The human eye : its optical construction popularly explained / by R. E. Dudgeon.

  • Robert Ellis Dudgeon
Date:
1878
Catalogue details

Licence: Public Domain Mark

Credit: The human eye : its optical construction popularly explained / by R. E. Dudgeon. Source: Wellcome Collection.

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

    26/136 page 6
    // position of the sun being in the Hne O S. But in spite of the considerable refractive power of the earth's atmosphere compared with that of interstellar space, the air being the least refractive of the transparent media in which our optical instruments are used, is regarded as unity in calculating the refractive powers of other transparent media employed for optical purposes. 10. The refractive properties of transparent sub- stances have been taken advantage of for constructing instruments, called lenses, by means of which the rays of light are deflected in certain required directions. Lenses, which form the basis of most optical in- struments, are generally constructed of glass, and the two chief uses of lenses being to concentrate and to scatter rays of light, the glass is shaped so as to effect these two objects. 11. The chief forms of glass lenses are shown in Fig. 3. A is a spherical lens, B is a double convex lens; the two surfaces may have the same convexity, as in the illustration, or may have different con- vexities. C is a plano-convex lens, one side being plane, the other convex. D is a meniscus^ where one A ,A rr e*»v«.^. side is convex, the other concave, the convexity being '-r*.^. greater than the concavity. E is a double co7icave lens. In such lenses the concavities may be the same
    digitised image 1
    digitised image 2
    digitised image 3