Instruments · Sundials; equinoctial sundials
Mechanical equinoctial sundial
- Maker / attribution
- Sisson, Jeremiah (maker); Jeremiah Sisson (maker)
- Date
- 1701-1752
- Historical period
- Early Modern Horology (1600 – 1750)
- Country of origin
- England
- Place
- London, Greater London, England, United Kingdom, London
- Object type
- Sundials; equinoctial sundials
- Dimensions
- overall: 155 mm x 50 mm x 120 mm, 0.3 kg
- Holding institution
- Science Museum Group, London
- Accession / object no.
- 1927-1465
- Credit line
- King’s College London
- Catalogue title (original)
- Mechanical equinoctial sundial, before 1752
Record summary
Held and catalogued by Science Museum Group, London (object number 1927-1465), this is a sundials; equinoctial sundials by Sisson, Jeremiah, made in London, Greater London, England, United Kingdom, London, dated 1701-1752. The Atlas places it in the Early Modern Horology period (1600 – 1750) of its Instruments collection. Recorded dimensions: overall: 155 mm x 50 mm x 120 mm, 0.3 kg. 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
Science Museum Group description
Mechanical equinoctial sundial, before 1752. The clock face was turned approximately south, the first pinhole was moved to the date, and the orientation of the dial was altered until the spot of light from the first pinhole coincided with the second. Turning the dial turned the hands on the clock, which then showed the time.The instrument was made by Jeremiah Sisson before 1752 as it shows the Julian calendar.
Historical context
Early Modern Horology (1600 – 1750)
Huygens' pendulum and balance spring transform accuracy; English makers develop the anchor and deadbeat escapements.
Pocket sundials, Butterfield dials and sandglasses remained essential companions to imperfect clocks; navigators used sandglasses and the log line; observatories began to combine telescopes with pendulum clocks.
Read the period in the timelineMore instruments from this periodEarlier: Renaissance 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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