The photophone was originally invented jointly by Alexander Graham Bell and his assistant Sumner Tainter on February 19, 1880. Then on June 3, 1880, Alexander Graham Bell transmitted the first wireless telephone message on his newly-invented photophone. Bell believed the photophone was his most important invention. The device allowed for the transmission of sound on a beam of light. Of the eighteen patents granted in Bell's name alone, and the twelve he shared with his collaborators, four were for the photophone. February 19 is the 50th day of the year in the Gregorian Calendar. ... 1880 (MDCCCLXXX) was a leap year starting on Thursday (see link for calendar). ... June 3 is the 154th day of the year in the Gregorian calendar (155th in leap years), with 211 days remaining. ... 1880 (MDCCCLXXX) was a leap year starting on Thursday (see link for calendar). ... Alexander Graham Bell (March 3, 1847 – August 2, 1922) was a Scottish-born scientist and inventor. ... The telephone or phone (Greek: tele = far away and phone = voice) is a telecommunications device which is used to transmit and receive sound (most commonly voice and speech) across distance. ... In general terms, an invention is an object, process or technique which displays an element of novelty. ... In communications, transmission is the act of transmitting electrical messages (and the associated phenonomena of radiant energy that pass through media). ... A schematic representation of hearing. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of wavelengths that are studied in the field of optics. ... A patent is a set of exclusive rights granted by a state to a person for a fixed period of time in exchange for the regulated, public disclosure of certain details of a device, method, process or composition of matter (substance) (known as an invention) which is new, inventive, and...

The photophone used crystalline selenium cells as the receiver. This material's electrical resistance varies inversely with the illumination, i.e., its resistance is higher when it is in the dark, and lower when it is lighted. The idea of the photophone was thus to modulate a light beam: the resulting varying illumination of the receiver would induce corresponding varying resistance in the selenium cells, which could be used by a telephone to regenerate the sounds captured at the receiver. The modulation of the light beam was done by a vibrating mirror: a thin mirror would alternate between concave and convex forms, thus focussing or dispersing the light from the light source. The photophone functioned similarly to the telephone, except the photophone used light as a means of projecting the information, while the telephone relied on electricity. SE redirects here. ... Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ... In geometry, concavity is a property of certain geometric figures, and in calculus, a property of certain graphs of functions. ... In mathematics, an object is convex if for any pair of points within the object, any point on the straight line segment that joins them is also within the object. ... Lightning strikes during a night-time thunderstorm. ...

Diagram of the Photophone. ...

In one experiment in Washington, D.C., Bell and his co-inventor Charles Sumner Tainter succeeded to communicate clearly over a distance of some 700 ft. (about 213 m), using plain sunlight as the light source. The receiver was a parabolic mirror with the selenium cells in its focal point. The selenium cells had an electrical resistance varying between 300 Ω and 100 Ω. Nickname: the District Motto: Justitia Omnibus (Justice for All) Official website: http://www. ... Charles Sumner Tainter, ca. ... A foot (plural: feet) is a non-SI unit of distance or length, measuring around a third of a meter. ... The metre, or meter (symbol: m) is the SI base unit of length. ... A parabola A parabola (from the Greek: παραβολή) is a conic section generated by the intersection of a cone, and a plane tangent to the cone or parallel to some plane tangent to the cone. ... The ohm (symbol: Ω) is the SI unit of electric resistance. ... The ohm (symbol: Ω) is the SI unit of electric resistance. ...

Although the photophone was an extremely important invention, it was many years before the significance of Bell's work was fully recognized. Bell's original photophone failed to protect transmissions from outside interferences, such as clouds, that easily disrupted transport. Until the development of modern fiber optics, technology for the secure transport of light inhibited use of Bell's invention. Bell's photophone is recognized as the progenitor of the modern fiber optics that today transport over eight percent of the world's telecommunications. Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). ... Fiber Optic strands An optical fiber in American English or fibre in British English is a transparent thin fiber for transmitting light. ... BlackBerry 7100t Telecommunication refers to the communication of information at a distance. ...

Literature

• Bell, A. G.: "On the Production and Reproduction of Sound by Light", American Journal of Sciences, Third Series, vol. XX, #118, October 1880, pp. 305 - 324; also published as "Selenium and the Photophone" in Nature, September 1880.

Look up October in Wiktionary, the free dictionary. ... 1880 (MDCCCLXXX) was a leap year starting on Thursday (see link for calendar). ... SE redirects here. ... First title page, November 4, 1869 Nature is one of the oldest and most reputable scientific journals, first published on 4 November 1869. ... Look up September in Wiktionary, the free dictionary. ... 1880 (MDCCCLXXX) was a leap year starting on Thursday (see link for calendar). ...

External links

• Bell's speech before the American Association for the Advancement of Science in Boston on August 27, 1880, in which he presented the above paper.