The electric current thus becomes stronger and stronger, and the armature therefore revolves in a magnetic field of the highest intensity, the limit of which is governed by the limit of saturation of the soft iron.
At each revolution the maximum magnetic effect upon each convolution of the armature is produced just after it passes through the middle of both magnetic fields, which are in a vertical plane passing through the axis of the machine (i. e. N1S1 in Fig. 173). The minimum effect is produced when in a plane at right angles to it, i. e. horizontal.
According to the law of Lenz already referred to, when a circuit starts from a neutral position on one side of an axis towards the pole of a magnet, it has a direct current induced in it, and the other part of the circuit which approaches the opposite pole of the magnet has an inverse current induced in it; these two induced currents are, however, in the same direction as regards circuit. A similar current will also be induced in all the convolutions of wire in succession as they approach the poles of the magnets.
These currents, almost as soon as they are induced, are collected by terminal rollers or brushes B, usually the latter, placed in contact with the commutator in the position which gives the strongest current. The position giving the strongest current gives also the least spark, so that when there are no sparks at the commutator the best lighting effect is produced. [Fig. 166] shows position of brushes when the armature revolves in the direction indicated by the arrow.
The circumference of the revolving armature is divided into an even number of equal parts, each opposite pair being filled with convolutions of insulated wire wound parallel to the axis of the armature.
The ends of these wires are brought to a commutator and connected to the segments either by screws or by soldering.