The compass is a device that indicates direction on the Earth's surface, relative to magnetic north. It is the principle instrument of Navigation; without it, a navigator would have difficulty in setting the course for a ship or airplane.
There are two basic type of compass, the
magnetic type and gyroscopic type. The magnetic type device its directional property from the Earth's magnetism, whereas the gyroscopic compass is a mechanical device that employee a spinning wheel and senses the Earth's rotation.
Magnetic compass:
The use of magnetic compass about Mediterranean seamen of the 12th century. There are two types of magnetic compass, the dry card and the liquid. The dry card compass use on ships consist of a system of magnetized needles suspended by silk threads from a graduated compass card about 25 cm (10 in) in diameter. In liquid compass the card is mounted in a sealed bowl filled with a liquid of low freezing point.
Gyroscopic compass:
The magnetic compass for ships and aircraft is now being superseded by the gyroscopic compass or gyrocompass. When it became possible to spin a wheel electrically, serious attention was given to use possibility of using a spinning wheel, the axis of which tends to maintains a fixed direction in space - for directional purposes. A spinning wheel that is free to move about three axes is known as a free gyroscope. In a meridian seeking gyroscope the Earth's force of gravity causes the spin axis of the gyroscope to oscillate horizontally around the vertical plane of the meridian, an oscillation that is continually reduced in amplitude by a damping device. Though the reduce, the spin axis settles horizontally in the vertical plane of the meridian, thereby acting as an efficient compass.
William Thomson (later Lord Kelvin) made an attempt in design a gyrocompass in 1883, but credit for inventing the first practical gyrocompass belongs to Hermann An schutz Kaempfe, whose first successful compass appeared in 1907, the first American gyrocompass, designed by Elmer A Sperry, was produced in 1911; the first English design, by S.G. Brown and J. Perry, is dated 1917.
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