, and during which repulsion can take place, is lengthened at
the expense of the period during which the currents are in the same
direction for attractive action. These differing periods are marked r,
a, etc., or the period during which _repulsion_ exists is from the zero
of the primary or inducing current to the succeeding zero of the
secondary or induced current; and the period during which _attraction_
exists is from the zero of the induced current to the zero of inducing
current.

But far more important still in giving prominence to the repulsive
effect than this difference of effective period is the fact that during
the period of repulsion both the inducing and induced currents have
their greatest values, while during the period of attraction the
currents are of small amounts comparatively. This condition may be
otherwise expressed by saying that the period during which repulsion
occurs includes all the maxima of current, while the period of
attraction includes no maxima. There is then a _repulsion due to the
summative effects of strong opposite currents_ for a _lengthened
period_, against an _attraction_ due to the summative effects of _weak
currents_ of the _same direction_ during a _shortened period_, the
resultant effect being a greatly _preponderating_ repulsion.

It is now not difficult to understand all the actions before described
as obtained with the varied relations of coils, magnetic fields, and
closed circuits. It will be easily understood, also, that an alternating
magnetic field is in all respects the same as an alternating current
coil in producing repulsion on the closed conductor, because the
repulsions between the two conductors are the result of magnetic
repulsions arising from opposing fields produced by the coils when the
currents are of opposite directions in them.

Thus far I have applied the repulsive action described in the
construction of alternating current indicators, alternating current arc
lamps, regulating devices for alternating currents, and to rotary motors
for such currents. For current indicators, a pivoted or suspended copper
band or ring composed of thin washers piled together and insulated from
one another, and made to carry a pointer or index has been placed in the
axis of a coil conveying alternating currents whose amount or potential
is to be indicated. Gravity or a spring is used to bring the index to
the zero of a divided scale, at which time the plane of the copper rin