Magnetism
Among the greatest Chinese contributions to physics were the discovery of magnetism and the development of the compass. Though references to magnetism in Chinese sources do not date before the third century BCE, knowledge of the phenomenon was clearly widespread by this time, and experiments were being undertaken and documented by the first century CE. There were many early lodestone devices, such as the "south-pointing spoon" of the first century CE (which may have been invented a century earlier), and there are several intriguing references to the use of magnets to make "automatic" chess boards.
But magnetism seems to have been used predominantly in geomancy until the tenth century. Geomancy, or feng shui, was concerned with regulating human dwellings in relation to those currents of the spirit of the earth that affect people. The fact that knowledge of the compass was reserved for imperial magicians greatly restricted its spread, and it seems that for many centuries the compass served only as a tool for divination. Even when the compass passed into more general use, the primacy of canal and river traffic slowed the spread of the device to ocean-going vessels. Nevertheless, there were many adaptations and improvements in the form of compasses, which culminated in their use in navigation by the eleventh century.
Two of the most critical components in the development of the compass were the use of a needle rather than a lodestone or piece of metal and the discovery of magnetic declination (the deviation between true or geographic north and the direction that a compass needle points). The magnetization of needles was an important step in the development of the compass, because needles could float or be suspended by a thread and turn with a great degree of freedom. Also, steel holds magnetization longer than iron, and it was relatively easy at an early date to make small needles of steel; such compasses with steel needles could be used on long voyages. Steel came to China from India in the fifth century, but the Chinese quickly began to produce their own supplies. There is evidence to suggest that magnetized needles were used as early as the fourth century CE, and their superiority in the construction of compasses was quickly recognized.
The discovery of declination was also relatively early, sometime between the seventh and tenth centuries. While the influence of nonscientific divinatory practices was clearly prominent in the development of the compass, much research and experimentation went into magnetism from the fifth century on.
Further Reading
Needham, Joseph. (1986) The Shorter Science and Civilisation in China. Vol. 3. Edited by Colin A. Ronan. Cambridge, U.K.: Cambridge University Press.
This is the complete article, containing 435 words
(approx. 1 page at 300 words per page).
