PRIOR TO COMPASS
By Yifan Yin
Yifan Yin is a Candidate PhD in Microwave
at Polytechnique School of Montreal
Nowadays, compass, due to its capacity to show directions relative to the geographic cardinal directions, is widely used in navigation and orientation. It is almost an universally accepted fact that the Chinese invented the magnetic compass early in Han Dynasty around 206 BC. But at that time, this sort of compass was used for geomancy and feng shui. For example, the selection of the suitable site for a house or a tomb, the indications of the fortune of a family, the telling of win or lose for a war, all kinds of divination. We should wait until the Song Dynasty in the 11th century when the magnetic compass was adapted for the navigational use. 1
During the period prior to the use of compass, the mariners use several other ways to tell the direction. The celestial heavens or the stars were considered as tools to navigate. But as a result of its limited use only at night, the movement of stars, the night blindness of some mariners, its accuracy left a lot to be desired. The sun was also a form of primary reference, as it always rises in the east and falls in the west. However, except the rainy, fog days as well as the night, the earth changes also its angle in relation to the sun owning to its axial tilt, the sun is not so reliable. In addition, the Vikings made use of cordierite or some other birefringent crystal to tell the direction and the elevation of the sun from the polarization of daylight.2
In order to cross large bodies of water, the Polynesians even invented a system based on oral tradition from navigator to apprentice, called Polynesian navigation.3
All theses methods above have their visible weakness in navigation. The development of navigational technology using the compass is a breakthrough in history. In ancient China, the Chinese did have the knowledge of magnetism and the lodestone’s power in showing the direction in early time, but the development of compass as a navigation instrument is slow and experiences three periods. Lodestones were primitively formed into the shape of spoon and this well-balanced spoon can be spun around in a circle and point the south due to its directive property. But at that time, it had no direct application to direction in navigation. Then, the magnetic needle was invented, however due to the demand for a stable environment free from the disturbances of winds and waves for the compass equipped with this magnetic needle, its use in navigation is rare.
It is not until the South Song Dynasty when the well-considered compass, a kind of device indicating the direction of the magnetic meridian, was generally used in navigation. This kind of compass had also made great progress in its accuracy. Gradually, the use of compass in navigation was transmitted first to the Arabs by the Silk Road, then to the European by the crusade.
1. Lowrie, William (2007). Fundamentals of Geophysics. London: Cambridge University Press. p. 281. “Early in the Han Dynasty, between 300-200 BC, the Chinese fashioned a rudimentary compass out of lodestone... the compass may have been used in the search for gems and the selection of sites for houses... their directive power led to the use of compasses for navigation”
2. Gábor Horváth; et al. (2011). "On the trail of Vikings with polarized skylight". Philosophical Transactions of the Royal Society B 366 (1565): 772–782