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Japanese water clock

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The first clocks made by human beings used the forces of nature. Learn about the inventions of ancient peoples, including sundials that directly tracked the movements of the sun and water clocks and combustion clocks that relied on the constant rates of physical processes.

Water clock

Sundials only tell time when the sun shines. The Egyptians also developed water clocks to tell time at night.
Water clocks were already in use in Egypt by around 1550 B.C. Water was poured into a mortar vessel to a prescribed level as soon as the sun went down. As the water leaked out from a small hole at the lower side of the vessel, the time could be determined by measuring the water level with a scale provided inside the vessel.
This water clock had a nighttime scale. This tells us that the Egyptians used sundials in the day and water clocks at night.

China also has a long history of water clocks. Official records of officers in charge of water clocks remain from the Zhou Dynasty (circa 1046 – 771 B.C.).

The Japanese adopted water clocks called “Rokoku” from China. Prince Naka no Oe (later Emperor Tenji) had a Rokoku produced in 660. In 671 the bells and drums were sounded to announce the time. This was the first time the Japanese public was notified of the time by sound. The bells and drums sounded on what would be June 10 in the present calendar. June 10 was established as Time Memorial Day in the Taisho period (in 1920).

The Rokoku works when water is poured in the first tank and flows to the lower tanks. The last tank is supplied with an arrow with a floater that floats higher as the water rises in the tank. The arrow has a scale to measure time.

Time was also constantly managed day and night in Japan.

The Water-powered Armillary (Sphere) and Celestial (Globe) Tower (astronomical observation clock tower) were invented by a scientist of the Northern Sung Dynasty (in 1088) named Su Song using the best available knowledge of Chinese astronomy and mechanical engineering of the day. The Sphere and Globe formed a precise water clock with an attached steelyard and driven by a waterwheel. The clock was also capable of astronomical observation.

Source: museum.seiko.co.jp
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