Quick Answer: How Did Chinese Water Clocks Work?
A Chinese water clock, or clepsydra (漏刻, lòukè), measures time through a change in water level. Water enters or leaves a vessel through a small opening. A float and an indicator can translate the change in level into a reading against a scale.[1][2][3]
- Outflow: Water leaves the vessel and the indicator descends.[2]
- Inflow: Water collects in a receiver, lifting the float and the pointer.[1][3]
- Regulation: Extra vessels can make the flow into the final receiver steadier.[1][3]
The time reading depends on a known relationship between water level and the scale.[1][3]
A water clock could give a reading after dark when a shadow instrument could no longer do so. Its practical problem was keeping the drip steady enough that equal marks corresponded to useful intervals. A surviving bronze clock from Guangzhou makes that problem visible.[1][3]
How a Changing Water Level Becomes a Time Reading
In a simple outflow design, water leaves a container and the level falls. A bronze clock in the National Museum of China had a graduated indicator that descended with the water. The indicator itself is missing. Its former position and the vessel’s form help explain where the reading would have been taken.[2]
An inflow clock reads the receiving vessel. As water enters, a float rises and moves the pointer. The height of the pointer relative to a scale gives a reading. With both designs, a calibration matters because the instrument is measuring water level directly and time through the relationship between level and flow.[1][3]
Why Chinese Water Clocks Used Several Vessels
A single draining reservoir can deliver water faster when full and more slowly when the level falls. Several vessels can separate the supply from the final reading. The last feeder can hold a steadier level, helping it send water into the measuring vessel at a steadier rate.[1][3]
In a late medieval astronomical bureau, a water clock could run by day or night as long as the water remained liquid. The bureau also used shadow measurements. The gnomon could supply a daylight reference, while the clepsydra provided readings between those observations.[3]
What the 1316 Guangzhou Water Clock Shows
The four bronze vessels made in Guangzhou in 1316 are arranged from top to bottom. Three feed the system and the lowest receives water. The National Museum’s description identifies an overflow in the third vessel. Excess water escaped there, helping keep the level supplying the receiver stable.[1][3]
In the receiver, a wooden float carried a pointer upward. The user could compare its height with a vertical scale marked with traditional double-hours. The scale and pointer are therefore part of the measurement system, alongside the vessels controlling the drip. The related study of Su Song’s astronomical clock shows how water could instead supply motion to a display mechanism.[1][3][4]
FAQs About Water Clocks in China
Could a water clock work at night?
It could provide a reading in darkness, with a steady supply and suitable conditions. The water needed to remain liquid, which mattered in winter.[3]
Is a clepsydra the same as Su Song’s clock?
A vessel clepsydra gives a reading through water level. In Su Song’s astronomical clock, water drove a regulated wheel and connected displays. Both use water, but its immediate job differs.[1][4]
What was the purpose of the float?
It followed the water level and carried an indicator. In the Guangzhou clock, the float rose as the lowest vessel filled, bringing the pointer to successively higher positions on the scale.[1]
出典
[1] National Museum of China. Four-Vessel Bronze Water Clock, 1316
[2] National Museum of China. Bronze Clepsydra With a Descending Indicator
[3] Journal of Chinese History. Becoming an Astronomer in Late Medieval China
[4] Chinese Annals of History of Science and Technology. Study of Clock Technology in China