Diptych Dial

France, 17th century AD

A beautifully decorated ivory sundial

Diptych dials are portable instruments, usually made from ivory. They were mainly produced in Nuremberg from the late fifteenth century onwards. They remained fashionable throughout the sixteenth and seventeenth centuries and were still in use in the eighteenth century.

They are based on the principles of vertical and horizontal sundials. The gnomon (shadow caster) is in this case not a solid piece, but a string, which 'points' to the celestial north pole.

This splendid example displays the typical colourful decoration of French dials. The string can be adjusted to suit different latitudes between 40° and 50°. A list is given of latitudes of different locations in Europe, so that the traveller can use the instrument to tell the time wherever he is, and to adjust his watch to local solar time.

F.A.B. Ward, Catalogue of European scientif (London, The British Museum Press, 1981)