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    In the year of 132 A.D., a piece of surprising news caused great sensation in the capital city (Luoyang of Henan). It was said that the Minister in charge of historical records, Zhang Heng, invented an apparatus, which could tell the time and location of earthquakes. Many people doubted this because they didn't think people could tell what happened far away in other parts of the world.
    The apparatus Zhang Heng invented was called the seismograph, which was the first one in the world history. According to the records in the Later Han Dynasty History, that apparatus was cast with bronze. The outer appearance of it was like a jar with an inner diameter of 8 feet. The mechanism was placed inside the apparatus, and 8 dragons were set in 8 directions outside the apparatus. Each dragon had a bronze ball in its mouth, and the earthquake waves could make the inside mechanism of the apparatus start to work and hit the pole on the head of the dragon. Then, the ball would fall from the dragon to the mouth of a corresponding frog in the direction of the earthquake. Therefore, the observer could get to know what time and in which direction an earthquake had happened.
    On March 1, 138 A.D., the dragon in the West of the seismograph opened its mouth and the bronze ball fell into the mouth of the frog. The seismograph indicated that there was an earthquake in the west of Luoyang, the capital city. But since people in Luoyang did not feel the shock, there were many gossips. Some people even said that the equipment was inaccurate. Days later, the messenger on horse came to report that an earthquake had happened in the west Gansu, which was more than 500 kilometers away from Luoyang. Thus, the seismograph made itself convinced both inside and outside the courthouse.
    The first modern seismograph was made in 1880. The tenet it used was similar to that of Zhang Heng's apparatus, only that it was made many years later.
    The first earthquake observation station in China was established in 1930 and was presided by Li Shanbang. Nowadays, China has built several hundreds of earthquake observation stations, which makes the earthquake forecast of China rank in the front row of the world.