The geography of the heavens and classbook of astronomy; (1863)
Burritt, Elijah H. (Elijah Hinsdale), 1794-1838, Mattison, Hiram, 1811-1868, Whitall, Henry, 1819-1887? Celestial planisphere. [from old catalog] · New York, Mason brothers; Boston, Mason & Hamlin; [etc., etc.] · leaf 313
674. What is a lens? Draw and describe different kinds. 675. Refracting power ofdouble-convex lens? Focal distance? Diagram, and illustrate. 676. How focal dis-tance governed ? Diagram, and illustrate, 677. What is the focal distance of a REFLECTION AND REFRACTION OF LIGHT. 311 … It must be borne in mind, that plano-concave—focal distance. light is refracted both when itenters, and when it leaves a doubleconvex lens, and in both instancesin the same direction ; and, so faras the distance of the focus isconcerned, to the same extent.But when the lens is convex onlyon one…
Constellations · Stars
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