When people think of something to help them find direction they think of the compass. The compass is one of the oldest instruments for navigation and surveying. Different types of compasses are used in ships, aircraft, and land vehicles.

The magnetic compass

During 10^th century, the idea of the magnetic compass had been brought to Europe, probably from China. Simple compasses were used in the Mediterranean as early as the 12^th century. The first compasses were not very reliable. Even though the magnetic compass was used during the Middle Ages, little was known about exactly how it worked.

How it works

The magnetic compass works because the Earth is like a large magnet surrounded by an even larger magnetic field. The Earth has two magnetic poles near both the North and South poles. The magnetic field around the Earth causes the magnetized needle of the compass to point in a north to south direction. Early compasses used a wooden stick floating in a water with lodestone, a naturally occurring magnetic ore, on one end that would point north.

In 1745 Gorwin Knight, an English inventor, developed a way of magnetizing steel, so it would retain magnetization for a longer time. His improved needle was bar-shaped and large enough to have a cap in the middle to rotate on. The new an improved compass was called the Knight compass, and it was widely used.

Why the compass is important

The compass has been an important part of navigation for ships at sea. The compass allows ships to steer in the direction they choose to follow. Columbus used a compass on his voyage across the Atlantic Ocean in the 1400’s. Ships today still have a compass on board. Tracy Edwards, captain of the yacht "Maiden" in the 1990 Whitebread Round-the-World Yacht race, used satellites to navigate her way, but found that it had so many errors, that she often used a magnetic compass.

Compass cards

The first compass cards, the paper below the magnetic needle, were marked out in points. There were 32 points on these cards, matching the direction of the winds sailors were familiar with at sea. Compasses are now marked in degrees. The four main points (or cardinal points) are North, South, East, and West. The North point on most compasses is usually decorated because it is the most important direction for navigation. It is like the North star, it is used as a marker to guide.

The liquid compass

Early compasses did not have water or liquid in them and were known as dry-card compasses. Their readings were effected by shock and vibration. Liquid-filled compasses were less effected by shock, but leaked and were difficult to repair. In 1862, the first reliable liquid compass was made with a float on the card that took the weight of the needle. Compasses were later filled with alcohol because it could only freeze at low temperatures. Because of these new improvements on liquid compasses, they started to be more popular than dry-card compasses by the end of the 19^th century.

The solar compass

A solar compass (also called the sun compass) uses the sun to tell its position. The solar compass operates similar to the sundial. It seems to have been developed by the Syrian Arabs as early as the 14^th century. It is useful for navigation in high latitudes, especially near the poles, where magnetic compasses become unreliable.

The gyrocompass

There is one problem with the magnetic compass, it is not always accurate, especially near metal. Some magnetic compasses do not work at all at the North or South poles. Elmer Sperry invented the gyrocompass, in the early 1900’s. The gyrocompass is not like a magnetic compass, and it isn’t effected by things that cause problems for a magnetic compass. An electric motor spins a wheel in the center of the gyrocompass. As long as the wheel is spinning, it will always point to the north. It will even point north if you are in outer space or underwater. This is why it is used on the International Space Station for steering and positioning.

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