String-gnomon dial. This dial comprises an octagonal-shaped dial plate on which is an hour scale set around a compass. The cardinal points on the compass are marked by Latin initials and an arrow is drawn west of North to indicate magnetic variation. A glass plate covers all. Hinged to the dial-plate is a shaped gnomon support which folds flat when not in use. It is pierced at its lower end for a plumb line and bob (both missing). Fixed to the top end of the support is a green string gnomon which is attached to the dial plate by means of a strut set across the compass glass. The dial is supported by three levelling screws. It has an eight-sided fishskin covered case with a red seal impression on its outside.
The dial was reputedly given by Admiral Nelson to Captain (later Vice-Admiral) Sir Thomas Boulden Thompson (circa 1766-1828) on the morning of the Battle of the Nile (1798).