Elementary treatise on physics experimental and applied for the use of colleges and schools (1890)
Ganot, A. (Adolphe), 1804-1887, Atkinson, E. (Edmund) · New York : W. Wood · leaf 509
rapidly than the square of the distance. The second law of intensity corresponds to the law which we have foundto prevail for heat : it may be theoretically deduced as follows :—Let DA,EB (fig. 446) be a pencil of parallel rays falling obliquely on a surface, ABand let ovt be the normal to… … Fig. 446. as S is only the projection of AB on a plane perpendicular to the pencil, we know from trigonometry that S = AB cos a, from which AB = This value substituted in the above equation gives I = -- cos a a formula which demonstrates the law of the cosine, for as a and S are constant…
Physics
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