What did Zhang Heng invent?

Zhang Heng invented the seismograph and the armillary sphere.

Seismograph: As early as A.D. 132, Zhang Heng developed the world's earliest post-earthquake measuring instrument, called the post-wind seismograph. According to the Book of the Later Han Dynasty, the vessel was made of copper, with a convex top and a diameter of about eight feet. The periphery was decorated with various characters of birds and animals, which was also very similar to the wine glasses at that time. The instrument has eight columns and a driving mechanism is installed. There are eight bronze pearl dragons outside the vessel, arranged on all sides. After the earthquake, there was a toad spider under each dragon, and the dragon ball in the corresponding direction fell and was picked up by toad's mouth.

2. Hunyi: As early as the Western Han Dynasty, Geng Shouchang made a Hunyi, and Zhang Heng improved it on this basis to make it more accurate. Zhang Heng's improved armillary sphere is a copper ball with a diameter of about four feet. The ball is engraved with twenty-four solar terms, north and south poles, twenty-eight stars, yellow equator and other elements, forming an elephant (similar to the present celestial sphere). By connecting the clepsydra with the elephant through a mechanical device, the elephant can be operated through the running water in the clepsydra, and the laws of celestial movement and seasonal solar terms can be obtained.

Zhang Heng is proficient in many aspects, including astronomy, mathematics, literature and geography. Especially in seismology and astronomy, it is the first in this field. Zhang Heng invented the seismograph, the armillary sphere, the shadow of the Swiss wheel, the drum car in the meter, the woodcut, the topographic map and so on.

Working principle of seismograph

The working principle of seismograph is based on the characteristics of seismic wave propagation and the action of gravity. Seismographs are mainly used to detect and record the direction and intensity of earthquakes. The basic principle of seismograph is to detect earthquakes by using gravity and vibration of seismic waves. It usually consists of a suspended copper spherical container and a vertical pillar. This spherical container is filled with mercury or other liquid. When an earthquake occurs, the vibration of seismic waves will make the liquid in the container tilt or swing, thus affecting the measuring device in the container.

Specifically, the measuring device in seismograph is usually a pointer or a vibrating plate. When the local seismic wave propagates to the seismograph, it will make the pointer or oscillating disk move accordingly. By observing the position change of pointer or pendulum, the direction and intensity of earthquake can be determined.

The working principle of seismograph is based on the propagation of seismic wave and the response of liquid to gravity. When the local seismic wave passes through the seismograph, it will cause the measuring device to move and then record the relevant information of the earthquake. This principle makes seismograph an important tool for monitoring and studying seismic activity.