The emergence of Zhang Heng's seismoscope has a profound historical background. This paper intends to explore the formation and material basis of Zhang Heng's scientific thought. It appears that the simple intention of "observing visions and distinguishing good fortune or misfortune"was his motivation to develop the seismoscope. Tracing its historical background,the authors proposed in this paper that the development of this seismoscope started around 128 A. D., and based on perceptual knowledge, two ideas about earthquakes came into being,i. e.,earthquake location could be judged according to the instrument shaking direction, and the earthquake and earth split were essentially different. In the instrument manufacture,Zhang Heng advocated a principle of "making utensils to imitate cosmos". By this principle,the following three problems were readily solved: the seismoscope imitated the response of the suspension system to earthquakes( i. e. natural seismoscope). Technically,the trigger mechanism of the latch was used for reference,and it recorded the physical evidence of earthquake occurrence by an ingenious way of a ball dropping from a dragon's mouth. The solution of these three key problems lead to the emergence of the seismoscope in 132 A. D. and the successful detection of an earthquake in 134 A. D. His invention deepened humanity's knowledge of natural laws, and promoted the development of science and technology in that time and later.
Historical data regarding Zhang Heng's seismoscope is not singular proof. Actually,the four earliest historical documents,i. e.,Continuation of Historiography of Han Dynasty, Historiography of the Later Han,Book of the Later Han and Ding Record all have relevant records of its structure,size,principle,response to earthquake and actual applications. These five aspects are supported by archaeological research,unearthed cultural relics, historical earthquakes and modern seismological study. These historical materials contain a great deal of specific information about this ancient seismoscope. In conclusion, the authenticity and reliability of Zhang Heng's seismoscope are verified.
The ancient idea of Heavenly Punishment confused natural phenomena with social issues,which resulted in Zhang Heng’s tragedy in his later years and seismoscope. The instrument might have been lost in the end of the Eastern Han Dynasty. A series of extremely serious chaotic social events caused by war took place,such as a fire in Luoyang,forging coins by destroying copper wares,relocation of the capital,sharp population decrease,and the destruction of the Ling Observatory. Zhang’s scientific thought and successful practice had played an important role in ideological enlightenments at the primary stage of modern seismology at the end of the nineteenth century. There is a glorious course of"innovation—inheritance—re-innovation"of scientific and technical development from the inception Zhang Heng’s seismoscope to the modern seismograph invented by Milne,et al.
In view of the important prestige of Zhang Heng’s seismoscope in world culture,scholars in different countries have performed restoration research,however,so far all restored models have only reached the drawing design and exhibition stage. In recent decades,new research achievements on historical materials,archaeology and historical seismology have been made in Chinese academic society,which lay a good foundation for the establishment of a new restored model. Not only does the new model more accord with historical materials,but it can be used to detect earthquakes for the first time. This paper will introduce the restoration in four aspects: scientific train of thought,structural restoration,formation restoration and scientific testing.
