Yeong-sil Jang (Unknown)

Abstract

Yeong-sil Jang (called Jang Yeong-sil in the Korean style, Unknown) was a Korean inventor and mechanical engineer who served as chief court engineer under King Sejong of the Joseon dynasty (AD 1392-1910). He made two Striking Clepsydras (Jagyeong-nu) in the course of equipping the Royal Observatory in AD 1432-38. He invented liquid-driven discrete ball-falling mechanisms and ball-driven discrete motion control mechanisms for operating dual-time-announcing devices, and applied these towards making the Striking Palace Clepsydra. He developed the mechanisms and employed them to make a functional astronomical clock, the Striking Heavenly Clepsydra, which worked in conjunction with a water-powered wheel drive. The clepsydra was a standard timekeeper capable of announcing twelve double-hours with a bell simultaneous with a visual display indicating the current time. Five night-watches and their twenty-five points could also be announced by way of a drum and gong without human involvement. The stories of his works are told in the Annals of Sejong issued in 1454 and are supplemented by accounts in the dynastic documents afterwards. His innovations on mechanism design led to subsequent astronomical clocks from the seventeenth century onwards in Korea. Not only did he assimilate the techniques of his Korean, Chinese and Islamic predecessors, but was also creative and innovative in the history of mechanism and machine design.