In 1885, Professor Ferraris constructed the motor depicted in plan in Fig 1, which was not, however, publicly shown till 1888. It was exhibited in 1893 at the Worid's Fair at Chicago. It consisted of two pairs of electromagnets A A and B B', having a common yoke made by winding iron wire around the exterior. Two alternate currents differing in phase were led into these two circuits, and the pivoted central body was observed to revolve.