Ophthalmic lenses : dioptric formulae for combined cylindrical lenses, the prism-dioptry and other optical papers / by Charles F. Prentice.

  • Prentice, Charles F. (Charles Frederick), 1854-
Date:
1907
Catalogue details

Licence: In copyright

Credit: Ophthalmic lenses : dioptric formulae for combined cylindrical lenses, the prism-dioptry and other optical papers / by Charles F. Prentice. Source: Wellcome Collection.

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

    49/216 (page 41)
    § 38. Identical refraction is also preferably obtained in this instance by combinations of spherical and cylindrical surfaces. The combination of a convex spherical surface with the active meridian of a stronger concave cylinder creates a periscopic section which is concave; whereas the combination of a concave spherical surface with the active meridian of a stronger convex cylinder results in a periscopic section which is convex. The identity of the refraction for these combinations becomes apparent by reference to the concavo-convex sphero-cylindrical lenses Figs. 31 and 32, in which, by a judicious selection of the respective spherical Concavo-convex Sphero-cylindrical Lens (—sl O + £2 axis 180°). and cylindrical curvatures, according to § 32, the demanded positive and negative elements of refraction for the principal meridians of the crossed cylindrical lens, Fig. 30, are fulfilled.