Instruments · Augsburg equinoctial sundial
Universal equinoctial sundial of the Augsburg type, signed on the base "Johan Schrettegger in Augsburg". In original case. German, c.1800
- Maker / attribution
- Schrettegger, Johan (maker)
- Date
- 1797-1843
- Historical period
- Precision & Scientific Horology (1750 – 1850)
- Country of origin
- Germany
- Place
- Augsburg, Schwaben, Bavaria, Germany, Augsburg
- Object type
- Augsburg equinoctial sundial
- Dimensions
- overall: 20 mm x 57 mm x 65 mm,
- Holding institution
- Science Museum Group, London
- Accession / object no.
- 1991-139
- Credit line
- On loan from the Wellcome Trust
- Catalogue title (original)
- Universal equinoctial sundial of the Augsburg type
Record summary
Held and catalogued by Science Museum Group, London (object number 1991-139), this is an augsburg equinoctial sundial by Schrettegger, Johan, made in Augsburg, Schwaben, Bavaria, Germany, Augsburg, dated 1797-1843. The Atlas places it in the Precision & Scientific Horology period (1750 – 1850) of its Instruments collection. Recorded dimensions: overall: 20 mm x 57 mm x 65 mm. The record is illustrated with 3 photographs.
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
Precision & Scientific Horology (1750 – 1850)
Harrison solves longitude; Mudge invents the lever; Breguet's Paris workshop defines the modern watch.
The longitude problem was solved by the marine chronometer and lunar distance methods; dividing engines made precision scales possible, and observatories set time by transit instruments.
Read the period in the timelineMore instruments from this periodEarlier: Early Modern Horology
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
Related records
Instruments · 1701-1800
"Astronomical circles" brass part silvered 4in diameter, German, 1701-1800, or " armillary astrolabe"
Science Museum Group, London
Instruments · 1701-1800
Perpetual calendar, gilt metal, 2½ x 9/16-inches, Germany, 1701-1800.
Science Museum Group, London
Instruments · 1701-1800
Sundial, Germany, 1701-1800
Science Museum Group, London
Instruments · 1701-1800
Universal pocket sundial, octagonal base, diameter of hour circle 2 7/8-inches, small plumbob, Germany, 1701-1800 (see note).
Science Museum Group, London
Instruments · 1726-1775
Universal equinoctial sundial of the Augsburg type, signed on the base "L T M" (Ludwig Theodatus Muller). In original case. German, mid 18th century. (B1670)
Science Museum Group, London
Instruments · 1734-1770
Sundial by Muller, Ludwig Theodatus, Germany, 1734-1770 (Science Museum Group 1938-415)
Science Museum Group, London
Instruments · 1734-1770
Sundial by Muller, Ludwig Theodatus, Germany, 1734-1770 (Science Museum Group 1991-138)
Science Museum Group, London
Instruments · 1734-1770
Sundial by Muller, Ludwig Theodatus, Germany, 1734-1770 (Science Museum Group 1991-192)
Science Museum Group, London