Excerpt from Treatise on Optics
Successive reflexions at plane surfaces, 78; successive refractions at plane surfaces, - critical angle, 79 - 81 a plate, 82; absolute and relative index of refraction, 8 3, 84; refraction through a plate, 85 - 87; Def. Of edge, faces, refr acting angle, principal section of a prism, 88; deviation through a prism, minimum deviation, 90 - 9 5; foci of a small pencil passing through a prism, 96; Def. Of a lens, axis of a lens, forms of lenses, 97, 98; geometrical focus of a pencil passing through a lens, 99, 100; principal focus, focal length, of a lens, - concave and convex lens, - power of alens, 101 - 104; a sphere regarded as a lens, its focal length, 105, 106; relative motion of conjugate foci in the case of a lens, 107; focal length of a lens determined practically, 108; cylindrical lenses, centre of a lens, 109; focal centres of a lens, 1 10; Discussion of an oblique pencil passing through a lens; 1 1 2, 1 13 combinations of lenses, 1 14; approximate determination of the focus of a small oblique pencil, 1 15 Lenses used in Lighthouses, 1 17.
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