This notebook covers the period December 1878-March 1879. All of the entries are by Edison, Charles Batchelor, and Francis Upton, with the exception of a few drawings by John Kruesi. The name of John Ott occasionally appears as a witness. Most of the material relates to experiments on electric lighting. There are drawings of lamps, including vacuum experiments; drawings of devices for making and testing wire spiral filaments; notes on platinum and platinum-iridium wire; notes and drawings of generators; calculations of system costs, including comparisons to gas lighting costs; and drawings and calculations about meters, including some labeled "Sprague's Exhibit Edison's Early Sketch No. [2-4] Jan. 12th 1886." There are also drawings of the electric pen and the phonograph. The book contains 241 numbered pages followed by 30 unnumbered pages.
Following the last page of Notebook #9 is a set of images, from this notebook and from Notebook #192 (N-78-12-15.2), that constitute Doc. 1621 in The Papers of Thomas A. Edison, Vol. 4. The images appear in the following order: Notebook #9, pages 3-13; Notebook #192, pages 23-39. Courtesy of Thomas Edison National Historical Park.