The relative positions of the respective brushes may be varied by moving the auxiliary brush or the brush c may remain quiescent and the core p be connected to the main brush holder A-1 so as to adjust the brushes a, b, in their relation to the brush c. If however an ajustment is applied to all the brushes as seen in Fig. 5 the solenoid should be connected to both A-1 and C so as to move them towards or away from each other. There are several known devices for giving motion in proportion to an electric current. I have shown moving cores in Figs. 4 and 5, as convenient devices for obtaining the required extent of motion with very slight changes in the current passing through the helices.
It is understood that the adjustment of the main brushes causes variations in the strength of the current independently of the relative position of said brushes to the auxiliary brush. In all cases the adjustment may be such that no current flows over the auxiliary brush when the dynamo is runing with its normal load.
I am aware that auxiliary brushes have been used in connection with the helices of the field wire, but in these instances the helices received the entire current through the auxiliary brush or brushes and said brushes could not be taken off without breaking the current through the field. These brushes caused however a great sparking upon the commutator. In my improvement the auxiliary brush causes very little or no sparking and can be ta[ken] off
