A high-school astronomy: in which the descriptive, physical, and practical are combined .. (1859)
Mattison, Hiram, 1811-1868 · New York, Mason brothers · leaf 222
497. What allowance for refraction ? Tables ? 498. What is a lens f (Draw and describe different kinds ?) 499. Refracting powei of dovMe-convex lens? Focal distance? (Diagramand illustrate.) ATMOSPHEKICAL REFRACTION. 217 … 500. The distance ofthe focus of a double-con-vex glass lens is the ra-dius of the sphere of itsconvexity. In this cut, it will be seen that theparallel rays A are refracted to a focusat C, by the double convex lens B, theconvexity of whose surfaces is justequal to the curve of the circle D. 501.…
Astronomy
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