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The phonoplex was a railway telegraphy system invented and patented by Edison in 1885. Beginning in 1886 the phonoplex was sold to railroad and telegraph companies in the United States and Canada through an unincorporated Edison business. These records cover the period 1886-1905, with the bulk of the material generated in 1886-1896. They consist of three letterbooks (1886-1888, 1890-1892) and a bound volume (1886-1905) titled "Cases Vol 1." A finding aid is available at the Edison National Historical Park.
A selection of correspondence from the third letterbook (1890-1892) has been reproduced in Part III. Selections from the two earlier letterbooks can be found in the Miscellaneous Letterbooks in Thomas A. Edison Papers, Part II (1879-1886). The case volume [not selected] provides account summaries for railroad, telegraph, and other installations of the phonoplex system. Included are circuit diagrams of installations; lists containing information on the types and costs of materials used; and tables relating to the dates of installation and royalties, station locations, and circuit lengths. Courtesy of Thomas Edison National Historical Park.