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 313
no-convex, or half a douhle con-vex lens ; one side being convex and the otherplane. B is & plano-concave ; one surface being con-cave, and the other plane. C is a double-convex lens, or one that isbounded by two convex surfaces. I) is a double-concave lens, or a circular pieceof glass hollowed… … 615. A double-convex lensconverges parallel rays to apoint called the focus; andthe distance of the focusdepends upon the degree ofconvexity. In the first of these cuts, the lens isquite thick, and the focus of the rays isquite near; but the other being less,convex, the focus is more distant. 616.…
Constellations · Stars
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