Electro-magnetic Attraction and Repulsion.
The attraction and repulsion due to electromagnetic lines of force,
which lines always tend to take as short a course as possible and also
seek the medium of the highest permeance. This causes them to
concentrate in iron and steel or other paramagnetic substance and to
draw them towards a magnet by shortening the lines of force connecting
the two. It is exactly the same attraction as that of the permanent
magnet for its armature, Ampére's theory bringing the latter under the
same title. In the case of two magnets like poles repel and unlike
attract. In the case of simple currents, those in the same direction
attract and those in opposite directions repel each other. This refers
to constant current reactions. Thus the attraction of unlike poles of
two magnets is, by the Ampérian theory, the attraction of two sets of
currents of similar direction, as is evident from the diagram. The
repulsion of like poles is the repulsion of unlike currents and the same
applies to solenoids, q. v. (See Magnetism and do. Ampére's Theory
of--Induction, Electro-dynamic--Electro-magnetic Induction.)