A photographophone is a device, first developed by Ernst Ruhmer of

Berlin Berlin ( ; ) is the Capital of Germany, capital and largest city of Germany, by both area and List of cities in Germany by population, population. With 3.7 million inhabitants, it has the List of cities in the European Union by population withi ...

, Germany in 1900, used to produce and play back audio recordings. Photographophone recording uses

celluloid Celluloids are a class of materials produced by mixing nitrocellulose and camphor, often with added dyes and other agents. Once much more common for its use as photographic film before the advent of safer methods, celluloid's common present-day ...

film. The process is started by speaking into a

microphone A microphone, colloquially called a mic (), or mike, is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and publi ...

, connected to a battery pack, whose modulated electrical output produces corresponding variations in the light of an arc (later an

incandescent lamp An incandescent light bulb, also known as an incandescent lamp or incandescent light globe, is an electric light that produces illumination by Joule heating a filament until it glows. The filament is enclosed in a glass bulb that is eith ...

) that passes through a cylindrical lens slot, which creates lines on the moving sensitive film. This film, after being taken out of the box and developed, shows a series of perpendicular striations parallel to one another, which are a photographic record of the sound waves created by the telephone transmitter output."Chapter IV: The Photographophone"
''Wireless Telephony In Theory and Practice'' by Ernst Ruhmer (translated from the German by James Erskine-Murray), 1908, Pages 36-40. To reproduce the recorded sound, a projector directs light through the film, which travels at an equal velocity to that with which the record is made. Behind the film, a sensitive selenium cell is mounted, receiving the variations in light, which produces a variation in its resistance, and corresponding audio in a connected telephone receiver. Ruhmer was quoted as saying: "It is truly a wonderful process: sound becomes electricity, becomes light, causes chemical action, becomes light and electricity again, and finally sound." In addition, it was described as "The reproduction of speech by this photographic phonograph is astonishingly clear, and in strength resembles the ennunciation of a good telephone when in ordinary use... It has the advantage of the ordinary wax-cylindered phonographs in that the reproduction is purer and is free from the unpleasant noises caused by imperfections in the mechanism."

References

Display technology History of film Film and video technology Film sound production Audiovisual introductions in 1900 {{film-tech-stub