Returning home to Brantford after six months abroad, Bell continued his experiments with his "harmonic telegraph".[N 12] The basic concept behind his device was that messages could be sent through a single wire if each message was transmitted at a different pitch, but work on both the transmitter and receiver was needed.

Answer this question, if possible (if impossible, reply "unanswerable"): How many wires did Bell send a signal through?
1