The magnetic compass is one of the oldest scientific instruments, and was the first known technological application of magnetism. For hundreds of years, it has been a vital tool for maritime navigators.
Despite modern equipment, which enables users to accurately determine their location to within a few meters, the magnetic compass is anything but obsolete. It is still a highly useful and practical tool for hikers and other people navigating while on foot, and is also often used by many smaller maritime vessels. Many airplanes and ships that are equipped with highly sophisticated navigational equipment often carry compasses as back up.
Depending on their intended use, compasses come in a wide variety of shapes and sizes. The type of compass used on a ship or aircraft, for example, is a highly complex electronic or mechanical device, designed to compensate for both the motion of the craft and its metallic structure. At the opposite end of the scale are the small pocket compasses designed for recreational use.
How Do They Work?
Whether they are big or small, sophisticated or humble, most magnetic compasses work in the same way, and are actually extremely simple devices. The magnetic compass is made up of a liquid camber filled with a special fluid that dampens a magnetic float with a compass card attached.
A small, elongated, permanently magnetized needle is placed on a small, frictionless pivot so it can rotate freely in the horizontal plane.
At the surface, the magnetic field of the Earth is fairly weak, having travelled a long way through the planet to affect your compass. This is why a compass needs to have a lightweight magnet and a frictionless bearing. Otherwise, there just isn’t enough strength in the Earth’s magnetic field to turn the needle.
The needle reacts to the magnetic field, rotating until it comes to rest in the same horizontal direction as the magnetic field. Over much of the Earth, this direction is roughly true north.
It’s important to note that magnetic north is not the same as map grid north, and it changes in different areas of the world. To get a completely accurate reading you have to adjust the bearing 2 degrees by turning the compass housing anticlockwise.
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