How it began
Water clocks had a long history in Korea, with the first mention of one in the Samguk Sagi, in records of the Three Kingdoms era. In 1434, the sixteenth year of King Sejong's reign, Jang Yeong-sil made a water clock on the king's order that marked the hours automatically with the sounds of a bell, a gong and a drum. It was called Jagyeongnu, the self-striking water clock, and was used to keep the standard of time in the Joseon dynasty. The surviving parts are held by the National Palace Museum of Korea in Seoul.
How it works
Water was poured into the largest bronze vessel, flowed down into smaller vessels and then into long water tanks. As the level rose, a floating rod lifted until it touched a lever device, which released a ball. The rolling ball struck another ball at the far end, and the falling balls triggered the gong, bell and drum. A wooden puppet also appeared holding a placard that showed the hour.
What lasted
The original clock was not well preserved, and in 1536 King Jungjong ordered it remade and improved, work done by Yu Jeon. Extensive records of the 1536 version remain, and the two clocks are believed to have been very similar. The surviving vessels, known as the Borugak Jagyeongnu, are described as the oldest and largest remains of an automatic water clock of this kind.
Where it stands today
The clock no longer runs because only its water vessels survive: large bronze containers 93.5 centimeters across and 70 centimeters high, and smaller ceramic vessels. They were designated National Treasure no. 229 on 3 March 1985. A working reconstruction of the clock was built in 2007.
