Clock

A clock or chronometer is a device that measures and displays time. It is one of the oldest human inventions, created to measure intervals shorter than natural units like the day, the lunar month, and the year. Early examples include the sundial, which uses the position of a shadow, and the hourglass, which uses flowing sand to track time.

The first mechanical clocks appeared around 1300 in Europe, using a verge escapement and balance wheels. A major improvement came in 1656 when Christiaan Huygens invented the pendulum clock, which was much more accurate. As navigation became more important, so did the need for precise timekeeping, leading to many advances in clock design.

Today, all modern clocks rely on a harmonic oscillator, such as a pendulum, balance wheel, tuning fork, quartz crystal, or even the vibrations of electrons in atoms. Clocks can display time in two main ways: analog clocks with hands on a clock face, and digital clocks that show numbers. Some clocks, like speaking clocks, are designed to be used by people who cannot see the display.

Etymology

The word clock comes from a medieval Latin term meaning 'bell,' called clocca. Many European languages share similar words. Clocks reached England from the Low Countries, and the English word evolved from terms like Klocke in Middle Low German and Middle Dutch, as well as clokke in Middle English, cloque in Old North French, all meaning 'bell'.

History of time-measuring devices

Main article: History of timekeeping devices

The apparent position of the Sun in the sky changes over the course of each day, reflecting the rotation of the Earth. Shadows cast by stationary objects move correspondingly, so their positions can be used to indicate the time of day. A sundial shows the time by displaying the position of a shadow on a (usually) flat surface that has markings that correspond to the hours. Sundials can be horizontal, vertical, or in other orientations. Sundials were widely used in ancient times. With knowledge of latitude, a well-constructed sundial can measure local solar time with reasonable accuracy, within a minute or two.

Many devices can be used to mark the passage of time without respect to reference time (time of day, hours, minutes, etc.) and can be useful for measuring duration or intervals. Examples of such duration timers are candle clocks, incense clocks, and the hourglass. Both the candle clock and the incense clock work on the same principle, wherein the consumption of resources is more or less constant, allowing reasonably precise and repeatable estimates of time passages. In the hourglass, fine sand pouring through a tiny hole at a constant rate indicates an arbitrary, predetermined passage of time.

Water clocks, along with sundials, are possibly the oldest time-measuring instruments, with the only exception being the day-counting tally stick. Given their great antiquity, where and when they first existed is not known and is perhaps unknowable. The bowl-shaped outflow is the simplest form of a water clock and is known to have existed in Babylon and Egypt around the 16th century BC. Other regions of the world, including India and China, also have early evidence of water clocks, but the earliest dates are less certain.

The Macedonian astronomer Andronicus of Cyrrhus supervised the construction of the Tower of the Winds in Athens in the 1st century BC, which housed a large clepsydra inside as well as multiple prominent sundials outside. The Greek and Roman civilizations advanced water clock design with improved accuracy. These advances were passed on through Byzantine and Islamic times, eventually making their way back to Europe. Independently, the Chinese developed their own advanced water clocks by 725 AD.

Some water clock designs were developed independently, and some knowledge was transferred through the spread of trade. Pre-modern societies did not have the same precise timekeeping requirements that exist in modern industrial societies. Instead, water clocks in ancient societies were used mainly for astrological reasons. These early water clocks were calibrated with a sundial. While never reaching the level of accuracy of a modern timepiece, the water clock was the most accurate and commonly used timekeeping device for millennia until it was replaced by the more accurate pendulum clock in 17th-century Europe.

The first known geared clock was invented by the great mathematician, physicist, and engineer Archimedes during the 3rd century BC. Archimedes created his astronomical clock, which was also a cuckoo clock with birds singing and moving every hour. The Archimedes clock works with a system of four weights, counterweights, and strings regulated by a system of floats in a water container with siphons that regulate the automatic continuation of the clock.

In Europe, between 1280 and 1320, there was 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.

An elaborate water clock, the 'Cosmic Engine', was invented by Su Song, a Chinese polymath, designed and constructed in China in 1092. This great astronomical hydromechanical clock tower was about ten metres high and was indirectly powered by a rotating wheel with falling water and liquid mercury, which turned an armillary sphere capable of calculating complex astronomical problems.

Spring-driven clocks appeared during the 15th century. Building smaller clocks was a technical challenge, as was improving accuracy and reliability. Clocks could be impressive showpieces to demonstrate skilled craftsmanship, or less expensive, mass-produced items for domestic use. The escapement in particular was an important factor affecting the clock's accuracy, so many different mechanisms were tried.

The next development in accuracy occurred after 1656 with the invention of the pendulum clock. Galileo had the idea to use a swinging bob to regulate the motion of a time-telling device earlier in the 17th century. Christiaan Huygens, however, is usually credited as the inventor. He determined the mathematical formula that related pendulum length to time and had the first pendulum-driven clock made. The first model clock was built in 1657 in the Hague, but it was in England that the idea was taken up. The longcase clock (also known as the grandfather clock) was created to house the pendulum and works by the English clockmaker William Clement in 1670 or 1671.

In 1675, Huygens and Robert Hooke invented the spiral balance spring, or the hairspring, designed to control the oscillating speed of the balance wheel. This crucial advance finally made accurate pocket watches possible.

A major stimulus to improving the accuracy and reliability of clocks was the importance of precise time-keeping for navigation. The position of a ship at sea could be determined with reasonable accuracy if a navigator could refer to a clock that lost or gained less than about 10 seconds per day.

The British had dominated watch manufacture for much of the 17th and 18th centuries, but maintained a system of production that was geared towards high quality products for the elite. It was in the United States that mass production took off. In 1816, Eli Terry and some other Connecticut clockmakers developed a way of mass-producing clocks by using interchangeable parts.

In 1815, the English scientist Francis Ronalds published the first electric clock powered by dry pile batteries. Alexander Bain, a Scottish clockmaker, patented the electric clock in 1840. The electric clock's mainspring is wound either with an electric motor or with an electromagnet and armature.

The piezoelectric properties of crystalline quartz were discovered in 1880. The first quartz clock was built by Warren Marrison and J.W. Horton at Bell Telephone Laboratories in Canada in 1927. Their inherent accuracy and low cost of production resulted in the subsequent proliferation of quartz clocks and watches.

Currently, atomic clocks are the most accurate clocks in existence. Atomic clocks were first theorized by Lord Kelvin in 1879. The first accurate atomic clock, a caesium standard based on a certain transition of the caesium-133 atom, was built by Louis Essen in 1955 at the National Physical Laboratory in the UK.

Operation

The invention of the mechanical clock in the 13th century changed how people kept track of time. Instead of using continuous processes like shadows on sundials or water flowing in a water clock, clocks began to use periodic oscillations, such as the swing of a pendulum or the vibration of a quartz crystal, which could be more accurate. All modern clocks work on the principle of oscillation.

Clocks have several key parts. An oscillator repeats the same motion over and over again at a constant rate. A controller keeps the oscillator moving and turns its motions into pulses. A counter adds up these pulses, turning them into units like seconds, minutes, and hours. Finally, an indicator shows this information in a way people can read. Power sources for clocks include weights and springs in mechanical clocks, and batteries or electricity in electric clocks. The timekeeping part of a clock, called an oscillator, can be a pendulum, a balance wheel, a tuning fork, a quartz crystal, or even the vibrations of atoms in atomic clocks. Some clocks, like slave clocks and radio clocks, get their time from more accurate external sources.

Types

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

Time display methods

Analog

Analog clocks show time with moving pointers called "hands" on a circle with numbers. The most common type has an hour hand and a minute hand. Some also have a second hand. Another type is the sundial, which uses the sun's shadow to show time.

Digital

Main article: Digital clock

Digital clocks show time with numbers. They can use a 24-hour format (00–23) or a 12-hour format with AM/PM. Many digital clocks use electronic screens, but some flip clocks change physical pages to show new numbers each minute.

Hybrid (analog-digital)

Some clocks mix styles, showing hours and minutes like analog clocks but displaying seconds digitally.

Auditory

Main article: Talking clock

Auditory clocks speak the time aloud, either in words or by sounds, helping people who are far away or unable to see the display.

Word

Word clocks show time using sentences, like "It's about three o'clock."

Projection

Main article: Projection clock

Projection clocks shine a bright image of the time onto a wall or ceiling, making it easy to read from a distance.

Tactile

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

Multi-display

Some clocks show time in many ways at once, like having several faces or showing different time zones.

Purposes

Clocks are found in many places, from homes and offices to public spaces like railway stations and churches. Smaller clocks, known as watches, are carried on wrists or kept in pockets, while computers, mobile phones, and MP3 players often display the time in a small corner of their screens.

The main purpose of a clock is to show the current time. Some clocks, called alarm clocks, can make a loud sound at a set time, such as to wake someone up. These alarms might start softly and get louder, or they can be paused briefly before resuming. Special clocks called training clocks help children learn to tell time by using visual cues instead of numbers. Clocks can also control other devices based on time, like heating systems, recording devices, or even telescopes that follow the stars. Computers use a steady signal called a clock signal to keep everything running smoothly and accurately.

Time standards

For scientific work, extremely accurate time measurement is important. Atomic clocks, which use the stable vibrations of atoms, provide the most precise timekeeping. These clocks are large, expensive, and need special conditions, but they help set the standard for all other clocks.

Navigation

In the past, sailors needed accurate clocks to determine their position at sea, especially for measuring longitude. This need led to the invention of precise marine chronometers by John Harrison. Today, satellite navigation systems like GPS provide extremely accurate time information directly from the satellites.

Sports and games

Clocks are also important in sports and games. Stopwatches time athletes, chess clocks limit how long players have to make moves, and various game clocks track the length of sports games or specific actions within them.

Culture

In the United Kingdom, clocks have been part of many interesting beliefs and stories. Some legends say that clocks have stopped on their own when someone important nearby passed away. For example, there are stories about clocks stopping at the time of famous kings and queens' deaths.

In Chinese culture, giving a clock as a gift is often avoided, especially to older people. This is because the word for "giving a clock" sounds similar to the phrase meaning "attending a funeral."

Specific types

Clocks come in many forms and are used in many ways. From the simple sundials of ancient times to the precise atomic clocks of today, these devices help us measure and keep track of time. There are many different kinds of clocks, each with its own unique way of telling time.

You can find clocks everywhere — on walls, in pockets, in computers, and even in vehicles. They all share the same basic purpose: to show us the time in a way that is easy to understand.

Awards

Some special awards for clocks and watch making include the Grand Prix d'Horlogerie de Genève (GPHG) and the Goldene Unruh. These awards recognize outstanding achievements in the design and craftsmanship of timepieces.