Brief description

A navigational instrument that shows the cardinal directions used for navigation and geographic orientation. It typically consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with magnetic north.

Use / Function

• Navigation: Determining direction of travel.
• Orientation: Aligning maps with the terrain.
• Surveying: Measuring horizontal angles for mapping.

Operating principle

Magnetism: The Earth acts like a giant magnet with magnetic poles near the geographic poles. A magnetized object (like a needle) that is free to rotate will align itself with the Earth’s magnetic field lines, pointing roughly North-South.

How to create it

Wet Compass (Simplest)

1. Magnetize a Needle: Rub a steel needle (or a straightened paperclip/wire) with a magnet or lodestone. Rub in one direction only (e.g., from eye to point), lifting the magnet at the end of each stroke. Do this 50-100 times.
2. Float: Place the needle on a small piece of cork, a leaf, or a piece of paper floating in a bowl of still water.
3. Read: The needle will rotate to align with the North-South line. You need to know which way is North (using the sun or stars) initially to mark the “North” end of your needle.

Dry Compass

1. Pivot: Push a pin vertically through a base (wood/cork).
2. Balance: Balance the magnetized needle horizontally on the tip of the pin. A small indentation or a glass bead in the center of the needle helps reduce friction.
3. Housing: Enclose in a box to protect from wind.

Materials needed

• Ferrous Metal: A needle, wire, or thin strip of steel/iron.
• Magnetizer: Lodestone (Magnetite) or an existing magnet. (Alternatively, electricity and a coil).
• Float/Pivot: Cork, leaf, or a sharp pin.
• Container: Bowl of water or a box.

Variants and improvements

• Lodestone Compass: An early Chinese version using a spoon-shaped lodestone on a bronze plate.
• Mariner’s Compass: Uses a gimbal (pivoting support) to keep the compass level on a rocking ship.
• Liquid-filled Compass: The housing is filled with liquid (oil/alcohol) to dampen the needle’s movement, making it stable.

Limits and risks

• Magnetic Declination: Magnetic North is not exactly True North. The difference varies by location and changes over time.
• Interference: Nearby iron objects (tools, weapons, ores) or electronic devices will deflect the needle (Deviation).
• Dip: Near the poles, the magnetic field lines point downwards, causing the needle to dip and potentially drag or get stuck.