Astronomical Regulators


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From their invention by Christiaan Huygens in 1656 until the introduction of quartz clocks in the 1930s, pendulum clocks were the most accurate form of timekeeper available. During that time, precision regulators played a central role as accurate time-keeping instruments in astronomical observatories and in the related fields of navigation and surveying. During the 18th and 19th century, London makers were at the forefront of innovation, introducing new and better escapements as well as the compensated pendulum.

Most of the Observatory’s regulators still survive, with the majority still in full working order. Many are now in the care of the National Maritime Museum at Greenwich. A few were regrettably sold in the 1930s and are now in private hands.

Prior to 1835, many of the clocks listed in the inventories were not named and only a description was given. It was Airy who assigned names to the clocks. These include the three clocks made by George Graham, now known as ‘Graham 1’, ‘Graham 2’ and ‘Graham 3’ and the clocks ‘Arnold 1’ and ‘Arnold 2’. The clocks were not however given identifying marks.


Clocks by maker (in alphabetical order)

Arnold 1
Arnold 2
Arnold (hour angle/degree clock)
Dent 2
Dent 1906
Dent 1914
Dent 1915
Dent 1916
Dent 2009
Dent 2010
Dent 2011 (transferred to Kew 1925/6)
Dent 2012
Dent 2013
Dent 2014
Dent 2015
Dent 2016
Dent 2017
Graham 1
Graham 2
Graham 3
Graham (Week Clock)
Grimaldi & Johnson
Mean Time (no name)
Molyneux (with flat steel pendulum)
Molyneux (with wooden pendulum)
Mudge & Dutton
Riefler 50
Shortt 3
Shortt 11
Shortt 16
Shortt 40
Shortt 49
Shortt 61
Shortt 66
Shortt 67
Tompion (hour angle/degree clock)
Tompion Great Clocks (x2)
Tompion (sextant clock)
Tompion (arc house clock)


Regulators on trial at the Observatory or there on a temporary basis

Earnshaw No. 1 (of the Armagh Observatory)

This clock by Earnshaw, which was destined for the new Observatory at Armagh, is said to have been delivered for trial at the Royal Observatory, Greenwich in February 1792 and to have remained there for two years until installed by Earnshaw at Armagh on 18 August 1794. For more information see A G Gunn’s article: Armagh’s Longcase Regulators, which was published in September 1993 (downloads as a pdf from the Armagh Observatory website). The Armagh website also has an excellent photograph of the clock together with an extensive description. Click here to view.


Other clocks

Arnold & Dent 708 (Dial Clock)