On November 17, 1797, Eli Terry received his first patent for a clock
Terry is known as the founder of the American clock-making industry.
Alexander Bain, Scottish clockmaker, patented the electric clock in 1840
The electric clock's mainspring is wound either with an electric motor or with an electro-magnet and armature
In 1841, he first patented the electromagnetic pendulum.
The development of electronics in the 20th century led to clocks with no clockwork parts at all
Time in these cases is measured in several ways, such as by the vibration of a tuning fork, the behaviour of quartz crystals, or the quantum vibrations of atoms
Even mechanical clocks have since come to be largely powered by batteries, removing the need for winding.
How clocks work
The invention of the mechanical clock in the 13th century initiated a change in timekeeping methods from continuous processes, such as the motion of the gnomon's shadow on a sundial or the flow of liquid in a water clock, to repetitive oscillatory processes, like the swing of a pendulum or the vibration of a quartz crystal, which were more accurate. All modern clocks use oscillation.
Although the methods they use vary, all oscillating clocks, mechanical and digital and atomic, work similarly and can be divided into analogous parts. They consist of an object that repeats the same motion over and over again, an oscillator, with a precisely constant time interval between each repetition, or 'beat'
Attached to the oscillator is a controller device, which sustains the oscillator's motion by replacing the energy it loses to friction, and converts its oscillations into a series of pulses
The pulses are then added up in a chain of some type of counters to express the time in convenient units, usually seconds, minutes, hours, etc
Then finally some kind of indicator displays the result in a human-readable form.
This provides power to keep the clock going.
In mechanical clocks, this is either a weight suspended from a cord wrapped around a pulley, a pendulum, or a spiral spring called a mainspring.
electric clocks, it is either a battery or the AC power line.
Since clocks must run continuously, there is often a small secondary power source to keep the clock going temporarily during interruptions in the main power
In old mechanical clocks, a maintaining power spring kept the clock turning while the mainspring was being wound
In quartz clocks that use AC power, a small backup battery is often included to keep the clock running if it is unplugged temporarily from the wall.