This is the fourth 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 July-September 1880. The front cover is labeled \"153\"" and is inscribed \""C. P. Mott No. 4 May 14. 80 to Septr. 23. 80.\"" The pages are unnumbered. Approximately 70 pages have been used."