What if someone recorded their voice but could never hear it played back? On April 9, 1860, a French inventor named Edouard-Leon Scott de Martinville sang into a strange-looking machine. The machine, called a phonautograph, used a horn to catch sound waves. Inside, a thin membrane vibrated when sound hit it. A needle attached to the membrane scratched wavy lines onto paper coated in black soot. These wavy lines were a visual picture of sound. Scott had done something no human had ever done before: he had recorded a voice. But he never heard his recording played back. The phonautograph could write sound but not read it. Thomas Edison would not invent the phonograph, a machine that could both record and replay sound, until 1877. Seventeen years later. Scott's recordings sat in French archives for nearly 150 years, forgotten. Then in 2008, researchers used a computer to scan the wavy lines. They were able to convert the scratches back into sound. When they played the result, they heard a ghostly voice singing in French. The oldest known recording of a human voice. Scott understood the principle of recording sound before anyone else.