The Standard Electrical Dictionary (part 4)

Pane, Luminous.
A pane of glass, one side of which has pasted to it a long zigzag strip
of tinfoil. A design is made by cutting through the strip. On
discharging a Leyden jar or an electric machine through the strip sparks
appear where the tinfoil is severed, thus producing the design in a
luminous effect. Many variations can be employed in their construction.

402 STANDARD ELECTRICAL DICTIONARY.

Pantelegraphy.
A system of telegraphy for transmitting designs, maps, drawing, and the
like by telegraphy. (See Telegraphy, Facsimile.)

Paper Filaments.
Filaments of carbon for incandescent lamps made from paper.

This is one of the earliest materials practically used. The paper is cut
out of proper shape, and is carbonized in a close vessel, while embedded
in powdered charcoal or some other form of carbon to absolutely cut off
access of air. It is then placed in the lamp chamber and flashed or
subjected to the regular treatment.

Parabola.
A curve; one of the conic sections. It is approximately represented by a
small arc of a circle, but if extended becomes rapidly deeper than a
half circle.

If, from a point within called the focus, lines are drawn to the curve
and then other lines are drawn from these points parallel to the axis,
the angles of incidence will he equal to the angles of reflection as
referred to tangents at the points where the lines touch the curve.

Parabolic Reflector.
A reflector for a light, a paraboloid or surface of revolution whose
section is a parabola. A light placed at its focus has its rays
reflected parallel to each other.

Examples of parabolic reflectors are seen in electric search lights and
in locomotive head-lights. They are employed in electric search lights.
The arc light must be of such construction as to maintain its ignited
points always at the same point, the focus of the paraboloid.

Paraffine. v.
To coat or saturate with paraffine wax. Paper may be paraffined by
dipping in the wax, or by being sprinkled with fragments of wax,
subsequently melted in with a hot iron or otherwise. The tops of battery
carbons are often paraffined to prevent the acid from rising in the
pores by capillary attraction and rusting the connections.

403 STANDARD ELECTRICAL DICTIONARY.

Paraffine Wax.
A hydro-carbon composed principally of mixtures of the higher members of
the paraffine series C n H2 n + 2. It is made from cannel coal, coal
tar, or petroleum by distillation. It is an insulator. Its resistance at
46° C. (114.8° F.) per centimeter cube is 3.4E16 ohms, or about the
highest resistance known.

Its specific inductive capacity (for milky wax) is 2.47 (Schiller). For
clear wax it is given as follows by different authorities:
1.92 Ayrton.
1.96 Wüllner.
1.977 Gibson & Barclay.
2.32 Baltzmann.

It is extensively used in condensers and other electric apparatus as a
dielectric and insulator.

Paragrêles.
Protectors against hail; lightning rods used to guard fields against
hail; of little or no real utility.

Parallax.
The apparent change in position of an object when looked at from two
points of view. By looking at an object a few feet distant first with
one eye and then with the other, the shifting in apparent position is
seen.

In reading the position of an indicator or needle over a scale parallax
introduces an error unless the eye is held vertically over the needle.
By making the dial of looking- glass and holding the eye so that the
reflection of its pupil is bisected by the needle this verticality is
ensured.

Parallel.
(a) In the nomenclature of electric circuits two or more conductors
leading from one point to another, are said to be in parallel.

(b) When two or more conductors connect two main leads of comparatively
large size and low resistance they are said to be in parallel or in
multiple arc. This order is easiest pictured as the rungs of a ladder in
parallel connecting its two sides representing the main leads.

It may be used as a noun as "arranged in parallel," or as an adjective
as "a parallel circuit," the opposite of series, q. v.

Paramagnetic. adj.
Possessing paramagnetic properties; tending to occupy a position with
the longer axis parallel to the lines of force of a magnetic field;
having magnetism; attracted by a magnet.

"If a homogeneous isotropic substance is placed in a magnetic field it
becomes magnetized at every point in the direction of the magnetic
intensity at that point, and with an intensity of magnetization
proportional to the magnetic intensity. When the positive direction of
the induced magnetization is the same as that of the magnetic intensity
the substance is called Magnetic or Paramagnetic; when it is opposite,
the substance is called Diamagnetic." (Emtage.)

A paramagnetic substance has high permeability or multiplying power for
lines of force, hence in a magnetic field a bar of iron, etc., is in
unstable equilibrium unless its longer axis is parallel with the lines
of force in order to reduce as much as possible the reluctance of the
circuit.

404 STANDARD ELECTRICAL DICTIONARY.

Iron is the most paramagnetic of all substances. Other paramagnetic
metals are: Nickel, cobalt, manganese, platinum, cerium, osmium,
palladium. Diamagnetic metals are bismuth, antimony, zinc, tin, mercury,
lead, silver, copper, gold, arsenic. Bismuth is the most diamagnetic of
all metals.

Of gases oxygen is most paramagnetic. Becquerel calculated that a cubic
yard of oxygen condensed would act on a magnetic needle as powerfully as
5.5 grains of metallic iron. Liquefied oxygen will adhere to the poles
of a magnet.

Changes of temperature and of other conditions may affect a body's
magnetism. Thus hot oxygen is diamagnetic, and a substance paramagnetic
in a vacuum may be diamagnetic in air.

Of liquids, solutions of iron or cobalt are paramagnetic; water, blood,
milk, alcohol, ether, oil of turpentine and most saline solutions are
diamagnetic.

Paramagnetism.
(a) The science or study of paramagnetic substances and phenomena.

(b) The magnetic property of a paramagnetic substance; that of being
attracted by a magnet, and of arranging itself with its longer axis
parallel with the lines of force of a magnetic field.

Parchmentizing.
If cellulose is treated with a mixture of two parts of sulphuric acid
and one part of water perfectly cold, it becomes like parchment. It
should at once be washed with water, and then with ammonia and water.
The Swan incandescent light fibres are made of parchmentized cotton
thread, which is afterward carbonized.

Partial Earth.
A fault in a conductor caused by imperfect connection with the earth,
where insulation from the earth is desired.

Passive State.
A state of a substance in virtue of which it is unattacked by a solvent
which ordinarily would dissolve or attack it. Iron in strong nitric acid
is unattacked or assumes the passive state. This particular case is
supposed to be due to a coating of magnetic oxide, so that there would
be properly speaking no question of a passive state, but only one of
superficial protection.

The existence of a true passive state of any substance is very doubtful.

P. D.
Abbreviation for potential difference or difference of potential, or for
electro-motive force.

405 STANDARD ELECTRICAL DICTIONARY.

Peltier Effect.
The thermal effect produced by the passage of a current through the
junction of two unlike conductors. Such junction is generally the seat
of thermo-electric effects, and a current is generally produced by
heating such a junction. If an independent current is passed in the same
direction as that of the thermoelectric current, it cools the junction,
and warms it if passed in the other direction. In general terms,
referring to thermo-electric couples, if passed through them it tends to
cool the hot and heat the cool junction. The phenomenon does not occur
in zinc-copper junctions.

Peltier's Cross.
A bar of bismuth and a bar of antimony soldered centre to centre at
right angles, being notched or halved there to receive or to set into
each other. It is used to demonstrate the Peltier effect, q. v. To one
pair of ends are connected the terminals of a battery circuit; to the
other pair are connected the terminals of a galvanometer.

The galvanometer by its deflections in one and then in the other
direction indicates that the junction is heated when the current passes
from antimony to bismuth and vice versa. It thus illustrates the heating
and cooling of a thermo-electric junction by a current of electricity.
The current from the battery by the Peltier effect either heats or cools
the junction, as the case may be. This heating or cooling them produces
a thermo-electric current in the galvanometer circuit. The battery has
no direct influence on the galvanometer.

Pendant Cord.
A double conductor or pair of conductors, insulated from each other and
covered with a worsted, silk, or cotton covering and used to suspend
incandescent lamps and at the same time to conduct the current to them.
It is also used for other similar service, such as acting as conductors
for small motors. Often each conductor is composed of a number of thin
wires laid together. This gives flexibility to the cord.

Synonym--Flexible Cord.

Pendulum, Electric.
(a) A pendulum operated by the intermittent action of an electro-magnet,
whose circuit is opened and closed by the pendulum itself. A point at
the lower end of the pendulum swinging through a globule of mercury may
close and open the circuit. Various other methods of accomplishing the
same end are employed ..

(b) A pith ball suspended by a thread from an insulating stand. It is
used to show the attraction exercised by a piece of sealing wax or other
substance excited by rubbing.

406 STANDARD ELECTRICAL DICTIONARY.

Pen, Electric.
A stylus for producing a series of perforations in paper, so that the
paper may act as a stencil for the reproduction of a great number of
copies of the original matter. Various kinds of electric pens have been
invented. One kind, invented by Edison, consists of a handle carrying an
electric motor actuating a needle, which is driven in and out of the
other end of the handle with high rapidity. It is used by being held
vertically on the paper with the needle end downward, and is moved so as
to describe perforated letters or designs. The paper is then used as a
stencil with an ink roller to reproduce the writing or design ad
libitum. A simpler kind dispenses with the motor and depends on the
perforations produced by the electric spark. As shown in the cut the
stylus is one terminal of an induction coil circuit. The support on
which the paper rests is the other terminal and must be a conductor. In
use the induction coil is started, and the stylus is moved over the
paper; a series of sparks pass through the paper from stylus to the
supporting tablet, perforating the paper and producing a stencil to be
used for reproduction.

Fig. 256. ELECTRIC PEN.

Pentane Standard, Harcourt's.
A standard of illuminating power; in it the combustible substance is a
gas made by mixing one cubic foot of air with three cubic inches of
liquid pentane, measured at 60° F. or, if measured as gases, 20 volumes
of air to 7 of pentane. It is burned at the rate of 0.5 cubic foot per
hour from a cylindrical tube one inch in diameter, closed at the top by
a disc 0.5 inch thick with a hole 0.25 inch in diameter, through which
the gas issues. It gives a flame 2.5 inches high.

The pentane used is the distillate of petroleum which boils at 50° C.
(122° F.) ; it has a specific gravity at 15° C. (60° F.) of from 0.628
to 0.631. It is almost pure pentane (C5H12).

As long as the rate of consumption is between 0.48 and 0.52 cubic foot
per hour the flame gives practically the same light.

407 STANDARD ELECTRICAL DICTIONARY.

Perforator.
An apparatus used in automatic high speed telegraphy for perforating
strips of paper. These are then used by drawing between a roller and
contact spring for making and breaking the telegraphic circuit for the
production of a record, such as the Morse record, at the distant
receiving station.

The perforated strip has different classes of holes punched in it to
represent dots or dashes. It is fed by machinery very rapidly, so that
the message is transmitted with the highest speed. Several operators may
simultaneously prepare the paper strips, and thus in conjunction with
its rapid feeding in the transmitter, far surpass the time of ordinary
direct transmission.

Fig. 257. PERFORATOR FOR
WHEATSTONE'S AUTOMATIC TELEGRAPH.

Perforators may be entirely mechanical but are sometimes pneumatic,
compressed air being used to operate them. The holes they make are on
different levels of the paper strip, as shown in the cut.

Period.
The time required for the completion of one complete element of periodic
motion. This may be a complete alternation (See Alternation, Complete)
of an alternating current, or of an oscillatory discharge.

Periodicity.
The rate of succession of alternations or of other fixed phases; the
rate of recurrence of phenomena.

408 STANDARD ELECTRICAL DICTIONARY.

Permanency.
In electric current conductors the property of possessing conductivity
unaffected by lapse of time. Generally the permanency of conductors is
very high. In some cases a slow annealing takes place which causes a
gradual change with the lapse of time. Annealed German silver wire has
been found to increase in conductivity at about .02 per cent. in a year.
(Matthiessen.) Wire, whether annealed or not, is left in a strained
condition after the drawing operations, and such a change is consonant
with this fact. The figure only applies to the samples tested by
Matthiessen.

Permanent State.
In a telegraph line or other current conductor, the condition when a
uniform current strength obtains over the whole line. When a current is
started it advances through the line with a sort of wave front gradually
increasing in strength. At the further end some time may elapse before
it attains its full intensity. When its does the permanent state
prevails. Until then the variable state, q. v., exists in the line.

Permeameter.
An apparatus for determining the permeability of samples of iron. It
consists of a large slotted block of iron. A coil is placed within the
slot. A hole is drilled through one end, and a rod of the iron to be
tested is passed through this hole and through the coil to the bottom of
the slot. The lower end of the rod must be accurately faced off. The
current is turned on, upon which the rod adheres to the bottom of the
slot. The force required to detach it is determined with a spring
balance. The permeation through its face is proportional to the square
of the force required.

Fig. 258. PERMEAMETER.

Permeance.
The multiplying or the conducting power for magnetic lines of force
possessed by a given mass of material. It varies with the shape and size
of the substance as well as with the inducing force. It is distinguished
from permeability, as the latter is a specific quality proper to the
material, and expressed as such; the permeance is the permeability as
affected by size and shape of the object as well as by its material.

409 STANDARD ELECTRICAL DICTIONARY.

Pflüger's Law.
A law of electro-therapeutics. It states that stimulation of a nerve is
only produced by successive appearance of the kathelectrotonic state,
and disappearance of the anelectrotonic state.

Phantom Wires.
The extra transmission circuits obtained in multiplex telegraph systems.
A single line arranged for four separate simultaneous transmissions by
quadruplex apparatus is said to establish three phantom wires.

Phase.
In wave motion, oscillating motion, simple harmonic motion, or similar
periodic phenomena, the interval of time passed from the time the moving
particle moved through the middle point of its course to the instant
when the phase is to be stated.

Pherope.
An apparatus for the electric transmission of pictures. (See Telephote.)

Philosopher's Egg.
An ellipsoidal vessel mounted with its long axis vertical and with two
vertical electrodes, the upper one sliding, and arranged to be attached
to an air pump. A discharge through it when the air is exhausted takes
the general shape of an egg.

Phonautograph.
An apparatus for registering the vibrations of a stylus, which is
mounted on a diaphragm and is acted on by sound waves.

It is virtually a resonating chamber, over one of whose ends a parchment
diaphragm is stretched. To the centre of the parchment a needle or
stylus is attached. A cylinder covered with soot is rotated in contact
with the point of the stylus. As the chamber is spoken into the
diaphragm and stylus vibrate and the vibrations are marked on the
cylinder. It is of some electric interest in connection with telephony.

Phone.
Colloquial abbreviation for telephone.

Phonic Wheel.
A form of small motor of very simple construction. It consists of a
toothed wheel of soft iron. A bar electro-magnet is fixed with one pole
facing the teeth of the wheel. By a tuning fork make and break a
succession of impulses of rapid frequency and short duration are sent
through the magnet. The teeth act as armatures and are successively
attracted by the magnet. The regulated speed is one tooth for each
impulse, but it may rotate at one-half the speed, giving two teeth for
each impulse, or at certain other sub-multiples of its regular speed. It
is the invention of Paul Lecour.

410 STANDARD ELECTRICAL DICTIONARY.

Phonograph.
An apparatus for reproducing articulate speech. It is not electric,
except as it may be driven by electricity.

It consists of a cylinder of wax-like material which is rotated and
moved slowly, longitudinally, screw fashion, at an even speed. A glass
diaphragm carrying a needle point is supported with the point barely
touching the wax. If the diaphragm is agitated, as by being spoken
against, the needle is driven back and forwards cutting a broken line or
groove following the direction of the thread of a screw in the wax, the
depth of which line or groove continually varies.

This imprints the message. If the needle is set back and the cylinder is
rotated so as to carry the needle point over the line thus impressed,
the varying depth throws the needle and diaphragm into motion and the
sound is reproduced.

The cylinder is rotated often by an electric motor, with a centrifugal
governor.

Phonozenograph.
An apparatus for indicating the direction of the point where a sound is
produced. It operates by a microphone and telephone in conjunction with
a Wheatstone bridge to determine the locality.

Phosphorescence.
The emission of light rays by a substance not heated, but whose
luminosity is due to the persistence of luminous vibration after light
has fallen upon it.

A phosphorescent body, after exposure to light, is luminous itself.
Phosphorescence may be induced by rubbing or friction, by heat, by
molecular bombardment, as in Crookes' tubes, and by static discharge of
electricity, as well as by simple exposure to light.

Another form of phosphorescence may be due to slow chemical combustion.
This is the cause of the luminosity of phosphorous.

Phosphorous, Electrical Reduction of.
Phosphorous is reduced from bone phosphate by the heat of the electric
arc. The phosphate mixed with charcoal is exposed to the heat of the
voltaic are, and reduction of the phosphorous with its volatilization at
once ensues. The phosphorous as it volatilizes is condensed and
collected.

Photo-electricity.
The development of electrical properties by exposure to light. Crystals
of fluor spar are electrified not only by heat (see Pyro-electricity)
but also by exposure to sunlight or to the light of the voltaic arc.

Photo-electric Microscope.
A projection, solar or magic-lantern microscope worked by the electric
light.

Photo-electro-motive Force.
Electro-motive force produced in a substance by the action of light.

411 STANDARD ELECTRICAL DICTIONARY.

Photometer.
An apparatus for measuring the intensity of light emitted by a given
lamp or other source of illuminating power. They may be classified into
several types.

Calorimetric or Heat Photometers act by measuring relatively the heat
produced by the ether waves (so-called radiant heat) emitted by the
source. The accuracy of the instrument is increased by passing the rays
through an alum solution. A thermopile, or an air thermometer, may be
used to receive the rays.

Chemical Photometers. In these the light falls upon sensitized
photographic paper. The depth of coloration is used as the index of
illuminating power.

Direct Visual Photometers. These include Rumford's Shadow Photometer,
Bunsen's Bar Photometer, and Wheatstone's Bead Photometer, in which the
light is estimated by direct visual comparison of its effects.

Optical Photometers. These include Polarization Photometers, in which
the light is polarized; Dispersion Photometers, in which a diverging
lens is placed in the path of the rays of light so as to reduce the
illuminating power in more rapid ratio than that of the square of the
distance.

Selenium Photometers, in which the variations in resistance of selenium
as light of varying intensity falls upon it is used as the indicator of
the intensity of the light.

Jet Photometers, for gas only, in which the height of a flame under
given conditions, or the conditions requisite to maintain a flame of
given height, is used to indicate the illuminating power.

The subject of photometers has acquired more importance than ever in
view of the extensive introduction of the electric light. (See Candle,
Standard--Carcel--Violé's Standard--and Photometers of various kinds.)

Photometer, Actinic.
A photometer whose registrations are produced by the action of the light
being tested upon sensitized paper or plates, such as used in
photography. Some efforts at self-registering photometers have been
based on actinic registration of the height of a flame of the gas to be
tested.

Photometer, Bar.
A photometer in which the two lights to be compared are fixed at or
opposite to the ends of a bar or scale of known length, generally 60 or
100 inches. The bar is divided by the rule of the inverse square of the
distances, so that if a screen is placed on any part of the bar where it
receives an equal amount of light from both sources, the figure on the
bar will indicate the relative illuminating power of the larger lamp or
light in terms of the smaller. The divisions of the bar are laid out on
the principle that the illuminating power of the two sources of light
will vary inversely with the square of their distance from the screen.

412 STANDARD ELECTRICAL DICTIONARY.

The screen used is sometimes the Bunsen disc. This is a disc of paper
with a spot of paraffine wax in the centre melted thoroughly into the
paper or with a ring of paraffine wax surrounding the untouched centre.
When this disc is equally illuminated on both sides the spot is nearly
invisible. Inequality of illumination brings it out more visibly.
Sometimes a Leeson disc is used. This consists of three pieces of paper,
two thin ones between which a thicker piece, out of which a star is cut,
is laid. When equally illuminated on both sides the star appears equally
bright on both sides.

The bar photometer is the standard form. A candle or pair of candles may
be burned at one end and an incandescent lamp at the other, or a gas
flame may first be rated by candles and used as a standard.

Synonyms--Bunsen's Photometer--Translucent Disc Photometer.

Fig. 259. BAR PHOTOMETER.

Photometer. Calorimetric.
A photometer in which the radiant energy, so called radiant heat, is
used as the measurer of the light.

In one type a differential air thermometer is used, one of whose bulbs
is blackened. On exposing this bulb to a source of light it will become
heated, and if lights of the same character are used the heating will be
in proportion to their illuminating power quite closely. The heating is
shown by the movements of the index. By careful calibration the
instrument may be made quite reliable.

Photometer, Dispersion.
A photometer in which the rays from one of the lights under comparison
are made more divergent by a concave lens. In this way a strong light,
such as all arc lamp can be photometered more readily than where only
the natural divergence of the beam exists. The law of the variation of
the intensity of light with the square of the distance is abrogated for
a law of more rapid variation by the use of a concave lens.

The diagram, Fig. 260, illustrates the principle. E represents a
powerful light, an arc light, to be tested. Its distance from the screen
is e. Its light goes through the concave lens L and is dispersed as
shown over an area A1, instead of the much smaller area A, which the
same rays would otherwise cover. Calling l the distance of the lens from
the screen, f its focus, and c the distance of the standard candle from
the screen when the shadows are of equal intensity, we have the
proportion.

Illuminating power of lamps: ditto of standard candle::
(l (e-l) + fe)2 : (c f)2

413 STANDARD ELECTRICAL DICTIONARY.

Fig. 260. DIAGRAM OF PRINCIPLE
OF THE DISPERSION PHOTOMETER.

The cut, Fig. 261, gives a perspective view of Ayrton's Dispersion
Photometer. C is the standard candle, L the concave lens, R the rod for
producing the two shadows on the screen S.

Fig. 261. AYRTON'S DISPERSION PHOTOMETER.

The mirror M is fixed at an angle of 45° with the stem on which it
rotates. The light of the arc lamp is received by the mirror and is
reflected through the lens. The candle holder slides along a graduated
bar C, and at D is an index plate to show the angle at which the spindle
carrying the mirror is set.

414 STANDARD ELECTRICAL DICTIONARY.

Dr. J. Hopkinson in his dispersion photometer uses a double convex lens.
This gives a focal image of the arc-lamp between the lens and screen,
whence the rays diverge very rapidly, thus giving the desired dispersion
effect.

It is principally for arc lamps that dispersion photometers are used.

Photometer, Shadow.
A photometer in which the relative intensity of the two lights is
estimated by the intensity or strength of shadows of the same object
which they respectively cast.

Fig. 262. RUMFORD'S SHADOW PHOTOMETER.

Fig. 263. RUMFORD'S SHADOW PHOTOMETER ARRANGED FOR TESTING
INCANDESCENT LAMPS.

415 STANDARD ELECTRICAL DICTIONARY.

A rod is supported in a vertical position. Back of it is a screen of
white paper. The two lights to be compared are arranged in front of the
rod and at a little distance from each other. They are shifted about
until the two shadows appear of equal darkness. The relative intensity
of the lights varies inversely with the square of their distances from
the shadows cast respectively by them on the screen.

The cut, Fig. 262, shows the simplest type of the shadow photometer. In
the cut, Fig. 263, a shadow photometer for testing incandescent lamps is
shown. In it E is the lamp under trial supported by a clamp H. A is an
ampere meter in circuit with the lamp, and V is a voltmeter. A candle C
can be moved along a graduated scale G G. R is the vertical rod, and S
is the screen on which the shadows fall.

Photophore.
An instrument for medical examination of the cavities of the body. It
includes an incandescent lamp mounted in a tube with a concave mirror
and convex lens.

Photo-voltaic Effect.
The change in resistance of some substances effected by light. Selenium,
of all substances, is most susceptible to this effect. (See Selenium.)

Piano, Electric.
A piano whose manual or key-board operates to close electric circuits,
whereby electro-magnets are caused to operate to drive the hammers
against the strings.

Pickle.
An acid solution for cleaning metal surfaces before electro-plating,
galvanizing or other deposition of metal upon them.

Picture, Electric.
A picture produced by passing a strong discharge through a piece of gold
leaf clamped or firmly pressed upon a sheet of paper. The gold leaf is
cut out of the desired shape, or else a stencil of paper overlays it.
The discharge dissipates the gold, and produces a purple colored
reproduction of the design upon the paper. The design is due to the
deposition of an exceedingly thin film of metallic gold.

Synonym--Electric Portrait.

Pile.
A galvanic or voltaic battery. It is sometimes restricted to a number of
voltaic couples connected. It should be only applied to batteries with
superimposed plates and no containing vessel such as the Dry Pile, q.
v., or Volta's Pile, q. v.

Pilot Transformer.
In alternating current distribution a small transformer placed at any
part of the system and connected to a voltmeter in the central station,
to indicate the potential difference of the leads.

Pilot Wires.
Wires brought from distant parts of electric light or power mains, and
leading to voltmeters at the central station, so that the potential of
distant parts of the system can be watched. The wires can be very small,
as they have but little current to transmit.

416 STANDARD ELECTRICAL DICTIONARY.

Pistol, Electric.
An experimental apparatus for exhibiting the power of electric
incandescence or of the electric spark. A tube is mounted with a handle
like a pistol. A plug is provided to screw in and out of its side. The
plug carries two wires connected on its inner side by a fine platinum
wire, or else disconnected but with their ends brought near together to
act as terminals for the production of a spark. To use it the tube is
filled with a mixture of air and gas, the latter either hydrogen,
hydro-carbon or other combustible gas. The tube when full is corked. The
wire is heated to incandescence by a current, or a spark is passed from
a Leyden jar or other source of electrostatic excitation. The mixture,
if properly proportioned, explodes and expels the cork violently.

Fig. 264. ELECTRIC PISTOL.

Pith.
A light and soft cellular tissue forming the central core of exogenous
trees and plants. In the older parts of the tree the woody tissue often
encroaches in and partly obliterates it.

For electrical pith-balls, the pith of the elder, of corn, or, best of
all, of sun-flower stems is used.

Pith-balls.
Ball made of pith. They are used in the construction of electroscopes
and for other experiments in static electricity.

They are cut out with a sharp knife and their shape may be improved by
gentle rolling in the hand or between the fingers.

Pivot Suspension.
Suspension poising or supporting of an object on a sharp pivot. This is
used for the needle in the ordinary compass. A cavity or inverted cup,
which may be made of agate, is attached to the middle of the needle
which has a hole for its reception. The centre of gravity of the needle
comes below the bottom of the cup.

Pivot suspension is not perfect, as it has considerable friction. There
is no restitution force, as with torsion filaments.

417 STANDARD ELECTRICAL DICTIONARY.

Plant.
The apparatus for commercial manufacturing or technical works. An
electric lighting plant includes the boilers, engines and dynamos for
producing the current, and the electric mains and subsidiary apparatus.

Plant Electricity.
Electricity manifested by plant life. By means of a galvanometer
potential differences are found to exist in different parts of trees or
fruits. The roots and interior portions are negative, and the flowers,
smaller branches and fruit are positive.

In some cases a contraction of the tissue of plants can be produced by
an electric current. The sensitive plant and others exhibit this
phenomenon, exactly analogous to the action of muscular tissue.

Plate, Arrester.
In a lightning arrester the plate connected to the circuit. Sometimes
both plates are designated arrester plates.

Plate Condenser.
A static condenser having a flat plate of glass for dielectric. (See
Epinus' Condenser.)

Plate Electrical Machine.
A frictional electric machine, in which a circular plate of glass is
excited by friction with the cushions. It is the most recent type of
frictional machine and has superseded the old cylinder machines. In its
turn it is superseded by influence machines, really plate machines, but
not so termed in practice.

Plate, Ground.
In a lightning arrester, the plate connected to the earth.

Plate, Negative.
In a voltaic battery, either primary or secondary, the plate which is
unattacked by the oxygen or negative radical or element of the fluid. It
corresponds to the carbon plate in the ordinary voltaic battery, and is
the one charged with positive electricity.

Plate, Positive.
In a voltaic battery, either primary or secondary, the plate which is
dissolved or attacked by the oxygen or negative radical or element of
the fluid. It is the plate corresponding to the zinc plate in the
ordinary voltaic battery, and is the one charged with negative
electricity.

Plating Balance.
A balance or scales to which articles in an electroplater's bath are
suspended. A weight exceeding by a known amount that of the article as
immersed overbalances the article. When the plating is being deposited
as soon as it exceeds the excess of weight of the counterpoise the
balance tips, the article descends a little, the electric circuit is
broken and the plating ceases. Thus the plating is automatically stopped
when a predetermined amount of metal is deposited.

418 STANDARD ELECTRICAL DICTIONARY.

Plating Bath.
A vessel of solution for the deposition of metal by electrolysis as used
in electro-plating.

Plating, Electro-.
The deposition of metal by electrolysis so as to coat the conducting
surface of objects therewith. The full details of the many processes are
very lengthy and cannot be given here.

The general principle includes a battery or source of electric current.
The object to be plated is connected to the negative terminal and is
immersed in the solution. Thus with a battery the object is in
electrical connection with the zinc plate. To the other terminal a
metallic plate is connected. The object and the plate termed the anode
being introduced into a suitable bath, the metal whose solution is in
the bath is deposited upon the surface of the object.

The bath is a solution of the metal in some form that will lend itself
to the electrolytic action. The anode is often a plate of the metal of
the bath, so that it dissolves as fast as metal is deposited on the
object, thus keeping up the strength of the solution.

The objects to be plated must be scrupulously clean, and great care must
be taken to keep the bath uncontaminated.

When the object has a non-conducting surface, it is made conducting by
being brushed over with plumbago q.v. In addition iron dust is sometimes
dusted over it. This acts by precipitating the metal of the bath
directly and thus giving a conducting basis for the metal to deposit on.
To avoid getting iron in a bath the object may be dipped in copper
sulphate solution. This precipitates copper in place of the iron and
leaves the article in good shape for silver or other plating.

Electro-plating, if made thick enough, gives a reverse of the article
when separated therefrom. A direct copy can be got by a second plating,
on the first plating after separation, or a wax impression can be
employed.

Under the different metals, formulae for the baths will be found. (See
also Quicking--
Steeling--Plating Balance.)

Platinoid.
An alloy of copper, nickel, zinc in the proportions of German silver
with 1 or 2 per cent of tungsten. It is used for resistances. It has a
specific resistance (or resistance per centimeter cube) of about 34
microhms. Its percentage variation in resistance per degree C. (1.8° F.)
is only about .021 per cent., or less than half that of German silver.
This is its most valuable feature.

419 STANDARD ELECTRICAL DICTIONARY.

Platinum.
A metal; one of the elements; symbol, Pt; atomic weight, 197.4;
equivalent, 49.35; valency, 4; specific gravity, 21.5.
It is a conductor of electricity.
The following data refer to the annealed metal at 0° C. (32° F.)
Relative Resistance (Silver annealed = 1), 6.022
Specific Resistance, 9.057 microhms.
Resistance of a wire,
(a) 1 foot long, weighing 1 grain, 2.779 ohms.
(b) 1 foot long, 1/1000 inch thick, 54.49 "
(c) 1 meter long, weighing 1 gram, 1.938 "
(d) 1 meter long, 1 millimeter thick, .1153 "
Resistance of a 1 inch cube, 3.565
Electro-chemical equivalent (Hydrogen = .0105), 0.5181.

The coefficient of expansion by heat is almost the same as that of
glass. It can be passed through holes in glass and the latter can be
melted about it so as to hermetically seal its place of passage through
the glass. It is used in incandescent lamps for leading-in wires and
other similar uses.

Platinum Black.
Finely divided platinum. It is made by boiling a solution of platinic
chloride with excess of sodium carbonate and a quantity of sugar, until
the precipitate is perfectly black and the supernatant liquid is
colorless. It seems to possess a great power of occluding oxygen gas.
When heated to redness it becomes spongy platinum. The negative plates
of a Smee battery are coated with platinum black.

Platinum-silver Alloy.
An alloy of 1 part platinum and 2 parts silver, used for resistance coils.

Relative Resistance (silver annealed = 1 ), 16.21 microhms.
Specific Resistance at 0°C. (32° F.), 24.39
Resistance of a wire,
(a) 1 foot long, weighing 1 grain, 4.197 ohms.
(b) 1 foot long, 1/1000 inch diameter, 146.70 "
(c) 1 meter long weighing 1 gram, 2.924 "
(d) 1 meter long, 1 millimeter diameter, 0.3106 "
Resistance of a 1 inch cube, 9.603 microhms.
Percentage Variation per degree C. (1.8° F.)
at about 20° C. (68° F.), 0.031 per cent.

Synonym--Platinum Alloy.

Platinum Sponge.
Finely divided platinum obtained by igniting platinum black, q.v., and
also by igniting salts of platinum. It has considerable power of
condensing or occluding oxygen. It will, if in good condition, set fire
to a jet of hydrogen impinging upon it.

Plow.
Contact arms projecting downwards from the motors, trucks, or bodies of
electric street cars, which enter the underground conduit through the
slot and carry contact pieces or brushes, to take the current for
driving the motors from the leads within the conduit.

420 STANDARD ELECTRICAL DICTIONARY.

Plücker Tubes.
A special form of Geissler tube designed for the production of
stratification and for observing the effects produced in the space
surrounding the negative electrode.

Plug.
(a) A piece of metal with a handle and a somewhat tapered end, used to
make connections by insertions between two plates or blocks of metal
slightly separated and with grooves to receive it.

(b) A plug or wedge with two metallic faces, insulated from each other
with a separate wire connected to each one. It is used in spring-jacks
q. v., to introduce a loop in a circuit.

Synonym--Wedge.

Plug. v.
To connect by inserting a plug, as in a resistance box.

Fig. 265. PLUGS FOR RESISTANCE COIL BOX.

Fig. 266. PLUG SWITCH.

Plug, Double.
A spring-jack plug or wedge with two pairs of insulated faces, one
behind the other, so as to simultaneously introduce two loops into a
circuit.

Plug, Grid.
A piece or mass of lead oxide, inserted into the holes in the lead
plates of storage batteries. The holes are often dovetailed or of uneven
section to better retain the plugs.

Plug Infinity.
In a box-bridge or resistance box, a plug whose removal from between two
disconnected discs opens the circuit. All the other discs are connected
by resistance coils of various resistance.

Plug Switch.
A switch composed of two contact blocks, not touching each other and
brought into electrical connection by the insertion of a metallic plug.
The latter is usually provided with an insulating handle, and a seat is
reamed out for it in the two faces of the contact blocks.

421 STANDARD ELECTRICAL DICTIONARY.

Plumbago.
Soft lustrous graphite, a native form of carbon; sometimes chemically
purified. It is used in electro-plating to give a conducting surface to
non-conducting objects, such as wax moulds. The surface, after coating
with plumbago, is sometimes dusted over with iron dust, which
precipitates the metal of the bath and starts the plating. It is
sometimes plated with copper, silver or gold, and is then termed
coppered, silvered, or gilt plumbago. It is gilded by moistening with
etherial solution of gold chloride and exposing to the air, and drying
and igniting.

Plunger.
A movable core which is used in connection with a so-called solenoid
coil, to be drawn in when the coil is excited. (See Coil and Plunger.)

Fig. 267 COIL AND PLUNGER WITH
SCALES TO SHOW ATTRACTION.

P. O.
Abbreviation for Post Office, q.v.

Poggendorf's Solution.
An acid depolarizing and exciting fluid for zinc-carbon batteries. The
following is its formula: Water, 100 parts; potassium bichromate, 12
parts; concentrated sulphuric acid, 25 parts. All parts by weight. Use
cold.

Point, Neutral.
(a) On a commutator of a dynamo the points at the ends of the diameter
of commutation, or where the brushes rest upon the surface of the
commutator, are termed neutral points. At these points there is no
generation of potential, they marking the union of currents of opposite
direction flowing from the two sides of the armature into the brushes.

(b) In electro-therapeutics, a place in the intra-polar region of a
nerve so situated with reference to the kathode and electrode as applied
in treatment, that its condition is unaffected.

Synonym--Indifferent Point.

(c) In a magnet the point of no attraction, situated between the two
poles, at about an equal distance from each, so as to mark the centre of
a magnet of even distribution of polarity.

(d) In thermo-electricity the point of temperature where the
thermo-electric powers of two metals are zero; in a diagram the point
where the lines representing their thermo-electric relations cross each
other; if the metals are arranged in a thermo-electric couple, one end
at a temperature a given amount above, the other at a temperature the
same amount below the neutral point, no current or potential difference
will be produced.

422 STANDARD ELECTRICAL DICTIONARY.

Point, Null.
A nodal point in electrical resonators; a point where in a system of
waves or oscillations, there is rest, the zero of motion being the
resultant of oppositely directed and equal forces. In electrical
resonators it is to be sought for in a point symmetrically situated,
with reference to the spark gap, or in a pair of points, which pair is
symmetrically placed.

The null point in resonators is found by connecting a lead from one of
the secondary terminals of an induction coil to different parts of the
resonator. The null point is one where the connection does not give rise
to any sparks between the micrometer knobs or spark gap, or where the
sparks are of diminished size.

The whole is exactly comparable to loops and nodes in a vibrating string
or in a Chladni plate as described in treatises on sound and acoustics.
(See Resonance, Electrical--Resonator, Electrical.)

Synonym--Nodal Point.

Point Poles.
Magnet poles that are virtually points, or of no magnitude. A long thin
magnet with little leakage except close to the ends may be supposed to
have point poles within itself a short distance back from the ends.

Points, Consequent.
In a magnet with consequent poles, the points where such poles are
situated.

Points, Corresponding.
In bound electrostatic charges the points of equal charges of opposite
potentials; the points at opposite extremities of electrostatic lines of
force. This definition implies that the bound charges shall be on equal
facing areas of conductors, as otherwise the spread or concentration of
the lines of force would necessitate the use of areas of size
proportionate to the spreading or concentrating of the lines of force.
At the same time it may figuratively be applied to these cases, the
penetration of the surface by a single line of force including the area
fixed by its relation to the surrounding lines.

Points, Isoelectric.
In electro-therapeutics, points of equal potential in a circuit.

423 STANDARD ELECTRICAL DICTIONARY.

Points of Derivation.
The point where a single conductor branches into two or more conductors,
operating or acting in parallel with each other.

Polar Angle.
The angle subtended by one of the faces of the pole pieces of the field-
magnet of a dynamo or motor. The centre of the circle of the angle lies
in the axis of the armature.

Synonym--Angle of Polar Span.

Polar Extension.
An addition made of iron to the poles of magnets. Various forms have
been experimented with. The pole pieces of dynamo field magnets are
polar extensions.

Synonyms--Pole Piece--Polar Tips.

Polarity, Diamagnetic.
The induced polarity of diamagnetic substances; it is the reverse of
paramagnetic polarity, or of the polarity of iron. A bar of diamagnetic
material held parallel with the lines of force in a magnetic field has a
like pole induced in the end nearest a given pole of the field magnet,
and vice versa. This theory accounts for the repulsion by a magnet of a
diamagnetic substance. The existence of this polarity is rather an
assumption. It originated with Faraday.

Polarity, Paramagnetic.
The induced polarity of paramagnetic substances, such as iron, nickel,
or cobalt.

When such a substance is brought into a magnetic field the part nearest
a specific pole of a magnet acquires polarity opposite to that of such
pole and is thereby attracted.

Another way of expressing it, in which the existence of a pole in or
near to the field is not implied, is founded on the conventional
direction of lines of force. Where these enter the substance a south
pole is formed and where they emerge a north pole is formed.

Such polarity tends always to be established in the direction of
greatest length, if the body is free to rotate.

424 STANDARD ELECTRICAL DICTIONARY.

Polarization.
(a) The depriving of a voltaic cell of its proper electro-motive force.
Polarization may be due to various causes. The solution may become
exhausted, as in a Smee battery, when the acid is saturated with zinc
and thus a species of polarization follows. But the best definition of
polarization restricts it to the development of counter-electro-motive
force in the battery by the accumulation of hydrogen on the negative
(carbon or copper) plate. To overcome this difficulty many methods are
employed. Oxidizing solutions or solids are used, such as solution of
chromic acid or powdered manganese dioxide, as in the Bunsen and
Leclanché batteries respectively; a roughened surface of platinum black
is used, as in the Smee battery; air is blown through the solution to
carry off the hydrogen, or the plates themselves are moved about in the
solution.

(b) Imparting magnetization to a bar of iron or steel, thus making a
permanent magnet, is the polarization of the steel of which it is made.
Polarization may be permanent, as in steel, or only temporary, as in
soft iron.

(c) The strain upon a dielectric when it separates two oppositely
charged surfaces. The secondary discharge of a Leyden jar, and its
alteration in volume testify to the strain put upon it by charging.

(d) The alteration of arrangement of the molecules of an electrolyte by
a decomposing current. All the molecules are supposed to be arranged
with like ends pointing in the same direction, positive ends facing the
positively-charged plate and negative ends the negatively-charged one.

(e) The production of counter-electro-motive force in a secondary
battery, or in any combination capable of acting as the seat of such
counter-electro-motive force. (See Battery, Secondary--Battery, Gas.)
The same can be found often in organized cellular tissue such as that of
muscles, nerves, or of plants. If a current is passed through this in
one direction, it often establishes a polarization or potential
difference that is susceptible of giving a return current in the
opposite direction when the charging battery is replaced by a conductor.

Polarization Capacity.
A voltaic cell in use becomes polarized by its negative plate
accumulating hydrogen, or other cause. This gradually gives the plate a
positive value, or goes to set up a counter-electro-motive force. The
quantity of electricity required to produce the polarization of a
battery is termed its Polarization Capacity or Capacity of Polarization.

Polarization of the Medium.
The dielectric polarization, q. v., of a dielectric, implying the
arrangement of its molecules in chains or filaments; a term due to
Faraday. He illustrated it by placing filaments of silk in spirits of
turpentine, and introduced into the liquid two conductors. On
electrifying one and grounding (or connecting to earth) the other one,
the silk filaments arranged themselves in a chain or string connecting
the points of the conductors.

Polar Region.
That part of the surface of a magnet whence the internal magnetic lines
emerge into the air. (S. P. Thompson.) As such lines may emerge from
virtually all parts of its surface, the polar regions are indefinite
areas, and are properly restricted to the parts whence the lines emerge
in greatest quantity.

Polar Span.
A proportion of the circle which represents the transverse section of
the armature space between the pole pieces of the field magnet in a
dynamo or motor; it is the proportion which is filled by the faces of
the pole pieces.

425 STANDARD ELECTRICAL DICTIONARY.

Pole, Analogous.
The end of a crystal of a pyroelectric substance, such as tourmaline,
which end when heated become positively electrified. On reduction of
temperature the reverse effect obtains.

Pole, Antilogous.
The end of a crystal of a pyroelectric substance, such as tourmaline,
which end, while increasing in temperature, becomes negatively
electrified. During reduction of its temperature the reverse effect
obtains.

Pole Changer.
(a) An automatic oscillating or vibrating switch or contact-breaker
which in each movement reverses the direction of a current from a
battery or other source of current of fixed direction, as such current
goes through a conductor.

(b) A switch moved by hand which for each movement effects the above
result.

Pole, Negative.
(a) In a magnet the south pole; the pole into which the lines of force
are assumed to enter from the air or outer circuit.

(b) In a current generator the pole or terminal into which the current
is assumed to flow from the external circuit. It is the negatively
charged terminal and in the ordinary voltaic battery is the terminal
connected to the zinc or positive plate.

Pole Pieces.
The terminations of the cores of field or other electro-magnets, or of
permanent magnets. These terminations are variously shaped, sometimes
being quite large compared to the core proper of the magnet.

They are calculated so as to produce a proper distribution of and
direction of the lines of force from pole to pole. As a general rule the
active field should be of uniform strength and the pole pieces may be of
contour calculated to attain this end.

Pole, Positive.
(a) In a magnet the north pole; the pole from which lines of force are
assumed to emerge into the air.

(b) In a current generator the pole or terminal whence the current is
assumed to issue into the outer circuit. It is the positively charged
terminal, and in the ordinary voltaic battery is the terminal connected
to the copper or carbon plate, termed the negative plate.

Poles.
(a) The terminals of an open electric circuit, at which there
necessarily exists a potential difference, produced by the generator or
source of electro-motive force in the circuit.

(b) The terminals of an open magnetic circuit; the ends of a magnetized
mass of steel, iron or other paramagnetic substance.

(c) The ends in general of any body or mass which show electric or
magnetic properties more developed than those of the central sections of
the body.

426 STANDARD ELECTRICAL DICTIONARY.

Pole, Salient.
In dynamo and motor field magnets, salient poles are those projecting
from the base or main body of the field magnet, as distinguished from
consequent poles formed by coils wound on the main body itself.

Fig. 268. SALIENT POLES OF FIELD MAGNET.

Poles, Compensating.
A device for avoiding the cross-magnetizing effect on the commutator
core due to the lead of the brushes. It consists in maintaining a small
bar electro-magnet perpendicularly between the pole pieces. This
compensates the cross-magnetizing effect.

Poles of Intensity.
The locus of highest magnetic force on the earth's surface. One such
pole is in Siberia, another is about lat. 52° N., long. 92° W.

Poles of Verticity.
The magnetic poles of the earth. (See Magnetic Poles.)

Pole Tips.
The extreme ends of the expanded poles of a field magnet. In some
machines some of the pole tips are made of cast iron, to alter the
distribution of the lines of force and resulting magnetic pull upon the
armatures. This is done to take off the weight of the armature from its
bearings.

Pole, Traveling.
A term applied to the poles produced in the action of a rotatory field,
whose poles constantly rotate around the circle of the field. (See
Field, Rotatory.)

417 STANDARD ELECTRICAL DICTIONARY.

Porous Cup.
A cup of pipe clay, unglazed earthenware or other equivalent material
used in voltaic cells to keep two liquids separate and yet to permit
electrolysis and electrolytic conduction.

They are necessarily only an expedient, as their porous nature permits
considerable diffusion, and were they not porous electrolytic action
would be impossible.

Synonym--Porous Cell.

Porret's Phenomenon.
In electro-physiology, an increase in the diameter of a nerve produced
by the positive pole of a voltaic circuit, when placed in contact with
the tissue and near to the nerve in question, the other pole being
connected to a more or less remote part of the body.

Portelectric Railroad.
A railroad worked by solenoidal attraction, the car forming the core of
the solenoids. It includes a series of solenoids or hollow coils of
copper wire distributed all along the road and inclosing within
themselves the track. On this a cylindrical car with pointed ends moves
on wheels. Current is supplied to the solenoid in advance of the car,
and attracts it. As it advances it breaks the contacts of the attracting
solenoid and turns the current into the one next in advance. This
operation is repeated as the car advances.

The solenoids are placed close together, each including in the trial
track 630 turns of No. 14 copper wire. The car was of wrought iron, 12
feet long, 10 inches in diameter and weighing 500 lbs. It was proposed
to employ the system for transportation of mail matter and similar uses.

Position Finder.
An instrument for determining the position of objects which are to be
fired at from forts. It is designed for use from forts situated on the
water.

Fiske's position finder may be thus generally described. On a chart the
channel is divided into squares, and the position finder determines the
square in which a vessel lies. For each square the direction and
elevation of the guns is calculated beforehand. The enemy can therefore
be continuously located and fired at, although from smoke or other cause
the object may be quite invisible to the gunner.

It comprises two telescopes situated at distant extremities of as long a
base line as is obtainable. These telescopes are kept directed upon the
object by two observers simultaneously. The observers are in constant
telephonic communication. As each telescope moves, it carries a contact
over an arc of conducting material. Below each telescope is an arm also
moving over an arc of conducting material. These arcs enter into a
Wheatstone bridge and are so connected that when the arm and the distant
telescope are at the same angle or parallel a balance is obtained. Thus
each observer has the power of establishing a balance. A chart is
provided for each of them, and over it the arm connected with the
distant telescope and an arm or indicator attached to the telescope at
that station move so that as long as both telescopes point at the object
and each observer maintains the electric balance, the intersection of
the arms shows the position on the chart.

The Position Finder is a simplification and amplification of the Range
Finder, q. v. In practice the observers may be placed far from the
forts, and may telephone their observations thereto. It has been found
accurate within one-third of one per cent.

428 STANDARD ELECTRICAL DICTIONARY.

Positive Direction.
The direction which lines of force are assumed to take in the air or
outer circuit from a positive to a negative region. It applies to
electrostatic, to magnetic and to electro-magnetic lines of force.

Positive Electricity.
The kind of electricity with which a piece of glass is charged when
rubbed with silk; vitreous electricity.

In a galvanic cell the surface of the copper or carbon plate is charged
with positive electricity. (See Electrostatic Series.)

According to the single fluid theory positive electrification consists
in a surplus of electricity.

Post Office. adj.
Many pieces of electric apparatus of English manufacture are thus
qualified, indicating that they are of the pattern of the apparatus used
by the British Post Office in its telegraph department.

Potential.
Potential in general may be treated as an attribute of a point in space,
and may express the potential energy which a unit mass would have if
placed at that point.

This conception of potential is that of a property attributable to a
point in space, such that if a unit mass were placed there the forces
acting upon it would supply the force factor of energy, while the body
would supply the mass factor. This property is expressible in units,
which produce, if the supposed mass is a unit mass, units of work or
energy, but potential itself is neither.

Thus taking gravitation, a pound mass on the surface of the earth
(assuming it to be a sphere of 4,000 miles radius) would require the
expenditure of 21,120,000 foot pounds to remove it to an infinite
distance against gravity. The potential of a point in space upon the
surface of the earth is therefore negative and is represented by
-21,120,000*32.2 foot poundals (32.2 = acceleration of gravity). (See
Poundal.) In practice and conventionally all points on the earth's
surface are taken as of zero potential.

429 STANDARD ELECTRICAL DICTIONARY.

Potential, Absolute.
The absolute electrical potential at a point possesses a numerical value
and measures the tendency which the existing electric forces would have
to drive an electrified particle away from or prevent its approach to
the point, if such a particle, one unit in quantity, were brought up to
or were situated at that point. It is numerically equal to the number of
ergs of work which must be done to bring a positive unit of electricity
from a region where there is absolutely no electric force up to the
point in question. (Daniell.) Two suppositions are included in this. The
region where there is an electric force has to be and only can be at an
infinite distance from all electrified bodies. The moving of the
particle must take place without any effect upon the distribution of
electricity on other particles.

Potential, Constant.
Unchanging potential or potential difference.

The ordinary system of incandescent lighting is a constant potential
system, an unvarying potential difference being maintained between the
two leads, and the current varying according to requirements.

Potential Difference, Electric.
If of any two points the absolute potentials are determined, the
difference between such two expresses the potential difference.
Numerically it expresses the quantity of work which must be done to
remove a unit of electricity from one to the other against electric
repulsion, or the energy which would be accumulated in moving it the
other way.

A positively charged particle is driven towards the point of lower
potential. A negatively charged body is driven in the reverse direction.

Potential Difference, Electro-motive.
A difference of potential in a circuit, or in part of a circuit, which
difference produces or is capable of producing a current, or is due to
the flow of such current.

It may be expressed as the fall in potential or the electro-motive force
included between any two points on a circuit. The current in an active
circuit is due to the total electro-motive force in the circuit. This is
distributed through the circuit in proportion to the resistance of its
parts. Owing to the distribution of electro-motive force throughout a
circuit including the generator, the terminals of a generator on closed
circuit may show a difference of potential far lower than the
electro-motive force of the generator on closed circuit. Hence potential
difference in such a case has been termed available electro-motive
force.

Potential, Electric Absolute.
The mathematical expression of a property of a point in space, measuring
the tendency which existing electric forces would have to drive an
electrified unit particle away from or prevent its approach to the point
in question, according to whether the point was situated at or was at a
distance from the point in question.

Potential is not the power of doing work, although, as it is expressed
always with reference to a unit body, it is numerically equal to the
number of ergs of work which must be done in order to bring a positive
unit of electricity from a region where there is no electric
force--which is a region at an infinite distance from all electrified
bodies--up to the point in question. This includes the assumption that
there is no alteration in the general distribution of electricity on
neighboring bodies. (Daniell.)

In practice the earth is arbitrarily taken as of zero electric potential.

430 STANDARD ELECTRICAL DICTIONARY.

Potential, Fall of.
The change in potential between any two points on an active circuit. The
change in potential due to the maintenance of a current through a
conductor.

The fall in potential multiplied by the current gives work or energy
units.

The fall of potential in a circuit and its subsequent raising by the
action of the generator is illustrated by the diagram of a helix. In it
the potential fall in the outer circuit is shown by the descent of the
helix. This represents at once the outer circuit and the fall of
potential in it. The vertical axis represents the portion of the circuit
within the battery or generator in which the potential by the action of
the generator is again raised to its original height.

In a circuit of even resistance the potential falls evenly throughout
it.

A mechanical illustration of the relation of fall of potential to
current is shown in the cut Fig. 269. A vertical wire is supposed to be
fixed at its upper end and a lever arm and cord at its lower end, with
weight and pulley imparts a torsional strain to it. The dials and
indexes show a uniform twisting corresponding to fall of potential. For
each unit of length there is a definite loss of twisting, corresponding
to fall of potential in a unit of length of a conductor of uniform
resistance. The total twisting represents the total potential
difference. The weight sustained by the twisting represents the current
maintained by the potential difference. For a shorter wire less twisting
would be needed to sustain the weight, as in a shorter piece of the
conductor less potential difference would be needed to maintain the same
current.

Fig. 269. MECHANICAL ILLUSTRATION OF
FALL OF POTENTIAL AND CURRENT STRENGTH.

431 STANDARD ELECTRICAL DICTIONARY.

Fig. 270. ILLUSTRATION OF THE FALL AND
REDEVELOPMENT OF POTENTIAL IN AN ELECTRIC CIRCUIT.

The fall of potential in a circuit in portions of it is proportional to
the resistance of the portions in question. This is shown in the
diagram. The narrow lines indicate high and the broad lines low
resistance. The fall in different portions is shown as proportional to
the resistance of each portion.

Fig. 271. DIAGRAM OF FALL OF POTENTIAL IN A
CONDUCTOR OF UNEVEN RESISTANCE.

Potential, Magnetic.
The magnetic potential at any point of a magnetic field expresses the
work which would be done by the magnetic forces of the field on a
positive unit of magnetism as it moves from that point to an infinite
distance therefrom. The converse applies to a negative unit.

It is the exact analogue of absolute electric potential.

The potential at any point due to a positive pole m at a distance r is
m/r;. that due to a negative pole - m at a distance r' is equal to
-m/r';. that due to both is equal to m/r - m/r' or m(1/r - 1/r').

Like electric potential and potential in general, magnetic potential
while numerically expressing work or energy is neither, although often
defined as such.

432 STANDARD ELECTRICAL DICTIONARY.

Potential, Negative.
The reverse of positive potential. (See Potential, Positive.)

Potential, Positive.
In general the higher potential. Taking the assumed direction of lines
of force, they are assumed to be directed or to move from regions of
positive to regions of negative potential. The copper or carbon plate of
a voltaic battery is at positive potential compared to the zinc plate.

Potential, Unit of Electric.
The arbitrary or conventional potential--or briefly, the potential of a
point in an electric field of force--is, numerically, the number of ergs
of work necessary to bring a unit of electricity up to the point in
question from a region of nominal zero potential--i. e., from the
surface of the earth. (Daniell.) This would give the erg as the unit of
potential.

Potential, Zero.
The potential of the earth is arbitrarily taken as the zero of electric
potential.

The theoretical zero is the potential of a point infinitely distant from
all electrified bodies.

Fig. 272. DIAGRAM OF POTENTIOMETER CONNECTIONS.

Potentiometer.
An arrangement somewhat similar to the Wheatstone Bridge for determining
potential difference, or the electro-motive force of a battery. In
general principle connection is made so that the cell under trial would
send a current in one direction through the galvanometer. Another
battery is connected, and in shunt with its circuit the battery under
trial and its galvanometer are connected, but so that its current is in
opposition. By a graduated wire, like that of a meter bridge, the
potential of the main battery shunt can be varied until no current
passes. This gives the outline of the method only.

433 STANDARD ELECTRICAL DICTIONARY.

In the cut A B is the graduated potentiometer wire through which a
current is passed in the direction of the arrow. E is the battery under
trial, placed in opposition to the other current, with a galvanometer
next it. Under the conditions shown, if the galvanometer showed no
deflection, the E. M. F. of the battery would be to the E. M. F. between
the ends of the potentiometer wire, 1 . . . . .10, as 1.5 the distance
between the points of connection, A and D of the battery circuit, is to
10, the full length of the potentiometer wire.

Poundal.
The British unit of force; the force which acting on a mass of one pound
for one second produces an acceleration of one foot.

Power. Activity;
the rate of activity, of doing work, or of expending energy. The
practical unit of electric power is the volt-ampere or watt, equal to
1E7 ergs per second. The kilowatt, one thousand watts or volt-amperes,
is a frequently adopted unit.

Power, Electric.
As energy is the capacity for doing work, electric energy is represented
by electricity in motion against a resistance. This possesses a species
of inertia, which gives it a species of kinetic energy. To produce such
motion, electro- motive force is required. The product of E. M. F. by
quantity is therefore electric energy. (See Energy, Electric.)

Generally the rate of energy or power is used. Its dimensions are
( ( (M^.5)*(L^.5) ) / T ) * ( ( (M^.5) *(L^1.5) )/( T^2) )
(intensity or current rate) * (electro-motive force or potential)
= (M * (L^2) ) / (T^3),
which are the dimensions of rate of work or activity. The practical unit
of electric rate of energy or activity is the volt-ampere or watt. By
Ohm's law, q. v., we have C = E/R (C = current; E = potential difference
or electro-motive force; R = resistance.) The watt by definition = C*E.
By substitution from Ohm's formula we deduce for it the following
values: ((C^2) * R) and ((E^2) /R). From these three expressions the
relations of electric energy to E.M.F., Resistance, and Current can be
deduced.

Power of Periodic Current.
The rate of energy in a circuit carrying a periodic current. In such a
circuit the electro-motive force travels in advance of the current it
produces on the circuit. Consequently at phases or intervals where,
owing to the alternations of the current, the current is at zero, the
electro-motive force may be quite high. At any time the energy rate is
the product of the electro-motive force by the amperage. To obtain the
power or average rate of energy, the product of the maximum
electro-motive force and maximum current must be divided by two and
multiplied by the cosine of the angle of lag, which is the angle
expressing the difference of phase.

434 STANDARD ELECTRICAL DICTIONARY.

Pressel.
A press-button often contained in a pear-shaped handle, arranged for
attachment to the end of a flexible conductor, so as to hang thereby. By
pressing the button a bell may be rung, or a distant lamp may be
lighted.

Pressure.
Force or stress exerted directly against any surface. Its dimensions are
force/area or ((M*L)/(T^2)) / (L^2) = M/(L* (T^2)).

Pressure, Electric.
Electro-motive force or potential difference; voltage. An expression of
metaphorical nature, as the term is not accurate.

Pressure, Electrification by.
A crystal of Iceland spar (calcium carbonate) pressed between the
fingers becomes positively electrified and remains so for some time.
Other minerals act in a similar way. Dissimilar substances pressed
together and suddenly separated carry off opposite charges. This is
really contact action, not pressure action.

Primary.
A term used to designate the inducing coil in an induction coil or
transformer; it is probably an abbreviation for primary coil.

Primary Battery.
A voltaic cell or battery generating electric energy by direct
consumption of material, and not regenerated by an electrolytic process.

The ordinary voltaic cell or galvanic battery is a primary battery.

Prime. vb.
To impart the first charge to one of the armatures of a Holtz or other
influence machine.

Fig. 273. PRIME CONDUCTOR AND PROOF PLANE.

435 STANDARD ELECTRICAL DICTIONARY.

Prime Conductor.
A metal or metal coated sphere or cylinder or other solid with rounded
ends mounted on insulating supports and used to collect electricity as
generated by a frictional electric machine.

According to whether the prime conductor or the cushions are grounded
positive or negative electricity is taken from the ungrounded part.
Generally the cushions are grounded, and the prime conductor yields
positive electricity.

Probe, Electric.
A surgeon's probe, designed to indicate by the closing of an electric
circuit the presence of a bullet or metallic body in the body of a
patient.

Two insulated wires are carried to the end where their ends are exposed,
still insulated from each other. In probing a wound for a bullet if the
two ends touch it the circuit is closed and a bell rings. If a bone is
touched no such effect is produced. The wires are in circuit with an
electric bell and battery.

Projecting Power of a Magnet.
The power of projecting its lines of force straight out from the poles.
This is really a matter of magnetic power, rather than of shape of the
magnet. In electromagnets the custom was followed by making them long to
get this effect. Such length was really useful in the regard of getting
room for a sufficient number of ampere turns.

436 STANDARD ELECTRICAL DICTIONARY.

Fig. 274. PRONY BRAKE.

Prony Brake.
A device for measuring the power applied to a rotating shaft. It
consists of a clamping device to be applied more or less rigidly to the
shaft or to a pulley upon it. To the clamp is attached a lever carrying
a weight. The cut shows a simple arrangement, the shaft A carries a
pulley B to which the clamp B1 B2 is applied. The nuts C1 C2 are used
for adjustment.

A weight is placed in the pan E attached to the end of the lever D. The
weight and clamp are so adjusted that the lever shall stand horizontally
as shown by the index E. If we call r the radius of the pulley and F the
friction between its surface and the clamp, it is evident that r F, the
moment of resistance to the motion of the pulley, is equal to the weight
multiplied by its lever arm or to W*R, where W indicates the weight and
R the distance of its point of application from the centre of the pulley
or r*F = R*W. The work represented by this friction is equal to the
distance traveled by the surface of the wheel multiplied by the
frictional resistance, or is 2*PI*r*n*F, in which n is the number of
turns per minute. But this is equal to 2*PI*R*W. These data being known,
the power is directly calculated therefrom in terms of weight and feet
per minute.

Proof-plane.
A small conductor, usually disc shaped, carried at the end of an
insulating handle. It is used to collect electricity by contact, from
objects electrostatically charged. The charge it has received is then
measured (see Torsion Balance) or otherwise tested. (See Prime
Conductor.)

Proof-sphere.
A small sphere, coated with gold-leaf or other conductor, and mounted on
an insulated handle. It is used instead of a proof-plane, for testing
bodies whose curvature is small.

Fig. 275. BOX BRIDGE.

437 STANDARD ELECTRICAL DICTIONARY.

Proportionate Arms.
In general terms the arms of a Wheatstone bridge
whose proportion has to be known to complete the measurement. There is a
different system of naming them. Some designate by this title the two
arms in parallel with each other branching at and running from one end
of the bridge to the two galvanometer connections. In the cut of the Box
Bridge, A C and A B are the proportionate arms. The third arm is then
termed the Rheostat arm. (Stewart & Gee.)

Others treat as proportionate arms the two side members of the bridge in
parallel with the unknown resistance and third or rheostat arm.

Synonym--Ratio Arms.

Prostration, Electric.
Too great exposure to the voltaic arc in its more powerful forms causes
symptoms resembling those of sunstroke. The skin is sometimes affected
to such a degree as to come off after a few days. The throat, forehead
and face suffer pains and the eyes are irritated. These effects only
follow exposure to very intense sources of light, or for very long
times.

Protector, Comb.
A lightning arrester, q. v., comprising two toothed plates nearly
touching each other.

Protector, Electric.
A protective device for guarding the human body against destructive or
injurious electric shocks. In one system, Delany's, the wrists and
ankles are encircled by conducting bands which by wires running along
the arms, back and legs are connected. A discharge it is assumed
received by the hands will thus be short circuited around the body and
its vital organs. India rubber gloves and shoe soles have also been
suggested; the gloves are still used to some extent.

Pull.
A switch for closing a circuit when pulled. It is used instead of a push
button, q.v., in exposed situations, as its contacts are better
protected than those of the ordinary push button.

Pump, Geissler.
A form of mercurial air pump. It is used for exhausting Geissler tubes,
incandescent lamp bulbs and similar purposes.

Referring to the cut, A is a reservoir of mercury with flexible tube C
connected to a tube at its bottom, and raised and lowered by a windlass
b, the cord from which passes over a pulley a. When raised the mercury
tends to enter the chamber B, through the tube T. An arrangement of
stopcocks surmounts this chamber, which arrangement is shown on a larger
scale in the three figures X, Y and Z. To fill the bulb B, the cocks are
set in the position Z; n is a two way cock and while it permits the
escape of air below, it cuts off the tube, rising vertically from it.
This tube, d in the full figure connects with a vessel o, pressure gauge
p, and tube c, the latter connecting with the object to be exhausted.
The bulb B being filled, the cock m is closed, giving the position Y and
the vessel A is lowered until it is over 30 inches below B.

438 STANDARD ELECTRICAL DICTIONARY.

This establishes a Torricellian vacuum in B. The cock n is now turned,
giving the position X, when air is at once exhausted from the vessel
connected to C. This process is repeated until full exhaustion is
obtained. In practice the first exhaustion is often effected by a
mechanical pump. By closing the cock on the outlet tube c but little air
need ever find its way to the chambers o and B.

Fig. 276. GEISSLER AIR PUMP.

439 STANDARD ELECTRICAL DICTIONARY.

Pumping.
In incandescent lamps a periodical recurring change in intensity due to
bad running of the dynamos, or in arc lamps to bad feeding of the
carbons.

Fig. 277. SPRENGEL AIR PUMP.

Pump, Sprengel.
A form of mercurial air pump. A simple form is shown in the cut. Mercury
is caused to flow from the funnel A, through c d to a vessel B. A side
connection x leads to the vessel R to be exhausted. As the mercury
passes x it breaks into short columns, and carries air down between
them, in this way exhausting the vessel R. In practice it is more
complicated. It is said to give a better vacuum than the Sprengel pump,
but to be slower in action.

440 STANDARD ELECTRICAL DICTIONARY.

Pump, Swinburne.
A form of mechanical air pump for exhausting incandescent lamp bulbs.
Referring to the cut, A is a bulb on the upper part of a tube G; above A
are two other bulbs C and D. From the upper end a tube runs to the bulb
E. Through the cock L, and tube F connection is made with a mechanical
air pump. The tube H leads to a drying chamber I, and by the tube J
connects with the lamp bulbs or other objects to be exhausted. The tube
G enters the bottle B through an airtight stopper, through which a
second tube with stopcock K passes. In use a vacuum is produced by the
mechanical pumps, exhausting the lamp bulbs to a half inch and drawing
up the mercury in G. The bent neck in the bulb E, acts with the bulb as
a trap to exclude mercury from F. When the mechanical pumps have
produced a vacuum equal to one half inch of mercury, the cock L is
closed and K is opened, and air at high pressure enters. This forces the
mercury up to the vessel D, half filling it. The high pressure is now
removed and the mercury descends. The valve in D closes it as the
mercury falls to the level G. Further air from the lamps enters A, and
by repetition of the ascent of the mercury, is expelled, through D. The
mercury is again lowered, producing a further exhaustion, and the
process is repeated as often as necessary.

Fig. 278. SWINBURNE'S AIR PUMP.

Push-Button.
A switch for closing a circuit by means of pressure applied to a button.
The button is provided with a spring, so that when pushed in and
released it springs back. Thus the circuit is closed only as long as the
button is pressed. The electric connection may be made by pressing
together two flat springs, each connected to one of the wires, or by the
stem of the button going between two springs, not in contact, forcing
them a little apart to secure good contact, and thereby bridging over
the space between them.

441 STANDARD ELECTRICAL DICTIONARY.

Pyro-electricity.
A phenomenon by which certain minerals when warmed acquire electrical
properties. (Ganot.) The mineral tourmaline exhibits it strongly. It was
originally observed in this mineral which was found to first attract and
then to repel hot ashes.

The phenomenon lasts while any change of temperature within certain
limits is taking place. In the case of tourmaline the range is from
about 10º C. (50º F.) to 150º C. (302º F.) Above or below this range it
shows no electrification.

The effect of a changing of temperature is to develop poles, one
positive and the other negative. As the temperature rises one end is
positive and the other negative; as the temperature becomes constant the
polarity disappears; as the temperature falls the poles are reversed.

If a piece of tourmaline excited by pyro-electricity is broken, its
broken ends develop new poles exactly like a magnet when broken.

The following minerals are pyro-electric: Boracite, topaz, prehnite,
zinc silicate, scolezite, axenite. The following compound substances are
also so: Cane sugar, sodium- ammonium racemate and potassium tartrate.

The list might be greatly extended.

The phenomenon can be illustrated by sifting through a cotton sieve upon
the excited crystal, a mixture of red lead and flowers of sulphur. By
the friction of the sifting these become oppositely electrified; the
sulphur adheres to the positively electrified end, and the red lead to
the negatively electrified end. (See Analogous Pole-Antilogous Pole.)

Pyromagnetic Motor.
A motor driven by the alternation of attraction and release of an
armature or other moving part, as such part or a section of it is
rendered more or less paramagnetic by heat.

Thus imagine a cylinder of nickel at the end of a suspension rod, so
mounted that it can swing like a pendulum. A magnet pole is placed to
one side to which it is attracted. A flame is placed so as to heat it
when in contact with the magnet pole. This destroys its paramagnetism
and it swings away from the magnet and out of the flame. It cools,
becomes paramagnetic, and as it swings back is reattracted, to be again
released as it gets hot enough. This constitutes a simple motor.

A rotary motor may be made on the same lines. Nickel is particularly
available as losing its paramagnetic property easily.

442 STANDARD ELECTRICAL DICTIONARY.

Various motors have been constructed on this principle, but none have
attained any practical importance. Owing to the low temperature at which
it loses its paramagnetic properties nickel is the best metal for
paramagnetic motors.

In Edison's motor, between the pole pieces of an electro-magnet a
cylinder made up of a bundle of nickel tubes is mounted, so as to be
free to rotate. A screen is placed so as to close or obstruct the tubes
farthest from the poles. On passing hot air or products of combustion of
a fire or gas flame through the tubes, the unscreened ones are heated
most and lose their paramagnetism. The screened tubes are then attracted
and the armature rotates, bringing other tubes under the screen, which
is stationary. Then the attracted tubes are heated while the others
cool, and a continuous rotation is the result.

Fig. 279. EDISON'S PYROMAGNETIC MOTOR.

Pyromagnetic Generator.
A current generator producing electric energy directly from thermal
energy by pyromagnetism.

Edison's pyromagnetic generator has eight electro-magnets, lying on
eight radii of a circle, their poles facing inward and their yokes
vertical. Only two are shown in the cut. On a horizontal iron disc are
mounted eight vertical rolls of corrugated nickel representing
armatures. On each armature a coil of wire, insulated from the nickel by
asbestus is wound. The coils are all in series, and have eight
connections with a commutator as in a drum armature. There are two main
divisions to the commutator. Each connects with an insulated collecting
ring, and the commutator and collecting rings are mounted on a spindle
rotated by power. Below the circle of vertical coils is a horizontal
screen, mounted on the spindle and rotating with it.

A source of heat, or a coal stove is directly below the machine and its
hot products of combustion pass up through the coils, some of which are
screened by the rotating screen. The effect is that the coils are
subjecting to induction owing to the change in permeability of the
nickel cores, according as they are heated, or as they cool when the
screen is interposed. The two commutator segments are in constant
relation to the screen, and current is collected therefrom and by the
collecting rings is taken to the outside circuit.

443 STANDARD ELECTRICAL DICTIONARY.

Pyromagnetism.
The development of new magnetic properties or alteration of magnetic
sensibility in a body by heat. Nickel and iron are much affected as
regards their paramagnetic power by rise of temperature.

Fig. 280. PYROMAGNETIC GENERATOR.

Pyrometer, Siemens' Electric.
An instrument for measuring high temperatures by the variations in
electric resistance in a platinum wire exposed to the heat which is to
be measured.

443 STANDARD ELECTRICAL DICTIONARY.

Q.
Symbol for electric quantity.

Quad.
(a) A contraction for quadrant, used as the unit of inductance; the henry.

(b) A contraction for quadruplex in telegraphy.

Quadrant.
A length equal to an approximate earth quadrant, equal to 1E9
centimeters. It has been used as the name for the unit of inductance,
the henry, q. v.

Synonym--Standard Quadrant.

444 STANDARD ELECTRICAL DICTIONARY.

Quadrant, Legal.
The accepted length of the quadrant of the earth, 9.978E8 instead of 1E9
centimeters; or to 9,978 kilometers instead of 10,000 kilometers.

Quadrature.
Waves or periodic motions the angle of lag of one of which, with
reference to one in advance of it, is 90°, are said to be in quadrature
with each other.

Qualitative.
Involving the determination only of the presence or absence of a
substance or condition, without regard to quantity. Thus a compass held
near a wire might determine qualitatively whether a current was passing
through the wire, but would not be sufficient to determine its quantity.
(See Quantitative.)

Quality of Sound.
The distinguishing characteristic of a sound other than its pitch; the
timbre.

It is due to the presence with the main or fundamental sound of other
minor sounds called overtones, the fundamental note prevailing and the
other ones being superimposed upon it. The human voice is very rich in
overtones; the telephone reproduces these, thus giving the personal
peculiarities of every voice.

Synonym--Timbre.

Quantitative.
Involving the determination of quantities. Thus a simple test would
indicate that a current was passing through a wire. This would be a
qualitative test. If by proper apparatus the exact intensity of the
current was determined, it would be a quantitative determination. (See
Qualitative.)

Quantity.
This term is used to express arrangements of electrical connections for
giving the largest quantity of current, as a quantity armature, meaning
one wound for low resistance.

A battery is connected in quantity when the cells are all in parallel.
It is the arrangement giving the largest current through a very small
external resistance.

The term is now virtually obsolete (Daniell); "in surface," "in
parallel," or "in multiple arc" is used.

Quantity, Electric.
Electricity may be measured as if it were a compressible gas, by
determining the potential it produces when stored in a defined
recipient. In this way the conception of a species of quantity is
reached. It is also measured as the quantity of current passed by a
conductor.

Thus a body whose surface is more or less highly charged with
electricity, is said to hold a greater or less quantity of electricity.

It may be defined in electrostatic or electro-magnetic terms. (See
Quantity, Electrostatic--Quantity, Electro-magnetic.)

445 STANDARD ELECTRICAL DICTIONARY.

Quantity.
Electro-magnetic. Quantity is determined electro-magnetically by the
measurement of current intensity for a second of time: its dimensions
are therefore given by multiplying intensity or current strength by
time. The dimensions of intensity are
( (M^.5) * (L^.5) ) / T
therefore the dimensions of electro-magnetic quantity are
( ( (M^.5) * (L^.5) ) / T ) * T = ( (M^.5) * (L^.5) )

Quantity, Electro-magnetic, Practical Unit of.
The quantity of electricity passed by a unit current in unit time; the
quantity passed by one ampere in one second; the coulomb.

It is equal to 3E9 electrostatic absolute units of quantity and to 0.1
of the electro- magnetic absolute unit of quantity.

One coulomb is represented by the deposit of
.00111815 gram, or .017253 grain of silver,
.00032959 gram, or .005804 grain of copper,
.0003392 gram, or .005232 grain of zinc.

If water is decomposed by a current each coulomb is represented by the
cubic centimeters of the mixed gases (hydrogen and oxygen) given by the
following formula.
( 0.1738 * 76 * (273 + Cº ) ) / ( h * 273 )
in which Cº is the temperature of the mixed gases in degree centigrade
and h is the
pressure in centimeters of mercury column; or by
( 0.01058 * 30 (491 + Fº - 32) ) / (h * 491 )
for degrees Fahrenheit and inches of barometer.

Quantity, Electrostatic.
Quantity is determined electro-statically by the repulsion a charge of
given quantity exercises upon an identical charge at a known distance.
The force evidently varies with the product of the two quantities, and
by the law of radiant forces also inversely with the square of the
distance. The dimensions given by these considerations is Q * Q/(L*L).
This is the force of repulsion. The dimensions of a force are
(M * L) /(T^2). Equating these two expressions we have:
(Q^2)/(L^2) = (M*L)/(T^2)
or
Q = ((M^.5)*(L^1.5)) / T
which are the dimensions of electrostatic quantity.

Quantity, Meter.
An electric meter for determining the quantity of electricity which
passes through it, expressible in coulombs or ampere hours. All
commercial meters are quantity meters.

446 STANDARD ELECTRICAL DICTIONARY.

Quartz.
A mineral, silica, SiO2. It has recently been used by C. V. Boys and
since by others in the making of filaments for torsion suspensions. The
mineral is melted, while attached to an arrow or other projectile. It is
touched to another piece of quartz or some substance to which it adheres
and the arrow is fired off from the bow. A very fine filament of
surpassingly good qualities for galvanometer suspension filaments is
produced.

As a dielectric it is remarkable in possessing but one-ninth the
residual capacity of glass.

Quicking.
The amalgamating of a surface of a metallic object before silver
plating. It secures better adhesion of the deposit. It is executed by
dipping the article into a solution of a salt of mercury. A solution of
mercuric nitrate 1 part, in water 100 parts, both by weight, is used.

446 STANDARD ELECTRICAL DICTIONARY.

R.
(a) Abbreviation and symbol for Reamur, as 10º R., meaning 10º by the
Reamur thermometer. (See Reamur Scale.)

(b) Symbol for resistance, as in the expression of Ohm's Law C=E/R.
(rho, Greek r) Symbol for specific resistance.

Racing of Motors.
The rapid acceleration of speed of a motor when the load upon it is
removed. It is quickly checked by counter-electro-motive force. (See
Motor, Electric.)

Radian.
The angle whose arc is equal in length to the radius; the unit angle.

Radiant Energy.
Energy, generally existing in the luminiferous ether, kinetic and
exercised in wave transmission, and rendered sensible by conversion of
its energy into some other form of energy, such as thermal energy.

If the ether waves are sufficiently short and not too short, they
directly affect the optic nerve and are known as light waves; they may
be so short as to be inappreciable by the eye, yet possess the power of
determining chemical change, when they are known as actinic waves; they
may be also so long as to be inappreciable by the eye, when they may be
heat-producing waves, or obscure waves.

Other forms of energy may be radiant, as sound energy dispersed by the
air, and gravitational energy, whose connection with the ether has not
yet been demonstrated.

Radiation.
The traveling or motion of ether waves through space.

Radicals.
A portion of a molecule, possessing a free bond and hence free to
combine directly. A radical never can exist alone, but is only
hypothetical. An atom is a simple radical, an unsaturated group of atoms
is a compound radical.

447 STANDARD ELECTRICAL DICTIONARY.

Radiometer.
An instrument consisting of four vanes poised on an axis so as to be
free to rotate, and contained in a sealed glass vessel almost perfectly
exhausted. The vanes of mica are blackened on one side.

On exposure to light or a source of heat (ether waves) the vanes rotate.
The rotation is due to the beating back and forth of air molecules from
the surface of the vanes to the inner surface of the glass globe.

Radiometer, Electric.
A radiometer in which the motion of the molecules of air necessary for
rotation of the vane is produced by electrification and not by heating.

Radio-micrometer.
An instrument for detecting radiant energy of heat or light form. It
consists of a minute thermopile with its terminals connected by a wire,
the whole suspended between the poles of a magnet. A minute quantity of
heat produces a current in the thermopile circuit, which, reacted on by
the field, produces a deflection. A convex mirror reflecting light is
attached so as to move with the thermopile. The instrument is of
extraordinary sensitiveness. It responds to .5E-6 of a degree Centigrade
or about 1E-6 degree Fahrenheit.

Radiophony.
The production of sound by intermittent action of a beam of light upon a
body. With possibly a few exceptions all matter may produce sound by
radiophouy.

Range Finder.
An apparatus for use on shipboard to determine the distance of another
ship or object. It is designed for ships of war, to give the range of
fire, so as to set the guns at the proper elevation. The general
principle involved is the use of the length of the ship if possible, if
not of its width, as a base line. Two telescopes are trained upon the
object and kept trained continuously thereon. The following describes
the Fiske range finder.

The range finder comprises two fairly powerful telescopes, each mounted
on a standard, which can be rotated round a vertical axis, corresponding
with the center of the large disc shown in the engraving. One-half of
the edge of this disc is graduated to 900 on either side of a zero
point, and below the graduation is fixed a length of platinum silver
wire. This wire only extends to a distance of 81.10 on either side of
zero, and is intended to form two arms of a Wheatstone bridge. The
sliding contact is carried by the same arm as the telescope standards,
so that it moves with the telescope. The two instruments are mounted at
a known distance apart on the ship, as shown diagrammatically in the
cut. Here A and B are the centers of the two discs, C and D the arms
carrying the telescopes, and E and F the platinum silver wires. Suppose
the object is at T, such that A B T is a right angle, then
AT=AB/sin(ATB).

448 STANDARD ELECTRICAL DICTIONARY.

If the two sectors are coupled up as shown, with a battery, h, and a
galvanometer, by the wires, a b and c d, then since the arm, e, on being
aligned on the object takes the position c1 while d remains at zero, the
Wheatstone bridge formed by these segments and their connections will be
out of balance, and a current will flow through the galvanometer, which
may be so graduated as to give the range by direct reading, since the
current through it will increase with the angle A T B.

Fig. 281. RANGE FINDER.

In general, however, the angle A B T will not be a right angle, but some
other angle. In this case AT = AB / sin(A T B) * sin( A B T), and hence
it will only be necessary to multiply the range reading on the
galvanometer by the sine of the angle A B T, which can be read directly
by the observer at B. This multiplication is not difficult, but by
suitably arranging his electrical appliances Lieutenant Fiske has
succeeded in getting rid of it, so that the reading of the galvanometer
always gives the range by direct reading, no matter what the angle at B
may be. To explain this, consider the two telescopes shown in the cut in
the positions C and D; the whole current then has a certain resistance.

449 STANDARD ELECTRICAL DICTIONARY.

Next suppose them, still remaining parallel, in the positions C1 and D1.
The total resistance of the circuit is now less than before, and hence
if C1, one of the telescopes, is moved out of parallel to the other,
through a certain angle, the current through the galvanometer will be
greater than if it were moved through an equal angle out of a parallel
when the telescopes were in the positions C and D. The range indicated
is, therefore, decreased, and by properly proportioning the various
parts it is found that the range can always be read direct from the
galvanometer, or in other words the multiplication of A B/sin( A T B )
by sin( A B T ) is to all intents and purposes performed automatically.
There is, it is true, a slight theoretical error; but by using a small
storage battery and making the contents carefully it is said to be
inappreciable. Each telescope is fitted with a telephone receiver and
transmitter, so that both observers can without difficulty decide on
what point to align their telescopes. It will be seen that it is
necessary that the lines of sight of two telescopes should be parallel
when the galvanometer indicates no current. It has been proposed to
accomplish this by sighting both telescopes on a star near the horizon,
which being practically an infinite distance away insures the
parallelism of the lines of sight.

Rate Governor.
An apparatus for securing a fixed rate of vibration of a vibrating reed.
It is applied in simultaneous telegraphy and telephoning over one wire.
The principle is that of the regular make and break mechanism, with the
feature that the contact is maintained during exactly one-half of the
swing of the reed. The contact exists during the farthest half of the
swing of the reed away from the attracting pole.

Fig. 282. LANGDON DAVIRS' RATE GOVERNOR.

In the left hand figure of the cut, K is the key for closing the
circuit. A is the base for attachment of the reed. V is the
contact-spring limited in its play to the right by the screw S. C is the
actuating magnet. By tracing the movements of the reed, shown on an
exaggerated scale in the three right hand figures, it will be seen that
the reed is in electric contact with the spring during about one-half
its movement. The time of this connection is adjustable by the screw S.

Synonym--Langdon Davies' Rate Governor or Phonophone.

450 STANDARD ELECTRICAL DICTIONARY.

Ray, Electric. Raia torpedo.
The torpedo, a fish having the same power of giving electric shocks as
that possessed by the electric eel, q. v. (See also Animal Electricity.)

Fig. 283. TORPEDO OR ELECTRIC RAY

Reaction of Dynamo, Field and Armature.
A principle of the dynamo current generator, discovered by Soren Hjorth
of Denmark.

When the armature is first rotated it moves in a field due to the
residual magnetism of the field magnet core. This field is very weak,
and a slight current only is produced. This passing in part or in whole
through the field magnet cores slightly strengthens the field, whose
increased strength reacts on the armature increasing its current, which
again strengthens the field. In this way the current very soon reaches
its full strength as due to its speed of rotation.

The operation is sometimes termed building up.

Sometimes, when there is but a trace of residual magnetism, it is very
hard to start a dynamo.

Reading Telescope.
A telescope for reading the deflections of a reflecting galvanometer.

A long horizontal scale is mounted at a distance from the galvanometer
and directly below or above the centre of the scale a telescope is
mounted. The telescope is so directed that the mirror of the
galvanometer is in its field of view, and the relative positions of
mirror, scale and telescope are such that the image of the scale in the
galvanometer mirror is seen by the observer looking through the
telescope.

Under these conditions it is obvious that the graduation of the scale
reflected by the mirror corresponds to the deflection of the
galvanometer needle.

The scale may be straight or curved, with the galvanometer in the latter
case, at its centre of curvature.

Reamur Scale.
A thermometer scale in use in some countries of Continental Europe. The
temperature of melting ice is 0°; the temperature of condensing steam
is 80°; the degrees are all equal in length. For conversion to
centigrade degrees multiply degrees Reamur by 5/4. For conversion to
Fahrenheit degrees multiply by 9/4 and add 32 if above 0° R., and if
below subtract 32. Its symbol is R., as 10° R.

451 STANDARD ELECTRICAL DICTIONARY.

Recalescence.
A phenomenon occurring during the cooling of a mass of steel, when it
suddenly emits heat and grows more luminous for an instant. It is a
phase of latent heat, and marks apparently the transition from a
non-magnetizable to a magnetiz able condition.

Receiver.
In telephony and telegraphy, an instrument for receiving a message as
distinguished from one used for sending or transmitting one.

Thus the Bell telephone applied to the ear is a receiver, while the
microphone which is spoken into or against is the transmitter.

Receiver, Harmonic.
A receiver including an electro-magnet whose armature is an elastic
steel reed, vibrating to a particular note. Such a reed responds to a
series of impulses succeeding each other with the exact frequency of its
own natural vibrations, and does not respond to any other rapid series
of impulses. (See Telegraph Harmonic.)

Reciprocal.
The reciprocal of a number is the quotient obtained by dividing one by
the number. Thus the reciprocal of 8 is 1/8.

Applied to fractions the above operation is carried out by simply
inverting the fraction. Thus the reciprocal of 3/4 is 4/3 or 1-1/3.

Record, Telephone.
Attempts have been made to produce a record from the vibrations of a
telephone disc, which could be interpreted by phonograph or otherwise.

Fig. 284. MORSE RECORDER OR EMBOSSER.

452 STANDARD ELECTRICAL DICTIONARY.

Recorder, Morse.
A telegraphic receiving apparatus for recording on a strip of paper the
dots and lines forming Morse characters as received over a telegraph
line. Its general features are as follows:

A riband or strip of paper is drawn over a roller which is slightly
indented around its centre. A stylus or blunt point carried by a
vibrating arm nearly touches the paper. The arm normally is motionless
and makes no mark on the paper. An armature is carried by the arm and an
electro-magnet faces the armature. When a current is passed through the
magnet the armature is attracted and the stylus is forced against the
paper, depressing it into the groove, thus producing a mark. When the
current ceases the stylus is drawn back by a spring.

Fig. 285. INKING ROLLER MECHANISM OF MORSE RECORDER.

In some instruments a small inking roller takes the place of the stylus,
and the roller is smooth. The cut, Fig. 285, shows the plan view of the
ink-roller mechanism. J is the roller, L is the ink well, Cl is the arm
by which it is raised or lowered by the electro-magnet, as in the
embosser. S S is the frame of the instrument, and B the arbor to which
the arm carrying the armature is secured, projecting to the right. A
spring is arranged to rub against the edge of the inking roller and
remove the ink from it.

The paper is fed through the apparatus by clockwork. At the present day
sound reading has almost entirely replaced the sight reading of the
recorder.

Recorder, Siphon.
A recording apparatus in which the inked marks are made on a strip of
paper, the ink being supplied by a siphon terminating in a capillary
orifice.

In the cut N S represents the poles of a powerful electro-magnet. A
rectangular coil bb of wire is suspended between the coils. A stationary
iron core a intensifies the field. The suspension wire f f 1 has its
tension adjusted at h. This wire acts as conductor for the current.

453 STANDARD ELECTRICAL DICTIONARY.

The current is sent in one or the other direction or is cut off in
practice to produce the desired oscillations of the coil b b. A glass
siphon n l works upon a vertical axis l. One end l is immersed in an ink
well m. Its longer end n touches a riband of paper o o. The thread k
attached to one side of the coil pulls the siphon back and forth
according to the direction of current going through the electro-magnet
cores. A spiral spring adjusted by a hand-screw controls the siphon. In
operation the siphon is drawn back and forth producing a zigzag line.
The upward marks represent dots, the downward ones dashes. Thus the
Telegraphic Code can be transmitted on it. To cause the ink to issue
properly, electrification by a static machine has been used, when the
stylus does not actually touch the paper, but the ink is ejected in a
series of dots.

Fig. 286. SIPHON RECORDER.

Reducteur for Ammeter.
A resistance arranged as a shunt to diminish the total current passing
through an ammeter. It is analogous to a galvanometer shunt. (See
Multiplying Power of Shunt.)

Reducteur for Voltmeter.
A resistance coil connected in series with a Voltmeter to diminish the
current passing through it. Its resistance being known in terms of the
resistance of the voltmeter it increases the range of the instrument so
that its readings may cover double or more than double their normal
range.

Reduction of Ores, Electric.
Treatment of ores by the electric furnace (see Furnace, Electric.) The
ore mixed with carbon and flux is melted by the combined arc and
incandescent effects of the current and the metal separates. In another
type the metal is brought into a fusible compound which is electrolyzed
while fused in a crucible. Finally processes in which a solution of a
salt of the metal is obtained, from which the metal is obtained by
electrolysis, may be included. Aluminum is the metal to whose extraction
the first described processes are applied.

454 STANDARD ELECTRICAL DICTIONARY.

Refraction, Electric Double.
Double refraction induced in some materials by the action of either an
electrostatic, magnetic or an electro-magnetic field.

The intensity or degree of refracting power is proportional to the
square of the strength of field.

Refreshing Action.
In electro-therapeutics the restoration of strength or of nerve force by
the use of voltaic alternatives, q. v.

Region, Extra-polar.
In electro-therapeutics the area or region of the body remote from the
therapeutic electrode.

Region, Polar.
In electro-therapeutics the area or region of the body near the
therapeutic electrode.

Register, Electric.
There are various kinds of electric registers, for registering the
movements of watchmen and other service. Contact or press buttons may be
distributed through a factory. Each one is connected so that when the
circuit is closed thereby a mark is produced by the depression of a
pencil upon a sheet or disc of paper by electro-magnetic mechanism. The
paper is moved by clockwork, and is graduated into hours. For each
push-button a special mark may be made on the paper. The watchman is
required to press the button at specified times. This indicates his
movements on the paper, and acts as a time detector to show whether he
has been attending to his duty.

Register, Telegraphic.
A term often applied to telegraph recorders, instruments for producing
on paper the characters of the Morse or other alphabet.

Regulation, Constant Current.
The regulation of a dynamo so that it shall give a constant current
against any resistance in the outer circuits, within practical limits.
It is carried out in direct current machines generally by independent
regulators embodying a controlling coil with plunger or some equivalent
electro-magnetic device inserted in the main circuit and necessarily of
low resistance. In some regulators the work of moving the regulator is
executed mechanically, but under electrical control; in others the
entire work is done by the current.

A typical regulator or governor (Golden's) of the first class comprises
two driven friction wheels between which is a driving friction wheel,
which can engage with one driven wheel only at once. It is brought into
engagement with one or the other by a solenoid and plunger.

455 STANDARD ELECTRICAL DICTIONARY.

As it touches one wheel it turns it in one direction. This moves a
sliding contact in one direction so as to increase a resistance. This
corresponds to a motion of the plunger in one direction. As the driving
wheel moves in the opposite direction by a reverse action it diminishes
the resistance. Thus the increase and decrease of resistance correspond
to opposite movements of the solenoid plunger, and consequently to
opposite variations in the current. The whole is so adjusted that the
variations in resistance maintain a constant amperage. The resistance is
in the exciting circuit of the dynamo.

In Brush's regulator, which is purely mechanical, a series dynamo is
made to give a constant current by introducing across the field magnets
a shunt of variable resistance, whose resistance is changed by an
electro-magnet, whose coils are in circuit with the main current. Carbon
resistance discs are used which the electro-magnet by its attraction for
its armature, presses with varying intensity. This alters the
resistance, decreasing it as the current increases and the reverse. As
the connection is in shunt this action goes to maintain a constant
current.

Regulation, Constant Potential.
The regulation of constant potential dynamos is executed on the same
lines as that of constant current dynamos. If done by a controlling
coil, it must for constant potential regulation be wound with fine wire
and connected as a shunt for some part of the machine.

Regulation of Dynamos.
The regulation of dynamos so that they shall maintain a constant
potential difference in the leads of their circuit for multiple arc
systems or shall deliver a constant current in series systems. Hence two
different systems of regulation are required, (a) constant potential
regulation--(b) constant current regulation. The first named is by far
the more important, as it concerns multiple arc lighting, which is the
system universally used for incandescent lighting.

S. P. Thompson thus summarizes the methods of governing or regulating
dynamos. Premising that alteration of the magnetic flux is the almost
universal way of control, it can be done in two ways; first, by varying
the excitation or ampere turns of the field, and second by varying the
reluctance of the magnetic circuit. The excitation or magnetic flux may
be varied

(a) by hand, with the aid of rheostats and commutators in the exciting
circuit;

(b) automatically, by governors, taking the place of the hand;

(c) by compound windings. The magnetic circuit may have its reluctance
caused to vary in several ways;

(d) by moving the pole pieces nearer to or further from the armature;

(e) by opening or closing some gap in the magnetic circuit (field-magnet
core);

(f) by drawing the armature endways from between the pole pieces;

(g) by shunting some of the magnetic lines away from the armature by a
magnetic shunt.

The latter magnetic circuit methods d, e, f, and g, have never met with
much success except on small machines or motors. Method e is adopted in
the Edison motor, the yoke being withdrawn or brought nearer the cores
of the coils. (See Regulation, Constant Current-Regulation, constant
Potential.)

456 STANDARD ELECTRICAL DICTIONARY.

Reguline. adj.
Having the characteristics of a piece of metal, being flexible,
adherent, continuous, and coherent. Applied to electrolytic deposits.

Relative.
Indicating the relation between two or more things without reference to
absolute value of any one of them. Thus one lamp may be of relatively
double resistance compared to another, but this states nothing of the
resistance in ohms of either lamp.

Relay.
A receiving instrument which moves in accordance with impulses of
currents received, and in so moving opens and closes a local circuit,
which circuit may include as powerful a battery as required or
desirable, while the relay may be on the other hand so delicate as to
work with a very weak current.

Fig. 287. RELAY.

The typical relay includes an electro-magnet and armature. To the latter
an arm is attached and the lower end of the arm works in pivots. As the
armature is attracted the arm swings towards the magnet. When the
current is cut off, the armature and arm are drawn back by a spring.
When the arm swings towards the magnet its upper end touching a contact
screw closes the local circuit. When it swings back it comes in contact
with a second screw, with insulated point, and opens the circuit as it
leaves the first named screw.

One terminal connects with the arm through the pivots and frame. The
other connects with the contact screw through the frame carrying it.

Synonym--Relay Magnet.

457 STANDARD ELECTRICAL DICTIONARY.

Relay Bells.
Bells connected by relay connection to a main line for acoustic
telegraphy. A stroke on one bell indicates a dot and on the other a
dash. The system is now nearly extinct.

Relay, Box-sounding.
A relay which is surrounded by or mounted on a resonator or wooden box
of such proportions and size as to reinforce the sound. This enables a
relay to act as a sounder, its weak sounds being virtually magnified so
as to be audible.

Relay Connection.
A connection used in telegraphy, including a local battery, with a short
circuit normally open, but closed by a switch and a sounder or other
appliance. The latter is made very sensitive so as to be worked by a
feeble current, and is connected to the main line. A very slight current
closes the switch and the local battery comes into operation to work a
sounder, etc. When the current ceases on the main line the switch opens
and throws the local battery out of action. The switch is termed a
relay, q. v. A long main line may thus produce strong effects at distant
stations, the intensity of action depending on the local battery.

Fig. 288. RELAY OR LOCAL CIRCUIT.

Relay, Differential.
A relay containing two coils wound differentially, and of the same
number of turns and resistance. If two equal currents pass through the
coils they counteract each other and no action takes place. If there is
a difference in the currents the relay acts as one coil preponderates.
The coils may be wound for uneven currents with different resistance and
number of turns.

Relay, Microphone.
A relay connection applied to a telephone circuit. It consists of a
microphone mounted in front of the diaphragm of a telephone receiver. In
circuit with the microphone is a battery and second telephone receiver.
The microphone is supposed to intensify the sounds of the first
telephone.

458 STANDARD ELECTRICAL DICTIONARY.

Relay, Polarized.
A relay whose armature is of steel, and polarized or permanently
magnetized, or in which a permanent magnet is used as the basis for the
electro-magnets. In the relay shown in the cut the coils shown are
mounted on cores carried on the end of a powerful bent permanent magnet.
Thus when no current passes their upper poles are both of the same sign,
and the horizontally vibrating tongue is held by the magnetic attraction
against one or the other pole piece. If a current is sent through the
electro-magnet it gives opposite polarity to the two polar extensions.
As the end of the vibrating tongue is of polarity determined by the
permanent magnet it is attracted to one pole and repelled from the
other. On cessation of current it remains attached by the permanent
magnetism. If now a current is sent in the opposite direction the two
poles again acquire opposite polarity, the reverse of the former, and
the tongue flies across to the opposite side. On cessation of current it
remains attached as before by the permanent magnetism.

In its movements to and fro the relay tongue opens and closes a contact,
so as to work a sounder or other apparatus. The polarized relay is of
high sensibility, and requires little or no change of adjustment.

Fig. 288. POLARIZED RELAY

Reluctance.
In a magnetic circuit or portion thereof, the resistance offered to the
flow of lines of force. The magnetic circuit as has already been stated
is treated like an electric circuit, and in it reluctance occupies the
place of resistance in the electric circuit. It is the reciprocal of
permeance. S. P. Thompson expresses the law thus:

Total number of magnetic lines = (magneto-motive force) / (magnetic
reluctance)

Synonyms--Magnetic Reluctance-Magnetic Resistance.

Reluctance, Unit of.
The reluctance of a circuit through which unit magnetizing power
(magneto-motive force) can produce a unit of induction or one line of
force. This value is very high; the reluctance of ordinary magnetic
circuits ranges from 1E-5 to 1E-8 unit of reluctance.

Reluctivity.
Specific reluctance; the reluctance of a cube of material whose edge
measures one centimeter in length. It is a quality bearing the same
relation to reluctance that permeability does to permeance.

It is defined as the reciprocal of magnetic permeability. (Kenelly.) If
plotted as a curve for different values of the magnetizing force it is
found to be nearly a straight line, a linear function of the magnetizing
force, H with the equation a + b H. Reluctivity is the property of a
substance; reluctance is the property of a circuit.

459 STANDARD ELECTRICAL DICTIONARY.

Remanence.
The residual magnetism left after magnetic induction, expressed in lines
of force per square centimeter.

Repeater.
In telegraphy an instrument for repeating the signals through a second
line. It is virtually a relay which is operated by the sender, and which
in turn operates the rest of the main line, being situated itself at
about the middle point of the distance covered. In the simpler forms of
repeater two relays are used, one for transmission in one direction the
other for transmission in the other. An attendant switches one or the
other in as required.

Thus a common relay is virtually a repeater for its local circuit. If
such a relay is placed half way down a line, and if the line beyond it
is connected as its local, it becomes a repeater.

Some forms of repeaters are automatic, and repeat both ways without the
need of an attendant.

It is the practice to somewhat prolong the signals sent through a
repeater.

Replenisher, Sir William Thomson's.
A static accumulating influence machine contained in Thomson's quadrant
electrometer and used to change the quadrants. The cut shows the
horizontal section and construction of the apparatus.

It contains two gilt brass inductors A B, and two eccentric sectors or
carriers, C, D, which are mounted on an ebonite spindle, which is spun
around by the fingers. The springs s s1 connect each with its inductor;
the springs S S1 connect only each other, and touch the sectors as they
turn around.

One of the inductors may be always assumed to be of slightly higher
potential than that of the other one. When the carriers are in contact
with the springs S S1 they are each charged by induction with
electricity opposite in sign to that of the nearest quadrant. As they
leave the springs S S1 in their rotation, they next touch the springs s
s1, but of the recently opposite inductor. They share each a portion of
its charge with the inductors building up their charges. The action is
repeated over and over again as they rotate.

Fig. 289. DIAGRAM OF THOMSON'S REPLENISHER.

Fig. 290. THOMSON'S REPLENISHER.

460 STANDARD ELECTRICAL DICTIONARY.

Reservoir, Common.
A term applied to the earth, because all electrified bodies discharge
into it if connected thereto.

Residual Atmosphere.
The air left in a receiver after exhaustion by an air pump. The
quantity, where good air pumps are used, is very minute.

Residue, Electric.
The residual charge of a condenser. (See Charge, Residual.)

Resin.
(a) The product obtained by non-destructive distillation of the juice of
the pitch pine. It is the solid residue left after the turpentine has
been evaporated or distilled. It is a mixture of abietic acid C44 H64 O5
and pinic acid C20 H30 O2. It is an insulator; its specific inductive
capacity is 2.55. (Baltzmann.)

Synonyms--Colophony--Rosin.

(b) The name is also generally applied to similar substances obtained
from the sap of other trees; thus shellac is a resin. The resins are a
family of vegetable products; the solid portions of the sap of certain
trees. Common resin, lac, dragons blood, are examples. They are all
dielectrics and sources of resinous or negative electricity when rubbed
with cotton, flannel, or silk. (See Electrostatic Series.)

461 STANDARD ELECTRICAL DICTIONARY.

Resinous Electricity.
Negative electricity; the electricity produced upon the surface of a
resinous body by rubbing it; such a body is shellac or sealing wax;
flannel and other substances may be used as the rubbing material. (See
Electrostatic Series.)

Resistance.
(a) The quality of an electric conductor, in virtue of which it opposes
the passage of an electric current, causing the disappearance of
electro-motive force if a current passes through it, and converting
electric energy into heat energy in the passage of a current through it.
If a current passes through a conductor of uniform resistance there is a
uniform fall of potential all along its length. If of uneven resistance
the fall in potential varies with the resistance. (See Potential, Fall
of.)

The fall of potential is thus expressed by Daniell. "In a conductor, say
a wire, along which a current is steadily and uniformly passing, there
is no internal accumulation of electricity, no density of internal
distribution; there is, on the other hand, an unequally distributed
charge of electricity on the surface of the wire, which results in a
potential diminishing within the wire from one end of the wire to the
other."

Resistance varies inversely with the cross section of a cylindrical or
prismatic conductor, in general with the average cross-section of any
conductor, and in the same sense directly with its true or average or
virtual length. It varies for different substances, and for different
conditions as of temperature and pressure for the same substance. A rise
of temperature in metals increases the resistance, in some bad
conductors a rise of temperature decreases the resistance.

462 STANDARD ELECTRICAL DICTIONARY.

Approximately, with the exception of iron and mercury, the resistance of
a metallic conductor varies with the absolute temperature. This is very
roughly approximate.

Except for resistance energy would not be expended in maintaining a
current through a circuit. The resistance of a conductor may be supposed
to have its seat and cause in the jumps from molecule to molecule, which
the current has to take in going through it. If so a current confined to
a molecule would, if once started, persist because there would be no
resistance in a molecule. Hence on this theory the Ampérian currents
(see Magnetism, Ampere's Theory of) would require no energy for their
maintenance and Ampére's theory would become a possible truth.

When metals melt their resistance suddenly increases.

Light rays falling on some substances, notably selenium, q. v., vary the
resistance.

Longitudinal stretching of a conductor decreases it, it increases with
longitudinal compression, and increases in iron and diminishes in tin
and zinc when a transverse stress tends to widen the conductor.

(b) The term resistance is used to express any object or conductor used
in circuit to develop resistance.

Resistance, Apparent.
Impedance; the virtual resistance of a circuit including the spurious
resistance due to counter-electromotive force. It may be made up of true
resistance and partly of an inductive reaction, as it represents the net
factor, the entire obstruction to the passage of a current, and not
merely a superadded resistance or counter-electro-motive force.

Synonym--Impedance.

Resistance, Asymmetrical.
Resistance which varies in amount in different directions through a
conductor. It implies a compound or composite conductor such as the
human system. The presence of counter-electro-motive force in different
parts of a conductor may bring about asymmetrical resistance.

Resistance, B. A. Unit of.
The British Association Ohm. (See Ohm, B. A.)

463 STANDARD ELECTRICAL DICTIONARY.

Resistance Box.
A box filled with resistance coils. The coils are connected in series so
that a circuit including any given number has their aggregate resistance
added to its own. The terminals of consecutive coils are connected to
short blocks of brass which are secured to the top of the box, lying
flatwise upon it, nearly but not quite in contact with each other. Plugs
of brass are supplied which can go in between pairs of blocks, which
have a pair of grooves reamed out to receive them. Such plugs short
circuit the coil below them when in position. The cut shows how such
coils are connected and the use of plugs to short circuit them. The
diagram shows the top of a Wheatstone bridge, q. v., resistance box with
connections for determining resistances.

Fig. 291. RESISTANCE BOX.

Resistance Box, Sliding.
A resistance box whose coils are set in a circle. Two metal arms with
handles are pivoted at the centre of the circle and by moving them
around they make and break contacts so as to throw the coils in and out
of circuit. The object is to permit an operator to adjust resistance
without looking at the box--an essential in duplex telegraphy.

Resistance, Breguet Unit of.
The same in origin as the Digney Unit. (See Resistance, Digney Unit of.)

It is equal to 9.652 Legal Ohms.

Resistance, Carbon.
A resistance, a substitute for a resistance coil; it is made of carbon,
and is of various construction. In the Brush dynamo regulator a set of
four vertical piles of plates of retort carbon, q. v., is used as a
resistance, whose resistance is made to vary by changing the pressure.
This pressure automatically increases as the current strength increases,
thus reducing the resistance.

464 STANDARD ELECTRICAL DICTIONARY.

Resistance Coil, Standard.
A standard or resistance issued by the Electric Standard Committee of
Great Britain. The cut shows the standard ohm. It is formed either of
German silver, or of an alloy of silver, 66.6 per cent. and platinum,
33.4 per cent. The wire is insulated and doubled before winding as
described before. (See Coil, Resistance.) The two ends of the wire are
soldered, each one to a heavy copper wire or rod r. The whole coil is
enclosed in a brass case, and is enclosed with paraffine melted in at A.
A place for a thermometer is provided at t. By immersing the lower part
of the case B in water of different degrees of heat any desired
temperature can be attained.

Fig. 292. STANDARD OHM COIL.

Resistance, Combined.
The actual resistance of several parallel conductors starting from the
same point and ending at the same point. If the individual resistance be
a b c d .. and the combined resistance be x then we have
x = 1 / (( 1/a) + (1/b) + (1/c) + (1/d) + …)

Synonym--Joint Resistance.

Resistance, Critical.
In a series wound dynamo the resistance of the outer circuit above which
the machine will refuse to excite itself.

Resistance, Dielectric.
The mechanical resistance of a dielectric to the tendency to perforation
or to the strains due to electrification. This is a phase of mechanical
resistance, and is distinct from the electrical or ohmic resistance of
the same substance.

Resistance, Digney Unit of.
The resistance of an iron wire, 1 kilometer long, 4 millimeters
diameter, temperature unknown.

It is equal to 9.163 legal ohms.

Resistance, Electrolytic.
The resistance of an electrolyte to the passage of a current decomposing
it. It is almost entirely due to electrolysis and is added to by
counter- electro-motive force, yet it is not treated specifically as
such, but as an actual resistance. When a current of a circuit of too
low voltage to decompose an electrolyte is caused by way of immersed
terminals to pass through an electrolyte the resistance appears very
high and sometimes almost infinite. If the voltage is increased until
the electrolyte is decomposed the resistance suddenly drops, and what
should be termed electrolytic resistance, far lower than the true
resistance, appears.

465 STANDARD ELECTRICAL DICTIONARY.

Resistance, English Absolute or Foot-Second Unit of.
A unit based on the foot and second. It is equal to (( foot / second ) *
1E7) , being based on these dimensions.

It is equal to 0.30140 legal ohm.

Resistance, Equivalent.
A resistance equivalent to other resistances, which may include
counter-electro-motive force.

Resistance, Essential.
The resistance of the generator in an electric circuit; the same as
internal resistance.

Resistance, External.
In an electric circuit the resistance of the circuit outside of the
generator, or battery.

Synonym--Non-essential Resistance.

Fig. 293. RESISTANCE FRAME.

Resistance Frame.
An open frame filled with resistance coils of iron, or German silver
wire. It is used as a resistance for dynamos and the larger or working
class of plant. The coils are sometimes connected so that by a switch
moving over a row of studs one or more can be thrown into series
according to the stud the switch is in contact with.

Resistance, German Mile Unit of.
The resistance of 8,238 yards of iron wire 1/6 inch in diameter. It is
equal to 56.81 legal ohms.

466 STANDARD ELECTRICAL DICTIONARY.

Resistance, Hittorf's.
A high resistance, often a megohm, composed of Hittorf's solution, q. v.
It is contained in a vertical glass tube near whose upper and lower ends
are electrodes of metallic cadmium attached to platinum wires. The
cadmium is melted in glass tubes, the platinum wire is inserted into the
melted metal and the tube is broken after all is solid. The resistance
should show no polarization current.

Fig. 294. HITTORF'S RESISTANCE

Resistance, Inductive.
A resistance in which self-induction is present; such as a coil of
insulated wire wound around an iron core.

Resistance, Insulation.
The resistance of the insulation of an insulated conductor. It is stated
in ohms per mile. It is determined by immersing a section of the line in
water and measuring the resistance between its conductor and the water.
The section must be of known length, and its ends must both be above the
liquid.

Resistance, Internal.
The resistance of a battery, or generator in an electric circuit as
distinguished from the resistance of the rest of the circuit, or the
external resistance.

Synonym--Essential Resistance.

Resistance, Jacobi's Unit of.
The resistance of a certain copper wire 25 feet long and weighing 345
grains.

It is equal to 0.6296 legal ohm.

Resistance, Matthiessen's Meter-gram Standard.
The resistance of a pure hard drawn copper wire of such diameter that
one meter of it weighs one gram. It is equal to .1434 Legal Ohms at 0º
C. (32º F.)

Resistance, Matthiessen's Unit of.
The resistance of a standard mile of pure annealed copper wire 1/16 inch
diameter, at a temperature of 15.5º C. (60º F.).

It is equal to 13.44 legal ohms.

467 STANDARD ELECTRICAL DICTIONARY.

Resistance, Meter-millimeter Unit of.
The resistance of a wire of copper one meter long and one square
millimeter in section. It is equal to .02057 ohms at 0º C. (32º F.) The
term may also be applied to the resistance of similar sized wire of
other metals.

Resistance, Mil-foot Unit of.
The resistance of a foot of copper wire one-thousandth of an inch in
diameter. It is equal to 9.831 ohms at 0º C. (32º F.) The term may also
be applied to the resistance of similar sized wire of other metals.

Resistance, Non-essential.
The resistance of the portion of an electric circuit not within the
generator; the same as external resistance.

Synonym--External Resistance.

Resistance, Non-inductive.
A resistance with comparatively little or negligible self-induction.

Resistance of Human Body.
The resistance of the human body is largely a matter of perfection of
the contacts between its surface and the electrodes. It has been
asserted that it is affected by disease. From 350 to 8,000 ohms have
been determined as resistances, but so much depends on the contacts that
little value attaches to the results.

Resistance, Ohmic.
True resistance measured in ohms as distinguished from
counter-electro-motive force, q. v. The latter is called often spurious
resistance.

Synonym--True Resistance.

Resistance, Reduced.
The resistance of a conductor reduced to ohms, or to equivalent lengths
of a column of mercury, 1 square millimeter in cross area.

Resistance, Siemen's Unit of.
The resistance of a column of mercury 1 meter long and 1 square
millimeter cross-sectional area at 0º C. (32º F.)

It is equal to .9431 legal ohm.

Resistance, Specific.
The relative resistance of a substance. It is expressed as the actual
resistance of a cube of the substance which is one centimeter on each
edge. For metals it is usually expressed in microhms, for liquids in
ohms.

The resistances of a specified length of wire of specified diameter of
different substances is often given, and is really a particular way of
stating specific resistances.

Synonym--Specific Conduction Resistance.

Resistance, Spurious.
The counter-electro-motive force, q. v., operating to prevent a current
being produced of what should be its full strength were the true
resistance and actuating electro-motive force only concerned. Such
counter-electro-motive force may be treated as a spurious resistance and
such a value in ohms assigned to it as would correspond to its proper
effect.

468 STANDARD ELECTRICAL DICTIONARY.

In its effect on opposing a current and in resisting its formation it
differs from true resistance. The latter in diminishing current strength
absorbs energy and develops heat; spurious resistance opposes and
diminishes a current without absorption of energy or production of heat.

Resistance, Steadying.
When arc lamps are connected in parallel or multiple arc a small
resistance coil is sometimes placed in series with each lamp for
steadying purposes. It reduces the percentage of variation of resistance
in each lamp, which may be caused by a change in the position of the
carbons.

Resistance, Swiss Unit of.
A unit constructed by the "Administration Suisse," based on the same
data as the Breguet and the Digney Units. (See Resistance, Digney Unit
of)

It is equal to 10.30 legal ohms.

Resistance, Thomson's Unit of.
A unit of resistance based on the foot and second.

It is equal to 0.3166 legal ohm.

Resistance, Unit.
Unit resistance is that of a conductor in which unit current is produced
by unit electro-motive force.

Resistance, Varley's Unit of.
The resistance of a standard mile of a special copper wire 1/16 inch
diameter.

It is equal to 25.33 ohms.

Resistance, Weber's Absolute Unit.
A metric system unit; (meter / second) * 1E7

It is equal to 0.9089 legal ohm.

Resonance, Electric.
A set of phenomena known as the Hertz experiments are grouped under this
title, which phenomena are incidents of and depend on the propagation of
electric waves through wires or current conductors, as well as through
the ether. Ordinarily a wire is only a seat of current, and is in its
nature inconsistent with wave propagation through its mass. Such waves
are virtually confined to the exterior of the wire. The point is that
the current-producing force is supposed to enter the wire at all points
from without, the current not being produced by an end-push. Hence in
rapidly recurring waves which are produced by a rapidly pulsatory or
alternating current, no time is afforded for the current-producing
force, in this case the wave-producing force, to penetrate into the
substance of the wire. In one of his experiments Dr. Hertz surrounded a
wire by a glass tube chemically silvered. The coating was so thin as to
be translucent. Through this metallic layer a current could be induced
in the wire in its interior. Any mechanical layer of metal took up the
induction itself, and protected the central wire. This gave a clue to
the thickness of metal penetrated by the rapid induced waves used by Dr.
Hertz.

469 STANDARD ELECTRICAL DICTIONARY.

Fig. 295. ELECTRICAL RESONANCE EXCITER.

The method used for the production of rapid oscillations is the
following. To the terminals of an induction coil two metal spheres AA1
are connected as shown. This apparatus is termed the exciter; in its
discharge a series of isochronous discharges takes place, alternating in
direction. The period of duration T of a single one is given by the
formula T= 2* PI * squareRoot( LC ), in which C is the capacity and L
is the self-induction. The spheres may be 30 centimeters (11.8 inches)
in diameter, connected each to conductors 0.5 centimeter (.2 inch) in
diameter and 40 centimeters (15.7 inches) long each. For the length of
an undulation the formula gives for this apparatus 4.8 meters (15.75
feet) as the length of a wave, assuming for them the velocity of
propagation equal to that of light. The exciter may have 10,000 times
the rate of oscillation possessed by the plain induction coil.

When this apparatus is worked it produces induced waves in every
neighboring conductor. The resonance effects appear in the size of the
spark induced. Thus a wire bent into a circle with its ends nearly
touching will give a spark, but if made of proper electrostatic
capacity, corresponding with the particular waves employed, the spark
will be very much larger. The ring, with its spark gap is termed a
resonator. It is used as an explorer to trace the waves.

Waves thus produced are transmitted by stone walls and nonconductors in
general. A plate of zinc reflects part and transmits part. The reflected
waves can be traced by the resonator, their angle of reflection being
equal to their angle of incidence. They can be received by one parabolic
reflector, reflected to another and brought to a focus. They can be
reflected so as to produce interference or loops and nodes, and the
loops and nodes can be traced by the resonator. By a prism of asphalt
they are refracted exactly like light.

From all this it is concluded that an additional proof is furnished of
the identity of light and electro-magnetic waves, and a very strong
experimental proof of Maxwell's theory of light is furnished.

Synonym--Hertz's Experiments.

470 STANDARD ELECTRICAL DICTIONARY.

Fig. 296. ELECTRICAL RESONATOR.

Resonator, Electric.
A small open electric circuit, with ends nearly touching. When exposed
to electric resonance, or to a sympathetic electric oscillatory
discharge, a spark passes from across the gap. The production of this
spark is altogether a matter of the inductance of the resonator. The
simplest form is a circle of copper wire with its ends nearly touching.
The length of the gap is adjustable by bending. A screw adjustment may
also be provided. Another form is shown in the cut, Fig. 296. Here
sheets of tinfoil are used to regulate the electrostatic capacity, while
at m is shown the finger piece for regulating the size of the spark gap
a.

Synonym--Spark Micrometer.

Resultant.
The line indicating the result of the application of two or more forces
to a point. Its direction and length give the elements of direction and
intensity. (See Forces, Resolution of Forces, Composition of
Components.)

Resultant Polarity.
The magnetic polarity imparted to a mass of iron acted on by two or more
separate inducing forces or currents. It appears in dynamos and motors.
The final polarity is the resultant of the inducing effect of the field
magnet poles and of the windings.

Retardation.
In telegraphy a retardation of the rate of transmission of signals. It
is due to several causes.

(a) The self-induction of the circuit, especially if it includes many
electro-magnets, produces extra currents (see Currents, Extra.) These
are opposed to the main current on closing it and hence retard the
action. They are in the same direction on opening it and hence again
retard the action.

(b) Every line has a certain static capacity. This is affected by the
proximity of the lines to the earth. For each signal electricity has to
be charged upon the line until the line is charged to its end with a
certain proportion of the initial density. This charging takes time and
hence introduces retardation.

(c) The cores of the electro-magnets of the relays or sounders are not
instantly magnetized and demagnetized. This magnetic lag, q. v.,
introduces retardation.

471 STANDARD ELECTRICAL DICTIONARY.

Retardation of Phase.
The fractional lagging behind of waves or alternating currents; by
lagging behind a portion of a wave length the corresponding phases, as
of full amplitude, are kept back or retarded. The phase of current
intensity may be retarded with reference to the electro-motive force by
the introduction of transformers of high capacity with high resistance
on open secondary circuits.

Retentivity.
Coercitive or coercive force; by virtue of which steel retains its
magnetism. It is the more modern name, "coercive force" as a term being
rejected by many.

Synonyms--Coercive Force--Coercitive Force.

Retort Carbon.
Carbon deposited in coal gas retorts from decomposition of the
hydrocarbons. It is a very hard, pure form, and is of graphitic
modification. Owing to its great hardness it is little used for
electrical purposes, the molded carbons being easier to make. The
deposition occurs in the regular gas-making process, and is a
disadvantage to the working.

Return.
A line or conductor which is supposed to carry current back to its
starting point, after it has traversed a line. It may be a wire or the
grounding of the ends of a line [or] may make the earth act as a return,
termed ground- or earth-return. The best distinction of a return is to
so term the portion of a circuit on which no apparatus is placed.

Reversibility.
The principal in virtue of which a device for producing a given form of
energy can absorb the same and do work. The reversibility of the dynamo
is its quality in virtue of which it can act as a current generator,
thereby converting mechanical energy into electric energy, or if a
current is passed through it, it rotates, doing work, and thereby
converting electric energy into mechanical energy. The knowledge of this
principle can be traced back to Jacobi in 1850.

Reversible Bridge.
A form of Wheatstone's Bridge adapted for reversal of the positions or
interchange of the proportionate arms, v., so that the accuracy of the
coils can be tested.

Rheochord.
An apparatus by means of which variable quantities of wire are thrown
into the circuit; a rheostat using wire. (See Rheostat, Wheatstone's.)

Rheometer.
A galvanometer. (Obsolete.)

472 STANDARD ELECTRICAL DICTIONARY.

Rheomotor.
A source of current; a current generator; a producer of potential
difference. (Obsolete.)

Rheophore.
The portion of an active circuit capable of deflecting a magnetic
needle. This properly includes all of the metallic conductor of a
circuit. (Obsolete.)

Rheoscope.
A galvanoscope; an instrument for qualitatively detecting potential
difference, fall or rise. (See Galvanoscope.)

Rheostat.
An adjustable resistance; an apparatus for changing the resistance
without opening the circuit. Its action may depend on the introduction
of variable lengths of mercury column, of some other liquid, or of wire
into a circuit. (See Rheostat, Wheatstone's.)

Rheostat Arm.
The third arm of known resistance in a Wheatstone bridge. (See
Proportionate Arms.)

Rheostatic Machine.
An apparatus for increasing potential difference. It consists of a
number of static condensers. They are charged in multiple arc or in
parallel, and are discharged in series. Secondary batteries may be used
for the charging; thus a static effect is produced from a galvanic
battery.

Rheostat, Wheatstone's.
This apparatus consists of two cylinders, one, A, made of brass, the
other, B, of wood, with a spiral groove. At its end is a copper ring a.
A fine brass wire has one end attached to this ring. Its other end is
fastened at e, and it is wound as shown; n and o are binding screws
connected, one with the cylinder-ring a, the other with the brass
cylinder, A. The current entering at o, traverses the wire on B, as
there the windings are insulated by the grooves, thence it passes to m
and by A, whose metal short circuits all the wire on it, to the
binding-post n. The handle, d, is turned one way or the other to
regulate the length of the wire through which the current must pass. On
each cylinder there is a square head, one of which is shown at c, so
that the handle can be shifted from one to the other as required; to A
if the wire is to be wound on that cylinder, to B if the reverse is
desired.

Fig. 297. WHEATSTONE'S RHEOSTAT.

473 STANDARD ELECTRICAL DICTIONARY.

Rheotome.
An automatic circuit breaker, one which rapidly opens and closes a
circuit, as in the case of the primary of an induction coil an
interrupter. (Obsolete.)

Rheotrope.
A pole changer, current reverser, or commutator, g., such as the
commutator of an induction coil. (Obsolete.)

Rhigolene.
A petroleum product; a hydrocarbon of low boiling point. Its vapor is
used in flashing (q. v.) carbon filaments for incandescent lamps.

Rhumbs.
In a mariners' compass, the thirty-two points, designated, north, north
by east, north north east, etc. (See Compass Mariner's-Compass, Points
of the.)

Rhumkorff Coil.
The induction coil, q. v.

Rigidity, Molecular.
The tendency of molecules to resist rotation or change of position; the
assumed cause of magnetic coercive force, or retentivity.

Ring Contact.
A contact formed by a terminal clip in the shape of a ring, split or cut
at one point so that its ends tend to spring together. The other
terminal is a bar which passes into the cut and is tightly pressed by
the elastic ring.

Fig. 298. SWITCH WITH RING CONTACTS.

474 STANDARD ELECTRICAL DICTIONARY.

Ring, Faraday.
A closed ring of iron used as the core of a transformer or induction
coil. The term is derived from Faraday's classic experiment with such an
apparatus when he produced a spark by induction in a secondary circuit.

Roaring.
A term applied to the noise sometimes produced in a voltaic arc, when
the electrodes are close together and a heavy current is passing.

Rocker.
In a dynamo the movable piece, mounted concentrically with the
commutator, and carrying the rocker-arms and brush-holders. By moving it
the brushes are adjusted for proper lead.

Rocker Arms.
The arms projecting from a rocker and each carrying one of the
brush-holders.

Roget's Spiral.
An experimental apparatus for illustrating the mutual attraction of
currents going in like direction. A cylindrical helix or spiral of wire
is suspended by one end. Its lower end just dips into a mercury cup. An
active circuit is connected, one terminal to the upper end, the other
terminal to the mercury cup, bringing the apparatus in series into the
circuit. The current as it passes causes the coil to shorten, each
spiral attracting its neighbors. This breaks the circuit by drawing the
lower end out of the mercury cup. The current being cut off the coils
cease to attract each other, and the end dips into the mercury cup
again. This closes the circuit, the coils again attract each other and
the same sequence follows and is repeated over and over again. A bright
spark is produced at each break of the mercury contact.

Rotation of Liquids, Electro-dynamic.
By passing a current through a liquid, such as dilute sulphuric acid, it
rotates if exposed to the induction of a current flowing at right angles
to it. The condition resolves itself into a liquid traversed by
horizontal currents from centre to circumference or vice versa, rotated
by a current passing through a circular conductor below it.

475 STANDARD ELECTRICAL DICTIONARY.

Rotation of Liquids, Electro-magnetic.
The rotation produced in a liquid carrying centripetal or centrifugal
currents by an electromagnet. It is practically an intensification of
electro-dynamic rotation. (See Rotation of Liquids, Electro-dynamic.)

Rubber.
In a frictional electric machine the cushion of leather which is pressed
against the plate as it rotates.

475 STANDARD ELECTRICAL DICTIONARY.

S.
(a) Symbol for second.

(b) Symbol for space, or length; L is preferable.

(c) Symbol for south-seeking pole of a magnet.

Saddle Bracket.
A bracket carried on the top of telegraph poles, carrying an insulator
for the upper wire.

Safety Device.
(a) A device to prevent overheating of any portion of a circuit by
excess of current. It generally consists of a slip of fusible metal
which if the current attains too much strength melts and opens the
circuit. To ensure its breaking a weight is sometimes suspended from the
strip. In one form an insulated German silver wire is wrapped around the
end of the fusible strip a number of times and its end is connected to
it. The other end of the German silver wire connects with the main lead,
so that all the current goes through both in series. If the German
silver wire becomes heated from excess of current the coil wrapped
tightly around the end of the fusible strip melts it and opens the
circuit.

(b) Lightning arresters, q. v., may be cited under this heading.

Synonyms--Automatic Cut Out--Safety Fuse, Plug, or Strip.

Fig. 299. COCKBURN SAFETY FUSE.

Safety Fuse.
A strip of metal inserted so as to form part of a circuit and of such
size that a smaller current [than] would heat the regular wire of the
circuit dangerously, so as to cause a conflagration for instance, would
melt the fuse and open the circuit. As it sometimes happens that a
safety fuse melts without parting a weight is sometimes hung upon it, so
as to break it as it softens.

Salt.
A salt is a chemical compound containing two atoms of two radicals,.
which saturate each other. One atom or radical is electro-positive
referred to the other, which is electro-negative. By electrolysis salts
are decomposed, the atoms or radicals separating and uniting to form new
molecules.

476 STANDARD ELECTRICAL DICTIONARY.

Saturated. adj.
A liquid is saturated with a substance when it has dissolved all that it
can, while an excess is present in the liquid. It is possible, by
dissolving some salts in hot water and allowing the solution to cool
without access of air, to obtain a supersaturated solution. On
introduction of a crystal of the salt, or often on mere access of air,
the solution forms crystals and the liquid left is saturated.

Saw, Electric.
A platinum coated steel wire mounted and connected to be raised to
incandescence for cutting purposes.

Schweigger's Multiplier.
An old term for the galvanometer as invented by Schweigger soon after
Oerstedt's discovery.

Scratch Brushes.
Brushes for cleaning the surface of articles to be electroplated to give
a good metallic surface suitable for deposition. They have often wire
instead of bristles.

477 STANDARD ELECTRICAL DICTIONARY.

Fig. 300. WIRE GAUZE ELECTRIC SCREEN.

Screen, Electric.
A large plate or a hollow case or cage of conducting material connected
with the earth, and used to protect any body placed within it from
electrostatic influences.

If within a hollow conducting sphere an electrified body is placed, the
inner surface of the sphere will be charged with electricity of opposite
kind to that of the sphere, and the outer surface with the same kind as
that of the sphere. Thus the sum of the electricities called into action
by induction is zero. The two inner charges are bound to each other. The
induced charge on the outer surface of the sphere is all that has any
effect on objects in the outer air.

If the outer surface is connected to the earth it becomes discharged,
and however highly electrified the body introduced into the sphere and
the inner surface of such sphere may be, they produce no external
effects, as they are bound one to the other.

If the sphere is connected to the earth and an unelectrified object is
placed within it, such object will be perfectly shielded from the
effects of an outer electrostatic field. Perforated tinfoil or wire
gauze has just as good a result. A large plate of metal connected to the
earth has the same effect. The screen whether plane or hollow simply
retains a bound charge due to the field of force, thereby neutralizing
it, and the electricity of the opposite sign escapes to the earth. Thus
a true shielding or screening effect is produced.

In the cut an experiment is shown in which an electric screen is carried
by a Leyden jar. Pith balls are suspended outside and inside of it. By
the approach of an electrified body the outer pith balls will diverge,
while no effect is produced upon the inner ones.

Secondary Actions.
In electrolysis the direct products of the electrical decomposition are
not always obtained at the electrodes, but products due to their
reaction on the water and other chemicals may appear. These constitute
secondary actions. Thus if a solution of copper sulphate is electrolyzed
with platinum electrodes, metallic copper appears at one pole and
sulphuric acid and oxygen gas at the other. But the products of
electrolysis by the current are copper (Cu) and sulphion (SO4). The
latter reacting on water sets free oxygen gas and forms sulphuric acid.
The latter is a secondary action.

Secondary Generator.
(a) An alternating current converter generating a so-called secondary
current.

(b) A secondary battery, q. v., may be thus termed.

Secondary, Movable.
The term movable secondaries has been applied to rings, spheres and
discs of conducting material, such as copper, whose behavior when near
the pole of an electro-magnet traversed by an alternating current, have
been studied by Elihu Thomson. Such masses are subjected to very
peculiar movements and mutual reactions. As the phenomena are due to
induced currents the above term has been applied to the masses in which
the currents are induced.

478 STANDARD ELECTRICAL DICTIONARY.

Secondary Plates, Colors of.
In a secondary battery of the lead plate type, the color of the plates
is a good indication of the condition of the battery. The negative plate
should be brown or deep-reddish, the other should be slate-colored.

Secondary Poles.
Poles sometimes found in magnets existing in positions intermediate
between the end or true poles.

Synonym--Consequent Poles.

Seebeck Effect.
The production of a current by heating the junction of two different
metals forming part of a circuit, or the thermo-electric production of
current, is stated as the Seebeck effect, having been discovered by that
investigator.

Selenium.
A non-metallic element. It is interesting electrically on account of the
changes its electric resistance undergoes when it is subjected to light.

In one set of experiments it was found that diffused light caused the
resistance to fall in the ratio of 11 to 9. Full sunlight reduced it to
one-half. Of the spectrum colors red was most powerful and the ultra red
region still more strongly affected its resistance.

The effect produced by exposure to light is instantaneous, but on
removal to the dark only slowly disappears.

A vessel of hot water was found to have no effect, showing that short
ether waves are essential to the effect.

Selenium Cell.
A selenium resistance box. Vitreous selenium is made by keeping ordinary
selenium for some hours at a temperature of about 220º C. (428º F.)
after fusing. It is placed in an electric circuit as part of the
conductor.

Its resistance can then be determined. It decreases in sunlight to about
one-half its resistance in the dark.

The selenium cell is used in the Photophone, q. v. Otherwise it is
little more than a subject of experiment.

Selenium Eye.
A model eye in which selenium in circuit with a battery and galvanometer
takes the place of the retina of the human eye.

Self-repulsion.
When a body is electrified each molecule repels its neighbor and the
condition in question is thus designated. An electrified soap-bubble
expands in virtue of self-repulsion.

Semi-conductors.
Substances which conduct static electricity poorly, but quite
appreciably and beyond the extent of leakage. The following are
examples: Alcohol and ether, powdered glass, flowers of sulphur, dry
wood, paper, ice at 0º C. (32º F.)

479 STANDARD ELECTRICAL DICTIONARY.

Sensibility.
The measure of the effect of a current upon a galvanometer,
or any similar case.

Sensitiveness, Angle of Maximum.
Every galvanometer has its angle of maximum sensitiveness, which is the
angle of deflection at which a small increment of current will produce
the greatest deflection. For every tangent galvanometer 45° is the angle
in question. In using a galvanometer for direct reading methods it is an
object to have it work at its angle of maximum sensitiveness.

Separately Excited Dynamo.
A dynamo-electric machine whose field magnet is excited from an outside
source, which may be another dynamo or a battery. Alternating current
dynamos are often of this description.

Separate Touch.
In magnetism a method of inducing magnetism in a steel bar. The opposite
poles of two magnets are applied at the center of the bar to be
magnetized, but without touching each other, and are drawn apart to its
ends. They are returned through the air and the process is repeated a
number of times and on both sides of the bar if necessary.

Separation of Electricities.
Under the double fluid theory of electricity the action of
electrification in accumulating positive electricity in one conductor
and negative on the other of the excited surfaces of two conductors.

Separator.
India rubber bands or other forms used in batteries to keep the plates
from touching in the cell; especially applied to secondary batteries,
where the plates are so near together as to require separators to
prevent short circuiting.

Fig. 301. SERIES CONNECTION.

Series.
(a) Arranged in succession as opposed to parallel. Thus if a set of
battery jars are arranged with the zinc of one connected to the carbon
of the next one for the entire number, it is said to be arranged in
series. When incandescent lamps are arranged in succession so that the
current goes through one after the other they are arranged in series.

The opposite of parallel, q. v., or multiple arc, q. v.; it may be used
as a noun or as an adjective.

(b) See Electro-Chemical Series;

(c) Thermo-Electric Series

(d) Electrostatic Series;

(e) Electro-motive Series.

Synonym--Cascade Connection (but little used.)

480 STANDARD ELECTRICAL DICTIONARY.

Series-multiple.
Arrangement of electric apparatus, in which the parts are grouped in
sets in parallel and these sets are connected in series. It is used as a
noun, as "arranged in series-multiple," or as an adjective, as "a
series-multiple circuit or system."

Fig. 302. SERIES-MULTIPLE CONNECTION.

Service Conductors.
In electric distribution the equivalents of service pipes in the
distribution of gas; wires leading from the street mains to the houses,
where current is to be supplied.

Serving.
The wrapping or winding of a cable composed of small size wire, laid
closely and smoothly with a tool called a serving mallet, or serving
block, or by machinery. It serves to protect the cable from wear.

Shackle.
In telegraph lines a swinging insulator bracket for use where wires make
an angle with the pole. A journal box is attached to the pole, like half
of a gate hinge. To this a short iron arm is pivoted so as to be free to
swing through a considerable angle. At its end an insulator is carried
to which the wire is attached. The shackle swings into line with the
wire, or takes a position for two wires corresponding to the resultant
of their directions of pull.

Fig. 303. DOUBLE SHACKLE

Shadow. Electric.
A term applied to a phenomenon of high vacua. If an electric discharge
is maintained in a Crookes' tube the glass opposite the negative
electrode tends to phosphoresce. A plate of aluminum, used also as the
positive electrode, protects the glass directly behind it so as to
produce the effect of a shadow.

Synonym--Molecular Shadow.

481 STANDARD ELECTRICAL DICTIONARY.

Sheath for Magnet Coils.
In 1867 C. E. Varley proposed the use of a copper sheath surrounding a
magnet core to diminish self-induction. It has since been used by Brush
and others. Sometimes metallic foil is laid between the successive coils
of wire.

Synonym--Mutual Induction Protector.

Sheath for Transformers.
A protective sheath of copper, interposed between the primary and
secondary circuits of an alternating current transformer. It is
connected to the earth. If the primary coil loses its insulation before
it can leak to the secondary it is grounded. This protects the secondary
circuit from the high electro-motive force of the primary circuit.

Shellac.
A resin; produced as an exudation upon the branches of certain Asiatic
trees, such as the banyan (Ficus religiosa). It is due to punctures in
the bark of the trees in question, which punctures are made by the
female of the insect coccus ficus or c. lacca.

Commercial shellac contains about 90 per cent. of resinous material, the
rest is made up of wax, gluten, coloring matter and other substances.

Shellac is soluble in alcohol, and in aqueous solutions of ammonium
chloride, of borax and in strong ammonia solution. Long standing is
required in the case of the last named solvent. Dilute hydrochloric and
acetic acids dissolve it readily; nitric acid slowly; strong sulphuric
acid is without action on it. Alkalies dissolve it.

In electric work it is used as an insulator and dielectric. Its
alcoholic solution is used to varnish glass plates of influence
machines, for the coils of induction coils and similar purposes.

Resistance in ohms per centimeter cube at 28° C. (82.4 F.)--(Ayrton),
9.0E15

Specific Inductive Capacity (Wüllner), 2.95 to 3.73

The same substance in less pure forms occurs in commerce, as stick lac,
lump lac, seed lac, button lac.

Shellac Varnish.
Solution of shellac in alcohol; methylic alcohol (wood alcohol or wood
naphtha) is often used as solvent.

Dr. Muirhead recommends button lac, dissolved in absolute alcohol, and
the top layers decanted. For highest insulation he dissolves the lac in
ordinary alcohol, precipitates by dropping into water, collects the
precipitate, dries and dissolves in absolute alcohol.

Shielded. adj.
An electric measuring instrument of the galvanometer type is shielded
when it is so constructed that its indications are not seriously
affected by the presence of neighboring magnets or by fields of force.
Shielding can be effected by using a very strong permanent magnet to
produce a field within which the magnetic needle moves and which reacts
upon it, or by enclosing the instrument in a thick iron box.

482 STANDARD ELECTRICAL DICTIONARY.

S. H. M.
Symbol or abbreviation for "simple harmonic motion."

Shock, Break.
A term in electro-therapeutics; the shock received when an electric
circuit, including the patient in series, is broken or opened.

Synonym--Opening Shock.

Shock, Electric.
The effect upon the animal system of the discharge through it of
electricity with high potential difference. Pain, nervous shock, violent
muscular contortions accompany it. Of currents, an alternating current
is reputed worse than a direct current; intermediate is the pulsatory
current.

The voltage is the main element of shock, amperage has also some direct
influence.

Shock, Static.
A term in electro-therapeutics. The application of static discharges
from small condensers or Leyden jars to a patient who is insulated from
the ground with one electrode applied to the conducting surface on which
he rests, while the other, a spherical electrode, is brought near the
body so as to produce a disruptive or spark discharge.

Short Circuit.
A connection between two parts of a circuit, which connection is of low
resistance compared to the intercepted portion. The term is used also as
a verb, as "to short circuit a lamp."

Fig. 304. DIAGRAM ILLUSTRATING SHORT CIRCUIT WORKING.

Short Circuit Working.
A method of working intermittently an electro-magnet so as to avoid
sparking. It consists in providing a short circuit in parallel with the
magnetic coils. This short circuit is of very low resistance. To throw
the magnet into action the short circuit is opened; to throw it out of
action the short circuit is closed. The shunt or short circuit must be
of negligibly small resistance and inductance.

483 STANDARD ELECTRICAL DICTIONARY.

Shovel Electrodes.
Large plate electrodes used in a medical bipolar bath. (See Bath,
Bipolar.)

Shunt.
In a current circuit a connection in parallel with a portion of the
circuit. Thus in a dynamo a special winding for the field may have its
ends connected to the bushes, from which the regular external circuit
also starts. The field is then wound in shunt with the armature. In the
case of a galvanometer a resistance coil may be put in parallel with it
to prevent too much current going through the galvanometer; this
connection is a shunt.

The word is used as a noun, as "a shunt," or "a connection or apparatus
in shunt with another," and as an adjective, as "a shunt connection," or
as a verb, as "to shunt a battery."

Shunt Box.
A resistance box designed for use as a galvanometer shunt. (See Shunt,
Galvanometer.) The box contains a series of resistance coils which can
be plugged in or out as required.

Shunt, Electro-magnetic.
In telegraphy a shunt for the receiving relay consisting of the coils of
an electro-magnet. It is placed in parallel with the relay. Its poles
are permanently connected by an armature. Thus it has high
self-induction.

On opening and closing the circuit by the sending key, extra currents
are produced in the shunt. The connections are so arranged that on
making the circuit the extra current goes through the relay in the same
direction as the principal current, while on breaking the circuit the
induced current goes in the opposite direction.

Thus the extra currents accelerate the production and also the cessation
of signalling currents, tending to facilitate the operations of sending
despatches.

Shunt, Galvanometer.
A resistance placed in parallel with a galvanometer, so as to short
circuit its coils and prevent enough current passing through it to
injure it. By knowing the resistance of the shunt and of the
galvanometer coils, the proportion of current affecting the galvanometer
is known. This gives the requisite factor for calculation. (See
Multiplying Power of Shunt.)

Shunt Ratio.
The coefficient expressing the ratio existing between the current in a
shunt and in the apparatus or conductor in parallel with it. (See
Multiplying Power of/ Shunt.)

Shunt Winding.
A dynamo or motor is shunt-wound when the field magnet winding is in
shunt or in parallel with the winding of the armature.

Shuttle Current.
A current alternating in direction; an alternating current.

484 STANDARD ELECTRICAL DICTIONARY.

Side-Flash.
A bright flashing lateral discharge from a conductor conveying a current
due to a static discharge.

Sighted Position.
In an absolute electrometer (see Electrometer, Absolute) the position of
the balanced arm carrying the movable disc or plate, when the disc and
guard plate are in one plane. The cross-hair on the lever-end is then
seen midway between two stops, or some other equivalent position is
reached which is discerned by sighting through a magnifying glass or
telescope.

Silver.
A metal; one of the elements; symbol Ag.; atomic weight, 108; valency, 1;
equivalent, 108; specific gravity, 10.5. It is a conductor of electricity.
Relative resistance, annealed, 1.0
Specific Resistance, annealed, at 0° C. (32° F.) 1.504 microhms.
Resistance of a wire at 0° C. (32° F.), Annealed. Hard Drawn.
(a) 1 foot long, weighing 1 grain, .2190 ohms .2389 ohms.
(b) 1 foot long, 1/1000 inch thick, 9.048 " 9.826 "
(c) 1 meter long, weighing 1 gram, .1527 " .1662 "
(d) 1 meter long, 1 millimeter thick, .01916 " .02080 "

Resistance annealed of a 1-inch cube, at 0° C. (32°F.) .5921 microhms.

Percentage increase in resistance per degree C.
(1.8 F.) at about 20° C. (68° F.), annealed, 0.377 per cent.

Electro-chemical equivalent, (Hydrogen = .0105) .1134 mgs.

Silver Bath.
A solution of a salt of silver for deposition in the electroplating
process.

The following is a typical formula:
Water, 10.0 parts by weight.
Potassium Cyanide, 5 " "
Metallic Silver, 2.5 " "

The silver is first dissolved as nitrate and converted into cyanide and
added in that form, or for 2.5 parts metallic silver we may read:
Silver cyanide, 3 parts by weight.

While many other formulas have been published the above is
representative of the majority. Other solvents for the silver than
potassium cyanide have been suggested, such as sodium hyposulphite, but
the cyanide solution remains the standard.

Silver Stripping Bath.
Various baths are used to remove silver from old electroplated articles.
Their composition depends upon the base on which the metal is deposited.
Silvered iron articles are placed as anodes in a solution of 1 part
potassium cyanide in 20 parts of water. As kathode a silver anode or a
copper one lightly oiled may be used. From the latter the silver easily
rubs off. For copper articles a mixture of fuming sulphuric acid and
nitric acid (40º Beaumé) may be used. The presence of any water in this
mixture will bring about the solution of the copper. Or fuming sulphuric
acid may be heated to between 300º and 400º F., some pinches of dry
pulverized potassium nitrate may be thrown in and the articles at once
dipped. These methods effect the solution of the silver, leaving the
copper unattacked.

485 STANDARD ELECTRICAL DICTIONARY.

Simple Substitution.
A method of obtaining a resistance equal to that of a standard. The
standard is put in circuit with a galvanometer and the deflection is
noted. For the standard another wire is substituted and its length
altered until the same deflection is produced. The two resistances are
then evidently identical. The standard can be again substituted to
confirm the result.

Sine Curve.
If we imagine a point moved back and forth synchronously with a
pendulum, and if such point made a mark upon paper, it would trace the
same line over and over again. If now the paper were drawn steadily
along at right angles to the line of motion of the point, then the point
would trace upon it a line like the profile of a wave. Such line is a
sine curve. It derives its name from the following construction. Let a
straight line be drawn, and laid off in fractions, such as degrees, of
the perimeter of a circle of given diameter. Then on each division of
the line let a perpendicular be erected equal in height to the sine of
the angle of the circle corresponding to that division; then if the
extremities of such lines be united by a curve such curve will be a sine
curve.

In such a curve the abscissas are proportional to the times, while the
ordinates are proportional to the sines of angles, which angles are
themselves proportional to the times. The ordinates pass through
positive and negative values alternately, while the abscissas are always
positive.

Any number of sine curves can be constructed by varying the diameter of
the original circle, or by giving to the abscissas a value which is a
multiple of the true length of the divisions of circle. If the pendulum
method of construction were used this would be attained by giving a
greater or less velocity to the paper as drawn under the pendulum.

A species of equation for the curve is given as follows: y = sin( x )

In this x really indicates the arc whose length is x, and reference
should be made to the value of the radius of the circle from which the
curve is described. It will also be noticed that the equation only
covers the case in which the true divisions of the circle are laid off
on the line. If a multiple of such divisions are used, say n times, or
1-n times, then the equation should read
y = n sin( x ) or y = sin( x ) / n

Synonyms--Curve of Sines--Sinusoidal Curve--Harmonic Curve.

486 STANDARD ELECTRICAL DICTIONARY.

Sine Law.
The force acting on a body is directly proportional to the sine of the
angle of deflection when--

I. The controlling force is constant in magnitude and direction; and

II. The deflecting force, although variable in its direction in space,
is fixed in direction relatively to the deflecting body.

Single Fluid Theory.
A theory of electricity. Electricity, as has been said, being
conveniently treated as a fluid or fluids, the single fluid theory
attributes electrical phenomena to the presence or absence of a single
fluid. The fluid repels itself but attracts matter; an excess creates
positive, a deficiency, negative electrification; friction, contact
action or other generating cause altering the distribution creates
potential difference or electrification. The assumed direction (see
Direction) of the current and of lines of force are based on the single
fluid theory. Like the double fluid theory, q. v., it is merely a
convenience and not the expression of a truth. (See Fluid, Electric, and
Double Fluid Theory.)

Synonym--Franklin's Theory.

Single Fluid Voltaic Cell.
A galvanic couple using only a single fluid, such as the Smee or Volta
cell.

Simple Harmonic Motion.
Motion of a point or body back and forth along a line; the motion of a
pendulum, as regards its successive swings back and forth, is an example
of harmonic motion.

Sinistrotorsal. adj.
The reverse of dextrotorsal, q. v. A helix with left-handed winding, the
reverse of an ordinary screw, such as a wood-screw or corkscrew.

Skin Effect.
A current of very brief duration does not penetrate the mass of a
conductor. Alternating currents for this reason are mainly conducted by
the outer layers of a conductor. The above is sometimes called the skin
effect.

Sled.
A contact for electric cars of the conduit system. It is identical with
the plow, q.v., but is drawn after the cars instead of being pushed
along with them.

Slide Meter Bridge.
A name for a Slide Bridge one meter long. There are also slide half
meter and slide quarter meter bridges and others. (See Meter Bridge.)

S. N. Code.
Abbreviation for single needle code, the telegraphic alphabet used with
the single needle system.

Soaking-in-and-out.
A term for the phenomena of the residual electrostatic charge; the
gradual acquirement or loss by a condenser of a portion of its
electrostatic charge.

487 STANDARD ELECTRICAL DICTIONARY.

Soldering, Electric.
(a) Soldering in which the solder is melted by means of electricity;
either current incandescence or the voltaic arc may be used. It is
identical in general with electric welding. (See Welding, Electric.)

(b) The deposition by electric plating of a metal over the ends of two
conductors held in contact. This secures them as if by soldering. It is
used in connecting the carbon filament of an incandescent lamp with the
platinum wires that pass through the glass. Copper is the metal usually
deposited.

Solenoid.
The ideal solenoid is a system of circular currents of uniform
direction, equal, parallel, of equal diameter of circle, and with their
centers lying on the same straight line, which line is perpendicular to
their planes.

Fig. 305. EXPERIMENTAL SOLENOID.

The simple solenoid as constructed of wire, is a helical coil, of
uniform diameter, so as to represent a cylinder. After completing the
coil one end of the wire is bent back and carried through the centre of
the coil, bringing thus both ends out at the same end. The object of
doing this is to cause this straight return member to neutralize the
longitudinal component of the helical turns. This it does approximately
so as to cause the solenoid for its practical action to correspond with
the ideal solenoid.

Instead of carrying one end of the wire through the centre of the coil
as just described, both ends may be bent back and brought together at
the centre.

A solenoid should always have this neutralization of the longitudinal
component of the helices provided for; otherwise it is not a true
solenoid.

Solenoids are used in experiments to represent magnets and to study and
illustrate their laws. When a current goes through them they acquire
polarity, attract iron, develop lines of force and act in general like
magnets.

A solenoid is also defined as a coil of insulated wire whose length is
not small as compared with its diameter.

488 STANDARD ELECTRICAL DICTIONARY.

Sonometer, Hughes'.
A sound measurer; a modification of a portion of Hughes' induction
balance, used for testing the delicacy of the ear or for determining the
relative intensity of sounds. (See Hughes' Induction Balance.) It is the
arrangement of three coils, two mounted one at each of the ends of a
graduated bar, and the third one between them and free to slide back and
forth thereon.

Sonorescence.
The property of producing sounds under the influence of momentary light
radiations rapidly succeeding each other. It is the property utilized in
the photophone, q. v.

Fig. 306. MORSE SOUNDER.

Sounder.
In telegraphy an instrument consisting of an electromagnet with armature
attached to an oscillating bar, the range of whose movements is
restricted by adjusting screws. The armature is drawn away from the
magnet by a spring. When a current is sent through the magnet the
armature is drawn towards the poles and produces a sound as the bar
strikes a striking piece or second adjusting screw. When the current
ceases the bar and armature are drawn back, striking the first mentioned
screw with a distinct sound, the back stroke.

The sounder is used to receive Morse and analogous character messages.
The forward strokes correspond to the beginnings of the dots or dashes
of the code, the back strokes to beginnings of the intervals. The
distinction between dots and dashes is made by observing the interval
between forward and back stroke.

Various devices are used to increase the sound. Sometimes a resonance
box is used on which the sounder is mounted.

In practice sounders are generally placed on local circuits and are
actuated by relays.

489 STANDARD ELECTRICAL DICTIONARY.

Sound Reading.
The art or method of receiving telegraph messages by ear. It is now
universally used by all expert Morse operators. It can only be applied
to telegraph systems producing audible sounds; in some cases, as in
needle telegraphy, it may be quite inapplicable.

Space, Clearance.
The space between faces of the pole pieces and the surface of the
armature in a dynamo. It is really the air gap, but in calculating
dynamo dimensions the thickness of the insulated copper wire windings of
the commutator are counted in as part of the air gap, because copper is
almost the same as air in impermeability. Clearance space is a
mechanical factor; the air gap is an electric or magnetic factor.

Synonym--Inter-air Space.

Space, Crookes' Dark.
In an exhausted tube, through which an electric discharge is caused to
pass, the space surrounding the negative electrode of the tube. This
space is free from any luminous effect, and by contrast with the light
of the discharge appears dark. The vacuum may be made so high that the
dark space fills the whole space between the electrodes. It is less for
a less vacuum and varies for other factors, such as the temperature of
the negative electrode from which it originates, the kind of residual
gas present, and the quality of the spark.

Space, Faraday's Dark.
The space in an exhausted tube between the luminous glows about the two
electrodes.

Space, Interferric.
A term for the air-gap in a magnetic circuit. It is etymologically more
correct than air-gap, for the latter is often two-thirds or more filled
with the insulating material and copper wire of the armature windings.
(See Space, Clearance.)

Spark Arrester.
A screen of wire netting fitting around the carbons of an arc lamp above
the globe to prevent the escape of sparks from the carbons.

Spark Coil.
A coil for producing a spark from a source of comparatively low
electro-motive force. It consists of insulated wire wound round a core
of soft iron, best a bundle of short pieces of wire. Such a coil may be
eight inches long and three inches thick, and made of No. 18-20 copper
wire, with a core one inch in diameter. On connecting a battery
therewith and opening or closing the circuit, a spark is produced by
self-induction, q. v. It is used for lighting gas.

490 STANDARD ELECTRICAL DICTIONARY.

Spark, Duration of Electric.
Wheatstone determined the duration of the spark given by a Leyden jar as
1/24000 second. Feddersen by interposing a tube of water 9 millimeters
(.36 inch) long in its path found that it lasted 14/10000 second, and
with one 180 millimeters (7.2 inches) long, 188/10000 second. Lucas and
Cazin for a 5 millimeter (.2 inch) spark, with different numbers of
Leyden jars, found the following:
Number of jars. Duration of Spark.
2 .000026 second
4 .000041 "
6 .000045 "
8 .000047 "

The duration increases with the striking distance, and is independent of
the diameter of the balls between which it is produced.

Spark Gap.
The space left between the ends of an electric resonator (see Resonator,
Electric) across which the spark springs. Its size may be adjustable by
a screw, something like the arrangement of screw calipers.

Sparking.
In dynamo-electric machines, the production of sparks at the commutator
between the brushes and commutator sections. The sparks are often true
voltaic arcs, and in all cases are injurious if in any quantity, wearing
out the commutator and brushes.

Sparking, Line or Points of Least.
In a dynamo or electric motor the diameter of the commutator
determining, or the points on the commutator marking the position of the
brushes where the sparking is a minimum. Field magnets powerful in
proportion to the armature are a preventative cause. The direction of
the line fixes the angle of lead to be given to the brushes.

Sparking, Resistance to.
The resistance to disruptive discharge through its substance offered by
a dielectric or insulator. It does not depend on its insulating
qualities, but on its rigidity and strength.

Spark, Length of.
The length of the spark accompanying the disruptive discharge is counted
as the distance from one electrode to the other in a straight line. It
is longer for an increased potential difference between the two
electrodes. If the gas or air between the electrodes is exhausted the
length increases, until the vacuum becomes too high, when the length
begins to decrease, and for a perfect vacuum no spark however small can
be produced. The shape of the conductor which is discharged, the
material of the electrodes, and the direction of the current are all
factors affecting the length of spark producible.

491 STANDARD ELECTRICAL DICTIONARY.

Spark Tube.
A tube used as a gauge or test to determine when the exhaustion of the
vacuum chamber or bulb of an incandescent lamp is sufficiently high.

The interior of the tube is connected with the interior of the bulb or
chamber of the lamps in process of exhaustion, and hence shares their
degree of exhaustion. From time to time connections with an induction
coil are made. When the exhaustion is carried far enough no discharge
will take place through the vacuum. As long as the tube acts like a
Geissler tube the exhaustion is not considered perfect.

Specific Heat of Electricity.
The heat absorbed or given out by a fluid in passing from one
temperature to another depends on its specific heat. In the Peltier and
the Thomson effects. q. v., the electric current acts as the producer of
a change of temperature, either an increase or decrease as the case may
be. This suggests an absorption of and giving out of heat which amount
of heat corresponding to a current of known amount is determinable, and
may be referred to any unit of quantity such as the coulomb. This or
some equivalent definite quantity of heat it has been proposed (Sir
William Thomson) to term the Specific Heat of Electricity.

Spent Acid.
Acid which has become exhausted. In a battery the acid becomes spent
from combination with zinc. It also loses its depolarizing power, if it
is a chromic acid solution or of that type, and then may be said to be
spent.

Spent Liquor.
The liquor of a plating bath which has become exhausted from use, the
metal it contained being all or partly deposited.

Sphygmograph, Electric.
An electric apparatus for recording the beat of the pulse, both as
regards its rate and strength.

Sphygmophone.
An apparatus for examination of the pulse by the microphone and
telephone.

Spiders.
Core-discs of a dynamo or motor armature are sometimes perforated with a
large central aperture, are fastened together with insulated bolts, and
the whole mass is secured to the shaft by three- or four-armed spiders.
These are like rimless wheels, the ends of their arms being secured to
the hollow cylinder constituting the armature core, and a central
aperture in their hub receiving the shaft.

492 STANDARD ELECTRICAL DICTIONARY.

Spiral.
This term is sometimes used instead of coil, as the primary spiral or
secondary spiral of an induction coil or transformer.

Spiral Winding.
The winding used on ring armatures. This may diagrammatically be
represented by a spiral carried around the ring shaped core. With two
field poles it gives two collecting points, positive and negative, with
four field poles it gives four collecting points, alternately positive
and negative.

Splice Box.
A box in which the splices in underground cables and electric lines are
contained. The splicing is generally done in the boxes with the cables
in place. They may be two-way for straight lines, or be four-way for two
side or lateral connections.

Spluttering.
A term applied to a sound sometimes produced in a voltaic arc, perhaps
caused by impure or insufficiently baked electrodes. (Elihu Thomson.)

Spring Control.
Control of or giving the restitutive force to the needle of a
galvanometer, core of a solenoid ammeter or moving part of any similar
instrument by a spring. As an example see Ammeter, Ayrton's.

Fig. 307. SPRING JACKS.

Spring Jack.
An arrangement for effecting, at one insertion of a species of plug, the
opening or breaking of a circuit and for the simultaneous connection to
the terminals formed by the breaking of two terminals of another system
or loop. Thus let a line include in its circuit two springs pressing
against each other, thereby completing the circuit. If a plug or wedge
of insulating material were inserted between the springs so as to press
them apart it would break the circuit and the whole would constitute a
spring jack cut-out. If each side of the plug had a strip of brass or
copper attached to it, and if the ends of another circuit were connected
to these strips, then the insertion of the plug would throw the new line
into the circuit of the other line.

493 STANDARD ELECTRICAL DICTIONARY.

Spring Jack Cut-out.
A cut-out, of the general construction of a spring jack, q. v., except
that a simple insulating plug or wedge is used in place of the
metal-faced wedge with its connections of the regular spring jack. The
insertion of an insulating wedge opens the circuit, which on its removal
is closed. The regular spring jack wedge will operate in the same way,
if its connections are kept open.

Spurious Voltage.
The voltage in excess of that developed by a secondary battery which is
required in the charging process. It is about .25 volt.

Square Wire.
Wire whose cross-section is a square. It has been used of iron for
building up the cores of armatures for dynamos or motors, for which it
is peculiarly suitable, and also of copper as a winding for armatures.

Staggering. adj.
When the brushes of a dynamo are set, one a little in advance of the
other on the surface of the commutator, they are said to be set
staggering. It is used to get over a break in the armature circuit.

State, Electrotonic.
A term expressing an abandoned theory. Faraday at one time proposed the
theory that a wire had to be in the electrotonic state to produce
electro-motive force by movement through an electric field. Any such
idea was ultimately abandoned by Faraday.

Static Breeze.
The electric breeze obtained by the silent discharge of high tension
electricity.

Static Electricity.
Electricity at rest or not in the current form ordinarily speaking. The
term is not very definite and at any rate only expresses a difference in
degree, not in kind. The recognition of the difference in degree has now
to a great extent also disappeared.

Station, Central.
The building or place in which are placed electrical apparatus, steam
engines and plant supplying a district with electric energy.

Station, Distant.
The place at the further end of a telegraph line, as referred to the
home station.

Station, Home.
The end of a telegraph line where the operators using the expression are
working.

494 STANDARD ELECTRICAL DICTIONARY.

Station, Transforming.
In alternating current distribution, a building or place where a number
of transformers are worked, so that low potential or secondary circuits
are distributed therefrom.

Steel.
A compound of iron with carbon. The carbon may range from a few
hundredths of one per cent. up to two per cent. For magnets, tool steel
drawn to a straw color or a little lower is good. All shaping and filing
should be done before magnetization.

Steeling.
The deposition of iron on copper plates by electrolysis. In
electrotyping a thin deposit of iron is thus given the relief plates
before printing from them. The deposit is very hard and exceedingly
thin, so that it does not interfere with the perfection of the
impression in the printing process. As the iron becomes worn it can be
dissolved off with hydrochloric acid, which does not dissolve the
copper, and a new deposit can be given it. Thus the plate may last for
an indefinite number of impressions.

The iron bath may be prepared by immersing in a solution of ammonium
chloride, two plates of iron, connected as anode and kathode in a
circuit. One plate dissolves while hydrogen is given off from the other.
The solution thus produced is used for a bath.

The hardness of the deposit, which is really pure iron, gives the name
of "steeling."

Synonym--Acierage.

St. Elmo's Fire.
Luminous static discharge effects sometimes seen on objects elevated in
the air. They are especially noticed on ships' masts. The sailors term
them corpusants (holy bodies). They resemble tongues or globes of fire.

Step-by-step Telegraphy.
A system of telegraphy in which in the receiving instrument a hand is
made to move step-by-step, with an escape movement around a dial. For
each step there is a letter and the hand is made to stop at one or the
other letter until the message is spelled out. (See Dial Telegraph.)

Step-down. adj.
A qualification applied to a converter or transformer in the alternating
current distribution, indicating that it lowers potential difference and
increases current from the secondary.

Step-up. adj.
The reverse of step-down; a qualification of a transformer or converter
indicating that it raises the potential and decreases the current in the
secondary.

Sticking.
The adherence, after the current is cut off, of the armature to the
poles of a magnet. In telegraphy it is a cause of annoyance and
obstructs the working. It may, in telegraphy, be due to too weak a
spring for drawing back the armature, or to imperfect breaking of the
contact by the despatcher's key or by the receiver's relay.

495 STANDARD ELECTRICAL DICTIONARY.

Stopping Off.
In electroplating the prevention of deposition of the plating metal on
any desired portions of the object. It is effected by varnishing the
places where no coating is desired. An article can be plated with
silver, stopped off in any desired design, and the unvarnished portions
may then be plated with gold in another bath. Various effects can be
produced by such means.

Storage Capacity.
A term for the ampere-hours of electricity, which can be taken in
current form from a storage battery.

Storage of Electricity.
Properly speaking electricity can only be stored statically or in static
condensers, such as Leyden jars. The term has been popularly applied to
the charging of secondary or storage batteries, in which there is really
no such thing as a storage of electricity, but only a decomposition and
opposite combination brought about, which leave the battery in a
condition to give a current.

Storms, Electric.
Wide-spread magnetic and electric disturbances, involving the
disturbance of the magnetic elements and other similar phenomena. (See
Magnetic Storms.)

Strain.
The condition of a body when subjected to a stress. Various consequences
may ensue from strain in the way of disturbance of electric and other
qualities of the body strained.

Stratification Tube.
A Geissler tube, q. v., for showing the stratification of the electric
discharge through a high vacuum.

The stratifications are greatly intensified by the presence of a little
vapor of turpentine, alcohol, bisulphide of carbon and other substances.

Stray Field.
In a dynamo or motor the portion of the field whose lines of force are
not cut by the armature windings.

Stray Power.
The proportion of the energy wasted in driving a dynamo, lost through
friction and other hurtful resistances.

Streamlets, Current.
A conception bearing the same relation to an electric current that lines
of force do to a field of force; elementary currents. If evenly
distributed the current is of uniform density; if unevenly distributed,
as in alternating currents, the current density varies in different
parts of the cross section of the conductor. This evenness or unevenness
may be referred to the number of streamlets per unit of area of
cross-section.

Stress.
Force exercised upon a solid tending to distort it, or to produce a
strain.

496 STANDARD ELECTRICAL DICTIONARY.

Stress, Dielectric.
The condition of a dielectric when maintaining a charge; its two
extremities are in opposite states of polarity, or are under permanent
potential difference. As the two opposite polarities tend to unite a
condition of stress is implied in the medium which separates them.

Stress, Electro-magnetic.
The stress produced upon transparent substances in an electro-magnetic
field of force. It is shown in the modified optical properties of glass
and similar substances placed between the poles of a strong
electro-magnet.

Stress, Electrostatic.
The stress produced upon substances in an electrostatic field of force;
the exact analogue of electro-magnetic stress, and affecting transparent
substances in the same general way.

Striae, Electric.
In Geissler tubes the light produced by the electric discharge is filled
with striae, bright bands alternating with dark spaces; these may be
termed electric striae.

Striking Distance.
The distance that separates two conductors charged with electricity of
different potential, when a spark starts between them.

Striking Solution.
In silver-plating a bath composed of a weak solution of silver
cyanide-with a large proportion of free potassium cyanide. It is used
with a strong current and a large silver anode. This gives an
instantaneous deposition of metallic silver over the surface of the
article which goes to insure a perfect coating in the silver bath
proper. After a few seconds in the striking solution, the article is at
once removed to the plating bath.

Stripping.
The removal of electroplating from an object. It may be effected in
several ways. An object whose plating is to be removed is placed in a
plating bath of the solution of the metal with which it is coated. It is
connected as the anode to the positive plate of the battery or
corresponding terminal of the generator. A kathode connected to the
other terminal being placed in the bath, the coating is dissolved by
electrolytic action. Sometimes simple treatment with acid is employed.
Different stripping baths are described under the heads of the different
metals.

S. U.
Symbol or abbreviation for Siemens' Unit of Resistance. (See Resistance,
Siemens' Unit of.)

Sub-branch.
A branch or lead of wire taken from a branch lead: a term used in
electric distribution.

Sub-main.
In electric distribution a conductor connected directly to a main; a
branch.

497 STANDARD ELECTRICAL DICTIONARY.

Subway, Electric.
A subterranean system of conduits for electric cables. As generally
constructed in this country it includes manholes, q. v., at the street
corners connected by ducts or pipes. These pipes are large enough to
hold a cable. To introduce a cable into a duct, which latter may be two
or three inches in diameter, and from two hundred to six or seven
hundred feet long, a wire or rope is first passed through the duct. This
is done by a set of short wooden rods with screws at the end so as to be
screwed together. Each rod must be shorter than the diameter of the
manhole. A rod is thrust in, another is screwed to it and thrust in, and
thus a set of rods is made to extend as far as desired. In pulling them
out a rope is attached and drawn through. This rope or a larger one is
used in drawing the cable through the duct. A windlass is employed to
draw the rope with cable attached through the ducts.

Sulphating.
In storage battery cells, the formation of a hard white basic lead
sulphate, Pb2 S05. Its formation is due to over-exhaustion of the cells.
As long as the voltage is not allowed to fall below 1.90 volts per cell
little of it forms. As it accumulates it is apt to drop off the plate
and fall to the bottom, thus weakening the plate possibly, and depriving
it of active material, and clogging up the cell. If it carries a film of
metallic lead with it, there is danger of short circuiting the cell.

The presence of some sodium sulphate in the solution is said to tend to
prevent sulphating, or to diminish it.

Sulphur Dioxide.
A compound gas, S O2; composed of
Sulphur, 32
Oxygen, 32
Molecular weight, 64
Specific gravity, 2.21.

It is a dielectric of about the same resistance as air. Its specific
inductive capacity at atmospheric pressure is: 1.0037 (Ayrton).

Synonyms--Sulphurous Acid--Sulphurous Acid Gas.

Sunstroke, Electric.
Exposure to the arc light sometimes produces the effects observed in
cases of sunstroke. It is said that, in the case of workmen at electric
furnaces, these effects are very noticeable. (See Prostration,
Electric.)

Supersaturated. adj.
A liquid is supersaturated when it has dissolved a substance at a
temperature favorable to its solubility and its temperature has been
allowed to change, the liquid being kept free from agitation or access
of air, provided crystallization or precipitation has not taken place.
It expresses the state of a liquid when it holds in solution more than
the normal quantity of any substance soluble in it.

Surface.
A galvanic battery is arranged in surface when all the positive plates
are connected together and all the negative plates are also connected.
This makes it equivalent to one large cell, the surface of whose plates
would be equal to the aggregate surface of the plates of the battery. It
is also used as an adjective, as "a surface arrangement of battery."

498 STANDARD ELECTRICAL DICTIONARY.

Surface Density.
The relative quantity of an electric charge upon a surface.

Surface, Equipotential.
A surface over all of which the potential is the same. In a general
sense equipotential surfaces are given by planes or surfaces which cut
lines of force at right angles thereto, or which are normal to lines of
force. The conception applies to electrostatic and electro-magnetic
fields of force, and for current conductors the planes normal to the
direction of the current are equipotential surfaces.

The contour of an equipotential surface of a field of force which is
drawn or represented by delineations of its lines of force can be
obtained by drawing a line normal thereto. This line will ordinarily be
more or less curved, and will be a locus of identical potentials.

An electric equipotential surface may be described as electro-static,
electro- magnetic, or magnetic; or may be an equipotential surface of a
current conductor. Besides these there are mechanical and physical
equipotential surfaces, such as those of gravitation.

Surface Leakage.
Leakage of current from one part of an insulating material to another by
the film of moisture or dirt on the surface.

Suspension.
This term is applied to methods of supporting galvanometer needles,
balance beams, magnetic compass needles and similar objects which must
be free to rotate. (See Suspension, Bifilar--Fibre and Spring
Suspension--Fibre Suspension--Knife Edge Suspension--Pivot
Suspension--Suspension, Torsion.)

Fig. 308. DIAGRAM OF BIFILAR SUSPENSION.

Suspension, Bifilar.
Suspension by two vertical parallel fibres, as of a galvanometer needle.
The restitution force is gravity, the torsion being comparatively slight
and negligible. Leaving torsion out of account the restitution force is
(a) proportional to the distance between the threads;. (b) inversely
proportional to their length; (c) proportional to weight of the needle
or other object suspended; (d) proportional to the angle of
displacement.

499 STANDARD ELECTRICAL DICTIONARY.

Assume two masses A and B at the end of a weightless rod, suspended by
the parallel cords a A, b B. Let the rod be rotated through an angle
theta. Consider the cord a A. Its lower end is swung through the angle
theta, as referred to the center O; the cord is deflected from the
vertical by an angle psi, such that a A tang(psi)= O A 2 sin (theta/2).
The component of gravitation tending to restore A to A, acting towards A
is equal to m g tan(psi). Its moment around O is equal to (m g tan(psi))
* (O A cos(theta/2). The whole moment of the couple is 2 m g tan(psi).
0 A. cos(theta/2) = 2 m g (O A2/ a A) 2 sin(theta/2). Cos(theta/2) =
2mgl(OA2/aA) sin(theta). The moment of the restoring force is thus
proportional to the sine of the angle of deflection, and the
oscillations of such a system are approximately simple harmonic.
(Daniell.)

If the twisting is carried so far as to cause the threads to cross and
come in contact with each other the suspension ceases to be a bifilar
suspension, but assumes the nature of a torsional suspension.

Swaging, Electric.
Mechanical swaging in which the objects to be swaged are heated by an
electric current as in electric welding.

S. W. G.
Abbreviation for Standard Wire Gauge.

Fig. 309. SIMPLE SWITCH.

Switch.
A device for opening and closing an electric circuit.

A simple type is the ordinary telegrapher's switch. A bar of metal is
mounted horizontally by a pivot at one end, so as to be free to rotate
through an arc of a circle. In one position its free end rests upon a
stud of metal. One terminal of a circuit is attached to its journal, the
other to the stud. Resting on the stud it closes the circuit, in other
positions it opens the circuit.

500 STANDARD ELECTRICAL DICTIONARY.

Switch, Automatic.
A switch opened and closed by the electric current. It is used for
lighting distant incandescent lamps. It includes one or two
electro-magnets operated by two push buttons. In the usual arrangement
one button is black and the other white, for extinguishing and lighting
respectively. When the white button is pushed it causes a current to
pass through one of the electro-magnets. This attracts its armature,
thereby making a contact and throwing the lamps into the lighting
circuit. Then they remain lighted until the black button is pressed.
This excites the other magnet, which attracts its armature, breaks the
contact and extinguishes the lights.

The object of the automatic switch is to enable distant lamps to be
lighted without the necessity of carrying the electric leads or wires to
the place whence the lighting is to be done. A very small wire will
carry enough current to operate the magnets, and open circuit batteries,
such as Leclanché batteries, may be used as the source of current for
the switch, but generally the lighting current is used for the purpose.

A single magnet may do the work. When the lighting button is pressed the
magnet is excited, attracts its armature and holds it attracted, until
by pressing the black button the current is turned off from it. In this
case the lighting current is used to excite the magnet.

Switch Board.
A board or tablet to which wires are led connecting with cross bars or
other switching devices, so as to enable connections among themselves or
with other circuits to be made.

Switch, Circuit Changing.
A switch whose arm in its swing breaks one contact and swinging over
makes another. It is employed to change the connections of circuits from
one dynamo to another.

Synonyms--Changing Switch--Changing Over Switch.

Switch, Double Break.
A form of switch in which double contact pieces are provided to give a
better contact. One form consists of a hinged bar whose end swings down
between two pairs of springs. Both pairs are connected to one terminal,
and the bar to the other terminal of a circuit.

Switch, Double Pole.
A heavy switch for central station work, that connects and disconnects
two leads simultaneously.

Switch, Feeder.
A heavy switch, often of double contact type, for connecting and
disconnecting feeders from bus bars in central stations.

501 STANDARD ELECTRICAL DICTIONARY.

Switch, Knife.
A switch whose movable arm is a narrow, deep bar of copper or brass, and
which in making contact is forced in edgeways between two springs
connected to one terminal. The bar is connected to the other terminal.

Synonyms--Knife Break Switch--Knife Edge Switch.

Switch, Multiple.
A switch which in the swing of its bar connects one by one with a number
of contacts so that ultimately the end of its bar is in contact with all
at once. It is used to throw lights in and out in succession, and it
can, if the multiple contacts connect with resistances, make them
operate as a rheostat.

Switch, Pole Changing.
A switch for changing the direction of the current in a circuit.

Switch, Reversing.
A switch, often of the plug type (see Plug Switch) for changing the
direction of current passing through a galvanometer.

Switch, Snap.
A switch constructed to give a quick, sharp break. It has a spiral
spring interposed between the handle and arm. As the handle is drawn
back to open it the spring is first extended, the bar being held by the
friction of the contacts, until the spring suddenly jerks it up, thus
breaking the contact.

Switch, Storage Battery Changing.
A switch for changing storage battery connections from series to
multiple and back again.

Switch, Three Way.
A switch, so constructed that by turning its handle connection can be
made from one lead to either of two other leads, and also so that
connection can be completely cut off.

Sympathetic Vibration.
The establishment of periodic movement in one body by impulses of the
same period communicated to it from another body in motion. Thus if two
tuning forks are of the same pitch and one is sounded the other will
begin to sound by sympathy, the sound waves communicating the necessary
periodic impulses to it.

Sympathetic vibrations are utilized in harmonic telegraphy. (See
Harmonic Receiver--Telegraph, Harmonic.)

501 STANDARD ELECTRICAL DICTIONARY.

T.
Symbol of time.

Tailings.
(a) In high speed transmission of telegraph signals by the automatic
system, the definiteness of the signal marks is sometimes interfered
with by retardation. Wrong marks are thus produced called tailings.

(b) The prolongation of the current at the distant receiving station of
a telegraph line due to the discharge of the line and to self-induction.

Synonyms--Tailing--Tailing Current.

502 STANDARD ELECTRICAL DICTIONARY.

Tamidine.
Reduced nitro-cellulose. Nitro-cellulose is dissolved in a proper
solvent and is obtained by evaporation as a translucent solid mass. By
ammonium sulphide or other reagent it is reduced so as to be virtually
cellulose. It is cut into shape for filaments of incandescent lamps,
which shapes are carbonized and flashed.

Tangent Law.
In a galvanometer the tangents of the angles of deflection of the needle
are proportional to the deflecting force--

I. When the controlling force is unaltered in absolute magnitude and
direction by the motion of the needle.

II. When the deflecting force acts at right angles always to the
controlling force.

These conditions are usually secured by having the actuating coil
through which the current passes flat and of large diameter compared to
the length of the needle; by using the uniform field of the earth as the
control; by having a short needle; by placing the coil with its plane in
the magnetic meridian.

For best proportions of tangent galvanometer coils see Bobbins.

Fig. 310. GRAPHIC CONSTRUCTION OF TANGENT SCALE.

Tangent Scale.
An arc of a circle in which the number of graduations in any arc
starting from zero are proportional to the tangent of the angle
subtended by such arc. The system is for use with tangent galvanometers.
Thus if for 45° a value of 100 is taken and marked on the scale then for
the arc 26° 33' + a value of 50 should be marked on the scale because
such are the relative values of the tangents.

Thus the scale instead of being divided into degrees is divided into
arcs of varying length, growing shorter as they are more distant from
the zero point, of such length that the first division being subtended
by a tangent of length 1, the first and second divisions added or taken
together as one arc are subtended by a tangent of length 2, and so on.

In the cut a simple method of graphically laying out a tangent scale is
shown. In it C is the centre of the arc, and H the radius running to the
zero of the instrument. From C a circle is described and on H a vertical
line tangent to the arc is erected. Taking any part of the tangent, as
the length shown ending at D, it is divided into any number of equal
parts. Radii of the circle are now drawn whose prolongations pass
through the divisions on the tangent. These radii, where they intersect
the arc of the circle, determine equal divisions of the tangent scale,
which, as is evident from the construction, are unequal angular
divisions of the arc.

503 STANDARD ELECTRICAL DICTIONARY.

Tanning, Electric.
The tanning of hides in the manufacture of leather by the aid of
electrolysis. A current of electricity is maintained through the tanning
vats in which regular tanning liquor is contained. Very extraordinary
claims are made for the saving of time in the tanning process. What is
ordinarily a process of several months, and sometimes of a year, is said
to be reduced to one occupying a few days only. The action of
electrolysis is the one relied on to explain the results.

Tapper.
The key used in single needle telegraph transmitters. It comprises two
flat springs L, E, each with a handle, normally pressed upward against
one contact bar Z, and when pressed down by the operator making contact
against a lower bar C when messages are to be transmitted. A double
tapper, such as shown, is used for each instrument.

Synonyms--Double Tapper Key--Pedal Key.

Fig. 311. TAPPER.

Target, Electric.
A target registering or indicating electrically upon an annunciator the
point of impact of each bullet.

Taste, Galvanic.
The effect produced upon the gustatory nerves by the passage of an
electric current, or by the maintenance of potential difference between
two portions of the tongue. It is very simply produced by placing a
silver coin above, and a piece of zinc below the tongue, or the reverse,
and touching their edges. A sour, peculiar taste is at once perceived.
It cannot be due to any measurable quantity of current or of
electrolytic decomposition, because the couple can do little more than
establish a potential difference. With a strong current the taste
becomes too strong for comfort, and if on a telegraph line the extra
currents produced by the signaling make the operation of tasting the
current a very unpleasant one. It is said that messages have been
received in this way, the receiver placing one terminal of the line on
his tongue, and a terminal attached to a grounded wire below it, and
then receiving the Morse characters by taste.

504 STANDARD ELECTRICAL DICTIONARY.

Teazer.
Originally a fine wire coil wound on the field magnets of a dynamo in
shunt with the regular winding to maintain the magnetism. It was
originally used in electroplating machines to prevent inversion of the
magnetism, but has since developed into a component part of the winding
of the compound dynamo. (See Dynamo, Compound.)

Tee, Lead.
A lead pipe of T shape used for connecting branches to electric cables.
The tee is soldered by wiped joints to the lead sheathings of the cable
and branches after the wires have been connected, and the junctions
coated with insulating tape or cement, or both.

It is sometimes made in two halves, and is known as a split tee.

Tel-autograph.
A telegraph for reproducing the hand-writing of the sender at the
receiving end of the line. To save time a special spelling is sometimes
used.

Teleautograph.
The special spelling used with the Tel-Autograph telegraph.

Tele-barometer, Electric.
A barometer with electric attachment for indicating or recording at a
distance the barometric readings.

Telegraph, ABC.
This term is applied to alphabet telegraphs indicating the message by
the movements of a pointer on a dial marked with the characters to be
sent. In England the Wheatstone ABC system is much employed.

Telegraph, Automatic.
A telegraph system based on the operation of the transmitting instrument
by a perforated strip of paper drawn through it. The perforations made
by an apparatus termed a perforator, are so arranged as to give
telegraphic characters of the Morse or International Code in the
transmitting instrument. (See Perforator.) Bain in the year 1846 was the
originator of the system. He punched a fillet of paper with dots and
dashes, and drew it between two terminals of the line, thus sending over
the line a corresponding series of short and long currents which were
received by his chemical receiver. (See Chemical Receiver.) The method
was not successful. Its modern development, the Wheatstone Automatic
Telegraph, is highly so. The perforated paper by its perforations
controls the reciprocating movement of two rods, which pass through each
hole in two rows, corresponding to the two rods respectively as the
holes come opposite to the ends of the rods. The rods are kept
constantly moving up and down. If unperforated paper is above them their
upward motion is limited. This gives three positions for the rods, (a)
both down, (b) one up and the other down, (c) both up. These positions
of the rods work a pole changing key by which dots, spaces, and dashes
are transmitted to the receiving instrument, which is an exceedingly
delicate ink-printer. The latter can have its speed adjusted to receive
from 200 to 450 words per minute.

505 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Dial.
A telegraph in which as receiver a dial instrument is used. A pointer or
index hand moves around a dial. The dial is marked with letters of the
alphabet. The movements of the pointer are controlled by the
transmitting operator at a distant station. He by the same actions moves
a pointer on a duplicate instrument before him and the two are
synchronized to give identical indications. Thus a message is spelled
out letter by letter on both dials simultaneously. The motions of the
index are generally produced by what is virtually a recoil escapement.
The scape wheel is carried by the axle of the index, and a pallet or
anchor is vibrated by an electro-magnet whose armature is attached to
the stem of the pallet. As the pallet is vibrated it turns the wheel and
index one tooth for each single movement. There are as many teeth in the
wheel as there are characters on the dial. The two instruments being in
duplicate and synchronized, the pallets move exactly in unison, so that
identical readings of the dials are given. The pallets may be moved by
any kind of make and break mechanism, such as an ordinary telegraph key.
The index moves by steps or jerks, so that the system is sometimes
called step-by-step telegraphy.

Fig. 312. DIAL TELEGRAPH.

In the cut the make and break transmitter is shown at v v, with its
handle and contacts g and t. This mechanism sends impulses of current by
F and Z to the receiving magnet l. This attracts and releases its
armature K from contact into the position indicated by the dotted lines.
This works the rocker n on the pin o, and actuates the double or anchor
pawl s r, which turns the pallet or scrape wheel m.

The system is dropping into disuse, being supplanted by the telephone.

Synonym--Step-by-step Telegraph.

506 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Double Needle.
A telegraph system in which the message is read by the motions of two
vertical needles on the face of the instrument in front of the receiving
operator. An identical instrument faces the transmitting operator. By
two handles, one for each hand, the needles are caused by electric
impulses to swing to right and to left so as to give a telegraphic code.
It has been generally superseded by the single needle telegraph.

Telegraph, Duplex.
A telegraph capable of transmitting simultaneously two messages over one
wire. The methods of effecting it are distinct from those of multiplex
telegraphy. This term is used as a distinction from diode multiplex
telegraphy, in which the work is done on other principles. There are two
systems of duplex telegraphy, the differential and the bridge systems.

Telegraph, Duplex Bridge.
A system of duplex telegraphy employing the principle of the Wheatstone
bridge. The other or differential system depends on equality or
difference of currents; the bridge method on equality or difference of
potentials. The cut shows the system known as Steam's Plan.

At the ends of the line wire are two cross connections like duplicate
galvanometer connections in a Wheatstone bridge, each including a
receiving relay. The rest of the connections are self-explanatory.

When A depresses his key the current splits at the point indicating the
beginning of the bridge. One portion goes through the line to B and to
earth, the other goes to earth at A through the rheostats indicated by
the corrugated lines.

On reaching B's end the current divides at the cross-connection and part
goes through the receiving relay shown in the center of that
cross-connection.

Thus if A sends to B or B to A it is without effect on the home
receiving instrument. Now suppose that both simultaneously are sending
in opposite directions. If the connections be studied it will be seen
that every movement of the transmitting key will affect the balance of
the distant or receiving end of the bridge and so its instrument will
record the signals as they are sent.

As shown in the cut the sending keys are on local circuits, and work
what are known as duplex transmitters. These are instruments which send
line signals without breaking the connection.

Fig. 313. STEARN'S PLAN OF DUPLEX BRIDGE TELEGRAPHY.

In Stearn's plan condensers are introduced as shown. By this plan
different receiving instruments can be used. The inventor once worked a
Morse instrument at one end of the line, and a Hughes' instrument at the
other end.

507 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Duplex, Differential.
A system of duplex telegraphy employing the differential action of two
exciting or magnetizing coils. The general principles are the following.
Suppose that at each of two stations, there is a magnet working as a
sounder or relay. Each magnet is differentially wound, with two coils of
opposite direction, of identical number of turns.

When the sending key at a station A is depressed two exactly equal
currents go through the magnet in opposite directions. One called the
compensation current goes to the earth at the stations. The other called
the line current goes through the line, through the line coil of the
distant station E, thereby actuating the relay or sounder armature.

The instrument of the sender A is unaffected because he is sending
opposite and equal currents through its two coils. A special resistance
is provided on the compensation circuit for keeping the currents exactly
equal in effect. Nothing the sender at A does affects his own
instrument.

Now suppose E desires to telegraph back at the same time that A is
telegraphing to his station. He works his key. This does not affect his
own instrument except by sending the equal and opposite currents through
its coils. When his key is depressed and A's key is untouched, he works
A's receiving instrument.

508 STANDARD ELECTRICAL DICTIONARY.

When A's key is depressed simultaneously with B's key, the two line
currents are in opposition and neutralize each other. This throws out
the balance in the instruments and both armatures are attracted by the
compensation currents left free to act by the neutralization of the line
currents.

Fig. 314. DUPLEX TELEGRAPH, DIFFERENTIAL SYSTEM

Suppose that B is sending a dash, and it begins while A's key is raised.
The line and compensation currents in B's receiving instrument
neutralize each other and no effect is produced, while A's receiving
instrument begins to register or indicate a dash. Now suppose A starts
to send a dash while B's is half over. He depresses his key. This sends
the two opposite currents through his magnet. His line current
neutralizes B's working current so that the compensation currents in
both receiving instruments hold the armatures attracted for the two
dashes. Meanwhile A's dash ends and he releases his key. At once his
line current ceases to neutralize B's line current, his receiving
instrument is actuated now by B's line current, while B's receiving
instrument ceases to be actuated by the compensation current.

Two assumptions are made in the above description. The line currents are
assumed to be equal in strength and opposite in direction at each
station. Neither of these is necessary. The line current received at a
station is always weaker than the outgoing line current, and it is the
preponderance of the compensation current over the partly neutralized
line current that does the work. As this preponderance is very nearly
equal to the line current received from the distant station, the signals
are actuated by almost the same current, whether it is compensation or
line current.

509 STANDARD ELECTRICAL DICTIONARY.

Both line currents may coincide in direction. Then when the two keys are
depressed, a line current of double strength goes through both receiving
instruments and both work by preponderance of the double line current
over the compensation current. In other respects the operation is the
same as before described.

Fig. 315. DUPLEX TELEGRAPH, DIFFERENTIAL SYSTEM.

Fig. 316. DIFFERENTIAL DUPLEX TELEGRAPH CONNECTIONS.

The cut shows a diagram of the operation of one end of the line. R and R
are resistances, E and E are earth contacts, and the two circles show
the magnet of the receiving instrument wound with two coils in
opposition. The battery and key are also shown. It also illustrates what
happens if the key of the receiver is in the intermediate position
breaking contact at both 1 and 2. The sender's line current then goes
through both coils of the receiving instrument magnet, but this time in
series, and in coincident direction. This actuates the instrument as
before. Owing to the resistance only half the normal current passes, but
this half goes through twice as many coils or turns as if the receiver's
key was in either of the other two positions.

In actual practice there are many refinements. To compensate for the
varying resistance of the line a rheostat or resistance with sliding
connection arm is connected in the compensation circuit so that the
resistance can be instantly changed. As the electro-static capacity of
the line varies sectional condensers are also connected in the
compensation circuits.

510 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Facsimile.
A telegraph for transmitting facsimiles of drawing or writing. The
methods employed involve the synchronous rotation of two metallic
cylinders, one at the transmitting end, the other at the receiving end.

On the transmitter the design is drawn with non-conducting ink. A tracer
presses upon the surface of each cylinder and a circuit is completed
through the two contacts. In operation a sheet of chemically prepared
paper is placed over the surface of the receiving cylinder. The two
cylinders are rotated in exact synchronism and the tracers are traversed
longitudinally as the cylinders rotate. Thus a number of makes and
breaks are produced by the transmitting cylinder, and on the receiving
cylinder the chemicals in the paper are decomposed, producing marks on
the paper exactly corresponding to those on the transmitting cylinder.

Synonyms--Autographic Telegraph--Pantelegraphy.

Telegraph, Harmonic Multiplex.
A telegraph utilizing sympathetic vibration for the transmission of
several messages at once over the same line. It is the invention of
Elisha Gray. The transmitting instrument comprises a series of vibrating
reeds or tuning-forks, each one of a different note, kept in vibration
each by its own electro-magnet. Each fork is in its own circuit, and all
unite with the main line so as to send over it a make and break current
containing as many notes superimposed as there are tuning forks. At the
other end of the line there are corresponding tuning forks, each with
its own magnet. Each fork at this end picks up its own note from the
makes and breaks on the main line, by the principle of sympathetic
vibration.

To each pair of operators a pair of forks of identical notes are
assigned. As many messages can be transmitted simultaneously as there
are pairs of forks or reeds.

The movements of a telegraph key in circuit with one of the transmitting
reeds sends signals of the Morse alphabet, which are picked out by the
tuning fork of identical note at the other end of the line.

511 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Hughes'.
A printing telegraph in very extensive use in continental Europe. Its
general features are as follows:

The instruments at each end of the line are identical. Each includes a
keyboard like a piano manual, with a key for each letter or character.
On each machine is a type wheel, which has the characters engraved in
relief upon its face. With the wheel a "chariot" as it is termed also
rotates. The type wheels at both stations are synchronized. When a key
is depressed, a pin is thrown up which arrests the chariot, and sends a
current to the distant station. This current causes a riband of paper to
be pressed up against the face of both type wheels so as to receive the
imprint of the character corresponding to the key. The faces of the
wheels are inked by an inking roller.

Fig. 317. ELECTRO-MAGNET OF HUGHES' PRINTING TELEGRAPH.

The most characteristic feature is the fact that the current sent by
depressing a key does not attract an armature, but releases one, which
is then pulled back by a spring. The armature is restored to its
position by the mechanical operation of the instrument. The magnet used
is a polarized electro-magnet. Coils are carried on the ends of a strong
powerful magnet. The coils are so connected that a current sent through
them by depressing a key is in opposition to the magnetism of the
permanent magnet so that it tends to release the armature, and in
practice does so. This release permits the printing mechanism to act.
The latter is driven by a descending weight, so that very slight
electric currents can actuate the instruments.

Synonym--Hughes' Type Printer.

Telegraphic Code.
(a) The telegraphic alphabet, as of the Morse System. (See Alphabet,
Telegraphic.)

(b) A code for use in transmitting messages either secretly, or
comprising several words or short sentences in one word, in order to
economize in transmission. Such codes are extensively used in commercial
cable messages.

512 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Magneto-electric.
A telegraph in which the current is produced by magneto-electric
generators. It has been applied to a considerable extent in England. The
Wheatstone ABC or dial telegraph is operated by a magneto-generator
turned by hand.

In this country the magneto-electric generator by which the calling bell
of a telephone is rung is an example. The magneto-electric key (See Key,
Magneto-electric) is for use in one kind of magneto-electric
telegraphing.

Telegraph, Morse.
A telegraph, characterized by the use of a relay, working a local
circuit, which circuit contains a sounder, or recorder for giving dot
and dash signals constituting the Morse alphabet. The signals are sent
by a telegraph key, which when depressed closes the circuit, and when
released opens it. The two underlying conceptions of the Morse Telegraph
system are the use of the dot and dash alphabet, and the use of the
local circuit, which circuit includes a receiving instrument, and is
worked by a relay, actuating a local battery. It would be difficult to
indicate any invention in telegraphy which has had such far-reaching
consequences as the one known as the Morse telegraph.

In other places the principal apparatus of the system will be found
described. The cut Fig. 318, repeated here gives the general disposition
of a Morse system. (See Circuit, Local.)

Fig. 318. DIAGRAM OF MORSE SYSTEM.

513 STANDARD ELECTRICAL DICTIONARY.

The key by which the messages are transmitted is shown in Fig. 319. M is
a base plate of brass. A is a brass lever, mounted on an arbor G carried
between adjustable set screws D. C is the anvil where contact is made by
depressing the key by the finger piece B of ebonite. E, Fl are adjusting
screws for regulating the vertical play of the lever. H is the switch
for opening or closing the circuit. It is opened for transmission, and
closed for receiving. By screws, L L, with wing nuts, K K, the whole is
screwed down to a table.

Fig. 319. MORSE TELEGRAPH KEY.

In the United States the simplest disposition of apparatus is generally
used. The main line is kept on closed circuit. In it may be included a
large number of relays at stations all along the line, each with its own
local circuit. There may be fifty of such stations. Battery is generally
placed at each end of the line. Very generally gravity batteries are
used, although dynamos now tend to supplant them in important stations.

As relays the ordinary relay is used. Its local circuit includes a
sounder and local battery. The latter is very generally of the gravity
type, but oxide of copper batteries (See Battery, Oxide of Copper) are
now being introduced. At main or central offices, the terminals of the
lines reach switch boards, where by spring-jacks and plugs, any desired
circuits can be looped into the main circuit in series therewith.

In European practise the main line is kept on open circuit. Polarized
relays are used to work the local circuits. The currents for these have
to be alternating in direction. When the line is not in use its ends are
connected to earth at both ends, leaving the battery out of circuit.
Each intermediate station has its own main, or line battery for use when
it desires to send a message. In the American system as first described,
it will be seen that the main batteries are at most two in number.

For the details of the different apparatus, the following definitions
may be consulted: Embosser, Telegraphic--Recorder, Morse--Relay--Relay
Connection--Sounder.

514 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Multiplex.
A system of telegraphy by which a number of messages can be transmitted
in both directions over a single wire. The principles underlying the
systems are the following:

Suppose that at the two extremities of a telegraph line two arms are
kept in absolute synchronous rotation. Let the arms in their rotation,
press upon as many conducting segments as there are to be transmissions
over the line. A transmitting and receiving set of instruments may be
connected to one segment at one end of the line, and another set to the
corresponding segment at the distant station. For each pair of segments
two sets can be thus connected. Then if the arm rotates so rapidly that
the contacts succeed each other rapidly enough each pair of sets of
instruments can be worked independently of the others. In practice this
rapid succession is effected by having a number of contacts made for
each pair during a single rotation of the arm or equivalent.

The multiplex system has been perfected by the use of La Cour's phonic
wheel (see Phonic Wheel), and brought into a practical success by
Patrick B. Delany, of New York.

Two phonic wheels rotate at each end of the line. They are kept in
synchronous motion by two vibrating steel reeds of exactly the same
fundamental note, and the axle of each wheel carries an arm whose end
trails over the contacts or distributor segments already spoken of. The
reeds are adjusted to vibrate at such speed that the trailer is in
contact with each segment about 1/500 second. The number of groups of
segments required for each working is determined by the retardation of
the signals owing to the static capacity of the line. To convert the
rapidly recurring impulses of current into practically a single current,
condensers are connected across the coils of the relay. One battery
serves for all the arms.

Multiplex telegraphy can effect from two to six simultaneous
transmissions over one wire. For two or four transmissions the method
only distinguishes it from duplex or quadruplex telegraphy. The terms
diode, triode, tetrode, pentode and hexode working are used to indicate
respectively the simultaneous transmission of two, three, four, five, or
six messages over one wire.

It will be seen that the multiplex process really assigns to each
transmission separate times, but divides these times into such short and
quickly recurring intervals that the work is executed as if there was
continuous contact. In no case is there the popular conception of the
sending of several messages actually simultaneously over one wire. Each
signal in reality has its own time assigned it, divided into short
periods of high frequency, and only utilizes the line when it is free.

515 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Over-house.
An English term for telegraph lines led over houses and supported on
standards on the roofs.

Telegraph Pole Brackets.
Arms for carrying insulators, which arms are attached to telegraph poles
or other support. They vary in style; sometimes they are straight bars
of wood gained into and bolted or spiked in place; sometimes they are of
iron.

Telegraph, Printing.
Various telegraphs have been invented for printing in the ordinary
alphabet the messages at the receiving end of the line.

Representative instruments of this class are used for transmitting
different market and stock reports to business offices from the
exchanges. The type faces are carried on the periphery of a printing
wheel, which is rotated like the hand of a dial telegraph, and against
whose face a paper riband is pressed whenever the proper letter comes
opposite to it. As each letter is printed the paper moves forward the
space of one letter. Spacing between words is also provided for. In the
recent instruments two lines of letters are printed on the paper one
above the other.

In England, and on the continent of Europe, printing instruments have
received considerable use for ordinary telegraphic work. Hughes' type
printer and Wheatstone's ABC telegraph meet with extensive use there for
ordinary transmission.

Telegraph, Quadruplex.
Duplex telegraphy is the sending of two messages in opposite directions
simultaneously through the same wire. Duplex telegraphy is the sending
of two messages simultaneously in the same direction. The two combined
constitute quadruplex telegraphy. [SIC]

The system was suggested by Stark of Vienna and Bosscha of Leyden in
1855; the successful problem was solved by Edison in 1874.

The principle is based on the two orders of difference in electric
currents; they may vary in strength or in direction. Thus we may have
one instrument which works with change of strength of current only, the
other with change of direction only. The two can be worked together if
the direction of the current can be altered without alteration of
strength, and if strength can be altered without alteration of
direction. Double current and single current working are so combined
that one relay works by one system of currents and another relay by the
other system. A current is constantly maintained through the line. The
relay operated by change in direction is a simple polarized relay which
works by change of direction of current. The relay operated by change in
strength is the ordinary unpolarized relay.

516 STANDARD ELECTRICAL DICTIONARY.

For the following description and the cuts illustrating it we are
indebted to Preece and Sivewright. The cut shows the arrangement of the
apparatus and connections for terminal offices.

"Sufficient table room is provided to seat four clerks. The apparatus is
arranged for the two senders to sit together in the centre, the messages
to be forwarded being placed between them. The section on the left of
the switch Q is known as the 'A' side, that on the right as the 'B' side
of the apparatus.

K1 the reversing key, reverses the direction of the current. K2 is a
simple key, known as the increment key; it is used simply to increase
the strength of the current.

Fig. 320. QUADRUPLEX TELEGRAPH CONNECTIONS.

The way in which the keys K1 and K2 combine their action is shown by
Fig. 321. E1 and E2 are the line batteries, the one having two and
one-third (2-1/3) the number of cells of the other, so that if E1 be the
electro-motive force of the smaller, that of the whole combined battery
will be 3.3 E1. The negative pole of E1 is connected to z and z1 of K1
and the positive pole of E2 to a of K2 through a resistance coil s. A
wire, called the 'tap' wire, connects the positive pole of E1 and the
negative pole of E2 to b of K2. This wire has in it a resistance coil
r2. The springs c and c1 of Kl are connected to the lever L of K2. Now,
when both keys are at rest, the negative pole of E1 is to line through
z, and the positive pole of E1 to earth through b of K2 and c of K1; the
positive pole of E2 being insulated at a of K2.

517 STANDARD ELECTRICAL DICTIONARY.

There is thus a weak negative current flowing to line. When K1 alone is
worked, the current of E1 is reversed. When K2 is worked alone, c of K1
is transferred from b to a, and the strength of the negative current
going to line is increased through the increase of the electro-motive
force from E1 to 3.3 E1 for the whole battery is brought into play. When
K1 and K2 are depressed together, then the negative pole of E1 goes to
earth through Z1; and the positive pole of E2 to line through a of K2
and c1 of K1 and a positive current, due to the whole electro-motive
force 3.3 E1 goes to line. Hence the effect of working K1 is simply to
reverse the current, whatever its strength, while that of K2 is to
strengthen it, whatever its direction.

The resistance coil s, of 100° resistance, is called a spark coil,
because it prevents the high electro-motive force of the whole battery
from damaging the points of contact by sparking or forming an arc across
when signals are sent; and the resistance r2 is made approximately equal
to the combined resistance of E2 and the spark coil, so that the total
resistance of the circuit may not be altered by the working of the
apparatus.

Fig. 321. QUADRUPLEX TELEGRAPH.

A1 and B1 (Fig. 320) are the relays which are used to respond to the
changes in the currents sent by the keys K1 and K2 at the distant
station.

A, is a simple polarized relay wound differentially, each wire having a
resistance of 200 [omega], and so connected up as to respond to the working of
the reversing key K1 of the distant station. It acts independently of
the strength of the current, and is therefore not affected by the
working of the increment key K2. It is connected up so as to complete

the local circuit of the sounder S1 and the local battery l1 and forms
the receiving portion of the 'A' side.

B, is a non-polarized relay also wound differentially, each coil having
a resistance of 200 [omega]. It responds only to an increase in the
strength of the current, and therefore only to the working of the
increment key K2 of the distant station.

518 STANDARD ELECTRICAL DICTIONARY.

The relay spring is so adjusted that the armatures are not actuated by
the weak current sent from E by the key K1.

In its normal position this relay completes the circuit of the local
battery through the sounder S. This sounder S, called the uprighting
sounder, acts as a relay to a second sounder, S2, called the reading
sounder, which is worked by another local battery, l2. Of course,
normally, the armature of S is held down and that of S2 is up, but when
the tongue t moves, as it does when the increment key K2 is depressed so
as to send the whole current to line, then the current from l is
interrupted, and the circuit of l2 is completed by the rising of the
armature of S, causing the reading sounder S2 to work. This is the 'B'
side.

R is a rheostat for balancing the resistance of the line, as used in
duplex working.

C is a condenser used for compensating the static charge of the line. It
is provided with an adjustable retardation coil, R1, to prolong the
effect of the compensating current from the condenser.

G is a differential galvanometer, used for testing, and for facilitating
adjustment and balancing.

Q is a switch for putting the line to earth, either for balancing, or
for any other purpose. There is on the earth wire leading from Q a
resistance coil, r1, equalling approximately the resistance of the whole
battery, 3.3 E1, and the resistance s.

The connections shown in Fig. 321, are for an 'up' office. At a 'down'
office it is necessary to reverse the wires on the two lower terminals
of the galvanometer and the two battery wires on the reversing key K1.

The keys K1 and K2 are, for repeaters, replaced by transmitters.

The adjustment of this apparatus requires great care and great accuracy.
Its good working depends essentially on technical skill that can only be
acquired by patience and perseverance.

Faults in working generally arise from careless adjustments, dirty
contacts, loose connections, battery failures, and the ordinary line
interruptions, but there are no troubles that are beyond the reach of
ordinary skill, and it can be safely said that, within moderate
distances, wherever and whenever duplex working is practicable, then
quadruplex working is so too."

The above is a typical quadruplex bridge system. There is also a
differential system, the full description of which, in addition to what
has been given, is outside of the scope of this work.

519 STANDARD ELECTRICAL DICTIONARY.

Telegraph Repeater.
An extension of the relay system, adopted for long lines. A repeating
station comprises in general terms duplicate repeating apparatus. One
set is connected for messages in one direction, the other for messages
in the opposite direction. The general operation of a repeating set is
as follows. The signals as received actuate a relay which by its local
circuit actuates a key, which in ordinary practise would be the sounder,
but in the repeater its lever opens and closes a circuit comprising a
battery and a further section of the line.

Repeaters are placed at intervals along the line. Each repeater repeats
the signals received for the next section of line with a new battery. It
represents an operator who would receive and repeat the message, except
that it works automatically.

The Indo-European line from London to Teheran, 3,800 miles long, is
worked directly without any hand retransmission, it being carried out by
five repeaters. This gives an average of over 500 miles for each
repeater.

Repeaters introduce retardation, and each repeater involves a reduction
in the rate of working. Yet in many cases they increase the speed of a
line greatly, as its speed is about equal to that of its worst section,
which may be far greater than that of the whole line in one.

Synonym--Translater.

Telegraph Signal.
In the telegraph alphabet, a dot, or dash; the signal or effect produced
by one closing of the circuit. A dash is equal in length to three dots.
The space between signals is equal to one dot; the space between letters
to three dots; and the space between words to six dots.

Telegraph, Single Needle.
A telegraph system in which the code is transmitted by the movements of
a needle shaped index which oscillates to right and left, the left hand
deflection corresponding to dots, the right hand deflection to dashes.
The instruments for sending and receiving are combined into one. The
needles are virtually the indexes of vertical galvanometers. In one form
by a tapper key (see Tapper), in another form by a key worked by a
drop-handle (the drop handle instrument), currents of opposite
directions are sent down the line. These pass through both instruments,
affecting both needles and causing them to swing to right or left, as
the operator moves his key.

As galvanometer needle or actuating needle a soft iron needle is
employed, which is polarized by the proximity of two permanent magnets.
This avoids danger of reversal of polarity from lightning, a trouble
incident to the old system.

520 STANDARD ELECTRICAL DICTIONARY.

The cut, Fig. 322, shows a single needle telegraph instrument of the
tapper form. The action of the tapper can be understood from the next
cut.

Fig. 322. SINGLE NEEDLE TELEGRAPH INSTRUMENT, DOUBLE
TAPPER FORM.

Fig. 323. DOUBLE TAPPER KEY FOR SINGLE NEEDLE TELEGRAPH.

C and Z are two strips of metal to which the positive and negative poles
of the battery are respectively connected. E and L are two metallic
springs; E is connected to earth, L is connected to the line; at rest
both press against Z. If L is depressed so as to touch C, the current
from the battery goes to the line by the key L, goes through the coils
of the distant instrument and deflects the needle to one side, and then
goes to the earth. If the key E is depressed, L retaining its normal
position, the direction of the current is reversed, for the other pole
of the battery is connected to the earth and the reverse current going
through the coils of the distant instrument deflects the galvanometer
needle to the other side.

In the drop-handle type an analogous form of commutator worked by a
single handle produces the same effects.

521 STANDARD ELECTRICAL DICTIONARY.

Telegraph, Wheatstone, A. B. C.
A magneto-electric telegraph of the dial system. An alternating current
magneto-generator is turned by hand and by depressing keys its current
is admitted to or cut off from the line and receiver's instrument. The
message is received by a dial instrument working by the escapement
motion described under Telegraph, Dial.

Telegraph, Writing.
A telegraph in which the message is received in written characters. The
transmitter includes a stylus which is held in the hand and whose point
bears against the upper end of a vertical rod. The rod is susceptible of
oscillation in all directions, having at its base a spring support
equivalent to a universal joint.

The stylus is moved about in the shape of letters. As it does this it
throws a series of resistances in and out of the circuit.

At the receiving end of the line the instrument for recording the
message includes two electro-magnets with their cores at right angles to
each other and their faces near together at the point of the angle. An
armature is supported between the faces and through it a vertical rod
carried by a spring at its bottom rises. These magnets receive current
proportional to the resistances cut in and out by the motions of the
other rod at the transmitting end of the line. These resistances are
arranged in two series at right angles to each other, one for each
magnet. Thus the movements of the transmitting stylus and rod are
repeated by the end of the rod in the receiving instrument. A species of
pen is carried at the end of the rod of the receiving instrument, which
marks the letters upon a riband of paper which is fed beneath it.

Telemanometer. Electric.
A pressure gauge with electric attachment for indicating or recording
its indications at a distance.

It is applicable to steam boilers, so as to give the steam pressure in
any desired place.

Telemeter, Electric.
An apparatus for electrically indicating or recording at a distance the
indications of any instrument such as a pressure gauge, barometer or
thermometer, or for similar work. The telemanometer applied to a boiler
comes into this class of instrument.

Telephotography.
The transmission of pictures by the electric current, the requisite
changes in the current being effected by the action of light upon
selenium. The picture is projected by a magic lantern. Its projection is
traversed by a selenium resistance through which the current passes.
This is moved systematically over its entire area, thus constituting the
transmitter, and synchronously with the motion of the selenium a contact
point at the other end of the line moves systematically over a sheet of
chemically prepared paper. The paper, which may be saturated with a
solution of potassium ferrocyanide and ammonium nitrate, is stained by
the passage of the current, and by the variation in intensity of
staining, which variation is due to variations in the current, produced
by the effects of the light upon the selenium, the picture is
reproduced.

522 STANDARD ELECTRICAL DICTIONARY.

Telepherage.
An electric transportation system, hitherto only used for the carrying
of ore, freight, etc. Its characteristic feature is that the electric
conductors, suspended from poles, supply the way on which carriages
provided with electric motors run. The motors take their current
directly from the conductors.

There are two conducting lines, running parallel with each other,
supported at the opposite ends of transverse brackets on a row of
supporting poles. At each pole the lines cross over so that right line
alternates with left, between consecutive pairs of poles.

The cars are suspended from pulleys running on one or the other of the
conductors. A train of such cars are connected and the current is taken
in near one end and leaves near the other end of the train. These
current connections are so distant, their distance being regulated by
the length of the train, that they are, for all but an instant at the
time of passing each of the poles, in connection with segments of the
line which are of opposite potential. To carry out this principle the
distance between contacts is equal to the distance between poles. Owing
to the crossing over of the lines the contacts are in connection as
described and thereby the actuating current is caused to go through the
motors.

Cars running in one direction go on the electric conductors on the one
side, those running in the other direction go on the other conductor.

A great many refinements have been introduced, but the system has been
very little used.

Telephone.
An instrument for the transmission of articulate speech by the electric
current. The current is defined as of the undulatory type. (See Current,
Undulatory.)

The cut shows what may be termed the fundamental telephone circuit. A
line wire is shown terminating in ground plates and with a telephone in
circuit at each end. The latter consists of a magnet N S with a coil of
insulated wire H surrounding one end. Facing the pole of the magnet is a
soft iron diaphragm D, held in a frame or mouthpiece T. Any change of
current in the line affects the magnetism of the magnet, causing it to
attract the diaphragm more or less. The magnet and diaphragm really
constitute a little electric motor, the diaphragm vibrating back and
forth through an exceedingly short range, for changes in the magnetic
attraction.

The principle of the reversibility of the dynamo applies here. If the
magnet is subjected to no change in magnetism, and if the diaphragm is
moved or vibrated in front of its poles, currents will be induced in the
wire bobbin which surrounds its end. If two such magnets with bobbins
and diaphragms are arranged as shown, vibrations imparted to one
diaphragm will send currents through the line which, affecting the
magnetism of the distant magnet, will cause its diaphragm to vibrate in
exact accordance with the motions of the first or motor diaphragm. In
the combination one telephone represents a dynamo, the other a motor.

If the vibrations of the diaphragm are imparted by the voice, the voice
with all its modulations will be reproduced by the telephone at the
distant end of the line.

523 STANDARD ELECTRICAL DICTIONARY.

Fig. 324. DIAGRAM OF BELL TELEPHONES
AND LINE WITH EARTH CONNECTIONS.

Fig. 325. SECTION OF BELL TELEPHONE.

The above gives the essential features of the Bell telephone. In
practice the telephone is used only as the receiver. As transmitter a
microphone is employed. To give the current a battery, generally of the
open circuit type, is used, and the current in the line is an induced or
secondary one.

The microphone which is talked to, and which is the seat of the current
variations which reproduce original sound, is termed the transmitter,
the telephone in which the sounds are produced at the distant end of the
line is termed the receiver.

Fig. 325 shows the construction of the Bell telephone in universal use
in this country as the receiver. M is a bar magnet, in a case L L. B B
is a bobbin or coil of insulated wire surrounding one end of the magnet.
D is the diaphragm of soft iron plate (ferrotype metal), and E is the
mouthpiece. The terminals of the coil B B connect with the binding
screws C C. The wire in the coil is No. 36, A. W. G., and is wound to a
resistance of about 80 ohms.

524 STANDARD ELECTRICAL DICTIONARY.

As typical transmitter the Blake instrument may be cited. It is a carbon
microphone. It is shown in section in the cut; a is the mouthpiece and e
is a diaphragm of iron plate, although other substances could be used; f
is a steel spring, with a platinum contact piece at its end. One end
bears against the diaphragm, the other against a carbon block k. The
latter is carried by a brass block p, and pressure is maintained between
these contacts by the spring g and weight of the piece c, which by
gravity tends to press all together. The current passes by way of the
spring f, carbon button k and spring g through the circuit indicated.

A battery is in circuit with these parts. If a telephone is also in
circuit, and the transmitter is spoken against, the diaphragm vibrating
affects the resistance of the carbon-platinum contact, without even
breaking the contact, and the telephone reproduces the sound. The heavy
piece of metal C acts by its inertia to prevent breaking of the contact.
The position of this piece c, which is carried by the brass plate m, is
adjusted by the screw n.

Fig. 326. SECTION OF BLAKE TRANSMITTER.

In practice the transmitter and battery are usually on a local circuit,
which includes the primary of an induction coil. The line and distant
receiving telephone are in circuit with the secondary of the induction
coil, without any battery.

Telephone, Bi-.
A pair of telephones carried at the ends of a curved bar or spring so
that they fit the head of a person using them. One telephone is held
against each ear without the use of the hands.

525 STANDARD ELECTRICAL DICTIONARY.

Telephone, Capillary.
A telephone utilizing electro-capillarity for the production of
telephonic effects. The following describes the invention of Antoine
Breguet.

The point of a glass tube, drawn out at its lower end to a capillary
opening dips vertically into a vessel. This vessel is partly filled with
mercury, over which is a layer of dilute sulphuric acid. The end of the
immersed tube dips into the acid, but does not reach the mercury. One
line contact is with mercury in the tube, the other with the mercury in
the vessel. The arrangement of tube and vessel is duplicated, giving one
set for each end of the line. On introducing a battery in the circuit
the level of the mercury is affected by electro-capillarity. The tubes
are closed by plates or diaphragms at their tops, so as to enclose a
column of air. It is evident that the pressure of this air will depend
upon the level of the mercury in the tube, and this depends on the
electro-motive force. On speaking against the diaphragm the sound waves
affect the air pressure, and consequently the level, enough to cause
potential differences which reproduce the sound in the other instrument.

Fig. 327. BREGURT'S CAPILLARY TELEPHONE.

Telephone, Carbon.
A telephone transmitter based on the use of carbon as a material whose
resistance is varied by the degree of pressure brought to bear upon it.
Undoubtedly the surface contact between the carbon and the other
conducting material has much to do with the action. Many carbon
telephones have been invented. Under Telephone the Blake transmitter is
described, which is a carbon telephone transmitter. The Edison carbon
transmitter is shown in section in the cut. E is the mouth piece and D
the diaphragm. I is a carbon disc with adjusting screw V. A platinum
plate B B, with ivory button b, is attached to the upper surface of the
carbon disc. C C is an insulating ring. The wire connections shown bring
the disc into circuit. It is connected like a Blake transmitter. It is
now but little used.

Fig. 328. SECTION OF EDISON CARBON TRANSMITTER.

526 STANDARD ELECTRICAL DICTIONARY.

Telephone, Chemical.
A telephone utilizing chemical or electrolytic action in transmitting or
receiving. The electro-motograph is an example of a chemical receiver.
(See Electro-motograph.)

Telephone, Electrostatic.
A telephone utilizing electrostatic disturbances for reproduction of the
voice. In the cut D and C are highly charged electrophori. The
diaphragms A and B when spoken to affect the potential of the
electrophorus so as to produce current variations which will reproduce
the sound. Dolbear and others have invented other forms of transmitters
based on electrostatic action. Receivers have also been constructed. A
simple condenser may be made to reproduce sound by being connected with
a powerful telephone current.

Fig. 329. DIAGRAM OF EDISON'S ELECTROSTATIC TELEPHONE.

Telephone Induction Coil.
The induction coil used in telephone circuits for inducing current on
the main line. It is simply a small coil wound with two separate
circuits of insulated wire. In the Edison telephone the primary coil, in
circuit with the transmitter, is of No. 18 to 24 wire and of 3 to 4 ohms
resistance. The secondary in circuit with the line and receiving
instrument is of No. 36 wire and of 250 ohms resistance. The Bell
telephone induction coil has its primary of No. 18 to 24 wire wound to a
resistance of 1/2 ohm, and its secondary of No. 36 wire, and of 80 ohms
resistance.

527 STANDARD ELECTRICAL DICTIONARY.

Telephone, Reaction.
A form of telephone containing two coils of insulated wire, one of which
is mounted on the disc, and the other on the magnet pole in the usual
way. These coils react upon each other so as to strengthen the effect.

Telephone, Thermo-electric.
A telephone transmitter including a thermo-electric battery, placed in
circuit with the line. A plate of vulcanite faces it. When the sound
waves strike the vulcanite they move it backward and forward. These
movements, owing to the elasticity of the vulcanite, produce minute
changes of temperature in it, which affecting the thermo-electric pile
produce in the circuit currents, which passing through a Bell telephone
cause it to speak. This type of instrument has never been adopted in
practice.

Telephote.
An apparatus for transmitting pictures electrically, the properties of
selenium being utilized for the purpose.

Synonym--Pherope.

Teleseme.
An annunciator, displaying on a dial the object wanted by the person
using it. It is employed to transmit messages from rooms in a hotel to
the office, or for similar functions.

Tele-thermometer.
A thermometer with electric attachment for indicating or recording its
indications at a distance.

Tempering, Electric.
A process of tempering metals by electrically produced heat. The article
is made part of an electric circuit. The current passing through it
heats it, thereby tempering it. For wire the process can be made
continuous. The wire is fed from one roll to another, and if required
one roll may be immersed in a liquid bath or the wire between the rolls
may be led therein. The current is brought to one roll and goes through
the wire to the other. As it does this the wire is constantly fed from
one roll to another. The bath may be used as described to cool it after
the heating. The amount of heating may be regulated by the rate of
motion of the wire.

528 STANDARD ELECTRICAL DICTIONARY.

Ten, Powers of.
This adjunct to calculations has become almost indispensable in working
with units of the C. G. S. system. It consists in using some power of 10
as a multiplier which may be called the factor. The number multiplied
may be called the characteristic. The following are the general
principles.

The power of 10 is shown by an exponent which indicates the number of
ciphers in the multiplier. Thus 10^2 indicates 100; 10^3 indicates 1,000
and so on.

The exponent, if positive, denotes an integral number, as shown in the
preceding paragraph. The exponent, if negative, denotes the reciprocal
of the indicated power of 10. Thus 10^-2 indicates 1/100; 10^-3 indicates
1/1000 and so on.

The compound numbers based on these are reduced by multiplication or
division to simple expressions. Thus: 3.14 X 10^7 = 3.14 X 10,000,000 =
31,400,000. 3.14 X 10^-7 = 3.14/10,000,000 or 314/1000000000. Regard must
be paid to the decimal point as is done here.

To add two or more expressions in this notation if the exponents of the
factors are alike in all respects, add the characteristics and preserve
the same factor. Thus:

(51X 10^6) + (54 X 10^6) = 105 X 10^6.
(9.1 X 10^-9) + (8.7 X 10^-9) = 17.8 X 10^-9.

To subtract one such expression from another, subtract the
characteristics and preserve the same factor. Thus:

(54 X 10^6) - (51 X 10^6) = 3 X 10^6.

If the factors have different exponents of the same sign the factor or
factors of larger exponent must be reduced to the smaller exponent, by
factoring. The characteristic of the expression thus treated is
multiplied by the odd factor. This gives a new expression whose
characteristic is added to the other, and the factor of smaller exponent
is preserved for both,

Thus:
(5 X 10^7) + (5 X10^9) = (5 X 10^7) + (5 X 100 X 10^7) = 505 X 10^7.

The same applies to subtraction. Thus:
(5 X 10^9) - (5 X 10^7) = (5 X 100 X 10^7) - (5 X 10^7) = 495 X 10^7.

If the factors differ in sign, it is generally best to leave the
addition or subtraction to be simply expressed. However, by following
the above rule, it can be done. Thus:

Add
5 X 10^-2 and 5 X 10^3.
5 X 10^3 = 5 X 10^5 X 10^-2
(5 X 10^5 X 10^-2) + (5 X 10^-2) = 500005 X 10^-2

This may be reduced to a fraction 500000/100 = 5000.05.

To multiply add the exponents of the factors, for the new factor, and
multiply the characteristics for a new characteristic. The exponents
must be added algebraically; that is, if of different signs the
numerically smaller one is subtracted from the other one, and its sign
is given the new exponent.

Thus;
(25 X 10^6) X (9 X 10^8) = 225 X 10^14.
(29 X 10^ -8) X (11 X 10^7) = 319 X 10^-1
(9 X 10^8) X (98 X 10^2) = 882 X 10^1

529 STANDARD ELECTRICAL DICTIONARY.

To divide, subtract (algebraically) the exponent of the divisor from
that of the dividend for the exponent of the new factor, and divide the
characteristics one by the other for the new characteristic. Algebraic
subtraction is effected by changing the sign of the subtrahend,
subtracting the numerically smaller number from the larger, and giving
the result the sign of the larger number.
(Thus to subtract 7 from 5 proceed thus; 5 - 7 = -2.)

Thus;
(25 X 10^6) / (5 X 10^8) = 5 X 10^-2
(28 X 10^-8) / (5 X 10^3) = 5.6 X 10^-11

Tension.
Electro-motive force or potential difference in a current system is
often thus termed. It is to be distinguished from intensity or current
strength, which word it too greatly resembles.

Tension, Electric.
(a) The condition an electrified body is brought into by
electrification, when each molecule repels its neighbor. The condition
is described as one of self-repulsion.

(b) The voltage or potential difference of a circuit is also thus
termed.

Terminal.
The end of any open electric circuit, or of any electric apparatus; as
the terminals of a circuit, dynamo, or battery.

Terminal Pole.
In telegraph line construction the last pole of a series; one beyond
which the line is not carried. Such pole, as the pull of the wires is
all in one direction, requires special staying or support. The regular
line poles are free from this strain, as the wire pulls in both
directions.

Tetanus, Acoustic.
A term in electro-therapeutics. An effect produced on a nerve by very
rapidly alternating induced currents. The currents are produced by an
induction coil with a vibrator giving a musical note. This is a species
of gauge of proper frequency of alternations.

Theatrophone.
An apparatus worked by automatic paying machinery by which a telephone
connection is made with a theatre or opera by the deposition of a coin
in a slot.

Therm.
A unit of heat. It has been proposed by the British Association and
amounts to a redefinition of the smaller calorie. It is the amount of
heat required to raise the temperature of one gram of water one degree
centigrade, starting at the temperature of maximum density of water.

530 STANDARD ELECTRICAL DICTIONARY.

Thermaesthesiometer.
An electro-therapeutic instrument for testing the sensitiveness of the
surface of the body to changes of temperature. Vessels of mercury are
provided with thermometers to indicate their temperature. One vessel is
surrounded by an electric conductor wound in a number of turns. The
temperature is raised by passing a current through this. By successive
applications of the vessels to the same spot upon the skin the power of
differentiating temperatures is determined.

Thermo Call.
(a) An electric alarm or call bell operated by thermo-electric currents.
It may serve as a fire alarm or heat indicator, always bearing in mind
the fact that differential heat is the requisite in a thermo-electric
couple.

(b) See Thermo-electric Call.

Thermo-chemical Battery.
A voltaic battery in which the electro-motive force is generated by
chemical action induced by heat.

The chemical used generally is sodium nitrate or potassium nitrate. The
positive plate is carbon. On heating the battery the nitrate attacks the
carbon, burning it and produces potential difference. For negative plate
some metal unattacked by the nitrate may be employed.

Fig. 330. POUILLET'S THERMO-ELECTRIC BATTERY.

Thermo-electric Battery or Pile.
A number of thermo-electric couples q. v., connected generally in
series.

In Nobili's pile the metals are bismuth and antimony; paper bands
covered with varnish are used to insulate where required. In Becquerel's
pile copper sulphide (artificial) and German silver, (90 copper, 10
nickel) are the two elements. The artificial copper sulphide is made
into slabs 4 inches long, 3/4 inch wide, and 1/2 inch thick (about).
Water is used to keep one set of junctions cool, and gas flames to heat
the other set. In Fig. 331, c, d represent the binding screws. The
couples are mounted on a vertical standard, with adjusting socket and
screw B, so that its lower end can be immersed in cold water, or raised
therefrom as desired.

531 STANDARD ELECTRICAL DICTIONARY.

FIG. 331. BECQUEREL'S THERMO-ELECTRIC BATTERIES.

Fig. 332 shows one couple of the battery. S is artificial antimony
sulphide; M is German silver; m is a protecting plate of German silver
to save the sulphide from wasting in the flame.

Fig. 332. ELEMENTS OF BECQUEREL'S THERMOELECTRIC BATTERIES.

Clamond's pile has been used in practical work. The negative element is
an alloy of antimony, 2 parts, zinc, 1 part. The positive element is tin
plate. Mica in some parts, and a paste of soluble glass and asbestus in
other parts are used as insulators. They are built up so as to form a
cylinder within which the fire is maintained. The air is relied on to
keep the outer junctions cool. The temperature does not exceed 200° C.
(392° F.)

Sixty such elements have an electro-motive force of 300 volts and an
internal resistance of 1.5 ohms. Such a battery requires the consumption
of three cubic feet of gas per hour. (See Currents, Thermo-electric. )

532 STANDARD ELECTRICAL DICTIONARY.

Thermo-electric Call.
A thermostat arranged to ring a bell or to give some indication when the
temperature rises or falls beyond certain points. It may be a compound
bar of brass and steel fixed at one end and free for the rest of its
length. Its end comes between two adjustable contacts. As the
temperature rises it bends one way (away from the brass side) and, if
hot enough, touching a contact gives one signal. If the temperature
falls it curves the other way, and if cold enough touches the other
contact, giving another signal. (See Thermostat, Electric.)

Thermo-electric Couple.
If two dissimilar conductors form adjacent parts of a closed circuit,
and their junction is at a different temperature than that of the rest
of the circuit, a current will result. Such pair of conductors are
called a thermo-electric couple. They may be joined in series so as to
produce considerable electro-motive force. (See Thermo-electricity and
other titles in thermo-electricity.)

The efficiency of a thermo-electric couple according to the second law
of thermo-dynamics is necessarily low--not over 10 per cent.

Thermo-electric Diagram.
A diagram indicating the change in potential difference for a fixed
difference of temperature between different metals at different
temperatures. It is laid out with rectangular co-ordinates. On one axis
temperatures are laid off, generally on the axis of abscissas. On the
other axis potential differences are marked. Different lines are then
drawn, one for each metal, which show the potential difference, say for
one degree centigrade difference of temperature between their junctions,
produced at the different temperatures marked on the axis of abscissas.

Fig. 333. THERMO-ELECTRIC DIAGRAM,
GIVING POTENTIAL DIFFERENCE IN C. G. S. UNITS.

Thus taking copper and iron we find at the temperature 0° C. (32° F.) a
difference of one degree C. (1.8° F.) in their junctions will produce a
potential difference of 15.98 micro volts, while at 274.5° C. (526.1°
F.) the lines cross, and zero difference of potential is indicated.
Taking the lead line on the same diagram it crosses the iron line a
little above 350° C. (662° F.), indicating that if one junction is
heated slightly above and the other is heated slightly below this

temperature no potential difference will be produced. Lead and copper
lines, on the other hand, diverge more and more as the temperature
rises.

533 STANDARD ELECTRICAL DICTIONARY.

Thermo-electric Inversion.
The thermo-electric relations of two conductors vary at different
temperatures. Sometimes at a definite point they have no electro-motive
force and after passing this point the positive plate becomes a negative
one and vice versa. This is inversion, or reversal. (See Thermo-electric
Diagram.)

Synonym-- Thermo-electric Reversal.

Thermo-electricity.
Electric energy, electro-motive force or electrification produced from
heat energy by direct conversion. It is generally produced in a circuit
composed of two electric conductors of unlike material, which circuit
must possess at least two junctions of the unlike substances. By heating
one of these to a higher temperature than that of the other, or by
maintaining one junction at a different temperature from that of the
other a potential difference is created accompanied by an electric
current.

In many cases differential application of heat to an identical material
will develop potential difference. This effect, the converse of the
Thomson effect, is not used to produce currents, as in a closed circuit
the potential differences due to differential heating would neutralize
each other.

Thermo-electric Junction.
A junction between two dissimilar conductors, which when heated or
cooled so as to establish a differential temperature, as referred to the
temperature of the other junction, produces potential difference and an
electric current.

Thermo-electric Pile, Differential.
A thermo-electric pile arranged to have opposite faces subjected to
different sources of heat to determine the identity or difference of
temperature of the two sources of heat. It corresponds in use to a
differential air thermometer.

Thermo-electric Power.
The coefficient which, multiplying the difference of temperature of the
ends of a thermo-electric couple, gives the potential difference,
expressed in micro-volts. It has always to be assigned to a mean or
average temperature of the junctions, because the potential difference
due to a fixed difference of temperature between two metals varies with
the average temperature of the two junctions. (See Thermo-electric
Diagram.)

For bismuth and antimony at 19.5° C. (67.1° F.) it is 103 microvolts per
degree Centigrade (1.8° F.). This means that if one junction is heated
to 19° C. and the other to 20° C. (66.2° F. and 68.0° F.) a potential
difference of 103 micro-volts will be produced.

The potential difference is approximately proportional to the difference
of temperature of the two junctions if such difference is small. Hence
for large differences of potential the thermo-electric power coefficient
does not apply.

As a differential function it is thus deduced by Sir William Thomson,
for expressing the E. M. F. in a thermo-electric circuit: If a circuit
is formed of two metals with the junctions at indefinitely near
temperatures, t and t + dt, and dE is the E. M. F. of the circuit, then
the differential coefficient dE/dt is called the thermo-electric power
of the two metals for the temperature t.

534 STANDARD ELECTRICAL DICTIONARY.