The apparatus consists of an ordinary sonometer with five feet clear space between the two end bridges, and having a wire stretched from one end to the other. A current from eight or ten Grove's cells, interrupted by a tuning fork which vibrates 128 times per second, is sent through the wire. At a distance about a fifth of its length from the end of the wire a large electro-magnet, with pointed poles, is placed so that the line joining the poles is at right angles to the wires. The poles are also put close to the wire, but leaving it freedom to vibrate. When a current from eight Grove's cells is sent through the coils of the electro-magnet, the wire begins to sound, and by altering its tension the fundamental note of the wire comes out loud and clear. The wire is also seen to be vibrating as a whole; and the vibrations are also seen to be in the plane perpendicular to the line joining the poles. By shifting the electro-magnet a little, and regulating the tension of the wire, it is seen to divide into nodes and loops with one, with two, with three nodes in its length, thus giving the harmonics of the fundamental note.