Synchronous electric time service

PREVIOUS to 1916 no commercial a-c. system was regulated with sufficient accuracy of speed to enable its use for indicating time. Two devices then were developed making commercial a-c. time service possible. The first of these was a selfstarting synchronous motor which utilized residual magnetism to enable the rotor to start and run at synchronous speed. The second consisted of an indicating instrument which would show to a generating station operator, directly in terms of time, deviations of average frequency from standard.