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.