Water Clock

Have you ever wondered how people measured time before clocks? You might think of the sundial. But for a sundial to work, you need... well, the sun. What if it was a cloudy day? Or

night time? How did they measure time then? To solve this problem, many cultures built water clocks. Experts believe that the earliest water-clock was buried in 1500 B.C. in the tomb of Amenhotep I. Around 325 B.C. Greeks began using water clocks to keep time. They built it by hand and made it from wood, iron or brass.

A water clock or clepsydra is a 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. A water clock uses the flow of water to measure time.

The earliest water clocks came in two types: inflow and outflow. Both designs involved two large containers. One container was filled with liquid and suspended over the second one. Water dripped through a hole in the bottom of the filled container to the bottom one.

On inflow water clocks, the bottom container was marked with the hours of the day. As the container fills, the observer can see where the water meets the lines and tell how much time has passed. For outflow clocks, it was just the opposite. 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.

Water clocks quickly became popular in other parts of the world. As they spread, they also evolved. The ancient Greeks built many of these devices, as did the Romans. Both of these cultures made clocks that used gears and depended on water pressure. They also added bells to sound at assigned times and other mechanical features that made the clocks much more complex. The Romans used these to set time limits for people speaking in court. When the water ran out, so did your time.

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Regional Development of Water Clock

Egypt

The oldest water clock for which there is physical evidence dates from c. 1417–1379 BC, during the reign of Amenhotep III. The oldest documentation of a water clock is the tomb inscription of the 16th century BC Egyptian court official, Amenemhet, which identifies him as its inventor. This simple outflow water clock, was a stone vessel with sloping sides that allowed water to drip at a nearly constant rate from a small hole near the base. There are twelve separate columns with consistently spaced marks on the inside to measure the passing of the "hours" as the water level reaches them. The columns are for each of the twelve months to allow for seasonal hour variations. This clock was used by the priests to determine the time of night so that ceremonies and sacrifices in the temple could be carried out 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 period (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.

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. In Babylonian times, time was measured with temporal hours. So, as the 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.\

China

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. The liquid in water clocks can freeze, and had to be kept warm with torches. This problem was solved in 976 by the Chinese astronomer and engineer Zhang Sixun. His invention used mercury instead of water.

Korea

In 1434, during Joseon rule, Jang Yeong-sil, Palace Guard and Chief Court Engineer, constructed the Jagyeongnu (self-striking water clock or striking clepsydra) for King Sejong. 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. The uniqueness of the clock was its capability to announce dual-times automatically with both visual and audible signals.

Febe Sihombing, Sepmiyanti Sitohang - 10D