موضوع
انجليزي عن البوصله
موضوع
انجليزي عن البوصله
A gusset compass.
A compass is a navigational
instrument consisting of a magnetized needle that aligns with the magnetic
field of the Earth. It thus indicates the Magnetic North, to be distinguished
from the geographic North Pole. The difference between the two directions in a
given place is called terrestrial magnetic declination. According to the
required precision, this difference is accommodated or a compensation chart is
used. Observed from France (in 2013), the two directions are essentially
identical.
The lines of the Earth's magnetic field on
which the compass needle aligns point underground at the north and south poles
(not at the surface). In the northern hemisphere, the north end of the compass
is drawn down. To compensate for this phenomenon, the southern end of the
compass needle is lightly weighted.
When using a "northern
hemisphere" compass in the southern hemisphere, the southern end of the
needle is drawn down by the magnetic field, even though it already has a
counterweight. Result, the southern point of the compass hangs on the bottom of
the cavity in which it is housed, and thus works much less well.
A compass provides a known reference
direction that aids navigation. The cardinal points are (clockwise): North,
East, South, and West. A compass can be used in conjunction with a clock to
provide an estimate of its navigation.
The compass is used mainly in land
navigation. It consists of a needle that rotates in front of graduations of the
instrument, usually held by hand, which is oriented in the desired direction.
In marine and air navigation, or on a vehicle, we use preferably a compass: it
is then the moving part that carries the graduations (in the opposite direction
to those of a compass). It turns in front of a fixed marker parallel to the
axis of the ship or the aircraft, called the line of faith, and gives directly
the course followed.
