Abstract:The actual existence of Zhangheng's seismograph is still controversial in science and historical circles, in great part because of contradictions within historical records. According to the History of the Later Han Dynasty: Biography of Zhang Heng, in the first year of Yang Jia (132 AD), Zhangheng made the seismograph and died in the fourth year of Yonghe (139 AD). During this time, there was only one earthquake that occurred in Longxi, Gansu Province, according to the History of the Later Han Dynasty, which occurred in the third year of Yonghe (138 AD). It is generally considered that this event must be the one the seismograph so famously recorded.The paradox lies in an inconsistency between historical records of the 138 AD Longxi earthquake. An accounting of property damage at the capital appears in the History of the Later Han Dynasty: WuXing Zhi, which means at the time of the Longxi earthquake, a destructive earthquake also struck the capital. However, according to the History of the Later Han Dynasty: Biography of Zhang Heng, when the Longxi earthquake occurred, no earthquake was felt at the capital.Therefore, in 138 AD, when the Houfeng seismograph recorded the earthquake, people in the capital should have strongly felt it. It would not be surprising that the seismograph could record the earthquake if people could feel it. Because of the conflict between the historical accounts, and because the seismograph was lost soon after its invention; many people believe that the seismograph did not really exist.This paper proposes another interpretation of the seemingly contradictory records. There were two capitals during the Eastern Han Dynasty: Chang'an and Luoyang. We know that the seismograph was tested in Luoyang. We propose that the capital that suffered earthquake damage was Chang'an, which would solve the paradox and serve as a powerful proof that the seismograph existed at that time.
