Alexander Graham Bell Experimental Telephone

An experimental telephone from 1876. Associated with United States patent 174465, “Improvement in Telegraphy,” issued 7 March 1876 to Alexander Graham Bell.

Alexander Graham Bell (1847–1922) demonstrated this and several other experimental telephones at the Philadelphia Centennial Exposition in 1876. This unit features a single electromagnet and could be used both as transmitter and receiver. Bell approached the problem of transmitting speech differently from other telephone inventors like Elisha Gray and Thomas Edison. They were mostly experienced telegraphers trying to make a better telegraph. Bell's in-depth study of hearing and speech strongly influenced his work as he sought to invent a device to help deaf people.

The object has a wooden base on which is mounted an electromagnet supported by a brass post. The cylinder-shaped electromagnet faces a parchment diaphragm that has a metal plate in the center. The diaphragm and a cone-shaped, tin mouthpiece are supported by two brass brackets. Two brass binding posts are set on one end of the base. A separate battery provides the electricity.

To transmit, a person speaks into the mouthpiece. The sound waves cause the diaphragm to vibrate like a drum. The metal plate on the diaphragm makes an electrical current in the electromagnet fluctuate. That current is transmitted by wires from the transmitted to an electromagnet on the receiver, which interacts with the metal plate on the receiver’s diaphragm. The diaphragm vibrates, recreating the sound waves for the listener.