Sight and touch : an attempt to disprove the received (or Berkeleian) theory of vision / by Thomas K. Abbott.
- Thomas Kingsmill Abbott
- Date:
- 1864
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.
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![certain limit, for example, two distinct impressions are per- ceived as one ; this limit being fifty times as great on some parts of the body as on others, and admitting of considerable transient diminution by practice.* Again, if with the eyes closed and the hand resting on a cushion, we allow another person to touch the tips of our fingers with glass, paper, leather, &c, moved over them, we shall confound substances and forms which with the hand free to move, we should dis- tinguish at once. Thus a plane plate of glass which is pressed first lightly, then more strongly, and again lightly on the finger-tip, will appear to be convex; if, on the contrary, it is pressed first strongly, then lightly, and again strongly, it will appear concave.-f- This is quite analogous to the illusion of the eye by light and shade. But is touch then to be pro- nounced incompetent to perceive the interval between two locally distinct impressions, or to distinguish the convex from the plane or concave? Or, again, must we deny the muscular sense the power of perceiving weight because this perception also is liable to be disturbed by accidental circumstances? For example, when we compare different substances, a very large body is judged lighter than a small one of the same weight. Weight and bulk being the same, an object which is easily grasped seems lighter than one which is more awkward. Even the same object may appear lighter or heavier, according to the extent of surface touched. Thus a truncated cone feels heavier when poised on the narrow than on the broad end. And all these circumstances being alike, a cold object feels heavier than one which is warmer.J And it has even been found that warmth is liable to be confounded * See E. H. Weber, Art. Tastsinn, in Wagner's Handworterb., p. 539. On the temporary effect of practice, see Volkmann, Berichte der Sachs. Gesellsch. zu Leipz., 1858, p. 38. t E. H. Weber, I.e., p. 542. I E. H. Weber, I.e., p 547, 551. [De Pulsu Resorptione Auditu et Tactu, pp. 135-7.]](https://iiif.wellcomecollection.org/image/b21037930_0049.jp2/full/800%2C/0/default.jpg)
