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PERMEABILITY, MAGNETIC

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Originally appearing in Volume V21, Page 176 of the 1911 Encyclopedia Britannica.
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PERMEABILITY, MAGNETIC , the ratio of the magnetic See also:induction or See also:flux-See also:density in any See also:medium to the inducing magnetic force. In the C.G.S. electromagnetic See also:system of See also:units the permeability is regarded as a pure number, and its value in empty space is taken as unity. The permeability of a See also:metal belonging to the ferromagnetic class—See also:iron, See also:nickel, See also:cobalt and some of their See also:alloys—is a See also:function of the magnetic force, and also depends upon the previous magnetic See also:history of the specimen. As the force increases from zero the permeability of a given specimen rises to a maximum, which may amount to several thousands, and then gradually falls off, tending to become unity when the force is increased without limit. Every other sub-stance has a See also:constant permeability, which differs from unity only by a very small fraction; if the substance is paramagnetic, its permeability is a little greater than 1; if diamagnetic, a little less. The conception of permeability (See also:Lat. per, through, and meare, to wander), is due to See also:Faraday, who spoke of it as " conducting See also:power for See also:magnetism " (Experimental Researches, See also:xxvi.), and the See also:term now in use was introduced by W. See also:Thomson (See also:Lord See also:Kelvin), in 1872, having been suggested by a hydrokinetic See also:analogy (Reprint of Papers on See also:Electrostatics and Magnetism, xxxi., xlii.). It is generally of importance that the iron employed in the construction of See also:electrical machinery should possess high permeability under the magnetic force to which it is to be subjected.

End of Article: PERMEABILITY, MAGNETIC

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