Land and Sea

One of the first problems that made high-sea navigation dangerous was the variation in the direction of the magnetic north. The compass needle is attracted by the lines of force of the Earth’s magnetic field toward a direction that diverges by a few degrees from the geographic north. This deviation is called magnetic declination and varies with longitude, making the use of the compass problematic during navigation. In the 15th century, the magnetic north pole was located east of geographic north, such that compasses declined clockwise. When nautical charts were designed with the direction of the Tramontana (or north wind) as the vertical axis, the resultant geographic representation thus shifted in a counter-clockwise direction at an angle equal to the magnetic declination.