10, the circuit being represented merely by two
circular spots or holes above and below the middle line, the current
flowing toward the spectator through the lower spot, and passing in
front of the figure to the upper hole, where it flows down. Into this
circuit the pole, N, is attracted, the tendency being to draw as many
lines of force as possible into the embrace of the circuit.
[Illustration: Fig. 11.]
So far as the reasoning about these mutual actions of magnets and
currents is concerned, it would therefore appear that the lines of force
are the really important feature to be understood and studied. All our
reasons about the attractions of magnets could be equally well thought
out if there were no corporeal magnets there at all, only collections
of lines of force. Bars of iron and steel may be regarded as convenient
conductors of the lines of force; and the poles of magnets are simply
the places where the lines of force run out of the metal into the air or
_vice versa_. Electric currents also may be reasoned about, and their
magnetic actions foretold quite irrespective of the copper wire that
acts as a conductor; for here there are not even any poles; the lines
of force or magnetic whirls are wholly outside the metal.
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