Jang Yeong-sil

Timeline

1. c. 1390–1420Dongnae · Gyeongsang ProvinceRegistered in Dongnae, Jang Yeong-sil was a state slave (of low status) because his mother was a government courtesan. He became renowned locally for making devices, with reports of his skill reaching Hanseong. Though of low social standing at this stage, he already had practical ability in metalwork, hydraulic mechanisms, and observational instruments, laying the groundwork for his later exceptional entry into court.
2. c. 1422–1432Gyeongbokgung, Hanseong · HanseongTaejong and Sejong heard of his ingenuity and, over objections from yangban sons, promoted Jang Yeong-sil to commoner status and summoned him to court. To improve timekeeping and agricultural administration, Sejong sent him to Ming China to study water clocks and astronomical instruments. After returning he entered the Seogungwan (Bureau of Astronomy) production system, preparing for large-scale instrument-making in the 1430s.
3. 1432–1441Gyeongbokgung, Hanseong · Jian Terrace · HanseongIn 1433 Sejong's court designed an automatic time-announcing water clock based on Chinese clepsydra traditions; after a trial run it was adopted on the first day of the seventh month of 1434 as the national standard clock, announcing the time automatically with bells and drums. Jang Yeong-sil also participated in making the armillary sphere, upturned-bowl sundial, and jade clepsydra. In 1441 the court began casting bronze rain gauges, naming them rain gauges in 1442 and promoting them to the eight provinces; the initiative is recorded as the crown prince's, and the records do not explicitly state that Jang Yeong-sil personally supervised their construction, though later ages often credit him along with the self-striking clock.
4. 1442Hanseong · Joseon dynastyIn 1442 the imperial palanquin supervised by Jang Yeong-sil broke during use, and censors impeached him for irreverence. Although Sejong had previously overridden status objections to employ him, he now dismissed him from office. The records thereafter no longer detail his activities, and both his place and year of death are unknown. His self-striking clock tradition was maintained by Seogungwan officials, becoming part of Joseon's timekeeping system.