(78 – 139 AD)

Zhang Heng was a polymath whose scientific works spanned across numerous fields. His contributions, which nourished generations of scholars, pertained to mathematics, mechanics, astronomy, seismology, geography and cartography. Even the great Liu Hui was inspired by his works. Likewise, many ancient scholars (who were not scientifically inclined) benefitted from his poems and other artistic works. Zhang Heng was also among the first scientists to methodically describe solar and lunar eclipses, as well as to conclude that moonlights do not originate from the moon: but are mere reflections of sun rays. He did improve several mathematical formulae, and derived better approximations for constants such as pi. One of his most notable engineering achievements involved the design and development of the first water-powered armillary sphere: with which he gained better cosmic insights. Another remarkable invention he made was the development of the first known seismoscope. This gadget was so sensitive as to accurately detect the cardinal direction of an earthquake occurring hundreds of kilometers away. The reinventions of both the odometer and the famous Chinese south-pointing chariot are attributed to him. Zhang Heng complimented his scientific exploits with erudite contributions to administration, ethics, literature and philosophy. He was highly influential in his lifetime; and remained so long after his death. His works inspired both Oriental and Western scholars. Named in his honor are: the 43-kilometer-wide Chang Heng lunar crater, the 1802 Zhang Heng asteroid, the Zhangheng-1 satellite, and the Zhanghengite (a golden-yellow mineral comprising mostly of copper, zinc, iron, aluminium and chromium).


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