Astronomical Regulators

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 most of the 19th centuries, 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 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 do not however appear to have been given identifying marks.

Although many of the telescopes at the Observatory were drawn or photographed, the same was not true of the regulators until the 1920s. But even then, the only ones that tended to get photographed were those associated with the Greenwich Time Service and in particular the "six-pip" time signals. Fortunately, a few Regulators make an appearance in the background of other images. They are important as they help track the changes made over time.

Some clocks were brought to the Observatory for trial before being sent on elsewhere.


Clocks by maker (in alphabetical order)

Arnold 1
Arnold 2
Arnold 3 (ref: RGO6/283/615 & as Arnold & Son in RGO39/10/53)
Arnold (hour angle/degree clock)


Dent 2
Dent 1906
Dent 1914*
Dent 1915
Dent 1916
Dent 2009
Dent 2010
Dent 2011
Dent 2012
Dent 2013
Dent 2014
Dent 2015
Dent 2016
Dent 2017

* Not owned by the Observatory


Göttingen mean-time clock (RGO6/730/229)
Graham 1
Graham 2
Graham 3
Graham (Week Clock)
Grimaldi & Johnson


Mean Time (no name)
Molyneux (with flat steel pendulum)
Molyneux (with wooden pendulum)

Molyneux & Cope
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: Astronomical Clocks at Armagh Observatory (1996).

Standard Clock with Gravity Escapement by Arnold & Dent, trialed from 20 Mar 1832 to 26 Apr 1833 and subsequently displayed at the galley of the "Society for the illustration and encouragement of practical science"

Cottingham Riefler made for the Observatory at Mauritius

Cottingham Riefler made by Mercer for the Observatory at Hong Kong

?Frodsham Regulator No.1039 (of the Palermo Observatory)?


Other clocks

Arnold & Dent 708 (Dial Clock)