Johnson's natural philosophy and key to philosophical charts : illustrated with 500 cuts; being reduced photographic copies of all the diagrams contained in the author's philosophical series of indestructible school charts ; for the use of schools and families (1878)
not exceed thirty orthirty-five feet. 654 Figure 6.—Reflection of-waves by parabolic curves. —The nature of a parabolic curve, as previously shown (393), is suchthat heat, light, and sound proceeding from its focus will be reflected,by the curve, in parallel lines; or, conversely, parallel rays,… … be made to tick in the focus, F, of one, it will be heard in the focus, L,of the other, although it tick so faintly that it cannot be heard at anyother point between them, even if the ear be placed quite near thewatch. Tins proves, again, that the angles of incidence and reflection areequal.…
Physics · Astronomy
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