Home | Membership | News | Diary | Courses | Noticeboard | Books | Journals | Links | Database | e-papers | Contact

Ripples in time: Conflict on the Greenwich Meridian

by Graham Dolan


Founded in 1675, the Royal Observatory was Britain's first government-funded scientific institution. The home of the Prime Meridian and also of Greenwich Mean Time, it sits on the edge of a plateau in the centre of Greenwich Park where it has commanding views of London and the nearby River Thames. Established by King Charles II for the specific and practical purpose of 'rectifying the Tables of the Motions of the Heavens, and the places of the fixed Stars, so as to find out the so much desired Longitude of Places for perfecting the art of Navigation'1, it is now a museum.

More than two centuries after its founding, work began on the construction of the Greenwich Generating Station. Designed and built by the London County Council (L.C.C), for the supply of electricity to its tramways, it was constructed in two phases, commencing in 1902. Sited on the banks of the Thames at a distance of just half a mile from the Royal Observatory and exactly on the line of the Greenwich Meridian it was only belatedly realised that its location represented a serious threat to the Observatory. As well as the more obvious problem of turbulent air and smoke from the chimneys, there was a potentially much more serious problem of vibration.

What seems rather curious is that no one associated with the Observatory was formally consulted about the location for the Generating Station. Nor was anyone there consulted about the design and nor did they ask to be. Even more curious, is that despite the fact that the Generating Station was being built right under his nose, William Christie, the Astronomer Royal, only began to raise objections in 1905 when phase one (the northern half) was nearing completion. On 30 May 1906, he shared his concerns with the Observatory's Board of Visitors (whose function was similar to that of a Board of Trustees) at their annual visitation.

By this time, phase one was largely up and running, having been officially opened just a few days earlier on Saturday 25 May. As was the norm, details of the visitation were reported in the press. In the ensuing weeks, numerous follow-up articles about the impact of the Generating Station on the Observatory were published and questions asked in Parliament. In all the hullaballoo, the finger of blame when pointed, was largely (and unfairly) directed towards the L.C.C. Very few asked why Christie, the Admiralty (who funded the Observatory) and the Board of Visitors were so slow in raising their objections ... and those who did ask, did not receive an answer.

A Parliamentary inquiry rapidly ensued. It made a number of recommendations in order to mitigate the impact of the Generating Station. These included finishing the two chimneys of phase two at a lower height than originally planned as well as taking steps to reduce vibrations.

The electrification of London's tramways

Under the Tramways Act, 1870 local authorities were permitted to acquire privately operated tramways in their area after they had been operating for twenty-one years. The London County Council, which had come into existence in 1889, acquired its first tram company by this means in 1895 and by 1909 owned most of the tramways in London.

The Greenwich tram depôt, which had opened 13 December 1870, stood on the banks of the Thames on land formally occupied by Crowley House and was acquired by the L.C.C. when it took over the London Tramways Company at the start of 1899. They in turn had acquired it as part of the assets of the Pimlico Peckham & Greenwich Street Tramway Company which they had taken over in 1873.

The London County Tramways Act, 1900 gave the Council, powers to electrify certain tramways and to construct a Generating Station on the site of its tramway depôt at Camberwell (now the site of Walworth Bus Garage). For various reasons, the Council then decided that their tram depôt at Greenwich would make a better site for the Generating Station. Amongst the advantages was that the river frontage would be convenient for the delivery of coal, the removal of ash and the supply of water for the condensers.

The London County Council (Tramways and Improvement) Act, 1902, gave the Council the powers needed to build its Generating Station at Greenwich. Much of the act dealt with the construction of new tramways and improvements to existing ones, with only a small section of its 34 pages being devoted to the Generating Station. As well as giving the Council the powers to acquire the additional land required, the act stated (without any further elaboration) that:

Prior to its completion, power for running the newly electrified section of line through Greenwich was obtained from the generating station operated by the London Electric Supply Corporation at Deptford.2

November 1905 — the panic begins

Work on constructing the Generating Station began almost immediately after the act of 1902 had been passed and by the end of 1903, the first two chimneys were nearly completed.3

Greenwich Generating Station as seen from the Royal Observatory in June 2007. Graham Dolan Archive

Although the height and position of the chimneys was one of the things Christie objected to, it was not until 2 November 1905, after another two years had passed, that he raised the matter for the first time with the Admiralty.4 What seems to have prompted his action was a report about a visit to the Generating Station by a group of Councillors from Paris that appeared in the 20 October edition of The Kentish Mercury. It seems that it was only at this point, that Christie realised, that what had been built so far, was only half of what was planned. What alarmed him further was an article in The Times on 30 October followed by another the following day that mentioned the Council's proposal to seek Parliamentary powers to enable it to supply electrical power to a wider market.

In his letter of 2 November to the Admiralty, Christie stressed that there was nothing in the 1902 act to indicate that the Generating Station would be of 'abnormal size' with 'exceptionally high chimneys'. He had, it seems, naively expected something similar to that of the rather smaller Generating Station that had been built on the banks of the Thames at Deptford around a mile to the north-west of the Observatory. Since its opening in 1889, (when it was London's biggest Generating Station), it had had, so Christie claimed, no discernable impact on the Observatory (more on this below). At about 150 feet in height, its chimneys were not only some 100 feet lower than those that had been built at Greenwich, but their tops were below the level of the plateau on which the Observatory's instruments stood.

The Observatory's most important instrument was a telescope known as the Airy Transit Circle. This instrument not only defined the Greenwich Meridian and the Prime Meridian of the World (which by definition is the north south line passing though its centre5), but was also the ultimate source of Greenwich

Mean Time. Designed by Christie's predecessor, the Astronomer Royal, George Airy, after whom it is named, it was brought into use at the start of 1851. It took the form of a refracting telescope mounted in such a way that it could only move in the plane of its own meridian. The stars all move across the sky in a similar way to the Sun, and like the Sun, they culminate, or reach their highest point, as they transit, or cross, the meridian of the observer.6

Because the Earth was believed to be spinning at a steady rate, it followed that each individual star would cross (transit) the meridian of the telescope at the same (sidereal) time each day. Provided the telescope was accurately aligned to the meridian, the right ascension of a star (the celestial equivalent of longitude) could be obtained directly from the time of transit. The celestial equivalent of latitude was found by measuring the angle up to the star at the same moment. In a bit of a chicken and egg scenario, certain of the brighter stars, whose positions had been refined by repeated observation over a long period of time, were used as 'clock stars' to determine the errors of the transit clock (the clock used with the telescope). This was done by comparing the observed times of transit with the theoretical ones. Crucially, it was from the transit clock at Greenwich that Greenwich Mean Time was ultimately determined.

Crowley House from the banks of the Thames

Whilst the two completed chimneys of Greenwich Generating Station were close to the Meridian of the Airy Transit Circle, they did not directly block the view along it. The issue here was going to be one of turbulence in the atmosphere as a result of the hot gases coming from it once the Generating Station came into use. The situation with the two chimneys that still needed to be finished was rather different as the most westerly of them would directly block the view of the Observatory's recently erected Altazimuth Telescope when it was aligned to the north.

Phase one of the Generating Station under construction in 1904

Phase one as it neared completion. Postcard published anonymously c.1905

Later, Christie was to stress the importance of the Greenwich Meridian as defined by the centre of the Airy Transit Circle together with the international obligations arising from its adoption as the Prime Meridian of the World at the 1884 International Meridian Conference. The subsequent adoption by many countries of a standard time based on the time on the Greenwich Meridian, in his opinion, strengthened those obligations further. Because of this, Christie argued, the Airy Transit Circle was sacrosanct and should not under any circumstances be moved and that if anything had to be moved it must be the Generating Station rather than the Observatory (for more on this see below).

As soon as they became aware of the conflict of interests, the Admiralty set in train a series of meetings with the L.C.C. with a view to resolving the dispute in a way that satisfied all of the parties and hopefully avoided any litigation.

Postcard published anonymously c.1904

Deptford Generating Station. From The Illustrated London News, the 26 October 1889

It soon became apparent that the height of the chimneys and the smoke they produced was only going to be part of the problem. Rather than use balanced turbine-generators, for phase one, the Council had chosen to install four less up to date vertical-horizontal steam reciprocating engine sets (by John Musgrave and Sons of Bolton) driving a flywheel-type alternator. These had the distinct disadvantage, from the observatory's point of view, that they were unbalanced and would potentially cause problems with vibration. It was arranged that as soon as the first of them was up and running, a series of vibration tests would be conducted in cooperation with the L.C.C. engineers. One was run for the first time on 23 March 1906.

Plan of the Generating Station

Sectional view

The vibrations from the engines caused tremors in the surface of the liquid mercury used to form a completely horizontal mirror in the four instruments where observations were made by reflection — the Airy Transit Circle, the Altazimuth, the Reflex Zenith Tube and the small reversible transit instrument in the pavilion in the courtyard. This was particularly serious as it was from these observations by reflection that the level errors of the instruments were obtained.

On 30 April, the first known mention of the problem appeared in the press in a general article about the nuisance of smoke from London's growing number of Generating Stations. This was published in The Daily News and carried a photograph of the new Generating Station at Greenwich, the caption of which ended with the sentence: 'It is contended that these works almost cut the meridian, and interfere with the work of the Observatory.' As far as is known, this was neither followed up by The Daily News, nor was it picked up by any other newspaper.

Despite the fact that progress was being made in the talks with the L.C.C., Christie rightly felt compelled to inform the Board of Visitors about the situation. By then, the two chimneys of phase two had risen to a height of 180 feet. Christie concluded his 1906 Report to the Board of Visitors, (completed on 26 May), with the following statement:

The chimneys as seen from the Airy Transit Circle The Altazimuth Telescope

The mercury trough of the Airy Transit Circle Taking an observation by reflection with the Airy Transit Circle

The question arises why the immediate neighbourhood of the Observatory should be selected for the planting of Generating Stations on an unprecedented scale to supply electric power to distant districts. The very powerful engines required for such a large output are liable to cause vibrations, the extent of which could hardly be anticipated from previous experience of ordinary engineering plant or of railway trains, which have hitherto not affected the work of the Observatory.

Furore in the press

As was the norm, after the meeting, the Astronomer Royal's report was circulated to the press. In the case of The Times, a brief report appeared the following day and a fuller one on 1 June. In the meantime, on 31 May, The Standard, The Tribune, The Daily Telegraph, The Morning Leader, The Daily Graphic and The Westminster Gazette had all published much fuller stories about the threat to the Observatory. On that same day, H.H. Turner, former Chief Assistant at Greenwich, Savilian Professor of Astronomy at Oxford and member of the Board of Visitors had penned a letter to The Times. This was published on 2 June.

In response, an unnamed member of the London County Council (Fitzroy Hemphill?) wrote to The Times the next day to defend the Council's actions. His letter, which was published on 7 June, ended as follows:

To this, there was no reply.

Questions in the House

On 21 June, the matter was raised in the House of Lords. During the debate that followed, the Earl of Crawford revealed a previously unknown fact:

The architect referred to was William Riley who in 1877 had joined the staff of the Director of Engineering and Works of the Admiralty, and rose to the rank of Assistant Director. In 1899 he had been appointed as 'Superintending Architect of Metropolitan Buildings and Architect to the London County Council'. Whilst it was true that Riley had had input into the recently constructed New Physical Building and Altazimuth Pavilion at the Observatory, he had had no input into the selection of the site for the Generating Station. Once this had been pointed out to Crawford, a graceful apology was issued via a letter to The Times (which had earlier reported on the debate).

As well as being reported in Hansard (as was the norm), the debate was also reported in the July 1906 edition of The Observatory. This was a monthly journal that had been founded by Christie and whose editors Thomas Lewis and Henry Hollis were both Assistants at the Royal Observatory. As such, its impartiality on the matter has to be questioned.

The Parliamentary Inquiry

Within weeks of the meeting of the Board of Visitors, a Parliamentary Committee had been put together. It had just three members: The 4th Earl of Rosse (representing the Royal Observatory), Sir Benjamin Baker (representing the London County Council) and James Alfred Ewing (representing the Admiralty). The Earl of Rosse, Lawrence Parsons, was an astronomer and one of the Observatory's visitors who had served on the Board since 1886. Baker was a civil engineer and Chief Engineer of the Council and probably best known today as the designer of the Forth Bridge. Ewing was a physicist and engineer who in 1903 had been appointed by the Board of the Admiralty as Director of Naval Education at the Royal Naval College, Greenwich, having previously been Professor of Mechanism and Applied Mechanics at the University of Cambridge.

The terms of reference were as follows:

The committee reported at the end of the year. In all, they made six recommendations which they summed up as follows:

The recommendations were subsequently accepted by both the Admiralty and the L.C.C., with the later finally agreeing to them in October 1907.8

A solution to the problems of vibration

Fortunately for all concerned, experiments conducted on the design of the mercury troughs (the trays that held the mercury) showed that the tremors in the surface of the mercury could be eliminated by altering the profile of the bottom surface and the depth of the mercury they contained. More details on this can be found in the Committee's report.9

Completion of phase two

Built from London stocks, with Portland stone cills, copings, and dressings and a roof covered with Bangor slate, the completed Generating Station had a total volume of 9,670,000 cubic feet. An early example of a steel framed building in Britain, it is today generally admired by architectural historians. The tapered octagonal chimneys as designed had crisply corbelled and machiolated tops.10

The decision not to complete the southern pair to their full height had a hugely disfiguring effect on the building's overall appearance. Phase two is believed to have been completed in about 1910. The total cost as estimated in 1906 was ₤900,000.

With regards to the turbines used in phase two; although the Committee recommended the use of balanced turbines, the decision to use such plant in phase two had in fact already been made before phase one was officially opened.

Although today the question of air quality is high on the political agenda, this was not the case when the Generating Station was built. No thought at all seems to have been given to the potential increase in air pollution that was likely to occur by failing to build the southern chimneys to their originally intended height.

Postcard by Perkins & Son

A failure of corporate memory?

As long ago as 1835, while the London and Greenwich Railway was still under construction, proposals had been under discussion for a line that would cross Greenwich Park on a viaduct between the Queen's House and the Observatory. The proposals were considered by the then Astronomer Royal (John Pond) and the Board of Visitors, both of whom raised their objections on the grounds that vibrations from the trains would almost certainly interfere with the observations by reflection that were made with the two Mural Circles (some of the most important telescopes in use at that time). So concerned were the Visitors that they asked one of their number, Captain Beaufort, to investigate the matter further. A series of tests were therefore carried out on his behalf alongside the Liverpool & Manchester Railroad. The results suggested that vibrations from trains running across Greenwich Park would almost certainly affect the Observatory.11

On 25 January of the following year, George Airy, the new Astronomer Royal, conducted further tests in the Glebe Meadow near the Surrey Canal and about 200 feet south of the London and Greenwich Railway, which by then was carrying test trains prior to its partial opening in February.12 They too suggested that there would be an impact, but that it could be mitigated by ensuring a minimum distance was maintained between the Observatory and the railway and that the trains be restricted in both their speed and their times of passage. The proposals continued to be pushed forward in various forms for the next 30 or so years and involved various further tests including a series that Airy undertook at Kensal Green in 1846.13 In the meantime, a line was built around the Park connecting the North Kent coast to London via a tunnel that ran from Charlton to Blackheath. This line opened in 1849.

Postcard by Perkins & Son, c.1909

In 1863, in response to yet another proposal to tunnel under the Park, Airy conducted further tests in two new locations, the two sites having similarities in soil structure with that of the Observatory. They were near the entrance to the existing Charlton to Blackheath tunnel by Morden College in Blackheath and near the Metropolitan Railway at the upper end of Portland Place near Regent's Park. From these experiments Airy concluded that any new tunnel should not pass closer to the Observatory than 1,000 feet.14 In the end, plans for a tunnel across the Park were abandoned and the line from Greenwich extended instead via a tunnel that passed under the grounds of the Royal Hospital School (now the National Maritime Museum). This eventually opened in 1878 and passed at a minimum distance of 570 yards from the Transit Circle.

Further tests were carried out in 1888, when amendments to the 1887 Bexley Heath Railway Act were being discussed in parliament as a result of a proposal to build a new tunnel under Blackheath that would pass within 840 yards of the Observatory. This time, tests were carried out by Christie at the Observatory itself, using the Airy Transit Circle.15 Worryingly, it was found not only 'that the disturbance was very great during the passage of trains between Greenwich and Maze Hill', but that 'there was considerable disturbance during the passage of trains through the Blackheath-Charlton tunnel, at a distance of a mile.' As a result, firstly, the construction of the new tunnel was not allowed and secondly modifications were made by Christie to the mercury troughs of the telescopes to damp out the vibrations.

Trains however weren't the only source of troublesome vibrations. Back in 1851, Airy had had to contend with the problems of vibrations with his newly installed Reflex Zenith Tube (a specialist telescope that can only point directly upwards). Installed in a small room next to the Airy Transit Circle, every time the adjacent courtyard gates were opened or shut, a jarring of the mercury would result. In 1853/4, Airy decided that a new room for the telescope should be constructed on the other side of the Transit Circle roughly 12 metres further from the gates. Here too there were problems, with the mercury suffering from an intolerably large and never ceasing tremor. It was eventually realised that the vibration problem was a result of the very structure of the hill itself, its compacted mix of sand and pebbles leading to the ready transmission of vibrations and tremors. The problem was eventually mitigated by backfilling the pit in which the mercury trough had stood with 'incoherent rubbish' and then suspending the mercury trough on a complex arrangement of staging.16 Interestingly, the problem of similarly transmitted vibrations does not appear to have affected the mercury troughs that had been used with the Mural Circles since 1822, nor the Transit Circle that replaced them in 1851.

Given the long history of both dealing with vibrations and seeing off schemes that would directly impact the work of the Observatory, one has to ask, when it came to the question of Greenwich Generating Station, was it a question of complacency on the part of the astronomers or was it a failure of corporate memory that caused the failure to respond?

The completed power station in 1911. Postcard by Mc.Queen Greenwich

A dereliction of duty? — The fitness for purpose of the Board of Visitors

Christie was not alone in failing to make the connection between the evolving Generating Station and its potential impact on the Observatory. What questions if any were asked by his two Chief Assistants, Frank Dyson and Philip Cowell, or more importantly the 15 or so members of the Board of Visitors, all Fellows of the Royal Society or the Royal Astronomical Society (or both), who were most certainly asleep on the job?

At their annual meeting at the Observatory in June 1903, the Visitors would have seen the chimneys under construction. By the time of their 1904 meeting, the first two chimneys would have been completed and by the time of the 1905 meeting, the whole of the external works of phase one would have been coming to an end. Even if they had failed to notice the Generating Station's looming presence on their way to and from the Observatory, they can hardly have failed to notice it from the vantage point of the Octagon Room where their meetings were held. Regrettably, the minutes of the meetings of the Board are, as a matter of course, somewhat rudimentary. As such, they shed no light on what may or may not have been discussed on either a formal or an informal basis.

It is apparent from Turner's letter to The Times (mentioned above) that the function of the Board as he (and presumably they) saw it, was largely to act as a sounding board for the Astronomer Royal and then to pass any appropriate resolutions. It does not seem to have occurred to him that the Board itself could (and should) have taken action an awful lot earlier.

The terms of reference of the Parliamentary inquiry were entirely about finding a resolution to the problems of the Observatory and the L.C.C. The Board of Visitors was never held to account and it was arguably to the long term detriment of the Observatory, that there was not a parallel inquiry into their role and the way in which they were constituted to see if they were still fit for purpose. It is hard to believe that a board with such a narrow range of interests would be allowed to exist today.

Stress & illness — a possible explanation for Christie's slowness to react?

By the start of the twentieth century, Christie's programme of expansion that had commenced in the early 1880s had finally come to an end. With his new telescopes and facilities came a significant increase in both the range and amount of work being done. With high staff turnover amongst his temporary Computers,17 Christie came under considerable personal pressure which inevitably took its toll.

Shortly before the meeting of the Board in 1905, Christie was ordered by his doctor to give up his work immediately, leave Greenwich, live in the open air and give up his duties and responsibilities altogether.18 The physician's report sent to the Board's then Chairman, Sir William Huggins, stated amongst other things that his capacity for work was small and for sustained work was nil. His reported symptoms suggest he was suffering from a combination of stress and heart failure. As a result, he missed the annual meeting of the Board.

According to Dyson, the illness was a repeat of one that he had had a few years earlier. Reading between the lines, it seems likely that Christie was afflicted throughout his last ten years as Astronomer Royal. Records are scanty, but we do know that the 1910 visitation (Christie's last as Astronomer Royal) was postponed by two weeks because of his illness.19 We also know from what Turner wrote in his obituary, that Christie lacked energy in his later years. This would have affected his ability to lead effectively and was almost certainly something of which the Visitors were aware, even though it is never formally alluded to in their records.

The weakness of some of Christie's scientific arguments

Some of Christie's scientific arguments do not necessarily stand up to proper scrutiny. Below are four areas where he could and perhaps should have been probed or challenged more deeply.

Existing obstructions on the Meridian of the Airy Transit Circle

Although no one ever asked at the time, it is worth noting that the Airy Transit Circle was never able to observe right down to a level horizon. To the north lay the summit of Pole Hill. At a distance of about 11 miles, its height was almost exactly 300 feet above sea level (and rather more when the height of the trees growing there was taken into account). To the south, at the same height above sea level as the Observatory and at a distance of just 480 metres, lay the Ranger's House. In between, there were lots of trees. Both would have been significant in terms of how low to the southern horizon the telescope could be pointed.

Vibrations from Deptford Generating Station

Deptford Generating Station supplied its first electricity in November 1889. A few weeks earlier however, on 26 September, the mercury trough of the Airy Transit Circle had been furnished with a bottom of amalgamated copper in an attempt to damp out the disturbing effects of tremors attributed to passing railway trains and road traffic.20 A similar change to the trough of the Reflex Zenith Tube had previously been made on 13 February 1889.21 The change to the Transit Circle produced very beneficial results as regards steadiness of the images and as a result, the trough was replaced by one of amalgamated copper the following year. It seems likely that the modified design would also have damped out any vibrations arising from the Deptford Generating Station once it came into use. Christie's claim therefore that the Generating Station had run with no discernable effect on the Observatory whilst being true, was potentially misleading.

Purpose of the Altazimuth

Christie's Altazimuth was erected in 1896. Similar in design to a transit circle, it could also be set up to point not only along a meridian, but at angles (azimuths) of 30, 60 and 90 degrees to it. Its main purpose was to make extra-meridian observations of the Moon, especially around the time of New Moon when it was close to the Sun and impossible to observe as it crossed the meridian. When used at an angle to the meridian, the presence of the Generating Station chimney would have been an irrelevance. Questions about the mode of use of the Altazimuth were never asked. Nor were questions about its effectiveness or reliability.

The truth about the inviolability of the Airy Transit Circle

The supposed importance of the 1884 International Meridian Conference and the so-called international obligations was somewhat over-egged. In 1906, the Airy Transit Circle was in its 56th year of operation. An identical instrument installed at the Cape Observatory in 1855 had just been replaced with one of more modern design. Although there were no immediate plans to replace the Greenwich Instrument, it would inevitably have needed to be replaced at some point. The physical nature of the Greenwich site (and historic precedent) would mean that any new instrument at Greenwich was unlikely to be placed on the same meridian as the old. As it turns out, the Airy Transit Circle ceased to be used to determine the clock errors in 1927 when it was decided to use the small reversible transit instrument in the nearby Transit Pavilion to the west instead. As a result, a small offset to the determined time was applied to bring it into line with the time on the Greenwich Meridian. The other functions of the Airy Transit Circle continued as before until eventually being taken over by the Cooke Reversible Transit Circle, a new telescope that was ordered in 1931 and originally set up in the Christie enclosure some 400 yards to the east of the Greenwich Meridian before being moved to Herstmonceux after the war.

It is worth noting too that the determinations of the difference in longitude between the observatories of Greenwich and Paris that were made in 1888, 1892 and 1902 while Christie was Astronomer Royal, were made from two observing stations on different meridians in the Observatory Courtyard and an offset applied to allow for their distance from the Greenwich Meridian.

Later, in 1912 when the Royal Society was consulted about plans to increase the power output from the Generating Station, it received a letter from one of its fellows suggesting that the Observatory might be moved to a potential site ten miles to its immediate south. In response, Dyson (who took over as Astronomer Royal in 1910) gave a more honest assessment of the position, writing '... it does not seem to me that any weight attaches to the fact that the suggested site is on the Greenwich Meridian, If the Observatory had to be moved, it would be as regards time and zero of longitude, comparatively an easy matter to make allowance for the difference between the new and old positions, but the conditions at present are not such as would justify the great expense and difficulty of moving the Observatory ...'22

Clutching at straws — the legal protection of observatories

In 1838, a new magnetic observatory was constructed at Greenwich, its purpose being to measure and record the changes that occurred in the Earth's magnetic field. These were of two types. The first, which includes the westward drift of magnetic north, arose because of what is happening within the Earth's core. The second, which were discovered in the nineteenth century, arise mainly from currents in the ionosphere and magnetosphere as a result of phenomena occurring on the Sun and take place over a much shorter timescale. In December 1890, small uncountable agitations had begun to be detected in the Horizontal and Vertical Force traces in the Magnetic Observatory. These corresponded to similar disturbances detected by the Earth Current registers. They started around 7 o'clock in the morning, ended around 11 o'clock at night, and were generally absent on Sundays.23 The following summer it was eventually realised that they were caused by the City and South London Railway (now part of the Northern Line) which ran from Stockwell to the City of London.24 Four years in the making, the railway was the first electric railway in London. Officially opened by the Prince of Wales on 4 November 1890, it opened to the public on 18 December. It operated at 500V DC using an insulated third rail to deliver the current, with the return being via the uninsulated running rails.

Had the power delivery system been such that all the return current flowed along the rails back to the substation, the magnetic fields produced by the outward and return currents would have more or less cancelled each other out, limiting the disturbed area to the vicinity of the railway. However, the return rail was not insulated from the ground, and part of the return current leaked into the earth. Not only did this reduce the cancellation effect (thereby affecting the Observatory), but the leakage currents created their own, smaller, magnetic fields as well.

Although, at this distance, the interference with the magnetic registers at Greenwich was not considered severe, it was only a matter of time before proposals would be made to electrify the multiplicity of existing lines and tramways in London. The closer they ran to the Observatory, the greater the impact they were likely to have on the magnetic instruments and the value of the magnetic records.

By 1893, a clause had been agreed for insertion in future Parliamentary railway or tramway bills authorising electrical power, in order to protect not only the Greenwich Observatory, but also the magnetic observatory at Kew (established in 1857) along with various other government scientific establishments in London. Amongst its provisions was the stipulation that 'either insulated returns or uninsulated metallic returns of low resistance' should be used. The clause was inserted in numerous bills, which in the case of Greenwich included any that related to a line that came within originally ten, but later five miles of the Observatory.

Although the 1902 Act did not in itself provide the Observatory with any protection in respect of the Generating Station, had the dispute with the L.C.C. gone to litigation, Christie suggested that this clause, which had been included in other acts and was designed to protect the observatory from the use and leakage of electricity, could be invoked on the grounds that test experiments had showed that when the electricity from the Generating Station was used with a constant load the vibration was smaller than when it was with the variable load of the tramways. Since it was the 'use' of electricity for the tramways that caused the excessive vibration, the generation of the electricity could not, so Christie argued, be dissociated from it.25

A brief history of the Generating Station from 1910 until today

One consequence of agreeing to abide by the recommendations of the Parliamentary Committee was that the L.C.C. found its hands tied when it wanted to upgrade the four 3,500 KW reciprocating engines of phase one with four turbines with more than double the output. They also wanted to raise the shorter chimneys by 60 feet. As a result, a new dialogue with the Admiralty was commenced in 1911. In early 1913 the Admiralty agreed to the turbines being substituted for the existing reciprocating engines subject to following three conditions that had previously agreed in 1907 being retained:

1. that the height of the chimneys would not be increased
2. that the temperature of the gases did not exceed 250° Fahrenheit
3. that no further development of the station would take place.

Although agreement was reached in 1913, it took until 1922 for the last of the reciprocating engines to be replaced. A few years later, in around 1927, a run of reinforced concrete high level reserve coal bunkers were built on the west side of the boiler house. Regrettably, as with the lowering of the southern chimneys, the architectural integrity of the original design was severely compromised in the process. Originally painted white, the bunkers still survive but have been black in colour since remedial work was carried out on them in 2013.

In 1930, a programme of modernisation began that involved the replacement of the turbine generators with new turbo-alternators of higher output. When the London Passenger Transport Board (London Transport) was formed in 1933, control of the Generating Station passed to it from the L.C.C. Over the following years further upgrades took place in part to meet the change in demand for electricity. Between 1969 and 1972, the Generating Station underwent a complete modernisation programme, with the coal-fired boilers and generators being replaced by eight gas turbine alternators fired by oil and the two northern chimneys being reduced to the same height as the others.26 From that time onwards, the Generating Station served as a backup to London Transport's Lots Road Generating Station at Chelsea which had originally been opened in 1905 to serve part of the underground network. In 1998 London Underground shut Lots Road and switched to the National Grid for its power supplies. At this point, the role of Greenwich changed, with the station becoming the provider of emergency power to the London Underground.

In 2015, the then Mayor of London, Boris Johnson, announced plans to install six new gas engines and introduce a district heating scheme for nearby homes and buildings. Although the scheme did not require planning permission, it did require approval by the Environment Agency to whom the proposal was submitted. Following local objections that the scheme would increase air pollution by adding to the already high levels of Nitrogen oxide, the proposal was withdrawn at the end of 2016 'to allow time for a review of the project to ensure it aligns with the priorities of the new Mayoral administration'.

The Author

Graham Dolan is a Fellow of the Royal Astronomical Society and was formerly Senior Education Officer at the Royal Observatory in Greenwich. He has spent much of the last ten years creating a website devoted to the history of the Observatory, its instruments and the people who worked there (

Notes and References

1 Royal Greenwich Observatory Archives, Cambridge University Library (subsequently RGO). RGO1/40/61
2 RGO7/66
3 RGO7/65
4 RGO7/66
5 International Conference Held at Washington for the Purpose of Fixing a Prime Meridian and a Universal Day: October, 1884. Protocols of the Proceedings. Resolution 2.
6 The north-south line on which the observer is standing
7 The National Archives (TNA). ADM190/6
8 RGO7/66
9 A copy of the report can be read at:
10 Peter Guillery. 'Greenwich Generating Station', London's Industrial Archaeology No 7 (2000)
11 Correspondence, &c., relative to a railway communication through Greenwich Park. Parliamentary Papers, Railways, Paper 375, 10 June 1846
12 ibid
13 ibid
14 Correspondence, &c., relative to a railway communication through Greenwich Park. Parliamentary Papers, Railways, Paper 259, 5 May 1865
15 RGO7/59
16 1856 Report of the Astronomer Royal to the Board of Visitors, p9
17 The role of the Computers was to turn observational data into something more useful by reducing it to a standard form. This necessarily involved long and tedious calculations which before the age of mechanical calculators and electronic computers, all had to be done by hand. Many Computers also took part in the observing programmes.
18 The National Archives (TNA). ADM190/16
19 ibid
20 RGO7/29
21 ibid
22 RGO7/66
23 1891 Report ... to the Board of Visitors, p13
24 1892 Report ... to the Board of Visitors, p15
25 RGO7/66
26 Modernization of Greenwich Generating Station. London Transport (1971)

© GLIAS, 2020