Magnetism
Magnetic effects from natural magnets have been known for a long time. Recorded observations from the Greeks more than 2500 years ago.
The word magnetism comes from the Greek word for a certain type of stone (lodestone) containing iron oxide found in Magnesia, a district in northern Greece.
Properties of lodestones: could exert forces on similar stones and could impart this property (magnetize) to a piece of iron it touched.
Small sliver of lodestone suspended with a string will always align itself in a north-south direction. ie can detect the magnetic field produced by the earth itself.