It is interesting that he was working on device to improve the speed of telegraph lines when he hit upon the idea of voice recording. He trying to build a device that would record an operator’s signal in what today would be called “real-time” and then play it back speeded up. The faster recording would be sent over a telegraph line, where it would recorded, and played back at the speed at which it was recorded. It occurred to him that the same device could record natural sounds, including, it turned out, the nursery rhyme “Mary had a little lamb”.