古代,中世インドにおける時間の尺度について

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概要

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• People used sundials and water clocks for measuring time in ancient and medieval India (from about the fifth century B. C. to the 12 th century A. D.). The sundial measured time by the length of gnomon's shadow. The Indian water clock divided a day and night into sixty durations. The smallest unit was one "nadika" (which was about 24 minutes). In my present paper I would like to study the size of Indian water clocks and the method to measure time. The Indian water clocks existed as two types in ancient and medieval India. One was a bowl which was made of copper with a hole in the bottom. The empty bowl was placed and floated on water in a larger vessel. It sunk to the bottom of the vessel as soon as one nadika passed. The other was a simple and small vessel which was made from clay with a tube at the lower part. The inside diameter of the tube was kept in a uniform size by the use of a needle. The needle was made of pure gold and was about 7 cm long. The vessel which had been filled with water, discharged the water for one nadika. This was the more ancient form of a water clock in India. The both types of water clocks were used to measure a smallest unit of time, e. g. one "nadika". However, people in those days needed a period which was longer than one nadika. A day or night was divided into four or five durations by the use of the period. This period was called "prahara" or "yama" and used in a solar time. The length of prahara or yama was varied according to each season. There might be water clocks for such a long period in those days (see also Figs. 1-3). (1) It seems that the water clock measuring one nadika was used as the basic instrument for any other size of water clocks measuring a longer period. ( 2 ) If the above water clock measuring one nadika was practically used for a day or night, it would have been used for adjusting the length of prahara or yama according to each season. It should be pointed out that this method corresponds to changing the time scale of a day or night according to each season in other countries such as China, Egypt, Greek and Roma.

• 日本科学史学会の論文
• 1979-07-16

著者

• 大網 功

  東洋大学工学部

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