The first mechanical clocks appeared about 1250 CE and employed weight-driven gears to keep time. Their invention represented an important step in the quest to discover a way to keep time accurately. The inventor of the first mechanical clock is unknown, but records indicate the timepiece originated in Europe. In all likelihood, the devices were invented in monasteries, where they were used to call the monks to prayer.
Mechanical clocks represented a vast improvement over previous timekeeping mechanisms of the day, including hourglasses and water clocks, which proved to be unreliable for accurate timekeeping.
The mechanical clock is composed of a few necessary parts, including a suspended weight that provides a driving force; a train of gear wheels that transmit power and turn a dial to indicate time; a time-controlling device that regulates the falling weight; and a mechanism known as an escapement. The escapement is a key component of the clock and is that which distinguishes it from its predecessors. This device takes energy from the power source, transmits it through gears, and releases it in beats, generally one per second. Early escapements were quite primitive and were unable to keep a regular beat. Later escapements were designed to fit on the top of the gears and were stimulated by the pendulum’s motion. Rocking back and forth on the wheel, the escapement allowed the gear to advance one notch but blocked advancement to the next notch. When the pendulum returned, the escapement released another notch. In this way the escapement controlled the rate at which the clock beat.
Clocks relied on the pull of gravity as a power source. A weight was attached to a cord that was tightly wound around a toothed spool known as a capstan. As the cord unwound, the capstan turned a set of gears that then caused the hands on the clock’s face to move. Although the early “modern” clocks represented a great leap forward, the devices were inaccurate at best, losing or gaining 15 minutes per day, and often much more than that. Such clocks often had to be reset daily at solar noon. Furthermore, their mechanical parts required a great deal of upkeep.
The next major advancement was the application of the pendulum to the clock in 1657, which provided a more reliable power source and hence represented a much more precise way to keep time. Clockmakers immediately began to employ the pendulum as a new type of “regulator,” and timekeeping errors were reduced even further. The pendulum allowed clockmakers to add a minute hand to the clock, which previously had sported only an hour hand. Furthermore, continued refinements to the shapes of clocks added to the increased accuracy of the devices because they could house and protect long pendulums. Thus were longcase clocks born, later known as grandfather clocks. Mechanical clocks continued in use for more than 400 years before the advent of the electric and, ultimately, the atomic clock in modern times.
patricia J. West
See also Atomic Clocks; Hourglass; Pendulums; Sundials; Measurements of Time; Timepieces
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