Signedunsigned
FunctionConversion of sound into varying intensities of light, which are converted into electrical impulses through the action of this light on selenium.
To operate the device, a concentrated beam of light is focused on the highly polished surface of a vibrating diaphragm, in this case made of glass. Reflections from the oscillating beam of light are passed through a lens and then on to the surface of a parabolic reflector/receiver made of silver-plated copper. The focused light rays are directed at a selenium cell. The selenium cell, which has the property of converting radiant energy into an electrical current, forms part of the telephonic circuit.
ProvenanceJefferson Laboratory, Physics Department, Harvard University
Published ReferencesThis instrument is described in:
Thomas G. Hedberg, "Catalogue: Telephones, Phonographs and Related Instruments in The Collection of Historical Scientific Instruments at Harvard University." William Andrewes, Project Director (unpublished manuscript, President and Fellows of Harvard College and Thomas G. Hedberg, 1989. Fifth Draft), pp. 79-80.
See also:
George B. Prescott, Bell's Electric Speaking Telephone: Its Invention, Construction, Application, Modification and History. (New York: D. Appleton and Company, 1884). pp. 315, 318. Available on Google Books here.