This is the fifth of six pocket notebooks used by Charles P. Mott, a member of the office staff at Menlo Park, to record daily activities at the laboratory. The entries from these notebooks were used as the basis for more extensive entries recorded by Mott in Menlo Park Notebooks #53 and #117. This pocket notebook covers the period September 1880-January 1881. The front cover is labeled "154" and is inscribed "No.5 Sept 23.80. to Jany 16.81. C. P. Mott." The pages are unnumbered. Approximately 100 pages have been used.