But after the wire has ceased moving, the attraction ceases; and so
far from any action occurring similar to that which draws the iron
sphere back to the magnet, we have to overcome a repulsion to bring
them together.
There is no potential energy conferred either by the removal or by
the approach of the wire, and the only power really transformed or
converted, in the experiment, is muscular power. Nothing that could
in strictness be called a conversion of magnetism into electricity
occurs. The muscular oxidation that moves the wire fails to produce
within the muscle its due amount of heat, a portion of that heat,
equivalent to the resistance overcome, appearing in the moving wire
instead.
Is this effect an attraction and a repulsion at a distance? If so,
why should both cease when the wire ceases to move? In fact, the
deportment of the wire resembles far more that of a body moving in a
resisting medium than anything else; the resistance ceasing when the
motion is suspended. Let us imagine the case of a liquid so mobile
that the hand may be passed through it to and fro, without
encountering any sensible resistance. It resembles the motion of a
conductor in the unexcited field of an electro-magnet. Now, let us
suppose a body placed in the liquid, or acting on it, which confers
upon it the property of viscosity; the hand would no longer move
freely. During its motion, but then only, resistance would be
encountered and overcome. Here we have rudely represented the case
of the excited magnetic field, and the result in both cases would be
substantially the same.
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