The Standard Electrical Dictionary (part 2)

Compass, Points of the.
The circle of the horizon may bc and is best referred to angular
degrees. It has also been divided into thirty-two equiangular and named
points. A point is 11.25°. The names of the points are as follows:
North, North by East, North North-east, North-east by North, North-east,
North-east by East, East North-east, East by North, East, East by South,
East South-east, South-east by East, South-east, South-east by South,
South South-east, South by East, South, South by West, South South-west,
South-west by South, South-west, South-west by West, West South-west,
West by South, West, West by North, West North-west, North-west by West,
North-west, North West by North, North North-west, North by West. They
are indicated by their initials as N. N. W., North North-west, N. by W.,
North by West.

Compass, Spirit.
A form of mariner's compass. The bowl or case is hermetically sealed and
filled with alcohol or other nonfreezing liquid. The compass card is
made with hollow compartments so as nearly to float. In this way the
friction of the pivot or point of support is greatly diminished, and the
compass is far more sensitive.

Compass, Surveyor's.
A species of theodolite; a telescope with collimation lines, mounted
above a compass, so as to be applicable for magnetic surveys. Its use is
to be discouraged on account of the inaccuracy and changes in
declination of the magnetic needle.

144 STANDARD ELECTRICAL DICTIONARY.

Compensating Resistances.
In using a galvanometer shunt the total resistance of the circuit is
diminished so that in some cases too much current flows through it; in
such case additional resistance, termed as above, is sometimes
introduced in series. The shunt in parallel with the galvanometer is
thus compensated for, and the experimental or trial circuit does not
take too much current.

Complementary Distribution.
Every distribution of electricity has somewhere a corresponding
distribution, exactly equal to it of opposite electricity; the latter is
the complimentary distribution to the first, and the first distribution
is also complimentary to it.

Component.
A force may always be represented diagrammatically by a straight line,
terminating in an arrow-head to indicate the direction, and of length to
represent the intensity of the force. The line may always be assumed to
represent the diagonal of a parallelogram, two of whose sides are
represented by lines starting from the base of the arrow, and of length
fixed by the condition that the original force shall be the diagonal of
the parallelogram of which they are two contiguous sides; such lines are
called components, and actually represent forces into which the original
force may always be resolved. The components can have any direction.
Thus the vertical component of a horizontal force is zero; its
horizontal component is equal to itself. Its 450 component is equal to
the square root of one-half of its square.

Condenser.
An appliance for storing up electrostatic charges: it is also called a
static accumulator. The telegraphic condenser consists of a box packed
full of sheets of tinfoil. Between every two sheets is a sheet of
paraffined paper, or of mica. The alternate sheets of tinfoil are
connected together, and each set has its own binding post. (See
Accumulator, Electrostatic.)

Condenser, Sliding.
An apparatus representing a Leyden jar whose coatings can be slid past
each other. This diminishes or increases the facing area, and
consequently in almost exactly similar ratio diminishes or increases the
capacity of the condenser.

Conductance.
The conducting power of a given mass of specified material of specified
shape and connections. Conductance varies in cylindrical or prismatic
conductors, inversely as the length, directly as the cross-section, and
with the conductivity of the material. Conductance is an attribute of
any specified conductor, and refers to its shape, length and other
factors. Conductivity is an attribute of any specified material without
direct reference to its shape, or other factors.

Conduction.
The process or act of conducting a current.

145 STANDARD ELECTRICAL DICTIONARY.

Conductivity.
The relative power of conducting the electric current possessed by
different substances. A path for the current through the ether is opened
by the presence of a body of proper quality, and this quality, probably
correlated to opacity, is termed conductivity. There is no perfect
conductor, all offer some resistance, q. v., and there is hardly any
perfect non-conductor. It is the reverse and reciprocal of resistance.

Conductivity, Specific.
The reciprocal of specific resistance. (See Resistance--Specific.)

Conductivity, Unit of.
The reciprocal of the ohm; it is a more logical unit, but has never been
generally adopted; as a name the title mho (or ohm written backwards)
has been suggested by Sir William Thomson, and provisionally adopted.

Conductivity, Variable.
The conductivity for electric currents of conductors varies with their
temperature, with varying magnetization, tension, torsion and
compression.

Conductor.
In electricity, anything that permits the passage of an electric
current. Any disturbance in the ether takes the form of waves because
the ether has restitutive force or elasticity. In a conductor, on the
other hand, this force is wanting; it opens a path through the ether and
a disturbance advances through it from end to end with a wave front, but
with no succession of waves. This advance is the beginning of what is
termed a current. It is, by some theorists, attributed to impulses given
at all points along the conductor through the surrounding ether, so that
a current is not merely due to an end thrust. If ether waves preclude a
current on account of their restitutive force, ether waves cannot be
maintained in a conductor, hence conductors should be opaque to light,
for the latter is due to ether waves. This is one of the more practical
every day facts brought out in Clerk Maxwell's electromagnetic theory of
light. The term conductor is a relative one, as except a vacuum there is
probably no substance that has not some conducting power. For relative
conducting power, tables of conductivity, q. v., should be consulted.
The metals beginning with silver are the best conductors, glass is one
of the worst.

Conductor, Anti-Induction.
A current conductor arranged to avoid induction from other lines. Many
kinds have been invented and made the subject of patents. A fair
approximation may be attained by using a through metallic circuit and
twisting the wires composing it around each other. Sometimes concentric
conductors, one a wire and the other a tube, are used, insulated, one
acting as return circuit for the other.

Conductor, Conical.
A prime conductor of approximately conical shape, but rounded on all
points and angles. Its potential is highest at the point.

146 STANDARD ELECTRICAL DICTIONARY.

Conductor, Imbricated.
A conductor used in dynamo armatures for avoiding eddy currents, made by
twisting together two or more strips of copper.

Conductor, Prime.
A body often cylindrical or spherical in shape, in any case with no
points or angles, but rounded everywhere, whose surface, if the
conductor itself is not metallic, is made conducting by tinfoil or gold
leaf pasted over it. It is supported on an insulating stand and is used
to collect or receive and retain static charges of electricity.

Conductors, Equivalent.
Conductors of identical resistance. The quotient of the length divided
by the product of the conductivity and cross-section must be the same in
each, if each is of uniform diameter.

Conjugate. adj.
Conjugate coils or conductors are coils placed in such relation that the
lines of force established by one do not pass through the coils of the
other. Hence variations of current in one produce no induced currents in
the other.

Connect. v.
To bring two ends of a conductor together, or to bring one end of a
conductor in connection with another, or in any way to bring about an
electrical connection.

Connector.
A sleeve with screws or other equivalent device for securing the ends of
wires in electrical contact. A binding-post, q. v., is an example.
Sometimes wire spring-catches are used, the general idea being a device
that enables wires to be connected or released at will without breaking
off or marring their ends. The latter troubles result from twisting
wires together.

Consequent Poles.
A bar magnet is often purposely or accidentally magnetized so as to have
both ends of the same polarity, and the center of opposite polarity. The
center is said to comprise two consequent poles. (See Magnet,
Anomalous.)

Conservation of Electricity.
As every charge of electricity has its equal and opposite charge
somewhere, near or far, more or less distributed, the sum of negative is
equal always to the sum of positive electrical charges. For this
doctrine the above title was proposed by Lippman.

Contact Breaker.
Any contrivance for closing a circuit, and generally for opening and
closing in quick succession. An old and primitive form consisted of a
very coarsely cut file. This was connected to one terminal, and the
other terminal was drawn over its face, making and breaking contact as
it jumped from tooth to tooth. (See Circuit Breaker--do. Automatic,
etc.--do. Wheel-do. Pendulum.)

147 STANDARD ELECTRICAL DICTIONARY.

Contact, Electric.
A contact between two conductors, such that a current can flow through
it. It may be brought about by simple touch or impact between the ends
or terminals of a circuit, sometimes called a dotting contact, or by a
sliding or rubbing of one terminal on another, or by a wheel rolling on
a surface, the wheel and surface representing the two terminals.

There are various descriptions of contact, whose names are
self-explanatory. The term is applied to telegraph line faults also, and
under this, includes different descriptions of contact with neighboring
lines, or with the earth.

Contact Electricity.
When two dissimilar substances are touched they assume different
electric potentials. If conductors, their entire surfaces are affected;
if dielectrics, only the surfaces which touch each other. (See Contact
Theory.)

Contact Faults.
A class of faults often called contacts, due to contact of the conductor
of a circuit with another conductor. A full or metallic contact is where
practically perfect contact is established; a partial contact and
intermittent contact are self-explanatory.

Contact Point.
A point, pin or stud, often of platinum, arranged to come in contact
with a contact spring, q. v., or another contact point or surface, under
any determined conditions.

Contact Potential Difference.
The potential difference established by the contact of two dissimilar
substances according to the contact theory, q. v.

Contact Series.
An arrangement or tabulation of substances in pairs, each intermediate
substance appearing in two pairs, as the last member of the first, and
first member of the succeeding pair, with the statement of the potential
difference due to their contact, the positively electrified substance
coming first. The following table of some contact potentials is due to
Ayrton and Perry:
CONTACT SERIES.
Difference of Potential in Volts.
Zinc--Lead .210
Lead--Tin .069
Tin--Iron .313
Iron--Copper .146
Copper--Platinum .238
Platinum-Carbon .113

The sum of these differences is 1.089, which is the contact potential
between zinc and carbon.

Volta's Law refers to this and states that--
The difference of potential produced by the contact of any two
substances is equal to the sum of the differences of potentials
between the intervening substances in the contact series.

It is to be remarked that the law should no longer be restricted to or
stated only for metals.

148 STANDARD ELECTRICAL DICTIONARY.

Contact-spring.
A spring connected to one lead of an electric circuit, arranged to press
against another spring, or contact point, q. v., under any conditions
determined by the construction of the apparatus. (See Bell,
Electric--Coil, Induction.)

Contact Theory.
A theory devised to explain electrification, the charging of bodies by
friction, or rubbing, and the production of current by the voltaic
battery. It holds that two bodies, by mere contact become oppositely
electrified. If such contact is increased in extent by rubbing together,
the intensity of their electrification is increased. This
electrification is accounted for by the assumption of different kinetic
energy, or energy of molecular motion, possessed by the two bodies;
there being a loss and gain of energy, on the two sides respectively,
the opposite electrifications are the result. Then when separated, the
two bodies come apart oppositely electrified.

The above accounts for the frictional production of electricity. In the
voltaic battery, a separation of the atoms of hydrogen and oxygen, and
their consolidation into molecules occurs, and to such separation and
the opposite electrification of the electrodes by the oxygen and
hydrogen, the current is attributed, because the hydrogen goes to one
electrode, and the oxygen to the other, each giving up or sharing its
own charge with the electrodes to which it goes. If zinc is touched to
copper, the zinc is positively and the copper negatively electrified. In
the separation of hydrogen and oxygen, the hydrogen is positively and
the oxygen negatively electrified. In the battery, the current is due to
the higher contact difference of oxygen and hydrogen compared to that
between zinc and copper. It will be seen that the two contact actions in
a battery work against each other, and that the current is due to a
differential contact action. The zinc in a battery is electrified
negatively because the negative electrification of the oxygen is greater
in amount than its own positive electrification due to contact with the
copper.

Contractures.
A muscular spasm or tetanus due to the passage of a current of
electricity; a term in electro-therapeutics.

Controlling Field.
The magnetic or electro-magnetic field, which is used in galvanometers
to control the magnetic needle, tending to restore it to a definite
position whenever it is turned therefrom. It may be the earth's field or
one artificially produced.

Controlling Force.
In galvanometers and similar instruments, the force used to bring the
needle or indicator back to zero. (See Controlling
Field--Electro-Magnetic Control--Gravity Control--Magnetic
Control--Spring Control.)

149 STANDARD ELECTRICAL DICTIONARY.

Convection, Electric.
The production of blasts or currents of air (convection streams) from
points connected to statically charged conductors. The term is sometimes
applied to electric convection of heat. (See Convection of Heat,
Electric.)

Convection, Electrolytic.
The resistance of acidulated water as a true conductor is known to be
very, almost immeasurably, high. As an electrolytic, its resistance is
very much lower. Hence the current produced between immersed electrodes
is theoretically almost null, unless the difference of potential between
them is high enough to decompose the liquid. Yet a feeble current too
great for a true conduction current is sometimes observed when two
electrodes with potential difference too low to cause decomposition are
immersed in it. Such a current is termed an electrolytic convection
current. It is supposed to be due to various causes. Some attribute it
to the presence of free oxygen from the air, dissolved in the water with
which the hydrogen combines. Others attribute it to the diffusion of the
gases of decomposition in the solution; others assume a partial
polarization of the molecules without decomposition. Other theories are
given, all of which are unsatisfactory. The term is due to Helmholtz.

Convection of Heat, Electric.
The effect of a current upon the distribution of heat in an unevenly
heated conductor. In some, such as copper, the current tends to equalize
the varying temperatures; the convection is then said to be positive, as
comparable to that of water flowing through an unequally heated tube. In
others, such as platinum or iron, it is negative, making the heated
parts hotter, and the cooler parts relatively cooler.

The effect of the electric current in affecting the distribution of heat
in unequally heated metal (Thomson's effect. q. v.), is sometimes so
termed. If a current passes through unequally heated iron it tends to
increase the difference of temperature, and the convection is negative;
in copper it tends to equalize the temperature, and the convection is
positive.

Converter.
An induction coil used with the alternating current for changing
potential difference and inversely therewith the available current. They
generally lower the potential, and increase the current, and are placed
between the primary high potential system that connects the houses with
the central station, and the secondary low potential system within the
houses. A converter consists of a core of thin iron sheets, wound with a
fine primary coil of many convolutions, and a coarse secondary coil of

few convolutions. The ratio of convolutions gives the ratio of maximum
potential differences of their terminals between the primary and
secondary coils. The coil may be jacketed with iron to increase the
permeance. (See Alternating Current System.)

Fig. 110. FERRANTI'S CONVERTER OR TRANSFORMER.

Fig. 111. SWINBURNE'S HEDGEHOG TRANSFORMER.

150 STANDARD ELECTRICAL DICTIONARY.

Co-ordinates, System of.
A system for indicating the position of points in space by reference to
fixed lines, intersecting at a determined and arbitrary point 0, termed
the origin of co-ordinates. In plane rectangular co-ordinates two lines
are drawn through the origin, one horizontal, termed the axis of
abscissas, or axis of X. All distances measured parallel to it, if
unknown, are indicated by x, and are termed abscissas. The other axis is
vertical, and is termed the axis of ordinates, or axis of Y. All
distances measured parallel to it, if unknown, are indicated by y and
are termed ordinates. Thus by naming its abscissa and ordinate a point
has its position with reference to the axes determined, and by
indicating the relation between a point, line or curve, and a system of
abscissas and ordinates, the properties of a line or curve can be
expressed algebraically. Co-ordinates may also be inclined to each other
at any other angles, forming oblique co-ordinates; relations may be
expressed partly in angles referred to the origin as a centre, giving
polar co-ordinates. For solid geometry or calculations in three
dimensions, a third axis, or axis of Z, is used, distances parallel to
which if unknown are indicated by z.

Fig. 112. AXES OF CO-ORDINATES.

151 STANDARD ELECTRICAL DICTIONARY.

Cooling Box.
In a hydroelectric machine, q. v., a conduit or chest through which the
steam passes on its way to the nozzles. Its object is to partially
condense the steam so as to charge it with water vesicles whose friction
against the sides of the nozzles produces the electrification .

152 STANDARD ELECTRICAL DICTIONARY.

Copper.
A metal; one of the elements. Symbol, Cu; atomic weight, 63.5;
equivalent, 63.5 and 31.75; valency, 1 and 2; specific gravity, 8.96.
It is a conductor of electricity, whose conductivity is liable to
vary greatly on account of impurities.

Annealed. Hard drawn.
Relative resistance (Silver = 1), 1.063 1.086
Specific resistance, 1.598 1.634 microhms.

Resistance of a wire at 0° C. (32° F.),
Annealed. Hard Drawn.
(a) 1 foot long, weighing 1 grain, .2041 ohms .2083 ohms.
(b) 1 foot long, 1/1000 inch thick, 9.612 " 9.831 "
(c) 1 meter long, weighing 1 gram, .1424 " .1453 "
(d) 1 meter long, 1 millimeter thick, .02034 " .02081 "

microhm. microhm.
Resistance of 1 inch cube at 0°C. (32° F.) .6292 .6433

Percentage of resistance change,
per 1° C. (1.8° F.) at about 20° C. (68° F.) = 0.388 per cent.

Electro-chemical Equivalent (Hydrogen = .0105) Cuprous .6667
Cupric .3334

In electricity it has been very extensively used as the negative plate
of voltaic batteries. It has its most extensive application as
conductors for all classes of electrical leads.

Copper Bath.
A solution of copper used for depositing the metal in the electroplating
process. For some metals, such as zinc or iron, which decompose copper
sulphate solution, special baths have to be used.

The regular bath for copper plating is the following:

To water acidulated with 8 to 10 percent. of sulphuric acid as much
copper sulphate is added as it will take up at the ordinary temperature.
The saturated bath should have a density of 1.21. It is used cold and is
kept in condition by the use of copper anodes, or fresh crystals may be
added from time to time.

For deposition on zinc, iron, tin and other metals more electropositive
than copper, the following baths may be used, expressed in parts by
weight:

Tin
Iron and Steel. Cast Iron
Cold Hot. and Zinc. Zinc.
Sodium Bisulphate, 500 200 300 100
Potassium Cyanide, 500 700 500 700
Sodium Carbonate, 1000 500 --- ---
Copper Acetate, 475 500 350 450
Aqua Ammoniae, 350 300 200 150
Water, 2500 2500 2500 2500

These are due to Roseleur.

153 STANDARD ELECTRICAL DICTIONARY.

Copper Stripping Bath.
There is generally no object in stripping copper from objects. It can be
done with any of the regular copper baths using the objects to be
stripped as anode. The danger of dissolving the base itself and thereby
injuring the article and spoiling the bath is obvious.

Cord Adjuster.
A device for shortening or lengthening the flexible cord, or flexible
wire supplying the current, and by which an incandescent lamp is
suspended. It often is merely a little block of wood perforated with two
holes through which the wires pass, and in which they are retained in
any desired position by friction and their own stiffness.

Fig. 113. FLEXIBLE CORD ADJUSTER.

Cord, Flexible.
A pair of flexible wire conductors, insulated lightly, twisted together
and forming apparently a cord. They are used for minor services, such as
single lamps and the like, and are designated according to the service
they perform, such as battery cords, dental cords (for supplying dental
apparatus) and other titles.

Core.
(a) The conductor or conductors of an electric cable. (See Cable Core.)

(b) The iron mass, generally central in an electro-magnet or armature,
around which the wire is coiled. It acts by its high permeance to
concentrate or multiply the lines of force, thus maintaining a more
intense field. (See Armature--Magnet, Electro--Magnet, Field--Core,
Laminated). In converters or transformers (See Converter) it often
surrounds the wire coils.

Core-discs.
Discs of thin wire, for building up armature cores. (See Laminated
Core.) The usual form of core is a cylinder. A number of thin discs of
iron are strung upon the central shaft and pressed firmly together by
end nuts or keys. This arrangement, it will be seen, gives a cylinder as
basis for winding the wire on.

Core-discs, Pierced.
Core-discs for an armature of dynamo or motor, which are pierced around
the periphery. Tubes of insulating material pass through the peripheral
holes, and through these the conductors or windings are carried. The
conductors are thus embedded in a mass of iron and are protected from
eddy currents, and they act to reduce the reluctance of the air gaps.
From a mechanical point of view they are very good. For voltages over
100 they are not advised.

Synonym--Perforated Core-discs.

154 STANDARD ELECTRICAL DICTIONARY.

Core-discs, Segmental.
Core-discs made in segments, which are bolted together to form a
complete disc or section of the core. The plan is adopted principally on
large cores. The discs thus made up are placed together to form the core
exactly as in the case of ordinary one piece discs.

Fig. 114. PIERCED OR PERFORATED CORE-DISC.

Core-discs, Toothed.
Core-discs of an armature of a dynamo or motor, which discs are cut into
notches on the periphery. These are put together to form the armature
core, with the notches corresponding so as to form a series of grooves
in which the wire winding is laid. This construction reduces the actual
air-gaps, and keeps the wires evenly spaced. Distance-pieces of
box-wood, m, m, are sometimes used to lead the wires at the ends of the
armature.

Fig. 115. TOOTHED CORE-DISC.

Core, Laminated.
A core of an armature, induction coil or converter or other similar
construction, which is made up of plates insulated more or less
perfectly from each other. The object of lamination is to prevent the
formation of Foucault currents. (See Currents, Foucault.) As insulation,
thin shellacked paper may be used, or sometimes the superficial
oxidation of the plates alone is relied on. The plates, in general, are
laid perpendicular to the principal convolutions of the wire, or
parallel to the lines of force. The object is to break up currents, and
such currents are induced by the variation in intensity of the field of
force, and their direction is perpendicular to the lines of force, or
parallel to the inducing conductors.

A core built up of core discs is sometimes termed a tangentially
laminated core. Made up of ribbon or wire wound coil fashion, it is
termed a radially laminated core.

155 STANDARD ELECTRICAL DICTIONARY.

Core Ratio.
In a telegraph cable the ratio existing between the diameter of the
conducting core and the insulator. To get a ratio approximately accurate
in practical calculations, the diameter of the core is taken at 5 per
cent. less than its actual diameter. The calculations are those
referring to the electric constants of the cable, such as its static
capacity and insulation resistance.

Core, Ribbon.
For discoidal ring-shaped cores of armatures, iron ribbon is often used
to secure lamination and prevent Foucault currents.

Synonym--Tangentially Laminated Core.

Core, Ring.
A core for a dynamo or motor armature, which core forms a complete ring.

Core, Stranded.
In an electric light cable, a conducting core made up of a group of
wires laid or twisted together.

Core, Tubular.
Tubes used as cores for electro-magnets. For very small magnetizing
power, tubular cores are nearly as efficient as solid ones in straight
magnets, because the principal reluctance is due to the air-path. On
increasing the magnetization the tubular core becomes less efficient
than the solid core, as the reluctance of the air-path becomes
proportionately of less importance in the circuit.

Corpusants.
The sailors' name for St. Elmo's Fire, q. v.

Coulomb.
The practical unit of quantity of electricity. It is the quantity passed
by a current of one ampere intensity in one second. It is equal to 1/10
the C. G. S. electro-magnetic unit of quantity, and to 3,000,000,000 C.
G. S. electrostatic units of quantity. It corresponds to the
decomposition of .0935 milligrams of water, or to the deposition of
1.11815 milligrams of silver.

Coulomb's Laws of Electrostatic Attraction and Repulsion.
1. The repulsions or attractions between two electrified bodies are in
the inverse ratio of the squares of their distance.

2. The distance remaining the same, the force of attraction or repulsion
between two electrified bodies is directly as the product of the
quantities of electricity with which they are charged.

156 STANDARD ELECTRICAL DICTIONARY.

Counter, Electric.
A device for registering electrically, or by electro-magnetic machinery,
the revolutions of shafts, or any other data or factors.

Counter-electro-motive Force.
A potential difference in a circuit opposed to the main potential
difference, and hence, resisting the operation of the latter, and
diminishing the current which would be produced without it. It appears
in electric motors, which, to a certain extent, operate as dynamos and
reduce the effective electro-motive force that operates them. It
appears in the primary coils of induction coils, and when the secondary
circuit is open, is almost equal to the main electro-motive force, so
that hardly any current can go through them under such conditions. It
appears in galvanic batteries, when hydrogen accumulates on the copper
plate, and in other chemical reactions. A secondary battery is charged
by a current in the reverse direction to that which it would normally
produce. Its own potential difference then appears as a
counter-electro-motive force.

Synonym--Back Electro-motive Force.

Counter-electro-motive Force of Polarization.
To decompose a solution by electrolysis, enough electro-motive force is
required to overcome the energy of composition of the molecule
decomposed. A part of this takes the form of a counter-electromotive
force, one which, for a greater or less time would maintain a current in
the opposite direction if the original source of current were removed.
Thus in the decomposition of water, the electrodes become covered, one
with bubbles of oxygen, the others with bubbles of hydrogen; this
creates a counter E. M. F. of polarization. In a secondary battery, the
working current may be defined as due to this cause.

Synonym--Back Electro-motive Force of Polarization.

Couple.
Two forces applied to different points of a straight line, when opposed
in direction or unequal in amount, tend to cause rotation about a point
intermediate between their points of application and lying on the
straight line. Such a pair constitute a couple.

Couple, Voltaic or Galvanic.
The combination of two electrodes, and a liquid or liquids, the
electrodes being immersed therein, and being acted on differentially by
the liquid or liquids. The combination constitutes a source of
electro-motive force and consequently of current. It is the galvanic or
voltaic cell or battery. (See Battery, Voltaic--Contact
Theory--Electro-motive Force--Electro-motive Series.)

Coupling.
The joining of cells of a galvanic battery, of dynamos or of other
devices, so as to produce different effects as desired.

157 STANDARD ELECTRICAL DICTIONARY

Couple, Astatic.
An astatic couple is a term sometimes applied to astatic needles, q.v.

C. P.
(a) An abbreviation of or symbol for candle power, q. v.

(b) An abbreviation of chemically pure. It is used to indicate a high
degree of purity of chemicals. Thus, in a standard Daniell battery, the
use of C. P. chemicals may be prescribed or advised.

Crater.
The depression that forms in the positive carbon of a voltaic arc. (See
Arc, Voltaic.)

Creeping.
A phenomenon of capillarity, often annoying in battery jars. The
solution, by capillarity, rises a little distance up the sides,
evaporates, and as it dries more creeps up through it, and to a point a
little above it. This action is repeated until a layer of the salts may
form over the top of the vessel. To avoid it, paraffine is often applied
to the edges of the cup, or a layer of oil, often linseed oil, is poured
on the battery solution,

Crith.
The weight of a litre of hydrogen at 0º C. (32º F.), and 760 mm. (30
inches) barometric pressure. It is .0896 grams. The molecular weight of
any gas divided by 2 and multiplied by the value of the crith, gives the
weight of a litre of the gas in question. Thus a litre of electrolytic
gas, a mixture of two molecules of hydrogen for one of oxygen, with a
mean molecular weight of 12, weighs (12/2) * .0896 or .5376 gram.

Critical Speed.
(a) The speed of rotation at which a series dynamo begins to excite its
own field.

(b) In a compound wound dynamo, the speed at which the same potential is
generated with the full load being taken from the machine, as would be
generated on open circuit, in which case the shunt coil is the only
exciter. The speed at which the dynamo is self-regulating.

(c) In a dynamo the rate of speed when a small change in the speed of
rotation produces a comparatively great change in the electro-motive
force. It corresponds to the same current (the critical current) in any
given series dynamo.

Cross.
(a) A contact between two electric conductors; qualified to express
conditions as a weather cross, due to rain, a swinging cross when a wire
swings against another, etc.

(b) vb. To make such contact.

Cross-Connecting Board.
A special switch board used in telephone exchanges and central telegraph
offices. Its function is, by plugs and wires, to connect the line wires
with any desired section of the main switchboard. The terminals of the
lines as they enter the building are connected directly to the
cross-connecting board.

158 STANDARD ELECTRICAL DICTIONARY.

Cross Connection.
A method of disposing of the effects of induction from neighboring
circuits by alternately crossing the two wires of a metallic telephone
circuit, so that for equal intervals they lie to right and left, or one
above, and one below.

Crossing Wires.
The cutting out of a defective section in a telegraph line, by carrying
two wires from each side of the defective section across to a
neighboring conductor, pressing it for the time into service and cutting
the other wire if necessary.

Cross-magnetizing Effect.
A phase of armature interference. The current in an armature of a dynamo
or motor is such as to develop lines of force approximately at right
angles to those of the field. The net cross-magnetizing effect is such
component of these lines, as is at right angles to the lines produced by
the field alone.

Cross-over Block.
A piece of porcelain or other material shaped to receive two wires which
are to cross each other, and hold them so that they cannot come in
contact. It is used in wiring buildings, and similar purposes. (See
Cleat, Crossing.)

Cross Talk.
On telephone circuits by induction or by contact with other wires sound
effects of talking are sometimes received from other circuits; such
effects are termed cross talk.

Crucible, Electric.
A crucible for melting difficultly fusible substances, or for reducing
ores, etc., by the electric arc produced within it. Sometimes the
heating is due more to current incandescence than to the action of an
arc.

Fig. 116. ELECTRIC FURNACE OR CRUCIBLE.

Crystallization, Electric.
Many substances under proper conditions take a crystalline form. The
great condition is the passage from the fluid into the solid state. When
such is brought about by electricity in any way, the term electric
crystallization may be applied to the phenomenon. A solution of silver
nitrate for instance, decomposed by a current, may give crystals of
metallic silver.

159 STANDARD ELECTRICAL DICTIONARY.

Cup, Porous.
A cup used in two-fluid voltaic batteries to keep the solutions separate
to some extent. It forms a diaphragm through which diffusion inevitably
takes place, but which is considerably retarded, while electrolysis and
electrolytic convection take place freely through its walls. As
material, unglazed pottery is very generally used.

In some batteries the cup is merely a receptacle for the solid
depolarizer. Thus, in the Leclanché battery, the cup contains the
manganese dioxide and graphite in which the carbon electrode is
embedded, but does not separate two solutions, as the battery only uses
one. Nevertheless, the composition of the solution outside and inside
may vary, but such variation is incidental only, and not an essential of
the operation.

Current.
The adjustment, or effects of a continuous attempt at readjustment of
potential difference by a conductor, q. v., connecting two points of
different potential. A charged particle or body placed in a field of
force tends to move toward the oppositely charged end or portion of the
field. If a series of conducting particles or a conducting body are held
so as to be unable to move, then the charge of the field tends, as it
were, to move through it, and a current results. It is really a
redistribution of the field and as long as such redistribution continues
a current exists. A current is assumed to flow from a positive to a
negative terminal; as in the case of a battery, the current in the outer
circuit is assumed to flow from the carbon to the zinc plate, and in the
solution to continue from zinc to carbon. As a memoria technica the zinc
may be thought of as generating the current delivering it through the
solution to the carbon, whence it flows through the wire connecting
them. (See Ohm's Law--Maxwell's Theory of Light--Conductor-Intensity.)

Current, After.
A current produced by the animal tissue after it has been subjected to a
current in the opposite direction for some time. The tissue acts like a
secondary battery. The term is used in electro-therapeutics.

Current, Alternating.
Usually defined and spoken of as a current flowing alternately in
opposite directions. It may be considered as a succession of currents,
each of short duration and of direction opposite to that of its
predecessor. It is graphically represented by such a curve as shown in
the cut. The horizontal line may denote a zero current, that is no
current at all, or may be taken to indicate zero electro-motive force.
The curve represents the current, or the corresponding electro-motive
forces. The further from the horizontal line the greater is either, and
if above the line the direction is opposite to that corresponding to the
positions below the line. Thus the current is alternately in opposite
directions, has periods of maximum intensity, first in one and then in
the opposite sense, and between these, passing from one direction to the
other, is of zero intensity. It is obvious that the current may rise
quickly in intensity and fall slowly, or the reverse, or may rise and
fall irregularly. All such phases may be shown by the curve, and a curve
drawn to correctly represent these variations is called the
characteristic curve of such current. It is immaterial whether the
ordinates of the curve be taken as representing current strength or
electromotive force. If interpreted as representing electro-motive
force, the usual interpretation and best, the ordinates above the line
are taken as positive and those below as negative.

Synonyms--Reversed Current--Periodic Currents.

Fig. 117. CHARACTERISTIC CURVE OF ALTERNATING CURRENT.

160 STANDARD ELECTRICAL DICTIONARY.

Current, Atomic.
A unit of current strength used in Germany; the strength of a current
which will liberate in 24 hours (86,400 seconds) one gram of hydrogen
gas, in a water voltameter. The atomic current is equal to 1.111
amperes. In telegraphic work the milliatom is used as a unit, comparable
to the milliampere. The latter is now displacing it.

Current, Charge.
If the external coatings of a charged and uncharged jar are placed in
connection, and if the inner coatings are now connected, after
separating them they are both found to be charged in the same manner. In
this process a current has been produced between the outside coatings
and one between the inner ones, to which Dove has given the name Charge
Current, and which has all the properties of the ordinary discharge
current. (Ganot.)

Current, Circular.
A current passing through a circular conductor; a current whose path is
in the shape of a circle.

Current, Commuted.
A current changed, as regards direction or directions, by a commutator,
q. v., or its equivalent.

Current, Constant.
An unvarying current. A constant current system is one maintaining such
a current. In electric series, incandescent lighting, a constant current
is employed, and the system is termed as above. In arc lighting systems,
the constant current series arrangement is almost universal.

161 STANDARD ELECTRICAL DICTIONARY.

Current, Continuous.
A current of one direction only; the reverse of an alternating current.
(See Current, Alternating.)

Current, Critical.
The current produced by a dynamo at its critical speed; at that speed
when a slight difference in speed produces a great difference in
electro-motive force. On the characteristic curve it corresponds to the
point where the curve bends sharply, and where the electro-motive force
is about two-thirds its maximum.

Current, Daniell/U.S. , Daniell/Siemens' Unit.
A unit of current strength used in Germany. It is the strength of a
current produced by one Daniell cell in a circuit of the resistance of
one Siemens' unit. The current deposits 1.38 grams of copper per hour.
It is equal to 1.16 amperes.

Current, Demarcation.
In electro-therapeutics, a current which can be taken from an injured
muscle, the injured portion acting electro-negatively toward the
uninjured portion.

Current Density.
The current intensity per unit of cross-sectional area of the conductor.
The expression is more generally used for electrolytic conduction, where
the current-density is referred to the mean facing areas of the
electrodes, or else to the facing area of the cathode only.

The quality of the deposited metal is intimately related to the current
density. (See Burning.)

Proper Current Density for Electroplating
Amperes Per Square Foot of Cathode.--(Urquhart.)
Copper, Acid Bath. 5.0 to 10.0
" Cyanide Bath, 3.0 " 5.0
Silver, Double Cyanide, 2.0 " 5.0
Gold, Chloride dissolved in Potassium Cyanide, 1.0 " 2.0
Nickel, Double Sulphate, 6.6 " 8.0
Brass, Cyanide, 2.0 " 3.0

Current, Diacritical.
A current, which, passing through a helix surrounding an iron core,
brings it to one-half its magnetic saturation, q. v.

Current, Diaphragm.
If a liquid is forced through a diaphragm, a potential difference
between the liquid on opposite sides of the diaphragm is maintained.
Electrodes or terminals of platinum may be immersed in the liquid, and a
continuous current, termed a diaphragm current, may be taken as long as
the liquid is forced through the diaphragm. The potential difference is
proportional to the pressure, and also depends on the nature of the
diaphragm and on the liquid.

162 STANDARD ELECTRICAL DICTIONARY.

Current, Direct.
A current of unvarying direction, as distinguished from an alternating
current. It may be pulsatory or intermittent in character, but must be
of constant direction.

Current, Direct Induced.
On breaking a circuit, if it is susceptible of exercising
self-induction, q. v., an extra current, in the direction of the
original is induced, which is called "direct" because in the same
direction as the original. The same is produced by a current in one
circuit upon a parallel one altogether separated from it. (See
Induction, Electro-Magnetic-Current, Extra.)

Synonym--Break Induced Current.

Current, Direction of.
The assumed direction of a current is from positively charged electrode
to negatively charged one; in a galvanic battery from the carbon or
copper plate through the outer circuit to the zinc plate and back
through the electrolyte to the carbon or copper plate. (See Current.)

Current, Displacement.
The movement or current of electricity taking place in a dielectric
during displacement. It is theoretical only and can only be assumed to
be of infinitely short duration. (See Displacement, Electric.)

Currents, Eddy Displacement.
The analogues of Foucault currents, hypothetically produced in the mass
of a dielectric by the separation of the electricity or by its
electrification. (See Displacement.)

Current, Extra.
When a circuit is suddenly opened or closed a current of very brief
duration, in the first case in the same direction, in the other case in
the opposite direction, is produced, which exceeds the ordinary current
in intensity. A high potential difference is produced for an instant
only. These are called extra currents. As they are produced by
electro-magnetic induction, anything which strengthens the field of
force increases the potential difference to which they are due. Thus the
wire may be wound in a coil around an iron core, in which case the extra
currents may be very strong. (See Induction, Self-Coil, Spark.)

Current, Faradic.
A term in medical electricity for the induced or secondary alternating
current, produced by comparatively high electro-motive force, such as
given by an induction coil or magneto-generator, as distinguished from
the regular battery current.

163 STANDARD ELECTRICAL DICTIONARY.

Current, Foucault.
A current produced in solid conductors, and which is converted into heat
(Ganot). These currents are produced by moving the conductors through a
field, or by altering the strength of a field in which they are
contained. They are the source of much loss of energy and other
derangement in dynamos and motors, and to avoid them the armature cores
are laminated, the plane of the laminations being parallel to the lines
of force. (See Core, Laminated.)

The presence of Foucault currents, if of long duration, is shown by the
heating of the metal in which they are produced. In dynamo armatures
they are produced sometimes in the metal of the windings, especially if
the latter are of large diameter.

Synonyms--Eddy Currents--Local Currents--Parasitical Currents.

Current, Franklinic.
In electro-therapeutics the current produced by a frictional electric
machine.

Current, Induced.
The current produced in a conductor by varying the conditions of a field
of force in which it is placed; a current produced by induction.

Current Induction.
Induction by one current on another or by a portion of a current on
another portion of itself. (See Induction.)

Current Intensity.
Current strength, dependent on or defined by the quantity of electricity
passed by such current in a given time. The practical unit of current
intensity is the ampere, equal to one coulomb of quantity per second of
time.

Current, Inverse Induced.
The current induced in a conductor, when in a parallel conductor or in
one having a parallel component a current is started, or is increased in
strength. It is opposite in direction to the inducing current and hence
is termed inverse. (See Induction, Electro-magnetic.) The parallel
conductors may be in one circuit or in two separate circuits.

Synonyms--Make-induced Current--Reverse-induced Current.

Current, Jacobi's Unit of.
A current which will liberate one cubic centimeter of mixed gases
(hydrogen and oxygen) in a water voltameter per minute, the gases being
measured at 0º C. (32º F.) and 760 mm. (29.92 inches) barometric
pressure. It is equal to .0961 ampere.

Current, Joint.
The current given by several sources acting together. Properly, it
should be restricted to sources connected in series, thus if two battery
cells are connected in series the current they maintain is their joint
current.

Current, Linear.
A current passing through a straight conductor; a current whose path
follows a straight line.

164 STANDARD ELECTRICAL DICTIONARY.

Current, Make and Break.
A succession of currents of short duration, separated by absolute
cessation of current. Such current is produced by a telegraph key, or by
a microphone badly adjusted, so that the circuit is broken at intervals.
The U. S. Courts have virtually decided that the telephone operates by
the undulatory currents, and not by a make and break current. Many
attempts have been made to produce a telephone operating by a
demonstrable make and break current, on account of the above
distinction, in hopes of producing a telephone outside of the scope of
the Bell telephone patent.

Current-meter.
An apparatus for indicating the strength of current. (See Ammeter.)

Current, Negative.
In the single needle telegraph system the current which deflects the
needle to the left.

Current, Nerve and Muscle.
A current of electricity yielded by nerves or muscles. Under proper
conditions feeble currents can be taken from nerves, as the same can be
taken from muscles.

Current, Opposed.
The current given by two or more sources connected in opposition to each
other. Thus a two volt and a one volt battery may be connected in
opposition, giving a net voltage of only one volt, and a current due to
such net voltage.

Current, Partial.
A divided or branch current. A current which goes through a single
conductor to a point where one or more other conductors join it in
parallel, and then divides itself between the several conductors, which
must join further on, produces partial currents. It produces as many
partial currents as the conductors among which it divides. The point of
division is termed the point of derivation.

Synonym--Derived Current.

Current, Polarizing.
In electro-therapeutics, a constant current.

Current, Positive.
In the single needle telegraph system the current which deflects the
needle to the right.

Current, Pulsatory.
A current of constant direction, but whose strength is constantly
varying, so that it is a series of pulsations of current instead of a
steady flow.

Current, Rectified.
A typical alternating current is represented by a sine curve, whose
undulations extend above and below the zero line. If by a simple two
member commutator the currents are caused to go in one direction, in
place of the sine curve a series of short convex curves following one
another and all the same side of the zero line results. The currents all
in the same direction, become what is known as a pulsating current.

Synonym--Redressed Current.

165 STANDARD ELECTRICAL DICTIONARY.

Current, Rectilinear.
A current flowing through a rectilinear conductor. The action of
currents depending on their distance from the points where they act,
their contour is a controlling factor. This contour is determined by the
conductors through which they flow.

Current Reverser.
A switch or other contrivance for reversing the direction of a
current in a conductor.

Currents, Ampérian.
The currents of electricity assumed by Ampere's theory to circulate
around a magnet. As they represent the maintenance of a current or of
currents without the expenditure of energy they are often assumed to be
of molecular dimensions. As they all go in the same sense of rotation
and are parallel to each other the result is the same as if a single set
of currents circulated around the body of the magnet. More will be found
on this subject under Magnetism. The Ampérian currents are purely
hypothetical and are predicated on the existence of a field of force
about a permanent magnet. (See Magnetism, Ampére's Theory of.)

If the observer faces the north pole of a magnet the Ampérian currents
are assumed to go in the direction opposite to that of a watch, and the
reverse for the south pole.

Figs. 118-119 DIRECTION OF AMPÉRIAN CURRENTS.

Currents, Angular.
Currents passing through conductors which form an angle with each other.

Currents, Angular, Laws of.
1. Two rectilinear currents, the directions of which form an angle with
each other, attract one another when both approach to or recede from the
apex of the angle.

2. They repel one another, if one approaches and the other recedes from
the apex of the angle.

166 STANDARD ELECTRICAL DICTIONARY

Currents, Earth.
In long telegraph lines having terminal grounds or connected to earth
only at their ends, potential differences are sometimes observed that
are sufficient to interfere with their working and which, of course, can
produce currents. These are termed earth-currents. It will be noted that
they exist in the wire, not in the earth. They may be of 40 milliamperes
strength, quite enough to work a telegraph line without any battery.
Lines running N. E. and S. W. are most affected; those running N.W. and
S. E. very much less so. These currents only exist in lines grounded at
both ends, and appear in underground wires. Hence they are not
attributable to atmospheric electricity. According to Wilde they are the
primary cause of magnetic storms, q. v., but not of the periodical
changes in the magnetic elements. (See Magnetic Elements.)

Synonym--Natural Currents.

Current, Secondary.
(a) A current induced in one conductor by a variation in the current in
a neighboring one; the current produced in the secondary circuit of an
induction coil or alternating current converter.

(b) The current given by a secondary battery. This terminology is not to
be recommended.

Current, Secretion.
In electro-therapeutics, a current due to stimulation of the secretory
nerves.

Current Sheet.
(a) If two terminals of an active circuit are connected to two points of
a thin metallic plate the current spreads over or occupies practically a
considerable area of such plate, and this portion of the current is a
current sheet.

The general contour of the current sheet can be laid out in lines of
flux. Such lines resemble lines of force. Like the latter, they are
purely an assumption, as the current is not in any sense composed of
lines.

(b) A condition of current theoretically brought about by the Ampérian
currents in a magnet. Each molecule having its own current, the
contiguous portions of the molecules counteract each other and give a
resultant zero current. All that remains is the outer sheet of electric
current that surrounds the whole.

Current, Sinuous.
A current passing through a sinuous conductor.

Currents, Multiphase.
A term applied to groups of currents of alternating type which
constantly differ from each other by a constant proportion of periods of
alternation. They are produced on a single dynamo, the winding being so
contrived that two, three or more currents differing a constant amount
in phase are collected from corresponding contact rings. There are
virtually as many windings on the armature as there are currents to be
produced. Separate conductors for the currents must be used throughout.

Synonyms--Polyphase Currents--Rotatory Currents.

167 STANDARD ELECTRICAL DICTIONARY.

Currents of Motion.
In electro-therapeutics, the currents produced in living muscle or
nerves after sudden contraction or relaxation.

Currents of Rest.
In electro-therapeutics, the currents traversing muscular or nervous
tissue when at rest. Their existence is disputed.

Currents, Orders of.
An intermittent current passing through a conductor will induce
secondary alternating currents in a closed circuit near it. This
secondary current will induce a tertiary current in a third closed
circuit near it, and so on. The induced currents are termed as of the
first, second, third and other orders. The experiment is carried out by
Henry's coils. (See Coils, Henry's.)

Currents, Thermo-electric.
These currents, as produced from existing thermo-electric batteries,
are generated by low potential, and are of great constancy. The opposite
junctions of the plates can be kept at constant temperatures, as by
melting ice and condensing steam, so that an identical current can be
reproduced at will from a thermopile.

Thermo-electric currents were used by Ohm in establishing his law. (See
Ohm's Law.)

Current, Swelling.
In electro-therapeutics, a current gradually increasing in strength.

Current, Undulatory.
A current varying in strength without any abrupt transition from action
to inaction, as in the make and break current. The current may be
continually changing in direction (see Current, Alternating), and hence,
of necessity, may pass through stages of zero intensity, but such
transition must be by a graduation, not by an abrupt transition. Such
current may be represented by a curve, such as the curve of sines. It is
evident that the current may pass through the zero point as it crosses
the line or changes direction without being a make and break current.
When such a current does alternate in direction it is sometimes called a
"shuttle current." The ordinary commercial telephone current and the
alternating current is of this type. (See Current, Make and Break.)

Current, Unit.
Unit current is one which in a wire of unit length, bent so as to form
an arc of a circle of unit length of radius, would act upon a unit pole
(see Magnetic Pole, Unit,) at the center of the circle with unit force.
Unit length is the centimeter; unit force is the dyne.

168 STANDARD ELECTRICAL DICTIONARY.

Current, Wattless.
Whenever there is a great difference in phase in an alternating current
dynamo between volts and current, the true watts are much less than the
product of the virtual volts and amperes, because the the watts are
obtained by multiplying the product of the virtual volts and amperes by
the cosine of the angle of lag (or lead). Any alternating current may be
resolved into two components in quadrature with each other, one in phase
with the volts, the other in quadrature therewith, the former is termed
by S. P. Thompson the Working Current, the latter the Wattless Current.
The greater the angle of lag the greater will be the wattless current.

Curve, Arrival.
A curve representing the rate of rise of intensity of current at the end
of a long conductor when the circuit has been closed at the other end.
In the Atlantic cable, for instance, it would require about 108 seconds
for the current at the distant end to attain 9/10 of its full value. The
curve is drawn with its abscissa representing time and its ordinates
current strength.

Curve, Characteristic.
A curve indicating, graphically, the relations between any two factors,
which are interdependent, or which vary simultaneously. Thus in a
dynamo, the voltage increases with the speed of rotation, and a
characteristic curve may be based on the relations between the speed of
rotation and voltage developed. The current produced by a dynamo varies
with the electro-motive force, and a curve can express the relations
between the electro-motive force and the current produced.

A characteristic curve is usually laid out by rectangular co-ordinates
(see Co-ordinates). Two lines are drawn at right angles to each other,
one vertical, and the other horizontal. One set of data are marked off
on the horizontal line, say one ampere, two amperes, and so on, in the
case of a dynamo's characteristic curve.

For each amperage of current there is a corresponding voltage in the
circuit. Therefore on each ampere mark a vertical is erected, and on
that the voltage corresponding to such amperage is laid off. This gives
a series of points, and these points may be connected by a curve. Such
curve will be a characteristic curve.

The more usual way of laying out a curve is to work directly upon the
two axes. On one is laid off the series of values of one set of data; on
the other the corresponding series of values of the other dependent
data. Vertical lines or ordinates, q. v., are erected on the horizontal
line or axis of abscissas at the points laid off; horizontal lines or
abscissas, q. v., are drawn from the points laid off on the vertical
line or axis of ordinates. The characteristic curve is determined by the
intersections of each corresponding pair of abscissa and ordinate.

169 STANDARD ELECTRICAL DICTIONARY.

Variations exist in characteristic curve methods. Thus to get the
characteristic of a commutator, radial lines may be drawn from a circle
representing its perimeter. Such lines may be of length proportional to
the voltage developed on the commutator at the points whence the lines
start. A cut giving an example of such a curve is given in Fig. 125.
(See Curve of Distribution of Potential in Armature.)

There is nothing absolute in the use of ordinates or abscissas. They may
be interchanged. Ordinarily voltages are laid off as ordinates, but the
practise may be reversed. The same liberty holds good for all
characteristic curves. Custom, however, should be followed.

Synonym--Characteristic.

Fig. 120. CHARACTERISTIC CURVE OF A DYNAMO
WITH HORSE POWER CURVES.

Curve, Characteristic, of Converter.
The characteristic curve of the secondary circuit of an alternating
current converter. It gives by the usual methods (see Curve,
Characteristic,) the relations between the electro-motive force and the
current in the secondary circuit at a fixed resistance. If connected in
parallel a constant electro-motive force is maintained, and the curve is
virtually a straight line. If connected in series an elliptical curve is
produced.

170 STANDARD ELECTRICAL DICTIONARY.

Curve, Charging.
In secondary battery manipulation, a curve indicating the increase of
voltage as the charging is prolonged. The rise in voltage with the
duration of the charging current is not uniform. In one case, shown in
the cut, there was a brief rapid rise of about 0.1 volt; then a long
slow rise for 0.15 volt; then a more rapid rise for nearly 0.40 volt,
and then the curve became a horizontal line indicating a cessation of
increase of voltage. The charging rate should be constant.

The horizontal line is laid off in hours, the vertical in volts, so that
the time is represented by abscissas and the voltage by ordinates of the
curve.

Fig. 121. CHARGING CURVE OF A SECONDARY BATTERY.

Curve, Discharging.
A characteristic curve of a storage battery, indicating the fall in
voltage with hours of discharge. The volts may be laid off on the axis
of ordinates, and the hours of discharging on the axis of abscissas. To
give it meaning the rate of discharge must be constant.

Curve, Electro-motive Force.
A characteristic curve of a dynamo. It expresses the relation between
its entire electromotive force, as calculated by Ohm's Law, and the
current intensities corresponding thereto. To obtain the data the dynamo
is driven with different resistances in the external circuit and the
current is measured for each resistance. This gives the amperes. The
total resistance of the circuit, including that of the dynamo, is known.
By Ohm's Law the electro-motive force in volts is obtained for each case
by multiplying the total resistance of the circuit in ohms by the
amperes of current forced through such resistance. Taking the voltages
thus calculated for ordinates and the corresponding amperages for
abscissas the curve is plotted. An example is shown in the cut.

171 STANDARD ELECTRICAL DICTIONARY.

Curve, External Characteristic.
A characteristic curve of a dynamo, corresponding to the electro-motive
force curve, except that the ordinates represent the voltages of the
external circuit, the voltages as taken directly from the terminals of
the machine, instead of the total electro-motive force of the circuit.
The dynamo is run at constant speed. The resistance of the external
circuit is varied. The voltages at the terminals of the machine and the
amperages of current corresponding thereto are determined. Using the
voltages thus determined as ordinates and the corresponding amperages as
abscissas the external characteristic curve is plotted.

This curve can be mechanically produced. A pencil may be moved against a
constant force by two electro-magnets pulling at right angles to each
other. One must be excited by the main current of the machine, the other
by a shunt current from the terminals of the machine. The point of the
pencil will describe the curve.

Fig. 122. CHARACTERISTIC CURVE OF A DYNAMO.

Curve, Horse Power.
Curves indicating electric horse power. They are laid out with
co-ordinates, volts being laid off on the axis of ordinates, and amperes
on the axis of abscissas generally. The curves are drawn through points
where the product of amperes by volts equals 746. On the same diagram 1,
2, 3 .... and any other horse powers can be plotted if within the
limits. See Fig. 120.

Curve, Isochasmen.
A line drawn on the map of the earth's surface indicating the locus of
equal frequency of auroras.

172 STANDARD ELECTRICAL DICTIONARY.

Curve, Life.
A characteristic curve showing the relations between the durability and
conditions affecting the same in any appliance. It is used most for
incandescent lamps. The hours of burning before failure give ordinates,
and the rates of burning, expressed indirectly in volts or in
candle-power, give abscissas. For each voltage or for each candle-power
an average duration is deducible from experience, so that two dependent
sets of data are obtained for the construction of the curve.

Curve, Load.
A characteristic curve of a dynamo, expressing the relation between its
voltage and the amount of excitation under a definite condition of
ampere load, at a constant speed. The ordinates represent voltage, the
abscissas ampere turns in the field, and the curves may be constructed
for a flow of 0, 50, 100, or .. , or any other number of amperes.

Fig. 123. LOAD CURVES.

Curve, Magnetization.
A characteristic curve of an electromagnet, indicating the relation of
magnetization to exciting current. Laying off on the axis of ordinates
the quantities of magnetism evoked, and the corresponding strengths of
the exciting current on the axis of abscissas, the curve can be plotted.
It first rises rapidly, indicating a rapid increase of magnetization,
but grows nearly horizontal as the iron becomes more saturated. The
effect due to the coils alone, or the effect produced in the absence of
iron is a straight line, because air does not change in permeability.

Curve of Distribution of Potential in Armature.
A characteristic curve indicating the distribution of potential
difference between adjoining sections of the commutator of an armature
in different positions all around it. The potential differences are
taken by a volt-meter or potential galvanometer, connection with the
armature being made by two small metal brushes, held at a distance apart
equal to the distance from centre to centre of two adjoining commutator
bars. The curve is laid out as if by polar co-ordinates extending around
the cross-section of the commutator, with the distances from the
commutator surface to the curve proportional to the potential
differences as determined by shifting the pair of brushes all around the
commutator.

The above is S. P. Thompson's method. Another method of W. M. Mordey
involves the use of a pilot brush. (See Brush, Pilot.) Otherwise the
method is in general terms identical with the above.

173 STANDARD ELECTRICAL DICTIONARY.

Fig. 124. MAGNETIZATION CURVE.

Fig. 125. ARMATURE: CURVE.

Fig. 126. DEVELOPMENT OF ARMATURE CURVE.

Curve of Dynamo.
The characteristic curve of a dynamo. (See Curve, Characteristic.)

Curve of Sines.
An undulating curve representing wave motion. It is produced by
compounding a simple harmonic motion, or a two and fro motion like that
of an infinitely long pendulum with a rectilinear motion. Along a
horizontal line points may be laid off to represent equal periods of
time. Then on each point a perpendicular must be erected. The length of
each must be equal to the length of path traversed by the point up to
the expiration of each one of the given intervals of time. The abscissas
are proportional to the times and the ordinates to the sines of angles
proportional to the times. Thus if a circle be drawn upon the line and
divided into thirty-two parts of equal angular value, the sines of these
angles may be taken as the ordinates and the absolute distance or length
of arc of the angle will give the abscissas.

Synonyms--Sine Curve--Sinusoidal Curve--Harmonic Curve.

Fig. 127. CURVE OF SINES.

174 STANDARD ELECTRICAL DICTIONARY.

Curve of Saturation of the Magnetic Circuit.
A characteristic curve whose ordinates may represent the number of
magnetic lines of force induced in a magnetic circuit, and whose
abscissas may represent the ampere turns of excitation or other
representative of the inducing force.

Curve of Torque.
A characteristic curve showing the relations between torque, q. v., and
current in a dynamo or motor.

Curve, Permeability Temperature.
A characteristic curve expressing the changes in permeability of a
paramagnetic substance as the temperature changes. The degrees of
temperature may be abscissas, and the permeabilities corresponding
thereto ordinates of the curve.

Cut In. v.
To connect any electric appliance, mechanism or conductor, into a
circuit.

Cut Out. v.
The reverse of to cut in; to remove from a circuit any conducting
device, and sometimes so arranged as to leave the circuit completed in
some other way.

Cut Out.
An appliance for removing any apparatus from an electric circuit, so
that no more current shall pass through such apparatus, and sometimes
providing means for closing the circuit so as to leave it complete after
the removal of the apparatus.

175 STANDARD ELECTRICAL DICTIONARY.

Cut Out, Automatic.
(a) A mechanism for automatically shunting an arc or other lamp when it
ceases to work properly. It is generally worked by an electro-magnet of
high resistance placed in parallel with the arc. If the arc grows too
long the magnet attracts its armature, thereby completing a shunt of
approximately the resistance of the arc, and which replaces it until the
carbons approach again to within a proper distance. Sometimes a strip or
wire of fusible metal is arranged in shunt with the arc. When the arc
lengthens the current through the wire increases, melts it and a spring
is released which acts to complete or close a shunt circuit of
approximately arc-resistance.

(b) See Safety Device--Safety Fuse.

(c) See below.

Cut-out, Magnetic.
A magnetic cut-out is essentially a coil of wire with attracted core or
armature. When the coil is not excited the core, by pressing down a
strip of metal or by some analogous arrangement, completes the circuit.
When the current exceeds a certain strength the core rises as it is
attracted and the circuit is opened.

Cut-out, Safety.
A block of porcelain or other base carrying a safety fuse, which melts
and breaks the circuit before the wire connected to it is dangerously
heated.

Synonyms--Fuse Block--Safety Catch--Safety Fuse.

Cut Out, Wedge.
A cut out operated by a wedge. The line terminals consist of a spring
bearing against a plate, the circuit being completed through their point
of contact. A plug or wedge composed of two metallic faces insulated
from each other is adapted to wedge the contact open. Terminals of a
loop circuit are connected to the faces of the wedge. Thus on sliding it
into place, the loop circuit is brought into series in the main circuit.

Synonym--Plug Cut Out--Spring Jack.

Cutting of Lines of Force.
A field of force is pictured as made up of lines of force; a conductor
swept through the field is pictured as cutting these lines. By so doing
it produces potential difference or electro-motive force in itself with
a current, if the conductor is part of a closed circuit.

Cycle of Alternation.
A full period of alternation of an alternating current. It begins
properly at the zero line, goes to a maximum value in one sense and
returns to zero, goes to maximum in the other sense and returns to zero.

Cystoscopy.
Examination of the human bladder by the introduction of a special
incandescent electric lamp. The method is due to Hitze.

176 STANDARD ELECTRICAL DICTIONARY.

Damper.
(a) A copper frame on which the wire in a galvanometer is sometimes
coiled, which acts to damp the oscillations of the needle.

(b) A tube of brass or copper placed between the primary and secondary
coils of an induction coil. It cuts off induction and diminishes the
current and potential of the secondary circuit. On pulling it out, the
latter increases. It is used on medical coils to adjust their strength
of action.

Damping.
Preventing the indicator of an instrument from oscillating in virtue of
its own inertia or elasticity. In a galvanometer it is defined as
resistance to quick vibrations of the needle, in consequence of which it
is rapidly brought to rest when deflected (Ayrton). In dead-beat
galvanometers (see Galvanometer, Dead-Beat,) damping is desirable in
order to bring the needle to rest quickly; in ballistic galvanometers
(see Galvanometer, Ballistic,) damping is avoided in order to maintain
the principle of the instrument. Damping may be mechanical, the
frictional resistance of air to an air-vane, or of a liquid to an
immersed diaphragm or loosely fitting piston, being employed. A
dash-pot, q. v., is an example of the latter. It may be
electro-magnetic. A mass of metal near a swinging magnetic needle tends
by induced currents to arrest the oscillations thereof, and is used for
this purpose in dead-beat galvanometers. This is termed, sometimes,
magnetic friction. The essence of damping is to develop resistance to
movement in some ratio proportional to velocity, so that no resistance
is offered to the indicator slowly taking its true position. (See
Galvanometer, Dead-Beat.)

Dash-Pot.
A cylinder and piston, the latter loosely fitting or perforated, or some
equivalent means being provided to permit movement. The cylinder may
contain a liquid such as glycerine, or air only. Thus the piston is
perfectly free to move, but any oscillations are damped (see Damping).
In some arc lamps the carbon holder is connected to a dash-pot to check
too sudden movements of the carbon. The attachment may be either to the
piston or to the cylinder. In the Brush lamp the top of the carbon
holder forms a cylinder containing glycerine, and in it a loosely
fitting piston works. This acts as a dash-pot.

Dead Beat. adj.
Reaching its reading quickly; applied to instruments having a moving
indicator, which normally would oscillate back and forth a number of
times before reaching its reading were it not prevented by damping. (See
Galvanometer, Aperiodic--Damping.)

Dead Earth.
A fault in a telegraph line which consists in the wire being thoroughly
grounded or connected to the earth.

177 STANDARD ELECTRICAL DICTIONARY.

Dead Point of an Alternator.
A two-phase alternator of the ordinary type connected as a motor to
another alternator cannot start itself, as it has dead points where the
relations and polarity of field and armature are such that there is no
torque or turning power.

Dead-Turns.
In the winding of an armature, a given percentage of the turns, it may
be 80 per cent., more or less, is assumed to be active; the other 20 per
cent. or thereabouts, is called dead-turns. This portion represents the
wire on such portions of the armature as comes virtually outside of the
magnetic field. They are termed dead, as not concurring to the
production of electro-motive force.

Dead Wire.
(a) The percentage or portion of wire on a dynamo or motor armature that
does not concur in the production of electromotive force. The
dead-turns, q. v., of a drum armature or the inside wire in a Gramme
ring armature are dead wire.

(b) A disused and abandoned electric conductor, such as a telegraph
wire.

(c) A wire in use, but through which, at the time of speaking, no
current is passing.

Death, Electrical.
Death resulting from electricity discharged through the animal system.
The exact conditions requisite for fatal results have not been
determined. High electro-motive force is absolutely essential; a
changing current, pulsatory or alternating, is most fatal, possibly
because of the high electro-motive force of a portion of each period.
Amperage probably has something to do with it, although the total
quantity in coulombs may be very small. As applied to the execution of
criminals, the victim is seated in a chair and strapped thereto. One
electrode with wet padded surface is placed against his head or some
adjacent part. Another electrode is placed against some of the lower
parts, and a current from an alternating dynamo passed for 15 seconds or
more. The potential difference of the electrodes is given at 1,500 to
2,000 volts, but of course the maximum may be two or three times the
measured amount, owing to the character of the current.

Decalescence.
The converse of recalescence, q. v. When a mass of steel is being heated
as it reaches the temperature of recalescence it suddenly absorbs a
large amount of heat, apparently growing cooler.

Deci.
Prefix originally used in the metric system to signify one-tenth of, now
extended to general scientific units. Thus decimeter means one-tenth of
a meter; decigram, one-tenth of a gram.

Declination, Angle of.
The angle intercepted between the true meridian and the axis of a
magnetic needle at any place. The angle is measured to east or west,
starting from the true meridian as zero.

178 STANDARD ELECTRICAL DICTIONARY.

Declination of the Magnetic Needle.
The deviation of the magnetic needle from the plane of the earth's
meridian. It is also called the variation of the compass. (See Magnetic
Elements.)

Decomposition.
The reduction of a compound substance into its constituents, as in
chemical analysis. The constituents may themselves be compounds or
proximate constituents, or may be elemental or ultimate constituents.

Decomposition, Electrolytic.
The decomposition or separation of a compound liquid into its
constituents by electrolysis. The liquid must be an electrolyte, q. v.,
and the decomposition proceeds subject to the laws of electrolysis, q.
v. See also Electrolytic Analysis.

Decrement.
When a suspension needle which has been disturbed is oscillating the
swings gradually decrease in amplitude if there is any damping, as there
always is. The decrement is the ratio of the amplitude of one
oscillation to the succeeding one. This ratio is the same for any
successive swings.

De-energize.
To cut off its supply of electric energy from an electric motor, or any
device absorbing and worked by electric energy.

Deflagration.
The explosive or violent volatilizing and dissipating of a substance by
heat, violent oxidation and similar means. It may be applied among other
things to the destroying of a conductor by an intense current, or the
volatilization of any material by the electric arc.

Deflecting Field.
The field produced in a galvanometer by the current which is being
tested, and which field deflects the needle, such deflection being the
measure of the current strength.

Deflection.
In magnetism the movement out of the plane of the magnetic meridian of a
magnetic needle, due to disturbance by or attraction towards a mass of
iron or another magnet.

Deflection Method.
The method of electrical measurements in which the deflection of the
index of the measuring instrument is used as the measure of the current
or other element under examination. It is the opposite of and is to be
distinguished from the zero or null method, q. v. In the latter
conditions are established which make the index point to zero and from
the conditions necessary for this the measurement is deduced. The
Wheatstone Bridge, q. v., illustrates a zero method, the sine or the
tangent compass, illustrates a deflection method. The use of deflection
methods involves calibration, q. v., and the commercial measuring
instruments, such as ammeters and volt meters, which are frequently
calibrated galvanometers, are also examples of deflection instruments.

179 STANDARD ELECTRICAL DICTIONARY.

Degeneration, Reaction of.
The diminished sensibility to electro-therapeutic treatment exhibited by
the human system with continuance of the treatment in question. The
general lines of variation are stated in works on the subject.

Deka.
Prefix originally used in the metric system to signify multiplying by
ten, as dekameter, ten meters, dekagram, ten grams; now extended to many
scientific terms.

De la Rive's Floating Battery.
A small galvanic couple, immersed in a little floating cell and
connected through a coil of wire immediately above them. When the
exciting battery solution is placed in the cell the whole, as it floats
in a larger vessel, turns until the coil lies at right angles to the
magnetic needle. Sometimes the two plates are thrust through a cork and
floated thus in a vessel of dilute sulphuric acid.

A magnet acts to attract or repel the coil in obedience to Ampére's
Theory, (See Magnetism, Ampere's Theory of.)

Delaurier's Solution.
A solution for batteries of the Bunsen and Grenet type. It is of the
following composition:
Water, 2,000 parts;
potassium bichromate, 184 parts;
sulphuric acid, 428 parts.

Demagnetization.
Removal of magnetism from a paramagnetic substance. It is principally
used for watches which have become magnetized by exposure to the
magnetic field surrounding dynamos or motors.

The general principles of most methods are to rotate the object, as a
watch, in a strong field, and while it is rotating to gradually remove
it from the field, or to gradually reduce the intensity of the field
itself to zero. A conical coil of wire within which the field is
produced in which the watch is placed is sometimes used, the idea being
that the field within such a coil is strongest at its base. Such a coil
supplied by an alternating current is found effectual (J. J. Wright).

If a magnetized watch is made to turn rapidly at the end of a twisted
string and is gradually brought near to and withdrawn from the poles of
a powerful dynamo it may be considerably improved.

A hollow coil of wire connected with a pole changer and dip-battery has
been used. The battery creates a strong field within the coil. The watch
is placed there and the pole changer is worked so as to reverse the
polarity of the field very frequently. By the same action of the pole
changer the plates of the battery are gradually withdrawn from the
solution so as to gradually reduce the magnetic field to zero while
constantly reversing its polarity. (G. M. Hopkins.)

Steel may be demagnetized by jarring when held out of the magnetic
meridian, or by heating to redness.

180 STANDARD ELECTRICAL DICTIONARY.

Density, Electric Superficial.
The relative quantity of electricity residing as an electric charge upon
a unit area of surface. It may be positive or negative.

Synonyms--Density of Charge--Surface Density.

Dental Mallet, Electric.
A dentist's instrument for hammering the fillings as inserted into
teeth. It is a little hammer held in a suitable handle, and which is
made to strike a rapid succession of blows by electro-magnetic motor
mechanism.

Depolarization.
(a) The removal of permanent magnetism. (See Demagnetization.)

(b) The prevention of the polarization of a galvanic cell. It is
effected in the Grove battery by the reduction of nitric acid; in the
Bunsen, by the reduction of chromic acid; in the Smee battery,
mechanically, by the platinum coated or rather platinized negative
plate. Other examples will be found under the description of various
cells and batteries. A fluid which depolarizes is termed a depolarizer
or depolarizing fluid or solution. (See Electropoion Fluid.)

Deposit, Electrolytic.
The metal or other substance precipitated by the action of a battery or
other current generator.

Derivation, Point of.
A point where a circuit branches or divides into two or more leads. The
separate branches then receive derived or partial currents.

Desk Push.
A press or push button, with small flush rim, for setting into the
woodwork of a desk.

Detector.
A portable galvanometer, often of simple construction, used for rough or
approximate work.

Detector, Lineman's.
A portable galvanometer with a high and a low resistance actuating coil,
constructed for the use of linemen and telegraph constructors when in
the field, and actually putting up, repairing or testing lines.

Deviation, Quadrantal.
Deviation of the compass in iron or steel ships due to the magnetization
of horizontal beams by the earth's induction. The effect of this
deviation disappears when the ship is in the plane of the electric
meridian, or at right angles thereto; its name is taken from the fact
that a swing of the ship through a quadrant brings the needle from zero
deviation to a maximum and back to zero.

181 STANDARD ELECTRICAL DICTIONARY.

Deviation, Semicircular.
Deviation of the compass in iron or steel ships due to vertical
induction. (See Induction, Vertical.) The effect of this induction
disappears when the ship is in the electric meridian. Its name is
derived from the fact that a swing of the ship through half the circle
brings the needle from zero deviation to a maximum and back to zero.

Dextrotorsal. adj.
Wound in the direction or sense of a right-handed screw; the reverse of
sinistrotorsal, q. v.

Fig. 128. DEXTROTORSAL HELIX.

Diacritical. adj.
(a) The number of ampere turns, q. v., required to bring an iron core to
one half its magnetic saturation, q. v., is termed the diacritical
number.

(b) The diacritical point of magnetic saturation is proposed by Sylvanus
P. Thompson as a term for the coefficient of magnetic saturation which
gives a magnet core one-half its maximum magnetization.

Diagnosis, Electro.
A medical diagnosis of a patient's condition based on the action of
different parts of the body under electric excitement.

Diamagnetic. adj.
Possessing a negative coefficient of magnetic susceptibility; having
permeability inferior to that of air. Such substances placed between the
poles of a magnet are repelled; if in the form of bars, they tend to
turn so as to have their long axis at right angles to the line joining
the poles. The reason is that the lines of force always seek the easiest
path, and these bodies having higher reluctance than air, impede the
lines of force, and hence are as far as possible pushed out of the way.
The above is the simplest explanation of a not well understood set of
phenomena. According to Tyndall, "the diamagnetic force is a polar
force, the polarity of diamagnetic bodies being opposed to that of
paramagnetic ones under the same conditions of excitement." Bismuth is
the most strongly diamagnetic body known; phosphorus, antimony, zinc,
and many others are diamagnetic. (See Paramagnetic.)

182 STANDARD ELECTRICAL DICTIONARY.

Diagometer.
An apparatus for use in chemical analysis for testing the purity of
substances by the time required for a charged surface to be discharged
through them to earth. It is the invention of Rousseau.

An electrometer is charged with a dry pile. One of its terminals is
connected with one surface of the solution or substance to be tested,
and the other with the other surface. The time of discharge gives the
index of the purity of the substance.

Diamagnetic Polarity.
Treating diamagnetism as due to a polar force, the polarity of a
diamagnetic body is the reverse of the polarity of iron or other
paramagnetic bodies. A bar-shaped diamagnetic body in a field of force
tends to place itself at right angles to the lines of force.

Diamagnetism.
(a) The science or study of diamagnetic substances and phenomena.

(b) The magnetic property of a diamagnetic substance.

Diameter of Commutation.
The points on the commutator of a closed circuit ring--or
drum--armature, which the brushes touch, and whence they take the
current, mark the extremities of the diameter of commutation. Were it
not for the lag this would be the diameter at right angles to the line
connecting the centers of the opposite faces of the field. It is always
a little to one side of this position, being displaced in the direction
of rotation. In open circuit armatures the brushes are placed on the
diameter at right angles to this one, and sometimes the term diameter of
commutation is applied to it. All that has been said is on the
supposition that the armature divisions correspond not only in
connection but in position with those of the armature coils. Of course,
the commutator could be twisted so as to bring the diameter of
commutation into any position desired.

Diapason, Electric.
A tuning-fork or diapason kept in vibration by electricity. In general
principle the ends of the fork act as armatures for an electro-magnet,
and in their motion by a mercury cup or other form of contact they make
and break the circuit as they vibrate. Thus the magnet alternately
attracts and releases the leg, in exact harmony with its natural period
of vibration.

Diaphragm.
(a) In telephones and microphones a disc of iron thrown into motion by
sound waves or by electric impulses, according to whether it acts as the
diaphragm of a transmitter or receiver. It is generally a plate of
japanned iron such as used in making ferrotype photographs. (See
Telephone and Microphone.)

(b) A porous diaphragm is often used in electric decomposition cells and
in batteries. The porous cup represents the latter use.

183 STANDARD ELECTRICAL DICTIONARY.

Dielectric.
A non-conductor; a substance, the different parts of which may, after an
electric disturbance, remain, without any process of readjustment, and
for an indefinite period of time, at potentials differing to any extent
(Daniell). There is no perfect dielectric. The term dielectric is
generally only used when an insulator acts to permit induction to take
place through it, like the glass of a Leyden jar.

Dielectric Constant.
The number or coefficient expressing the relative dielectric capacity of
a medium or substance. (See Capacity, Specific Inductive.)

Dielectric, Energy of.
In a condenser, the conducting coatings are merely to conduct the
current all over the surface they cover; the keeping the electricities
separated is the work of the dielectric, and represents potential energy
which appears in the discharge. The amount of energy is proportional to
the charge, and to the potential difference. As any electrified body
implies an opposite electrification somewhere, and a separating
dielectric, the existence of a condenser is always implied.

Dielectric Polarization.
A term due to Faraday. It expresses what he conceived to be the
condition of a dielectric when its opposite faces are oppositely
electrified. The molecules are supposed to be arranged by the
electrification in a series of polar chains, possibly being originally
in themselves seats of opposite polarities, or having such imparted to
them by the electricities. The action is analogous to that of a magnet
pole on a mass of soft iron, or on a pile of iron filings.

Dielectric Strain.
The strain a solid dielectric is subjected to, when its opposite
surfaces are electrified. A Leyden jar dilates under the strain, and
when discharged gives a dull sound. The original condition is not
immediately recovered. Jarring, shaking, etc., assist the recovery from
strain. The cause of the strain is termed Electric Stress. (See Stress,
Electric.) This is identical with the phenomenon of residual charge.
(See Charge, Residual.) Each loss of charge is accompanied with a
proportional return of the dielectric towards its normal condition.

Dielectric Resistance.
The mechanical resistance a body offers to perforation or destruction by
the electric discharge.

Dielectric Strength.
The resistance to the disruptive discharge and depending on its
mechanical resistance largely or entirely. It is expressible in volts
per centimeter thickness. Dry air requires 40,000 volts per centimeter
for a discharge.

184 STANDARD ELECTRICAL DICTIONARY.

Differential Winding Working.
A method of working an electro-magnet intermittently, so as to avoid
sparking. The magnet is wound with two coils. One is connected straight
into the circuit, the other is connected in parallel therewith with a
switch inserted. The coils are so connected that when the switch is
closed the two are in opposition, the current going through them in
opposite senses. Thus one overcomes the effect of the other and the
magnet core shows no magnetism, provided the two coils are of equal
resistance and equal number of convolutions or turns.

Fig. 129. DIFFERENTIAL WINDING WORKING
OF ELECTRO-MAGNETIC APPARATUS.

Diffusion.
A term properly applied to the varying current density found in
conductors of unequal cross sectional area. In electro-therapeutics it
is applied to the distribution of current as it passes through the human
body. Its density per cross-sectional area varies with the area and
with the other factors.

Diffusion Creep.
When electrodes of an active circuit are immersed in a solution of an
electrolyte, a current passes electrolytically if there is a sufficient
potential difference. The current passes through all parts of the
solution, spreading out of the direct prism connecting or defined by the
electrodes. To this portion of the current the above term is applied. If
the electrodes are small enough in proportion to the distance between
them the current transmission or creep outside of the line becomes the
principal conveyor of the current so that the resistance remains the
same for all distances.

Dimensions and Theory of Dimensions.
The expression of the unitary value of a physical quantity in one or
more of the units of length (L), time (T) and mass (M) is termed the
dimensions of such quantity. Thus the dimension or dimensions of a
distance is simply L; of an angle, expressible by dividing the arc by
the radius is L/L; of a velocity, expressible by distance divided by
time--L/T; of acceleration, which is velocity acquired in a unit of
time, and is therefore expressible by velocity divided by time--L/T/T or
L/T2; of momentum, which is the product of mass into velocity--M*L/T; of
kinetic energy taken as the product of mass into the square of
velocity--M*(L2/T2); of potential energy taken as the product of mass
into acceleration into space-M*(L/T2)*L reducing to M*(L2/T2). The
theory is based on three fundamental units and embraces all electric
quantities. The simple units generally taken are the gram, centimeter
and second and the dimensions of the fundamental compound units are
expressed in terms of these three, forming the centimeter-gram-second or
C. G. S. system of units. Unless otherwise expressed or implied the
letters L, M and T, may be taken to indicate centimeter, gram and second
respectively. It is obvious that very complicated expressions of
dimensions may be built up, and that a mathematical expression of
unnamed quantities may be arrived at. Dimensions in their application by
these symbols are subject to the laws of algebra. They were invented by
Fourier and were brought into prominence by J. Clerk Maxwell. Another
excellent definition reads as follows: "By the dimensions of a physical
quantity we mean the quantities and powers of quantities, involved in
the measurement of it." (W. T. A. Emtage.)

185 STANDARD ELECTRICAL DICTIONARY.

Dimmer.
An adjustable choking coil used for regulating the intensity of electric
incandescent lights. Some operate by the introduction and withdrawal of
an iron core as described for the choking coil (see Coil, Choking),
others by a damper of copper, often a copper ring surrounding the coil
and which by moving on or off the coil changes the potential of the
secondary circuit.

Dip of Magnetic Needle.
The inclination of the magnetic needle. (See Elements, Magnetic.)

Dipping.
(a) Acid or other cleaning processes applied by dipping metals in
cleaning or pickling solutions before plating in the electroplater's
bath.

(b) Plating by dipping applies to electroplating without a battery by
simple immersion. Copper is deposited on iron from a solution of copper
sulphate in this way.

Synonym--Simple Immersion.

Dipping Needle.
A magnet mounted in horizontal bearings at its centre of gravity. Placed
in the magnetic meridian it takes the direction of the magnetic lines of
force of the earth at that point. It is acted on by the vertical
component of the earth's magnetism, as it has no freedom of horizontal
movement. (See Magnetic Elements, and Compass, Inclination.)

Directing Magnet.
In a reflecting galvanometer the magnet used for controlling the
magnetic needle by establishing a field. It is mounted on the spindle of
the instrument above the coil and needle.

Synonym--Controlling Magnet.

186 STANDARD ELECTRICAL DICTIONARY.

Direction.
(a) The direction of an electric current is assumed to be from a
positively charged electrode or terminal to a negatively charged one in
the outer circuit. (See Current.)

(b) The direction of magnetic and electro-magnetic lines of force is
assumed to be from north to south pole of a magnet in the outer circuit.
It is sometimes called the positive direction. Their general course is
shown in the cuts diagrammatically. The circles indicate a compass used
in tracing their course. The magnetic needle tends to place itself in
the direction of or tangential to the lines of force passing nearest it.

(c) The direction of electrostatic lines of force is assumed to be out
of a positively charged and to a negatively charged surface.

Fig. 130. DIRECTION OF LINES OF FORCE OF A PERMANENT MAGNET.

Fig. 131, DIRECTION OF LINES OF FORCE OF AN ELECTRO-MAGNET.

187 STANDARD ELECTRICAL DICTIONARY.

Directive Power.
In magnetism the power of maintaining itself in the plane of the
magnetic meridian, possessed by the magnetic needle.

Discharge, Brush.
The static discharge of electricity into or through the air may be of
the brush or spark form. The brush indicates the escape of electricity
in continuous flow; the spark indicates discontinuity. The conditions
necessary to the production of one or the other refer to the nature of
the conductor, and of other conductors in its vicinity and to the
electro-motive force or potential difference; small alterations may
transform one into the other. The brush resembles a luminous core whose
apex touches the conductor. It is accompanied by a slight hissing noise.
Its luminosity is very feeble. The negative conductor gives a smaller
brush than that of the positive conductor and discharges it more
readily. When electricity issues from a conductor, remote from an
oppositely excited one, it gives an absolutely silent discharge, showing
at the point of escape a pale blue luminosity called electric glow, or
if it escapes from points it shows a star-like centre of light. It can
be seen in the dark by placing a point on the excited conductor of a
static-electric machine.

Synonyms--Silent Discharge--Glow Discharge.

Discharge, Conductive.
A discharge of a static charge by conduction through a conductor.

Discharge, Convective.
The discharge of static electricity from an excited conductor through
air or rarefied gas; it is also called the quiet or silent discharge.
The luminous effect in air or gas at atmospheric pressures takes the
form of a little brush from a small positive electrode; the negative
shows a star. The phenomena of Gassiot's cascade, the philosopher's egg
and Geissler tubes, all of which may be referred to, are instances of
convective discharge.

Discharge, Dead Beat.
A discharge that is not oscillatory in character.

Discharge, Disruptive.
A discharge of a static charge through a dielectric. It involves
mechanical perforation of the dielectric, and hence the mere mechanical
strength of the latter has much to do with preventing it. A disruptive
discharge is often oscillatory in character; this is always the case
with the discharge of a Leyden jar.

188 STANDARD ELECTRICAL DICTIONARY.

Discharge, Duration of.
The problem of determining this factor has been attacked by various
observers. Wheatstone with his revolving mirror found it to be 1/24000
second. Fedderson, by interposing resistance, prolonged it to 14/10000
and again to 138/10000 second. Lucas & Cazin made it from 26 to 47
millionths of a second. All these experiments were performed with Leyden
jars.

Discharge, Impulsive.
A disruptive discharge produced between conductors by suddenly produced
potential differences. The self-induction of the conductor plays an
especially important part in discharges thus produced.

Discharge, Lateral.
(a) A lightning discharge, which sometimes takes place between a
lightning rod and the building on which it is.

(b) In the discharge of a Leyden jar or condenser the discharge which
takes the alternative path, q. v.

Discharge, Oscillatory.
The sudden or disruptive discharge of a static condenser, such as a
Leyden jar, or of many other charged conductors, is oscillatory in
character. The direction of the currents rapidly changes, so that the
discharge is really an alternating current of excessively short total
duration. The discharge sends electro-magnetic waves through the ether,
which are exactly analogous to those of light but of too long period to
affect the eye.

Synonym--Surging Discharge.

Fig. 132. DISCHARGER.

Discharger.
An apparatus for discharging Leyden jars. It consists of a conductor
terminating in balls, and either jointed like a tongs or bent with a
spring-action, so that the balls can be set at distances adapted to
different sized jars. It has an insulating handle or a pair of such. In
use one ball is brought near to the coating and the other to the spindle
ball of the jar. When nearly or quite in contact the jar discharges.

Synonyms--Discharging Rod--Discharging Tongs.

189 STANDARD ELECTRICAL DICTIONARY.

Discharger, Universal.
An apparatus for exposing substances to the static discharge spark. It
consists of a base with three insulating posts. The central post carries
an ivory table to support the object. The two side posts carry
conducting rods, terminating in metal balls, and mounted with universal
joints. A violent shock can be given to any object placed on the table.

Synonym--Henley's Universal Discharger.

Discharge, Silent.
This term is sometimes applied to the glow or brush discharge and
sometimes to the condition of electric effluvium. (See Discharge,
Brush--Effluvium, Electric.)

Discharge, Spark.
The discontinuous discharge of high tension electricity through a
dielectric or into the air produces electric sparks. These are quite
strongly luminous, of branching sinuous shape, and in long sparks the
luminosity varies in different parts of the same spark. A sharp noise
accompanies each spark. High density of charge is requisite for the
formation of long sparks.

Disconnection.
The separation of two parts of, or opening a circuit, as by turning a
switch, unscrewing a binding screw, or the like. The term is sometimes
used to indicate a class of faults in telegraph circuits. Disconnections
may be total, partial or intermittent, and due to many causes, such as
open or partially replaced switches, oxidized or dirty contact points,
or loose joints.

Displacement, Electric.
A conception of the action of charging a dielectric. The charge is all
on the surface. This fact being granted, the theory of displacement
holds that charging a body is the displacing of electricity, forcing it
from the interior on to the surface, or vice versa, producing a positive
or negative charge by displacement of electricity. While displacement is
taking place in a dielectric there is assumed to be a movement or
current of electricity called a displacement current.

Disruptive Tension.
When the surface of a body is electrified, it tends to expand, all
portions of the surface repelling each other. The film of air
surrounding such a body is electrified too, and is subjected to a
disruptive tension, varying in intensity with the square of the density.

Dissimulated Electricity.
The electricity of a bound charge. (See Charge, Bound.)

Dissociation.
The separation of a chemical compound into its elements by a
sufficiently high degree of heat. All compounds are susceptible of
dissociation, so that it follows that combustion is impossible at high
temperatures.

190 STANDARD ELECTRICAL DICTIONARY.

Distance, Critical, of Alternative Path.
The length of air gap in an alternative path whose resistance joined to
the impedance of the rest of the conductors of the path just balances
the impedance of the other path.

Distance, Sparking.
The distance between electrodes, which a spark from a given Leyden jar
or other source will pass across.

Synonym--Explosive Distance.

Distillation.
The evaporation of a liquid by heat, and sometimes in a vacuum, followed
by condensation of the vapors, which distil or drop from the end of the
condenser. It is claimed that the process is accelerated by the liquid
being electrified.

Distributing Box.
In an electric conduit system, a small iron box provided for giving
access to the cable for the purpose of making house and minor
connections.

Synonym--Hand Hole.

Distributing Switches.
Switch systems for enabling different dynamos to supply different lines
of a system as required. Spring jacks, q. v., are used for the lines,
and plug switches for the dynamo leads. Thus, dynamos can be thrown in
or out as desired, without putting out the lights.

Distribution of Electric Energy, Systems of.
The systems of electric current distribution from central stations or
from private generating plants, mechanical or battery, the latter
primary or secondary. They include in general the alternating current
system and direct current systems. Again, these may be subdivided into
series and multiple arc, multiple-series and series-multiple
distribution, and the three, four, or five wire system may be applied to
multiple arc or multiple series systems. (See Alternating
Current--Current System--Multiple Arc--Multiple Series--Series
Multiple--Three Wire System.)

Door Opener, Electric.
An apparatus for opening a door by pushing back the latch. A spring then
draws the door open, and it is closed against the force of the spring by
the person entering. Electro-magnetic mechanism actuates the latch, and
is operated by a switch or press-button. Thus a person on the upper
floor can open the hall door without descending.

Dosage, Galvanic.
In electro-therapeutics the amount of electric current or discharge, and
duration of treatment given to patients.

Double Carbon Arc Lamp.
An arc lamp designed to burn all night, usually constructed with two
parallel sets of carbons, one set replacing the other automatically, the
current being switched from the burnt out pair to the other by the
action of the mechanism of the lamp.

191 STANDARD ELECTRICAL DICTIONARY.

Double Fluid Theory.
A theory of electricity. Electricity is conveniently treated as a fluid
or fluids. According to the double fluid hypothesis negative electricity
is due to a preponderance of negative fluid and vice versa. Like fluid
repels like, and unlike attracts unlike; either fluid is attracted by
matter; the presence in a body of one or the other induces
electrification; united in equal proportions they neutralize each other,
and friction, chemical decomposition and other causes effect their
separation. The hypothesis, while convenient, is overshadowed by the
certainty that electricity is not really a fluid at all. (See Single
Fluid Theory--Fluid, Electric.)

Synonym--Symmer's Theory.

Double Fluid Voltaic Cell.
A cell in which two fluids are used, one generally as depolarizer
surrounding the negative plate, the other as excitant surrounding the
positive plate. A porous diaphragm or difference in specific gravities
is used to keep the solutions separate and yet permit the essential
electrolytic diffusion. Grove's Cell, Bunsen's Cell, and Daniell's Cell,
all of which may be referred to, are of this type, as are many others.

Double Wedge.
A plug for use with a spring-jack. It has connection strips at its end
and another pair a little distance back therefrom, so that it can make
two loop connections at once.

Synonym--Double Plug.

Doubler.
A continuously acting electrophorous, q.v.; an early predecessor of the
modern electric machines. It is now no longer used.

D. P.
Abbreviation for Potential Difference.

Drag.
The pull exercised by a magnetic field upon a conductor moving through
it or upon the motion of an armature in it.

Dreh-strom. (German)
Rotatory currents; a system of currents alternating in periodic
succession of phases and producing a rotatory field. (See Field,
Rotatory--Multiphase Currents.)

Drill Electric.
A drill for metals or rock worked by an electro-magnetic motor. For
metals a rotary motion, for rocks a reciprocating or percussion action
is imparted. It is used by shipbuilders for drilling holes in plates
which are in place in ships, as its flexible conductors enable it to be
placed anywhere. For rock-drilling a solenoid type of construction is
adopted, producing rapid percussion.

192 STANDARD ELECTRICAL DICTIONARY.

Drip Loop.
A looping downward of wires entering a building, so that rain water, as
it runs along the wire, will drip from the lowest part of the loop
instead of following the wire into or against the side of the building.

Driving Horns.
Projections on the periphery of an armature of a dynamo for holding the
winding in place and preventing its displacement. Various arrangements
have been adopted. They are sometimes wedges or pins and are sometimes
driven into spaces left in the drum core. The toothed disc armature
cores make up an armature in which the ridges formed by the teeth form
practically driving horns.

Dronier's Salt.
A substance for solution for use in bichromate batteries. It is a
mixture of one-third potassium bichromate and two-thirds potassium
bisulphate. It is dissolved in water to make the exciting fluid.

Drop, Automatic.
A switch or circuit breaker, operating to close a circuit by dropping
under the influence of gravity. It is held up by a latch, the circuit
remaining open, until the latch is released by a current passing through
an electro-magnet. This attracting an armature lets the drop fall. As it
falls it closes a local or second circuit, and thus may keep a bell
ringing until it is replaced by hand. It is used in burglar alarms, its
function being to keep a bell ringing even though the windows or door by
which entrance was made is reclosed.

193 STANDARD ELECTRICAL DICTIONARY.

Fig. 133. THE MAGIC DRUM.

Drum, Electric.
A drum with a mechanism within for striking the head with a hammer or
some equivalent method so as to be used as a piece of magical apparatus.
In the one shown in the cut a sort of telephone action is used to
produce the sound, the electro-magnet D and armature being quite
screened from observation through the hole. (See Fig. 133) A ring, C,
shown in Fig. 133, with two terminals, the latter shown by the unshaded
portions a a, and a suspending hook E, also with two terminals, and two
suspending conductors A, B, carry the current to the magnet. A sudden
opening or closing of the circuit produces a sound.

Dub's Laws.
1. The magnetism excited at any transverse section of a magnet is
proportional to the square root of the distance between the given
section and the end.

2. The free magnetism at any given transverse section of a magnet is
proportional to the difference between the square root of half the
length of the magnet and the square root of the distance between the
given section and the nearest end.

Duct.
The tube or compartment in an electric subway for the reception of a
cable. (See Conduit, Electric Subway.)

Dyad.
A chemical term; an element which in combination replaces two monovalent
elements; one which has two bonds or is bivalent.

Dyeing, Electric.
The producing mordanting or other dyeing effects on goods in dyeing by
the passage of an electric current.

Dynamic Electricity.
Electricity of relatively low potential and large quantity; current
electricity as distinguished from static electricity; electricity in
motion.

194 STANDARD ELECTRICAL DICTIONARY.

Dynamo, Alternating Current.
A dynamo-electric machine for producing an alternating current; an
alternator. They are classified by S. P. Thompson into three classes--I.
Those with stationary field-magnet and rotating armature. II. Those with
rotating field magnet and stationary armature. III. Those with both
field magnet part and armature part stationary, the amount of magnetic
induction from the latter through the former being caused to vary or
alternate in direction by the revolution of appropriate pieces of iron,
called inductors. Another division rests on whether they give one simple
alternating current, a two phase current, or whether they give multi
phase currents. (See Current, Alternating--Currents, Multiphase.)

A great many kinds of alternators have been constructed. Only an outline
of the general theory can be given here. They are generally multipolar,
with north and south poles alternating around the field. The armature
coils, equal in number in simple current machines, to the poles, are
wound in opposite senses, so that the current shall be in one direction,
though in opposite senses, in all of them at anyone time. As the
armature rotates the coils are all approaching their poles at one time
and a current in one sense is induced in every second coil, and one in
the other sense in the other coils. They are all in continuous circuit
with two open terminals, each connected to its own insulated connecting
ring on the shaft. As the coils pass the poles and begin to recede from
them the direction changes, and the current goes in the other direction
until the next poles are reached and passed. Thus there are as many
changes of direction of current per rotation as there are coils in the
armature or poles in the field.

Fig. 134. ALTERNATING CURRENT DYNAMO WITH
SEPARATE EXCITER MOUNTED ON MAIN SHAFT.

195 STANDARD ELECTRICAL DICTIONARY.

The field-magnets whose windings may be in series are often excited by a
separate direct current generation. Some are self-exciting, one or more
of the armature coils being separated from the rest, and connected to a
special commutator, which rectifies its current.

By properly spacing the coils with respect to the poles of the field,
and connecting each set of coils by itself to separate connecting rings,
several currents can be taken from the same machine, which currents
shall have a constant difference in phase. It would seem at first sight
that the same result could be attained by using as many separate
alternators as there were currents to be produced. But it would be
almost impossible to preserve the exact relation of currents and current
phase where each was produced by its own machine. The currents would
overrun each other or would lag behind. In a single machine with
separate sets of coils the relation is fixed and invariable.

Fig. I35. DIAGRAM OF ARRANGEMENT OF ARMATURE COILS AND
COLLECTING RINGS IN AN ALTERNATING CURRENT DYNAMO.

Dynamo, Alternating Current, Regulation of.
Transformers, converters, or induction coils are used to regulate
alternating current dynamos, somewhat as compound winding is applied in
the case of direct-current dynamos. The arrangement consists in
connecting the primary of an induction coil or transformer into the
external circuit with its secondary connected to the field circuit. Thus
the transformer conveys current to the field picked up from the main
circuit, and represents to some extent the shunt of a direct-current
machine.

Dynamo, Commercial Efficiency of.
The coefficient, q. v., obtained by dividing the mechanically useful or
available work of a dynamo by the mechanical energy absorbed by it. This
only includes the energy available in the outer circuit, for doing
useful work.

196 STANDARD ELECTRICAL DICTIONARY.

Fig. 136. COMPOUND WOUND DYNAMO.

Dynamo. Compound.
A compound wound dynamo; one which has two coils on its field magnet;
one winding is in series with the external circuit and armature; the
other winding is in parallel with the armature winding, or else with the
armature winding and field winding, both in series. (See Winding, Long
Shunt--Winding, Short Shunt.)

Such a dynamo is, to a certain extent, self-regulating, the two coils
counteracting each other, and bringing about a more regular action for
varying currents than that of the ordinary shunt or series dynamo.

The extent of the regulation of such a machine depends on the
proportions given its different parts. However good the self-regulating
may be in a compound wound machine, it can only be perfect at one
particular speed.

To illustrate the principle on which the approximate regulation is
obtained the characteristic curve diagram may be consulted.

Fig. 137. CURVES OF SERIES AND SHUNT WINDINGS SUPERIMPOSED.

One curve is the curve of a series winding, the other that of a shunt
winding, and shows the variation of voltage in each with resistance in
the external or working circuit. The variation is opposite in each case.
It is evident that the two windings could be so proportioned on a
compound machine that the resultant of the two curves would be a
straight line. This regulation would then be perfect and automatic, but
only for the one speed.

197 STANDARD ELECTRICAL DICTIONARY.

Dynamo, Direct Current.
A dynamo giving a current of unvarying direction, as distinguished from
an alternator or alternating current dynamo.

Dynamo, Disc.
A dynamo with a disc armature, such as Pacinotti's disc, q. v. (See also
Disc, Armature.) The field magnets are disposed so that the disc rotates
close to their poles, and the poles face or are opposite to the side or
sides of the disc. The active leads of wire are those situated on the
face or faces of the disc.

Fig. 138. POLECHKO'S DISC DYNAMO.

Dynamo-electric Machine.
A machine driven by power, generally steam power, and converting the
mechanical energy expended on driving it into electrical energy of the
current form. The parts of the ordinary dynamo may be summarized as
follows: First, A circuit as complete as possible of iron. Such circuit
is composed partly of the cores of an electro-magnet or of several
electro-magnets, and partly of the cylindrical or ring-shaped core of an
armature which fits as closely as practicable between the magnet ends or
poles which are shaped so as to partly embrace it. Second, of coils of
insulated wire wound upon the field-magnet cores. When these coils are
excited the field-magnets develop polarity and the circuit just spoken
of becomes a magnetic circuit, interrupted only by the air gaps between
the poles and armatures. Thirdly, of coils of insulated wire upon the
armature core. These coils when rotated in the magnetic field cut
magnetic lines of force and develop electro-motive force.

198 STANDARD ELECTRICAL DICTIONARY.

Fourthly, of collecting mechanism, the commutator in direct current
dynamos, attached to the armature shaft and rotating with it. This
consists of insulated rings, or segments of rings to which the wire
coils of the armature are connected, and on which two springs of copper
or plates of carbon or some other conductor presses. The electro-motive
force developed by the cutting of lines of force, by the wires of the
armature, shows itself as potential difference between the two springs.
If the ends of a conductor are attached, one to each of these brushes,
the potential difference will establish a current through the wire. By
using properly divided and connected segments on the commutator the
potential difference and consequent direction of the current may be kept
always in the same sense or direction. It is now clear that the external
wire may be connected with the windings of the field-magnet. In such
case the excitement of the field-magnets is derived from the armature
and the machine is self-excited and entirely self-contained.

The above is a general description of a dynamo. Sometimes the coils of
the field-magnets are not connected with the armature, but derive their
current from an outside source. Such are termed separately excited
dynamos.

Some general features of dynamo generators may be seen in the
definitions under this head and elsewhere. The general conception is to
cut lines of force with a conductor and thus generate electromotive
force, or in some way to change the number of lines of force within a
loop or circuit with the same effect.

Dynamo, Electroplating.
A dynamo designed for low potential and high current intensity. They are
wound for low resistance, frequently several wires being used in
parallel, or ribbon, bar or rectangular conductors being employed. They
are of the direct current type. They should be shunt wound or they are
liable to reverse. They are sometimes provided with resistance in the
shunt, which is changed as desired to alter the electro-motive force.

Dynamo, Equalizing.
A combination for three and five-wire systems. A number of armatures or
of windings on the same shaft are connected across the leads. If the
potential drops at any pair of mains, the armature will begin to be
driven by the other mains, acting to an extent as an element of a motor,
and will raise the potential in the first pair.

Dynamo, Far Leading.
A motor dynamo, used to compensate the drop of potential in long mains.
Into the mains at a distant point a series motor is connected, driving a
dynamo placed in shunt across the mains. The dynamo thus driven raises
the potential difference between the two mains.

199 STANDARD ELECTRICAL DICTIONARY.

Dynamograph.
A printing telegraph in which the message is printed at both
transmitting and receiving ends.

Dynamo, Inductor.
A generator in which the armature or current-generating windings are all
comprised upon the poles of the field magnets. Masses of iron, which
should be laminated and are the inductors, are carried past the field
magnet poles concentrating in their passage the lines of force, thus
inducing currents in the coils. In one construction shown in the cut the
field magnets a, a .. are U shaped and are arranged in a circle, their
poles pointing inwards. A single exciting coil c, c ... is wound around
the circle in the bend of the V-shaped segments. The poles carry the
armature coils e, e ... The laminated inductors i, i ... are mounted on
a shaft S, by spiders h, to be rotated inside the circle of magnets,
thus generating an alternating current.

Synonym--Inductor Generator.

Fig. 139. INDUCTOR DYNAMO.

Dynamo, Interior Pole.
A dynamo with a ring armature, with field magnet pole pieces which
extend within the ring.

200 STANDARD ELECTRICAL DICTIONARY.

Dynamo, Iron Clad.
A dynamo in which the iron of the field magnet is of such shape as to
enclose the field magnet coils as well as the armature.

Dynamometer.
A device or apparatus for measuring force applied, or rate of
expenditure of energy by, or work done in a given time by a machine. A
common spring balance can be used as a force dynamometer, viz: to
determine how hard a man is pulling and the like. The steam engine
indicator represents an energy-dynamometer of the graphic type, the
instrument marking an area whence, with the aid of the fixed factors of
the engine, the work done may be determined. Prony's Brake, q. v., is a
type of the friction dynamometer, also of the energy type. In the latter
type during the experiment the whole power must be turned on or be
expended on the dynamometer.

Dynamo, Motor.
A motor dynamo is a machine for (a) converting a continuous current at
any voltage to a continuous current of different strength at a different
voltage or for (b) transforming a continuous current into an alternating
one, and vice versa.

For the first type see Transformer, Continuous Current; for the second
type see Transformer, Alternating Current.

Dynamo, Multipolar.
A dynamo having a number of field magnet poles, not merely a single
north and a single south pole. The field magnet is sometimes of a
generally circular shape with the poles arranged radially within it, the
armature revolving between the ends.

Dynamo, Non-polar.
A name given by Prof. George Forbes to a dynamo invented by him. In it a
cylinder of iron rotates within a perfectly self-contained iron-clad
field magnet. The current is taken off by brushes bearing near the
periphery, at two extremities of a diameter. A machine with a disc 18
inches in diameter was said to give 3,117 amperes, with 5.8 volts E. M.
F. running at 1,500 revolutions per second. The E. M. F. of such
machines varies with the square of the diameter of the disc or cylinder.

Dynamo, Open Coil.
A dynamo the windings of whose armatures may be grouped in coils, which
are not connected in series, but which have independent terminals. These
terminals are separate divisions of the commutator and so spaced that
the collecting brushes touch each pair belonging to the same coil
simultaneously. As the brushes come in contact with the sections forming
the terminals they take current from the coil in question. This coil is
next succeeded by another one, and so on according to the number of
coils employed.

Dynamo, Ring.
A dynamo the base of whose field magnets is a ring in general shape, or
perhaps an octagon, and with poles projecting inwardly therefrom.

201 STANDARD ELECTRICAL DICTIONARY.

Dynamo, Coupling of.
Dynamos can be coupled exactly like batteries and with about the same
general results. An instance of series coupling would be given by the
dynamos in the three wire system when no current is passing through the
neutral wire, and when the lamps on each side of it are lighted in equal
number.

Dynamo, Self-exciting.
A dynamo which excites its own field. The majority of dynamos are of
this construction. Others, especially alternating current machines, are
separately excited, the field magnets being supplied with current from a
separate dynamo or current generator.

Dynamo, Separate Circuit.
A dynamo in which the field magnet coils are entirely disconnected from
the main circuit, and in which current for the field is supplied by
special coils carried for the purpose by the same armature, or by a
special one, in either case a special commutator being provided to
collect the current.

Dynamo, Separately Excited.
A dynamo whose field magnets are excited by a separate current
generator, such as a dynamo or even a battery. Alternating current
dynamos are often of this construction. Direct current dynamos are not
generally so. The term is the opposite of self-exciting.

Fig. 140. SERIES DYNAMO.

Dynamo, Series.
A dynamo whose armature, field winding, and external circuit are all in
series.

In such a dynamo short circuiting or lowering the resistance of the
external circuit strengthens the field, increases the electro-motive
force and current strength and may injure the winding by heating the
wire, and melting the insulation.

202 STANDARD ELECTRICAL DICTIONARY.

Dynamo, Shunt.
A dynamo whose field is wound in shunt with the external circuit. Two
leads are taken from the brushes; one goes around the field magnets to
excite them; the other is the external circuit.

In such a dynamo the lowering of resistance on the outer circuit takes
current from the field and lowers the electro-motive force of the
machine. Short circuiting has no heating effect.

Fig. 141. SHUNT DYNAMO.

Dynamo, Single Coil.
A dynamo whose field magnet is excited by a single coil. Several such
have been constructed, with different shapes of field magnet cores, in
order to obtain a proper distribution of poles.

Dynamo, Tuning Fork.
A dynamo in which the inductive or armature coils were carried at the
ends of the prongs of a gigantic tuning fork, and were there maintained
in vibration opposite the field magnets. It was invented by T. A.
Edison, but never was used.

Dynamo, Uni-polar.
A dynamo in which the rotation of a conductor effects a continuous
increase in the number of lines cut, by the device of arranging one part
of the conductor to slide on or around the magnet. (S. P. Thomson.)
Faraday's disc is the earliest machine of this type.

203 STANDARD ELECTRICAL DICTIONARY.

Dyne.
The C. G. S. or fundamental unit of force. It is the force which can
impart an acceleration of one centimeter per second to a mass of one
gram in one second. It is equal to about 1/981 the weight of a gram,
this weight varying with the latitude.

Earth.
(a) The earth is arbitrarily taken as of zero electrostatic potential.
Surfaces in such condition that their potential is unchanged when
connected to the earth are said to be of zero potential. All other
surfaces are discharged when connected to the earth, whose potential,
for the purposes of man at least, never changes.

(b) As a magnetic field of force the intensity of the earth's field is
about one-half a line of force per square centimeter.

(c) The accidental grounding of a telegraph line is termed an earth, as
a dead, total, partial, or intermittent earth, describing the extent and
character of the trouble.

Earth, Dead.
A fault, when a telegraph or other conductor is fully connected to earth
or grounded at some intermediate point.

Synonyms--Solid Earth--Total Earth.

Earth, Partial.
A fault, when a telegraph or other conductor is imperfectly connected to
earth or grounded at some intermediate point.

Earth Plate.
A plate buried in the earth to receive the ends of telegraph lines or
other circuits to give a ground, q. v. A copper plate is often used. A
connection to a water or gas main gives an excellent ground, far better
than any plate. When the plate oxidizes it is apt to introduce
resistance.

Earth Return.
The grounding of a wire of a circuit at both ends gives the circuit an
earth return.

Earth, Swinging.
A fault, when a telegraph or other conductor makes intermittent
connection with the earth. It is generally attributable to wind action
swinging the wire, whence the name.

Ebonite.
Hard vulcanized India rubber, black in color. Specific resistance in
ohms per cubic centimeter at 46º C. (115º F.): 34E15 (Ayrton); specific
inductive capacity, (air = 1): 2.56 (Wüllner); 2.76 (Schiller); 3.15
(Boltzmann). It is used in electrical apparatus for supporting members
such as pillars, and is an excellent material for frictional generation
of potential. Its black color gives it its name, and is sometimes made a
point of distinction from Vulcanite, q. v.

204 STANDARD ELECTRICAL DICTIONARY.

Economic Coefficient.
The coefficient of electric efficiency. (See Efficiency, Electric.)

Edison Effect.
A continuous discharge resulting in a true current which takes place
between a terminal of an incandescent lamp filament and a plate placed
near it. The lamp must be run at a definitely high voltage to obtain it.

Ediswan.
An abbreviation for Edison-Swan; the trade name of the incandescent lamp
used in Great Britain, and of other incandescent system apparatus.

Fig. 142. GYMNOTUS ELECTRICUS.

Eel, Electric (Gymnotus Electricus).
An eel capable of effecting the discharge of very high potential
electricity, giving painful or dangerous shocks. Its habitat is the
fresh water, in South America. Faraday investigated it and estimated its
shock as equal to that from fifteen Leyden jars, each of 1.66 square
feet of coating. (See Animal Electricity and Ray, Electric.)

Effect, Counter-inductive.
A counter-electro-motive force due to induction, and opposing a current.

Efficiency.
The relation of work done to energy absorbed. A theoretically perfect
machine would have the maximum efficiency in which the two qualities
named would be equal to each other. Expressed by a coefficient, q. v.,
the efficiency in such case would be equal to 1. If a machine produced
but half the work represented by the energy it absorbed, the rest
disappearing in wasteful expenditure, in heating the bearings, in
overcoming the resistance of the air and in other ways, its efficiency
would be expressed by the coefficient 1/2 or .5, or if one hundred was
the basis, by fifty per centum. There are a number of kinds of
efficiencies of an electric generator which are given below.

Efficiency, Commercial.
Practical efficiency of a machine, obtained by dividing the available
output of work or energy of a machine by the energy absorbed by the same
machine. Thus in a dynamo part of the energy is usefully expended in
exciting the field magnet, but this energy is not available for use in
the outer circuit, is not a part of the output, and is not part of the
dividend.

If M represents the energy absorbed, and W the useful or available
energy, the coefficient of commercial efficiency is equal to W/M. M is
made up of available, unavailable and wasted (by Foucault currents,
etc.,) energy. Calling available energy W, unavailable but utilized
energy w, and wasted energy m, the expression for the coefficient of
commercial efficiency becomes

W / ( W + w + m )
when M = W + w + m

Synonym--Net efficiency.

205 STANDARD ELECTRICAL DICTIONARY.

Efficiency, Electrical.
In a dynamo or generator the relation of total electric energy produced,
both wasted and useful or available to the useful or available
electrical energy. If we call W the useful electric and w the wasted
electric energy, the coefficient of electrical efficiency is equal to

W / ( W + w )

Synonyms--Intrinsic Efficiency--Economic Coefficient--Coefficient of
Electrical Efficiency.

Efficiency of Conversion.
In a dynamo or generator the relation of energy absorbed to total
electric energy produced. Part of the electric energy is expended in
producing the field and in other ways. Thus a generator with high
efficiency of conversion may be a very poor one, owing to the
unavailable electric energy which it produces. The coefficient of
Efficiency of Conversion is obtained by dividing the total electric
energy produced by the energy absorbed in working the dynamo. If M
represents the energy absorbed, or work done in driving the dynamo or
generator, W the useful electric, and w the wasted electrical energy,
then the coefficient of efficiency of conversion is equal to

(W + w ) / M

In the quantity M are included besides available (W) and unavailable (w)
electric energy, the totally wasted energy due to Foucault currents,
etc., calling the latter m, the above formula may be given

( W+ w ) / (W + w + m )

This coefficient may refer to the action of a converter, q. v., in the
alternating system. Synonym--Gross Efficiency.

Efficiency of Secondary Battery, Quantity.
The coefficient obtained by dividing the ampere-hours obtainable from a
secondary battery by the ampere hours required to charge it.

Efficiency of Secondary Battery, Real.
The coefficient obtained by dividing the energy obtainable from a
secondary battery by the energy absorbed in charging it. The energy is
conveniently taken in watt-hours and includes the consideration of the
spurious voltage. (See Battery, Secondary.)

206 STANDARD ELECTRICAL DICTIONARY.

Efflorescence.
The appearance of a dry salt upon the walls of a vessel containing a
solution above the normal water-line from evaporation of a liquid. It
appears in battery jars and in battery carbons, in the latter
interfering with the electrical connections, and oxidizing or rusting
them. (See Creeping.)

Effluvium, Electric.
When a gas is made to occupy the position of dielectric between two
oppositely electrified surfaces a peculiar strain or condition of the
dielectric is produced, which promotes chemical change. The condition is
termed electrical effluvium or the silent discharge. By an apparatus
specially constructed to utilize the condition large amounts of ozone
are produced.

Synonym--Silent Discharge.

Elastic Curve.
A crude expression for a curve without projections or sudden
sinuosities; such a curve as can be obtained by bending an elastic strip
of wood.

Electrepeter.
An obsolete name for a key, switch or pole changer of any kind.

Elasticity, Electric.
The phenomenon of the dielectric is described under this term. When a
potential difference is established between two parts of the dielectric,
a flow of electricity displacement current starts through the
dielectric, which current is due to the electric stress, but is
instantly arrested by what has been termed the electric elasticity of
the dielectric. This is expressed by
( electric stress ) / ( electric strain )
and in any substance is inversely proportional to the specific inductive
capacity.

Electricity.
It is impossible in the existing state of human knowledge to give a
satisfactory definition of electricity. The views of various authorities
are given here to afford a basis for arriving at the general consensus
of electricians.

We have as yet no conception of electricity apart from the electrified
body; we have no experience of its independent existence. (J. E. H.
Gordon.)

What is Electricity? We do not know, and for practical purposes it is
not necessary that we should know. (Sydney F. Walker.)

Electricity … is one of those hidden and mysterious powers of nature
which has thus become known to us through the medium of effects.
(Weale's Dictionary of Terms.)

This word Electricity is used to express more particularly the cause,
which even today remains unknown, of the phenomena that we are about to
explain. (Amédée Guillemin.)

207 STANDARD ELECTRICAL DICTIONARY.

Electricity is a powerful physical agent which manifests itself mainly
by attractions and repulsions, but also by luminous and heating effects,
by violent commotions, by chemical decompositions, and many other
phenomena. Unlike gravity, it is not inherent in bodies, but it is
evoked in them by a variety of causes … (Ganot's Physics.)

Electricity and magnetism are not forms of energy; neither are they
forms of matter. They may, perhaps, be provisionally defined as
properties or conditions of matter; but whether this matter be the
ordinary matter, or whether it be, on the other hand, that
all-pervading ether by which ordinary matter is surrounded, is a question
which has been under discussion, and which now may be fairly held to be
settled in favor of the latter view. (Daniell's Physics.)

The name used in connection with an extensive and important class of
phenomena, and usually denoting the unknown cause of the phenomena or
the science that treats of them. (Imperial Dictionary.)

Electricity. . . is the imponderable physical agent, cause, force or the
molecular movement, by which, under certain conditions, certain
phenomena, chiefly those of attraction and repulsion, . . . are
produced. (John Angell.)

It has been suggested that if anything can rightly be called
"electricity," this must be the ether itself; and that all electrical
and magnetic phenomena are simply due to changes, strains and motions in
the ether. Perhaps negative electrification. . .means an excess of
ether, and positive electrification a defect of ether, as compared with
the normal density. (W. Larden.)

Electricity is the name given to the supposed agent producing the
described condition (i. e. electrification) of bodies. (Fleeming
Jenkin.)

There are certain bodies which, when warm and dry, acquire by friction,
the property of attracting feathers, filaments of silk or indeed any
light body towards them. This property is called Electricity, and bodies
which possess it are said to be electrified. (Linnaeus Cumming.)

What electricity is it is impossible to say, but for the present it is
convenient to look upon it as a kind of invisible something which
pervades all bodies. (W. Perren Maycock.)

What is electricity? No one knows. It seems to be one manifestation of
the energy which fills the universe and which appears in a variety of
other forms, such as heat, light, magnetism, chemical affinity,
mechanical motion, etc. (Park Benjamin.)

208 STANDARD ELECTRICAL DICTIONARY.

The theory of electricity adopted throughout these lessons is, that
electricity, whatever its true nature, is one, not two; that this
Electricity, whatever it may prove to be, is not matter, and is not
energy; that it resembles both matter and energy in one respect,
however, in that it can neither be created nor destroyed. (Sylvanus P.
Thomson.)

In Physics a name denoting the cause of an important class of phenomena
of attraction and repulsion, chemical decomposition, etc., or,
collectively, these phenomena themselves. (Century Dictionary.)

A power in nature, often styled the electric fluid, exhibiting itself,
when in disturbed equilibrium or in activity, by a circuit movement, the
fact of direction in which involves polarity, or opposition of
properties in opposite directions; also, by attraction for many
substances, by a law involving attraction between substances of unlike
polarity, and repulsion between those of like; by exhibiting accumulated
polar tension when the circuit is broken; and by producing heat, light,
concussion, and often chemical changes when the circuit passes between
the poles, or through any imperfectly conducting substance or space. It
is evolved in any disturbance of molecular equilibrium, whether from a
chemical, physical, or mechanical cause. (Webster's Dictionary.)

In point of fact electricity is not a fluid at all, and only in a few of
its attributes is it at all comparable to a fluid. Let us rather
consider electricity to be a condition into which material substances
are thrown. . .(Slingo & Brooker.)

Electricity, Cal.
The electricity produced in the secondary of a transformer by changes of
temperature in the core. This is in addition to the regularly induced
current.

Synonym--Acheson Effect.

Electrics.
Substances developing electrification by rubbing or friction; as
Gilbert, the originator of the term, applied it, it would indicate
dielectrics. He did not know that, if insulated, any substance was one
of his "electrics." A piece of copper held by a glass handle becomes
electrified by friction.

Electrification.
The receiving or imparting an electric charge to a surface; a term
usually applied to electrostatic phenomena.

Electrization.
A term in electro-therapeutics; the subjection of the human system to
electric treatment for curative, tonic or diagnostic purposes.

Electro-biology.
The science of electricity in its relation to the living organism,
whether as electricity is developed by the organism, or as it affects
the same when applied from an external source.

209 STANDARD ELECTRICAL DICTIONARY.

Electro-capillarity.
The relations between surface tension, the potential difference and the
electrostatic capacity of fluids in contact. Although nominally in
contact such surfaces are separated by about one-twenty-millionth of a
centimeter (1/50000000 inch) ; thus a globule of mercury and water in
which it is immersed constitute an electrostatic accumulator of definite
electrostatic capacity. Again the mercury and water being in electric
connection differ in potential by contact (see Contact Theory). A
definite surface tension is also established. Any change in one of these
factors changes the other also. A current passed through the contact
surfaces will change the surface tension and hence the shape of the
mercury globule. Shaking the globule will change its shape and capacity
and produce a current. Heating will do the same. (See Electrometer,
Capillary; and Telephone, Capillary.) Mercury and water are named as
liquids in which the phenomena are most conveniently observed. They are
observable in other parallel cases.

Electro-chemical Equivalent.
The quantity of an element or compound liberated from or brought into
combination, electrolytically, by one coulomb of electricity. The
electro-chemical equivalent of hydrogen is found by experiment to be
.0000105 gram. That of any other substance is found by multiplying this
weight by its chemical equivalent referred to hydrogen, which is its
atomic or molecular weight divided by its valency. Thus the atomic
weight of oxygen is 16, its valency is 2, its equivalent is 16/2 = 8;
its electro-chemical equivalent is equal to .0000105 X 8 = .000840 gram.

Electro-chemical Series.
An arrangement of the elements in the order of their relative electrical
affinities so that each element is electro-negative to all the elements
following it, and electro-positive to the elements preceding it. The
usual series begins with oxygen as the most electro-negative and ends
with potassium as the most electro-positive element. There is, of
course, no reason why other series of compound radicals, such as
sulphion (SO4), etc., should not also be constructed. For each liquid
acting on substances a separate series of the substances acted on may be
constructed. Thus for dilute sulphuric acid the series beginning with
the negatively charged or most attacked one is zinc, amalgamated or
pure, cadmium, iron, tin, lead, aluminum, nickel, antimony, bismuth,
copper, silver, platinum. In other liquids the series is altogether
different.

Electro--chemistry.
The branch of electricity or of chemistry treating of the relations
between electric and chemical force in different compounds and
reactions. (See Electrolysis--Electrochemical series--Electro-chemical
Equivalent .)

210 STANDARD ELECTRICAL DICTIONARY.

Electro-culture.
The application of electricity to the cultivation of plants. In one
system wires are stretched or carried across the bed under the surface,
and some are connected to one pole and others to the other pole of a
galvanic battery of two or more elements. In some experiments improved
results have thus been obtained.

Another branch refers to the action of the electric arc light on
vegetation. This has an effect on vegetation varying in results.

Electrode.
(a) The terminal of an open electric circuit.

(b) The terminals of the metallic or solid conductors of an electric
circuit, immersed in an electrolytic solution.

(c) The terminals between which a voltaic arc is formed, always in
practice made of carbon, are termed electrodes.

(d) In electro-therapeutics many different electrodes are used whose
names are generally descriptive of their shape, character, or uses to
which they are to be applied. Such are aural electrodes for the ears,
and many others.

(e) The plates of a voltaic battery.

Electrode, Indifferent.
A term in electro-therapeutics. An electrode to which no therapeutic
action is attributed but which merely provides a second contact with the
body to complete the circuit through the same. The other electrode is
termed the therapeutic electrode.

Electrodes, Erb's Standards of.
Proposed standard sizes for medical electrodes as follows:
Name. Diameter.
Fine Electrode, 1/2 centimeter .2 inch
Small " 2 " .8 "
Medium " 7.5 " 3.0 "
Large " 6X2 " 2.4 X .8 "
Very large " 16x8 " 6.4 x 3.2 "

Electrodes, Non-polarizable.
In electro-therapeutics electrodes whose contact surface is virtually
porous clay saturated with zinc chloride solution. The series terminate
in amalgamated zinc ends, enclosed each in a glass tube, and closed with
clay. Contact of metal with the tissues is thus avoided.

Electrode, Therapeutic.
A term in electro-therapeutics. An electrode applied to the body for the
purpose of inducing therapeutic action, or for giving the basis for an
electric diagnosis of the case. The other electrode is applied to
complete the circuit only; it is termed the indifferent electrode.

Electro-diagnosis.
The study of the condition of a patient by the reactions which occur at
the terminals or kathode and anode of an electric circuit applied to the
person. The reactions are divided into kathodic and anodic reactions.

211 STANDARD ELECTRICAL DICTIONARY.

Electro-dynamic. adj.
The opposite of electrostatic; a qualification of phenomena due to
current electricity.

Synonym--Electro-kinetic.

Electro-dynamic Attraction and Repulsion.
The mutual attraction and repulsion exercised by currents of electricity
upon each other. The theory of the cause is based upon stress of the
luminiferous ether and upon the reaction of lines of force upon each
other. For a resumé of the theory see Induction, Electro-magnetic.

Electro-dynamics.
The laws of electricity in a state of motion; the inter-reaction of
electric currents. It is distinguished from electro-magnetic induction
as the latter refers to the production of currents by induction. The
general laws of electro-dynamics are stated under Induction,
Electro-magnetic, q. v.

Synonym--Electro-kinetics.

Fig. 143. DIAGRAM OF CONNECTIONS OF
SIEMENS' ELECTRO-DYNAMOMETER.

212 STANDARD ELECTRICAL DICTIONARY.

Electro-dynamometer, Siemens'.
An apparatus for measuring currents by the reaction between two coils,
one fixed and one movable, through which the current to be measured
passes. It is one of the oldest commercial ammeters or current
measurers. It comprises a fixed coil of a number of convolutions and a
movable coil often of only one convolution surrounding the other. The
movable coil is suspended by a filament or thread from a spiral spring.
The spring is the controlling factor. Connection is established through
mercury cups so as to bring the two coils in series. In use the spring
and filament are adjusted by turning a milled head to which they are
connected until the coils are at right angles. Then the current is
turned on and deflects the movable coil. The milled head is turned until
the deflection is overcome. The angle through which the head is turned
is proportional to the square of the current. The movable coil must in
its position at right angles to the fixed one lie at right angles to the
magnetic meridian.

Thus in the diagram, Fig. 143 A B C D is the fixed coil; E F G H is the
movable coil; S is the spiral spring attached at K to the movable coil.
The arrows show the course of the current as it goes through the coils.

Electrolier.
A fixture for supporting electric lamps; the analogue in electric
lighting of the gasolier or gas chandelier. Often both are combined, the
same fixture being piped and carrying gas burners, as well as being
wired and carrying electric lamps.

Electrolysis.
The separation of a chemical compound into its constituent parts or
elements by the action of the electric current. The compound may be
decomposed into its elements, as water into hydrogen and oxygen, or into
constituent radicals, as sodium sulphate into sodium and sulphion, which
by secondary reactions at once give sodium hydrate and sulphuric acid.
The decomposition proceeds subject to the laws of electrolysis. (See
Electrolysis, Laws of.) For decomposition to be produced there is for
each compound a minimum electro-motive force or potential difference
required. The current passes through the electrolyte or substance
undergoing decomposition entirely by Electrolytic Conduction, q. v. in
accordance with Grothüss' Hypothesis, q. v. The electrolyte therefore
must be susceptible of diffusion and must be a fluid.

The general theory holds that under the influence of a potential
difference between electrodes immersed in an electrolyte, the molecules
touching the electrodes are polarized, in the opposite sense for each
electrode. If the potential difference is sufficient the molecules will
give up one of their binary constituents to the electrode, and the other
constituent will decompose the adjoining molecule, and that one being
separated into the same two constituents will decompose its neighbor,
and so on through the mass until the other electrode is reached. This
one separates definitely the second binary constituent from the
molecules touching it.

213 STANDARD ELECTRICAL DICTIONARY.

Thus there is an exact balance preserved. Just as many molecules are
decomposed at one electrode as at the other, and the exact chain of
decomposition runs through the mass. Each compound electrolyzed develops
a binary or two-fold composition, and gives up one constituent to one
electrode and the other to the other.

Fig. 144. ACTION OF MOLECULES IN A SOLUTION
BEFORE AND DURING ELECTROLYSIS.

The cut shows the assumed polarization of an electrolyte. The upper row
shows the molecules in irregular order before any potential difference
has been produced, in other words, before the circuit is closed. The
next row shows the first effects of closing the circuit, and also
indicates the polarization of the mass, when the potential difference is
insufficient for decomposition. The third row indicates the
decomposition of a chain of molecules, one constituent separating at
each pole.

214 STANDARD ELECTRICAL DICTIONARY.

Electrolysis, Laws of.
The following are the principal laws, originally discovered by
Faraday, and sometimes called Faraday's Laws of Electrolysis:

1. Electrolysis cannot take place unless the electrolyte is a conductor.
Conductor here means an electrolytic conductor, one that conducts by its
own molecules traveling, and being decomposed. (See Grothüss'
Hypothesis.)

II. The energy of the electrolytic action of the current is the same
wherever exercised in different parts of the circuit.

III. The same quantity of electricity--that is the same current for the
same period----- decomposes chemically equivalent quantities of the
bodies it decomposes, or the weights of elements separated in
electrolytes by the same quantity of electricity (in coulombs or some
equivalent unit) are to each other as their chemical equivalent.

IV. The quantity of a body decomposed in a given time is proportional to
the strength of the current.

To these may be added the following:

V. A definite and fixed electro-motive force is required for the
decomposition of each compound, greater for some and less for others.
Without sufficient electro-motive force expended on the molecule no
decomposition will take place. (See Current, Convective.)

Electrolyte.
A body susceptible of decomposition by the electric current, and capable
of electrolytic conduction. It must be a fluid body and therefore
capable of diffusion, and composite in composition. An elemental body
cannot be an electrolyte.

Electrolytic Analysis.
Chemical analysis by electrolysis. The quantitative separation of a
number of metals can be very effectively executed. Thus, suppose that a
solution of copper sulphate was to be analyzed. A measured portion of
the solution would be introduced into a weighed platinum vessel. The
vessel would be connected to the zinc plate terminal of a battery. From
the other terminal of the battery a wire would be brought and would
terminate in a plate of platinum. This would be immersed in the solution
in the vessel. As the current would pass the copper sulphate would be
decomposed and eventually all the copper would be deposited in a firm
coating on the platinum. The next operations would be to wash the metal
with distilled water, and eventually with alcohol, to dry and to weigh
the dish with the adherent copper. On subtracting the weight of the dish
alone from the weight of the dish and copper, the weight of the metallic
copper in the solution would be obtained.

In similar ways many other determinations are effected. The processes of
analysis include solution of the ores or other substances to be analyzed
and their conversion into proper form for electrolysis. Copper as just
described can be precipitated from the solution of its sulphate. For
iron and many other metals solutions of their double alkaline oxalates
are especially available forms for analysis.

The entire subject has been worked out in considerable detail by
Classen, to whose works reference should be made for details of
processes.

Electrolytic Convection.
It is sometimes observed that a single cell of Daniell battery, for
instance, or other source of electric current establishing too low a
potential difference for the decomposition of water seems to produce a
feeble but continuous decomposition. This is very unsatisfactorily
accounted for by the hydrogen as liberated combining with dissolved
oxygen. (Ganot.) The whole matter is obscure. (See Current, Convection.)

215 STANDARD ELECTRICAL DICTIONARY.

Electrolytic Conduction.
Conduction by the travel of atoms or radicals from molecule to molecule
of a substance with eventual setting free at the electrodes of the atoms
or radicals as elementary molecules or constituent radicals. A substance
to be capable of acting as an electrolytic conductor must be capable of
diffusion, and must also have electrolytic conductivity. Such a body is
called an electrolyte. (See Grothüss' Hypothesis--Electrolysis--
Electrolysis, Laws of--Electro-chemical Equivalent.)

Electro-magnet.
A mass, in practice always of iron, around which an electric circuit is
carried, insulated from the iron. When a current is passed through the
circuit the iron presents the characteristics of a magnet. (See
Magnetism, Ampére's Theory of--Solenoid--Lines of Force.) In general
terms the action of a circular current is to establish lines of force
that run through the axis of the circuit approximately parallel thereto,
and curving out of and over the circuit, return into themselves outside
of the circuit. If a mass of iron is inserted in the axis or elsewhere
near such current, it multiplies within itself the lines of force, q. v.
(See also Magnetic Permeability--Permeance--Magnetic Induction,
Coefficient of Magnetic Susceptibility--Magnetization, Coefficient of
Induced.) These lines of force make it a magnet. On their direction,
which again depends on the direction of the magnetizing current, depends
the polarity of the iron. The strength of an electro-magnet, below
saturation of the core (see Magnetic Saturation), is proportional nearly
to the ampere-turns, q. v. More turns for the same current or more
current for the same turns increase its strength.

In the cut is shown the general relation of current, coils, core and
line of force. Assume that the magnet is looked at endwise, the observer
facing one of the poles; then if the current goes around the core in the
direction opposite to that of the hands of a clock, such pole will be
the north pole. If the current is in the direction of the hands of a
clock the pole facing the observer will be the south pole. The whole
relation is exactly that of the theoretical Ampérian currents, already
explained. The direction and course of the lines of force created are
shown in the cut.

The shapes of electro-magnets vary greatly. The cuts show several forms
of electro- magnets. A more usual form is the horseshoe or double limb
magnet, consisting generally of two straight cores, wound with wire and
connected and held parallel to each other by a bar across one end, which
bar is called the yoke.

In winding such a magnet the wire coils must conform, as regards
direction of the current in them to the rule for polarity already cited.
If both poles are north or both are south poles, then the magnet cannot
be termed a horseshoe magnet, but is merely an anomalous magnet. In the
field magnets of dynamos the most varied types of electro-magnets have
been used. Consequent poles are often produced in them by the direction
of the windings and connections.

To obtain the most powerful magnet the iron core should be as short and
thick as possible in order to diminish the reluctance of the magnetic
circuit. To obtain a greater range of action a long thin shape is
better, although it involves waste of energy in its excitation.

216 STANDARD ELECTRICAL DICTIONARY.

Fig. 145 DIAGRAM OF AN ELECTRO-MAGNET SHOWING RELATION OF
CURRENT AND WINDING TO ITS POLARITY AND LINES OF FORCE.

Fig. 146. ANNULAR ELECTRO-MAGNET

Electro-magnet, Annular.
An electro-magnet consisting of a cylinder with a circular groove cut in
its face, in which groove a coil of insulated wire is placed. On the
passage of a current the iron becomes polarized and attracts an armature
towards or against its grooved face. The cut shows the construction of
an experimental one. It is in practice applied to brakes and clutches.
In the cut of the electro-magnetic brake (see Brake, Electro-magnetic),
C is the annular magnet receiving its current through the brushes, and
pressed when braking action is required against the face of the moving
wheel. The same arrangement, it can be seen, may apply to a clutch.

217 STANDARD ELECTRICAL DICTIONARY.

Fig. 147. BAR ELECTRO-MAGNET.

Electro-magnet, Bar.
A straight bar of iron surrounded with a magnetizing coil of wire. Bar
electromagnets are not much used, the horseshoe type being by far the
more usual.

Electro-magnet, Club-foot.
An electro-magnet, one of whose legs only is wound with wire, the other
being bare.

Fig. 148. CLUB-FOOT ELECTRO-MAGNETS WITH HINGED ARMATURES.

Electro-magnet, Hinged.
An electro-magnet whose limbs are hinged at the yoke. On excitation by a
current the poles tend to approach each other.

Fig. 149. ELECTRO-MAGNET, HINGED

Electro-magnetic Attraction and Repulsion.
The attraction and repulsion due to electromagnetic lines of force,
which lines always tend to take as short a course as possible and also
seek the medium of the highest permeance. This causes them to
concentrate in iron and steel or other paramagnetic substance and to
draw them towards a magnet by shortening the lines of force connecting
the two. It is exactly the same attraction as that of the permanent
magnet for its armature, Ampére's theory bringing the latter under the
same title. In the case of two magnets like poles repel and unlike
attract. In the case of simple currents, those in the same direction
attract and those in opposite directions repel each other. This refers
to constant current reactions. Thus the attraction of unlike poles of
two magnets is, by the Ampérian theory, the attraction of two sets of
currents of similar direction, as is evident from the diagram. The
repulsion of like poles is the repulsion of unlike currents and the same
applies to solenoids, q. v. (See Magnetism and do. Ampére's Theory
of--Induction, Electro-dynamic--Electro-magnetic Induction.)

218 STANDARD ELECTRICAL DICTIONARY.

Electro-magnetic Control.
Control of a magnet, iron armature, or magnetic needle in a
galvanometer, ammeter, voltmeter or similar instrument by an
electro-magnetic field, the restitutive force being derived from an
electro-magnet. The restitutive force is the force tending to bring the
index to zero.

Electro-magnetic Field of Force.
A field of electro-magnetic lines of force, q. v., established through
the agency of an electric current. A wire carrying a current is
surrounded by circular concentric lines of force which have the axis of
the wire as the locus of their centres. Electro-magnets produce lines of
force identical with those produced by permanent magnets. (See Field of
Force--Magnetic Field of Force--Controlling Field--Deflecting Field.)

Electro-magnetic Induction.
When two currents of unlike direction are brought towards each other,
against their natural repulsive tendency work is done, and the
consequent energy takes the form of a temporary increase in both
currents. When withdrawn, in compliance with the natural tendency of
repulsion, the currents are diminished in intensity, because energy is
not expended on the withdrawal, but the withdrawal is at the expense of
the energy of the system. The variations thus temporarily produced in
the currents are examples of electro-magnetic induction. The currents
have only the duration in each case of the motion of the circuits. One
circuit is considered as carrying the inducer current and is termed the
primary circuit and its current the primary current, the others are
termed the secondary circuit and current respectively. We may assume a
secondary circuit in which there is no current. It is probable that
there is always an infinitely small current at least, in every closed
circuit. Then an approach of the circuits will induce in the secondary
an instantaneous current in the reverse direction. On separating the two
circuits a temporary current in the same direction is produced in the
secondary.

219 STANDARD ELECTRICAL DICTIONARY.

A current is surrounded by lines of force. The approach of two circuits,
one active, involves a change in the lines of force about the secondary
circuit. Lines of force and current are so intimately connected that a
change in one compels a change in the other. Therefore the induced
current in the secondary may be attributed to the change in the field of
force in which it lies, a field maintained by the primary circuit and
current. Any change in a field of force induces a current or change of
current in any closed circuit in such field, lasting as long as the
change is taking place. The new current will be of such direction as to
oppose the change. (See Lenz's Law.)

The action as referred to lines of force may be figured as the cutting
of such lines by the secondary circuit, and such cutting may be brought
about by moving the secondary in the field. (See Lines of Force--Field
of Force.) The cutting of 1E8 lines of force per second by a closed
circuit induces an electro-motive force of one volt. (See Induction,
Mutual, Coefficient of.)

Electro-magnet, Iron Clad.
A magnet whose coil and core are encased in a iron jacket, generally
connected to one end of the core. This gives at one end two poles, one
tubular, the other solid, and concentric with each other. It is
sometimes called a tubular magnet.

Electro-magnet, One Coil.
An electro-magnet excited by one coil. In some dynamos the field magnets
are of this construction, a single coil, situated about midway between
the poles, producing the excitation.

Electro-magnetic Leakage.
The leakage of lines of force in an electro-magnet; the same as magnetic
leakage. (See Magnetic Leakage.)

Electro-magnetic Lines of Force.
The lines of force produced in an electro-magnetic field. They are
identical with Magnetic Lines of Force, q. v. (See also Field of
Force-Line of Force.)

Electro-magnetic Stress.
The stress in an electro-magnetic field of force, showing itself in the
polarization of light passing through a transparent medium in such a
field. (See Magnetic Rotary Polarization.)

Electro-magnetic Theory of Light.
This theory is due to J. Clark Maxwell, and the recent Hertz experiments
have gone far to prove it. It holds that the phenomena of light are due
to ether waves, identical in general factors with those produced by
electro-magnetic induction of alternating currents acting on the ether.
In a non-conductor any disturbance sets an ether wave in motion owing to
its restitutive force; electricity does not travel through such a
medium, but can create ether waves in it. Therefore a non-conductor of
electricity is permeable to waves of ether or should transmit light, or
should be transparent. A conductor on the other hand transmits
electrical disturbances because it has no restitutive force and cannot
support an ether wave. Hence a conductor should not transmit light, or
should be opaque. With few exceptions dielectrics or non-conductors are
transparent, and conductors are opaque.

220 STANDARD ELECTRICAL DICTIONARY.

Again, the relation between the electrostatic and electro-magnet units
of quantity is expressed by 1 : 30,000,000,000; the latter figure in
centimeters gives approximately the velocity of light. The
electro-magnetic unit depending on electricity in motion should have
this precise relation if an electro-magnetic disturbance was propagated
with the velocity of light. If an electrically charged body were whirled
around a magnetic needle with the velocity of light, it should act in
the same way as a current circulating around it. This effect to some
extent has been shown experimentally by Rowland.

A consequence of these conclusions is (Maxwell) that the specific
inductive capacity of a non-conductor or dielectric should be equal to
the square of its index of refraction for waves of infinite length. This
is true for some substances--sulphur, turpentine, petroleum and benzole.
In others the specific inductive capacity is too high, e. g., vegetable
and animal oils, glass, Iceland spar, fluor spar, and quartz.

Electro-magnetic Unit of Energy.
A rate of transference of energy equal to ten meg-ergs per second.

Electro-magnetism.
The branch of electrical science treating of the magnetic relations of a
field of force produced by a current, of the reactions of
electro-magnetic lines of force, of the electromagnetic field of force,
of the susceptibility, permeability, and reluctance of diamagnetic and
paramagnetic substances, and of electro-magnets in general.

Electro-magnet, Long Range.
An electro-magnet so constructed with extended pole pieces or otherwise,
as to attract its armature with reasonably constant force over a
considerable distance. The coil and plunger, q. v., mechanisms
illustrate one method of getting an extended range of action. When a
true electro-magnet is used, one with an iron core, only a very limited
range is attainable at the best. (See Electro-magnet, Stopped Coil--do.
Plunger.)

Electro-magnet, Plunger.
An electro-magnet with hollow coils, into which the armature enters as a
plunger. To make it a true electro-magnet it must have either a yoke,
incomplete core, or some polarized mass of iron.

Electro-magnet, Polarized.
An electro-magnet consisting of a polarized or permanently magnetized
core wound with magnetizing coils, or with such coils on soft iron cores
mounted on its ends. The coils may be wound and connected so as to
cooperate with or work against the permanent magnet on which it is
mounted. In Hughes' magnet shown in the cut it is mounted in opposition,
so that an exceedingly feeble current will act to displace the armature,
a, which is pulled away from the magnet by a spring, s.

221 STANDARD ELECTRICAL DICTIONARY.

Fig. 150 HUGHES' POLARIZED ELECTRO-MAGNET

Electro-magnets, Interlocking.
Electro-magnets so arranged that their armatures interlock. Thus two
magnets, A A and B B, may be placed with their armatures, M and N, at
right angles and both normally pulled away from the poles. When the
armature M is attracted a catch on its end is retained by a hole in the
end of the other armature N, and when the latter armature N is attracted
by its magnet the armature M is released. In the mechanism shown in the
cut the movements of the wheel R are controlled. Normally it is held
motionless by the catch upon the bottom of the armature M, coming
against the tooth projecting from its periphery. A momentary current
through the coils of the magnet A A releases it, by attracting M, which
is caught and retained by N, and leaves it free to rotate. A momentary
current through the coils of the magnet B B again releases M, which
drops down and engages the tooth upon R and arrests its motion.

Fig. 151. INTERLOCKING ELECTRO-MAGNETS.

222 STANDARD ELECTRICAL DICTIONARY.

Electro-magnet, Stopped Coil.
An electro-magnet consisting of a tubular coil, in which a short fixed
core is contained, stopping up the aperture to a certain distance, while
the armature is a plunger entering the aperture. This gives a longer
range of action than usual.

Electro-magnet, Surgical.
An electro-magnet, generally of straight or bar form, fitted with
different shaped pole pieces, used for the extraction of fragments of
iron or steel from the eyes. Some very curious cases of successful
operations on the eyes of workmen, into whose eyes fragments of steel or
iron had penetrated, are on record.

Electro-medical Baths.
A bath for the person provided with connections and electrodes for
causing a current of electricity of any desired type to pass through the
body of the bather. Like all electro-therapeutical treatment, it should
be administered under the direction of a physician only.

Electro-metallurgy.
(a) In the reduction of ores the electric current has been proposed but
never extensively used, except in the reduction of aluminum and its
alloys. (See Reduction of Ores, Electric.)

(b) Electro-plating and deposition of metal from solutions is another
branch. (See Electroplating and Electrotyping.)

(c) The concentration of iron ores by magnetic attraction may come under
this head. (See Magnetic Concentration of Ores.)

Electrometer.
An instrument for use in the measurement of potential difference, by the
attraction or repulsion of statically charged bodies. They are
distinguished from galvanometers as the latter are really current
measurers, even if wound for use as voltmeters, depending for their
action upon the action of the current circulating in their coils.

Electrometer, Absolute.
An electrometer designed to give directly the value of a charge in
absolute units. In one form a plate, a b, of conducting surface is
supported or poised horizontally below a second larger plate C, also of
conducting surface. The poised plate is surrounded by a detached guard
ring--an annular or perforated plate, r g r' g'--exactly level and even
with it as regards the upper surface. The inner plate is carried by a
delicate balance. In use it is connected to one of the conductors and
the lower plate to earth or to the other. The attraction between them is
determined by weighing. By calculation the results can be made absolute,
as they depend on actual size of the plates and their distance, outside
of the potential difference of which of course nothing can be said. If S
is the area of the disc, d the distance of the plates, V-V1 the
difference of their potential, which is to be measured, and F the force
required to balance their attraction, we have:

F = ( ( V - V1 )^2 * S ) / ( 8 * PI * d^2 )

223 STANDARD ELECTRICAL DICTIONARY.

If V = 0 this reduces to

F = ( V^2 * S ) / ( 8 * PI * d^2 ) (2)
or
V = d * SquareRoot( (8 * PI * F ) / S ) (3)

As F is expressed as a weight, and S and a as measures of area and
length, this gives a means of directly obtaining potential values in
absolute measure. (See Idiostatic Method--Heterostatic Method.)

Synonyms--Attracted Disc Electrometer--Weight Electrometer.

Fig. 152. SECTION OF BASE OF PORTABLE ELECTROMETER.

In some forms the movable disc is above the other, and supported at the
end of a balance beam. In others a spring support, arranged so as to
enable the attraction to be determined in weight units, is adopted. The
cuts, Figs. 152 and 154, show one of the latter type, the portable
electrometer. The disc portion is contained within a cylindrical vessel.

Fig. 153. DIAGRAM ILLUSTRATING
THEORY OF ABSOLUTE ELECTROMETER.

Referring to Fig. 152 g is the stationary disc, charged through the
wire connection r; f is the movable disc, carried by a balance beam
poised at i on a horizontal and transverse stretched platinum wire,
acting as a torsional spring. The position of the end k of the balance
beam shows when the disc f is in the plane of the guard ring h h. The
end k is forked horizontally and a horizontal sighting wire or hair is
fastened across the opening of the fork. When the hair is midway between
two dots on a vertical scale the lever is in the sighted position, as it
is called, and the disc is in the plane of the guard ring.

224 STANDARD ELECTRICAL DICTIONARY.

Fig. 154. PORTABLE ELECTROMETER.

The general construction is seen in Fig. 154. There the fixed disc D is
carried by insulating stem g1. The charging electrode is supported by an
insulating stem g2, and without contact with the box passes out of its
cover through a guard tube E, with cover, sometimes called umbrella, V.
The umbrella is to protect the apparatus from air currents. At m is the
sighting lens. H is a lead box packed with pumice stone, moistened with
oil of vitriol or concentrated sulphuric acid, to preserve the
atmosphere dry. Before use the acid is boiled with some ammonium
sulphate to expel any corrosive nitrogen oxides, which might corrode the
brass.

In use the upper disc is charged by its insulated electrode within the
tube E; the movable disc is charged if desired directly through the case
of the instrument. The upper disc is screwed up or down by the
micrometer head M, until the sighted position is reached. The readings
of the micrometer on the top of the case give the data for calculation.

225 STANDARD ELECTRICAL DICTIONARY.

Fig. 155. LIPPMAN'S CAPILLARY ELECTROMETER.

Electrometer, Capillary.
An electrometer for measuring potential difference by capillary action,
which latter is affected by electrostatic excitement. A tube A contains
mercury; its end drawn out to a fine aperture dips into a vessel B which
contains dilute sulphuric acid with mercury under it, as shown. Wires
running from the binding-posts a and b connect one with the mercury in
A, the other with that in B. The upper end of the tube A connects with a
thick rubber mercury reservoir T, and manometer H. The surface tension
of the mercury-acid film at the lower end of the tube A keeps all in
equilibrium. If now a potential difference is established between a and
b, as by connecting a battery thereto, the surface tension is increased
and the mercury rises in the tube B. By screwing down the compressing
clamp E, the mercury is brought back to its original position. The
microscope M is used to determine this position with accuracy. The
change in reading of the manometer gives the relation of change of
surface tension and therefore of potential. Each electrometer needs
special graduation or calibration, but is exceedingly sensitive and
accurate. It cannot be used for greater potential differences than .6
volt, but can measure .0006 volt. Its electrostatic capacity is so small
that it can indicate rapid changes. Another form indicates potential
difference by the movement of a drop of sulphuric acid in a horizontal
glass tube, otherwise filled with mercury, and whose ends lead into two
mercury cups or reservoirs. The pair of electrodes to be tested are
connected to the mercury vessels. The drop moves towards the negative
pole, and its movement for small potential differences (less than one
volt) is proportional to the electro-motive force or potential
difference.

226 STANDARD ELECTRICAL DICTIONARY.

Electrometer Gauge.
An absolute electrometer (see Electrometer, Absolute) forming an
attachment to a Thomson quadrant electrometer. It is used to test the
potential of the flat needle connected with the inner surface of the
Leyden jar condenser of the apparatus. This it does by measuring the
attraction between itself and an attracting disc, the latter connected
by a conductor with the interior of the jar.

Electrometer, Lane's.
A Leyden jar with mounted discharger, so that when charged to a certain
point it discharges itself. It is connected with one coating of any jar
whose charge is to be measured, which jar is then charged by the other
coating. As the jar under trial becomes charged to a certain point the
electrometer jar discharges itself, and the number of discharges is the
measure of the charge of the other jar. It is really a unit jar, q. v.

Fig. 156. THOMSON'S QUADRANT ELECTROMETER.

Fig. 157. HENLEY'S QUADRANT ELECTROSCOPE.

227 STANDARD ELECTRICAL DICTIONARY.

Electrometer, Quadrant.
(a) Sir William Thomson's electrometer, a simple form of which is shown
in the cut, consists of four quadrants of metal placed horizontally;
above these a broad flat aluminum needle hangs by a very fine wire,
acting as torsional suspension. The quadrants are insulated from each
other, but the opposite ones connect with each other by wires. The
apparatus is adjusted so that, when the quadrants are in an unexcited
condition the needle is at rest over one of the diametrical divisions
between quadrants. The needle by its suspension wire is in communication
with the interior of a Leyden jar which is charged. The whole is covered
with a glass shade, and the air within is kept dry by a dish of
concentrated sulphuric acid so that the jar retains its charge for a
long time and keeps the needle at approximately a constant potential. If
now two pairs of quadrants are excited with opposite electricities, as
when connected with the opposite poles of an insulated galvanic cell,
the needle is repelled by one pair and attracted by the other, and
therefore rotates through an arc of greater or less extent. A small
concave mirror is attached above the needle and its image is reflected
on a graduated screen. This makes the smallest movement visible.
Sometimes the quadrants are double, forming almost a complete box,
within which the needle moves.

(b) Henley's quadrant electrometer is for use on the prime conductor of
an electric machine, for roughly indicating the relative potential
thereof. It consists of a wooden standard attached perpendicularly to
the conductor. Near one end is attached a semi-circular or quadrant arc
of a circle graduated into degrees or angular divisions. An index,
consisting of a straw with a pith-bell attached to its end hangs from
the center of curvature of the arc. When the prime conductor is charged
the index moves up over the scale and its extent of motion indicates the
potential relatively.

When the "quadrant electrometer" is spoken of it may always be assumed
that Sir William Thomson's instrument is alluded to. Henley's instrument
is properly termed a quadrant electroscope. (See Electroscope.)

Electro-motive Force.
The cause which produces currents of electricity. In general it can be
expressed in difference of potentials, although the term electro-motive
force should be restricted to potential difference causing a current. It
is often a sustained charging of the generator terminals whence the
current is taken. Its dimensions are

(work done/the quantity of electricity involved),

or ( M * (L^2) /(T^2 ) ) / ((M^.5) * (L^.5)) = ( (M^.5) * (L^1.5) ) /(T^2)

The practical unit of electro-motive force is the volt, q. v. It is
often expressed in abbreviated form, as E. M. D. P., or simply as D. P.,
i. e., potential difference.

Electro-motive force and potential difference are in many cases
virtually identical, and distinctions drawn between them vary with
different authors. If we consider a closed electric circuit carrying a
current, a definite electro-motive force determined by Ohm's law from
the resistance and current obtains in it. But if we attempt to define
potential difference as proper to the circuit we may quite fail.
Potential difference in a circuit is the difference in potential between
defined points of such circuit. But no points in a closed circuit can be
found which differ in potential by an amount equal to the entire
electro-motive force of the circuit. Potential difference is properly
the measure of electro-motive force expended on the portion of a circuit
between any given points. Electro-motive force of an entire circuit, as
it is measured, as it were, between two consecutive points but around
the long portion of the circuit, is not conceivable as merely potential
difference. Taking the circle divided in to degrees as an analogy, the
electro-motive force of the entire circuit might be expressed as 360º,
which are the degrees intervening between two consecutive points,
measured the long way around the circle. But the potential difference
between the same two points would be only 1º, for it would be measured
by the nearest path.

228 STANDARD ELECTRICAL DICTIONARY.

Electro-motive Force, Counter.
A current going through a circuit often has not only true or ohmic
resistance to overcome, but meets an opposing E. M. F. This is termed
counter-electro-motive force. It is often treated in calculations as
resistance, and is termed spurious resistance. It may be a part of the
impedance of a circuit.

In a primary battery hydrogen accumulating on the negative plate
develops counter E. M. F. In the voltaic arc the differential heating of
the two carbons does the same. The storage battery is changed by a
current passing in the opposite direction to its own natural current;
the polarity of such a battery is counter E. M. F.

Electro-motive Force, Unit.
Unit electro-motive force is that which is created in a conductor moving
through a magnetic field at such a rate as to cut one unit line of force
per second. It is that which must be maintained in a circuit of unit
resistance to maintain a current of unit quantity therein. It is that
which must be maintained between the ends of a conductor in order that
unit current may do unit work in a second.

Electro-motive Intensity.
The force acting upon a unit charge of electricity. The mean force is
equal to the difference of potential between two points within the field
situated one centimeter apart, such distance being measured along the
lines of force. The term is due to J. Clerk Maxwell.

Electro-motive Series.
Arrangement of the metals and carbon in series with the most
electro-positive at one end, and electronegative at the other end. The
following are examples for different exciting liquids:

Dilute Sulphuric Dilute Hydrochloric Caustic Potassium
Acid Acid. Potash. Sulphide.

Zinc Zinc Zinc Zinc
Cadmium Cadmium Tin Copper
Tin Tin Cadmium Cadmium
Lead Lead Antimony Tin
Iron Iron Lead Silver
Nickel Copper Bismuth Antimony
Bismuth Bismuth Iron Lead
Antimony Nickel Copper Bismuth
Copper Silver Nickel Nickel
Silver Antimony Silver Iron
Gold
Platinum
Carbon

In each series the upper metal is the positive, dissolved or attacked
element.

229 STANDARD ELECTRICAL DICTIONARY.

Electro-motograph.
An invention of Thomas A. Edison. A cylinder of chalk, moistened with
solution of caustic soda, is mounted so as to be rotated by a handle. A
diaphragm has an arm connected to its center. This arm is pressed
against the surface of the cylinder by a spring. When the cylinder is
rotated, a constant tension is exerted on the diaphragm. If a current is
passed through the junction of arm and cylinder the electrolytic action
alters the friction so as to change the stress upon the diaphragm.

If the current producing this effect is of the type produced by the
human voice through a microphone the successive variations in strain
upon the diaphragm will cause it to emit articulate sounds. These are
produced directly by the movement of the cylinder, the electrolytic
action being rather the regulating portion of the operation. Hence very
loud sounds can be produced by it. This has given it the name of the
loud- speaking telephone.

The same principle may be applied in other ways. But the practical
application of the motograph is in the telephone described.

Fig. 158. ELECTRO-MOTOGRAPH TELEPHONE

Electro-motor.
This term is sometimes applied to a current generator, such as a voltaic
battery.

Electro-muscular Excitation.
A term in medical electricity indicating the excitation of muscle as the
effect of electric currents of any kind.

Electro-negative. adj.
Appertaining to negative electrification; thus of the elements oxygen is
the most electro-negative, because if separated by electrolytic action
from any combination, it will be charged with negative electricity.

230 STANDARD ELECTRICAL DICTIONARY.

Electro-optics.
The branch of natural science treating of the relations between light
and electricity. Both are supposed to be phenomena of or due to the
luminiferous ether. To it may be referred the following:

(a) Electro-magnetic Stress and Magnetic Rotary Polarization;

(b) Dielectric Strain; all of which may be referred to in this book;

(c) Change in the resistance of a conductor by changes in light to which
it is exposed (see Selenium);

(d) The relation of the index of refraction of a dielectric to the
dielectric constant (see Electro-magnetic Theory of Light);

(e) The identity (approximate) of the velocity of light in centimeters
and the relative values of the electrostatic and electro-magnet units
of intensity, the latter being 30,000,000,000 times greater than the
former, while the velocity of light is 30,000,000,000 centimeters per
second.

Electrophoric Action.
The action of an electrophorous; utilized in influence machines. (See
Electrophorous.)

Fig. 159. ELECTROPHOROUS.

Electrophorous.
An apparatus for the production of electric charges of high potential by
electrostatic induction, q. v. It consists of a disc of insulating
material B, such as resin or gutta percha, which is held in a shallow
metal-lined box or form. The disc may be half an inch thick and a foot
or more in diameter, or may be much smaller and thinner. A metal disc A,
smaller in diameter is provided with an insulating handle which may be
of glass, or simply silk suspension strings. To use it the disc B is
excited by friction with a cat-skin or other suitable substance. The
metallic disc is then placed on the cake of resin exactly in its centre,
so that the latter disc or cake projects on all sides. Owing to
roughness there is little real electric contact between the metal and
dielectric. On touching the metal disc a quantity of negative
electricity escapes to the earth. On raising it from the cake it comes
off excited positively, and gives a spark and is discharged. It can be
replaced, touched, removed and another spark can be taken from it, and
so on as long as the cake stays charged.

The successive discharges represent electrical energy expended. This is
derived from the muscular energy expended by the operator in separating
the two discs when oppositely excited. As generally used it is therefore
an apparatus for converting muscular or mechanical energy into electric
energy.

231 STANDARD ELECTRICAL DICTIONARY.

Electro-physiology.
The science of the electric phenomena of the animal system. It may also
be extended to include plants. The great discovery of Galvani with the
frog's body fell into this branch of science. The electric fishes,
gymnotus, etc., present intense phenomena in the same.

Electroplating.
The deposition by electrolysis of a coating of metal upon a conducting
surface. The simplest system makes the object to be plated the negative
electrode or plate in a galvanic couple. Thus a spoon or other object
may be connected by a wire to a plate of zinc. A porous cup is placed
inside a battery jar. The spoon is placed in the porous cup and the zinc
outside it. A solution of copper sulphate is placed in the porous cup,
and water with a little sodium or zinc sulphate dissolved in it,
outside. A current starts through the couple, and copper is deposited on
the spoon.

A less primitive way is to use a separate battery as the source of
current; to connect to the positive plate by a wire the object to be
plated, and a plate of copper, silver, nickel or other metal to the
other pole of the battery. On immersing both object and plate (anode) in
a bath of proper solution the object will become plated.

In general the anode is of the same material as the metal to be
deposited, and dissolving keeps up the strength of the bath. There are a
great many points of technicality involved which cannot be given here.
The surface of the immersed object must be conductive. If not a fine
wire network stretched over it will gradually fill up in the bath and
give a matrix. More generally the surface is made conductive by being
brushed over with plumbago. This may be followed by a dusting of iron
dust, followed by immersion in solution ot copper sulphate. This has the

effect of depositing metallic copper over the surface as a starter for
the final coat.

Attention must be paid to the perfect cleanliness of the objects, to the
condition of the bath, purity of anodes and current density.

Voltaic batteries are largely used for the current as well as special
low resistance dynamos. Thermo-electric batteries are also used to some
extent but not generally.

Electro-pneumatic Signals.
Signals, such as railroad signals or semaphores, moved by compressed
air, which is controlled by valves operated by electricity. The House
telegraph, which was worked by air controlled by electricity, might come
under this term, but it is always understood as applied to railroad
signals, or their equivalent.

232 STANDARD ELECTRICAL DICTIONARY.

Electropoion Fluid.
An acid depolarizing solution for use in zinc-carbon couples, such as
the Grenet battery. The following are formulae for its preparation:

(a) Dissolve one pound of potassium bichromate in ten pounds of water,
to which two and one-half pounds of concentrated sulphuric acid have
been gradually added. The better way is to use powdered potassium
bichromate, add it to the water first, and then gradually add the
sulphuric acid with constant stirring.

(b) To three pints of water add five fluid ounces of concentrated
sulphuric acid; add six ounces pulverized potassium bichromate.

(c) Mix one gallon concentrated sulphuric acid and three gallons of
water. In a separate vessel dissolve six pounds potassium bichromate in
two gallons of boiling water. Mix the two.

The last is the best formula. Always use electropoion fluid cold. (See
Trouvé's Solution--Poggendorff's Solution--Kakogey's Solution--
Tissandrier's Solution--Chutaux's Solution.)

Electro-positive. adj.
Appertaining to positive electrification; thus potassium is the most
electro-positive of the elements. (See Electro-negative.)

Electro-puncture.
The introduction into the system of a platinum point or needle,
insulated with vulcanite, except near its point, and connected as the
anode of a galvanic battery. The kathode is a metal one, covered with a
wet sponge and applied on the surface near the place of puncture. It is
used for treatment of aneurisms or diseased growths, and also for
removal of hair by electrolysis. (See Hair, Removal of by Electrolysis.)

Synonym--Galvano-puncture.

Electro-receptive. adj.
A term applied to any device or apparatus designed to receive and absorb
electric energy. A motor is an example of an electro-receptive
mechanism.

Electroscope.
An apparatus for indicating the presence of an electric charge, and also
for determining the sign, or whether the charge is positive or negative.
The simplest form consists of a thread doubled at its centre and hung
therefrom. On being charged, or on being connected to a charged body the
threads diverge. A pair of pith balls may be suspended in a similar way,
or a couple of strips of gold leaf within a flask (the gold leaf
electroscope). To use an electroscope to determine the sign of the
charge it is first slightly charged. The body to be tested is then
applied to the point of suspension, or other charging point. If at once
further repelled the charge of the body is of the same sign as the
slight charge first imparted to the electroscope leaves; the leaves as
they become more excited will at once diverge more. If of different sign
they will at first approach as their charge is neutralized and will
afterwards diverge.

The gold-leaf electroscope is generally enclosed in a glass bell jar or
flask. Sometimes a pair of posts rise, one on each side, to supply
points of induction from the earth to intensify the action. (See
Electrometer, Quadrant--Electroscope, Gold leaf, and others.)

233 STANDARD ELECTRICAL DICTIONARY.

Electroscope, Bennett's.
A gold-leaf electroscope, the suspended leaves of which are contained in
a glass shade or vessel of dry air. On the inside of the glass shade are
two strips of gold leaf, which rise from the lower edge a short
distance, being pasted to the glass, and connected to the ground. These
act by induction to increase the sensitiveness of the instruments.

Electroscope, Bohenberger's.
A condensing electroscope (see Electroscope, Condensing) with a single
strip of gold leaf suspended within the glass bell. This is at an equal
distance from the opposite poles of two dry piles (see Zamboni's Dry
Pile) standing on end, one on each side of it. As soon as the leaf is
excited it moves toward one and away from the other pile, and the sign
of its electrification is shown by the direction of its motion.

Electroscope, Condensing.
A gold leaf electroscope, the glass bell of which is surmounted by an
electrophorous or static condenser, to the lower plate of which the
leaves of gold are suspended or connected.

In use the object to be tested is touched to the lower plate, and the
upper plate at the same time is touched by the finger. The plates are
now separated. This reduces the capacity of the lower plate greatly and
its charge acquires sufficient potential to affect the leaves, although
the simple touching may not have affected them at all.

Electroscope, Gold Leaf.
An electroscope consisting of two leaves of gold leaf hung in contact
with each other from the end of a conductor. When excited they diverge.
The leaves are enclosed in a glass vessel.

Fig. 160. GOLD LEAF ELECTROSCOPE.

234 STANDARD ELECTRICAL DICTIONARY.

Electroscope, Pith Ball.
Two pith balls suspended at opposite ends of a silk thread doubled in
the middle. When charged with like electricity they repel each other.
The extent of their repulsion indicates the potential of their charge.

Electrostatic Attraction and Repulsion.
The attraction and repulsion of electrostatically charged bodies for
each other, shown when charged with electricity. If charged with
electricity of the same sign they repel each other. If with opposite
they attract each other. The classic attraction and subsequent repulsion
of bits of straw and chaff by the excited piece of amber is a case of
electrostatic attraction and repulsion. (See Electricity,
Static--Electrostatics--Coulomb's Laws of Electrostatic Attraction and
Repulsion.)

Electrostatic Induction, Coefficient of.
The coefficient expressing the ratio of the charge or change of charge
developed in one body to the potential of the inducing body.

Electrostatic Lines of Force.
Lines of force assumed to exist in an electrostatic field of force, and
to constitute the same. In general they correspond in action and
attributes with elcctro-magnetic lines of force. They involve in almost
all cases either a continuous circuit, or a termination at both ends in
oppositely charged surfaces.

Fig. 161. ELECTROSTATIC LINES OF FORCE
BETWEEN NEAR SURFACES.

Fig. 162. ELECTROSTATIC LINKS OF FORCE
BETWEEN DISTANT SURFACES.

235 STANDARD ELECTRICAL DICTIONARY.

The cut, Fig. 161, shows the general course taken by lines of force
between two excited surfaces when near together. Here most of them are
straight lines reaching straight across from surface to surface, while a
few of them arch across from near the edges, tending to spread. If the
bodies are drawn apart the spreading tendency increases and the
condition of things shown in the next cut, Fig. 162, obtains. There is
an axial line whose prolongations may be supposed to extend
indefinitely, as occupying a position of unstable equilibrium. Here the
existence of a straight and unterminated line of force may be assumed.

A direction is predicated to lines of force corresponding with the
direction of an electric current. They are assumed to start from a
positively charged and to go towards a negatively charged surface. A
positively charged body placed in an electrostatic field of force will
be repelled from the region of positive into or towards the region of
negative potential following the direction of the lines of force, not
moving transversely to them, and having no transverse component in its
motion.

Electrostatics.
The division of electric science treating of the phenomena of electric
charge, or of electricity in repose, as contrasted with electro-dynamics
or electricity in motion or in current form. Charges of like sign repel,
and of unlike sign attract each other. The general inductive action is
explained by the use of the electrostatic field of force and
electrostatic lines of force, q. v. The force of attraction and
repulsion of small bodies or virtual points, which are near enough to
each other, vary as the square of the distance nearly, and with the
product of the quantities of the charges of the two bodies.

Electrostatic Refraction.
Dr. Kerr found that certain dielectrics exposed to electric strain by
being placed between two oppositely excited poles of a Holtz machine or
other source of very high tension possess double refracting powers, in
other words can rotate a beam of polarized light, or can develop two
complimentary beams from common light. Bisulphide of carbon shows the
phenomenon well, acting as glass would if the glass were stretched in
the direction of the electrostatic lines of force. To try it with glass,
holes are drilled in a plate and wires from an influence machine are
inserted therein. The discharge being maintained through the glass it
polarizes light.

Synonym--Kerr Effect.

Electrostatic Series.
A table of substances arranged in the order in which they are
electrostatically charged by contact, generally by rubbing against each
other. The following series is due to Faraday. The first members become
positively excited when rubbed with any of the following members, and
vice versa. The first elements correspond to the carbon plate in a
galvanic battery, the succeeding elements to the zinc plate.

Cat, and Bear-skin--Flannel--Ivory--Feathers--Rock Crystal--Flint
Glass--Cotton--Linen--Canvas--White Silk--the Hand--Wood--Shellac--the
Metals (Iron-Copper-Brass-Tin-Silver-Platinum)--Sulphur. There are some
irregularities. A feather lightly drawn over canvas is negatively
electrified; if drawn through folds pressed against it it is positively
excited. Many other exceptions exist, so that the table is of little
value.

236 STANDARD ELECTRICAL DICTIONARY.

Electrostatic Stress.
The stress produced upon a transparent medium in an electrostatic field
of force by which it acquires double refracting or polarizing properties
as regards the action of such medium upon light. (See Electrostatic
Refraction.)

Electro-therapeutics or Therapy.
The science treating of the effects of electricity upon the animal
system in the treatment and diagnosis of disease.

Electrotonus.
An altered condition of functional activity occurring in a nerve
subjected to the passage of an electric current. If the activity is
decreased, which occurs near the anode, the state is one of
anelectrotonus, if the activity is increased which occurs near the
kathode the condition is one of kathelectrotonus.

Electrotype.
The reproduction of a form of type or of an engraving or of the like by
electroplating, for printing purposes. The form of type is pressed upon
a surface of wax contained in a shallow box. The wax is mixed with
plumbago, and if necessary some more is dusted and brushed over its
surface and some iron dust is sprinkled over it also. A matrix or
impression of the type is thus obtained, on which copper is deposited by
electroplating, q. v.

Element, Chemical.
The original forms of matter that cannot be separated into constituents
by any known process. They are about seventy in number. Some of the
rarer ones are being added to or cancelled with the progress of chemical
discovery. For their electric relations see Electro-chemical
Equivalents--Electro-chemical Series.

The elements in entering into combination satisfy chemical affinity and
liberate energy, which may take the form of electric energy as in the
galvanic battery, or of heat energy, as in the combustion of carbon or
magnesium. Therefore an uncombined element is the seat of potential
energy. (See Energy, Potential.) In combining the elements always
combine in definite proportions. A series of numbers, one being proper
to each element which denote the smallest common multipliers of these
proportions, are called equivalents. Taking the theory of valency into
consideration the product of the equivalents by the valencies gives the
atomic weights.

237 STANDARD ELECTRICAL DICTIONARY.

Element, Mathematical.
A very small part of anything, corresponding in a general way to a
differential, as the element of a current.

Element of a Battery Cell.
The plates in a galvanic couple are termed elements, as the carbon and
zinc plates in a Bunsen cell. The plate unattacked by the solution, as
the carbon plate in the above battery, is termed the negative plate or
element; the one attacked, as the zinc plate, is termed the positive
plate or element.

Synonym--Voltaic Element.

Elements, Electrical Classification of.
This may refer to Electro-chemical Series, Electrostatic Series, or
Thermo-electric Series, all of which may be referred to.

Element, Thermo-electric.
One of the metals or other conductors making a thermo-electric couple,
the heating of whose junction produces electro-motive force and a
current, if on closed circuit. The elements of a couple are respectively
positive and negative, and most conductors can be arranged in a series
according to their relative polarity. (See Thermo-electric Series.)

Elongation.
The throw of the magnetic needle. (See Throw.)

Synonym--Throw.

Embosser, Telegraph.
A telegraphic receiver giving raised characters on a piece of paper. It
generally refers to an apparatus of the old Morse receiver type, one
using a dry point stylus, which pressing the paper into a groove in the
roller above the paper, gave raised characters in dots and lines.

Fig. 163. MORSE RECEIVER.

238 STANDARD ELECTRICAL DICTIONARY.

E. M. D. P.
Abbreviation for "electro-motive difference of potential" or for
electro-motive force producing a current as distinguished from mere
inert potential difference.

E. M. F.
Abbreviation for "electro-motive force."

Fig. 164. END-ON METHOD.

End-on Method.
A method of determining the magnetic moment of a magnet. The magnet
under examination, N S, is placed at right angles to the magnetic
meridian, M O R, and pointing directly at or "end on" to the centre of a
compass needle, n s. From the deflection a of the latter the moment is
calculated.

Endosmose, Electric.
The inflowing current of electric osmose. (See Osmose, Electric.)

End Play.
The power to move horizontally in its bearings sometimes given to
armature shafts. This secures a more even wearing of the commutator
faces. End play is not permissible in disc armatures, as the attraction
of the field upon the face of the armature core would displace it
endwise. For such armatures thrust-bearings preventing end play have to
be provided.

Energy.
The capacity for doing work. It is measured by work units which involve
the exercise of force along a path of some length. A foot-pound,
centimeter-gram, and centimeter-dyne are units of energy and work.

The absolute unit of energy is the erg, a force of one dyne exercised
over one centimeter of space. (See Dyne.)

The dimensions of energy are
force (M * L / T^2) * space (L) = M * (L^2 / T^2).
Energy may be chemical (atomic or molecular), mechanical,
electrical, thermal, physical, potential, kinetic, or actual, and other
divisions could be formulated.

239 STANDARD ELECTRICAL DICTIONARY.

Energy, Atomic.
The potential energy due to atomic relations set free by atomic change;
a form of chemical energy, because chemistry refers to molecular as well
as to atomic changes. When atomic energy loses the potential form it
immediately manifests itself in some other form, such as heat or
electric energy. It may be considered as always being potential energy.
(See Energy, Chemical.)

Energy, Chemical.
A form of potential energy (see Energy, Potential) possessed by elements
in virtue of their power of combining with liberation of energy, as in
the combination of carbon with oxygen in a furnace; or by compounds in
virtue of their power of entering into other combinations more
satisfying to the affinities of their respective elements or to their
own molecular affinity. Thus in a galvanic couple water is decomposed
with absorption of energy, but its oxygen combines with zinc with
evolution of greater amount of energy, so that in a voltaic couple the
net result is the setting free of chemical energy, which is at once
converted into electrical energy in current form, if the battery is on a
closed circuit.

Energy, Conservation of.
A doctrine accepted as true that the sum of energy in the universe is
fixed and invariable. This precludes the possibility of perpetual
motion. Energy may be unavailable to man, and in the universe the
available energy is continually decreasing, but the total energy is the
same and never changes.

Energy, Degradation of.
The reduction of energy to forms in which it cannot be utilized by man.
It involves the reduction of potential energy to kinetic energy, and the
reduction of kinetic energy of different degrees to energy of the same
degree. Thus when the whole universe shall have attained the same
temperature its energy will have become degraded or non-available. At
present in the sun we have a source of kinetic energy of high degree, in
coal a source of potential energy. The burning of all the coal will be
an example of the reduction of potential to kinetic energy, and the
cooling of the sun will illustrate the lowering in degree of kinetic
energy. (See Energy, Conservation of--Energy, Potential--Energy,
Kinetic.)

Energy, Electric.
The capacity for doing work possessed by electricity
under proper conditions. Electric energy may be either kinetic or
potential. As ordinary mechanical energy is a product of force and
space, so electric energy is a product of potential difference and
quantity. Thus a given number of coulombs of electricity in falling a
given number of volts develop electric energy. The dimensions are found
therefore by multiplying electric current intensity quantity
((M^.5) * (L^.5)),
by electric potential
((M^.5)*(L^1.5) / (T^2)),
giving (M * (L^2)/(T^2)),
the dimensions of energy in general as it should be.

The absolute unit of electric energy in electro-magnetic measure is
(1E-7) volt coulombs.

240 STANDARD ELECTRICAL DICTIONARY.

The practical unit is the volt-coulomb. As the volt is equal to 1E8
absolute units of potential and the coulomb to 0.1 absolute units of
quantity, the volt-coulomb is equal to 1E7 absolute units of energy.

The volt-coulomb is very seldom used, and the unit of Electric Activity
or Power (see Power, Electric), the volt-ampere, is universally used.
This unit is sometimes called the Watt, q. v., and it indicates the rate
of expenditure or of production of electric energy.

The storing up in a static accumulator or condenser of a given charge of
electricity, available for use with a given change of potential
represents potential electric energy.

The passing of a given quantity through a conductor with a given fall of
potential represents kinetic electric energy.

In a secondary battery there is no storage of energy, but the charging
current simply accumulates potential chemical energy in the battery,
which chemical energy is converted into electric energy in the discharge
or delivery of the battery.

It is customary to discuss Ohm's law in this connection; it is properly
treated under Electric Power, to which the reader is referred. (See
Power, Electric.)

Energy, Electric Transmission of.
If an electric current passes through a conductor all its energy is
expended in the full circuit. Part of the circuit may be an electrical
generator that supplies energy as fast as expended. Part of the circuit
may be a motor which absorbs part of the energy, the rest being expended
in forcing a current through the connecting wires and through the
generator. The electric energy in the generator and connecting wires is
uselessly expended by conversion into heat. That in the motor in great
part is utilized by conversion into mechanical energy which can do
useful work. This represents the transmission of energy. Every electric
current system represents this operation, but the term is usually
restricted to the transmission of comparatively large quantities of
energy.

A typical installation might be represented thus. At a waterfall a
turbine water wheel is established which drives a dynamo. From the
dynamo wires are carried to a distant factory, where a motor or several
motors are established, which receive current from the dynamo and drive
the machinery. The same current, if there is enough energy, may be used
for running lamps or electroplating. As electric energy (see Energy,
Electric,) is measured by the product of potential difference by
quantity, a very small wire will suffice for the transmission of a small
current at a high potential, giving a comparatively large quantity of
energy. It is calculated that the energy of Niagara Falls could be
transmitted through a circuit of iron telegraph wire a distance of over
1,000 miles, but a potential difference of 135,000,000 volts would be
required, something quite impossible to obtain or manage.

241 STANDARD ELECTRICAL DICTIONARY.

Energy, Kinetic.
Energy due to matter being actually in motion. It is sometimes called
actual energy. The energy varies directly with the mass and with the
square of the velocity. It is represented in formula by .5 *M * (v^2).

Synonyms--Actual Energy--Energy of Motion--Dynamic Energy.

Energy, Mechanical.
The energy due to mechanical change or motion, virtually the same as
molar energy. (See Energy, Molar.)

Energy, Molar.
The energy of masses of matter due to movements of or positions of
matter in masses; such as the kinetic energy of a pound or of a ton in
motion, or the potential energy of a pound at an elevation of one
hundred feet.

Energy, Molecular.
The potential energy due to the relations of molecules and set free by
their change in the way of combination. It is potential for the same
reason that applies to atomic and chemical energy, of which latter it is
often a form, although it is often physical energy. The potential energy
stored up in vaporization is physical and molecular energy; the
potential energy stored up in uncombined potassium oxide and water, or
calcium oxide (quicklime) and water is molecular, and when either two
substances are brought together kinetic, thermal or heat energy is set
free, as in slaking lime for mortar.

Energy of an Electrified Body.
An electrified body implies the other two elements of a condenser. It is
the seat of energy set free when discharged. (See Dielectric, Energy
of.) The two oppositely charged bodies tend to approach. This tendency,
together with the distances separating them, represents a potential
energy.

Energy of Stress.
Potential energy due to stress, as the stretching of a spring. This is
hardly a form of potential energy. A stressed spring is merely in a
position to do work at the expense of its own thermal or kinetic energy
because it is cooled in doing work. If it possessed true potential
energy of stress it would not be so cooled.

Energy of Position.
Potential energy due to position, as the potential energy of a pound
weight raised ten feet (ten foot lbs.). (See Energy, Potential.)

Energy, Physical.
The potential energy stored up in physical position or set free in
physical change. Thus a vapor or gas absorbs energy in its vaporization,
which is potential energy, and appears as heat energy when the vapor
liquefies.

242 STANDARD ELECTRICAL DICTIONARY.

Energy, Potential, or Static Energy.
The capacity for doing work in a system due to advantage of position or
other cause, such as the stress of a spring. A pound weight supported
ten feet above a plane has ten foot lbs. of potential energy of position
referred to that plane. A given weight of an elementary substance
represents potential chemical energy, which will be liberated as actual
energy in its combination with some other element for which it has an
affinity. Thus a ton of coal represents a quantity of potential chemical
energy which appears in the kinetic form of thermal energy when the coal
is burning in a furnace. A charged Leyden jar represents a source of
potential electric energy, which becomes kinetic heat energy as the same
is discharged.

Energy, Thermal.
A form of kinetic molecular energy due to the molecular motion of bodies
caused by heat.

Entropy.
Non-available energy. As energy may in some way or other be generally
reduced to heat, it will be found that the equalizing of temperature,
actual and potential, in a system, while it leaves the total energy
unchanged, makes it all unavailable, because all work represents a fall
in degree of energy or a fall in temperature. But in a system such as
described no such fall could occur, therefore no work could be done. The
universe is obviously tending in that direction. On the earth the
exhaustion of coal is in the direction of degradation of its high
potential energy, so that the entropy of the universe tends to zero.
(See Energy, Degradation of.)

Entropy, Electric.
Clerk Maxwell thought it possible to recognize in the Peltier effect, q.
v., a change in entropy, a gain or loss according to whether the
thermo-electric junction was heated or cooled. This is termed Electric
Entropy. (See Energy, Degradation of.)

243 STANDARD ELECTRICAL DICTIONARY.

Fig. 165. EPINUS' CONDENSER,

Epinus' Condenser.
Two circular brass plates, A and B, are mounted on insulating supports,
and arranged to be moved towards or away from each other as desired.
Between them is a plate of glass, C, or other dielectric. Pith balls may
be suspended back of each brass plate as shown. The apparatus is charged
by connecting one plate to an electric machine and the other to the
earth. The capacity of the plate connected to the machine is increased
by bringing near to it the grounded plate, by virtue of the principle of
bound charges. This apparatus is used to illustrate the principles of
the electric condenser. It was invented after the Leyden jar was
invented.

Fig. 166. EPINUS' CONDENSER.

E. P. S.
Initials of Electrical Power Storage; applied to a type of secondary
battery made by a company bearing that title.

Fig. 167. CAM EQUALIZER.

244 STANDARD ELECTRICAL DICTIONARY.

Equalizer.
In electro-magnetic mechanism an arrangement for converting the pull of
the electro-magnet varying in intensity greatly over its range of
action, into a pull of sensibly equal strength throughout. The use of a
rocking lever acting as a cam, with leverage varying as the armature
approaches or recedes from the magnet core is one method of effecting
the result. Such is shown in the cut. E is an electro-magnet, with
armature a. A and B are the equalizer cams. The pull on the short end of
the cam B is sensibly equal for its whole length.

Many other methods have been devised, involving different shapes of pole
pieces, armatures or mechanical devices other than the one just shown.

Equipotential. adj.
Equal in potential; generally applied to surfaces. Thus every magnetic
field is assumed to be made up of lines of force and intersecting those
lines, surfaces, plane, or more or less curved in contour, can be
determined, over all parts of each one of which the magnetic intensity
will be identical. Each surface is the locus of equal intensity. The
same type of surface can be constructed for any field of force, such as
an electrostatic field, and is termed an equipotential surface.

Equipotential Surface, Electrostatic.
A surface in an electrostatic field of force, which is the locus of all
points of a given potential in such field; a surface cutting all the
lines of force at a point of identical potential. Lines of force are cut
perpendicularly by an equipotential surface, or are normal thereto.

Equipotential Surface, Magnetic and Electro-magnetic.
A surface bearing the same relation to a magnetic or electro-magnetic
field of force that an electrostatic equipotential surface (see
Equipotential Surface, Electrostatic,) does to an electrostatic field of
force.

Equivalent, Chemical.
The quotient obtained by dividing the atomic weight of an element by its
valency.

Equivalents, Electro-chemical.
The weight of any substance set free by one coulomb of electricity. The
following give some equivalents expressed in milligrams:

Hydrogen .0105 Mercury (mercurous) 2.10
Gold .6877 Iron (ferric) .1964
Silver 1.134 Iron (ferrous) .294
Copper (cupric) .3307 Nickel .3098
Mercury (mercuric) 1.05 Zinc .3413
Lead 1.0868 Chlorine .3728
Oxygen .89

245 STANDARD ELECTRICAL DICTIONARY.

Equivalent, Electro-mechanical.
The work or energy equivalent to unit quantities of electric energy, q.
v.; or equivalent to a unit current in a conductor whose ends differ one
unit of potential. The unit of electric energy taken is the watt-second

or volt-coulomb. One volt-coulomb is equal to
Ergs 1E7 [10000000]
Foot Pound .737337
Gram-degree C. .24068
Horse Power Second .0013406
Pound-degree F. .000955
One horse power is equal to 745.943 volt coulombs per second.

Equivalent, Electro-thermal.
The heat produced by a unit current passing through a conductor with
unit difference of potential at its ends; the heat equivalent of a
volt-coulomb or watt-second. It is equal to
Gram-degree C. .24068
Pound-degree F. .000955

Equivalent, Thermo-chemical.
The calories evolved by the combination of one gram of any substance
with its equivalent of another substance being determined, the product
obtained by multiplying this number by the equivalent (atomic or
molecular weight / valency) of the first element or substance is the
thermo-chemical equivalent. If expressed in kilogram calories, the
product of the thermo-chemical equivalent by 0.43 gives the voltage
required to effect such decomposition.

The following are thermo-chemical equivalents of a few combinations:
Water 34.5
Zinc oxide 43.2
Iron protoxide 34.5
Iron Sesquioxide 31.9 X 3
Copper oxide 19.2

Equivolt.
"The mechanical energy of one volt electro-motive force exerted under
unit conditions through one equivalent of chemical action in grains."
(J. T. Sprague.) This unit is not in general use as the unit of electric
energy, the volt-coulomb and (for rate of electric energy) the
volt-ampere being always used.

Erg.
The absolute or fundamental C. G. S. unit of work or energy. The work
done or energy expended in moving a body through one centimeter against
a resistance of one dyne.

Erg-ten.
Ten millions of ergs, or ten meg-ergs.

Escape.
A term applied to leakage of current.

Etching, Electric.
A process of producing an etched plate. The plate is coated with wax,
and the design traced through as in common etching. It is then placed in
a bath and is connected to the positive terminal from a generator, whose
negative is immersed in the same bath, so that the metal is dissolved by
electrolytic action. By attaching to the other terminal and using a
plating bath, a rough relief plate may be secured, by deposition in the
lines of metal by electroplating.

Synonym--Electric Engraving.

246 STANDARD ELECTRICAL DICTIONARY.

Ether.
The ether is a hypothetical thing that was invented to explain the
phenomena of light. Light is theoretically due to transverse vibrations
of the ether. Since the days of Young the conception of the ether has
extended, and now light, "radiant heat," and electricity are all treated
as phenomena of the ether. Electrical attraction and repulsion are
explained by considering them due to local stresses in the ether;
magnetic phenomena as due to local whirlpools therein. The ether was
originally called the luminiferous ether, but the adjective should now
be dropped. Its density is put at 936E-21 that of water, or equal to
that of the atmosphere at 210 miles above the earth's surface. Its
rigidity is about 1E-9 that of steel (see Ten, Powers of); as a whole it
is comparable to an all-pervading jelly, with almost perfect elasticity.
The most complete vacuum is filled with ether.

All this is a hypothesis, for the ether has never been proved to exist.
Whether gravitation will ever be explained by It remains to be seen.

Eudiometer.
A graduated glass tube for measuring the volumes of gases. In its
simplest form it is simply a cylindrical tube, with a scale etched or
engraved upon it, closed at one end and open at the other. The gas to be
measured is collected in it over a liquid, generally water, dilute
sulphuric acid in the gas voltameter, or mercury. Many different shapes
have been given them by Hoffmann, Ure, Bunsen and others.

Evaporation, Electric.
The superficial sublimation or evaporation of a substance under the
influence of negative electricity. It is one of the effects investigated
by Crookes in his experiments with high vacua. He found that when a
metal, even so infusible as platinum, was exposed to negative
electrification in one of his high vacuum tubes, that it was volatilized
perceptibly. A cadmium electrode heated and electrified negatively was
found to give a strong coating of metal on the walls of the tube. Even
in the open air the evaporation of water was found to be accelerated by
negative electrification.

Exchange, Telephone.
The office to which telephone wires lead in a general telephone system.
In the office by a multiple switch board, or other means, the different
telephones are interconnected by the office attendants, so that any
customers who desire it may be put into communication with each other.
The exchange is often termed the Central Office, although it may be only
a branch office.

Excitability, Faradic.
The action produced in nerve or muscle of the animal system by an
alternating or intermitting high potential discharge from an induction
coil.

247 STANDARD ELECTRICAL DICTIONARY.

Excitability, Galvanic.
The same as Faradic excitability, except that it refers to the effects
of the current from a galvanic battery.

Excitability of Animal System, Electric.
The susceptibility of a nerve or muscle to electric current shown by the
effect produced by its application.

Exciter.
A generator used for exciting the field magnet of a dynamo. In
alternating current dynamos, e. g., of the Westinghouse type, a special
dynamo is used simply to excite the field magnet. In central station
distribution the same is often done for direct current dynamos.

Exosmose, Electric.
The outflowing current of electric osmose. (See Osmose, Electric.)

Expansion, Coefficient of.
The number expressing the proportional increase in size, either length,
area or volume, of a substance under the influence generally of heat.
There are three sets of coefficients, (1) of linear expansion, (2) of
superficial expansion, (3) of cubic expansion or expansion of volume.
The first and third are the only ones much used. They vary for different
substances, and for the same substance at different temperatures. They
are usually expressed as decimals indicating the mixed number referred
to the length or volume of the body at the freezing point as unity.

Expansion, Electric.
(a) The increase in volume of a condenser, when charged
electrostatically. A Leyden jar expands when charged, and contracts when
discharged.

(b) The increase in length of a bar of iron when magnetized.

This is more properly called magnetic expansion or magnetic elongation.

Exploder.
(a) A small magneto-generator for producing a current for heating the
wire in an electric fuse of the Abel type (see Fuse, Electric), and
thereby determining an explosion.

(b) The term may also be applied to a small frictional or influence
machine for producing a spark for exploding a spark fuse.

Explorer.
A coil, similar to a magnetizing coil (see Coil, Magnetizing), used for
investigating the electro-magnetic circuit and for similar purposes. If
placed around an electro-magnet and connected with a galvanometer, it
will produce a deflection, owing to a momentary induced current, upon
any change in the magnet, such as removing or replacing the armature. It
is useful in determining the leakage of lines of force and for general
investigations of that nature. It is often called an exploring coil.
Hughes' Induction Balance (see Induction Balance, Hughes') is sometimes
called a Magnetic Explorer. The exploring coil may be put in circuit
with a galvanometer for quantitative measurements or with a telephone
for qualitative ones.

248 STANDARD ELECTRICAL DICTIONARY.

Extension Bell Call.
A system of relay connection, q. v., by which a bell is made to continue
ringing after the current has ceased coming over the main line. It is
designed to prolong the alarm given by a magneto call bell, q. v., which
latter only rings as long as the magneto handle is turned. A vibrating
electric bell (see Bell, Electric,) is connected in circuit with a local
battery and a switch normally open, but so constructed as to close the
circuit when a current is passed and continue to do so indefinitely. The
distant circuit is connected to this switch. When the magneto is worked
it acts upon the switch, closes the local battery circuit and leaves it
closed, while the bell goes on ringing until the battery is exhausted or
the switch is opened by hand.

Eye, Electro-magnetic.
An apparatus used in exploring a field of electro-magnetic radiations.
It is a piece of copper wire 2 millimeters (.08 inch) in diameter, bent
into an almost complete circle 70 millimeters (.28 inch) in diameter,
with terminals separated by an air gap. This is moved about in the
region under examination, and by the production of a spark indicates the
locality of the loops or venters in systems of stationary waves.

248 STANDARD ELECTRICAL DICTIONARY.

F.
Abbreviation for Fahrenheit, as 10º F., meaning 10º Fahrenheit. (See
Fahrenheit Scale.)

Fahrenheit Scale.
A thermometer scale in use in the United States and England. On this
scale the temperature of melting ice is 32°; that of condensing steam is
212°; the degrees are all of equal length. Its use is indicated by the
letter F., as 180° F. To convert its readings into centigrade, subtract
32 and multiply by 5/9. (b) To convert centigrade into F. multiply by
9/5 and add 32. Thus 180° F. = ((180-32) * 5/9)° C. = 82.2° C. Again
180° C. = (180 * 9/5) + 32 = 324° F.

The additions and subtractions must be algebraic in all cases. Thus when
the degrees are minus or below zero the rules for conversion might be
put thus: To convert degrees F. below zero into centigrade to the number
of degrees F. add 32, multiply by 5/9 and place a minus sign (-) before
it. (b) To convert degrees centigrade below zero into Fahrenheit,
multiply the number of degrees by 9/5, subtract from 32 if smaller; if
greater than 32 subtract 32 therefrom, and prefix a minus sign, thus:
-10° C. = 32 - (10 * 9/5) = 14°. Again, -30°C. = (30 * 9/5) - 32 = 22 =
-22° F.

249 STANDARD ELECTRICAL DICTIONARY.

Farad.
The practical unit of electric capacity; the capacity of a conductor
which can retain one coulomb of electricity at a potential of one volt.

The quantity of electricity charged upon a conducting surface raises its
potential; therefore a conductor of one farad capacity can hold two
coulombs at two volts potential, and three coulombs at three volts, and
so on. The electric capacity of a conductor, therefore, is relative
compared to others as regards its charge, for the latter may be as great
as compatible with absence of sparking and disruptive discharge. In
other words, a one farad or two farad conductor may hold a great many
coulombs. Charging a conductor with electricity is comparable to pumping
air into a receiver. Such a vessel may hold one cubic foot of air at
atmospheric pressure and two at two atmospheres, and yet be of one cubic
foot capacity however much air is pumped into it.

The farad is equal to one fundamental electrostatic unit of capacity
multiplied by 9E11 and to one electro-magnetic unit multiplied by 1E-9.

The farad although one of the practical units is far too large, so the
micro-farad is used in its place. The capacity of a sphere the size of
the earth is only .000636 of a farad.

Faraday, Effect.
The effect of rotation of its plane produced upon a polarized beam of
light by passage through a magnetic field. (See Magnetic Rotary
Polarization.)

Faraday's Cube.
To determine the surface action of a charge, Faraday constructed a room,
twelve feet cube, insulated, and lined with tinfoil. This room he
charged to a high potential, but within it he could detect no excitement
whatever. The reason was because the electricity induced in the bodies
within the room was exactly equal to the charge of the room-surface, and
was bound exactly by it. The room is termed Faraday's cube.

Faraday's Dark Space.
A non-luminous space between the negative and positive glows, produced
in an incompletely exhausted tube through which a static discharge, as
from an induction coil, is produced. It is perceptible in a rarefaction
of 6 millimeters (.24 inch) and upwards. If the exhaustion is very high
a dark space appears between the negative electrode and its discharge.
This is known as Crookes' dark space.

Faraday's Disc.
A disc of any metal, mounted so as to be susceptible of rotation in a
magnetic field of force, with its axis parallel to the general direction
of the lines of force. A spring bears against its periphery and another
spring against its axle. When rotated, if the springs are connected by a
conductor, a current is established through the circuit including the
disc and conductor. The radius of the disc between the spring contacts
represents a conductor cutting lines of force and generating a potential
difference, producing a current. If a current is sent through the
motionless wheel from centre to periphery it rotates, illustrating the
doctrine of reversibility. As a motor it is called Barlow's or
Sturgeon's Wheel. If the disc without connections is rapidly rotated it
produces Foucault currents, q. v., within its mass, which resist its
rotation and heat the disc.

250 STANDARD ELECTRICAL DICTIONARY.

Fig. 168. "FARADAY'S NET."

Faraday's Net.
An apparatus for showing that the electric charge resides on the
surface. It consists of a net, conical in shape and rather deep, to
whose apex two threads, one on each side, are attached. Its mouth is
fastened to a vertical ring and the whole is mounted on an insulating
support.

It is pulled out to its full extent and is electrified. No charge can be
detected inside it. By pulling one of the threads it is turned with the
other side out. Now all the charge is found on the outside just as
before, except that it is of course on the former inside surface of the
bag. The interior shows no charge.

Faraday's Transformer.
The first transformer. It was made by Michael Faraday. It was a ring of
soft iron 7/8 inch thick, and 6 inches in external diameter. It was
wound with bare wire, calico being used to prevent contact of the wire
with the ring and of the layers of wire with each other, while twine was
wound between the convolutions to prevent the wires from touching.
Seventy-two feet of copper wire, 1/20 inch diameter, were wound in three
superimposed coils, covering about one-half of the ring. On the other
half sixty feet of copper wire were wound in two superimposed coils.
Faraday connected his coils in different ways and used a galvanometer to
measure the current produced by making and breaking one of the circuits
used as a primary.

The coil is of historic interest.

Faraday's Voltameter.
A voltameter, in which the coulombs of current are measured by the
volume of the gas evolved from acidulated water. (See Voltameter, Gas.)

Faradic. adj.
Referring to induced currents, produced from induction coils. As Faraday
was the original investigator of the phenomena of electro-magnetic
induction, the secondary or induced electro-magnetic currents and their
phenomena and apparatus are often qualified by the adjective Faradic,
especially in electro-therapeutics. A series of alternating
electrostatic discharges, as from an influence machine (Holtz), are
sometimes called Franklinic currents. They are virtually Faradic, except
as regards their production.

251 STANDARD ELECTRICAL DICTIONARY.

Faradic Brush.
A brush for application of electricity to the person. It is connected as
one of the electrodes of an induction coil or magneto generator. For
bristles wire of nickel plated copper is generally employed.

Faradization.
In medical electricity the analogue of galvanization; the effects due to
secondary or induced currents; galvanization referring to currents from
a galvanic battery; also the process of application of such currents.

Faults.
Sources of loss of current or of increased resistance or other troubles
in electric circuits.

Feeder.
A lead in an electric central station distribution system, which lead
runs from the station to some point in the district to supply current.
It is not used for any side connections, but runs direct to the point
where current is required, thus "feeding" the district directly. In the
two wire system a feeder may be positive or negative; in the three wire
system there is also a neutral feeder. Often the term feeder includes
the group of two or of three parallel lines.

Feeder Equalizer.
An adjustable resistance connected in circuit with a feeder at the
central station. The object of the feeder being to maintain a definite
potential difference at its termination, the resistance has to be varied
according to the current it is called on to carry.

Feeder, Main or Standard.
The main feeder of a district. The standard regulation of pressure
(potential difference between leads) in the district is often determined
by the pressure at the end of the feeder.

Feeder, Negative.
The lead or wire in a set of feeders, which is connected to the negative
terminal of the generator.

Feeder, Neutral.
In the three wire system the neutral wire in a set of feeders. It is
often made of less diameter than the positive and negative leads.

Feeder, Positive.
The lead or wire in a set of feeders, which wire is connected to the
positive terminal of the generator.

Ferranti Effect.
An effect as yet not definitely explained, observed in the mains of the
Deptford, Eng., alternating current plant. It is observed that the
potential difference between the members of a pair of mains rises or
increases with the distance the place of trial is from the station.

252 STANDARD ELECTRICAL DICTIONARY.

Ferro-magnetic. adj.
Paramagnetic; possessing the magnetic polarity of iron.

Fibre and Spring Suspension.
A suspension of the galvanometer needle used in marine galvanometers.
The needle is supported at its centre of gravity by a vertically
stretched fibre attached at both its ends, but with a spring
intercalated between the needle and one section of the fibre.

Fibre Suspension.
Suspension, as of a galvanometer needle, by a vertical or hanging fibre
of silk or cocoon fibre, or a quartz fibre. (See Quartz.)

This suspension, while the most delicate and reliable known, is very
subject to disturbance and exacts accurate levelling of the instrument.

Fibre suspension is always characterized by a restitutive force. Pivot
suspension, q. v., on the other hand, has no such force.

Field, Air.
A field the lines of force of which pass through air; the position of a
field comprised within a volume of air.

Field, Alternating.
Polarity or direction being attributed to lines of force, if such
polarity is rapidly reversed, an alternating field results. Such field
may be of any kind, electro-magnetic or electrostatic. In one instance
the latter is of interest. It is supposed to be produced by high
frequency discharges of the secondary of an induction coil, existing in
the vicinity of the discharging terminals.

Field Density.
Field density or density of field is expressed in lines of force per
unit area of cross-section perpendicular to the lines of force.

Field, Distortion of.
The lines of force reaching from pole to pole of an excited field magnet
of a dynamo are normally symmetrical with respect to some axis and often
with respect to several. They go across from pole to pole, sometimes
bent out of their course by the armature core, but still symmetrical.
The presence of a mass of iron in the space between the pole pieces
concentrates the lines of force, but does not destroy the symmetry of
the field.

When the armature of the dynamo is rotated the field becomes distorted,
and the lines of force are bent out of their natural shape. The new
directions of the lines of force are a resultant of the lines of force
of the armature proper and of the field magnet. For when the dynamo is
started the armature itself becomes a magnet, and plays its part in
forming the field. Owing to the lead of the brushes the polarity of the
armature is not symmetrical with that of the field magnets. Hence the
compound field shows distortion. In the cut is shown diagrammatically
the distortion of field in a dynamo with a ring armature. The arrow
denotes the direction of rotation, and n n * * * and s s * * * indicate
points of north and south polarity respectively.

253 STANDARD ELECTRICAL DICTIONARY.

The distorted lines must be regarded as resultants of the two induced
polarities of the armature, one polarity due to the induction of the
field, the other to the induction from its own windings. The positions
of the brushes have much to do with determining the amount and degree of
distortion. In the case of the ring armature it will be seen that some
of the lines of force within the armature persist in their polarity and
direction, almost as induced by the armature windings alone, and leak
across without contributing their quota to the field. Two such lines are
shown in dotted lines.

In motors there is a similar but a reversed distortion.

Fig. 169. DISTORTION OF FIELD IN A
RING ARMATURE OF AN ACTIVE DYNAMO.

Fig. 170. DISTORTION OF FIELD IN A
RING ARMATURE OF AN ACTIVE MOTOR.

254 STANDARD ELECTRICAL DICTIONARY.

Field, Drag of.
When a conductor is moved through a field so that a current is generated
in it, the field due to that current blends with the other field and
with its lines of force, distorting the field, thereby producing a drag
upon its own motion, because lines of force always tend to straighten
themselves, and the straightening would represent cessation of motion in
the conductor. This tendency to straightening therefore resists the
motion of the conductor and acts a drag upon it.

Field of Force.
The space in the neighborhood of an attracting or repelling mass or
system. Of electric fields of force there are two kinds, the
Electrostatic and the Magnetic Fields of Force, both of which may be
referred to. A field of force may be laid out as a collection of
elements termed Lines of Force, and this nomenclature is universally
adopted in electricity. The system of lines may be so constructed that
(a) the work done in passing from one equipotential surface to the next
is always the same; or (b) the lines of force are so laid out and
distributed that at a place in which unit force is exercised there is a
single line of force passing through the corresponding equipotential
surface in each unit of area of that surface. The latter is the
universal method in describing electric fields. It secures the following
advantages:--First: The potential at any point in the field of space
surrounding the attracting or repelling mass or masses is found by
determining on which imaginary equipotential surface that point lies.
Second: If unit length of a line of force cross n equipotential
surfaces, the mean force along that line along the course of that part
of it is equal to n units; for the difference of potential of the two
ends of that part of the line of force = n; it is also equal to F s (F
= force), because it represents numerically a certain amount of work;
but s = I, whence n = F. Third: The force at any part of the field
corresponds to the extent to which the lines of force are crowded
together; and thence it may be determined by the number of lines of
force which pass through a unit of area of the corresponding
equipotential surface, that area being so chosen as to comprise the
point in question. (Daniell.)

Field of Force, Electrostatic.
The field established by the attracting, repelling and stressing
influence of an electrostatically charged body. It is often termed an
Electrostatic Field. (See Field of Force.)

255 STANDARD ELECTRICAL DICTIONARY.

Field of Force of a Current.
A current establishes a field of force around itself, whose lines of
force form circles with their centres on the axis of the current. The
cut, Fig. 172, shows the relation of lines of force to current.

Fig. 171. EXPERIMENT SHOWING LINES OF FORCE
SURROUNDING AN ACTIVE CONDUCTOR.

Fig. 172. DIAGRAM OF FIELD OF FORCE
SURROUNDING AN ACTIVE CONDUCTOR.

Fig. 173. LINK OF FORCE INDUCED BY A
CURRENT SHOWING THE MAGNETIC WHIRLS.

The existence of the field is easily shown by passing a conductor
vertically through a horizontal card. On causing a current to go through
the wire the field is formed, and iron filings dropped upon the card,
tend, when the latter is gently tapped, to take the form of circles. The
experiment gives a version of the well-known magnetic figures, q. v. See
Fig. 171.

The cut shows by the arrows the relation of directions of current to the
direction of the lines of force, both being assumptions, and merely
indicating certain fixed relations, corresponding exactly to the
relations expressed by the directions of electro-magnetic or magnetic
lines of force

256 STANDARD ELECTRICAL DICTIONARY.

Field, Pulsatory.
A field produced by pulsatory currents. By induction such field can
produce an alternating current.

Field, Rotating.
In a dynamo the field magnets are sometimes rotated instead of the
armature, the latter being stationary. In Mordey's alternator the
armature, nearly cylindrical, surrounds the field, and the latter
rotates within it, the arrangement being nearly the exact reverse of the
ordinary one. This produces a rotating field.

Field, Rotatory.
A magnetic field whose virtual poles keep rotating around its centre of
figure. If two alternating currents differing one quarter period in
phase are carried around four magnetizing coils placed and connected in
sets of two on the same diameter and at right angles to each other, the
polarity of the system will be a resultant of the combination of their
polarity, and the resultant poles will travel round and round in a
circle. In such a field, owing to eddy currents, masses of metal,
journaled like an armature, will rotate, with the speed of rotation of
the field.

Field, Stray.
The portion of a field of force outside of the regular circuit;
especially applied to the magnetic field of force of dynamos expressing
the portion which contributes nothing to the current generation.

Synonym--Waste Field.

Field, Uniform.
A field of force of uniform density. (See Field Density.)

Figure of Merit.
In the case of a galvanometer, a coefficient expressing its delicacy. It
is the reciprocal of the current required to deflect the needle through
one degree. By using the reciprocal the smaller the current required the
larger is the figure of merit. The same term may be applied to other
instruments.

It is often defined as the resistance of a circuit through which one
Daniell's element will produce a deflection of one degree on the scale
of the instrument. The circuit includes a Daniell's cell of resistance
r, a rheostat R, galvanometer G and shunt S. Assume that with the shunt
in parallel a deflection of a divisions is obtained. The resistance of
the shunted galvanometer is (GS/G+S ; the multiplying power m of the
shunt is S+G/S; the formula or figure of merit is m d (r+R +G S/G+S).

The figure of merit is larger as the instrument is more sensitive.
Synonym--Formula of Merit.

257 STANDARD ELECTRICAL DICTIONARY.

Filament.
A thin long piece of a solid substance. In general it is so thin as to
act almost like a thread, to be capable of standing considerable
flexure. The distinction between filament and rod has been of much
importance in some patent cases concerning incandescent lamps. As used
by electricians the term generally applies to the carbon filament of
incandescent lamps. This as now made has not necessarily any fibres, but
is entitled to the name of filament, partly by convention, partly by its
relative thinness and want of stiffness. (See Incandescent
Lamps--Magnetic Filament.)

Fire Alarm, Electric, Automatic.
A system of telegraph circuits, at intervals supplied with thermostats
or other apparatus affected by a change of temperature, which on being
heated closes the circuit and causes a bell to ring. (See Thermostat.)

Fire Alarm Telegraph System.
A system of telegraphic lines for communicating the approximate location
of a fire to a central station and thence to the separate fire-engine
houses in a city or district. It includes alarm boxes, distributed at
frequent intervals, locked, with the place where the key is kept
designated, or in some systems left unlocked. On opening the door of the
box and pulling the handle or otherwise operating the alarm, a
designated signal is sent to the central station. From this it is
telegraphed by apparatus worked by the central station operator to the
engine houses. The engines respond according to the discipline of the
service.

Fire Cleansing.
Freeing the surface of an article to be plated from grease by heating.

Fire Extinguisher, Electric, Automatic.
A modification of the electric fire alarm (see Fire Alarm, Electric,
Automatic), in which the thermostats completing the circuits turn on
water which, escaping through the building, is supposed to reach and
extinguish a fire.

Flashing in a Dynamo or Magneto-electric Generator.
Bad adjustment of the brushes at the commutator, or other fault of
construction causes the production of voltaic arcs at the commutator of
a generator, to which the term flashing is applied.

Flashing of Incandescent Lamp Carbons.
A process of treatment for the filaments of incandescent lamps. The
chamber before sealing up is filled with a hydro-carbon vapor or gas,
such as the vapor of a very light naphtha (rhigolene). A current is then
passed through the filament heating it to redness. The more attenuated
parts or those of highest resistance are heated the highest, and
decompose most rapidly the hydro-carbon vapor, graphitic carbon being
deposited upon these parts, while hydrogen is set free. This goes on
until the filament is of uniform resistance throughout. It gives also a
way of making the resistance of the filament equal to any desired number
of ohms, provided it is originally of high enough resistance. The
process increases the conductivity of the filament.

After flashing the chambers are pumped out and sealed up.

258 STANDARD ELECTRICAL DICTIONARY.

Flashing Over.
A phenomenon observed in high potential dynamos. On a sudden alteration
of the resistance of the circuit a long blue spark will be drawn out
around the surface of the commutator from brush to brush. The spark is
somewhat of the nature of an arc, and may seriously injure commutators
whose sections are only separated by mica, or other thin insulation. In
the case of commutators whose sections are separated by air spaces it is
not so injurious.

Flats.
In a commutator of a dynamo, the burning or wearing away of a commutator
segment to a lower level than the rest. Sometimes two adjacent bars will
be thus affected, causing a flat place on the commutator. It is not
always easy to account for the formation of flats. They may have their
origin in periodic vibrations due to bad mounting, or to sparking at the
particular point.

Floor Push.
A press or push button constructed to be set into the floor to be
operated by pressing with the foot. It is used to ring an alarm bell,
sound a buzzer or for similar service.

Fluid, Depolarizing.
A fluid used in voltaic batteries to dispose of the hydrogen, which goes
to the negative plate. This it does by oxidizing it. Chromic acid,
nitric acid, and chloric acids are among the constituents of liquid
depolarizers. (See Electropoion Fluid.)

Fluid, Electric.
The electric current and charge have sometimes been attributed to a
fluid. The theory, which never was much more than hypothetical, survives
to some extent in the single and double fluid theory. (See Single Fluid
Theory-Double Fluid Theory.)

Fluorescence.
The property of converting ether waves of one length, sometimes of
invisible length, into waves of another length (visible). AEsculin,
quinine salts, uranium glass and other substances exhibit this
phenomenon. The phenomenon is utilized in the production of Geissler
tubes.

Flush Boxes.
A heavy iron box covered with a heavy hand plate and laid flush (whence
the name), or even with the surface of a roadway. Into it conductors of
an underground system lead, and it is used to make connections therewith
and for examining the leakage of the conductors and for similar
purposes. It is a "man-hole" (q. v.) in miniature.

Fluviograph.
An electric registering tide gauge or water level gauge.

259 STANDARD ELECTRICAL DICTIONARY.

Fly or Flyer, Electric.
A little wheel, ordinarily poised on a point, like a compass needle. It
carries several tangentially directed points, all pointing in the same
sense. When connected with a source of electricity of high potential it
revolves by reaction. The tension of its charge is highest at the
points, the air there is highly electrified and repelled, the reaction
pushing the wheel around like a Barker's mill or Hero's steam engine.
Sometimes the flyer is mounted with its axis horizontal and across the
rails on a railroad along which it travels.

Synonym--Reaction Wheel.

Foci Magnetic.
The two points on the earth's surface where the magnetic intensity is
greatest. They nearly coincide in position with the magnetic poles.

Fog, Electric.
Fogs occurring when the atmosphere is at unusually high potential and
accompanied by frequent change of such polarity.

Following Horns.
In dynamo-electric machines the projecting ends of the pole pieces
towards which the outer uncovered perimeter of the armature turns in its
regular operations. The leading horns are those away from which the
armature rotates. In considering rotation the exposed portion of the
superficies of the armature is considered. The definition would have to
be reversed if the part facing the pole pieces were considered.

Synonym--Trailing Horns.

Foot-candle.
A unit of illuminating power; the light given by one standard candle at
a distance of one foot. The ordinary units of illuminating power are
entirely relative; this is definite. It is due to Carl Herring.

Foot-pound.
A practical unit of work or energy. The quantity of work required to
raise a pound one foot, or one hundred pounds one-hundredth of a foot,
and so on; or the potential energy represented by a weight at an
elevation under these conditions.

Foot-step.
In a dynamo with armature at the lower end of its field magnets, the
plate generally of zinc, interposed between it and the iron base plate
to prevent the leakage of lines of force outside of the circuit. Any
diamagnetic material which is mechanically suitable may be used.

Force.
Force may be variously defined.
(a) Any cause of change of the condition of matter with respect to
motion or rest.

(b) A measurable action upon a body under which the state of rest of
that body, or its state of uniform motion in a straight line, suffers
change.

(c) It may be defined by its measurement as the rate of change of
momentum, or

(d) as the rate at which work is done per unit of space traversed.

Force is measured by the acceleration or change of motion it can impart
to a body of unit mass in a unit of time, or, calling
force, F,
mass, m
acceleration per second a
we have F = m a.

The dimensions of force are
mass (M) * acceleration (L/(T^2)) = (M*L)/(T^2).

260 STANDARD ELECTRICAL DICTIONARY.

Force de Cheval. Horse power (French).
It is the French or metric horse power.
It is equal to:
542.496 Foot lbs. per second.
.9864 English Horse Power.
75.0 Kilogram-meters per second.

Force, Electro-magnetic.
The mechanical force of attraction or repulsion acting on the
electro-magnetic unit of quantity. Its intensity varies with the square
of the distance. It may also be defined as electric force in the
electro-magnetic system.

Its dimensions are equal to
mechanical force ((M*L)/(T^2)) divided by quantity ((M^.5)*(L^.5))
= ((M^.5)*(L^.5))/(T^2).

Force, Electrostatic.
The force by which electric matter or electrified surfaces attract or
repel each other. It is also termed electric force (not good) and
electro-motive intensity. It is the mechanical force acting upon a unit
quantity of electricity. Its intensity varies with the square of the
distance.

Its dimensions are therefore equal to
(quantity * unity / (square of distance) Q. * 1 / (L^2)
= ((M^.5) * (L^1.5) )/ T*1 / (L^2)
= ((M^.5) * (L^.5)) / T
These dimensions are also those of potential difference.

The objection to the term electric force is that it may be applied also
to electro-magnetic force, and hence be a source of confusion.

Forces, Parallelogram of.
The usual method of composing forces or resolving a force. The sides of
a parallelogram of forces represent component forces and the diagonal
represents the resultant. See Component--Resultant--Forces, Composition
of--Forces, Resolution of.

Forces, Composition of.
When several forces act in a different direction upon a point they may
be drawn or graphically represented as arrows or lines emanating from
the point in the proper direction and of lengths proportional to the
force they exercise. Any two can be treated as contiguous sides of a
parallelogram and the parallelogram can be completed. Then its diagonal,
called the resultant, will represent the combined action of the two
forces, both as regards direction and intensity. This is the composition
of two forces.

If more than two forces act upon the given point the resultant can be
composed with any of the others and a new force developed. The new
resultant can be combined with another force, and the process kept up,
eliminating the components one by one until a final resultant of all is
obtained. This will give the exact direction and intensity of the
forces, however many or varied.

261 STANDARD ELECTRICAL DICTIONARY.

Forces, Resolution of.
The developing from a single force treated as a resultant, two other
forces in any desired direction. The reverse of composition of forces.
(See Forces, Composition of--Forces, Parallelogram
of--Components--Resultant.)

Force, Tubes of.
Aggregations of lines of force, either electrostatic or magnetic. They
generally have a truncated, conical or pyramidal shape and are not
hollow. Every cross-section contains the same number of lines. The name
it will seem is not very expressive.

Force, Unit of.
The fundamental or C. G. S. unit or force is the dyne, q. v.

The British unit of force is the poundal (the force which will produce
an acceleration of one foot per second in a mass of one pound). It is
equal to about 10/322 pound. A force cannot be expressed accurately in
weight units, because weight varies with the latitude.

Forming.
The process of producing secondary battery plates from lead plates by
alternately passing a charging current through the cell and then
allowing it to discharge itself and repeating the operation. (See
Battery, Secondary, Planté's.)

Foundation Ring.
In a dynamo armature the ring-shaped core on which Gramme ring armatures
and other ring armatures are wound.

Fourth State of Matter.
Gas so rarefied that its molecules do not collide, or rarely do so;
radiant matter, q. v.

Frame.
In a dynamo the bed-piece is sometimes called the frame.

Franklin's Experiment.
Franklin proved the identity of lightning and electricity by flying a
kite in a thunder storm. The kite was of silk so as to endure the
wetting. When the string became wet sparks could be taken from a key
attached to its end. The main string was of hemp; at the lower end was a
length of silk to insulate it. The key was attached near the end of and
to the hemp string.

Franklin's Plate.
A simple form of condenser. It consists of a plate of glass coated on
each side with tinfoil with a margin of about an inch of clear glass.
One coating may be grounded as indicated in the cut, and the plate
charged like a Leyden jar. Or one side may be connected with one
terminal, and the other with the other terminal of an influence machine
and the pane will be thus charged.

Synonym--Fulminating Pane.

262 STANDARD ELECTRICAL DICTIONARY.

Fig. 174. FRANKLIN'S PLATE.

Franklin's Theory.
The single fluid theory, q. v., of electricity.

Frequency.
The number of double reversals or complete alternations per second in an
alternating current.

Synonym--Periodicity.

Frictional Electricity.
Electricity produced by friction of dissimilar substances. (See
Electrostatic Series.) The contact theory holds that friction plays only
a secondary rôle in this process; that it increases the thoroughness of
contact, and tends to dry the rubbing surfaces, but that the charges
induced are due to contact of dissimilar substances, not to friction of
one against the other.

Frictional Heating.
The heating of a conductor by the passage of a current; the Joule
effect, q. v.

Fringe.
The outlying edge of a magnetic field.

Frog, Galvani's Experiment With.
A classic experiment in electricity, leading to the discovery of current
or dynamic electricity. If a pair of legs of a recently killed frog are
prepared with the lumbar nerves exposed near the base of the spinal
column, and if a metallic conductor, one half-length zinc and the other
half-length copper, is held, one end between the lumbar nerves and the
spine, and the other end against one of the muscles of the thigh or
lower legs, the moment contact occurs and the circuit is completed
through the animal substance the muscles contract and the leg is
violently drawn upwards. Galvani, in 1786, first performed, by accident,
this famous experiment, it is said, with a scalpel with which he was
dissecting the animal. He gave his attention to the nerves and muscles.
Volta, more happily, gave his attention to the metals and invented the
voltaic battery, described by him in a letter to Sir Joseph Banks, dated
1800.

Frog, Rheoscopic.
If the nerve or living muscle of a frog is suddenly dropped upon another
living muscle so as to come in contact with its longitudinal and
transverse sections, the first muscle will contract on account of the
stimulation of its nerve due to the passage of a current derived from
the second muscle (Ganot). The experiment goes under the above title.

263 STANDARD ELECTRICAL DICTIONARY.

Frying.
A term applied to a noise sometimes produced in a voltaic arc due to too
close approach of the carbons to each other. It has been suggested that
it may be due to volatilization of the carbon. (Elihu Thomson.)

Fulgurite.
An irregular and tubular mass of vitrified quartz, believed to be formed
by melting under the lightning stroke.

Fig. 175. CRUCIBLE, ELECTRIC.

Furnace, Electric.
A furnace in which the heat is produced by the electric current. It has
hitherto been practically used only in the extraction of aluminum and
silicium from their ores. The general principle involves the formation
of an arc between carbon electrodes. The substances to be treated are
exposed to the heat thus produced. Sometimes the substances in the arc
form imperfect conductors, and incandescence takes a part in the action.
Sometimes the substances are merely dropped through the arc.

Fuse Board.
A tablet on which a number of safety fuses are mounted. Slate is
excellent material for the tablet, as it is incombustible, and is easily
drilled and worked.

Fuse Box.
A box containing a safety fuse. Porcelain is an excellent material for
its base. No combustible material should enter into its composition.

Fuse, Cockburn.
A safety fuse or cut off which consists of a wire of pure tin running
from terminal to terminal, to whose centre a leaden ball is secured by
being cast into position. The connection with the terminals is made by
rings at the ends of the wire through which the terminal screws are
passed and screwed home. When the tin softens under too heavy a current
the weight of the shot pulls it apart.

Fig. 176 COCKBURN SAFETY FUSE.

264 STANDARD ELECTRICAL DICTIONARY.

Fig. 177. ELECTRIC FUSE.

Fuse, Electric.
A fuse for igniting an explosive by electricity. There are two kinds. In
one a thin wire unites the ends of the two conducting wires as they
enter the case of the fuse. The larger wires are secured to the case, so
that no strain comes on the fine wire. On passing a current of
sufficient strength the small wire is heated. In use the fuse is bedded
in powder, which again may be surrounded by fulminating powder, all
contained in a copper or other metallic case. Such a detonator is used
for exploding guncotton and other high explosives.

The other kind of fuse is similar, but has no thin connecting wire. The
ends of the conductors are brought nearer together without touching. In
use a static discharge is produced across from end to end of the
conductors, igniting a proper explosive placed there as in the other
case.

The first kind of fuse is generally operated by a battery or small
mechanical generator--the latter by a spark coil, frictional or
influence machine or by a Leyden jar.

264 STANDARD ELECTRICAL DICTIONARY.

Galvanic. adj.
Voltaic; relating to current electricity or the electrolytic and
electro-chemical relations of metals. (For titles in general under this
head see Voltaic--or the main title.)

Galvanic Element.
A galvanic couple with exciting fluid and adjuncts; a galvanic cell. The
word element is sometimes applied to the electrodes of a cell, as the
carbon element or zinc element.

265 STANDARD ELECTRICAL DICTIONARY.

Galvanic Polarization.
The polarization of a voltaic couple. (See Polarization.)

Galvanism.
The science of voltaic or current electricity.

Galvanization.
(a) Electroplating or depositing a metal over the surface of another by
electrolysis.

(b) In medical electricity the effects produced on any part of the
system by the current of voltaic battery. Various descriptive
qualifications are prefixed, such as "general" galvanization, indicating
its application as applied to the whole body, "local" for the reverse
case, and so on.

Galvanization, Labile.
Application of the galvanic current in electro-therapeutics where one
sponge electrode is employed which is rubbed or moved over the body, the
other being in constant contact with the body.

Galvanized Iron.
Iron coated with zinc by cleaning and immersion in melted zinc. The iron
is prevented from rusting by galvanic action. It forms the negative
element in a couple of which the zinc is the positive element. From this
electric protective action the name is derived.

Galvano-cautery, Chemical.
Electro-therapeutic treatment with sharp electrodes, one of which is
inserted in the tissue and a current passed by completing the circuit
through the tissue so as to electrolyze or decompose the fluids of the
tissue. It is applied in the removal of hair or extirpation of the
follicle. The process is not one of heating, and is improperly named
cautery.

Galvano-faradization.
In medical electricity the application of the voltaic and induced or
secondary current simultaneously to any part of the system.

Galvanometer.
An instrument for measuring current strength and sometimes for measuring
inferentially potential difference, depending on the action of a
magnetic field established by the current, such action being exerted on
a magnetic needle or its equivalent.

A current passing through a conductor establishes circular lines of
force. A magnetic needle placed in their field is acted on and tends to
place itself parallel with the lines, in accordance with the principles
of current induction. (See Induction, Electro-magnetic.) A common
compass held near a conductor through which a current is passing tends
to place itself at right angles to such conductor. For a maximum effect
the conductor or the part nearest the needle should lie in the magnetic
meridian. If at right angles thereto its action will only strengthen the
directive force of the earth's induction or magnetic field, as the
needle naturally points north and south. Such combination is virtually a
galvanometer.

266 STANDARD ELECTRICAL DICTIONARY.

A typical galvanometer comprises a flat coil of wire placed horizontally
within which a magnetic needle is delicately poised, so as to be free to
rotate with the least possible friction. The needle may be supported on
a sharp point like a compass needle, or may be suspended by a long fine
filament. It should be covered by a glass plate and box, or by a glass
shade. Finally a graduated disc may be arranged to show the amount of
deflection of the needle.

In use the apparatus is turned about until the needle, as acted on by
the earth's magnetic field, lies parallel to the direction of the coils
of wire. On passing a current through the coil the needle is deflected,
more or less, according to its strength.

By using exceedingly fine wire, long enough to give high resistance, the
instrument can be used for very high potentials, or is in condition for
use in determining voltage. By using a coil of large wire and low
resistance it can be employed in determining amperage. In either case
the deflection is produced by the current.

The needle is often placed above or below the coil so as only to receive
a portion of its effect, enough for all practical purposes in the
commoner class of instruments.

The galvanometer was invented by Schweigger a short time after Oersted's
discovery, q. v.

Galvanometer, Absolute.
A galvanometer giving absolute readings; properly one whose law of
calibration can be deduced from its construction. Thus the diameter of
the coil, and the constants and position of a magnetic needle suspended
in its field being known, the current intensity required to deflect the
needle a given number of degrees could be calculated.

Galvanometer, Aperiodic.
A galvanometer whose needle is damped (see Damping) as, for instance, by
the proximity of a plate of metal, by an air vane or otherwise, so that
it reaches its reading with hardly any oscillation. A very light needle
and a strong magnetic field also conduce to vibrations of short period
dying out very quickly. Such galvanometers are termed "dead-beat." No
instrument is absolutely dead-beat, only relatively so.

267 STANDARD ELECTRICAL DICTIONARY.

Fig. 178. ASTATIC GALVANOMETER.

Galvanometer, Astatic.
A galvanometer with a pair of magnetic needles connected astatically, or
parallel with their poles in opposition. (See Astatic Needle.) Each
needle has its own coil, the coils being wound in opposite directions so
as to unite in producing deflections in the same sense. As there should
be some directive tendency this is obtained by one of the magnets being
slightly stronger than the other or by the proximity of a fixed and
adjustable controlling magnet, placed nearer one needle than the other.

For small deflections the currents producing them are proportional to
their extent.

Galvanometer, Ballistic.
A galvanometer whose deflected element has considerable moment of
inertia; the exact opposite of an aperiodic or dead beat galvanometer.
(See Galvanometer, Aperiodic.) All damping by air vanes or otherwise
must be carefully done away with.

Fig. 179. SIEMENS & HALSKE'S GALVANOMETER.

Siemens & Halske's galvanometer is of the reflecting or mirror type (see
Galvanometer, Reflecting) with suspended, bell-shaped magnet, in place
of the ordinary magnetic needle, or astatic combination of the lightest
possible weight in the regular instrument. A copper ball drilled out to
admit the magnet is used as damper in the ordinary use of the
instrument. To convert it into a ballistic galvanometer the copper ball
is removed. The heavy suspended magnet then by its inertia introduces
the desired element into the instrument.

268 STANDARD ELECTRICAL DICTIONARY.

Referring to the cut, Fig. 179, M is the suspended magnet, with north
and south poles n and s; S is the reflecting mirror; r is the tube
containing the suspending thread; R is the damper removed for ballistic
work.

The ballistic galvanometer is used to measure quantities of electricity
in an instantaneous discharge, which discharge should be completed
before the heavy needle begins to move. The extreme elongation or throw
of the needle is observed, and depends (1) on the number of coulombs (K)
that pass during the discharge; (2) on the moment of inertia of the
needle and attached parts; (3) on the moment of the controlling forces,
i. e., the forces tending to pull the needle back to zero; (4) on the
moment of the damping forces; (5) on the moment of the deflecting forces
due to a given constant current. The formula is thus expressed:

K = (P / PI ) * A * sin( kº / 2 ) / tan( aº )

in which K = coulombs discharged; P = periodic time of vibration of
needle; A = amperes producing a steady deflection equal to aº ; kº =
first angular deflection of needle. For accuracy kº and aº should both
be small and the damping so slight as to be negligible. Otherwise a
correction for the latter must be applied. For approximate work for kº
and aº the deflections read on the scale may be used with the following
formula:

K = (P / PI ) * ( A / 2 ) * ( kº / aº )

Galvanometer Constant.
Assume a galvanometer with a very short needle and so placed with
respect to its coils that the magnetic field produced by a current
circulating in them is sensibly uniform in the neighborhood of the
needle, with its lines of force at right angles thereto. The field is
proportional to the current i, so that it may be denoted by G i. Then G
is the galvanometer constant. If now the angle of deflection of the
needle is ? against the earth's field H, M being the magnetic moment of
the needle we have G i M cos ? = H M sin ? or i = (H/G)* tan ?. H/G is
the reduction factor; variable as H varies for different places.

For a tangent galvanometer the constant G is equal to 2*PI*(n/a), in
which n denotes the number of turns of wire, and a denotes the radius of
the circle.

Galvanometer, Differential.
A galvanometer in which the needle is acted on by two coils wound in
opposition, each of equal deflecting action and of equal resistance. If
a current is divided between two branches or parallel conductors, each
including one of the coils, when the needle points to zero the
resistances of the two branches will bc equal. In the cut, C C'
represent the coils, and A and B the two leads into which the circuit, P
Q, is divided.

269 STANDARD ELECTRICAL DICTIONARY.

Fig. 180. THEORY OF DIFFERENTIAL GALVANOMETER.

Fig. 181. DIFFERENTIAL GALVANOMETER.

Galvanometer, Direct Reading.
A calibrated galvanometer, whose scale is graduated by volts or amperes,
instead of degrees.

Galvanometer, Marine. (Sir William Thomson's.)
A galvanometer of the reflecting type, for use on shipboard. A fibre
suspension is adopted for the needle. The fibre is attached to a fixed
support at one end and to a spring at the other, and the needle is
suspended by its centre of gravity. This secures it to a considerable
extent from disturbance due to the rolling of the ship. A thick iron box
encloses the needle, etc., to cut off any magnetic action from the ship.
(See Galvanometer, Reflecting.)

Galvanometer, Potential.
A galvanometer wound with fine German silver wire to secure high
resistance used for determination of potential difference.

Galvanometer, Proportional.
A galvanometer so constructed that the deflections of its index are
proportional to the current passing. It is made by causing the
deflecting force to increase as the needle is deflected, more and more,
or by causing the restitutive force to diminish under like conditions,
or by both. The condition is obtained in some cases by the shape and
position of the deflecting coils.

Galvanometer, Quantity.
A galvanometer for determining quantities of electricity, by the
deflections produced by discharging the quantities through their coils.
It is a ballistic galvanometer with very little or no damping.

270 STANDARD ELECTRICAL DICTIONARY.

Fig. 182. PRINCIPLE OF REFLECTING GALVANOMETER.

Fig. 183. REFLECTING GALVANOMETER.

Galvanometer, Reflecting.
A galvanometer the deflections of whose needle are read by an image
projected by light reflected from a mirror attached to the needle or to
a vertical wire carrying the needle. A lamp is placed in front of the
instrument facing the mirror. The light of the lamp is reflected by the
mirror upon a horizontal scale above the lamp. An image of a slit or of
a wire may be caused thus to fall upon the scale, the mirror being
slightly convex, or a lens being used to produce the projection.

271 STANDARD ELECTRICAL DICTIONARY.

If the mirror swings through a horizontal arc, the reflected image will
move, in virtue of a simple geometrical principle, through an arc of
twice as many degrees. The scale can be placed far from the mirror, so
that the ray of light will represent a weightless index of very great
length, and minute deflections of the needle will be shown distinctly
upon the scale.

In the cut, Fig. 182, the ray of light from the lamp passes through the
aperture, m m, and is made parallel by the lens, L. At s is the mirror
attached to the needle and moving with it. A scale placed at t receives
the reflection from the mirror. The cut, Fig. 183, shows one form of the
instrument set up for use.

Synonym--Mirror Galvanometer.