Hong Kong

According to the Hong Kong Post website:  Scientists and inventors from China attained impressive achievements and made notable contribution to the world and science. This set of stamps features four ancient Chinese scientists, viz. Zhang Heng, Zu Chongzhi, Guo Shoujing and Li Shizhen who made substantial contribution to science, mathematics and astronomy, as well as Chinese medicine and herbal studies.

Zhang Heng (AD 78-139), an astronomer in the Eastern Han Dynasty, invented the world’s first seismoscope in the first year of the Yangjia Reign (AD 132). At the centre of the cavity of this bronze instrument was a hanging pendulum which carried eight mobile arms and cranks connected to eight corresponding dragons around the instrument’s surface. Each dragon held a bronze ball in its mouth and beneath the head of each dragon sat a toad with its mouth opening upwards. In the event of an earthquake, the vibrating pendulum would move the crank of a mobile arm in a specific direction and cause the corresponding dragon to release the small bronze ball into the open mouth of a toad. The time and direction of the earthquake could thus be deduced.