Sundial and Copper Clepsydra

Today, all kinds of clocks and watches bring convenience to daily life. But in ancient times, how did Chinese people measure time?

At first, they judged the time according to the position of the sun, the moon and stars in the sky, which was not very accurate. Later, people designed a kind of hour counter using the sun to determine the time ——the sundial. In the Qin (221-207 BC) and Han (206 BC-220 AD) dynasties, the sundial had become popular. The sundial is a round plate, the surface is carved with 12 hours (zi, chou, yin, mao, chen, si, wu, wei, shen, you, xu and hai), with a copper needle embedded in the center of the surface. Under the sun, the shadow of the copper needle moves slowly on the surface of the sundial to provide an accurate indication of time.

But when it is cloudy or at night, the sundial does not function. Later, people used the method of dropping water or sand to measure time, and invented a new tool ——the copper clepsydra.

The copper clepsydra was also called a water clock, hourglass, and sandglass. The earliest clepsydra was a copper pot holding water with a small opening at the bottom and a pole with scales standing in the center. When the water dropped through the small hole, people determined time by the scale on the pole as the water level decreased. This method of measuring time through clepsydra was still not accurate.

As the clepsydra was passed on from generation to generation, it gradually evolved into a set of four pots. These are placed in order on a four-level wooden stand, the one on the highest level called the Sun Pot, and below it the Moon Pot, Star Pot and Water-receiving Pot, respectively. The Sun Pot, Moon Pot and Star Pot all have an opening at the bottom for water to drop, and the Water-receiving Pot has a gauge inside. The water drops from the Sun Pot into the Moon Pot and then into the Star Pot and at last into the Water-receiving Pot. As more and more water drops into the Water-receiving Pot, the gauge gradually increases with the buoyancy of water. And thus people could tell the time through the scale above the water. The more levels the clepsydra has, the more accurate it is to measure time. Now, the four-level clepsydra of the Yuan (1271-1368 AD) and Qing (1644-1911 AD) dynasties are preserved respectively in the Museum of Chinese History and the Palace Museum in Beijing.

The sundial and copper clepsydra are the crystallization of ancient Chinese wisdom and creativeness. They not only tell us how ancient Chinese measured time, but also provide precious materials on the development of science and technology in ancient China.