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.