Anatomy of a compass

The magnetic compass opened up unreachable parts of the ocean and made precise navigation possible. Duncan Haskell explores its innards for us...

Illustration: Aidan Meighan

Illustration: Aidan Meighan

GIMBAL The gimbal system was introduced for compasses used aboard ships on rough seas and had to remain level to give an accurate reading.To do this, two sets of pivots at right-angles are mounted in brass hoops around the compass and are able to rotate independently in the centre.

PIN For the needle to swivel freely it is positioned upon a sharp balance pin, which reduces any friction that may restrict its movement. 

ROSE CARD Fitted under the needle and pin, this circular card is annotated with the cardinal points N, S, E, W. Initially it was used to indicate the main winds sailors were familiar with at sea. 

NEEDLE The key component of the compass is the magnet itself, often referred to as the needle. The magnetised needle detects the Earth’s magnetic field and aligns itself accordingly, with the south pole of the needle being attracted to Earth’s magnetic North Pole.The end of the needle is often marked to indicate this.

This was taken from print issue 2 of Ernest Journal, on sale now.