Instruments · Diptych dial
Diptych dial, France, 1573
- Maker / attribution
- Unrecorded in source
- Date
- 1573
- Historical period
- Renaissance Horology (1400 – 1600)
- Country of origin
- France
- Place
- French
- Object type
- Diptych dial
- Materials / technique
- ebony, ivory
- Dimensions
- 70x56 mm
- Holding institution
- Museo Galileo, Florence
- Accession / object no.
- Inv. 2489
- Credit line
- Museo Galileo, Florence
- Catalogue title (original)
- Diptych dial (English)
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Record summary
Held and catalogued by Museo Galileo, Florence (object number Inv. 2489), this is a diptych dial, made in French, France, dated 1573. The Atlas places it in the Renaissance Horology period (1400 – 1600) of its Instruments collection. Materials and techniques recorded by the source: ebony, ivory. Recorded dimensions: 70x56 mm. The record is illustrated with 1 photograph.
Assembled from the source record's structured fields. Dates and attributions are given as the source states them; where a field is missing the Atlas leaves it blank rather than estimating.
Catalogue description
Catalogue description — Museo Galileo
Dial consisting of an oval ebony box with a decorated and painted lid. Inside the lid are marked latitudes 43°, 45°, and 48°, with three corresponding holes. These latitude values suggest the instrument came from France. The base is fitted with a compass for orientating the dial and hour lines marked on three concentric bands. A string is stretched between the lid and the base. When the box is opened, the string, inserted in the hole corresponding to the selected latitude, casts its shadow on the hour lines. The instrument was already documented in the reign of Grand Duke Cosimo I de' Medici. Probable provenance: Medici collections.
Provenance
Medici collections
Historical context
Renaissance Horology (1400 – 1600)
Spring power makes clocks portable; Nuremberg and Augsburg produce the first watches; the Prague Orloj is built.
Instrument-making flourished in Nuremberg, Augsburg, Louvain and London: ivory diptych dials, astronomical compendia, astrolabes and nocturnals for wealthy patrons, navigators and scholars.
Read the period in the timelineMore instruments from this periodEarlier: Medieval Period
Atlas type guide
Sundials and solar time-finders
A sundial tells time from the position of a shadow cast by a gnomon or style. Because the sun's apparent motion depends on latitude, every fixed dial is laid out for a particular latitude, and portable dials either carry a latitude scale or are made for one region. Sundials show local apparent solar time, which drifts against mean (clock) time by up to about sixteen minutes over the year — the equation of time.
Portable dials were the pocket instruments of the sixteenth to eighteenth centuries. Nuremberg and Augsburg workshops produced folding ivory diptych dials with inset compasses; English and French makers sold brass horizontal dials, ring dials and the Butterfield type; Japanese and Chinese makers had their own traditions of compass dials. After mechanical watches became reliable, dials remained in use for setting them, and nineteenth-century heliochronometers were built to correct directly for the equation of time.
What to look for
- The latitude engraved on the dial plate or a latitude arc on the gnomon — it shows where the dial was meant to be used.
- The type of hour lines: equal (equinoctial) hours, Italian or Babylonian hours counted from sunset or sunrise, or unequal temporal hours on early and Islamic instruments.
- An inset magnetic compass and whether a magnetic-declination mark is drawn on its card — a useful dating clue because declination changes over time.
- Maker's signatures and town marks: Nuremberg compass-makers (Kompassmacher) often struck a personal mark and the town's punch.
- Additional scales such as lunar volvelles, wind roses, perpetual calendars or lists of cities with their latitudes.
Dating clues
- Ivory diptych dials are characteristic of Nuremberg between about 1500 and 1700.
- Butterfield-type dials with a bird-shaped adjustable gnomon point to Paris workshops from the late seventeenth century onward.
- Equation-of-time tables engraved on the plate became common after the mid-seventeenth century, once pendulum clocks made the difference between solar and mean time obvious.
General guidance written by the Atlas editors about this kind of object. It is not a statement about this particular piece; for that, rely on the source record above and on physical examination.
Read next:The history timeline
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