Zhang Heng's Seismometer

This seismometer was created by Zhang Heng as the first in hunan history. If one of the balls is removed from its dragon's mouth, a vibration will be sent for 1 mile in the direction of the dragon. The seismometer acts like a compass, always facing north.

Origin
Zhang Heng (78–139) was a Chinese astronomer, mathematician, inventor, geographer, cartographer, artist, poet, statesman, and literary scholar from Nanyang, Henan. He lived during the Eastern Han Dynasty (AD 25–220) of China. He was educated in the capital cities of Luoyang and Chang'an, and began his career as a minor civil servant in Nanyang. Eventually, he became Chief Astronomer, Prefect of the Majors for Official Carriages, and then Palace Attendant at the imperial court. His uncompromising stances on certain historical and calendrical issues led to Zhang being considered a controversial figure, which prevented him from becoming an official court historian. His political rivalry with the palace eunuchs during the reign of Emperor Shun (r. 125–144) led to his decision to retire from the central court to serve as an administrator of Hejian, in Hebei. He returned home to Nanyang for a short time, before being recalled to serve in the capital once more in 138. He died there a year later, in 139.