William J. Hammer (1858-1934) began working with Thomas Edison in 1879, assisting in the development of the incandescent light bulb. In time he was known as an electrical engineer and expert on electric power distribution. Other interests included radium, selenium cells, aeronautics, and the transmission of sounds. This paper disc is part of his apparatus for measuring light.
Ref: William J. Hammer, “Method of Measuring Light,” U.S. Patent 333,308 (May 26, 1908).
