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)
ACOUSTICS. 305 Such galleries are of ellipsoidal shape; and the whispering takesplace at one focus and is heard at the other. The reason the whisper-ing cannot be heard at other points, is because there is no other pointwhere the rays converge. For this reason, too, the whispering cannotbe heard…
Physics · Astronomy
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