Fagen, M. D. (1975). A history of engineering and science in the bell system: The early years (1875-1925). The United States of America: Bell Telephone Laboratories.

Fagen, M. D. A History of Engineering and Science in the Bell System: The Early Years (1875-1925). The United States of America: Bell Telephone Laboratories, 1975.

Fagen, M. D. A History of Engineering and Science in the Bell System: The Early Years (1875-1925). The United States of America: Bell Telephone Laboratories, 1975.