Instruments · Compass horizontal sundial
Horizontal compass sundial for latitude 51 degrees, signed "J. Abraham BATH", English, first half of the 19th century. (B1691)
- Maker / attribution
- Abraham, Jacob (maker); Jacob Abraham (maker)
- Date
- 1809-1842
- Historical period
- Precision & Scientific Horology (1750 – 1850)
- Country of origin
- England
- Place
- Bath, Bath and North East Somerset, England, United Kingdom, Bath
- Object type
- Compass horizontal sundial
- Dimensions
- overall: 98 mm x 24 mm
- Holding institution
- Science Museum Group, London
- Accession / object no.
- 1991-173
- Credit line
- Wellcome Trust
- Catalogue title (original)
- Horizontal compass sundial, for latitude 51 degrees
Record summary
Held and catalogued by Science Museum Group, London (object number 1991-173), this is a compass horizontal sundial by Abraham, Jacob, made in Bath, Bath and North East Somerset, England, United Kingdom, Bath, dated 1809-1842. The Atlas places it in the Precision & Scientific Horology period (1750 – 1850) of its Instruments collection. Recorded dimensions: overall: 98 mm x 24 mm. The record is illustrated with 2 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
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