In the Eastern Han Dynasty, earthquakes often occurred. Sometimes once a year and twice a year. A major earthquake affected dozens of counties. The city walls and houses collapsed, and many people and animals were injured. The feudal emperors and ordinary people at the time regarded the earthquake as an ominous sign, and some took the opportunity to promote superstition and deceive the people. However, he did not believe in God or evil. After careful investigation and repeated experiments on the recorded earthquake phenomenon, he invented an instrument for measuring and reporting earthquakes, called a earthquake instrument.
The ground motion instrument is made of fine copper, with a length of eight feet and a raised lid, similar to a wine bottle. The surface is golden yellow, and eight golden dragons are cast on the upper part, which lie in eight directions: east, west, south, north, northeast, southeast, northwest, and southwest. The dragon fell, with the dragon s head down, and each dragon s mouth held a small copper ball, which was opposite to the toad who squatted and opened his mouth on the ground. A copper pillar is erected in the center of the cavity of the ground motion instrument. There are eight crossbars around the copper pillars, called Badao, each connected to a dragon head. The copper pillar is a pendulum device. Eight channels are used to control and conduct the direction of copper pillar movement. When the ground motion instrument was shocked by the earthquake wave, the copper pillars fell down in the direction of the earthquake, pushing the crossbar and the faucet in the same direction to open the dragon s mouth, the copper ball dropped into the toad s mouth, and a sound was made to remind people to notice Earthquake and its time and direction.
Hold a bead on the platform, and if you press down slightly on which side, the bead will roll to which side. Another example is when we light a candle and place it on an uneven table, it will always fall to the lower side. The ground motion instrument is designed based on these simple principles. The ground motion can be transmitted far away, but it is too far for people to feel it, but the ground motion meter can accurately measure it.
One day in February 138, Zhang Hengs ground motion instrument suddenly opened up to the western dragon s mouth and spit out a copper ball. According to Zhang Heng s design, this is to report an earthquake in the west. However, that day there was no sign of an earthquake in Luoyang, and no one had heard of an earthquake nearby. Therefore, everybody talked a lot, saying that Zhang Heng s ground-moving instrument was a deceptive thing, and some even said that he intended to cause rumors. A few days later, some people rode fast to report to the court that a large earthquake occurred in Jincheng and Longxi, more than a thousand miles away from Luoyang, and even the mountains collapsed. Longxi is more than a thousand miles away from Luoyang, and the ground motion instrument is correctly marked, indicating that its seismic sensitivity is relatively high. At the same time, Zhang Heng also had a certain understanding of the propagation and directivity of seismic waves. These achievements were very remarkable at that time. In Europe, it was not until 1880 that instruments similar to the ground motion instruments were made. It is more than 1,700 years later than Zhang Heng ’s invention..