Water clock

clepsydrawater clockswater-clockclepsydrasclepsydra clockclepsydraeClepsydreinflow clepsydrasklepsydraMechanical water clock
A water clock or clepsydra (Greek κλεψύδρα from κλέπτειν, 'to steal'; ὕδωρ, 'water') is any timepiece by which time is measured by the regulated flow of liquid into (inflow type) or out from (outflow type) a vessel, and where the amount is then measured.wikipedia
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Escapement

detent escapementCross-beat escapementduplex escapements
The Greeks and Romans advanced water clock design to include the inflow clepsydra with an early feedback system, gearing, and escapement mechanism, which were connected to fanciful automata and resulted in improved accuracy. Zhang's ingenuity led to the creation by the Tang dynasty mathematician and engineer Yi Xing (683–727) and Liang Lingzan in 725 of a clock driven by a waterwheel linkwork escapement mechanism.
The invention of the first all-mechanical escapement, the verge escapement, in 13th-century Europe initiated a change in timekeeping methods from continuous processes, such as the flow of water in water clocks, to repetitive oscillatory processes, such as the swing of pendulums, which could yield more accuracy.

Torricelli's law

Spouting can
If viscosity is neglected, the physical principle required to study such clocks is Torricelli's law.
A clepsydra is a clock that measures time by the flow of water.

Zhang Heng

Chang Hunggrid systemHeng Zhang
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.
He invented the world's first water-powered armillary sphere to assist astronomical observation; improved the inflow water clock by adding another tank; and invented the world's first seismoscope, which discerned the cardinal direction of an earthquake 500 km away.

Epicyclic gearing

epicyclicepicyclic gearboxplanetary
Further advances were made in Byzantium, Syria and Mesopotamia, where increasingly accurate water clocks incorporated complex segmental and epicyclic gearing, water wheels, and programmability, advances which eventually made their way to Europe.
His geared water clock employed a complex gear train mechanism that included both segmental and epicyclic gearing.

Astronomical clock

astronomicalastronomical clock towerastronomical clock towers
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.
In the 11th century, the Song dynasty Chinese horologist, mechanical engineer, and astronomer Su Song created a water-driven astronomical clock for his clock-tower of Kaifeng City.

Armillary sphere

armillaryarmillary spheresArmil
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.
The world's first water-powered celestial globe was created by Zhang Heng, who operated his armillary sphere by use of an inflow clepsydra clock (see Zhang's article for more detail).

Zhang Sixun

In 976, the Song dynasty military engineer and astronomer Zhang Sixun addressed the problem of the water in clepsydrae freezing in cold weather by using liquid mercury instead.
He is credited with creating an armillary sphere for his astronomical clock tower that employed the use of liquid mercury (dripped periodically from a clepsydra clock).

Su Song

Su SungEndless power-transmitting chain driveSong, Su
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.
European Jesuit visitors to China like Matteo Ricci and Nicolas Trigault briefly wrote about Chinese clocks with wheel drives, but others mistakenly believed that the Chinese had never advanced beyond the stage of the clepsydra, incense clock, and sundial.

Acropolis of Athens

AcropolisAthenian Acropolisthe Acropolis
Just northeast of the entrance to the Acropolis of Athens there was a famous natural spring named Clepsydra.
Nevertheless, it seems that a nine-gate wall, the Enneapylon, had been built around the biggest water spring, the Clepsydra, at the northwestern foot.

Horology

horologisthorologicalhorologists
Between 270 BC and AD 500, Hellenistic (Ctesibius, Hero of Alexandria, Archimedes) and Roman horologists and astronomers were developing more elaborate mechanized water clocks.
Clocks, watches, clockwork, sundials, hourglasses, clepsydras, timers, time recorders, marine chronometers, and atomic clocks are all examples of instruments used to measure time.

Elephant clock

the Elephant
In al-Jazari's 1206 treatise, he describes one of his water clocks, the elephant clock.
The elephant clock was a medieval invention by Al-Jazari (1136–1206), an Arab engineer and inventor of various clocks including the Elephant clock which consisted of a weight powered water clock in the form of an Asian elephant.

Tower of the Winds

Temple of Winds in AthensThe Tower of the Windstower
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.
The structure features a combination of sundials, a water clock, and a wind vane.

Yi Xing

Xing, YiZhang Sui
Zhang's ingenuity led to the creation by the Tang dynasty mathematician and engineer Yi Xing (683–727) and Liang Lingzan in 725 of a clock driven by a waterwheel linkwork escapement mechanism.
It was the earlier Chinese inventor Zhang Heng during the Han dynasty who was the first to apply hydraulic power (i.e. a waterwheel and water clock) in mechanically-driving and rotating his equatorial armillary sphere.

Vitruvius

Marcus Vitruvius PollioVitruvianVitruv
The Roman engineer Vitruvius described early alarm clocks, working with gongs or trumpets.
In Book I, Chapter 3 (The Departments of Architecture), Vitruvius divides architecture into three branches, namely; building; the construction of sundials and water clocks; and the design and use of machines in construction and warfare.

Water wheel

waterwheelwater wheelsovershot wheel
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. Further advances were made in Byzantium, Syria and Mesopotamia, where increasingly accurate water clocks incorporated complex segmental and epicyclic gearing, water wheels, and programmability, advances which eventually made their way to Europe. Their timekeeping is governed by a pendulum, but they use water for other purposes, such as providing the power needed to drive the clock by using a water wheel or something similar, or by having water in their displays.
They also employed water wheels to power a variety of devices, including various water clocks and automata.

Ismail al-Jazari

Al-Jazarial-Jazari, Ismailal-Jazarī
The water clocks by the Arabic engineer Al-Jazari, however, are credited for going "well beyond anything" that had preceded them.
A camshaft, a shaft to which cams are attached, was introduced in 1206 by al-Jazari, who employed them in his automata, water clocks (such as the candle clock) and water-raising machines.

Qanat

falajkarezfoggara
According to Callisthenes, the Persians were using water clocks in 328 BC to ensure a just and exact distribution of water from qanats to their shareholders for agricultural irrigation.
According to Callisthenes, the Persians were using water clocks in 328 BCE to ensure a just and exact distribution of water from qanats to their shareholders for agricultural irrigation.

Hour

htime of dayhr
It featured a 24-hour mechanized clepsydra and indicators for the eight winds from which the tower got its name, and it displayed the seasons of the year and astrological dates and periods.
By the time of Amenhotep III, the priests at Karnak were using water clocks to determine the hours.

The use of water clocks in Iran, especially in Zibad, dates back to 500 BC.

Clock tower

clocktowertower clockcastle clock
This octagonal clocktower showed scholars and shoppers both sundials and mechanical hour indicators.
In its interior, there was also a water clock (or clepsydra), driven by water coming down from the Acropolis.

Herophilos

HerophilusHerophilus of ChalcedonHerophilean
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.
To measure this pulse, he made use of a water clock.

Bernard Gitton

In 1979, French scientist Bernard Gitton began creating his Time-Flow Clocks, which are a modern-day approach to the historical version.
Bernard Gitton (born 24 June 1935 ) is a French physicist and artist who has built modern water clocks, fountains and other devices relating art and science.

Ctesibius

Ctesibius of AlexandriaKtesibios
Between 270 BC and AD 500, Hellenistic (Ctesibius, Hero of Alexandria, Archimedes) and Roman horologists and astronomers were developing more elaborate mechanized water clocks. Ctesibius invented an indicator system typical for later clocks such as the dial and pointer.
His other inventions include the hydraulis, a water organ that is considered the precursor of the modern pipe organ, and improved the water clock or clepsydra ("water thief").

Borugak Jagyeongnu

JagyeongnuWater clockWater clock of Borugak Pavilion
In 1434 during the Choson (or Joseon) Dynasty, Chang Yongsil (or Jang Young Sil) (장영실 in Korean), Palace Guard and later Chief Court Engineer, constructed the Jagyeongnu (self-striking water clock or striking clepsydra) for King Sejong.
The water clock is currently held and managed by the National Palace Museum of Korea in Seoul.

Sejong the Great

King SejongSejongKing Sejong the Great
In 1434 during the Choson (or Joseon) Dynasty, Chang Yongsil (or Jang Young Sil) (장영실 in Korean), Palace Guard and later Chief Court Engineer, constructed the Jagyeongnu (self-striking water clock or striking clepsydra) for King Sejong.
Jang created new significant designs for water clocks, armillary spheres, and sundials.