senses. The fruit of that (labour shall I call it or) diversion is what I now present you with, in hopes it may give some entertainment to one who, in the midst of business and vulgar enjoyments, preserves a relish for the more refined pleasures of thought and reflexion. My thoughts concerning Vision have led me into some notions, so far out of the common road that it had been improper to address them to one of a narrow and contracted genius. But, you, SIR, being master of a large and free understanding, raised above the power of those prejudices that enslave the far greater part of mankind, may deservedly be thought a proper patron for an attempt of this kind. Add to this, that you are no less disposed to forgive than qualified to discern whatever faults may occur in it. Nor do I think you defective in any one point necessary to form an exact judgment on the most abstract and difficult things, so much as in a just confidence of your own abilities. And, in this one instance, give me leave to say, you shew a manifest weakness of judgment. With relation to the following Essay, I shall only add that I beg your pardon for laying a trifle of that nature in your way, at a time when you are engaged in the important affairs of the nation, and desire you to think that I am, with all sincerity and respect, CONTENTS. 3. Remote distance perceived rather by experience than by sense. 4. Near distance thought to be perceiv'd by the angle of the optic axes. 5. Difference between this and the former manner of perceiving distance, 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 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-First, the sensation arising from the 17. Betwixt which and distance there is no necessary connexion. 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. Secondly, confusedness of appearance. 22. This the occasion of those judgments attributed to diverging rays. 24. What deceives the writers of optics in this matter. 25. The cause why one idea may suggest another. 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 extremely 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 anything 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 farther enlarged on. 58. No necessary connexion 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 connexion 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. 77. It is shewn 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 visibile 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 shewn 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,' &c. 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 hath 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 pictures 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. Farther 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. Ques. 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. D |