Monochord

Monochord, or Sonometer, is an apparatus by which the vibrations of strings may be observed. A single string or wire is stretched over two pieces of wood fixed to a sounding-board. One end of the string is fixed, the other passes over a pulley and is loaded with weights. The length of the vibrating string is altered by placing a movable bridge between the two fixed ones, only that part of the string between the movable bridge and the bridge nearest to the pulley being considered. The number of vibrations of the wire per second is found to increase with the load applied, and to decrease when a greater length is used.