An elementary treatise on optics / by I.W. Jackson.

  • Jackson, I. W. (Isaac Wilber), 1804-1877.
Date:
1867
Catalogue details

Licence: Public Domain Mark

Credit: An elementary treatise on optics / by I.W. Jackson. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

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    47. Conditions of emergence. Since light, when passing from one medium into another of less refractive power may fall so obliquely upon the common surface as to suffer internal reflec- tion instead of transmission, we shall consider for a moment the conditions of emergence. Let L equal the limiting angle for the passage of light from the glass of the prism into air, and G the refracting angle of the prism. We shall examine only the cases in which . G = 2L, G — L, G < L. §1. Let G = 2L. [Fig. 35.] Here the ray incident at I and parallel to AI, will be refracted in the direction II' making with the normal the angle Nil' = L = \G = \ISI'; so that II' will be perpendicular to SM, which bisects the angle ISI'. Hence the ray will fall upon the second surface at the limiting angle. Every other incident ray, as LI, will fall upon the second surface in some direction II more oblique than II', and hence will suffer total reflection. In this case, therefore, none of the light incident upon, the sur- face AS can pass through the surface A'S. A cham- ber with a single aperture closed by such a prism, would be perfectly dark. §2. LetG = L. [Fig. 36.] Here it is evident that the incident ray, which coincides with the normal, will fall upon the second [ Optics.] 6