A watchwork or clockwork is made up of a set of gears connected together. The gears in a watch or clock are called wheels, and there are usually five of them. The first of the series is the largest. Each succeeding one is usually smaller and turns faster. The wheels are powered by a spring known as the mainspring, which is coiled inside a drum attached to the largest wheel.
When the stiff mainspring is wound up tightly and released, it starts to unwind again. As it unwinds, it moves the largest wheel. The large wheel turns the center wheels, the center one turns the third wheel, and the third one turns the fourth. If the spring were allowed to unwind at its own speed, the clock or watch, would not keep time because the speed of the turning wheels could not be controlled. The fifth wheel is part of the escapement, and it fixes the rate at which all them turn.
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The escapement in a watch and some clocks is made up of a balance wheel, a hairspring, and an escape wheel. The hairspring, a tiny elastic strip inside the balance, links the balance wheel with the rest of the watch. When the balance one begins to move, it pulls against the hairspring, which immediately pulls back and changes the direction of the movement of the balance wheel. As the balance wheel regularly turns back and forth, two fingerlike prongs hit the notched edges, of the escape wheel.
Each time the escape wheel begins to move freely, it is stopped by one of the prongs controlled by the balance and held briefly. One tooth of the escape wheel has time to move before the other prong stops the escape wheel again. The regular back-and-forth movement of the balance wheel keeps the escape wheel turning one tooth at a time. The tick we hear in a watch is from the escape wheel each time a tooth escapes. If the watch gains or loses time, it is because the balance wheel is too fast or too slow.
In a pendulum clock the escapement is regulated by a pendulum in place of the balance wheel. The escape wheel is attached to the fourth wheel, and its regular turning holds the movement of the other wheels to a set speed. The fourth wheel turns once each minute. The second hand is attached to the fourth wheel. The center wheel turns once each hour. The minute hand is attached to the center wheel.
Each axle, or pivot, of the gears turns in a bearing. Jewels are often used as bearings in watches and clocks. The hard, smooth surface of a jewel allows the axle to move freely, and the jewel outlasts a metal bearing. High- quality timepieces have many jewel bearings, but jewels alone do not make a high quality ometer is a very large, accurate watch mounted in a special bracket to keep it level on a rolling sea.
The chronograph is an accurate timer that includes the timing action of the stopwatch and also indicates the time of day. Chronographs are valuable aids in laboratory tests and in studying the movements of stars or the time it takes a ship to sail from place to place. The most accurate astronomical clocks are used in observatories to time the movements of stars to the second.