Magnetism
Magnetism is a class of physical phenomena that are mediated by magnetic fields. Electric currents and the magnetic moments of elementary particles give rise to a magnetic field, which acts on other currents and magnetic moments. The most familiar effects occur in ferromagnetic materials, which are strongly attracted by magnetic fields and can be magnetized to become permanent magnets, producing magnetic fields themselves. Only a few substances are ferromagnetic; the most common ones are iron, nickel and cobalt and their alloys. The prefix "" refers to iron, because permanent magnetism was first observed in lodestone, a form of natural iron ore called magnetite, FeO.
Magnetism
Magnetism was first discovered in the ancient world, when people noticed that lodestones, naturally magnetized pieces of the mineral magnetite, could attract iron. The word "magnet" comes from the Greek term μαγνῆτις λίθος "magnētis lithos", "the Magnesian stone, lodestone." In ancient Greece, Aristotle attributed the first of what could be called a scientific discussion of magnetism to the philosopher Thales of Miletus, who lived from about 625 BC to about 545 BC. The ancient Indian medical text "Sushruta Samhita" describes using magnetite to remove arrows embedded in a person's body.
In ancient China, the earliest literary reference to magnetism lies in a 4th-century BC book named after its author, "The Sage of Ghost Valley".
The 2nd-century BC annals, "Lüshi Chunqiu", also notes:
"The lodestone makes iron approach, or it attracts it."
The earliest mention of the attraction of a needle is in a 1st-century work "Lunheng" ("Balanced Inquiries"): "A lodestone attracts a needle."
The 11th-century Chinese scientist Shen Kuo was the first person to write—in the "Dream Pool Essays"—of the magnetic needle compass and that it improved the accuracy of navigation by employing the astronomical concept of true north.
By the 12th century the Chinese were known to use the lodestone compass for navigation. They sculpted a directional spoon from lodestone in such a way that the handle of the spoon always pointed south.