Gage, Alfred P. (Alfred Payson), 1836-1903 · Boston, London, Ginn · leaf 343
of light were a single luminous point, as A (Fig. 227), theshadow of an opaque body B would be of infinite length, and would con-sist only of an umbra. But, if the source of light have a sensible size,the opaque body will intercept just as many separate pencils of light asthere are luminous points,… … Fig. 228. the lines C F and D G, and the pencil vfrom B will be intercepted betweenthe lines C E and T> F. Hence, the light will be wholly excluded onlyfrom the space between the lines C F and D F, which enclose the umbra.The enveloping penumbra, a section of which is included between thelines C…
Physics
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