Accumulator.—Another name for secondary batteries.

Alternate Current Dynamo.—Produces currents which are alternately positive and negative.

Amalgamation.—Zinc is protected from local action by having its surface coated with mercury.

AmpÈre.—The Unit of current. A volt divided by an ohm.
(See Electrical Measurements, page 104.)

AmpÈre Meter.—An instrument used for measuring strength of current.

Anode.—The positive electrode or pole of a decomposing cell, the wire or plate connected to the copper or other negative element of a battery. In electro-plating, it is usually the soluble pole of the metal to be deposited. (v. Cathode.)

Arc.—The air space in which the electric light forms.

Armature.—The keeper of a magnet: the part which closes the magnetic lines of the field-magnet, or the rotary part.

Battery.—A combination of two or more voltaic cells coupled together.

B. A.—British Association.

Block Station.—A central-station for the supply of continuous buildings.

Board of Trade Unit.—One thousand watt hours equals 10 ampÈres at 100 volts per hour, or 1·35 HP. working for one hour.

Bobbin.—A coil of wire, or a number of such coils, generally so mounted that they can be rapidly revolved.

Bridge (Wheatstone’s).—An apparatus for measuring resistances by balancing the unknown resistance against one known and capable of adjustment.

B. W. G.—Birmingham wire gauge.

Candle-Power.—Term used to denote the amount of light as compared with a standard sperm candle, which is a spermaceti candle, burning at the rate of 2 grains per minute.

Carbons.—The electrodes of arc lamps; the negative plate of a battery.

Carcel Lamp.—The French standard, equal to 9·4 candles.

Capacity (K).—The powder of a surface to hold electricity as “static charge.” A coulomb divided by a volt. Its Unit is the Farad.

Cathode.—The negative pole of a battery; the wire or plate connected with the zinc or positive element of the battery. The object on which a metallic deposit is to be formed. (v. Anode).

Centimetre.—The hundredth part of a metre.

Cell.—Each separate vessel in which a chemical action occurs, by which electricity is capable of being developed.

Central-station.—A building containing plant for supplying electricity to the public.

C. G. S.—The centimetre-gramme-second system.

Circuit Conductive.—The wires which form the path for the passage of the current.

Commutator.—A circuit changer, or switch. The collector of currents on a dynamo.

Compound Winding.—A method of increasing or decreasing the energy developed in a dynamo in proportion to the demand.

Conductivity.—Is the reciprocal to resistance, and applies to that property of any substance whereby the passage of electricity through it is effected with the least opposition.

Conductors.—Substances which most freely permit electricity to pass.

Connections.—Wires, &c., completing the circuit between different apparatus.

Contact Breaker.—The electric lighting equivalent for a gas tap.

Coulomb (Q).—The Unit of quantity, which passes in one second of an ampÈre current.

Cut-out.—An instrument placed in the circuit which will open it automatically.

Current (C).—The Unit is the AmpÈre. The supposed flow or passage of electricity or electrical force in the direction from + to -, or positive to negative.

Current Reverse.—A current in the opposite direction to the normal current.

Decimetre.—The tenth part of a metre.

Deflection.—The angle or number of degrees through which the needle of a galvanometer moves when a current is passing through its coils.

Diaphragm.—A porous division between two liquids through which electric current passes.

Duplex Cut-out.—An instrument which enables a spare fuse to be immediately substituted for that melted.

Duty.—A term used to denote the economy of any motor.

Dynamo.—A name given to machines which produce electricity for commercial purposes.

Dynamometer.—An instrument for ascertaining the horse-power absorbed by any machine.

Dyne.—The Unit of force which gives a velocity of 1 centimetre per second to 1 gramme weight after acting for 1 second.

Direct-Current Dynamo.—An electric generator producing currents passing in one direction.

Earth.—A term for the return circuit, which for economy is formed through the earth in telegraph work. A return conductor common to many circuits is sometimes called “earth.”

Electrodes.—A term for the poles or plates leading the current into and out of a cell.

Electrolysis.—The act of decomposition by the electric current.

Electrolyte.—The liquid in a cell.

Electrometer.—An instrument for measuring electric potential.

Electro-motive Force (E. M. F.) (E).—The electric force tending to produce electric current. The Unit is the volt.

Erg.—The C. G. S. Unit of energy. The work of moving a body through 1 centimetre against the force of a dyne.

Extra Current.—The induced current of higher E. M. F., which appears in a wire wound in a helix when the current is broken.

Farad.—The Unit of capacity: a coulomb divided by a volt.

Field of Force.—The space between or around the poles of a magnet.

Filament.—That part of an incandescent lamp which gives out the light.

Field-Magnets.—In a dynamo the magnets between which the armature revolves.

Foot Pound.—The British Unit of work, or 1 lb. raised 1 foot high.

Galvanometer.—An instrument for measuring current.

Generator.—Another term for a dynamo.

Governor.—An apparatus for controlling the speed of any motor.

Horse-Power (HP.)—indicated HP.—The Unit is 33,000 lbs. lifted 1 foot high per minute. The nominal HP. of any motor is generally fixed considerably less than the indicated.

The French “force cheval” represents 32,560 foot pounds.

Horse-Power of Water.—Indian Government rule, 15 cube feet per second falling through 1 foot = 1 HP.

Indicator Diagram.—The drawing produced by an instrument which is fixed to the cylinder of a steam-engine for the purpose of ascertaining its duty.

Induction.—The name given to effects produced out of a force-exerting body or out of the circuit to which the force is directly applied. A current in a wire induces currents in other conductors parallel to it.

Inertia.—The resistance to change of state of rest or motion.

Insulators.—Bodies possessing high electrical resistance. All insulating substances, however, allow some electricity to pass.

Intensity.—The old term for the properties now described as E. M. F. and potential.

Joule, also called Joulad (W).—The Unit of heat or work, it has also been applied to the mechanical equivalent of heat, 772 foot lbs.

Kilowatt.—One thousand watts.

Knot.—The geographical and nautical mile.

Leads.—Terms usually applied to copper conductors.

Magnetism.—A condition which can be highly developed in iron and steel, by electric action or otherwise.

Measurement.—See Units.

Metre.—The French standard of length = 3·28 feet.

Meg Ohm.—The prefix meg signifies a million.

Millimetre.—The thousandth part of a metre.

MilliampÈre.—The thousandth of an ampÈre.

Mica-foil.—The fusible portion of a Hedges cut-out.

Multiple Arc.—Galvanic cells or dynamos connected parallel, or lamps so arranged that each furnishes a separate path for the current.

Negative.—In a machine the wire returning from the lamp. In a galvanic battery the copper, carbon, or platinum plate. Sign -.

Nigger.—An American term used to denote an electrical fault.

Ohm.—The Unit of resistance. A volt divided by an ampÈre.

Ohm’s Laws.—Laws, investigated by Ohm, regulating electrical current magnitudes. Calling the current C, electro-motive force E, and resistance R: the expression is

Osmose.—The process of diffusion of liquids through a porous division.

Paraffin.—An insulating substance much used in telegraphic work.

Plummer Block.—The bearing on which a shaft revolves.

Polarity.—The distinct features of the two separate poles of a magnet.

Poles.—The two ends of a magnet. The wires, plates, &c., leading from a battery.

Positive.—In a machine the wire proceeding to the lamp. In a battery the zinc plate. Sign +.

Potential.—A word used to indicate a condition for work. Difference of potential is a difference of electrical condition. Potential of a battery means its E. M. F.

Power (P).—The rate of doing work. When an ampÈre passes through an ohm, the unit power, called a watt, is required.

Quantity (Q).—The Unit is the Coulomb.

Relay.—An electro-magnet which, receiving its current from a distance, closes the circuit of a local battery so as to produce the required effect of strength.

Resistance (R).—The opposition presented by the circuit to the development of the current. The Unit of resistance is the Ohm.

Rheostat.—An instrument for inserting resistances. A valuable artificial resistance employed for measuring unknown resistances.

Return Current.—The current in the wire leading to the machine.

Rigger.—The pulley or wheel by which power is transmitted.

Secondary Battery.—Wrongly termed an accumulator, is an appliance for storing energy in such a form that it shall be available for the reproduction of electric currents.

Secondary Generator.—A transformer of a current of high potential into a current of less E. M. F.

Series.—The plan of connecting lamps so that the current passes one after the other.

Shunt.—A coil of wire arranged to take a certain proportion of any current.

Solenoids.—Helices of wire which act like magnets.

Switch.—An apparatus for changing one circuit on to another.

Spectrum.—The elongated figure of the prismatic colours.

Torque.—Term used to express the strain on a shaft due to electro-magnetic action.

Units.—The various bases of any system of measurement.

Volt.—The Unit of electro-motive force and potential. An ampÈre multiplied by an ohm. (See Electrical Measurements.)

Voltameter.—An apparatus for measuring the current by its chemical action.

Voltmeter.—An instrument used for measuring E. M. F.

Watt.—The Unit of power. A volt-ampÈre. The horse-power electrical, taken as 746 B A watts, is equivalent to only 736 true watts. The horse-power electrical is equal to 756 B A watts, which is equal to 746 true watts. The “force de cheval,” or horse-power in use abroad, is defined as 75 kilogrammetres, and is, therefore, 736 true watts.

Work (W.)—Is a volt multiplied by a coulomb, or (amp.² × sec × ohm) or (amp. × sec × volt). The Unit is the Joule.

Yoke.—Is a term applied to the apparently neutral mass of iron which connects the poles of a horse-shoe magnet at the back.