The Standard Electrical Dictionary (part 3)

Galvanometer Shunt.
To prevent too much current passing through a galvanometer (for fear of
injury to its insulation) a shunt is sometimes placed in parallel with
it. The total current will be distributed between galvanometer and shunt
in the inverse ratio of their respective resistances. (See Multiplying
Power of a Shunt.)

272 STANDARD ELECTRICAL DICTIONARY.

Fig. 184. SINE GALVANOMETER.

Galvanometer, Sine.
A galvanometer whose measurements depend upon the sine of the angle of
deflection produced when the coil and needle lie in the same vertical
plane.

The needle, which may be a long one, is surrounded by a coil, which can
be rotated about a vertical axis passing through the point of suspension
of the needle. Starting with the needle at rest in the plane of the
coil, a current is passed through the coil deflecting the needle, the
coil is swung around deflecting the needle still more, until the needle
lies in the plane of the coil; the intensity of the current will then be
in proportion to the sine of the angle through which the coil and needle
move.

In the galvanometer M is a circle carrying the coil, N is a scale over
which the needles, m and n, move, the former being a magnetic needle,
the latter an index at right angles and attached thereto; a and b are
wires carrying the current to be measured. The circles, M and N, are
carried by a base, O, around which they rotate. H is a fixed horizontal
graduated circle. In use the circle, M, is placed in the magnetic
meridian, the current is passed through the coil, M; the needle is
deflected; M is turned until its plane coincides with the direction of
the needle, m. The current strength is proportional to the sine of the
angle of deflection. This angle is measured by the vernier, C, on the
circle, H. The knob, A, is used to turn the circle, M.

273 STANDARD ELECTRICAL DICTIONARY.

Fig. 185. TANGENT GALVANOMETER.

Galvanometer, Tangent.
A galvanometer in which the tangents of the angles of deflection are
proportional to the currents producing such deflections.

For this law to apply the instrument in general must fulfill the
following conditions:

(1) The needle must be controlled by a uniform magnetic field such as
that of the earth;

(2) the diameter of the coil must be large compared to the length of the
needle;

(3) the centre of suspension of the needle must be at the centre of the
coil;

(4) the magnetic axis of the needle must lie in the plane of the coil
when no current is passing.

If a single current strength is to be measured the best results will be
attained when the deflection is 45°; in comparing two currents the best
results will be attained when the deflections as nearly as possible are
at equal distances on both sides of 45°.

The needle should not exceed in length one-tenth the diameter of the
coil.

For very small deflections any galvanometer follows the law of
tangential deflection.

As for very small deflections the tangents are practically equal to the
arcs subtended, for such deflections the currents are proportional to
the deflections they produce.

The sensibility is directly proportional to the number of convolutions
of wire and inversely proportional to their diameter.

The tangent law is most accurately fulfilled when the depth of the coil
in the radial direction is to the breadth in the axial direction as
squareRoot(3):squareRoot(2), or about as 11:9.

Galvanometer, Torsion.
A galvanometer whose needle is suspended by a long filament or by a
thread and spiral spring against whose force of torsion the movements of
the needle are produced. The current strength is determined by bringing
the needle back to its position of rest by turning a hand-button or
other arrangement. The angle through which this is turned gives the
angle of torsion. From this the current strength is calculated on the
general basis that it is proportional to the angle of torsion.

Fig. 186. TORSION GALVANOMETER.

274 STANDARD ELECTRICAL DICTIONARY.

Galvanometer, Vertical.
A galvanometer whose needle is mounted on a horizontal axis and is
deflected in a vertical plane. One of the poles is weighted to keep it
normally vertical, representing the control. It is not used for accurate
work.

Synonym--Upright Galvanometer.

Fig. 187. VERTICAL GALVANOMETER.

Galvanometer, Volt- and Ampere-meter.
A galvanometer of Sir William Thomson's invention embodying the tangent
principle, and having its sensibility adjustable by moving the magnetic
needle horizontally along a scale (the "meter") towards or away from the
coil. A curved magnet is used to adjust the control. The leads are
twisted to prevent induction.

The instrument is made with a high resistance coil for voltage
determinations, and with a low resistance coil for amperage
determinations.

At one end of a long base board a vertical coil with its plane at right
angles to the axis of the board is mounted. A scale (the "meter" of the
name) runs down the centre of the board. A groove also runs down the
centre. The magnetic needle is contained in a quadrant-shaped
glass-covered box which slides up and down the groove. A number of short
parallel needles mounted together, with an aluminum pointer are used.

Fig. 188. SIR WILLIAM THOMSON'S
AMPERE-METER GALVANOMETER.

275 STANDARD ELECTRICAL DICTIONARY.

In the cut P is the base board, M is a glass covered case containing the
magnetic needle, and sliding along the base board, being guided by the
central groove, C, is the coil. Between the coil and the needle is the
arched or bent controlling magnet. The long twisted connecting wires are
seen on the right hand.

Galvano-plastics.
The deposition of metals by electrolysis, a disused term replaced
by electro-deposition, electroplating, and electro-metallurgy.

Galvano-puncture.
An operation in medical electricity. (See Electro-puncture.)

Galvanoscope.
An instrument, generally of the galvanometer type, used for ascertaining
whether a current is flowing or not. Any galvanoscope, when calibrated,
if susceptible thereof, becomes a galvanometer.

Gas, Electrolytic.
Gas produced by the decomposition, generally of water, by electrolysis.
It may be hydrogen or oxygen, or a mixture of the two, according to how
it is collected. (See Gases, Mixed.)

Gases, Mixed.
The mixture of approximately one volume of oxygen and two volumes of
hydrogen collected in the eudiometer of a gas voltameter or other
electrolytic apparatus.

Gassing.
The evolution of gas from the plates of a storage battery in the
charging process, due to too high voltage in the circuit of the charging
dynamo.

Gastroscope.
An apparatus for illuminating by an incandescent lamp the interior of
the stomach, and with prisms to refract the rays of light so that the
part can be seen. The stomach is inflated with air, if desirable, to
give a better view. An incandescent platinum spiral in a water jacket
has been employed for the illumination.

Gassiot's Cascade.
A goblet lined for half its interior surface with tinfoil. It is placed
in the receiver of an air pump from the top of whose bell a conductor
descends into it, not touching the foil. On producing a good
rarefaction, and discharging high tension electricity from between the
conductor just mentioned and the metal of the machine, a luminous effect
is produced, as if the electricity, pale blue in color, was overflowing
the goblet.

Gauss.
A name suggested for unit intensity of magnetic field. Sylvanus P.
Thomson proposed for its value the intensity of a field of 1E8 C. G. S.
electro-magnetic units. J. A. Fleming proposed the strength of field
which would develop one volt potential difference in a wire 1E6
centimeters long, moving through such field with a velocity of one
centimeter per second. This is one hundred times greater than Thomson's
standard. Sir William Thomson suggested the intensity of field produced
by a current of one ampere at a distance of one centimeter

The gauss is not used to any extent; practical calculations are based on
electro-magnetic lines of force.

276 STANDARD ELECTRICAL DICTIONARY.

Gauss' Principle.
An electric circuit acts upon a magnetic pole in such a way as to make
the number of lines of force that pass through the circuit a maximum.

Fig. 189. GAUSS' TANGENT POSITION.

Gauss, Tangent Positions of.
The "end on" and "broadside" methods of determining magnetization
involve positions which have been thus termed. (See Broadside Method and
End on Method.)

Gear, Magnetic Friction.
Friction gear in which the component wheels are pressed against each
other by electromagnetic action. In the cut, repeated from Adherence,
Electro-magnetic, the magnetizing coil makes the wheels, which are of
iron, press strongly together.

Fig. 190. MAGNETIC FRICTION GEAR.

277 STANDARD ELECTRICAL DICTIONARY.

Geissler Tubes.
Sealed tubes of glass containing highly rarefied gases, and provided
with platinum electrodes extending through the glass tightly sealed as
they pass through it, and often extending a short distance beyond its
interior surface.

On passing through them the static discharge luminous effects are
produced varying with the degree of exhaustion, the contents (gas), the
glass itself, or solutions surrounding it. The two latter conditions
involve fluorescence phenomena often of a very beautiful description.

The pressure of the gas is less than one-half of a millimeter of
mercury. If a complete vacuum is produced the discharge will not pass.
If too high rarefaction is produced radiant matter phenomena (see
Radiant State) occur.

Geissler tubes have been used for lighting purposes as in mines, or for
illuminating the interior cavities of the body in surgical or medical
operations.

Generating Plate.
The positive plate in a voltaic couple, or the plate which is dissolved;
generally a plate of zinc.

Synonyms--Positive Plate--Positive Element.

Generator, Current.
Any apparatus for maintaining an electric current. It may be as regards
the form of energy it converts into electrical energy, mechanical, as a
magneto or dynamo electric machine or generator; thermal, as a
thermo-electric battery; or chemical, as a voltaic battery; all of which
may be consulted.

Generator, Secondary.
A secondary or storage battery. (See Battery, Secondary.)

German Silver.
An alloy of copper, 2 parts, nickel, 1 part, and zinc, 1 part. Owing to
its high resistance and moderate cost and small variation in resistance
with change of temperature, it is much used for resistances. From Dr.
Mathiessen's experiment the following constants are deduced in legal
ohms:
Relative Resistance (Silver = 1), 13.92
Specific Resistance at 0° C. (32F.), 20.93 microhms.
Resistance of a wire,
(a) 1 foot long, weighing 1 grain, 2.622 ohms.
1 foot long, 1/1000 inch thick, 125.91 "
1 meter long, weighing 1 gram, 1.830 "
1 meter long, 1 millimeter thick, 0.2666 "
Resistance of a 1 inch cube at 0°C. (32° F.), 8.240 microhms.

Approximate percentage increase of resistance per 1° C. (1.8° F.) at
about 20° C. (68° F.), 0.044 per cent.

Gilding, Electro-.
The deposition of gold by an electric current, or electrolytically in
the electroplating bath.

Gilding Metal.
A special kind of brass, with a high percentage of copper, used to make
objects which are to be gilded by electrolysis.

278 STANDARD ELECTRICAL DICTIONARY.

Gimbals.
A suspension used for ships' compasses and sometimes for other
apparatus. It consists of a ring held by two journals, so as to bc free
to swing in one plane. The compass is swung upon this ring, being placed
concentrically therewith. Its journals are at right angles to those of
the ring. This gives a universal joint by which the compass, weighted
below its line of support, is always kept horizontal.

Fig. 191. COMPASS SUSPENDED IN GIMBALS.

Glass.
A fused mixture of silicates of various oxides. It is of extremely
varied composition and its electric constants vary greatly. Many
determinations of its specific resistance have been made. For flint
glass at 100° C. (212° F.) about (2.06E14) ohms --at 60° C (140° F.)
(1.020E15) (Thomas Gray) is given, while another observer (Beetz) gives
for glass at ordinary temperatures an immeasurably high resistance. It
is therefore a non-conductor of very high order if dry. As a dielectric
the specific inductive capacity of different samples of flint glass is
given as 6.57--6.85--7.4--10.1 (Hopkinson), thus exceeding all other
ordinary dielectrics. The densest glass, other things being equal, has
the highest specific inductive capacity.

Gold.
A metal, one of the elements; symbol Au. c .; atomic weight, 196.8;
equivalent, 65.6; valency, 3; specific gravity 19.5.
It is a conductor of electricity.

Annealed. Hard drawn.
Relative Resistance (Annealed Silver = 1), 1.369 1.393
Specific Resistance, 2.058 2.094
Resistance of a wire at 0° C. (32°F.)
(a) 1 foot long, weighing 1 grain, 57.85 58.84 ohms
(b) 1 foot long, 1/1000 inch thick, 12.38 12.60 "
(c) 1 meter long, weighing 1 gram, .4035 .4104 "
(d) 1 meter long, 1 millimeter thick, .02620 .02668 "
Resistance of a 1 inch cube at 0° C.(32° F.) .8102 .8247

Approximate increase in resistance per 0° C., (1.8° F)
at about 20° C. (68° F.), 0.365 per cent.

Electro-chemical equivalent (Hydrogen = .0105), .6888

279 STANDARD ELECTRICAL DICTIONARY.

Gold Bath.
A solution of gold used for depositing the metal in the electroplating
process.

A great number of formulae have been devised, of which a few
representative ones are given here.
COLD BATHS. HOT BATHS.
Water, 10,000 10,000 10,000 10,000 5,000 3,000
Potassium Cyanide, 200 -- 200 10 -- 50
Gold, 100 15 100 10 10 10
Potassium Ferrocyanide, -- 200 -- -- 150 --
Potassium Carbonate, -- 150 -- -- 50 --
Ammonium Chloride, -- 30 -- -- 20 --
Aqua Ammoniae, -- -- 500 -- -- --
Sodium Phosphate, -- -- -- 600 -- --
Sodium Bisulphite, -- -- -- 100 -- --

(Roseleur.)

In the baths the gold is added in the form of neutral chloride, Auric
chloride (Au Cl6).

Gold Stripping Bath.
A bath for removing gold from plated articles without dissolving the
base in order to save the precious metal. A bath of 10 parts of
potassium cyanide and 100 parts of water may be used, the articles to be
stripped being immersed therein as the anode of an active circuit. If
the gilding is on a silver or copper basis, or on an alloy of these
metals the same solution attacks the base and dissolves it, which is
objectionable. For silver articles it is enough to heat to cherry red
and throw into dilute sulphuric acid. The gold scales off in metallic
spangles. For copper articles, a mixture of 10 volumes concentrated
sulphuric acid, 1 volume nitric acid, and 2 volumes hydrochloric acid
may be used by immersion only, or with a battery. The sulphuric acid in
such large excess is supposed to protect the copper. For copper articles
concentrated sulphuric acid alone with the battery may be used. This
does not sensibly attack the copper if it is not allowed to become
diluted. Even the dampness of the air may act to dilute it.

Graduator.
Apparatus for enabling the same line to be used for telegraph signals
and telephoning.

One type consists in coils with iron cores or simply electromagnets.
These act to retard the current in reaching its full power and also
prolong it. This gives a graduated effect to the signals, so that the
telephone diaphragm is not audibly affected by the impulses.

The telephoning current is so slight and so rapid in its characteristic
changes that it is without effect upon the ordinary telegraph.

280 STANDARD ELECTRICAL DICTIONARY.

Gram.
The unit of weight in the metric system; accepted as the unit of
mass in the absolute of C. G. S. system of units. It is the
one-thousandth part of mass of a standard weight preserved under proper
conditions in Paris, and supposed to be the mass of a cubic decimeter of
distilled water at the temperature of the maximum density of water. The
standard is the kilogram; the temperature is 3.9º C. (39º F.). The
standard kilogram is found to be not exactly the weight of a cubic
decimeter of water, the latter weighing 1.000013 kilogram.

If therefore the defined gram on the water basis is taken as the unit it
varies very slightly from the accepted gram.

1 gram is equal to 15.43234874 grains. (Prof. W. H. Miller.)

Gram-atom.
The number of grams of an element equal numerically to the atomic
weight, as 16 grams of oxygen, 1 gram of hydrogen, 35.5 grams of
chlorine; all which might be expressed as gram-atoms of oxygen, hydrogen
and chlorine respectively.

The gram-atom approximately expresses the number of gram-calories
required to heat one gram of the substance 1º C. (1.8º F.). This is in
virtue of Dulong and Petit's discovery that the atomic weight of an
element multiplied by its specific heat gives approximately a constant
for all elements.

Gram-molecule.
The number of grams of a substance equal numerically to its molecular
weight.

Graphite.
Carbon; one of three allotropic modifications of this element. It occurs
in nature as a mineral.

It is used as a lubricant for machinery; for commutator brushes; for
making surfaces to be plated conductive, and for mixing with manganese
binoxide in Leclanché cells.

Gravitation.
A natural force which causes all masses of matter to attract each other.
Its cause is unknown; it is often supposed to be due to the luminiferous
ether.

281 STANDARD ELECTRICAL DICTIONARY.

Gravity, Acceleration of.
The velocity imparted to a body in one second by the action of
gravitation at any standard point upon the earth's surface in a vacuum.
This will vary at different places, owing principally to the variation
in centrifugal force due to the earth's rotation. For standard valuation
it must be reduced to sea level. The following are examples of its
variation:

Equator, 978.1028 centimeters per second
Paris, 980.94 "
Greenwich 981.I7 "
Edinburgh, 981.54 "
Pole (N. or S.), 983.1084 (theoretical) "

As round numbers for approximate calculations 981 centimeters or 32.2
feet may be employed.

Gravity, Control.
Control by weight. In some ammeters and voltmeters gravity is the
controlling force.

Grid.
A lead plate perforated or ridged for use in a storage battery as the
supporter of the active materials and in part as contributing thereto
from its own substance.

Ground.
The contact of a conductor of an electric circuit with the earth,
permitting the escape of current if another ground exists.

Ground-wire.
A metaphorical term applied to the earth when used as a return circuit.

Fig. 192. GROVE'S GAS BATTERY.

Grove's Gas Battery.
A voltaic battery depending for its action on the oxidation of hydrogen
instead of the oxidation of zinc. Its action is more particularly
described under Battery, Gas. In the cut B, B1 * * * are the terminals
of the positive or hydrogen electrodes, marked H, and A, Al * * * are
the terminals of the negative or oxygen electrodes marked O, while M, M1
* * * is dilute sulphuric acid.

282 STANDARD ELECTRICAL DICTIONARY.

Guard Ring.
An annular horizontal surface surrounding the balanced disc in the
absolute electrometer. (See Electrometer, Absolute.)

Guard Tube.
A metal tube surrounding a dry pile used with a quadrant electrometer,
or other electrometers of that type. It prevents the capacity of the
lower brass end of the pile (which brass end closes the glass tube
containing the discs) from momentary change by approach of some
conductor connected to the earth. There are other guard tubes also.

Gun, Electro-magnetic.
An electro-magnet with tubular core. If, when it is excited a piece of
an iron rod is pushed into the central aperture of the core and is
released, the magnetic circle will try to complete itself by pushing the
rod out so that it can thus be discharged, as if from a popgun.

Synonym--Electric Popgun.

Fig. 193. "ELECTRIC POPGUN."

Gutta Percha.
The hardened milky juice of a tree, the Isonandra gutta, growing in
Malacca and other parts of the Eastern Archipelago. It is much used as
an insulator or constituent of insulators.

Resistance after several minutes electrification per 1 centimeter cube
at 54º C. (75º F.), 4.50E14 ohms.

The specific resistance varies--from 2.5E13 to 5.0E14 ohms. A usual
specification is 2.0E14 ohms. The influence of temperature on its
resistance is given in Clark & Bright's empirical formula, R = R0 at, in
which R is the resistance at temperature tº C--Ro the resistance at 0º C
(32º F), a is the coefficient .8944.

The resistance increases with the time of passage of the current, the
variation being less the higher the temperature.

283 STANDARD ELECTRICAL DICTIONARY.

Time of Relative Resistance Relative Resistance
Electrification. at 0º C (32º F.) at 24º C (75º F.)
1 minute 100 5.51
2 " 127.9 6.
5 " 163.1 6.66
10 " 190.9 6.94
20 " 230.8 7.38
30 " 250.6 7.44
60 " 290.4 7.6
90 " 318.3 7.66

In cable testing one minute is generally taken as the time of
electrification.

Pressure increases the resistance by the formula Rp=R (1+ .00327 P) in
which Rp is the resistance at pressure p--R resistance at atmospheric
pressure--p pressure in atmospheres. Thus in the ocean at a depth of
4,000 meters (2.4855 miles), the resistance is more than doubled. The
longer the pressure is applied, the greater is the resistance.

The specific inductive capacity of gutta percha is 4.2.

Good gutta percha should not break when struck with a hammer, should
recover its shape slowly, and it should support much more than 300 times
its own weight.

Gyrostatic Action of Armatures.
Owing to gyrostatic action a rotating armature resists any change of
direction of its axis. On ships and in railway motors which have to turn
curves this action occurs. A 148 lb. armature running at 1,300
revolutions per minute may press with 30 lbs. on each journal as the
ship rolls through an angle of 20° in 16 seconds.

283 STANDARD ELECTRICAL DICTIONARY.

H.
(a) The symbol for the horizontal component of the earth's
magnetization.

(b) The symbol for the intensity of a magnetizing force or field. The
symbol H, as it is generally used, may mean either the number of dynes
which act upon a unit pole, or the number of lines of force per
centimeter.

(c) The symbol for the unit of self-induction.

Hair, Removal of, by Electrolysis.
A method of depilation by destruction of individual hair follicles by
electrolysis.

A fine platinum electrode is thrust into a hair follicle. It is the
negative electrode. The positive electrode is in contact with the body
of the person under treatment; it is often a sponge electrode simply
held in his hand. A current of two to four milliamperes from an E. M. F.
of 15 to 20 volts, is passed. This destroys the follicle, the hair is
removed and never grows again. A gradual increase of current is advised
for the face. As only one hair is removed at once, but a small number
are taken out at a sitting.

284 STANDARD ELECTRICAL DICTIONARY.

Haldat's Figures.
With a pole of a strong bar magnet, used like a pencil, imaginary
figures are drawn upon a hard steel plate, such as a saw-blade. The
pattern is gone over several times. By dusting iron filings on a sheet
of paper laid over the steel plate, while horizontal, very complicated
magnetic figures are produced.

Hall's Experiment.
A cross of thin metal, such as gold leaf, is secured upon a pane of
glass. To two opposite arms a battery is connected in circuit with them.
To the other two arms a galvanometer is connected in circuit. If the
cross is put into a field of force whose lines are perpendicular
thereto, the galvanometer will disclose a constant current. The current
is pushed, as it were, into the galvanometer circuit. Other metals have
been used with similar results. They must be thin or the experiment
fails. If the arm receiving the battery current is horizontal, and if it
flows from left to right, and if the lines of force go from downward
through the cross, the current in the galvanometer circuit will flow
from the observer through the other arms of the cross, if the cross is
of gold, silver, platinum or tin, and the reverse if of iron. The
experiment has indicated a possible way of reaching the velocity of
electricity in absolute measure.

Hall Effect.
The effect observed in Hall's experiment, q. v.

Hall Effect, Real.
A transverse electro-motive force in a conductor through which a current
is passing produced by a magnetic field.

Hall Effect, Spurious.
A spurious electro-motive force produced in a conductor, through which a
current is passing by changes in conductivity of the conductor brought
about by a magnetic field.

Hanger Board.
A board containing two terminals, a suspending hook, and a switch, so
that an arc lamp can be introduced into a circuit thereby, or can be
removed as desired.

Harmonic Receiver.
A receiver containing a vibrating reed, acted on by an electro-magnet.
Such a reed answers only to impulses tuned to its own pitch. If such are
received from the magnet it will vibrate. Impulses not in tune with it
will not affect it. (See Telegraph, Harmonic.)

Head Bath, Electric.
A fanciful name for an electro-medical treatment of the head. The
patient is insulated by an insulating stool or otherwise. His person is
connected with one terminal of an influence machine. An insulated
metallic circle, with points of metal projecting inward or downward, is
placed about the head. The circle is connected with the other pole of
the machine. On working it a silent or brush discharge with air
convection streams occurs between the patient's head and the circle of
points.

285 STANDARD ELECTRICAL DICTIONARY.

Head-light, Electric.
An electric head-light for locomotives has been experimented with. It
includes the parabolic reflection of the regular light with an arc-lamp
in place of the oil lamp. An incandescent lamp may be used in the same
place, but has no great advantage over oil as regards illuminating
power.

Heat.
A form of kinetic energy, due to a confused oscillatory movement of the
molecules of a body. Heat is not motion, as a heated body does not
change its place; it is not momentum, but it is the energy of motion. If
the quantity of molecular motion is doubled the momentum of the
molecules is also doubled, but the molecular mechanical energy or heat
is quadrupled.

As a form of energy it is measured by thermal units. The calorie is the
most important, and unfortunately the same term applies to two units,
the gram-degree C. and the kilogram-degree C. (See Calorie.) Calories
are determined by a calorimeter, q. v.

Independent of quantity of heat a body may be hotter or colder.
Thermometers are used to determine its temperature.

Heat is transmitted by conduction, a body conducting it slowly for some
distance through its own substance. Bodies vary greatly in their
conductivity for heat. It is also transmitted by convection of gases or
liquids, when the heated molecules traveling through the mass impart
their heat to other parts. Finally it is transmitted by ether waves with
probably the speed of light. This mode of transmission and the phenomena
of it were attributed to radiant heat. As a scientific term this is now
dropped by many scientists. This practice very properly restricts the
term "heat" to kinetic molecular motion.

The mechanical equivalent of heat is the number of units of work which
the energy of one unit quantity of heat represents. (See Equivalents,
Mechanical and Physical.)

Heat, Atomic.
The product of the specific heat of an element by its atomic weight. The
product is approximately the same for all the elements, and varies as
determined between 5.39 and 6.87. The variations are by some attributed
principally to imperfection of the work in determining them. The atomic
heat represents the number of gram calories required to raise the
temperature of a gram atom (a number of grams equal numerically to the
atomic weight) one degree centigrade.

286 STANDARD ELECTRICAL DICTIONARY.

Heat, Electric.
This term has been given to the heat produced by the passage of a
current of electricity through a conductor. It is really electrically
produced heat, the above term being a misnomer.

The rise of temperature produced in a cylindrical conductor by a current
depends upon the diameter of the conductor and on the current. The
length of the wire has only the indirect connection that the current
will depend upon the resistance and consequently upon its length.

The quantity of heat produced in a conductor by a current is in
gram-degree C. units equal to the product of the current, by the
electro-motive force or potential difference maintained between the ends
of the wire, by .24.

The cube of the diameter of a wire for a given rise of temperature
produced in such conductor by a current is equal approximately to the
product of the square of the current, by the specific resistance (q. v.)
of the material of the conductor, by .000391, the whole divided by the
desired temperature in centigrade units.

Heat, Electrical Convection of.
A term applied to the phenomena included under the Thomson effect, q.
v., the unequal or differential heating effect produced by a current of
electricity in conductors whose different parts are maintained at
different temperatures.

Heater, Electric.
An apparatus for converting electrical energy into thermal energy.

An incandescent lamp represents the principle, and in the Edison meter
has been used as such to maintain the temperature of the solutions.
Heaters for warming water and other purposes have been constructed,
utilizing conductors heated by the passage of the current as a source of
heat. (See also Heating Magnet.)

Heating Error.
In voltmeters the error due to alteration of resistance of the coil by
heating. If too strong a current is sent through the instrument, the
coils become heated and their resistance increased. They then do not
pass as much current as they should for the potential difference to
which they may be exposed. Their readings then will be too low. One way
of avoiding the trouble is to have a key in circuit, and to pass only an
instantaneous or very brief current through the instrument and thus get
the reading before the coils have time to heat.

The heating error does not exist for ammeters, as they are constructed
to receive the entire current, and any heating "error" within their
range is allowed for in the dividing of the scale.

Heating Magnet.
An electro-magnet designed to be heated by Foucault currents induced in
its core by varying currents in the windings. It has been proposed as a
source of artificial heat, a species of electric heating apparatus for
warming water, or other purposes.

287 STANDARD ELECTRICAL DICTIONARY.

Heat, Irreversible.
The heat produced by an electric current in a conductor of identical
qualities and temperature throughout. Such heat is the same whatever the
direction of the current. The heating effect is irreversible because of
the absence of the Thomson effect, q. v.) or Peltier effect, q. v.

Heat, Mechanical Equivalent of.
The mechanical energy corresponding to a given quantity of heat energy.
Mechanical energy is generally represented by some unit of weight and
height, such as the foot-pound; and heat energy is represented by a
given weight of water heated a given amount, such as a pound-degree
centigrade. Joule's equivalent is usually accepted; it states that
772.55 foot pounds of mechanical energy are equivalent to 1 pound-degree
F. (one pound avds. of water raised in temperature one degree
Fahrenheit). Other equivalencies have also been deduced.

Heat, Molecular.
The product of a specific heat of the compound by its molecular weight.
It is approximately equal to the sum of the atomic heats of its
constituent elements.

The molecular heat represents the number of gram calories required to
raise the temperature of a gram-molecule (a number of grams equal
numerically to the molecular weight) one degree centigrade.

The molecular heat is approximately equal for all substances.

Heat, Specific.
The capacity of a body for heat; a coefficient representing the relative
quantity of heat required to raise the temperature of an identical
weight of a given body a defined and identical amount.

The standard of comparison is water; its specific heat is taken as
unity. The specific heats by weight of other substances are less than
unity. The specific heat varies with the temperature. Thus the specific
heat of water is more strictly 1+.00015 tº C.

Specific heat is greater when a substance is in the liquid than when it
is in the solid state. Thus the specific heat of ice is 0.489; less
than half that of water. It differs with the allotropic modifications of
bodies; the specific heat of graphite is .202; of diamond, .147.

The product of the specific heat by the atomic weight of elements gives
a figure approximately the same. A similar law applies in the case of
molecules. (See Heat, Atomic-Heat, Molecular.)

The true specific heat of a substance should be separated from the heat
expended in expanding a body against molecular and atomic forces, and
against the atmospheric pressure. So far this separation has not been
possible to introduce in any calculations.

288 STANDARD ELECTRICAL DICTIONARY.

Heat, Specific, of Electricity.
A proposed term to account for the heat absorbed or given out in
unhomogeneous conductors, by the Thomson effect, or Peltier effect (see
Effect, Thomson--Effect, Peltier.) If a current of electricity be
assumed to exist, then under the action of these effects it may be
regarded as absorbing or giving out so many coulombs of heat, and thus
establishing a basis for specific heat.

Heat Units.
The British unit of heat is the pound degree F--the quantity of heat
required to raise the temperature of a pound of water from 32° to 33° F.

The C. G. S. unit is the gram-degree C.; another metric unit is the
kilogram-degree C. The latter is the calorie; the former is sometimes
called the small calorie or the joule; the latter is sometimes called
the large calorie. The term joule is also applied to a quantity of heat
equivalent to the energy of a watt-second or volt-coulomb. This is equal
to .24l gram degree calorie.

Hecto.
A prefix to terms of measurement--meaning one hundred times, as
hectometer, one hundred meters.

Heliograph.
An apparatus for reflecting flashes of light to a distant observer. By
using the Morse telegraph code messages may thus be transmitted long
distances. When possible the sun's light is used.

Helix.
A coil of wire; properly a coil wound so as to follow the outlines of a
screw without overlaying itself.

Fig. 194. LEFT-HANDED HELIX.

Fig. 195. RIGHT-HANDED HELIX.

Henry.
The practical unit of electro-magnetic or magnetic inductance. It is
equal to 1E9 C. G. S., or absolute units of inductance. As the
dimensions of inductance are a length the henry is equal to 1E9
centimeters, or approximately to one quadrant of the earth measured on
the meridian.

Synonyms--Secohm--Quadrant--Quad.

289 STANDARD ELECTRICAL DICTIONARY.

Hermetically Sealed.
Closed absolutely tight. Glass vessels, such as the bulbs of
incandescent lamps, are hermetically sealed often by melting the glass
together over any opening into their interior.

Heterostatic Method.
A method of using the absolute or attracted disc electrometer. (See
Electrometer Absolute.) The formula for its idiostatic use, q. v.,
involves the determination of d, the distance between the suspended and
fixed discs. As this is difficult to determine the suspended disc and
guard ring may be kept at one potential and the lower fixed disc is then
connected successively with the two points whose potential difference is
to be determined. Their difference is determined by the difference
between d and d', the two distances between the discs. This difference
is the distance through which the micrometer screw is moved. The
heterostatic formula is:

V' - V = (d' - d)* squareRoot( 8*PI*F / S )

in which V and V' are potentials of the two points; d' and d the two
distances between the discs necessary for equilibrium; S the area of the
disc and F the force of attraction in dynes. (See Idiostatic Method.)

High Bars of Commutator.
Commutator bars, which in the natural wear of the commutator, project
beyond the others. The surface then requires turning down, as it should
be quite cylindrical.

High Frequency.
A term used as a noun or as an adjective to indicate in an alternating
current, the production of a very great number of alternations per unit
of time--usually expressed as alternations per second.

Hissing.
A term applied to a noise sometimes produced by a voltaic arc; probably
due to the same cause as frying, q. v.

Hittorf's Solution.
A solution used as a resistance. It is a solution of cadmium iodide in
amylic alcohol. Ten per cent. of the salt is used. It is contained in a
tube with metallic cadmium electrodes. (See Resistance, Hittorf' s.)

Fig. 196. HITTORF'S RESISTANCE TUBE.

290 STANDARD ELECTRICAL DICTIONARY.

Holders.
(a) The adjustable clamps for holding the armature brushes of dynamos
and motors.

(b) The clamps for holding the carbons of arc lamps.

(c) The clamps for holding safety fuses, q. v.

(d) Holders for Jablochkoff candles and other electric candles. (See
Candle Holders.)

(e) A box or block of porcelain for holding safety fuses.

Hood.
A tin hood placed over an arc-lamp. Such hoods are often truncated cones
in shape, with the small end upwards. They reflect a certain amount of
light besides protecting the lamp to some extent from rain.

Horns.
The extensions of the pole pieces of a dynamo or motor. (See Following
Horns-Leading Horns.)

Synonym--Pole Tips.

Horse Power.
A unit of rate of work or activity. There are two horse powers.

The British horse power is equal to 33,000 pounds raised one foot per
minute, or 550 foot pounds per second, or 1.0138 metric horse power.

The metric horse power (French) is equal to 75 kilogram-meters, or 542
foot pounds per second, or .986356 British horse power.

H. P. is the abbreviation for horse power. (See Horse Power, Electric.)

Horse Power, Actual.
The rate of activity of a machine, as actually developed in condition
for use. It is less than the indicated or total horse power, because
diminished by the hurtful resistances of friction, and other sources of
waste. It is the horse power that can be used in practise, and which in
the case of a motor can be taken from the fly-wheel.

Horse Power, Electric.
The equivalent of a mechanical horse power in electric units, generally
in volt-amperes or watts; 745.943 watts are equivalent to the activity
of one British horse power; 735.75 are equivalent to one metric horse
power. The number 746 is usually taken in practical calculations to give
the equivalency.

Horse Power, Indicated.
The horse power of an engine as indicated by its steam pressure, length
of stroke, and piston area, and vacuum, without making any deduction for
friction or hurtful resistances. The steam pressure is in accurate work
deduced from indicator diagrams.

Horse Power, Hour.
A horse power exerted for one hour, or the equivalent thereof. As the
horse power is a unit of activity, the horse power hour is a unit of
work or of energy. It is equal to 1,980,000 foot pounds.

H. P.
Abbreviation for "horse power."

291 STANDARD ELECTRICAL DICTIONARY.

Hughes' Electro-magnet.
A horseshoe electro-magnet with polarized core. It is made by mounting
two bobbins of insulated wire on the ends of a permanent horseshoe
magnet. It was devised for use in Hughes' printing telegraph, where very
quick action is required. The contact lasts only .053 second, 185
letters being transmitted per minute.

Fig. 197 HUGHES' ELECTRO-MAGNET.

Fig. 198. HUGHES' INDUCTION BALANCE.

Hughes' Induction Balance.
An apparatus for determining the presence of a concealed mass of metal.
The apparatus is variously connected. The cut shows a representative
form; a and a' are two primary coils, each consisting of 100 meters (328
feet) of No. 32 silk covered copper wire (0.009 inch diameter) wound on
a boxwood spool ten inches in depth; b and b' are secondary coils. All
coils are supposed to be alike. The primary coils are joined in series
with a battery of three or four Daniell cells. A microphone m is
included in the same circuit. The secondary coils are joined in series
with a telephone and in opposition with each other. The clock is used to
produce a sound affecting the microphone. If all is exactly balanced
there will be no sound produced in the telephone. This balance is
brought about by slightly varying the distance of one of the secondaries
from the primary, until there is no sound in the telephone. If now a
piece of metal is placed within either of the coils, it disturbs the
balance and the telephone sounds.

292 STANDARD ELECTRICAL DICTIONARY.

To measure the forces acting a sonometer or audiometer is used. This is
shown in the upper part of the cut. Two fixed coils, c and e are mounted
at the ends of a graduated bar. A movable coil d is connected in the
telephone circuit; c and e by a switch can be connected with the battery
and microphone circuit, leaving out the induction balance coils. The
ends of the coils c and e, facing each other are of the same polarity.
If these coils, c and e, were equal in all respects, no sound would be
produced when d was midway between them. But they are so wound that the
zero position for d is very near one of them, c.

Assume that a balance has been obtained in the induction balance with
the coil d at zero. No sound is heard whether the switch is moved to
throw the current into one or the other circuit. A piece of metal placed
in one of the balance coils will cause the production of a sound. The
current is turned into the sonometer and d is moved until the same
sound, as tested by rapid movements of the switch, is heard in both
circuits. The displacement of d gives the value of the sound.

A milligram of copper is enough to produce a loud sound. Two coins can
be balanced against each other, and by rubbing one of them, or by
breathing on one of them, the balance will be disturbed and a sound will
be produced.

Prof. Hughes has also dispensed with the audiometer. He has used a strip
of zinc tapering from a width of 4 mm. (.16 inch) at one end to a sharp
edge or point at the other. The piece to be tested being in place in one
coil, the strip is moved across the face of the other until a balance is
obtained.

As possible uses the detection of counterfeit coins, the testing of
metals for similarity of composition and the location of bullets in the
body have been suggested. Care has to be taken that no masses of metal
interfere. Thus in tests of the person of a wounded man, the presence of
an iron truss, or of metallic bed springs may invalidate all
conclusions.

The same principle is carried out in an apparatus in which the parts are
arranged like the members of a Wheatstone bridge. One pair of coils is
used, which react on each other as primary and secondary coils. One of
the coils is in series with a telephone in the member of the bridge
corresponding to that containing the galvanometer of the Wheatstone
bridge. The latter is more properly termed an induction bridge.

Synonyms--Inductance Bridge--Inductance Balance--Induction Bridge.

293 STANDARD ELECTRICAL DICTIONARY.

Hydro-electric. adj.
(a) A current produced by a voltaic couple or the couple itself is
sometimes thus characterized or designated as a "hydro-electric current"
or a "hydro-electric couple." It distinguishes them from
thermo-electric.

(b) Armstrong's steam boiler electric machine (see Hydroelectric
Machine) is also termed a hydro-electric machine.

Hydro-electric Machine.
An apparatus for generating high potential difference by the escape of
steam through proper nozzles.

It consists of a boiler mounted on four glass legs or otherwise
insulated. An escape pipe terminates in a series of outlets so shaped as
to impede the escape of the steam by forcing it out of the direct
course. These jets are lined with hard wood. They are enclosed in or led
through a box which is filled with cold water.

Fig. 199. ARMSTRONG'S HYDRO-ELECTRIC MACHINE.

This is to partly condense the steam so as to get it into the vesicular
state, which is found essential to its action. Dry steam produces no
excitation. If the boiler is fired and the steam is permitted to escape
under the above conditions the vesicles presumably, or the "steam" is
found to be electrified. A collecting comb held against the jet becomes
charged and charges any connected surface.

294 STANDARD ELECTRICAL DICTIONARY.

The boiler in the above case is negatively and the escaping "steam" is
positively charged. By changing the material of the linings of the jets,
or by adding turpentine the sign of the electricity is reversed. If the
water contains acid or salts no electricity is produced. The regular
hydro-electric machine is due to Sir William Armstrong.

Faraday obtained similar results with moist air currents.

Hydrogen.
An element existing under all except the most extreme artificial
conditions of pressure and cold as a gas. It is the lightest of known
substances. Atomic weight, 1; molecular weight, 2; equivalent, 1;
valency, 1; specific gravity, .0691-.0695. (Dumas & Boussingault.)

It is a dielectric of about the same resistance as air. Its specific
inductive capacity at atmospheric pressure is:
.9997 (Baltzman) .9998 (Ayrton)

Electro-chemical equivalent, .0105 milligram.
The above is usually taken as correct. Other values are as follows:
.010521 (Kohllrausch) .010415 (Mascart)

The electro-chemical equivalent of any element is obtained by
multiplying its equivalent by the electro-chemical equivalent of
hydrogen. The value .0105 has been used throughout this book.

Hygrometer.
An instrument for determining the moisture in the air. One form consists
of a pair of thermometers, one of which has its bulb wrapped in cloth
which is kept moist during the observation. The evaporation is more or
less rapid according to the dryness or moisture of the air, and as the
temperature varies with this evaporation the relative readings of the
two thermometers give the basis for calculating the hygrometric state of
the air. Another form determines the temperature at which dew is
deposited on a silver surface, whence the calculations are made.

Hysteresis, Magnetic.
A phenomenon of magnetization of iron. It may be attributed to a sort of
internal or molecular friction, causing energy to be absorbed when iron
is magnetized. Whenever therefore the polarity or direction of
magnetization of a mass of iron is rapidly changed a considerable
expenditure of energy is required. It is attributed to the work done in
bringing the molecules into the position of polarity.

295 STANDARD ELECTRICAL DICTIONARY.

The electric energy lost by hysteresis may be reduced by vibrations or
jarring imparted to the iron, thus virtually substituting mechanical for
electrical work.

On account of hysteresis the induced magnetization of a piece of iron or
steel for fields of low intensity will depend on the manner in which the
material has been already magnetized. Let the intensity of field
increase, the magnetization increasing also; then lower the intensity;
the substance tends to and does retain some of its magnetism. Then on
again strengthening the field it will have something to build on, so
that when it attains its former intensity the magnetization will exceed
its former value. For a moderate value of intensity of field the
magnetization can have many values within certain limits.

Synonym--Hysteresis--Hysteresis, Static--Magnetic Friction.

Hysteresis, Viscous.
The gradual increase or creeping up of magnetization when a magnetic
force is applied with absolute steadiness to a piece of iron. It may
last for half an hour or more and amount to several per cent. of the
total magnetization. It is a true magnetic lag.

295 STANDARD ELECTRICAL DICTIONARY.

I.
A symbol sometimes used to indicate current intensity. Thus Ohm's law is
often expressed I = E/R, meaning current intensity is equal to
electro-motive force divided by resistance. C is the more general symbol
for current intensity.

Ideoelectrics or Idioelectrics.
Bodies which become electric by friction. This was the old definition,
the term originating with Gilbert. It was based on a misconception, as
insulation is all that is requisite for frictional electrification,
metals being thus electrified if held by insulating handles. The term is
virtually obsolete; as far as it means anything it means insulating
substances such as scaling wax, sulphur, or glass.

Idle Coils.
Coils in a dynamo, in which coils no electro-motive force is being
generated. This may occur when, as a coil breaks connection with the
commutator brush, it enters a region void of lines of magnetic force, or
where the lines are tangential to the circle of the armature.

Idiostatic Method.
A method of using the absolute or attracted disc electrometer. (See
Electrometer, Absolute.) The suspended disc and guard ring are kept at
the same potential, which is that of one of the points whose potential
difference is to be determined; the lower fixed disc is connected to the
other of the points whose potential difference is to be determined. Then
we have the formula

V = d * SquareRoot( 8 * PI * F ) / S

in which d is the distance between the discs, V is the difference of
potential of the two points, F the force of attraction between the discs
in dynes, and S the area of the suspended disc. (See Heterostatic
Method.)

296 STANDARD ELECTRICAL DICTIONARY.

Idle Poles.
Poles of wire sealed into Crookes' tubes, not used for the discharge
connections, but for experimental connections to test the effect of
different excitation on the discharge.

Idle Wire.
In a dynamo the wire which plays no part in generating electro-motive
force. In a Gramme ring the wire on the inside of the ring is idle wire.

Igniter.
In arc lamps with fixed parallel carbons of the Jablochkoff type (see
Candle, Jablochkoff) a strip of carbon connects the ends of the carbons
in the unused candle. This is necessary to start the current. Such strip
is called an igniter. It burns away in a very short time when an arc
forms producing the light, and lasts, if all goes well, until the candle
burns down to its end. Without the igniter the current would not start
and no arc would form.

I. H. P.
Symbol for indicated horse-power.

Illuminating Power.
The relative light given by any source compared with a standard light,
and stated in terms of the same, as a burner giving an illuminating
power of sixteen candles. For standards see Candle, Carcel--Methven
Standard--Pentane Standard.

Illuminating Power, Spherical.
The illuminating power of a lamp or source of light may vary in
different directions, as in the case of a gas burner or incandescent
lamp. The average illuminating power determined by photometric test or
by calculation in all directions from the source of light is called the
spherical illuminating power, or if stated in candles is called the
spherical candle power.

Illumination, Unit of.
An absolute standard of light received by a surface. Preece proposed as
such the light received from a standard candle (see Candle, Standard) at
a distance of 12.7 inches. The object of selecting this distance was to
make it equal to the Carcel Standard (see Carcel), which is the light
given by a Carcel lamp at a distance of one meter.

From one-tenth to one-fiftieth this degree of illumination was found in
gas-lighted streets by Preece, depending on the proximity of the gas
lamps.

Image, Electric.
An electrified point or system of points on one side of a surface which
would produce on the other side of that surface the same electrical
action which the actual electrification of that surface really does
produce. (Maxwell.)

The method of investigating the distribution of electricity by electric
images is due to Sir William Thomson. The conception is purely a
theoretical one, and is of mathematical value and interest.

297 STANDARD ELECTRICAL DICTIONARY.

Impedance.
The ratio of any impressed electro-motive force to the current which it
produces in a conductor. For steady currents it is only the resistance.
For variable currents it may include besides resistance inductance and
permittance. It is the sum of all factors opposing a current, both ohmic
and spurious resistances. It is often determined and expressed as ohms.

Synonym--Apparent Resistance--Virtual Resistance.

Impedance, Oscillatory.
The counter-electro-motive force offered to an oscillatory discharge, as
that of a Leyden jar. It varies with the frequency of the discharge
current.

Synonym--Impulsive Impedance.

Impressed Electro-motive Force.
The electro-motive force expending itself in producing current induction
in a neighboring circuit.

Impulse.
(a) An electro-magnetic impulse is the impulse produced upon the
luminiferous ether by an oscillatory discharge or other varying type of
current; the impulse is supposed to be identical, except as regards
wave-length, with a light wave.

(b) An electro-motive impulse is the electro-motive force which rises so
high as to produce an impulsive or oscillatory discharge, such as that
of a Leyden jar.

Incandescence, Electric.
The heating or a conductor to red, or, more etymologically, to white
heat by the passage of an electric current. The practical conditions are
a high intensity of current and a low degree of conductance of the
conductor relatively speaking.

Inclination Map.
A map showing the locus of equal inclination or dips of the magnetic
needle. The map shows a series of lines, each one of which follows the
places at which the dip of the magnetic needle is identical. The map
changes from year to year. (See Magnetic Elements.)

Independence of Currents in Parallel Circuits.
If a number of parallel circuits of comparatively high resistance are
supplied by a single generator of comparatively low resistance, the
current passed through each one will be almost the same whether a single
one or all are connected. Under the conditions named the currents are
practically independent of each other.

Indicating Bell.
An electric bell arranged to drop a shutter or disclose in some other
way a designating number or character when rung.

298 STANDARD ELECTRICAL DICTIONARY.

Indicator.
(a) An apparatus for indicating the condition of a distant element, such
as the water level in a reservoir, the temperature of a drying room or
cold storage room or any other datum. They are of the most varied
constructions.

(b) The receiving instrument in a telegraph system is sometimes thus
termed.

Indicator, Circuit.
A galvanometer used to show when a circuit is active, and to give an
approximate measurement of its strength. It is a less accurate and
delicate form of instrument than the laboratory appliance.

Inductance.
The property of a circuit in virtue of which it exercises induction and
develops lines of force. It is defined variously. As clear and
satisfactory a definition as any is the following, due to Sumpner and
Fleming: Inductance is the ratio between the total induction through a
circuit to the current producing it. "Thus taking a simple helix of five
turns carrying a current of two units, and assuming that 1,000 lines of
force passed through the central turn, of which owing to leakage only
900 thread the next adjacent on each side, and again only 800 through
the end turns, there would be 800 + 900 + 1000 + 900 + 800, or 4,400
linkages of lines with the wire, and this being with 2 units of current,
there would be 2,200 linkages with unit current, and consequently the
self-inductance of the helix would be 2,200 centimetres." (Kennelly.)
Inductance, as regards its dimensions is usually reduced to a length,
hence the last word of the preceding quotation.

The practical unit of inductance is termed the henry, from Prof. Joseph
Henry; the secohm, or the quad or quadrant. The latter alludes to the
quadrant of the earth, the value in length of the unit in question.

Induction, Coefficient of Self.
The coefficient of self-induction of a circuit is the quantity of
induction passing through it per unit current in it. If a given circuit
is carrying a varying current it is producing a varying quantity of
magnetic induction through itself. The quantity of induction through the
circuit due to its current is generally proportional to its current. The
quantity for unit current is the coefficient of self-induction.
(Emtage.)

Induction, Cross.
The induction of magnetic lines of force in a dynamo armature core by
the current passing around such armature. These lines in a symmetrical
two pole machine are at right angles to the lines of force which would
normally extend across the space between the two magnet poles. The joint
magnetizing effect of the field and of the cross induction produces a
distorted field between the poles .

Synonym--Cross-magnetizing Effect.

299 STANDARD ELECTRICAL DICTIONARY.

Induction, Electro-magnetic.
The inter-reaction of electromagnetic lines of force with the production
of currents thereby.

A current passing through a conductor establishes around it a field of
force representing a series of circular lines of force concentric with
the axis of the conductor and perpendicular thereto. These lines of
force have attributed to them, as a representative of their polarity,
direction. This is of course purely conventional. If one is supposed to
be looking at the end of a section of conductor, assuming a current be
passing through it towards the observer, the lines of force will have a
direction opposite to the motion of the hands of a watch. The idea of
direction may be referred to a magnet. In it the lines of force are
assumed to go from the north pole through the air or other surrounding
dielectric to the south pole.

Two parallel wires having currents passing through them in the same
direction will attract each other. This is because the oppositely
directed segments of lines of force between the conductors destroy each
other, and the resultant of the two circles is an approximation to an
ellipse. As lines of force tend to be as short as possible the
conductors tend to approach each other to make the ellipse become of as
small area as possible, in other words to become a circle.

If on the other hand the currents in the conductors are in opposite
directions the segments of the lines of force between them will have
similar directions, will, as it were, crowd the intervening ether and
the wires will be repelled.

Fig. 200. ATTRACTION OF CONDUCTORS CARRYING SIMILAR CURRENTS.

By Ampére's theory of magnetism, (see Magnetism, Ampére's Theory of,) a
magnet is assumed to be encircled by currents moving in the direction
opposite to that of the hands of a watch as the observer faces the north
pole. A magnet near a wire tends to place the Ampérian currents parallel
to the wire, and so that the portion of the Ampérian currents nearest
thereto will correspond in direction with the current in the wire.

300 STANDARD ELECTRICAL DICTIONARY.

This is the principle of the galvanometer. A number of methods of
memoria technica have been proposed to remember it by.

Thus if we imagine a person swimming with the current and always facing
the axis of the conductor, a magnetic needle held where the person is
supposed to be will have its north pole deflected to the right hand of
the person.

Fig. 201. REPULSION OF CONDUCTORS
CARRYING OPPOSITE CURRENTS.

Again if we think of a corkscrew, which as it is turned screws itself
along with the current, the motion of the handle shows the direction of
the lines of force and the direction in which the north pole of a needle
is deflected. This much is perhaps more properly electro-dynamics, but
is necessary as a basis for the expression of induction.

If a current is varied in intensity in one conductor it will induce a
temporary current in another conductor, part of which is parallel to the
inducing current and which conductor is closed so as to form a circuit.
If the inducing current is decreased the induced current in the near and
parallel portion of the other circuit will be of identical direction; if
increased the induced current will be of opposite direction.

This is easiest figured by thinking of the lines of force surrounding
the inducing conductor. If the current is decreased these can be
imagined as receiving a twist or turn contrary to their normal
direction, as thereby establishing a turn or twist in the ether
surrounding the other wire corresponding in direction with the direction
of the original lines of force, or what is the same thing, opposite in
direction to the original twist. But we may assume that the
establishment of such a disturbance causes a current, which must be
governed in direction with the requirements of the new lines of force.

The same reasoning applies to the opposite case.

301 STANDARD ELECTRICAL DICTIONARY.

The general statement of a variable current acting on a neighboring
circuit also applies to the approach or recession of an unvarying
current, and to the cutting of lines of force by a conductor at right
angles thereto. For it is evident that the case of a varying current is
the case of a varying number of lines of force cutting or being cut by
the neighboring conductor. As lines of force always imply a current,
they always imply a direction of such current. The cutting of any lines
of force by a closed conductor always implies a change of position with
reference to all portions of such conductor and to the current and
consequently an induced current or currents in one or the other
direction in the moving conductor.

As the inducing of a current represents energy abstracted from that of
the inducing circuit, the direction of the induced current is determined
by (Lenz's Law) the rule that the new current will increase already
existing resistances or develop new ones to the disturbance of the
inducing field.

In saying that a conductor cutting lines of force at right angles to
itself has a current induced in it, it must be understood that if not at
right angles the right angle component of the direction of the wire acts
in generating the current. The case resolves itself into the number of
lines of force cut at any angle by the moving wire.

The lines of force may be produced by a magnet, permanent or electro.
This introduces no new element. The magnet may be referred, as regards
direction of its lines of force, to its encircling currents, actual or
Ampérian, and the application of the laws just cited will cover all
cases.

Induction, Coefficient of Mutual.
The coefficient of mutual induction of two circuits is the quantity of
magnetic induction passing through either of them per unit current in
the other. (Emtage.) It is also defined as the work which must be done
on either circuit, against the action of unit current in each, to take
it away from its given position to an infinite distance from the other;
and also as the work which would be done by either circuit on the other
in consequence of unit current in each, as the other moves from an
infinite distance to its given position with respect to the other
conductor. It depends on the form, size, and relative position of the
two circuits; and on the magnetic susceptibilities of neighboring
substances.

The ether surrounding two circuits of intensity i' and i" must possess
energy, expressible (Maxwell) as 1/2 L i2 + M i i + 1/2 N i12. It can be
shown that M i i1 in any given position of the two circuits is
numerically equal (1) to the mutual potential energy of the two circuits
(2) to the number of lines of induction, which being due to A, pass from
A through B, or equally being due to B, pass from B through A, and M is
styled the coefficient of mutual induction. (Daniell.)

302 STANDARD ELECTRICAL DICTIONARY.

Induction, Electrostatic.
An electrostatic charge has always an opposite and bound charge. This
may be so distributed as not to be distinguishable, in which case the
charge is termed, incorrectly but conventionally, a free charge. But
when a charge is produced an opposite and equal one always is formed,
which is the bound charge. The region between the two charges and
permeated by their lines of force, often curving out so as to embrace a
volume of cross-sectional area larger than the mean facing area of the
excited surfaces, is an electrostatic field of force. The establishing
of an electrostatic field, and the production of a bound charge are
electrostatic induction.

An insulated conductor brought into such a field suffers a
redistribution of its electricity, or undergoes electrostatic induction.
The parts nearest respectively, the two loci of the original and the
bound charges, are excited oppositely to such charges. The conductor
presents two new bound charges, one referred to the original charge, the
other to the first bound charge.

Induction, Horizontal.
In an iron or steel ship the induction exercised upon the compass needle
by the horizontal members of the structure, such as deck-beams, when
they are polarized by the earth's magnetic induction. This induction
disappears four times in swinging a ship through a circle; deviation due
to it is termed quadrantal deviation. (See Deviation, Quadrantal.)

Induction, Lateral.
A term formerly used to express the phenomenon of the alternative
discharge of a Leyden jar or other oscillatory discharge of electricity.
(See Discharge, Alternative.)

Induction, Magnetic.
The magnetization of iron or other paramagnetic substance by a magnetic
field.

On account of its permeability or multiplying power for lines of force,
a paramagnetic body always concentrates lines of force in itself if
placed in a magnetic field, and hence becomes for the time being a
magnet, or is said to be polarized.

As the tendency of lines of force is to follow the most permeable path,
a paramagnetic bar places itself lengthwise or parallel with the
prevailing direction of the lines of force so as to carry them as far on
their way as possible. Every other position of the bar is one of
unstable equilibrium or of no equilibrium. The end of the bar where the
lines of force enter (see Lines of Force) is a south pole and is
attracted towards the north pole of the magnet.

The production of magnetic poles under these conditions in the bar is
shown by throwing iron filings upon it. They adhere to both ends but not
to the middle.

Induction, Mutual, Electro-magnetic.
The induction due to two electric currents reacting on each other.

303 STANDARD ELECTRICAL DICTIONARY.

Induction, Mutual, Electrostatic.
A charged body always induces a charge upon any other body near it; and
the same charge in the second body will induce the other charge in the
first body if the latter is unexcited. In other words the second body's
induction from the first is the measure of the charge the second would
require to induce in the first its own (the second's) induced charge.
This is the law of mutual electrostatic induction.

Induction, Open Circuit.
Inductive effects produced in open circuits. By oscillatory discharges a
discharge can be produced across a break in a circuit otherwise
complete. The requirements for its production involve a correspondence
or relation of its dimensions to the inducing discharge. The whole is
analogous to the phenomena of sound resonators and sympathetic
vibrations. Synonym--Oscillatory induction.

Induction, Self-.
(a) A phenomenon of electric currents analogous to the inertia of
matter. Just as water which fills a pipe would resist a sudden change in
its rate of motion, whether to start from rest, to cease or decrease its
motion, so an electric current requires an appreciable time to start and
stop. It is produced most strongly in a coiled conductor, especially if
a core of iron is contained within it.

As in the case of two parallel wires, one bearing currents which vary,
momentary currents are induced in the other wire, so in a single
conductor a species of inertia is found which retards and prolongs the
current. If a single conductor is twisted into a helix or corresponding
shape, its separate turns react one on the other in accordance with the
general principles of electromagnetic induction. (See Induction,
Electro-magnetic.) Thus when a current is suddenly formed the coils
acting upon each other retard for an instant its passage, producing the
effect of a reverse induced current or extra current opposing the
principal current. Of course no extra current is perceptible, but only
the diminution. When the current is passing regularly and the current is
broken, the corresponding action prolongs the current or rather
intensifies it for an instant, producing the true extra current. This is
current self-induction.

Synonyms--Electric Inertia--Electro-dynamic Capacity.

(b) A permanent magnet is said to tend to repel its own magnetism, and
thus to weaken itself; the tendency is due to magnetic self-induction.

Induction Sheath.
In the brush dynamo a thin sheet of copper surrounding the magnet cores
with edges soldered together. The winding is outside of it. Its object
is to absorb extra currents set up by variations in magnetic intensity
in the cores. These currents otherwise would circulate in the cores.

304 STANDARD ELECTRICAL DICTIONARY.

Induction, Unit of Self-.
The unit of self-induction is the same as that of induction in general.
It is the henry, q. v.

Induction, Unipolar.
Induction produced in a conductor which continuously cuts the lines of
force issuing from one pole of a magnet. As the lines of force are
always cut in the same sense a continuous and constant direction current
is produced.

Induction, Vertical.
In an iron or steel ship the induction or attraction exercised in the
compass by vertical elements of the structure. Such vertical masses of
iron in the northern hemisphere would have their upper ends polarized as
south poles, and would affect the magnet as soon as the vessel swung out
of the magnetic meridian. Thus this induction disappears twice in
swinging a ship through a complete circle; deviation due to it is termed
semi-circular deviation. (See Deviation, Semi-circular.)

Fig. 202. INDUCTOR DYNAMO.

Inductophone.
A method of train telegraphy. The train carries a circuit including a
coil, and messages are picked up by it from coils along the line into
which an alternating current is passed. A telephone is used as a
receiver in place of a sounder or relay. The invention, never
practically used, is due to Willoughby Smith.

305 STANDARD ELECTRICAL DICTIONARY.

Inductor.
(a) In a current generator a mass of iron, generally laminated, which is
moved past a magnet pole to increase the number of lines of force
issuing therefrom. It is used in inductor dynamos. (See Dynamo
Inductor.) In the cut Fig. 202, of an inductor dynamo i, i, are the
laminated inductors.

(b) In influence machines the paper or tinfoil armatures on which the
electrification is induced.

Inertia.
A force in virtue of which every body persists in its state of motion or
rest except so far as it is acted on by some force.

Inertia, Electro-magnetic.
This term is sometimes applied to the phenomena of self-induction, or
rather to the cause of these phenomena.

Infinity Plug.
A plug in a resistance box, which on being pulled out of its seat opens
the circuit or makes it of infinite resistance. The plug seats itself
between two brass plates which are not connected with each other in any
way. The other plates are connected by resistance coils of varying
resistance.

Influence, Electric.
Electric induction, which may be either electrostatic, current, or
electro-magnetic.

Insolation, Electric.
Exposure to powerful arc-light produces effects resembling those of
sun-stroke. The above term or the term "electric sun-stroke" has been
applied to them.

Installation.
The entire apparatus, buildings and appurtenances of a technical or
manufacturing establishment. An electric light installation, for
instance, would include the generating plant, any special buildings, the
mains and lamps.

Insulating Stool.
A support for a person, used in experiments with static generators. It
has ordinarily a wooden top and glass legs. It separates one standing on
it from the earth and enables his surface to receive an electrostatic
charge. This tends to make his hair stand on end, and anyone on the
floor who touches him will receive a shock.

Insulating Tape.
Prepared tape used in covering the ends of wire where stripped for
making joints. After the stripped ends of two pieces are twisted
together, and if necessary soldered and carefully cleaned of soldering
fluid, they may be insulated by being wound with insulating tape.

The tape is variously prepared. It may be common cotton or other tape
saturated with any insulating compound, or may be a strip of gutta
percha or of some flexible cement-like composition.

306 STANDARD ELECTRICAL DICTIONARY.

Insulating Varnish.
Varnish used to coat the surface of glass electrical apparatus, to
prevent the deposition of hygrometric moisture, and also in the
construction of magnetizing and induction coils and the like. Shellac
dissolved in alcohol is much used. Gum copal dissolved in ether is
another. A solution of sealing wax in alcohol is also used. If applied
in quantities these may need baking to bring about the last drying. (See
Shellac Varnish.)

Insulator.
(a) Any insulating substance.

(b) A telegraph or line insulator for telegraph wires. (See Insulator,
Line or Telegraph.)

Synonyms--Dielectric--Non-conductor.

Insulator Cap.
A covering or hood, generally of iron, placed over an insulator to
protect it from injury by fracture with stones or missiles.

Insulator, Fluid.
(a) For very high potentials, as in induction coils or alternating
circuits, fluid insulators, such as petroleum or resin oil, have been
used. Their principal merit is that if a discharge does take place
through them the opening at once closes, so that they are self-healing.

(b) Also a form of telegraph or line insulator in which the lower rim is
turned up and inwards, so as to form an annular cup which is filled with
oil.

Insulator, Line or Telegraph.
A support often in the shape of a collar or cap, for a telegraph or
other wire, made of insulating material. Glass is generally used in the
United States, porcelain is adopted for special cases; pottery or stone
ware insulators have been used a great deal in other countries.
Sometimes the insulator is an iron hook set into a glass screw, which is
inserted into a hole in a telegraph bracket. Sometimes a hook is caused
to depend from the interior of an inverted cup and the space between the
shank of the hook and cup is filled with paraffine run in while melted.

Insulators are tested by measuring their resistance while immersed in a
vessel of water.

Intensity. Strength.
The intensity of a current or its amperage or strength; the intensity or
strength of a magnetic field or its magnetic density; the intensity or
strength of a light are examples of its use. In the case of dynamic
electricity it must be distinguished from tension. The latter
corresponds to potential difference or voltage and is not an attribute
of current; intensity has no reference to potential and is a
characteristic of current.

Intensity of a Magnetic Field.
The intensity of a magnetic field at any point is measured by the force
with which it acts on a unit magnet pole placed at that point. Hence
unit intensity of field is that intensity of field which acts on a unit
pole with a force of one dyne. (S. P. Thomson.) (See Magnetic Lines of
Force.)

307 STANDARD ELECTRICAL DICTIONARY.

Intercrossing.
Crossing a pair of conductors of a metallic circuit from side to side to
avoid induction from outside sources.

Intermittent.
Acting at intervals, as an intermittent contact, earth, or grounding of
a telegraph wire.

Interpolar Conductor.
A conductor connecting the two poles of a battery or current generator;
the external circuit in a galvanic circuit.

Interpolation.
A process used in getting a closer approximation to the truth from two
varying observations, as of a galvanometer. The process varies for
different cases, but amounts to determining an average or deducing a
proportional reading from the discrepant observed ones.

Interrupter.
A circuit breaker. It may be operated by hand or be automatic. (See
Circuit Breaker--Circuit Breaker, Automatic--and others.)

Interrupter, Electro-magnetic, for a Tuning Fork.
An apparatus for interrupting a current which passes through an
electromagnet near and facing one of the limbs of a tuning fork. The
circuit is made and broken by the vibrations of another tuning fork
through which the current passes. The second one is thus made to
vibrate, although it may be very far off and may not be in exact unison
with the first. The first tuning fork has a contact point on one of its
limbs, to close the circuit; it may be one which dips into a mercury
cup.

Intrapolar Region.
A term in medical electricity, denoting the part of a nerve through
which a current is passing.

Ions.
The products of decomposition produced in any given electrolysis are
termed ions, the one which appears at the anode or negative electrode is
the anion. The electrode connected to the carbon or copper plate of a
wet battery is an anode. Thus in the electrolysis of water oxygen is the
anion and hydrogen is termed the kation. In this case both anion and
kation are elements. In the decomposition of copper sulphate the anion
is properly speaking sulphion (S O4), a radical, and the kation is
copper, an element. Electro-negative elements or radicals are anions,
such as oxygen, sulphion, etc., while electro-positive ones are kations,
such as potassium. Again one substance may be an anion referred to one
below it and a kation referred to one above it, in the electro-chemical
series, q. v. Anion means the ion which goes to the anode or positive
electrode; kation, the ion which goes to the kathode or negative
electrode.

308 STANDARD ELECTRICAL DICTIONARY.

Iron.
A metal; one of the elements; symbol, Fe; atomic weight, 56;
equivalent, 28 and 14, ; valency, 4 and 2.
It is a conductor of electricity. The following data are at
0° C. 32° F., with annealed metal.

Specific Resistance, 9.716 microhms.
Relative Resistance. 6.460
Resistance of a wire,
(a) 1 foot long weighing 1 grain, 1.085 ohms.
(b) 1 foot long 1/1000 inch thick, 58.45 "
(c) 1 meter long weighing 1 gram, .7570 "
(d) 1 meter long, 1 millimeter thick, .1237 "
Percentage increase in resistance per degree C. (1.8° F.)
at about 20° C. (68°F.), about 0.5 per cent.
Resistance of a 1 inch cube, 3.825 microhms.
Electro-chemical equivalent (Hydrogen = .0105), .147 and .294

Iron, Electrolytic.
Iron deposited by electrolytic action. Various baths are employed for
its formation. (See Steeling.) It has very low coercive power, only
seven to ten times that of nickel.

Ironwork Fault of a Dynamo.
A short circuiting of a dynamo by, or any connection of its coils with,
the iron magnet cores or other iron parts.

Isochronism.
Equality of periodic time; as of the times of successive beats of a
tuning fork, or of the times of oscillations of a pendulum.

Isoclinic Lines.
The lines denoting the locus of sets of equal dips or inclinations of
the magnetic needle upon the earth's surface, the magnetic parallels, q.
v. These lines are very irregular. (See Magnetic Elements.)

Isoclinic Map.
A map showing the position of isoclinic lines.

Isodynamic Lines.
Lines marking the locus of places of equal magnetic intensity on the
earth's surface. (See Magnetic Elements, Poles of Intensity.)

Isodynamic Map.
A map showing the position of isodynamic lines. (See Poles of
Intensity.)

Isogonic Lines.
Lines on a map marking the locus of or connecting those points where the
declination or variation of the magnetic needle is the same. (See
Magnetic Elements--Declination of Magnetic Needle.)

Synonyms--Isogonal Lines--Halleyan Lines.

309 STANDARD ELECTRICAL DICTIONARY.

Isogonic Map.
A map showing the isogonic lines. On such a map each line is
characterized and marked with the degrees and direction of variation of
the compass upon itself.

Synonym--Declination Map.

Isolated Plant, Distribution or Supply.
The system of supplying electric energy by independent generating
systems, dynamo or battery, for each house, factory or other place, as
contra-distinguished from Central Station Distribution or Supply.

Isotropic.

(Greek, equal in manner.)

Having equal properties in all directions; the reverse of anisotropic,
q. v. Thus a homogeneous mass of copper or silver has the same specific
resistance in all directions and is an isotropic conductor. Glass has
the same specific inductive capacity in all directions and is an
isotropic medium or dielectric. The same applies to magnetism. Iron is
an isotropic paramagnetic substance. (See Anisotropic.) The term applies
to other branches of physics also.

I. W. G.
Contraction for Indian Wire Gauge--the gauge adopted in British India.

309 STANDARD ELECTRICAL DICTIONARY.

J.
Symbol for the unit joule, the unit of electric energy.

Jacobi's Law.
A law of electric motors. It states that the maximum work of a motor is
performed when the counter-electromotive force is equal to one-half the
electro-motive force expended on the motor.

Jewelry.
Small incandescent lamps are sometimes mounted as articles of jewelry in
scarf-pins or in the hair. They may be supplied with current from
storage or from portable batteries carried on the person.

Joint, American Twist.
A joint for connecting telegraph wires, especially aerial lines. Its
construction is shown in the cut. The end of each wire is closely wound
around the straight portion of the other wire for a few turns.

Fig. 203. AMERICAN TWIST JOINT.

310 STANDARD ELECTRICAL DICTIONARY.

Joint, Britannia.
A joint for uniting the ends of telegraph and electric wires. The ends
of the wires are scraped clean and laid alongside each other for two
inches, the extreme ends being bent up at about right angles to the
wire. A thin wire is wound four or five times around one of the wires,
back of the joint, the winding is then continued over the lapped
portion, and a few more turns are taken around the other single wire.
The whole is then soldered.

Fig. 204. BRITANNIA JOINT.

Joint, Butt.
A joint in belting or in wire in which the ends to be joined are cut off
square across, placed in contact and secured. It ensures even running
when used in belting. Any irregularity in thickness of a belt affects
the speed of the driven pulley. As dynamos are generally driven by
belts, and it is important to drive them at an even speed to prevent
variations in the electro-motive force, butt joints should be used on
belting for them, unless a very perfect lap joint is made, which does
not affect either the thickness or the stiffness of the belt.

When a butt joint is used in wire a sleeve may be used to receive the
abutting ends, which may be secured therein by soldering. This species
of joint has been used on lightning rods and may more properly be termed
a sleeve joint.

Joint, Lap.
(a) In belting a joint in which the ends are overlapped, and riveted or
otherwise secured in place. If made without reducing the thickness of
the ends it is a bad joint for electrical work, as it prevents even
running of machinery to which it is applied. Hence dynamo belts should
be joined by butt joints, or if by lap joints the ends should be shaved
off so that when joined and riveted, there will be no variation in the
thickness of the belt.

(b) In wire lap joints are made by overlapping the ends of the wire and
soldering or otherwise securing. The Britannia joint (see Joint,
Britannia,) may be considered a lap-joint.

Joint, Marriage.
A joint for stranded conductors used for Galende's cables. It is made
somewhat like a sailor's long splice. Each one of the strands is wound
separately into the place whence the opposite strand is unwound and the
ends are cut off so as to abutt. In this way all are smoothly laid in
place and soldering is next applied.

Fig. 205. MARRIAGE JOINT.

311 STANDARD ELECTRICAL DICTIONARY.

Joint, Sleeve.
A joint in electric conductors, in which the ends of the wires are
inserted into and secured in a metallic sleeve or tube, whose internal
diameter is just sufficient to admit them.

Joint, Splayed.
The method of joining the ends of stranded conductors. The insulating
covering is removed, the wires are opened out, and the center wire,
heart or core of the cable is cut off short. The two ends are brought
together, the opened out wires are interlaced or crotched like the
fingers of the two hands, and the ends are wound around the body of the
cable in opposite directions. The joint is trimmed and well soldered.
Tinned wire with rosin flux for the soldering is to be recommended.
Insulating material is finally applied by hand, with heat if necessary.

Joints in Belts.
Belt-joints for electric plants where the belts drive dynamos should be
made with special care. The least inequality affects the electro-motive
force. Butt joints are, generally speaking, the best, where the ends of
the belt are placed in contact and laced. Lap-joints are made by
overlapping the belt, and unless the belt is carefully tapered so as to
preserve uniform strength, the speed of the dynamo will vary and also
the electromotive force.

Joulad.
A name proposed to be substituted for "joule," q. v. It has not been
adopted.

Joule.
This term has been applied to several units.

(a) The practical C. G. S. unit of electric energy and work--the
volt-coulomb. It is equal to 1E7 ergs--0.73734 foot pound.--.00134 horse
power seconds. A volt-ampere represents one joule per second.

(b) It has also been used as the name of the gram-degree C. thermal
unit--the small calorie.

Synonym--Joulad.

Joule Effect.
The heating effect of a current passing through a conductor. It varies
with the product of the resistance by the square of the current, or with
(C^2)*R.

Joule's Equivalent.
The mechanical equivalent of heat, which if stated in foot-pounds per
pound-degree F. units, is 772 (772.55). (See Equivalents.)

Junction Box.
In underground distribution systems, an iron casing or box in which the
feeders and mains are joined, and where other junctions are made.

Synonym--Fishing Box.

311 STANDARD ELECTRICAL DICTIONARY.

K.
The symbol for electrostatic capacity.

Kaolin.
A product of decomposition of feldspar, consisting approximately of
silica, 45, alumina, 40, water, 15. It was used in electric candles of
the Jablochkoff type as a constituent of the insulating layer or
colombin. Later it was abandoned for another substance, as it was found
that it melted and acted as a conductor.

312 STANDARD ELECTRICAL DICTIONARY.

Kapp Line of Force.
A line of force proposed by Kapp. It is equal to 6,000 C. G. S. lines of
force, and the unit of area is the square inch. Unfortunately it has
been adopted by many manufacturers, but its use should be discouraged,
as it is a departure from the uniform system of units.

One Kapp line per square inch = 930 C. G. S. lines per square
centimeter.

Kathelectrotonus.
A term used in medical electricity or electro-therapeutics to indicate
the increased functional activity induced in a nerve by the proximity of
the kathode of an active circuit which is completed through the nerve.
The converse of anelectrotonus.

Kathode.
The terminal of an electric circuit whence an electrolyzing current
passes from a solution. It is the terminal connected to the zinc plate
of a primary battery.

Kathodic Closure Contraction.
A term in electro-therapeutics; the contractions near where the kathode
of an active circuit is applied to the body, which are observed at the
instant when the circuit is closed.

Kathodic Duration Contraction.
A term in electro-therapeutics; the contraction near where the kathode
of an active circuit is applied to the body for a period of time.

K. C. C.
Abbreviation for Kathodic Closure Contraction, q. v.

K. D. C.
Abbreviation for Kathodic Duration Contraction, q. v.

Keeper.
A bar of soft iron used to connect the opposite poles of a horseshoe
magnet or the opposite poles of two bar magnets placed side by side. It
is designed to prevent loss of magnetism. The armature of a horseshoe
magnet is generally used as its keeper. For bar magnets a keeper is used
for each end, the magnets being laid side by side, with their poles in
opposite direction but not touching, and a keeper laid across at each
end connecting the opposite poles.

Kerr Effect.
The effect of an electrostatic field upon polarized light traversing a
dielectric contained within the field. (See Electrostatic Refraction.)

Kerr's Experiment.
Polarized light reflected from the polished face of a magnet pole has
its plane of polarization rotated; when it is reflected from the north
pole the rotation is from left to right.

313 STANDARD ELECTRICAL DICTIONARY.

Key.
A switch adapted for making and breaking contact easily when worked by
hand, as a Morse telegraph key.

Key Board.
A board or tablet on which keys or switches are mounted.

Key-board.
(a) A switch board, q. v.

(b) A set of lettered keys similar to those of a typewriter employed in
some telegraph instruments. As each key is depressed it produces the
contact or break requisite for the sending of the signal corresponding
to the letter marked upon the key. The signal in printing telegraphs, on
which such key-boards are used, is the reprinting of the letter at the
distant end of the line.

Key, Bridge.
A key for use with a Wheatstone Bridge, q.v. It is desirable to first
send a current through the four arms of the bridge in using it for
testing resistances and then through the galvanometer, because it takes
a definite time for the current to reach its full strength. This is
especially the case if the element being measured has high static
capacity, as a long ocean cable. If the galvanometer connections were
completed simultaneously with the bridge connections a momentary swing
would be produced even if the arms bore the proper relation to each
other. This would cause delay in the testing. A bridge key avoids this
by first connecting the battery circuit through the arms of the bridge,
and then as it is still further depressed the galvanometer circuit is
completed.

314 STANDARD ELECTRICAL DICTIONARY.

Fig. 206. CHARGE AND DISCHARGE KEY

Key, Charge and Discharge.
A key for use in observing the discharge of a condenser immediately
after removing the battery. In one typical form it has two contacts, one
below and one above, and being a spring in itself is pressed up against
the upper one. Connections are so made that when in its upper position
it brings the two coatings of the condenser in circuit with the
galvanometer. When depressed it does the same for a battery. In use it
is depressed and suddenly released when the galvanometer receives the
full charge, before there has been time for leakage. This is one method
of connection illustrating its principle.

In the cut L is the spring-key proper. S2, is the upper contact screw
against which the spring normally presses. In this position the
galvanometer G is in circuit with the opposite coatings of the condenser
C. On depressing the contact S2, is broken and S1, is made. This brings
the battery B in circuit with the condenser coatings. On releasing the
key it springs up and the galvanometer receives the effect of the charge
of the condenser as derived from the battery.

Key, Double Contact.
A key arranged to close two distinct circuits, holding the first closed
until the second is completed. It is used for Wheatstone bridge work.

Key, Double Tapper.
A telegraph key giving contacts alternately for currents in opposite
directions, used in needle telegraphy.

Key, Increment.
A key for use in duplex and quadruplex telegraphy. Its action is to
increase the line current, not merely to suddenly turn current into it.

315 STANDARD ELECTRICAL DICTIONARY.

Fig. 207. KEMPE'S DISCHARGE KEY.

Key, Kempe's Discharge.
A key giving a charging, discharging and insulating connection, for
static condenser work. Referring to the cut l is a lever or spring with
upper discharging contact s, and lower charging contact s'. In use it is
pressed down by the insulating handle or finger piece C, until caught by
the hook attached to the key I. This hook is lower down than that on the
key D, and holds it in contact with the charging contact piece S'. On
pressing the key I, marked or designated "Insulate," it springs up,
breaks contact at S', and catching against the hook on D, which key is
designated "Discharge," remains insulated from both contacts; next on
pressing D it is released and springs up and closes the discharge
contact S. It is a form of charge and discharge key. (See Key, Charge
and Discharge.)

Key, Magneto-electric.
A telegraph key whose movements operate what is virtually a small
magneto-generator, so as to produce currents of alternating direction,
one impulse for each motion of the key. It is employed for telegraphing
without a line battery, a polarized relay being used. In one very simple
form a key is mounted on a base with a permanent magnet and connected to
the armature, so that when the key is pressed downwards it draws the
armature away from the poles of the magnet. If the magnet or its
armature is wound with insulated wire this action of the key will cause
instantaneous currents to go through a circuit connected to the magnet
or armature coils.

Fig. 208. SIEMENS' MAGNETO-ELECTRIC KEY.

In Siemens & Halske's key an H armature E is pivoted between the poles N
S, of a powerful compound horseshoe magnet, G G. It is wound with fine
wire and a key handle H is provided for working it. In its normal
position the handle is drawn upward, and the end S S of the armature
core is in contact with the south pole S of the permanent magnet, and
the end D D with the north pole. This establishes the polarity of the
armature. On depressing the key the contacts are broken and in their
place the end D D comes in contact with the south pole and the end S S
with the north pole. This suddenly reverses the polarity of the armature
and sends a momentary current through the armature coil which is in
circuit with the line. The cut only shows the principle of the key,
whose construction is quite complicated.

316 STANDARD ELECTRICAL DICTIONARY.

Key, Make and Break.
An ordinary electric key, usually making a contact when depressed, and
rising by spring action when released, and in its rise breaking the
contact.

Fig. 209. PLUG KEY

Key, Plug.
An appliance for closing a circuit. Two brass blocks are connected to
the terminals, but are disconnected from each other. A brass plug
slightly coned or with its end split so as to give it spring action is
thrust between the blocks to complete the circuit. It is used in
Resistance coils and elsewhere. (See Coil, Resistance.) Grooves are
formed in the blocks to receive the plug.

Key, Reversing.
(a) A double key, arranged so that by depressing one key a current flows
in one direction, and by depressing the other a current flows in the
opposite direction. It is used in connection with a galvanometer in
experimental, testing or measuring operations.

(b) A key effecting the same result used in quadruplex telegraphy.

Key, Sliding-Contact.
A name given to the key used for making instantaneous contacts with the
metre wire of a metre bridge, q. v. The name is not strictly correct,
because it is important that there should be no sliding contact made, as
it would wear out the wire and make it of uneven resistance.

It is a key which slides along over the wire and which, when depressed,
presses a platinum tipped knife edge upon the wire. On being released
from pressure the key handle springs up and takes the knife edge off the
wire. This removal is essential to avoid wearing the wire, whose
resistance per unit of length must be absolutely uniform.

Key, Telegraph.
The key used in telegraphy for sending currents as desired over the
line. It consists of a pivoted lever with finger piece, which lever when
depressed makes contact between a contact point on its end and a
stationary contact point on the base. This closes the circuit through
the line. When released it springs up and opens the line circuit.

Kilo.
A prefix to the names of units; it indicates one thousand times, as
kilogram, one thousand grams. A few such units are given below.

Kilodyne.
A compound unit; one thousand dynes. (See Dyne.)

Kilogram.
A compound unit; one thousand grams; 2.2046 pounds avds.

317 STANDARD ELECTRICAL DICTIONARY.

Kilojoule.
A compound unit; one thousand joules, q. v.

Kilometer.
A compound unit; one thousand meters; 3280.899 feet; 0.621382 statute
miles. (See Meter.)

Kilowatt.
A compound unit; one thousand watts, q. v.

Kine.
An absolute or C. G. S. unit of velocity or rate of motion; one
centimeter per second; proposed by the British Association.

Kirchoff's Laws.
These relate to divided circuits.

I. When a steady current branches, the quantity of electricity arriving
by the single wire is equal to the quantity leaving the junction by the
branches. The algebraical sum of the intensities of the currents passing
towards (or passing from) the junction is equal to zero; Summation(C) =
0 (Daniell.) In the last sentence currents flowing towards the point are
considered of one sign and those flowing away from it of the other.

II. In a metallic circuit comprising within it a source of permanent
difference of potential, E, the products of the intensity of the current
within each part of the circuit into the corresponding resistance are,
if the elements of current be all taken in cyclical order together,
equal to E; Summation(C * r) =E. In a metallic circuit in which there is
no source of permanent difference of potential E = 0, and Summation(C *
r) = 0.

This law applies to each several mesh of a wire network as well as to a
single metallic loop, and it holds good even when an extraneous current
is passed through the loop. (Daniell.)

In this statement of the two laws E stands for electro-motive force, C
for current intensity; and r for resistance of a single member of the
circuit.

Knife-edge Suspension.
The suspension of an object on a sharp edge of steel or agate. The knife
edge should abut against a plane. The knife edge is generally carried by
the poised object. Its edge then faces downward and on the support one
or more plane or approximately plane surfaces are provided on which it
rests. In the ordinary balance this suspension can be seen. It is
sometimes used in the dipping needle.

It is applied in cases where vertical oscillations are to be provided
for.

Knot.
The geographical mile; a term derived from the knots on the log line,
used by navigators. It is equal to 6,087 feet.

Synonyms--Nautical Mile--Geographical Mile.

318 STANDARD ELECTRICAL DICTIONARY.

Kohlrausch's Law.
A law of the rate of travel of the elements and radicals in solutions
under the effects of electrolysis. It states that each element under the
effects of electrolysis has a rate of travel for a given liquid, which
is independent of the element with which it was combined. The rates of
travel are stated for different elements in centimeters per hour for a
potential difference of one or more volts per centimeter of path.

[Friedrich Wilhelm Georg Kohlrausch (1840-1910)]

Kookogey's Solution.
An acid exciting and depolarizing solution for a zinc-carbon couple,
such as a Bunsen battery. Its formula is: Potassium bichromate, 227
parts; water, boiling, 1,134 parts; while boiling add very carefully and
slowly 1,558 parts concentrated sulphuric acid. All parts are by weight.
Use cold.

Krizik's Cores.
Cores of iron for use with magnetizing coils, q. v. They are so shaped,
the metal increasing in quantity per unit of length, as the centre is
approached, that the pull of the excited coil upon them will as far as
possible be equal in all positions. A uniform cylinder is attracted with
varying force according to its position; the Krizik bars or cores are
attracted approximately uniformly through a considerable range.

318 STANDARD ELECTRICAL DICTIONARY.

L.
Symbol for length and also for the unit of inductance or coefficient of
induction, because the dimensions of inductance are length.

Lag, Angle of.
(a) The angle of displacement of the magnetic axis of an armature of a
dynamo, due to its magnetic lag. The axis of magnetism is displaced in
the direction of rotation. (See Magnetic Lag.)

(b) The angle expressing the lag of alternating current and
electro-motive force phases.

Laminated. adj.
Made up of thin plates, as a laminated armature core or converter core.

Lamination.
The building up of an armature core or other thing out of plates. The
cores of dynamo armatures or of alternating current converters are often
laminated. Thus a drum armature core may consist of a quantity of thin
iron discs, strung upon a rod and rigidly secured, either with or
without paper insulation between the discs. If no paper is used the film
of oxide on the iron is relied on for insulation. The object of
lamination is to break up the electrical continuity of the core, so as
to avoid Foucault currents. (See Currents, Foucault.) The laminations
should be at right angles to the direction of the Foucault currents
which would be produced, or in most cases should be at right angles to
the active parts of the wire windings.

319 STANDARD ELECTRICAL DICTIONARY.

Lamination of Armature Conductors.
These are sometimes laminated to prevent the formation of eddy currents.
The lamination should be radial, and the strips composing it should be
insulated from each other by superficial oxidation, oiling or
enamelling, and should be united only at their ends.

Fig. 210. PILSEN ARC LAMP.

Lamp, Arc.
A lamp in which the light is produced by a voltaic arc. Carbon
electrodes are almost universally employed. Special mechanism, operating
partly by spring or gravity and partly by electricity, is employed to
regulate the distance apart of the carbons, to let them touch when no
current passes, and to separate them when current is first turned on.

The most varied constructions have been employed, examples of which will
be found in their places. Lamps may in general be divided into classes
as follows, according to their regulating mechanism and other features:

(a) Single light regulators or monophotes. Lamps through whose
regulating mechanism the whole current passes. These are only adapted to
work singly; if several are placed in series on the same circuit, the
action of one regulator interferes with that of the next one.

(b) Multiple light regulators or polyphotes. In these the regulating
mechanism and the carbons with their arc are in parallel; the regulating
device may be a single magnet or solenoid constituting a derived or
shunt-circuit lamp, or it may include two magnets working differentially
against or in opposition to each other constituting a differential lamp.

320 STANDARD ELECTRICAL DICTIONARY.

(c) Lamps with fixed parallel carbons termed candles (q. v., of various
types).

(d) Lamps without regulating mechanism. These include lamps with
converging carbons, whose object was to dispense with the regulating
mechanism, but which in some cases have about as much regulating
mechanism as any of the ordinary arc lamps.

Lamp, Contact.
A lamp depending for its action on loose contact between two carbon
electrodes. At the contact a species of incandescence with incipient
arcs is produced. One of the electrodes is usually flat or nearly so,
and the other one of pencil shape rests upon it.

Lamp, Differential Arc.
An arc lamp, the regulation of the distance between whose carbons
depends on the differential action of two separate electrical coils. The
diagram illustrates the principle. The two carbons are seen in black;
the upper one is movable, The current arrives at A. It divides, and the
greater part goes through the low resistance coil M to a contact roller
r, and thence by the frame to the upper carbon, and through the arc and
lower carbon to B, where it leaves the lamp. A smaller portion of the
current goes through the coil M1 of higher resistance and leaves the
lamp also at B. A double conical iron core is seen, to which the upper
carbon holder is attached. This is attracted in opposite directions by
the two coils. If the arc grows too long its resistance increases and
the coil M1 receiving more current draws it down and thus shortens the
arc. If the arc grows too short, its resistance falls, and the coil M
receives more current and draws the core upwards, thus lengthening the
arc. This differential action of the two cores gives the lamp its name.
R is a pulley over which a cord passes, one end attached to the core and
the other to a counterpoise weight, W.

Fig. 211. DIAGRAM OF THE PILSEN DIFFERENTIAL ARC LAMP.

321 STANDARD ELECTRICAL DICTIONARY.

Lamp, Holophote.
A lamp designed for use alone upon its own circuit. These have the
regulating mechanism in series with the carbon and arc, so that the
whole current goes through both. (See Lamp, Arc.)

Synonym--Monophote Lamp.

Lamp-hour.
A unit of commercial supply of electric energy; the volt-coulombs
required to maintain an electric lamp for one hour. A sixteen-candle
power incandescent lamp is practically the lamp alluded to, and requires
about half an ampere current at 110 volts, making a lamp-hour equal to
about 198,000 volt-coulombs.

Lamp, Incandescent.
An electric lamp in which the light is produced by heating to whiteness
a refractory conductor by the passage of a current of electricity. It is
distinguished from an arc lamp (which etymologically is also an
incandescent lamp) by the absence of any break in the continuity of its
refractory conductor. Many different forms and methods of construction
have been tried, but now all have settled into approximately the same
type.

The incandescent lamp consists of a small glass bulb, called the
lamp-chamber, which is exhausted of air and hermetically sealed. It
contains a filament of carbon, bent into a loop of more or less simple
shape. This shape prevents any tensile strain upon the loop and also
approximates to the outline of a regular flame.

Fig. 212. INCANDESCENT ELECTRIC LAMP.

322 STANDARD ELECTRICAL DICTIONARY.

The loop is attached at its ends to two short pieces of platinum wire,
which pass through the glass of the bulb and around which the glass is
fused. As platinum has almost exactly the same coefficient of
heat-expansion as glass, the wires do not cause the glass to crack.

The process of manufacture includes the preparation of the filament.
This is made from paper, silk, bamboo fibre, tamidine, q. v., or other
material. After shaping into the form of the filament the material is
carbonized at a high heat, while embedded in charcoal, or otherwise
protected from the air. The flashing process (see Flashing of
incandescent Lamp Carbons) may also be applied. The attachment to the
platinum wires is effected by a minute clamp or by electric soldering.
The loop is inserted and secured within the open globe, which the glass
blower nearly closes, leaving one opening for exhaustion.

The air is pumped out, perhaps first by a piston pump, but always at the
end by a mercurial air pump. (See Pump, Geissler--and others.) As the
exhaustion becomes high a current is passed through the carbons heating
them eventually to white heat so as to expel occluded gas. The occluded
gases are exhausted by the pump and the lamp is sealed by melting the
glass with a blowpipe or blast-lamp flame. For the exhaustion several
lamps are usually fastened together by branching glass tubes, and are
sealed off one by one.

The incandescent lamps require about 3.5 watts to the candle power, or
give about 12 sixteen-candle lamps to the horse power expended on them.

Generally incandescent lamps are run in parallel or on multiple arc
circuits. All that is necessary in such distribution systems is to
maintain a proper potential difference between the two leads across
which the lamps are connected. In the manufacture of lamps they are
brought to an even resistance and the proper voltage at which they
should be run is often marked upon them. This may be fifty volts and
upward. One hundred and ten volts is a very usual figure. As current one
ampere for a fifty-volt, or about one-half an ampere for a one hundred
and ten volt lamp is employed.

Lamp, Incandescent, Three Filament.
A three filament lamp is used for three phase currents. It has three
filaments whose inner ends are connected, and each of which has one
leading-in wire. The three wires are connected to the three wires of the
circuit. Each filament receives a current varying in intensity, so that
there is always one filament passing a current equal to the sum of the
currents in the other two filaments.

Lamp, Lighthouse.
A special type of arc light. It is adapted for use in a lighthouse
dioptric lantern, and hence its arc has to be maintained in the same
position, in the focus of the lenses. The lamps are so constructed as to
feed both carbons instead of only one, thereby securing the above
object.

323 STANDARD ELECTRICAL DICTIONARY.

Lamp, Pilot.
A lamp connected to a dynamo, and used by its degree of illumination to
show when the dynamo on starting becomes excited, or builds itself up.

Lamp, Polyphote.
An arc lamp adapted to be used, a number in series, upon the same
circuit. The electric regulating mechanism is placed in shunt or in
parallel with the carbons and arc. (See Lamp, Arc.)

Lamps, Bank of.
A number of lamps mounted on a board or other base, and connected to
serve as voltage indicator or to show the existence of grounds, or for
other purposes.

Lamp, Semi-incandescent.
A lamp partaking of the characteristics of both arc and incandescence; a
lamp in which the imperfect contact of two carbon electrodes produces a
part of or all of the resistance to the current which causes
incandescence.

The usual type of these lamps includes a thin carbon rod which rests
against a block of carbon. The species of arc formed at the junction of
the two heats the carbons. Sometimes the upper carbon or at least its
end is heated also by true incandescence, the current being conveyed
near to its end before entering it.

Semi-incandescent lamps are not used to any extent now.

Lamp Socket.
A receptacle for an incandescent lamp; the lamp being inserted the
necessary connections with the two leads are automatically made in most
sockets. The lamps may be screwed or simply thrust into the socket and
different ones are constructed for different types of lamps. A key for
turning the current on and off is often a part of the socket.

Latent Electricity.
The bound charge of static electricity. (See Charge, Bound.)

Law of Intermediate Metals.
A law of thermo-electricity. The electro-motive force between any two
metals is equal to the sum of electro-motive forces between each of the
two metals and any intermediate metal in the thermo-electric series, or
the electro-motive force between any two metals is equal to the sum of
the electromotive forces between all the intermediate ones and the
original two metals; it is the analogue of Volta's Law, q. v.

Law of Inverse Squares.
When force is exercised through space from a point, its intensity varies
inversely with the square of the distance. Thus the intensity of light
radiated by a luminous point at twice a given distance therefrom is of
one-fourth the intensity it had at the distance in question.
Gravitation, electric and magnetic attraction and repulsion and other
radiant forces are subject to the same law.

324 STANDARD ELECTRICAL DICTIONARY.

Law of Successive Temperatures.
A law of thermo-electricity. The electro-motive force due to a given
difference of temperature between the opposite junctions of the metals
is equal to the sum of the electro-motive forces produced by fractional
differences of temperature, whose sum is equal to the given difference
and whose sum exactly fills the given range of temperature.

Law, Right-handed Screw.
This rather crude name is given by Emtage to a law expressing the
relation of direction of current in a circuit to the positive direction
of the axis of a magnet acted on by such current. It is thus expressed:
A right-handed screw placed along the axis of the magnet and turned in
the direction of the current will move in the positive direction, i. e.,
towards the north pole of the axis of the magnet.

Lead.
A metal; one of the elements; symbol Pb. Atomic weight, 207;
equivalent, 103-1/2; valency, 2.
Lead may also be a tetrad, when its equivalent is 51.75.
The following data are at 0º C. (32º F.) with compressed metal:
Relative Resistance, (Silver = l) 13.05
Specific Resistance, 19.63 microhms.
Resistance of a wire,
(a) 1 ft. long, weighing 1 grain, 3.200 ohms.
(b) 1 meter long, weighing 1 gram, 2.232 "
(c) 1 meter long, 1 millimeter thick, .2498 "
Resistance of 1 inch cube, 7.728 microhms.
Electro-Chemical Equivalent (Hydrogen = .0105) 1.086 mgs.

Leading Horns.
The tips of pole pieces in a dynamo, which extend in the direction of
movement of the armature.

Leading-in Wires.
The platinum wires passing through the glass of an incandescent
lamp-chamber, to effect the connection of the carbon filament with the
wires of the circuit.

Lead of Brushes, Negative.
In a motor the brushes are set backwards from their normal position, or
in a position towards the direction of armature rotation or given a
negative lead instead of a positive one, such as is given to dynamo
brushes.

Leak.
A loss or escape of electricity by accidental connection either with the
ground or with some conductor. There are various kinds of leak to which
descriptive terms are applied.

Leakage.
The loss of current from conductors; due to grounding at least at two
places, or to very slight grounding at a great many places, or all along
a line owing to poor insulation. In aerial or pole telegraph lines in
wet weather there is often a very large leakage down the wet poles from
the wire. (See Surface Leakage--Magnetic Leakage.)

325 STANDARD ELECTRICAL DICTIONARY.

Leakage Conductor.
A conductor placed on telegraph poles to conduct directly to earth any
leakage from a wire and thus prevent any but a very small portion
finding its way into the other wires on the same pole. It presents a
choice of evils, as it increases the electrostatic capacity of the line,
and thus does harm as well as good. It consists simply of a wire
grounded and secured to the pole.

Leg of Circuit.
One lead or side of a complete metallic circuit.

Lenz's Law.
A law expressing the relations of direction of an inducing current or
field of force to the current induced by any disturbance in the
relations between such field and any closed conductor within its
influence. It may be variously expressed.

(a) If the relative position of two conductors, A and B, be changed, of
which A is traversed by a current, a current is induced in B in such a
direction that, by its electro-dynamic action on the current in A, it
would have imparted to the conductors a motion of the contrary kind to
that by which the inducing action was produced. (Ganot.)

(b) The new (induced) current will increase the already existing
resistances, or develop new resistance to that disturbance of the field
which is the cause of induction. (Daniell.)

(c) When a conductor is moving in a magnetic field a current is induced
in the conductor in such a direction as by its mechanical action to
oppose the motion. (Emtage.)

(d) The induced currents are such as to develop resistance to the change
brought about.

Letter Boxes, Electric.
Letter boxes with electrical connections to a bell or indicator of some
sort, which is caused to act by putting a letter into the box.

Leyden Jar.
A form of static condenser.

In its usual form it consists of a glass jar. Tinfoil is pasted around
the lower portions of its exterior and interior surfaces, covering from
one-quarter to three-quarters of the walls in ordinary examples. The
rest of the glass is preferably shellacked or painted over with
insulating varnish, q. v. The mouth is closed with a wooden or cork
stopper and through its centre a brass rod passes which by a short chain
or wire is in connection with the interior coating of the jar. The top
of the rod carries a brass knob or ball.

If such a jar is held by the tinfoil-covered surface in one hand and its
knob is held against the excited prime conductor of a static machine its
interior becomes charged; an equivalent quantity of the same electricity
is repelled through the person of the experimenter to the earth and when
removed from the conductor it will be found to hold a bound charge. If
the outer coating and knob are both touched or nearly touched by a
conductor a disruptive discharge through it takes place.

326 STANDARD ELECTRICAL DICTIONARY.

Fig. 213. LEYDEN JAR WITH DISCHARGER.

If one or more persons act as discharging conductors they will receive a
shock. This is done by their joining hands, a person at one end touching
the outer coating and another person at the other end touching the knob.

From an influence machine a charge can be taken by connecting the
coating to one electrode and the knob to the other.

Fig. 214. SULPHURIC ACID LEYDEN JAR.

327 STANDARD ELECTRICAL DICTIONARY.

Leyden Jar, Sir William Thomson's.
An especially efficient form of Leyden jar. It consists of a jar with
outer tinfoil coating only. For the interior coating is substituted a
quantity of concentrated sulphuric acid. The central rod is of lead with
a foot, which is immersed in the acid and from which the rod rises. A
wooden cover partly closes the jar, as the central tube through which
the rod passes is so large as not to allow the wood to touch it. Thus
any leakage from inner to outer coating has to pass over the inside and
outside glass surfaces. In the common form of jar the wooden cover may
short circuit the uncoated portion of the inner glass surface. In the
cut a simplified form of Thomson's Leyden jar is shown, adapted for
scientific work.

Lichtenberg's Figures.
If the knob of a Leyden jar or other exited electrode is rubbed over the
surface of ebonite, shellac, resin or other non-conducting surface it
leaves it electrified in the path of the knob. If fine powder such as
flowers of sulphur or lycopodium is dusted over the surface and the
excess is blown away, the powder will adhere where the surface was
electrified, forming what are called Lichtenberg's Figures, Lycopodium
and sulphur show both positive and negative figures, that is to say,
figures produced by a positively or negatively charged conductor. Red
lead adheres only to negative figures. If both positive and negative
figures are made and the surface is sprinkled with both red lead and
flowers of sulphur each picks out its own figure, the sulphur going
principally to the positive one.

The red lead takes the form of small circular heaps, the sulphur
arranges itself in tufts with numerous diverging branches. This
indicates the difference in the two electricities. The figures have been
described as "a very sensitive electrosope for investigating the
distribution of electricity on an insulating surface." (Ganot.)

Life of Incandescent Lamps.
The period of time a lamp remains in action before the carbon filament
is destroyed. The cause of a lamp failing may be the volatilization of
the carbon of the filament, causing it to become thin and to break; or
the chamber may leak. The life of the lamp varies; 600 hours is a fair
estimate. Sometimes they last several times this period.

The higher the intensity at which they are used the shorter is their
life. From their prime cost and the cost of current the most economical
way to run them can be approximately calculated.

Lightning.
The electrostatic discharge to the earth or among themselves of clouds
floating in the atmosphere. The discharge is accompanied by a spark or
other luminous effect, which may be very bright and the effects, thermal
and mechanical, are often of enormous intensity.

The lightning flash is white near the earth, but in the upper regions
where the air is rarefied it is of a blue tint, like the spark of the
electric machine. The flashes are often over a mile in length, and
sometimes are four or five miles long. They have sometimes a curious
sinuous and often a branching shape, which has been determined by
photography only recently. To the eye the shape seems zigzag.

328 STANDARD ELECTRICAL DICTIONARY.

In the case of a mile-long flash it has been estimated that 3,516,480 De
la Rue cells, q. v., would be required for the development of the
potential, giving the flash over three and one-half millions of volts.
But as it is uncertain how far the discharge is helped on its course by
the rain drops this estimate may be too high.

There are two general types of flash. The so-called zigzag flash
resembles the spark of an electric machine, and is undoubtedly due to
the disruptive discharge from cloud to earth. Sheet lightning has no
shape, simply is a sudden glow, and from examination of the spectrum
appears to be brush discharges (see Discharge, Brush) between clouds.
Heat lightning is attributed to flashes below the horizon whose light
only is seen by us. Globe or ball lightning takes the form of globes of
fire, sometimes visible for ten seconds, descending from the clouds. On
reaching the earth they sometimes rebound, and sometimes explode with a
loud detonation. No adequate explanation has been found for them.

The flash does not exceed one-millionth of a second in duration; its
absolute light is believed to be comparable to that of the sun, but its
brief duration makes its total light far less than that of the sun for
any period of time.

If the disruptive discharge passes through a living animal it is often
fatal. As it reaches the earth it often has power enough to fuse sand,
producing fulgurites, q. v. (See also Back Shock or Stroke of
Lightning.)

Volcanic lightning, which accompanies the eruptions of volcanoes, is
attributed to friction of the volcanic dust and to vapor condensation.

Lightning Arrester.
An apparatus for use with electric lines to carry off to earth any
lightning discharge such lines may pick up. Such discharge would imperil
life as well as property in telegraph offices and the like.

Arresters are generally constructed on the following lines. The line
wires have connected to them a plate with teeth; a second similar plate
is placed near this with its teeth opposite to those of the first plate
and nearly touching it. The second plate is connected by a low
resistance conductor to ground. Any lightning discharge is apt to jump
across the interval, of a small fraction of an inch, between the
oppositely placed points and go to earth.

Another type consists of two plates, placed face to face, and pressing
between them a piece of paper or mica. The lightning is supposed to
perforate this and go to earth. One plate is connected to the line, the
other one is grounded.

The lightning arrester is placed near the end of the line before it
reaches any instrument. (See Alternative Paths.)

329 STANDARD ELECTRICAL DICTIONARY.

Fig. 215. COMB OR TOOTHED LIGHTNING ARRESTER.

Fig. 216. FILM OR PLATE LIGHTNING ARRESTER.

Lightning Arrester, Counter-electro-motive Force.
An invention of Prof. Elihu Thompson. A lightning arrester in which the
lightning discharge sets up a counter-electro-motive force opposed to
its own. This it does by an induction coil. If a discharge to earth
takes place it selects the primary of the coil as it has low
self-induction. In its discharge it induces in the secondary a reverse
electro-motive force which protects the line.

Lightning Arrester Plates.
The toothed plates nearly in contact, tooth for tooth, or the flat
plates of a film lightning arrester, which constitute a lightning
arrester. Some advocate restricting the term to the plate connected to
the line.

Lightning Arrester, Vacuum.
A glass tube, almost completely exhausted, into which the line wire is
fused, while a wire leading to an earth connection has its end fused in
also.

A high tension discharge, such as that of lightning, goes to earth
across the partial vacuum in preference to going through the line, which
by its capacity and self-induction opposes the passage through it of a
lightning discharge.

It is especially adapted for underground and submarine lines.

330 STANDARD ELECTRICAL DICTIONARY.

Lightning, Ascending.
Lightning is sometimes observed which seems to ascend. It is thought
that this may be due to positive electrification of the earth and
negative electrification of the clouds.

Lightning, Globe or Globular.
A very unusual form of lightning discharge, in which the flashes appear
as globes or balls of light. They are sometimes visible for ten seconds,
moving so slowly that the eye can follow them. They often rebound on
striking the ground, and sometimes explode with a noise like a cannon.
They have never been satisfactorily explained. Sometimes the phenomenon
is probably subjective and due to persistence of vision.

Lightning Jar.
A Leyden jar whose coatings are of metallic filings dusted on to the
surface while shellacked, and before the varnish has had time to dry. In
its discharge a scintillation of sparks appears all over the surface.

Line of Contact.
The line joining the points of contact of the commutator brushes in a
dynamo or motor.

Synonym--Diameter of Commutation.

Lines of Force.
Imaginary lines denoting the direction of repulsion or attraction in a
field of force, q. v. They may also be so distributed as to indicate the
relative intensity of all different parts of the field. They are normal
to equipotential surfaces. (See Electro-magnetic Lines of
Force--Electrostatic Lines of Force--Magnetic Lines of Force.)

Lines of Induction.
Imaginary lines within a body marking the direction taken within it by
magnetic induction. These are not necessarily parallel to lines of
force, but may, in bodies of uniform agglomeration, or in crystalline
bodies, take various directions.

Synonym--Lines of Magnetic Induction.

Lines of Slope.
Lines in a field of force which mark the directions in which the
intensity of force in the field most rapidly falls away.

Links, Fuse.
Links made of more or less easily fusible metal, for use as safety
fuses.

Listening Cam.
In a telephone exchange a cam or species of switch used to connect the
operator's telephone with a subscriber's line.

331 STANDARD ELECTRICAL DICTIONARY.

Lithanode.
A block of compressed lead binoxide, with platinum connecting foils for
use as an electrode in a storage battery. It has considerable capacity,
over 5 ampere-hours per pound of plates, but has not met with any
extended adoption.

Load.
In a dynamo the amperes of current delivered by it under any given
conditions.

Local Action.
(a) In its most usual sense the electric currents within a battery, due
to impurities in the zinc, which currents may circulate in exceedingly
minute circuits, and which waste zinc and chemicals and contribute
nothing to the regular current of the battery. Amalgamated or chemically
pure zinc develops no local action.

(b) The term is sometimes applied to currents set up within the armature
core or pole pieces of a dynamo. (See Currents, Foucault.)

Local Battery.
A battery supplying a local circuit (q. v.); in telegraphy, where it is
principally used, the battery is thrown in and out of action by a relay,
and its current does the work of actuating the sounder and any other
local or station instruments. (See Relay.)

Local Circuit.
A short circuit on which are placed local apparatus or instruments. Such
circuit is of low resistance and its current is supplied by a local
battery, q. v. Its action is determined by the current from the main
line throwing its battery in and out of circuit by a relay, q. v., or
some equivalent.

Local Currents.
Currents within the metal parts of a dynamo. (See Currents, Foucault.)
In a galvanic battery. where there is local action, q. v., there are
also local currents, though they are not often referred to.

Localization.
Determining the position of anything, such as a break in a cable, or a
grounding in a telegraph line. In ocean cables two typical cases are the
localization of a break in the conductor and of a defect in the
insulation admitting water. The first is done by determining the static
capacity of the portion of the line which includes the unbroken portion
of the conductor; the other by determining the resistance of the line on
a grounded circuit.

Locus.
A place. The word is used to designate the locality or position of, or
series of positions of definite conditions and the like. Thus an
isogonic line is the locus of equal declinations of the magnetic needle;
it is a line passing through all places on the earth's surface where the
condition of a given declination is found to exist.

332 STANDARD ELECTRICAL DICTIONARY.

Lodestone.
Magnetic magnetite; magnetite is an ore of iron, Fe3 04 which is
attracted by the magnet. Some samples possess polarity and attract iron.
The latter are lodestones.

Synonym--Hercules Stone

Logarithm.
The exponent of the power to which it is necessary to raise a fixed
number to produce a given number. The fixed number is the base of the
system. There are two systems; one, called the ordinary system, has 10
for its base, the other, called the Naperian system, has 2.71828 for its
base. The latter are also termed hyperbolic logarithms, and are only
used in special calculations.

Log, Electric.
An apparatus for measuring the speed of a ship. A rotating helical vane
of known pitch is dragged behind the vessel. As the helix rotates its
movements may actuate electric machinery for registering its rotations.
The number of these in a given time, multiplied by the pitch of the
vane, gives the distance traversed in such time.

Loop.
A portion of a circuit introduced in series into another circuit. The
latter circuit is opened by a spring-jack, q. v. or other device, and
the loop inserted. By loops any number of connections can be inserted
into a circuit in series therewith, and in series or in parallel with
one another.

Loop Break.
A double bracket or similar arrangement for holding on insulators the
ends of a conductor which is cut between them, and to which are
connected the ends of a loop. The space between the insulators may be
about a foot.

Luces.
This may be used as the plural of lux, q. v. It is the Latin plural.

Luminous Jar.
A Leyden jar whose coatings are of lozenge-shaped pieces of tinfoil
between which are very short intervals. When discharged, sparks appear
all over the surface where the lozenges nearly join.

Lux.
A standard of illumination, q. v., as distinguished from illuminating
power.

It is the light given by one candle at a distance of 12.7 inches--by a
carcel, q. v., at a distance of one meter---or by 10,000 candles at
105.8 feet.

It was proposed by W. H. Preece. All the above valuations are identical.

332 STANDARD ELECTRICAL DICTIONARY.

M.
(a) Symbol of gaseous pressure equal to one-millionth of an atmosphere.

(b) The Greek m, µ, is used as the symbol of magnetic permeability.

333 STANDARD ELECTRICAL DICTIONARY.

Machine, Cylinder Electric.
A frictional electric machine whose rotating glass is in the shape of a
cylinder instead of a disc as in the more recent machines.

Fig. 217. PLATE FRICTIONAL ELECTRIC MACHINE.

Machine, Frictional Electric.
An apparatus for development of high tension electricity by contact
action, brought about by friction.

It consists of a plate or cylinder of glass mounted on insulating
standards and provided with a handle for turning it. One or more
cushions of leather are held on an insulated support, so as to rub
against the plate or cylinder as it is turned. A metal comb or combs are
held on another insulating support so as to be nearly in contact with
the surface of the glass plate at a point as far removed as possible
from the rubbers. The combs are attached to a brass ball or round-ended
cylinder, which is termed the prime conductor.

In use either the prime conductor or cushions are connected by a chain
or otherwise with the earth. Assume it to be the cushions. As the
machine is worked by turning the plate, the glass and cushion being in
contact develop opposite electricities. The glass is charged with
positive electricity, and as it turns carries it off and as it reaches
the prime conductor by induction and conduction robs it of its negative
electricity. Meanwhile the cushions negatively excited deliver their
charge to the earth. The action thus goes on, the prime conductor being
charged with positive electricity.

334 STANDARD ELECTRICAL DICTIONARY.

If the prime conductor is connected to the earth and the cushions are
left insulated, negative electricity can be collected from the cushions.

In some machines both prime conductor and cushions are kept insulated
and without ground contact. Electrodes connecting with each are brought
with their ends close enough to maintain a sparking discharge.

Machine Influence.
A static electric machine working by induction to build up charges of
opposite nature on two separate prime conductors. In general they are
based on the principle of the electrophorous. Work is done by the
operator turning the handle. This rotates a disc and draws excited parts
of it away from their bound charges. This represents a resistance to
mechanical motion. The work absorbed in overcoming this mechanical
resistance appears as electric energy. There are various types of
influence machines, the Holtz, Toeppler-Holtz and Wimshurst being the
most used. The electrophorous, q. v., is a type of influence machine.

Machine, Holtz Influence.
A static electric machine. It includes two plates, one of which is
rapidly rotated in front of the other. Two armatures of paper are
secured to the back of the stationary plate at opposite ends of a
diameter. To start it one of these is charged with electricity. This
charge by induction acts through the two thicknesses of glass upon a
metal bar carrying combs, which lies in front of the further side of the
movable plate. The points opposite the armature repel electrified air,
which strikes the movable disc and charges it. A second rod with comb at
the opposite end of the same diameter acts in the reverse way. Thus
opposite sections of the disc are oppositely charged and the combs with
them. By induction these portions of the disc react upon the two
armatures. The opposite electricities escape from the armatures by paper
tongues which are attached thereto and press against the back of the
movable plate. As the plate rotates the opposite electricities on its
face neutralize the electricity repelled from the combs. The charges on
the back strengthen the charges of the armatures and brass combs. Thus
the machine builds up, and eventually a discharge of sparks takes place
from the poles of the brass combs.

335 STANDARD ELECTRICAL DICTIONARY.

Machine, Toeppler-Holtz.
A modification of the Holtz machine. The priming charge of the armatures
is produced by friction of metallic brushes against metallic buttons on
the face of the rotating plate. (See Machine, Holtz.)

Machine, Wimshurst.
A form of static influence machine. It consists of two plates of glass,
on which radial sectors of tinfoil are pasted. Both plates are rotated
in opposite directions. The sectors of the two plates react one upon the
other, and electric charges of opposite sign accumulate on the opposite
sides of the plates and are collected therefrom by collecting combs.

Mack.
A name, derived from Maxwell, and suggested for the unit of inductance.
It is due to Oliver Heaviside, but has never been adopted. (See Henry.)

Magne-Crystallic Action.
The action of a supposed force of the same name, proposed by Faraday. It
relates to the different action of a magnetic field upon crystalline
bodies, according to the position of their axes of crystallization. A
needle of tourmaline, normally paramagnetic, if poised with its axis
horizontal, is diamagnetic. Bismuth illustrates the same phenomenon. The
subject is obscure. Faraday thought that he saw in it the action of a
specific force.

Magnet.
A body which tends when suspended by its centre of gravity to lay itself
in a definite direction, and to place a definite line within it, its
magnetic axis, q. v., in a definite direction, which, roughly speaking,
lies north and south. The same bodies have the power of attracting iron
(Daniell), also nickel and cobalt.

Magnets are substances which possess the power of attracting iron.
(Ganot.)

Magnet, Anomalous.
A magnet possessing more than the normal number (two) of poles. If two
straight magnets are placed end to end with their south poles in
juxtaposition the compound bar will seem to possess three poles, one at
each end and one in the middle. The apparent pole in the middle is
really made up of two consequent poles, q. v. It sometimes happens that
when a single long thin bar is magnetized consequent poles are produced,
although such magnet is in one piece. This may be accidental, as in such
case it is quite hard to avoid anomalous poles, or, as in the field
magnets of some forms of dynamos, anomalous poles may be purposely
produced.

Magnet, Artificial.
A magnet formed artificially by any method of magnetization (see
Magnetism) applicable to permanent magnets, electro-magnets and
solenoids. It expresses the distinction from the natural magnets or
lodestone, q. v. It is made of steel in practice magnetized by some of
the methods described under Magnetization.

336 STANDARD ELECTRICAL DICTIONARY.

Magnet, Axial.
A straight-solenoid with axial core.

Magnet, Bar.
A bar magnet is one in the shape of a bar, i. c., straight with parallel
sides and considerably longer than wide or deep.

Magnet, Bell-shaped.
A form of permanent magnet used in some galvanometers. In shape it is a
thick-sided cylindrical box with two slots cut out of opposite sides, so
as to make it represent a horseshoe magnet. Its shape enables it to be
surrounded closely by a mass of copper, for damping its motion, to
render the instrument dead-beat. Such a magnet is used in Siemens &
Halske's galvanometer.

Magnet Coil.
A coil to be thrust over an iron core, to make an electro-magnet. They
are often wound upon paper or wooden bobbins or spools, so as to be
removable from the core if desired.

Magnet, Compensating.
(a) A magnet fastened near a compass on an iron or steel ship to
compensate the action of the metal of the ship upon the magnetic needle.
The ship itself always has some polarity and this is neutralized by one
or more compensating magnets.

(b) See below.

Magnet, Controlling.
A magnet attached to a galvanometer by which the directive tendency of
its magnetic needle is adjusted. In the reflecting galvanometer it often
is a slightly curved magnet carried by a vertical brass spindle rising
from the center of the instrument, and which magnet may be slid up and
down on the spindle to regulate or adjust its action.

Synonym--Compensating Magnet.

Magnet, Compound.
A permanent magnet, built up of a number of magnets. Small bars can be
more strongly magnetized than large. Hence a compound magnet may be made
more powerful than a simple one.

Magnet Core.
The iron bar or other mass of iron around which insulated wire is wound
for the production of an electro-magnet. The shapes vary greatly,
especially for field magnets of dynamos and motors. For these they are
usually made of cast iron, although wrought iron is preferable from the
point of view of permeability.

Magnet, Damping.
A damping magnet is one used for bringing an oscillating body to rest.
The body may be a metallic disc or needle, and the action of the magnet
depends on its lines of force which it establishes, so that the body has
to cut them, and hence has its motion resisted.

337 STANDARD ELECTRICAL DICTIONARY.

Magnet, Deflection of.
The change of position of a magnet from the plane of the earth's
meridian in which it normally is at rest into another position at some
angle thereto, by the effect of an artificial magnetic field, as the
deflection of a galvanometer needle.

Magnet, Electro-.
A magnet consisting of a bar of iron, bundle of iron wires, iron tube or
some equivalent, around which a coil of insulated wire is wound. Such
combination becomes polarized when a current is passed through it and is
an active magnet. On the cessation of the current its magnetism in part
or almost completely disappears. (See Electro-magnet.)

Magnet, Equator of.
In a magnet the locus of points of no attractive power and of no
polarity. In a symmetrical, evenly polarized magnet it is the imaginary
line girdling the centre. The terms Neutral Point or Neutral Line have
displaced it.

Synonyms--Neutral Line--Neutral Point.

Magnet, Field.
A magnet, generally an electro-magnet, used to produce the field in a
dynamo or motor.

Magnet, Haarlem.
Celebrated magnets made in Haarlem, Holland. Logeman, Van Wetteren,
Funckler and Van der Willigen were the makers who gave the celebrity to
the magnets. They were generally horseshoe magnets, and would carry
about twenty times their own weight.

Magnet, Horseshoe.
A magnet of U shape--properly one with the poles brought a little closer
together than the rest of the limbs. For direct lifting and attractive
effects it is the most generally adopted type. Its advantage as regards
lifting effect is due to small reluctance, q. v., offered by a complete
iron circuit, such as the armature and magnet together produce. As the
term is now used it is applied to any U shaped magnet.

Fig. 218. JOULE'S ELECTRO-MAGNET.

Magnet, Joule's Electro.
An electro-magnet of the shape of a cylinder with a longitudinal segment
cut-off. It is wound with wire as shown. The segment cut-off is a piece
of the same shape as the armature. It is of high power.

338 STANDARD ELECTRICAL DICTIONARY.

Magnetic Adherence.
The tendency of a mass of iron to adhere to the poles of a magnet. It is
best figured as due to the virtual shortening of lines of force, as the
more permeable iron gives a better path for them than the air can
afford, and consequently a virtually shorter one.

Magnetic Attraction and Repulsion.
The attraction of a magnet for iron, steel, nickel and cobalt and of
unlike poles of magnets for each other. It is identical with
electro-magnetic attraction, q.v. (Also see Electro-magnetism.)

Magnetic Attraction and Repulsion, Coulomb's Law of.
Magnetic attraction and repulsion are inversely as the square of the
distance. (Ganot.)

While theoretically true in the case of isolated poles, in practise it
does not generally apply on account of the large diameter and relative
shortness of magnets.

Magnetic Axis.
The line connecting the poles of a magnet. It does not generally
coincide exactly with any symmetrical axis of figure. In such cases an
error is introduced into the indications of the needle which must be
determined and allowed for in compasses. To determine it with a magnetic
needle the suspension cup is made removable, so that the needle can be
reversed. Readings are taken with one side of the needle and then with
the other side of the needle up, and the average corresponds with the
position of the magnetic axis in both positions of the needle.

Magnetic Azimuth.
The angle, measured on a horizontal circle, between the magnetic
meridian and a great circle of the earth passing through the observer
and any observed body. It is the astronomical azimuth of a body referred
to the magnetic meridian and therefore subject to the variation of the
compass. The angle is the magnetic azimuth of the observed body.

Magnetic Battery.
A name for a compound permanent magnet; one made up by bolting or
clamping together, or to single soft iron pole pieces, a number of
single permanent magnets. There are a number of forms of compound
magnets. In making them care has to be taken to have them of even
strength. It is also well to have them slightly separated. The object of
both these precautions is to prevent a stronger element or magnet from
depolarizing its neighbor.

Synonym--Compound Magnet.

Magnetic Bridge.
An apparatus for testing the relative permeability of iron. It consists
of a rectangular system of iron cores. Three of the sides are wound with
wire as shown. The other side is built up of double bars, and from the
centre two curved arms rise, as shown in the cut. The arms do not touch.
Between them a short magnet is suspended by a filament, which also
carries a mirror and an index.

339 STANDARD ELECTRICAL DICTIONARY.

Fig. 219. MAGNETIC BRIDGE.

A lamp and scale are provided as in the reflecting galvanometer. When
adjusted the magnetic needle hangs as shown in the cut, Fig. 219,
without any tendency to turn towards either curved pole piece. If all
iron parts are symmetrical and of similar metal, a current through the
coils will make no difference. It will work in magnetic opposition upon
the two arms, or, in other words, will maintain both arms at identical
potential.

Fig. 220. POLE PIECES, MAGNETIC NEEDLE
AND MIRROR OF MAGNETIC BRIDGE.

If there is the least difference in permeability, length or thickness
between any of the iron bars the magnetic potential of the two curved
arms will differ, and the magnetic needle will turn one way or the
other. In practical use different samples of iron are substituted for
the unwound members of the fourth side of the parallelogram, and the
needle by its motions indicates the permeability.

In the cut, Fig. 220, D D are the ends of the curved pole pieces; A the
wire carrying the mirror B and magnetic needle N, and E is the index
which shows the larger deflections.

340 STANDARD ELECTRICAL DICTIONARY.

Magnetic Circuit.
A magnetic field of force is characterized by the presence of lines of
force, which, while approximately parallel, curve around and tend to
form closed curves. The polarity of a field of force is referred to an
imaginary direction of the lines of force from the north pole through
space to the south pole, and in the part of the field corresponding to
the body of the magnet, from the south to the north pole. The cut
indicates these features. Hence the magnetic field of force is termed
the magnetic circuit, and to it are attributed a species of resistance
termed reluctance, q. v., and the producing cause of the field or lines
of force is termed sometimes magneto-motive force, q. v.) corresponding
to the electro-motive force. The modern treatment of the magnetic
circuit is similar to the application of Ohm's law and the laws of
resistance and conductivity to the electric circuit.

Magnetic Circuit, Double.
A magnetic circuit which virtually represents two horseshoe magnets
placed with their like poles in contact. It is used for field magnets,
the armatures occupying a place between the consequent poles.

Fig. 221. ONE-HALF PORTION OF A DOUBLE MAGNETIC CIRCUIT.

Magnetic Concentration of Ores.
The concentration of ores or the freeing them from their gangue by
magnetic attraction. It is only applicable to those cases in which
either the ore itself or the gangue is attracted by the magnet. Its
principal application is to the concentration of magnetic iron sands.
(See Magnetic Concentration.)

Magnetic Concentrator.
An apparatus similar to a magnetic separator, q. v., but used to
concentrate magnetic iron sands. By the action of electro-magnets the
magnetic iron sand (magnetite) is separated from the sand with which it
is mixed.

Magnetic Conductivity and Conductance.
The first notion of permeance and of the magnetic circuit included the
idea of magnetic conductivity, which conducted lines of force urged by
magneto-motive force through a magnetic circuit. The terms are displaced
by permeability and permeance.

341 STANDARD ELECTRICAL DICTIONARY.

Magnetic Continuity.
The completeness of a magnetic circuit, as when the armature of a
horseshoe magnet is in contact with both poles. It is an attribute of a
paramagnetic substance only and is identical for permanent magnets or
for electro-magnets. An air space intervening between armature and
magnet poles, or a space filled with any diamagnetic substance prevents
continuity, although the lines of force to some extent still find their
way around. The leakage is increased by discontinuity.

Magnetic Control.
Control of a magnetic needle, magnet, iron index or armature, in a
galvanometer, ammeter or voltmeter by a magnetic field; the restitutive
force being derived from a permanent magnet.

Magnetic Couple.
The couple of magnetic force which tends to bring the magnetic needle
into the plane of the magnetic meridian. One force is represented by the
imaginary pull upon the north pole, and the other by the opposite pull
upon the south pole of the needle. The moment of the couple varies from
a maximum when the needle is at right angles to the plane of the
magnetic meridian to zero when it is in such plane.

Magnetic Creeping.
Viscous hysteresis; the slow increase of magnetism in a paramagnetic
body when exposed to induction.

Fig. 222. MAGNETIC CURVES OR FIGURES.

Magnetic Curves.
The pictorial representation of magnetic lines of force. It is generally
produced by scattering filings on a sheet of paper or pane of glass held
over a magnet. The filings arrange themselves in characteristic curves.
Tapping the paper or pane of glass facilitates the arrangement, or
jarring the filings off a smaller magnet, so that they fall polarized
upon the paper, is thought by some to improve the effect. The group of
curves forms what are termed magnetic figures, q. v.

342 STANDARD ELECTRICAL DICTIONARY.

Magnetic Declination.
The angular deviation of the magnetic needle, causing it to rest at an
angle with the true meridian; the variation of the compass. (See
Magnetic Elements.)

Magnetic Density.
The intensity of magnetization expressed in lines of force per stated
area of cross-section in a plane at right angles to the lines of force.

Magnetic Dip.
The inclination from the horizontal assumed by a magnetic needle free to
move in the vertical plane. (See Magnetic Elements.) The angle of dip or
inclination is entirely a function of the earth, not of the needle.

Magnetic Discontinuity.
A break or gap in a magnetic circuit. To make a complete circuit the
iron or other core must be continuous. If the armature of a horseshoe
magnet is in contact with both poles the continuity is complete. If the
armature is not in contact magnetic continuity gives place to
discontinuity. It is an attribute of a paramagnetic substance only, and
is identical for permanent magnets, or for electro-magnets.

Magnetic Elements.
The qualities of the terrestrial magnetism at any place as expressed in
its action upon the magnetic needle. Three data are involved.

I. The Declination or Variation.
II. The Inclination or Dip.
III. The Force or Intensity.

I. The Declination is the variation expressed in angular degrees of the
magnetic needle from the true north and south, or is the angle which the
plane of the magnetic meridian makes with that of the geographical
meridian. It is expressed as east or west variation according to the
position of the north pole; east when the north pole of the needle is to
the east of the true meridian, and vice versa. Declination is different
for different places; it is at present west in Europe and Africa, and
east in Asia and the greater part of North and South America. The
declination is subject to (a) secular, (b) annual and (c) diurnal
variations. These are classed as regular; others due to magnetic storms
are transitory and are classed as irregular, (a) Secular variations. The
following table shows the secular variations during some three hundred
years at Paris. These changes are termed secular, because they require
centuries for their completion.

343

STANDARD ELECTRICAL DICTIONARY.

Table of Declination or Variation at Paris.
Year. Declination.
1580 11º 30' E.
1663 0°
1700 8° 10' W.
1780 19º 55' W.
1785 22º 00' W.
1805 22º 5' W.
1814 22º 34' W.
1825 22° 22' W.
1830 22º 12' W.
1835 22º 4' W.
1850 20º 30' W.
1855 19º 57' W.
1860 19º 32' W.
1865 18º 44' W.
1875 17º 21' W.
1878 17º 00' W.

On scrutinizing these figures it will be seen that there is part of a
cycle represented and that the declination is slowly returning to the
zero point after having reached its maximum western variation in 1814.
Upwards of 300 years would be required for its completion on the basis
of what is known. In other places, notably the coast of Newfoundland,
the Gulf of the St. Lawrence and the rest of the North American seaboard
and in the British Channel, the secular variations are much more rapid
in progress. (b) Annual variations--These were first discovered in 1780
by Cassini. They represent a cycle of annual change of small extent,
from 15' to 18' only. In Paris and London the annual variation is
greatest about the vernal equinox, or March 21st, and diminishes for the
next three months, and slowly increases again during the nine following
months. It varies during different epochs. (c) Diurnal variations were
discovered in 1722 by Graham. A long needle has to be employed, or the
reflection of a ray of light, as in the reflecting galvanometer, has to
be used to observe them. In England the north pole of the magnetic
needle moves every day from east to west from sunrise until 1 or 2 P.
M.; it then tends towards the east and recovers its original position by
10 P. M. During the night the needle is almost stationary. As regards
range the mean amplitude of diurnal variations at Paris is from April to
September 13' to 15'; for the other months from 8' to 10'. On some days
it amounts to 25' and sometimes is no more than 5'. The amplitude of
diurnal variations decreases from the poles to the equator. Irregular
variations accompany earthquakes, the aurora borealis and volcanic
eruptions. In Polar regions the auroral variations may be very great;
even at 40° latitude they may be 1° or 2°. Simultaneous irregularities
sometimes extend over large areas. Such are attributed to magnetic
storms. II. The Inclination is the angle which the magnetic needle makes
with the horizon, when the vertical plane in which the needle is assumed
to be free to move coincides with the magnetic meridian. It is sometimes
called the dip of the needle. It varies as does the declination, as
shown in the following table of inclinations of London.

344 STANDARD ELECTRICAL DICTIONARY.

Table of Inclination or Dip at London
Year. Inclination.
1576 71° 50'
1600 72°
1676 73° 30'
1723 74° 42'
1773 72° 19'
1780 72° 8'
1790 71° 33'
1800 70° 35'
1821 70° 31'
1828 69° 47'
1838 69° 17'
1854 68° 31'
1859 68° 21'
1874 67° 43'
1876 67° 39'
1878 67° 36'
1880 67° 35'
1881 67° 35'

III. Force or Intensity is the directive force of the earth. It varies
with the squares of the number of oscillations the magnetic needle will
make if caused to oscillate from a determined initial range. The
intensity is supposed to be subject to secular change. According to
Gauss the total magnetic intensity of the earth is equal to that which
would be exerted if in each cubic yard there were eight bar magnets,
each weighing one pound. This is, of course, a rough way of expressing
the degree of intensity. Intensity is least near the magnetic equator
and greatest near the magnetic poles; the places of maximum intensity
are termed the magnetic foci. It varies with the time of day and
possibly with changes in altitude.

Magnetic Elongation.
The elongation a bar of iron or steel undergoes when magnetized. By
magnetization it becomes a little longer and thinner, there being no
perceptible change in volume. The change is accompanied by a slight
sound--the magnetic tick. An exceedingly delicate adjustment of
apparatus is required for its observation.

Magnetic Equator.
A locus of the earth's surface where the magnet has no tendency to dip.
It is, approximately speaking, a line equally distant from the magnetic
poles, and is called also the aclinic line. It is not a great circle of
the earth.

345 STANDARD ELECTRICAL DICTIONARY.

Magnetic Field of Force.
The field of force established by a magnet pole. The attractions and
repulsions exercised by such a field follow the course of the electro-
magnetic lines of force. (See also Field of Force.) Thus the tendency of
a polarized needle attracted or repelled is to follow, always keeping
tangential to curved lines, the direction of the lines of force, however
sweeping they may be. The direction of magnetic lines of force is
assumed to be the direction in which a positive pole is repelled or a
negative one attracted; in other words, from the north pole of a magnet
to its south pole in the outer circuit. The direction of lines of force
at any point, and the intensity or strength of the field at that point,
express the conditions there. The intensity may bc expressed in terms of
that which a unit pole at unit distance would produce. This intensity as
unitary it has been proposed to term a Gauss. (See Weber.)

The direction of the lines of force in a magnetic field are shown by the
time-honored experiment of sprinkling filings of iron upon a sheet of
paper held over a magnet pole or poles. They arrange themselves, if the
paper is tapped, in more or less curved lines tending to reach from one
pole of the magnet to the other. Many figures may be produced by
different conditions. Two near poles of like name produce lines of force
which repel each other. (See Magnetic Curves.)

A magnetic and an electro-magnetic field are identical in all essential
respects; the magnetic field may be regarded as a special form of the
electro-magnetic field, but only special as regards its production and
its defined north and south polar regions.

Synonyms--Magnetic Spin (not much used).

Magnetic Field, Uniform.
A field of identical strength in all parts, such as the earth's magnetic
field. If artificially produced, which can only be approximately done,
it implies large cross-section of magnet pole in proportion to the
length of the magnetic needle affected by it, which is used in
determining its uniformity.

Magnetic Figures.
The figures produced by iron filings upon paper or glass held near
magnetic poles. By these figures the direction of lines of force is
approximately given, and a species of map of the field is shown. (See
Magnetic Field of Force--Magnetic Curves.)

Magnetic Filament.
The successive rows of polarized molecules assumed to exist in
magnetized iron. Each molecule represents an infinitely small magnet,
and its north pole points to the south pole of the next molecule. Such a
string or row is a theoretical conception based on the idea that the
molecules in a magnet are all swung in to parallelism in the magnetizing
process. A magnetic filament may be termed the longitudinal element of a
magnet. (See Magnetism, Hughes' Theory of.)

Magnetic Fluids.
A two-fluid theory of magnetism has been evolved, analogous to the
two-fluid theory of electricity. It assumes north fluid or "red
magnetism" and a south fluid or "blue magnetism." Each magnetism is
supposed to predominate at its own pole and to attract its opposite.
Before magnetization the fluids are supposed to neutralize each other
about each molecule; magnetization is assumed to separate them,
accumulating quantities of them at the poles.

Magnetic Flux.
Magnetic induction; the number of lines of force that pass through a
magnetic circuit.

Synonym--Magnetic Flow.

346 STANDARD ELECTRICAL DICTIONARY.

Magnetic Force.
The forces of attraction and repulsion exercised by a magnet. By
Ampere's theory it is identical with the forces of attraction and
repulsion of electric currents.

Magnetic Friction.
The damping effect produced on the movements of a mass of metal by
proximity to a magnet; the phenomenon illustrated in Arago's wheel, q.
v. When a mass of metal moves in the vicinity of a magnet it cuts the
lines of force emanating from its poles, thereby producing currents in
its mass; as the production of these currents absorbs energy a damping
effect is produced upon the movements of the mass.

Magnetic Gear.
Friction gear in which electro-magnetic adherence is employed to draw
the wheels together. (See Adherence, Electro-magnetic--Electro-magnetic
Friction Gear.)

Magnetic Inclination.
The inclination from the horizontal of a magnetic needle placed in the
magnetic meridian. (See Magnetic Element--Inclination Map.)

Synonym--Magnetic Dip.

Magnetic Induction.
The force of magnetization within an induced magnet. It is in part due
to the action of the surrounding particles of polarized material; in
part to the magnetic field. (See Magnetic Induction, Coefficient of.)

In a more general way it is the action of a magnet upon bodies in its
field of force. In some cases the magnetism induced causes the north
pole of the induced magnet to place itself as far as possible from the
north pole of the inducing magnet and the same for the south poles. Such
substances are called paramagnetic or ferromagnetic. They lie parallel
or tangential to the lines of force. In other cases the bodies lie at
right angles or normal to the lines of force. Such bodies are called
diamagnetic.

Some bodies are crystalline or not homogeneous in structure, and in them
the lines of magnetic induction may take irregular or eccentric paths.
(See AEolotropic.)

Synonym--Magnetic Influence.

Magnetic Induction, Apparent Coefficient of.
The apparent permeability of a paramagnetic body as affected by the
presence of Foucault currents in the material itself. These currents act
exactly as do the currents in the coils surrounding the cores of
electro-magnets. They produce lines of force which may exhaust the
permeability of the iron, or may, if in an opposite direction, add to
its apparent permeability.

Magnetic Induction, Coefficient of.
The number, obtained by dividing the magnetization of a body, expressed
in lines of force produced in it, by the magnetizing force which has
produced such magnetization, expressed in lines of force producible by
the force in question in air. It always exceeds unity for iron, nickel
and cobalt. It is also obtained by multiplying the coefficient of
induced magnetization by 4 PI (4 * 3.14159) and adding 1. (See Magnetic
Susceptibility--Magnetization, Coefficient of Induced.)

347 STANDARD ELECTRICAL DICTIONARY.

The coefficient of magnetic induction varies with the material of the
induced mass, and varies with the intensity of the magnetizing force.
This variation is due to the fact that as the induced magnetism in a
body increases, the magnetizing force required to maintain such
induction, increases in a more rapid ratio. The coefficient of magnetic
induction is the same as magnetic permeability, and in a certain sense
is the analogue of conductivity. It is also termed the multiplying power
of the body or core magnetized. It is the coefficient of induced
magnetization (see Magnetization, Coefficient of Induced) referred to a
mass of matter. For diamagnetic bodies the coefficient has a negative
sign; for paramagnetic bodies it has a positive sign.

Synonyms--Permeability--Multiplying Power--Magnetic Inductive Capacity.

Magnetic Induction, Dynamic.
The induction produced by a magnetic field which moves with respect to a
body, or where the body if moving moves at a different rate, or where
the body moves and the field is stationary. In the case where both move,
part of the induction may be dynamic and part static. (See Magnetic
Induction, Static.)

Magnetic Induction, Static.
Magnetic induction produced by a stationary field acting upon a
stationary body.

Magnetic Induction, Tube of.
An approximate cylinder or frustrum of a cone whose sides are formed of
lines of magnetic induction. (See Magnetic Induction, Lines of.) The
term tube is very curiously applied in this case, because the element or
portion of a magnetic field thus designated is in no sense hollow or
tubular.

Magnetic Inertia.
A sensible time is required to magnetize iron, or for it to part with
its magnetism, however soft it may be. This is due to its magnetic
inertia and is termed the lag. Permanent or residual magnetism is a
phase of it. It is analogous to self-induction of an electric circuit,
or to the residual capacity of a dielectric.

Magnetic Insulation.
Only approximate insulation of magnetism is possible. There is no
perfect insulator. The best ones are only 10,000 times less permeable
than iron. Hence lines of force find their way through air and all other
substance, being simply crowded together more in paths of iron or other
paramagnetic substance.

348 STANDARD ELECTRICAL DICTIONARY.

Magnetic Intensity.
The intensity of the magnetization of a body. It is measured by the
magnetic lines of force passing through a unit area of the body, such
area being at right angles to the direction of the lines of force.

Magnetic Lag.
In magnetism the tendency of hard iron or steel especially to take up
magnetism slowly, and to part with it slowly. (See Magnetic Inertia.)
The lag affects the action of a dynamo, and is a minor cause of those
necessitating the lead of the brushes.

Synonym--Magnetic Retardation.

Magnetic Latitude.
Latitude referred to the magnetic equator and isoclinic lines.

Magnetic Leakage.
The lines of force in a field magnet which pass through the air and not
through the armature are useless and represent a waste of field. Such
lines constitute magnetic leakage.

Magnetic Limit.
The temperature beyond which a paramagnetic metal cannot be magnetized.
The magnetic limit of iron is from a red to a white heat; of cobalt, far
beyond a white heat; of chromium, below a red heat; of nickel at about
350° C. (662°F.) of manganese, from 15° C. to 20° C. (59° to 68° F.)

Magnetic Lines of Force.
Lines of force indicating the distribution of magnetic force, which is
due presumably to whirls of the ether. A wire or conductor through which
a current is passing is surrounded by an electro-magnetic field of
force, q. v., whose lines of force form circles surrounding the
conductor in question. A magnet marks the existence of a similar
electro-magnetic field of force whose lines form circuits comprising
part of and in some places all of the body of the magnet, and which are
completed through the air or any surrounding paramagnetic or diamagnetic
body. They may be thought of as formed by the Ampérian sheet of current,
and analogous to those just mentioned as surrounding a conductor.

Fig. 223. MAGNETIC LINES OF FORCE, DIRECTION OF.

A magnetic line of force may be thought of as a set of vortices or
whirls, parallel to each other, and strung along the line of force which
is the locus of their centres.

If as many lines are drawn per square centimeter as there are dynes (per
unit pole) of force at the point in question, each such line will be a
unitary c. g. s. line of force.

349 STANDARD ELECTRICAL DICTIONARY.

Magnetic Mass.
A term for a quantity of magnetism. Unit mass is the quantity which at
unit distance exercises unit force.

Magnetic Matter.
Imaginary matter assumed as a cause of magnetism. Two kinds, one
positive and one negative, may be assumed as in the two fluid theory of
electricity, or only one kind, as in the single fluid theory of
electricity. Various theories of magnetic matter have been presented
whose value is only in their convenience.

Magnetic Memory.
The property of retaining magnetism; coercive force; magnetic inertia;
residual magnetism.

Magnetic Meridian.
A line formed on the earth's surface by the intersection therewith of a
plane passing through the magnetic axis. It is a line determined by the
direction of the compass needle. The meridians constantly change in
direction and correspond in a general way to the geographical meridians.

Magnetic Moment.
The statical couple with which a magnet would be acted on by a uniform
magnetic field of unit intensity if placed with its magnetic axis at
right angles to the lines of force of the field. (Emtage.) A uniformly
and longitudinally magnetized bar has a magnetic moment equal to the
product of its length by the strength of its positive pole.

Magnetic Needle.
A magnet with a cup or small depression at its centre and poised upon a
sharp pin so as to be free to rotate or oscillate in a horizontal plane.
The cup is often made of agate. Left free to take any position, it
places its magnetic axis in the magnetic meridian.

Magnetic Parallels.
Lines roughly parallel to the magnetic equator on all parts of each of
which the dip of the magnetic needle is the same; also called Isoclinic
Lines. These lines mark the places of the intersection of equipotential
surfaces with the earth's surface. They are not true circles, and near
the poles are irregular ellipses; the magnet there points toward their
centres of curvature. They correspond in a general way with the
Geographical Parallels of Latitude.

Magnetic Permeability.
The specific susceptibility of any substance, existing in a mass, for
magnetic induction. (See Magnetic Induction, Coefficient of, synonym for
Magnetic Permeability and Magnetization, Coefficient of Induced.)

Synonyms--Magnetic Inductive Capacity--Multiplying Power--Coefficient of
Magnetic Induction.

350 STANDARD ELECTRICAL DICTIONARY.

Magnetic Perturbations.
Irregular disturbances of the terrestrial magnetism, as by the aurora
and in electric storms.

Magnetic Poles.
The points where the equipotential surfaces of the terrestrial field of
force graze the earth's surface; the points toward which the north or
south poles of the magnetic needle is attracted. Over a magnetic pole
the magnetic needle tends to stand in a vertical position. There are two
poles, Arctic or negative, and Antarctic or positive. Magnetic needles
surrounding them do not necessarily point toward them, as they point to
the centres of curvature of their respective magnetic parallels. The
poles constantly change in position. The line joining them does not
coincide with anything which may be termed the magnetic axis of the
earth.

Magnetic Poles, False.
Poles on the earth's surface other than the two regular magnetic poles.
There seem by observation to be several such poles, while analogy would
limit true magnetic poles to two in number.

Magnetic Potential.
The potential at any point of a magnetic field is the work which would
be done by the magnetic forces of the field upon a positive unit of
magnetism as it moves from that point to an infinite distance. (Emtage.)

Magnetic Proof Piece.
A piece of iron used for testing magnets and the distribution of
magnetism in bars, by suspending or supporting above or near the magnet,
by detaching after adherence, and in other ways.

Magnetic Proof Plane.
An exploring coil used for testing the distribution of magnetism. It is
connected in circuit with a galvanometer, and exposed to alternation of
current, or to other disturbing action produced by the magnet or field
under examination. This affects the galvanometer, and from its movements
the current produced in the coil, and thence the magnetic induction to
which it was exposed, are calculated.

Synonym--Exploring Coil.

Magnetic Quantity.
The magnetism possessed by a body; it is proportional to the action of
similar poles upon each other, or to the field produced by the pole in
question. It is also called the strength of a pole.

The force exercised by two similar poles upon each other varies with
their product and inversely with the square of the distance separating
them; or it may be expressed thus (m * m) / (L^2). This is a force, and
the dimensions of a force are ML/(T^2). Therefore, (m^2)/(L^2) =
ML/(T^2) or m = (M^.5)*(L^1.5)/T.

351 STANDARD ELECTRICAL DICTIONARY.

Magnetic Reluctance.
The reciprocal of permeance; magnetic resistance; the relative
resistance to the passage of lines of force offered by different
substances. The idea is derived from treating the magnetic circuit like
an electric one, and basing its action on magneto-motive force acting
through a circuit possessing magnetic reluctance.

Magnetic Reluctivity.
The reciprocal of magnetic permeability, q. v.

Synonym--Magnetic Resistance.

Magnetic Retentivity.
The property of steel or hard iron by which it slowly takes up and
slowly parts with a magnetic condition--traditionally (Daniell) called
coercitive force.

Magnetic Rotary Polarization.
If a plane polarized beam of light is sent through a transparent medium
in a magnetic field its plane of polarization is rotated, and this
phenomenon is denoted as above. (Compare Refraction, Electric, and see
Electro-magnetic Stress.) This has been made the basis of a method for
measuring current. A field of force varies with the current; the
polarization produced by such field is therefore proportional to the
current. (Becquerel & Rayleigh.)

A plane polarized beam of light passing through the transparent medium
in the magnetic field by the retardation or acceleration of one of its
circular components has its plane of polarization rotated as described.
The direction of the lines of force and the nature of the medium
determine the sense of the rotation; the amount depends upon the
intensity of the field resolved in the direction of the ray, and on the
thickness and nature of the medium.

Magnetic Saturation.
The maximum magnetic force which can be permanently imparted to a steel
bar. A bar may be magnetized beyond this point, but soon sinks to it.
The magnetism produced in a bar is prevented from depolarization by the
retentivity or coercive force of the bar. The higher the degree of
magnetization the greater the tendency to depolarization.

It is also defined as the maximum intensity of magnetism produced in a
paramagnetic substance by a magnetic field as far as affected by the
permeability of the substance in question. The more lines of force
passed through such a substance the lower is its residual permeability.
It is assumed that this becomes zero after a certain point, and then the
point of saturation is reached. After this point is reached the addition
of any lines of force is referred entirely to the field and not at all
to the permeability of the substance. But such a zero is only definable
approximately.

Magnetic Screen.
A box or case of soft iron, as thick as practicable, for protecting
bodies within it from the action of a magnetic field. The lines of force
to a great extent keep within the metal of the box on account of its
permeability, and but a comparatively few of them cross the space within
it.

Such screens are used to prevent watches from being magnetized, and are
a part of Sir William Thomson's Marine galvanometer.

A magnetic screen may be a sphere, an infinite or very large plane, or
of the shape of any equipotential surface.

Synonym--Magnetic Shield.

352 STANDARD ELECTRICAL DICTIONARY.

Magnetic Self-induction.
The cause of a magnet weakening is on account of this quality, which is
due to the direction of the lines of force within a magnet from the
positive towards the negative pole. "A magnet thus tends to repel its
own magnetism and to weaken itself by self-induction." (Daniell.)

Magnetic Separator.
An apparatus for separating magnetic substances from mixtures. Such
separators depend on the action of electro-magnets. In one form the
material falls upon an iron drum, magnetized by coils. Any magnetic
substance adheres to the drum and is thereby separated. They are used by
porcelain makers for withdrawing iron particles from clay, by machinists
to separate iron filings and chips from brass, and for similar purposes.

Fig. 224. MAGNETIC SEPARATOR.

Magnetic Shell.
A theoretical conception of a cause of a magnetic field or of a
distribution of magnetism. If we imagine a quantity of very short
magnets arranged in contact with their like poles all pointing in the
same direction so as to make a metal sheet, we have a magnetic shell.
Its magnetic moment is equal to the sum of the magnetic moment of all
its parts. If the shell is of uniform strength the magnetic moment of a
unit area gives the strength of the shell; it is equal to the magnetic
quantity per unit of area, multiplied by the thickness of the shell.

If its strength is uniform throughout a magnetic shell is called simple;
if its strength varies it is termed complex.

Emtage thus defines it: A magnetic shell is an indefinitely thin sheet
magnetized everywhere in the direction normal to itself.

Magnetic Shell, Strength of.
The magnetic quantity per unit of area of the shell multiplied by the
thickness of the shell.

353 STANDARD ELECTRICAL DICTIONARY.

Magnetic Shield.
In general a magnetic screen, q. v. Sometimes a strong local field is
made to act as a shield, by its predominance overcoming any local or
terrestrial field to which the needle to be protected may be exposed.

Magnetic Shunt.
The conception of a magnetic circuit being formed, the shunt is a
corollary of the theory. It is any piece of iron which connects points
of a magnet differing in polarity, so as to divert part of the lines of
force from the armature or yoke. The shunt is especially applicable in
the case of horseshoe magnets. Thus a bar of iron placed across from
limb to limb a short distance back from the poles would act as a shunt
to the armature and would divert to itself part of the lines of force
which would otherwise go through the armature and would weaken the
attraction of the magnet for the latter. In dynamos a bar of iron used
as a magnetic shunt has been used to diminish the lines of force going
through the armature and hence to weaken the field and diminish the
electro-motive force. By moving the shunt nearer or further from the
poles the dynamo is regulated.

In the cut the projections between the yoke and poles of the magnet
shown act as a shunt to the yoke, taking some lines of force therefrom.

Fig. 225. MAGNETIC SHUNT.

Magnetic Storms.
Terrestrial magnetic disturbances sometimes covering very wide areas,
and affecting the magnetic declination and inclination. One such
disturbance was felt simultaneously at Toronto, Canada, the Cape of Good
Hope, Prague and Van Diemen's Land. (Sabine.)

354 STANDARD ELECTRICAL DICTIONARY.

Magnetic Strain.
The strain produced by magnetic lines of force in substances exposed to
their action. It is observed in substances placed between the poles of a
strong electro-magnet, and evinces itself in the alteration of the
optical properties of transparent substances.

Magnetic Stress.
The stress produced by magnetic lines of force on substances through
which they pass, evidenced in alteration of the optical properties of
transparent bodies thus treated.

Magnetic Susceptibility.
The specific intrinsic susceptibility of any material for magnetic
induction. It refers to the particle of matter, and not to the mass, as
in the latter its own particles react on each other and bring about what
is termed permeability, q. v. (See also Magnetization, Coefficient of
Induced, and Magnetic Induction, Coefficient of.)

Synonym--Coefficient of Induced Magnetization.

Magnetic Tick.
When a bar of iron is suddenly magnetized or demagnetized it emits a
slight sound, called the Page sound, or the magnetic tick. This has been
utilized in a telephone by Reiss. The telephone will receive sound, but
is very weak. It consists of a bar surrounded with a coil of insulated
wire. Variations in current produce sounds, which may be articulate if
the currents are produced by a telephonic transmitter.

Magnetic Twist.
A bar of iron held in the magnetic meridian and pointing to the pole and
twisted becomes to some extent permanently magnetized. Conversely a bar
when magnetized seems to have a twist set up in it. The latter is
magnetic twist.

Magnetic Variations.
Changes in the value of magnetic declination or inclination. (See
Magnetic Elements.)

Magnetism, Ampére's Theory of.
A theory accounting for magnetic phenomena by assuming the existence of
currents circulating around the molecules of permanent magnets. If such
currents so circulate and all in the same direction, the result is the
same as if the body of the magnet was enveloped in currents representing
those of an electro-magnet or solenoid. This is because in the interior
the current around one molecule would counteract the current around its
neighboring ones in part, so that the only virtual currents left would
be represented by those on the outer surfaces of the outer shell of
molecules, and these virtually resolve themselves into one general
current sheet, surrounding the magnet and coinciding with its surface.

The theory assumes that such currents permanently circulate around the
molecules of paramagnetic substances. Under ordinary conditions there is
no coincidence in their direction and no resultant current is produced.
When magnetized or polarized the molecules are brought into order, so
that the direction of their current coincides and the body becomes a
magnet.

355 STANDARD ELECTRICAL DICTIONARY.

Fig. 226. AMPÉRIAN CURRENTS IN MAGNETS.

At the north pole of the magnet the direction of the Ampérian currents
is the reverse of that of a watch when the observer faces the pole; the
reverse obtains for the south pole.

The attraction of opposite and repulsion of similar poles is explained
by the actions of the Ampérian currents upon each other. If north and
south pole are placed together these currents will coincide in direction
and hence will attract each other. If two like poles are put together
the currents will have opposite directions and will repel each other.

No energy is supposed to be required to maintain currents around or in a
single molecule.

Fig. 227. NORTH AND SOUTH POLES OF A MAGNET
SHOWING DIRECTION OF AMPÉRIAN CURRENTS.

Magnetism, Blue.
A term arising from the two fluid theory of magnetism; the magnetism of
the south pole of a magnet. (See Magnetic Fluids.) The magnetism of the
north pole is termed red magnetism. Both terms originated presumably in
the painting of magnets, and are little used.

Synonym--South Magnetic Fluid.

356 STANDARD ELECTRICAL DICTIONARY.

Magnetism, Components of Earth's.
The magnetic force of the earth acts in the plane of the magnetic
meridian and in direction generally lies oblique to the plane of the
horizon. It can be resolved into two components, one vertical, which has
no directive effect upon the magnetic needle, the other horizontal,
which represents the directive element for the usual compass needle. For
the dipping needle, q. v., the vertical component is the only active
one. A magnetic needle mounted on a universal joint at its centre of
gravity would be acted on by both components.

Magnetism, Creeping of.
The gradual increase of magnetism when a magnetic force is applied with
absolute steadiness to a piece of iron. It is a form of magnetic lag. It
may last for half an hour and involve an increase of several per cent.
of the total magnetism.

Synonym--Viscous Hysteresis.

Magnet, Iron Clad.
A magnet with a casing of iron connected at one end to the core. The
term is generally applied to electromagnets of this form.

Synonyms--Tubular Magnet--Jacketed Magnet.

Magnetism, Decay of.
The gradual loss of magnetism by permanent magnets, due to accidental
shocks, changes of temperature, slow spontaneous annealing of the iron
and other similar causes.

Magnetism, Discharge of.
The loosing of magnetization. Thus in a shunt-wound dynamo there is a
critical resistance for the outer circuit, below which the field ceases
to be magnetized, as enough current ceases to be shunted into it to
magnetize it. The machine is said to unbuild itself, and a discharge of
magnetism occurs from the field magnet.

Magnetism, Ewing's Theory of.
Ewing found by a model consisting of a number of pivoted magnetic
needles that the observed phenomena of magnetization could be
represented thereby. Thus there would be no need of assuming internal
frictional forces of Maxwell, nor the closed rings or chains of Hughes.
The theory retains the notion, however, of paramagnetic matter,
consisting of an assemblage of molecular magnets. The loss of energy by
hysteresis is represented in the model by the energy lost by the needles
in beating against the air.

357 STANDARD ELECTRICAL DICTIONARY.

Magnetism, Free.
The magnetism or magnetic field outside of a magnetic circuit. It is due
to escape of lines of force and to the magnetic leakage through the air.
The lines of force are never, under the most favorable circumstances,
confined to the metallic circuit of the magnet and armature. In a simple
magnet without armature all the lines of force have to follow an air
path, and the field is at its strongest. As the magnetism is strongest
at the surface near the poles, the term is sometimes understood as
applying to the surface attraction. In such case it is defined as the
distribution, on a magnetized bar or mass, of magnetic lines of force as
they emerge from its surface.

Synonym--Surface Magnetization.

Magnetism, Hughes' Theory of.
A theory accounting for magnetic phenomena by assuming that each
molecule is a magnet, and that in a polarized or magnetized body they
are all arranged with their poles in the same direction, while in an
unmagnetized body their poles, alternating in direction, neutralize each
other.

Magnetization consists in a partial rotation of the molecules so as to
make them agree in position, thus, as a resultant developing north and
south poles at the ends of the bar.

The theory is in a certain sense simpler than Ampere's theory, but is
not so generally adopted.

Magnetism, Lamellar Distribution of.
The distribution of magnetism in thin and uniform or "simple magnetic
shells," q. v. A given distribution is termed lamellar if the substance
in which it exists can be divided into simple magnetic shells, which
either form closed surfaces, or have their edges in the surface of the
substance. In lamellar distribution the polar area is very large
compared with the distance between opposite poles.

Magnetism of Gases.
Faraday experimented on this point by coloring gases with a little vapor
of iodine or other colored gas, and letting them flow between the two
poles of a powerful electromagnet. In this way he found some are
repelled, some attracted, and in the case of oxygen, it is attracted at
one temperature and repelled at another. At ordinary temperatures a
cubic yard of oxygen possesses the magnetism of 5.5 grains of iron and
when liquefied it is strongly attracted.

Magnetism or Magnetization, Temporary.
When a mass of iron is magnetized by a current, when the current ceases
the portion of its magnetism which disappears is the temporary
magnetism; the portion retained is the residual or permanent magnetism.

Magnetism, Red.
A term arising from the two fluid theory of magnetism; the magnetism of
the north pole of a magnet. (See Magnetic Fluids.) The magnetism of the
south pole is termed blue magnetism. Both terms originated in the
painting of magnets. They are but little used.

Synonym--North Magnetic Fluid.

358 STANDARD ELECTRICAL DICTIONARY.

Magnetic Remanence.
The residual magnetism left in a bar of steel or other paramagnetic
material after the application of a powerful magnet. It is distinguished
from coercive force, as the latter is the amount of negative magnetizing
or of demagnetizing force required to reduce the remanent magnetism to
zero.

Synonym--Remanence--Residual Magnetism.

Magnetism, Solenoidal Distribution of.
The distribution of magnetism in such a way that the poles are very far
apart in proportion to their area. The magnetization of a long thin bar
of steel illustrates solenoidal distribution.

Magnetism Sub-permanent.
The magnetism of a paramagnetic substance which presents a considerable
degree of permanency, but which gradually disappears, leaving the
permanent magnetism present. It is noticeable in iron or steel ships
whose magnetism gradually reduced in quantity, eventually becomes fully
permanent.

Magnetism, Weber's Theory of.
The molecules of a magnetizable material by this theory are supposed to
be magnets with their poles lying in every direction, and hence
neutralizing each other. By magnetization these are supposed to be
turned with their similar poles in the same direction, and their axis
parallel, hence acting like a group of magnets. It is practically
identical with Hughes' theory.

Magnetism, Terrestrial.
The magnetism of the earth. (See Magnetic Elements.)

Fig. 228. MAGNETIZATION BY DOUBLE TOUCH.

Magnetization by Double Touch.
The process of magnetizing a steel bar by simultaneously stroking it
with two poles of a horseshoe magnet or with two opposite poles of two
bar magnets. The poles must be close but not touching. A block of wood
may be placed between the ends if single magnets are used. The poles are
placed on the middle of the bar and carried back and forth to one end,
then to the other, and so on, ending at the middle of the bar in such
direction as to give each end the same number of strokes. The poles must
be close together or consequent poles will be produced. If bar magnets
are used they may be held inclined at an angle of 15º to 20º with the
horizontal bar to be magnetized. The ends of the latter may rest on
poles of two other magnets, each end on a pole of the same name as that
of the magnetizing magnet on its side. (See Magnetization, Hoffer's
Method.)

359 STANDARD ELECTRICAL DICTIONARY.

Magnetization by Separate Touch.
A method of magnetization. Two magnets are used. Held in an inclined
position two opposite poles are touched to the bar near its centre, and
are drawn off to the two ends. They are returned through the air and the
process is repeated.

Magnetization by Single Touch.
A method of polarizing or magnetizing steel bars, by stroking them
always in one direction with one pole of a magnet, returning it through
the air. The stroking is best done on both sides. The stroking may begin
at one end and end at the other, or it may be commenced in the center of
the bar and be carried to one end with one pole, and the same done for
the other half with the other pole.

Magnetization by the Earth.
The earth imparts magnetism to iron masses. If a rod of steel is held
parallel to the inclination and in the magnetic meridian it exhibits
polarity, which by jarring or hammering, can be made to some extent
permanent. A piece of soft iron held vertically, or still better in the
line of the dip as above, and which is twisted when in that position,
becomes magnetized with some degree of permanence. Many other instances
are cited, such as fire-irons, lamp-posts, iron gates, lathe turnings,
all of which often exhibit polarity, having been magnetized by the
earth's field.

Magnetization, Coefficient of Induced.
The coefficient (q. v.) expressing the relation between the specific
intensity of magnetization of a particle and the magnetizing force. The
magnetizing force is measured by the lines of force it can produce in a
field of air. The coefficient of induced magnetization is the factor by
which the intensity of a magnetizing field must be multiplied to produce
the magnetization imparted by it to a particle of any substance. This
coefficient varies for different substances, and is also called magnetic
susceptibility. It is distinguished from permeability as referring only
to a particle isolated from influence of a mass of surrounding particles
of its own kind. It is definable as the intensity of the magnetization
assumed by an exceedingly long and exceedingly thin bar placed in a unit
field. If a mass of metal were placed in such a field all its particles
would become affected and within the mass no unit field could exist.
Hence magnetic susceptibility (another name for this coefficient) does
not apply to the case of large cores of electro-magnets and
dynamo-armatures, but is really a theoretical rather than a practical
figure.

The sign of the coefficient of diamagnetic bodies is negative; of
paramagnetic bodies is positive.

Synonym--Magnetic Susceptibility. \

360 STANDARD ELECTRICAL DICTIONARY.

Magnetization, Cycle of.
A cycle of positive or of positive and negative magnetization represents
the application of a magnetizing force beginning at a fixed value,
generally zero, rising to a maximum, or to a value of maximum distance
from the initial and then returning to the original basis. It is
virtually a full wave of magnetization and may extend on both sides of a
zero line giving positive and negative values.

Cycles of magnetization apply especially to transformers and other
apparatus of that character used with the alternating current system.

Magnetization, Hoffer's Method.
For horseshoe bars an armature is placed against the poles of the magnet
bar to be treated. The poles of a strong horseshoe magnet are stroked
over it from poles to bend and returned through the air, or vice versa.
In the first case the poles will be the same as those of the inducing
magnet; in the second case they will be opposite. A maximum effect is
produced in ten strokes. The stroking should be applied to both sides.
An electro-magnet may be used as inducer as shown, but an armature
should be used; in the cut it is omitted.

Fig. 229. MAGNETIZING A HORSESHOE MAGNET.

Magnetization, Intensity of.
The amount of magnetism induced in or present in a body. It is expressed
in Magnetic Lines of Force, q. v., per cross-sectional area.

Magnetization, Isthmus Method of.
A method used by Ewing in a research on the magnetization of iron in
very strong fields. He used samples of iron turned down in the centre to
a narrow neck, and thus concentrated the lines of force greatly.

Magnetization, Elias' Method.
The bar to be magnetized is surrounded by a magnetizing coil, q. v. A
strong current is passed through it, and the coil is moved back and
forth a few times.

Magnetization, Jacobi's Method.
For horseshoe bars. The bar is placed with its poles against those of a
horseshoe magnet. A bar of soft iron, long enough to reach from outside
to outside of the legs, is laid across near the junction and is drawn
along towards the bend of the new bar and away from it. This is repeated
a few times on both sides.

361 STANDARD ELECTRICAL DICTIONARY.

Magnetization, Limit of.
As the induction of magnetizing force increases, magnetization of
paramagnetic metals tends towards a limit, the increase in magnetization
being continually less and less as the metal becomes more highly
magnetized. In diamagnetic substances no limit is discernible.

Synonym--Maximum Magnetization.

Magnetization, Specific.
The magnetic moment per gram of a substance.

Magnet-keeper.
A bar of iron connecting the two poles of a permanent magnet. Often the
same bar serves as armature and keeper.

Magnet, Lamination of.
It is advantageous to make magnets of laminated construction, or of thin
plates of steel. The thin metal can be better tempered or hardened than
thick metal. A slight separation of the plates is advantageous from some
points of view. If in actual contact there is some danger that the
weaker members will have their polarity reversed by the stronger ones.
This is counteracted to some extent by separation.

Magnet, Long Coil.
A high resistance electro-magnet; one whose coil is of thin wire of
considerable length.

Magnet, Natural.
The lodestone, q. v.; a variety of magnetite or magnetic oxide of iron,
exhibiting permanent magnetism, attracting iron, and possessing north
and south poles.

Magnet, Neutral Line of.
A line at right angles to the magnetic axis of a magnet, q.v., and
nearly or quite at the centre, so situated with reference to the poles
on either end that it marks the locus of no polarity. It has been called
the equator of the magnet. It is defined by the intersection of the
plane of no magnetism with the surface of the bar.

Synonym--Magnetic Equator.

Magnet, Normal.
A bar or compound bar magnet, magnetized to such an extent that the
curves of the lines of force run into each other in the middle, is thus
termed by Jamin.

Magneto.
Abbreviation for Magneto-electric Generator. (See Magneto-electric
Generator.)

Magneto Call Bell.
A call operated by current from a magneto-electric generator. It is very
generally used in telephone systems.

362 STANDARD ELECTRICAL DICTIONARY.

Magneto-electric. adj.
Relating to induced electric effects due to the cutting of true magnetic
lines of force by, or equivalent action of or upon a conductor. These
effects are identical with electro-magnetic effects and are only
distinguished from them by the field being due to a permanent magnet
instead of an electromagnet.

Magneto-electric Brake.
A device for bringing to rest an oscillating galvanometer needle. It
consists essentially of a coil in circuit with a key and with the
galvanometer. On opening the circuit an inverse current is established
by induction, tending to bring the needle to rest.

Magneto-electric Generator.
A current generator operating by maintaining a potential difference at
its terminals, by reactions in a field of force, which field is
established by a permanent magnet.

The cut, Fig. 230, shows the general principle of construction of a
direct current generator. The armature is rotated between the poles of a
permanent magnet. Any of the regular types of dynamo armature can be
used. From its commutator the current is taken by brushes.

Fig. 230. MAGNETO-ELECTRIC GENERATOR.

Fig. 231. MAGNETO-ELECTRIC GENERATOR.

363 STANDARD ELECTRICAL DICTIONARY.

The cut, Fig. 231, shows an alternating current machine. In it a pair of
bobbins, wound in series, and both either right-handed or left-handed,
are rotated between permanent magnet poles. The current may be taken off
by two brushes bearing on two collecting rings on the axis of the
bobbins, the ends of the wire being connected thereto. Or if a shocking
current is desired, one of the brushes or springs may strike a series of
pins forming virtually a broken or interrupted collecting ring. This
gives a current for medical purposes.

Synonyms--Magneto-dynamo--Magneto-electric Machine.

Magnetograph.
An apparatus for recording variations in magnetic elements. One type
includes a magnetic needle to which a concave mirror is attached. The
light ray from the mirror is reflected upon sensitized paper where its
movements are photographically reproduced. The movements of the spot are
due to the movements of the needle and act as the record of the same.

Magneto-Inductor.
An instrument for use with a ballistic galvanometer to reproduce a
definite current impulse. Two magnets are fastened together in one
straight line, the north poles almost touching. This is mounted at the
end of a rod like a pendulum, the axis of the magnets transverse to the
rod. The magnets are carried by a frame and oscillate at the end of the
rod, back and forth within a fixed coil, which is one-half the length
of the double magnet. A bob is attached to the bottom of the frame by
which the whole can be swung. As the magnets are of fixed value, their
time of oscillation constant, and the coil fixed in size, the apparatus
provides a means of getting a definite instantaneous current of
identical value whenever needed.

Fig. 232. MAGNETO-INDUCTOR.

364 STANDARD ELECTRICAL DICTIONARY.

Magnetometer.
(a) A reflecting galvanometer, with heavy magnetic needle, dampened by a
copper frame. It was devised by Weber.

(b) An apparatus for measuring the intensity of magnetic force. It may
consist of a magnet suspended by bifilar or by torsion suspension. A
reflecting mirror and scale as in the reflecting galvanometer may be
used to act as indicator of its motions. It is used in investigations of
the intensity of the earth's field.

If the motions of the spot of light are received on a moving strip of
sensitized paper and are thereby reproduced photographically, the
instrument is self-recording. Such an apparatus is used in the Kew
Observatory, Eng., for recording the terrestrial magnetic elements.

Magnetometry.
The determination of the magnetic moment of a magnet.

It involves the determination by experiment of--( a) the product of the
magnetic moment, M, of the magnet by the horizontal component, H, of the
earth's magnetism; (b) the quotient of M divided by H. Knowing these two
quantities, M is given by the formula M = SquareRootM * H) * (M/H) )
and if desired H is given by the formula H = SquareRoot( (M*H) / (M/H)).

M*H is determined by the method of vibrations. A very long, thin magnet
suspended by a torsion filament is caused to oscillate, and its period
is determined. Calling such period T and the moment of inertia of the
magnet I, we have the formula T= 2* PI * SquareRoot( I / (H*M) ) (a),
whence H*M is calculated, I of course being known or separately
determined.

Fig. 233 END-ON METHOD.

Fig. 234. BROADSIDE METHOD.

M/H is determined by the End-on deflection method, or the Broadside
deflection method. In both cases the deflection of a compass needle by
the magnet in question is the basis of the work.

In the end-on method AB is the magnet under examination; DE the compass
needle; a the angle of deflection; d the distance between C and the
middle of AB, which should be considerable compared with the length of
DE; 2l, the length of AB. We then have the formula
tan a = (M/H) * (2d / (d^2 - l^2)^2),
which if 2l is small compared to d reduces to
tan a = M/Hd 3

(b), which gives M/H, a and d being known.

365 STANDARD ELECTRICAL DICTIONARY.

In the broadside method the line d is the magnetic meridian, and the
diagram shows the relative positions. We then have the formula
tan a = (M/H) / (d2 + l2)^1.5;
which if 1 is relatively small reduces to
tan a = M/(H * d3 )(C.)

a and c or a and b can be combined giving M and H in C.G.S. measurement.

Magnetometer, Differential.
An apparatus, invented by Eickemeyer, for testing the magnetic qualities
of different samples of iron. It is very similar in construction and
principle to the magnetic bridge, q. v.

Magneto-motive Force.
The force producing a magnetic field or forcing lines of force around a
magnetic circuit. It is usually applied only to electro-magnets and is
expressible in turns of the wire winding multiplied by amperes of
current, or in ampere-turns.

Magnet Operation.
A term in surgery; the use of the electro-magnet or permanent magnet for
removing particles of iron from the eye.

Magnetoscope.
An apparatus for detecting the presence of magnetism, without measuring
its intensity. A simple magneto-scope consists of a magnetized bit of
watch-spring suspended in a vertical glass tube by a fine filament. A
bit of unmagnetized soft iron wire may be used in the same way. The
first has the advantage of indicating polarity; the latter merely shows
magnetic attraction. A cork may be used as base of the instrument.

Fig. 235. MAGNETOSCOPE.

366 STANDARD ELECTRICAL DICTIONARY.

Magnet, Permanent.
A bar of steel charged with residual magnetism. Steel possesses high
coercive force in virtue of which when once magnetized it retains part
of the magnetization.

Permanent magnets are generally straight bars or U shaped; they are
termed bar magnets, magnetic needles, horseshoe magnets, machine magnets
and otherwise, according to their shape or uses.

Magnet Pole.
The part of a magnet showing strongest polarity; the part which attracts
iron the most powerfully, and acts as the starting point for lines of
force.

Magnet Poles, Secondary.
Magnet poles are often not situated at the ends. Owing to inequality of
the material or other causes they may occupy intermediate positions on
the magnet. Such poles are called secondary poles.

Magnet Pole, Unit.
A unit magnet pole is one which exerts unit force on another unit pole
placed at unit distance from it. Unit force is the dyne; unit distance
is one centimeter.

Magnet, Portative Power of.
The power of sustaining a weight by attraction of its armature possessed
by a magnet. In general terms the adherence of the armature of a magnet
to the pole varies with the square of the number of lines of force which
pass through the point of contact. Hence an increased adherence of the
armature to a horseshoe electro-magnet is sometimes obtained by
diminishing the area of contact of one pole which concentrates the lines
of force. Steel magnets were frequently made with rounded ends to
increase the portative power.

Magnet, Simple.
A magnet made of one piece of metal, or at least magnetized as such; the
reverse of a compound magnet, which is magnetized piece by piece and
then fastened together.

Magnet, Solenoidal.
A magnet which is so uniformly magnetized and is so long in proportion
to its other dimensions that it virtually establishes two magnetic
poles, one at either end. It is a long thin bar so magnetized that all
its molecules would, considered as magnets, be absolutely equal.
(Daniell.) It acts like a solenoid, except that it is longer in
proportion than the solenoid generally is constructed.

Magnet, Sucking.
A magnet coil with movable or loose axial bar of soft iron.

The whole is usually mounted vertically. When a strong enough current is
passed the bar is drawn up into the coil as if by suction, whence the
name.

367 STANDARD ELECTRICAL DICTIONARY.

Magnet, Unipolar.
No such thing as a unipolar magnet is possible. The name is given to
poised or suspended magnets, one of whose poles lies in the axis of
suspension. It is obvious that such a magnet will act, as far as its
directive tendency and rotatory movements are concerned, as if it had
only one pole. As shown in the cut, the pole s in both magnets lies in
the axis of suspension or directly under the filament by which they are
suspended, while the other pole n is the active pole in causing rotation
or directive tendency; c c are counterweights or counterpoises.

Fig. 236. UNIPOLAR MAGNETS.

Magnetophone.
An apparatus for producing a loud sound, involving the principles of the
telephone. A rapidly alternating or make and break current being
produced by any means and being transmitted through the telephone gives
a loud note of pitch dependent on the current producing it. Sometimes a
perforated metallic disc is rotated in a magnetic field, and produces
the requisite type of current.

Magnus' Law.
A law of thermo-electricity. In a homogeneous circuit, however, the
temperature varies from point to point; there is no current.

Whatever potential differences may be established by the variations in
temperature it is evident that they must counteract each other and
reduce to zero.

Mains, Electric.
The larger conductors in a system of electric light or power
distribution.

Make. v.
To complete a circuit, as by closing a switch.

Make and Break Current.
A current which is continually broken or interrupted and started again.
It is applied only where the "makes" and "breaks" succeed each other
with great rapidity, as in the action of an induction coil or pole
changer, etc. It has had considerable importance in litigation affecting
the Bell telephone patents, the courts holding that the original Bell
patent (No. 174,465, of 1876,) covered the undulating current, for the
transmission of speech. Many efforts have been made by litigants to
prove that specific telephones have transmitted articulate speech by the
make and break current, but without success. If this could have been
proved the assumption is that the courts would have sustained the use of
such device as not infringing upon the claims of the Bell patent.

Malapterurus.
A fish, sometimes called the thunder fish, an inhabitant of African
rivers, occurring in the Nile and Senegal. It possesses considerable
electric power, similar to that of the gymnotus and torpedo, although
inferior in amount.

368 STANDARD ELECTRICAL DICTIONARY.

Fig. 237. MALAPTERURUS.

Man-hole.
The cistern-like depression in the ground for giving access to the ends
of tubes in electric conduits. (See Conduit, Electric Subway.)

Marked End or Pole.
The north pole or north seeking pole of a magnet, so called because it
is usually marked with a notch or scratch by the maker. The south pole
is called the unmarked end.

Mass.
The quantity of matter in a body. The C. G. S. unit of mass is the
quantity of matter in a gram. While weight varies with latitude and
other circumstances, mass is invariable.

The unit of mass is also defined as the quantity of matter which in a
balance will counterpoise a standard mass, the gram or pound. As the
gram is intended to be the mass of one cubic centimeter of water at
3.09º C. (39º F.), the C. G. S. unit of mass is really 1.000013 gram.

As a primary unit its dimensions are indicated by M.

Mass, Electric.
A term for quantity of electricity. The unit mass is such a quantity as
at unit distance will act with unit force.

Matter, Electric.
The imaginary substance constituting electricity; a conception used
purely as a matter of convenience.

Matter, Radiant.
Matter in the ultra-gaseous or so-called fourth state. In the gaseous
state the molecules of a gas are in perpetual kinetic motion, colliding
actually or virtually with each other, rebounding from such approach,
and striking also the walls of the containing vessel. But except for
these deflections, which are of enormous frequency, the paths of the
molecules would be perfectly straight.

In the radiant state matter exists in so high a vacuum that collisions
of the molecules rarely occur, and the molecules simply beat back and
forth in straight lines from side to side of the containing vessel.

A layer of gas in this condition is termed a Crookes' layer, from Prof.
William Crookes, who discovered and investigated these phenomena.

369 STANDARD ELECTRICAL DICTIONARY.

Luminous streams of the molecules are produced by electric high
potential discharges between electrodes. The course of the discharge is
normal, in general terms, to the surfaces of the electrodes, and reaches
from one to the other in a curve or straight line, as the case may be.

These luminous streams are deflected by a magnetic field; if brought to
a focus can heat refractory material in that focus to a full white heat,
and can develop phosphorescence. The latter is termed electric
phosphorescence. A great variety of experiments have been devised to
illustrate the phenomena of radiant matter. The vacuum is generally
produced in a hermetically sealed glass vessel into which the electrodes
are sealed, and which contain the phosphorescent substances or other
essentials for the experiments. The vessels are termed Crookes' Tubes.

Matteueci's Experiment.
An experiment for showing the inductive effect of the discharge of a
Leyden jar. Two glass plates are supported on standards in a vertical
position. Flat coils of wire are wound or coiled and secured to one
surface of each plate. One plate has much finer and longer wire than the
other. Metal handles are connected to the ends of the coarser wire coil.
The plates are placed with their coils facing each other. A Leyden jar
is discharged through the coarser coil, while the handles are grasped by
a person. The shock of the discharge is felt by him.

Matting, Electric Floor.
Matting or floor covering underlaid with burglar alarm contacts, so
arranged as to be closed by anyone walking on the matting. The contacts
are connected to a burglar alarm system. The object is to provide an
alarm if a burglar enters a house, in case he should enter a door or
window without sounding the bell. The latter can be done by cutting out
the window or part of the door instead of opening it.

Maxwell's Theory of Light.
A theory of light. It is due to J. Clerk Maxwell.

It supposes the phenomena of electric induction to be due to the ether,
q. v. It supposes the condition of the ether when conveying light to be
the same as if exposed to the induction of rapidly alternating currents
or discharges (in this case synonymous). It therefore is an
electro-magnetic effect if the theory is correct.

An electric stress such as one due to the induction of an
electrostatically charged body is not a wave-creating element or factor,
but is a simple stress. But let this stress be stopped and renewed and
at once it appears as a wave-forming agency.

This stoppage and renewal represents evidently a discharge succeeded by
a charge, or if repeated is equivalent to an intermittent current or an
alternating one.

370 STANDARD ELECTRICAL DICTIONARY.

Again the electrostatic stress kept constant may by being carried
through space carry with it a wave, just as a moving projectile carries
a wave of air in advance of itself.

Admitting this much the following consequences follow:

Since in non-conductors the displacement produces a restitution force,
which varies as the displacement which is requisite or is a criterion
for the propagation of waves, while in conductors no such force is
manifested and the electric energy appears as heat, it follows that
light vibrations are not possible in conductors, because
electro-magnetic waves do not exist in them when they are in circuit,
and conductors should be opaque, while the reverse is true for
non-conductors. (Daniell.)

This is carried out often enough to make a striking evidence in favor of
Maxwell's theory.

The velocity of propagation of an electro-magnetic disturbance in a
non-conductor should be equal to that of light. This constant is proved
by mathematical considerations, to be approximately the same as the
ratio of the electrostatic to the electromagnetic unit of intensity or
quantity. This ratio is 3E10 (30,000,000,000), which is almost exactly
the velocity of light.

It also follows from what has been said that if an electrostatically
charged body were whirled around a galvanometer needle at the rate of
3E10 revolutions per second it should affect it like a circulating
current. This rate of rotation cannot be attained, but Rowland has made
manifest the effect of a rotating statically charged body upon a
magnetic needle.

The above is the merest outline of Maxwell's theory. The full
development must be studied in his own and succeeding works.

Mayer's Floating Magnets.
An experiment due to Prof. Mayer. A number of sewing needles are
magnetized and thrust into bits of cork, almost all the way through,
with their like poles projecting. They are floated in a basin of water
and take, under the effects of attraction and repulsion, when approached
by a magnet pole, regular geometric positions, marking out the positions
of angles of polygons.

Measurements.
The determination of the value of quantities; determination of the
factor by which the unitary value must be multiplied to produce the
quantity under examination. Such are the measurement of the voltage of a
galvanic battery, or of the ohms of resistance of a conductor.
Electricity has been termed the science of measurement.

Meg or Mega.
A prefix, meaning one million times. A megohm is one million ohms; a
megerg is one million ergs; a megadyne is one million dynes.

371 STANDARD ELECTRICAL DICTIONARY.

Fig. 238. MAYER'S FLOATING MAGNETS.

Mercury.
A metal; one of the elements; symbol, Hg; atomic weight, 200 ;
equivalent, 200 or 100; valency, 1 and 2.
It is a conductor of electricity.
The following data are 0º C. (32º F.)
Relative Resistance, 62.73
Specific Resistance, 94.32 microhms.
Resistance of a wire,
(a) 1 foot long, weighing 1 grain, 18.51 ohms.
(b) 1 foot long, 1/1000 inch thick, 572.3 "
(c) 1 meter long, weighing 1 gram, 12.91 "
(d) I meter long, 1 millimeter thick 1.211 "
Resistance of a 1 inch cube, 37.15 microhms.
Percentage increase of resistance per degree C. 1.8° F.
at about 20° C. (68° F.), .72 per cent.
Electro-chemical equivalent (Hydrogen = .0105), 2.10 mgs.
1.05 "

372 STANDARD ELECTRICAL DICTIONARY.

Mercury Cup.
A cup of iron, wood or some material that does not amalgamate or is
unattacked by mercury, which is filled with mercury and made an
electrode of a circuit. By dipping the other terminal of the circuit
into the mercury a very good contact is obtained. It is well to cover
the mercury with alcohol. The cup may be filled so that the mercury
rises in a meniscus or semi-globule above its edges.

For some purposes this form is useful, as for contacts with the end of a
swinging wire or pendulum, because in such cases the contact can be made
without the contact point entering the cup. The point swings through the
projecting meniscus without touching the edges of the cup. A mercury cup
and contact constitute a mercury break.

Meridian, Astronomical.
The great circle passing through the north and south poles of the
celestial sphere. It lies in a plane with the corresponding geographical
or terrestrial meridian.

Meridian, Geographic.
The true north and south meridian; the approximate great circle formed
by the intersection of a plane passing through north and south poles of
the earth with the earth's surface.

373 STANDARD ELECTRICAL DICTIONARY.

Fig. 239. SCHALLENBERG'S ALTERNATING CURRENT METER.

Meter, Alternating Current.
A meter for measuring alternating current, as supplied to consumers,
from an alternating current system. Like most commercial meters its only
function is the measurement of quantity; the potential difference is
maintained at a constant figure by the generating plant.

The cut shows the Schallenberg meter. It is simply an alternating
current motor (see Motor, Alternating Current), with air vanes mounted
on its spindle. A main coil passes all the current. Within this is a
second coil complete in itself, and not touching or connecting with the
other. The latter is built up of copper rings. Within the two coils, and
concentric with both is a disc of copper carried by a vertical spindle.
The same spindle carries air vanes, and is free to rotate. As it does so
it moves the indicating machinery.

The current in the outer coil induces one in the inner coil. Owing to
lag, the current in the inner one differs in phase from that in the
outer one, and a rotatory field is produced. The copper disc acquires
induced polarity, and rotates with speed which normally would be in
proportion to the square of the current. But the object of the meter is
to register the current only. The air vanes effect this. The resistance
of the air to their motion causes the rate of rotation to vary directly
as the speed.

Meter Bridge.
A form of Wheatstone's bridge in which one lateral pair of arms is
represented by a straight wire. The other pair comprise a known
resistance, and the resistance to be determined. The galvanometer is
connected on one side between the known and unknown resistance. On the
other side its connection is moved back and forth along the straight
wire until the balance is secured and the galvanometer reads zero.

The relative lengths of wire intercepted between the two ends thereof
and the movable galvanometer connection are proportional to the
resistance of these parts and give the necessary data with the one known
resistance for determining the unknown resistance.

374 STANDARD ELECTRICAL DICTIONARY.

In the original meter bridge the wire was one meter long, whence its
name, and was stretched straight. In more recent examples the wire
varies in length and in one form is bent into a circle or spiral, so as
to make the instrument more compact.

The contact is not a sliding one, but is adjusted by trial. The contact
piece is slid along, but not touching the wire, and from time to time is
pressed down against the wire. This prevents wear of the wire. The wire
may be made of platinum or of platinum-iridium alloy. The latter is
very hard and not easily worn out.

Sometimes, as shown in the cut, three parallel wires are stretched along
the baseboard of the instrument, and arranged so that a single wire, two
wires or three wires in series can be used for the proportional sides of
the bridge, thus making it a two-meter or three-meter bridge as desired.
On the other hand some are made of restricted length, as a half or
quarter meter only.

Fig. 240. METER BRIDGE.

In the cut J K is the wire, traversed by the contact key. By moving the
contact C back and forth in the slot it can be brought over any of the
three divisions of the wire. H is the handle for depressing the key. S
is a flat spring, carrying the contact piece and holding it up from the
wires, except when pressed downwards. As shown in the cut, it is in use
for calibrating a voltmeter V, by Poggendorff's method, G being the
galvanometer and r1 and r2 being resistances.

Synonyms--Slide Bridge--Slide Balance.

Meter Candle.
A unit of illuminating power; the light given by one standard candle at
a distance of one meter. The ordinary units of illuminating power are
altogether relative; this one is definite.

375 STANDARD ELECTRICAL DICTIONARY.

Meter, Chemical Electric.
A current meter in which the current is determined by the amount of
chemical decomposition which it can effect. In the Edison meter the
solution is one of zinc sulphate. Two electrodes of zinc are immersed in
it, and a fractional part of the current is passed through it. The gain
in weight of one electrode and the loss in the other are proportional to
the current. Both electrodes are weighed periodically, one acting as
check upon the other.

Meter, Current.
An instrument for measuring the quantity of electricity in current form
supplied to consumers. It may be of various types. The general principle
involved is that in commercial installations for incandescent light and
power supply a fixed potential is usually maintained, the multiple arc
system being employed. Hence all that is requisite is to measure the
coulombs or the ampere-hours to know what quantity of energy has been
supplied.

Meter, Electro-magnetic.
A current meter in which the current is measured by its electro-magnetic
effects.

Meter-millimeter.
A unit of resistance. (See Resistance, Meter-millimeter.)

Meter, Thermal Electric.
A current meter in which the current is measured by the heat it imparts
to a conductor. In one meter a very light helix of mica is poised
horizontally over a conductor, and the whole is enclosed in a case. As
the wire is heated it causes an ascending current of air which rotates
the vane, and the latter moves delicate clockwork which moves indicating
hands. The hotter the wire the more rapidly the air ascends, and
consequently the speed of the vane is proportional to the current,
because the heat of the conductor is proportional thereto.

Meter, Time Electric.
An electric meter which measures the length of time during which current
is used. It assumes a constant current and potential. It is virtually a
clock, which is turned on when the current passes, and is turned off
with the current.

Meter, Watt.
A combined current and potential meter. It is constructed on the general
lines of a Siemens' Electro Dynamometer. If in it one coil is made of
coarse wire and is placed in series with the current conductor, and if
the other is wound with fine wire and is connected as a shunt from point
to point whose potential difference is to be determined, the instrument
becomes a watt meter.

Synonym--Energy Meter.

Methven Standard or Screen.
A standard of illuminating power. It is the light emitted by a
three-inch Argand gas flame through a rectangular aperture in a silver
plate carried by a screen. The aperture is of such size and so far
distant from the flame as to permit the passage of exactly two candles
illuminating power.

Fig. 241. METHVEN SCREEN

376 STANDARD ELECTRICAL DICTIONARY.

Mho.
A unit of conductance, not in very general use. It is the reciprocal of
the ohm. Thus a resistance of ten ohms is a conductance of one-tenth
mho.

Mica.
A natural mineral, a silicate of several oxides; muscovite. It is used
as an insulator and dielectric. Its resistance per centimeter cube after
several minutes electrification at 20º C. (68º F.) is 8.4E13 ohms
(Ayrton). Its specific inductive capacity is 5, air being taken at 1.

Mica, Moulded.
An insulating material, whose body is made of mica pulverized and
cemented together with heat and pressure and some suitable cement.
Shellac is often used as the cement.

Micro.
A prefix meaning "one-millionth of;" a micro-farad is one-millionth of a
farad.

Micrometer.
An instrument for measuring small distances or small differences. It
generally is based upon an accurate screw which may have a worm wheel
for head, actuated by a worm or helix with graduated head, so that
exceedingly small advances of the screw may be produced. The pitch of
the screw being known its actual advance is known.

Micrometer, Arc.
A micrometer for measuring the distance between voltaic arc electrodes.

Micron.
A unit of length. It is one-millionth of a meter or four
one-hundred-thousandths of an inch.

377 STANDARD ELECTRICAL DICTIONARY.

Microphone.
An apparatus which includes a contact of variable resistance; such
resistance can be varied in amount by slight vibrations, such as those
produced by sound waves. The apparatus in use forms part of a circuit
including a telephone and current generator. As the contact is varied
the resistance of the circuit and consequently the current intensity
changes and sounds are emitted by the telephone corresponding to such
changes. If the microphone is spoken to, the telephone will emit
corresponding sounds, reproducing the voice.

It has been found in practice that carbon gives the best microphone
contact. One of the simplest and earliest forms is shown in the cut. A
short rod or pencil of carbon, A, such as used in batteries, is
sharpened at the ends and rests loosely in a vertical position between
two blocks of carbon, C C, in each of which a hole is drilled to receive
one of the points. The blocks are carried on a standard and base D. The
blocks are connected with two terminals x, y, of a circuit, including a
telephone and battery. There are two contacts to be disturbed.

If delicately adjusted a fly walking over the base-board will disturb
the contacts enough to produce sounds in the telephone. These sounds are
possibly not due only to sound waves, but in part to absolute mechanical
disturbances.

The various forms of telephone transmitter are generally microphones.

Fig. 242. MICROPHONE.

Microphone Relay.
A combined microphone and telephone. A microphone is placed close to the
diaphragm of a telephone. The slight sound waves emitted by the
telephone affect the microphone and are repeated in its circuit. The
microphone circuit includes a local battery and telephone.

Microtasimeter.
An apparatus for indicating minute changes in temperature or atmospheric
moisture.

378 STANDARD ELECTRICAL DICTIONARY.

A button of compressed lampblack is placed in series with a battery and
galvanometer. A strip of some substance, affected in its length either
by heat or by moisture, is held pressing against the button. A slight
change in length of the strip varies the resistance of the button and
hence affects the galvanometer. In this way exceedingly slight changes
in heat or moisture may be indicated.

For heat indications vulcanite may be used. The heat of the hand held
near it is enough to affect the galvanometer. For moisture a slip of
gelatine is used. The moisture of a damp slip of paper two or three
inches distant is sufficient to affect the galvanometer.

In the cut, Fig. 2, shows the general distribution of the apparatus in
circuit with a battery and galvanometer. C is the base of the apparatus,
from which the standard, B, with adjusting screw, H, rises. The strip of
vulcanite is held between I and G. Within D is the carbon button (F in
Fig. 3) pressed between G and E; A is a standard to carry the parts last
described. In Fig. I it is shown as part of a Wheatstone bridge, a, b
and c being resistance coils; l the tasimeter, and g the galvanometer.
If a balance is secured, any variation in the resistance of the
tasimeter will disturb the galvanometer.

Synonym--Tasimeter.

Fig. 243. MICROTASIMETER.

379 STANDARD ELECTRICAL DICTIONARY.

Mil.
A unit of length; one-thousandth part of a lineal inch.

It is equal to
.025399 millimeter;
.000083 foot;
.001000 inch.

Mil, Circular.
A unit of area; employed in designating the cross-sectional area of
wires and other circular conductors.

It is equal to
.78540 square mil;
.000507 square millimeter;
7.8E-7 (.00000078) square inch.

If the diameter of a wire is given in mils, the square of its diameter
gives its cross-sectional area in circular mils.

Mil-foot.
A unit of resistance. (See Resistance, Mil-foot, Unit of).

Mil, Square.
A unit of area; one-millionth of a square inch.

It is equal to
.000645 square millimeter;
1.2733 circular mil;
.000001 square inch.

Milli.
A prefix; one-thousandth. Thus a milligram is one-thousandth of a gram;
a millimeter is one thousandth of a meter.

Milligram.
A unit of weight ; one-thousandth of a gram, q. v.

It is equal to
.015432 grain;
.000032 troy ounce.

Millimeter.
A unit of length; one-thousandth of a meter.

It is equal to
39.37079 mils;
.03937 inch;
.00109 yard.

380 STANDARD ELECTRICAL DICTIONARY.

Milli-oerstedt.
A proposed but not adopted unit of current; one-thousandth of an
oerstedt. It is equal to one-thousandth of an ampere.

mm.
Contraction for millimeters.

Molar.
Referring to phenomena of mass as gravitation. Mechanics
generally treats of molar laws and phenomena.

Molar Attraction.
The attraction of mass for mass; gravitation. Synonyms--Mass
Attraction--Gravitation.

Molecular Affinity.
The attraction of molecules for each other as seen in the formation of
double salts, the combining of water of crystallization with a salt, and
in other cases; a phase of affinity belonging to chemistry, although
outside of true atomic attraction.

Molecular Attraction.
The attraction of molecules; physical affinity. Cohesion, the attraction
of similar molecules for each other, and adhesion, that of dissimilar
molecules, are examples. This should be distinguished from molecular
affinity, a phase of chemical force.

Molecular Bombardment.
When a gas contained in a vessel is brought to a sufficient state of
rarefaction the molecules cease to be subject to the laws of diffusion,
but move back and forth in straight lines from side to side of the
vessel. Their courses can be affected by electric discharge, which can
cause them to all impinge upon one of the electrodes, the positive one,
producing luminous effects. The path, if referred to the negative
electrode, tends to be normal to its surface, so that the resultant path
may be curved, as the stream of molecules go to the positive electrode.
The fanciful name of molecular bombardment is given to the phenomenon,
the luminous effect being attributed to the impinging of the molecules
against the positive electrode as they are projected from the positive.
The course of the molecules is comparable to the stream of carbon
particles from the positive to the negative electrode in an arc lamp.
(See Matter, Radiant.)

Molecular Chain.
The theoretical rows of molecules supposed to extend from anode to
cathode in an electrolytic cell (see Cell, Electric--Grothüss'
Hypothesis) are called molecular chains.

381 STANDARD ELECTRICAL DICTIONARY.

Molecular Rigidity.
The tendency of the molecules of a mass to retain their position in a
mass in resistance to polarizing or depolarizing force, the first being
the effect of a magnetic field. It is the theoretical cause of coercive
force, q. v., and of residual magnetism. (See Magnetism, Residual.)

Molecule.
The smallest particle of matter that can exist alone. It is made up of
atoms, but an atom can never exist alone, but only, with one or two
possible exceptions, combined with one or more other atoms as a
molecule. The molecules under present conditions are not in constant
contact with each other, but are perpetually vibrating through paths, in
solids probably in defined paths, in liquids and gases in perpetually
new paths. The molecules collide with each other and rebound. This
motion is the kinetic motion termed heat. At the absolute zero--minus
273.72° C. (-460.7° F.) the molecules would be in contact and quiescent.
In the gaseous state the molecules of most substances occupy the same
volume; those of a few elements occupy one-half and of others twice the
normal volume. The mean free path of the molecule of hydrogen is about
1/20,000 mm. (1/508,000 inch) (Maxwell) or twice this length (Crookes),
the collisions in hydrogen are about 17,750 millions per second; the
diameter is about 8/10,000,000 mm. (8/254,000,000 inch) ; A particle of
matter 1/4,000 mm. (1/102,000 inch) contains, it is supposed, about
40,000 molecules. The results of different authorities vary so widely as
to deprive the subject of much of its interest. A Sprengel pump, such as
used for exhausting Geissler tubes, or incandescent lamp bulbs, may
leave only one hundred-millionth (1/100,000,000,) of an atmosphere
present, giving the molecules a capability of an average free path of
vibration 33 feet long.

Moment.
When a force is applied so as to tend to produce rotation around a
point, the product of the force by the shortest distance from the point
of rotation to the extension of the line of the force. Such distance is
the perpendicular to the extension of the line through the point of
rotation.

Mordey Effect.
A phenomenon observed in dynamo armatures. At full loads the hysteresis
decreases. The effect is thus expressed by S. P. Thompson. "When an
armature core is rotated in a strong magnetic field, the magnetization
of the iron is being continually carried through a cycle, but in a
manner quite different from that in which it is carried when the
magnetizing force is periodically reversed, as in the core of a
transformer. Mordey has found the losses by hysteresis to be somewhat
smaller in the former case than in the latter."

Morse Receiver.
The receiving instrument formerly universally used in the Morse system.
It is now but little employed, the sounder having displaced it. Several
types were invented.

It consists of machinery which carries a reel of paper ribbon arranged
to be fed over a roller by clockwork. A pencil, inking roller, or
embossing stylus (for the latter the roller must have a groove) is
carried by an arm with restricted range of vibration just over the paper
and roller. The armature of an electro-magnet is attached to the arm.
When the magnet is excited the armature is attracted and the marking
device is pressed on the paper. If the clockwork is in operation the
marker will make a line as long as the armature is attracted. When
released no mark will be produced. In this way the dots and dashes of
the Morse code are made on a ribbon of paper.

As an inking arrangement a small roller is carried by the end of the
vibrating arm. The embosser, or dry point stylus, was very extensively
used. The clockwork was generally driven by descending weights.

Synonym--Morse Recorder.

382 STANDARD ELECTRICAL DICTIONARY.

Mortar, Electric.
An electric toy which may have various modifications. In the cut a
wooden mortar with recess to receive a ball is shown. Two wires enter
the base but do not touch. On placing the ball in position and passing a
spark from a Leyden jar across the interval between the wires, the heat
and disturbance are enough to project the ball. Gunpowder may be used,
the discharge being passed through a wet string to prolong the spark.

Fig. 244. ELECTRIC MORTAR.

Motor, Compound or Compound Wound.
A motor which has two windings on the field magnets, one in parallel
with that on the armature, the other in series therewith, exactly as in
a compound dynamo. (See Dynamo, Compound.)

Motor, Differential.
A differentially wound motor; with a compound wound field, whose series
coil and shunt coil are wound in opposition to each other. It is
virtually a compound wound dynamo. (See Dynamo, Compound Wound.)

Motor, Electric.
A machine or apparatus for converting electric energy into mechanical
kinetic energy. The electric energy is generally of the dynamic or
current type, that is to say, of comparatively low potential and
continuous or virtually continuous flow. Some electrostatic motors have,
however, been made, and an influence machine can often be operated as a
static motor.

Electric motors of the current type may be divided into two
classes--direct current and alternating current motors.

Direct current motors are generally based on the same lines of
construction as dynamos. One of the great discoveries in modern
electricity was that if a current is passed through a dynamo, the
armature will rotate. This fact constitutes the principle of the
reversibility of the dynamo.

383 STANDARD ELECTRICAL DICTIONARY.

Motors built on the dynamo model may be series wound, shunt wound, or
compound wound, or of the magneto type, in the latter case having a
fixed field irrespective of any current sent through them. The field may
be produced by an electro-magnet separately excited and unaffected by
the current sent through the motor.

A current passed through a magneto or motor with separately excited
field will turn it in the direction opposite to that required to produce
the same current from it were it worked as a generator.

A current passed through a series wound motor acts exactly as above.

Both these facts follow from Lenz's law, q. v.

A current passed through a shunt wound motor acts oppositely to the
above. The direction of rotation is the same as that required to produce
a current of the same direction. This is because the field being in
parallel with the armature the motor current goes through the magnet
coils in the direction the reverse of that of the current produced in
the armature when it is used as a dynamo. Hence this also carries out
Lenz's law.

The compound wound motor acts one way or the other according as its
shunt or series winding preponderates. The two may exactly balance each
other, when there will be no motion at all. The series connections of a
compound wound dynamo should therefore be reversed, making both series
and shunt work in unison, if the dynamo is to be used as a motor.

The general principles of the electric motor of the dynamo, or
continuous rotation type, can only be outlined here. The current passing
through the field magnets polarizes them and creates a field. Entering
the armature by the brushes and commutators it polarizes its core, but
in such a way that the north pole is away from the south pole of the
field magnet, and the same for the south pole. Hence the armature
rotates. As it does this the brushes connect with other commutator
sections, and the poles of the armature are shifted back. This action
continues indefinitely.

Another class of motors is of the reciprocating type. These are now very
little used. (See Motor, Reciprocating.)

One valuable feature of continuous rotation electric motors is the fact
that they absorb energy, to a great extent proportional in amount to the
work they have to do. The rotation of the armature in the field of the
motor involves the cutting of lines of force by its coils. This
generates an electro-motive force contrary in direction to that
producing the actuating current. The more rapid the rotation the greater
is this counter-electro-motive force. The motor armature naturally
revolves faster with diminished resistance to the motion of the
armature. This increases the counter-electromotive force, so that less
energy is absorbed. When the motor is called on to do work, the armature
rotates more slowly, and the counter-electro-motive force diminishes, so
that the machine absorbs more energy. (See Jacobi's Law.)

384 STANDARD ELECTRICAL DICTIONARY.

Motor Electro-motive Force.
The counter-electro-motive force of a motor. (F. J. Sprague.)

A motor rotates in virtue of the pull of the field magnet upon the poles
of the core of its armature. In responding to this pull the windings of
the armature cuts lines of force and hence generates a
counter-electro-motive force, for which the above term was suggested.

Motor-Generator.
A combined motor and generator used to lower the potential difference in
a portion of a circuit, e. g., that part within a building.

A motor-generator is a dynamo whose armature carries two commutators,
with two separate windings, one of fine wire of many turns, the other of
coarse wire of few turns. If the potential of the system is to be
lowered, the main current is passed through the fine winding. This
causes the armature to turn motor-fashion, and a potential difference is
generated by the rotation of the large coils in the field. This
potential difference is comparatively low and by properly proportioning
the windings may be lowered to as great a degree as required.

The same apparatus may be inverted so as to raise potential difference.
It acts for continuous current systems as the induction coil transformer
does for alternating current systems.

Synonym--Continuous Current Transformer.

Motor, Multiphase.
A motor driven by multiphase currents. It is arranged in general terms
for distribution of the multi phase currents in coils symmetrically
arranged around the circle of the field. These coils are wound on cores
of soft iron. A rotating field is thus produced, and a permanent magnet
or a polarized armature pivoted in such a field will rotate with the
field, its poles following the poles of the rotatory field.

The cut, Fig. 245, illustrates the principles of action of a four phase
current motor, connected to a four phase current dynamo or generator.
The generator is shown on the left hand of the cut and the motor on the
right hand. In the generator the armature N S is supposed to be turned
by power in the direction shown by the arrow. Each one of the pair of
coils is wound in the reverse sense of the one opposite to it, and the
two are connected in series with each other, and with a corresponding
pair in the motor. The connection can be readily traced by the letters A
A', a a' for one set of coils and B B' b b' for the other set.

385 STANDARD ELECTRICAL DICTIONARY.

For each rotation of the armature two currents, each in opposite
direction, are produced in A A', and the same is the case for B B'.
These currents which have an absolutely constant relation of phase, and
which it will be seen alternate four times for each rotation of the
armature, regulate the polarity of the field of the motor. The resultant
of their action is to keep the poles of the field magnet of the motor
constantly traveling around its circle. Hence the armature N S of the
motor, seen on the right hand of the cut, tends to travel around also
its north and south poles, following the south and north poles of the
rotatory field respectively.

Fig. 245. FOUR-PHASE CURRENT GENERATOR AND MOTOR.

It is not essential that the armature should be a magnet or polarized.
Any mass of soft iron will by induction be polarized and will be
rotated, although not necessarily synchronously, with the rotatory
field. Any mass of copper, such as a disc or cylinder, will have
Foucault currents induced in it and will also rotate. The only
components of such currents which are useful in driving the motor are
those which are at right angles to the lines of force and to the
direction of motion. A very good type of armature based on these
considerations is a core of soft iron wound with insulated copper wire
in one or more closed coils; and so wound as to develop the currents of
proper direction.

Such an armature is used in the Tesla alternating current motor. An
efficiency of 85 per cent. has been attained with some of the Tesla
motors.

Motor, Prime.
A machine used for producing mechanical motion against resistance. It
may operate by converting heat or any other form of kinetic or potential
energy into mechanical energy of the moving type. A steam-engine and a
water-wheel are examples of prime motors.

Motor, Reciprocating.
The early type of motor depending upon reciprocating motion, such as the
motion of a coil in a solenoid. These were based upon the lines of a
steam engine, and have been abandoned except for special purposes where
reciprocating motion is especially required, as in the case of rock
drills.

386 STANDARD ELECTRICAL DICTIONARY.

Fig. 246. RICORDON'S RECIPROCATING MOTOR.

In the cut, B is an electro-magnet; A is an armature; E a pole piece.
The current enters by the springs, b b, and by commutation is supplied
and cut off alternately, thus maintaining a reciprocating movement of
the armature and rotation of the fly-wheel.

Synonym--Pulsating Motor.

Motor, Series.
A motor whose winding on the armature is in series with the winding on
the field. It is similar to a series dynamo. (See Dynamo, Series.)

Motor, Shunt.
A motor whose winding on the armature is in parallel with the winding on
the field magnets. It is similar to a shunt wound dynamo. (See Dynamo,
Shunt.)

Fig. 247. MULTIPLE ARC CONNECTION.

Multiple.
A term expressing connection of electric apparatus such as battery
couples, or lamps in parallel with each other. In the ordinary
incandescent lamp circuits the lamps are connected in multiple.

Synonym--Multiple Arc.

387 STANDARD ELECTRICAL DICTIONARY.

Multiple Arc Box.
A resistance box arranged so that the coils may be plugged in multiple
instead of in series. Such can be used as a rheostat, as the resistance
can be very gradually changed by putting the coils one by one into
parallel with each other. Thus by adding in parallel with a 10 ohm coil
a 10,000 ohm coil the resistance is decreased to 9.999001 ohms, and thus
the resistance can be very slowly changed without sudden stops or abrupt
changes.

Multiple Series.
Arrangements of electric apparatus in a circuit in a number of series,
which minor series are then arranged in parallel. The term may be used
as a noun, as "arranged in multiple-series," or as an adjective, as "a
multiple-series circuit."

Fig. 248. MULTIPLE SERIES CONNECTION.

Multiple Switch Board.
A switch board on whose face connecting spring jacks or other devices
are repeated for the same circuits, so that different operators have
each the entire set of connections repeated on the section of the board
immediately in front of and within their reach. This multiplication of
the same set of connections, giving one complete set to each operator,
gives the title "multiple" to the type of switch board in question. The
typical multiple switch board used in telephone exchanges is the best
example of this construction. The calling annunciators of the
subscribers are distributed along the bottom of the board extending its
full length. To each operator a given number is assigned, all within
reach of the right or left hand. This gives five or six feet length of
board to each, and an operator only responds to those subscribers within
his range. But anyone of his subscribers may want to connect with any of
the others in the entire central station. Accordingly in front of each
operator spring jacks are arranged, one for each of the entire set of
subscribers connected in that office. The operator connects as required
any of the calling subscribers, who are comparatively few, to any one of
the large number served by the central station. Thus the entire set of
subscribers' spring jacks are multiplied over and over again so as to
give one set to each operator.

388 STANDARD ELECTRICAL DICTIONARY.

Multiple Wire Method for Working Electro-magnets.
A method for suppressing sparking in working electro-magnets
intermittently. The magnet core is wound with a number (from four to
twenty) of separate layers of fine wire. A separate wire is taken for
each layer and all are wound in the same direction, from one end to the
other of the space or bobbin without returning. The ends are then joined
so as to bring all the wires in parallel. The effect of this is that as
the coils vary in diameter the time constants of each is different from
that of the others, the coefficient of self-induction being less, and
the resistance being greater for the coils farthest from the central
axis. Thus the extra currents run differently in the different coils,
and only a comparatively small spark can be produced owing to the
division of forces thus brought about.

Fig. 249. DIAGRAM ILLUSTRATING MULTIPLE WIRE WORKING.

Multiplex Telegraphy.
Any system of telegraphy transmitting more than four messages
simultaneously over a single wire. Properly it should apply to all
transmitting more than one, but conventionally has the above restricted
meaning, distinguishing it from duplex and quadruplex telegraphy.

Multiplying Power of a Shunt.
When a resistance is placed in parallel with a galvanometer on a circuit
the following relation obtains. Let s and g equal the resistances of the
shunt and galvanometer respectively, S and G the currents in amperes
passing through them, V the potential difference between their common
terminals, and A the whole current in amperes. Then we have
A = ( (s + g ) / s ) * G
and ( (s + g ) / s ) is termed the multiplying power of the shunt, as it
is the factor by which the current passing through the galvanometer must
be multiplied by to produce the total current.

Muscular Pile.
A species of voltaic battery, often termed Matteueci's pile, made up of
alternate pieces of muscle cut longitudinally and transversely
respectively. The different pieces represent the elements of a battery,
and their difference of potential is naturally possessed by the pieces.

Myria.
A prefix; one million times. Thus myriavolt means one million volts.

389 STANDARD ELECTRICAL DICTIONARY.

N.
(a) Symbol for north pole or north-seeking pole of a magnet.

(b) Symbol for the number of lines of force in a magnetic circuit.

Nairne's Electrical Machine.
The cylinder electrical machine, q.v.

Napierian Logarithms.
A series of logarithms the base of whose system is 2.72818. They are
also called hyperbolic logarithms.

Nascent State.
An element just separating from a combination possesses at that time
higher affinities than after separation, and can effect more powerful
chemical changes.

It is sometimes attributed to a differential time of existence in the
atomic modification, before the freed atoms have united to form
molecules.

Natural Currents.
A term for earth currents. (See Current, Earth.)

Needle.
(a) A term applied to a bar magnet poised horizontally upon a vertical
point, or suspended in a horizontal position by a filament. Thus the
magnet in a mariner's compass, which may be a substantial bar magnet, is
called a magnetic needle.

(b) An indicator in general shape like the hand of a clock. (Sec
Annunciator, Needle- Telegraph, Needle.)

Needle of Oscillation.
The magnetic needle poised horizontally, and used for measuring the
intensity of the earth's magnetic field, or of an artificial magnetic
field, by the method of oscillations. The intensities of the field is
inversely as the square of the number of oscillations performed in a
given time.

Needle, Telegraphic.
The index in needle telegraphy (see Telegraph, Needle), whose motions
indicate the characters it is desired to transmit.

Negative Charge.
One of the two kinds of electric charges. The other is the positive.

By the double fluid hypothesis this is assumed to be a charge of a
particular kind of electricity--negative electricity.

By the single fluid hypothesis it is supposed to be caused by the
absence of part of the normal electricity of a surface. The reverse is
held by some theorists.

The subject is so purely theoretical that neither of the two hypotheses
is accepted as final.

390 STANDARD ELECTRICAL DICTIONARY.

Negative Electricity.
The kind of electricity with which a piece of amber is charged by
friction with flannel; resinous electricity. (See Electrostatic Series.)

In a galvanic battery the surface of the zinc plate is charged with
negative electricity.

According to the single fluid theory negative electrification consists
in a deficiency of electricity.

Negative Element.
In a voltaic cell the plate not dissolved by the solution; the one which
is positively charged; the copper, platinum, or carbon plate in the
usual type of battery.

The current is assumed to flow from negative element to positive element
(the zinc plate) through the wire or other external conductor.

Nerve Currents.
Currents of electricity obtained from nerves. They are much more feeble
than those obtained from muscle, but are produced in the same general
ways.

Network.
Conductors in parallel and crossing each other, with connections at the
junctions.

The term is sometimes so loosely applied as to include parallel
conductors.

Neutral Line of Commutator.
The diameter of a commutator which connects its Neutral Points, q. v.;
sometimes termed the diameter of commutation; the diameter approximately
at right angles with the lines of force. The commutator brushes are
applied at the extremities of this diameter.

Neutral Point of a Commutator.
The points of a commutator at which no lines of force are cut; the
points at the extremities of a diameter which, except for the lag, would
be at right angles to the lines of force; the points at which the
brushes touch the commutator.

Neutral Point, Thermo-electric.
A temperature marking a point of no thermo-electric difference of
potential. If the junctions of a thermo-electric couple are at
temperatures, one a little over and the other an equal amount under the
neutral point, no current will be developed. At the neutral point the
thermo-electric polarities are reversed. Differences of temperature
above it give currents of reverse direction to those given by
corresponding differences below it. For an iron-copper couple the
neutral point is 274.5° C. (526° F.)

Synonym--Neutral Temperature.

Neutral Relay Armature.
An unpolarizable armature for use with a relay; an armature of soft iron
or iron wire; as distinguished from a polarized armature.

391 STANDARD ELECTRICAL DICTIONARY.

Neutral Wire.
The central wire in the three wire system, q. v., of electric
distribution; the wire connected to a point between the two dynamos, or
otherwise to the central point of the current generator.

Fig. 250. DIAGRAM OF THREE WIRE SYSTEM SHOWING NEUTRAL WIRE.

Neutral Wire Ampere Meter.
An ampere meter connected in the circuit of the neutral wire to
determine the current passing through it. Such determination is for the
purpose of ascertaining how much more work is being done by one of the
lateral leads than by the other.

Synonym--Balance Ampere Meter.

N. H. P.
Symbol or contraction for "nominal horse power." This is a basis for
rating the size of an engine.

Nickel.
A metal; one of the elements; atomic weight, 58.8 ; equivalent, 29.4;
valency, 2; specific gravity, 8.8. It is a conductor of electricity.
Relative resistance, annealed (Silver = 1), 8.285
Specific Resistance, 12.47 microhms.
Resistance of a wire
(a) 1 foot long, weighing 1 grain, 15.206 ohms.
(b) 1 foot long, 1/1000 inch thick, 74.963 "
(c) 1 meter long, weighing 1 gram, 1.060 "
(d) 1 meter long, 1 millimeter thick, .1587 "
Resistance of a 1-inch cube, 4.907 microhms.
Electro-chemical equivalent, (Hydrogen = .0105) .3087 mgs.

It is strongly paramagnetic, but loses this quality at 350º C. (662º F.)

It is important as a constituent of German silver, an alloy much used
for resistance coils.

Nickel, Bath.
A bath for the electro-deposition of nickel. A great many
formulae have been given. Metallic nickel is dissolved in 1 vol.
sulphuric acid mixed with 2 vols. water. Neutralize with ammonia, and
add of ammonium sulphate one-half the weight of metallic nickel
originally used; 135 parts of nickel will be enough for a bath of 10,000
parts.

392 STANDARD ELECTRICAL DICTIONARY.

Other formulae are as follows:
Double nickel-ammonium sulphate, 4 parts.
Ammonium carbonate, 3 "
Water 100 "
Nickel sulphate, nitrate or chloride, 1 "
Sodium bisulphate, 1 "
Water, 20 "

Nickel anodes are used in the bath to maintain the strength. Too much
care cannot be exercised in the absolute cleanliness of the articles to
be plated. A too alkaline bath gives a disagreeable yellow color to the
deposit; too acid a bath gives badly adhering deposits.

Night Bell.
An alarm bell in a telegraph office, which bell is connected at night to
give a loud signal to attract the operator's attention. It is used in
telephone exchanges and is connected so as to ring as long as a
subscriber remains unanswered after calling.

Nobili's Rings.
When a dilute solution of copper acetate is placed on a bright silver
plate and a strip of zinc is touched to the silver beneath the copper, a
series of rings of copper are formed by electrolysis around the zinc.
These are Nobili's rings.

If for the copper acetate a solution of lead oxide in potassium hydrate
solution is substituted, and if the polished plate which may be German
silver is connected to the positive electrode of a battery, and a
platinum wire connected to the negative pole is immersed in the liquid,
it determines the formation of beautiful iridescent rings of lead
binoxide. The platinum wire is sometimes sealed in glass so that only
its point projects.

The colors are due to interference of light, the layers of lead oxide
being extremely thin.

The lead binoxide is formed by secondary reaction. Metallic lead is
first deposited on the negative pole. The oxygen which goes to the
positive pole formed by the polished plate produces lead binoxide which
is deposited there in rings. The reaction is comparable to that of a
storage battery.

Synonyms--Metallochromes--Electric Rings.

Nodular Deposit.
A deposit obtained in electroplating, characterized by irregular
thickness; due to too low density of current.

Non-conductor.
A material that does not conduct electricity except with great
difficulty; a substance of very high resistance.

Synonym--Insulator--Dielectric.

North Pole.
(a) The north-seeking pole of a magnet; the pole of a magnet which tends
to point to the north, and whence lines of force are assumed to issue on
their course to the other pole of the magnet.

(b) The North Pole of the earth. Treating the earth as a magnet, and
accepting the above nomenclature the north pole should be termed the
south pole. (See Austral Pole--Boreal Pole.)

393 STANDARD ELECTRICAL DICTIONARY.

North-seeking Pole.
The pole of a magnet which tends to point to the north; the north pole
of a magnet.

Null Method.
Any method of obtaining measurements or comparisons, in which the
measurement is correct when the deflection of the galvanometer or other
indicator is zero, nought or null. The Wheatstone Bridge (see Bridge,
Wheatstone) is an example of a null method.

Two obvious advantages attach to null methods in electric galvanometer
work. One is that an uncalibrated galvanometer can be employed. The
other is that a galvanometer of any high degree of sensitiveness can be
employed, there being no restriction as to its fineness of winding or
highness of resistance.

393 STANDARD ELECTRICAL DICTIONARY.

"Upper case Omega Graphic".
(Greek capital" Omega") symbol for megohm.

"Lower case Omega Graphic".
(Greek omega) symbol for ohm.

Occlusion.
An absorption of gases by metals. Palladium will, if used as the
hydrogen evolving electrode in decomposing water, absorb 980 times its
volume of hydrogen, which is said to be occluded. The metal may also be
heated in hydrogen and allowed to cool therein, when occlusion occurs.
Platinum will occlude 4 times its volume of hydrogen; iron, 4.15 times
its volume of carbon-monoxide; silver, 7 times its volume of oxygen.
Metals with occluded gases may serve as elements in a galvanic couple.
(See Gas Battery.) A metal expands in occluding a gas.

In the storage battery it is believed that occlusion plays a part,
hydrogen and oxygen being respectively absorbed by the two sets of
plates, and acting as they do in Groves' gas battery.

Oerstedt.
Name proposed for the unit of current strength, but not adopted. The
ampere is the accepted name.

394 STANDARD ELECTRICAL DICTIONARY.

Oerstedt's Discovery.
Oerstedt discovered in 1820 that a magnetic needle tended to place
itself at right angles to a current of electricity. This fundamental
experiment is the basis of the galvanometer.

Fig. 251. OERSTEDT'S DISCOVERY.

Ohm.
The practical unit of resistance; 1E9 C. G. S. electro-magnetic units.
The legal ohm is the resistance of a mercury column 1 square millimeter
in cross-sectional area and 106 centimeters in length. There has been
considerable confusion, owing to inaccuracy in early determinations, in
the valuation of the ohm. In this work the legal ohm is used. The
different ohms will be found defined in their place. Resistance units of
various names may also be consulted.

The following table gives the relative values of the different ohms.

Length of
Mercury Board of
Column in True B. A. Trade Legal
Centimetre. Ohm. Ohm. Ohm. Ohm.

True Ohm, 106.24 1. 1.0128 .9994 1.0022
B. A. Ohm, 104.9 .9874 1. .9868 .9889
Board of Trade Ohm 106.3 1.00050 1.0133 1. 1.0028
Legal Ohm, 106.0 .9977 1.0112 .9971 1.

Ohmage.
The Resistance of a circuit expressed in ohms.

Ohm, B. A.
The British Association unit of resistance; the resistance of a column
of mercury 1 square millimeter in cross sectional area and 104.9
centimeters long; the B. A. Unit of Resistance.

Ohm, Board of Trade.
The approximate ohm as recommended by the British Board of Trade on the
advice of a committee (Sir W. Thomson, Dr. J. Hopkinson, Lord Rayleigh
and others). It is the resistance of a mercury column one square
millimeter in section, and 106.3 centimeters long at 0º C. (32º F.)

Synonym--New Ohm.

395 STANDARD ELECTRICAL DICTIONARY.

Ohmic Resistance.
True resistance as distinguished from spurious resistance, or
counter-electro-motive force.

Ohm, Legal.
The practical unit of resistance. The resistance of a column of mercury
one square millimeter in cross-sectional area and 106 centimetres long
at 0º C. (32º F.) The ohm used previously to 1884 is the B. A. Unit of
Resistance, q. v.

One legal ohm = 1.0112 B. A. Units, and I B. A. Unit = 0.9889 legal ohm.

The resistance of a copper wire 1 foot long and 1/1000 inch in diameter
is about 10 ohms. The resistance of 1 mile of iron wire 1/3 inch in
diameter is about 10 ohms.

Synonym--Congress Ohm.

396 STANDARD ELECTRICAL DICTIONARY.

Fig. 252. THEORY OF OHMMETER.

Fig. 253. OHMMETER.

Ohmmeter.
An instrument for measuring directly the resistance of a conductor or of
any part of a circuit through which a strong current is passing. It is
the invention of Prof. W. E. Ayrton.

It contains two fixed coils at right angles to each other acting on the
same needle of soft iron. One coil is of thick wire and is placed in
series with the resistance to be measured. The other is of very thin
wire and is placed in parallel with the same resistance. One wire acts
by the total current, the other by the potential difference between the
ends of the resistance. The action on the soft iron needle is due to the
ratio of potential difference to total currents, or to the resistance
itself. By properly designing and proportioning the coils the angular
deflections of the needle are made proportional to the resistance.

In use the thick wire may be kept permanently in circuit. On connecting
the binding posts of the thin wire coil to any two parts of the circuit
its resistance is at once given by the deflection of the needle.

When no current is passing the needle rests in any position. A current
in the thick coil brings it to zero. A current simultaneously passing
through the thin high resistance coil brings about the deflection.

The instrument is a commercial rather than a scientific one.

Ohm's Law.
The fundamental law expressing the relations between current,
electro-motive force and resistance in an active electric circuit. It
may be expressed thus:

(a) The current strength is equal to the electro-motive force divided by
the resistance.

(b) The electro-motive force is equal to the current strength multiplied
by the resistance.

(c) The resistance is equal to the electro-motive force divided by the
current strength. All these are different forms of the same statement.
Algebraically the law is usually expressed thus, (a) C = E/R. It may
also be expressed thus: (b) E = C*R and (c) R= E/C, in which R denotes
resistance, C denotes current strength, and E denotes electro-motive
force.

Ohm, True.
The true ohm is the resistance of a column of mercury 1 square
millimeter in cross-sectional area, and 106.24 centimeters long. (See
Ohm.)

Synonym-Rayleigh Ohm.

Oil Insulation.
Oil insulation has received several applications in electrical work. It
has been proposed for use in underground conduits. These it was proposed
to fill with oil after the insertion of the conductors, the latter
properly wrapped with cotton or other covering. For induction coils it
has been very successfully used. Its principal utility depends on the
fact that it is liquid, so that if pierced by a spark it at once closes
again. A solid insulator if pierced is permanently injured. It is also
used in telegraph insulators (see Insulator, Liquid) to prevent surface
leakage.

397 STANDARD ELECTRICAL DICTIONARY.

Olefiant Gas.
A compound gas; C2H4; composed of carbon, 24; hydrogen, 4; molecular
weight, 28; specific gravity, .981.

It is a dielectric of about the resistance of air. Its specific
inductive capacity at atmospheric pressure is 1.000722 (Boltzman.)

Synonym--Ethene; heavy carburetted hydrogen.

Open. adj.
An electric circuit is said to be open when it is cut or broken so that
no current can pass through it. The term may be recollected by thinking
of a switch; when open no current can pass through it. The same
adjective is applied to magnetic circuits, an air gap implying an open
circuit.

Open Circuit Oscillation.
An oscillation of current in open circuit so that a spark discharge
accompanies it. It is produced by electric resonance in a simple circle
or loop of wire with ends placed near together but not touching, if the
circuit is of such size that its period of oscillation corresponds with
that of the inducing discharge. (See Resonance, Electric.) Its period
depends entirely on the self-induction of the circuit.

Ordinate.
In a system of plane co-ordinates (see Co-ordinates), the distance of
any point from the axis of abscissas measured parallel to the axis of
ordinates.

Ordinates, Axis of.
The vertical axis in a system of co-ordinates, q. v.

Synonym--Axis of Y.

Organ, Electric.
An organ in which the air blast is admitted or excluded from the
different pipes by electric mechanism.

The outlines of the system are a series of contacts worked by the keys
and stops, which cause, when operated by the organist, a current to pass
through electro-magnets, opening the valves of the different pipes. Thus
the manual may be at any distance from the organ, and a number of organs
may be worked upon the same manual. As many as five in a single
cathedral are thus connected to a manual in the chancel.

Orientation of a Magnetic Needle.
The acquirement by a magnetic needle of its position of rest, with its
magnetic axis in the magnetic meridian.

Origin of Co-ordinates.
In a system of linear co-ordinates the point of intersection of the
axes; the point whose co-ordinates are both zero.

398 STANDARD ELECTRICAL DICTIONARY.

Oscillating Needle.
A small light bar magnet suspended by a filament and employed in
determining the intensity of a magnetic field by the oscillations it
completes in a given time after a given disturbance.

Oscillations, Electric.
In static electricity the sudden and very rapid alternations in the
discharge of a static condenser. This discharge of the disruptive order
seems a single one, but is really composed of a number of discharges
alternating in direction and producing electro-magnetic ether waves,
probably identical with light waves except that they are longer and far
less rapid.

Oscillatory Electro-motive Force.
Electro-motive force rapidly changing in sense or in direction, so that
it presents an oscillatory character. The alternating current and the
telephone current as used in practice are actuated by this type of
electro-motive force.

Osmose, Electric.
When two liquids are separated by a porous diaphragm, and a strong
current of electricity is passed through from the liquid on one side,
through the diaphragm, to the liquid on the other side, the liquid on
the side towards which the current is passing rises in level. The
process is termed electric osmose. When a liquid is forced through a
diaphragm a current is produced; in other words electric osmose is
reversible. The current thus produced is termed a diaphragm current.

Oscillation, Electric.
The phase of discharge of a static condenser in one direction. It is
usually followed by a discharge in the opposite direction constituting a
second oscillation, and so on, so that a great number of exceedingly
short oscillations are comprised. Thus, in the discharge of the Leyden
jar a large number of oscillations of current back and forth are
produced, the current alternating like the swings of a pendulum.

These oscillations are supposed to affect the ether, producing waves in
it identical with light waves, except that we have not been able yet to
produce them short enough to affect the visual organs. The waves thus
produced can be reflected or refracted; some substances are transparent
for them and others opaque. There is a possibility that man may yet
succeed in producing electric oscillations of sufficient frequency to
bring about the direct production of light.

Oscillatory Displacement.
Hypothetical displacement currents of rapidly alternating direction
produced in the oscillatory discharge of a Leyden jar or static
condenser.

Oscillatory Induction.
Induction produced by sympathetic action of an oscillatory discharge or
by electric resonance. (See Oscillations, Electric--Resonance,
Electric--Resonator, Electric.)

399 STANDARD ELECTRICAL DICTIONARY.

Outlet.
The part of an electrolier or electric light fixture out of which the
wires are led for attachment of an incandescent light socket.

Output.
The rate of energy delivered or of work done by a machine. In the case
of a current generator it is the volt-coulombs per given second, or
better the volt-amperes delivered at its outer circuit terminals.

Output, Magnetic.
The analogue in a magnetic circuit of the output of an electric circuit.
It is the product of the magnetizing force by the induced magnetism.

Output, Unit of.
As a unit of output of a dynamo Prof. Sylvanus P. Thompson has proposed
1,000 watts, or one kilowatt. This unit is now frequently used. To
completely define the dynamo, however, the amperage or the voltage must
also be given, as a 10 kilowatt--110 volt machine, or a 10 kilowatt--99
ampere machine.

Over-Compounding.
A proportioning of the series and shunt windings of a compound dynamo,
so that the voltage of the terminals rises with the load or output
enough to allow for the drop in mains, thus maintaining the potential
for full load at distant points in a district. It is carried out by an
increase of ampere-turns in the series winding.

Overload.
In an electric motor a mechanical load put upon it so great as to
prevent economical working. One effect of such a load is to make the
armature run so slowly as to unduly reduce the counter-electro-motive
force and hence to permit so much current to pass through the coils as
to heat them, perhaps injuriously. In this case the production of heat
implies the waste of energy.

Overtype Dynamo or Motor.
A dynamo or motor whose armature is placed above or in the upper part of
the field magnets, the yoke piece of the magnets being in or resting
upon the base of the machine.

Ozone.
An allotropic form of oxygen. It possesses much more energetic chemical
properties than oxygen. It is supposed to contain three atoms of oxygen
in its molecule, represented thus:
O
/ \
O---O

It is produced by electric discharges and it is its peculiar odor which
is noticed about an electric machine, and sometimes in a thunderstorm
near the path of a lightning flash.

In the electrolysis of water some ozone may be produced, thus
diminishing the volume of the oxygen or of the mixed gases given off.
This is a source of inaccuracy in a gas voltameter.

400 STANDARD ELECTRICAL DICTIONARY.

Pacinotti's Inductor.
The Pacinotti or Gramme Ring. (See Pacinotti's Ring.)

Pacinotti's Ring.
A ring of iron wire wound with coils of insulated wire at right angles
to its circular axis, and used as the armature of a dynamo or motor. A
number of connections are taken from the coils to a central commutator.

Fig. 254. PACINOTTI'S MACHINE, WITH RING ARMATURE.

If such a ring with its coils is rotated in a field, current can be
taken from points of the commutator on a line at right angles to the
lines of force entering the ring.

The ring was discovered in 1862 by Pacinotti, and later was
independently discovered by Gramme. It is often known as the Gramme
ring.

Pacinotti Teeth.
Projections on a cylindrical or drum armature, between which in the
grooves formed thereby, the wire is wound. The teeth being of iron tend
to diminish the reluctance or magnetic resistance of the interpolar
space, or interval between the poles of the field magnet.

Synonym--Pacinotti Projections.

Paillard Alloys.
Non-magnetic palladium alloys, invented by Paillard, of
Switzerland, used in anti-magnetic watches. The following are given as
the compositions of several such alloys:

I. II.
Palladium, 60 to 75 parts 50 to 75 parts
Copper, I5 to 25 " 20 to 30 "
Iron. 1 to 5 " 5 to 20 "

401 STANDARD ELECTRICAL DICTIONARY.

The following are more complex:
I. II.
Palladium, 65 to 75 parts 45 to 50 parts
Copper, 15 to 25 " 15 to 25 "
Nickel, 1 to 5 " 2 to 5 "
Silver, 3 to 10 " 20 to 25 "
Gold, 1 to 2-1/2 " 2 to 5 "
Platinum, 1/2 to 2 " 2 to 5 "
Steel, 1 to 5 " 2 to 5 "

These alloys are used for balance springs, as well as for the balance
wheels and escapement parts of watches. The elasticity of recently
produced springs has been found to be very satisfactory.

Page Effect.
The sounds produced by magnetizing and demagnetizing a bar of iron or
steel; the magnetic tick. The sounds are strong enough to produce a
telephonic effect. (See Magnetic Tick.)

Palladium.
A metal of the platinum series. It has the highest power of occlusion,
q.v., of all metals. It is the characteristic ingredient of non-magnetic
watch alloys.

Palladium used as an electrode in the electrolysis of water will occlude
936 volumes of hydrogen, and the hydrogen-palladium alloy will exceed in
size the original electrode.

Fig. 255. LUMINOUS PANE.