_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.