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

by T. O'Conor Sloane

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.
[Transcriber's note: The earth's magnetic field is believed to originate
it electric currents in the moving molten core.]
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.