English: A model of the first telephone transmitter/receiver (microphone/speaker) invented by US scientist Alexander Graham Bell in 1875. It is now known as 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 built by his 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 work before intelligible speech could be transmitted. This is probably not the transmitter used in Bell's famous first communication of speech on March 10, 1876: "Come here, Watson, I need you"; Bell had improved electromagnetic transmitter designs by then, and some sources say a liquid transmitter was used on that occasion.

It consists of a parchment diaphragm stretched over a cup-shaped sound collector, attached to an iron armature on a springy metal reed, near a pickup coil of wire wound on an iron core attached to the binding posts at top. It was included in Bell's telephone patent of March 7, 1876. This image shows a model of the original device; Thomas A. Watson wrote in 1915 (p. 1017 below) that "all that is left" of the original was in the National Museum in Washington. 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

Plaque on model says: "This model of Bell's first telephone is a duplicate of the instrument through which speech sounds were first transmitted, 1875"