Clocks · Long case clock
Sidereal degree clock by Thomas Tompion
- Maker / attribution
- Thomas Tompion (maker)
- Date
- 1691
- Historical period
- Early Modern Horology (1600 – 1750)
- Country of origin
- England
- Object type
- Long case clock
- Materials / technique
- metal; wood; glass
- Dimensions
- Overall: 150 x 500 x 255 mm
- Holding institution
- Royal Museums Greenwich
- Accession / object no.
- ZAA0559
- Credit line
- National Maritime Museum, Greenwich, London
- Catalogue title (original)
- Sidereal degree clock (English)
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Record summary
Held and catalogued by Royal Museums Greenwich (object number ZAA0559), this is a long case clock by Thomas Tompion, made in England, dated 1691. The Atlas places it in the Early Modern Horology period (1600 – 1750) of its Clocks collection. Materials and techniques recorded by the source: metal; wood; glass. Recorded dimensions: Overall: 150 x 500 x 255 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
Catalogue description — Royal Museums Greenwich
This clock was designed by John Flamsteed, first Astronomer Royal, to show the time in degrees, minutes and seconds of arc. In astronomy it is often more convenient to express time in this way. The earth turns through 360°on its axis every 24 sidereal hours. 24 hours = 360° 1 hour = 15° 4 minutes of time = 1° 4 seconds of time = 1' of arc 1 second of time = 15" of arc The clock reads as follows: small window right of centre – tens of degrees; 'minute' hand – degrees, with 10-minute of arc subdivisions; 'second' hand – minutes of arc with 10-second of arc subdivisions. The pendulum is 17.3 inches long instead of the usual 39.1 inches and so beats 2/3 second of time (or 10 seconds of arc) instead of 1 second of time. To convert the clock to read normal hours a pendulum of 39.1 inches can be fitted and the small dial behind the aperture reversed to show I to XII hours. The clock then shows hours and decimal parts of an hour. In practice this system was not very useful for astronomers and it is believed that only two 'angle clocks' were ever made: this one, and one by John Arnold, currently on display in the Meridian gallery at the Royal Observatory, Greenwich.
Historical context
Early Modern Horology (1600 – 1750)
Huygens' pendulum and balance spring transform accuracy; English makers develop the anchor and deadbeat escapements.
Huygens's pendulum (1656–57) improved clock accuracy from about a quarter of an hour to under a minute a day. The anchor escapement (c. 1670) and the long seconds pendulum created the longcase clock; London makers such as Fromanteel, Knibb, Tompion and Quare led European clockmaking, and French makers created the Boulle pendule.
Read the period in the timelineMore clocks from this periodEarlier: Renaissance Horology
Atlas type guide
Longcase (tall-case or grandfather) clocks
The longcase clock was born from two seventeenth-century innovations: Christiaan Huygens's pendulum (1656–57) and the anchor escapement (c. 1670). A long seconds pendulum, nearly a metre long, swings with a small arc, and enclosing it together with the driving weights in a tall wooden case protected the mechanism and created a new piece of furniture. London makers such as Ahasuerus Fromanteel, Thomas Tompion and Joseph Knibb set the pattern.
By the eighteenth century longcase clocks were made throughout Britain, the Netherlands, Scandinavia (the Swedish Mora clock), France (the Comtoise from the Franche-Comté), Germany and colonial America. Eight-day movements with two weights became standard in better clocks; thirty-hour clocks with one weight and a rope or chain were cheaper alternatives.
What to look for
- Winding holes in the dial: two (eight-day, going and striking) or none (thirty-hour, pulled up by a chain).
- Brass dials with applied chapter rings (earlier) versus painted iron 'white' dials (after c. 1770 in Britain).
- Moon-phase arches, date apertures, seconds dials and maker's name on the dial.
- Case woods and style: ebonised, walnut marquetry, lacquer, oak or mahogany; regional styles from London, Lancashire, Scotland or America.
- Whether the movement and dial match the case — 'marriages' are common.
Dating clues
- Square brass dials suggest c. 1670–1720; arched brass dials c. 1715–1790.
- Painted (white) dials were made by Birmingham dial-makers from about 1772.
- Comtoise clocks with repoussé pendulums are mostly nineteenth century.
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:Anchor (recoil) escapementDeadbeat escapementAnchor escapement
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