Zhang Heng, a Pioneering Scientist
Zhang Heng (78-140 AD) was born in Nanyang, Henan Province. He was one of the world's first astronomers. He was also a learned mathematician. He was appointed official with historiographic duties, and was also in charge of drawing up the calendar and observing astronomical phenomena.
He developed an armillary sphere, on which were carved all the astronomical phenomena known at that time.
Contrary to the popular belief at that time, Zhang Heng maintained that earthquakes were not signs of Heaven's anger but natural disasters. As a result of careful observations of earthquakes, he invented a seismograph in 132, which was the world's first instrument to identify and ascertain the direction of earthquakes. When an earthquake occurred, even if it could not be felt in Luoyang, the capital, a bronze ball would fall from the mouth of one of the carved dragon's heads on the instrument facing the direction of the epicenter of the earthquake into the mouth of a bronze toad below. It was not until the 13th century that similar instruments appeared outside China.
Zhang Heng's Seismograph
The seismograph was made entirely of bronze. Inside, there was a balanced post and eight rods connected to eight dragon's heads on the outside. When an earthquake occurred, the balanced post would tilt in the direction of the quake, push a rod, and cause the corresponding dragon's head to disgorge a bronze ball, which would then fall into the mouth of a bronze toad below.