A compass, magnetic compass
or mariner's compass is a navigational instrument for determining
direction relative to the earth's
magnetic poles. It consists of a magnetized pointer (usually marked
on the North end) free to align itself with
Earth's magnetic field. The face of the compass generally highlights
the
cardinal points of north, south, east and west. The compass greatly
improved maritime trade by making travel safer and more efficient. A
compass can be used to calculate
heading, used with a
sextant
to calculate
latitude, and with a
marine chronometer to calculate
longitude. It thus provides a much improved
navigational capability, that has only been recently supplanted by
modern devices such as the
gyrocompass and the
Global Positioning System (GPS).
Fundamentally, the classic compass is any magnetically sensitive device
able to indicate the direction of the
magnetic north of a planet's
magnetosphere. Often compasses are built as a stand alone sealed
instrument with a magnetized bar or needle turning freely upon a
pivot, or
moving in a fluid, thus able to point in a
northerly
and southerly
direction. An early form of the compass (a magnetized needle floating in
water) was invented in
ancient China
sometime before 1044. The dry compass was invented in
medieval
Europe
around 1300.
This was supplanted in the early 20th century by the liquid-filled
magnetic compass.
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