A non-self-starting type synchronous motor comprises a pair of permanent-magnet rotors rotatable in directions opposite to each other by means of magnetic coupling in order to prevent the rotational motion of the rotators from being stopped by step-out of the synchronous motion because of vibration or impact and also a field coil for giving a turning force to said pair of rotors.

A self-starting type synchronous motor comprising a pair of permanent-magnet rotors rotatable in directions opposite to each other by means of magnetic coupling, and a magnetic pole arranged adjacent to at least one of said rotors and capable of making said rotors rest at positions shifted from such positions where the magnetic coupling is strongest, for the purpose of achieving reliable self-starting.

An electronic clock having a clock circuit in which reference clock pulses are frequency divided so as to be applied to a time indicating device for stepwise switching the time indication therein one by one unit of time for indicating the time, and the time indication is corrected stepwise one by one unit of time in timed relationship to the reference clock pulses by applying time correction pulses to the clock circuit until the correction of time is achieved. The device for correcting the time ...