action as a result.

[Illustration: Fig. 3]

The experiment was, however, varied, as in Fig. 1. The disk, D, was held
over the magnet pole, as shown, and the current in the magnet coils cut
off by shunting them. There was felt an attraction of the disk or a dip
toward the pole. The current was then put on by opening the shunting
switch, and a repulsive action or lift of the disk was felt. The actions
just described are what would be expected in such a case, for when
attraction took place, currents had been induced in the disk, D, in the
same direction as those in the magnet coils beneath it, and when
repulsion took place the induced current in the disk was of opposite
character or direction to that in the coils.

[Illustration: Fig. 4]

Now let us imagine the current in the magnet coils to be not only cut
off, but reversed back and forth.

For the reasons just given, we will find that the disk, D, is attracted
and repelled alternately; for, whenever the currents induced in it are
of the same direction with those in the inducing or magnet coil,
attraction will ensue, and when they are opposite in direction,
repulsion will be produced. Moreover, the repulsion will be produced
when the current in the magnet coil is rising to a maximum in either
direction, and attraction will be the result when the current of either
direction is falling to zero, since in the former case opposite currents
are induced in the disk, D, in accordance with well known laws, and in
the latter case currents of the same direction will exist in the disk,
D, and the magnet coil. The disk might, of course, be replaced by a ring
of copper or other good conductor, or by a closed coil of bare or
insulated wire, or by a series of disks, rings or coils superposed, and
the results would be the same. Thus far, indeed, we have nothing of a
particularly novel character, and, doubtless, other experimenters have
made very similar experiments and noted similar results to those
described.

[Illustration: FIG. 5]

The account just given of the effects produced by alternating currents,
while true, is not the whole truth, and just here we may supplement it
by the following statements:

_An alternating current circuit or coil repels and attracts a closed
circuit or coil placed in direct or magnetic inductive relation
therewith; but the repulsive effect is in excess of the attractive
effect.

When the closed circuit or coil is so placed, and is of such low
r