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Proceeding south on King William Walk, your path is blocked by the gold trimmed St. Mary’s Gate. To the east is a landscaped promenade featuring prominently a ship in the bottle, perhaps ten feet in diameter and twenty-five in length. To the west is the Greenwich Tavern "The Mature Neighbourly Gastric Pub, Please Enjoy Responsibly and Quietly." Straight ahead, high on a hill, surrounded by the 183 acre Greenwich Park sits the Observatory.
Climbing that long steep grade, digesting a breakfast of fried uncured bacon, eggs, bangers, pork and beans and tomatoes are five land surveyors: 4 Yanks and 1 Brit. The climb is a culmination, the hajj for these surveyors, the once in a lifetime journey to our Mecca: the Prime Meridian, Longitude and Time.
The Observatory grounds proper, dominated by Flamsteed House, is a hodge-podge of structures assembled over three centuries of time. The contemporary surveyors would spend a number of hours traversing through narrow hallways, up and down stairs and along stone pathways in beautiful weather through early spring gardens. These same paths were once trodden by the footsteps of Edmond Halley (the comet), Charles Mason (and Dixon), Isaac Newton (falling apples), Christopher Wren (St. Paul’s Cathedral) and any number of surveyors and astronomers and Kings and Queens of the realm.
The entire "astronomick" enterprise was begun long before the fabled sinking of the Shovell fleet and the Board of Longitude. The observatory’s origin might possibly have been due to pillow talk, a whisper in the ear or a conversation over wine. Charles II, the Merrie Monarch, had as a mistress, Louise de Keroualle, later the Duchess of Portsmouth, "the face that saved a thousand ships." She related to Charles an exciting story about a fellow Frenchman, Le Sieur de St. Pierre and his work solving the problem of longitude using only the heavens.
During Charles’ reign, the Great Plague and Great Fire of London occurred. Seeking diversions, Charles turned to the sciences to complement his investments in nautical enterprises. Besides having an acknowledged dozen children and seven mistresses, Charles greatly expanded the powers of the East India Company as well as chartering the Hudson’s Bay Company. On March 4, 1675 the King named 28 year old John Flamsteed "Royal Astronomical Observator." Shortly thereafter, financed through the sale of spoiled gunpowder, work began on Flamsteed’s new home and observatory. The site was chosen by Wren; a deserted castle with very strong existing foundation stones on high ground away from the lights and smoke of London. The Royal Warrant stated in part: "Whereas, in order to the finding out of longitude of places for perfecting navigation and astronomy, we have resolved to build a small observatory within our park at Greenwich, upon the highest ground, at or near the place where the Castle stood, with lodging-rooms for our astronomical observator and assistant . . ." Flamsteed’s first order of business was that he immediately proved the Frenchman incompetent.
The Greenwich Meridian
A meridian is a line running in a north/ south direction through the poles of the earth’s rotation. There have been numerous meridians established for differing purposes over the years. Our country’s rectangular system of survey has the meridian as a primary element.
Astronomers establish meridians to map the heavens. The primary instruments of the observatory, the mural quadrants and circles and the zenith sectors are mounted to solid stone walls oriented with the meridian. The stars are mapped and charted based on the precise time of their passing the meridian and by their elevation above the "horizon." The prime meridian of the world, now illuminated at night by a laser, passes through the eyepiece of George Biddel Airy’s 1851 transit circle.
In 1884, the international community met in Washington, DC and agreed to use the Greenwich meridian as the world’s prime meridian. In 1913, France finally adopted the meridian which they referred to as "Paris time diminished by 9 minutes and 21 seconds." As part of this agreement, it is said that Britain promised to adopt the metric system. The Brits just didn’t say when.
The world chose Airy’s meridian but all of England is mapped using Bradley’s meridian situated about 8 meters west. James Bradley became 3rd Astronomer Royal in 1742. The focal point in Bradley’s transit room is the telescope he used to chart more than 3,000 stars and establish the meridian that eventually served as the basis for the famous Ordnance Survey.
Flamsteed’s meridian disappeared following his death and his wife selling his instruments. Evidence said to be remnants of his 100 foot deep well zenith sector and a portion of a quadrant built by Abraham Sharp are the few remaining objects of Flamsteed’s 42 year tenure. Edmund Halley’s iron quadrant by Graham (and meridian) is on the west side of the same wall holding Bradley’s (later) quadrant.
There is yet a 5th meridian at Greenwich (unmarked). WGS84 placed the 00 degrees location shown on one’s GPS receiver about 102.5 meters east of Airy’s meridian. This is due to adjustments based on the earth’s center and not its surface. However, the good news is that because of the movement of tectonic plates, the GPS meridian is moving toward Airy’s line about 2.5 cm a year.
Using a pretty good, but inexpensive pocket compass, the American delegation checked Airy’s meridian. We found that it was fairly accurate, being just about 11-1/4 degrees east of north. Perhaps on the next trip we’ll check declination.
Lines of longitude are converging meridians going either north or south from the equator. As mentioned, "longitude naught" (from an old English astronomer) passes through the observatory. Numeric designations increase east and west until both achieve 180 degrees at the international date-line. This is an arbitrary system, but one agreed to in 1884.
Latitude is somewhat easy to determine based on the position of Polaris or the sun at noon. Longitude, not so easy. One factor, known early on was a comparison of local times. Any number of solutions have been proposed over the centuries.
A 1687 pamphlet advocated taking a wounded dog to sea. At a predetermined time, a timekeeper on shore would dip a bandage from the dog into a powder. The dog at sea would yelp at that precise time and the crew would know the time ashore.
Edmond Halley, 2nd Royal Observator thought the answer might lie in magnetism. Halley charted declination on a number of voyages at sea, developing the first isogonic lines. Unfortunately, declination does not remain stationary.
Tobias Mayer of Gottingen University in Germany was developing a system (the one St. Pierre shared) of Lunar distances. This system is fairly simple and straight forward. Basically, the moon would be in a certain position in relation to certain stars at precise times. Observations and computations weren’t that simple and straight forward though.
Nevil Maskelyne, the 5th Astronomer Royal as well as Charles Mason devoted much of their time observing and computing, adding to Mayer’s work. Unlike any of his predecessors, Maskelyne devoted his efforts solely to the original charge of the Royal Warrant. The end result was the Nautical Almanac, published in 1766, immediately selling over 10,000 copies. Lunars remained in use into the 19th century, well after the advent of a reliable chronometer.
The chronometer. The story of Jo
hn Harrison and the years of clock design leading to H4 is well known. Though Maskelyne directed that the £20,000 Longitude Reward be evenly split between Lunars and time, eventually Harrison received £14,315 with Mayer’s widow getting a mere £3000. For his work on Lunars Charles Mason received £1317.
ack at the courtyard, the lads from the States were entertained with the solution to the longitude by a wonderful performer. Clearly and concisely, Lady Vanessa related the story of longitude in a most interesting way. The mischievous surveyors brought up sidereal time. Time to change the subject.
With the longitude problem all but conquered, efforts at the Observatory turned to improving the quality of chronometers and standardizing time. The site became a proving ground for the Admiralty, putting a variety of chronometers through a variety of tests. Charles Darwin’s conveyance, The Beagle carried an astounding 22 chronometers.
Atop Flamsteed House is the red time ball. Each day since 1833, the ball has been raised partially at 12:55. At two minutes before the hour, it is brought all the way to the top. At precisely 1:00 (1300), it is dropped. A ritual that long ago allowed navigators of vessels anchored in the Thames to synchronize their times. Ha.
When the rails were joined in Utah (1869), the American railroad system had over 70 standard local times. In 1883, Dowd’s American system of one hour of time per 15 degrees of longitude using GMT for the benchmark was implemented. It’s no coincidence that one year later, the Greenwich meridian and mean time were agreed to internationally in Washington City.
In the 19th century, subscriptions to Greenwich Mean Time became available using telegraph lines. Each hour, on the hour, the time was broadcast. With the introduction of intercontinental underwater cables, direct and near instantaneous communication with the clock at Greenwich became possible across the world, ceasing the necessity to view the heavens.
Behind The Success
While Flamsteed established that the speed of the rotation of the earth was constant (not really), Bradley discovered aberration of light and nutation and Halley paid to have Newton’s papers published, the true craftsmen, geniuses and scientists were producing the remarkable machines that allowed these unprecedented discoveries. There could be no precise measurements made consistently without the fruits of the early instrument and clock makers’ labors. The precision necessary (accuracy was a given, paramount and unspoken) to derive almanacs and ephemera from observations evolved as the skill and innovation of the time keeping and sighting devices evolved. Prior to Ramsden’s engine, Graham and Bird devised an ingenious method of dividing the scales on the quadrant. This involved 96 degrees per quadrant because it’s easily divisible by two. A conversion chart was then applied. The early clocks rivaled Harrison’s timepiece for accuracy. Unfortunately, they were stationary and impractical at sea. Tampion’s (c.1670) clock still keeps up with the hours and minutes in the Octagon Room of Flamsteed house. The unknown personalities of Greenwich have directly impacted the surveyor far more, perhaps, than any of the works of the star gazers.
Reluctantly, it was time to go. The five surveyors had consumed an enormous amount of sights, memories and knowledge. The time now was for consuming liver, onions and mash, Sunday pot roast and maybe some fish and chips. Over lunch, in a 400 year old pub, and over glasses of ale and bitters, talk turned to the current subject of utilizing coordinates as monumentation in our home country. Flamsteed and those that followed had developed a system over nearly 3 centuries that the entire world grasped, creating a truly international community. It occurred to me that it seems inevitable that we, as surveyors would happily utilize the technology now available to benefit the public we serve. Just as the mariners and aviators of old lived the importance of that system perfected within that cluster of buildings on that hill in Greenwich Park high above that River Thames.
C. Barton Crattie is a land surveyor in Tennessee and Georgia. Visiting London and Paris in March of this year, he expects more good surveying stories to come out of that experience.
A 5.454Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE