By the motion of
the wire, say with the hand, towards the magnet, what the Germans
call a Scheidungs-Kraft--a separating force--is brought into play.
This force tears the mixed fluids asunder, and drives them in two
currents, the one positive and the other negative, in two opposite
directions through the wire. The presence of these currents evokes
a force of repulsion between the magnet and the wire; and to cause
the one to approach the other, this repulsion must be overcome.
The overcoming of this repulsion is, in fact, the work done in
separating and impelling the two electricities. When the wire is
moved away from the magnet, a Scheidungs-Kraft, or separating force,
also comes into play; but now it is an attraction that has to be
surmounted. In surmounting it, currents are developed in directions
opposed to the former; positive takes the place of negative, and
negative the place of positive; the overcoming of the attraction
being the work done in separating and impelling the two
electricities.
The mechanical action occurring here is different from that
occurring where a sphere of soft iron is withdrawn from a magnet,
and again attracted. In this case muscular force is expended during
the act of separation; but the attraction of the magnet effects the
reunion. In the case of the moving wire also we overcome a
resistance in separating it from the magnet, and thus far the action
is mechanically the same as the separation of the sphere of iron.
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