Instruments · Universal equinoctial sundial
Universal equinoctial sundial. French, c.1930
- Maker / attribution
- Unrecorded in source
- Date
- 1921-1940
- Historical period
- Golden Age of Mechanical Watchmaking (1900 – 1945)
- Country of origin
- France
- Place
- France, France
- Object type
- Universal equinoctial sundial
- Holding institution
- Science Museum Group, London
- Accession / object no.
- 1991-147
- Credit line
- Wellcome Trust
- Catalogue title (original)
- Universal equinoctial sundial. French
Record summary
Held and catalogued by Science Museum Group, London (object number 1991-147), this is an universal equinoctial sundial, made in France, France, dated 1921-1940. The Atlas places it in the Golden Age of Mechanical Watchmaking period (1900 – 1945) of its Instruments collection. 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
The source record does not include a narrative description. The structured fields above are reproduced from it.
Historical context
Golden Age of Mechanical Watchmaking (1900 – 1945)
The wristwatch displaces the pocket watch; waterproof cases, self-winding and grand complications.
Timing instruments became electrical and specialised: industrial time recorders, sports timers and aviation instruments.
Read the period in the timelineMore instruments from this periodEarlier: Industrial Revolution
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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