‘Cannon dial for latitude 49° North. 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. Engraved on the dial-plate is the maker’s signature, Victor Chevalier Ingr. Breveté quai l'horlage 77 à Paris.’ (via National Maritime Museum)