SOUND BY LOOSE ELECTRICAL CONTACT. 283 
long flat files. These were put edgewise on the lead blocks, with their tails 
resting on the edges of three-cornered files. The current was sent through the 
rockers by means of these lead blocks and three-cornered files. One of these 
rockers was placed at A along with the automatic make-and-break, while the 
other was placed at B. An arrangement was provided whereby the make-and- 
break could be at any moment shunted out of the circuit without interrupting 
the current. The make-and-break was then started, and having ascertained 
that the rockers at A and B were both sounding, the make-and-break was 
shunted off in hopes of hearing A and B still continuing to sound from the one 
acting as make-and-break to the other. These hopes, however, were doomed 
to disappointment, as, after many trials, I failed to hear any sound after the 
shunt was made. 
Experiment 4.—Being still not satisfied that there was not an actual vibra- 
tion at B in these experiments, I determined to test for it in another way. 
This time I took a tin can and riveted into the centre of its bottom a pointed 
piece of steel wire. The can was fixed to a wooden board, and an arrangement 
made whereby another pointed piece of-steel wire could be moved up opposite 
to the former piece, and as close to it as might be desired. The current was 
now led through the can and these pieces of steel, and the make-and-break 
started as usual, when very minute to-and-fro vibrations of the can were observ- 
able, especially when the steel points were not pressing hard against each other 
but loosely in contact, so that little sparks could be seen between them. To 
make perfectly certain of this observation, I hope to repeat the experiment with 
still greater care. 
From this experiment, notwithstanding the negative evidence of the others, 
it seems not unlikely that when a strong interrupted current is sent through a 
circuit where there is a loose contact, more or less of an actual separation of 
the surfaces there takes place, so as to make something of a make-and-break 
similar to the original make-and-break which causes the interrupted current. 
Should this suggestion be established, it will follow that it is something of the 
same kind, but only differing in degree, which sends the undulatory currents 
which transmit musical sounds and articulate speech from any form of micro- 
phone transmitter to a similar form of microphone receiver. 
As to the cause or causes of this separation of the surface at the loose con- 
tact B, or of whatever agitation else it may be which gives forth the sound, it 
is impossible in the present state of knowledge to speak with confidence. I am 
inclined, however, to look for one cause at least in that produced by the cur- 
rent at the loose contact. There the resistance and, in consequence, the rise 
of temperature produced by the current is greatest, and an effect similar to 
the TREVELYAN rocker will be set up, although immensely smaller in amount. 
Experiment 5.—This experiment has reference to the sounds heard in a 
