Elementary natural philosophy : designed for high schools and academies (1881)
Griffin, La Roy F. (La Roy Freese), 1844-1916 · Philadelphia : Sower, Potts & Co. · leaf 194
series of luminous points, each of which gives offdivergent rays. 653. Shadows result from the interception of thesedivergent rays. If rays of light are intercepted by anopaque bodj^, darkness exists beyond that body. This spacewhere light is wanting is called the Umbra, or complete 184 OPTICS.… … Fig. 204. whose light is interceptedby an opaque body, asa sphere. Here theshadow, or Umbra, isdetermined by linesdrawn from the pointtangent to the sphere,Lac and Lbd, Fig. 204.* That is, the Umbrais the frustum of a conewhose apex is at the luminous point. A section of theshadow made by a screen…
Physics
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