A
Civilization advance.
The
electromagnetic force of
attraction and
repulsion between various substances, especially known as
ferrous metals, is due to the alignment of tiny
electric charges and is known as magnetism. (Magnetism can also be induced using a moving electrical charge.) All known magnetic objects have two poles, one north-seeking and one south-seeking. The poles are so named because a freely floating magnet aligns itself with the Earth's
magnetic field, which runs approximately north-south (though it has not always been that way).
Prerequisites: Navigation and
Physics.
Allows for: Electricity.