Sight and Touch; An Attempt to Disprove the Received (or Berkeleian) Theory of Vision

Overview

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1864 Excerpt: ...long familiarly known, although not alluded to by Mr. Mansel or Mr. Mill. It may be readily verified by looking through a pane of glass at a more distant object, when a small mark on the glass will appear confused and enlarged; while by a voluntary muscular effort, directing our gaze to the latter, we see it...
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Overview

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1864 Excerpt: ...long familiarly known, although not alluded to by Mr. Mansel or Mr. Mill. It may be readily verified by looking through a pane of glass at a more distant object, when a small mark on the glass will appear confused and enlarged; while by a voluntary muscular effort, directing our gaze to the latter, we see it distinctly, and the remote object now confused. With a little practice, it is easy to alter the adjustment at will while looking at the same object, as for instance, a mark on the paper or on glass. In particular, I find if I adjust the eye for distant vision, while looking pIG g_ at a black dot on the paper, the ยป dot becomes a circle with grayish centre; a small circle appears larger, but with a black dot in Q the centre; a larger spot appears as a dark nucleus surrounded with a penumbra; a straight line appears double, the middle space being gray; and a square, by suitable adjustment, will appear larger, but with a cross in the middle. These appearances may be gradually Besides it is plain that the impression of light ought to be received on a definite surface. Now the rods terminate in such a definite surface in contact with a dark pigment. Here first the light ceases to be transmitted as light. It has been supposed therefore by Draper, that the absorption of light in this pigment develops heat, and that the rods conduct the impression to the nerve cells, which constitute a ganglion capable of perceiving light, the fibres of the optic nerve merely communicating the impression to the sensorium. On an entoptic observation suggested by PurkynS, in which the distribution of the rods and cones appears to be rendered sensible, see Czermak, in the Vienna " Sitzungsberichte," vol. xli., p. 644; xliii., pt. ii., p. 167. Draper, op. cit., p. 38...
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Product Details

  • ISBN-13: 9781150596162
  • Publisher: General Books LLC
  • Publication date: 5/28/2012
  • Pages: 56
  • Product dimensions: 7.44 (w) x 9.69 (h) x 0.12 (d)

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