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).
