This undated notebook was probably used in 1888. The entries are by Edison and his wife, Mina Miller Edison. The book contains notes regarding the melting properties of numerous chemical compounds used for insulation. Some of the compounds are identified for potential use in phonograph cylinders or lamp filaments. The pages are unnumbered. One page has been removed from the back of the book. Approximately 60 pages have been used. Courtesy of Thomas Edison National Historical Park.