Navigational Tools in the Fifteenth and Sixteenth Centuries

The earliest documentation of the use of a mariner's compass in the Middle ages is found in the writings of an Englishman, Alexander Neckham of St. Albans. Neckham wrote in his treatise, De Utensilibus, of a needle carried on shipboard, which, when balanced on a pivot and allowed to come to rest, showed mariners their direction even when the stars were obscured.

The box compass was invented by Petrus Peregrinus. It involved a pivoting needle revolving around a graduated disc similar to an astrolabe. Around 1302, the priniciples of Peregrinus' box compass and the wind rose (rosa ventorum) were combined, positioning the magnetic needle to rotate on the center of the wind rose, where it still rests today. The wind rose, consisting of eight winds, with subdivisions for half-winds and quarter-winds, was fitted to a metal cap and one or more magnetic needles. This basic mechanical design has changed very little in over 600 years of navigation.

With the use of a compass, a Navigator could follow a rhumb line on a sailing chart. Prior to the use of a compass, sailors could not safely navigate the open ocean accurately, so many of the charts made during these times were Portolan charts, or coastlines plotted for sailing from port to port. If a navigator set out from a known port and measured the direction of sail using a compass, he could accurately project where he would land in relation to the origin point and to the north pole (originally, many navigators thought that a compass point was attracted to the north star). This is the basic instrument navigators used to determine direction of travel.