Liang Ling-Tsan

fl. 700s

Chinese Engineer

Liang Ling-Tsan, also known as Liang Ling-Zan, made his reputation in eighth century China. He was half of a two-man team that led the construction of the first clock escapement in history.

An engineer, Liang was also a member of the Crown Prince's bodyguard. When officials of the K'ai-Yuan reign issued an edict for the construction of an astronomical instrument, they selected Liang and a Chinese monk named I-Hsing (I-Xing) to oversee the project. I-Hsing was also a noted astronomer and mathematician. The two men and a team of artisans and technicians designed a water clock with an escapement, or mechanism, to control the speed and regularity of the clock's movements, and thus allow more accurate timekeeping ability.

Water clocks dated back nearly 4,000 years before the Liang-I-Hsing project began. A very simple water clock might involve two vessels, one placed higher than the other. The empty, lower container would be placed so that it would collect drips issuing from a tiny hole in the higher container. When a day had passed (such as sunrise to sunrise), the lower vessel's water level would be marked, along with equal increments of that level. If the day was to be divided into 24 hours, which was becoming a more common time division in China, the lower vessel would be marked into 24 divisions. Once this water clock was constructed, an observer could determine the time by simply viewing the water level as it related to the hour marks on the lower vessel.

The water clocks, unlike sundials, allowed the ability to envision hours as stable entities with unchanging lengths. For hundreds of years, people from many cultures divided each day and each night into a set number of hours, regardless of the length of the day or night. In the summer, the longer days were divided into a set number of equal-length hours, and the shorter nights into a set number of equal-length hours. A daytime hour in the summer might last 70 minutes, whereas a nighttime hour might last only 50 minutes. As the days became shorter with the approach of autumn, a daytime hour would decrease in length and a nighttime hour would increase. With the water clocks, which relied on a near-constant drip rate rather than time of year and length of daylight, the opportunity arose for unchanging hour lengths.

Although water clocks can be simple devices, the water clock constructed by Liang and I-Hsing was anything but. They used water to turn a driving wheel that set the clock in motion. To regulate the clock's movements, they also employed what is credited as the first mechanical escapement. The resulting bronze clock presented a celestial map, gave the time and the location of the sun and moon, and depicted the movement of the equatorial constellations. The bronze astronomical instrument was a showpiece in the palace, rivaled in notoriety only some three centuries later when Chang Ssu-Hsün used many of the ideas of I-Hsing and Liang to construct a large and intricate water-clock tower.

LESLIE A. MERTZ