The sailors, aviators and explorers use various methods to navigate. Sometimes appeal to the position of the sun or stars, or various types of measures, some built with gyroscopes and magnetic. The most common of these tools is the compass that was designed around the twelfth century by Chinese sailors. It is believed that the idea came from the observation of certain rocks with magnetic properties, the pieces of wood floating on the water, naturally oriented towards the North. In its current form, the compass is a magnetic needle placed on a vertical support that allows you to rotate freely. The imam of this needle is attracted by the magnetic south pole, because of this, points north. Thus, one can determine the position of the other cardinal points, and therefore provides a useful tool in widespread use.
The point of the attraction coming from the south magnetic pole does not coincide with the North. But the distance between them is relatively small, so that the compass is useful as a means of orientation.