Apparatus for sounding an adjustable number of beats per minute and therefore for fixing the tempo of a comp. An early form, called chronomètre, was available at end of 17th cent. and further experiments followed. The idea of the clockwork model patented by Maelzel seems to have been appropriated from the Dutch inventor D. N. Winkel. Maelzel est. a metronome factory in Paris, 1816. The one most commonly used is a pyramidal wooden instrument at the front of which a perpendicular steel strip, about 7½″ long by ⅛″ wide, is pivoted. The principle is that of a double pendulum (an oscillating rod weighted at both ends). The upper weight is movable along the steel strip, and according to its position on the rod the number of oscillations per minute can be made to vary between 40 and 208. The rod beats (or ‘ticks’) as it swings back and forth and a bell may be incorporated which can be set to ring every 2, 3, or 4 beats. Maelzel's graduated scale, fixed to the case, gives speed of oscillation. A composer who wants 78 quarter‐note (crotchet) beats in a minute will write ‘M.M. (Maelzel metronome) 𝅘𝅥 = 78’. A spiral spring, which is wound up like a clock, keeps the instrument beating for a considerable period. Battery and electronically operated metronomes have been marketed. A pocket metronome shaped like a wrist‐watch was designed in Switzerland about 1945 and others have been invented which can be synchronized to cope with the complex rhythms found in many modern scores.
It should be mentioned that some composers' metronome markings are suspect. Editors of early works have in many cases added metronome marks which they think are feasible. The ticking of Maelzel's metronome is supposed to have inspired the theme of the 2nd movt. of Beethoven's 8th sym. Several 20th‐cent. composers have incorporated the ticking of actual metronomes into their scores, e.g. Ligeti's sym.‐poem for 100 metronomes and Gordon Crosse's Play Ground.