General and practical optics / by Lionel Laurance.

  • Laurance, Lionel.
Date:
1914
Catalogue details

Licence: In copyright

Credit: General and practical optics / by Lionel Laurance. 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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    ray is refracted as if it came in the direction K G, so that if S is on the principal axisj /g is its image. If the object point S (Fig. 78) is within F^, draw H S connecting S with the focal plane and the surface. Draw HC cutting D E in K; connect K S ] a1 c ~ Fig. 77. K with the surface to meet there S H, crossing the axis in f.^, which is the image of S if the latter is on the principal axis. Construction for the Course of a Ray.—When and F^ are not known the construction as is illustrated in Fig. 79 can be employed. Let A B he the incident ray on a surface of the medium whose centre is C and /x= TG. H K ^ \ ^-^c j-^ Fig. 78. Draw DEC normally at the point of incidence, and draw a tangent to the surface at and at right angles to D B C \ then H K is the refracting plane. From any point G drop GH normally to E F. Measure ^ 5 and mark off B K equal to 10/16 of H B. Drop the normal K L and mark off the line B M whose length equals that of B G. Then B M N is the course of the refracted ray. Fig. 79. This method serves also for spheres and lenses by making a second construc- tion for the second surface. Formula for Conjugate Foci.—The formula, previously given, for calcu- lating conjugate foci of a single surface is fh + /^^ ^ or = ^2 ~ f^i _ f^i