South-Pointing Chariot

The south-pointing chariot was an ancient Chinese two-wheeled vehicle carrying a pivoted pointer, usually shaped as a small figure with an outstretched arm, that kept indicating the same compass direction no matter which way the chariot itself turned. It achieved this without any magnetic compass, using a geared mechanism, in some versions a differential gear, connected to the chariot's wheels so that whenever the vehicle turned, the gearing rotated the pointer relative to the chariot's body by exactly enough to cancel out the turn and keep it aimed at the same heading. Although later legend attributed similar devices to the much earlier Western Zhou dynasty, the earliest south-pointing chariot supported by reliable historical texts was built by the mechanical engineer Ma Jun, who worked for the state of Cao Wei during China's Three Kingdoms period in the third century AD; no original chariot survives, but Chinese texts describe such vehicles being built and used for roughly another thousand years, into the vicinity of 1300.