These documents cover the years 1868-1921. Included are several letters from Edison to John C. Van Duzer, a civilian electrician with the U.S. Signal Corps. The letters, which date from the period September-December 1868, concern Edison's proposed invention of a facsimile telegraph and a method of secret signaling. Also included is an 1878 letter from Edison to John H. Long, an American student in Germany who later became a professor of chemistry at Northwestern University. It pertains to Edison's tasimeter, which was designed to measure heat. There is also a letter from Hannah Swan, wife of inventor Joseph W. Swan, who wrote Edison in 1888 requesting a phonograph. A similar request from 1890 is from Coleman Sellers, a prominent engineer. In addition, there is a 1921 letter to William M. Van der Weyde, president of the Thomas Paine National Historical Association, in which Edison describes Paine as "one of the greatest men of all time." Courtesy of American Philosophical Society.