The ancient Chinese were the first to use magnets as compasses for navigation. Though they did not know it, these “south-pointing needles” worked because the magnets aligned themselves with Earth’s magnetic field. Since Earth’s magnetic poles have been very close to the rotational north and south poles, compasses point almost exactly north and south in most parts of the world.

Over time, scientists started making a connection between lodestones (permanent magnets) and the nature of Earth itself. The English astronomer Edmund Halley (1656–1742), for example, spent two years crossing the Atlantic on a Royal Navy ship, studying Earth’s magnetic field. Later, the German mathematician and scientist Karl Friedrich Gauss (1777–1855) made important discoveries about how magnets and magnetic fields work in general. He also created the first specialized observatory for the study of Earth’s magnetic field. With his colleague Wilhelm Weber (1804–1891), who was also famous for his work with electricity, Gauss calculated the location of Earth’s magnetic poles. (Today, a unit of magnetic flux density is called a gauss in his honor.)