The Rhythmicon—also known as the Polyrhythmophone—was an electro-mechanical musical instrument designed and built by Leon Theremin for composer Henry Cowell, intended to reveal connections between rhythms, pitches and the harmonic series. It used a series of perforated spinning disks, similar to a Nipkow disk, to interrupt the flow of light between bulbs and phototoreceptors aligned with the disk perforations. The interrupted signals created oscillations which were perceived as rhythms or tones depending on the speed of the disks. Although it generated both pitches and rhythms, it has often been described as the world's first drum machine. Development In 1930, the avant-garde American composer and musical theorist Henry Cowell collaborated with Russian inventor Léon Theremin in designing and building the remarkably innovative Rhythmicon. Cowell wanted an instrument with which to play compositions involving multiple rhythmic patterns impossible for one person to perform simultaneously on acoustic keyboard or percussion instruments. The invention, completed by Theremin in 1931, can produce up to sixteen different rhythms—a periodic base rhythm on a selected fundamental pitch and fifteen progressively more rapid rhythms, each associated with one of the ascending notes of the fundamental pitch's overtone series. Like the overtone series itself, the rhythms follow an arithmetic progression, so that for every single beat of the fundamental, the first overtone (if played) beats twice, the second overtone beats three times, and so forth. Using the device's keyboard, each of the sixteen rhythms can be produced individually or in any combination. A seventeenth key permits optional syncopation. The instrument produces its percussion-like sound using a system, proposed by Cowell, that involves light being passed through radially indexed holes in a series of spinning "cogwheel" disks before arriving at electric photoreceptors. Nicolas Slonimsky described its capabilities in 1933:The rhythmicon can play triplets against quintuplets, or any other combination up to 16 notes in a group. The metrical index is associated ... with the corresponding frequence of vibrations.... Quintuplets are ... sounded on the fifth harmonic, nonuplets on the ninth harmonic, and so forth. A complete chord of sixteen notes presents sixteen rhythmical figures in sixteen harmonics within the range of four octaves. All sixteen notes coincide, with the beginning of each period, thus producing a synthetic harmonic series of tones. Schillinger once calculated that it would take 455 days, 2 hours, and 30 minutes to play all the combinations available on the Rhythmicon, assuming an average duration of 10