Maker's Name: 
unknown, UK, s/n 18774D
Where made: 
10 × 10 × 20 cm

Hollow wooden handle with screw on bottom supporting brass bowl. Glass face. Moveable prism with marker for sighting . Mother of pearl magnetic disc mounted on type of universal joint immersed in discoloured liquid in center of bowl. Disc marked with degrees in mirror writing.
To sight compass hold level, look over glass face to prism, line up arrow on prism with pin that protrudes over disc and read of disc.
A Crown with the letters AM etched into the face probably indicate the compass was used on a government boat.
AM means Air Ministry. It is also possible this was used on aircraft by the navigator.