_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.
2(A P R S)
Ind. HP. of any engine = —————————
33,000
A = Area of piston in square inches.
P = Average pressure of steam in lbs. per square inch.
R = Number of revolutions per minute.
S = Length of stroke in feet (if in inches, × 33,000 by 12).
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
Current E. M. F. Resistance.
E E
C = ——, amps. E = C × R, volts. R = —— ohms.
R C
(See Electrical Measurements.)
_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.
[Illustration]