Coil, Resistance. A coil so wound that it will offer a resistance to a steady current, or reduce the flow of electricity. Commutator. A cylinder on the end of the armature of a dynamo or motor and provided with a pair of contact plates for each particular coil in the armature, in order to change the direction of the current. Compass. An apparatus which indicates the direction or flow of the earth's magnetism. Condenser. A device for storing up electro-static charges. Conductance. That quality of a conductor to carry a current of electricity, dependent on its shape for the best results. Conduction. The transmission of a current through a rod, wire or conductor. Conductivity. That quality which has reference to the capacity to conduct a current. Conductor. Any body, such as a bar, rod, wire, or machine, which will carry a current. Connector. A binding post, clamp, screw, or other means to hold the end of a wire, or electric conductor. Contact. To unite any parts in an electric circuit. Controller. The handle of a switchboard, or other contact making and breaking means in a circuit. Converter. An induction coil in an alternating circuit for changing potential difference, such as high alternating voltage into low direct current voltage. Convolution. To wind like a clock spring. Core. The inner portion of an electro-magnet. The inside part of an armature wound with wire. Core, Laminated. When the core is built up of a number of separate pieces of the same material, but not insulated from each other. Coulomb. The unit of electrical quantity. It is the quantity passed by a current of one ampere intensity in one second of time. Couple, Electric. Two or more electrodes in a liquid to produce an electric force. Current, Alternating. A natural current produced by the action of electro-magnets. It is a succession of short impulses in opposite directions. Current, Constant. A current which is uniformly maintained in a steady stream. Current, Induced. A current produced by electro-dynamic induction. Current Meter. An apparatus for indicating the strength of a current. An ammeter. Current, Oscillating. A current which periodically alternates. Current, Periodic. A periodically varying current strength. Current, Undulating. A current which has a constant direction, but has a continuously varying strength.