The black isometric mineral, magnetite, is among the most abundant of the Earth's minerals and can be found in beach sand, in meteorites, and in the natural abrasive emery. The naturally magnetic variety is known as a lodestone, first discovered in the Chinese desert around 3000 B.C.

The magnetic property of lodestone was first studied by the Greek philosopher Thales (624 B.C.-546 B.C.); his samples were found in the region of Magnesia, undoubtedly giving rise to the name "magnet." Thales also noted the "magnetic" property of amber which, when rubbed, could attracted light objects. Amber, however, is not a natural magnet; its ability to attract objects is due to the build-up of static electricity.

Magnets were useful in making compasses, the invention of which is credited to the Chinese. The next advance did not occur for nearly 2,000 years when French scholar Petrus Peregrinus (1240-?) considered the...