The one dated entry in this notebook is from May 19, 1890. According to an inscription by Clarke at the front of the book, the notebook was used during the years 1890-1894 for research into the "prior art" of electric meters and motors that could be used in meters. The research was conducted in defense of Edison's U.S. Patent 242,901 in unspecified litigation. The entries consist primarily of summaries of British and American patents and articles in books and journals. There are also several pages of notes and formulas for determining the flow of air and steam. Most of the entries concern water and electric meters and electric motors; a few pages at the end of the book relate to generators. The label on the front cover is inscribed "Electric Meters" and "1890." Clarke's name and address are also inscribed on the label. The pages are unnumbered; approximately 130 pages have been used. Courtesy of the Henry Ford Museum and Greenfield Village Research Center.