Editing Clock (section)

===Early electric===

{{main|Electric clock}}

[[File:Pendule electrique l maitrier 05117.jpg|thumb|upright|Early French electromagnetic clock]]

In 1815, the English scientist [[Francis Ronalds]] published the [[Electric clock#History|first electric clock]] powered by [[Voltaic pile#Dry pile|dry pile]] batteries.<ref>{{Cite book|title=Sir Francis Ronalds: Father of the Electric Telegraph|last=Ronalds|first=B.F.|publisher=Imperial College Press|year=2016|isbn=978-1-78326-917-4|location=London}}</ref> [[Alexander Bain (inventor)|Alexander Bain]], a Scottish clockmaker, patented the [[electric clock]] in 1840. The electric clock's mainspring is wound either with an electric motor or with an [[electromagnet]] and armature. In 1841, he first patented the [[Electromagnetism|electromagnetic]] pendulum. By the end of the nineteenth century, the advent of the dry cell battery made it feasible to use electric power in clocks. Spring or weight-driven clocks that use electricity, either [[alternating current]] (AC) or [[direct current]] (DC), to rewind the spring or raise the weight of a mechanical clock would be classified as an [[electromechanical clock]]. This classification would also apply to clocks that employ an electrical impulse to propel the pendulum. In electromechanical clocks, electricity serves no time-keeping function. These types of clocks were made as individual timepieces but are more commonly used in synchronized time installations in schools, businesses, factories, railroads and government facilities as a [[master clock]] and [[slave clocks]].

Where an [[Alternating current|AC]] electrical supply of stable frequency is available, timekeeping can be maintained very reliably by using a [[synchronous motor]], essentially counting the cycles. The supply current alternates with an accurate frequency of 50&nbsp;[[hertz]] in many countries, and 60&nbsp;hertz in others. While the frequency may vary slightly during the day as the load changes, generators are designed to maintain an accurate number of cycles over a day, so the clock may be a fraction of a second slow or fast at any time, but will be perfectly accurate over a long time. The [[Rotor (electric)|rotor]] of the motor rotates at a speed that is related to the alternation frequency. Appropriate gearing converts this rotation speed to the correct ones for the hands of the analog clock. Time in these cases is measured in several ways, such as by counting the cycles of the AC supply, vibration of a [[tuning fork]], the behaviour of [[quartz]] crystals, or the quantum vibrations of atoms. Electronic circuits divide these high-frequency oscillations into slower ones that drive the time display.