This condition can be illustrated by a diagram, Fig. 12.  Here the lines of zero current are the horizontal straight lines.  The wavy lines represent the variations of current strength in each conductor, the current in one direction being indicated by that portion of the curve above the zero line, and in the other direction by that portion below it.  The vertical dotted lines simply mark off corresponding portions of phase or succession of times.

[Illustration:  FIG. 15]

Here it will be seen that in the positive primary current descending from m, its maximum, to the zero line, the secondary current has risen from its zero to m, its maximum.  Attraction will therefore ensue, for the currents are in the same direction in the two conductors.  When the primary current increases from zero to its negative maximum, n, the positive current in the secondary closed circuit will be decreasing from m, its positive maximum, to zero; but, as the currents are in opposite directions, repulsion will occur.  These actions of attraction and repulsion will be reproduced continually, there being a repulsion, then an attraction, then a repulsion, and again an attraction, during one complete wave of the primary current.  The letters, r, a, at the foot of the diagram, Fig. 12, indicate this succession.

In reality, however, the effects of self-induction in causing a lag, shift, or retardation of phase in the secondary current will considerably modify the results, and especially so when the secondary conductor is constructed so as to give to such self-induction a large value.  In other words, the maxima of the primary or inducing current will no longer be found coincident with the zero points of the secondary currents.  The effect will be the same as if the line representing the wave of the secondary current in Fig. 12 had been shifted forward to a greater or less extent.  This is indicated in diagram, Fig. 13.  It gives doubtless an exaggerated view of the action, though from the effects of repulsion which I have produced, I should say it is by no means an unrealizable condition.

[Illustration:  Fig. 16.]

It will be noticed that the period during which the currents are opposite, 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.