Diptych sundial (detail)

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Diptych sundials have two plates hinged together, and in use open out to form a right angle, with the string hinge operating as a gnomon. This ivory example was made in the 17th century in Dieppe in France. The photograph shows the inside of the lid.

There is a pewter moon dial on the inside of the lid. It has two rotating discs and a fixed outer scale. The top rotating disc has no scale, a single pointer and a hole through which the relative phase of the moon can be seen.

The moon dial, or lunar volvelle, relates the time at night to local solar time.

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• Online ID: 000-190-001-026-C
• Image Rights Holder: National Museums Scotland
• Project: National Museums Scotland
  Project description   View all records in project
• Ref: National Museums Scotland  T.1924.13
• Date: 17th century
  
• Material: Ivory, metal disc. Inscription: [On base] Names of French towns with information concerning them
  Sundial, universal
  
• Dimensions: 2.88" x 2.38"
  
• What: Sundial, universal
  
• Subject: 20. TIME MEASUREMENT, Sundials (Departmental Classification)
  
• Who:
• Where: FRANCE
  France, Dieppe
  
• Event:
• Description: French universal sundial in ivory, book form, base with sunk compass surrounded by horizontal dial, analemmatic dial, moon dial and equinoctial and polar dials, unsigned, Dieppe, 17th century
  
• References:
  • For a similar example, see Lloyd, Steven A., Ivory Diptych Sundials 1570-1750. London & Cambridge, Massachusetts: Harvard, 1992. p 128, also pp 25-6 
• Translations:
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