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 501
penumbra.—When light falls upon an opaque body itcannot penetrate into the space immediately behind it, and this space iscalled the shadow. In determining the extent and the shape of a shadow projected by a body,two cases are to be distinguished ; that in which the source of light is asingle point,… … move round the sphere M tangentially, always passing through the point S,this line will produce a conical surface, which, beyond the sphere, separatesthat portion of space which is in shadow from that which is illuminated. Inthe present case, on placing a screen, PQ, behind the opacjue body the…
Physics
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