It will be apparent that the respective cores of the field magnets are subjected to the neutralising or intensifying effects of the current in the shunt through c-1 and the magnetism of the cores will be partially neutralized or the point of the greatest magnetism shifted, so that it will be more or less remote from or approaching to, the armature, and hence the aggregate energizing action of the field magnets on the armature will be correspondingly varied. In the form indicated in Fig. 1 the regulation is effected by shifting the point of greatest magnetism, and in Figs. 2 and 3 the same effect is produced by the action of the current in the shunt passing through the neutralizing helix.
In Figs. 4 and 5, A-1, A-1, indicate the main brush holder carrying the main brushes, and C, the auxiliary brush holder carrying the auxiliary brush. These brush holders are movable in arcs concentric with the center of the commutator shaft.
An from piston P of the solenoid S, (Fig. 4) is attached to the auxiliary brush holder C. The adjustment is effected by means of a spring and screw or tightened.
In Fig. 5 instead of a solenoid an iron tube enclosing a coil is shown. The piston P of the coil is attached to both brush holders A-1, A-1 and C. When the brushes are moved directly by electrical devices as shown in Figs. 4 and 5, these are so costructed that the force exerted for adjusting is practically uniform through the whole length of motion.
