The invention of the phonograph happened quite by accident. Thomas Edison moved to Menlo Park, New Jersy in 1876, where he established an industrial research laboratory. There, Edison was working on a carbon telephone transmitter to improve the existing Bell telephone system.
In that laboratory a year later, Edison invented the phonograph while he was trying to improve a telegraph repeater. He attached a telephone diaphragm to the needle in the telegraph repeater; in this way, he was able to reproduce a recording that could be played back. After he made some improvements to the machine, he tested it. He recited "Mary Had a Little Lamb" into the machine and played his voice back to a very surprised audience.