On the mechanism of the eye / by Thomas Young.

  • Young, Thomas, 1773-1829.
Date:
1801
Catalogue details

Licence: Public Domain Mark

Credit: On the mechanism of the eye / by Thomas Young. Source: Wellcome Collection.

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

    11/84 (page 7)
    Corollary 3. For parallel rays, d = 00, and e = . Scholium 1. It may be observed, that the caustic by refraction stops short at its cusp, not geometrically, but physically, the total reflection interfering. Corollary 4. Call muu „ 6, and * * c ; then * = -p^-, and ? — 6 == jzrc'-> or> m words, the rectartgle contained by the focal lengths of parallel rays, passing and repassing any surface in the same lines, is equal to the rectangle contained by the differences between these lengths and the distances of any con- jugate foci. Corollary 5. For perpendicular rays, e = p^ = m-\- pzTt '■> or, if the radius be a, e = ,mad ; and if d and e be given to find ' ' d — n a 0 the radius, a = —7—— • m a -f n e Corollary 6. For rays perpendicular and parallel, e = m, or e — ma. Corollary*]. For a double convex lens, neglecting the thick- ness, call the first radius g, the second h. and e = , f.eb Hence n = -7^- . s-^p- ; and, for parallel rays, e = -~r, and dg-\-db-~ngh llel rays, n = c . • lfg = b = a, e = ^ 7p^n g; and for parallel rays e=24: calling this principal focal length b, e =as in Cor. 4 ; whence we have the joint focus of two lenses; also, de b d + e Corollary 8. In a sphere, e = ma. 2 d __ ^pzrjj-^ {or me distance from the centre, and b — —■ 2'