Abstract
THE form of microphone described by Mr. Gerald B. Francis (NATURE, vol. xviii. p. 383) is easily made and very efficient. It not only did for me all its inventor promised, but with a common tumbler inverted over it upon the sounding-board so as to prevent direct impact of sound waves upon the ball, it became a powerful transmitter of the human voice. I conversed easily and satisfactorily with a friend a half-mile from my end of the wire. The exact contact of the lower wire with the ball was effected by a screw with a very fine thread passing through without touching the lower block or cup. The voice must be kept low to prevent bounding of the ball so as to break contact. Bell telephones were used as receiving instruments, the batteries being Hill and Calland gravity batteries used extensively in this country upon telegraph lines. These batteries agree exactly in every respect with the one used by Prof. Hughes in his interesting experiments excepting the clay, which is not necessary, and must be a great inconvenience in a permanent arrangement.
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BARRETT, S. The Microphone. Nature 18, 540 (1878). https://doi.org/10.1038/018540d0
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DOI: https://doi.org/10.1038/018540d0
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