A Study on the Operation Mechanism of Ongnu, the Astronomical Clock in Sejong Era

Abstract

Ongnu (Jade Clepsydra; also called Heumgyeonggaknu) is a water clock was made by Jang Yeong-sil in 1438. It is not only an automatic water clock that makes the sound at every hour on the hour by striking bell, drum and gong, but also an astronomical clock that shows the sun's movement over time. Ongnu's power mechanism used is a water-hammering method applied to automatic time-signal device. The appearance of Ongnu is modeled by Gasan (pasted-paper imitation mountain) and Binpungdo (landscape of farming work scene) is drawn at the foot of the mountain. The structure of Ongnu is divided into the top of the mountain, the foot of the mountain and the flatland. There located are sunmovement device, Ongnyeo (jade female immortal; I) and Four gods (shaped of animal-like immortals) at the top of the mountain, Sasin (jack hour) and Musa (warrior) at the foot of the mountain, and Twelve gods, Ongnyeo (II) and Gwanin on the flatland. In this study, we clearly and systematically understood the time-announcing mechanism of each puppet. Also, we showed the working mechanism of the sun-movement device. Finally, we completely established the 3D model of Ongnu based on this study.

A Study on the Internal Structure of Heumgyeonggaknu

“…8 The fixed quantity supply of water and constant speed operating of the water wheel is most important to the waterhammering type water clock. Kim et al (2011) suggested that a fixed quantity water in Uigi (欹器, inclining vessel) which is supplied from southern Gwanin (官人, government official)'s golden bottle spilled into Nusudae as time passed and this water move into a small vessel which is hanging from the water wheel in Heumgyeonggaknu and then this water-filled device is operating Cheonhyeong system (天衡, oriental escapement device).…”

“…1 was made so that every puppet is standing up. 9 For the study of Kim et al (2011), it is hard to be regarded as the key device related with water-hammering type control considering that the Uigi is installed separately as stated in the literature record (Myeongjong Sillok 10:92a:10 ~ 14). (Myeongjong Sillok 10:92a:10 ~ 14; 領觀象監事李芑啓曰 前者, 以欽敬閣欹器, 虛而不欹, 故今改造而進.…”

“…For example, at O-Si (午時), the Ongnyeo is raised with the corresponding Sipae by the motion of rotation wheel. 14 Regarding this part, Kim et al (2011) stated that "by the working mechanism of Nusudae that had the escapement system" (Kim et al 2011, p.84). However, in the following research, the Nusudae was analyzed as the space which simply accommodates Uigi.…”

A Study for the Restoration of Hong Dae-Yong Honsangui - Focusing on the structure and operating mechanism -

“…Shui yün i hsiang t'ai of 11th century and Borugaknu of 15th century had such a function. Kim et al (2011) and Lee & Kim (2012) presumed that the overflow method was also applied to Heumgyeonggaknu and the water-hammering type celestial globe. The generation and control of the driving force using the alarm clock Tongcheonui, which is another instrument in the Nongsugak, the personal observatory of Hong Dae-Yong, is by a weight and a foliot type escapement system.…”