An Essay Towards a New Theory of Vision | Page 3

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