The measurement of the capacity of insulated wires can be easily carried out by means of an appliance devised by the author and Mr. W. C. Clinton, consisting of a rotating commutator which alternately charges the insulated wire at a source of known electromotive force and then discharges it through a galvanometer.
"Hertzian Wave Wireless Telegraphy"
John Ambrose Fleming
Then, associated with this form of induction coil is a commutator of a peculiar kind, which performs the following functions when a battery is connected to it and when it is made to revolve by a motor or by clockwork.
"Hertzian Wave Wireless Telegraphy"
John Ambrose Fleming
Where it is desired to give the patient a galvanic shock, it is only necessary rapidly to reverse the current by means of the commutator.
"The Electric Bath"
George M. Schweig