From The Art and Popular Culture Encyclopedia
He is perhaps most famous as the man who almost, but not quite, invented the phonograph. No one before M. Charles Cros had thought of reproducing sound by making an apparatus capable of registering and reproducing sounds which had been engraved with a diagraphm. The inventor gave the name of Paleophone (voix du passé) to his invention. On April 30, 1877 he submitted a sealed envelope containing a letter to the Academy of Sciences in Paris explaining his proposed method. The letter was read in public on the 3rd December following. In his letter, after having shown that his method consisted of obtaining an oscillation of a membrane and using the tracing to reproduce the same oscillation, having regard for its duration and intensity Cros added that the cylindrical form of the receiving apparatus seemed to him to be the most practical, as it allowed for the graphic inscription of the vibrations by means of a very fine wormed screw. An article on the Paleophone was published in "la semaine du Clergé" on October 10th, written by l'Abbé Leblanc. Cros proposed metal for both engraving tool attached to the diagraphm and receiving material for durability.
Before Cros had a chance to follow up on this idea or attempt to construct a working model, Thomas Alva Edison introduced his first working phonograph in the USA. Edison used a cylinder covered in tinfoil for his first phonograph, patenting this method for reproducing sound on January 15, 1878. Edison and Cros apparently did not know of each other's work in advance.
Cros was convinced that pinpoints of light observed on Mars and Venus (probably high clouds illuminated by the sun, were the lights of large cities on those planets. He spent years petitioning for the French government to build a giant mirror that could be used to communicate with the martians and selenites by burning giant lines on the deserts of those planets. He was never convinced that the martians were not a proven fact, nor that mirror he wanted was technically impossible to build.
Charles Cros died in Paris.