The theory of ocular defects and of spectacles / translated from the German of Hermann Scheffler by Robert Brudenell Carter with prefatory notes and a chapter of practical instructions.
- Hermann Scheffler
- Date:
- 1869
Licence: Public Domain Mark
Credit: The theory of ocular defects and of spectacles / translated from the German of Hermann Scheffler by Robert Brudenell Carter with prefatory notes and a chapter of practical instructions. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
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![where a! is substituted for — /; that is, the distance of the original luminous point is measured from a point which lies at a distance f from the front of the lens, or of the cornea of the eye, to which this last formula, though with different characters, is applied in pages 23 and 35. The expression [1] is the foundation for the whole theory of the lens; but, where great accuracy is required, it admits of a second and nearer approximation, and also a correction for the central thickness of the lens, where that is too con- siderable to be neglected. It is, however, sufficient for our present purpose. 2. To find the total deviation of a ray, or axis of a pencil of rays, passing through a thin prism, in terms of the base and sides of the prism. In Fig. a in the last ai'ticle, suppose tangents to be drawn Fig. b. r> to the curves at p and p' ; then we shall have a figure like 5, representing a section of a prism by a plane perpendicular to its edges; and since at the points p, p' the faces of the prism](https://iiif.wellcomecollection.org/image/b2236397x_0018.jp2/full/800%2C/0/default.jpg)
