Sight and touch : an attempt to disprove the received (or Berkeleian) theory of vision / by Thomas K. Abbott.

  • Abbott, Thomas Kingsmill, 1829-1913.
Date:
1864
Catalogue details

Licence: Public Domain Mark

Credit: Sight and touch : an attempt to disprove the received (or Berkeleian) theory of vision / by Thomas K. Abbott. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

    115/196 (page 103)
    experimentally, since space being so familiar easily slips into our perception. But if we try to gaze fixedly before us, we shall observe that space disappears, and that in endeavouring to recover it we can detect ourselves in a scarcely perceptible movement of the eye.* But that there is a perception of depth even when the eye is at rest appears from the follow- ing observation. If we make a small spot with ink on a pane of glass, and look at it with the eye adjusted for distant vision, it will, as already mentioned, appear surrounded with a penumbra, but the central nucleus will seem sunk within this penumbra, as if seen at the end of a minute tube. And when we look through the wrong end of a telescope there is a very decided appearance of remoteness although the eye is at rest. It is true that in order to measure distance it is necessary to look successively from one object to another, and for reasons already mentioned this motion is also fitted to evoke the idea of distance; but to obtain the impression or perception of distance, it is sufficient to see at once objects at different distances. With respect to the measure of distance as distinguished from the positive perception, it might be supposed that the medium is supplied by the muscular sensations accompanying the motions of adjustment, &c.; but this view appears to be untenable. The voluntary muscles generally are provided with nerves of sensation, so that when we will a move- ment we learn by means of these whether the muscles have answered to our effort. But the muscles of the eye seem nearly devoid of sensory nerves.-|- The reason is obvious; the motions of these muscles are to be guided by the im- pressions in the retina, not by any sensation of their own position; and it is by the same impressions we learn that our effort has succeeded. It is nevertheless supposable that the * Psychologie als Wissenschaft, sec. Ill, p. 128. t See Alison, in Edinb. Trans., vol. xv., p. 62.