What is a Magnetic Compass, its principle, types and errors?

The Principles of the compass

A Magnetic compass is a critical piece of marine navigational equipment. Simply put, a magnetised needle, suspended freely, points North because of the forces caused by the Earth’s magnetic field. Once North is known, the other directions are easily found.

The ship magnetic compass is usually housed on the ‘monkey island’ above the navigating bridge and reflected into the bridge by means of a periscope like device, so a helmsman can easily read the compass when he is steering the ship.

Note :

• The true meridian is the longitude and always points True North
• The Magnetic Meridian is at an angle to the True Meridian. Since the Magnetic North and South poles of the Earth are not the same. It can be imagined as ‘magnetic longitude’.

How does a magnetic compass work?

A magnetic compass works because the Earth is like a giant magnet, surrounded by a huge magnetic field. The Earth has two magnetic poles which lie near the North and South poles. The magnetic field of the Earth causes a magnetized ‘needle’ of iron or steel to swing into a north-south position if it is hung from a thread, or if it is stuck through a straw or piece of wood floating in a bowl of water.