Music was sent down a telephone line for the first time in 1876, the year the phone was invented.
During the 1870s, two well-known inventors both independently designed devices that could transmit sound along with electrical cables. Those inventors were Alexander Graham Bell and Elisha Gray. Both devices were registered at the patent office within hours of each other. There followed a bitter legal battle over the invention of the telephone, which Bell subsequently won.
The telegraph and telephone are very similar in concept, and it was through Bell's attempts to improve the telegraph that he found success with the telephone.
The telegraph had been a highly successful communication system for about 30 years before Bell began experimenting. The main problem with the telegraph was that it used Morse code, and was limited to sending and receiving one message at a time. Bell had a good understanding of the nature of sound and music. This enabled him to perceive the possibility of transmitting more than one message along the same wire at one time. Bell's idea was not new, others before him had envisaged multiple telegraphs. Bell offered his own solution, the "Harmonic Telegraph". This was based on the principle that musical notes could be sent simultaneously down the same wire if those notes differed in pitch.
By the latter part of 1874 Bell's experiment had progressed enough for him to inform close family members about the possibility of multiple telegraphs. Bell's future father in law, attorney Gardiner Green Hubbard saw the opportunity to break the monopoly exerted by the Western Union Telegraph Company. He gave Bell the financial backing required for him to carry on his work developing the multiple telegraphs. However, Bell failed to mention that he and his accomplice, another brilliant young electrician Thomas Watson, were developing an idea that occurred to him during the summer. This idea was to create a device that could transmit the human voice electrically.
Bell and Watson continued to work on the harmonic telegraph at the insistence of Hubbard and a few other financial backers. During March 1875 Bell met with a man called Joseph Henry without the knowledge of Hubbard. Joseph Henry was the respected director of the Smithsonian Institution. He listened closely to Bell's ideas and offered words of encouragement. Both Bell and Watson were spurred on by Henry's opinions and continued their work with even greater enthusiasm and determination. By June 1875 they realized their goal of creating a device that could transmit speech electrically would soon be realized. Their experiments had proven different tones would vary the strength of an electric current in a wire.