On this Day

December 3, 1877

French Academy opens Charles Cros' Sealed Envelope



On April 30, 1877, Charles Cros submitted a sealed letter to the Academy of Sciences in Paris describing how to reproduce sound from a recording of sound waves.


"The letter stated in French, "Un index léger est solidaire du centre de figure d'une membrane vibrante ; il se termine par une pointe [...] qui repose sur une surface noircie à la flamme." The English translation is one close to this: "A lightweight armature is fixed to the center of the face of a vibrating membrane; it ends with a sharp point [...] which rests on a lamp-blacked surface." This surface is integral with a disc driven by a double movement of rotation and linear progression. The system is reversible: when the tip follows the furrow the membrane restores the original acoustic signal.

In his letter, after having shown that his method consisted of detecting an oscillation of a membrane and using the tracing to reproduce the oscillation with respect to its duration and intensity, Cros added that a cylindrical form for 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-threaded screw.

"As far as is known, no one before him had thought of a practical way to reproduce sound from a recording of airborne sound waves. He gave the Greek name 'Paleophone' ('voix du passé', tr. 'voice of the past') to his invention."

An article on the Paleophone was published in "la semaine du Clergé" on October 10, 1877, written by l'Abbé Leblanc. Cros proposed metal for both engraving tool attached to the diaphragm and receiving material for durability" (1).

On December 3, 1877, the sealed envelope was opened and the Cros letter was read in public.

The First Day cover below celebrates the 100 year anniversary of the opening of that sealed letter by the Academy of Sciences in Paris and is postmarked December 3, 1977.

Cros is therefore credited "with anticipating, though barely, what Edison was to accomplish" (2) which is why the First Day cover reads 100 years of the Phonographe (and not 100 years of the Paleophone which was never built).



(1) Wikipedia

(2) Charles Cros, as described in “The Talking Machine”, by Timothy C. Fabrizio and George F. Paul





December 3 - On this Day Factola