Elementary natural philosophy : designed for high schools and academies (1881)
Griffin, La Roy F. (La Roy Freese), 1844-1916 · Philadelphia : Sower, Potts & Co. · leaf 196
186 OPTICS. … 660. Light furnishes the best means of proving the lawof inverse squares. For if a piece of paper or boardwhose side is unity, Fig. 208, be placedat a distance of unity from the sourceof light, its shadow will just cover an-other whose side is two, placed at twicethe distance: or whose side is…
Physics
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