Expo Club
Zhou Dry
Time is an important reference for human life. Modern people often time and arrange work and life through clocks and watches, but China did not have clocks before the Qing Dynasty, and it is not easy to time them. Of course, this does not mean that there were no chronograph tools in ancient times. In the long-term life and production practice, through the continuous observation of some natural phenomena, ancient people gradually grasped the periodic changes in the sunrise and sunset, the stars appearing, the moon is missing, and took this as an opportunity to invent a variety of timing tools. The "sundial" is one of them. The so-called sundial is a tool for human beings to measure time according to the change of the position of the sun's shadow. As the Forbidden City of the Ming and Qing Dynasties, there are sundials in front of the Taihe Hall, Qianqing Palace, Kunning Palace, Yangxin Hall, Cining Palace and other buildings.
The sundial consists of a base, a dial, and a pointer. The base is parallel to the ground, the dial is parallel to the equator, and the pointer is parallel to the earth's axis (pointing to the north and south poles). The angle between the pointer and the ground plane must be the same as the local geographic latitude. The latitude of Beijing is 39.9 degrees north latitude, so the angle between the sundial of the Taihe Temple and the ground is also 39.9 degrees. The hands are generally copper, passing vertically through the dial, and their most important role is to determine the north-south direction. Since the dial is parallel to the equatorial plane, the upper end of the pointer points exactly to the north celestial pole and the lower end to the southern celestial pole. Therefore, the pointer of the sundial of the Taihe Temple is set in a north-south direction, and the pointer is fixed towards the North Pole. The second function of the pointer is to determine the time. The determination of its time is mainly achieved by the projection of the sun's illumination pointer on the dial. The dial is disc-shaped and stony, with 12 hours carved on both sides. When the sun shines on the sundial, the shadow of the pointer is cast on the dial. The sun moves from east to west, and the pointer shadow slowly moves from west to east. The scale of the dial is uniform, and the shadow of the moving hands is like the hands of modern clocks. As the position of the sun changes, the time it takes for a dial needle shadow to move an inch on the disk is called "an inch of time", and the idiom of "an inch of time and an inch of gold" is derived from this.
Sundials measure time using the direction of the sun's projection, but they lose their utility on rainy days and at night, and cannot be used during the vernal and autumnal equinoxes. Therefore, China's ancient craftsmen invented the missing engraving. As a timer, the use of missed engravings is more common and longer than sundials. Inside the Jiaotai Hall of the Forbidden City, there is a copper pot that is leaking. Leaks refer to water leaky pots, used to drain or hold water; engraving, refers to the time unit divided into days, which measures the time of day and night through the floating arrows of the leaky pot. The copper pot in the Jiaotai Hall was first created in the qianlong decade of the Qing Dynasty (1745) and was made by the Qing Palace Manufacturing Office. On October 21, the sixty-second year of Qianlong (1797), the Qianqing Palace was destroyed, and not only was the Qianqing Palace destroyed, but also the Jiaotai Hall and the copper pots in it were missing. The copper pot that exists in the Jiaotai Hall is leak-engraved, which was made and installed here by the imitation original of the third year of Qing Jiaqing (1798). When the leak is used, the water is injected into the leaky pot, and the water flows out of the pot hole and flows to the container placed under the kettle, which has a marker rod engraved with a moment in the container, called an arrow. The arrow is supported by a boat and floats on the surface of the water. When water flows out or flows into the pot, the arrow shaft sinks or rises accordingly, and the ancients can know the specific moment by looking at the mark on the arrow shaft from the lid hole.
During the Western Zhou Dynasty in China, there were missing engravings. Most of the early leaks use a single leaky pot, and the dripping rate is affected by the height of the liquid level in the pot, the liquid level is high, the dripping speed is faster, the liquid level is low, and the dripping rate is slower. In order to solve this problem, the ancients further created a multi-stage missing device. The so-called multi-level leakage engraving, that is, the use of multiple leaky pots, up and down in turn into a group, each leaky pot in turn to its next leaky pot dripping water. In this way, for the lowest receiving kettle, a drainage kettle above it has the same rate of water replenishment, the liquid level in the pot is basically kept constant, and its own dripping rate can be maintained uniformly.
The copper pot in the Forbidden City, like the sundial, became the main timekeeping tool in the Forbidden City for a long time. In the late Qing Dynasty, the chiming bell became popular, and sundials and missing engravings gradually withdrew from the historical stage and became an integral part of the royal ceremonial culture. However, they are simple in construction, scientific in design, and practical, providing time judgment guarantee for the lives of ancients for a long period of time, so they are the embodiment of the wisdom of ancient craftsmen.
(The author is a research librarian of the Palace Museum)