550 Proceedings of the Royal Society 
fastened in their places two metallic strips, one of copper and the, 
other of iron, so arranged that they could he made to rub against 
each other by moving the upper rod up and down in its air-tight 
socket. Before being fixed on, the metal surfaces were both well 
cleaned by scraping. When this apparatus was included in the 
circuit either of a galvanometer or telephone, no difference could be 
detected either in the deflection or the sound produced, by exhaust- 
ing the air, as far as could be done, with an ordinary good air-pump. 
It is possible, however, that there may be films ' of air adhering to 
the metals which cannot be removed by pumping. Indeed, in the 
whole of this inquiry, the great difficulty is to be sure of what are 
the surfaces that are in contact. 
Having ascertained that the current produced by the friction of 
antimony and bismuth is of some strength, and fairly constant when 
the friction is constant, I proceeded to make a small dynamo machine 
for producing currents on this principle. It consists of a cylinder 
of antimony 3 inches long and 2J inches in diameter, mounted on 
an axis which runs in centres. By a fly-wheel and band this 
cylinder is driven rapidly round against a plate of bismuth pressed 
tight against it by a stiff spring, Wires are led from the plate of 
bismuth and from one of the pivots on which the cylinder revolves 
to two binding screws, which form the electrodes of the machine. 
When this machine is included in the circuit with a microphone 
transmitter and a telephone, the current from it can be fised for the 
transmission of musical sounds and even loud speaking. There is, 
however* heard along with the transmitted sound the noise arising 
from the friction of the antimony and bismuth. I have succeeded 
in transmitting, in this way, very distinctly, tunes played on a violin 
to which a microphone was attached. It is very curious, in this 
experiment, to hear so distinctly the music, notwithstanding the 
friction noise which accompanies it. It is to be noticed that the 
sound heard in the telephone of the rubbing of two pieces of metal 
together in a distant room is an effect precisely identical to this. 
In this case the rubbing produces the current, and the more or less 
loose contact of the metals acts as the microphone whereby the 
sound is transmitted through means of that current to the telephone. 
- I have also tried, with varying success, several other forms of this 
friction current-producer. In one of the most effective of these the 
