02/12/1877 Batchelor, Charles and Edison, Thomas Alva -- Technical Notes and Drawings
(Bell, Alexander Graham) Telephone; Acoustic telegraphy
[MBN002]  Special Collections Series -- Charles Batchelor Collection -- Notebooks: Cat. 1317 (1875-1878)
[MBN002033; TAEM 90:673]
Courtesy of Thomas Edison National Historical Park.