, cause + of mistake in this matter + 92 The case of one born blind, proper to be considered + 93 Such a one might by touch attain to have IDEAS of UPPER and LOWER + 94 Which modes of situation he would attribute only to things + tangible + 95 He would not at first sight think anything he saw, high or low, + erect or inverted + 96 This illustrated by an example + 97 By what means he would come to denominate visible OBJECTS, + high or low, etc. + 98 Why he should think those OBJECTS highest, which are painted on + the lowest part of his eye, and VICE VERSA + 99 How he would perceive by sight, the situation of external objects + 100 Our propension to think the contrary, no argument against + what has been said + 101 Objection + 102 Answer + 103 An object could not be known at first sight by the colour + 104 Nor by the magnitude thereof + 105 Nor by the figure + 106 In the first act of vision, no tangible thing would be suggested + by sight + 107 Difficulty proposed concerning number + 108 Number of things visible, would not at first sight suggest + the like number of things tangible + 109 Number the creature of the mind + 110 One born blind would not at first sight number visible things + as others do + 111 The situation of any object determined with respect only to + objects of the same sense + 112 No distance, great or small, between a visible and tangible thing + 113 The not observing this, cause of difficulty in erect vision + 114 Which otherwise includes nothing unaccountable + 115 What is meant by the picture being inverted + 116 Cause of mistake in this matter + 117 Images in the eye, not pictures of external objects + 118 In what sense they are pictures + 119 In this affair we must carefully distinguish between ideas + of sight and touch + 120 Difficult to explain by words the true Theory of Vision + 121 The question, whether there is any IDEA common to sight + and touch, stated + 122 Abstract extension inquired into + 123 It is incomprehensible + 124 Abstract extension not the OBJECT of geometry + 125 The general IDEA of a triangle, considered + 126 Vacuum, or pure space, not common to sight and touch + 127 There is no idea, or kind of idea, common to both senses + 128 First argument in proof hereof + 129 Second argument + 130 Visible figure and extension, not distinct IDEAS from colour + 131 Third argument + 132 Confirmation drawn from Mr. Molyneux's problem of a sphere + and a cube, published by Mr. Locke + 133 Which is falsely solved, if the common supposition be true + 134 More might be said in proof of our tenet, but this suffices + 135 Further reflection on the foregoing problem + 136 The same thing doth not affect both sight and touch + 137 The same idea of motion not common to sight and touch + 138 The way wherein we apprehend motion by sight, easily collected + from what hath been said + 139 QU. How visible and tangible IDEAS came to have the same name + if not of the same kind + 140 This accounted for without supposing them of the same kind + 141 OBJ. That a tangible square is liker to a visible square than + to a visible circle + 142 ANS. That a visible square is fitter than a visible circle, + to represent a tangible square + 143 But it doth not hence follow, that a visible square + is like a tangible square + 144 Why we are more apt to confound visible with tangible IDEAS, + than other signs with the things signified + 145 Several other reasons hereof, assigned + 146 Reluctancy in rejecting any opinion, no argument of its truth + 147 Proper objects of vision the language of nature + 148 In it there is much admirable, and deserving our attention + 149 Question proposed, concerning the object of geometry + 150 At first view we are apt to think visible extension the object + of geometry + 151 Visible extension shown not to be the object of geometry + 152 Words may as well be thought the object of geometry, + as visible extension + 153 It is proposed to inquire, what progress an intelligence that + could see, but not feel, might make in geometry + 154 He cannot understand those parts which relate to solids, and + their surfaces, and lines generated by their section + 155 Nor even the elements of plane geometry + 156 The proper objects of sight incapable of being managed as + geometrical figures + 157 The opinion of those who hold plane figures to be the immediate + objects of sight, considered + 158 Planes no more the immediate objects of sight, than solids + 159 Difficult to enter precisely into the thoughts of the + above-mentioned intelligence + 160 The object of geometry, its not being sufficiently understood, + cause of difficulty, and useless labour in that science + + + + +AN ESSAY TOWARDS A NEW THEORY OF VISION + + +1. My design is to show the manner wherein we perceive by sight the +distance, magnitude, and situation of OBJECTS. Also to consider the +difference there is betwixt the IDEAS of sight and touch, and whether +there be any IDEA common to both senses. + +2. It is, I think, agreed by all that DISTANCE, of itself and +immediately, cannot be seen. For DISTANCE being a Line directed end-wise +to the eye, it projects only one point in the fund of the eye, which +point remains invariably the same, whether the distance be longer or +shorter. + +3. I find it also acknowledged that the estimate we make of the distance +of OBJECTS considerably remote is rather an act of judgment grounded on +EXPERIENCE than of SENSE. For example, when I perceive a great number of +intermediate OBJECTS, such as houses, fields, rivers, and the like, which +I have experienced to take up a considerable space, I thence form a +judgment or conclusion that the OBJECT I see beyond them is at a great +distance. Again, when an OBJECT appears faint and small, which at a near +distance I have experienced to make a vigorous and large appearance, I +instantly conclude it to be far off: And this, it is evident, is the +result of EXPERIENCE; without which, from the faintness and littleness I +should not have inferred anything concerning the distance of OBJECTS. + +4. But when an OBJECT is placed at so near a distance as that the +interval between the eyes bears any sensible proportion to it, the +opinion of speculative men is that the two OPTIC AXES (the fancy that we +see only with one eye at once being exploded) concurring at the OBJECT do +there make an ANGLE, by means of which, according as it is greater or +lesser, the OBJECT is perceived to be nearer or farther off. + +5. Betwixt which and the foregoing manner of estimating distance there is +this remarkable difference: that whereas there was no apparent, necessary +connection between small distance and a large and strong appearance, or +between great distance and a little and faint appearance, there appears a +very necessary connection between an obtuse angle and near distance, and +an acute angle and farther distance. It does not in the least depend upon +experience, but may be evidently known by anyone before he had +experienced it, that the nearer the concurrence of the OPTIC AXES, the +greater the ANGLE, and the remoter their concurrence is, the lesser will +be the ANGLE comprehended by them. + +6. There is another way mentioned by optic writers, whereby they will +have us judge of those distances, in respect of which the breadth of the +PUPIL hath any sensible bigness: And that is the greater or lesser +divergency of the rays, which issuing from the visible point do fall on +the PUPIL, that point being judged nearest which is seen by most +diverging rays, and that remoter which is seen by less diverging rays: +and so on, the apparent distance still increasing, as the divergency of +the rays decreases, till at length it becomes infinite, when the rays +that fall on the PUPIL are to sense parallel. And after this manner it is +said we perceive distance when we look only with one eye. + +7. In this case also it is plain we are not beholding to experience: it +being a certain, necessary truth that the nearer the direct rays falling +on the eye approach to a PARALLELISM, the farther off is the point of +their intersection, or the visible point from whence they flow. + +8. I have here set down the common, current accounts that are given of +our perceiving near distances by sight, which, though they are +unquestionably received for true by MATHEMATICIANS, and accordingly made +use of by them in determining the apparent places of OBJECTS, do, +nevertheless seem to me very unsatisfactory: and that for these following +reasons:-- + +9. FIRST, It is evident that when the mind perceives any IDEA, not +immediately and of itself, it must be by the means of some other IDEA. +Thus, for instance, the passions which are in the mind of another are of +themselves to me invisible. I may nevertheless perceive them by sight, +though not immediately, yet by means of the colours they produce in the +countenance. We often see shame or fear in the looks of a man, by +perceiving the changes of his countenance to red or pale. + +10. Moreover it is evident that no IDEA which is not itself perceived can +be the means of perceiving any other IDEA. If I do not perceive the +redness or paleness of a man's face themselves, it is impossible I should +perceive by them the passions which are in his mind. + +11. Now from sect. 2 it is plain that distance is in its own nature +imperceptible, and yet it is perceived by sight. It remains, therefore, +that it be brought into view by means of some other IDEA that is itself +immediately perceived in the act of VISION. + +12. But those LINES and ANGLES, by means whereof some MATHEMATICIANS +pretend to explain the perception of distance, are themselves not at all +perceived, nor are they in truth ever thought of by those unskilful in +optics. I appeal to anyone's experience whether upon sight of an OBJECT he +computes its distance by the bigness of the ANGLE made by the meeting of +the two OPTIC AXES? Or whether he ever thinks of the greater or lesser +divergency of the rays, which arrive from any point to his PUPIL? Everyone +is himself the best judge of what he perceives, and what not. In vain +shall all the MATHEMATICIANS in the world tell me, that I perceive certain +LINES and ANGLES which introduce into my mind the various IDEAS of +DISTANCE, so long as I myself am conscious of no such thing. + +13. Since, therefore, those ANGLES and LINES are not themselves perceived +by sight, it follows from sect. 10 that the mind doth not by them judge +of the distance of OBJECTS. + +14. Secondly, the truth of this assertion will be yet farther evident to +anyone that considers those LINES and ANGLES have no real existence in +nature, being only an HYPOTHESIS framed by the MATHEMATICIANS, and by them +introduced into OPTICS, that they might treat of that science in a +GEOMETRICAL way. + +15. The third and last reason I shall give for rejecting that doctrine is, +that though we should grant the real existence of those OPTIC ANGLES, +etc., and that it was possible for the mind to perceive them, yet these +principles would not be found sufficient to explain the PHENOMENA of +DISTANCE, as shall be shown hereafter. + +16. Now, it being already shown that distance is suggested to the mind by +the mediation of some other IDEA which is itself perceived in the act of +seeing, it remains that we inquire what IDEAS or SENSATIONS there be that +attend VISION, unto which we may suppose the IDEAS of distance are +connected, and by which they are introduced into the mind. And FIRST, it +is certain by experience that when we look at a near OBJECT with both +eyes, according as it approaches or recedes from us, we alter the +disposition of our eyes, by lessening or widening the interval between +the PUPILS. This disposition or turn of the eyes is attended with a +sensation, which seems to me to be that which in this case brings the +IDEA of greater or lesser distance into the mind. + +17. Not that there is any natural or necessary connection between the +sensation we perceive by the turn of the eyes and greater or lesser +distance, but because the mind has by constant EXPERIENCE found the +different sensations corresponding to the different dispositions of the +eyes to be attended each with a different degree of distance in the +OBJECT: there has grown an habitual or customary connection between those +two sorts of IDEAS, so that the mind no sooner perceives the sensation +arising from the different turn it gives the eyes, In order to bring the +PUPILS nearer or farther asunder, but it withal perceives the different +IDEA of distance which was wont to be connected with that sensation; just +as upon hearing a certain sound, the IDEA is immediately suggested to the +understanding which custom had united with it. + +18 Nor do I see how I can easily be mistaken in this matter. I know +evidently that distance is not perceived of itself. That by consequence +it must be perceived by means of some other IDEA which is immediately +perceived, and varies with the different degrees of distance. I know also +that the sensation arising from the turn of the eyes is of itself +immediately perceived, and various degrees thereof are connected with +different distances, which never fail to accompany them into my mind, +when I view an OBJECT distinctly with both eyes, whose distance is so +small that in respect of it the interval between the eyes has any +considerable magnitude. + +19. I know it is a received opinion that by altering the disposition of +the eyes the mind perceives whether the angle of the OPTIC AXES is made +greater or lesser. And that accordingly by a kind of NATURAL +GEOMETRY it judges the point of their intersection to be nearer +or farther off. But that this is not true I am convinced by my own +experience, since I am not conscious that I make any such use of the +perception I have by the turn of my eyes. And for me to make those +judgments, and draw those conclusions from it, without knowing that I do +so, seems altogether incomprehensible. + +20. From all which it follows that the judgment we make of the distance +of an OBJECT, viewed with both eyes, is entirely the RESULT OF +EXPERIENCE. If we had not constantly found certain sensations arising +from the various disposition of the eyes, attended with certain degrees +of distance, we should never make those sudden judgments from them +concerning the distance of OBJECTS; no more than we would pretend to +judge a man's thoughts by his pronouncing words we had never heard +before. + +21. Secondly, an OBJECT placed at a certain distance from the eye, to +which the breadth of the PUPIL bears a considerable proportion, being +made to approach, is seen more confusedly: and the nearer it is brought +the more confused appearance it makes. And this being found constantly to +be so, there ariseth in the mind an habitual CONNECTION between the +several degrees of confusion and distance; the greater confusion still +implying the lesser distance, and the lesser confusion the greater +distance of the OBJECT. + +22. This confused appearance of the OBJECT doth therefore seem to be the +MEDIUM whereby the mind judgeth of distance in those cases wherein the +most approved writers of optics will have it judge by the different +divergency with which the rays flowing from the radiating point fall on +the PUPIL. No man, I believe, will pretend to see or feel those imaginary +angles that the rays are supposed to form according to their various +inclinations on his eye. But he cannot choose seeing whether the OBJECT +appear more or less confused. It is therefore a manifest consequence from +what bath been demonstrated, that instead of the greater or lesser +divergency of the rays, the mind makes use of the greater or lesser +confusedness of the appearance, thereby to determine the apparent place +of an OBJECT. + +23 Nor doth it avail to say there is not any necessary connection between +confused VISION and distance, great or small. For I ask any man what +necessary connection he sees between the redness of a blush and shame? And +yet no sooner shall he behold that colour to arise in the face of +another, but it brings into his and the IDEA of that passion which hath +been observed to accompany it. + +24. What seems to have misled the writers of optics in this matter is +that they imagine men judge of distance as they do of a conclusion in +mathematics, betwixt which and the premises it is indeed absolutely +requisite there be an apparent, necessary connection: but it is far +otherwise in the sudden judgments men make of distance. We are not to +think that brutes and children, or even grown reasonable men, whenever +they perceive an OBJECT to approach, or depart from them, do it by virtue +of GEOMETRY and DEMONSTRATION. + +25. That one IDEA may suggest another to the mind it will suffice that +they have been observed to go together, without any demonstration of the +necessity of their coexistence, or without so much as knowing what it is +that makes them so to coexist. Of this there are innumerable instances of +which no one can be ignorant. + +26. Thus, greater confusion having been constantly attended with nearer +distance, no sooner is the former IDEA perceived, but it suggests the +latter to our thoughts. And if it had been the ordinary course of Nature +that the farther off an OBJECT were placed, the more confused it should +appear, it is certain the very same perception that now makes us think an +OBJECT approaches would then have made us to imagine it went farther off. +That perception, abstracting from CUSTOM and EXPERIENCE, being equally +fitted to produce the IDEA of great distance, or small distance, or no +distance at all. + +27. Thirdly, an OBJECT being placed at the distance above specified, and +brought nearer to the eye, we may nevertheless prevent, at least for some +time, the appearances growing more confused, by straining the eye. In +which case that sensation supplies the place of confused VISION in aiding +the mind to judge of the distance of the OBJECT; it being esteemed so +much the nearer by how much the effort or straining of the eye in order +to distinct VISION is greater. + +28. I have here set down those sensations or IDEAS that seem to be the +constant and general occasions of introducing into the mind the different +IDEAS of near distance. It is true in most cases that divers other +circumstances contribute to frame our IDEA of distance, to wit, the +particular number, size, kind, etc., of the things seen. Concerning +which, as well as all other the forementioned occasions which suggest +distance, I shall only observe they have none of them, in their own +nature, any relation or connection with it: nor is it possible they should +ever signify the various degrees thereof, otherwise than as by EXPERIENCE +they have been found to be connected with them. + +29. I shall proceed upon these principles to account for a phenomenon +which has hitherto strangely puzzled the writers of optics, and is so far +from being accounted for by any of their THEORIES OF VISION that it is, +by their own confession, plainly repugnant to them; and of consequence, +if nothing else could be objected, were alone sufficient to bring their +credit in question. The whole difficulty I shall lay before you in the +words of the learned Dr. Barrow, with which he concludes his optic +lectures:-- + +'I have here delivered what my thoughts have suggested to me concerning +that part of optics which is more properly mathematical. As for the other +parts of that science (which being rather physical, do consequently +abound with plausible conjectures instead of certain principles), there +has in them scarce anything occurred to my observation different from what +has been already said by Kepler, Scheinerus, Descartes, and others. And +methinks, I had better say nothing at all, than repeat that which has +been so often said by others. I think it therefore high time to take my +leave of this subject: but before I quit it for good and all, the fair +and ingenuous dealing that I owe both to you and to truth obligeth me to +acquaint you with a certain untoward difficulty, which seems directly +opposite to the doctrine I have been hitherto inculcating, at least, +admits of no solution from it. In short it is this. Before the double +convex glass or concave speculum EBF, let the point A be placed at such a +distance that the rays proceeding from A, after refraction or reflection, +be brought to unite somewhere in the AxAB. And suppose the point of union +(i.e. the image of the point A, as hath been already set forth) to be Z; +between which and B, the vertex of the glass or speculum, conceive the +eye to be anywhere placed. The question now is, where the point A ought +to appear? Experience shows that it does not appear behind at the point +Z, and it were contrary to nature that it should, since all the +impression which affects the sense comes from towards A. But from our +tenets it should seem to follow that it would appear before the eye at a +vast distance off, so great as should in some sort surpass all sensible +distance. For since if we exclude all anticipations and prejudices, every +OBJECT appears by so much the farther off, by how much the rays it sends +to the eye are less diverging. And that OBJECT is thought to be most +remote from which parallel rays proceed unto the eye. Reason would make +one think that OBJECT should appear at yet a greater distance which is +seen by converging rays. Moreover it may in general be asked concerning +this case what it is that determines the apparent place of the point A, +and maketh it to appear after a constant manner sometimes nearer, at +other times farther off? To which doubt I see nothing that can be +answered agreeable to the principles we have laid down except only that +the point A ought always to appear extremely remote. But on the contrary +we are assured by experience that the point A appears variously distant, +according to the different situations of the eye between the points B and +Z. And that it doth never (if at all) seem farther off, than it would if +it were beheld by the naked eye, but on the contrary it doth sometimes +appear much nearer. Nay, it is even certain that by how much the rays +falling on the eye do more converge by so much the nearer doth the OBJECT +seem to approach. For the eye being placed close to the point B, the +OBJECT A appears nearly in its own natural place, if the point B is taken +in the glass, or at the same distance, if in the speculum. The eye being +brought back to O, the OBJECT seems to draw near: and being come to P it +beholds it still nearer. And so on little and little, till at length the +eye being placed somewhere, suppose at Q, the OBJECT appearing extremely +near, begins to vanish into mere confusion. All which doth seem repugnant +to our principles, at least not rightly to agree with them. Nor is our +tenet alone struck at by this experiment, but likewise all others that +ever came to my knowledge are, every whit as much, endangered by it. The +ancient one especially (which is most commonly received, and comes +nearest to mine) seems to be so effectually overthrown thereby that the +most learned Tacquet has been forced to reject that principle, as false +and uncertain, on which alone he had built almost his whole CATOPTRICS; +and consequently by taking away the foundation, hath himself pulled down +the superstructure he had raised on it. Which, nevertheless, I do not +believe he would have done had he but considered the whole matter more +thoroughly, and examined the difficulty to the bottom. But as for me, +neither this nor any other difficulty shall have so great an influence on +me as to make me renounce that which I know to be manifestly agreeable to +reason: especially when, as it here falls out, the difficulty is founded +in the peculiar nature of a certain odd and particular case. For in the +present case something peculiar lies hid, which being involved in the +subtilty of nature will, perhaps, hardly be discovered till such time as +the manner of vision is more perfectly made known. Concerning which, I +must own, I have hitherto been able to find out nothing that has the +least show of PROBABILITY, not to mention CERTAINTY. I shall, therefore, +leave this knot to be untied by you, wishing you may have better success +in it than I have had.' + +30. The ancient and received principle, which Dr. Barrow here mentions as +the main foundation of Tacquet's CATOPTRICS, is that: 'every visible point +seen by reflection from a speculum shall appear placed at the intersection +of the reflected ray, and the perpendicular of incidence:' which +intersection in the present case, happening to be behind the eye, it +greatly shakes the authority of that principle, whereon the +aforementioned author proceeds throughout his whole CATOPTRICS in +determining the apparent place of OBJECTS seen by reflection from any kind +of speculum. + +31. Let us now see how this phenomenon agrees with our tenets. The eye +the nearer it is placed to the point B in the foregoing figures, the more +distinct is the appearance of the OBJECT; but as it recedes to O the +appearance grows more confused; and at P it sees the OBJECT yet more +confused; and so on till the eye being brought back to Z sees the OBJECT +in the greatest confusion of all. Wherefore by sect. 21 the OBJECT should +seem to approach the eye gradually as it recedes from the point B, that +is, at O it should (in consequence of the principle I have laid down in +the aforesaid section) seem nearer than it did at B, and at P nearer than +at O, and at Q nearer than at P; and so on, till it quite vanishes at Z. +Which is the very matter of fact, as anyone that pleases may easily +satisfy himself by experiment. + +32. This case is much the same as if we should suppose an Englishman to +meet a foreigner who used the same words with the English, but in a +direct contrary signification. The Englishman would not fail to make a +wrong judgment of the IDEAS annexed to those sounds in the mind of him +that used them. Just so, in the present case the OBJECT speaks (if I may +so say) with words that the eye is well acquainted with, that is, +confusions of appearance; but whereas heretofore the greater confusions +were always wont to signify nearer distances, they have in this case a +direct, contrary signification, being connected with the greater +distances. Whence it follows that the eye must unavoidably be mistaken, +since it will take the confusions in the sense it has been used to, which +is directly opposed to the true. + +33. This phenomenon as it entirely subverts the opinion of those who will +have us judge of distance by lines and angles, on which supposition it is +altogether inexplicable, so it seems to me no small confirmation of the +truth of that principle whereby it is explained. But in order co a more +full explication of this point, and to show how far the hypothesis of the +mind's judging by the various divergency of rays may be of use in +determining the apparent place of an OBJECT, it will be necessary to +premise some few things, which are already well known to those who have +any skill in dioptrics. + +34. FIRST, any radiating point is then distinctly seen when the rays +proceeding from it are, by the refractive power of the crystalline, +accurately reunited in the retina or fund of the eye: but if they are +reunited, either before they arrive at the retina, or after they have +passed it, then there is confused vision. + + + +35. SECONDLY, suppose in the adjacent figures NP represent an eye duly +framed and retaining its natural figure. In Fig. 1 the rays falling +nearly parallel on the eye, are by the crystalline AB refracted, so as +their focus or point of union F falls exactly on the retina: but if the +rays fall sensibly diverging on the eye, as in Fig. 2, then their focus +falls beyond the retina: or if the rays are made to converge by the lens +QS before they come at the eye, as in Fig. 3, their focus F will fall +before the retina. In which two last cases it is evident from the +foregoing section that the appearance of the point Z is confused. And by +how much the greater is the convergency, or divergency, of the rays +falling on the pupil, by so much the farther will the point of their +reunion be from the retina, either before or behind it, and consequently +the point Z will appear by so much the more confused. And this, by the +bye, may show us the difference between confused and faint vision. +Confused vision is when the rays proceedings from each distinct point of +the OBJECT are not accurately recollected in one corresponding point on +the retina, but take up some space thereon, so that rays from different +points become mixed and confused together. This is opposed to a distinct +vision, and attends near objects. Faint vision is when by reason of the +distance of the object or grossness of the interjacent medium few rays +arrive from the object to the eye. This is opposed to vigorous or clear +vision, and attends remote objects. But to return. + +36. The eye, or (to speak truly) the mind, perceiving only the confusion +itself, without ever considering the cause from which it proceeds, doth +constantly annex the same degree of distance to the same degree of +confusion. Whether that confusion be occasioned by converging or by +diverging rays, it matters not. Whence it follows that the eye viewing +the object Z through the glass QS (which by refraction causeth the rays +ZQ, ZS, etc., to converge) should judge it to be at such a nearness at +which if it were placed it would radiate on the eye with rays diverging +to that degree as would produce the same confusion which is now produced +by converging rays, i.e. would cover a portion of the retina equal to DC +(VID. Fig. 3 supra). But then this must be understood (to use Dr. +Barrow's phrase) SECLUSIS PRAENOTIONIBUS ET PRAEJUDICIIS, in case we +abstract from all other circumstances of vision, such as the figure, +size, faintness, etc. of the visible objects; all which do ordinarily +concur to form our idea of distance, the mind having by frequent +experience observed their several sorts or degrees to be connected with +various distances. + +37. It plainly follows from what hath been said that a person perfectly +purblind (i.e. that could not see an object distinctly but when placed +close to his eye) would not make the same wrong judgment that others do +in the forementioned case. For to him greater confusions constantly +suggesting greater distances, he must, as he recedes from the glass and +the object grows more confused, judge it to be at a farther distance, +contrary to what they do who have had the perception of the objects +growing more confused connected with the idea of approach. + +38. Hence also it doth appear there may be good use of computation by +lines and angles in optics; not that the mind judgeth of distance +immediately by them, but because it judgeth by somewhat which is +connected with them, and to the determination whereof they may be +subservient. Thus the mind judging of the distance of an object by the +confusedness of its appearance, and this confusedness being greater or +lesser to the naked eye, according as the object is seen by rays more or +less diverging, it follows that a man may make use of the divergency of +the rays in computing the apparent distance, though not for its own sake, +yet on account of the confusion with which it is connected. But, so it +is, the confusion itself is entirely neglected by mathematicians as +having no necessary relation with distance, such as the greater or lesser +angles of divergency are conceived to have. And these (especially for +that they fall under mathematical computation) are alone regarded in +determining the apparent places of objects, as though they were the sole +and immediate cause of the judgments the mind makes of distance. Whereas, +in truth, they should not at all be regarded in themselves, or any +otherwise, than as they are supposed to be the cause of confused vision. + +39. The not considering of this has been a fundamental and perplexing +oversight. For proof whereof we need go no farther than the case before +us. It having been observed that the most diverging rays brought into the +mind the idea of nearest distance, and that still, as the divergency +decreased, the distance increased: and it being thought the connexion +between the various degrees of divergency and distance was immediate; +this naturally leads one to conclude, from an ill-grounded analogy, that +converging rays shall make an object appear at an immense distance: and +that, as the convergency increases, the distance (if it were possible) +should do so likewise. That this was the cause of Dr. Barrow's mistake is +evident from his own words which we have quoted. Whereas had the learned +doctor observed that diverging and converging rays, how opposite soever +they may seem, do nevertheless agree in producing the same effect, to +wit, confusedness of vision, greater degrees whereof are produced +indifferently, either as the divergency or convergency and the rays +increaseth. And that it is by this effect, which is the same in both, +that either the divergency or convergency is perceived by the eye; I say, +had he but considered this, it is certain he would have made a quite +contrary judgment, and rightly concluded that those rays which fall on +the eye with greater degrees of convergency should make the object from +whence they proceed appear by so much the nearer. But it is plain it was +impossible for any man to attain to a right notion of this matter so long +as he had regard only to lines and angles, and did not apprehend the true +nature of vision, and how far it was of mathematical consideration. + +40. Before we dismiss this subject, it is fit we take notice of a query +relating thereto, proposed by the ingenious Mr. Molyneux, is his TREATISE +OF DIOPTRICS,[Par. I. Prop. 31, Sect. 9.] where speaking of this +difficulty, he has these words: 'And so he (i.e. Dr. Barrow) leaves this +difficulty to the solution of others, which I (after so great an example) +shall do likewise; but with the resolution of the same admirable author of +not quitting the evident doarine which we have before laid down, for +determining the LOCUS OBJECTI, on account of being pressed by one +difficulty which seems inexplicable till a more intimate knowledge of the +visive faculty be obtained by mortals. In the meantime, I propose it to +the consideration of the ingenious, whether the LOCUS APPARENS of an +object placed as in this 9th section be not as much before the eye as the +distinct base is behind the eye!' To which query we may venture to answer +in the negative. For in the present case the rule for determining the +distance of the distinct base, or respective focus from the glass, is this: +as the difference between the distance of the object and focus is to the +focus or focal length, so the distance of the object from the glass is to +the distance of the respective focus or distinct base from the glass. +[Molyneux Dioptr., Par. I. Prop. 5.] Let us now suppose the object to be +placed at the distance of the focal length, and one half of the focal +length from the glass, and the eye close to the glass, hence it will follow +by the rule that the distance of the distinct base behind the eye is double +the true distance of the object before the eye. If therefore Mr. Molyneux's +conjecture held good, it would follow that the eye should see the object +twice as far off as it really is; and in other cases at three or four times +its due distance, or more. But this manifestly contradicts experience, the +object never appearing, at farthest, beyond its due distance. Whatever, +therefore, is built on this supposition (VID. COROL. I. PROP. 57, IBID.) +comes to the ground along with it. + +41. From what hath been premised it is a manifest consequence that a man +born blind, being made to see, would, at first, have no idea of distance +by sight; the sun and stars, the remotest objects as well as the nearer, +would all seem to be in his eye, or rather in his mind. The objects +intromitted by sight would seem to him (as in truth they are) no other +than a new set of thoughts or sensations, each whereof is as near to him +as the perceptions of pain or pleasure, or the most inward passions of +his soul. For our judging objects provided by sight to be at any +distance, or without the mind, is (VID. sect. 28) entirely the effect of +experience, which one in those circumstances could not yet have attained +to. + +42. It is indeed otherwise upon the common supposition that men judge of +distance by the angle of the optic axes, just as one in the dark, or a +blind-man by the angle comprehended by two sticks, one whereof he held in +each hand. For if this were true, it would follow that one blind from his +birth being made to see, should stand in need of no new experience in +order to perceive distance by sight. But that this is false has, I think, +been sufficiently demonstrated. + +43. And perhaps upon a strict inquiry we shall not find that even those +who from their birth have grown up in a continued habit of seeing are +irrecoverably prejudiced on the other side, to wit, in thinking what they +see to be at a distance from them. For at this time it seems agreed on +all hands, by those who have had any thoughts of that matter, that +colours, which are the proper and immediate object of sight, are not +without the mind. But then it will be said, by sight we have also the +ideas of extension, and figure, and motion; all which may well be thought +without, and at some distance from the mind, though colour should not. In +answer to this I appeal to any man's experience, whether the visible +extension of any object doth not appear as near to him as the colour of +that object; nay, whether they do not both seem to be in the very same +place. Is not the extension we see coloured, and is it possible for us, +so much as in thought, to separate and abstract colour from extension? +Now, where the extension is there surely is the figure, and there the +motion too. I speak of those which are perceived by sight. + +44. But for a fuller explication of this point, and to show that the +immediate objects of sight are not so much as the ideas or resemblances +of things placed at a distance, it is requisite that we look nearer into +the matter and carefully observe what is meant in common discourse, when +one says that which he sees is at a distance from him. Suppose, for +example, that looking at the moon I should say it were fifty or sixty +semidiameters of the earth distant from me. Let us see what moon this is +spoken of: it is plain it cannot be the visible moon, or anything like +the visible moon, or that which I see, which is only a round, luminous +plane of about thirty visible points in diameter. For in case I am +carried from the place where I stand directly towards the moon, it is +manifest the object varies, still as I go on; and by the time that I am +advanced fifty or sixty semidiameters of the earth, I shall be so far +from being near a small, round, luminous flat that I shall perceive +nothing like it; this object having long since disappeared, and if I +would recover it, it must be by going back to the earth from whence I set +out. Again, suppose I perceive by sight the faint and obscure idea of +something which I doubt whether it be a man, or a tree, or a tower, but +judge it to be at the distance of about a mile. It is plain I cannot mean +that what I see is a mile off, or that it is the image or likeness of +anything which is a mile off, since that every step I take towards it the +appearance alters, and from being obscure, small, and faint, grows clear, +large, and vigorous. And when I come to the mile's end, that which I saw +first is quite lost, neither do I find anything in the likeness of it. + +45. In these and the like instances the truth of the matter stands thus: +having of a long time experienced certain ideas, perceivable by touch, as +distance, tangible figure, and solidity, to have been connected with +certain ideas of sight, I do upon perceiving these ideas of sight +forthwith conclude what tangible ideas are, by the wonted ordinary course +of Nature like to follow. Looking at an object I perceive a certain +visible figure and colour, with some degree of faintness and other +circumstances, which from what I have formerly observed, determine me to +think that if I advance forward so many paces or miles, I shall be +affected with such and such ideas of touch: so that in truth and +strictness of speech I neither see distance itself, nor anything that I +take to be at a distance. I say, neither distance nor things placed at a +distance are themselves, or their ideas, truly perceived by sight. This I +am persuaded of, as to what concerns myself: and I believe whoever will +look narrowly into his own thoughts and examine what he means by saying +he sees this or that thing at a distance, will agree with me that what he +sees only suggests to his understanding that after having passed a +certain distance, to be measured by the motion of his body, which is +perceivable by touch, he shall come to perceive such and such tangible +ideas which have been usually connected with such and such visible ideas. +But that one might be deceived by these suggestions of sense, and that +there is no necessary connexion between visible and tangible ideas +suggested by them, we need go no farther than the next looking-glass or +pictures to be convinced. Note that when I speak of tangible ideas, I +take the word idea for any the immediate object of sense or +understanding, in which large signification it is commonly used by the +moderns. + +46. From what we have shown it is a manifest consequence that the ideas +of space, outness, and things placed at a distance are not, strictly +speaking, the object of sight; they are not otherwise perceived by the +eye than by the ear. Sitting in my study I hear a coach drive along the +street; I look through the casement and see it; I walk out and enter into +it; thus, common speech would incline one to think I heard, saw, and +touched the same thing, to wit, the coach. It is nevertheless certain, +the ideas intromitted by each sense are widely different and distinct +from each other; but having been observed constantly to go together, they +are spoken of as one and the same thing. By the variation of the noise I +perceive the different distances of the coach, and know that it +approaches before I look out. Thus by the ear I perceive distance, just +after the same manner as I do by the eye. + +47. I do not nevertheless say I hear distance in like manner as I say +that I see it, the ideas perceived by hearing not being so apt to be +confounded with the ideas of touch as those of sight are. So likewise a +man is easily convinced that bodies and external things are not properly +the object of hearing; but only sounds, by the mediation whereof the idea +of this or that body or distance is suggested to his thoughts. But then +one is with more difficulty brought to discern the difference there is +betwixt the ideas of sight and touch: though it be certain a man no more +sees and feels the same thing than he hears and feels the same thing. + +48. One reason of which seems to be this. It is thought a great absurdity +to imagine that one and the same thing should have any more than one +extension, and one figure. But the extension and figure of a body, being +let into the mind two ways, and that indifferently either by sight or +touch, it seems to follow that we see the same extension and the same +figure which we feel. + +49. But if we take a close and accurate view of things, it must be +acknowledged that we never see and feel one and the same object. That +which is seen is one thing, and that which is felt is another. If the +visible figure and extension be not the same with the tangible figure and +extension, we are not to infer that one and the same thing has divers +extensions. The true consequence is that the objects of sight and touch +are two distinct things. It may perhaps require some thought rightly to +conceive this distinction. And the difficulty seems not a little +increased, because the combination of visible ideas hath constantly the +same name as the combination of tangible ideas wherewith it is connected: +which doth of necessity arise from the use and end of language. + +50. In order therefore to treat accurately and unconfusedly of vision, we +must bear in mind that there are two sorts of objects apprehended by the +eye, the one primarily and immediately, the other secondarily and by +intervention of the former. Those of the first sort neither are, nor +appear to be, without the mind, or at any distance off; they may indeed +grow greater or smaller, more confused, or more clear, or more faint, but +they do not, cannot approach or recede from us. Whenever we say an object +is at a distance, whenever we say it draws near, or goes farther off, we +must always mean it of the latter sort, which properly belong to the +touch, and are not so truly perceived as suggested by the eye in like +manner as thoughts by the ear. + +51. No sooner do we hear the words of a familiar language pronounced in +our ears, but the ideas corresponding thereto present themselves to our +minds: in the very same instant the sound and the meaning enter the +understanding: so closely are they united that it is not in our power to +keep out the one, except we exclude the other also. We even act in all +respects as if we heard the very thoughts themselves. So likewise the +secondary objects, or those which are only suggested by sight, do often +more strongly affect us, and are more regarded than the proper objects of +that sense; along with which they enter into the mind, and with which +they have a far more strict connexion, than ideas have with words. Hence +it is we find it so difficult to discriminate between the immediate and +mediate objects of sight, and are so prone to attribute to the former +what belongs only to the latter. They are, as it were, most closely +twisted, blended, and incorporated together. And the prejudice is +confirmed and riveted in our thoughts by a long tract of time, by the use +of language, and want of reflexion. However, I believe anyone that shall +attentively consider what we have already said, and shall say, upon this +subject before we have done (especially if he pursue it in his own +thoughts) may be able to deliver himself from that prejudice. Sure I am +it is worth some attention, to whoever would understand the true nature +of vision. + +52. I have now done with distance, and proceed to show how it is that we +perceive by sight the magnitude of objects. It is the opinion of some +that we do it by angles, or by angles in conjunction with distance: but +neither angles nor distance being perceivable by sight, and the things we +see being in truth at no distance from us, it follows that as we have +shown lines and angles not to be the medium the mind makes use of in +apprehending the apparent place, so neither are they the medium whereby +it apprehends the apparent magnitude of objects. + +53. It is well known that the same extension at a near distance shall +subtend a greater angle, and at a farther distance a lesser angle. And by +this principle (we are told) the mind estimates the magnitude of an +object, comparing the angle under which it is seen with its distance, and +thence inferring the magnitude thereof. What inclines men to this mistake +(beside the humour of making one see by geometry) is that the same +perceptions or ideas which suggest distance do also suggest magnitude. +But if we examine it we shall find they suggest the latter as immediately +as the former. I say, they do not first suggest distance, and then leave +it to the judgment to use that as a medium whereby to collect the +magnitude; but they have as close and immediate a connexion with the +magnitude as with the distance; and suggest magnitude as independently of +distance as they do distance independently of magnitude. All which will +be evident to whoever considers what hath been already said, and what +follows. + +54. It hath been shown there are two sorts of objects apprehended by +sight; each whereof hath its distinct magnitude, or extension. The one, +properly tangible, i.e. to be perceived and measured by touch, and not +immediately falling under the sense of seeing: the other, properly and +immediately visible, by mediation of which the former is brought in view. +Each of these magnitudes are greater or lesser, according as they contain +in them more or fewer points, they being made up of points or minimums. +For, whatever may be said of extension in abstract, it is certain sensible +extension is not infinitely divisible. There is a MINIMUM TANGIBILE and a +MINIMUM VISIBILE, beyond which sense cannot perceive. This everyone's +experience will inform him. + +55. The magnitude of the object which exists without the mind, and is at +a distance, continues always invariably the same: but the visible object +still changing as you approach to, or recede from, the tangible object, +it hath no fixed and determinate greatness. Whenever, therefore, we speak +of the magnitude of anything, for instance a tree or a house, we must +mean the tangible magnitude, otherwise there can be nothing steady and +free from ambiguity spoken of it. But though the tangible and visible +magnitude in truth belong to two distinct objects: I shall nevertheless +(especially since those objects are called by the same name, and are +observed to coexist), to avoid tediousness and singularity of speech, +sometimes speak of them as belonging to one and the same thing. + +56. Now in order to discover by what means the magnitude of tangible +objects is perceived by sight. I need only reflect on what passes in my +own mind, and observe what those things be which introduce the ideas of +greater or lesser into my thoughts, when I look on any object. And these +I find to be, FIRST, the magnitude or extension of the visible object, +which being immediately perceived by sight, is connected with that other +which is tangible and placed at a distance. SECONDLY, the confusion or +distinctness. And thirdly, the vigorousness or faintness of the aforesaid +visible appearance. CETERIS PARIBUS, by how much the greater or lesser +the visible object is, by so much the greater or lesser do I conclude the +tangible object to be. But, be the idea immediately perceived by sight +never so large, yet if it be withal confused, I judge the magnitude of +the thing to be but small. If it be distinct and clear, I judge it +greater. And if it be faint, I apprehend it to be yet greater. What is +here meant by confusion and faintness hath been explained in sect. 35. + +57. Moreover the judgments we make of greatness do, in like manner as +those of distance, depend on the disposition of the eye, also on the +figure, number, and situation of objects and other circumstances that +have been observed to attend great or small tangible magnitudes. Thus, +for instance, the very same quantity of visible extension, which in the +figure of a tower doth suggest the idea of great magnitude, shall in the +figure of a man suggest the idea of much smaller magnitude. That this is +owing to the experience we have had of the usual bigness of a tower and a +man no one, I suppose, need be told. + +58. It is also evident that confusion or faintness have no more a +necessary connexion with little or great magnitude than they have with +little or great distance. As they suggest the latter, so they suggest the +former to our minds. And by consequence, if it were not for experience, +we should no more judge a faint or confused appearance to be connected +with great or little magnitude, than we should that it was connected with +great or little distance. + +59. Nor will it be found that great or small visible magnitude hath any +necessary relation to great or small tangible magnitude: so that the one +may certainly be inferred from the other. But before we come to the proof +of this, it is fit we consider the difference there is betwixt the +extension and figure which is the proper object of touch, and that other +which is termed visible; and how the former is principally, though not +immediately taken notice of, when we look at any object. This has been +before mentioned, but we shall here inquire into the cause thereof. We +regard the objects that environ us in proportion as they are adapted to +benefit or injure our own bodies, and thereby produce in our minds the +sensation of pleasure or pain. Now bodies operating on our organs, by an +immediate application, and the hurt or advantage arising therefrom, +depending altogether on the tangible, and not at all on the visible, +qualities of any object: this is a plain reason why those should be +regarded by us much more than these: and for this end the visive sense +seems to have been bestowed on animals, to wit, that by the perception of +visible ideas (which in themselves are not capable of affecting or any +wise altering the frame of their bodies) they may be able to foresee +(from the experience they have had what tangible ideas are connected with +such and such visible ideas) and damage or benefit which is like to +ensue, upon the application of their own bodies to this or that body +which is at a distance. Which foresight, how necessary it is to the +preservation of an animal, everyone's experience can inform him. Hence it +is that when we look at an object, the tangible figure and extension +thereof are principally attended to; whilst there is small heed taken of +the visible figure and magnitude, which, though more immediately +perceived, do less concern us, and are not fitted to produce any +alteration in our bodies. + +60. That the matter of fact is true will be evident to anyone who +considers that a man placed at ten foot distance is thought as great as +if he were placed at a distance only of five foot: which is true not with +relation to the visible, but tangible greatness of the object: the +visible magnitude being far greater at one station: than it is at the +other. + +61. Inches, feet, etc., are settled stated lengths whereby we measure +objects and estimate their magnitude: we say, for example, an object +appears to be six inches or six foot long. Now, that this cannot be meant +of visible inches, etc., is evident, because a visible inch is itself no +constant, determinate magnitude, and cannot therefore serve to mark out +and determine the magnitude of any other thing. Take an inch marked upon +a ruler: view it, successively, at the distance of half a foot, a foot, a +foot and a half, etc., from the eye: at each of which, and at all the +intermediate distances, the inch shall have a different visible +extension, i.e. there shall be more or fewer points discerned in it. Now +I ask which of all these various extensions is that stated, determinate +one that is agreed on for a common measure of other magnitudes? No reason +can be assigned why we should pitch on one more than another: and except +there be some invariable, determinate extension fixed on to be marked to +the word inch, it is plain it can be used to little purpose; and to say a +thing contains this or that number of inches shall imply no more than +that it is extended, without bringing any particular idea of that +extension into the mind. Farther, an inch and a foot, from different +distances, shall both exhibit the same visible magnitude, and yet at the +same time you shall say that one seems several times greater than the +other. From all which it is manifest that the judgments we make of the +magnitude of objects by sight are altogether in reference to their +tangible extension. Whenever we say an object is great, or small, of this +or that determinate measure, I say it must be meant of the tangible, and +not the visible extension, which, though immediately perceived, is +nevertheless little taken notice of. + +62. Now, that there is no necessary connexion between these two distinct +extensions is evident from hence: because our eyes might have been framed +in such a manner as to be able to see nothing but what were less than the +MINIMUM TANGIBILE. In which case it is not impossible we might have +perceived all the immediate objects of sight, the very same that we do +now: but unto those visible appearances there would not be connected +those different tangible magnitudes that are now. Which shows the +judgments we make of the magnitude of things placed at a distance from +the various greatness of the immediate objects of sight do not arise from +any essential or necessary but only a customary tie, which has been +observed between them. + +63. Moreover, it is not only certain that any idea of sight might not +have been connected with this or that idea of touch, which we now observe +to accompany it: but also that the greater visible magnitudes might have +been connected with, and introduced into our minds lesser tangible +magnitudes and the lesser visible magnitudes greater tangible magnitudes. +Nay, that it actually is so we have daily experience; that object which +makes a strong and large appearance, not seeming near so great as +another, the visible magnitude whereof is much less, but more faint, and +the appearance upper, or which is the same thing painted lower on the +RETINA, which faintness and situation suggest both greater magnitude and +greater distance. + +64. From which, and from sect. 57 and 58, it is manifest that as we do +not perceive the magnitudes of objects immediately by sight, so neither +do we perceive them by the mediation of anything which has a necessary +connexion with them. Those ideas that now suggest unto us the various +magnitudes of external objects before we touch them, might possibly have +suggested no such thing: or they might have signified them in a direct +contrary manner: so that the very same ideas, on the perception whereof +we judge an object to be small, might as well have served to make us +conclude it great. Those ideas being in their own nature equally fitted +to bring into our minds the idea of small or great, or no size at all of +outward objects; just as the words of any language are in their own +nature indifferent to signify this or that thing or nothing at all. + +65. As we see distance, so we see magnitude. And we see both in the same +way that we see shame or anger in the looks of a man. Those passions are +themselves invisible, they are nevertheless let in by the eye along with +colours and alterations of countenance, which are the immediate object of +vision: and which signify them for no other reason than barely because +they have been observed to accompany them. Without which experience we +should no more have taken blushing for a sign of shame than of gladness. + +66. We are nevertheless exceeding prone to imagine those things which are +perceived only by the mediation of others to be themselves the immediate +objects of sight; or, at least, to have in their own nature a fitness to +be suggested by them, before ever they had been experienced to coexist +with them. From which prejudice everyone, perhaps, will not find it easy +to emancipate himself, by any [but] the clearest convictions of reason. +And there are some grounds to think that if there was one only invariable +and universal languages in the world, and that men were born with the +faculty of speaking it, it would be the opinion of many that the ideas of +other men's minds were properly perceived by the ear, or had at least a +necessary and inseparable tie with the sounds that were affixed to them. +All which seems to arise from want of a due application of our discerning +faculty, thereby to discriminate between the ideas that are in our +understandings, and consider them apart from each other; which would +preserve us from confounding those that are different, and make us see +what ideas do, and what do not include or imply this or that other idea. + +67. There is a celebrated phenomenon, the solution whereof I shall +attempt to give by the principles that have been laid down, in reference +to the manner wherein we apprehend by sight the magnitude of objects. The +apparent magnitude of the moon when placed in the horizon is much greater +than when it is in the meridian, though the angle under which the +diameter of the moon is seen be not observed greater in the former case +than in the latter: and the horizontal moon doth not constantly appear of +the same bigness, but at some times seemeth far greater than at others. + +68. Now in order to explain the reason of the moon's appearing greater +than ordinary in the horizon, it must be observed that the particles +which compose our atmosphere intercept the rays of light proceeding from +any object to the eye; and by how much the greater is the portion of +atmosphere interjacent between the object and the eye, by so much the +more are the rays intercepted; and by consequence the appearance of the +object rendered more faint, every object appearing more vigorous or more +faint in proportion as it sendeth more or fewer rays into the eye. Now +between the eye and the moon, when situated in the horizon, there lies a +far greater quantity of atmosphere than there does when the moon is in +the meridian. Whence it comes to pass that the appearance of the +horizontal moon is fainter, and therefore by sect. 56 it should be +thought bigger in that situation than in the meridian, or in any other +elevation above the horizon. + +69. Farther, the air being variously impregnated, sometimes more and +sometimes less, with vapours and exhalations fitted to retund and +intercept the rays of light, it follows that the appearance of the +horizontal moon hath not always an equal faintness, and by consequence +that luminary, though in the very same situation, is at one time judged +greater than at another. + +70. That we have here given the true account of the phenomena of the +horizontal moon will, I suppose, be farther evident to anyone from the +following considerations. FIRST, it is plain that which in this case +suggests the idea of greater magnitude must be something which is itself +perceived; for that which is unperceived cannot suggest to our perception +any other thing. SECONDLY, it must be something that does not constantly +remain the same, but is subject to some change or variation, since the +appearance of the horizontal moon varies, being at one time greater than +at another. And yet, THIRDLY, it cannot be the visible figure or +magnitude, since that remains the same, or is rather lesser, by how much +the moon is nearer to the horizon. It remains therefore that the true +cause is that affection or alteration of the visible appearance which +proceeds from the greater paucity of rays arriving at the eye, and which +I term FAINTNESS: since this answers all the forementioned conditions, +and I am not conscious of any other perception that doth. + +71. Add to this that in misty weather it is a common observation that the +appearance of the horizontal moon is far larger than usual, which greatly +conspires with and strengthens our opinion. Neither would it prove in the +least irreconcilable with what we have said, if the horizontal moon +should chance sometimes to seem enlarged beyond its usual extent, even in +more serene weather. For we must not only have regard to the mist which +happens to be in the place where we stand; we ought also to take into our +thoughts the whole sum of vapours and exhalations which lie betwixt the +eye and the moon: all which cooperating to render the appearance of the +moon more faint, and thereby increase its magnitude, it may chance to +appear greater than it usually does, even in the horizontal position, at +a time when, though there be no extraordinary fog or haziness, just in +the place where we stand, yet the air between the eye and the moon, taken +all together, may be loaded with a greater quantity of interspersed +vapours and exhalations than at other times. + +72. It may be objected that in consequence of our principles the +interposition of a body in some degree opaque, which may intercept a +great part of the rays of light, should render the appearance of the moon +in the meridian as large as when it is viewed in the horizon. To which I +answer, it is not faintness anyhow applied that suggests greater +magnitude, there being no necessary but only an experimental connexion +between those two things. It follows that the faintness which enlarges +the appearance must be applied in such sort, and with such circumstances, +as have been observed to attend the vision of great magnitudes. When from +a distance we behold great objects, the particles of the intermediate air +and vapours, which are themselves unperceivable, do interrupt the rays of +light, and thereby render the appearance less strong and vivid: now, +faintness of appearance caused in this sort hath been experienced to +coexist with great magnitude. But when it is caused by the interposition +of an opaque sensible body, this circumstance alters the case, so that a +faint appearance this way caused doth not suggest greater magnitude, +because it hath not been experienced to coexist with it. + +73. Faintness, as well as all other ideas or perceptions which suggest +magnitude or distance, doth it in the same way that words suggest the +notions to which they are annexed. Now, it is known a word pronounced +with certain circumstances, or in a certain context with other words, +hath not always the same import and signification that it hath when +pronounced in some other circumstances or different context of words. The +very same visible appearance as to faintness and all other respects, if +placed on high, shall not suggest the same magnitude that it would if it +were seen at an equal distance on a level with the eye. The reason +whereof is that we are rarely accustomed to view objects at a great +height; our concerns lie among things situated rather before than above +us, and accordingly our eyes are not placed on the top of our heads, but +in such a position as is most convenient for us to see distant objects +standing in our way. And this situation of them being a circumstance +which usually attends the vision of distant objects, we may from hence +account for (what is commonly observed) an object's appearing of +different magnitude, even with respect to its horizontal extension, on +the top of a steeple, for example, an hundred feet high to one standing +below, from what it would if placed at an hundred feet distance on a +level with his eye. For it hath been shown that the judgment we make on +the magnitude of a thing depends not on the visible appearance alone, but +also on divers other circumstances, any one of which being omitted or +varied may suffice to make some alteration in our judgment. Hence, the +circumstances of viewing a distant object in such a situation as is +usual, and suits with the ordinary posture of the head and eyes being +omitted, and instead thereof a different situation of the object, which +requires a different posture of the head taking place, it is not to be +wondered at if the magnitude be judged different: but it will be demanded +why an high object should constantly appear less than an equidistant low +object of the same dimensions, for so it is observed to be: it may indeed +be granted that the variation of some circumstances may vary the judgment +made on the magnitude of high objects, which we are less used to look at: +but it does not hence appear why they should be judged less rather than +greater? I answer that in case the magnitude of distant objects was +suggested by the extent of their visible appearance alone, and thought +proportional thereto, it is certain they would then be judged much less +than now they seem to be (VIDE sect. 79). But several circumstances +concurring to form the judgment we make on the magnitude of distant +objects, by means of which they appear far larger than others, whose +visible appearance hath an equal or even greater extension; it follows +that upon the change or omission of any of those circumstances which are +wont to attend the vision of distant objects, and so come to influence +the judgments made on their magnitude, they shall proportionably appear +less than otherwise they would. For any of those things that caused an +object to be thought greater than in proportion to its visible extension +being either omitted or applied without the usual circumstances, the +judgment depends more entirely on the visible extension, and consequently +the object must be judged less. Thus in the present case the situation of +the thing seen being different from what it usually is in those objects +we have occasion to view, and whose magnitude we observe, it follows that +the very same object, being an hundred feet high, should seem less than +if it was an hundred feet off on (or nearly on) a level with the eye. +What has been here set forth seems to me to have no small share in +contributing to magnify the appearance of the horizontal moon, and +deserves not to be passed over in the explication of it. + +74. If we attentively consider the phenomenon before us, we shall find +the not discerning between the mediate and immediate objects of sight to +be the chief cause of the difficulty that occurs in the explication of +it. The magnitude of the visible moon, or that which is the proper and +immediate object of vision, is not greater when the moon is in the +horizon than when it is in the meridian. How comes it, therefore, to seem +greater in one situation than the other? What is it can put this cheat on +the understanding? It has no other perception of the moon than what it +gets by sight: and that which is seen is of the same extent, I say, the +visible appearance hath the same, or rather a less, magnitude when the +moon is viewed in the horizontal than when in the meridional position: +and yet it is esteemed greater in the former than in the latter. Herein +consists the difficulty, which doth vanish and admit of a most easy +solution, if we consider that as the visible moon is not greater in the +horizon than in the meridian, so neither is it thought to be so. It hath +been already shown that in any act of vision the visible object +absolutely, or in itself, is little taken notice of, the mind still +carrying its view from that to some tangible ideas which have been +observed to be connected with it, and by that means come to be suggested +by it. So that when a thing is said to appear great or small, or whatever +estimate be made of the magnitude of any thing, this is meant not of the +visible but of the tangible object. This duly considered, it will be no +hard matter to reconcile the seeming contradiction there is, that the +moon should appear of a different bigness, the visible magnitude thereof +remaining still the same. For by sect. 56 the very same visible +extension, with a different faintness, shall suggest a different tangible +extension. When therefore the horizontal moon is said to appear greater +than the meridional moon, this must be understood not of a greater +visible extension, but a of greater tangible or real extension, which by +reason of the more than ordinary faintness of the visible appearance, is +suggested to the mind along with it. + +75. Many attempts have been made by learned men to account for this +appearance. Gassendus, Descartes, Hobbes, and several others have +employed their thoughts on that subject; but how fruitless and +unsatisfactory their endeavours have been is sufficiently shown in THE +TRANSACTIONS,[Phil. Trans. Num. 187. p. 314] where you may +see their several opinions at large set forth and confuted, not without +some surprize at the gross blunders that ingenious men have been forced +into by endeavouring to reconcile this appearance with the ordinary +Principles of optics. Since the writing of which there hath been published +in the TRANSACTIONS [Numb. 187. P. 323] another paper relating to the same +affair by the celebrated Dr. Wallis, wherein he attempts to account for +that phenomenon which, though it seems not to contain anything new or +different from what had been said before by others, I shall nevertheless +consider in this place. + +76. His opinion, in short, is this; we judge not of the magnitude of an +object by the visual angle alone, but by the visual angle in conjunction +with the distance. Hence, though the angle remain the same, or even +become less, yet if withal the distance seem to have been increased, the +object shall appear greater. Now, one way whereby we estimate the +distance of anything is by the number and extent of the intermediate +objects: when therefore the moon is seen in the horizon, the variety of +fields, houses, etc., together with the large prospect of the wide +extended land or sea that lies between the eye and the utmost limb of the +horizon, suggest unto the mind the idea of greater distance, and +consequently magnify the appearance. And this, according to Dr. Wallis, +is the true account of the extraordinary largeness attributed by the mind +to the horizontal moon at a time when the angle subtended by its diameter +is not one jot greater than it used to be. + +77. With reference to this opinion, not to repeat what hath been already +said concerning distance, I shall only observe, FIRST, that if the +prospect of interjacent objects be that which suggests the idea of +farther distance, and this idea of farther distance be the cause that +brings into the mind the idea of greater magnitude, it should hence +follow that if one looked at the horizontal moon from behind a wall, it +would appear no bigger than ordinary. For in that case the wall +interposing cuts off all that prospect of sea and land, etc. which might +otherwise increase the apparent distance, and thereby the apparent +magnitude of the moon. Nor will it suffice to say the memory doth even +then suggest all that extent of land, etc., which lies within the +horizon; which suggestion occasions a sudden judgment of sense that the +moon is farther off and larger than usual. For ask any man who, from such +a station beholding the horizontal moon, shall think her greater than +usual, whether he hath at that time in his mind any idea of the +intermediate objects, or long tract of land that lies between his eye and +the extreme edge of the horizon? And whether it be that idea which is the +cause of his making the aforementioned judgment? He will, I suppose, +reply in the negative, and declare the horizontal moon shall appear +greater than the meridional, though he never thinks of all or any of +those things that lie between him and it. SECONDLY, it seems impossible +by this hypothesis to account for the moon's appearing in the very same +situation at one time greater than at another; which nevertheless has +been shown to be very agreeable to the principles we have laid down, and +receives a most easy and natural explication from them. For the further +clearing' up of this point it is to be observed that what we immediately +and properly see are only lights and colours in sundry situations and +shades and degrees of faintness and clearness, confusion and +distinctness. All which visible objects are only in the mind, nor do they +suggest ought external, whether distance or magnitude, otherwise than by +habitual connexion as words do things. We are also to remark that, beside +the straining of the eyes, and beside the vivid and faint, the distinct +and confused appearances (which, bearing some proportion to lines and +angles, have been substituted instead of them in the foregoing part of +this treatise), there are other means which suggest both distance and +magnitude; particularly the situation of visible points of objects, as +upper or lower; the one suggesting a farther distance and greater +magnitude, the other a nearer distance and lesser magnitude: all which is +an effect only of custom and experience; there being really nothing +intermediate in the line of distance between the uppermost and lowermost, +which are both equidistant, or rather at no distance from the eye, as +there is also nothing in upper or lower, which by necessary connexion +should suggest greater or lesser magnitude. Now, as these customary, +experimental means of suggesting distance do likewise suggest magnitude, +so they suggest the one as immediately as the other. I say they do not +(VIDE sect. 53) first suggest distance, and then leave the mind from +thence to infer or compute magnitude, jut suggest magnitude as +immediately and directly as they suggest distance. + +78. This phenomenon of the horizontal moon is a clear instance of the +insufficiency of lines and angles for explaining the way wherein the mind +perceives and estimates the magnitude of outward objects. There is +nevertheless a use of computation by them in order to determine the +apparent magnitude of things, so far as they have a connexion with, and +are proportional to, those other ideas or perceptions which are the true +and immediate occasions that suggest to the mind the apparent magnitude +of things. But this in general may, I think, be observed concerning +mathematical computation in optics: that it can never be very precise and +exact since the judgments we make of the magnitude of external things do +often depend on several circumstances, which are not proportionable to, +or capable of being defined by, lines and angles. + +79. From what has been said we may safely deduce this consequence; to +wit, that a man born blind and made to see would, at first opening of his +eyes, make a very different judgment of the magnitude of objects +intromitted by them from what others do. He would not consider the ideas +of sight with reference to, or as having any connexion with, the ideas of +touch: his view of them being entirely terminated within themselves, he +can no otherwise judge them great or small than as they contain a greater +or lesser number of visible points. Now, it being certain that any +visible point can cover or exclude from view only one other visible +point, it follows that whatever object intercepts the view of another +hath an equal number of visible points with it; and consequently they +shall both be thought by him to have the same magnitude. Hence it is +evident one in those circumstances would judge his thumb, with which he +might hide a tower or hinder its being seen, equal to that tower, or his +hand, the interposition whereof might conceal experimental means the +firmament from his view, equal to the firmament: how great an inequality +soever there may in our apprehensions seem to be betwixt those two +things, because of the customary and close connexion that has grown up in +our minds between the objects of sight and touch; whereby the very +different and distinct ideas of those two senses are so blended and +confounded together as to be mistaken for one and the same thing; out of +which prejudice we cannot easily extricate ourselves. + +80. For the better explaining the nature of vision, and setting the +manner wherein we perceive magnitudes in a due light, I shall proceed to +make some observations concerning matters relating thereto, whereof the +want of reflexion, and duly separating between tangible and visible +ideas, is apt to create in us mistaken and confused notions. And FIRST, I +shall observe that the MINIMUM VISIBILE is exactly equal in all beings +whatsoever that are endowed with the visive faculty. No exquisite +formation of the eye, no peculiar sharpness of sight, can make it less in +one creature than in another; for it not being distinguishable into +parts, nor in any wise a consisting of them, it must necessarily be the +same to all. For suppose it otherwise, and that the MINIMUM VISIBILE of a +mite, for instance, be less than the MINIMUM VISIBILE of a man: the +latter therefore may by detraction of some part be made equal to the +former: it doth therefore consist of parts, which is inconsistent with +the notion of a MINIMUM VISIBILE or point. + +81. It will perhaps be objected that the MINIMUM VISIBILE of a man doth +really and in itself contain parts whereby it surpasses that of a mite, +though they are not perceivable by the man. To which I answer, the +MINIMUM VISIBILE having (in like manner as all other the proper and +immediate objects of sight) been shown not to have any existence without +the mind of him who sees it, it follows there cannot be any pan of it +that is not actually perceived, and therefore visible. Now for any object +to contain distinct visible parts, and at the same time to be a MINIMUM +VISIBILE, is a manifest contradiction. + +82. Of these visible points we see at all times an equal number. It is +every whit as great when our view is contracted and bounded by near +objects as when it is extended to larger and remoter. For it being +impossible that one MINIMUM VISIBILE should obscure or keep out of sight +mote than one other, it is a plain consequence that when my view is on +all sides bounded by the walls of my study see just as many visible +points as I could, in case that by the removal of the study-walls and all +other obstructions, I had a full prospect of the circumjacent fields, +mountains, sea, and open firmament: for so long as I am shut up within +the walls, by their interposition every point of the external objects is +covered from my view: but each point that is seen being able to cover or +exclude from sight one only other corresponding point, it follows that +whilst my sight is confined to those narrow walls I see as many points, +or MINIMA VISIBILIA, as I should were those walls away, by looking on all +the external objects whose prospect is intercepted by them. Whenever +therefore we are said to have a greater prospect at one time than +another, this must be understood with relation, not to the proper and +immediate, but the secondary and mediate objects of vision, which, as +hath been shown, properly belong to the touch. + +83. The visive faculty considered with reference to its immediate objects +may be found to labour of two defects. FIRST, in respect of the extent or +number of visible points that are at once perceivable by it, which is +narrow and limited to a certain degree. It can take in at one view but a +certain determinate number of MINIMA VISIBILIA, beyond which it cannot +extend its prospect. Secondly, our sight is defective in that its view is +not only narrow, but also for the most part confused: of those things +that we take in at one prospect we can see but a few at once clearly and +unconfusedly: and the more we fix our sight on any one object, by so much +the darker and more indistinct shall the rest appear. + +84. Corresponding to these two defects of sight, we may imagine as many +perfections, to wit, 1ST, that of comprehending in one view a greater +number of visible points. 2DLY, of being able to view them all equally +and at once with the utmost clearness and distinction. That those +perfections are not actually in some intelligences of a different order +and capacity from ours it is impossible for us to know. + +85. In neither of those two ways do microscopes contribute to the +improvement of sight; for when we look through a microscope we neither +see more visible points, nor are the collateral points more distinct than +when we look with the naked eye at objects placed in a due distance. A +microscope brings us, as it were, into a new world: it presents us with a +new scene of visible objects quite different from what we behold with the +naked eye. But herein consists the most remarkable difference, to wit, +that whereas the objects perceived by the eye alone have a certain +connexion with tangible objects, whereby we are taught to foresee what +will ensue upon the approach or application of distant objects to the +parts of our own body, which much conduceth to its preservation, there is +not the like connexion between things tangible and those visible objects +that are perceived by help of a fine microscope. + +86. Hence it is evident that were our eyes turned into the nature of +microscopes, we should not be much benefited by the change; we should be +deprived of the forementioned advantage we at present receive by the +visive faculty, and have left us only the empty amusement of seeing, +without any other benefit arising from it. But in that case, it will +perhaps be said, our sight would be endued with a far greater sharpness +and penetration than it now hath. But it is certain from what we have +already shown that the MINIMUM VISIBILE is never greater or lesser, but +in all cases constantly the same: and in the case of microscopical eyes I +see only this difference, to wit, that upon the ceasing of a certain +observable connexion betwixt the divers perceptions of sight and touch, +which before enabled us to regulate our actions by the eye, it would now +be rendered utterly unserviceable to that purpose. + +87. Upon the whole it seems that if we consider the use and end of sight, +together with the present state and circumstances of our being, we shall +not find any great cause to complain of any defect or imperfection in it, +or easily conceive how it could be mended. With such admirable wisdom is +that faculty contrived, both for the pleasure and convenience of life. + +88. Having finished what I intended to say concerning the distance and +magnitude of objects, I come now to treat of the manner wherein the mind +perceives by sight their situation. Among the discoveries of the last +age, it is reputed none of the least that the manner of vision hath been +more clearly explained than ever it had been before. There is at this day +no one ignorant that the pictures of external objects are painted on the +RETINA, or fund of the eye: that we can see nothing which is not so +painted: and that, according as the picture is more distinct or confused, +so also is the perception we have of the object: but then in this +explication of vision there occurs one mighty difficulty. The objects are +painted in an inverted order on the bottom of the eye: the upper part of +any object being painted on the lower part of the eye, and the lower part +of the object on the upper part of the eye: and so also as to right and +left. Since therefore the pictures are thus inverted, it is demanded how +it comes to pass that we see the objects erect and in their natural +posture? + +89. In answer to this difficulty we are told that the mind, perceiving an +impulse of a ray of light on the upper part of the eye, considers this +ray as coming in a direct line from the lower part of the object; and in +like manner tracing the ray that strikes on the lower part of the eye, it +is directed to the upper part of the object. Thus in the adjacent figure, +C, the lower point of the object ABC, is projected on C the upper part of +the eye. So likewise the highest point A is projected on A the lowest +part of the eye, which makes the representation CBA inverted: but the +mind considering the stroke that is made on C as coming in the straight +line CC from the lower end of the object; and the stroke or impulse on a +as coming in the line AA from the upper end of the object, is directed to +make a right judgment of the situation of the object ABC, notwithstanding +the picture of it is inverted. This is illustrated by conceiving a blind +man who, holding in his hands two sticks that cross each other, doth with +them touch the extremities of an object, placed in a perpendicular +situation. It is certain this man will judge that to be the upper part of +the object which he touches with the stick held in the undermost hand, +and that to be the lower part of the object which he touches with the +stick in his uppermost hand. This is the common explication of the erect +appearance of objects, which is generally received and acquiesced in, +being (as Mr. Molyneux tells us [Diopt. par. 2. c. 7. P. 289.]) 'allowed +by all men as satisfactory'. + +90. But this account to me does not seem in any degree true. Did I +perceive those impulses, decussations, and directions of the rays of +light in like manner as hath been set forth, then indeed it would not be +altogether void of probability. And there might be some pretence for the +comparison of the blind man and his cross sticks. But the case is far +otherwise. I know very well that I perceive no such thing. And of +consequence I cannot thereby make an estimate of the situation of +objects. I appeal to anyone's experience, whether he be conscious to +himself that he thinks on the intersection made by the radious [SIC] +pencils, or pursues the impulses they give in right lines, whenever he +perceives by sight the position of any object? To me it seems evident +that crossing and tracing of the rays is never thought on by children, +idiots, or in truth by any other, save only those who have applied +themselves to the study of optics. And for the mind to judge of the +situation of objects by those things without perceiving them, or to +perceive them without knowing it, is equally beyond my comprehension. Add +to this that the explaining the manner of vision by the example of cross +sticks and hunting for the object along the axes of the radious pencils, +doth suppose the proper objects of sight to be perceived at a distance +from us, contrary to what hath been demonstrated. + +91. It remains, therefore, that we look for some other explication of +this difficulty: and I believe it not impossible to find one, provided we +examine it to the bottom, and carefully distinguish between the ideas of +sight and touch; which cannot be too oft inculcated in treating of +vision: but more especially throughout the consideration of this affair +we ought to carry that distinction in our thoughts: for that from want of +a right understanding thereof the difficulty of explaining erect vision +seems chiefly to arise. + +92. In order to disentangle our minds from whatever prejudices we may +entertain with relation to the subject in hand, nothing seems more +apposite than the taking into our thoughts the case of one born blind, +and afterwards, when grown up, made to see. And though, perhaps, it may +not be an easy task to divest ourselves entirely of the experience +received from sight, so as to be able to put our thoughts exactly in the +posture of such a one's, we must, nevertheless, as far as possible, +endeavour to frame true conceptions of what might reasonably be supposed +to pass in his mind. + +93. It is certain that a man actually blind, and who had continued so +from his birth, would by the sense of feeling attain to have ideas of +upper and lower. By the motion of his hand he might discern the situation +of any tangible object placed within his FI reach. That part on which he +felt himself supported, or towards which he perceived his body to +gravitate, he would term lower, and the contrary to this upper; and +accordingly denominate whatsoever objects he touched. + +94. But then, whatever judgments he makes concerning the situation of +objects are confined to those only that are perceivable by touch. All +those things that are intangible and of a spiritual nature, his thoughts +and desires, his passions, and in general all the modifications of the +soul, to these he would never apply the terms UPPER and LOWER, except +only in a metaphorical sense. He may, perhaps, by way of allusion, speak +of high or low thoughts: but those terms in their proper signification +would never be applied to anything that was not conceived to exist +without the mind. For a man born blind, and remaining in the same state, +could mean nothing else by the words HIGHER and LOWER than a greater or +lesser distance from the earth; which distance he would measure by the +motion or application of his hand or some other part of his body. It is +therefore evident that all those things which, in respect of each other, +would by him be thought higher or lower, must be such as were conceived +to exist without his mind, in the ambient space. + +95. Whence it plainly follows that such a one, if we suppose him made to +see, would not at first sight think anything he saw was high or low, +erect or inverted; for it hath been already demonstrated in sect. 41 that +he would not think the things he perceived by sight to be at any distance +from him, or without his mind. The objects to which he had hitherto been +used to apply the terms UP and DOWN, HIGH and LOW, were such only as +affected or were some way perceived by his couch: but the proper objects +of vision make a new set of ideas, perfectly distinct and different from +the former, and which can in no sort make themselves perceived by touch. +There is, therefore, nothing at all that could induce him to think those +terms applicable to them: nor would he ever think it till such time as he +had observed their connexion with tangible objects, and the same +prejudice began to insinuate itself into his understanding, which from +their infancy had grown up in the understandings of other men. + +96. To set this matter in a clearer light I shall make use of an example. +Suppose the above-mentioned blind person by his touch perceives a man to +stand erect. Let us inquire into the manner of this. By the application +of his hand to the several parts of a human body he had perceived +different tangible ideas, which being collected into sundry complex ones, +have distinct names annexed to them. Thus one combination of a certain +tangible figure, bulk, and consistency of parts is called the head, +another the hand, a third the foot, and so of the rest: all which complex +ideas could, in his understanding, be made up only of ideas perceivable +by touch. He had also by his touch obtained an idea of earth or ground, +towards which he perceives the parts of his body to have a natural +tendency. Now, by ERECT nothing more being meant than that perpendicular +position of a man wherein his feet are nearest to the earth, if the blind +person by moving his hand over the parts of the man who stands before him +perceives the tangible ideas that compose the head to be farthest from, +and those that compose the feet to be nearest to, that other combination +of tangible ideas which he calls earth, he will denominate that man +erect. But if we suppose him on a sudden to receive his sight, and that +he behold a man standing before him, it is evident in that case he would +neither judge the man he sees to be erect nor inverted; for he never +having known those terms applied to any other save tangible things, or +which existed in the space without him, and what he sees neither being +tangible nor perceived as existing without, he could not know that in +propriety of language they were applicable to it. + +97. Afterwards, when upon turning his head or eyes up and down to the +right and left he shall observe the visible objects to change, and shall +also attain to know that they are called by the same names, and connected +with the objects perceived by touch; then indeed he will come to speak of +them and their situation, in the same terms that he has been used to +apply to tangible things; and those that he perceives by turning up his +eyes he will call upper, and those that by turning down his eyes he will +call lower. + +98. And this seems to me the true reason why he should think those +objects uppermost that are painted on the lower part of his eye: for by +turning the eye up they shall be distinctly seen; as likewise those that +are painted on the highest part of the eye shall be distinctly seen by +turning the eye down, and are for that reason esteemed lowest; for we +have shown that to the immediate objects of sight considered in +themselves, he would not attribute the terms HIGH and LOW. It must +therefore be on account of some circumstances which are observed to +attend them: and these, it is plain, are the actions of turning the eye +up and down, which suggest a very obvious reason why the mind should +denominate the objects of sight accordingly high or low. And without this +motion of the eye, this turning it up and down in order to discern +different objects, doubtless ERECT, INVERSE, and other the like terms +relating to the position of tangible objects, would never have been +transferred, or in any degree apprehended to belong to the ideas of +sight: the mere act of seeing including nothing in it to that purpose; +whereas the different situations of the eye naturally direct the mind to +make a suitable judgment of the situation of objects intromitted by it. + +99. Farther, when he has by experience learned the connexion there is +between the several ideas of sight and touch, he will be able, by the +perception he has of the situation of visible things in respect of one +another, to make a sudden and true estimate of the situation of outward, +tangible things corresponding to them. And thus it is he shall perceive +by sight the situation of external objects which do not properly fall +under that sense. + +100. I know we are very prone to think that, if just made to see, we +should judge of the situation of visible things as we do now: but we are +also as prone to think that, at first sight, we should in the same way +apprehend the distance and magnitude of objects as we do now: which hath +been shown to be a false and groundless persuasion. And for the like +reasons the same censure may be passed on the positive assurance that +most men, before they have thought sufficiently of the matter, might have +of their being able to determine by the eye at first view, whether +objects were erect or inverse. + +101. It will, perhaps, be objected co our opinion that a man, for +instance, being thought erect when his feet are next the earth, and +inverted when his head is next the earth, it doth hence follow that by +the mere act of vision, without any experience or altering the situation +of the eye, we should have determined whether he were erect or inverted: +for both the earth itself, and the limbs of the man who stands thereon, +being equally perceived by sight, one cannot choose seeing what part of +the man is nearest the earth, and what part farthest from it, i.e. +whether he be erect or inverted. + +102. To which I answer, the ideas which constitute the tangible earth and +man are entirely different from those which constitute the visible earth +and man. Nor was it possible, by virtue of the visive faculty alone, +without superadding any experience of touch, or altering the position of +the eye, ever to have known, or so much as suspected, there had been any +relation or connexion between them. Hence a man at first view would not +denominate anything he saw earth, or head, or foot; and consequently he +could not tell by the mere act of vision whether the head or feet were +nearest the earth: nor, indeed, would we have thereby any thought of +earth or man, erect or inverse, at all: which will be made yet more +evident if we nicely observe, and make a particular comparison between, +the ideas of both senses. + +103. That which I see is only variety of light and colours. That which I +feel is hard or soft, hot or cold, rough or smooth. What similitude, what +connexion have those ideas with these? Or how is it possible that anyone +should see reason to give one and the same name to combinations of ideas +so very different before he had experienced their coexistence? We do not +find there is any necessary connexion betwixt this or that tangible +quality and any colour whatsoever. And we may sometimes perceive colours +where there is nothing to be felt. All which doth make it manifest that +no man, at first receiving of his sight, would know there was any +agreement between this or that particular object of his sight and any +object of touch he had been already acquainted with: the colours, +therefore, of the head would to him no more suggest the idea of head than +they would the idea of foot. + +104. Farther, we have at large shown (VID. sect. 63 and 64) there is no +discoverable necessary connexion between any given visible magnitude and +any one particular tangible magnitude; but that it is entirely the result +of custom and experience, and depends on foreign and accidental +circumstances that we can by the perception of visible extension inform +ourselves what may be the extension of any tangible object connected with +it. Hence it is certain that neither the visible magnitude of head or +foot would bring along with them into the mind, at first opening of the +eyes, the respective tangible magnitudes of those parts. + +105. By the foregoing section it is plain the visible figure of any part +of the body hath no necessary connexion with the tangible figure thereof, +so as at first sight to suggest it to the mind. For figure is the +termination of magnitude; whence it follows that no visible magnitude +having in its own nature an aptness to suggest any one particular +tangible magnitude, so neither can any visible figure be inseparably +connected with its corresponding tangible figure: so as of itself and in +a way prior to experience, it might suggest it to the understanding. This +will be farther evident if we consider that what seems smooth and round +to the touch may to sight, if viewed through a microscope, seem quite +otherwise. + +106. From all which laid together and duly considered, we may clearly +deduce this inference. In the first act of vision no idea entering by the +eye would have a perceivable connexion with the ideas to which the names +EARTH, MAN, HEAD, FOOT, etc., were annexed in the understanding of a +person blind from his birth; so as in any sort to introduce them into his +mind, or make themselves be called by the same names, and reputed the +same things with them, as afterwards they come to be. + +107. There doth, nevertheless, remain one difficulty, which perhaps may +seem to press hard on our opinion, and deserve not to be passed over: for +though it be granted that neither the colour, size, nor figure of the +visible feet have any necessary connexion with the ideas that compose the +tangible feet, so as to bring them at first sight into my mind, or make +me in danger of confounding them before I had been used to, and for some +time experienced their connexion: yet thus much seems undeniable, namely, +that the number of the visible feet being the same with that of the +tangible feet, I may from hence without any experience of sight +reasonably conclude that they represent or are connected with the feet +rather than the head. I say, it seems the idea of two visible feet will +sooner suggest to the mind the idea of two tangible feet than of one +head; so that the blind man upon first reception of the visive faculty +might know which were the feet or two, and which the head or one. + +108. In order to get clear of this seeming difficulty we need only +observe that diversity of visible objects doth not necessarily infer +diversity of tangible objects corresponding to them. A picture painted +with great variety of colours affects the touch in one uniform manner; it +is therefore evident that I do not by any necessary consecution, +independent of experience, judge of the number of things tangible from +the number of things visible. I should not, therefore, at first opening +my eyes conclude that because I see two I shall feel two. How, therefore, +can I, before experience teaches me, know that the visible legs, because +two, are connected with the tangible legs, or the visible head, because +one, is connected with the tangible head? The truth is, the things I see +are so very different and heterogeneous from the things I feel that the +perception of the one would never have suggested the other to my +thoughts, or enabled me to pass the least judgment thereon, until I had +experienced their connexion. + +109. But for a fuller illustration of this matter it ought to be +considered that number (however some may reckon it amongst the primary +qualities) is nothing fixed and settled, really existing in things +themselves. It is entirely the creature of the mind, considering either +an idea by itself, or any combination of ideas to which it gives one +name, and so makes it pass for an unit. According as the mind variously +combines its ideas the unit varies: and as the unit, so the number, which +is only a collection of units, doth also vary. We call a window one, a +chimney one, and yet a house in which there are many windows and many +chimneys hath an equal right to be called one, and many houses go to the +making of the city. In these and the like, instances it is evident the +unit constantly relates to the particular draughts the mind makes of its +ideas, to which it affixes names, and wherein it includes more or less as +best suits its own ends and purposes. Whatever, therefore, the mind +considers as one, that is an unit. Every combination of ideas is +considered as one thing by the mind, and in token thereof is marked by +one name. Now, this naming and combining together of ideas is perfectly +arbitrary, and done by the mind in such sort as experience shows it to be +most convenient: without which our ideas had never been collected into +such sundry distinct combinations as they now are. + +110. Hence it follows that a man born blind and afterwards, when grown +up, made to see, would not in the first act of vision parcel out the +ideas of sight into the same distinct collections that others do, who +have experienced which do regularly coexist and are proper to be bundled +up together under one name. He would not, for example, make into one +complex idea, and thereby esteem an unit, all those particular ideas +which constitute the visible head or foot. For there can be no reason +assigned why he should do so, barely upon his seeing a man stand upright +before him. There crowd into his mind the ideas which compose the visible +man, in company with all the other ideas of sight perceived at the same +time: but all these ideas offered at once to his view, he would not +distribute into sundry distinct combinations till such time as by +observing the motion of the parts of the man and other experiences he +comes to know which are to be separated and which to be collected +together. + +111. From what hath been premised it is plain the objects of sight and +touch make, if I may so say, two sets of ideas which are widely different +from each other. To objects of either kind we indifferently attribute the +terms high and low, right and left, and suchlike, denoting the position +or situation of things: but then we must well observe that the position +of any object is determined with respect only to objects of the same +sense. We say any object of touch is high or low, according as it is more +or less distant from the tangible earth: and in like manner we denominate +any object of sight high or low in proportion as it is more or less +distant from the visible earth: but to define the situation of visible +things with relation to the distance they bear from any tangible thing, +or VICE VERSA, this were absurd and perfectly unintelligible. For all +visible things are equally in the mind, and take up no part of the +external space: and consequently are equidistant from any tangible thing +which exists without the mind. + +112. Or rather, to speak truly, the proper objects of sight are at no +distance, neither near nor far, from any tangible thing. For if we +inquire narrowly into the matter we shall find that those things only are +compared together in respect of distance which exist after the same +manner, or appertain unto the same sense. For by the distance between any +two points nothing more is meant than the number of intermediate points: +if the given points are visible the distance between them is marked out +by the number of the interjacent visible points: if they are tangible, +the distance between them is a line consisting of tangible points; but if +they are one tangible and the other visible, the distance between them +doth neither consist of points perceivable by sight nor by touch, i.e. it +is utterly inconceivable. This, perhaps, will not find an easy admission +into all men's understanding: however, I should gladly be informed +whether it be not true by anyone who will be at the pains to reflect a +little and apply it home to his thoughts. + +113. The not observing what has been delivered in the two last sections +seems to have occasioned no small part of the difficulty that occurs in +the business of erect appearances. The head, which is painted nearest the +earth, seems to be farthest from it: and on the other hand the feet, +which are painted farthest from the earth, are thought nearest to it. +Herein lies the difficulty, which vanishes if we express the thing more +clearly and free from ambiguity, thus: how comes it that to the eye the +visible head which is nearest the tangible earth seems farthest from the +earth, and the visible feet, which are farthest from the tangible earth +seem nearest the earth? The question being thus proposed, who sees not +the difficulty is founded on a supposition that the eye, or visive +faculty, or rather the soul by means thereof, should judge of the +situation of visible objects with reference to their distance from the +tangible earth? Whereas it is evident the tangible earth is not perceived +by sight: and it hath been shown in the two last preceding sections that +the location of visible objects is determined only by the distance they +bear from one another; and that it is nonsense to talk of distance, far +or near, between a visible and tangible thing. + +114. If we confine our thoughts to the proper objects of sight, the whole +is plain and easy. The head is painted farthest from, and the feet +nearest to, the visible earth; and so they appear to be. What is there +strange or unaccountable in this? Let us suppose the pictures in the fund +of the eye to be the immediate objects of the sight. The consequence is +that things should appear in the same posture they are painted in; and is +it not so? The head which is seen seems farthest from the earth which is +seen; and the feet which are seen seem nearest to the earth, which is +seen; and just so they are painted. + +115. But, say you, the picture of the man is inverted, and yet the +appearance is erect: I ask, what mean you by the picture of the man, or, +which is the same thing, the visible man's being inverted? You tell me it +is inverted, because the heels are uppermost and the head undermost? +Explain me this. You say that by the head's being undermost you mean that +it is nearest to the earth; and by the heels being uppermost that they +are farthest from the earth. I ask again what earth you mean? You cannot +mean the earth that is painted on the eye, or the visible earth: for the +picture of the head is farthest from the picture of the earth, and the +picture of the feet nearest to the picture of the earth; and accordingly +the visible head is farthest from the visible earth, and the visible feet +nearest to it. It remains, therefore, that you mean the tangible earth, +and so determine the situation of visible things with respect to tangible +things; contrary to what hath been demonstrated in sect. 111 and 112. The +two distinct provinces of sight and touch should be considered apart, and +as if their objects had no intercourse, no manner of relation one to +another, in point of distance or position. + +116. Farther, what greatly contributes to make us mistake in this matter +is that when we think of the pictures in the fund of the eye, we imagine +ourselves looking on the fund of another's eye, or another looking on the +fund of our own eye, and beholding the pictures painted thereon. Suppose +two eyes A and B: A from some distance looking on the pictures in B sees +them inverted, and for that reason concludes they are inverted in B: but +this is wrong. There are projected in little on the bottom of A the +images of the pictures of, suppose, man, earth, etc., which are painted +on B. And besides these the eye B itself, and the objects which environ +it, together with another earth, are projected in a larger size on A. +Now, by the eye A these larger images are deemed the true objects, and +the lesser only pictures in miniature. And it is with respect to those +greater images that it determines the situation of the smaller images: so +that comparing the little man with the great earth, A judges him +inverted, or that the feet are farthest from and the head nearest to the +great earth. Whereas, if A compare the little man with the little earth, +then he will appear erect, i.e. his head shall seem farthest from, and +his feet nearest to, the little earth. But we must consider that B does +not see two earths as A does: it sees only what is represented by the +little pictures in A, and consequently shall judge the man erect. For, in +truth, the man in B is not inverted, for there the feet are next the +earth; but it is the representation of it in A which is inverted, for +there the head of the representation of the picture of the man in B is +next the earth, and the feet farthest from the earth, meaning the earth +which is without the representation of the pictures in B. For if you take +the little images of the pictures in B, and consider them by themselves, +and with respect only to one another, they are all erect and in their +natural posture. + +117. Farther, there lies a mistake in our imagining that the pictures of +external objects are painted on the bottom of the eye. It hath been shown +there is no resemblance BETWEEN the ideas of sight and things tangible. +It hath likewise been demonstrated that the proper objects of sight do +not exist without the mind. Whence it clearly follows that the pictures +painted on the bottom of the eye are not the pictures of external +objects. Let anyone consult his own thoughts, and then say what affinity, +what likeness there is between that certain variety and disposition of +colours which constitute the visible man, or picture of a man, and that +other combination of far different ideas, sensible by touch, which +compose the tangible man. But if this be the case, how come they to be +accounted pictures or images, since that supposes them to copy or +represent some originals or other? + +118. To which I answer: in the forementioned instance the eye A takes the +little images, included within the representation of the other eye B, to +be pictures or copies, whereof the archetypes are not things existing +without, but the larger pictures projected on its own fund: and which by +A are not thought pictures, but the originals, or true things themselves. +Though if we suppose a third eye C from a due distance to behold the fund +of A, then indeed the things projected thereon shall, to C, seem pictures +or images in the same sense that those projected on B do to A. + +119. Rightly to conceive this point we must carefully distinguish between +the ideas of sight and touch, between the visible and tangible eye; for +certainly on the tangible eye nothing either is or seems to be painted. +Again, the visible eye, as well as all other visible objects, hath been +shown to exist only in the mind, which perceiving its own ideas, and +comparing them together, calls some PICTURES in respect of others. What +hath been said, being rightly comprehended and laid together, doth, I +think, afford a full and genuine explication of the erect appearance of +objects; which phenomenon, I must confess, I do not see how it can be +explained by any theories of vision hitherto made public. + +120. In treating of these things the use of language is apt to occasion +some obscurity and confusion, and create in us wrong ideas; for language +being accommodated to the common notions and prejudices of men, it is +scarce possible to deliver the naked and precise truth without great +circumlocution, impropriety, and (to an unwary reader) seeming +contradictions; I do therefore once for all desire whoever shall think it +worth his while to understand what I have written concerning vision, that +he would not stick in this or that phrase, or manner of expression, but +candidly collect my meaning from the whole sum and tenor of my discourse, +and laying aside the words as much as possible, consider the bare notions +themselves, and then judge whether they are agreeable to truth and his +own experience, or no. + +121. We have shown the way wherein the mind by mediation of visible ideas +doth perceive or apprehend the distance, magnitude and situation of +tangible objects. We come now to inquire more particularly concerning the +difference between the ideas of sight and touch, which are called by the +same names, and see whether there be any idea common to both senses. From +what we have at large set forth and demonstrated in the foregoing parts +of this treatise, it is plain there is no one selfsame numerical +extension perceived both by sight and touch; but that the particular +figures and extensions perceived by sight, however they may be called by +the same names and reputed the same things with those perceived by touch, +are nevertheless different, and have an existence distinct and separate +from them: so that the question is not now concerning the same numerical +ideas, but whether there be any one and the same sort of species of ideas +equally perceivable to both senses; or, in other words, whether +extension, figure, and motion perceived by sight are not specifically +distinct from extension, figure, and motion perceived by touch. + +122. But before I come more particularly to discuss this matter, I find +it proper to consider extension in abstract: for of this there is much +talk, and I am apt to think that when men speak of extension as being an +idea common to two senses, it is with a secret supposition that we can +single out extension from all other tangible and visible qualities, and +form thereof an abstract idea, which idea they will have common both to +sight and touch. We are therefore to understand by extension in abstract +an idea of extension, for instance, a line or surface entirely stripped +of all other sensible qualities and circumstances that might determine it +to any particular existence; it is neither black nor white, nor red, nor +hath it any colour at all, or any tangible quality whatsoever and +consequently it is of no finite determinate magnitude: for that which +bounds or distinguishes one extension from another is some quality or +circumstance wherein they disagree. + +123. Now I do not find that I can perceive, imagine, or any wise frame in +my mind such an abstract idea as is here spoken of. A line or surface +which is neither black, nor white, nor blue, nor yellow, etc., nor long, +nor short, nor rough, nor smooth, nor square, nor round, etc., is +perfectly incomprehensible. This I am sure of as to myself: how far the +faculties of other men may reach they best can tell. + +124. It is commonly said that the object of geometry is abstract +extension: but geometry contemplates figures: now, figure is the +termination of magnitude: but we have shown that extension in abstract +hath no finite determinate magnitude. Whence it clearly follows that it +can have no figure, and consequently is not the object of geometry. It is +indeed a tenet as well of the modern as of the ancient philosophers that +all general truths are concerning universal abstract ideas; without +which, we are told, there could be no science, no demonstration of any +general proposition in geometry. But it were no hard matter, did I think +it necessary to my present purpose, to show that propositions and +demonstrations in geometry might be universal, though they who make them +never think of abstract general ideas of triangles or circles. + +125. After reiterated endeavours to apprehend the general idea a +triangle, I have found it altogether incomprehensible. And surely if +anyone were able to introduce that idea into my mind, it must be the +author of the ESSAY CONCERNING HUMAN UNDERSTANDING; he who has so far +distinguished himself from the generality of writers by the clearness +and significancy of what he says. Let us therefore see how this +celebrated author describes the general or abstract idea of a triangle. +'It must be (says he) neither oblique nor rectangular, neither +equilateral, equicrural, nor scalenum; but all and none of these at once. +In effect, it is somewhat imperfect that cannot exist; an idea, wherein +some parts of several different and inconsistent ideas are put together' +ESSAY ON HUM. UNDERSTAND. B. iv. C. 7. S.9. This is the idea which he +thinks needful for the enlargement of knowledge, which is the subject of +mathematical demonstration, and without which we could never come to know +any general proposition concerning triangles. That author acknowledges it +doth 'require some pains and skill to form this general idea of a +triangle.' IBID. But had he called to mind what he says in another place, +to wit, 'That ideas of mixed modes wherein any inconsistent ideas are put +together cannot so much as exist in the mind, i.e. be conceived.' VID. B. +iii. C. 10. S. 33. IBID. I say, had this occurred to his thoughts, it is +not improbable he would have owned it above all the pains and skill he +was master of to form the above-mentioned idea of a triangle, which is +made up of manifest, staring contradictions. That a man who laid so great +a stress on clear and determinate ideas should nevertheless talk at this +rate seems very surprising. But the wonder will lessen if it be +considered that the source whence this opinion flows is the prolific womb +which has brought forth innumerable errors and difficulties in all parts +of philosophy and in all the sciences: but this matter, taken in its full +extent, were a subject too comprehensive to be insisted on in this place. +And so much for extension in abstract. + +126. Some, perhaps, may think pure space, VACUUM, or trine dimension to +be equally the object of sight and touch: but though we have a very great +propension to think the ideas of outness and space to be the immediate +object of sight, yet, if I mistake not, in the foregoing parts of this +essay that hath been clearly demonstrated to be a mere delusion, arising +from the quick and sudden suggestion of fancy, which so closely connects +the idea of distance with those of sight, that we are apt to think it is +itself a proper and immediate object of that sense till reason corrects +the mistake. + +127. It having been shown that there are no abstract ideas of figure, and +that it is impossible for us by any precision of thought to frame an idea +of extension separate from all other visible and tangible qualities which +shall be common both to sight and touch: the question now remaining is, +whether the particular extensions, figures, and motions perceived by +sight be of the same kind with the particular extensions, figures, and +motions perceived by touch? In answer to which I shall venture to lay +down the following proposition: THE EXTENSION, FIGURES, AND MOTIONS +PERCEIVED BY SIGHT ARE SPECIFICALLY DISTINCT FROM THE IDEAS OF TOUCH +CALLED BY THE SAME NAMES, NOR is THERE ANY SUCH THING as ONE IDEA OR KIND +OF IDEA COMMON TO BOTH SENSES. This proposition may without much +difficulty be collected from what hath been said in several places of +this essay. But because it seems so remote from, and contrary to, the +received notions and settled opinion of mankind, I shall attempt to +demonstrate it more particularly and at large by the following arguments. + +128. When upon perception of an idea I range it under this or that sort, +it is because it is perceived after the same manner, or because it has a +likeness or conformity with, or affects me in the same way as, the ideas +of the sort I rank it under. In short, it must not be entirely new, but +have something in it old and already perceived by me. It must, I say, +have so much at least in common with the ideas I have before known and +named as to make me give it the same name with them. But it has been, if +I mistake not, clearly made out that a man born blind would not at first +reception of his sight think the things he saw were of the same nature +with the objects of touch, or had anything in common with them; but that +they were a new set of ideas, perceived in a new manner, and entirely +different from all he had ever perceived before: so that he would not +call them by the same name, nor repute them to be of the same sort with +anything he had hitherto known. + +129. SECONDLY, light and colours are allowed by all to constitute a son +or species entirely different from the ideas of touch: nor will any man, +I presume, say they can make themselves perceived by that sense: but +there is no other immediate object of sight besides light and colours. It +is therefore a direct consequence that there is no idea common to both +senses. + +130. It is a prevailing opinion, even amongst those who have thought and +writ most accurately concerning our ideas and the ways whereby they enter +into the understanding, that something more is perceived by sight than +barely light and colours with their variations. Mr. Locke termeth sight, +'The most comprehensive of all our senses, conveying to our minds the +ideas of light and colours, which are peculiar only to that sense; and +also the far different ideas of space, figure, and motion. ESSAY ON HUMAN +UNDERSTAND. B. ii. C. 9. S. 9. Space or distance, we have shown, is not +otherwise the object of sight than of hearing. VID. sect. 46. And as for +figure and extension, I leave it to anyone that shall calmly attend to +his own clear and distinct ideas to decide whether he had any idea +intromitted immediately and properly by sight save only light and +colours: or whether it De possible for him to frame in his mind a +distinct abstract idea of visible extension or figure exclusive of all +colour: and on the other hand, whether he can conceive colour without +visible extension? For my own part, I must confess I am not able to +attain so great a nicety of abstraction: in a strict sense, I see nothing +but light and colours, with their several shades and variations. He who +beside these doth also perceive by sight ideas far different and distinct +from them hath that faculty in a degree more perfect and comprehensive +than I can pretend to. It must be owned that by the mediation of light +and colours other far different ideas are suggested to my mind: but so +they are by hearing, which beside sounds which are peculiar to that +sense, doth by their mediation suggest not only space, figure, and +motion, but also all other ideas whatsoever that can be signified by +words. + +131. THIRDLY, it is, I think, an axiom universally received that +quantities of the same kind may be added together and make one entire +sum. Mathematicians add lines together: but they do not add a line to a +solid, or conceive it as making one sum with a surface: these three kinds +of quantity being thought incapable of any such mutual addition, and +consequently of being compared together in the several ways of +proportion, are by then esteemed entirely disparate and heterogeneous. +Now let anyone try in his thoughts to add a visible line or surface to a +tangible line or surface, so as to conceive them making one continued sum +or whole. He that can do this may think them homogeneous: but he that +cannot, must by the foregoing axiom think them heterogeneous. A blue and +a red line I can conceive added together into one sum and making one +continued line: but to make in my thoughts one continued line of a +visible and tangible line added together is, I find, a task far more +difficult, and even insurmountable: and I leave it to the reflexion and +experience of every particular person to determine for himself. + +132. A farther confirmation of our tenet may be drawn from the solution +of Mr. Molyneux's problem, published by Mr. Locke in his ESSAY: which I +shall set down as it there lies, together with Mr. Locke's opinion of it, +'"Suppose a man born blind, and now adult, and taught by his touch to +distinguish between a cube and a sphere of the same metal, and nighly +[SIC] of the same bigness, so as to tell, when he felt one and t'other, +which is the cube and which the sphere. Suppose then the cube and sphere +placed on a table, and the blind man to be made to see: QUAERE, whether +by his sight, before he touched them, he could now distinguish and tell +which is the globe, which the cube?" To which the acute and judicious +proposer answers: "Not. For though he has obtained the experience of how +a globe, how a cube, affects his touch, yet he has not yet attained the +experience that what affects his touch so or so must affect his sight so +or so: or that a protuberant angle in the cube that pressed his hand +unequally shall appear to his eye as it doth in the cube." I agree with +this thinking gentleman, whom I am proud to call my friend, in his answer +to this his problem; and am of opinion that the blind man at first sight +would not be able with certainty to say which was the globe, which the +cube, whilst he only saw them.' (ESSAY ON HUMAN UNDERSTANDING, B. ii. C. +9. S. 8.) + +133. Now, if a square surface perceived by touch be of the same sort with +a square surface perceived by sight, it is certain the blind man here +mentioned might know a square surface as soon as he saw it: it is no more +but introducing into his mind by a new inlet an idea he has been already +well acquainted with. Since, therefore, he is supposed to have known by +his touch that a cube is a body terminated by square surfaces, and that a +sphere is not terminated by square surfaces: upon the supposition that a +visible and tangible square differ only IN NUMERO it follows that he +might know, by the unerring mark of the square surfaces, which was the +cube, and which not, while he only saw them. We must therefore allow +either that visible extension and figures are specifically distinct from +tangible extension and figures, or else that the solution of this problem +given by those two thoughtful and ingenious men is wrong. + +134. Much more might be laid together in proof of the proposition I have +advanced: but what has been said is, if I mistake not, sufficient to +convince anyone that shall yield a reasonable attention: and as for those +that will not be at the pains of a little thought, no multiplication of +words will ever suffice to make them understand the truth, or rightly +conceive my meaning. + +135. I cannot let go the above-mentioned problem without some reflexion +on it. It hath been evident that a man blind from his birth would not, at +first sight, denominate anything he saw by the names he had been used to +appropriate to ideas of touch, VID. sect. 106. Cube, sphere, table are +words he has known applied to things perceivable by touch, but to things +perfectly intangible he never knew them applied. Those words in their +wonted application always marked out to his mind bodies or solid things +which were perceived by the resistance they gave: but there is no +solidity, no resistance or protrusion, perceived by sight. In short, the +ideas of sight are all new perceptions, to which there be no names +annexed in his mind: he cannot therefore understand what is said to him +concerning them: and to ask of the two bodies he saw placed on the table, +which was the sphere, which the cube? were to him a question downright +bantering and unintelligible; nothing he sees being able to suggest to +his thoughts the idea of body, distance, or in general of anything he had +already known. + +136. It is a mistake to think the same thing affects both sight and +touch. If the same angle or square which is the object of touch be also +the object of vision, what should hinder the blind man at first sight +from knowing it? For though the manner wherein it affects the sight be +different from that wherein it affected his touch, yet, there being +beside his manner or circumstance, which is new and unknown, the angle or +figure, which is old and known, he cannot choose but discern it. + +137. Visible figure and extension having been demonstrated to be of a +nature entirely different and heterogeneous from tangible figure and +extension, it remains that we inquire concerning. Now that visible motion +is not of the same sort with tangible motion seems to need no farther +proof, it being an evident corollary from what we have shown concerning +the difference there is between visible and tangible extension: but for a +more full and express proof hereof we need only observe that one who had +not yet experienced vision would not at first sight know motion. Whence +it clearly follows that motion perceivable by sight is of a sort distinct +from motion perceivable by touch. The antecedent I prove thus: by touch +he could not perceive any motion but what was up or down, to the right or +left, nearer or farther from him; besides these and their several +varieties or complications, it is impossible he should have any idea of +motion. He would not therefore think anything to be motion, or give the +name motion to any idea which he could not range under some or other of +those particular kinds thereof. But from sect. 95 it is plain that by the +mere act of vision he could not know motion upwards or downwards, to the +right or left, or in any other possible direction. From which I conclude +he would not know motion at all at first sight. As for the idea of motion +in abstract, I shall not waste paper about it, but leave it to my reader +to make the best he can of it. To me it is perfectly unintelligible. + +138. The consideration of motion may furnish a new field for inquiry: but +since the manner wherein the mind apprehends by sight the motion of +tangible objects, with the various degrees thereof, may be easily +collected from what hath been said concerning the manner wherein that +sense doth suggest their various distances, magnitudes, and situations, I +shall not enlarge any farther on this subject, but proceed to consider +what may be alleged, with greatest appearance of reason, against the +proposition we have shown to be true. For where there is so much +prejudice to be encountered, a bare and naked demonstration of the truth +will scarce suffice. We must also satisfy the scruples that men may raise +in favour of their preconceived notions, show whence the mistake arises, +how it came to spread, and carefully disclose and root out those false +persuasions that an early prejudice might have implanted in the mind. + +139. FIRST, therefore, it will be demanded how visible extension and +figures come to be called by the same name with tangible extension and +figures, if they are not of the same kind with them? It must be something +more than humour or accident that could occasion a custom so constant and +universal as this, which has obtained in all ages and nations of the +world, and amongst all ranks of men, the learned as well as the +illiterate. + +140. To which I answer, we can no more argue a visible and tangible +square to be of the same species from their being called by the same +name, than we can that a tangible square and the monosyllable consisting +of six letters whereby it is marked are of the same species because they +are both called by the same name. It is customary to call written words +and the things they signify by the same name: for words not being +regarded in their own nature, or otherwise than as they are marks of +things, it had been superfluous, and beside the design of language, to +have given them names distinct from those of the things marked by them. +The same reason holds here also. Visible figures are the marks of +tangible figures, and from sect. 59 it is plain that in themselves they +are little regarded, or upon any other score than for their connexion +with tangible figures, which by nature they are ordained to signify. And +because this language of nature doth not vary in different ages or +nations, hence it is that in all times and places visible figures are +called by the same names as the respective tangible figures suggested by +them, and not because they are alike or of the same sort with them. + +141. But, say you, surely a tangible square is liker to a visible square +than to a visible circle: it has four angles and as many sides: so also +has the visible square: but the visible circle has no such thing, being +bounded by one uniform curve without right lines or angles, which makes +it unfit to represent the tangible square but very fit to represent the +tangible circle. Whence it clearly follows that visible figures are +patterns of, or of the same species with, the respective tangible figures +represented by them: that they are like unto them, and of their own +nature fitted to represent them, as being of the same sort: and that they +are in no respect arbitrary signs, as words. + +142. I answer, it must be acknowledged the visible square is fitter than +the visible circle to represent the tangible square, but then it is not +because it is liker, or more of a species with it, but because the +visible square contains in it several distinct parts, whereby to mark the +several distinct corresponding parts of a tangible square, whereas the +visible circle doth not. The square perceived by touch hath four +distinct, equal sides, so also hath it four distinct equal angles. It is +therefore necessary that the visible figure which shall be most proper to +mark it contain four distinct equal parts corresponding to the four sides +of the tangible square, as likewise four other distinct and equal parts +whereby to denote the four equal angles of the tangible square. And +accordingly we see the visible figures contain in them distinct visible +parts, answering to the distinct tangible parts of the figures signified +or suggested by them. + +143. But it will not hence follow that any visible figure is like unto, +or of the same species with, its corresponding tangible figure, unless it +be also shown that not only the number but also the kind of the parts be +the same in both. To illustrate this, I observe that visible figures +represent tangible figures much after the same manner that written words +do sounds. Now, in this respect words are not arbitrary, it not being +indifferent what written word stands for any sound: but it is requisite +that each word contain in it so many distinct characters as there are +variations in the sound it stands for. Thus the single letter A is proper +to mark one simple uniform sound; and the word ADULTERY is accommodated +to represent the sound annexed to it, in the formation whereof there +being eight different collisions or modifications of the air by the +organs of speech, each of which produces a difference of sound, it was +fit the word representing it should consist of as many distinct +characters, thereby to mark each particular difference or part of the +whole sound. And yet nobody, I presume, will say the single letter a, or +the word ADULTERY, are like unto, or of the same species with, the +respective sounds by them represented. It is indeed arbitrary that, in +general, letters of any language represent sounds at all: but when that +is once agreed, it is not arbitrary what combination of letters shall +represent this or that particular sound. I leave this with the reader to +pursue, and apply it in his own thoughts. + +144. It must be confessed that we are not so apt to confound other signs +with the things signified, or to think them of the same species, as we +are visible and tangible ideas. But a little consideration will show us +how this may be without our supposing them of a like nature. These signs +are constant and universal, their connexion with tangible ideas has been +learnt at our first entrance into the world; and ever since, almost every +moment of our lives, it has been occurring to our thoughts, and fastening +and striking deeper on our minds. When we observe that signs are +variable, and of human institution; when we remember there was a time +they were not connected in our minds with those things they now so +readily suggest; but that their signification was learned by the slow +steps of experience: this preserves us from confounding them. But when we +find the same signs suggest the same things all over the world; when we +know they are not of human institution, and cannot remember that we ever +learned their signification, but think that at first sight they would +have suggested to us the same things they do now: all this persuades us +they are of the same species as the things respectively represented by +them, and that it is by a natural resemblance they suggest them to our +minds. + +145. Add to this that whenever we make a nice survey of any object, +successively directing the optic axis to each point thereof, there are +certain lines and figures described by the motion of the head or eye, +which being in truth perceived by feeling, do nevertheless so mix +themselves, as it were, with the ideas of sight, that we can scarce think +but they appertain to that sense. Again, the ideas of sight enter into +the mind several at once, more distinct and unmingled than is usual in +the other senses beside the touch. Sounds, for example, perceived at the +same instant, are apt to coalesce, if I may so say, into one sound: but +we can perceive at the same time great variety of visible objects, very +separate and distinct from each other. Now tangible extension being made +up of several distinct coexistent parts, we may hence gather another +reason that may dispose us to imagine a likeness or an analogy between +the immediate objects of sight and touch. But nothing, certainly, doth +more contribute to blend and confound them together than the strict and +close connexion they have with each other. We cannot open our eyes but +the ideas of distance, bodies, and tangible figures are suggested by +them. So swift and sudden and unperceived is the transition from visible +to tangible ideas that we can scarce forbear thinking them equally the +immediate object of vision. + +146. The prejudice which is grounded on these, and whatever other causes +may be assigned thereof, sticks so fast that it is impossible without +obstinate striving and labour of the mind to get entirely clear of it. +But then the reluctancy we find in rejecting any opinion can be no +argument of its truth to whoever considers what has been already shown +with regard to the prejudices we entertain concerning the distance, +magnitude, and situation of objects; prejudices so familiar to our minds, +so confirmed and inveterate, as they will hardly give way to the clearest +demonstration. + +147. Upon the whole, I think we may fairly conclude that the proper +objects of vision constitute an universal language of the Author of +Nature, whereby we are instructed how to regulate our actions in order to +attain those things that are necessary to the preservation and well-being +of our bodies, as also to avoid whatever may be hurtful and destructive +of them. It is by their information that we are principally guided in all +the transactions and concerns of life. And the manner wherein they +signify and mark unto us the objects which are at a distance is the same +with that of languages and signs of human appointment, which do not +suggest the things signified by any likeness or identity of nature, but +only by an habitual connexion that experience has made us to observe +between them. + +148. Suppose one who had always continued blind be told by his guide that +after he has advanced so many steps he shall come to the brink of a +precipice, or be stopped by a wall; must not this to him seem very +admirable and surprizing? He cannot conceive how it is possible for +mortals to frame such predictions as these, which to him would seem as +strange and unaccountable as prophesy doth to others. Even they who are +blessed with the visive faculty may (though familiarity make it less +observed) find therein sufficient cause of admiration. The wonderful art +and contrivance wherewith it is adjusted to those ends and purposes for +which it was apparently designed, the vast extent, number, and variety of +objects that are at once with so much ease and quickness and pleasure +suggested by it: all these afford subject for much and pleasing +speculation, and may, if anything, give us some glimmering analogous +prenotion of things which are placed beyond the certain discovery and +comprehension of our present state. + +149. I do not design to trouble myself with drawing corollaries from the +doctrine I have hitherto laid down. If it bears the test others may, so +far as they shall think convenient, employ their thoughts in extending it +farther, and applying it to whatever purposes it may be subservient to: +only, I cannot forbear making some inquiry concerning the object of +geometry, which the subject we have been upon doth naturally lead one to. +We have shown there is no such idea as that of extension in abstract, and +that there are two kinds of sensible extension and figures which are +entirely distinct and heterogeneous from each other. Now, it is natural +to inquire which of these is the object of geometry. + +150. Some things there are which at first sight incline one to think +geometry conversant about visible extension. The constant use of the +eyes, both in the practical and speculative parts of that science, doth +very much induce us thereto. It would, without doubt, seem odd to a +mathematician to go about to convince him the diagrams he saw upon paper +were not the figures, or even the likeness of the figures, which make the +subject of the demonstration. The contrary being held an unquestionable +truth, not only by mathematicians, but also by those who apply themselves +more particularly to the study of logic; I mean, who consider the nature +of science, certainty, and demonstration: it being by them assigned as +one reason of the extraordinary clearness and evidence of geometry that +in this science the reasonings are free from those inconveniences which +attend the use of arbitrary signs, the very ideas themselves being copied +out and exposed to view upon paper. But, by the bye, how well this agrees +with what they likewise assert of abstract ideas being the object of +geometrical demonstration I leave to be considered. + +151. To come to a resolution in this point we need only observe what hath +been said in sect. 59, 60, 61, where it is shown that visible extensions +in themselves are little regarded, and have no settled determinable +greatness, and that men measure altogether, by the application of +tangible extension to tangible extension. All which makes it evident that +visible extension and figures are not the object of geometry. + +152. It is therefore plain that visible figure are of the same use in +geometry that words are: and the one may as well be accounted the object +of that science as the other, neither of them being otherwise concerned +therein than as they represent or suggest to the mind the particular +tangible figures connected with them. There is indeed this difference +between the signification of tangible figures by visible figures, and of +ideas by words: that whereas the latter is variable and uncertain, +depending altogether on the arbitrary appointment of men, the former is +fixed and immutably the same in all times and places. A visible square, +for instance, suggests to the mind the same tangible figure in Europe +that it doth in America. Hence it is that the voice of the Author of' +Nature which speaks to our eyes, is not liable to that misinterpretation +and ambiguity that languages of human contrivance are unavoidably subject +to. + +153. Though what has been said may suffice to show what ought to be +determined with relation to the object of geometry, I shall nevertheless, +for the fuller illustration thereof, consider the case of an +intelligence, or unbodied spirit, which is supposed to see perfectly +well, i.e. to have a clear perception of the proper and immediate objects +of sight, but to have no sense of touch. Whether there be any such being +in Nature or no is beside my purpose to inquire. It sufficeth that the +supposition contains no contradiction in it. Let us now examine what +proficiency such a one may be able to make in geometry. Which speculation +will lead us more clearly to see whether the ideas of sight can possibly +be the object of that science. + +154. FIRST, then, it is certain the aforesaid intelligence could have no +idea of a solid, or quantity of three dimensions, which followeth from +its not having any idea of distance. We indeed are prone to think that we +have by sight the ideas of space and solids, which ariseth from our +imagining that we do, strictly speaking, see distance and some parts of +an object at a greater distance than others; which hath been demonstrated +to be the effect of the experience we have had, what ideas of touch are +connected with such and such ideas attending vision: but the intelligence +here spoken of is supposed to have no experience of touch. He would not, +therefore, judge as we do, nor have any idea of distance, outness, or +profundity, nor consequently of space or body, either immediately or by +suggestion. Whence it is plain he can have no notion of those parts of +geometry which relate to the mensuration of solids and their convex or +concave surfaces, and contemplate the properties of lines generated by +the section of a solid. The conceiving of any part whereof is beyond the +reach of his faculties. + +155. Farther, he cannot comprehend the manner wherein geometers describe +a right line or circle; the rule and compass with their use being things +of which it is impossible he should have any notion: nor is it an easier +matter for him to conceive the placing of one plane or angle on another, +in order to prove their equality: since that supposeth some idea of +distance or external space. All which makes it evident our pure +intelligence could never attain to know so much as the first elements of +plane geometry. And perhaps upon a nice inquiry it will be found he +cannot even have an idea of plane figures any more than he can of solids; +since some idea of distance is necessary to form the idea of a +geometrical plane, as will appear to whoever shall reflect a little on +it. + +156. All that is properly perceived by the visive faculty amounts to no +more than colours, with their variations and different proportions of +light and shade. But the perpetual mutability and fleetingness of those +immediate objects of sight render them incapable of being managed after +the manner of geometrical figures; nor is it in any degree useful that +they should. It is true there are divers of them perceived at once, and +more of some and less of others: but accurately to compute their +magnitude and assign precise determinate proportions between things so +variable and inconstant, if we suppose it possible to be done, must yet +be a very trifling and insignificant labour. + +157. I must confess men are tempted to think that flat or plane figures +are immediate objects of sight, though they acknowledge solids are not. +And this opinion is grounded on what is observed in painting, wherein (it +seems) the ideas immediately imprinted on the mind are only of planes +variously coloured, which by a sudden act of the judgment are changed +into solids. But with a little attention we shall find the planes here +mentioned as the immediate objects of sight are not visible but tangible +planes. For when we say that pictures are planes, we mean thereby that +they appear to the touch smooth and uniform. But then this smoothness and +uniformity, or, in other words, this planeness of the picture, is not +perceived immediately by vision: for it appeareth to the eye various and +multiform. + +158. From all which we may conclude that planes are no more the immediate +object of sight than solids. What we strictly see are not solids, nor yet +planes variously coloured: they are only diversity of colours. And some +of these suggest to the mind solids, and other plane figures, just as +they have been experienced to be connected with the one or the other: so +that we see planes in the same way that we see solids, both being equally +suggested by the immediate objects of sight, which accordingly are +themselves denominated planes and solids. But though they are called by +the same names with the things marked by them, they are nevertheless of a +nature entirely different, as hath been demonstrated. + +159. What hath been said is, if I mistake not, sufficient to decide the +question we proposed to examine, concerning the ability of a pure spirit, +such as we have described, to know GEOMETRY. It is, indeed, no easy +matter for us to enter precisely into the thoughts of such an +intelligence, because we cannot without great pains cleverly separate and +disentangle in our thoughts the proper objects of sight from those of +touch which are connected with them. This, indeed, in a complete degree +seems scarce possible to be performed: which will not seem strange to us +if we consider how hard it is for anyone to hear the words of his native +language pronounced in his ears without understanding them. Though he +endeavour to disunite the meaning from the sound, it will nevertheless +intrude into his thoughts, and he shall find it extreme difficult, if not +impossible, to put himself exactly in the posture of a foreigner that +never learned the language, so as to be affected barely with the sounds +themselves, and not perceive the signification annexed to them. + +160. By this time, I suppose, it is clear that neither abstract nor +visible extension makes the object of geometry; the not discerning of +which may perhaps have created some difficulty and useless labour in +mathematics. Sure I am, that somewhat relating thereto has occurred to my +thoughts, which, though after the most anxious and repeated examination I +am forced to think it true, doth, nevertheless, seem so far out of the +common road of geometry, that I know not whether it may not be thought +presumption, if I should make it public in an age, wherein that science +hath received such mighty improvements by new methods; great part whereof, +as well as of the ancient discoveries, may perhaps lose their reputation, +and much of that ardour with which men study the abstruse and fine +geometry be abated, if what to me, and those few to whom I have imparted +it, seems evidently true, should really prove to be so. + + + + + + + + + + +End of the Project Gutenberg EBook of An Essay Towards a New Theory of Vision, by +George Berkeley + +*** END OF THIS PROJECT GUTENBERG EBOOK ESSAY--NEW THEORY OF VISION *** + +***** This file should be named 4722.txt or 4722.zip ***** +This and all associated files of various formats will be found in: + https://www.gutenberg.org/4/7/2/4722/ + +Produced by Col Choat. 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Please read this +important information, as it gives you specific rights and +tells you about restrictions in how the file may be used. + + + + + + + + + + + +An Essay Towards a New Theory of Vision +by George Berkeley (1685-1753) + + + +CONTENTS + + +Sect. + 1 Design + 2 Distance of itself invisible + 3 Remote distance perceived rather by experience than by sense + 4 Near distance thought to be perceived by the ANGLE of the OPTIC AXES + 5 Difference between this and the former manner of perceiving distance + 6 Also by diverging rays + 7 This depends not on experience + 8 These the common accounts, but not satisfactory + 9 Some IDEAS perceived by the mediation of others + 10 No IDEA which is not itself perceived, can be the means of + perceiving another + 11 Distance perceived by means of some other IDEA + 12 Those lines and angles mentioned in optics, are not themselves + perceived + 13 Hence the mind does not perceive distance by lines and angles + 14 Also because they have no real existence + 15 And because they are insufficient to explain the phenomena + 16 The IDEAS that suggest distance are, 1st, the sensation arising from + the turn of the eyes + 17 Betwixt which and distance there is no necessary connection + 18 Scarce room for mistake in this matter + 19 No regard had to the angle of the OPTIC AXES + 20 Judgment of distance made with both eyes, the result of EXPERIENCE + 21 2ndly, Confusedness of appearance + 22 This the occasion of those judgments attributed to diverging rays + 23 Objection answered + 24 What deceives the writers of optics in this matter + 25 The cause why one IDEA may suggest another + 26 This applied to confusion and distance + 27 Thirrdly, the straining of the eye + 28 The occasions which suggest distance have in their own nature + no relation to it + 29 A difficult case proposed by Dr. Barrow as repugnant to + all the known theories + 30 This case contradicts a received principle in catoptrics + 31 It is shown to agree with the principles we have laid down + 32 This phenomenon illustrated + 33 It confirms the truth of the principle whereby it is explained + 34 Vision when distinct, and when confused + 35 The different effects of parallel diverging and converging rays + 36 How converging and diverging rays come to suggest the same distance + 37 A person extreme purblind would judge aright in the + forementioned case + 38 Lines and angles, why useful in optics + 39 The not understanding this, a cause of mistake + 40 A query proposed, by Mr. Molyneux in his DIOPTRICS, considered + 41 One born blind would not at first have any IDEA of distance by sight + 42 This not agreeable to the common principles + 43 The proper objects of sight, not without the mind, nor the images + of any thing without the mind + 44 This more fully explained + 45 In what sense we must be understood to see distance + and external things + 46 Distance, and things placed at a distance, not otherwise perceived + by the eye than by the ear + 47 The IDEAS of sight more apt to be confounded with the IDEAS of touch + than those of hearing are + 48 How this comes to pass + 49 Strictly speaking, we never see and feel the same thing + 50 Objects of SIGHT twofold, mediate and immediate + 51 These hard to separate in our thoughts + 52 The received accounts of our perceiving magnitude by sight, false + 53 Magnitude perceived as immediately as distance + 54 Two kinds of sensible extension, neither of which is + infinitely divisible + 55 The tangible magnitude of an OBJECT steady, the visible not + 56 By what means tangible magnitude is perceived by sight + 57 This further enlarged on + 58 No necessary connection between confusion or faintness + of appearance, and small or great magnitude + 59 The tangible magnitude of an OBJECT more heeded than the visible, + and why + 60 An instance of this + 61 Men do not measure by visible feet or inches + 62 No necessary connection between visible and tangible extension + 63 Greater visible magnitude might signify lesser tangible magnitude + 64 The judgments we make of magnitude depend altogether on experience + 65 Distance and magnitude seen as shame or anger + 66 But we are prone to think otherwise, and why + 67 The moon seems greater in the horizon than in the meridian + 68 The cause of this phenomenon assigned + 69 The horizontal moon, why greater at one time than another. + 70 The account we have given proved to be true + 71 And confirmed by the moon's appearing greater in a mist + 72 Objection answered + 73 The way wherein faintness suggests greater magnitude illustrated + 74 Appearance of the horizontal moon, why thought difficult to explain + 75 Attempts towards the solution of it made by several, but in vain + 76 The opinion of Dr. Wallis + 77 It is shown to be unsatisfactory + 78 How lines and angles may be of use in computing apparent magnitudes + 79 One born blind, being made to see, what judgment he would make + of magnitude + 80 The MINIMUM VISIBLE the same to all creatures + 81 Objection answered + 82 The eye at all times perceives the same number of visible points + 83 Two imperfections in the VISIVE FACULTY + 84 Answering to which, we may conceive two perfections + 85 In neither of these two ways do microscopes improve the sight + 86 The case of microscopical eyes, considered + 87 The sight, admirably adapted to the ends of seeing + 88 Difficulty concerning erect vision + 89 The common way of explaining it + 90 The same shown to be false + 91 Not distinguishing between IDEAS of sight and touch, cause + of mistake in this matter + 92 The case of one born blind, proper to be considered + 93 Such a one might by touch attain to have IDEAS of UPPER and LOWER + 94 Which modes of situation he would attribute only to things tangible + 95 He would not at first sight think anything he saw, high or low, + erect or inverted + 96 This illustrated by an example + 97 By what means he would come to denominate visible OBJECTS, + high or low, etc. + 98 Why he should think those OBJECTS highest, which are painted on + the lowest part of his eye, and VICE VERSA + 99 How he would perceive by sight, the situation of external objects +100 Our propension to think the contrary, no argument against + what has been said +101 Objection +102 Answer +103 An object could not be known at first sight by the colour +104 Nor by the magnitude thereof +105 Nor by the figure +106 In the first act of vision, no tangible thing would be suggested + by sight +107 Difficulty proposed concerning number +108 Number of things visible, would not at first sight suggest + the like number of things tangible +109 Number the creature of the mind +110 One born blind would not at first sight number visible things + as others do +111 The situation of any object determined with respect only to objects + of the same sense +112 No distance, great or small, between a visible and tangible thing +113 The not observing this, cause of difficulty in erect vision +114 Which otherwise includes nothing unaccountable +115 What is meant by the picture being inverted +116 Cause of mistake in this matter +117 Images in the eye, not pictures of external objects +118 In what sense they are pictures +119 In this affair we must carefully distinguish between ideas + of sight and touch +120 Difficult to explain by words the true Theory of Vision +121 The question, whether there is any IDEA common to sight + and touch, stated +122 Abstract extension inquired into +123 It is incomprehensible +124 Abstract extension not the OBJECT of geometry +125 The general IDEA of a triangle, considered +126 Vacuum, or pure space, not common to sight and touch +127 There is no idea, or kind of idea, common to both senses +128 First argument in proof hereof +129 Second argument +130 Visible figure and extension, not distinct IDEAS from colour +131 Third argument +132 Confirmation drawn from Mr. Molyneux's problem of a sphere + and a cube, published by Mr. Locke +133 Which is falsely solved, if the common supposition be true +134 More might be said in proof of our tenet, but this suffices +135 Further reflection on the foregoing problem +136 The same thing doth not affect both sight and touch +137 The same idea of motion not common to sight and touch +138 The way wherein we apprehend motion by sight, easily collected + from what hath been said +139 QU. How visible and tangible IDEAS came to have the same name + if not of the same kind +140 This accounted for without supposing them of the same kind +141 OBJ. That a tangible square is liker to a visible square than + to a visible circle +142 ANS. That a visible square is fitter than a visible circle, + to represent a tangible square +143 But it doth not hence follow, that a visible square + is like a tangible square +144 Why we are more apt to confound visible with tangible IDEAS, + than other signs with the things signified +145 Several other reasons hereof, assigned +146 Reluctancy in rejecting any opinion, no argument of its truth +147 Proper objects of vision the language of nature +148 In it there is much admirable, and deserving our attention +149 Question proposed, concerning the object of geometry +150 At first view we are apt to think visible extension the object + of geometry +151 Visible extension shown not to be the object of geometry +152 Words may as well be thought the object of geometry, + as visible extension +153 It is proposed to inquire, what progress an intelligence that + could see, but not feel, might make in geometry +154 He cannot understand those parts which relate to solids, and their + surfaces, and lines generated by their section +155 Nor even the elements of plane geometry +156 The proper objects of sight incapable of being managed as + geometrical figures +157 The opinion of those who hold plane figures to be the immediate + objects of sight, considered +158 Planes no more the immediate objects of sight, than solids +159 Difficult to enter precisely into the thoughts of the + above-mentioned intelligence +160 The object of geometry, its not being sufficiently understood, + cause of difficulty, and useless labour in that science + + + +AN ESSAY TOWARDS A NEW THEORY OF VISION + + +1. My design is to show the manner wherein we perceive by sight the +distance, magnitude, and situation of OBJECTS. Also to consider the +difference there is betwixt the IDEAS of sight and touch, and whether +there be any IDEA common to both senses. + +2. It is, I think, agreed by all that DISTANCE, of itself and +immediately, cannot be seen. For DISTANCE being a Line directed end-wise +to the eye, it projects only one point in the fund of the eye, which +point remains invariably the same, whether the distance be longer or +shorter. + +3. I find it also acknowledged that the estimate we make of the distance +of OBJECTS considerably remote is rather an act of judgment grounded on +EXPERIENCE than of SENSE. For example, when I perceive a great number of +intermediate OBJECTS, such as houses, fields, rivers, and the like, which +I have experienced to take up a considerable space, I thence form a +judgment or conclusion that the OBJECT I see beyond them is at a great +distance. Again, when an OBJECT appears faint and small, which at a near +distance I have experienced to make a vigorous and large appearance, I +instantly conclude it to be far off: And this, it is evident, is the +result of EXPERIENCE; without which, from the faintness and littleness I +should not have inferred anything concerning the distance of OBJECTS. + +4. But when an OBJECT is placed at so near a distance as that the +interval between the eyes bears any sensible proportion to it, the +opinion of speculative men is that the two OPTIC AXES (the fancy that we +see only with one eye at once being exploded) concurring at the OBJECT do +there make an ANGLE, by means of which, according as it is greater or +lesser, the OBJECT is perceived to be nearer or farther off. + +5. Betwixt which and the foregoing manner of estimating distance there is +this remarkable difference: that whereas there was no apparent, necessary +connection between small distance and a large and strong appearance, or +between great distance and a little and faint appearance, there appears a +very necessary connection between an obtuse angle and near distance, and +an acute angle and farther distance. It does not in the least depend upon +experience, but may be evidently known by anyone before he had +experienced it, that the nearer the concurrence of the OPTIC AXES, the +greater the ANGLE, and the remoter their concurrence is, the lesser will +be the ANGLE comprehended by them. + +6. There is another way mentioned by optic writers, whereby they will +have us judge of those distances, in respect of which the breadth of the +PUPIL hath any sensible bigness: And that is the greater or lesser +divergency of the rays, which issuing from the visible point do fall on +the PUPIL, that point being judged nearest which is seen by most +diverging rays, and that remoter which is seen by less diverging rays: +and so on, the apparent distance still increasing, as the divergency of +the rays decreases, till at length it becomes infinite, when the rays +that fall on the PUPIL are to sense parallel. And after this manner it is +said we perceive distance when we look only with one eye. + +7. In this case also it is plain we are not beholding to experience: it +being a certain, necessary truth that the nearer the direct rays falling +on the eye approach to a PARALLELISM, the farther off is the point of +their intersection, or the visible point from whence they flow. + +8. I have here set down the common, current accounts that are given of +our perceiving near distances by sight, which, though they are +unquestionably received for true by MATHEMATICIANS, and accordingly made +use of by them in determining the apparent places of OBJECTS, do, +nevertheless seem to me very unsatisfactory: and that for these following +reasons:-- + +9. FIRST, It is evident that when the mind perceives any IDEA, not +immediately and of itself, it must be by the means of some other IDEA. +Thus, for instance, the passions which are in the mind of another are of +themselves to me invisible. I may nevertheless perceive them by sight, +though not immediately, yet by means of the colours they produce in the +countenance. We often see shame or fear in the looks of a man, by +perceiving the changes of his countenance to red or pale. + +10. Moreover it is evident that no IDEA which is not itself perceived can +be the means of perceiving any other IDEA. If I do not perceive the +redness or paleness of a man's face themselves, it is impossible I should +perceive by them the passions which are in his mind. + +11. Now from sect. 2 it is plain that distance is in its own nature +imperceptible, and yet it is perceived by sight. It remains, therefore, +that it be brought into view by means of some other IDEA that is itself +immediately perceived in the act of VISION. + +12. But those LINES and ANGLES, by means whereof some MATHEMATICIANS +pretend to explain the perception of distance, are themselves not at all +perceived, nor are they in truth ever thought of by those unskilful in +optics. I appeal to anyone's experience whether upon sight of an OBJECT he +computes its distance by the bigness of the ANGLE made by the meeting of +the two OPTIC AXES? Or whether he ever thinks of the greater or lesser +divergency of the rays, which arrive from any point to his PUPIL? Everyone +is himself the best judge of what he perceives, and what not. in vain +shall all the MATHEMATICIANS in the world tell me, that I perceive certain +LINES and ANGLES which introduce into my mind the various IDEAS of +DISTANCE, so long as I myself am conscious of no such thing. + +13. Since, therefore, those ANGLES and LINES are not themselves perceived +by sight, it follows from sect. 10 that the mind doth not by them judge +of the distance of OBJECTS. + +14. Secondly, the truth of this assertion will be yet farther evident to +anyone that considers those LINES and ANGLES have no real existence in +nature, being only an HYPOTHESIS framed by the MATHEMATICIANS, and by them +introduced into OPTICS, that they might treat of that science in a +GEOMETRICAL way. + +15. The third and last reason I shall give for rejecting that doctrine is, +that though we should grant the real existence of those OPTIC ANGLES, +etc., and that it was possible for the mind to perceive them, yet these +principles would not be found sufficient to explain the PHENOMENA of +DISTANCE, as shall be shown hereafter. + +16. Now, it being already shown that distance is suggested to the mind by +the mediation of some other IDEA which is itself perceived in the act of +seeing, it remains that we inquire what IDEAS or SENSATIONS there be that +attend VISION, unto which we may suppose the IDEAS of distance are +connected, and by which they are introduced into the mind. And FIRST, it +is certain by experience that when we look at a near OBJECT with both +eyes, according as it approaches or recedes from us, we alter the +disposition of our eyes, by lessening or widening the interval between +the PUPILS. This disposition or turn of the eyes is attended with a +sensation, which seems to me to be that which in this case brings the +IDEA of greater or lesser distance into the mind. + +17. Not that there is any natural or necessary connection between the +sensation we perceive by the turn of the eyes and greater or lesser +distance, but because the mind has by constant EXPERIENCE found the +different sensations corresponding to the different dispositions of the +eyes to be attended each with a different degree of distance in the +OBJECT: there has grown an habitual or customary connection between those +two sorts of IDEAS, so that the mind no sooner perceives the sensation +arising from the different turn it gives the eyes, In order to bring the +PUPILS nearer or farther asunder, but it withal perceives the different +IDEA of distance which was wont to be connected with that sensation; just +as upon hearing a certain sound, the IDEA is immediately suggested to the +understanding which custom had united with it. + +18 Nor do I see how I can easily be mistaken in this matter. I know +evidently that distance is not perceived of itself. That by consequence +it must be perceived by means of some other IDEA which is immediately +perceived, and varies with the different degrees of distance. I know also +that the sensation arising from the turn of the eyes is of itself +immediately perceived, and various degrees thereof are connected with +different distances, which never fail to accompany them into my mind, +when I view an OBJECT distinctly with both eyes, whose distance is so +small that in respect of it the interval between the eyes has any +considerable magnitude. + +19. I know it is a received opinion that by altering the disposition of +the eyes the mind perceives whether the angle of the OPTIC AXES is made +greater or lesser. And that accordingly by a kind of NATURAL +GEOMETRY it judges the point of their intersection to be nearer +or farther off. But that this is not true I am convinced by my own +experience, since I am not conscious that I make any such use of the +perception I have by the turn of my eyes. And for me to make those +judgments, and draw those conclusions from it, without knowing that I do +so, seems altogether incomprehensible. + +20. From all which it follows that the judgment we make of the distance +of an OBJECT, viewed with both eyes, is entirely the RESULT OF +EXPERIENCE. If we had not constantly found certain sensations arising +from the various disposition of the eyes, attended with certain degrees +of distance, we should never make those sudden judgments from them +concerning the distance of OBJECTS; no more than we would pretend to +judge a man's thoughts by his pronouncing words we had never heard +before. + +21. Secondly, an OBJECT placed at a certain distance from the eye, to +which the breadth of the PUPIL bears a considerable proportion, being +made to approach, is seen more confusedly: and the nearer it is brought +the more confused appearance it makes. And this being found constantly to +be so, there ariseth in the mind an habitual CONNECTION between the +several degrees of confusion and distance; the greater confusion still +implying the lesser distance, and the lesser confusion the greater +distance of the OBJECT. + +22. This confused appearance of the OBJECT doth therefore seem to be the +MEDIUM whereby the mind judgeth of distance in those cases wherein the +most approved writers of optics will have it judge by the different +divergency with which the rays flowing from the radiating point fall on +the PUPIL. No man, I believe, will pretend to see or feel those imaginary +angles that the rays are supposed to form according to their various +inclinations on his eye. But he cannot choose seeing whether the OBJECT +appear more or less confused. It is therefore a manifest consequence from +what bath been demonstrated, that instead of the greater or lesser +divergency of the rays, the mind makes use of the greater or lesser +confusedness of the appearance, thereby to determine the apparent place +of an OBJECT. + +23 Nor doth it avail to say there is not any necessary connection between +confused VISION and distance, great or small. For I ask any man what +necessary connection he sees between the redness of a blush and shame? And +yet no sooner shall he behold that colour to arise in the face of +another, but it brings into his and the IDEA of that passion which hath +been observed to accompany it. + +24. What seems to have misled the writers of optics in this matter is +that they imagine men judge of distance as they do of a conclusion in +mathematics, betwixt which and the premises it is indeed absolutely +requisite there be an apparent, necessary connection: but it is far +otherwise in the sudden judgments men make of distance. We are not to +think that brutes and children, or even grown reasonable men, whenever +they perceive an OBJECT to approach, or depart from them, do it by virtue +of GEOMETRY and DEMONSTRATION. + +25. That one IDEA may suggest another to the mind it will suffice that +they have been observed to go together, without any demonstration of the +necessity of their coexistence, or without so much as knowing what it is +that makes them so to coexist. Of this there are innumerable instances of +which no one can be ignorant. + +26. Thus, greater confusion having been constantly attended with nearer +distance, no sooner is the former IDEA perceived, but it suggests the +latter to our thoughts. And if it had been the ordinary course of Nature +that the farther off an OBJECT were placed, the more confused it should +appear, it is certain the very same perception that now makes us think an +OBJECT approaches would then have made us to imagine it went farther off. +That perception, abstracting from CUSTOM and EXPERIENCE, being equally +fitted to produce the IDEA of great distance, or small distance, or no +distance at all. + +27. Thirdly, an OBJECT being placed at the distance above specified, and +brought nearer to the eye, we may nevertheless prevent, at least for some +time, the appearances growing more confused, by straining the eye. In +which case that sensation supplies the place of confused VISION in aiding +the mind to judge of the distance of the OBJECT; it being esteemed so +much the nearer by how much the effort or straining of the eye in order +to distinct VISION is greater. + +28. I have here set down those sensations or IDEAS that seem to be the +constant and general occasions of introducing into the mind the different +IDEAS of near distance. It is true in most cases that divers other +circumstances contribute to frame our IDEA of distance, to wit, the +particular number, size, kind, etc., of the things seen. Concerning +which, as well as all other the forementioned occasions which suggest +distance, I shall only observe they have none of them, in their own +nature, any relation or connection with it: nor is it possible they should +ever signify the various degrees thereof, otherwise than as by EXPERIENCE +they have been found to be connected with them. + +29. I shall proceed upon these principles to account for a phenomenon +which has hitherto strangely puzzled the writers of optics, and is so far +from being accounted for by any of their THEORIES OF VISION that it is, +by their own confession, plainly repugnant to them; and of consequence, +if nothing else could be objected, were alone sufficient to bring their +credit in question. The whole difficulty I shall lay before you in the +words of the learned Dr. Barrow, with which he concludes his optic +lectures:-- + +'I have here delivered what my thoughts have suggested to me concerning +that part of optics which is more properly mathematical. As for the other +parts of that science (which being rather physical, do consequently +abound with plausible conjectures instead of certain principles), there +has in them scarce anything occurred to my observation different from what +has been already said by Kepler, Scheinerus, Descartes, and others. And +methinks, I had better say nothing at all, than repeat that which has +been so often said by others. I think it therefore high time to take my +leave of this subject: but before I quit it for good and all, the fair +and ingenuous dealing that I owe both to you and to truth obligeth me to +acquaint you with a certain untoward difficulty, which seems directly +opposite to the doctrine I have been hitherto inculcating, at least, +admits of no solution from it. In short it is this. Before the double +convex glass or concave speculum EBF, let the point A be placed at such a +distance that the rays proceeding from A, after refraction or reflection, +be brought to unite somewhere in the AxAB. And suppose the point of union +(i.e. the image of the point A, as hath been already set forth) to be Z; +between which and B, the vertex of the glass or speculum, conceive the +eye to be anywhere placed. The question now is, where the point A ought +to appear? Experience shows that it does not appear behind at the point +Z, and it were contrary to nature that it should, since all the +impression which affects the sense comes from towards A. But from our +tenets it should seem to follow that it would appear before the eye at a +vast distance off, so great as should in some sort surpass all sensible +distance. For since if we exclude all anticipations and prejudices, every +OBJECT appears by so much the farther off, by how much the rays it sends +to the eye are less diverging. And that OBJECT is thought to be most +remote from which parallel rays proceed unto the eye. Reason would make +one think that OBJECT should appear at yet a greater distance which is +seen by converging rays. Moreover it may in general be asked concerning +this case what it is that determines the apparent place of the point A, +and maketh it to appear after a constant manner sometimes nearer, at +other times farther off? To which doubt I see nothing that can be +answered agreeable to the principles we have laid down except only that +the point A ought always to appear extremely remote. But on the contrary +we are assured by experience that the point A appears variously distant, +according to the different situations of the eye between the points B and +Z. And that it doth never (if at all) seem farther off, than it would if +it were beheld by the naked eye, but on the contrary it doth sometimes +appear much nearer. Nay, it is even certain that by how much the rays +falling on the eye do more converge by so much the nearer doth the OBJECT +seem to approach. For the eye being placed close to the point B, the +OBJECT A appears nearly in its own natural place, if the point B is taken +in the glass, or at the same distance, if in the speculum. The eye being +brought back to O, the OBJECT seems to draw near: and being come to P it +beholds it still nearer. And so on little and little, till at length the +eye being placed somewhere, suppose at Q, the OBJECT appearing extremely +near, begins to vanish into mere confusion. All which doth seem repugnant +to our principles, at least not rightly to agree with them. Nor is our +tenet alone struck at by this experiment, but likewise all others that +ever came to my knowledge are, every whit as much, endangered by it. The +ancient one especially (which is most commonly received, and comes +nearest to mine) seems to be so effectually overthrown thereby that the +most learned Tacquet has been forced to reject that principle, as false +and uncertain, on which alone he had built almost his whole CATOPTRICS; +and consequently by taking away the foundation, hath himself pulled down +the superstructure he had raised on it. Which, nevertheless, I do not +believe he would have done had he but considered the whole matter more +thoroughly, and examined the difficulty to the bottom. But as for me, +neither this nor any other difficulty shall have so great an influence on +me as to make me renounce that which I know to be manifestly agreeable to +reason: especially when, as it here falls out, the difficulty is founded +in the peculiar nature of a certain odd and particular case. For in the +present case something peculiar lies hid, which being involved in the +subtilty of nature will, perhaps, hardly be discovered till such time as +the manner of vision is more perfectly made known. Concerning which, I +must own, I have hitherto been able to find out nothing that has the +least show of PROBABILITY, not to mention CERTAINTY. I shall, therefore, +leave this knot to be untied by you, wishing you may have better success +in it than I have had.' + +30. The ancient and received principle, which Dr. Barrow here mentions as +the main foundation of Tacquet's CATOPTRICS, is that: 'every visible point +seen by reflection from a speculum shall appear placed at the intersection +of the reflected ray, and the perpendicular of incidence:' which +intersection in the present case, happening to be behind the eye, it +greatly shakes the authority of that principle, whereon the +aforementioned author proceeds throughout his whole CATOPTRICS in +determining the apparent place of OBJECTS seen by reflection from any kind +of speculum. + +31. Let us now see how this phenomenon agrees with our tenets. The eye +the nearer it is placed to the point B in the foregoing figures, the more +distinct is the appearance of the OBJECT; but as it recedes to O the +appearance grows more confused; and at P it sees the OBJECT yet more +confused; and so on till the eye being brought back to Z sees the OBJECT +in the greatest confusion of all. Wherefore by sect. 21 the OBJECT should +seem to approach the eye gradually as it recedes from the point B, that +is, at O it should (in consequence of the principle I have laid down in +the aforesaid section) seem nearer than it did at B, and at P nearer than +at 0, and at Q nearer than at P; and so on, till it quite vanishes at Z. +Which is the very matter of fact, as anyone that pleases may easily +satisfy himself by experiment. + +32. This case is much the same as if we should suppose an Englishman to +meet a foreigner who used the same words with the English, but in a +direct contrary signification. The Englishman would not fail to make a +wrong judgment of the IDEAS annexed to those sounds in the mind of him +that used them. Just so, in the present case the OBJECT speaks (if I may +so say) with words that the eye is well acquainted with, that is, +confusions of appearance; but whereas heretofore the greater confusions +were always wont to signify nearer distances, they have in this case a +direct, contrary signification, being connected with the greater +distances. Whence it follows that the eye must unavoidably be mistaken, +since it will take the confusions in the sense it has been used to, which +is directly opposed to the true. + +33. This phenomenon as it entirely subverts the opinion of those who will +have us judge of distance by lines and angles, on which supposition it is +altogether inexplicable, so it seems to me no small confirmation of the +truth of that principle whereby it is explained. But in order co a more +full explication of this point, and to show how far the hypothesis of the +mind's judging by the various divergency of rays may be of use in +determining the apparent place of an OBJECT, it will be necessary to +premise some few things, which are already well known to those who have +any skill in dioptrics. + +34. FIRST, any radiating point is then distinctly seen when the rays +proceeding from it are, by the refractive power of the crystalline, +accurately reunited in the retina or fund of the eye: but if they are +reunited, either before they arrive at the retina, or after they have +passed it, then there is confused vision. + + + +35. SECONDLY, suppose in the adjacent figures NP represent an eye duly +framed and retaining its natural figure. In Fig. 1 the rays falling +nearly parallel on the eye, are by the crystalline AB refracted, so as +their focus or point of union F falls exactly on the retina: but if the +rays fall sensibly diverging on the eye, as in Fig. 2, then their focus +falls beyond the retina: or if the rays are made to converge by the lens +QS before they come at the eye, as in Fig. 3, their focus F will fall +before the retina. In which two last cases it is evident from the +foregoing section that the appearance of the point Z is confused. And by +how much the greater is the convergency, or divergency, of the rays +falling on the pupil, by so much the farther will the point of their +reunion be from the retina, either before or behind it, and consequently +the point Z will appear by so much the more confused. And this, by the +bye, may show us the difference between confused and faint vision. +Confused vision is when the rays proceedings from each distinct point of +the OBJECT are not accurately recollected in one corresponding point on +the retina, but take up some space thereon, so that rays from different +points become mixed and confused together. This is opposed to a distinct +vision, and attends near objects. Faint vision is when by reason of the +distance of the object or grossness of the interjacent medium few rays +arrive from the object to the eye. This is opposed to vigorous or clear +vision, and attends remote objects. But to return. + +36. The eye, or (to speak truly) the mind, perceiving only the confusion +itself, without ever considering the cause from which it proceeds, doth +constantly annex the same degree of distance to the same degree of +confusion. Whether that confusion be occasioned by converging or by +diverging rays, it matters not. Whence it follows that the eye viewing +the object Z through the glass QS (which by refraction causeth the rays +ZQ, ZS, etc., to converge) should judge it to be at such a nearness at +which if it were placed it would radiate on the eye with rays diverging +to that degree as would produce the same confusion which is now produced +by converging rays, i.e. would cover a portion of the retina equal to DC +(VID. Fig. 3 supra). But then this must be understood (to use Dr. +Barrow's phrase) SECLUSIS PRAENOTIONIBUS ET PRAEJUDICIIS, in case we +abstract from all other circumstances of vision, such as the figure, +size, faintness, etc. of the visible objects; all which do ordinarily +concur to form our idea of distance, the mind having by frequent +experience observed their several sorts or degrees to be conneted with +various distances. + +37 It plainly follows from what hath been said that a person perfectly +purblind (i.e. that could not see an object distinctly but when placed +close to his eye) would not make the same wrong judgment that others do +in the forementioned case. For to him greater confusions constantly +suggesting greater distances, he must, as he recedes from the glass and +the object grows more confused, judge it to be at a farther distance, +contrary to what they do who have had the perception of the objects +growing more confused connected with the idea of approach. + +38. Hence also it doth appear there may be good use of computation by +lines and angles in optics; not that the mind judgeth of distance +immediately by them, but because it judgeth by somewhat which is +connected with them, and to the determination whereof they may be +subservient. Thus the mind judging of the distance of an object by the +confusedness of its appearance, and this confusedness being greater or +lesser to the naked eye, according as the object is seen by rays more or +less diverging, it follows that a man may make use of the divergency of +the rays in computing the apparent distance, though not for its own sake, +yet on account of the confusion with which it is connected. But, so it +is, the confusion itself is entirely neglected by mathematicians as +having no necessary relation with distance, such as the greater or lesser +angles of divergency are conceived to have. And these (especially for +that they fall under mathematical computation) are alone regarded in +determining the apparent places of objects, as though they were the sole +and immediate cause of the judgments the mind makes of distance. Whereas, +in truth, they should not at all be regarded in themselves, or any +otherwise, than as they are supposed to be the cause of confused vision. + +39. The not considering of this has been a fundamental and perplexing +oversight. For proof whereof we need go no farther than the case before +us. It having been observed that the most diverging rays brought into the +mind the idea of nearest distance, and that still, as the divergency +decreased, the distance increased: and it being thought the connexion +between the various degrees of divergency and distance was immediate; +this naturally leads one to conclude, from an ill-grounded analogy, that +converging rays shall make an object appear at an immense distance: and +that, as the convergency increases, the distance (if it were possible) +should do so likewise. That this was the cause of Dr. Barrow's mistake is +evident from his own words which we have quoted. Whereas had the learned +doctor observed that diverging and converging rays, how opposite soever +they may seem, do nevertheless agree in producing the same effect, to +wit, confusedness of vision, greater degrees whereof are produced +indifferently, either as the divergency or convergency and the rays +increaseth. And that it is by this effect, which is the same in both, +that either the divergency or convergency is perceived by the eye; I say, +had he but considered this, it is certain he would have made a quite +contrary judgment, and rightly concluded that those rays which fall on +the eye with greater degrees of convergency should make the object from +whence they proceed appear by so much the nearer. But it is plain it was +impossible for any man to attain to a right notion of this matter so long +as he had regard only to lines and angles, and did not apprehend the true +nature of vision, and how far it was of mathematical consideration. + +40. Before we dismiss this subject, it is fit we take notice of a query +relating thereto, proposed by the ingenious Mr. Molyneux, is his TREATISE +OF DIOPTRICS,[Par. I. Prop. 31, Sect. 9.] where speaking of this +difficulty, he has these words: 'And so he (i.e. Dr. Barrow) leaves this +difficulty to the solution of others, which I (after so great an example) +shall do likewise; but with the resolution of the same admirable author of +not quitting the evident doarine which we have before laid down, for +determining the LOCUS OBJECTI, on account of being pressed by one +difficulty which seems inexplicable till a more intimate knowledge of the +visive faculty be obtained by mortals. In the meantime, I propose it to +the consideration of the ingenious, whether the LOCUS APPARENS of an +object placed as in this 9th section be not as much before the eye as the +distinct base is behind the eye!' To which query we may venture to answer +in the negative. For in the present case the rule for determining the +distance of the distinct base, or respective focus from the glass, is this: +as the difference between the distance of the object and focus is to the +focus or focal length, so the distance of the object from the glass is to +the distance of the respective focus or distinct base from the glass. +[Molyneux Dioptr., Par. I. Prop. 5.] Let us now suppose the object to be +placed at the distance of the focal length, and one half of the focal +length from the glass, and the eye close to the glass, hence it will follow +by the rule that the distance of the distinct base behind the eye is double +the true distance of the object before the eye. If therefore Mr. Molyneux's +conjecture held good, it would follow that the eye should see the object +twice as far off as it really is; and in other cases at three or four times +its due distance, or more. But this manifestly contradicts experience, the +object never appearing, at farthest, beyond its due distance. Whatever, +therefore, is built on this supposition (VID. COROL. I. PROP. 57, IBID.) +comes to the ground along with it. + +41. From what hath been premised it is a manifest consequence that a man +born blind, being made to see, would, at first, have no idea of distance +by sight; the sun and stars, the remotest objects as well as the nearer, +would all seem to be in his eye, or rather in his mind. The objects +intromitted by sight would seem to him (as in truth they are) no other +than a new set of thoughts or sensations, each whereof is as near to him +as the perceptions of pain or pleasure, or the most inward passions of +his soul. For our judging objects provided by sight to be at any +distance, or without the mind, is (VID. sect. 28) entirely the effect of +experience, which one in those circumstances could not yet have attained +to. + +42. It is indeed otherwise upon the common supposition that men judge of +distance by the angle of the optic axes, just as one in the dark, or a +blind-man by the angle comprehended by two sticks, one whereof he held in +each hand. For if this were true, it would follow that one blind from his +birth being made to see, should stand in need of no new experience in +order to perceive distance by sight. But that this is false has, I think, +been sufficiently demonstrated. + +43. And perhaps upon a strict inquiry we shall not find that even those +who from their birth have grown up in a continued habit of seeing are +irrecoverably prejudiced on the other side, to wit, in thinking what they +see to be at a distance from them. For at this time it seems agreed on +all hands, by those who have had any thoughts of that matter, that +colours, which are the proper and immediate object of sight, are not +without the mind. But then it will be said, by sight we have also the +ideas of extension, and figure, and motion; all which may well be thought +without, and at some distance from the mind, though colour should not. In +answer to this I appeal to any man's experience, whether the visible +extension of any object doth not appear as near to him as the colour of +that object; nay, whether they do not both seem to be in the very same +place. Is not the extension we see coloured, and is it possible for us, +so much as in thought, to separate and abstract colour from extension? +Now, where the extension is there surely is the figure, and there the +motion too. I speak of those which are perceived by sight. + +44. But for a fuller explication of this point, and to show that the +immediate objects of sight are not so much as the ideas or resemblances +of things placed at a distance, it is requisite that we look nearer into +the matter and carefully observe what is meant in common discourse, when +one says that which he sees is at a distance from him. Suppose, for +example, that looking at the moon I should say it were fifty or sixty +semidiameters of the earth distant from me. Let us see what moon this is +spoken of: it is plain it cannot be the visible moon, or anything like +the visible moon, or that which I see, which is only a round, luminous +plane of about thirty visible points in diameter. For in case I am +carried from the place where I stand directly towards the moon, it is +manifest the object varies, still as I go on; and by the time that I am +advanced fifty or sixty semidiameters of the earth, I shall be so far +from being near a small, round, luminous flat that I shall perceive +nothing like it; this object having long since disappeared, and if I +would recover it, it must be by going back to the earth from whence I set +out. Again, suppose I perceive by sight the faint and obscure idea of +something which I doubt whether it be a man, or a tree, or a tower, but +judge it to be at the distance of about a mile. It is plain I cannot mean +that what I see is a mile off, or that it is the image or likeness of +anything which is a mile off, since that every step I take towards it the +appearance alters, and from being obscure, small, and faint, grows clear, +large, and vigorous. And when I come to the mile's end, that which I saw +first is quite lost, neither do I find anything in the likeness of it. + +45. In these and the like instances the truth of the matter stands thus: +having of a long time experienced certain ideas, perceivable by touch, as +distance, tangible figure, and solidity, to have been connected with +certain ideas of sight, I do upon perceiving these ideas of sight +forthwith conclude what tangible ideas are, by the wonted ordinary course +of Nature like to follow. Looking at an object I perceive a certain +visible figure and colour, with some degree of faintness and other +circumstances, which from what I have formerly observed, determine me to +think that if I advance forward so many paces or miles, I shall be +affected with such and such ideas of touch: so that in truth and +strictness of speech I neither see distance itself, nor anything that I +take to be at a distance. I say, neither distance nor things placed at a +distance are themselves, or their ideas, truly perceived by sight. This I +am persuaded of, as to what concerns myself: and I believe whoever will +look narrowly into his own thoughts and examine what he means by saying +he sees this or that thing at a distance, will agree with me that what he +sees only suggests to his understanding that after having passed a +certain distance, to be measured by the motion of his body, which is +perceivable by touch, he shall come to perceive such and such tangible +ideas which have been usually connected with such and such visible ideas. +But that one might be deceived by these suggestions of sense, and that +there is no necessary connexion between visible and tangible ideas +suggested by them, we need go no farther than the next looking-glass or +pictures to be convinced. Note that when I speak of tangible ideas, I +take the word idea for any the immediate object of sense or +understanding, in which large signification it is commonly used by the +moderns. + +46. From what we have shown it is a manifest consequence that the ideas +of space, outness, and things placed at a distance are not, strictly +speaking, the object of sight; they are not otherwise perceived by the +eye than by the ear. Sitting in my study I hear a coach drive along the +street; I look through the casement and see it; I walk out and enter into +it; thus, common speech would incline one to think I heard, saw, and +touched the same thing, to wit, the coach. It is nevertheless certain, +the ideas intromitted by each sense are widely different and distinct +from each other; but having been observed constantly to go together, they +are spoken of as one and the same thing. By the variation of the noise I +perceive the different distances of the coach, and know that it +approaches before I look out. Thus by the ear I perceive distance, just +after the same manner as I do by the eye. + +47. I do not nevertheless say I hear distance in like manner as I say +that I see it, the ideas perceived by hearing not being so apt to be +confounded with the ideas of touch as those of sight are. So likewise a +man is easily convinced that bodies and external things are not properly +the object of hearing; but only sounds, by the mediation whereof the idea +of this or that body or distance is suggested to his thoughts. But then +one is with more difficulty brought to discern the difference there is +betwixt the ideas of sight and touch: though it be certain a man no more +sees and feels the same thing than he hears and feels the same thing. + +48. One reason of which seems to be this. It is thought a great absurdity +to imagine that one and the same thing should have any more than one +extension, and one figure. But the extension and figure of a body, being +let into the mind two ways, and that indifferently either by sight or +touch, it seems to follow that we see the same extension and the same +figure which we feel. + +49. But if we take a close and accurate view of things, it must be +acknowledged that we never see and feel one and the same object. That +which is seen is one thing, and that which is felt is another. If the +visible figure and extension be not the same with the tangible figure and +extension, we are not to infer that one and the same thing has divers +extensions. The true consequence is that the objects of sight and touch +are two distinct things. It may perhaps require some thought rightly to +conceive this distinction. And the difficulty seems not a little +increased, because the combination of visible ideas hath constantly the +same name as the combination of tangible ideas wherewith it is connected: +which doth of necessity arise from the use and end of language. + +50. In order therefore to treat accurately and unconfusedly of vision, we +must bear in mind that there are two sorts of objects apprehended by the +eye, the one primarily and immediately, the other secondarily and by +intervention of the former. Those of the first sort neither are, nor +appear to be, without the mind, or at any distance off; they may indeed +grow greater or smaller, more confused, or more clear, or more faint, but +they do not, cannot approach or recede from us. Whenever we say an object +is at a distance, whenever we say it draws near, or goes farther off, we +must always mean it of the latter sort, which properly belong to the +touch, and are not so truly perceived as suggested by the eye in like +manner as thoughts by the ear. + +51. No sooner do we hear the words of a familiar language pronounced in +our ears, but the ideas corresponding thereto present themselves to our +minds: in the very same instant the sound and the meaning enter the +understanding: so closely are they united that it is not in our power to +keep out the one, except we exclude the other also. We even act in all +respects as if we heard the very thoughts themselves. So likewise the +secondary objects, or those which are only suggested by sight, do often +more strongly affect us, and are more regarded than the proper objects of +that sense; along with which they enter into the mind, and with which +they have a far more strict connexion, than ideas have with words. Hence +it is we find it so difficult to discriminate between the immediate and +mediate objects of sight, and are so prone to attribute to the former +what belongs only to the latter. They are, as it were, most closely +twisted, blended, and incorporated together. And the prejudice is +confirmed and riveted in our thoughts by a long tract of time, by the use +of language, and want of reflexion. However, I believe anyone that shall +attentively consider what we have already said, and shall say, upon this +subject before we have done (especially if he pursue it in his own +thoughts) may be able to deliver himself from that prejudice. Sure I am +it is worth some attention, to whoever would understand the true nature +of vision. + +52. I have now done with distance, and proceed to show how it is that we +perceive by sight the magnitude of objects. It is the opinion of some +that we do it by angles, or by angles in conjunction with distance: but +neither angles nor distance being perceivable by sight, and the things we +see being in truth at no distance from us, it follows that as we have +shown lines and angles not to be the medium the mind makes use of in +apprehending the apparent place, so neither are they the medium whereby +it apprehends the apparent magnitude of objects. + +53. It is well known that the same extension at a near distance shall +subtend a greater angle, and at a farther distance a lesser angle. And by +this principle (we are told) the mind estimates the magnitude of an +object, comparing the angle under which it is seen with its distance, and +thence inferring the magnitude thereof. What inclines men to this mistake +(beside the humour of making one see by geometry)is that the same +perceptions or ideas which suggest distance do also suggest magnitude. +But if we examine it we shall find they suggest the latter as immediately +as the former. I say, they do not first suggest distance, and then leave +it to the judgment to use that as a medium whereby to collect the +magnitude; but they have as close and immediate a connexion with the +magnitude as with the distance; and suggest magnitude as independently of +distance as they do distance independently of magnitude. All which will +be evident to whoever considers what hath been already said, and what +follows. + +54. It hath been shown there are two sorts of objects apprehended by +sight; each whereof hath its distinct magnitude, or extension. The one, +properly tangible, i.e. to be perceived and measured by touch, and not +immediately falling under the sense of seeing: the other, properly and +immediately visible, by mediation of which the former is brought in view. +Each of these magnitudes are greater or lesser, according as they contain +in them more or fewer points, they being made up of points or minimums. +For, whatever may be said of extension in abtract, it is certain sensible +extension is not infinitely divisible. There is a MINIMUM TANGIBILE and a +MINIMUM VISIBILE, beyond which sense cannot perceive. This everyone's +experience will inform him. + +55. The magnitude of the object which exists without the mind, and is at +a distance, continues always invariably the same: but the visible object +still changing as you approach to, or recede from, the tangible object, +it hath no fixed and determinate greatness. Whenever, therefore, we speak +of the magnitude of anything, for instance a tree or a house, we must +mean the tangible magnitude, otherwise there can be nothing steady and +free from ambiguity spoken of it. But though the tangible and visible +magnitude in truth belong to two distinct objects: I shall nevertheless +(especially since those objects are called by the same name, and are +observed to coexist), to avoid tediousness and singularity of speech, +sometimes speak of them as belonging to one and the same thing. + +56. Now in order to discover by what means the magnitude of tangible +objects is perceived by sight. I need only reflect on what passes in my +own mind, and observe what those things be which introduce the ideas of +greater or lesser into my thoughts, when I look on any object. And these +I find to be, FIRST, the magnitude or extension of the visible object, +which being immediately perceived by sight, is connected with that other +which is tangible and placed at a distance. SECONDLY, the confusion or +distinctness. And thirdly, the vigorousness or faintness of the aforesaid +visible appearance. CETERIS PARIBUS, by how much the greater or lesser +the visible object is, by so much the greater or lesser do I conclude the +tangible object to be. But, be the idea immediately perceived by sight +never so large, yet if it be withal confused, I judge the magnitude of +the thing to be but small. If it be distinct and clear, I judge it +greater. And if it be faint, I apprehend it to be yet greater. What is +here meant by confusion and faintness hath been explained in sect. 35. + +57. Moreover the judgments we make of greatness do, in like manner as +those of distance, depend on the disposition of the eye, also on the +figure, number, and situation of objects and other circumstances that +have been observed to attend great or small tangible magnitudes. Thus, +for instance, the very same quantity of visible extension, which in the +figure of a tower doth suggest the idea of great magnitude, shall in the +figure of a man suggest the idea of much smaller magnitude. That this is +owing to the experience we have had of the usual bigness of a tower and a +man no one, I suppose, need be told. + +58. It is also evident that confusion or faintness have no more a +necessary connexion with little or great magnitude than they have with +little or great distance. As they suggest the latter, so they suggest the +former to our minds. And by consequence, if it were not for experience, +we should no more judge a faint or confused appearance to be connected +with great or little magnitude, than we should that it was connected with +great or little distance. + +59. Nor will it be found that great or small visible magnitude hath any +necessary relation to great or small tangible magnitude: so that the one +may certainly be inferred from the other. But before we come to the proof +of this, it is fit we consider the difference there is betwixt the +extension and figure which is the proper object of touch, and that other +which is termed visible; and how the former is principally, though not +immediately taken notice of, when we look at any object. This has been +before mentioned, but we shall here inquire into the cause thereof. We +regard the objects that environ us in proportion as they are adapted to +benefit or injure our own bodies, and thereby produce in our minds the +sensation of pleasure or pain. Now bodies operating on our organs, by an +immediate application, and the hurt or advantage arising therefrom, +depending altogether on the tangible, and not at all on the visible, +qualities of any object: this is a plain reason why those should be +regarded by us much more than these: and for this end the visive sense +seems to have been bestowed on animals, to wit, that by the perception of +visible ideas (which in themselves are not capable of affecting or any +wise altering the frame of their bodies) they may be able to foresee +(from the experience they have had what tangible ideas are connected with +such and such visible ideas) and damage or benefit which is like to +ensue, upon the application of their own bodies to this or that body +which is at a distance. Which foresight, how necessary it is to the +preservation of an animal, everyone's experience can inform him. Hence it +is that when we look at an object, the tangible figure and extension +thereof are principally attended to; whilst there is small heed taken of +the visible figure and magnitude, which, though more immediately +perceived, do less concern us, and are not fitted to produce any +alteration in our bodies. + +60. That the matter of fact is true will be evident to anyone who +considers that a man placed at ten foot distance is thought as great as +if he were placed at a distance only of five foot: which is true not with +relation to the visible, but tangible greatness of the object: the +visible magnitude being far greater at one station: than it is at the +other. + +61. Inches, feet, etc., are settled stated lengths whereby we measure +objects and estimate their magnitude: we say, for example, an object +appears to be six inches or six foot long. Now, that this cannot be meant +of visible inches, etc., is evident, because a visible inch is itself no +constant, determinate magnitude, and cannot therefore serve to mark out +and determine the magnitude of any other thing. Take an inch marked upon +a ruler: view it, successively, at the distance of half a foot, a foot, a +foot and a half, etc., from the eye: at each of which, and at all the +intermediate distances, the inch shall have a different visible +extension, i.e. there shall be more or fewer points discerned in it. Now +I ask which of all these various extensions is that stated, determinate +one that is agreed on for a common measure of other magnitudes? No reason +can be assigned why we should pitch on one more than another: and except +there be some invariable, determinate extension fixed on to be marked to +the word inch, it is plain it can be used to little purpose; and to say a +thing contains this or that number of inches shall imply no more than +that it is extended, without bringing any particular idea of that +extension into the mind. Farther, an inch and a foot, from different +distances, shall both exhibit the same visible magnitude, and yet at the +same time you shall say that one seems several times greater than the +other. From all which it is manifest that the judgments we make of the +magnitude of objects by sight are altogether in reference to their +tangible extension. Whenever we say an object is great, or small, of this +or that determinate measure, I say it must be meant of the tangible, and +not the visible extension, which, though immediately perceived, is +nevertheless little taken notice of. + +62. Now, that there is no necessary connexion between these two distinct +extensions is evident from hence: because our eyes might have been framed +in such a manner as to be able to see nothing but what were less than the +MINIMUM TANGIBILE. In which case it is not impossible we might have +perceived all the immediate objects of sight, the very same that we do +now: but unto those visible appearances there would not be connected +those different tangible magnitudes that are now. Which shows the +judgments we make of the magnitude of things placed at a distance from +the various greatness of the immediate objects of sight do not arise from +any essential or necessary but only a customary tie, which has been +observed between them. + +63. Moreover, it is not only certain that any idea of sight might not +have been connected with this or that idea of touch, which we now observe +to accompany it: but also that the greater visible magnitudes might have +been connected with, and introduced into our minds lesser tangible +magnitudes and the lesser visible magnitudes greater tangible magnitudes. +Nay, that it actually is so we have daily experience; that object which +makes a strong and large appearance, not seeming near so great as +another, the visible magnitude whereof is much less, but more faint, and +the appearance upper, or which is the same thing painted lower on the +RETINA, which faintness and situation suggest both greater magnitude and +greater distance. + +64. From which, and from sect. 57 and 58, it is manifest that as we do +not perceive the magnitudes of objects immediately by sight, so neither +do we perceive them by the mediation of anything which has a necessary +connexion with them. Those ideas that now suggest unto us the various +magnitudes of external objects before we touch them, might possibly have +suggested no such thing: or they might have signified them in a direct +contrary manner: so that the very same ideas, on the perception whereof +we judge an object to be small, might as well have served to make us +conclude it great. Those ideas being in their own nature equally fitted +to bring into our minds the idea of small or great, or no size at all of +outward objects; just as the words of any language are in their own +nature indifferent to signify this or that thing or nothing at all. + +65. As we see distance, so we see magnitude. And we see both in the same +way that we see shame or anger in the looks of a man. Those passions are +themselves invisible, they are nevertheless let in by the eye along with +colours and alterations of countenance, which are the immediate object of +vision: and which signify them for no other reason than barely because +they have been observed to accompany them. Without which experience we +should no more have taken blushing for a sign of shame than of gladness. + +66. We are nevertheless exceeding prone to imagine those things which are +perceived only by the mediation of others to be themselves the immediate +objects of sight; or, at least, to have in their own nature a fitness to +be suggested by them, before ever they had been experienced to coexist +with them. From which prejudice everyone, perhaps, will not find it easy +to emancipate himself, by any [but] the clearest convictions of reason. +And there are some grounds to think that if there was one only invariable +and universal languages in the world, and that men were born with the +faculty of speaking it, it would be the opinion of many that the ideas of +other men's minds were properly perceived by the ear, or had at least a +necessary and inseparable tie with the sounds that were affixed to them. +All which seems to arise from want of a due application of our discerning +faculty, thereby to discriminate between the ideas that are in our +understandings, and consider them apart from each other; which would +preserve us from confounding those that are different, and make us see +what ideas do, and what do not include or imply this or that other idea. + +67. There is a celebrated phenomenon, the solution whereof I shall +attempt to give by the principles that have been laid down, in reference +to the manner wherein we apprehend by sight the magnitude of objects. The +apparent magnitude of the moon when placed in the horizon is much greater +than when it is in the meridian, though the angle under which the +diameter of the moon is seen be not observed greater in the former case +than in the latter: and the horizontal moon doth not constantly appear of +the same bigness, but at some times seemeth far greater than at others. + +68. Now in order to explain the reason of the moon's appearing greater +than ordinary in the horizon, it must be observed that the particles +which compose our atmosphere intercept the rays of light proceeding from +any object to the eye; and by how much the greater is the portion of +atmosphere interjacent between the object and the eye, by so much the +more are the rays intercepted; and by consequence the appearance of the +object rendered more faint, every object appearing more vigorous or more +faint in proportion as it sendeth more or fewer rays into the eye. Now +between the eye and the moon, when situated in the horizon, there lies a +far greater quantity of atmosphere than there does when the moon is in +the meridian. Whence it comes to pass that the appearance of the +horizontal moon is fainter, and therefore by sect. 56 it should be +thought bigger in that situation than in the meridian, or in any other +elevation above the horizon. + +69. Farther, the air being variously impregnated, sometimes more and +sometimes less, with vapours and exhalations fitted to retund and +intercept the rays of light, it follows that the appearance of the +horizontal moon hath not always an equal faintness, and by consequence +that luminary, though in the very same situation, is at one time judged +greater than at another. + +70. That we have here given the true account of the phenomena of the +horizontal moon will, I suppose, be farther evident to anyone from the +following considerations. FIRST, it is plain that which in this case +suggests the idea of greater magnitude must be something which is itself +perceived; for that which is unperceived cannot suggest to our perception +any other thing. SECONDLY, it must be something that does not constantly +remain the same, but is subject to some change or variation, since the +appearance of the horizontal moon varies, being at one time greater than +at another. And yet, THIRDLY, it cannot be the visible figure or +magnitude, since that remains the same, or is rather lesser, by how much +the moon is nearer to the horizon. It remains therefore that the true +cause is that affection or alteration of the visible appearance which +proceeds from the greater paucity of rays arriving at the eye, and which +I term FAINTNESS: since this answers all the forementioned conditions, +and I am not conscious of any other perception that doth. + +71. Add to this that in misty weather it is a common observation that the +appearance of the horizontal moon is far larger than usual, which greatly +conspires with and strengthens our opinion. Neither would it prove in the +least irreconcilable with what we have said, if the horizontal moon +should chance sometimes to seem enlarged beyond its usual extent, even in +more serene weather. For we must not only have regard to the mist which +happens to be in the place where we stand; we ought also to take into our +thoughts the whole sum of vapours and exhalations which lie betwixt the +eye and the moon: all which cooperating to render the appearance of the +moon more faint, and thereby increase its magnitude, it may chance to +appear greater than it usually does, even in the horizontal position, at +a time when, though there be no extraordinary fog or haziness, just in +the place where we stand, yet the air between the eye and the moon, taken +all together, may be loaded with a greater quantity of interspersed +vapours and exhalations than at other times. + +72. It may be objected that in consequence of our principles the +interposition of a body in some degree opaque, which may intercept a +great part of the rays of light, should render the appearance of the moon +in the meridian as large as when it is viewed in the horizon. To which I +answer, it is not faintness anyhow applied that suggests greater +magnitude, there being no necessary but only an experimental connexion +between those two things. It follows that the faintness which enlarges +the appearance must be applied in such sort, and with such circumstances, +as have been observed to attend the vision of great magnitudes. When from +a distance we behold great objects, the particles of the intermediate air +and vapours, which are themselves unperceivable, do interrupt the rays of +light, and thereby render the appearance less strong and vivid: now, +faintness of appearance caused in this sort hath been experienced to +coexist with great magnitude. But when it is caused by the interposition +of an opaque sensible body, this circumstance alters the case, so that a +faint appearance this way caused doth not suggest greater magnitude, +because it hath not been experienced to coexist with it. + +73. Faintness, as well as all other ideas or perceptions which suggest +magnitude or distance, doth it in the same way that words suggest the +notions to which they are annexed. Now, it is known a word pronounced +with certain circumstances, or in a certain context with other words, +hath not always the same import and signification that it hath when +pronounced in some other circumstances or different context of words. The +very same visible appearance as to faintness and all other respects, if +placed on high, shall not suggest the same magnitude that it would if it +were seen at an equal distance on a level with the eye. The reason +whereof is that we are rarely accustomed to view objects at a great +height; our concerns lie among things situated rather before than above +us, and accordingly our eyes are not placed on the top of our heads, but +in such a position as is most convenient for us to see distant objects +standing in our way. And this situation of them being a circumstance +which usually attends the vision of distant objects, we may from hence +account for (what is commonly observed) an object's appearing of +different magnitude, even with respect to its horizontal extension, on +the top of a steeple, for example, an hundred feet high to one standing +below, from what it would if placed at an hundred feet distance on a +level with his eye. For it hath been shown that the judgment we make on +the magnitude of a thing depends not on the visible appearance alone, but +also on divers other circumstances, any one of which being omitted or +varied may suffice to make some alteration in our judgment. Hence, the +circumstances of viewing a distant object in such a situation as is +usual, and suits with the ordinary posture of the head and eyes being +omitted, and instead thereof a different situation of the object, which +requires a different posture of the head taking place, it is not to be +wondered at if the magnitude be judged different: but it will be demanded +why an high object should constantly appear less than an equidistant low +object of the same dimensions, for so it is observed to be: it may indeed +be granted that the variation of some circumstances may vary the judgment +made on the magnitude of high objects, which we are less used to look at: +but it does not hence appear why they should be judged less rather than +greater? I answer that in case the magnitude of distant objects was +suggested by the extent of their visible appearance alone, and thought +proportional thereto, it is certain they would then be judged much less +than now they seem to be (VIDE sect. 79). But several circumstances +concurring to form the judgment we make on the magnitude of distant +objects, by means of which they appear far larger than others, whose +visible appearance hath an equal or even greater extension; it follows +that upon the change or omission of any of those circumstances which are +wont to attend the vision of distant objects, and so come to influence +the judgments made on their magnitude, they shall proportionably appear +less than otherwise they would. For any of those things that caused an +object to be thought greater than in proportion to its visible extension +being either omitted or applied without the usual circumstances, the +judgment depends more entirely on the visible extension, and consequently +the object must be judged less. Thus in the present case the situation of +the thing seen being different from what it usually is in those objects +we have occasion to view, and whose magnitude we observe, it follows that +the very same object, being an hundred feet high, should seem less than +if it was an hundred feet off on (or nearly on) a level with the eye. +What has been here set forth seems to me to have no small share in +contributing to magnify the appearance of the horizontal moon, and +deserves not to be passed over in the explication of it. + +74. If we attentively consider the phenomenon before us, we shall find +the not discerning between the mediate and immediate objects of sight to +be the chief cause of the difficulty that occurs in the explication of +it. The magnitude of the visible moon, or that which is the proper and +immediate object of vision, is not greater when the moon is in the +horizon than when it is in the meridian. How comes it, therefore, to seem +greater in one situation than the other? What is it can put this cheat on +the understanding? It has no other perception of the moon than what it +gets by sight: and that which is seen is of the same extent, I say, the +visible appearance hath the same, or rather a less, magnitude when the +moon is viewed in the horizontal than when in the meridional position: +and yet it is esteemed greater in the former than in the latter. Herein +consists the difficulty, which doth vanish and admit of a most easy +solution, if we consider that as the visible moon is not greater in the +horizon than in the meridian, so neither is it thought to be so. It hath +been already shown that in any act of vision the visible object +absolutely, or in itself, is little taken notice of, the mind still +carrying its view from that to some tangible ideas which have been +observed to be connected with it, and by that means come to be suggested +by it. So that when a thing is said to appear great or small, or whatever +estimate be made of the magnitude of any thing, this is meant not of the +visible but of the tangible object. This duly considered, it will be no +hard matter to reconcile the seeming contradiction there is, that the +moon should appear of a different bigness, the visible magnitude thereof +remaining still the same. For by sect. 56 the very same visible +extension, with a different faintness, shall suggest a different tangible +extension. When therefore the horizontal moon is said to appear greater +than the meridional moon, this must be understood not of a greater +visible extension, but a of greater tangible or real extension, which by +reason of the more than ordinary faintness of the visible appearance, is +suggested to the mind along with it. + +75. Many attempts have been made by learned men to account for this +appearance. Gassendus, Descartes, Hobbes, and several others have +employed their thoughts on that subject; but how fruitless and +unsatisfactory their endeavours have been is sufficiently shown in THE +TRANSACTIONS,[Phil. Trans. Num. 187. p. 314] where you may +see their several opinions at large set forth and confuted, not without +some surprize at the gross blunders that ingenious men have been forced +into by endeavouring to reconcile this appearance with the ordinary +Principles of optics. Since the writing of which there hath been published +in the TRANSACTIONS [Numb. 187. P. 323] another paper relating to the same +affair by the celebrated Dr. Wallis, wherein he attempts to account for +that phenomenon which, though it seems not to contain anything new or +different from what had been said before by others, I shall nevertheless +consider in this place. + +76. His opinion, in short, is this; we judge not of the magnitude of an +object by the visual angle alone, but by the visual angle in conjunction +with the distance. Hence, though the angle remain the same, or even +become less, yet if withal the distance seem to have been increased, the +object shall appear greater. Now, one way whereby we estimate the +distance of anything is by the number and extent of the intermediate +objects: when therefore the moon is seen in the horizon, the variety of +fields, houses, etc., together with the large prospect of the wide +extended land or sea that lies between the eye and the utmost limb of the +horizon, suggest unto the mind the idea of greater distance, and +consequently magnify the appearance. And this, according to Dr. Wallis, +is the true account of the extraordinary largeness attributed by the mind +to the horizontal moon at a time when the angle subtended by its diameter +is not one jot greater than it used to be. + +77. With reference to this opinion, not to repeat what hath been already +said concerning distance, I shall only observe, FIRST, that if the +prospect of interjacent objects be that which suggests the idea of +farther distance, and this idea of farther distance be the cause that +brings into the mind the idea of greater magnitude, it should hence +follow that if one looked at the horizontal moon from behind a wall, it +would appear no bigger than ordinary. For in that case the wall +interposing cuts off all that prospect of sea and land, etc. which might +otherwise increase the apparent distance, and thereby the apparent +magnitude of the moon. Nor will it suffice to say the memory doth even +then suggest all that extent of land, etc., which lies within the +horizon; which suggestion occasions a sudden judgment of sense that the +moon is farther off and larger than usual. For ask any man who, from such +a station beholding the horizontal moon, shall think her greater than +usual, whether he hath at that time in his mind any idea of the +intermediate objects, or long tract of land that lies between his eye and +the extreme edge of the horizon? And whether it be that idea which is the +cause of his making the aforementioned judgment? He will, I suppose, +reply in the negative, and declare the horizontal moon shall appear +greater than the meridional, though he never thinks of all or any of +those things that lie between him and it. SECONDLY, it seems impossible +by this hypothesis to account for the moon's appearing in the very same +situation at one time greater than at another; which nevertheless has +been shown to be very agreeable to the principles we have laid down, and +receives a most easy and natural explication from them. For the further +clearing' up of this point it is to be observed that what we immediately +and properly see are only lights and colours in sundry situations and +shades and degrees of faintness and clearness, confusion and +distinctness. All which visible objects are only in the mind, nor do they +suggest ought external, whether distance or magnitude, otherwise than by +habitual connexion as words do things. We are also to remark that, beside +the straining of the eyes, and beside the vivid and faint, the distinct +and confused appearances (which, bearing some proportion to lines and +angles, have been substituted instead of them in the foregoing part of +this treatise), there are other means which suggest both distance and +magnitude; particularly the situation of visible points of objects, as +upper or lower; the one suggesting a farther distance and greater +magnitude, the other a nearer distance and lesser magnitude: all which is +an effect only of custom and experience; there being really nothing +intermediate in the line of distance between the uppermost and lowermost, +which are both equidistant, or rather at no distance from the eye, as +there is also nothing in upper or lower, which by necessary connexion +should suggest greater or lesser magnitude. Now, as these customary, +experimental means of suggesting distance do likewise suggest magnitude, +so they suggest the one as immediately as the other. I say they do not +(VIDE sect. 53) first suggest distance, and then leave the mind from +thence to infer or compute magnitude, jut suggest magnitude as +immediately and directly as they suggest distance. + +78. This phenomenon of the horizontal moon is a clear instance of the +insufficiency of lines and angles for explaining the way wherein the mind +perceives and estimates the magnitude of outward objects. There is +nevertheless a use of computation by them in order to determine the +apparent magnitude of things, so far as they have a connexion with, and +are proportional to, those other ideas or perceptions which are the true +and immediate occasions that suggest to the mind the apparent magnitude +of things. But this in general may, I think, be observed concerning +mathematical computation in optics: that it can never be very precise and +exact since the judgments we make of the magnitude of external things do +often depend on several circumstances, which are not proportionable to, +or capable of being defined by, lines and angles. + +79. From what has been said we may safely deduce this consequence; to +wit, that a man born blind and made to see would, at first opening of his +eyes, make a very different judgment of the magnitude of objects +intromitted by them from what others do. He would not consider the ideas +of sight with reference to, or as having any connexion with, the ideas of +touch: his view of them being entirely terminated within themselves, he +can no otherwise judge them great or small than as they contain a greater +or lesser number of visible points. Now, it being certain that any +visible point can cover or exclude from view only one other visible +point, it follows that whatever object intercepts the view of another +hath an equal number of visible points with it; and consequently they +shall both be thought by him to have the same magnitude. Hence it is +evident one in those circumstances would judge his thumb, with which he +might hide a tower or hinder its being seen, equal to that tower, or his +hand, the interposition whereof might conceal experimental means the +firmament from his view, equal to the firmament: how great an inequality +soever there may in our apprehensions seem to be betwixt those two +things, because of the customary and close connexion that has grown up in +our minds between the objects of sight and touch; whereby the very +different and distinct ideas of those two senses are so blended and +confounded together as to be mistaken for one and the same thing; out of +which prejudice we cannot easily extricate ourselves. + +80. For the better explaining the nature of vision, and setting the +manner wherein we perceive magnitudes in a due light, I shall proceed to +make some observations concerning matters relating thereto, whereof the +want of reflexion, and duly separating between tangible and visible +ideas, is apt to create in us mistaken and confused notions. And FIRST, I +shall observe that the MINIMUM VISIBILE is exactly equal in all beings +whatsoever that are endowed with the visive faculty. No exquisite +formation of the eye, no peculiar sharpness of sight, can make it less in +one creature than in another; for it not being distinguishable into +parts, nor in any wise a consisting of them, it must necessarily be the +same to all. For suppose it otherwise, and that the MINIMUM VISIBILE of a +mite, for instance, be less than the MINIMUM VISIBILE of a man: the +latter therefore may by detraction of some part be made equal to the +former: it doth therefore consist of parts, which is inconsistent with +the notion of a MINIMUM VISIBILE or point. + +81. It will perhaps be objected that the MINIMUM VISIBILE of a man doth +really and in itself contain parts whereby it surpasses that of a mite, +though they are not perceivable by the man. To which I answer, the +MINIMUM VISIBILE having (in like manner as all other the proper and +immediate objects of sight) been shown not to have any existence without +the mind of him who sees it, it follows there cannot be any pan of it +that is not actually perceived, and therefore visible. Now for any object +to contain distinct visible parts, and at the same time to be a MINIMUM +VISIBILE, is a manifest contradiction. + +82. Of these visible points we see at all times an equal number. It is +every whit as great when our view is contracted and bounded by near +objects as when it is extended to larger and remoter. For it being +impossible that one MINIMUM VISIBILE should obscure or keep out of sight +mote than one other, it is a plain consequence that when my view is on +all sides bounded by the walls of my study see just as many visible +points as I could, in case that by the removal of the study-walls and all +other obstructions, I had a full prospect of the circumjacent fields, +mountains, sea, and open firmament: for so long as I am shut up within +the walls, by their interposition every point of the external objects is +covered from my view: but each point that is seen being able to cover or +exclude from sight one only other corresponding point, it follows that +whilst my sight is confined to those narrow walls I see as many points, +or MINIMA VISIBILIA, as I should were those walls away, by looking on all +the external objects whose prospect is intercepted by them. Whenever +therefore we are said to have a greater prospect at one time than +another, this must be understood with relation, not to the proper and +immediate, but the secondary and mediate objects of vision, which, as +hath been shown, properly belong to the touch. + +83. The visive faculty considered with reference to its immediate objects +may be found to labour of two defects. FIRST, in respect of the extent or +number of visible points that are at once perceivable by it, which is +narrow and limited to a certain degree. It can take in at one view but a +certain determinate number of MINIMA VISIBILIA, beyond which it cannot +extend its prospect. Secondly, our sight is defective in that its view is +not only narrow, but also for the most part confused: of those things +that we take in at one prospect we can see but a few at once clearly and +unconfusedly: and the more we fix our sight on any one object, by so much +the darker and more indistinct shall the rest appear. + +84. Corresponding to these two defects of sight, we may imagine as many +perfections, to wit, 1ST, that of comprehending in one view a greater +number of visible points. 2DLY, of being able to view them all equally +and at once with the utmost clearness and distinction. That those +perfections are not actually in some intelligences of a different order +and capacity from ours it is impossible for us to know. + +85. In neither of those two ways do microscopes contribute to the +improvement of sight; for when we look through a microscope we neither +see more visible points, nor are the collateral points more distinct than +when we look with the naked eye at objects placed in a due distance. A +microscope brings us, as it were, into a new world: it presents us with a +new scene of visible objects quite different from what we behold with the +naked eye. But herein consists the most remarkable difference, to wit, +that whereas the objects perceived by the eye alone have a certain +connexion with tangible objects, whereby we are taught to foresee what +will ensue upon the approach or application of distant objects to the +parts of our own body, which much conduceth to its preservation, there is +not the like connexion between things tangible and those visible objects +that are perceived by help of a fine microscope. + +86. Hence it is evident that were our eyes turned into the nature of +microscopes, we should not be much benefited by the change; we should be +deprived of the forementioned advantage we at present receive by the +visive faculty, and have left us only the empty amusement of seeing, +without any other benefit arising from it. But in that case, it will +perhaps be said, our sight would be endued with a far greater sharpness +and penetration than it now hath. But it is certain from what we have +already shown that the MINIMUM VISIBILE is never greater or lesser, but +in all cases constantly the same: and in the case of microscopical eyes I +see only this difference, to wit, that upon the ceasing of a certain +observable connexion betwixt the divers perceptions of sight and touch, +which before enabled us to regulate our actions by the eye, it would now +be rendered utterly unserviceable to that purpose. + +87. Upon the whole it seems that if we consider the use and end of sight, +together with the present state and circumstances of our being, we shall +not find any great cause to complain of any defect or imperfection in it, +or easily conceive how it could be mended. With such admirable wisdom is +that faculty contrived, both for the pleasure and convenience of life. + +88. Having finished what I intended to say concerning the distance and +magnitude of objects, I come now to treat of the manner wherein the mind +perceives by sight their situation. Among the discoveries of the last +age, it is reputed none of the least that the manner of vision hath been +more clearly explained than ever it had been before. There is at this day +no one ignorant that the pictures of external objects are painted on the +RETINA, or fund of the eye: that we can see nothing which is not so +painted: and that, according as the picture is more distinct or confused, +so also is the perception we have of the object: but then in this +explication of vision there occurs one mighty difficulty. The objects are +painted in an inverted order on the bottom of the eye: the upper part of +any object being painted on the lower part of the eye, and the lower part +of the object on the upper part of the eye: and so also as to right and +left. Since therefore the pictures are thus inverted, it is demanded how +it comes to pass that we see the objects erect and in their natural +posture? + +89. In answer to this difficulty we are told that the mind, perceiving an +impulse of a ray of light on the upper part of the eye, considers this +ray as coming in a direct line from the lower part of the object; and in +like manner tracing the ray that strikes on the lower part of the eye, it +is directed to the upper part of the object. Thus in the adjacent figure, +C, the lower point of the object ABC, is projected on C the upper part of +the eye. So likewise the highest point A is projected on A the lowest +part of the eye, which makes the representation CBA inverted: but the +mind considering the stroke that is made on C as coming in the straight +line CC from the lower end of the object; and the stroke or impulse on a +as coming in the line AA from the upper end of the object, is directed to +make a right judgment of the situation of the object ABC, notwithstanding +the picture of it is inverted. This is illustrated by conceiving a blind +man who, holding in his hands two sticks that cross each other, doth with +them touch the extremities of an object, placed in a perpendicular +situation. It is certain this man will judge that to be the upper part of +the object which he touches with the stick held in the undermost hand, +and that to be the lower part of the object which he touches with the +stick in his uppermost hand. This is the common explication of the erect +appearance of objects, which is generally received and acquiesced in, +being (as Mr. Molyneux tells us [Diopt. par. 2. c. 7. P. 289.]) 'allowed +by all men as satisfactory'. + +90. But this account to me does not seem in any degree true. Did I +perceive those impulses, decussations, and directions of the rays of +light in like manner as hath been set forth, then indeed it would not be +altogether void of probability. And there might be some pretence for the +comparison of the blind man and his cross sticks. But the case is far +otherwise. I know very well that I perceive no such thing. And of +consequence I cannot thereby make an estimate of the situation of +objects. I appeal to anyone's experience, whether he be conscious to +himself that he thinks on the intersection made by the radious [SIC] +pencils, or pursues the impulses they give in right lines, whenever he +perceives by sight the position of any object? To me it seems evident +that crossing and tracing of the rays is never thought on by children, +idiots, or in truth by any other, save only those who have applied +themselves to the study of optics. And for the mind to judge of the +situation of objects by those things without perceiving them, or to +perceive them without knowing it, is equally beyond my comprehension. Add +to this that the explaining the manner of vision by the example of cross +sticks and hunting for the object along the axes of the radious pencils, +doth suppose the proper objects of sight to be perceived at a distance +from us, contrary to what hath been demonstrated. + +91. It remains, therefore, that we look for some other explication of +this difficulty: and I believe it not impossible to find one, provided we +examine it to the bottom, and carefully distinguish between the ideas of +sight and touch; which cannot be too oft inculcated in treating of +vision: but more especially throughout the consideration of this affair +we ought to carry that distinction in our thoughts: for that from want of +a right understanding thereof the difficulty of explaining erect vision +seems chiefly to arise. + +92. In order to disentangle our minds from whatever prejudices we may +entertain with relation to the subject in hand, nothing seems more +apposite than the taking into our thoughts the case of one born blind, +and afterwards, when grown up, made to see. And though, perhaps, it may +not be an easy task to divest ourselves entirely of the experience +received from sight, so as to be able to put our thoughts exactly in the +posture of such a one's, we must, nevertheless, as far as possible, +endeavour to frame true conceptions of what might reasonably be supposed +to pass in his mind. + +93. It is certain that a man actually blind, and who had continued so +from his birth, would by the sense of feeling attain to have ideas of +upper and lower. By the motion of his hand he might discern the situation +of any tangible object placed within his FI reach. That part on which he +felt himself supported, or towards which he perceived his body to +gravitate, he would term lower, and the contrary to this upper; and +accordingly denominate whatsoever objects he touched. + +94. But then, whatever judgments he makes concerning the situation of +objects are confined to those only that are perceivable by touch. All +those things that are intangible and of a spiritual nature, his thoughts +and desires, his passions, and in general all the modifications of the +soul, to these he would never apply the terms UPPER and LOWER, except +only in a metaphorical sense. He may, perhaps, by way of allusion, speak +of high or low thoughts: but those terms in their proper signification +would never be applied to anything that was not conceived to exist +without the mind. For a man born blind, and remaining in the same state, +could mean nothing else by the words HIGHER and LOWER than a greater or +lesser distance from the earth; which distance he would measure by the +motion or application of his hand or some other part of his body. It is +therefore evident that all those things which, in respect of each other, +would by him be thought higher or lower, must be such as were conceived +to exist without his mind, in the ambient space. + +95. Whence it plainly follows that such a one, if we suppose him made to +see, would not at first sight think anything he saw was high or low, +erect or inverted; for it hath been already demonstrated in sect. 41 that +he would not think the things he perceived by sight to be at any distance +from him, or without his mind. The objects to which he had hitherto been +used to apply the terms UP and DOWN, HIGH and LOW, were such only as +affected or were some way perceived by his couch: but the proper objects +of vision make a new set of ideas, perfectly distinct and different from +the former, and which can in no sort make themselves perceived by touch. +There is, therefore, nothing at all that could induce him to think those +terms applicable to them: nor would he ever think it till such time as he +had observed their connexion with tangible objects, and the same +prejudice began to insinuate itself into his understanding, which from +their infancy had grown up in the understandings of other men. + +96. To set this matter in a clearer light I shall make use of an example. +Suppose the above-mentioned blind person by his touch perceives a man to +stand erect. Let us inquire into the manner of this. By the application +of his hand to the several parts of a human body he had perceived +different tangible ideas, which being collected into sundry complex ones, +have distinct names annexed to them. Thus one combination of a certain +tangible figure, bulk, and consistency of parts is called the head, +another the hand, a third the foot, and so of the rest: all which complex +ideas could, in his understanding, be made up only of ideas perceivable +by touch. He had also by his touch obtained an idea of earth or ground, +towards which he perceives the parts of his body to have a natural +tendency. Now, by ERECT nothing more being meant than that perpendicular +position of a man wherein his feet are nearest to the earth, if the blind +person by moving his hand over the parts of the man who stands before him +perceives the tangible ideas that compose the head to be farthest from, +and those that compose the feet to be nearest to, that other combination +of tangible ideas which he calls earth, he will denominate that man +erect. But if we suppose him on a sudden to receive his sight, and that +he behold a man standing before him, it is evident in that case he would +neither judge the man he sees to be erect nor inverted; for he never +having known those terms applied to any other save tangible things, or +which existed in the space without him, and what he sees neither being +tangible nor perceived as existing without, he could not know that in +propriety of language they were applicable to it. + +97. Afterwards, when upon turning his head or eyes up and down to the +right and left he shall observe the visible objects to change, and shall +also attain to know that they are called by the same names, and connected +with the objects perceived by touch; then indeed he will come to speak of +them and their situation, in the same terms that he has been used to +apply to tangible things; and those that he perceives by turning up his +eyes he will call upper, and those that by turning down his eyes he will +call lower. + +98. And this seems to me the true reason why he should think those +objects uppermost that are painted on the lower part of his eye: for by +turning the eye up they shall be distinctly seen; as likewise those that +are painted on the highest part of the eye shall be distinctly seen by +turning the eye down, and are for that reason esteemed lowest; for we +have shown that to the immediate objects of sight considered in +themselves, he would not attribute the terms HIGH and LOW. It must +therefore be on account of some circumstances which are observed to +attend them: and these, it is plain, are the actions of turning the eye +up and down, which suggest a very obvious reason why the mind should +denominate the objects of sight accordingly high or low. And without this +motion of the eye, this turning it up and down in order to discern +different objects, doubtless ERECT, INVERSE, and other the like terms +relating to the position of tangible objects, would never have been +transferred, or in any degree apprehended to belong to the ideas of +sight: the mere act of seeing including nothing in it to that purpose; +whereas the different situations of the eye naturally direct the mind to +make a suitable judgment of the situation of objects intromitted by it. + +99. Farther, when he has by experience learned the connexion there is +between the several ideas of sight and touch, he will be able, by the +perception he has of the situation of visible things in respect of one +another, to make a sudden and true estimate of the situation of outward, +tangible things corresponding to them. And thus it is he shall perceive +by sight the situation of external objects which do not properly fall +under that sense. + +100. I know we are very prone to think that, if just made to see, we +should judge of the situation of visible things as we do now: but we are +also as prone to think that, at first sight, we should in the same way +apprehend the distance and magnitude of objects as we do now: which hath +been shown to be a false and groundless persuasion. And for the like +reasons the same censure may be passed on the positive assurance that +most men, before they have thought sufficiently of the matter, might have +of their being able to determine by the eye at first view, whether +objects were erect or inverse. + +101. It will, perhaps, be objected co our opinion that a man, for +instance, being thought erect when his feet are next the earth, and +inverted when his head is next the earth, it doth hence follow that by +the mere act of vision, without any experience or altering the situation +of the eye, we should have determined whether he were erect or inverted: +for both the earth itself, and the limbs of the man who stands thereon, +being equally perceived by sight, one cannot choose seeing what part of +the man is nearest the earth, and what part farthest from it, i.e. +whether he be erect or inverted. + +I02. To which I answer, the ideas which constitute the tangible earth and +man are entirely different from those which constitute the visible earth +and man. Nor was it possible, by virtue of the visive faculty alone, +without superadding any experience of touch, or altering the position of +the eye, ever to have known, or so much as suspected, there had been any +relation or connexion between them. Hence a man at first view would not +denominate anything he saw earth, or head, or foot; and consequently he +could not tell by the mere act of vision whether the head or feet were +nearest the earth: nor, indeed, would we have thereby any thought of +earth or man, erect or inverse, at all: which will be made yet more +evident if we nicely observe, and make a particular comparison between, +the ideas of both senses. + +103. That which I see is only variety of light and colours. That which I +feel is hard or soft, hot or cold, rough or smooth. What similitude, what +connexion have those ideas with these? Or how is it possible that anyone +should see reason to give one and the same name to combinations of ideas +so very different before he had experienced their coexistence? We do not +find there is any necessary connexion betwixt this or that tangible +quality and any colour whatsoever. And we may sometimes perceive colours +where there is nothing to be felt. All which doth make it manifest that +no man, at first receiving of his sight, would know there was any +agreement between this or that particular object of his sight and any +object of touch he had been already acquainted with: the colours, +therefore, of the head would to him no more suggest the idea of head than +they would the idea of foot. + +104. Farther, we have at large shown (VID. sect. 63 and 64) there is no +discoverable necessary connexion between any given visible magnitude and +any one particular tangible magnitude; but that it is entirely the result +of custom and experience, and depends on foreign and accidental +circumstances that we can by the perception of visible extension inform +ourselves what may be the extension of any tangible object connected with +it. Hence it is certain that neither the visible magnitude of head or +foot would bring along with them into the mind, at first opening of the +eyes, the respective tangible magnitudes of those parts. + +105. By the foregoing section it is plain the visible figure of any part +of the body hath no necessary connexion with the tangible figure thereof, +so as at first sight to suggest it to the mind. For figure is the +termination of magnitude; whence it follows that no visible magnitude +having in its own nature an aptness to suggest any one particular +tangible magnitude, so neither can any visible figure be inseparably +connected with its corresponding tangible figure: so as of itself and in +a way prior to experience, it might suggest it to the understanding. This +will be farther evident if we consider that what seems smooth and round +to the touch may to sight, if viewed through a microscope, seem quite +otherwise. + +106. From all which laid together and duly considered, we may clearly +deduce this inference. In the first act of vision no idea entering by the +eye would have a perceivable connexion with the ideas to which the names +EARTH, MAN, HEAD, FOOT, etc., were annexed in the understanding of a +person blind from his birth; so as in any sort to introduce them into his +mind, or make themselves be called by the same names, and reputed the +same things with them, as afterwards they come to be. + +107. There doth, nevertheless, remain one difficulty, which perhaps may +seem to press hard on our opinion, and deserve not to be passed over: for +though it be granted that neither the colour, size, nor figure of the +visible feet have any necessary connexion with the ideas that compose the +tangible feet, so as to bring them at first sight into my mind, or make +me in danger of confounding them before I had been used to, and for some +time experienced their connexion: yet thus much seems undeniable, namely, +that the number of the visible feet being the same with that of the +tangible feet, I may from hence without any experience of sight +reasonably conclude that they represent or are connected with the feet +rather than the head. I say, it seems the idea of two visible feet will +sooner suggest to the mind the idea of two tangible feet than of one +head; so that the blind man upon first reception of the visive faculty +might know which were the feet or two, and which the head or one. + +108. In order to get clear of this seeming difficulty we need only +observe that diversity of visible objects doth not necessarily infer +diversity of tangible objects corresponding to them. A picture painted +with great variety of colours affects the touch in one uniform manner; it +is therefore evident that I do not by any necessary consecution, +independent of experience, judge of the number of things tangible from +the number of things visible. I should not, therefore, at first opening +my eyes conclude that because I see two I shall feel two. How, therefore, +can I, before experience teaches me, know that the visible legs, because +two, are connected with the tangible legs, or the visible head, because +one, is connected with the tangible head? The truth is, the things I see +are so very different and heterogeneous from the things I feel that the +perception of the one would never have suggested the other to my +thoughts, or enabled me to pass the least judgment thereon, until I had +experienced their connexion. + +109. But for a fuller illustration of this matter it ought to be +considered that number (however some may reckon it amongst the primary +qualities) is nothing fixed and settled, really existing in things +themselves. It is entirely the creature of the mind, considering either +an idea by itself, or any combination of ideas to which it gives one +name, and so makes it pass for an unit. According as the mind variously +combines its ideas the unit varies: and as the unit, so the number, which +is only a collection of units, doth also vary. We call a window one, a +chimney one, and yet a house in which there are many windows and many +chimneys hath an equal right to be called one, and many houses go to the +making of the city. In these and the like, instances it is evident the +unit constantly relates to the particular draughts the mind makes of its +ideas, to which it affixes names, and wherein it includes more or less as +best suits its own ends and purposes. Whatever, therefore, the mind +considers as one, that is an unit. Every combination of ideas is +considered as one thing by the mind, and in token thereof is marked by +one name. Now, this naming and combining together of ideas is perfectly +arbitrary, and done by the mind in such sort as experience shows it to be +most convenient: without which our ideas had never been collected into +such sundry distinct combinations as they now are. + +110. Hence it follows that a man born blind and afterwards, when grown +up, made to see, would not in the first act of vision parcel out the +ideas of sight into the same distinct collections that others do, who +have experienced which do regularly coexist and are proper to be bundled +up together under one name. He would not, for example, make into one +complex idea, and thereby esteem an unit, all those particular ideas +which constitute the visible head or foot. For there can be no reason +assigned why he should do so, barely upon his seeing a man stand upright +before him. There crowd into his mind the ideas which compose the visible +man, in company with all the other ideas of sight perceived at the same +time: but all these ideas offered at once to his view, he would not +distribute into sundry distinct combinations till such time as by +observing the motion of the parts of the man and other experiences he +comes to know which are to be separated and which to be collected +together. + +111. From what hath been premised it is plain the objects of sight and +touch make, if I may so say, two sets of ideas which are widely different +from each other. To objects of either kind we indifferently attribute the +terms high and low, right and left, and suchlike, denoting the position +or situation of things: but then we must well observe that the position +of any object is determined with respect only to objects of the same +sense. We say any object of touch is high or low, according as it is more +or less distant from the tangible earth: and in like manner we denominate +any object of sight high or low in proportion as it is more or less +distant from the visible earth: but to define the situation of visible +things with relation to the distance they bear from any tangible thing, +or VICE VERSA, this were absurd and perfectly unintelligible. For all +visible things are equally in the mind, and take up no part of the +external space: and consequently are equidistant from any tangible thing +which exists without the mind. + +112. Or rather, to speak truly, the proper objects of sight are at no +distance, neither near nor far, from any tangible thing. For if we +inquire narrowly into the matter we shall find that those things only are +compared together in respect of distance which exist after the same +manner, or appertain unto the same sense. For by the distance between any +two points nothing more is meant than the number of intermediate points: +if the given points are visible the distance between them is marked out +by the number of the interjacent visible points: if they are tangible, +the distance between them is a line consisting of tangible points; but if +they are one tangible and the other visible, the distance between them +doth neither consist of points perceivable by sight nor by touch, i.e. it +is utterly inconceivable. This, perhaps, will not find an easy admission +into all men's understanding: however, I should gladly be informed +whether it be not true by anyone who will be at the pains to reflect a +little and apply it home to his thoughts. + +113. The not observing what has been delivered in the two last sections +seems to have occasioned no small part of the difficulty that occurs in +the business of erect appearances. The head, which is painted nearest the +earth, seems to be farthest from it: and on the other hand the feet, +which are painted farthest from the earth, are thought nearest to it. +Herein lies the difficulty, which vanishes if we express the thing more +clearly and free from ambiguity, thus: how comes it that to the eye the +visible head which is nearest the tangible earth seems farthest from the +earth, and the visible feet, which are farthest from the tangible earth +seem nearest the earth? The question being thus proposed, who sees not +the difficulty is founded on a supposition that the eye, or visive +faculty, or rather the soul by means thereof, should judge of the +situation of visible objects with reference to their distance from the +tangible earth? Whereas it is evident the tangible earth is not perceived +by sight: and it hath been shown in the two last preceding sections that +the location of visible objects is determined only by the distance they +bear from one another; and that it is nonsense to talk of distance, far +or near, between a visible and tangible thing. + +114. If we confine our thoughts to the proper objects of sight, the whole +is plain and easy. The head is painted farthest from, and the feet +nearest to, the visible earth; and so they appear to be. What is there +strange or unaccountable in this? Let us suppose the pictures in the fund +of the eye to be the immediate objects of the sight. The consequence is +that things should appear in the same posture they are painted in; and is +it not so? The head which is seen seems farthest from the earth which is +seen; and the feet which are seen seem nearest to the earth, which is +seen; and just so they are painted. + +115. But, say you, the picture of the man is inverted, and yet the +appearance is erect: I ask, what mean you by the picture of the man, or, +which is the same thing, the visible man's being inverted? You tell me it +is inverted, because the heels are uppermost and the head undermost? +Explain me this. You say that by the head's being undermost you mean that +it is nearest to the earth; and by the heels being uppermost that they +are farthest from the earth. I ask again what earth you mean? You cannot +mean the earth that is painted on the eye, or the visible earth: for the +picture of the head is farthest from the picture of the earth, and the +picture of the feet nearest to the picture of the earth; and accordingly +the visible head is farthest from the visible earth, and the visible feet +nearest to it. It remains, therefore, that you mean the tangible earth, +and so determine the situation of visible things with respect to tangible +things; contrary to what hath been demonstrated in sect. 111 and 112. The +two distinct provinces of sight and touch should be considered apart, and +as if their objects had no intercourse, no manner of relation one to +another, in point of distance or position. + +116. Farther, what greatly contributes to make us mistake in this matter +is that when we think of the pictures in the fund of the eye, we imagine +ourselves looking on the fund of another's eye, or another looking on the +fund of our own eye, and beholding the pictures painted thereon. Suppose +two eyes A and B: A from some distance looking on the pictures in B sees +them inverted, and for that reason concludes they are inverted in B: but +this is wrong. There are projected in little on the bottom of A the +images of the pictures of, suppose, man, earth, etc., which are painted +on B. And besides these the eye B itself, and the objects which environ +it, together with another earth, are projected in a larger size on A. +Now, by the eye A these larger images are deemed the true objects, and +the lesser only pictures in miniature. And it is with respect to those +greater images that it determines the situation of the smaller images: so +that comparing the little man with the great earth, A judges him +inverted, or that the feet are farthest from and the head nearest to the +great earth. Whereas, if A compare the little man with the little earth, +then he will appear erect, i.e. his head shall seem farthest from, and +his feet nearest to, the little earth. But we must consider that B does +not see two earths as A does: it sees only what is represented by the +little pictures in A, and consequently shall judge the man erect. For, in +truth, the man in B is not inverted, for there the feet are next the +earth; but it is the representation of it in A which is inverted, for +there the head of the representation of the picture of the man in B is +next the earth, and the feet farthest from the earth, meaning the earth +which is without the representation of the pictures in B. For if you take +the little images of the pictures in B, and consider them by themselves, +and with respect only to one another, they are all erect and in their +natural posture. + +117. Farther, there lies a mistake in our imagining that the pictures of +external objects are painted on the bottom of the eye. It hath been shown +there is no resemblance BETWEEN the ideas of sight and things tangible. +It hath likewise been demonstrated that the proper objects of sight do +not exist without the mind. Whence it clearly follows that the pictures +painted on the bottom of the eye are not the pictures of external +objects. Let anyone consult his own thoughts, and then say what affinity, +what likeness there is between that certain variety and disposition of +colours which constitute the visible man, or picture of a man, and that +other combination of far different ideas, sensible by touch, which +compose the tangible man. But if this be the case, how come they to be +accounted pictures or images, since that supposes them to copy or +represent some originals or other? + +118. To which I answer: in the forementioned instance the eye A takes the +little images, included within the representation of the other eye B, to +be pictures or copies, whereof the archetypes are not things existing +without, but the larger pictures projected on its own fund: and which by +A are not thought pictures, but the originals, or true things themselves. +Though if we suppose a third eye C from a due distance to behold the fund +of A, then indeed the things projected thereon shall, to C, seem pictures +or images in the same sense that those projected on B do to A. + +119. Rightly to conceive this point we must carefully distinguish between +the ideas of sight and touch, between the visible and tangible eye; for +certainly on the tangible eye nothing either is or seems to be painted. +Again, the visible eye, as well as all other visible objects, hath been +shown to exist only in the mind, which perceiving its own ideas, and +comparing them together, calls some PICTURES in respect of others. What +hath been said, being rightly comprehended and laid together, doth, I +think, afford a full and genuine explication of the erect appearance of +objects; which phenomenon, I must confess, I do not see how it can be +explained by any theories of vision hitherto made public. + +120. In treating of these things the use of language is apt to occasion +some obscurity and confusion, and create in us wrong ideas; for language +being accommodated to the common notions and prejudices of men, it is +scarce possible to deliver the naked and precise truth without great +circumlocution, impropriety, and (to an unwary reader) seeming +contradictions; I do therefore once for all desire whoever shall think it +worth his while to understand what I have written concerning vision, that +he would not stick in this or that phrase, or manner of expression, but +candidly collect my meaning from the whole sum and tenor of my discourse, +and laying aside the words as much as possible, consider the bare notions +themselves, and then judge whether they are agreeable to truth and his +own experience, or no. + +121. We have shown the way wherein the mind by mediation of visible ideas +doth perceive or apprehend the distance, magnitude and situation of +tangible objects. We come now to inquire more particularly concerning the +difference between the ideas of sight and touch, which are called by the +same names, and see whether there be any idea common to both senses. From +what we have at large set forth and demonstrated in the foregoing parts +of this treatise, it is plain there is no one selfsame numerical +extension perceived both by sight and touch; but that the particular +figures and extensions perceived by sight, however they may be called by +the same names and reputed the same things with those perceived by touch, +are nevertheless different, and have an existence distinct and separate +from them: so that the question is not now concerning the same numerical +ideas, but whether there be any one and the same sort of species of ideas +equally perceivable to both senses; or, in other words, whether +extension, figure, and motion perceived by sight are not specifically +distinct from extension, figure, and motion perceived by touch. + +122. But before I come more particularly to discuss this matter, I find +it proper to consider extension in abstract: for of this there is much +talk, and I am apt to think that when men speak of extension as being an +idea common to two senses, it is with a secret supposition that we can +single out extension from all other tangible and visible qualities, and +form thereof an abstract idea, which idea they will have common both to +sight and touch. We are therefore to understand by extension in abstract +an idea of extension, for instance, a line or surface entirely stripped +of all other sensible qualities and circumstances that might determine it +to any particular existence; it is neither black nor white, nor red, nor +hath it any colour at all, or any tangible quality whatsoever and +consequently it is of no finite determinate magnitude: for that which +bounds or distinguishes one extension from another is some quality or +circumstance wherein they disagree. + +123. Now I do not find that I can perceive, imagine, or any wise frame in +my mind such an abstract idea as is here spoken of. A line or surface +which is neither black, nor white, nor blue, nor yellow, etc., nor long, +nor short, nor rough, nor smooth, nor square, nor round, etc., is +perfectly incomprehensible. This I am sure of as to myself: how far the +faculties of other men may reach they best can tell. + +124. It is commonly said that the object of geometry is abstract +extension: but geometry contemplates figures: now, figure is the +termination of magnitude: but we have shown that extension in abstract +hath no finite determinate magnitude. Whence it clearly follows that it +can have no figure, and consequently is not the object of geometry. It is +indeed a tenet as well of the modern as of the ancient philosophers that +all general truths are concerning universal abstract ideas; without +which, we are told, there could be no science, no demonstration of any +general proposition in geometry. But it were no hard matter, did I think +it necessary to my present purpose, to show that propositions and +demonstrations in geometry might be universal, though they who make them +never think of abstract general ideas of triangles or circles. + +125. After reiterated endeavours to apprehend the general idea a +triangle, I have found it altogether incomprehensible. And surely if +anyone were able to introduce that idea into my mind, it must be the +author of the ESSAY CONCERNING HUMAN UNDERSTANDING; he who has so far +distinguished himself from the generality of writers by the clearness +and significancy of what he says. Let us therefore see how this +celebrated author describes the general or abstract idea of a triangle. +'It must be (says he) neither oblique nor rectangular, neither +equilateral, equicrural, nor scalenum; but all and none of these at once. +In effect, it is somewhat imperfect that cannot exist; an idea, wherein +some parts of several different and inconsistent ideas are put together' +ESSAY ON HUM. UNDERSTAND. B. iv. C. 7. S.9. This is the idea which he +thinks needful for the enlargement of knowledge, which is the subject of +mathematical demonstration, and without which we could never come to know +any general proposition concerning triangles. That author acknowledges it +doth 'require some pains and skill to form this general idea of a +triangle.' IBID. But had he called to mind what he says in another place, +to wit, 'That ideas of mixed modes wherein any inconsistent ideas are put +together cannot so much as exist in the mind, i.e. be conceived.' VID. B. +iii. C. 10. S. 33. IBID. I say, had this occurred to his thoughts, it is +not improbable he would have owned it above all the pains and skill he +was master of to form the above-mentioned idea of a triangle, which is +made up of manifest, staring contradictions. That a man who laid so great +a stress on clear and determinate ideas should nevertheless talk at this +rate seems very surprising. But the wonder will lessen if it be +considered that the source whence this opinion flows is the prolific womb +which has brought forth innumerable errors and difficulties in all parts +of philosophy and in all the sciences: but this matter, taken in its full +extent, were a subject too comprehensive to be insisted on in this place. +And so much for extension in abstract. + +126. Some, perhaps, may think pure space, VACUUM, or trine dimension to +be equally the object of sight and touch: but though we have a very great +propension to think the ideas of outness and space to be the immediate +object of sight, yet, if I mistake not, in the foregoing parts of this +essay that hath been clearly demonstated to be a mere delusion, arising +from the quick and sudden suggestion of fancy, which so closely connects +the idea of distance with those of sight, that we are apt to think it is +itself a proper and immediate object of that sense till reason corrects +the mistake. + +127. It having been shown that there are no abstract ideas of figure, and +that it is impossible for us by any precision of thought to frame an idea +of extension separate from all other visible and tangible qualities which +shall be common both to sight and touch: the question now remaining is, +whether the particular extensions, figures, and motions perceived by +sight be of the same kind with the particular extensions, figures, and +motions perceived by touch? In answer to which I shall venture to lay +down the following proposition: THE EXTENSION, FIGURES, AND MOTIONS +PERCEIVED BY SIGHT ARE SPECIFICALLY DISTINCT FROM THE IDEAS OF TOUCH +CALLED BY THE SAME NAMES, NOR is THERE ANY SUCH THING as ONE IDEA OR KIND +OF IDEA COMMON TO BOTH SENSES. This proposition may without much +difficulty be collected from what hath been said in several places of +this essay. But because it seems so remote from, and contrary to, the +received notions and settled opinion of mankind, I shall attempt to +demonstrate it more particularly and at large by the following arguments. + +128. When upon perception of an idea I range it under this or that sort, +it is because it is perceived after the same manner, or because it has a +likeness or conformity with, or affects me in the same way as, the ideas +of the sort I rank it under. In short, it must not be entirely new, but +have something in it old and already perceived by me. It must, I say, +have so much at least in common with the ideas I have before known and +named as to make me give it the same name with them. But it has been, if +I mistake not, clearly made out that a man born blind would not at first +reception of his sight think the things he saw were of the same nature +with the objects of touch, or had anything in common with them; but that +they were a new set of ideas, perceived in a new manner, and entirely +different from all he had ever perceived before: so that he would not +call them by the same name, nor repute them to be of the same sort with +anything he had hitherto known. + +129. SECONDLY, light and colours are allowed by all to constitute a son +or species entirely different from the ideas of touch: nor will any man, +I presume, say they can make themselves perceived by that sense: but +there is no other immediate object of sight besides light and colours. It +is therefore a direct consequence that there is no idea common to both +senses. + +130. It is a prevailing opinion, even amongst those who have thought and +writ most accurately concerning our ideas and the ways whereby they enter +into the understanding, that something more is perceived by sight than +barely light and colours with their variations. Mr. Locke termeth sight, +'The most comprehensive of all our senses, conveying to our minds the +ideas of light and colours, which are peculiar only to that sense; and +also the far different ideas of space, figure, and motion. ESSAY ON HUMAN +UNDERSTAND. B. ii. C. 9. S. 9. Space or distance, we have shown, is not +otherwise the object of sight than of hearing. VID. sect. 46. And as for +figure and extension, I leave it to anyone that shall calmly attend to +his own clear and distinct ideas to decide whether he had any idea +intromitted immediately and properly by sight save only light and +colours: or whether it De possible for him to frame in his mind a +distinct abstract idea of visible extension or figure exclusive of all +colour: and on the other hand, whether he can conceive colour without +visible extension? For my own part, I must confess I am not able to +attain so great a nicety of abstraction: in a strict sense, I see nothing +but light and colours, with their several shades and variations. He who +beside these doth also perceive by sight ideas far different and distinct +from them hath that faculty in a degree more perfect and comprehensive +than I can pretend to. It must be owned that by the mediation of light +and colours other far different ideas are suggested to my mind: but so +they are by hearing, which beside sounds which are peculiar to that +sense, doth by their mediation suggest not only space, figure, and +motion, but also all other ideas whatsoever that can be signified by +words. + +131. THIRDLY, it is, I think, an axiom universally received that +quantities of the same kind may be added together and make one entire +sum. Mathematicians add lines together: but they do not add a line to a +solid, or conceive it as making one sum with a surface: these three kinds +of quantity being thought incapable of any such mutual addition, and +consequently of being compared together in the several ways of +proportion, are by then esteemed entirely disparate and heterogeneous. +Now let anyone try in his thoughts to add a visible line or surface to a +tangible line or surface, so as to conceive them making one continued sum +or whole. He that can do this may think them homogeneous: but he that +cannot, must by the foregoing axiom think them heterogeneous. A blue and +a red line I can conceive added together into one sum and making one +continued line: but to make in my thoughts one continued line of a +visible and tangible line added together is, I find, a task far more +difficult, and even insurmountable: and I leave it to the reflexion and +experience of every particular person to determine for himself. + +132. A farther confirmation of our tenet may be drawn from the solution +of Mr. Molyneux's problem, published by Mr. Locke in his ESSAY: which I +shall set down as it there lies, together with Mr. Locke's opinion of it, +'"Suppose a man born blind, and now adult, and taught by his touch to +distinguish between a cube and a sphere of the same metal, and nighly +[SIC] of the same bigness, so as to tell, when he felt one and t'other, +which is the cube and which the sphere. Suppose then the cube and sphere +placed on a table, and the blind man to be made to see: QUAERE, whether +by his sight, before he touched them, he could now distinguish and tell +which is the globe, which the cube?" To which the acute and judicious +proposer answers: "Not. For though he has obtained the experience of how +a globe, how a cube, affects his touch, yet he has not yet attained the +experience that what affects his touch so or so must affect his sight so +or so: or that a protuberant angle in the cube that pressed his hand +unequally shall appear to his eye as it doth in the cube." I agree with +this thinking gentleman, whom I am proud to call my friend, in his answer +to this his problem; and am of opinion that the blind man at first sight +would not be able with certainty to say which was the globe, which the +cube, whilst he only saw them.' (ESSAY ON HUMAN UNDERSTANDING, B. ii. C. +9. S. 8.) + +133. Now, if a square surface perceived by touch be of the same sort with +a square surface perceived by sight, it is certain the blind man here +mentioned might know a square surface as soon as he saw it: it is no more +but introducing into his mind by a new inlet an idea he has been already +well acquainted with. Since, therefore, he is supposed to have known by +his touch that a cube is a body terminated by square surfaces, and that a +sphere is not terminated by square surfaces: upon the supposition that a +visible and tangible square differ only IN NUMERO it follows that he +might know, by the unerring mark of the square surfaces, which was the +cube, and which not, while he only saw them. We must therefore allow +either that visible extension and figures are specifically distinct from +tangible extension and figures, or else that the solution of this problem +given by those two thoughtful and ingenious men is wrong. + +134. Much more might be laid together in proof of the proposition I have +advanced: but what has been said is, if I mistake not, sufficient to +convince anyone that shall yield a reasonable attention: and as for those +that will not be at the pains of a little thought, no multiplication of +words will ever suffice to make them understand the truth, or rightly +conceive my meaning. + +135. I cannot let go the above-mentioned problem without some reflexion +on it. It hath been evident that a man blind from his birth would not, at +first sight, denominate anything he saw by the names he had been used to +appropriate to ideas of touch, VID. sect. 106. Cube, sphere, table are +words he has known applied to things perceivable by touch, but to things +perfectly intangible he never knew them applied. Those words in their +wonted application always marked out to his mind bodies or solid things +which were perceived by the resistance they gave: but there is no +solidity, no resistance or protrusion, perceived by sight. In short, the +ideas of sight are all new perceptions, to which there be no names +annexed in his mind: he cannot therefore understand what is said to him +concerning them: and to ask of the two bodies he saw placed on the table, +which was the sphere, which the cube? were to him a question downright +bantering and unintelligible; nothing he sees being able to suggest to +his thoughts the idea of body, distance, or in general of anything he had +already known. + +136. It is a mistake to think the same thing affects both sight and +touch. If the same angle or square which is the object of touch be also +the object of vision, what should hinder the blind man at first sight +from knowing it? For though the manner wherein it affects the sight be +different from that wherein it affected his touch, yet, there being +beside his manner or circumstance, which is new and unknown, the angle or +figure, which is old and known, he cannot choose but discern it. + +137. Visible figure and extension having been demonstrated to be of a +nature entirely different and heterogeneous from tangible figure and +extension, it remains that we inquire concerning. Now that visible motion +is not of the same sort with tangible motion seems to need no farther +proof, it being an evident corollary from what we have shown concerning +the difference there is between visible and tangible extension: but for a +more full and express proof hereof we need only observe that one who had +not yet experienced vision would not at first sight know motion. Whence +it clearly follows that motion perceivable by sight is of a sort distinct +from motion perceivable by touch. The antecedent I prove thus: by touch +he could not perceive any motion but what was up or down, to the right or +left, nearer or farther from him; besides these and their several +varieties or complications, it is impossible he should have any idea of +motion. He would not therefore think anything to be motion, or give the +name motion to any idea which he could not range under some or other of +those particular kinds thereof. But from sect. 95 it is plain that by the +mere act of vision he could not know motion upwards or downwards, to the +right or left, or in any other possible direction. From which I conclude +he would not know motion at all at first sight. As for the idea of motion +in abstract, I shall not waste paper about it, but leave it to my reader +to make the best he can of it. To me it is perfectly unintelligible. + +138. The consideration of motion may furnish a new field for inquiry: but +since the manner wherein the mind apprehends by sight the motion of +tangible objects, with the various degrees thereof, may be easily +collected from what hath been said concerning the manner wherein that +sense doth suggest their various distances, magnitudes, and situations, I +shall not enlarge any farther on this subject, but proceed to consider +what may be alleged, with greatest appearance of reason, against the +proposition we have shown to be true. For where there is so much +prejudice to be encountered, a bare and naked demonstration of the truth +will scarce suffice. We must also satisfy the scruples that men may raise +in favour of their preconceived notions, show whence the mistake arises, +how it came to spread, and carefully disclose and root out those false +persuasions that an early prejudice might have implanted in the mind. + +139. FIRST, therefore, it will be demanded how visible extension and +figures come to be called by the same name with tangible extension and +figures, if they are not of the same kind with them? It must be something +more than humour or accident that could occasion a custom so constant and +universal as this, which has obtained in all ages and nations of the +world, and amongst allranks of men, the learned as well as the +illiterate. + +140. To which I answer, we can no more argue a visible and tangible +square to be of the same species from their being called by the same +name, than we can that a tangible square and the monosyllable consisting +of six letters whereby it is marked are of the same species because they +are both called by the same name. It is customary to call written words +and the things they signify by the same name: for words not being +regarded in their own nature, or otherwise than as they are marks of +things, it had been superfluous, and beside the design of language, to +have given them names distinct from those of the things marked by them. +The same reason holds here also. Visible figures are the marks of +tangible figures, and from sect. 59 it is plain that in themselves they +are little regarded, or upon any other score than for their connexion +with tangible figures, which by nature they are ordained to signify. And +because this language of nature doth not vary in different ages or +nations, hence it is that in all times and places visible figures are +called by the same names as the respective tangible figures suggested by +them, and not because they are alike or of the same sort with them. + +141. But, say you, surely a tangible square is liker to a visible square +than to a visible circle: it has four angles and as many sides: so also +has the visible square: but the visible circle has no such thing, being +bounded by one uniform curve without right lines or angles, which makes +it unfit to represent the tangible square but very fit to represent the +tangible circle. Whence it clearly follows that visible figures are +patterns of, or of the same species with, the respective tangible figures +represented by them: that they are like unto them, and of their own +nature fitted to represent them, as being of the same sort: and that they +are in no respect arbitrary signs, as words. + +142. I answer, it must be acknowledged the visible square is fitter than +the visible circle to represent the tangible square, but then it is not +because it is liker, or more of a species with it, but because the +visible square contains in it several distinct parts, whereby to mark the +several distinct corresponding parts of a tangible square, whereas the +visible circle doth not. The square perceived by touch hath four +distinct, equal sides, so also hath it four distinct equal angles. It is +therefore necessary that the visible figure which shall be most proper to +mark it contain four distinct equal parts corresponding to the four sides +of the tangible square, as likewise four other distinct and equal parts +whereby to denote the four equal angles of the tangible square. And +accordingly we see the visible figures contain in them distinct visible +parts, answering to the distinct tangible parts of the figures signified +or suggested by them. + +143. But it will not hence follow that any visible figure is like unto, +or of the same species with, its corresponding tangible figure, unless it +be also shown that not only the number but also the kind of the parts be +the same in both. To illustrate this, I observe that visible figures +represent tangible figures much after the same manner that written words +do sounds. Now, in this respect words are not arbitrary, it not being +indifferent what written word stands for any sound: but it is requisite +that each word contain in it so many distinct characters as there are +variations in the sound it stands for. Thus the single letter A is proper +to mark one simple uniform sound; and the word ADULTERY is accommodated +to represent the sound annexed to it, in the formation whereof there +being eight different collisions or modifications of the air by the +organs of speech, each of which produces a difference of sound, it was +fit the word representing it should consist of as many distinct +characters, thereby to mark each particular difference or part of the +whole sound. And yet nobody, I presume, will say the single letter a, or +the word ADULTERY, are like unto, or of the same species with, the +respective sounds by them represented. It is indeed arbitrary that, in +general, letters of any language represent sounds at all: but when that +is once agreed, it is not arbitrary what combination of letters shall +represent this or that particular sound. I leave this with the reader to +pursue, and apply it in his own thoughts. + +144. It must be confessed that we are not so apt to confound other signs +with the things signified, or to think them of the same species, as we +are visible and tangible ideas. But a little consideration will show us +how this may be without our supposing them of a like nature. These signs +are constant and universal, their connexion with tangible ideas has been +learnt at our first entrance into the world; and ever since, almost every +moment of our lives, it has been occurring to our thoughts, and fastening +and striking deeper on our minds. When we observe that signs are +variable, and of human institution; when we remember there was a time +they were not connected in our minds with those things they now so +readily suggest; but that their signification was learned by the slow +steps of experience: this preserves us from confounding them. But when we +find the same signs suggest the same things all over the world; when we +know they are not of human institution, and cannot remember that we ever +learned their signification, but think that at first sight they would +have suggested to us the same things they do now: all this persuades us +they are of the same species as the things respectively represented by +them, and that it is by a natural resemblance they suggest them to our +minds. + +145. Add to this that whenever we make a nice survey of any object, +successively directing the optic axis to each point thereof, there are +certain lines and figures described by the motion of the head or eye, +which being in truth perceived by feeling, do nevertheless so mix +themselves, as it were, with the ideas of sight, that we can scarce think +but they appertain to that sense. Again, the ideas of sight enter into +the mind several at once, more distinct and unmingled than is usual in +the other senses beside the touch. Sounds, for example, perceived at the +same instant, are apt to coalesce, if I may so say, into one sound: but +we can perceive at the same time great variety of visible objects, very +separate and distinct from each other. Now tangible extension being made +up of several distinct coexistent parts, we may hence gather another +reason that may dispose us to imagine a likeness or an analogy between +the immediate objects of sight and touch. But nothing, certainly, doth +more contribute to blend and confound them together than the strict and +close connexion they have with each other. We cannot open our eyes but +the ideas of distance, bodies, and tangible figures are suggested by +them. So swift and sudden and unperceived is the transition from visible +to tangible ideas that we can scarce forbear thinking them equally the +immediate object of vision. + +146. The prejudice which is grounded on these, and whatever other causes +may be assigned thereof, sticks so fast that it is impossible without +obstinate striving and labour of the mind to get entirely clear of it. +But then the reluctancy we find in rejecting any opinion can be no +argument of its truth to whoever considers what has been already shown +with regard to the prejudices we entertain concerning the distance, +magnitude, and situation of objects; prejudices so familiar to our minds, +so confirmed and inveterate, as they will hardly give way to the clearest +demonstration. + +147. Upon the whole, I think we may fairly conclude that the proper +objects of vision constitute an universal language of the Author of +Nature, whereby we are instructed how to regulate our actions in order to +attain those things that are necessary to the preservation and well-being +of our bodies, as also to avoid whatever may be hurtful and destructive +of them. It is by their information that we are principally guided in all +the transactions and concerns of life. And the manner wherein they +signify and mark unto us the objects which are at a distance is the same +with that of languages and signs of human appointment, which do not +suggest the things signified by any likeness or identity of nature, but +only by an habitual connexion that experience has made us to observe +between them. + +148. Suppose one who had always continued blind be told by his guide that +after he has advanced so many steps he shall come to the brink of a +precipice, or be stopped by a wall; must not this to him seem very +admirable and surprizing? He cannot conceive how it is possible for +mortals to frame such predictions as these, which to him would seem as +strange and unaccountable as prophesy doth to others. Even they who are +blessed with the visive faculty may (though familiarity make it less +observed) find therein sufficient cause of admiration. The wonderful art +and contrivance wherewith it is adjusted to those ends and purposes for +which it was apparently designed, the vast extent, number, and variety of +objects that are at once with so much ease and quickness and pleasure +suggested by it: all these afford subject for much and pleasing +speculation, and may, if anything, give us some glimmering analogous +prenotion of things which are placed beyond the certain discovery and +comprehension of our present state. + +149. I do not design to trouble myself with drawing corollaries from the +doctrine I have hitherto laid down. If it bears the test others may, so +far as they shall think convenient, employ their thoughts in extending it +farther, and applying it to whatever purposes it may be subservient to: +only, I cannot forbear making some inquiry concerning the object of +geometry, which the subject we have been upon doth naturally lead one to. +We have shown there is no such idea as that of extension in abstract, and +that there are two kinds of sensible extension and figures which are +entirely distinct and heterogeneous from each other. Now, it is natural +to inquire which of these is the object of geometry. + +150. Some things there are which at first sight incline one to think +geometry conversant about visible extension. The constant use of the +eyes, both in the practical and speculative parts of that science, doth +very much induce us thereto. It would, without doubt, seem odd to a +mathematician to go about to convince him the diagrams he saw upon paper +were not the figures, or even the likeness of the figures, which make the +subject of the demonstration. The contrary being held an unquestionable +truth, not only by mathematicians, but also by those who apply themselves +more particularly to the study of logic; I mean, who consider the nature +of science, certainty, and demonstration: it being by them assigned as +one reason of the extraordinary clearness and evidence of geometry that +in this science the reasonings are free from those inconveniences which +attend the use of arbitrary signs, the very ideas themselves being copied +out and exposed to view upon paper. But, by the bye, how well this agrees +with what they likewise assert of abstract ideas being the object of +geometrical demonstration I leave to be considered. + +151. To come to a resolution in this point we need only observe what hath +been said in sect. 59, 60, 61, where it is shown that visible extensions +in themselves are little regarded, and have no settled determinable +greatness, and that men measure altogether, by the application of +tangible extension to tangible extension. All which makes it evident that +visible extension and figures are not the object of geometry. + +152. It is therefore plain that visible figure are of the same use in +geometry that words are: and the one may as well be accounted the object +of that science as the other, neither of them being otherwise concerned +therein than as they represent or suggest to the mind the particular +tangible figures connected with them. There is indeed this difference +between the signification of tangible figures by visible figures, and of +ideas by words: that whereas the latter is variable and uncertain, +depending altogether on the arbitrary appointment of men, the former is +fixed and immutably the same in all times and places. A visible square, +for instance, suggests to the mind the same tangible figure in Europe +that it doth in America. Hence it is that the voice of the Author of' +Nature which speaks to our eyes, is not liable to that misinterpretation +and ambiguity that languages of human contrivance are unavoidably subject +to. + +153. Though what has been said may suffice to show what ought to be +determined with relation to the object of geometry, I shall nevertheless, +for the fuller illustration thereof, consider the case of an +intelligence, or unbodied spirit, which is supposed to see perfectly +well, i.e. to have a clear perception of the proper and immediate objects +of sight, but to have no sense of touch. Whether there be any such being +in Nature or no is beside my purpose to inquire. It sufficeth that the +supposition contains no contradiction in it. Let us now examine what +proficiency such a one may be able to make in geometry. Which speculation +will lead us more clearly to see whether the ideas of sight can possibly +be the object of that science. + +154. FIRST, then, it is certain the aforesaid intelligence could have no +idea of a solid, or quantity of three dimensions, which followeth from +its not having any idea of distance. We indeed are prone to think that we +have by sight the ideas of space and solids, which ariseth from our +imagining that we do, strictly speaking, see distance and some parts of +an object at a greater distance than others; which hath been demonstrated +to be the effect of the experience we have had, what ideas of touch are +connected with such and such ideas attending vision: but the intelligence +here spoken of is supposed to have no experience of touch. He would not, +therefore, judge as we do, nor have any idea of distance, outness, or +profundity, nor consequently of space or body, either immediately or by +suggestion. Whence it is plain he can have no notion of those parts of +geometry which relate to the mensuration of solids and their convex or +concave surfaces, and contemplate the properties of lines generated by +the section of a solid. The conceiving of any part whereof is beyond the +reach of his faculties. + +155. Farther, he cannot comprehend the manner wherein geometers describe +a right line or circle; the rule and compass with their use being things +of which it is impossible he should have any notion: nor is it an easier +matter for him to conceive the placing of one plane or angle on another, +in order to prove their equality: since that supposeth some idea of +distance or external space. All which makes it evident our pure +intelligence could never attain to know so much as the first elements of +plane geometry. And perhaps upon a nice inquiry it will be found he +cannot even have an idea of plane figures any more than he can of solids; +since some idea of distance is necessary to form the idea of a +geometrical plane, as will appear to whoever shall reflect a little on +it. + +156. All that is properly perceived by the visive faculty amounts to no +more than colours, with their variations and different proportions of +light and shade. But the perpetual mutability and fleetingness of those +immediate objects of sight render them incapable of being managed after +the manner of geometrical figures; nor is it in any degree useful that +they should. It is true there are divers of them perceived at once, and +more of some and less of others: but accurately to compute their +magnitude and assign precise determinate proportions between things so +variable and inconstant, if we suppose it possible to be done, must yet +be a very trifling and insignificant labour. + +157. I must confess men are tempted to think that flat or plane figures +are immediate objects of sight, though they acknowledge solids are not. +And this opinion is grounded on what is observed in painting, wherein (it +seems) the ideas immediately imprinted on the mind are only of planes +variously coloured, which by a sudden act of the judgment are changed +into solids. But with a little attention we shall find the planes here +mentioned as the immediate objects of sight are not visible but tangible +planes. For when we say that pictures are planes, we mean thereby that +they appear to the touch smooth and uniform. But then this smoothness and +uniformity, or, in other words, this planeness of the picture, is not +perceived immediately by vision: for it appeareth to the eye various and +multiform. + +158. From all which we may conclude that planes are no more the immediate +object of sight than solids. What we strictly see are not solids, nor yet +planes variously coloured: they are only diversity of colours. And some +of these suggest to the mind solids, and other plane figures, just as +they have been experienced to be connected with the one or the other: so +that we see planes in the same way that we see solids, both being equally +suggested by the immediate objects of sight, which accordingly are +themselves denominated planes and solids. But though they are called by +the same names with the things marked by them, they are nevertheless of a +nature entirely different, as hath been demonstrated. + +159. What hath been said is, if I mistake not, sufficient to decide the +question we proposed to examine, concerning the ability of a pure spirit, +such as we have described, to know GEOMETRY. It is, indeed, no easy +matter for us to enter precisely into the thoughts of such an +intelligence, because we cannot without great pains cleverly separate and +disentangle in our thoughts the proper objects of sight from those of +touch which are connected with them. This, indeed, in a complete degree +seems scarce possible to be performed: which will not seem strange to us +if we consider how hard it is for anyone to hear the words of his native +language pronounced in his ears without understanding them. Though he +endeavour to disunite the meaning from the sound, it will nevertheless +intrude into his thoughts, and he shall find it extreme difficult, if not +impossible, to put himself exactly in the posture of a foreigner that +never learned the language, so as to be affected barely with the sounds +themselves, and not perceive the signification annexed to them. + +160. By this time, I suppose, it is clear that neither abstract nor +visible extension makes the object of geometry; the not discerning of +which may perhaps have created some difficulty and useless labour in +mathematics. Sure I am, that somewhat relating thereto has occurred to my +thoughts, which, though after the most anxious and repeated examination I +am forced to think it true, doth, nevertheless, seem so far out of the +common road of geometry, that I know not whether it may not be thought +presumption, if I should make it public in an age, wherein that science +hath received such mighty improvements by new methods; great part whereof, +as well as of the ancient discoveries, may perhaps lose their reputation, +and much of that ardour with which men study the abstruse and fine +geometry be abated, if what to me, and those few to whom I have imparted +it, seems evidently true, should really prove to be so. + + + + + + + + + +The Project Gutenberg Etext of An Essay Towards a New Theory of Vision +by George Berkeley +This file should be named trvsn10.txt or trvsn10.zip + +Corrected EDITIONS of our etexts get a new NUMBER, trvsn11.txt +VERSIONS based on separate sources get new LETTER, trvsn10a.txt + +Prepared by Col Choat colc@gutenberg.net.au + +More information about this book is at the top of this file. + +We are now trying to release all our etexts one year in advance +of the official release dates, leaving time for better editing. +Please be encouraged to tell us about any error or corrections, +even years after the official publication date. + +Please note neither this listing nor its contents are final til +midnight of the last day of the month of any such announcement. +The official release date of all Project Gutenberg Etexts is at +Midnight, Central Time, of the last day of the stated month. 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