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Home arrow Archives   The American Surveyor     

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Written by Various Letters to the Editor   
Friday, 23 August 2013

A 248Kb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

The Royal Observatory
Your author Fred Roeder (who has written of the various Prime Meridians) may be interested to learn of the discrepancy between the Bradley Prime Meridian (in use until December 31, 1850) and the Airy Prime Meridian (in use after January 4, 1851). This is impliedly referred to in Barton Crattie's recently published "The Royal Observatory--Mistresses, Meridians, Longitude & Time."

Because the Airy telescope could only be constructed at a location that would not interfere with observations using the Bradley telescope, the Airy telescope was located some 8 metres east of the Bradley Prime Meridian.

My interest arises because of a 3.6 km discrepancy (or "dogleg") in the eastern border of the state of South Australia. It is commonly attributed to lesser earlier surveying technique (pre 1850) for the southern leg when the northern leg was more accurately positioned (~ 1868). However, approximately 11 metres of the discrepancy (at the latitude of the discrepancy) is properly attributed to the change in the location of the Prime Meridian (8 m at the latitude of Greenwich). The pre-1850 surveyors were using one Prime Meridian & the 1868 surveyors were using another PM.

They only had to transfer it about 200 miles (on horseback !!!) from the observatory in Melbourne and they were off by 3500 metres (= 3.5 km). By 1868 the latter day surveyors had the benefit of the telegraph to give "almost' instantaneous communications including time signals. The meridian had already been transferred halfway around the world to the Sydney & Melbourne Observatories--it was the last 200 miles that was the killer!

Part of the confusion was every surveyor & his dog had their own unique view of the accuracy of their starting point. You know the story - ask 5 economists & you get 5 different answers (6 different answers if one of the economists went to Harvard). And every surveyor & his dog was pretty vocal about why their assessment of the location of the starting point was correct.

[I have enjoyed reading Mark Stein's book, How the States Got Their Shapes and in Australia we have a drier version (for the Australian states) by David Taylor, The States of a Nation. Maybe our PBS will pick up the US TV series of How the States Got Their Shapes.]

The discrepancy caused by the different locations of the Bradley & Airy meridians went undetected for over a 100 years until in the 1950s some modern day UK surveyors were unable to verify or reconcile the Ordnance Survey (pre-1851) with their 1950s surveys. Their subsequent investigation uncovered what had previously been ignored and/or forgotten.

Best wishes & thanks for all the interesting stories I read in The American Surveyor.
Prof. Mal Park
University of Melbourne

Crattie replies:
Thank you for your words and clarification. I guess it was remiss of me not to explicitly say each astronomer royal established their own meridians for the exact reason you stated, the physical location of their respective sighting devises (telescope, quadrant etc). Walking within the observatory, this is obvious. --BC

I greatly enjoyed Mr Crattie's article on the Royal Observatory in the June 2013 edition of "The American Surveyor", and I thought that your readers might like to know something of its more recent history.

By the late 1940s, the smog and streetlights of London made practical astronomy all but impossible at Greenwich, so the observatory moved sixty miles south to a new home at Herstmonceux Castle, close to the south coast of England. The historic connection with Greenwich was retained in its new name, the Royal Greenwich Observatory (RGO), and its role was expanded to include support for research in astrophysics at British universities. A 100-inch reflecting telescope was built at Herstmonceux and inaugurated by the Queen in 1967. At the time, this was one of the largest astronomical telescopes in the world, and it was named after Sir Isaac Newton, inventor of the reflecting telescope.

Time-keeping and geodesy continued to be an important part of the Observatory's work. A group of atomic clocks was maintained by the Time Department to define Greenwich Mean Time, and Her Majesty's Nautical Almanac Office (HMNAO) produced annual almanacs for sailors, airmen and surveyors. In the early 1980s, a satellite laser ranging station was built as part of an international project to determine the precise details of the Earth's complex gravitational field.

Major changes were imminent, however. In 1985, the National Physical Laboratory took over the responsibility for maintaining the U.K.'s national time standard, severing the centuries-old link between the Observatory and Greenwich Mean Time. The 100-inch Isaac Newton Telescope was moved to a new international observatory atop an extinct volcano on La Palma in the Canary Islands, where observing conditions were far superior to anything in England. And in 1990, the Royal Greenwich Observatory itself was transferred to Cambridge.

In its new home, next door to Cambridge University's famed Institute of Astronomy, the RGO acted primarily as a laboratory for the development of astronomical instrumentation. HMNAO continued to produce its range of almanacs, but with a much reduced complement of staff. The final blow fell in 1998, when the government closed the RGO. Some groups were relocated to the Royal Observatory in Edinburgh, others to the Institute of Astronomy. HMNAO moved to the Rutherford Appleton Laboratory, near Oxford, and then, in 2006, to Taunton, in Somerset, to become part of the Hydrographic Office of the Royal Navy. It still publishes publish annual almanacs of star positions for astronomers, sailors and surveyors, and in doing so, it continues the proud tradition of the old Royal Observatory which began with John Flamsteed in 1675.
Dr David Harper
Wellcome Trust Sanger Institute,
Hinxton, Cambridge, England

P.S. I should explain that I am an astronomer by training. My connection to the RGO began in 1984, whilst I was a graduate student working with members of HMNAO. I was on the staff of HMNAO for two years, from 1996 until the closure of the RGO. I read Mr Crattie's article in a copy of "The American Surveyor" belonging to my late father-in-law, Bill Stockman, of Sandpoint, Idaho. Bill was a land surveyor in north Idaho for more than 50 years, much of it in the U.S. Forest Service. He passed away June 21, 2013.

Crattie replies: Your letter is of the best type, one full of information. Thank you for expanding on the article and bringing us to date. It is (was) a great institution that was of enormous value to the entire navigating world. We made it over to your neighborhood on our recent trip to your fine country. We took a trip over to the British Antarctic Survey as well as the Scott Polar Museum. We were fortunate to meet Mr. Alan Wright just about 4 months prior to his demise. Mr. Wright spent a year and a half in the early 60s surveying in that cold clime. --BC

A 248Kb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

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