History of 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. Such measurement requires devices. Devices operating on several different physical processes have been used over the millennia, culminating in the clocks of today.

Sundials and other devices

The sundial, which measures the time of day by the direction of shadows cast by the sun, was widely used in ancient times.

Candle clocksand sticks of incense that burn down at approximately, predictable speeds have also been used to estimate the passing of time. In an hourglass, fine sandpours through a tiny hole at a constant rate and indicates a predetermined passage of an arbitrary period of time.

Water clocks

Water clocks, along with the sundials, are possibly the oldest time-measuring instruments, with the only exceptions being the vertical gnomon and the day-counting tally stick. Given their great antiquity, where and when they first existed are not known and perhaps unknowable. The bowl-shaped outflow is the simplest form of a water clock and is known to have existed in Babylon and in Egypt around the 16th century BC. Some authors, however, write about water clocks appearing as early as 4000 BC.

Early clocks

In 797 (or possibly 801), the Abbasidcaliphof Baghdad, Harun al-Rashid, presented Charlemagnewith an Asian Elephantnamed Abul-Abbastogether with a "particularly elaborate example" of a water clock.

None of the first clocks survived from 13th century Europe, but various mentions in church records reveal some of the early history of the clock.

These early clocks may not have used hands or dials, but “told” the time with audible signals.

A new mechanism

The word clock (from the Latin word clocca, "bell") suggests that it was the sound of bells which also characterized the prototype mechanical clocks that appeared during the 13th century in Europe.

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 powerwere 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.

Outside of Europe, the escapement mechanism had been known and used in medieval China, as the Song Dynastyhorologist and engineer Su Song(1020 - 1101) incorporated it into his astronomical clock-tower of Kaifeng in 1088. However, his astronomical clock and rotating armillary spherestill relied on the use of flowing water (ie. hydraulics), while European clockworks of the following centuries shed this old habit for a more efficient driving power of weights, in addition to the escapement mechanism.

The first mechanical clocks to be driven by weightsand gearswere invented by medieval Muslim engineers. The first geared mechanical clock was invented by the 11th-century Arabengineer Ibn Khalaf al-Muradi in Islamic Spain; the first weight-drivenmechanical clocks, employing a mercury escapement mechanism and a clock facesimilar to an astrolabedial, were also invented by Muslim engineers in the 11th century. A similar weight-driven mechanical clock later appeared in a Spanish languagework compiled from earlier Arabic sources for Alfonso Xin 1277.The knowledge of weight-driven mechanical clocks produced

These mechanical clocks were intended for two main purposes: for signalling 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 interest in astronomy, science, astrology, and how these subjects integrated with the religious philosophy of the time. The astrolabewas 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 dials or hands. They would have announced the canonical hoursor 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.

In 1283, a large clock was installed at Dunstable Priory; its location above the rood screensuggests that it was not a water clock. In 1292, Canterbury Cathedralinstalled a 'great horloge'. Over the next 30 years there are brief mentions of clocks at a number of ecclesiastical institutions in England, Italy, and France. In 1322, a new clock was installed in Norwich, an expensive replacement for an earlier clock installed in 1273. This had a large (2 metre) astronomical dial with automata and bells. The costs of the installation included the full-time employment of two clockkeepersfor two years.

Early astronomical clocks

Besides the Chinese astronomical clock of Su Song in 1088 mentioned above, in Europe there were the clocks constructed by Richard of Wallingfordin St Albansby 1336, and by Giovanni de Dondiin Paduafrom 1348 to 1364. They no longer exist, but detailed descriptions of their design and construction survive, and modern reproductions have been made. They illustrate how quickly the theory of the mechanical clock had been translated into practical constructions, and also that one of the many impulses to their development had been the desire of astronomers to investigate celestial phenomena.

Wallingford's clock had a large astrolabe-type dial, showing the sun, the moon's age, phase, and node, a star map, and possibly the planets. In addition, it had a wheel of fortune and an indicator of the state of the tide at London Bridge. Bells rang every hour, the number of strokes indicating the time.

Dondi's clock was a seven-sided construction, 1 metre high, with dials showing the time of day, including minutes, the motions of all the known planets, an automatic calendar of fixed and movable feasts, and an eclipse prediction hand rotating once every 18 years.

It is not known how accurate or reliable these clocks would have been. They were probably adjusted manually every day to compensate for errors caused by wear and imprecise manufacture.

The Salisbury Cathedral clock, built in 1386, is considered to be the world's oldest surviving mechanical clock that strikes the hours.

Later developments

Clockmakers developed their art in various ways. 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.

Spring-driven clocks appeared during the 1400s, although they are often erroneously credited to Nürnberg watchmaker Peter Henlein (or Henle, or Hele) around 1511. The earliest existing spring driven clock is the chamber clock given to Peter the Good, Duke of Burgundy, around 1430, now in the Germanisches Nationalmuseum. Spring power presented clockmakers with a new problem; how to keep the clock movement running at a constant rate as the spring ran down. This resulted in the invention of the stackfreed and the fusee in the 1400s, and many other innovations, down to the invention of the modern going barrel in 1760.

The first record of a minute hand on a clock is 1475, in the Almanus Manuscript of Brother Paul.

During the 15th and 16th centuries, clockmaking flourished, particularly in the metalworking towns of Nurembergand Augsburg, and in France, Blois. Some of the more basic table clocks have only one time-keeping hand, with the dial between the hour markers being divided into four equal parts making the clocks readable to the nearest 15 minutes. Other clocks were exhibitions of craftsmanship and skill, incorporating astronomical indicators and musical movements. The cross-beat escapement was developed in 1585 by Jost Burgi, who also developed the remontoire. Burgi's accurate clocks helped Tycho Braheto observe astronomical events with much greater precision than before.

The first mechanical alarm clock was invented by the Ottomanengineer Taqi al-Din. His alarm clock was capable of sounding at a specified time, achieved by placing a peg on the dial wheel. At the requested time, the peg activated a ringing device. In the same treatise, he described a mechanical astronomical clockcalled the "observational clock", which was the first to measure time in minutes. He made use of his mathematical knowledgeto design three dialswhich showed the hours, degrees and minutes. He later improved the design of his observational clock to measure time in secondsin an astronomical treatise written at his Istanbul observatory of al-Din(1577-1580). He described his observational clock as "a mechanical clock with three dials which show the hours, the minutes, and the seconds." This was an important innovation in 16th-century practical astronomy, as previous clocks were not accurate enough to be used for astronomical purposes. He further improved the observational clock, using only one dial to represent the hours, minutes and seconds, describing it as "a mechanical clock with a dial showing the hours, minutes and seconds and we divided every minute into five seconds.

Another early record of a second hand on a clock dates back to about 1560, on a clock now in the Fremersdorf collection. However, this clock could not have been accurate, and the second hand was probably for indicating that the clock was working.

The next development in accuracy occurred after 1657 with the invention of the pendulum clock. Galileohad 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 (99.38 cm or 39.13 inches for the one second movement) and had the first pendulum-driven clock made. In 1670, the English clockmaker William Clementcreated the anchor escapement, an improvement over Huygens' crown escapement. Within just one generation, minute hands and then secondhands were added.

The excitement over the pendulum clock had attracted the attention of designers resulting in a proliferation of clock forms. Notably, the longcase clock (also known as the grandfather clock) was created to house the pendulum and works. The English clockmaker William Clementis also credited with developing this form in 1670 or 1671. It was also at this time that clock cases began to be made of wood and clock faces to utilize enamelas well as hand-painted ceramics.

On November 17, 1797, Eli Terry received his first patent for a clock. Terry is known as the founder of the American clock-making industry.

Alexander Bain, Scottish clockmaker, patented the electric clock in 1840. The electric clock's mainspring is wound either with an electric motoror with an electro-magnetand armature. In 1841, he first patented the electromagnetic pendulum.