Note on a simple device for finding the slip of an induction motor

There are a number of devices for finding the slip of an induction motor; but the following device, adopted more than a year ago in the laboratory of the University of Tennessee, is more simple and inexpensive than any other accurate device known to the writer. It does not even require the contact-maker and voltmeter described by B. F. Bailey in the Electrical World for April 22, 1905.