Elementary natural philosophy : designed for high schools and academies (1881)
Griffin, La Roy F. (La Roy Freese), 1844-1916 · Philadelphia : Sower, Potts & Co. · leaf 122
audibleat a distance, while it remains inaudible at all intermediateplaces. This is accomplished by means of two concavereflectors. One person produces the sound at the focus ofthe first reflector, and it is heard by a person situated atthe focus of the second. 396. Fig. 139 shows the principle… … TRUMPETS. ■ 113 according to the first law parallel. When they reach M, they areonce more reflected, and reach the focus F, where they can bereadily heard. In this way, two persons can carry on a conversa-tion inaudible to all persons between F and F. 397. Resonance. The sound of a person speaking…
Physics
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