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48 HANDBOOK OF PROJECTION FOR
TWO-WIRE SYSTEM.— A system in which only two wires arc employed.
ULTRA VIOLET RAYS.— Rays of light existing beyond the violet light of the visible spectrum. These rays have a vioration in excess of eight hundred billion per second.
UNBALANCED LOAD.— As applies to the 3-wire system, a condition in which more current is consumed on one side of the system than on the other, which has the effect of compelling one generator to carry a heavier load than the other,
UNDERWRITERS' RULES.— See "National Electric Code."
USEFUL LIFE. — A term applied to many things, but in electrics particularly to incandescent lamps, which deteriorate with age. It is the time an incandescent lamp will burn before its output of light has decreased more than 20 per cent. When a lamp has fallen below 80 per cent, of its rated c. p. it is the part of true economy to replace it with a new one.
VOLATILIZATION. — In projection, the transforming of carbon into vapor through heat.
VOLT. — Unit of electrical pressure. See page 50.
VOLTAGE DROP.— The drop in voltage due to the resistance of the conductors. Voltage drop exists in every circuit. See "Copper Loss."
VOLT-AMMETER. — An instrument for measuring current consumption in watts.
VOLTMETER. — An instrument of high resistance for measuring electrical pressure.
WATER GLASS.— Soluble glass. Used as a binder for carbon cores. It is the residue of water glass which forms the white, light weight ash with which the interior of the. lamphouse becomes coated.
WATT. — The practical unit of electrical power. See page 53.
WATT HOUR.— The energy consumed when one watt of electrical energy has been used for one hour.
WATT-HOUR METER.— A meter used for measuring electrical consumption in watt hours.
WATTS PER CANDLE POWER.— The specific consumption of an electric lamp is its watt consumption per mean spherical candle power. In connection with incandescent lamps, the term "watts per candle power" is used commercially to denote the watts consumed per mean horizontal c. p.
WESTERN UNION WIRE JOINT.— See figure 26.
WIRE GAUGE. — A gauge for measuring round wires according to an arbitrary standard. See page 78.