Astronomical Regulator: Hardy


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Made by William Hardy (d.1832), and known as 'Hardy' since Airy's time this particular regulator was delivered to the Observatory in 1811 and remained in continuous use as a Transit Clock until 1954. It can be considered as one of the most important clocks that the Observatory ever owned. During its lifetime, it underwent a number of significant modifcations.

Until 1871, when Dent 1906 was brought into use, the Transit Clock was the Observatory's de-facto sidereal standard. Intitially used as the Transit Clock with Troughton's 6-foot Mural Circle, Hardy was later used with its successors, firstly Troughton's 10-foot Transit Instrument and then the Airy Transit Circle.

Today, Hardy can be seen in its location on the south side of the Airy Transit Circle that it has occupied since 1850, where it is cared for by the National Maritime Museum (Object ID: ZAA0591). A replica pier (erected by the Museum in the mid-1960s) alongside the Troughton Transit Instrument marks the position Hardy occupied from 1823 until 1850.

Hardy in use with the Airy Transit Circle. The observer is in a pit below the level of the floor. The dial can be seen towards the top left. From the 8 August 1885 edition of The Graphic (detail)

The dial

In the early 1800s, using a mural circle at his Observatory in Somerset, the astronomer John Pond showed that the Greenwich Quadrants were defective. Impressed by the results, in 1807, the fifth Astronomer Royal Neville Maskelyne ordered a similar but larger instrument for Greenwich with the intention that it would superceed both the Mural Quadrants and the 8-foot transit telescope (which was used for measuring right ascension and determining the time). At around the same time, the clockmaker William Hardy persuaded the Board of Longitude to test a clock containing a new form of escapement he had invented. The clock was put on trial at the Royal Observatory where Maskelyne was so impressed with its perfomance that in 1809, he ordered a clock from Hardy for use with the new Mural Circle. Maskelyne died before either instrument was delivered and it fell to Pond, who was appointed as his successor, to bring the new instruments into use. The clock was delivered in 1811 and the Mural Circle in 1812.

In the event, the Mural Circle proved insufficiently stable for making transit observations, so in 1813, Pond ordered a new Transit Instrument from Troughton. It was brought into use in 1816 and used intitially with the existing Transit Clock, Graham 3. Meanwhile, transit observations with the Mural Circle ceased on 3 March 1814 (Greenwich Obs 1814) . In 1821, Graham 3 was dismounted and replaced by a series of clocks in quick succession (some or all of which appear to have been supplied on a trail basis), starting with a clock by Mollyneux and Cope. None appear to have been satisfactory, so in 1823 Pond transferrred Hardy from the Circle Room to the Transit Room for use with the Transit Instrument.

In 1850, the Airy Transit Circle, replaced both the Transit Circle and the Mural Circle. Hardy remained as the Transit Clock, but without its orignal case as in its new location, rather than being mounted on a stone pier, it was set into a niche in the base of the stonework supporting the south collimator of the Transit Circle. Hardy continued to be used with the Transit Circle until the last observation was taken in 1954.


1807: A new form of escapement by Hardy is tested by the Board of Longitude

Trial Results of showing the rate of Hardy

The rate of Graham 3 during the same period


1809: Maskelyne places an order


Hardy's escapement

In 1820, William Hardy was awarded a gold medal and an award of fifty guineas for his design by the Society Instituted at London for the Encouragement of Arts, Manufactures and Commerce (the present Royal Society of Arts), who published a set of plates with an accompanying description together with an introductory letter from Hardy that set out the circumstances of the first clock's trial at Greenwich, his relationship with Maskelyne and the ordering of a clock by the Observatory.

Letter and description:Transactions of the Society Instituted at London for the Encouragement of Arts, Manufactures and Commerce. Volume 38, (1820) pp.168–185.

Plates: 34–38.

William Pearson (1767-1847), one of the founders of the Royal Astronomical Society and a member of the Observatory's Board of Visitors from 1826 described the escapement in his magnum opus An introduction to practical astronomy, which was published in three volumes in the second half or the 1820s. His account and illustrations were adapted (without acknowlegement) directly from the account by Hardy mentione above. Links to the relevant pages are provided below.

Description: An introduction to practical astronomy, Vol 2 pp.306-8

Illustrations: An introduction to practical astronomy, Vol 3, Plate 14, figs 5, 6, 7, 8, 9

Instructions on cleaning the mechanism: An introduction to practical astronomy Vol 2 p.315


1823: Moved for use with the Transit Instrument instead of the Mural Circle(s)

Mural circle used when Transit intrument was out of use until at least 1832 and used with a journeyman clock set to beat in time with Hardy


1830: Dent replaces the escapement and an argument ensues

Table of times when Hardy had to come and clean the clock (pallets)


1850: Moved for use with the Airy Transit Circle


Alterations to the pendulum

As supplied by Hardy, the clock came with a mercurial pendulum. The first modification came in 1828 when:  'Mr Hardy applied a new glass cylinder to the pendulum of the clock containing a column of quicksilver nearly half and inch longer than the former.' (Greenwich Obs 1828).

The present pendulum is a compensated one of zinc & steel. The earliest published reference to such a pendulum having been fitted to the clock comes in the Introduction to the 1908 volume of Greenwich Observations and was repeated in the volume for 1909, which was the last volume to have an introdcution. After this date, there appears to be no further mention of the pendulum in the published output of the Observatory.

Information about changes and repairs made to the more important clocks was normally published in the Reports of the Astronomer Royal. No such information about changes to Hardy's pendulum was ever published. The location of the more important clocks was also published in the Introductions to the volumes of Greenwich Observations (1836-1909). Information about the type of pendulum was often included as well. The nature of these entries tends to be inconsistent, particularly between 1881 and 1909 during the tenure of Christie as Astronomer Royal, who mentioned Hardy's pendulum was mentioned for the first time in the volume for 1907, when the clock was recorded as being fitted with a gridiron pendulum. On this basis, it might seem reasonable to assume that a mercurial pendulum was replaced by a gridiron one in 1907 which was then changed for a zinc and steel one in 1908. But was this really the case, or did the Astronomer Royal simply fail to report the chaneovers in the year in which they happened?

The first clocks at the observatory to have zinc & steel pendulums were all ordered by Airy and delivered in 1871. They were the new sidereal standard, Dent 1906, and the three clocks Dent 1914, 1915 & 1916, which were orderd for the forthcoming 1874 Transit of Venus expeditions. Airy also arranged for zinc & steel pendulums to be fitted to three of the existing Observatory clocks that were being loaned for the expeditions (Earnshaw, Graham 2 & Arnold 2). Prior to the 1882 Transit of Venus Expeditions, five and possibly six of the Dent clocks that had been supplied for the 1874 Expeditiion with wooden pendulums had them upgraded to zinc and steel. They were Dents 1916, 2010, 2011, 2012, 2016, 2017 and possibly 2015.

In his 1874 Report to the Board of Visitors Airy wrote:

'The clock Hardy, which was in a bad state, has been thoroughly renovated by Messrs. E. Dent & Co., the principal alterations being the substitution of new contact­ apparatus and of a new escape-pinion for the old parts. While these repairs were being executed, the clock Arnold 1 was placed in the Transit-Circle-pit for use in observations of Circumpolar Stars, &c. The rate of this clock would probably be improved by the substitution of a zinc and steel pendulum (which has been found to answer so well in the Sidereal Standard and Transit of Venus clocks) for its old grid­iron pendulum.'

The published results show that Hardy was dismounted on 19 February 1874 and remounted at some point between 1 and 6 May. The exact date was not recorded in either the published observations or the journal of the Astonomer Royal or his chief assistant.

Given that Airy clearly rated the zinc & steel pendulums, the question therefore arises, did he have Hardy's pendulum changed for one of zinc & steel in 1874, but fail to mention the fact? Assuming that he didn't change it and that Christie was not in error when he recorded in 1907 that Hardy had a gridiron pendulm in 1907, one has to ask why was this apparently retrograde step taken. One possibility is that the mercury pendulum was damaged that year and one of the old gridiorn pendulums from one of the other clocks fitted as an interim measure while a new one of zinc & steel was ordered to replace it. A search of the correspondence with tradesman in the archives may shed more light on the matter.


The reserve Transit Clocks


Historical summary with references
1809? Ordered by Nevil Maskelyne
1811/12 Hardy submitted a bill of £350 for the clock. This was much larger than expected and referred by the Board of Ordnance (the Observatory's funder at the time) to the Council of the Royal Society (in their role as Visitors to the Observatory) for an explanation. An investigation was commenced by William Wollaston (one of the secretaries) who sought the opinion of the clockmaker A Cumming who interviewed Hardy and wrote back to Wollason in 19 January (RS MS372/149). Others were apparently alos consulted and a report compiled that  was read at the meeting of Council on 30 Jan 1812 in which they recommended that Hardy be paid a sum of £200 guineas. (RS MS 372/153 & RGO6/22/68). Hardy was not at all happy writing to RH Crew (for the Board of Ordnance) on 17 Feb requesting either that they get two or three of the superior chronometer makers to arbitrate or that he take back the clock (RS MS372/150). On 19 Feb, his letter was sent on to William Wollaston (one of the secretaries at the Royal Society asking him to get the view of the Royal Society on the matter. The matter was discussed at the next council meeting on 5 Mar. ...
... The minutes covering the period to the end of 1813 (RGO6/22) make no further mention of the clock suggesting that in the matter did not go to arbitration, and Hardy clearly did not take the clock back. Whether the Ordance paid hime more than 200 guineas reamins to be discovered.
1816 New 10-foot Transit Instrument by Troughton replaces Bradley's 8-foot Transit Instrument of 1750 on raised piers in the same location.
1823 4 Nov: Moved from Circle Room to Transit Room for use as the Transit Clock, with the new Transit Telescope (the 10-foot Transit Instrument) that had been installed by Troughton in 1816. (Greenwich Observations 1823)
1828 3 May: 'Mr Hardy applied a new glass cylinder to the pendulum of the clock containing a column of quicksilver nearly half and inch longer than the former.' (Greenwich Obs 1828)
1830 13 Feb: 'After the passage of the Sun the clock was taken down by Mr. Dent in order to apply a new escapment, and a clock of his own substituted in place thereof.' (Greenwich Observations 1830). This was done because the The rate of the clock had become extremely unsteady (Intro to Greenwich Obs 1836)
30 Mar: 'Hardy's clock was put up again by Mr.Dent, having had a dead-beat escapement applied (Greenwich Observations 1830).
Hardy later complained to the Royal Society as Dent also inscribed the dial (in keeping), with the words 'New Dead Beat Escapement by Dent
1836 In Airy's first year in office, a number of clocks were altered by Dent. in December 1836 Hardy had its jewelled holes removed by Dent. After the alterations the pivots turned in brass holes (Intro to Greenwich Obs 1836)
1850 The Troughton 10-foot Transit Instrument replaced by the Airy Transit Cicle which had been erected in the Circle Room which had been adapted to receive it. In December, Hardy transferred to the Transit Circle Room for use as the Transit Clock. To this end, it was dismounted from its case and mounted so that the dial was in the lower part of the south collimator pier facing nothwards, in which position it remains today. The telescope was bought into use at the start of 1851
1871 Dent 1906 installed in Magnetic Basement as the new sidereal standard providing impulses for the chrononograph and reducing Hardys role to that of a reserve clock.
1893 Described in 1893 inventory as 'Clock by Hardy' and being in the Transit Circle Room, with no infromation about the pendulum (RGO39/10/29). Nor is there any reference to an earlier pendulum being stored in either of the two Chronometer Rooms or the Museum that had been set up in teh partially constructed New  Physical Building.
1954 30 March: last published observation made with the Airy Transit Cicle taken by Gilbert Saterthwaite (Greenwich Observations 1954). By November, the movement and driving weight were being stored in the East Library at Greenwich (Inventory, Nov 1954). The location of the pendulum was not recorded



Board of Longitude 1