• A boxwood pocket sundial signed on the compass dial paper Negretti & Zambra, London.
   
• Dials of this type are known as diptych dials. This dial dates from the second half of the 19^th century
   
• The hinged boxwood instrument opens to reveal a compass and sundial in the base and a circular paper disc in the lid with a printed equation of time.
   
• The lid is held open by a brass latch which keeps the string gnomen under tension. The sundial is graduated from 4 am to 8 pm in quarter hour intervals.
   
• The compass is graduated in one degree intervals and has a 16 point compass rose to the centre. When the dial is closed a small pin operates a lever to stop the compass needle rotating.
   
• The instrument measures 3” x 2¼” x ¾” when closed.
   

Henry Negretti and Joseph Zambra became partners in 1850 and were one of the major makers of scientific instruments in the 19^th and early 20^th century.