The geography of the heavens : and class-book of astronomy : accompanied by a celestial atlas (1860)
Burritt, Elijah H. (Elijah Hinsdale), 1794-1838, Mattison, Hiram, 1811-1868 · New York : Mason Brothers · leaf 314
, half its refractingpower is gone, so that the raysare not so soon refracted to afocus. In this case, the focal dis-tance is equal to the diameter ofthe sphere formed by extendingthe convex surface of the lens;while with the double-convex lens,the focal distance is only equal tothe radius of such… … * focus atthe circle cave lens disperses pa-rallel rays, as if theydiverged from the cen-ter of a circle formedby the convex surfaceproduced. In this cut, the parallel raysA are dispersed by the double-concave lens C, as shown atB; and their direction, asthus refracted, is the sameas if they…
Constellations · Stars
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