[2] According to the History of Song, Zhang Sixun passed the state examinations in astronomy and mathematics, for this he was appointed to service in the national astronomical observatory (Si Tian Jian), within two years of taking office he had finished construction of an armillary sphere either in 977 or 979.
It was polymathic scientist and engineer Zhang Heng (78–139 AD) during the Han dynasty who invented the first hydraulic-powered (i.e. with waterwheel and clepsydra) armillary sphere.
In addition, it was the Tang dynasty era Buddhist monk, engineer, and mathematician Yi Xing (683–727 AD) who invented the first hydraulic-powered armillary sphere that incorporated the escapement mechanism.
armillary sphere, hun i) and presented the designs to the emperor Thai Tsung, who ordered artisans of the Imperial Workshops to construct it within the Palace.
On a kuei-mao day in the first month of the 4th year (+979) the elaborate machine was completed, and the emperor caused it to be placed under the eastern drum-tower of the Wen-Ming Hall.
Moreover, as during winter the water partly froze and its flow was greatly reduced, the machinery lost its exactness, and there was no constancy between the hot and cold weather.
(Chang) Ssu-Hsun was considered the equal of the Thang clock-makers and was made Special Assistant in charge of the Armillary Sphere (Engine)(Ssu-Thien Hun I Chheng).