the leading tone

The rhythmicon, essentially the world’s first drum machine, built by Leon Theremin in the 1930s at the request and according to the concept of Henry Cowell. The rhythmicon, or “polyrhythmophone,” was designed to facilitate the execution of complex polyrhythms impossible for a single performer using conventional means. It works by projecting light onto photoreceptors; the rhythms are achieved by having the light pass through holes on discs which rotate at controlled speeds.