This form has the advantage that the vibrating body exhibits the two
phases at the same time; relatively to the liquid, one of its ends
advances while the other recedes. Thus with a vibrating sphere
presented to the movable drum, there may be obtained repulsion or
attraction, according as the side which is approached is concordant or
discordant with the end of the drum that it faces.

[Illustration: FIG. 3.]

With the arrangement shown in Fig. 3 there may be performed an
interesting series of experiments. The two spheres supported by the
frame are set in simultaneous vibration, and the frame, moreover, is
free to revolve about its axis. The effect is analogous to that which
would be produced by two short magnets carried by the same revolving
support; on presenting the vibrating sphere to the extremities the
whole affair is attracted or repulsed, according to its phase and
according to the point at which it is presented; on replacing the
transverse support by a single sphere (as indicated in the figure by a
dotted line) we obtain the analogue of a short magnet carried on a
pivot like a small compass needle. This sphere follows the pole of a
vibrating sphere which is presented to it, as the pole of a magnet
would do, with this difference always, that in the magnet, like poles
repel, while in oscillating bodies like phases attract.

In all the preceding experiments the bodies brought in presence were
both in motion and the phenomena were analogous to those of permanent
magnetism. We may also reproduce those which result from magnetism by
induction. For this purpose we employ small balls of different
materials suspended from floats, as shown in Fig. 4 (a, b, c).