This study aims to develop a restoration model of an armillary sphere of Tongcheon-ui (Pan-celestial Armillary Sphere) by referring to the records of Damheonseo (Hong Dae-Yong Anthology) and the artifact of an armillary sphere in the Korean Christian Museum of Soongsil University. Between 1760 and 1762, Hong, Dae-Yong (1731-1783) built Tongcheon-ui, with Na, Kyung-Jeok (1690-1762) designing the basic structure and Ann, Cheo-In (1710-1787) completing the assembly. The model in this study is a spherical body with a diameter of 510 mm. Tongcheon-ui operates the armillary sphere by transmitting the rotational power from the lantern clock. The armillary sphere is constructed in the fashion of a two-layer sphere: the outer one is Yukhab-ui that is fixed; and the inner one, Samsin-ui, is rotated around the polar axis. In the equatorial ring possessed by Samsin-ui, an ecliptic ring and a lunar-path ring are successively fixed and are tilted by 23.5° and 28.5° over the equatorial ring, respectively. A solar miniature attached to a 365-toothed inner gear on the ecliptic ring reproduces the annual motion of the Sun. A lunar miniature installed on a 114-toothed inner gear of the lunar-path ring can also replay the moon's orbital motion and phase change. By the set of ‘a ratchet gear, a shaft and a spur gear’ installed in the solstice-colure double- ring, the inner gears in the ecliptic ring and lunar-path ring can be rotated in the opposite direction to the rotation of Samsin-ui and then the solar and lunar miniatures can simulate their revolution over the period of a year and a month, respectively. In order to indicate the change of the moon phases, 27 pins were arranged in a uniform circle around the lunar-path ring, and the 29-toothed wheel is fixed under the solar miniature. At the center of the armillary sphere, an earth plate representing a world map is fixed horizontally. Tongcheon-ui is the armillary sphere clock developed by Confucian scholars in the late Joseon Dynasty, and the technical level at which astronomical clocks could be produced at the time is of a high standard.

Hong, Dae-Yong manufactured the Tongcheon-ui (Pan-celestial Armillary Sphere) with cooperating clock researcher Na, Kyeong-Jeok, and its craftsman An, Cheo-In, in Naju of Jeolla Province in 1760 ~ 1762. Tongcheon-ui is a kind of astronomical clock with an armillary sphere which is rotated by the force generated by a lantern clock’s weight. In our study, we examine the lantern clock model of Tongcheon-ui through its description of the articles written by Hong himself. As his description, however, did not explain the detail of the mechanical process of the lantern clock, we investigate the remains of lantern clocks in the possession of Korea University Museum and Seoul National University Museum. Comparing with the clocks of these museums, we designed the lantern clock model of Tongcheon-ui which measures 115 mm (L) × 115 mm (W) × 307 mm (H). This model has used the structure of the striking train imitated from the Korea University Museum artifact and is also regulated by a foliot escapement which is connected to a going train for timekeeping. The orientation of the rotation of the going train and the striking train of our model makes a difference with the remains of both university museums. That is, on the rotation axis of the first gear set of Tongcheon-ui’s lantern clock, the going and the striking trains take on a counterclockwise and clockwise direction, respectively. The weight of 6.4 kg makes a force driving these two trains to stick to the pulley on the twine pulling across two spike gears corresponding to the going train and the striking train. This weight below the pulley may travel down about 560 mm per day. We conclude that the mechanical system of Tongcheon-ui’s lantern clock is slightly different from the Japanese style.