Egypt The oldest water clock of which there is physical evidence dates to c. 1417–1379 BC in the
New Kingdom of Egypt, during the reign of the pharaoh
Amenhotep III, where it was used in the
Precinct of Amun-Re at
Karnak. The oldest documentation of the water clock is the tomb inscription of the 16th century BC Egyptian court official Amenemhet, which identifies him as its inventor. These simple water clocks, which were of the outflow type, were
stone vessels with sloping sides that allowed water to drip at a nearly constant rate from a small hole near the bottom. There were twelve separate columns with consistently spaced markings on the inside to measure the passage of "hours" as the water level reached them. The columns were for each of the twelve
months to allow for the variations of the seasonal hours. Priests used these clocks to determine the time at night so that the temple rites and sacrifices could be performed at the correct hour.
Babylon In Babylon, water clocks were of the outflow type and were cylindrical in shape. Use of the water clock as an aid to astronomical calculations dates back to the
Old Babylonian Empire (
c. 2000 –
c. 1600 BC). While there are no surviving water clocks from the Mesopotamian region, most evidence of their existence comes from writings on
clay tablets. Two collections of tablets, for example, are the
Enuma Anu Enlil (1600–1200 BC) and the
MUL.APIN (7th century BC). In these tablets, water clocks are used for payment of the night and day watches (guards). These clocks were unique, as they did not have an indicator such as hands (as are typically used today) or grooved notches (as were used in Egypt). Instead, these clocks measured time "by the weight of water flowing from" it. The volume was measured in capacity units called
qa. The weight,
mana or
mina (the Greek unit for about one pound), is the weight of water in a water clock. In Babylonian times, time was measured with temporal hours. So, as seasons changed, so did the length of a day. "To define the length of a 'night watch' at the
summer solstice, one had to pour two mana of water into a cylindrical clepsydra; its emptying indicated the end of the watch. One-sixth of mana had to be added each succeeding half-month. At the
equinox, three mana had to be emptied in order to correspond to one watch, and four mana was emptied for each watch of the
winter solstitial night."'' According to N. Kameswara Rao, pots excavated from the
Indus Valley Civilisation site of
Mohenjo-daro may have been used as water clocks. They are tapered at the bottom, have a hole on the side, and are similar to the utensil used to perform
abhiṣeka (ritual water pouring) on
lingams. The
Jyotisha, one of the six
Vedanga disciplines, describes water clocks called
ghati or
kapala that measure time in units of
nadika (around 24 minutes). A clepsydra in the form of a floating and sinking copper vessel is mentioned in the
Sürya Siddhānta (5th century AD). At
Nalanda mahavihara, an
ancient Buddhist university, four-hour intervals were measured by a water clock, which consisted of a similar copper bowl holding two large floats in a larger bowl filled with water. The bowl was filled with water from a small hole at its bottom; it sank when filled and was marked by the beating of a drum in the daytime. The amount of water added varied with the seasons, and students at the university operated the clock. Descriptions of similar water clocks are also given in the
Pañca Siddhāntikā by the polymath
Varāhamihira in the 6th century, which adds further detail to the account given in the
Sūrya Siddhānta. Further descriptions are recorded in the
Brāhmasphuṭasiddhānta by the mathematician
Brahmagupta in the 7th century. A detailed description with measurements is also recorded by the astronomer
Lalla in the 8th century, who describes the
ghati as a hemispherical copper vessel with a hole that is fully filled after one
nadika.
China 's astronomical clock tower, featuring a clepsydra tank,
waterwheel,
escapement mechanism, and
chain drive to power an
armillary sphere and 113
striking clock jacks to sound the hours and to display informative plaques In
ancient China, as well as throughout East Asia, water clocks were very important in the study of
astronomy and
astrology. The oldest written reference dates the use of the water clock in China to the 6th century BC. From about 200 BC onwards, the outflow clepsydra was replaced almost everywhere in China by the inflow type with an indicator-rod borne on a float(浮箭漏, fú jiàn lòu). The liquid in water clocks was liable to freezing, and had to be kept warm with torches, a problem that was solved in 976 by the Chinese astronomer and engineer
Zhang Sixun. His invention—a considerable improvement on Yi Xing's clock—used
mercury instead of water. Mercury is a liquid at room temperature, and freezes at , lower than any air temperature common outside polar regions. Again, instead of using water, the early Ming Dynasty engineer
Zhan Xiyuan (c. 1360–1380) created a sand-driven wheel clock, improved upon by Zhou Shuxue (c. 1530–1558). The use of clepsydrae to drive mechanisms
illustrating astronomical phenomena began with the Han Dynasty polymath
Zhang Heng (78–139) in 117, who also employed a
waterwheel. Zhang Heng was the first in China to add an extra compensating tank between the reservoir and the inflow vessel, which solved the problem of the falling
pressure head in the reservoir tank. The same mechanism would be used by the Song dynasty polymath
Su Song (1020–1101) in 1088 to power his
astronomical clock tower, as well as a
chain drive.
Su Song's clock tower, over tall, possessed a
bronze power-driven armillary sphere for observations, an automatically rotating
celestial globe, and five front panels with doors that permitted the viewing of changing
mannequins which rang bells or gongs, and held tablets indicating the hour or other special times of the day. In the 2000s, in
Beijing's
Drum Tower an outflow clepsydra is operational and displayed for tourists. It is connected to automata so that every quarter-hour a small brass statue of a man claps his cymbals.
Persia The use of water clocks in
Greater Iran, especially in the desert areas such as
Yazd,
Isfahan,
Zibad, and
Gonabad, dates back to 500 BC. Later, they were also used to determine the exact holy days of pre-Islamic religions such as
Nowruz (
March equinox),
Mehregan (
September equinox),
Tirgan (
summer solstice) and
Yaldā Night (
winter solstice) – the shortest, longest, and equal-length days and nights of the years. The water clocks, called
pengan (and later
fenjan) used were one of the most practical ancient tools for timing the yearly calendar. The water clock was the most accurate and commonly used timekeeping device for calculating the amount or the time that a farmer must take water from a
qanat or well for irrigation until more accurate current clocks replaced it. Persian water clocks were a practical, useful, and necessary tool for the qanat's shareholders to calculate the length of time they could divert water to their farms or gardens. The qanat was the only water source for agriculture and irrigation in arid area so a just and fair water distribution was very important. Therefore, a very fair and clever old person was elected to be the manager of the water clock or
mir āb, and at least two full-time managers were needed to control and observe the number of hours and announce the exact time of the days and nights from sunrise to sunset because shareholders usually divided between day and night owners. The Persian water clock consisted of a large pot full of water and a bowl with a small hole in the center. When the bowl became full of water, it would sink into the pot, and the manager would empty the bowl and again put it on the top of the water in the pot. He would record the number of times the bowl sank by putting small stones into a jar. of
Ctesibius's (285–222 BC) clepsydra from the 3rd century BC. The hour indicator ascends as water flows in. Also, a series of gears rotate a cylinder to correspond to the temporal hours. ' hydraulic clock (clepsydra), at the
Kotsanas Museum of Ancient Greek Archaeology in
Athens. The word "
clepsydra" comes from the Greek meaning "water thief". The Greeks considerably advanced the water clock by tackling the problem of the diminishing flow. They introduced several types of the inflow clepsydra, one of which included the earliest feedback control system.
Ctesibius invented an indicator system typical for later clocks such as the dial and pointer. The
Roman engineer
Vitruvius described early alarm clocks, working with gongs or trumpets.
Clepsydrae for keeping time Some scholars suspect that the clepsydra may have been used as a stop-watch for imposing a time limit on clients' visits in
Athenian brothels. Slightly later, in the early 3rd century BC, the
Hellenistic physician
Herophilos employed a portable clepsydra on his house visits in
Alexandria for measuring his patients' pulse-beats. By comparing the rate by age group with empirically obtained data sets, he was able to determine the intensity of the disorder. The biggest achievement of the invention of clepsydrae during this time, however, was by Ctesibius with his incorporation of gears and a dial indicator to automatically show the time as the lengths of the days changed throughout the year, because of the temporal timekeeping used during his day. Also, a Greek astronomer,
Andronicus of Cyrrhus, supervised the construction of his Horologion, known today as the
Tower of the Winds, in the
Athens marketplace (or
agora) in the first half of the 1st century BC. This
octagonal
clocktower showed scholars and shoppers both
sundials and a
windvane. Inside it was a mechanized clepsydra, although the type of display it used cannot be known for sure; some possibilities are: a rod that moved up and down to display the time, a water-powered
automaton that struck a bell to mark the hours, or a moving star disk in the ceiling.
Medieval Islamic world 's
elephant water clock (1206). In the
medieval Islamic world (632-1280), the use of water clocks has its roots from Archimedes during the rise of
Alexandria in
Egypt and continues on through
Byzantium. The water clocks by the Arabic engineer
Al-Jazari, however, are credited for going "well beyond anything" that had preceded them. In Al-Jazari's 1206 treatise, he describes one of his water clocks, the
elephant clock. 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. Basically, 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. of
Al-Jazari, 12th century. The most sophisticated water-powered
astronomical clock was
Al-Jazari's
castle clock, considered by some to be an early example of a programmable
analog computer, in 1206. It was a complex device that was about high, and had multiple functions alongside timekeeping. It included a display of the
zodiac and the solar and lunar orbits, and a pointer in the shape of the crescent moon which traveled across the top of a gateway, moved by a hidden cart and causing automatic doors to open, each revealing a mannequin, every hour. It was possible to re-program the length of day and night in order to account for the changing lengths of day and night throughout the year, and it also featured five musician automata who automatically play music when moved by levers operated by a hidden camshaft attached to a water wheel. The first water clocks to employ complex segmental and
epicyclic gearing was invented earlier by the
Arab engineer
Ibn Khalaf al-Muradi in
Islamic Iberia c. 1000. His water clocks were driven by
water wheels, as was also the case for several Chinese water clocks in the 11th century.
Korea In 718,
Unified Silla established the system of clepsydra for the first time in Korean history, imitating the Tang Dynasty. In 1434, during
Joseon rule,
Chang Yŏngsil (), a palace guard and later chief court engineer, constructed the
Borugak Jagyeongnu or self-striking water clock of Borugak Pavilion for
Sejong the Great. What made his water clock self-striking (or automatic) was using jack-work mechanisms: three wooden figures or "jacks" struck objects to signal the time. This innovation no longer required the reliance of human workers, known as "rooster men", to constantly replenish it. The uniqueness of the clock was its capability to announce dual-times automatically with visual and audible signals. Chang developed a signal conversion technique that made it possible to measure analog time and announce digital time simultaneously as well as to separate the water mechanisms from the ball-operated striking mechanisms. The conversion device was called
pangmok, and was placed above the inflow vessel that measured the time, the first device of its kind in the world. Thus, the Borugak water clock is the first hydro-mechanically engineered dual-time clock in the history of horology.
Japan Emperor Tenji made Japan's first water clock called a . They were highly socially significant and run by ==Temperature, water viscosity, and clock accuracy==