46 Proceedings of the Royal Society 
In order to augment the currents, and consequently the sounds 
produced in this way, I took a large iron fly-wheel mounted on an 
axis which ran in centres. By a wire attached to one of the centres 
this wheel was connected to one of the terminals of the circuit, 
while a file was connected to the other terminal. The wheel was 
then driven rapidly round, and the file held hard on to its rim, — so 
hard that sparks of fire were produced by the friction. In this way 
a very distinct noise was heard in the receiving telephone. I have 
also made a variety of the above experiment by mounting a small 
cylinder of antimony in a turning-lathe, and driving it round 
against a bar of bismuth. This produces the loudest and most 
distinct noise of anything which I have yet tried. 
These experiments demonstrate, without doubt, the existence of 
currents produced in conducting substances by friction alone, but it 
becomes a question whether they are to be regarded as merely 
thermo-electric, or whether they are not the very currents referred 
to by Sir William Thomson as the probable cause of friction, and 
by Professor Tait, in his “ Thermo -dynamics,” where he says, “ it is 
possible that all friction, not excepting that caused by actual abrasion, 
is due to the production of electricity.” 
Instead of rubbing the substances together, I next proceeded to 
try the effect of knocking the one against the other. For this pur- 
pose a small anvil was put into metallic connection with one of the 
terminals of the circuit, and a hammer similarly connected to the 
other. Each stroke of the hammer on the anvil was very faintly 
heard in the distant telephone. As a variety of this experiment I 
put a small quantity of detonating powder on the anvil, and came 
down upon it with a blow from the hammer. I thought that it 
might be possible to hear something of the sharp snap produced 
by such a blow. The souud, however, heard in the telephone was 
not appreciably louder than before. Another variety of this ex- 
periment- was made by driving a wheel, with large teeth, rapidly 
round in the turning- lathe, and holding against it a strong metal 
spring. The rapid clicks produced in this way were heard even 
when the telephone was a short distance from the ear. Here, how- 
ever, it is plain that we have a mixture of the effects produced by 
rubbing and knocking. 
In my next experiment I took a phonograph, and so arranged it 
