The compass is
the most basic and essential of aircraft instruments for determining position
and direction. In some airplanes it is the only source of direction information.
The compass was developed by sailors in the 14th century who
placed a magnetic ‘lodestone,’ or needle, to a card that depicted
a compass rose. The earliest compass roses depicted the four wind directions,
north, south, east, and west as well as up to 28 more points between these.
The needle was usually mounted in some type of liquid to allow it to point
magnetically towards true north.
compass is not much different. A ball with a compass card showing north,
south, east, and west as well as 360 different degrees of heading is placed
inside a container filled with liquid (sometimes pilots have substituted
whiskey when this fluid leaked out). The ball is designed to point towards
magnetic north no matter which direction the aircraft is moving.