This notebook covers the period March-July 1880. Most of the entries are by William J. Hammer. Some are by Charles Batchelor. Some entries may also be by Francis Jehl and Charles Flammer, whose names appear as witnesses. Most of the material relates to tests on experimental lamps, numbers 974 to 1323. There is also a drawing on the inside back cover of a Japanese bamboo filament lamp. Related material can be found in Menlo Park Notebook #41. The label on the front cover is marked \"From No 974- Electric Lights.\"" The book contains 276 numbered pages.

Blank pages: 150-159, 162-171, 174-209, 212-249, 252-256, 273-275.

Missing page numbers: 1-54, 257-272."