Magnetic Compass
The magnetic compass is the oldest instrument used for navigation. It has been a vital tool for navigators at sea for centuries. A magnetic compass is an important type of instrument which indicates direction relative to the earth's magnetic poles, using a magnetized steel bar or needle . It allows ships to steer a selected course. By taking bearings of visible objects with a compass, the navigator is also able to fix a ship's position on a chart. It is an ideal meriner's compass.
In its simplest form magnetic compass consists of a magnetized needle mounted on a pivot at the center of a fixed graduated card, so as to permit the needle to swing freely in the horizontal plane. The mariner's compass, a large magnetic type used aboard ships, has bundles of parallel magnetic needles attached to the underside of the compass card, which pivots about its center in a glass-covered bronze bowl. The bowl is hung in gimbals, and hence the card retains a horizontal position despite the pitching and rolling of the ship.
How does a magnetic compass works?
The magnetic compass operates on the principle that unlike magnetic poles attract each other whereas like magnetic poles repel each other. A magnetic compass works because the Earth is like a giant magnet, with a huge magnetic field surrounding it. The Earth has two magnetic poles. These two poles lie near the North and South poles. The magnetic field of the Earth makes a magnetized 'needle' of steel or iron when hung in a thread to swing into a north-south position. The needle shows the same movement when stuck through a straw or piece of wood floating in a bowl of water.
