The Standard Electrical Dictionary Part 103

Magnetic Stress.

The stress produced by magnetic lines of force on substances through which they pa.s.s, 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 ma.s.s, 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, Amp?re's Theory of.

A theory accounting for magnetic phenomena by a.s.suming 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 sh.e.l.l of molecules, and these virtually resolve themselves into one general current sheet, surrounding the magnet and coinciding with its surface.

The theory a.s.sumes 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. AMP?RIAN CURRENTS IN MAGNETS.

At the north pole of the magnet the direction of the Amp?rian 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 Amp?rian 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 AMP?RIAN 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 compa.s.s 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 a.s.suming 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 a.s.semblage 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 circ.u.mstances, 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 ma.s.s, 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 a.s.suming 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.