A navigator’s charts show him that he must, for example, sail to the northeast. His problem is to know the northeast direction. He finds this using a magnetic compass.
Already 800 years ago, sailors used a compass to show them the direction of the north. They discovered that if a small, thin piece of magnetized iron swings freely, it will always point in a north-south direction. They called such a piece of iron a magnetic needle.
The first sailor’s -or sailor’s- compasses were made by fixing a magnetic needle to a piece of straw. The straw was then floated in a container of water. Later, the needle was fixed on a round card in such a way that it could rotate freely on the card. The card was marked with all the points of the compass. Later still, the compass card was placed in a container filled with liquid. The liquid absorbed the blows of the rocking ship. This made the needle move more constantly.
A magnetic compass does not point to the geographic North Pole of the earth. Instead, it points to the north magnetic pole, which is in a slightly different location. However, browsers may allow this and other conditions that move the needle away from its correct position.
However, a magnetic compass cannot be used inside modern steel ships. These ships have a lot of metal that affects the direction the needle points. A different type of instrument, called a gyrocompass, is used on most large modern ships.
The gyro compass is actually a gyroscope mounted in a special way. Like all gyroscopes, the gyro has a heavy wheel that rotates on an axis. An electric motor drives the gyro wheel. No matter how the boat is moving, the gyro compass axis automatically adjusts to point true north. Because it does not have a magnetic needle, the gyro compass works well on a steel ship.