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Water clock

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A water clock or clepsydra is a device for measuring time by letting water regularly flow out of a container, usually through a tiny aperture. While never reaching the level of accuracy based on today's standards of timekeeping, the water clock was the most accurate and commonly used timekeeping device for millennia, until it was replaced by the more accurate pendulum clock in the 17th century.
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Water Clock Overview

According to researcher Jim Maciejewski, water clocks were among the earliest timekeepers created by mankind. While there is no consensus on where or when the first water clock was created, early water clocks have been shown to have existed in the Mesopotamian region (Sumer, Babylonia, Assyria), in India (Vedic people), and in China. The general timeframe is 1500 BC - 3000 BC, and perhaps even earlier. Some water clock designs were developed independently and some knowledge was transferred through the spread of trade. It is important to point out that the need for the common person to 'know what time it is' largely did not exist until the Industrial Revolution, when it became important to keep track of hours worked. In the earliest of time, however, the purpose for using a water clock was for astronomical and astrological reasons. These early water clocks were calibrated with a sundial. Through the centuries, water clocks were used for timing lawyer's speeches during a trial, labors of prostitutes, night watches of guards, sermons and masses in church, to name only a few.

One of the oldest archaelogical finds of a water clock was in the tomb of the Egyptian pharaoh Amenhotep I (1525 - 1504 BC). This outflow water clock was built in honor of Amenhotep I by Amenemhet, an 18th dynasty dignitary. These were stone vessels with sloping sides that allowed water to drip at a nearly constant rate from a small hole near the bottom. Other clepsydras were cylindrical or bowl-shaped containers designed to slowly fill with water entering at a constant rate. Markings on the inside surfaces measured the passage of "hours" as the water level reached them. These clocks were used to determine hours at night, but may have been used in daylight as well. Another version consisted of a metal bowl with a hole in the bottom; when placed in a container of water the bowl would fill and sink in a certain time. These were still in use in northern Africa in the 20th century.

In Greece, a water clock was known as a clepsydra (water thief). Between 270 BC and AD 500, Greek (Ctesibius, Hero of Alexandria, Archimedes) and Roman horologists and astronomers were developing more elaborate mechanized water clocks. The added complexity was aimed at making the flow more constant by regulating the pressure, and at providing fancier displays of the passage of time. Some water clocks rang bells and gongs, while others opened doors and windows to show figurines of people, or moved pointers, and dials. Some even displayed astrological models of the universe.

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 structure showed scholars and shoppers both sundials and mechanical hour indicators. 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. The Romans also developed mechanized clepsydras, though their complexity accomplished little improvement over simpler methods for determining the passage of time.

A scale model of Su Song's Astronomical Clock Tower.
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A scale model of Su Song's Astronomical Clock Tower.

Celestial globe on third floor.
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Celestial globe on third floor.

Armillary sphere on roof.
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Armillary sphere on roof.

Time display panel.
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Time display panel.

Water powered mechanism.
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Water powered mechanism.

In eastern Asia, water clocks were very important in astronomy and astrology. Third century Chinese clepsydras drove various mechanisms that illustrated astronomical phenomena. One of the most elaborate clock towers was built by Su Sung (蘇頌) and his associates in 1088. Su Sung's mechanism incorporated a water-driven escapement invented about 725. The Su Sung clock tower, over 30 feet 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 manikins which rang bells or gongs, and held tablets indicating the hour or other special times of the day. From the earliest of times, Chinese timekeeping devices were introduced to the Korean peninsula.

In Korea, timekeeping was both a royal duty and a royal prerogative from its Three Kingdom Period (c. 37 BC) onwards. By 1434 during the Choson Dynasty, Jang Young Sil, a chief engineer of Korea, constructed the Chagyongnu (self-striking water clock) for King Sejong. What made the Chagyongnu self-striking was the use of jack-work mechanisms, by which three wooden figures (jacks) struck objects to signal the time. The Chagyongnu was a fully automatic device that didn't require any human worker, known as "rooster men", to constantly replenish it. [link] By 554, the water clock spread from Korea to Japan. Water clocks were used and improved upon throughout Asia well into the 15th century.

Today, few water clocks exist. In 1979, Bernard Gitton began creating his Time-Flow Clocks, which are a modern-day approach to water clocks. His unique design can be found in a couple places in the United States and in over 30 locations throughout the world. Also, there are some other modern designs of water clocks, but overall the use of water flow to power a clock largely remains a lost art.

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References

Further reading

Overview of Water Clocks and other Time Instruments Babylonian Water Clocks Chinese Water Clocks Egyptian Water Clocks Greek and Alexandrian Water Clocks Indian Water Clocks Islamic Water Clocks Korean Water Clocks Mesopotamian Water Clocks Present-day Water Clocks Other Topics on Water Clocks and Related Material Non-English Resources

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