Clock

A clock or chronometer is a device that measures and shows time. It is one of the oldest human inventions. People made clocks to measure short periods, instead of waiting for a day, a lunar month, or a year.

Early ways to tell time included tools like the sundial, which uses the position of a shadow, and the hourglass, which uses flowing sand.

The first mechanical clocks appeared around 1300 in Europe. They used parts like balance wheels to keep time. Later, Christiaan Huygens invented the pendulum clock in 1656, which was much more accurate. As technology grew, clocks became smaller and easier to carry. Today, most clocks use electronic parts, such as quartz crystal or the movement of electrons in atoms, to keep very exact time.

Clocks can show time in different ways. Analog clocks use a clock face with moving hands. Digital clocks show numbers. Some clocks, called speaking clocks, tell the time using words. This helps people who cannot see the display. Clocks help us organize our days, from waking up to going to bed.

Etymology

The word clock comes from a medieval Latin word for 'bell,' called clocca. Many European languages have similar words. Clocks came to England from the Low Countries. The English word for 'bell' is Klocke, from Middle Low German and Middle Dutch. This word also has roots in Middle English, Old North French, and Middle Dutch, all meaning 'bell'.

Main articles: Latin, cognates, Low Countries, Middle English, Old North French, Middle Dutch

History of time-measuring devices

Main article: History of timekeeping devices

The Sun’s position in the sky changes during the day because the Earth rotates. Shadows from objects move too, and these shadows can show what time it is. A sundial uses a shadow’s position on a flat surface with markings to show the time. Sundials can be flat, upright, or other shapes. People used sundials in ancient times. If you know where you are, a sundial can show the local solar time fairly well, usually within a minute or two. People used sundials to check clocks until the 1830s when trains and the telegraph made time the same in different places.

Many tools can track how time passes without needing to show the exact hour or minute. Examples include candle clocks, incense clocks, and the hourglass. Candle and incense clocks work because the candle or incense burns at a steady rate, letting people guess how much time has passed. In an hourglass, sand falls through a small hole at a steady rate, showing a set amount of time. The sand isn’t used up—it can be used again.

Water clocks, like sundials, may be some of the oldest time tools. We don’t really know when or where they were first made. The simplest water clock is a bowl-shaped outlet, and we know they existed in Babylon and Egypt around the 16th century BC. Other places like India and China also used water clocks, but we don’t know exactly when they started using them.

The Macedonian astronomer Andronicus of Cyrrhus built the Tower of the Winds in Athens in the 1st century BC. It held a large water clock inside and had sundials on the outside, acting like an early clocktower. The Greeks and Romans improved water clocks. These ideas moved through Byzantine and Islamic times back to Europe. China also made advanced water clocks by 725 AD, sharing their ideas with Korea and Japan.

Some water clocks were made separately, and some ideas moved through trade. Pre-modern societies didn’t need very exact timekeeping like we do today. Water clocks in the past were mostly used for astrology. They were checked against sundials. Water clocks were the best time tools for thousands of years until the more exact pendulum clock replaced them in 17th-century Europe.

The first known geared clock was made by the mathematician, physicist, and engineer Archimedes in the 3rd century BC. Archimedes built an astronomical clock that also acted like a cuckoo clock, with birds moving and singing every hour. This clock used four weights, counterweights, and strings, controlled by floats in a water container with siphons.

In the 12th century, Al-Jazari, an engineer from Mesopotamia, made many clocks of different shapes and sizes. Famous ones included elephant, scribe, and castle clocks. These clocks not only told time but also showed the wealth and status of the Artuqid State.

The word horologia comes from the Greek ὥρα (hour) and λέγειν (to tell). It was used for early mechanical clocks, but it covered many types of timekeepers. For example, in 1176, Sens Cathedral in France had an ‘horologe’, but we don’t know what it looked like. In 1198, a fire at St Edmundsbury abbey (now Bury St Edmunds) caused monks to run to the clock for water, showing their water clock had a big enough tank to help put out fires.

In Europe, between 1280 and 1320, more people wrote about clocks and horologes in church records. This probably shows a new type of clock was made. Older water clocks were changed to use falling weights instead of water. This power was controlled by a swaying part, probably from bell-ringing devices. This controlled power release – the escapement – started the true mechanical clock, different from earlier cogwheel clocks.

These mechanical clocks were used mainly for two things: to signal events like services and public meetings, and to model the Solar System. The first purpose was for managing things; the second came from people’s interest in astronomy, science, and astrology, mixed with religious ideas at the time. The astrolabe was used by astronomers and astrologers, and adding a clock drive to its moving plate made a working model of the solar system.

In 1283, a big clock was placed at Dunstable Priory in Bedfordshire in southern England; its spot above the rood screen suggests it wasn’t a water clock. In 1292, Canterbury Cathedral installed a ‘great horloge’. Over the next 30 years, clocks appeared at many churches in England, Italy, and France. In 1322, a new clock was put in Norwich, replacing an earlier one from 1273. This clock had a large (2 metre) astronomical dial with automata and bells.

A fancy water clock called the ‘Cosmic Engine’ was made by Su Song, a Chinese polymath, in China in 1092. This ten-metre-high (about 30 feet) astronomical clock tower used a wheel turned by falling water and liquid mercury to move an armillary sphere that could solve complex astronomy problems.

In Europe, clocks were built by Richard of Wallingford in Albans by 1336, and by Giovanni de Dondi in Padua from 1348 to 1364. Though they don’t exist anymore, we have detailed descriptions of how they were made, and modern copies have been built. These show how quickly mechanical clock theory became practical, and also that one reason for developing them was astronomers’ desire to study the heavens.

The Astrarium of Giovanni Dondi dell'Orologio was a complex astronomical clock built between 1348 and 1364 in Padua, Italy, by Giovanni Dondi dell'Orologio. The Astrarium had seven faces and 107 moving gears; it showed the positions of the Sun, the Moon and the five planets known at the time, as well as religious holy days. It was about 1 metre high, made of brass or iron, and stood on seven decorative feet. The lower part had a 24-hour dial and a large calendar drum showing church holidays, moving holidays, and the Moon’s position in the zodiac. The upper part had seven dials, each about 30 cm across, showing data for the Primum Mobile, Venus, Mercury, the Moon, Saturn, Jupiter, and Mars. Above the 24-hour dial was the Primum Mobile dial, showing the stars’ daily motion and the Sun’s yearly motion. Each ‘planetary’ dial used complex clockwork to model the planets’ movements fairly well, matching both Ptolemaic theory and actual observations.

Wallingford’s clock had a large astrolabe-style dial showing the Sun, the Moon’s age and phase, a star map, and possibly the planets. It also had a wheel of fortune and a tide indicator for London Bridge. Bells rang every hour, with the number of chimes showing the hour. Dondi’s clock was a seven-sided, 1-metre-high structure with dials for the time, all known planets’ motions, a calendar of holidays, and a prediction hand for eclipses moving once every 18 years. We don’t know how accurate or reliable these clocks were. They were probably adjusted by hand each day to fix errors from wear and imperfect making.

Spring-driven clocks appeared in the 15th century, though they are often wrongly credited to Nuremberg watchmaker Peter Henlein around 1511. The earliest existing spring-driven clock is a chamber clock given to Phillip the Good, Duke of Burgundy, around 1430, now in the Germanisches Nationalmuseum. Springs gave clockmakers a new challenge: keeping the clock running at the same speed as the spring weakened. This led to inventions like the stackfreed and the fusee in the 15th century, and later the modern going barrel in 1760.

Early clock faces didn’t show minutes or seconds. A clock with minutes was shown in a 1475 manuscript by Paulus Almanus, and some 15th-century clocks in Germany showed minutes and seconds. An early record of a seconds hand appears around 1560 on a clock now in the Fremersdorf collection.

During the 15th and 16th centuries, clockmaking grew strongly in metalworking towns like Nuremberg and Augsburg in Germany, and Blois in France. Some simple table clocks had only one hand, with the dial split into four parts, showing time to the nearest 15 minutes. Other clocks showed off craftsmanship, with astronomy indicators and musical movements.

The first pendulum clock was designed by Christiaan Huygens in 1656

The next big step in accuracy came after 1656 with the pendulum clock. Galileo first thought of using a swinging weight to keep time earlier in the 17th century. But Christiaan Huygens is usually credited with the invention. He found the math linking pendulum length to time (about 99.4 cm or 39.1 inches for a one-second swing) and made the first pendulum clock. The first model was built in 1657 in the Hague, but the idea was taken up in England. The longcase clock (or grandfather clock) was made to hold the pendulum by English clockmaker William Clement in 1670 or 1671. Around this time, clock cases began to use wood and faces used enamel or painted ceramics.

In 1670, William Clement created the anchor escapement, an improvement over Huygens’ crown escapement. Clement also added the pendulum suspension spring in 1671. The concentric minute hand was added by Daniel Quare, a London clockmaker, and others, and the second hand was introduced.

In 1675, Huygens and Robert Hooke invented the spiral balance spring, or hairspring, to control the balance wheel’s [/w/45]. This key step finally made accurate pocket watches possible. The great English clockmaker Thomas Tompion was one of the first to use this in his pocket watches, and he adopted the minute hand, which later settled into its modern shape. The rack and snail striking mechanism for striking clocks was introduced in the 17th century and was better than the ‘countwheel’ mechanism.

A big reason to improve clock accuracy was the need for exact time at sea. A ship’s position could be found fairly well if the navigator had a clock that lost or gained less than about 10 seconds a day. This clock couldn’t have a pendulum, which wouldn’t work on a moving ship. In 1714, the British government offered up to 20,000 pounds to anyone who could find the exact longitude. John Harrison, who spent his life improving his clocks, later received large sums under the Longitude Act.

In 1735, Harrison built his first chronometer, improving it over the next thirty years before showing it. The clock had many new ideas, like bearings to reduce friction, weighted balances to handle the ship’s movement, and two metals to prevent heat changes.

The British led watchmaking in the 17th and 18th centuries, but focused on high-quality products for wealthy people. Though Britain tried to make clockmaking modern with mass production in 1843, it was in the United States that this succeeded. In 1816, Eli Terry and other Connecticut clockmakers found a way to mass-produce clocks using interchangeable parts. Aaron Lufkin Dennison started a factory in 1851 in Massachusetts using interchangeable parts, and by 1861 was a successful company called the Waltham Watch Company.

In 1815, English scientist Francis Ronalds made the first electric clock using dry pile batteries. Alexander Bain, a Scottish clockmaker, patented the electric clock in 1840. The electric clock’s spring was wound by an electric motor or an electromagnet. By the late 1800s, dry cell batteries made electric power practical for clocks. Spring or weight-driven clocks using electricity, either alternating current (AC) or direct current (DC), to wind the spring or lift the weight are called electromechanical clocks. These clocks don’t use electricity to keep time but can be used in schools, businesses, factories, railroads, and government places as a master clock and slave clocks.

The piezoelectric effect in quartz crystals was found by Jacques and Pierre Curie in 1880. The first crystal oscillator was made in 1917 by Alexander M. Nicolson, and the first quartz crystal oscillator by Walter G. Cady in 1921. In 1927 the first quartz clock was built by Warren Marrison and J.W. Horton at Bell Telephone Laboratories in Canada. Over the next years, quartz clocks became precise time tools in labs—though their complex vacuum tube electronics limited use elsewhere. The National Bureau of Standards (now NIST) used quartz clocks as the U.S. time standard from late 1929 to the 1960s, when it switched to atomic clocks. In 1969, Seiko made the world’s first quartz wristwatch, the Astron. Their accuracy and low cost led to many quartz clocks and watches.

Today, atomic clocks are the most accurate. They’re much better than quartz clocks, accurate to a few seconds over trillions of years. Atomic clocks were first suggested by Lord Kelvin in 1879. In the 1930s, magnetic resonance made practical methods. A prototype ammonia maser was built in 1949 at the U.S. National Bureau of Standards (NBS, now NIST). Though less accurate than quartz clocks, it showed the idea worked. The first exact atomic clock, a caesium standard based on a certain change in the caesium-133 atom, was built by Louis Essen in 1955 at the National Physical Laboratory in the UK. The caesium standard was checked using the astronomical time scale ephemeris time (ET). As of 2013, the most exact atomic clocks are ytterbium clocks, stable to within less than two parts in 1 quintillion (2×10⁻¹⁸).

Operation

The invention of the mechanical clock in the 13th century changed how people kept track of time. Before this, people used things like the shadow of a stick or the flow of water to tell time. Mechanical clocks used a swinging weight or a spring to keep time, but they were not very accurate.

All modern clocks, whether they are mechanical, electric, or atomic, work in a similar way. They have a part that moves back and forth very regularly, called an oscillator. This could be a swinging pendulum, a tiny wheel, or even the vibrations of atoms. The clock counts these movements to show the time in seconds, minutes, and hours. Some clocks, like those in schools, get their time from a master clock and adjust to stay in sync. Others use signals from the power grid or radio stations to keep very accurate time.

Types

Clocks can be grouped by how they show time and how they keep track of it.

Time display methods

Analog

See also: Clock face

Analog clocks show time using moving pointers called "hands" on a numbered circle. The most common type has a short "hour hand" and a longer "minute hand." Some also have a "second hand." These hands move around a circle divided into 12 sections to show the hours.

Digital

Main article: Digital clock

Digital clocks show time using numbers. They can display time in two ways: the 24-hour format (00–23) or the 12-hour format with AM/PM (like 12AM, 1AM up to 11PM). Most digital clocks use electronic screens like LCD or LED.

Hybrid (analog-digital)

Some clocks mix both styles, showing hours and minutes like analog clocks but displaying seconds with numbers.

Auditory

Main article: Talking clock

Auditory clocks speak the time out loud, either in words ("It is three thirty") or by sounds, like bell rings. Many phone services offer this as a speaking clock.

Word

Word clocks show time using phrases, like "It’s about three o’clock."

Projection

Main article: Projection clock

Projection clocks shine the time onto a wall or ceiling, making large numbers easy to read. They usually have a battery backup to keep accurate time.

Tactile

Some clocks are made for people who cannot see well. These may use touch or Braille to show the time.

Multi-display

Some clocks show time in many ways—on different faces, in different time zones, or with both analog and digital displays.

Purposes

Clocks are found in many places, like homes, offices, schools, and even on computers and phones. They help us know what time it is. Some clocks, called alarm clocks, can make a loud sound at a certain time, like to wake someone up. These can be helpful for kids who are learning to tell time.

Clocks are also used to help control other devices, like turning on heating systems or timing games and sports. In sports, stopwatches measure how fast athletes run, and in chess, special clocks help players keep track of their time.

Culture

In different cultures, clocks have special meanings. In the United Kingdom, some people believe that if a clock stops, it might mean that something big is happening.

In China, people sometimes avoid giving clocks as gifts to older people. This is because the words for "clock" and "funeral" sound similar.

Specific types

Clocks help us measure and show time. People have made clocks for thousands of years to track shorter periods than natural cycles like days or years. Many different methods and technologies have been used to create clocks over time.

You can see a list of different kinds of clocks here.

Awards

Clocks that are made very well often win special prizes. Two famous awards for great clocks are the Grand Prix d'Horlogerie de Genève and Goldene Unruh.