725 AD – Mechanical Clock

This post continues our  Computer Systems History series.

Through most of the middle ages, technological advancement was almost at standstill. Before large mechanical clocks began to appear in the towers of several large Italian cities, in the early-to-mid-14th century, there was a Liang Ling-Tsan, an 8th century military engineer. Together with Buddhist monk I-Hsing, Ling-Tsan was trying to devise a more precise calendar. He constructed a great astronomical clock on the grounds of the palace in Ch’ang-An. This ancestor of all modern clocks, built in 721-725AD, was the first machine known to employ an escapement, the basic device that is still used to regulated clocks. It divided the power from a water-wheel into exactly similar unit impulses so that the apparent motions of stars and the less regular wanderings of the planets could be duplicated by the measurable movements of a bronze dial made of rings and little spheres, while wooden figurines kept the sequence of the hours.

Clock Tower from Su Songs Book
Clock Tower from Su Songs Book

It was described this way:It was made in the image of the round heavens and on it were shown the lunar mansions in their order, the equator and the degrees of the heavenly circumference. Water, flowing into scoops, turned a wheel automatically, rotating it one complete revolution in one day and night. Besides this, there were two rings fitted around the celestial sphere outside, having the sun and moon threaded on them, and these were made to move in circling orbit … And they made a wooden casing the surface of which represented the horizon, since the instrument was half sunk in it. It permitted the exact determinations of the time of dawns and dusks, full and new moons, tarrying and hurrying. Moreover, there were two wooden jacks standing on the horizon surface, having one a bell and the other a drum in front of it, the bell being struck automatically to indicate the hours, and the drum being beaten automatically to indicate the quarters. All these motions were brought about by machinery within the casing, each depending on wheels and shafts, hooks, pins and interlocking rods, stopping devices and locks checking mutually.

Independently, The Greek and Roman civilizations are also credited for initially advancing water clock design to include complex gearing, which was connected to fanciful automata and also resulted in improved accuracy. Elaborate and impressive mechanized water clocks were developed between 100 B.C. and 500 A.D. by Greek and Roman horologists and astronomers. The added complexity was aimed at making the flow more constant by regulating the pressure, and at providing fancier displays of the passage of time. Some water clocks rang bells and gongs; others opened doors and windows to show little figures of people, or moved pointers, dials, and astrological models of the universe. These advances were passed on through Byzantium and Islamic times, eventually making their way back to Europe, until new types of mechanisms emerged in 13th century.

In the Far East, mechanized astronomical/astrological clock making developed from 200 to 1300 A.D. Third-century Chinese clepsydras drove various mechanisms that illustrated astronomical phenomena. One of the most elaborate clock towers was built by Su Sung and his associates in 1088 A.D. Su Sung’s mechanism incorporated a water-driven escapement invented back in 721-725 AD by Liang Ling-Tsan.


Resources used and recommended for further reading: