Merchant, F. W. (Francis Walter), 1855-1937, Chant, Clarence Augustus, 1865-1956 · Toronto : Copp Clark · leaf 343
tes in dioptres the powers of the lenses required. 383. Experimental Determination of Focal Length. By holding various lenses in sunlight or in a parallel beam from aprojecting lantern, and shaking chalk-dust in the air, thenature of a lens can easily be observed. If it is convex the principal… … Fig. 383.—Finding the focallength of a concave lena. As the focus of a concave lens is virtual the determinationof its focal length is not so simple, but it may be found in thefollowing way, which is similar to that used for a convexmirror (§ 357). Make two slits in, p in a circular disc (a, Fig.…
Physics
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