In the 12th century, seamen in China and Europe discovered that a piece of lodestone (magnetic ore), when floated on a stick in water, aligns itself so that it points in the direction of the North Star. This is because the Earth itself acts as a huge magnet with a north-south field, which causes freely moving magnets to take on the same direction.
The direction of the Earth's magnetic field isn't perfectly parallel to the north-south axis of the globe, but it is close enough to make an uncorrected compass a practical guide. The inaccuracy or declination differs in scale from point to point upon the Earth. The deflection of a compass needle due to local magnetic influences is called deviation.
The direction of the Earth's magnetic field isn't perfectly parallel to the north-south axis of the globe, but it is close enough to make an uncorrected compass a practical guide. The inaccuracy or declination differs in scale from point to point upon the Earth. The deflection of a compass needle due to local magnetic influences is called deviation.
