The Standard Electrical Dictionary / A Popular Dictionary of Words and Terms Used in the Practice of Electrical Engineering

by T. O'Conor Sloane

Fig. 212. INCANDESCENT ELECTRIC LAMP.
322 STANDARD ELECTRICAL DICTIONARY.
The loop is attached at its ends to two short pieces of platinum wire,
which pass through the glass of the bulb and around which the glass is
fused. As platinum has almost exactly the same coefficient of
heat-expansion as glass, the wires do not cause the glass to crack.
The process of manufacture includes the preparation of the filament.
This is made from paper, silk, bamboo fibre, tamidine, q. v., or other
material. After shaping into the form of the filament the material is
carbonized at a high heat, while embedded in charcoal, or otherwise
protected from the air. The flashing process (see Flashing of
incandescent Lamp Carbons) may also be applied. The attachment to the
platinum wires is effected by a minute clamp or by electric soldering.
The loop is inserted and secured within the open globe, which the glass
blower nearly closes, leaving one opening for exhaustion.
The air is pumped out, perhaps first by a piston pump, but always at the
end by a mercurial air pump. (See Pump, Geissler--and others.) As the
exhaustion becomes high a current is passed through the carbons heating
them eventually to white heat so as to expel occluded gas. The occluded
gases are exhausted by the pump and the lamp is sealed by melting the
glass with a blowpipe or blast-lamp flame. For the exhaustion several
lamps are usually fastened together by branching glass tubes, and are
sealed off one by one.
The incandescent lamps require about 3.5 watts to the candle power, or
give about 12 sixteen-candle lamps to the horse power expended on them.
Generally incandescent lamps are run in parallel or on multiple arc
circuits. All that is necessary in such distribution systems is to
maintain a proper potential difference between the two leads across
which the lamps are connected. In the manufacture of lamps they are
brought to an even resistance and the proper voltage at which they
should be run is often marked upon them. This may be fifty volts and
upward. One hundred and ten volts is a very usual figure. As current one
ampere for a fifty-volt, or about one-half an ampere for a one hundred
and ten volt lamp is employed.
Lamp, Incandescent, Three Filament.
A three filament lamp is used for three phase currents. It has three
filaments whose inner ends are connected, and each of which has one
leading-in wire. The three wires are connected to the three wires of the
circuit. Each filament receives a current varying in intensity, so that
there is always one filament passing a current equal to the sum of the
currents in the other two filaments.
Lamp, Lighthouse.
A special type of arc light. It is adapted for use in a lighthouse
dioptric lantern, and hence its arc has to be maintained in the same
position, in the focus of the lenses. The lamps are so constructed as to
feed both carbons instead of only one, thereby securing the above
object.
323 STANDARD ELECTRICAL DICTIONARY.
Lamp, Pilot.
A lamp connected to a dynamo, and used by its degree of illumination to
show when the dynamo on starting becomes excited, or builds itself up.
Lamp, Polyphote.
An arc lamp adapted to be used, a number in series, upon the same
circuit. The electric regulating mechanism is placed in shunt or in
parallel with the carbons and arc. (See Lamp, Arc.)
Lamps, Bank of.
A number of lamps mounted on a board or other base, and connected to
serve as voltage indicator or to show the existence of grounds, or for
other purposes.
Lamp, Semi-incandescent.
A lamp partaking of the characteristics of both arc and incandescence; a
lamp in which the imperfect contact of two carbon electrodes produces a
part of or all of the resistance to the current which causes
incandescence.
The usual type of these lamps includes a thin carbon rod which rests
against a block of carbon. The species of arc formed at the junction of
the two heats the carbons. Sometimes the upper carbon or at least its
end is heated also by true incandescence, the current being conveyed
near to its end before entering it.
Semi-incandescent lamps are not used to any extent now.
Lamp Socket.
A receptacle for an incandescent lamp; the lamp being inserted the
necessary connections with the two leads are automatically made in most
sockets. The lamps may be screwed or simply thrust into the socket and
different ones are constructed for different types of lamps. A key for
turning the current on and off is often a part of the socket.
Latent Electricity.
The bound charge of static electricity. (See Charge, Bound.)
Law of Intermediate Metals.
A law of thermo-electricity. The electro-motive force between any two
metals is equal to the sum of electro-motive forces between each of the
two metals and any intermediate metal in the thermo-electric series, or
the electro-motive force between any two metals is equal to the sum of
the electromotive forces between all the intermediate ones and the
original two metals; it is the analogue of Volta's Law, q. v.
Law of Inverse Squares.
When force is exercised through space from a point, its intensity varies
inversely with the square of the distance. Thus the intensity of light
radiated by a luminous point at twice a given distance therefrom is of
one-fourth the intensity it had at the distance in question.
Gravitation, electric and magnetic attraction and repulsion and other
radiant forces are subject to the same law.
324 STANDARD ELECTRICAL DICTIONARY.
Law of Successive Temperatures.
A law of thermo-electricity. The electro-motive force due to a given
difference of temperature between the opposite junctions of the metals
is equal to the sum of the electro-motive forces produced by fractional
differences of temperature, whose sum is equal to the given difference
and whose sum exactly fills the given range of temperature.
Law, Right-handed Screw.
This rather crude name is given by Emtage to a law expressing the
relation of direction of current in a circuit to the positive direction
of the axis of a magnet acted on by such current. It is thus expressed:
A right-handed screw placed along the axis of the magnet and turned in
the direction of the current will move in the positive direction, i. e.,
towards the north pole of the axis of the magnet.
Lead.
A metal; one of the elements; symbol Pb. Atomic weight, 207;
equivalent, 103-1/2; valency, 2.
Lead may also be a tetrad, when its equivalent is 51.75.
The following data are at 0º C. (32º F.) with compressed metal:
Relative Resistance, (Silver = l) 13.05
Specific Resistance, 19.63 microhms.
Resistance of a wire,
(a) 1 ft. long, weighing 1 grain, 3.200 ohms.
(b) 1 meter long, weighing 1 gram, 2.232 "
(c) 1 meter long, 1 millimeter thick, .2498 "
Resistance of 1 inch cube, 7.728 microhms.
Electro-Chemical Equivalent (Hydrogen = .0105) 1.086 mgs.
Leading Horns.
The tips of pole pieces in a dynamo, which extend in the direction of
movement of the armature.
Leading-in Wires.
The platinum wires passing through the glass of an incandescent
lamp-chamber, to effect the connection of the carbon filament with the
wires of the circuit.
Lead of Brushes, Negative.
In a motor the brushes are set backwards from their normal position, or
in a position towards the direction of armature rotation or given a
negative lead instead of a positive one, such as is given to dynamo
brushes.
Leak.
A loss or escape of electricity by accidental connection either with the
ground or with some conductor. There are various kinds of leak to which
descriptive terms are applied.
Leakage.
The loss of current from conductors; due to grounding at least at two
places, or to very slight grounding at a great many places, or all along
a line owing to poor insulation. In aerial or pole telegraph lines in
wet weather there is often a very large leakage down the wet poles from
the wire. (See Surface Leakage--Magnetic Leakage.)
325 STANDARD ELECTRICAL DICTIONARY.
Leakage Conductor.
A conductor placed on telegraph poles to conduct directly to earth any
leakage from a wire and thus prevent any but a very small portion
finding its way into the other wires on the same pole. It presents a
choice of evils, as it increases the electrostatic capacity of the line,
and thus does harm as well as good. It consists simply of a wire
grounded and secured to the pole.
Leg of Circuit.
One lead or side of a complete metallic circuit.
Lenz's Law.
A law expressing the relations of direction of an inducing current or
field of force to the current induced by any disturbance in the
relations between such field and any closed conductor within its
influence. It may be variously expressed.
(a) If the relative position of two conductors, A and B, be changed, of
which A is traversed by a current, a current is induced in B in such a
direction that, by its electro-dynamic action on the current in A, it
would have imparted to the conductors a motion of the contrary kind to
that by which the inducing action was produced. (Ganot.)
(b) The new (induced) current will increase the already existing
resistances, or develop new resistance to that disturbance of the field
which is the cause of induction. (Daniell.)
(c) When a conductor is moving in a magnetic field a current is induced
in the conductor in such a direction as by its mechanical action to
oppose the motion. (Emtage.)
(d) The induced currents are such as to develop resistance to the change
brought about.
Letter Boxes, Electric.
Letter boxes with electrical connections to a bell or indicator of some
sort, which is caused to act by putting a letter into the box.
Leyden Jar.
A form of static condenser.
In its usual form it consists of a glass jar. Tinfoil is pasted around
the lower portions of its exterior and interior surfaces, covering from
one-quarter to three-quarters of the walls in ordinary examples. The
rest of the glass is preferably shellacked or painted over with
insulating varnish, q. v. The mouth is closed with a wooden or cork
stopper and through its centre a brass rod passes which by a short chain
or wire is in connection with the interior coating of the jar. The top
of the rod carries a brass knob or ball.
If such a jar is held by the tinfoil-covered surface in one hand and its
knob is held against the excited prime conductor of a static machine its
interior becomes charged; an equivalent quantity of the same electricity
is repelled through the person of the experimenter to the earth and when
removed from the conductor it will be found to hold a bound charge. If
the outer coating and knob are both touched or nearly touched by a
conductor a disruptive discharge through it takes place.
326 STANDARD ELECTRICAL DICTIONARY.

Fig. 213. LEYDEN JAR WITH DISCHARGER.
If one or more persons act as discharging conductors they will receive a
shock. This is done by their joining hands, a person at one end touching
the outer coating and another person at the other end touching the knob.
From an influence machine a charge can be taken by connecting the
coating to one electrode and the knob to the other.

Fig. 214. SULPHURIC ACID LEYDEN JAR.
327 STANDARD ELECTRICAL DICTIONARY.
Leyden Jar, Sir William Thomson's.
An especially efficient form of Leyden jar. It consists of a jar with
outer tinfoil coating only. For the interior coating is substituted a
quantity of concentrated sulphuric acid. The central rod is of lead with
a foot, which is immersed in the acid and from which the rod rises. A
wooden cover partly closes the jar, as the central tube through which
the rod passes is so large as not to allow the wood to touch it. Thus
any leakage from inner to outer coating has to pass over the inside and
outside glass surfaces. In the common form of jar the wooden cover may
short circuit the uncoated portion of the inner glass surface. In the
cut a simplified form of Thomson's Leyden jar is shown, adapted for
scientific work.
Lichtenberg's Figures.
If the knob of a Leyden jar or other exited electrode is rubbed over the
surface of ebonite, shellac, resin or other non-conducting surface it
leaves it electrified in the path of the knob. If fine powder such as
flowers of sulphur or lycopodium is dusted over the surface and the
excess is blown away, the powder will adhere where the surface was
electrified, forming what are called Lichtenberg's Figures, Lycopodium
and sulphur show both positive and negative figures, that is to say,
figures produced by a positively or negatively charged conductor. Red
lead adheres only to negative figures. If both positive and negative
figures are made and the surface is sprinkled with both red lead and
flowers of sulphur each picks out its own figure, the sulphur going
principally to the positive one.
The red lead takes the form of small circular heaps, the sulphur
arranges itself in tufts with numerous diverging branches. This
indicates the difference in the two electricities. The figures have been
described as "a very sensitive electrosope for investigating the
distribution of electricity on an insulating surface." (Ganot.)
Life of Incandescent Lamps.
The period of time a lamp remains in action before the carbon filament
is destroyed. The cause of a lamp failing may be the volatilization of
the carbon of the filament, causing it to become thin and to break; or
the chamber may leak. The life of the lamp varies; 600 hours is a fair
estimate. Sometimes they last several times this period.
The higher the intensity at which they are used the shorter is their
life. From their prime cost and the cost of current the most economical
way to run them can be approximately calculated.
[Transcriber's note: Contemporary incandecent buls are rated for 1000
hours; flourescent bulbs up to 24000 hours; LED lamps up to 100000 hours.]
Lightning.
The electrostatic discharge to the earth or among themselves of clouds
floating in the atmosphere. The discharge is accompanied by a spark or
other luminous effect, which may be very bright and the effects, thermal
and mechanical, are often of enormous intensity.
The lightning flash is white near the earth, but in the upper regions
where the air is rarefied it is of a blue tint, like the spark of the
electric machine. The flashes are often over a mile in length, and
sometimes are four or five miles long. They have sometimes a curious
sinuous and often a branching shape, which has been determined by
photography only recently. To the eye the shape seems zigzag.
328 STANDARD ELECTRICAL DICTIONARY.
In the case of a mile-long flash it has been estimated that 3,516,480 De
la Rue cells, q. v., would be required for the development of the
potential, giving the flash over three and one-half millions of volts.
But as it is uncertain how far the discharge is helped on its course by
the rain drops this estimate may be too high.
There are two general types of flash. The so-called zigzag flash
resembles the spark of an electric machine, and is undoubtedly due to
the disruptive discharge from cloud to earth. Sheet lightning has no
shape, simply is a sudden glow, and from examination of the spectrum
appears to be brush discharges (see Discharge, Brush) between clouds.
Heat lightning is attributed to flashes below the horizon whose light
only is seen by us. Globe or ball lightning takes the form of globes of
fire, sometimes visible for ten seconds, descending from the clouds. On
reaching the earth they sometimes rebound, and sometimes explode with a
loud detonation. No adequate explanation has been found for them.
The flash does not exceed one-millionth of a second in duration; its
absolute light is believed to be comparable to that of the sun, but its
brief duration makes its total light far less than that of the sun for
any period of time.
If the disruptive discharge passes through a living animal it is often
fatal. As it reaches the earth it often has power enough to fuse sand,
producing fulgurites, q. v. (See also Back Shock or Stroke of
Lightning.)
Volcanic lightning, which accompanies the eruptions of volcanoes, is
attributed to friction of the volcanic dust and to vapor condensation.
[Transcriber's note: The origin of lightning is still (2008) not fully
understood, but is thought to relate to charge separation in the
vertical motion of water droplets and ice crystals in cloud updrafts. A
lightning bolt carries a current of 40,000 to 120,000 amperes, and
transfers a charge of about five coulombs. Nearby air is heated to about
10,000 °C (18,000 °F), almost twice the temperature of the Sun’s
surface.]
Lightning Arrester.
An apparatus for use with electric lines to carry off to earth any
lightning discharge such lines may pick up. Such discharge would imperil
life as well as property in telegraph offices and the like.
Arresters are generally constructed on the following lines. The line
wires have connected to them a plate with teeth; a second similar plate
is placed near this with its teeth opposite to those of the first plate
and nearly touching it. The second plate is connected by a low
resistance conductor to ground. Any lightning discharge is apt to jump
across the interval, of a small fraction of an inch, between the
oppositely placed points and go to earth.
Another type consists of two plates, placed face to face, and pressing
between them a piece of paper or mica. The lightning is supposed to
perforate this and go to earth. One plate is connected to the line, the
other one is grounded.
The lightning arrester is placed near the end of the line before it
reaches any instrument. (See Alternative Paths.)
329 STANDARD ELECTRICAL DICTIONARY.

Fig. 215. COMB OR TOOTHED LIGHTNING ARRESTER.

Fig. 216. FILM OR PLATE LIGHTNING ARRESTER.
Lightning Arrester, Counter-electro-motive Force.
An invention of Prof. Elihu Thompson. A lightning arrester in which the
lightning discharge sets up a counter-electro-motive force opposed to
its own. This it does by an induction coil. If a discharge to earth
takes place it selects the primary of the coil as it has low
self-induction. In its discharge it induces in the secondary a reverse
electro-motive force which protects the line.
Lightning Arrester Plates.
The toothed plates nearly in contact, tooth for tooth, or the flat
plates of a film lightning arrester, which constitute a lightning
arrester. Some advocate restricting the term to the plate connected to
the line.
Lightning Arrester, Vacuum.
A glass tube, almost completely exhausted, into which the line wire is
fused, while a wire leading to an earth connection has its end fused in
also.
A high tension discharge, such as that of lightning, goes to earth
across the partial vacuum in preference to going through the line, which
by its capacity and self-induction opposes the passage through it of a
lightning discharge.
It is especially adapted for underground and submarine lines.
330 STANDARD ELECTRICAL DICTIONARY.
Lightning, Ascending.
Lightning is sometimes observed which seems to ascend. It is thought
that this may be due to positive electrification of the earth and
negative electrification of the clouds.
Lightning, Globe or Globular.
A very unusual form of lightning discharge, in which the flashes appear
as globes or balls of light. They are sometimes visible for ten seconds,
moving so slowly that the eye can follow them. They often rebound on
striking the ground, and sometimes explode with a noise like a cannon.
They have never been satisfactorily explained. Sometimes the phenomenon
is probably subjective and due to persistence of vision.
Lightning Jar.
A Leyden jar whose coatings are of metallic filings dusted on to the
surface while shellacked, and before the varnish has had time to dry. In
its discharge a scintillation of sparks appears all over the surface.
Line of Contact.
The line joining the points of contact of the commutator brushes in a
dynamo or motor.
Synonym--Diameter of Commutation.
Lines of Force.
Imaginary lines denoting the direction of repulsion or attraction in a
field of force, q. v. They may also be so distributed as to indicate the
relative intensity of all different parts of the field. They are normal
to equipotential surfaces. (See Electro-magnetic Lines of
Force--Electrostatic Lines of Force--Magnetic Lines of Force.)
Lines of Induction.
Imaginary lines within a body marking the direction taken within it by
magnetic induction. These are not necessarily parallel to lines of
force, but may, in bodies of uniform agglomeration, or in crystalline
bodies, take various directions.
Synonym--Lines of Magnetic Induction.
Lines of Slope.
Lines in a field of force which mark the directions in which the
intensity of force in the field most rapidly falls away.
Links, Fuse.
Links made of more or less easily fusible metal, for use as safety
fuses.
Listening Cam.
In a telephone exchange a cam or species of switch used to connect the
operator's telephone with a subscriber's line.
331 STANDARD ELECTRICAL DICTIONARY.
Lithanode.
A block of compressed lead binoxide, with platinum connecting foils for
use as an electrode in a storage battery. It has considerable capacity,
over 5 ampere-hours per pound of plates, but has not met with any
extended adoption.
Load.
In a dynamo the amperes of current delivered by it under any given
conditions.
Local Action.
(a) In its most usual sense the electric currents within a battery, due
to impurities in the zinc, which currents may circulate in exceedingly
minute circuits, and which waste zinc and chemicals and contribute
nothing to the regular current of the battery. Amalgamated or chemically
pure zinc develops no local action.
(b) The term is sometimes applied to currents set up within the armature
core or pole pieces of a dynamo. (See Currents, Foucault.)
Local Battery.
A battery supplying a local circuit (q. v.); in telegraphy, where it is
principally used, the battery is thrown in and out of action by a relay,
and its current does the work of actuating the sounder and any other
local or station instruments. (See Relay.)
Local Circuit.
A short circuit on which are placed local apparatus or instruments. Such
circuit is of low resistance and its current is supplied by a local
battery, q. v. Its action is determined by the current from the main
line throwing its battery in and out of circuit by a relay, q. v., or
some equivalent.
Local Currents.
Currents within the metal parts of a dynamo. (See Currents, Foucault.)
In a galvanic battery. where there is local action, q. v., there are
also local currents, though they are not often referred to.
Localization.
Determining the position of anything, such as a break in a cable, or a
grounding in a telegraph line. In ocean cables two typical cases are the
localization of a break in the conductor and of a defect in the
insulation admitting water. The first is done by determining the static
capacity of the portion of the line which includes the unbroken portion
of the conductor; the other by determining the resistance of the line on
a grounded circuit.
Locus.
A place. The word is used to designate the locality or position of, or
series of positions of definite conditions and the like. Thus an
isogonic line is the locus of equal declinations of the magnetic needle;
it is a line passing through all places on the earth's surface where the
condition of a given declination is found to exist.
332 STANDARD ELECTRICAL DICTIONARY.
Lodestone.
Magnetic magnetite; magnetite is an ore of iron, Fe3 04 which is
attracted by the magnet. Some samples possess polarity and attract iron.
The latter are lodestones.
Synonym--Hercules Stone
Logarithm.
The exponent of the power to which it is necessary to raise a fixed
number to produce a given number. The fixed number is the base of the
system. There are two systems; one, called the ordinary system, has 10
for its base, the other, called the Naperian system, has 2.71828 for its
base. The latter are also termed hyperbolic logarithms, and are only
used in special calculations.
Log, Electric.
An apparatus for measuring the speed of a ship. A rotating helical vane
of known pitch is dragged behind the vessel. As the helix rotates its
movements may actuate electric machinery for registering its rotations.
The number of these in a given time, multiplied by the pitch of the
vane, gives the distance traversed in such time.
Loop.
A portion of a circuit introduced in series into another circuit. The
latter circuit is opened by a spring-jack, q. v. or other device, and
the loop inserted. By loops any number of connections can be inserted
into a circuit in series therewith, and in series or in parallel with
one another.
Loop Break.
A double bracket or similar arrangement for holding on insulators the
ends of a conductor which is cut between them, and to which are
connected the ends of a loop. The space between the insulators may be
about a foot.
Luces.
This may be used as the plural of lux, q. v. It is the Latin plural.
Luminous Jar.
A Leyden jar whose coatings are of lozenge-shaped pieces of tinfoil
between which are very short intervals. When discharged, sparks appear
all over the surface where the lozenges nearly join.
Lux.
A standard of illumination, q. v., as distinguished from illuminating
power.
It is the light given by one candle at a distance of 12.7 inches--by a
carcel, q. v., at a distance of one meter---or by 10,000 candles at
105.8 feet.
It was proposed by W. H. Preece. All the above valuations are identical.