Accession No

0185

Brief Description

ivory diptych dial; French; early 18th century

Origin

France

Maker

Class

dials

Earliest Date

1700

Latest Date

1725

Inscription Date

Material

ivory; metal (brass, steel); glass; paper

Dimensions

length 64 mm; breadth 51 mm; height 14 mm

Special Collection

Robert Whipple collection

Provenance

Purchased by Robert Stewart Whipple from R. Middegaels, Paris, France, on 10/01/1925.

Inscription

Description Notes

Ivory with brass fittings; plain tablets. Leaf IIa carries horizontal dial calibrated for 40˚, 45˚ and 50˚N. Hour scales divided V - XII, I - VII, numbered by I, subdivided to 30 minutes. Inset compass with paper card; 8-point compass rose; fleur-de-lys for North; 12 points marked, with North offset 10˚W for magnetic variation. Unusual compass needle with jewelled bearing (a replacement?). Paper a poor fit (possibly from German dial). (Needle detached; glass missing; 2-2-2000).
Leaf Ia carries scale of latitudes divided 40˚ - 50˚, numbered 40, 42, 43, 50, subdivided to 1˚ (numbers in wrong places then; 2-2-2000). Sliding index for setting string gnomon (string gnomon missing; 2-2-2000). Brass plate with a table of latitudes (see history file).

Condition: fair (ivory warped (?); needle detached); incomplete (gnomon missing; glass missing).

References

Events

Description
The Diptych dial is a common form of portable multi-function sundial. Diptych dials were made popular by the instrument makers in Nuremberg during the sixteenth and seventeenth centuries. They are usually made of ivory with brass fittings, and are often elaborately decorated. The name of the device derives from the Greek diptychos for a pair of folding writing tablets, which the instrument resembles.

Diptych dials consist of two leaves hinged together, with a string ‘gnomon’ stretched between the inner surfaces of the leaves for casting a shadow. To use the device as a sundial the lower leaf must be placed parallel to the horizon and the upper leaf must be at a right angle vertically to it. The gnomon must then be aligned with the meridian of the place where it is being used by using the inbuilt magnetic compass. Time can then be read from the horizontal or vertical dial by the location of the shadow cast by the string gnomon.

In addition to the horizontal and vertical dials, diptych dials normally carry a number of other features, such as equinoctial dials, windroses, tables of latitude for adjusting the string gnomon for different locations, epact tables, lunar volvelles for telling time at night by the moon, and various pin-gnomon dials for telling the time according to Babylonian or Italian hours, or for calculating the position of the Sun in the zodiac.
27/05/2009
Created by: Joshua Nall on 27/05/2009

FM:43290