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The Photophone, also known as a radiophone, was invented jointly by Alexander Graham Bell and his then-assistant Charles Sumner Tainter on February 19, 1880, at Bell's 1325 'L' Street laboratory in Washington, D.C.[1][2] Both were later to become full associates in the Volta Laboratory Association, created and financed by Bell.

Bell believed the Photophone was his most important invention. The device allowed for the transmission of both articulated sounds and normal human conversations on a beam of light. On April 1, 1880, and also described by plaque as occurring on June 3, Bell's assistant transmitted the world's first wireless telephone message to him on their newly invented form of telecommunication, the far advanced precursor to fiber-optic communications that came into widespread use during the 1980s. The wireless call was sent from the roof of the Franklin School to the window of Bell's laboratory, some 213 metres (700 ft) away.[3][4][5]

Of the eighteen patents granted in Bell's name alone, and the twelve he shared with his collaborators, four were for the Photophone, which Bell referred to as his 'greatest achievement', writing that the Photophone was "the greatest invention [I have] ever made, greater than the telephone".[6]

Bell transferred the Photophone's rights to the American Bell Telephone Company in May 1880.[7] The master patent for the Photophone (U.S. Patent 235,199 Apparatus for Signalling and Communicating, called Photophone), was issued in December 1880,[5] many decades before its principles could be applied to practical applications.


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