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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![however as nearly spherical. Now in any system of sphe- rical surfaces having a common axis FF\ we can find the position of the image of a point P by the following simple construction:—F F' being the two foci, and H IT, CC, four Fig. 5. a b e P^—^ F\v H A hi c c1^--—^ P ^-^ ~^^-^P' points easily determined, draw PC, and parallel to it C'P'. Draw also PF, and let it meet in A the plane through H perpendicular to F F'. Then let A P parallel to F F' meet C P' in F; this is the place of the image* In the eye, the interval between the points C C is less than half a milli- metre, they may therefore be regarded as coincident, and called the optical centre. The point F' (fig. 6), where the optical axis meets the retina, is not the most sensitive point. This, which also determines the centre of the field, is in the yellow spot Y, which in normal eyes is considerably to the outer side of F'. The line Y C. being the direction of distinct vision, may be called the visual axis, and it forms an angle with the optic axis of 5° on an average.-f- The surfaces of the cornea and the lens are not, however, * To find the course of any ray P a draw C c parallel to it to meet the focal plane F', and a b parallel to F F ; then b c is the final direction. Listing M Dioptrik der Auges,' in Wagner's Handworterb. ; [Gauss '•Dioptrische Untersuchungen, Abhandlungen der Gbtt. Gesellsch. Bd. i.. 1-38-1843]. t I.e., in normal eyes: less in myopic and greater in hypermetropic eyes. Donders De ligging van het draaipunt van het Oog.M Versla- gen en Mededeel. der K. Akad. van Wetensch. (Amsterd.), vol. xiv., p. 3<U.](https://iiif.wellcomecollection.org/image/b21037930_0098.jp2/full/800%2C/0/default.jpg)
