Coil, Ruhmkorff. A common type of induction-coil with a vibrator or circuit-breaker. Used with constant and direct current.
A step-up transformer with a circuit-breaker attachment.
Coils, Idle. Coils in a dynamo in which no electro-motive force is being generated or developed.
Coils that, through broken connections or short circuits, are inactive.
Column, Electric. An old name for the voltaic pile. The apparatus made up of a pile of disks of copper and zinc, separated by pieces of flannel wet with acidulated water.
Comb. A bar from which a number of teeth project like the teeth of a comb. It is used as a collector of electricity from the plate of a frictional electric machine.
Commutator. An apparatus used on motors and dynamos and induction-coils for changing the direction of currents. It is made in a variety of types, but usually in the shape of insulated bars closely packed about an armature shaft.
Commutator-bars. The metallic segments of a dynamo or motor-commutator.
Commutators, Quiet. Commutators that do not spark during the revolutions of the armature.
Compass. An apparatus for indicating the directive force of the earth upon the magnetic needle. It consists of a case covered with glass, in which a magnetized needle, normally pointing to the north, is balanced on a point at the centre. Under the needle a card is arranged on which the degrees or points of the compass are inscribed. A valuable instrument in electrical work, magnetism, etc.