The polyphase induction motor, the discovery of which was announced by Tesla in 1887, occurred at such a time as to have a tremendous effect on the economic and the industrial history of this country. The relative ease with which electric power could be transmitted and distributed by virtue of alternating current, and the availability of a reliable ac drive motor, made the conversion of electric power to mechanical power a relatively simple operation. This, in large measure, made possible the enormous expansion of industry that has occurred during the twentieth century.