III.

Electric Timepieces

In the electric clocks used in homes today, a small motor runs in unison with the power-station generator, which is regulated to deliver an alternating current of precisely 60 cycles per second. Electric currents may also be used to keep the movements of several “slave” clocks synchronized with the pendulum in a master clock.

The quartz-crystal clock developed in 1929 for precision timekeeping employs a ring of quartz that is connected to an electrical circuit and made to oscillate between 10,000 and 100,000 hertz (cycles per second). The high-frequency oscillation is converted to an alternating current, reduced to a frequency more convenient for time measurement, and thus made to drive the motor of a synchronous clock or a digital display. The maximum error of the most accurate quartz-crystal clocks is plus or minus one second in ten years.

The electric or electronic watch is powered by a small battery that functions for about one year without replacement. The battery may drive the balance wheel of an otherwise mechanical clock, or it may be used to drive the oscillations of either a small tuning fork or a quartz crystal.