Mechanical Clock (Edited from Wikipedia) SUMMARY A clock is an instrument to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". A silent instrument missing such a striking mechanism has traditionally been known as a timepiece. In general usage today a "clock" refers to any device for measuring and displaying the time. Watches and other timepieces that can be carried on one's person are often distinguished from clocks. The clock is one of the oldest human inventions, meeting the need to consistently measure intervals of time shorter than the natural units: the day, the lunar month, and the year. Devices operating on several physical processes have been used over the millennia. A sundial shows the time by displaying the position of a shadow on a flat surface. There are a range of duration timers, a well-known example being the hourglass. Water clocks, along with the sundials, are possibly the oldest time-measuring instruments. A major advance occurred in ancient China around 725 with the invention of the escapement by the Han Chinese mechanical engineer and buddhist monk Yi Xing, which allowed construction of the world's first mechanical clocks in China by both Yi Xing, Zhang Sixun and Su Song. By the year 1300, clock escapements were being developed for mechanical clocks in Europe which used oscillating timekeepers like balance wheels. Spring-driven clocks appeared during the 15th century. During the 15th and 16th centuries, clockmaking flourished. The next development in accuracy occurred after 1656 with the invention of the pendulum clock. A major stimulus to improving the accuracy and reliability of clocks was the importance of precise time-keeping for navigation. The electric clock was patented in 1840. The development of electronics in the 20th century led to clocks with no clockwork parts at all. The timekeeping element in every modern clock is a harmonic oscillator, a physical object (resonator) that vibrates or oscillates repetitively at a precisely constant frequency. This object can be a pendulum, a tuning fork, a quartz crystal, or the vibration of electrons in atoms as they emit microwaves. Analog clocks usually indicate time using angles. Digital clocks display a numeric representation of time. Two numeric 1 display formats are commonly used on digital clocks: 24-hour notation and 12-hour notation. Most digital clocks use electronic mechanisms and LCD, LED, or VFD displays. For convenience, distance, telephony or blindness, auditory clocks present the time as sounds. There are also clocks for the blind that have displays that can be read by using the sense of touch. Some of these are similar to normal analog displays, but are constructed so the hands can be felt without damaging them. The evolution of the technology of clocks continues today. HISTORY The first mechanical clock in the world was invented in China in AD 725 by Yi Xing and Liang Lingzan. The world's first escapement mechanism had been invented and used in medieval China, as the Song dynasty polymath and genius Su Song (1020–1101) incorporated it into his monumental innovation of the astronomical clock-tower of Kaifeng in 1088. His astronomical clock and rotating armillary sphere still relied on the use of either flowing water during the spring, summer, autumn seasons and liquid mercury during the freezing temperature of winter. 600 years later European clockworks of the 14th and 15th centuries shed this method for a more efficient driving power of weights, in addition to the Han Chinese escapement mechanism. Between 1280 and 1320, there is an increase in the number of references to clocks and horologes in church records, and this probably indicates that a new type of clock mechanism had been devised. Existing clock mechanisms that used water power were being adapted to take their driving power from falling weights. This power was controlled by some form of oscillating mechanism, probably derived from existing bell- ringing or alarm devices. This controlled release of power—the escapement—marks the beginning of the true mechanical clock. The earliest medieval European clockmakers were Christian monks. Medieval religious institutions required clocks because they regulated daily prayer- and work-schedules strictly, using various types of time-telling and recording devices, such as water clocks, sundials and marked candles, probably in combination. When mechanical clocks came into use, they were often wound at least twice a day to ensure accuracy. Monasteries broadcast important times and durations with bells, rung either by hand or by a mechanical device, such as by a falling weight or by rotating beater. These mechanical clocks were intended for two main purposes: for signaling and notification (e.g. the timing of services and public events), and for modeling the solar system. The former purpose is administrative, the latter arises naturally given the scholarly interests in astronomy, science, astrology, and how these subjects integrated 2 with the religious philosophy of the time. The astrolabe was used both by astronomers and astrologers, and it was natural to apply a clockwork drive to the rotating plate to produce a working model of the solar system. Simple clocks intended mainly for notification were installed in towers, and did not always require faces or hands. They would have announced the canonical hours or intervals between set times of prayer. Canonical hours varied in length as the times of sunrise and sunset shifted. The more sophisticated astronomical clocks would have had moving dials or hands, and would have shown the time in various time systems, including Italian hours, canonical hours, and time as measured by astronomers at the time. Both styles of clock started acquiring extravagant features such as automata. The religious necessities and technical skill of the medieval monks were crucial factors in the development of clocks, as the historian [and RPC instructor] Thomas Woods writes: The monks also counted skillful clock-makers among them. The first recorded clock was built by the future Pope Sylvester II for the German town of Magdeburg, around the year 996. Much more sophisticated clocks were built by later monks. Peter Lightfoot, a 14th-century monk of Glastonbury, built one of the oldest clocks still in existence, which now sits in excellent condition in London's Science Museum. The appearance of clocks in writings of the 11th century implies that they were well known in Europe in that period. In the early 14th-century, the Florentine poet Dante Alighieri referred to a clock in his Paradiso; the first known literary reference to a clock that struck the hours. An astronomical clock was constructed at Wells Cathedral around 1390. The dial represents a geocentric view of the universe, with the Sun and Moon revolving around a central fixed Earth. It is unique in having its original medieval face, showing a philosophical model of the pre-Copernican universe. Above the clock is a set of figures, which hit the bells, and a set of jousting knights who revolve around a track every 15 minutes. The clock was converted to pendulum-and-anchor escapement in the 17th century, and was installed in London's Science Museum in 1884, where it continues to operate. One clock that has not survived is that of the Abbey of St Albans, built by the 14th- century abbot Richard of Wallingford. It may have been destroyed during Henry VIII's Dissolution of the Monasteries, but the abbot's notes on its design have allowed a full- scale reconstruction. As well as keeping time, the astronomical clock could accurately 3 predict lunar eclipses, and may have shown the Sun, Moon (age, phase, and node), stars and planets, as well as a wheel of fortune, and an indicator of the state of the tide at London Bridge. According to Thomas Woods, "a clock that equaled it in technological sophistication did not appear for at least two centuries". During the Middle Ages, clocks primarily served religious purposes; the first employed for secular timekeeping emerged around the 15th century. In Dublin, the official measurement of time became a local custom, and by 1466 a public clock stood on top of the Tholsel (the city court and council chamber). It was the first of its kind to be clearly recorded in Ireland, and would only have had an hour hand. The increasing lavishness of castles led to the introduction of turret clocks. A 1435 example survives from Leeds castle; its face is decorated with the images of the Crucifixion of Jesus, Mary and St George. Early clock dials showed hours: the display of minutes and seconds evolved later. A clock with a minutes dial is mentioned in a 1475 manuscript, and clocks indicating minutes and seconds existed in Germany in the 15th century. Timepieces which indicated minutes and seconds were occasionally made from this time on, but this was not common until the increase in accuracy made possible by the pendulum clock and, in watches, by the spiral balance spring. The 16th-century astronomer Tycho Brahe used clocks with minutes and seconds to observe stellar positions. ESCAPEMENT An escapement is a device in mechanical watches and clocks that transfers energy to the timekeeping element (the "impulse action") and allows the number of its oscillations to be counted (the "locking action"). The impulse action transfers energy to the clock's timekeeping element (usually a pendulum or balance wheel) to replace the energy lost to friction during its cycle and keep the timekeeper oscillating. The escapement is driven by force from a coiled spring or a suspended weight, transmitted through the timepiece's gear train. Each swing of the pendulum or balance wheel releases a tooth of the escapement's escape wheel gear, allowing the clock's gear train to advance or "escape" by a fixed amount.