Water clock
A water clock or clepsydra (from
Water clocks are one of the oldest time-measuring instruments.[1] The simplest form of water clock, with a bowl-shaped outflow, existed in Babylon, Egypt, and Persia around the 16th century BC. Other regions of the world, including India and China, also provide early evidence of water clocks, but the earliest dates are less certain. Water clocks were used in ancient Greece and in ancient Rome, as described by technical writers such as Ctesibius (died 222 BC) and Vitruvius (died after 15 BC).
Designs
A water clock uses the flow of water to measure time. If viscosity is neglected, the physical principle required to study such clocks is Torricelli's law. There are two types of water clocks: inflow and outflow. In an outflow water clock, a container is filled with water, and the water is drained slowly and evenly out of the container. This container has markings that are used to show the passage of time. As the water leaves the container, an observer can see where the water is level with the lines and tell how much time has passed. An inflow water clock works in basically the same way, except instead of flowing out of the container, the water is filling up the marked container. As the container fills, the observer can see where the water meets the lines and tell how much time has passed. Some modern timepieces are called "water clocks" but work differently from the ancient ones. 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. A water clock is one of the oldest and most important instruments.[citation needed]
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. 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. Independently, the Chinese developed their own advanced water clocks, incorporating gears, escapement mechanisms, and water wheels, passing their ideas on to Korea and Japan.[citation needed]
Some water clock designs were developed independently, and some knowledge was transferred through the spread of trade. These early water clocks were calibrated with a sundial. While never reaching a level of accuracy comparable to today's standards of timekeeping, the water clock was the most accurate and commonly used timekeeping device for millennia, until it was replaced by more accurate pendulum clocks in 17th-century Europe.[citation needed]
Regional development
Egypt
The oldest water clock of which there is physical evidence dates to c. 1417–1379 BC, during the reign of
Babylon
Clay tablet | |
---|---|
Akkadian | |
Created | 600BC-500BC |
Present location | Room 55, British Museum |
Identification | 29371 |
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
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.[8] 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.[citation needed]
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."[8]
India
N. Narahari Achar and Subhash Kak suggest that water clocks were used in ancient India as early as the 2nd millennium BC, based on their appearance in Atharvaveda'.[9][10] According to N. Kameswara Rao, pots excavated from the
The
Descriptions of similar water clocks are also given in the
China
In
The use of clepsydrae to drive mechanisms
Persia
The use of water clocks in Persia or Greater Iran, especially in desert area of Iran such as Yazd, Isfahan, Zibad, and Gonabad, dates back to 500 BC.[24] Later they were also used to determine the exact holy days of pre-Islamic religions such as Nowruz (March equinox), Chelleh Night (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 used in Iran were one of the most practical ancient tools for timing the yearly calendar.[25][26] 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 it was replaced by more accurate current clocks.[27][28] Persian water clocks were a practical and 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 (called Mir Aab), and at least two full-time managers were needed to control and observe the number of Fenjans or Pengan (hours) and announce the exact time of the days and nights from sunrise to sunset because share holder usually were divided to the days owners and night owners.[29] The Fenjaan 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.[29] The place where the clock was situated, and its managers, were collectively known as khaneh Fenjaan (times house). Usually this would be the top floor of a public-house, with west- and east-facing windows to show the time of Sunset and Sunrise. The Zibad Gonabad water clock was in use until 1965[26] when it was substituted by modern clocks.[25]
Greco-Roman world
The word "clepsydra" comes from the Greek meaning "water thief".[31] 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.[32] Ctesibius invented an indicator system typical for later clocks such as the dial and pointer.[33] The Roman engineer Vitruvius described early alarm clocks, working with gongs or trumpets.[33] A commonly used water clock was the simple outflow clepsydra. This small earthenware vessel had a hole in its side near the base. In both Greek and Roman times, this type of clepsydra was used in courts for allocating periods of time to speakers. In important cases, such as when a person's life was at stake, it was filled completely, but for more minor cases, only partially. If proceedings were interrupted for any reason, such as to examine documents, the hole in the clepsydra was stopped with wax until the speaker was able to resume his pleading.[34]
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
Between 270 BC and AD 500,
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,
Medieval Islamic world
In the
The most sophisticated water-powered
The first water clocks to employ complex segmental and
Korea
In 718,
What made the Jagyeongnu self-striking (or automatic) was the use of jack-work mechanisms, by which three wooden figures (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.[citation needed]
The uniqueness of the clock was its capability to announce dual-times automatically with both visual and audible signals.[45] Jang 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.[46] 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.[47] Thus, the Striking Palace Clepsydra is the first hydro-mechanically engineered dual-time clock in the history of horology.[48][49]
Japan
Emperor Tenji made Japan's first water clock called a Rokoku (漏刻). They were highly socially significant and run by Doctors of Water Clock
Temperature, water viscosity, and clock accuracy
When viscosity can be neglected, the outflow rate of the water is governed by
See also
Notes
- ^ Turner 1984, p. 1
- ^ a b Cotterell & Kamminga 1990, pp. 59–61.
- ISBN 0-226-15555-2.
- ^ Cotterell & Kamminga 1990
- ISBN 0-19-814946-8.
- ISBN 0-19-509539-1.
- ^ Neugebauer 1947.
- ^ a b Neugebauer 1947, pp. 39–40
- ^ Achar, N. Narahari (December 1998). "On the meaning of AV XIX. 53.3: Measurement of Time?". Electronic Journal of Vedic Studies. Archived from the original on 2015-09-23. Retrieved 2007-05-11.
- Bibcode:2003physics...1078K.
- Bibcode:2005BASI...33..499R. Retrieved 2007-05-11.
It appears that two artifacts from Mohenjo-daro and Harappa might correspond to these two instruments. Joshi and Parpola (1987) lists a few pots tapered at the bottom and having a hole on the side from the excavations at Mohenjadaro (Figure 3). A pot with a small hole to drain the water is very similar to clepsydras described by Ohashi to measure the time (similar to the utensil used over the lingum in Shiva temple for abhishekam).
- ^ "A copper vessel (in the shape of the lower half of the water jar) which has a small hole in its bottom and being placed upon clean water in a basin sinks exactly 60 times in a day and at night." – Chapter 13, verse 23 of the Sürya Siddhānta.
- ISBN 90-04-12556-6.
- ^ "A copper vessel weighing 10 palas, 6 angulas in height and twice as much in breadth at the mouth—this vessel of the capacity of 60 palas of water and hemispherical in form is called a ghati." This copper vessel, which was bored with a needle and made of 3 1/8 masas of gold and 4 angulas long, gets filled in one nadika."[full citation needed]
- ^ a b c Needham 2000, p. 479
- ^ Needham 1995, pp. 321–322
- ^ Temple & Needham 1998, p. 107.
- ^ Mercury at the Encyclopædia Britannica
- ^ Needham 1986, pp. 510–511
- ^ Needham 2000, pp. 30, 532
- ^ Needham 2000, pp. 471, 490, 532
- ^ Needham 2000, p. 462
- ^ Ellywa (1 August 2007). "Clepsydra in the Drum Tower, Beijing, China" – via Wikimedia Commons.
- ^ Rahimi, G.H. "Water Sharing Management in Ancient Iran, with Special Reference to Pangān (cup) in Iran" (PDF). Tehran university science magazine.
- ^ a b "Conference of Qanat in Iran – water clock in Persia 1383". www.aftabir.com (in Persian).
- ^ a b "Qanat is cultural and social and scientific heritage in Iran".
- ^ "Water clock or Pengan in Iran, National conference 2004 Gonabad". parssea.org. Archived from the original on 2017-06-10.
- ^ vista.ir. "Qanat iscultural and social and scientific heritage in Iran".
- ^ a b "water clock in persia". amordadnews.com. Archived from the original on 2014-04-29.
- ^ This engraving is taken from "Rees's Clocks, Watches, and Chronometers 1819–20. The design of the illustration was modified from Claude Perrault's illustrations in his 1684 translation of Vitruvius's Les Dix Livres d'Architecture (1st century BC), of which he describes Ctesibius's clepsydra in great length.
- ISBN 9780823989171.
The Greeks named the water clock 'clepsydra' (KLEP-suh-druh), which means 'water thief'.
- ^ Goodenow, Orr & Ross (2007), p. 7
- ^ a b John G. Landels: "Water-Clocks and Time Measurement in Classical Antiquity", "Endeavour", Vol. 3, No. 1 (1979), pp. 32–37 (35)
- ^ Hill 1981, p. 6
- ^ .
- ^ Lewis 2000, pp. 356f.
- ISBN 969-8016-25-2.
- ^ al-Hassan & Hill 1986, pp. 57–59
- ^ History Channel. Archived from the originalon March 1, 2014. Retrieved 2008-09-06.
- ISBN 0-292-78149-0.
- )
- ^ "two falcon automata dropping balls into vases – Google Search". www.google.com.my.
- ^ , History of Science and Technology in Islam
- .
- ISBN 9789400741324. Retrieved 27 March 2017.
- ISBN 9789400741324. Retrieved 27 March 2017.
- ^ Fifty Wonders of Korea - Vol. 2. KSCPP. Archived from the original on 2017-03-27. Retrieved 27 March 2017.
- ISBN 9789401789479. Retrieved 27 March 2017.
- ISBN 9789401796453. Retrieved 27 March 2017.
- ^ Goodenow, Orr & Ross (2007), p. 6
- ^ CRC Handbook of Chemistry and Physics, page F-36
Sources used
- Cowan, Harrison J. (1958). Time and Its Measurement: From the stone age to the nuclear age. Ohio: The World Publishing Company. Bibcode:1958tmfs.book.....C.
- Turner, Anthony J. (1984). The Time Museum. Vol. I: Time Measuring Instruments, Part 3: Water-clocks, Sand-glasses, Fire-clocks. Rockford, IL: The Museum. OCLC 159866762.
- Cotterell, Brian; Kamminga, Johan (1990). Mechanics of pre-industrial technology: An introduction to the mechanics of ancient and traditional material culture. Cambridge University Press. OCLC 18520966.
- S2CID 120229480. (Reprinted in Neugebauer, Otto (1983). Astronomy and History: Selected Essays. pp. 239–245.)
- Needham, Joseph (1986). Science & Civilization in China: Volume 4, Physics and Physical Technology, Part 2, Mechanical Engineering. Taipei: Caves Books.
- OCLC 153247126.
- OCLC 153247141.
Bibliography
External links
- The Clock of Flowing Time in Berlin Archived 2019-01-18 at the Wayback Machine
- NIST: A Walk Through Time – Early Clocks
- Bernard Gitton's Time-Flow Clocks Archived 2011-08-09 at the Wayback Machine
- Qanat is cultural,social and scientific heritage in Iran
- Egypt's Water Clock
- Encyclopedia Americana. 1920. .
- A Brief History of Clocks: From Thales to Ptolemy
- The Indianapolis Children's Museum Water Clock
- Nanaimo, BC Water Clock Archived 2007-08-11 at the Wayback Machine
- Animation: Ctesibius Water Clock
- Rees's Universal Dictionary article on Clepsydra, 1819
- The Royal Gorge Bridge Water Clock Archived 2007-05-01 at the Wayback Machine
- New International Encyclopedia. 1905.
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- The Mechanical Water Clock Of Ibn Al-Haytham
- computer servies on site on clocks