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ELECTRIC-LIGHT BUG

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ELECTRIC MOTOR

ELECTRIC BUG

fore, either to apply a match or to heat it with an electrically heated platinum wire. It is almost needless to add that they are patented in all civilized countries. For the various methods of distributing incandescent lamps, the three-wire and five-wire systems, etc., see any good treatise on electric engineering.

Electric=Light Bug, a large water-bug common in the United States. The bugs fly readily from pond to pond. Formerly they attracted no general attention; but, since our cities have been lighted by electrical lights placed on high elevations, they are at times very common in cities. They fly into the electric light and are killed by hundreds and have been the occasion of frequent mention by the public press. They are not, however, of recent appearance in this country, as is sometimes supposed. They are true bugs, living in the water, with a sharp beak used for puncturing their prey. They attack snails, small fish and, occasionally, a frog, and suck the blood. They reach a length of more than two inches, and have long been known to observers of insects under the names giant water-bug and water-scorpion.

Electric Meter, a piece of apparatus for measuring and recording the electric energy consumed in a circuit. Several forms of electric meter have been devised, but the only kinds in general use are the clock and the motor-meter. The clock-form of meter is much used in Europe, but not in the United States, In the Aaron meter, a clock-form, the pendulum of a clock has a magnetic bob, which swings over a coil carrying the current, and thus the change in the rate of the clock depends on the current. This change in rate is recorded on one or more dials, and these are graduated in electrical units. The only meters in general use in the United States are motor-meters. A motor-meter is a small electric motor so made that the number of revolutions of the armature is proportional to the electric energy consumed in the circuit in which the motor is placed. The total number of revolutions is recorded on a dial by a simple mechanism. The meter is usually incased like a gas-meter with only the dial visible. Electric meters record in some unit representing power multiplied by time, as watt-hour, measur-

ing a watt of electric energy for one hour, or lamp-hour, measuring the energy required to run one 16-candle-power incandescent lamp for one hour. For incandescent-lighting circuits where the pressure remains

AN ELECTRIC  METER

constant, the meter need record only current (amperes), but on motor-circuits the meter must be a true watt-meter, that is, record pressure times current (volts X amperes).

Meters are either for direct or for alternating circuits. A. C. meters are usually some form of induction-motor. (See ELECTRIC MOTOR.) Among the best-known electric meters are the Shallenberger, Thomson and Stanley meters. Meters are now-used by most large central stations in measuring electric energy supplied for all purposes. The accuracy for their whole range of loads is within 2% for the best meters, while for mean loads the accuracy is much greater.

Electric Motor, a machine for transforming the energy of an electric current into mechanical power. The modern direct-current motor may be looked upon as a reversed dynamo. In fact, any direct-current generator will run as a motor if current is passed through its armature and field-magnets, and in general an efficient generator is an efficient motor. But not all electric motors are good generators, for motors are often constructed for special purposes. Thus the street-car motor, for obvious reasons, is made with light field-magnets. But the general description of a D. C. dynamo applies directly to a D. C. motor.

An alternating-current dynamo will run as a motor when supplied with the proper alternating current, provided it is first brought up to its normal speed as a generator. After that it runs synchronously