First in point of time and importance is the Macdonald Spring Motor, the invention of Thomas Hood Macdonald, a prolific inventor and contributor of many valuable improvements to the talking machine art and industry. The Bell and Tainter machine was operated by a storage battery and this was an inconvenient and expensive form of power. To meet this condition the Macdonald Spring Motor was invented and from the start proved a tremendous success. Today most of the clockwork motor talking machines are built upon the principles disclosed in the Macdonald Spring Motor patent. [Illustration: AN UP-TO-DATE TALKING MACHINE MODEL] The next important step was the discovery by Macdonald that a critical speed for the surface of the record must be obtained in order to secure best results, and this wonderful principle in the art of sound recording was protected by United States patent issued to Macdonald covering what is known as the Macdonald Graphophone Grand. This discovery and invention has been largely instrumental in the rapid development of sound recording. Although Bell and Tainter disclosed a method of recording sound on a flat surface, all of the earlier forms of talking-machine records were what are known as cylindrical, records in a cylindrical form. Later the disc record came into use and is now the most popular form. Relatively very few cylinder records are manufactured at the present time. The process of sound recording, as applied to disc records, is covered by United States patent to J. W. Jones, and marks a further important stage in the development of the art and industry.