Synonym--Magnetic r.e.t.a.r.dation.

Magnetic Lat.i.tude.

Lat.i.tude referred to the magnetic equator and isoclinic lines.

Magnetic Leakage.

The lines of force in a field magnet which pa.s.s through the air and not through the armature are useless and represent a waste of field. Such lines const.i.tute 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 pa.s.sing 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 Amp?rian sheet of current, and a.n.a.logous 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 Ma.s.s.

A term for a quant.i.ty of magnetism. Unit ma.s.s is the quant.i.ty which at unit distance exercises unit force.

Magnetic Matter.

Imaginary matter a.s.sumed as a cause of magnetism. Two kinds, one positive and one negative, may be a.s.sumed 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.

[Transcriber's note: See "magnet" and Edward Purcell's explanation of magnetism using general relativity.]

Magnetic Memory.

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

[Transcriber's note: Small ferrite magnetic donuts were used as computer main memory from 1950 to 1970.]

Magnetic Meridian.

A line formed on the earth's surface by the intersection therewith of a plane pa.s.sing through the magnetic axis. It is a line determined by the direction of the compa.s.s 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 Lat.i.tude.

Magnetic Permeability.

The specific susceptibility of any substance, existing in a ma.s.s, 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 a.n.a.logy 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.