=Contact.= The electrical union of two conductors, whether temporary or permanent. It may be established by touching the ends or terminals of a circuit through the agency of a push-button, a telegraph-key, an electric switch, etc. =Contact-breaker.= (The same as Circuit-breaker, _which see_.) =Contact, Loose.= A contact formed by two or several surfaces imposed one upon another and held by their weight alone. =Contact-point.= A point, or stud, often of silver or platinum, arranged to come into touch with a contact-spring, such as the vibrating armature of an electric bell. =Contact-spring.= A spring connected at one end of a lead and arranged to press against another spring or plate, so that a plug may be inserted between the contact-points. =Controller.= The lever or handle on the switch-board of a resistance-coil, by means of which electric current is let in or kept out of a circuit. =Controlling Force.= In galvanometers and similar instruments, the force used to bring the needle or indicator back to zero. =Converter.= An induction-coil used with the alternating current for changing the potential difference and inverting the available current. High alternating voltage may be converted into lower direct-current voltage, thereby increasing the amperage or current. A converter consists of a core of thin iron sheets, wound with a primary coil of fine insulated wire, with many convolutions or turns. Also, a secondary coil made up of coarse insulated wire with fewer convolutions. The coil may be jacketed with iron to increase the permanence. =Converter, Rotary.= A combined motor and dynamo whose function is to transform a current of high or low voltage (A-C., or D-C.) into any other kind of current desired. =Convolution.= The state of being convolved; a turn, wrap, fold, or whorl. A clock-spring is a familiar example. =Copper-bath.= A solution of sulphate of copper used in electro-plating, electrotyping, and copper-refining by electricity. =Cord, Flexible.= A flexible-wire conductor made up of many strands of fine wire and properly insulated so that it may be easily twisted, bent, or wrapped. Flexible wire is used as the conductors for portable electric lights, push-buttons, medical coils, etc. =Core.= The iron mass (generally located in the centre of a coil or helix) which becomes highly magnetic when a current is flowing around it, but which looses its magnetism immediately that the current ceases to flow. A conductor or the conductors of an electric cable made up of a single strand or many strands laid together and twisted. These may be of bare metal, or each one insulated from the others.