Zhang Heng

Henglg.jpg (7993 bytes)

Born: 78 in Nan-yang, China
Died: 139 in China

Heng was a mathematician, astronomer and geographer. He became chief astrologer and minister under the Emperor An'ti of China.

In the year 123 he corrected the calendar to bring it into line with the seasons.

In 132 Heng invented the first seismoscope for measuring earthquakes. Heng's device was in the shape of a cylinder with eight dragon heads around the top, each with a ball in its mouth. Around the bottom were eight frogs, each directly under a dragon head. When an earthquake occurred, a ball fell out of a the dragon's mouth into a frog's mouth, making a noise.

Heng was the first person in China to construct a rotating celestial globe. He wrote about this in his work Hun-i chu where he describes his version of the universe as follows:-

The sky is like a hen's egg, and is as round as a crossbow pellet; the Earth is like the yolk of the egg, lying alone at the centre. The sky is large and the Earth small.

In another work Lin Hsien, he describes the stars:-

North and south of the equator there are 124 groups which are always brightly shining. 320 stars can be named. There are in all 2500, not including those which the sailors observe. Of the very small stars there are 11520.

Heng also proposed p = 10 or approximately 3.162.

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