A thin steel rod (called vibrator) is clamped at one end and passes through a small solenoid. The rod is slightly flattened at the free end and a hole is drilled in it so that a string can be tied through it. The solenoid is connected to A.C. mains through a suitable lamp resistance. A permanent horse shoe magnet is mounted on the base board and a steel rod passes between them. The thin rod is magnetized longitudinally. The solenoid and a horse shoe shaped magnet cause it to vibrate with the frequency of A.C. supply. The length of the vibrator is adjusted until its natural frequency corresponds with that of the supply. The whole unit is mounted on a polished wooden base, complete with pulley, pan and cord.