Bell and Watson experiment with speech
Alexander Graham Bell studied sound and hearing, as well as ways to carry sound electrically. With his assistant Thomas Watson, he built apparatus to convert speech vibrations into variations in a circuit and reproduce sound at the receiving end.
The electrical variation had to follow the changing voice closely enough for words to be understood. Mechanical vibration, current and human hearing met in the same experiment.
The experiment of March 10, 1876
On March 10, 1876, Bell spoke into the apparatus: “Mr. Watson, come here, I want to see you.” Watson understood him in another room and came to Bell. Speech had passed through the circuit, and the listener responded to its meaning.
The liquid transmitter used in the experiment changed the electrical contact with the vibration, varying the current with sound. Bell recorded the work in his notebook and reported it in a letter to his father that day.
Understanding a complete sentence
A telegraph encoded written letters; the telephone experiment sought to preserve the continuous variation of speech. The speaker did not have to translate each letter into code, nor did the listener first have to decode a written message.
Bell’s notebook recorded speaking, listening and checking the result. The apparatus had progressed from producing a sound to conveying an intelligible instruction.
Connecting voices through a line
Intelligible speech brought electrical communication into conversation. With instruments at the two ends of a line, people could speak in turn, hear replies and adjust what they said immediately. Transmitters, receivers, wires and switching connections became the basis of telephone service.
The letters and notebook preserve a concrete experimental scene: two rooms, two experimenters, a transmitter and an understood sentence. Longer-distance service required further work on signal loss and network connections.