Cannon dial for latitude 49° North. This dial has a circular white marble base on which is an hour scale engraved in black with a shaped brass gnomon. There are two quadrant supports for the limbs holding the burning glass, both marked on the outside with a declination scale. The limbs are pivoted to the centres of the quadrants and held in position by screws. The burning glass, also fixed on by screws, has a biconvex lens mounted in a brass ring. The brass cannon is pivoted between two supports and has an elongated slit to accommodate the fuse. Engraved on the dial-plate is the maker's signature, 'Victor Chevalier Ingr. Breveté quai de l'horloge 77 à Paris'.

Cannon dials (or 'time guns' as they were occasionally known) were popular in the 18th century. A burning glass mounted above the plate would receive the sun's rays at noon, so providing the heat to light the fuse at the end of the miniature cannon, causing it to fire and thus provide a signal for midday.

For more information regarding this dial please refer to the OUP & NMM catalogue, 'Sundials at Greenwich'.