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22 HANDBOOK OF PROJECTION FOR
BLOWING POINT.— The number of amperes (flow of current) necessary to blow a given fuse is the "blowing point" of that fuse.
BRUSH. — A device for making electrical contact between the rotating commutator, or collecting rings of a generator, and the stationary circuit wires. Brushes are made from carbon, copper wires, copper strips and copper gauze, but carbon brushes are most largely used.
BRUSH LOSS.— Loss, in watts, due to lack of perfect electrical contact between brush and commutator or collector ring. May be greatly increased by dirty brushes, dirty, rough commutator or lack of sufficient pressure between brushes and commutator.
BRUSH ROCKER.— The rocker or yoke to which dynamo and motor brush holders are attached. Its purpose is to permit the shifting of the brushes around the commutator to the neutral point.
BUS BARS. — Name commonly applied to the heavy copper bars used on switchboards where a large number of circuits are to be served. Strictly speaking, this name may only be properly applied to power house heavy copper bars connecting with the generators.
BUZZER. — An electric signal which makes a buzzing sound.
B. X. — A flexible metal tubing for the protection of electric wires, much used for interior work. A flexible metal conduit.
CABLE. — A single copper wire, or strand of such wires, heavily insulated and covered with a metal sheath, usually of a lead composition.
CALCIUM LIGHT.— An intense white light produced by0the incandescence of a spot on a pencil of lime when a mixture of oxygen and hydrogen gases is burned in contact therewith. Also called "lime light." Used for projection where electric current is not available, but is a very unsatisfactory illuminant for motion picture projection as compared with electric light.
CALIPERS. — Instruments with which to measure external and internal diameters.
CAM. — A revolving disc fixed to a shaft and designed to impart to a second element, with which it is in constant or intermittent contact, a variable velocity or motion, or an intermittent motion.
CAMERAMAN. — The one who does the actual photograph:ng in the production of motion pictures.
CANDLE. — The unit of illumination, as one candle power.