We learned last post that the Earth’s core is surrounded by molten metal, which exerts a magnetic field around the planet. Some metals can be magnetized. They can be made into a magnet, so they exert a force on other metals without touching them. Iron and steel can be magnetized.
The thing about Earth’s giant magnetic field is that magnetized metals—if they can—try to line up with it. If you were to take a small piece of iron or steel (like a needle) and rub it a few times with a magnet, it will try to align itself with Earth’s North and South. You could make it easier for the needle if you float it on a piece of styrofoam or cork in a bowl of water. After the needle settles down it will point North-South. Congratulations! You built a compass.
Back to the beginning of The Western Civ User’s Guide to Time & Space