Elementary natural philosophy : designed for high schools and academies (1881)
Griffin, La Roy F. (La Roy Freese), 1844-1916 · Philadelphia : Sower, Potts & Co. · leaf 211
dges than in the middle, as D,E, and F, Fig. 230. 702. Foci of Convex Lenses. Onlythe double convex need be consid-ered, as the others produce similareffects, but at greater distances.Fi^ 230. Double convex lenses usually have sections of spheres for their surfaces. Hence the centreof curvature of… … 202 HEAT. through the centre of the lens itself, called the Optical Centre. 704. Focus of Parallel Rays. The focus of parallel rays,called the Principal Focus, is found by drawing perpen-diculars to the surface, and tracing the direction of the rajsthrough the glass. Thus the ray L, Fig. 231, meets…
Physics
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