This proposition, which
has been termed "Maxwell's Rule," is very important, because it can be
so readily applied to so many cases, and will enable one so easily
to think out the actual reaction in any particular case. The rule is
illustrated by the sketch shown in Fig. 10, where a bar magnet has been
placed with its north pole opposite the south face of the circuit of
the cell. The lines of force of the magnet are drawn into the ring and
coalesce with those due to the current. According to Faraday's mode of
regarding the actions in the magnetic field there is a tendency for the
lines of force to shorten themselves. This would occur if either the
magnet were pulled into the circuit, or the circuit were moved up toward
the magnet. Each attracts the other, and whichever of them is free to
move will move in obedience to the attraction. And the motion will in
either case be such as to increase the total number of lines of force
that pass through the circuit. Lest it should be thought that Fig. 10 is
fanciful or overdrawn, we reproduce an actual magnetic "field" made in
the manner described in the preceding article. Fig. 11 is a kind of
sectional view of Fig.
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