Thursday, February 6, 2014

Stones of Magnesia

A perpetual motion machine powered by magnetism,
described by Peter Peregrinus
Magnets/lodestones have fascinated people for at least 25 centuries. We should first clarify the names. The word "lodestone" was first used in the 16th century and refers to the metal ore with magnetic properties. The word "magnet" was coined by the Greeks far earlier and refers to "stones from Magnesia." Magnesia was a region in Thessaly where it was easy to find the magnetic ore.

Aristotle informs us that Thales of Miletus (625 - c.525 BCE) was certain that magnetism, since it caused the rock to move, was a sign that all things—even rocks—were imbued with divine power; essentially, with "soul." Pliny the Elder mentioned a mountain near the Indus River that was a giant magnet. Superstitions about magnets abounded, and it was incorporated into legends. A mid-twelfth century romance about Aeneas claimed that the walls of Carthage had meanest in them that drew and incapacitated the weapons of Aeneas' men.

Bishop of Paris William of Auvergne in 1231-6 used magnetism as an analogy for the motion of the celestial spheres. A generation later, a French scholar named Peter Peregrinus, or Peter of Maricourt, wrote Epistolæ de Magnete ["Letters on the Magnet"] to a friend, explaining the observable properties of magnets. He describes the two poles, attraction and repulsion, and how to make efficient compasses. His work was so thorough that no one bothered to write another work on magnets until 1600, and that person quoted Peter's work.

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