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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![coincide witii tlie curved surflices, the direction of a ray Q p p' q passing through these points will be the same for the prism and the lens, and the equation — + — = (n — 1) r ^ will still hold good. ax \r r J Let PN, DF, p'n' be drawn perpendicular to qq, and qp, q p' be produced to k and i, meeting in i. Since the angles at Q, q and d are small, we may consider approximately that QN = Q p = a; q N'=Qp'=a;; pn = p'n'=6 ; and d h = de. Then, the total deviation if/ = the exterior angle q i k = angles Q + q- tan. ip = tan. (q q- q) = tan. q + tan. q'' (since the angles are small), pnp'n' /1,1\ . inAI , q N q n' \ a x j V b r J T, , e PN FE e p'n' fh, ... But ——= ; and ■=. — = by similar tri- r P 0 D E r Y o' D H angles; /I.IAfe + FH he r/n e - + = T = =m. . . [5] V r' r y D E D H /i = tan. \p = e (n — + • (™~ l)j asinp. 6. where 7>i = the ratio of the base to the side of the prism, or = the chord, to radius unity, of ^ the refracting angle of the prism. 3. To find the relation between the lens and the prism which form an orthoscopic glass as in p. 6. Let the reader, after considering the explanation given in pages 5 and 6, suppose b and b', the centres of the glasses (Figs. 1 and 2), to be joined by a line b m V cntting the frontal axis a/ at right angles at m. Then b m = b'm = hJ/_ d nearly.](https://iiif.wellcomecollection.org/image/b2236397x_0019.jp2/full/800%2C/0/default.jpg)
