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                Home History and Culture Zhang Heng and the Seismograph
                Zhang Heng and the Seismograph
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                The first seismograph (dì dǒng yí?地動儀) of the world was invented by Zhang Heng (zhāng héng?張衡), a famous scientist in the Eastern Han Dynasty (dōng hàn 東漢, 25-220). Zhang Heng (78-139) was from Nanyang (nán yáng?南陽) in Henan Province (hé nán shěng?河南省). He studied diligently, and was especially keen on astronomy, calendars and mathematics. As a whole, Zhang Heng can be regarded as an erudite and talented scientist.

                Earthquakes of ancient times
                From the earliest times, the Chinese were concerned with the destructive force of earthquakes. It was recorded in Sima Qian's (sīmǎ qiān 司馬遷) Records of the Grand Historian(shǐ jì 史記) of 91 BC that in 780 BC an earthquake had been powerful enough to divert the courses of three rivers. The ancient Chinese did not understand that earthquakes were zhanghengcaused by the shifting of tectonic plates in the Earth's crust; instead, the people of the ancient Zhou Dynasty (zhōu cháo 周朝) explained them as disturbances with cosmic yin and yang (yīn yáng 陰陽), along with the heavens' displeasure with acts committed (or the common peoples' grievances ignored) by the current ruling dynasty. These theories were ultimately derived from the ancient text of the Yijing (yì jīng 易經, Book of Changes), in its fifty-first hexagram.

                During the Han Dynasty (hàn cháo 漢朝), many learned scholars—including Zhang Heng—believed in the "oracles of the winds". These oracles of the occult observed the direction, force, and timing of the winds, to speculate about the operation of the cosmos and to predict events on Earth. These ideas influenced Zhang Heng's views on the cause of earthquakes. Against the grain of earlier theories proposed by his fellow Chinese and contemporary Greeks, Zhang Heng believed that earthquakes were caused by wind and air.

                Structure of the Seismometer
                In 132, Zhang Heng presented to the Han court what many historians consider to be his most Seismographimpressive invention, the first seismometer. It was named Houfeng didong yi (hòu fēng dì dòng yí 候風地動儀, instrument for measuring the seasonal winds and the movements of the Earth). The description we have, from the History of the Later Han Dynasty (hòu hàn shū 后漢書), says that it was a large bronze vessel, about 2 meters in diameter and looked like a big cup with a lid. The surface of the instrument was cast with eight dragons, whose bodies were downward vertically and heads pointed to eight directions (east, south, west, north, southeast, northeast, southwest, and northwest), and each dragon had a copper ball in the mouth. On the ground vertically below the mouths of dragons, there were eight copper toads raising their heads and opening their mouths. The inner side of the seismograph was elaborately constructed. When an earthquake occurring at that direction, to which the dragon pointed would open its mouth, and the ball would fall into the toad’s mouth, automatically indicating the earthquake occurring at that direction.
                One day in 138 AD, the dragon pointing to the west expelled its ball. As expected, an restored modelearthquake had occurred on that day in Longxi? (lǒng xī 隴西, in present-day Gansu Province) four hundred miles away from Luoyang (luò yáng 洛陽). It was the first time that mankind had used the instrument to sense an earthquake. This was essential for the Han government in sending quick aid and relief to regions devastated by this natural disaster.??
                ????????????????? (click to enlarge)

                huntianyiApart from the Seismograph, Zhang Heng also invented the first water-driven armillary sphere (shuǐ yùn hún tiān yí 水運渾天儀) in the world to measure the position of celestial bodies. With so many contributions, Zhang Heng was highly esteemed by most people. A crater on the moon was named after him.


                ????? 張衡的一個杰出貢獻的科學領域是地震學。他的代表作就是震爍古今的候風地動儀的發明?,F在中國所見到的地動儀,并不是張衡發明的地動儀,而是后人復原的。張衡發明的地動儀早就毀于戰火了。候風地動儀發明于陽嘉元年(公元132年),全部用精銅鑄成,外形像一個帶蓋的大茶杯。儀器表面鑄有八條垂直向下的龍,龍頭分別對準東、南、西、北、東南、東北、西南、西北八個方向,每條龍的嘴里都含有一個銅球。在正對龍嘴的地上,蹲著八個仰頭、張嘴的銅蟾蜍(chán chú)。地動儀的內部結構非常精細巧妙,當某個方向發生地震時儀器上對著那個方向的龍嘴就會張開,銅球就會掉進銅蟾蜍的嘴里,自動報告發生地震的方向。公元138年的一天,地動儀西邊的龍嘴吐出了銅球。果然,遠在千里之外的隴西(今甘肅?。┰谶@一天發生了地震。這是人類第一次用儀器報地震。??????????????????????????????????????????????????????????????????????????????????
                ????? seismograph 這臺儀器不僅博得當時人們的嘆服,就是在今天的科學家看來也無不贊嘆。世界上地震頻繁,但真正能用儀器來觀測地震,在國外那是19世紀以后的事。候風地動儀乃是世界上的地震儀之祖。雖然它的功能尚只限于測知震中的大概方位,但它卻超越了世界科技的發展約1800年。
                ????? 張衡還制造出了世界上第一架測量天體位置的水運渾天儀,為古代科學發展做出了突出貢獻,并被人們所崇敬。聯合國天文組織曾將太陽系中的1802號小行星命名為“張衡星”。人們還將月球背面的一環形山命名為“張衡環形山”。


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