Su Song - Su Song's Armillary Sphere

Su Song's Armillary Sphere

In Joseph Needham's third volume of Science and Civilization in China, the drawing for Fig. 159 displays a drawing of Su Song's armillary sphere (as depicted in his 11th century treatise), complete with three 'nests' or layers of mechanically-rotated rings. It was the earlier Chinese astronomer Li Chun-feng of the Tang Dynasty who in 633 AD created the first armillary sphere with three layers to calibrate multiple aspects of astronomical observation. Zhang's armillary sphere has often been compared to that of the 13th century monarch Alfonso X of Castile in Islamic-era Spain. The chief difference was that Alfonso's instrument featured an arrangement for making measurements of the azimuth and altitude, which was present in the Arabic tradition, while Su Song's armillary sphere was duly graduated. For the drawing of Su's armillary sphere, the listing of components are:

• The Outer Nest
  • meridian circle
  • horizon circle
  • outer equator circle

• The Middle Nest
  • solstitial colure circle
  • ecliptic circle
  • diurnal motion gear-ring, connecting with the power-drive

• The Inner Nest
  • polar-mounted declination ring or hour-angle circle, with
  • sighting tube attached to it and strengthened by a
  • diametral brace

• Other Parts
  • vertical column concealing the transmission shaft
  • supporting columns in the form of dragons
  • cross-piece of the base, incorporating water-levels
  • south polar pivot
  • north polar pivit