A pendulum clock is a clock that uses a swinging weight known as a pendulum as its timekeeping element. The pendulum is an approximate harmonic oscillator that swings in a time interval that depends on its length, and that resists swinging at other rates. From its invention in 1656 by Christiaan Huygens, inspired by Galileo Galilei, until the 1930s, the pendulum clock was the world's most precise type of timekeeper. Throughout the 18th and 19th centuries, pendulum clocks in homes, factories, offices, and railroad stations served as primary time standards for scheduling daily life activities, work shifts, and public transportation. Their accuracy allowed for the fast pace of life during the Industrial Revolution. The home pendulum clock, which was replaced by cheaper synchronous electric clocks in the 1930s and 1940s, are now kept mostly for their decorative and antique value.
As pendulum clocks must be stationary in order to avoid affecting the motion of the pendulum, other mechanisms are used in portable timepieces.
History
The pendulum clock was invented on 25 December 1656 by Dutch scientist and inventor Christiaan Huygens. The invention was patented the following year. Huygens described it in his manuscript (1658). Huygens contracted the construction of his clock to Salomon Coster.Andrewes, W.J.H. Clocks and Watches: The leap to precision in
Huygens was inspired by investigations of pendulums by Galileo Galilei in around 1602, who had discovered the key property that makes pendulums useful timekeepers—they behave isochronically, so that they swing with a period that is independent of the size of the swing. In 1637, Galileo described a mechanism to his son, Vincenzo that could keep a pendulum swinging. The mechanism was partly constructed by his son in 1649.A modern reconstruction can be seen at
Prior to the discovery of the pendulum many clock makers during the 1580s were given commission to create clocks showing minutes and second on them, this was not possible though since clocks mechanisms at the time were not accurate enough to add these markers.Andrewes, William J. H. “A Chronicle of Timekeeping.” Scientific American 287, no. 3 (2002): 78. http://www.jstor.org/stable/26059969. Before the use of pendulums in clocks, they were accurate to about 15 minutes per day. The introduction of the pendulum, the first harmonic oscillator used in timekeeping, increased their accuracy to 15 seconds per day,, p.3, also published in Proceedings of the Royal Society of London, A 458, 563–579 an improvement that led to their rapid spread. Many existing "verge and foliot" clocks were fitted with pendulums. By 1659 pendulum clocks were being manufactured by the French clockmaker Nicolaus Hanet, and in England by Ahasuerus Fromanteel.
These early clocks, due to their verge escapements, had wide pendulum swings of 80–100°. In his 1673 analysis of pendulums, Horologium Oscillatorium, Huygens showed that wide swings made the pendulum inaccurate, causing its period, and thus the rate of the clock, to vary with unavoidable variations in the driving force provided by the movement. In this Huygens concluded that it was best to create a clock with a cycloid shape rather than a circular shape, so the clock would oscillate in the same time regardless of amplitude.Andrewes, William J. H. “A Chronicle of Timekeeping.” Scientific American 287, no. 3 (2002): 79. http://www.jstor.org/stable/26059969. Clockmakers' realization that only pendulums with small swings of a few degrees are isochronous motivated the invention of the anchor escapement by Robert Hooke around 1658, which reduced the pendulum's swing to 4–6°. The anchor became the standard escapement used in pendulum clocks. In addition to increased accuracy, the anchor's narrow pendulum swing allowed the clock's case to accommodate longer, slower pendulums, which needed less power and caused less wear on the movement.The seconds pendulum (also called the Royal pendulum), long, in which the time period is two seconds, became widely used in quality clocks. Huygens took this the creation of the pendulum clock a step further and in 1675 added the spiral balance spring. Similar to how gravity controls a pendulum clock the balance spring would control the rotary oscillation of a balance wheel in a portable clock.Andrewes, William J. H. “A Chronicle of Timekeeping.” Scientific American 287, no. 3 (2002): 79. http://www.jstor.org/stable/26059969. This discovery of using a similar motion in a pendulum clock in a portal clocks revolutionized the industry forever. The long narrow freestanding clocks built around these pendulums, first made by William Clement around 1680, who also claimed invention of the anchor escapement, became known as grandfather clocks. The increased accuracy resulting from these developments caused the minute hand, previously rare, to be added to clock faces beginning around 1690.Milham 1945, p. 190
The 18th and 19th century wave of horological innovation that followed the invention of the pendulum brought many improvements to pendulum clocks. The deadbeat escapement invented in 1675 by Richard Towneley and popularized by George Graham around 1715 in his precision "regulator" clocks gradually replaced the anchor escapementMilham 1945, p.181, 441 and is now used in most modern pendulum clocks. Observation that pendulum clocks slowed down in summer brought the realization that thermal expansion and contraction of the pendulum rod with changes in temperature was a source of error. This was solved by the invention of temperature-compensated pendulums; the mercury pendulum by Graham in 1721 and the gridiron pendulum by John Harrison in 1726.Milham 1945, pp. 193–195 With these improvements, by the mid-18th century precision pendulum clocks achieved accuracies of a few seconds per week.
Until the 19th century, clocks were handmade by individual craftsmen and were very expensive. The rich ornamentation of pendulum clocks of this period indicates their value as status symbols of the wealthy. The clockmakers of each country and region in Europe developed their own distinctive styles. By the 19th century, factory production of clock parts gradually made pendulum clocks affordable by middle-class families.
During the Industrial Revolution, the faster pace of life and scheduling of shifts and public transportation like trains depended on the more accurate timekeeping made possible by the pendulum. Daily life was organized around the home pendulum clock. More accurate pendulum clocks, called regulators, were installed in places of business and railroad stations and used to schedule work and set other clocks. The need for extremely accurate timekeeping in celestial navigation to determine longitude on ships during long sea voyages drove the development of the most accurate pendulum clocks, called astronomical regulators. These precision instruments, installed in clock vaults in naval observatories and kept accurate within a fraction of a second by observation of star transits overhead, were used to set marine chronometers on naval and commercial vessels. Beginning in the 19th century, astronomical regulators in naval observatories served as primary standards for national time distribution services that distributed time signals over telegraph wires.Milham 1945, p.83 From 1909, US National Bureau of Standards (now NIST) based the US time standard on Riefler pendulum clocks, accurate to about 10 milliseconds per day. In 1929 it switched to the Shortt-Synchronome free pendulum clock before phasing in quartz standards in the 1930s. With an error of less than one second per year, the Shortt was the most accurate commercially produced pendulum clock at the time of its creation.
Pendulum clocks remained the world standard for accurate timekeeping for 270 years, until the invention of the quartz clock in 1927, and were used as time standards through World War II. The French Time Service included pendulum clocks in their ensemble of standard clocks until 1954. The home pendulum clock began to be replaced as domestic timekeeper during the 1930s and 1940s by the synchronous electric clock, which kept more accurate time because it was synchronized to the oscillation of the electric power grid. Behind the Iron Curtain, where quartz technology was unavailable, experiments with pendulum clocks continued for much longer, with corresponding developments in accuracy: the AChF-3 isochronous pendulum clock developed by physicist Feodosii Fedchenko in 1955 archived: NASA Astronomical Data System has an accuracy in the range of quartz clocks and is the most accurate pendulum clock ever to have gone into production. The most accurate experimental pendulum clock ever made may be the Littlemore Clock built by Edward T. Hall in the 1990s (donated in 2003 to the National Watch and Clock Museum, Columbia, Pennsylvania, USA). The largest pendulum clocks, exceeding , were built in Geneva (1972) and Gdańsk (2016).
Mechanism
The mechanism which runs a mechanical clock is called the movement. The movements of all mechanical pendulum clocks have these five parts:Milham 1945, pp. 74, 197 – 212 A power source; either a weight on a cord or chain that turns a pulley or sprocket, or a mainspring. A gear train (wheel train) that steps up the speed of the power so that the pendulum can use it. The gear ratios of the gear train also divide the rotation rate down to give wheels that rotate once every hour and once every 12 or 24 hours, to turn the hands of the clock. An escapement that gives the pendulum precisely timed impulses to keep it swinging, and which releases the gear train wheels to move forward a fixed amount at each swing. This is the source of the "ticking" sound of an operating pendulum clock. The pendulum, a weight on a rod, which is the timekeeping element of the clock. An indicator or dial that records how often the escapement has rotated and therefore how much time has passed, usually a traditional clock face with rotating hands.
Additional functions in clocks besides basic timekeeping are called complications. More elaborate pendulum clocks may include these complications: Striking train: strikes a bell or gong on every hour, with the number of strikes equal to the number of the hour. Some clocks will also signal the half hour with a single strike. More elaborate types, technically called chiming clocks, strike on the quarter hours, and may play melodies or Cathedral chimes, usually Westminster quarters. Calendar dials: show the day, date, and sometimes month. Moon phase dial: shows the phase of the moon, usually with a painted picture of the moon on a rotating disk. These were useful historically for people planning nighttime journeys. Equation of time dial: this rare complication was used in early days to set the clock by the passage of the sun overhead at noon. It displays the difference between the time indicated by the clock and the time indicated by the position of the sun, which varies by as much as ±16 minutes during the year. Repeater attachment: repeats the hour chimes when triggered by hand. This rare complication was used before artificial lighting to check what time it was at night.
In electromechanical pendulum clocks such as used in mechanical Master clocks the power source is replaced by an electrically powered solenoid that provides the impulses to the pendulum by magnetic force, and the escapement is replaced by a switch or photodetector that senses when the pendulum is in the right position to receive the impulse. These should not be confused with more recent quartz pendulum clocks in which an electronic quartz clock module swings a pendulum. These are not true pendulum clocks because the timekeeping is controlled by a quartz crystal in the module, and the swinging pendulum is merely a decorative simulation.
Gravity-swing pendulum