The principles and systems of electric motor control

There is hardly anything which stands out so prominently today in our industrial activities, as the efficiency obtained by the electric driving of machinery. The duty or performance cycle of the motor naturally depends on the controlling apparatus, and the writer, after describing several types of resistance, endeavors to explain the various forms of magnetic control in vogue today for both d-c. and a-c. motors, hoping to bring out a full discussion on the merits of each, also regarding the characteristics embodied in contactor or magnetic switch design.