The magnetic compass is the most well-known of all instruments used in finding direction. It is the oldest navigational instrument and has been aiding sailors to cross the seas for many centuries. Mariners can use magnetic compasses to fix a ship’s position on a chart by using it to take bearings of visible objects as well as allowing them to steer a particular course.
History
The exact origins of the magnetic compass and the date that it was first used are unknown. However, it is certain the Ancient Greeks were aware of the attractive properties of magnetism, and the Chinese probably knew that iron bars acquired a directional north-south property when stroked with a lodestone up to 2,000 years ago. This idea reached Europe in the 10th century and was probably introduced by Arab traders who gained the information from China. Simple magnetic compasses were used in the Mediterranean in the 12th century, although they were often unreliable. In the Middle Ages, magnetic compasses were used widely, but little was known about how they worked.
How it Works
Earth’s two magnetic poles, which are located close to the North and South Poles, mean that the Earth is similar to a giant magnet, surrounded by a magnetic field. This magnetic field causes magnetized iron needles to swing into a north-south position when hung from a thread or put through a piece of wood floating in water. Originally, needles became magnetized by stroking them with a lump of magnetic rock known as a lodestone. As this effect was temporary, ships would carry lodestones in order to stroke the needle of the compass when its magnetism wore off.