GyrocompassA gyrocompass is a compass which finds North by using an (electrically powered) fast spinning wheel and friction forces in order to exploit the rotation of the Earth. Gyrocompasses are widely used on ships. They have two main advantages over magnetic compasses:
- they find true North, i.e. the direction of Earth's rotational axis, as opposed to magnetic North,
- they are not affected by metal in a ship's hull.
This is because true North is the only direction for which the gyroscope can remain on the surface of the earth and not be required to change. This is considered to be a point of minimum potential energy.
Since the operation of a gyrocompass crucially depends on its rotation on Earth, it won't function correctly if the vessel it is mounted on is fast moving, especially in East-West direction.
The gyrocompass was patented in 1885 by the Dutch Martinus Gerardus van den Bos; however, his device never worked properly. In 1903, the German Herman Anschütz-Kaempfe constructed a working gyrocompass and obtained a patent on the design. In 1908, the American inventor Elmer Ambrose Sperry patented a gyrocompass in the US. When he attempted to sell this device to the German navy in 1914, Anschütz-Kaempfe sued for patent infringement. Sperry argued that Anschütz-Kaempfe's patent was invalid because it did not significantly improve on the earlier van den Bos patent. Albert Einstein testified in the case, first agreeing with Sperry but then reversing himself and finding that Anschütz-Kaempfe's patent was valid and that Sperry had infringed by using a specific dampening method. Anschütz-Kaempfe won the case in 1915.