History of timekeeping devices - AbsoluteAstronomy.com

For thousands of years, devices have been used to measure and keep track of time

Time

Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

. The current sexagesimal system

Numeral system

A numeral system is a writing system for expressing numbers, that is a mathematical notation for representing numbers of a given set, using graphemes or symbols in a consistent manner....

of time measurement

Systems of measurement

A system of measurement is a set of units which can be used to specify anything which can be measured and were historically important, regulated and defined because of trade and internal commerce...

dates to approximately 2000 BC, in Sumer

Sumer

Sumer was a civilization and historical region in southern Mesopotamia, modern Iraq during the Chalcolithic and Early Bronze Age....

. The Ancient Egypt

Ancient Egypt

Ancient Egypt was an ancient civilization of Northeastern Africa, concentrated along the lower reaches of the Nile River in what is now the modern country of Egypt. Egyptian civilization coalesced around 3150 BC with the political unification of Upper and Lower Egypt under the first pharaoh...

ians divided the day into two 12-hour periods, and used large obelisk

Obelisk

An obelisk is a tall, four-sided, narrow tapering monument which ends in a pyramid-like shape at the top, and is said to resemble a petrified ray of the sun-disk. A pair of obelisks usually stood in front of a pylon...

s to track the movement of the Sun. They also developed water clock

Water clock

A water clock or clepsydra is any timepiece in which time is measured by the regulated flow of liquid into or out from a vessel where the amount is then measured.Water clocks, along with sundials, are likely to be the oldest time-measuring instruments, with the only exceptions...

s, which were probably first used in the Precinct of Amun-Re, and later outside Egypt as well; they were employed frequently by the Ancient Greeks

Ancient Greece

Ancient Greece is a civilization belonging to a period of Greek history that lasted from the Archaic period of the 8th to 6th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and the Byzantine era. Included in Ancient Greece is the...

, who called them clepsydrae. The Shang Dynasty

Shang Dynasty

The Shang Dynasty or Yin Dynasty was, according to traditional sources, the second Chinese dynasty, after the Xia. They ruled in the northeastern regions of the area known as "China proper" in the Yellow River valley...

is believed to have used the outflow water clock around the same time, devices which were introduced from Mesopotamia

Mesopotamia

Mesopotamia is a toponym for the area of the Tigris–Euphrates river system, largely corresponding to modern-day Iraq, northeastern Syria, southeastern Turkey and southwestern Iran.Widely considered to be the cradle of civilization, Bronze Age Mesopotamia included Sumer and the...

as early as 2000 BC. Other ancient timekeeping devices include the candle clock

Candle clock

A candle clock is a thin candle with consistently spaced markings , that when burned, indicate the passage of periods of time. While no longer used today, candle clocks provided an effective way to tell time indoors, at night, or on a cloudy day...

, used in China, Japan, England and Iraq; the timestick, widely used in India and Tibet, as well as some parts of Europe; and the hourglass

Hourglass

An hourglass measures the passage of a few minutes or an hour of time. It has two connected vertical glass bulbs allowing a regulated trickle of material from the top to the bottom. Once the top bulb is empty, it can be inverted to begin timing again. The name hourglass comes from historically...

, which functioned similarly to a water clock.

The earliest clock

Clock

A clock is an instrument used 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 mechanism has traditionally been known as a timepiece...

s relied on shadows cast by the sun, and hence were not useful in cloudy weather or at night and required recalibration as the seasons changed (if the gnomon

Gnomon

The gnomon is the part of a sundial that casts the shadow. Gnomon is an ancient Greek word meaning "indicator", "one who discerns," or "that which reveals."It has come to be used for a variety of purposes in mathematics and other fields....

was not aligned with the Earth's axis). The earliest known clock with a water-powered escapement

Escapement

In mechanical watches and clocks, an escapement is a device that transfers energy to the timekeeping element and enables counting the number of oscillations of the timekeeping element...

mechanism, which transferred rotational energy into intermittent motions, dates back to 3rd century BC ancient Greece

Ancient Greece

; Chinese engineers later invented clocks incorporating mercury

Mercury (element)

Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

-powered escapement mechanisms in the 10th century, followed by Arabic engineers inventing water clocks driven by gear

Gear

A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....

s and weights

Maintaining power

In horology, a maintaining power is a mechanism for keeping a clock or watch going while it is being wound.-Huygens:The weight drive used by Christiaan Huygens in his early clocks acts as a maintaining power...

in the 11th century.

Mechanical clocks employing the verge escapement

Verge escapement

The verge escapement is the earliest known type of mechanical escapement, the mechanism in a mechanical clock that controls its rate by advancing the gear train at regular intervals or 'ticks'. Its origin is unknown. Verge escapements were used from the 14th century until about 1800 in clocks...

mechanism were invented in Europe at the turn of the 14th century, and became the standard timekeeping device until the spring

Spring (device)

A spring is an elastic object used to store mechanical energy. Springs are usually made out of spring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after fabrication...

-powered clock and pocket watch

Pocket watch

A pocket watch is a watch that is made to be carried in a pocket, as opposed to a wristwatch, which is strapped to the wrist. They were the most common type of watch from their development in the 16th century until wristwatches became popular after World War I during which a transitional design,...

in the 16th century, followed by the pendulum clock

Pendulum clock

A pendulum clock is a clock that uses a pendulum, a swinging weight, as its timekeeping element. The advantage of a pendulum for timekeeping is that it is a resonant device; it swings back and forth in a precise time interval dependent on its length, and resists swinging at other rates...

in the 17th century. During the 20th century, quartz oscillators were invented, followed by atomic clock

Atomic clock

An atomic clock is a clock that uses an electronic transition frequency in the microwave, optical, or ultraviolet region of the electromagnetic spectrum of atoms as a frequency standard for its timekeeping element...

s. Although first used in laboratories, quartz oscillators were both easy to produce and accurate, leading to their use in wristwatches. Atomic clocks are far more accurate than any previous timekeeping device, and are used to calibrate other clocks and to calculate the proper time

International Atomic Time

International Atomic Time is a high-precision atomic coordinate time standard based on the notional passage of proper time on Earth's geoid...

on Earth; a standardized civil system, Coordinated Universal Time

Coordinated Universal Time

Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...

, is based on atomic time.

Early timekeeping devices

Many ancient civilizations observed astronomical bodies

Astronomical object

Astronomical objects or celestial objects are naturally occurring physical entities, associations or structures that current science has demonstrated to exist in the observable universe. The term astronomical object is sometimes used interchangeably with astronomical body...

, often the Sun

Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

and Moon

Moon

The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

, to determine times, dates, and seasons. Methods of sexagesimal timekeeping, now common in Western society

Western world

The Western world, also known as the West and the Occident , is a term referring to the countries of Western Europe , the countries of the Americas, as well all countries of Northern and Central Europe, Australia and New Zealand...

, first originated nearly 4,000 years ago in Mesopotamia

Mesopotamia

and Egypt

Egypt

Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...

; a similar system was developed later in Mesoamerica

Mesoamerica

Mesoamerica is a region and culture area in the Americas, extending approximately from central Mexico to Belize, Guatemala, El Salvador, Honduras, Nicaragua, and Costa Rica, within which a number of pre-Columbian societies flourished before the Spanish colonization of the Americas in the 15th and...

. The first calendar

Calendar

A calendar is a system of organizing days for social, religious, commercial, or administrative purposes. This is done by giving names to periods of time, typically days, weeks, months, and years. The name given to each day is known as a date. Periods in a calendar are usually, though not...

s may have been created during the last glacial period, by hunter-gatherer

Hunter-gatherer

A hunter-gatherer or forage society is one in which most or all food is obtained from wild plants and animals, in contrast to agricultural societies which rely mainly on domesticated species. Hunting and gathering was the ancestral subsistence mode of Homo, and all modern humans were...

s who employed tools such as sticks and bones to track the phases of the moon or the seasons. Stone circle

Stone circle

A stone circle is a monument of standing stones arranged in a circle. Such monuments have been constructed across the world throughout history for many different reasons....

s, such as England's Stonehenge

Stonehenge

Stonehenge is a prehistoric monument located in the English county of Wiltshire, about west of Amesbury and north of Salisbury. One of the most famous sites in the world, Stonehenge is composed of a circular setting of large standing stones set within earthworks...

, were built in various parts of the world, especially in Prehistoric Europe

Prehistoric Europe

Prehistoric Europe refers to the prehistorical period of Europe, usually taken to refer to human prehistory since the Lower Paleolithic, but in principle also extending to geological time scale - for which see Geological history of Europe....

, and are thought to have been used to time and predict seasonal and annual events such as equinox

Equinox

An equinox occurs twice a year, when the tilt of the Earth's axis is inclined neither away from nor towards the Sun, the center of the Sun being in the same plane as the Earth's equator...

es or solstice

Solstice

A solstice is an astronomical event that happens twice each year when the Sun's apparent position in the sky, as viewed from Earth, reaches its northernmost or southernmost extremes...

s. As those megalith

Megalith

A megalith is a large stone that has been used to construct a structure or monument, either alone or together with other stones. Megalithic describes structures made of such large stones, utilizing an interlocking system without the use of mortar or cement.The word 'megalith' comes from the Ancient...

ic civilizations left no recorded history

Recorded history

Recorded history is the period in history of the world after prehistory. It has been written down using language, or recorded using other means of communication. It starts around the 4th millennium BC, with the invention of writing.-Historical accounts:...

, little is known of their calendars or timekeeping methods.

3500 BC – 500 BC

Sundials have their origin in shadow clocks, which were the first devices used for measuring the parts of a day. The oldest known shadow clock is from Egypt, and was made from green schist

Schist

The schists constitute a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is...

. Ancient Egyptian obelisks, constructed about 3500 BC, are also among the earliest shadow clocks.

Egyptian shadow clocks divided daytime

Daytime (astronomy)

On Earth, daytime is roughly the period on any given point of the planet's surface during which it experiences natural illumination from indirect or direct sunlight....

into 10 parts, with an additional four "twilight

Twilight

Twilight is the time between dawn and sunrise or between sunset and dusk, during which sunlight scattering in the upper atmosphere illuminates the lower atmosphere, and the surface of the earth is neither completely lit nor completely dark. The sun itself is not directly visible because it is below...

hours"—two in the morning, and two in the evening. One type of shadow clock consisted of a long stem with five variable marks and an elevated crossbar which cast a shadow over those marks. It was positioned eastward in the morning, and was turned west at noon. Obelisks functioned in much the same manner: the shadow cast on the markers around it allowed the Egyptians to calculate the time. The obelisk also indicated whether it was morning or afternoon, as well as the summer

Summer solstice

The summer solstice occurs exactly when the axial tilt of a planet's semi-axis in a given hemisphere is most inclined towards the star that it orbits. Earth's maximum axial tilt to our star, the Sun, during a solstice is 23° 26'. Though the summer solstice is an instant in time, the term is also...

and winter

Winter solstice

Winter solstice may refer to:* Winter solstice, astronomical event* Winter Solstice , former band* Winter Solstice: North , seasonal songs* Winter Solstice , 2005 American film...

solstice

Solstice

A solstice is an astronomical event that happens twice each year when the Sun's apparent position in the sky, as viewed from Earth, reaches its northernmost or southernmost extremes...

s. A third shadow clock, developed c.

Circa

Circa , usually abbreviated c. or ca. , means "approximately" in the English language, usually referring to a date...

1500 BC, was similar in shape to a bent T-square

T-square

A T-square is a technical drawing instrument used by draftsmen primarily as a guide for drawing horizontal lines on a drafting table. It may also guide a triangle to draw vertical or diagonal lines. Its name comes from the general shape of the instrument where the horizontal member of the T slides...

. It measured the passage of time by the shadow cast by its crossbar on a non-linear rule. The T was oriented eastward in the mornings, and turned around at noon

Noon

Noon is usually defined as 12 o'clock in the daytime. The word noon is also used informally to mean midday regarding the location of the sun not the middle of a persons day. Although this is a time around the middle of the day when people in many countries take a lunch break...

, so that it could cast its shadow in the opposite direction.

Although accurate, shadow clocks relied on the sun, and so were useless at night and in cloudy weather. The Egyptians therefore developed a number of alternative timekeeping instruments, including water clocks, hourglasses, and a system for tracking star movements. The oldest description of a water clock is from the tomb inscription of the 16th-century BC Egyptian court official Amenemhet, identifying him as its inventor. There were several types of water clocks, some more elaborate than others. One type consisted of a bowl with small holes in its bottom, which was floated on water and allowed to fill at a near-constant rate; markings on the side of the bowl indicated elapsed time, as the surface of the water reached them. The oldest-known waterclock was found in the tomb of pharaoh

Pharaoh

Pharaoh is a title used in many modern discussions of the ancient Egyptian rulers of all periods. The title originates in the term "pr-aa" which means "great house" and describes the royal palace...

Amenhotep I

Amenhotep I was the second Pharaoh of the 18th dynasty of Egypt. His reign is generally dated from 1526 to 1506 BC. He was born to Ahmose I and Ahmose-Nefertari, but had at least two elder brothers, Ahmose-ankh and Ahmose Sapair, and was not expected to inherit the throne...

(1525–1504 BC), suggesting that they were first used in ancient Egypt. The ancient Egyptians are also believed to be the inventors of the hourglass

Hourglass

, which consisted of two vertically aligned glass chambers connected by a small opening. When the hourglass was turned over, grains of sand fell at a constant rate from one chamber to the other. Another Egyptian method of determining the time during the night was using plumb-lines

Plumb-bob

A plumb-bob or a plummet is a weight, usually with a pointed tip on the bottom, that is suspended from a string and used as a vertical reference line, or plumb-line....

called merkhet

Merkhet

The merkhet was an ancient timekeeping instrument. It involved the use of a bar with a plumb line, attached to a wooden handle...

s. In use since at least 600 BC, two of these instruments were aligned with Polaris

Polaris

Polaris |Alpha]] Ursae Minoris, commonly North Star or Pole Star, also Lodestar) is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole, making it the current northern pole star....

, the north pole star

Pole star

The term "Pole Star" usually refers to Polaris, which is the current northern pole star, also known as the North Star.In general, however, a pole star is a visible star, especially a prominent one, that is approximately aligned with the Earth's axis of rotation; that is, a star whose apparent...

, to create a north–south meridian

Meridian (astronomy)

This article is about the astronomical concept. For other uses of the word, see Meridian.In the sky, a meridian is an imaginary great circle on the celestial sphere. It passes through the north point on the horizon, through the celestial pole, up to the zenith, through the south point on the...

. The time was accurately measured by observing certain stars as they crossed the line created with the merkhets.

500 BC – 1 BC

Water clock

s, or clepsydrae, were commonly used in Ancient Greece

Ancient Greece

following their introduction by Plato

Plato

Plato , was a Classical Greek philosopher, mathematician, student of Socrates, writer of philosophical dialogues, and founder of the Academy in Athens, the first institution of higher learning in the Western world. Along with his mentor, Socrates, and his student, Aristotle, Plato helped to lay the...

, who also invented a water-based alarm clock

Alarm clock

An alarm clock is a clock that is designed to make a loud sound at a specific time. The primary use of these clocks is to awaken people from their night's sleep or short naps; they are sometimes used for other reminders as well. To stop the sound, a button or handle on the clock is pressed; but...

. One account of Plato's alarm clock describes it as depending on the nightly overflow of a vessel containing lead balls, which floated in a columnar vat. The vat held a steadily increasing amount of water, supplied by a cistern. By morning, the vessel would have floated high enough to tip over, causing the lead balls to cascade onto a copper platter. The resultant clangor would then awaken Plato's students at the Academy

Platonic Academy

The Academy was founded by Plato in ca. 387 BC in Athens. Aristotle studied there for twenty years before founding his own school, the Lyceum. The Academy persisted throughout the Hellenistic period as a skeptical school, until coming to an end after the death of Philo of Larissa in 83 BC...

. Another possibility is that it comprised two jars, connected by a siphon

Siphon

The word siphon is sometimes used to refer to a wide variety of devices that involve the flow of liquids through tubes. But in the English language today, the word siphon usually refers to a tube in an inverted U shape which causes a liquid to flow uphill, above the surface of the reservoir,...

. Water emptied until it reached the siphon, which transported the water to the other jar. There, the rising water would force air through a whistle, sounding an alarm. The Greeks and Chaldeans regularly maintained timekeeping records as an essential part of their astronomical observations.

Greek

Ancient Greece

astronomer, Andronicus of Cyrrhus

Andronicus of Cyrrhus

Andronicus of Cyrrhus or Andronicus Cyrrhestes,son of Hermias, was a Greek astronomer who flourished about 100 BC....

, supervised the construction of the Tower of the Winds

Tower of the Winds

The Tower of the Winds, also called horologion , is an octagonal Pentelic marble clocktower on the Roman agora in Athens. The structure features a combination of sundials, a water clock and a wind vane...

in Athens in the 1st century B.C.

In Greek tradition, clepsydrae were used in court

Court

A court is a form of tribunal, often a governmental institution, with the authority to adjudicate legal disputes between parties and carry out the administration of justice in civil, criminal, and administrative matters in accordance with the rule of law...

; later, the Romans

Ancient Rome

Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....

adopted this practice, as well. There are several mentions of this in historical records and literature of the era; for example, in Theaetetus
Theaetetus (dialogue)
The Theaetetus is one of Plato's dialogues concerning the nature of knowledge. The framing of the dialogue begins when Euclides tells his friend Terpsion that he had written a book many years ago based on what Socrates had told him of a conversation he'd had with Theaetetus when Theaetetus was...

, Plato

Plato

says that "Those men, on the other hand, always speak in haste, for the flowing water urges them on". Another mention occurs in Lucius Apuleius' The Golden Ass
The Golden Ass
The Metamorphoses of Apuleius, which St. Augustine referred to as The Golden Ass , is the only Latin novel to survive in its entirety....

: "The Clerk of the Court began bawling again, this time summoning the chief witness for the prosecution to appear. Up stepped an old man, whom I did not know. He was invited to speak for as long as there was water in the clock; this was a hollow globe into which water was poured through a funnel in the neck, and from which it gradually escaped through fine perforations at the base". The clock in Apuleius' account was one of several types of water clock used. Another consisted of a bowl with a hole in its centre, which was floated on water. Time was kept by observing how long the bowl took to fill with water.

Although clepsydrae were more useful than sundials—they could be used indoors, during the night, and also when the sky was cloudy—they were not as accurate; the Greeks, therefore, sought a way to improve their water clocks. Although still not as accurate as sundials, Greek water clocks became more accurate around 325 BC, and they were adapted to have a face with an hour hand, making the reading of the clock more precise and convenient. One of the more common problems in most types of clepsydrae was caused by water pressure: when the container holding the water was full, the increased pressure caused the water to flow more rapidly. This problem was addressed by Greek and Roman horologists

Horology

Horology is the art or science of measuring time. Clocks, watches, clockwork, sundials, clepsydras, timers, time recorders and marine chronometers are all examples of instruments used to measure time.People interested in horology are called horologists...

beginning in 100 BC, and improvements continued to be made in the following centuries. To counteract the increased water flow, the clock's water containers—usually bowls or jugs—were given a conical shape; positioned with the wide end up, a greater amount of water had to flow out in order to drop the same distance as when the water was lower in the cone. Along with this improvement, clocks were constructed more elegantly in this period, with hours marked by gongs, doors opening to miniature figurines, bells, or moving mechanisms. There were some remaining problems, however, which were never solved, such as the effect of temperature. Water flows more slowly when cold, or may even freeze.

Although the Greeks and Romans did much to advance water clock technology, they still continued to use shadow clocks. The mathematician and astronomer Theodosius of Bithynia

Theodosius of Bithynia

Theodosius of Bithynia was a Greek astronomer and mathematician who wrote the Sphaerics, a book on the geometry of the sphere. Born in Tripolis, in Bithynia, Theodosius is cited by Vitruvius as having invented a sundial suitable for any place on Earth...

, for example, is said to have invented a universal sundial that was accurate anywhere on Earth, though little is known about it. Others wrote of the sundial in the mathematics and literature of the period. Marcus Vitruvius Pollio, the Roman author of De Architectura
De architectura
' is a treatise on architecture written by the Roman architect Vitruvius and dedicated to his patron, the emperor Caesar Augustus, as a guide for building projects...

, wrote on the mathematics of gnomon

Gnomon

s, or sundial blades. During the reign of Emperor Augustus

Augustus

Augustus ;23 September 63 BC – 19 August AD 14) is considered the first emperor of the Roman Empire, which he ruled alone from 27 BC until his death in 14 AD.The dates of his rule are contemporary dates; Augustus lived under two calendars, the Roman Republican until 45 BC, and the Julian...

, the Romans constructed the largest sundial ever built, the Solarium Augusti

Solarium Augusti

The Solarium Augusti was a sundial in ancient Rome, the largest of the ancient era. It was erected by Emperor Augustus, with a 30-metre Egyptian red granite obelisk that he had imported from Heliopolis...

. Its gnomon was an obelisk from Heliopolis

Heliopolis (ancient)

Heliopolis was one of the oldest cities of ancient Egypt, the capital of the 13th Lower Egyptian nome that was located five miles east of the Nile to the north of the apex of the Nile Delta...

. Similarly, the obelisk from Campus Martius

Campus Martius

The Campus Martius , was a publicly owned area of ancient Rome about in extent. In the Middle Ages, it was the most populous area of Rome...

was used as the gnomon for Augustus' zodiacal sundial. Pliny the Elder

Pliny the Elder

Gaius Plinius Secundus , better known as Pliny the Elder, was a Roman author, naturalist, and natural philosopher, as well as naval and army commander of the early Roman Empire, and personal friend of the emperor Vespasian...

records that the first sundial in Rome arrived in 264 BC, looted from Catania

Catania

Catania is an Italian city on the east coast of Sicily facing the Ionian Sea, between Messina and Syracuse. It is the capital of the homonymous province, and with 298,957 inhabitants it is the second-largest city in Sicily and the tenth in Italy.Catania is known to have a seismic history and...

, Sicily

Sicily

Sicily is a region of Italy, and is the largest island in the Mediterranean Sea. Along with the surrounding minor islands, it constitutes an autonomous region of Italy, the Regione Autonoma Siciliana Sicily has a rich and unique culture, especially with regard to the arts, music, literature,...

; according to him, it gave the incorrect time until the markings and angle appropriate for Rome's latitude were used—a century later.

Water clocks

Joseph Needham

Noel Joseph Terence Montgomery Needham, CH, FRS, FBA , also known as Li Yuese , was a British scientist, historian and sinologist known for his scientific research and writing on the history of Chinese science. He was elected a fellow of the Royal Society in 1941, and as a fellow of the British...

speculated that the introduction of the outflow clepsydra to China, perhaps from Mesopotamia

Mesopotamia

, occurred as far back as the 2nd millennium BC, during the Shang Dynasty

Shang Dynasty

, and at the latest by the 1st millennium BC. By the beginning of the Han Dynasty

Han Dynasty

The Han Dynasty was the second imperial dynasty of China, preceded by the Qin Dynasty and succeeded by the Three Kingdoms . It was founded by the rebel leader Liu Bang, known posthumously as Emperor Gaozu of Han. It was briefly interrupted by the Xin Dynasty of the former regent Wang Mang...

, in 202 BC, the outflow clepsydra was gradually replaced by the inflow clepsydra, which featured an indicator rod on a float. To compensate for the falling pressure head

Pressure head

Pressure head is a term used in fluid mechanics to represent the internal energy of a fluid due to the pressure exerted on its container. It may also be called static pressure head or simply static head...

in the reservoir, which slowed timekeeping as the vessel filled, Zhang Heng

Zhang Heng

Zhang Heng was a Chinese astronomer, mathematician, inventor, geographer, cartographer, artist, poet, statesman, and literary scholar from Nanyang, Henan. He lived during the Eastern Han Dynasty of China. He was educated in the capital cities of Luoyang and Chang'an, and began his career as a...

added an extra tank between the reservoir and the inflow vessel. Around 550 AD, Yin Gui was the first in China to write of the overflow or constant-level tank added to the series, which was later described in detail by the inventor Shen Kuo

Shen Kuo

Shen Kuo or Shen Gua , style name Cunzhong and pseudonym Mengqi Weng , was a polymathic Chinese scientist and statesman of the Song Dynasty...

. Around 610, this design was trumped by two Sui Dynasty

Sui Dynasty

The Sui Dynasty was a powerful, but short-lived Imperial Chinese dynasty. Preceded by the Southern and Northern Dynasties, it ended nearly four centuries of division between rival regimes. It was followed by the Tang Dynasty....

inventors, Geng Xun and Yuwen Kai, who were the first to create the balance clepsydra, with standard positions for the steelyard balance

Steelyard balance

A steelyard balance or steelyard is a straight-beam balance with arms of unequal length. It incorporates a counterweight which slides along the calibrated longer arm to counterbalance the load and indicate its weight...

. Joseph Needham states that:
Between 270 BC

270 BC

Year 270 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Clepsina and Blasio...

and 500 AD, Hellenistic

Hellenistic civilization

Hellenistic civilization represents the zenith of Greek influence in the ancient world from 323 BCE to about 146 BCE...

(Ctesibius

Ctesibius

Ctesibius or Ktesibios or Tesibius was a Greek inventor and mathematician in Alexandria, Ptolemaic Egypt. He wrote the first treatises on the science of compressed air and its uses in pumps...

, Hero of Alexandria

Hero of Alexandria

Hero of Alexandria was an ancient Greek mathematician and engineerEnc. Britannica 2007, "Heron of Alexandria" who was active in his native city of Alexandria, Roman Egypt...

, Archimedes

Archimedes

Archimedes of Syracuse was a Greek mathematician, physicist, engineer, inventor, and astronomer. Although few details of his life are known, he is regarded as one of the leading scientists in classical antiquity. Among his advances in physics are the foundations of hydrostatics, statics and an...

) and Roman

Ancient Rome

horologists

Horology

and astronomer

Astronomer

An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...

s were developing more elaborate mechanized water clocks. The added complexity was aimed at regulating the flow and at providing fancier displays of the passage of time. For example, some water clocks rang bells

Bell (instrument)

A bell is a simple sound-making device. The bell is a percussion instrument and an idiophone. Its form is usually a hollow, cup-shaped object, which resonates upon being struck...

and gong

Gong

A gong is an East and South East Asian musical percussion instrument that takes the form of a flat metal disc which is hit with a mallet....

s, while others opened doors and windows to show figurines of people, or moved pointers, and dials. Some even displayed astrological

Astrology

Astrology consists of a number of belief systems which hold that there is a relationship between astronomical phenomena and events in the human world...

models of the universe.

Some of the most elaborate water clocks were designed by Muslim engineers. In particular, the water clocks by Al-Jazari

Al-Jazari

Abū al-'Iz Ibn Ismā'īl ibn al-Razāz al-Jazarī was a Muslim polymath: a scholar, inventor, mechanical engineer, craftsman, artist, mathematician and astronomer from Al-Jazira, Mesopotamia, who lived during the Islamic Golden Age...

in 1206 are credited for going "well beyond anything" that had preceded them. In his treatise, he describes one of his water clocks, the elephant clock

Elephant clock

The elephant clock was a medieval islamic invention by al-Jazari , consisting of a weight powered water clock in the form of an elephant. The various elements of the clock are in the housing on top of the elephant...

. The clock recorded the passage of temporal hours, which meant that the rate of flow had to be changed daily to match the uneven length of days throughout the year. To accomplish this, the clock had two tanks: the top tank was connected to the time indicating mechanisms and the bottom was connected to the flow control regulator

Regulator (automatic control)

In automatic control, a regulator is a device which has the function of maintaining a designated characteristic. It performs the activity of managing or maintaining a range of values in a machine. The measurable property of a device is managed closely by specified conditions or an advance set...

. At daybreak the tap was opened and water flowed from the top tank to the bottom tank via a float regulator that maintained a constant pressure in the receiving tank.

Candle clocks

It is not known specifically where and when candle clock

Candle clock

s were first used; however, their earliest mention comes from a Chinese poem, written in 520 by You Jianfu. According to the poem, the graduated candle was a means of determining time at night. Similar candles were used in Japan until the early 10th century.

The candle clock most commonly mentioned and written of is attributed to King Alfred the Great

Alfred the Great

Alfred the Great was King of Wessex from 871 to 899.Alfred is noted for his defence of the Anglo-Saxon kingdoms of southern England against the Vikings, becoming the only English monarch still to be accorded the epithet "the Great". Alfred was the first King of the West Saxons to style himself...

. It consisted of six candles made from 72 pennyweight

Pennyweight

A pennyweight is a unit of mass that is equal to 24 grains, 1/20 of a troy ounce, 1/240 of a troy pound, approximately 0.054857 avoirdupois ounce and exactly 1.55517384 grams....

s of wax, each 12 inches (30.5 cm) high, and of uniform thickness, marked every inch (2.5 cm). As these candles burned for about four hours, each mark represented 20 minutes. Once lit, the candles were placed in wooden framed glass boxes, to prevent the flame from extinguishing.

The most sophisticated candle clocks of their time were those of Al-Jazari

Al-Jazari

in 1206. One of his candle clocks included a dial

Dial (measurement)

A dial is generally a flat surface, circular or rectangular, with numbers or similar markings on it, used for displaying the setting or output of a timepiece, radio, clock, watch, or measuring instrument...

to display the time and, for the first time, employed a bayonet fitting

Bayonet mount

A bayonet mount or bayonet connector is a fastening mechanism consisting of a male side with one or more pins, and a female receptor with matching L slots and spring to keep the two parts locked together....

, a fastening mechanism

Fastener

A fastener is a hardware device that mechanically joins or affixes two or more objects together.Fasteners can also be used to close a container such as a bag, a box, or an envelope; or they may involve keeping together the sides of an opening of flexible material, attaching a lid to a container,...

still used in modern times. Donald Routledge Hill

Donald Routledge Hill

Donald Routledge Hill was an English engineer and historian of science and technology.Alongside more general works on the history of technology, he wrote works on the history of medieval Arabic science and technology, and translated The Book of Knowledge of Ingenious Mechanical Devices of the...

described Al-Jazari's candle clocks as follows:

A variation on this theme were oil-lamp clock

Oil-lamp clock

Oil-lamp clocks are clocks consisting of a graduated glass reservoir to hold oil - usually whale oil, which burned cleanly and evenly - supplying the fuel for a built-in lamp. As the level in the reservoir dropped, it provided a rough measure of the passage of time....

s. These early timekeeping devices consisted of a graduated glass reservoir to hold oil — usually whale oil, which burned cleanly and evenly — supplying the fuel for a built-in lamp. As the level in the reservoir dropped, it provided a rough measure of the passage of time.

Incense clocks

In addition to water, mechanical, and candle clocks, incense clock

Incense clock

The incense clock is a Chinese timekeeping device that appeared during the Song Dynasty and spread to neighboring countries such as Japan. The clocks' bodies are effectively specialized censers that hold incense sticks or powdered incense that have been manufactured and calibrated to a known rate...

s were used in the Far East

Far East

The Far East is an English term mostly describing East Asia and Southeast Asia, with South Asia sometimes also included for economic and cultural reasons.The term came into use in European geopolitical discourse in the 19th century,...

, and were fashioned in several different forms. Incense

Incense

Incense is composed of aromatic biotic materials, which release fragrant smoke when burned. The term "incense" refers to the substance itself, rather than to the odor that it produces. It is used in religious ceremonies, ritual purification, aromatherapy, meditation, for creating a mood, and for...

clocks were first used in China around the 6th century; in Japan, one still exists in the Shōsōin

Shosoin

The is the treasure house that belongs to Tōdai-ji, Nara The building is in the azekura log-cabin style, with a raised floor. It lies to the northwest of the Daibutsuden...

, although its characters are not Chinese, but Devanagari

Devanagari

Devanagari |deva]]" and "nāgarī" ), also called Nagari , is an abugida alphabet of India and Nepal...

. Due to their frequent use of Devanagari characters, suggestive of their use in Buddhist ceremonies, Edward H. Schafer

Edward H. Schafer

Edward Hetzel Schafer, was a leading historian of Tang Dynasty China. He wrote ground-breaking works such as The Golden Peaches of Samarkand: A study of Tang exotics and The Vermilion Bird: T'ang images of the South. Schafer wrote his Ph.D...

speculated that incense clocks were invented in India

India

India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

. Although similar to the candle clock, incense clocks burned evenly and without a flame; therefore, they were more accurate and safer for indoor use.

Several types of incense clock have been found, the most common forms include the incense stick and incense seal. An incense stick clock was an incense stick with calibrations; most were elaborate, sometimes having threads, with weights attached, at even intervals. The weights would drop onto a platter or gong below, signifying that a certain amount of time had elapsed. Some incense clocks were held in elegant trays; open-bottomed trays were also used, to allow the weights to be used together with the decorative tray. Sticks of incense with different scents were also used, so that the hours were marked by a change in fragrance. The incense sticks could be straight or spiraled; the spiraled ones were longer, and were therefore intended for long periods of use, and often hung from the roofs of homes and temples.

In Japan, a geisha

Geisha

, Geiko or Geigi are traditional, female Japanese entertainers whose skills include performing various Japanese arts such as classical music and dance.-Terms:...

was paid for the number of senkodokei (incense sticks) that had been consumed while she was present, a practice which continued until 1924. Incense seal clocks were used for similar occasions and events as the stick clock; while religious purposes were of primary importance, these clocks were also popular at social gatherings, and were used by Chinese scholars and intellectuals. The seal was a wooden or stone disk with one or more grooves etched in it into which incense was placed. These clocks were common in China, but were produced in fewer numbers in Japan. To signal the passage of a specific amount of time, small pieces of fragrant woods, resins, or different scented incenses could be placed on the incense powder trails. Different powdered incense clocks used different formulations of incense, depending on how the clock was laid out. The length of the trail of incense, directly related to the size of the seal, was the primary factor in determining how long the clock would last; all burned for long periods of time, ranging between 12 hours and a month.

While early incense seals were made of wood or stone, the Chinese gradually introduced disks made of metal, most likely beginning during the Song dynasty

Song Dynasty

The Song Dynasty was a ruling dynasty in China between 960 and 1279; it succeeded the Five Dynasties and Ten Kingdoms Period, and was followed by the Yuan Dynasty. It was the first government in world history to issue banknotes or paper money, and the first Chinese government to establish a...

. This allowed craftsmen to more easily create both large and small seals, as well as design and decorate them more aesthetically. Another advantage was the ability to vary the paths of the grooves, to allow for the changing length of the days in the year. As smaller seals became more readily available, the clocks grew in popularity among the Chinese, and were often given as gifts. Incense seal clocks are often sought by modern-day clock collectors; however, few remain that have not already been purchased or been placed on display at museums or temples.

Clocks with gears and escapements

The earliest instance of a liquid-driven escapement was described by the Greek

Ancient Greece

engineer Philo of Byzantium

Philo of Byzantium

Philo of Byzantium , also known as Philo Mechanicus, was a Greek engineer and writer on mechanics, who lived during the latter half of the 3rd century BC...

(fl. 3rd century BC) in his technical treatise Pneumatics (chapter 31) where he likens the escapement mechanism of a washstand

Washstand

A washstand is a table or stand containing conveniences for washing oneself.- Ancient Greece:In his Pneumatics, Philo of Byzantium, a Greek engineer and writer on mechanics, describes an escapement mechanism, the earliest known, as part of a washstand...

automaton

Automaton

An automaton is a self-operating machine. The word is sometimes used to describe a robot, more specifically an autonomous robot. An alternative spelling, now obsolete, is automation.-Etymology:...

with those as employed in (water) clocks. Another early clock to use escapement

Escapement

In mechanical watches and clocks, an escapement is a device that transfers energy to the timekeeping element and enables counting the number of oscillations of the timekeeping element...

s was built during the 7th century AD in Chang'an

Chang'an

Chang'an is an ancient capital of more than ten dynasties in Chinese history, today known as Xi'an. Chang'an literally means "Perpetual Peace" in Classical Chinese. During the short-lived Xin Dynasty, the city was renamed "Constant Peace" ; yet after its fall in AD 23, the old name was restored...

, by Tantric

Vajrayana

Vajrayāna Buddhism is also known as Tantric Buddhism, Tantrayāna, Mantrayāna, Secret Mantra, Esoteric Buddhism and the Diamond Vehicle...

monk and mathematician, Yi Xing

Yi Xing

Yi Xing , born Zhang Sui , was a Chinese astronomer, mathematician, mechanical engineer,and Buddhist monk of the Tang Dynasty...

, and government official Liang Lingzan

Liang Lingzan

Liang Lingzan was a Tang Dynasty military engineer and government official of the Kaiyuan era. He invented a mechanized water clock with the Tantric monk and mathematician Yi Xing . It was actually an astronomical instrument that served as a clock, made of bronze in the capital of Chang'an in the...

. An astronomical instrument that served as a clock, it was discussed in a contemporary text as follows:

[It] was made in the image of the round heavens and on it were shown the lunar mansions in their order, the equator and the degrees of the heavenly circumference. Water, flowing into scoops, turned a wheel automatically, rotating it one complete revolution in one day and night. Besides this, there were two rings fitted around the celestial sphere outside, having the sun and moon threaded on them, and these were made to move in circling orbit ... And they made a wooden casing the surface of which represented the horizon, since the instrument was half sunk in it. It permitted the exact determinations of the time of dawns and dusks, full and new moons, tarrying and hurrying. Moreover, there were two wooden jacks standing on the horizon surface, having one a bell and the other a drum in front of it, the bell being struck automatically to indicate the hours, and the drum being beaten automatically to indicate the quarters. All these motions were brought about by machinery within the casing, each depending on wheels and shafts, hooks, pins and interlocking rods, stopping devices and locks checking mutually.

Since Yi Xing's clock was a water clock

Water clock

, it was affected by temperature variations. That problem was solved in 976 by Zhang Sixun

Zhang Sixun

Zhang Sixun was a Chinese astronomer and military engineer from Bazhong, Sichuan during the early Song Dynasty . He is credited with creating an armillary sphere for his astronomical clock tower that employed the use of liquid mercury...

by replacing the water with mercury

Mercury (element)

Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

, which remains liquid down to −39 °C (−38 °F). Zhang implemented the changes into his clock tower

Clock tower

A clock tower is a tower specifically built with one or more clock faces. Clock towers can be either freestanding or part of a church or municipal building such as a town hall. Some clock towers are not true clock towers having had their clock faces added to an already existing building...

, which was about 10 metres (32.8 ft) tall, with escapements to keep the clock turning and bells to signal every quarter-hour. Another noteworthy clock, the elaborate Cosmic Engine, was built by Su Song

Su Song

Su Song was a renowned Chinese polymath who specialized himself as a statesman, astronomer, cartographer, horologist, pharmacologist, mineralogist, zoologist, botanist, mechanical and architectural engineer, poet, antiquarian, and ambassador of the Song Dynasty .Su Song was the engineer of a...

, in 1088. It was about the size of Zhang's tower, but had an automatically rotating armillary sphere

Armillary sphere

An armillary sphere is a model of objects in the sky , consisting of a spherical framework of rings, centred on Earth, that represent lines of celestial longitude and latitude and other astronomically important features such as the ecliptic...

—also called a celestial globe—from which the positions of the stars could be observed. It also featured five panels with mannequins ringing gongs or bells, and tablets showing the time of day, or other special times. Furthermore, it featured the first known endless power-transmitting chain drive

Chain drive

Chain drive is a way of transmitting mechanical power from one place to another. It is often used to convey power to the wheels of a vehicle, particularly bicycles and motorcycles...

in horology. Originally built in the capital of Kaifeng

Kaifeng

Kaifeng , known previously by several names , is a prefecture-level city in east-central Henan province, Central China. Nearly 5 million people live in the metropolitan area...

, it was dismantled by the Jin army and sent to the capital of Yanjing

Fanyang

Yanjing for administrative purposes was an ancient city and capital of the State of Yan in northern China. It was located in modern Beijing.- History :...

(now Beijing

Beijing

Beijing , also known as Peking , is the capital of the People's Republic of China and one of the most populous cities in the world, with a population of 19,612,368 as of 2010. The city is the country's political, cultural, and educational center, and home to the headquarters for most of China's...

), where they were unable to put it back together. As a result, Su Song's son Su Xie was ordered to build a replica.

The clock towers built by Zhang Sixun and Su Song, in the 10th and 11th centuries, respectively, also incorporated a striking clock

Striking clock

A striking clock is a clock that sounds the hours audibly on a bell or gong. In 12 hour striking, used most commonly in striking clocks today, the clock strikes once at 1 AM, twice at 2 AM, continuing in this way up to twelve times at 12 noon, then starts over, striking once at 1 PM, twice at 2...

mechanism, the use of clock jacks to sound the hours. A striking clock outside of China was the Jayrun Water Clock

Jayrun Water Clock

The Jayrun Water Clock, a water clock built by the Arab engineer Muhammad al-Sa'ati, was positioned at the gate of Damascus, Syria, at the exit of the Umayyad Mosque in the 12th century during the reign of Nur ad-Din Zangi.-Construction:...

, at the Umayyad Mosque

Umayyad Mosque

The Umayyad Mosque, also known as the Great Mosque of Damascus or formerly the Basilica of Saint John the Baptist , is located in the old city of Damascus, is one of the largest and oldest mosques in the world...

in Damascus

Damascus

Damascus , commonly known in Syria as Al Sham , and as the City of Jasmine , is the capital and the second largest city of Syria after Aleppo, both are part of the country's 14 governorates. In addition to being one of the oldest continuously inhabited cities in the world, Damascus is a major...

, Syria

Syria

Syria , officially the Syrian Arab Republic , is a country in Western Asia, bordering Lebanon and the Mediterranean Sea to the West, Turkey to the north, Iraq to the east, Jordan to the south, and Israel to the southwest....

, which struck once every hour. It was constructed by Muhammad al-Sa'ati in the 12th century, and later described by his son Ridwan ibn al-Sa'ati, in his On the Construction of Clocks and their Use (1203), when repairing the clock. In 1235, an early monumental water-powered alarm clock

Alarm clock

that "announced the appointed hours of prayer

Salat times

Salat times refers to times when Muslims perform prayers . The term is primarily used for the five daily prayers plus the Friday prayer. According to Muslim beliefs, the salat times were taught by Allah through Gabriel to Muhammad....

and the time both by day and by night" was completed in the entrance hall of the Mustansiriya Madrasah in Baghdad

Baghdad

Baghdad is the capital of Iraq, as well as the coterminous Baghdad Governorate. The population of Baghdad in 2011 is approximately 7,216,040...

.

The first gear

Gear

ed clock was invented in the 11th century by the Arab engineer Ibn Khalaf al-Muradi

Al-Muradi

Alī Ibn Khalaf al-Murādī, Al-Andalus, was an engineer and author of the unique technological manuscript entitled Kitāb al-asrār fī natā'ij al-afkār . It was copied and used at the court of Alfonso VI of León and Castile in Christian Spain in the 11th century...

in Islamic Iberia

Al-Andalus

Al-Andalus was the Arabic name given to a nation and territorial region also commonly referred to as Moorish Iberia. The name describes parts of the Iberian Peninsula and Septimania governed by Muslims , at various times in the period between 711 and 1492, although the territorial boundaries...

; it was a water clock that employed a complex gear train

Gear train

A gear train is formed by mounting gears on a frame so that the teeth of the gears engage. Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, this provides a smooth transmission of rotation from one gear to the next.The transmission of...

mechanism, including both segmental and epicyclic gearing

Epicyclic gearing

Epicyclic gearing or planetary gearing is a gear system consisting of one or more outer gears, or planet gears, revolving about a central, or sun gear. Typically, the planet gears are mounted on a movable arm or carrier which itself may rotate relative to the sun gear...

, capable of transmitting high torque

Torque

Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....

. The clock was unrivalled in its use of sophisticated complex gearing, until the mechanical clocks of the mid-14th century. Al-Muradi's clock also employed the use of mercury in its hydraulic linkages

Linkage (mechanical)

A mechanical linkage is an assembly of bodies connected together to manage forces and movement. The movement of a body, or link, is studied using geometry so the link is considered to be rigid. The connections between links are modeled as providing ideal movement, pure rotation or sliding for...

, which could function mechanical automata

Automaton

An automaton is a self-operating machine. The word is sometimes used to describe a robot, more specifically an autonomous robot. An alternative spelling, now obsolete, is automation.-Etymology:...

. Al-Muradi's work was known to scholars working under Alfonso X of Castile

Alfonso X of Castile

Alfonso X was a Castilian monarch who ruled as the King of Castile, León and Galicia from 1252 until his death...

, hence the mechanism may have played a role in the development of the European mechanical clocks. Other monumental water clocks constructed by medieval Muslim engineers also employed complex gear trains and arrays of automata

Automaton

An automaton is a self-operating machine. The word is sometimes used to describe a robot, more specifically an autonomous robot. An alternative spelling, now obsolete, is automation.-Etymology:...

. Like the earlier Greeks and Chinese, Arab engineers at the time also developed a liquid-driven escapement

Escapement

In mechanical watches and clocks, an escapement is a device that transfers energy to the timekeeping element and enables counting the number of oscillations of the timekeeping element...

mechanism which they employed in some of their water clocks. Heavy floats were used as weights and a constant-head system was used as an escapement

Escapement

In mechanical watches and clocks, an escapement is a device that transfers energy to the timekeeping element and enables counting the number of oscillations of the timekeeping element...

mechanism, which was present in the hydraulic controls they used to make heavy floats descend at a slow and steady rate.

A mercury clock, described in the Libros del saber de Astronomia, a Spanish

Spanish language

Spanish , also known as Castilian , is a Romance language in the Ibero-Romance group that evolved from several languages and dialects in central-northern Iberia around the 9th century and gradually spread with the expansion of the Kingdom of Castile into central and southern Iberia during the...

work from 1277 consisting of translations and paraphrases of Arabic works, is sometimes quoted as evidence for Muslim knowledge of a mechanical clock. However, the device was actually a compartmented cylindrical water clock, which the Jewish author of the relevant section, Rabbi

Rabbi

In Judaism, a rabbi is a teacher of Torah. This title derives from the Hebrew word רבי , meaning "My Master" , which is the way a student would address a master of Torah...

Isaac, constructed using principles described by a philosopher named "Iran", identified with Heron of Alexandria

Hero of Alexandria

Hero of Alexandria was an ancient Greek mathematician and engineerEnc. Britannica 2007, "Heron of Alexandria" who was active in his native city of Alexandria, Roman Egypt...

(fl. 1st century AD), on how heavy objects may be lifted.

Astronomical clocks

During the 11th century in the Song Dynasty

Technology of the Song Dynasty

The Song Dynasty provided some of the most significant technological advances in Chinese history, many of which came from talented statesmen drafted by the government through imperial examinations....

, the Chinese astronomer

Chinese astronomy

Astronomy in China has a very long history, with historians considering that "they [the Chinese] were the most persistent and accurate observers of celestial phenomena anywhere in the world before the Arabs."...

, horologist and mechanical engineer Su Song

Su Song

created a water-driven astronomical clock

Astronomical clock

An astronomical clock is a clock with special mechanisms and dials to display astronomical information, such as the relative positions of the sun, moon, zodiacal constellations, and sometimes major planets.-Definition:...

for his clock tower of Kaifeng

Kaifeng

Kaifeng , known previously by several names , is a prefecture-level city in east-central Henan province, Central China. Nearly 5 million people live in the metropolitan area...

City. It incorporated an escapement mechanism as well as the earliest known endless power-transmitting chain drive

Chain drive

Chain drive is a way of transmitting mechanical power from one place to another. It is often used to convey power to the wheels of a vehicle, particularly bicycles and motorcycles...

, which drove the armillary sphere

Armillary sphere

.

Contemporary Muslim astronomers

Islamic astronomy

Islamic astronomy or Arabic astronomy comprises the astronomical developments made in the Islamic world, particularly during the Islamic Golden Age , and mostly written in the Arabic language. These developments mostly took place in the Middle East, Central Asia, Al-Andalus, and North Africa, and...

also constructed a variety of highly accurate astronomical clocks for use in their mosques and observatories

Observatory

An observatory is a location used for observing terrestrial or celestial events. Astronomy, climatology/meteorology, geology, oceanography and volcanology are examples of disciplines for which observatories have been constructed...

, such as the water-powered astronomical clock by Al-Jazari

Al-Jazari

in 1206, and the astrolabic clock by Ibn al-Shatir

Ibn al-Shatir

Ala Al-Din Abu'l-Hasan Ali Ibn Ibrahim Ibn al-Shatir was an Arab Muslim astronomer, mathematician, engineer and inventor who worked as muwaqqit at the Umayyad Mosque in Damascus, Syria.-Astronomy:...

in the early 14th century. The most sophisticated timekeeping astrolabes were the gear

Gear

ed astrolabe mechanisms designed by Abū Rayhān Bīrūnī in the 11th century and by Muhammad ibn Abi Bakr in the 13th century. These devices functioned as timekeeping devices and also as calender

Calender

The calender is a series of hard pressure rollers used to form or smooth a sheet of material. In a principal application, the calender is located at the end of a papermaking process . Those that are used separate from the process are also called supercalenders...

s.
A sophisticated water-powered astronomical clock was built by Al-Jazari

Al-Jazari

in 1206. This castle clock

Castle clock

A castle clock is a clock whose face is mounted outside a castle or perhaps a church tower. They may be elaborate or simple.Al-Jazari constructed an elaborate clock and described it in his Book of Knowledge of Ingenious Mechanical Devices in 1206. It was about 3,3 metres high , and had multiple...

was a complex device that was about 11 feet (3.4 m) high, and had multiple functions alongside timekeeping. It included a display of the zodiac

Zodiac

In astronomy, the zodiac is a circle of twelve 30° divisions of celestial longitude which are centred upon the ecliptic: the apparent path of the Sun across the celestial sphere over the course of the year...

and the solar and lunar paths, and a pointer in the shape of the crescent moon

Lunar phase

A lunar phase or phase of the moon is the appearance of the illuminated portion of the Moon as seen by an observer, usually on Earth. The lunar phases change cyclically as the Moon orbits the Earth, according to the changing relative positions of the Earth, Moon, and Sun...

which travelled across the top of a gateway, moved by a hidden cart and causing doors to open, each revealing a mannequin

Mannequin

A mannequin is an often articulated doll used by artists, tailors, dressmakers, and others especially to display or fit clothing...

, every hour. It was possible to reset the length of day and night in order to account for the changing lengths of day and night throughout the year. This clock also featured a number of automata

Automaton

An automaton is a self-operating machine. The word is sometimes used to describe a robot, more specifically an autonomous robot. An alternative spelling, now obsolete, is automation.-Etymology:...

including falcons and musicians who automatically played music when moved by levers operated by a hidden camshaft

Camshaft

A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...

attached to a water wheel

Water wheel

A water wheel is a machine for converting the energy of free-flowing or falling water into useful forms of power. A water wheel consists of a large wooden or metal wheel, with a number of blades or buckets arranged on the outside rim forming the driving surface...

Modern devices of ancient origin

Sundial

A sundial is a device that measures time by the position of the Sun. In common designs such as the horizontal sundial, the sun casts a shadow from its style onto a surface marked with lines indicating the hours of the day. The style is the time-telling edge of the gnomon, often a thin rod or a...

s were further developed by Muslim astronomers

Islamic astronomy

. As the ancient dials were nodus-based with straight hour-lines, they indicated unequal hours—also called temporary hours—that varied with the seasons. Every day was divided into 12 equal segments regardless of the time of year; thus, hours were shorter in winter and longer in summer. The idea of using hours of equal length throughout the year was the innovation of Abu'l-Hasan Ibn al-Shatir

Ibn al-Shatir

Ala Al-Din Abu'l-Hasan Ali Ibn Ibrahim Ibn al-Shatir was an Arab Muslim astronomer, mathematician, engineer and inventor who worked as muwaqqit at the Umayyad Mosque in Damascus, Syria.-Astronomy:...

in 1371, based on earlier developments in trigonometry

Trigonometry

Trigonometry is a branch of mathematics that studies triangles and the relationships between their sides and the angles between these sides. Trigonometry defines the trigonometric functions, which describe those relationships and have applicability to cyclical phenomena, such as waves...

by Muhammad ibn Jābir al-Harrānī al-Battānī (Albategni). Ibn al-Shatir was aware that "using a gnomon

Gnomon

that is parallel to the Earth's axis will produce sundials whose hour lines indicate equal hours on any day of the year". His sundial is the oldest polar-axis sundial still in existence. The concept appeared in Western sundials starting in 1446.

Following the acceptance of heliocentrism

Heliocentrism

Heliocentrism, or heliocentricism, is the astronomical model in which the Earth and planets revolve around a stationary Sun at the center of the universe. The word comes from the Greek . Historically, heliocentrism was opposed to geocentrism, which placed the Earth at the center...

and equal hours, as well as advances in trigonometry, sundials appeared in their present form during the Renaissance

Renaissance

The Renaissance was a cultural movement that spanned roughly the 14th to the 17th century, beginning in Italy in the Late Middle Ages and later spreading to the rest of Europe. The term is also used more loosely to refer to the historical era, but since the changes of the Renaissance were not...

, when they were built in large numbers. In 1524, the French astronomer Oronce Finé

Oronce Finé

Oronce Fine was a French mathematician and cartographer.-Life:...

constructed an ivory

Ivory

Ivory is a term for dentine, which constitutes the bulk of the teeth and tusks of animals, when used as a material for art or manufacturing. Ivory has been important since ancient times for making a range of items, from ivory carvings to false teeth, fans, dominoes, joint tubes, piano keys and...

sundial, which still exists; later, in 1570, the Italian astronomer Giovanni Padovani

Giovanni Padovani

Giovanni Padovani was an Italian mathematician and astronomer. He lived in Verona and was a student of Pietro Pitati...

published a treatise including instructions for the manufacture and laying out of mural (vertical) and horizontal sundials. Similarly, Giuseppe Biancani's

Giuseppe Biancani

Giuseppe Biancani was an Italian Jesuit astronomer, mathematician, and selenographer, after whom the crater Blancanus on the Moon is named...

Constructio instrumenti ad horologia solaria (c. 1620) discusses how to construct sundials.

The Portuguese

Portugal

Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...

navigator Ferdinand Magellan

Ferdinand Magellan

Ferdinand Magellan was a Portuguese explorer. He was born in Sabrosa, in northern Portugal, and served King Charles I of Spain in search of a westward route to the "Spice Islands" ....

used 18 hourglasses on each ship during his circumnavigation of the globe in 1522. Since the hourglass was one of the few reliable methods of measuring time at sea, it is speculated that it had been used on board ships as far back as the 11th century, when it would have complemented the magnetic compass as an aid to navigation. However, the earliest evidence of their use appears in the painting Allegory of Good Government, by Ambrogio Lorenzetti

Ambrogio Lorenzetti

Ambrogio Lorenzetti was an Italian painter of the Sienese school. He was active between approximately 1317 to 1348. His elder brother was the painter Pietro Lorenzetti....

, from 1338. From the 15th century onwards, hourglasses were used in a wide range of applications at sea, in churches, in industry, and in cooking; they were the first dependable, reusable, reasonably accurate, and easily constructed time-measurement devices. The hourglass also took on symbolic meanings, such as that of death, temperance, opportunity, and Father Time

Father Time

Father Time is usually depicted as an elderly bearded man, somewhat worse for wear, dressed in a robe, carrying a scythe and an hourglass or other timekeeping device...

, usually represented as a bearded, old man. Though also used in China, the hourglass

Hourglass

's history there is unknown.

Clocks

Clock

s encompass a wide spectrum of devices, ranging from wristwatches to the Clock of the Long Now

Clock of the Long Now

The Clock of the Long Now, also called the 10,000-year clock, is a proposed mechanical clock designed to keep time for 10,000 years. The project to build it is part of the Long Now Foundation....

. The English word clock is said to derive from the Middle English

Middle English

Middle English is the stage in the history of the English language during the High and Late Middle Ages, or roughly during the four centuries between the late 11th and the late 15th century....

clokke, Old North French

Old French

Old French was the Romance dialect continuum spoken in territories that span roughly the northern half of modern France and parts of modern Belgium and Switzerland from the 9th century to the 14th century...

cloque, or Middle Dutch

Middle Dutch

Middle Dutch is a collective name for a number of closely related West Germanic dialects which were spoken and written between 1150 and 1500...

clocke, all of which mean bell
Bell (instrument)
A bell is a simple sound-making device. The bell is a percussion instrument and an idiophone. Its form is usually a hollow, cup-shaped object, which resonates upon being struck...

, and are derived from the Medieval Latin

Medieval Latin

Medieval Latin was the form of Latin used in the Middle Ages, primarily as a medium of scholarly exchange and as the liturgical language of the medieval Roman Catholic Church, but also as a language of science, literature, law, and administration. Despite the clerical origin of many of its authors,...

clocca, also meaning bell. Indeed, bells were used to mark the passage of time; they marked the passage of the hours at sea and in abbey

Abbey

An abbey is a Catholic monastery or convent, under the authority of an Abbot or an Abbess, who serves as the spiritual father or mother of the community.The term can also refer to an establishment which has long ceased to function as an abbey,...

s.

Throughout history, clocks have had a variety of power sources, including gravity, springs

Spring (device)

, and electricity. The invention of mechanical clockwork itself is usually credited to the Chinese official Liang Lingzan and monk Yi Xing. However, mechanical clocks were not widely used in the West until the 14th century. Clocks were used in medieval monasteries

Monastery

Monastery denotes the building, or complex of buildings, that houses a room reserved for prayer as well as the domestic quarters and workplace of monastics, whether monks or nuns, and whether living in community or alone .Monasteries may vary greatly in size – a small dwelling accommodating only...

to keep the regulated schedule of prayers. The clock continued to be improved, with the first pendulum clock

Pendulum clock

being designed and built in the 17th century by Christiaan Huygens, a Dutch scientist.

Early Western mechanical clocks

The earliest medieval European clockmaker

Clockmaker

A clockmaker is an artisan who makes and repairs clocks. Since almost all clocks are now factory-made, most modern clockmakers only repair clocks. Modern clockmakers may be employed by jewellers, antique shops, and places devoted strictly to repairing clocks and watches...

s were Christian monks. Medieval religious institutions required clocks because daily prayer and work schedules were strictly regulated. This was done by various types of time-telling and recording devices, such as water clocks, sundials and marked candles, probably used in combination. When mechanical clocks were used, they were often wound at least twice a day to ensure accuracy. Important times and durations were broadcast by bells, rung either by hand or by a mechanical device, such as a falling weight or rotating beater.

As early as 850, Pacificus, archdeacon of Verona

Verona

Verona ; German Bern, Dietrichsbern or Welschbern) is a city in the Veneto, northern Italy, with approx. 265,000 inhabitants and one of the seven chef-lieus of the region. It is the second largest city municipality in the region and the third of North-Eastern Italy. The metropolitan area of Verona...

, constructed a water clock (horologium nocturnum).

The religious necessities and technical skill of the medieval monks were crucial factors in the development of clocks, as the historian Thomas Woods

Thomas Woods

Thomas E. "Tom" Woods, Jr. is an American historian, economist, political analyst, and New York Times-bestselling author. He has written extensively on the subjects of American history, contemporary politics, and economic theory...

writes:

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

Florence

Florence is the capital city of the Italian region of Tuscany and of the province of Florence. It is the most populous city in Tuscany, with approximately 370,000 inhabitants, expanding to over 1.5 million in the metropolitan area....

poet Dante Alighieri

Dante Alighieri

Durante degli Alighieri, mononymously referred to as Dante , was an Italian poet, prose writer, literary theorist, moral philosopher, and political thinker. He is best known for the monumental epic poem La commedia, later named La divina commedia ...

referred to a clock in his Paradiso; considered to be the first literary reference to a clock that struck the hours. The earliest detailed description of clockwork was presented by Giovanni da Dondi, Professor of Astronomy at Padua

University of Padua

The University of Padua is a premier Italian university located in the city of Padua, Italy. The University of Padua was founded in 1222 as a school of law and was one of the most prominent universities in early modern Europe. It is among the earliest universities of the world and the second...

, in his 1364 treatise Il Tractatus Astrarii. This has inspired several modern replicas, including some in London's Science Museum

Science Museum (London)

The Science Museum is one of the three major museums on Exhibition Road, South Kensington, London in the Royal Borough of Kensington and Chelsea. It is part of the National Museum of Science and Industry. The museum is a major London tourist attraction....

and the Smithsonian Institution

Smithsonian Institution

The Smithsonian Institution is an educational and research institute and associated museum complex, administered and funded by the government of the United States and by funds from its endowment, contributions, and profits from its retail operations, concessions, licensing activities, and magazines...

. Other notable examples from this period were built in Milan

Milan

Milan is the second-largest city in Italy and the capital city of the region of Lombardy and of the province of Milan. The city proper has a population of about 1.3 million, while its urban area, roughly coinciding with its administrative province and the bordering Province of Monza and Brianza ,...

(1335), Strasbourg

Strasbourg astronomical clock

The Strasbourg astronomical clock is located in the Cathédrale Notre-Dame of Strasbourg, Alsace, France. It is the third clock on that spot and dates from the time of the first French possession of the city...

(1354), Lund

Lund Cathedral

The Lund Cathedral is the Lutheran cathedral in Lund, Scania, Sweden. It is the seat of the bishop of Lund of the Church of Sweden.- History :...

(1380), Rouen

Rouen

Rouen , in northern France on the River Seine, is the capital of the Haute-Normandie region and the historic capital city of Normandy. Once one of the largest and most prosperous cities of medieval Europe , it was the seat of the Exchequer of Normandy in the Middle Ages...

(1389), and Prague

Prague

Prague is the capital and largest city of the Czech Republic. Situated in the north-west of the country on the Vltava river, the city is home to about 1.3 million people, while its metropolitan area is estimated to have a population of over 2.3 million...

(1462).

Salisbury cathedral clock

Salisbury cathedral clock

The Salisbury Cathedral clock, a large iron-framed clock without a dial located in the aisle of Salisbury Cathedral. Supposedly dating from about 1386, it is claimed to be the oldest working clock in the world....

, dating from about 1386, is the oldest working clock in the world, still with most of its original parts. It has no dial, as its purpose was to strike a bell

Striking clock

at precise times. The wheels and gears are mounted in an open, box-like iron frame, measuring about 1.2 metres (3.9 ft) square. The framework is held together with metal dowels and pegs, and the escapement is the verge and foliot type, standard for clocks of this age. The power is supplied by two large stones, hanging from pulleys. As the weights fall, ropes unwind from the wooden barrels. One barrel drives the main wheel, which is regulated by the escapement, and the other drives the striking mechanism and the air brake.

Peter Lightfoot's Wells Cathedral clock

Wells Cathedral clock

The Wells Cathedral clock is an astronomical clock in the north transept of Wells Cathedral, England.The clock is one of the group of famous 14th to 16th century astronomical clocks to be found in the West of England....

, constructed c. 1390, is also of note. The dial represents a geocentric view of the universe, with the Sun

Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

and Moon

Moon

revolving around a centrally fixed Earth

Earth

Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

. It is unique in having its original medieval face, showing a philosophical model of the pre-Copernican

Copernican Revolution

The Copernican Revolution refers to the paradigm shift away from the Ptolemaic model of the heavens, which postulated the Earth at the center of the galaxy, towards the heliocentric model with the Sun at the center of our Solar System...

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

Pendulum

A pendulum is a weight suspended from a pivot so that it can swing freely. When a pendulum is displaced from its resting equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position...

and anchor escapement

Anchor escapement

In horology, the recoil or anchor escapement is a type of escapement used in pendulum clocks. An escapement is the mechanism in a mechanical clock that maintains the swing of the pendulum and allows the clock's wheels to advance a fixed amount with each swing, moving the hands forward...

in the 17th century, and was installed in London's Science Museum in 1884, where it continues to operate. Similar astronomical clocks, or horologes, can be seen at Exeter, Ottery St Mary, and Wimborne Minster.

One clock that has not survived to the present-day is that of the Abbey of St Albans, built by the 14th-century abbot Richard of Wallingford

Richard of Wallingford

Richard of Wallingford was an English mathematician who made major contributions to astronomy/astrology and horology while serving as abbot of St Albans Abbey in Hertfordshire.-Biography:...

. It may have been destroyed during Henry VIII

Henry VIII of England

Henry VIII was King of England from 21 April 1509 until his death. He was Lord, and later King, of Ireland, as well as continuing the nominal claim by the English monarchs to the Kingdom of France...

's Dissolution of the Monasteries

Dissolution of the Monasteries

The Dissolution of the Monasteries, sometimes referred to as the Suppression of the Monasteries, was the set of administrative and legal processes between 1536 and 1541 by which Henry VIII disbanded monasteries, priories, convents and friaries in England, Wales and Ireland; appropriated their...

, but the abbot's notes on its design have allowed a full-scale reconstruction. As well as keeping time, the astronomical clock could accurately predict lunar eclipse

Lunar eclipse

A lunar eclipse occurs when the Moon passes behind the Earth so that the Earth blocks the Sun's rays from striking the Moon. This can occur only when the Sun, Earth, and Moon are aligned exactly, or very closely so, with the Earth in the middle. Hence, a lunar eclipse can only occur the night of a...

s, and may have shown the Sun, Moon (age, phase, and node), stars and planets, as well as a wheel of fortune

The Wheel of Fortune

The Wheel of Fortune, or Rota Fortunae, is a concept in medieval and ancient philosophy referring to the capricious nature of Fate. The wheel belongs to the goddess Fortuna, who spins it at random, changing the positions of those on the wheel - some suffer great misfortune, others gain windfalls...

, and an indicator of the state of the tide at London Bridge

London Bridge

London Bridge is a bridge over the River Thames, connecting the City of London and Southwark, in central London. Situated between Cannon Street Railway Bridge and Tower Bridge, it forms the western end of the Pool of London...

. According to Thomas Woods

Thomas Woods

, "a clock that equaled it in technological sophistication did not appear for at least two centuries". Giovanni de Dondi was another early mechanical clockmaker, whose clock did not survive, but has been replicated based on the designs. De Dondi's clock was a seven-faced construction with 107 moving parts, showing the positions of the Sun, Moon, and five planets, as well as religious feast days. Around this period, mechanical clocks were introduced into abbeys and monasteries to mark important events and times, gradually replacing water clocks which had served the same purpose.

During the Middle Ages, clocks were primarily used for 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

Tholsel

The term Tholsel refers to extant and former public buildings in Ireland's towns and cities.The actual meaning of the word is uncertain...

(the city court and council chamber). It was probably the first of its kind 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

Leeds Castle

Leeds Castle, southeast of Maidstone, Kent, England, dates back to 1119, though a Saxon fort stood on the same site from the 9th century. The castle is built on islands in a lake formed by the River Len to the east of the village of Leeds....

; its face is decorated with the images of the Crucifixion of Jesus

Crucifixion of Jesus

The crucifixion of Jesus and his ensuing death is an event that occurred during the 1st century AD. Jesus, who Christians believe is the Son of God as well as the Messiah, was arrested, tried, and sentenced by Pontius Pilate to be scourged, and finally executed on a cross...

, Mary

Mary (mother of Jesus)

Mary , commonly referred to as "Saint Mary", "Mother Mary", the "Virgin Mary", the "Blessed Virgin Mary", or "Mary, Mother of God", was a Jewish woman of Nazareth in Galilee...

and St George.

Clock tower

Clock tower

s in Western Europe

Western Europe

Western Europe is a loose term for the collection of countries in the western most region of the European continents, though this definition is context-dependent and carries cultural and political connotations. One definition describes Western Europe as a geographic entity—the region lying in the...

in the Middle Ages were also sometimes striking clock

Striking clock

s. The most famous original still standing is possibly St Mark's Clock

St Mark's Clock

For the building containing the clock see the article on the ClocktowerSt Mark's Clock is the clock housed in the Clocktower on the Piazza San Marco in Venice adjoining the Procuratie Vecchie...

on the top of St Mark's Clocktower

St Mark's Clocktower

The Clock Tower in Venice is an early renaissance building on the north side of the Piazza San Marco at the entrance to the Merceria. It comprises a tower, which contains the clock, and lower buildings on each side. It adjoins the eastern end of the Procuratie Vecchie...

in St Mark's Square, Venice

Venice

Venice is a city in northern Italy which is renowned for the beauty of its setting, its architecture and its artworks. It is the capital of the Veneto region...

, assembled in 1493, by the clockmaker Gian Carlo Rainieri from Reggio Emilia

Reggio Emilia

Reggio Emilia is an affluent city in northern Italy, in the Emilia-Romagna region. It has about 170,000 inhabitants and is the main comune of the Province of Reggio Emilia....

. In 1497, Simone Campanato moulded the great bell that every definite time-lapse is beaten by two mechanical bronze statues (h. 2,60 m.) called Due Mori (Two Moors
Moors
The description Moors has referred to several historic and modern populations of the Maghreb region who are predominately of Berber and Arab descent. They came to conquer and rule the Iberian Peninsula for nearly 800 years. At that time they were Muslim, although earlier the people had followed...

), handling a hammer. Possibly earlier (1490 by clockmaster Jan Růže also called Hanuš) is the Prague Astronomical Clock, that according to another source was assembled as early as 1410 by clockmaker Mikuláš of Kadaň

Mikulas of Kadan

Mikuláš of Kadaň was an Imperial clockmaker who designed the clock machine of Prague Orloj together with Jan Šindel around 1410 . The Orloj was modified by Master Hanuš who was mistaken to be the creator of the clock according to the legend recorded by Alois Jirásek....

and mathematician Jan Šindel

Jan Šindel

Jan Šindel was a professor at Charles University and became the rector of the University in 1410. He lectured on mathematics and astronomy....

. The allegorical parade of animated sculptures rings on the hour every day.

Early clock dials did not use minutes and seconds. A clock with a minutes dial is mentioned in a 1475 manuscript, and clocks indicating minutes and seconds existed in Germany

Germany

Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

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, the spiral balance spring. The 16th-century astronomer Tycho Brahe

Tycho Brahe

Tycho Brahe , born Tyge Ottesen Brahe, was a Danish nobleman known for his accurate and comprehensive astronomical and planetary observations...

used clocks with minutes and seconds to observe stellar positions.

Ottoman mechanical clocks

The Ottoman

Ottoman Empire

The Ottoman EmpireIt was usually referred to as the "Ottoman Empire", the "Turkish Empire", the "Ottoman Caliphate" or more commonly "Turkey" by its contemporaries...

engineer Taqi al-Din described a weight-driven clock with a verge-and-foliot escapement

Verge escapement

, a striking train of gears, an alarm

Alarm clock

, and a representation of the moon's phases in his book The Brightest Stars for the Construction of Mechanical Clocks (Al-Kawākib al-durriyya fī wadh' al-bankāmat al-dawriyya), written around 1556. Similarly to earlier 15th-century European mechanical alarm clocks, the alarm was set by placing a peg on the dial wheel at the appropriate time. The clock had three dials

Dial (measurement)

reading in hours, degrees and minutes. Taqi al-Din later constructed a clock for the Istanbul Observatory, where he used it to make observations of right ascension

Right ascension

Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...

s, stating: “We constructed a mechanical clock with three dials which show the hours, the minutes, and the seconds. We divided each minute into five seconds.” This was an important innovation in 16th-century practical astronomy

Astronomy

Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

, as at the start of the century clocks were not accurate enough to be used for astronomical purposes.

An example of a watch which measured time in minutes was created by an Ottoman

Ottoman Empire

The Ottoman EmpireIt was usually referred to as the "Ottoman Empire", the "Turkish Empire", the "Ottoman Caliphate" or more commonly "Turkey" by its contemporaries...

watchmaker, Meshur Sheyh Dede, in 1702.

Pendulum clocks

Innovations to the mechanical clock continued, with miniaturization leading to domestic clocks in the 15th century, and personal watches in the 16th. In the 1580s, the Italian polymath

Polymath

A polymath is a person whose expertise spans a significant number of different subject areas. In less formal terms, a polymath may simply be someone who is very knowledgeable...

Galileo Galilei

Galileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...

investigated the regular swing of the pendulum

Pendulum

, and discovered that it could be used to regulate a clock. Although Galileo studied the pendulum as early as 1582, he never actually constructed a clock based on that design. The first pendulum clock was designed and built by Dutch

Netherlands

The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...

scientist Christiaan Huygens, in 1656. Early versions erred by less than one minute per day, and later ones only by 10 seconds, very accurate for their time.

The Jesuits

Society of Jesus

The Society of Jesus is a Catholic male religious order that follows the teachings of the Catholic Church. The members are called Jesuits, and are also known colloquially as "God's Army" and as "The Company," these being references to founder Ignatius of Loyola's military background and a...

were another major contributor to the development of pendulum clocks in the 17th and 18th centuries, having had an "unusually keen appreciation of the importance of precision". In measuring an accurate one-second pendulum, for example, the Italian astronomer Father Giovanni Battista Riccioli

Giovanni Battista Riccioli

Giovanni Battista Riccioli was an Italian astronomer and a Catholic priest in the Jesuit order...

persuaded nine fellow Jesuits "to count nearly 87,000 oscillations in a single day". They served a crucial role in spreading and testing the scientific ideas of the period, and collaborated with contemporary scientists, such as Huygens.

The modern longcase clock

Longcase clock

A longcase clock, also tall-case clock, floor clock, or grandfather clock, is a tall, freestanding, weight-driven pendulum clock with the pendulum held inside the tower, or waist of the case. Clocks of this style are commonly 1.8–2.4 metres tall...

, also known as the grandfather clock, has its origins in the invention of the anchor escapement

Anchor escapement

mechanism in about 1670. Before then, pendulum clocks had used the older verge escapement

Verge escapement

mechanism, which required very wide pendulum swings of about 100°. To avoid the need for a very large case, most clocks using the verge escapement had a short pendulum. The anchor mechanism, however, reduced the pendulum's necessary swing to between 4° to 6°, allowing clockmakers to use longer pendulums with consequently slower beats. These required less power to move, caused less friction and wear, and were more accurate than their shorter predecessors. Most longcase clocks use a pendulum about a metre (39 inches) long to the center of the bob, with each swing taking one second. This requirement for height, along with the need for a long drop space for the weights that power the clock, gave rise to the tall, narrow case.

In 1675, 18 years after inventing the pendulum clock, Huygens devised the spiral balance spring

Balance spring

A balance spring, or hairspring, is a part used in mechanical timepieces. The balance spring, attached to the balance wheel, controls the speed at which the wheels of the timepiece turn, and thus the rate of movement of the hands...

for the balance wheel

Balance wheel

The balance wheel is the timekeeping device used in mechanical watches and some clocks, analogous to the pendulum in a pendulum clock. It is a weighted wheel that rotates back and forth, being returned toward its center position by a spiral spring, the balance spring or hairspring...

of pocket watches, an improvement on the straight spring invented by English natural philosopher Robert Hooke

Robert Hooke

Robert Hooke FRS was an English natural philosopher, architect and polymath.His adult life comprised three distinct periods: as a scientific inquirer lacking money; achieving great wealth and standing through his reputation for hard work and scrupulous honesty following the great fire of 1666, but...

. This resulted in a great advance in accuracy of pocket watches, from perhaps several hours per day to 10 minutes per day, similar to the effect of the pendulum upon mechanical clocks.

Clockmakers

The first professional clockmakers came from the guild

Guild

A guild is an association of craftsmen in a particular trade. The earliest types of guild were formed as confraternities of workers. They were organized in a manner something between a trade union, a cartel, and a secret society...

s of locksmiths and jewellers. Clockmaking developed from a specialized craft into a mass production industry over many years. Paris

Paris

Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...

and Blois

Blois

Blois is the capital of Loir-et-Cher department in central France, situated on the banks of the lower river Loire between Orléans and Tours.-History:...

were the early centers of clockmaking in France. French clockmakers such as Julien Le Roy

Julien Le Roy

Julien Le Roy was a major 18th-century Parisian clockmaker and watchmaker.He was born in Tours in 1686, and by the age of 13, had already made his first clock. In 1699, he moved to Paris for further training. He became maitre horloger in 1713 and later juré of his guild...

, clockmaker of Versailles

Versailles

Versailles , a city renowned for its château, the Palace of Versailles, was the de facto capital of the kingdom of France for over a century, from 1682 to 1789. It is now a wealthy suburb of Paris and remains an important administrative and judicial centre...

, were leaders in case design and ornamental clocks. Le Roy belonged to the fifth generation of a family of clockmakers, and was described by his contemporaries as "the most skillful clockmaker in France, possibly in Europe". He invented a special repeating mechanism which improved the precision of clocks and watches, a face that could be opened to view the inside clockwork, and made or supervised over 3,500 watches. The competition and scientific rivalry resulting from his discoveries further encouraged researchers to seek new methods of measuring time more accurately.

Between 1794 and 1795, in the aftermath of the French Revolution

French Revolution

The French Revolution , sometimes distinguished as the 'Great French Revolution' , was a period of radical social and political upheaval in France and Europe. The absolute monarchy that had ruled France for centuries collapsed in three years...

, the French government briefly mandated decimal clocks

Decimal time

Decimal time is the representation of the time of day using units which are decimally related. This term is often used to refer specifically to French Revolutionary Time, which divides the day into 10 decimal hours, each decimal hour into 100 decimal minutes and each decimal minute into 100 decimal...

, with a day divided into 10 hours of 100 minutes each. The astronomer and mathematician Pierre-Simon Laplace

Pierre-Simon Laplace

Pierre-Simon, marquis de Laplace was a French mathematician and astronomer whose work was pivotal to the development of mathematical astronomy and statistics. He summarized and extended the work of his predecessors in his five volume Mécanique Céleste...

, among other individuals, modified the dial of his pocket watch to decimal time. A clock in the Palais des Tuileries kept decimal time as late as 1801, but the cost of replacing all the nation's clocks prevented decimal clocks from becoming widespread. Because decimalized clocks only helped astronomers rather than ordinary citizens, it was one of the most unpopular changes associated with the metric system

Metric system

The metric system is an international decimalised system of measurement. France was first to adopt a metric system, in 1799, and a metric system is now the official system of measurement, used in almost every country in the world...

, and it was abandoned.

In Germany, Nuremberg

Nuremberg

Nuremberg[p] is a city in the German state of Bavaria, in the administrative region of Middle Franconia. Situated on the Pegnitz river and the Rhine–Main–Danube Canal, it is located about north of Munich and is Franconia's largest city. The population is 505,664...

and Augsburg

Augsburg

Augsburg is a city in the south-west of Bavaria, Germany. It is a university town and home of the Regierungsbezirk Schwaben and the Bezirk Schwaben. Augsburg is an urban district and home to the institutions of the Landkreis Augsburg. It is, as of 2008, the third-largest city in Bavaria with a...

were the early clockmaking centers, and the Black Forest

Black Forest

The Black Forest is a wooded mountain range in Baden-Württemberg, southwestern Germany. It is bordered by the Rhine valley to the west and south. The highest peak is the Feldberg with an elevation of 1,493 metres ....

came to specialize in wooden cuckoo clocks. The English became the predominant clockmakers of the 17th and 18th centuries. In 1802, British Philosopher, William Paley, applied the analogy of a watch's design to the idea that creation is designed, and therefore must have a designer. Switzerland established itself as a clockmaking center following the influx of Huguenot

Huguenot

The Huguenots were members of the Protestant Reformed Church of France during the 16th and 17th centuries. Since the 17th century, people who formerly would have been called Huguenots have instead simply been called French Protestants, a title suggested by their German co-religionists, the...

craftsmen, and in the 19th century, the Swiss industry "gained worldwide supremacy in high-quality machine-made watches". The leading firm of the day was Patek Philippe, founded by Antoni Patek

Antoni Patek

Antoni Norbert Patek , is a Polish pioneer in watchmaking and a creator of Patek Philippe & Co. one of the most famous watchmaker companies.- Early life :...

of Warsaw

Warsaw

Warsaw is the capital and largest city of Poland. It is located on the Vistula River, roughly from the Baltic Sea and from the Carpathian Mountains. Its population in 2010 was estimated at 1,716,855 residents with a greater metropolitan area of 2,631,902 residents, making Warsaw the 10th most...

and Adrien Philippe

Adrien Philippe

Jean Adrien Philippe was French horologist and cofounder of watchmaker Patek Philippe & Co. of Geneva, Switzerland.In 1842 Adrien Philippe invented a mechanism for watches which allowed them to be wound and set by means of crown rather than a key. His patented invention earned him a Gold Medal at...

of Berne

Berne

The city of Bern or Berne is the Bundesstadt of Switzerland, and, with a population of , the fourth most populous city in Switzerland. The Bern agglomeration, which includes 43 municipalities, has a population of 349,000. The metropolitan area had a population of 660,000 in 2000...

Wristwatches

In 1904, Alberto Santos-Dumont

Alberto Santos-Dumont

Alberto Santos-Dumont , was a Brazilian early pioneer of aviation. The heir of a wealthy family of coffee producers, Santos Dumont dedicated himself to science studies in Paris, France, where he spent most of his adult life....

, an early aviator, asked his friend, a French watchmaker

Watchmaker

A watchmaker is an artisan who makes and repairs watches. Since virtually all watches are now factory made, most modern watchmakers solely repair watches. However, originally they were master craftsmen who built watches, including all their parts, by hand...

called Louis Cartier

Louis Cartier

Louis Cartier was a famous French watchmaker and businessman known worldwide for elegant and extravagant watch designs. He was passionate about mechanical pocket watches and had the goal of creating his own line of timepieces...

, to design a watch that could be useful during his flights. The wristwatch had already been invented by Patek Philippe, in 1868, but only as a "lady’s bracelet watch", intended as jewelry. As pocket watches were unsuitable, Louis Cartier created the Santos wristwatch, the first man's wristwatch and the first designed for practical use.

Wristwatches gained in popularity during World War I, when officers found them to be more convenient than pocket watch

Pocket watch

es in battle. Also, because the pocket watch was mainly a middle class

Middle class

The middle class is any class of people in the middle of a societal hierarchy. In Weberian socio-economic terms, the middle class is the broad group of people in contemporary society who fall socio-economically between the working class and upper class....

item, the enlisted men

Enlisted rank

An enlisted rank is, in most Militaries, any rank below a commissioned officer or warrant officer. The term can also be inclusive of non-commissioned officers...

usually owned wristwatches, which they brought with them. Artillery and infantry officers depended on their watches as battles became more complicated and coordinated attacks became necessary. Wristwatches were found to be needed in the air as much as on the ground: military pilots found them more convenient than pocket watches for the same reasons as Santos-Dumont had. Eventually, army contractors manufactured watches en masse, for both infantry and pilots. In World War II, the A-11 was a popular watch among American airmen, with its simple black face and clear white numbers for easy readability.

Marine chronometers

Marine chronometer

A marine chronometer is a clock that is precise and accurate enough to be used as a portable time standard; it can therefore be used to determine longitude by means of celestial navigation...

s are clocks used at sea as time standard

Time standard

A time standard is a specification for measuring time: either the rate at which time passes; or points in time; or both. In modern times, several time specifications have been officially recognized as standards, where formerly they were matters of custom and practice. An example of a kind of time...

s, to determine longitude

Longitude

Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....

by celestial navigation

Celestial navigation

Celestial navigation, also known as astronavigation, is a position fixing technique that has evolved over several thousand years to help sailors cross oceans without having to rely on estimated calculations, or dead reckoning, to know their position...

. They were first developed by Yorkshire

Yorkshire

Yorkshire is a historic county of northern England and the largest in the United Kingdom. Because of its great size in comparison to other English counties, functions have been increasingly undertaken over time by its subdivisions, which have also been subject to periodic reform...

carpenter John Harrison

John Harrison

John Harrison was a self-educated English clockmaker. He invented the marine chronometer, a long-sought device in solving the problem of establishing the East-West position or longitude of a ship at sea, thus revolutionising and extending the possibility of safe long distance sea travel in the Age...

, who won the British government's Longitude Prize

Longitude prize

The Longitude Prize was a reward offered by the British government for a simple and practical method for the precise determination of a ship's longitude...

in 1759. Marine chronometers keep the time of a fixed location—usually Greenwich Mean Time

Greenwich Mean Time

Greenwich Mean Time is a term originally referring to mean solar time at the Royal Observatory in Greenwich, London. It is arguably the same as Coordinated Universal Time and when this is viewed as a time zone the name Greenwich Mean Time is especially used by bodies connected with the United...

—allowing seafarers to determine longitude by comparing the local high noon

High Noon

High Noon is a 1952 American Western film directed by Fred Zinnemann and starring Gary Cooper and Grace Kelly. The film tells in real time the story of a town marshal forced to face a gang of killers by himself...

to the clock.

Chronometers

A chronometer

Chronometer

Chronometer may refer to:* Chronometer watch, a watch tested and certified to meet certain precision standards* Hydrochronometer, a water clock* Marine chronometer, a timekeeper used for celestial navigation...

is a portable timekeeper that meets certain precision standards. Initially, the term was used to refer to the marine chronometer

Marine chronometer

A marine chronometer is a clock that is precise and accurate enough to be used as a portable time standard; it can therefore be used to determine longitude by means of celestial navigation...

, a timepiece used to determine longitude

Longitude

by means of celestial navigation

Celestial navigation

. More recently, the term has also been applied to the chronometer watch

Chronometer watch

A chronometer watch is a specific type of watch tested and certified to meet certain precision standards. In Switzerland, only timepieces certified by the COSC may use the word 'Chronometer' on them....

, a wristwatch that meets certain precision standards set by the Swiss agency COSC

COSC

COSC aka C.O.S.C. is Contrôle Officiel Suisse des Chronomètres, the Official Swiss Chronometer Testing Institute, which is the institute responsible for certifying the accuracy and precision of wristwatches in Switzerland.-Background:...

. Over 1,000,000 "Officially Certified Chronometer" certificates, mostly for mechanical wrist-chronometers—wristwatches—with sprung balance oscillators, are delivered each year, after passing the COSC's most severe tests, and being singly identified by an officially recorded individual serial number

Serial number

A serial number is a unique number assigned for identification which varies from its successor or predecessor by a fixed discrete integer value...

. According to COSC, a chronometer is a high-precision watch, capable of displaying the seconds and housing a movement that has been tested over several days, in different positions, and at different temperatures, by an official, neutral body. To meet this requirement, each movement is individually tested for several consecutive days, in five positions, and at three temperatures. Any watch with the designation chronometer has a certified movement.

Quartz oscillators

The piezoelectric properties of crystalline quartz

Quartz

Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

were discovered by Jacques

Jacques Curie

Paul-Jacques Curie was a French physicist and professor at the University of Montpellier. He and his brother, Pierre Curie, studied pyroelectricity in the 1880s, leading to their discovery of some of the mechanisms behind piezoelectricity....

and Pierre Curie

Pierre Curie

Pierre Curie was a French physicist, a pioneer in crystallography, magnetism, piezoelectricity and radioactivity, and Nobel laureate. He was the son of Dr. Eugène Curie and Sophie-Claire Depouilly Curie ...

in 1880. The first quartz crystal oscillator

Crystal oscillator

A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency...

was built by Walter G. Cady

Walter Guyton Cady

Dr. Walter Guyton Cady was a noted American physicist and electrical engineer. He was a pioneer in piezoelectricity, and in 1921 developed the first crystal oscillator....

in 1921, and in 1927 the first quartz clock

Quartz clock

A quartz clock is a clock that uses an electronic oscillator that is regulated by a quartz crystal to keep time. This crystal oscillator creates a signal with very precise frequency, so that quartz clocks are at least an order of magnitude more accurate than good mechanical clocks...

was built by Warren Marrison and J. W. Horton at Bell Telephone Laboratories in Canada. The following decades saw the development of quartz clocks as precision time measurement devices in laboratory settings—the bulky and delicate counting electronics, built with vacuum tube

Vacuum tube

In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...

s, limited their practical use elsewhere. In 1932, a quartz clock able to measure small weekly variations in the rotation rate of the Earth was developed. The National Bureau of Standards (now NIST) based the time standard of the United States on quartz clocks from late 1929 until the 1960s, when it changed to atomic clocks. In 1969, Seiko

Seiko

, more commonly known simply as Seiko , is a Japanese watch company.-History and ongoing developments:The company was founded in 1881, when Kintarō Hattori opened a watch and jewelry shop called in the Ginza area of Tokyo, Japan. Eleven years later, in 1892, he began to produce clocks under the...

produced the world's first quartz wristwatch

Watch

A watch is a small timepiece, typically worn either on the wrist or attached on a chain and carried in a pocket, with wristwatches being the most common type of watch used today. They evolved in the 17th century from spring powered clocks, which appeared in the 15th century. The first watches were...

, the Astron

Astron (wristwatch)

The Astron wristwatch, formally known as the Seiko Quartz-Astron 35SQ, was the world's first "quartz clock" wristwatch, i.e., one based on a quartz crystal oscillator...

. Their inherent accuracy and low cost of production has resulted in the subsequent proliferation of quartz clocks and watches.

Atomic clocks

Atomic clock

s are the most accurate timekeeping devices known to date. Accurate to within a few seconds over many thousands of years, they are used to calibrate other clocks and timekeeping instruments. The first atomic clock, invented in 1949, is on display at the Smithsonian Institution

Smithsonian Institution

. It was based on the absorption line in the ammonia

Ammonia

Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

molecule, but most are now based on the spin

Spin (physics)

In quantum mechanics and particle physics, spin is a fundamental characteristic property of elementary particles, composite particles , and atomic nuclei.It is worth noting that the intrinsic property of subatomic particles called spin and discussed in this article, is related in some small ways,...

property of the cesium atom. The International System of Units

International System of Units

The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

standardized its unit of time, the second, on the properties of cesium in 1967. SI

International System of Units

defines the second as 9,192,631,770 cycles of the radiation

Radiation

In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...

which corresponds to the transition between two electron spin energy levels of the ground state

Ground state

The ground state of a quantum mechanical system is its lowest-energy state; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state...

of the ¹³³Cs atom. The cesium atomic clock, maintained by the National Institute of Standards and Technology

National Institute of Standards and Technology

The National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory, otherwise known as a National Metrological Institute , which is a non-regulatory agency of the United States Department of Commerce...

, is accurate to 30 billionths of a second per year. Atomic clocks have employed other elements, such as hydrogen

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

and rubidium

Rubidium

Rubidium is a chemical element with the symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group. Its atomic mass is 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other elements in group 1, such as very rapid...

vapor, offering greater stability—in the case of hydrogen clocks—and smaller size, lower power consumption, and thus lower cost (in the case of rubidium clocks).

External links

www.germanclocks.org - for a comprehensive timeline of horology
A pilot's view on civilian, military, and vintage aviator time-pieces.
A walk through time
Measuring time in ancient Egypt
A basic Overview

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Early timekeeping devices

3500 BC – 500 BC

500 BC – 1 BC

Water clocks

Candle clocks

Incense clocks

Clocks with gears and escapements

Astronomical clocks

Modern devices of ancient origin

Clocks

Early Western mechanical clocks

Ottoman mechanical clocks

Pendulum clocks

Clockmakers

Wristwatches

Marine chronometers

Chronometers

Quartz oscillators

Atomic clocks

Further reading

External links