[NM001070], Technical Note, Thomas Alva Edison, William Unger, July 23rd, 1870
[NM001-F] Notebook Series -- Miscellaneous Shop and Laboratory Notebooks
https://edisondigital.rutgers.edu/document/NM001070
Thomas A. Edison Papers, School of Arts and Sciences, Rutgers University
Archive.org Viewer, Microfilm Series Reel 5