The action and uses of prismatic combinations / by Archibald Percival.

  • Percival, A. S. (Archibald Stanley), 1862-
Date:
[1881]
Catalogue details

Licence: Public Domain Mark

Credit: The action and uses of prismatic combinations / by Archibald Percival. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    eflfect on the eye is, of course, identical with that on luminous rays (Fig. i). A Strabismus of i£° requires a prism of 15°^ to correct it; when a diplopia is cor- rected by a prism of io0^ it corresponds to a Strabismus of io°, and so on.* FlG. 2.—Parallel rays of light on traversing the prism as beforeundergo a deviation S. ün reacting the lens, since the pencil of rays is oblique, they will converge to the (secondary) focus F, which is not on the principal axis. The visual line must consequently undergo a deviation X. The ray of light which it receives on its macula passes through an eccentric portion of the lens, which therefore acts as an additional prism. Accordingly in this case X is greater than S. When, however, a spherical lens is used in conjunc- tion with the prism, this simple relation no longer * Vide paper by Dr. Landolt, ün the Numbering of Prismatic Glasses, Knapp's Archiveso/ Ophthalmology, vol. xix., No. 4, p. 49S.
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