272 Scientific Proceedings, Royal Dublin Socrety. 
notice of the Royal Society of Edinburgh, the sound heard in a 
telephone when a file and wire were rubbed together, and others 
have pointed out similar facts. The experiments I am about to 
describe were likewise made before I had read Forbes's note, but 
as | have noticed some additional facts it may be of sufficient 
interest to bring them before the Society. 
Interruptor.—A steady current in one direction has no audible 
effect on the telephone after the first contact, hence to use the 
telephone as an electric re-agent, the current must be interrupted. 
For this purpose I find it convenient tomakeuse of a rapidly revolvy- 
ing wheel, W, Fig. 1, the periphery of which is nicked, and the 
nicks filled with shell-lac, so that a smooth continuous surface is 
presented to the springs which bears on the edge of the wheel. 
The wheel is driven by clockwork, and makes about 100 inter- 
ruptions ‘per second. Binding screws attached to the frame of 
the clockwork enable the interruptor to be thrown into circuit 
