Instruments · Magnetic horizontal sundial
Sundial by Porter, Samuel (maker), England, 1824
- Maker / attribution
- Porter, Samuel (maker) (maker)
- Date
- 1824
- Historical period
- Precision & Scientific Horology (1750 – 1850)
- Country of origin
- England
- Place
- London, Greater London, England, United Kingdom, London
- Object type
- Magnetic horizontal sundial
- Holding institution
- Science Museum Group, London
- Accession / object no.
- 1984-181
- Credit line
- Harley, G.
- Catalogue title (original)
- Portable horizontal sundial in wooden case
Record summary
Held and catalogued by Science Museum Group, London (object number 1984-181), this is a magnetic horizontal sundial by Porter, Samuel (maker), made in London, Greater London, England, United Kingdom, London, dated 1824. The Atlas places it in the Precision & Scientific Horology period (1750 – 1850) of its Instruments collection. 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
Related records
Instruments · 1731-1776
Azimuth compass sundial by James Ferguson, London, England, 1731-1776. Could also be used as a tablet sundial - string gnomon is missing (see note).
Science Museum Group, London
Instruments · 1738-1777
Azimuth sundial 4 3/8" diam, with folding gnomon fitted in mahogany case, made by B. Martin
Science Museum Group, London
Instruments · 1750–1799
Ship's log glass. Single sand-glass in cylindrical brass mount (end cap missing). 15 seconds. Horne Type B. ?English, second half of the 18th century
Science Museum Group, London
Instruments · 1750–1799
Ship's log glass. Single sand-glass in cylindrical brass mount. 30 seconds. Horne Type B. ?English, second half of the 18th century (Science Museum Group 1991-207)
Science Museum Group, London
Instruments · 1750–1799
Ship's log glass. Single sand-glass in cylindrical brass mount. 30 seconds. Horne Type B. ?English, second half of the 18th century (Science Museum Group 1991-208)
Science Museum Group, London
Instruments · 1750-1800
Single sand glass in four pillared wooden mount. 17 minutes. Horne Type B. Second half of the 18th century
Science Museum Group, London
Instruments · 1751-1825
Sundial, by Troughton, in case. Invented and made by Troughton
Science Museum Group, London
Instruments · 1751-1850
Universal Sundial; by Dollond and large brass stand, engraved "Dollond London" 6-inch hours circle, divided to 2 min, 3 levelling screws
Science Museum Group, London