Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eyeglasses, etc. / by James Thorrington.

  • James Thorington
Date:
1910
Catalogue details

Licence: In copyright

Credit: Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eyeglasses, etc. / by James Thorrington. Source: Wellcome Collection.

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

    33/350 (page 11)
    ] I a A ray of light passing from a dense into a rarer medium is deviated or refracted away from the perpen- dicular. . Aside from these laws, there are other facts m regard to rays of light that should have consideration. A ray of light will continue its straight course through any number of different transparent media, no matter what their densities, so long as it forms right angles with the surface or surfaces. Such a ray is spoken of as the normal or per- pendicular; such surfaces are plane, the surfaces and per- pendicular forming right angles. (See Fig. 12.) In any case of refraction the incident and refracted rays may be supposed to change places. r ^ ICE / FLINT GLASS *P J- CROWN J PLATE % r Fig. 12. Fig. 13. Figure 13 shows the perpendicular (P P) to a piece of plate glass with plane surfaces. Part of the ray A in air incident at 0 on the surface S F is bent in the glass toward the perpendicular, P P. The dotted line shows the direction the ray would have taken had it not been refracted. As the ray in the glass comes to the second surface at R, and passes into a rarer medium, it is deviated from the perpen- dicular, P P. The ray now continues its original direction, but has been deviated from its course; it has undergone