Jagyeongnu Clock Production

Overview

Jagyeongnu (自擊漏) means "self-striking water clock." It measured time by the amount of water flowing in and was an automatic time-signaling device in which figures struck a bell, a drum, and a gong at prescribed times to announce the hour. It was made in 1434 (the 16th year of King Sejong) by Jang Yeong-sil, Yi Cheon, Kim Jo, and others under royal order, and was used from the first day of the seventh lunar month of that year (August 5 in the solar calendar).

Background of Production

In the early Joseon period, officials who tended the water clock watched the graduated markings and struck a drum or bell by hand to announce the hour. Because this depended on people, the hours were often missed. King Sejong regarded the accurate announcement of time as a basic element of state governance and ordered the creation of a clock that announced the hours on its own, without human hands. Jang Yeong-sil, a former government slave of Dongrae who was recognized for his technical talent and recruited, was the central figure in the production.

Structure and Operation

• Water-receiving part: Water flowed at a constant rate from a large water jar at the top, through a smaller jar, into a tall cylindrical receiving vessel (susuho 受水壺), and a float rod (jatdae, also called salttae) inside the vessel rose.
• Time-signaling part: When the float rod reached a certain height, it touched a bronze ball and set it rolling; the ball then moved a lever and figures, which struck the bell, drum, and gong.
• Signaling method: The bell was struck at every double-hour (si 時), and at night the drum and gong were struck in accordance with the night watches (gyeong 更) and points (jeom 點). There was also a mechanism in which a figure appeared holding a time tablet (sipae 時牌) to indicate the hour.

Installation and Use

Jagyeongnu was installed in Boruga (報漏閣), built south of Gyeonghoeru in Gyeongbok Palace, and was also called "Boruga-ru." Its location is presumed to be near the present site of Sujeongjeon. The signal sounded at Boruga was relayed through palace gate towers to the Jongno bell tower in the capital, so that the city's residents could know the times of the curfew (injeong) and the lifting of the curfew (paru).

Later History

The Jagyeongnu of King Sejong's era was not used for long and fell into disrepair, so a new one was made in 1536 (the 31st year of King Jungjong). Part of the water jars and receiving vessel of the Jagyeongnu made at that time survives as the "Changgyeonggung Jagyeongnu Nugi" (Water Clock of Changgyeonggung Palace), which has been designated a National Treasure. The striking mechanism does not survive, so today's reconstructions were made on the basis of records and research.

Significance

Jagyeongnu is a representative scientific instrument of fifteenth-century East Asia that combined a water clock with an automatic mechanical device. Together with the Angbuilgu (sundial), the Ganui (astronomical instrument), and the made in the same period, it shows the level of science and technology in the reign of King Sejong.