An Essay Towards a New Theory of Vision

by George Berkeley

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]