28 
Proceedings of the Boyal Society 
4. Note on an Electric Sonometer. By Prof. James Blytli. 
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 funda- 
mental note. 
This effect is due to the interrupted current causing the wire to 
vibrate across the lines of force due to the electro-magnet ; in fact, 
the magnet appears very much to perform the function of the bow 
when employed to agitate the wire in the ordinary way. 
I have tried different wires — iron, steel, and copper — all with the 
same result, which shows that the effect is not confined to wires 
formed of the magnetic metals alone. 
This experiment helps to explain the action of the wire telephone, 
and shows that it is due mainly, if not entirely, to the transverse 
and not to the longitudinal vibrations of the wire. 
By damping the wire at the requisite points along its length, the 
various notes of the scale can be distinctly reproduced. 
All the notes produced are remarkably clear and beautiful, and 
the effect of a slight alteration of tension in altering the tone is very 
marked. 
It is easy to see how an apparatus on this principle could be 
constructed for repeating Helmholtz’s experiments on the vowel 
sounds. 
