The seismograph is a masterpiece created by scientist Zhang Heng during the Eastern Han Dynasty in China. The time of the initial construction of the seismometer is unknown, but it was rebuilt in the first year of the Yangjia reign of Emperor Shun of Han (132 AD). It was the world's first seismometer and the first instrument in history to use scientific methods to determine the direction of earthquakes. The seismometer has eight directions, each with a dragon head containing a dragon ball, and below each head there is a toad corresponding to it. If an earthquake occurs on either side, the dragon ball contained in the dragon mouth in that direction will fall into the mouth of the toad, thus determining the direction of the earthquake.