Page:Canadian patent 29537.djvu/15

 amount of current passes through the energizing circuit s.

The phenomenon alluded to, viz: The variation of the resistance of the motor, apparently like that in ordinary motors, is probably attributable to the variation in the amount of self-induction in the primary or energizing circuit.

In lieu of the field magnets for the motors shown in the drawings soft iron field magnets excited by a continuous current may be used.

This plan is a very advantageous one, but it is characteristic of a motor so operated that if the field magnet be strongly energized by its coils and the circuits through the armature coils closed, assuming the generator to be running at a certain speed, the motor will not start but if the field be but slightly energized or in general in such condition that the magnetic influence of the armature preponderates in determining its magnetic condition, the motor will start and with sufficient current, will reach its normal or maximum speed. For this reason it is desirable to keep, at the start and until the motor has attained its normal speed, or nearly so; the field circuit open, or to permit but little current to pass through it.

Another characteristic of this form of motor is that its direction of rotation is not reversed by reversing the direction of the current through its field coils, for the direction of rotation depends, not upon the polarity of the field, but upon the direction in which the poles of the armature are shifted. To reverse the motor the connections of either of the energizing circuits must