1 - A Short History of Magnetism and Magnetic Materials

Summary

The magnetite iron ore FeO - Fe₂O₃ (or Fe₃O₄), famously known as lodestone, is the first known natural magnet. Folklore is that roughly around 2500 BC a Greek shepherd was tending his sheep in a region of ancient Greece called Magnesia (now in modern Turkey), and the nails that held his shoe together were stuck to the rock he was standing on. There were more such ancient stories about iron parts being pulled out from hulls of the ships sailing past the islands in the south Pacific and ones about the disarming and immobilizing of knights in their iron armor. Depending on the time and places where Fe₃O₄ or magnetite ore was found, it was variously known as the Magnesia stone, lodestone, the stone of Lydia, l’aimant in France, chumbak in India, or ts’u she in China. The modern name magnet is possibly derived from early lodestones found in the ancient Greek region of Magnesia.

The chronicled history of magnetism dates back to 600 BC. Lodestone's magnetic properties were studied and documented by the famous Greek philosopher Thales of Miletus (Fig. 1.1) in 600 BC [1]. Around the same period, the magnetic properties of lodestone were known in India, and the well-known ancient physician sage Sushruta (see Fig. 1.1) applied it to draw out metal splinters from bodies of injured soldiers [2]. However, Chinese writings dating back to 4000 BC mention magnetite, and indicate the possibility that original discoveries of magnetism might have taken place in China [3]. The Chinese were the first to notice that lodestone would orient itself to point north if not hindered by gravity and friction. The early Chinese compasses, however, were used in fortune-telling through the interpretation of lines and geographic alignments as symbols of the divine. These were also used for creating harmony in a room or building with the alignment of various features to different compass points. The first navigational lodestone compasses emerged from China. They had a unique design with the lodestone being shaped as a ladle (Fig. 1.2). The lodestone ladle sat in the center of a bronze or copper plate/disc. These compasses rotated freely when pushed and usually came to rest with the handle part of the ladle pointing south and so were known as south pointers. The copper/bronze base would be inscribed with cardinal direction points and other important symbols.