Reconstruction of Mechanical Principles of Zhang Heng's Seismoscope

The difficulties in the reconstruction of Zhang Heng’s Seismoscope come mainly from the lack of understanding of its mechanical principles. Such a discrepancy affects the rational reconstruction of the external form of the seismoscope and the fair assessment of its position in science. In connection with the two basic conjectures on its basic principles over the past hundred years: namely, the suspended pendulum and the upright rod, the authors have conducted a comprehensive study from the viewpoint of modern seismology. In this study, various aspects are involved, such as the properties of the seismoscope, its description in the “History of the Latter Han Dynasty", the structure and movement of the central pillar, historical earthquakes in the Longxi region, earthquake intensity in Luoyang, and modern seismograms from the Luoyang seismic station. The result shows that Zhang Heng’s seismoscope works following a suspended pendulum principle; it is triggered to move by seismic Rayleigh waves; and resonance plays the role of amplification. The long-prevailing conjecture of the upright rod, which was mistakenly called the “inverted pendulum" for a time, is believed to be improper. Both theory and practice show that it cannot be used in a seismoscope and will lead to an irrational reconstruction of the external form.