Though it is surely an apt moniker, the south-pointing chariot is not one-hundred percent true to its name. One might suspect that these carriages could only travel south, which makes little sense but would be spot-on for their unique sobriquet. However, they are, in fact, named for the movable pointer each one carried, which was designed to point south, regardless of the direction of travel. Most likely used as a compass for navigation, these pointers where often shaped like a doll or other humanoid figure with an outstretched arm indicating south.
Unfortunately, no historical examples of the south-pointing chariot still exist today. A good amount was written about the carriages at the time of their invention and use, however. The oldest reliable resource to mention the south-pointing chariot was written circa 250 CE by Chinese engineer and government official Ma Jun. This places the vehicle’s creation some eight centuries before the first navigational use of the magnetic compass.
Fully Mechanical, Analog GPS
Multiple variations of these ancient, two-wheeled vehicles likely existed. Most types of south-pointing chariot used a special geared mechanism, connected to the rotating drive wheels, that kept the point aimed southward. No magnetics were involved, and so the mechanism did not automatically detect the correct direction; instead, the pointer was aimed south by hand at the start of a journey.
As the chariot turned left or right, the gear mechanism rotated the pointer relative to the carriage’s movement to keep it pointed south. This mechanism’s dead reckoning action proved less than perfect, and so was highly susceptible to cumulative errors which required manual correction. The curvature of the earth itself and the unavoidable topographical changes along any given route are enough to nudge the pointer well away from true south over a relatively short distance.
It is widely believed that most south-pointing chariots utilized differential gears to maintain their directional pointer, which likely makes them the first devices in human history to use differential gears, centuries before Europeans began using similar mechanisms. Modern recreations of south-pointing chariots that use differential gears have been relatively successful in automatically maintaining their pointer direction.
Descriptions in Song Shu
The Song Shu (translated: “Book of Song”), written in 493 CE by the poet and historian Shen Yue of the Southern Qi dynasty, contains extensive descriptions of south-pointing chariots and their use throughout the Three Kingdoms. Shen Yue wrote:
The south-pointing carriage was first constructed by the Duke of Zhou as a means of conducting homewards certain envoys who had arrived from a great distance beyond the frontiers. The country to be traversed was a boundless plain, in which people lost their bearings as to east and west. [The Duke] caused this vehicle to be made in order that the ambassadors should be able to distinguish north and south […]
During the Qing-long reign period [233-237 CE], the emperor Ming Di commissioned the scholar Ma Jun to construct one, and he duly succeeded. [The vehicle and its design were lost] during the troubles attending the establishment of the Jin Dynasty […]
Later on, Shi Hu [Emperor of the Jie Later Zhao dynasty] had one made by Xie Fei [and] Linghu Shang made one for [Emperor of the Later Qin dynasty] Yao Xing. […] Its appearance and construction was like that of a drum-carriage. A wooden figure of a man was placed at the top, with its arm raised and pointing to the south. Although the carriage turned round and round, the pointer-arm still indicated the south. In State processions, the south-pointing carriage led the way, accompanied by the imperial guard.
These vehicles […] did not function particularly well. Though called ‘south-pointing carriages,’ they very often did not pint true, and had to negotiate curves step by step, with the help of someone inside to adjust the machinery.