Water clock

A clock that measures time by using the dripping, flowing, and inflowing of water. Sundials and star clocks indicate time, so they cannot be used in places where the sun or stars are not visible, and are not suitable for measuring from any point in time or for dividing up time. Water clocks have been used since ancient times to compensate for this in Egypt and China, the birthplaces of ancient civilization. The oldest surviving example is an Egyptian water clock from around 1400 BC, a bucket-like container with a small hole in the bottom that measures time by the change in the water level. The Greeks called it a clepsydra (meaning water thief). In the 2nd century BC, water clocks were significantly developed by Ctesibius of Alexandria and his disciple Heron. Ctesibius' clock not only shows the month, date, and time, but also the 12 signs of the zodiac. Water clocks were widely used until around the 17th century, and some were equipped with striking devices. The Japanese water clock, which is said to have first told time in 671 (the 10th year of the reign of Emperor Tenchi), is also a type of water clock.

[Kuniyuki Motomochi]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

水のしたたりや流出・流入を利用して時間を測る時計。日時計や星時計は時刻を示すもので太陽や恒星が見えない場所では使用できず、また任意時点からの測定、時間の細分には適していない。古代文明の発祥地エジプトや中国などではこれを補うため古くから水時計が用いられた。現存最古のものは紀元前1400年ごろのエジプトの水時計で、バケツ状の容器の底に小穴があり、満たした水の水位変化によって時間を測る。ギリシア人はこれをクレプシドラclepsydra（水泥棒の意）とよんだ。前2世紀、水時計はアレクサンドリアのクテシビオスとその弟子ヘロンなどによって著しい発達を遂げた。クテシビオスの時計は月、日、時刻ばかりか黄道十二宮を示すものである。水時計は17世紀ごろまでも広く用いられ、なかには時打ち装置を備えたものもある。671年（天智天皇10）に初めて時を報じたとされる日本の漏刻(ろうこく)も水時計の一種である。

［元持邦之］

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