Wujing Zongyao - Compass and Navigation

Compass and Navigation

In the 3rd century, the Chinese engineer Ma Jun invented the South Pointing Chariot. This was a wheeled vehicle that employed differential gearing in order to lock a figurine of an immortal in place on the end of a long wooden staff, the figure having its arm stretched out and always pointing to the southern cardinal direction. Although the authors of the Wujing Zongyao were mistaken in believing that the design of the South Pointing Chariot was not handed down (as it was reinvented during the Song period and combined with an odometer), they described a new device which allowed one to navigate. This was the 'south pointing fish' (a thermoremanence compass), essentially a heated iron (or preferably steel) object cut in the shape of a fish and suspended in a bowl of water. The Wujing Zongyao part 1 vol 15 text stated:

When troops encountered gloomy weather or dark nights, and the directions of space could not be distinguished, they let an old horse go on before to lead them, or else they made use of the south-pointing carriage, or the south-pointing fish to identify the directions. Now the carriage method has not been handed down, but in the fish method a thin leaf of iron is cut into the shape of a fish two inches long and half an inch broad, having a pointed head and tail. This is then heated in a charcoal fire, and when it has become thoroughly red-hot, it is taken out by the head with iron tongs and placed so that its tail points due north. In this position it is quenched with water in a basin, so that its tail is submerged for several tenths of an inch. It is then kept in a tightly closed box. To use it, a small bowl filled with water is set up in a windless place, and the fish is laid as flat as possible upon the water-surface so that it floats, whereupon its head will point south.

Writing several decades after the Wujing Zongyao was written, the scientist and statesman Shen Kuo (1031–1095 AD) wrote of the first truly magnetized compass needle in his book Dream Pool Essays (1088 AD). With a more efficient compass magnetized by lodestone, the thermoremanence compass fell out of use. The later maritime author Zhu Yu soon wrote of the magnetic needle compass as a means to navigate at sea, in his book Pingzhou Table Talks of 1119 AD.