Index
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
