These two documents are from 1886 and 1908. The first is a letter from engineer and former Edison associate Frank J. Sprague to Edward H. Johnson, vice president of the Edison Electric Light Co., on the value of alternating current systems for power transmission. The second item was prepared by Johnson for T. Commerford Martin, co-author of the official two-volume biography, Edison: His Life and Inventions (New York: Harper & Brothers, 1910). His reminiscences describe how he and Edison first met while working on the automatic telegraph in the early 1870s. Other recollections include Sir William Thomson's visit to the Philadelphia Centennial Exhibition in 1876 and early demonstrations of Edison's phonograph in New York.

Courtesy of the Henry Ford Museum and Greenfield Village Research Center.