Self-Striking Water Clock (Jagyeongnu)

Timeline

1. 1432–1434Gyeongbokgung Palace, Hanyang · HanyangSejong ordered Jang Yeong-sil, together with Yi Chae, Kim Yo, and others, to develop a water clock that would automatically strike bells and drums according to the hour. The design drew on China's water-powered astronomical clock and West Asian automatic time-announcing traditions, while multi-tiered clepsydra, floating arrows, and ball-bearing levers achieved unattended announcement of the double-hours, watches, and quarters.
2. 1434Borugak Pavilion, Gyeongbokgung · HanyangThe court built the Borugak pavilion south of Gyeonghoeru and installed the self-striking water clock as the national standard timepiece. Outflowing water drove the floating arrow, triggering levers that made figures strike a bell, drum, and gong, conveying opening and closing times of the palace and city gates of Hanyang and the time of court audiences; Sejong accordingly proposed promoting Jang Yeong-sil in rank.
3. 1435–1505Borugak Pavilion, Hanyang royal palace · HanyangThe self-striking water clock long served timekeeping for the court and the capital, with repair records in years such as 1469. In 1505 Yeonsangun relocated it to the Borugak pavilion of Changdeokgung, showing that the mechanism had evolved from a new invention of Sejong's reign into a national time standard that could be moved with the principal palace.
4. 1536Changdeokgung–Deoksugung · HanyangThe original instrument of Sejong's reign was later lost. In 1536 the Jungjong reign recast the water-supplying and receiving vessels according to the old design; they were subsequently repaired repeatedly and interacted with the water-clock system of the astronomical bureau in the 1590s. The surviving vessels are designated national treasures, and modern full-scale reconstructions of the self-striking water clock are used in exhibitions, allowing the 1434 invention to endure both as a cultural artifact and as a reconstructed mechanism.