boussole

Boussole is the French term for a compass, a navigational instrument that shows direction relative to the magnetic north. It typically consists of a magnetized needle or a magnetic card that can rotate freely inside a housing. In many models the needle is mounted in a liquid-filled capsule to damp oscillations, and a rotating bezel or a protractor-scale allows the user to read bearings in degrees. When oriented, the device aligns with Earth’s magnetic field, providing a reference for navigation.

The magnetic compass originated in China, with navigation use dating to the Song dynasty in the 11th century, and spread to the Islamic world and Europe by the 12th century. The term boussole entered French during the Middle Ages, probably via Italian or Old French, reflecting its long maritime and land-navigation use.

There are several types used today: marine compasses (magnetic and gyro-stabilized), pocket compasses, and baseplate or orienteering compasses. Reading a bearing entails aligning the direction of travel with the bezel and noting the value on the scale. Because magnetic north differs from true north, navigators apply magnetic declination (variation) to convert to true bearings when using maps. Compasses can be affected by nearby ferrous metals, electrical devices, or intense magnetic fields, requiring calibration or adjustment.

In modern contexts, digital compasses with magnetometers are common in smartphones, tablets, and cars, often integrated with maps and GPS. Even with electronic systems, traditional magnetic compasses remain a standard backup in navigation, especially in wilderness, marine, and aviation settings, where redundancy and cross-checks ensure reliability.