The actions produced and producible by the agency of alternating
currents of considerable energy are assuming greater importance in the
electric arts. I mean, of course, by the term alternating currents,
currents of electricity reversed at frequent intervals, so that a
positive flow is succeeded by a negative flow, and that again by a
positive flow, such reversals occurring many times in a second, so that
the curve of current of electromotive force will, if plotted, be a wave
line, the amplitude of which is the arithmetical sum of the positive and
negative maxima of current or electromotive force, as the case may be,
while a horizontal middle line joins the zero points of current or
electromotive force.

[Illustration: FIG. 1]

It is well known that such a current passing in a coil or conductor laid
parallel with or in inductive relation to a second coil or conductor,
will induce in the second conductor, if on open circuit, alternating
electromotive forces, and that if its terminals be closed or joined,
alternating currents of the same rhythm, period, or pitch, will
circulate in the second conductor. This is the action occurring in any
induction coil whose primary wire is traversed by alternating currents,
and whose secondary wire is closed either upon itself directly or
through a resistance. What I desire to draw attention to in the present
paper are the mechanical actions of attraction and repulsion which will
be exhibited between the two conductors, and the novel results which may
be obtained by modifications in the relative dispositions of the two
conductors.

[Illustration: FIG. 2.]