File:Bell "gallows" telephone 1875 side view.jpg

English: The first telephone transmitter/receiver (microphone/speaker) invented by US scientist Alexander Graham Bell in 1875, called the "Gallows" instrument due to its shape. It was the first device through which sounds were transmitted, but could not transmit intelligible speech. Bell designed it after his seminal June 2, 1875 experiment in which he realized that a vibrating metal reed could transmit not only musical tones but the more complicated waveforms of speech, and it was constructed by Bell's collaborator Thomas A. Watson. It functioned as both a dynamic microphone and a speaker. Bell found that two of these devices wired in a circuit with a battery functioned as a crude bidirectional telephone; sounds spoken into one would be heard faintly from the other. It took another year of development before intelligible speech was transmitted. It is probably not the transmitter used in Bell's famous first communication of speech on March 10, 1876: "Come here, Watson, I need you"; by then Bell had developed improved electromagnetic transmitter designs, and some sources say he used a liquid transmitter on that occasion. Watson wrote in 1915 (p. 1017 below) that "all that is left" of this instrument was in the National Museum in Washington.

It consists of a parchment diaphragm stretched over a cup-shaped sound collector in back of the hole, touching an iron armature on a springy metal reed, near a pickup coil of wire wound on an iron core. It was included in Bell's famous telephone patent of March 7, 1876. Information from Thomas A. Watson (May 18, 1915) How Bell invented the telephone, Trans. of the American Inst. of Electrical Engineers, Vol. 34, Part I, p. 1011-1021

Caption: Bell's original telephone, exhibited at the Philadelphia Centennial Exposition, 1876