Opinion: How the Prime Meridian Changed the World

The prime meridian line.

Photograph by Danita Delimont, Alamy

Astronomer Nevil Maskelyne. Illustration from Universal History Archive/Getty Images

Mark Anderson

Published May 26, 2013

Some 250 years ago, a British astronomer published the first of a series of guidebooks that would ultimately establish Greenwich, England, as the world's zero-degree longitude location, the "prime meridian."

Nevil Maskelyne's 1763 The British Mariner's Guide—and his follow-up The Nautical Almanac and Astronomical Ephemeris, published annually beginning in 1766—would set the standard for nautical navigation for decades to come.

And though the world has largely forgotten the Guide and Almanac, modern technology has not. Any device that uses maps and geolocation—from smartphones to global positioning system (GPS) devices to GPS-enabled trucks, airplanes, and ships—still hails the prime meridian flag that Maskelyne planted at his observatory, the Royal Observatory in Greenwich, two-and-a-half centuries ago.

That's because defining zero degrees longitude—which effectively divides the world into East and West—is the first step toward finding every other point of longitude on the map, and finding your way in general. And that was once a very big deal.

A Longitude Problem

Indeed, before the Guide and Almanac, the world had a deadly longitude problem. Navigation at sea was extremely difficult, resulting in countless disasters and disappearances over the centuries because ships' captains simply could not figure out where they were.

For instance, on October 22, 1707, more than 1,400 British sailors died because a storm caused the fleet's navigators to lose their location; then the navigators and naval officers mistook the craggy archipelago on which the fleet wrecked for the western entrance to the English Channel.

Pre-Meridian sailing was difficult, as depicted in this illustration of the Vitus Bering expedition wrecked upon the Aleutian Isles in 1741.

Illustration from North Wind Picture Archive/Alamy

But by the spring of 1763, after decades of hardscrabble observations and calculations, astronomers had finally cracked the code to predict the moon's meandering path across the sky. No mere academic exercise, this breakthrough would enable mariners around the world to locate their longitude at sea—turning the moon into the world's first global positioning satellite.

Though he was not the first scientist who attempted to resolve the longitude issue, Maskelyne was the first to put forward a practical solution, one that wound up being so good it effectively enshrined Greenwich as the prime meridian for the entire world, says Rebekah Higgitt, curator of history of science and technology at the Royal Observatory in Greenwich. Thus he was, she says, "very central to creating Greenwich as it has come to be known.

An Arbitrary Matter

Unlike latitude, which represents angular distance from the equator, longitude on a spinning Earth is based on a zero-degree prime meridian that's simply a matter of arbitrary convention. By the 1760s, many seagoing nations had established their own zero-degree longitude point. The Royal Observatory in Paris, for example, was France's prime meridian, while the tip of the most southwestern of the Canary Islands was Spain's prime meridian.

Naturally, Great Britain produced maps and charts based on its prime meridian in Greenwich. But what transformed the country's standard into the worldwide standard was the precision, practicality, and utility of Britain's longitude solution.

For more than two centuries before Maskelyne, scholars across Europe had been talking about using the moon to find longitude at sea. But two vast problems stood in the way.

The first involved measurement. No simple, portable device existed to precisely gauge the angular separation between the moon and the sun or a known reference star—the raw numbers navigators needed to derive longitude. But between 1730 and 1760, various technologists across Europe devised ever-better quadrants, octants, and sextants that solved the measurement problem.

Mapping the Moon's Position

The second and larger issue was prediction: In order for a sailor or anyone else to know his longitude, one must compare local time (via a sundial, for instance) with the exact local time at the prime meridian, using some sort of universal clock.

And the best universal timepiece, scientists throughout the 17th and 18th centuries recognized, is the moon, which slowly moves through the sky over a 28-day cycle. So its position compared with the location of the sun or the stars could serve as the celestial clock's hand.

Unfortunately, the moon's precise motion through the sky is anything but regular. Tugged as it is variously by the Earth and sun and following an oblong orbit that never is quite the same, the moon's exact path was extraordinarily difficult to forecast in advance.

That is, until the 1750s, when German mapmaker Tobias Mayer finally mastered the pages of complex equations that would enable astronomers to precisely forecast the moon's position a year or more ahead of time. This discovery would finally provide navigators with the lunar almanacs they needed.

In the spring of 1763, Maskelyne published the first lunar charts based on Mayer's work in his British Mariner's Guide, allowing navigators to measure the moon's position in the sky and to derive Greenwich time at that very instant. Ships' captains and navigators could better do their jobs, kicking off a decade of revolutionary innovation that solved one of the greatest technological problems of the 18th century—navigation at sea.

"This method carried into practice," Maskelyne wrote in the Mariner's Guide, "will ... bring the longitude to great nearness."

Still, the British Mariner's Guide left a lot of legwork to be done. Navigators using the Guide could spend up to four hours calculating their location. Maskelyne's solution was feasible, in other words, but it was still not practical.

A Navigational Breakthrough

However, with Maskelyne's subsequent innovation, the Nautical Almanac, it took just 30 minutes to crank out lunar longitudes. The Almanac anticipated every possible calculation that could be done in advance and simply listed the answers in a reference table, so mariners at sea did not have to run the numbers themselves.

To do this, Maskelyne employed a cottage industry of human "computers"—mathematical prodigies whose only job was to crunch the numbers that would ultimately appear in the Almanac—working day and night beginning in 1765.

Now to find a boat's longitude at sea, all a navigator needed to know was the local time and the position of the moon and a nearby reference point, whether that was the sun or a well-known evening star.

Thus, the Almanac was a breakthrough for mariners, including one of its first customers, Lieutenant (ultimately Captain) James Cook, who field-tested the reference book on his first voyage around the world, finding it superior to any way-finding technique he'd yet seen.

The normally reserved Cook recorded in his journals his pleasure with the Almanac's precision and ease of use. "It is only by this means that this method of finding the longitude at sea can be brought into universal practice," Cook wrote. "[It is] a method which we have found may be depended on to within a half a degree! Which is a degree of accuracy more than sufficient for all nautical purposes."

It's Official

Higgitt says that soon after the Almanac—which like the Mariner's Guide before it used the Greenwich Observatory as its prime meridian—was published, merchant fleets and navies beyond British shores began to adopt Britain's superior navigational technology.

For example, France's nautical almanacs, Connoissance des Temps, simply reprinted Maskelyne's lunar charts verbatim from 1772 onward—effectively appointing Greenwich as their prime meridian too.

Moreover, British cartographers used the Mariner's Guide and Almanac to help them map the planet. This opened up another channel to disseminate the Greenwich prime meridian around the world, as navies and merchant fleets from France, Holland, Spain, and elsewhere came to rely on the often superlative British maps.

By 1884, some 72 percent of the world's shipping tonnage was following the Greenwich standard. And that year, a congress of nations around the world made it official, declaring the Royal Observatory in Greenwich, England, as the Earth's true prime meridian.

Greenwich Time

After Greenwich was appointed the Earth's geographical standard-bearer, a similar need for a global time standard led it to become the world's default timekeeper too. So whenever NASA today launches a rocket into outer space, its clocks are set not to Houston or Kennedy Space Center time but rather to absolute Greenwich time, also called "Universal time," which doesn't change with the seasons like in other time zones. Airplane pilots also use Greenwich as their fallback time zone, calling it "Zulu Time."

Moreover, the selection of Greenwich as the prime meridian helped establish the international date line exactly halfway around the globe from Greenwich. Transpacific travelers must set their calendars ahead by one day when they travel west across the date line, and back by one day when they cross it going east.

And so today, the prime meridian at Greenwich, England, stands as a quiet testimonial on every modern map, navigational chart, and GPS device to the astronomers who finally cracked the longitude puzzle, changing the world—including how easily we get from place to place and tell what time it is when we arrive—forever.

Editor's Note: Mark Anderson is a science and technology journalist based in Massachusetts. This article was adapted from his 2012 book, The Day the World Discovered the Sun: An Extraordinary Story of 18th Century Scientific Adventure and the Race to Track the Transit of Venus (Da Capo Press).

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Frank Reed

A preliminary note: I teach classes in the history and practice of navigation at Mystic Seaport Museum in Mystic, Connecticut, and in July I am teaching a weekend class in lunars. Details here: http://ReedNavigation.com. Also for broad discussions of all topics in celestial navigation and other forms of traditional position-finding, I highly recommend the message boards of the "NavList" community located at http://fer3.com/arc. There is no place on the internet that has hosted more discussions of lunars, longitude, and related topics.

A few of the comments here expressed disappointment that Harrison and his time-keepers weren't mentioned. They may have missed the point. The dominance of a specific choice for the Prime Meridian began with the lunar tables and NOT with the use or function of chronometers. Furthermore, lunars (or "lunar observations" or "longitude by lunar distances") were available almost immediately starting in the early 1760s when Maskelyne published his "British Mariners' Guide" and especially after the annual publication of the "Nautical Almanac and Astronomical Ephemeris" starting in 1767. That "Nautical Almanac", unlike its modern descendant with a similar name, was almost entirely devoted to finding longitude by lunars. And those longitudes, right from day one, were based on the meridian of the Royal Observatory in Greenwich. Chronometers, meanwhile, were rare and temperamental until the early 19th century. In 1802 when Edmund Blunt began publishing the first edition of Nathaniel Bowditch's famous "New American Practical Navigator", Bowditch wrote that chronometers could not be relied upon and in general they were quite rare at that time. He advocated lunars. Put it in historical perspective: chronometers were the original "black box" --mysterious machines that had to function perfectly with minimal interaction from users. Navigators only really began to trust chronometers decades later especially when ships began carrying three or even more chronometers which could serve as checks on each other.

The real proof of the significance of lunars exists in the mundane documents that fill libraries around the globe: ships' logbooks. Lunars were indeed widely used at sea from 1767 until about 1850 when they nearly disappear. That's over 75 years of active use of this method. It's worth noting that lunars faded into history much earlier in those parts of the maritime world where chronometers became common sooner. In the Royal Navy, for example, lunars were nearly over and done by about 1825 and they are only rarely encountered after that. It's also important to recognize that lunars were never used "just like" chronometers. Lunar observations were typically taken over the course of a few days right around First Quarter and Last Quarter phases of the Moon, when the Sun and Moon were conveniently "in distance". Between these fortnightly resets, the longitude was either determined by "dead reckoning" (before roughly 1835 on American commercial vessels) or in later years by a chronometer of uncertain reliability (up until about 1850 on American commercial vessels). Even on voyages where chronometers were available, it was common practice to observe lunars regularly, too, as a means of resetting the chronometer's error.

The "myth" of lunars is one of the flaws in Dava Sobel's otherwise terrific "Longitude". She intentionally paints Maskelyne as a villain and even says so. She mistakenly characterizes lunars as exceedingly difficult, which they were not at all after 1767 (though they did require an unusually good and well-adjusted sextant). These mis-characterizations of lunars and sputtering at Maskelyne are found in the era, too, by the "partisans" of the Harrison family. And it's important to recognize that they were indeed "partisans". Scathing attacks were published on both sides. Late 18th century Britain would remind many people today of the modern internet. "Posts" were made defending various points of view and attacking other points of view. Printed in pamphlets, they reached a much smaller community, of course, but the exchanges had the same dynamic that we see today in heated online exchanges. Unfortunately some modern commentators (and Sobel was hardly the first to make this mistake) do not understand this context. Harrison was by no means some innocent victim of the astronomers and mathematicians, pleasing as that image may be to some modern readers. Follow the money. He was amply rewarded long before the successful time-keeper known today as "H4". The awards from the Board of Longitude were princely sums in those days. In addition, Harrison received the Copley Prize, the greatest scientific honor in all of Britain in that era, long before the success of H4. Thanks to the huge commercial success of Sobel's "Longitude", Harrison's side of the story is now very well known. And let's be clear, lunars were eventually inferior to chronometers. There's no doubt about that. The Harrison partisans were right in the long-term, but it took 75 years for their case to be conclusively proven.

Finally, it's intriguing to note that "lunars" were shot by the Apollo astronauts, especially by Jim Lovell on Apollo 8. They served as a backup to ground-based tracking and rather than determining GMT or some other time variable, their purpose was to fix the spacecraft's position in space and correct the computer-managed "state vector". I presented a paper on "Lunars in the Space Age" at the "After Longitude" conference at the National Maritime Museum in Greenwich last year.

Rok Dolnicar

Very interesting illustration. What a life in the times of middle eve. So we can enjoy the beauty of todays techs. My best from Slovenia, Rok Dolnicar - http://www.rok-dolnicar.blogspot.com/

Mark Chilton

This was an enjoyable read. As a Geography major in college (long ago) I learned the outlines of this tale, but have never taken such a close-up view of the matter.

However, I think it would have been appropriate to acknowledge the role of Colonialism. You can call the establishment of the Prime Meridian at Greenwich "arbitrary," but it isn't actually arbitrary. The Prime Meridian's location at England is anything but arbitrary. It is an artifact of the English Imperialism - you can't subjugate the rest of the world without knowing where it is (with respect to your navy and/or merchant marine).

I don't say this to suggest that any other system should be used, but simply to acknowledge the reality that the desire to subjugate the non-European world in service to the accumulation of wealth in England was the ultimate motive here. The obliteration of indigenous cultures, the efficient propagation of the trans-Atlantic slave trade and the transformation of most of the earth's landscape were not merely un-intended consequences of English Naval supremacy, they were the direct intentional object of it.

However, it's important to also acknowledge that English scientific breakthroughs around longitudinal measurement were only one of many factors that brought about the so-called Pax Brittanica. And the motives of the French, Spanish and Dutch were, of course, no different.

Arthur Cohn

Locating the prime meridian at Greenwich is also why Japan and China, which are on the western edge of the Pacific Ocean are called the far east

Rebekah Higgitt

The fact that Greenwich became the world's prime meridian is proof of the importance of the astronomers at the Royal Observatory in the business of finding a solution to the longitude problem. There would have been no reason for Harrison's clocks or later chronometers to be set to Greenwich time had the Nautical Almanac and charts produced on that astronomical data not been a hugely important tool. Clocks could have been set to a reference time at any known location.

Harrison's sea watch, wonderful though it was, was not a solution to the problem of finding longitude - it was only one clock, very expensive and took a long time to make. It took years more of work, innovation and support by - yes! - Maskleyne and the Board of Longitude to make timekeepers widely available and affordable. It was Maskelyne who ensured that other makers had access to Harrisons ideas to help make more watches and, ultimately, simplify them. It was Maskelyne who made sure that Larcum Kendall's copy of Harrison's H4 and two of John Arnold's timekeepers were sent out with Cook, and Maskelyne who made sure that the Almanac included instructions on how to use a timekeeper at sea.

Meanwhile, the Nautical Almanac and octant were much more widely available and, until the availability of wireless signals or positioning systems, astronomy was the ONLY way to find longitude at sea if you had lost it (the only way to check a chronometer was working properly or to re-set it). The Board of Longitude would have been foolish indeed if they had rewarded Harrison and not bothered to support the lunar distance method.

For more reading you may be interested in having a look at the blog of the History of the Board of Longitude Project, including four posts that look at the story from Maskleyne's point of view: http://blogs.rmg.co.uk/longitude/?s=%22rehabilitating+nevil+maskelyne+-%22 and my post reminding readers that 'There was no such thing as the Longitude Prize' http://blogs.rmg.co.uk/longitude/2012/03/07/there-was-no-such-thing-as-the-longitude-prize/ .

Mark Anderson

Hello. I wrote this article and am certainly familiar with John Harrison. Thanks in part to the excellent Dava Sobel book *Longitude*, Harrison's life and work and genius is well chronicled elsewhere. However, perhaps as a result, the popular view today of the race for longitude is also a little more unfairly biased toward Harrison. In Sobel's account, Maskelyne plays the role of moustache-twirling villain who obstructs Harrison's chronometer out of petty jealousy and bullying boosterism for his own inferior longitude solution, lunar navigation.

Yet the historians I have interviewed are coming around to a more balanced approach to understanding the longitude race. First of all, to be clear, Harrison was a genius, and his chronometer was a world-changing technology, no dispute. But the founding document of the Board of Longitude -- the Longitude Act of 1714 -- demanded that the longitude-finding solution they sought should be "practicable and useful at sea."

Certainly, by the early decades of the 19th century, the nautical chronometer was indeed just that. But in the 1760s, when the action of this story takes place, nautical chronometers cost almost as much as the ship itself! Not surprisingly, with those pricetags, the chronometers remained *theoretically* promising and interesting solutions to the longitude problem. But they were far too costly to imagine rolling out to merchant and naval ships around the world. Throughout most of the 18th century, in other words, the chronometer remained anything but "practicable and useful."

Yet by 1767, when the first Nautical Almanac was published and accurate longitudes could be determined in less than 30 minutes for an outlay of just a few pounds (the cost of a quadrant or sextant plus the shilling cover price of the Almanac itself), the "practicable and useful" hurdle had been cleared. So Maskelyne was not just being parochial or narrow-minded in seeing lunar longitudes as a much more attractive solution to the vast majority of mariners in his day.

Ultimately the ideal solution is a combination of the two - the very combination that Lieutenant Cook set sail with in 1772 in his legendary second voyage. Cook had field tested the Nautical Almanac in his first voyage and came away very impressed. Now in his second voyage, he had both the Almanac and a chronometer. And he and his officers wound up using one to cross-check the other.

That's of course another story. But Maskelyne has no Sobel today to champion his side of the argument, so I thought it was worthwhile here to make the case that, yes, even though Harrison has any number of passionate and outspoken advocates today, his adversary also has a story and a longitude solution that is equally interesting and impressive. And, indeed, practicable and useful too.

Bruce Mergele

Doesn't surprise me. I served as a Quartermaster in the Coast Guard and Navy and was disgusted when the NG published an article claiming Perry reached the Pole based on photographic evidence. Kind of like the Smithsonian and Langley's Aerodrome. Time for more scholarly journalism and less half-truths and sensationalism NG... How about some objective editing?

Andrew Booth

No mention of John Harrison? That's amazing! It was Harrison's timepieces (H1 - H4) that finally cracked the longitude problem by using Greenwich as the Prime Meridian. Poor John Harrison was snubbed and had every obstacle put in his way when he was working on his chronometers simply because he wasn't born into the right social circle. Even when his chronometers had proved themselves and the longitude problem solved Harrison was snubbed and it was Maskelyne who made sure he didn't receive any recognition or the prize.

James Muccio

@ Lee -- going to Google Earth it appears your GPS was working correctly. The Prime Meridian runs about 200 feet to the right of the Royal Observatory. It seems that, perhaps for tourism purposes they moved the line indoors, or perhaps when they established the line, 200 feet was close enough. Who would have thought you could measure it's accuracy to within 10 feet in the palm of your hand two centuries later?

Lee Berg

John Harrison's genius was key to solving the longitude problem. Mr. Harrison's chronometers, especially considering his background, were nothing short of amazing, even today. The Royal Observatory at Greenwich still houses some of his early timepieces.

I was somewhat dismayed, however, to find that my GPS (pre-smartphone) did not read zero degrees longitude while standing on the marked prime meridian at the Royal Observatory, pictured in the article. I had to move away some 200 ft., well beyond the precision of the device. When asked, one of the guides mumbled something about the ellipsoid, etc. Perhaps I don't understand or my GPS was not functioning properly.

James Muccio

@ Mark Cuson - I also wish there was a mention of John Harrison. Thanks for your comment. It's seems exceedingly strange that no mention whatsoever is given to time keeping, which in fact is the real genius behind GPS and any future navigation aides. Without exquisite time, GPS has atomic clocks on-board, and a reference point, the Prime meridian, navigation becomes exceedingly difficult. Harrison's chronometer produced portable exquisite time. GPS then turned that on it's head and made exquisite time available to everyone. The reference point is still necessary and a standard had to emerge in order for it to work universally.

Mark Cuson

I wish there was a mention of John Harrison (http://en.wikipedia.org/wiki/John_Harrison) in this article. I would argue that he was the real genius behind solving the longitude problem by his invention of a marine chronometer. John Harrison was a self-taught carpenter from Lincolnshire. He built his first longcase clock in 1713, entirely out of wood. Over the next 50 years, he dedicated his life to designing a timekeeper that would be accurate to two minutes (or half a degree) on an extended nautical voyage. His last design, named H4, was actually a watch just 13cm in diameter and lost only 5.1 seconds after 61 days at sea. Despite having completely fulfilled the requirements of the £20,000 longitude prize posted by the British government over 40 years earlier, his watch was dismissed by the Board of Longitude as a fluke, and they only awarded him half of the prize money. The rest was granted to him only after he disclosed his designs to the Board, and also constructed two additional watches with the same accuracy. Explorer James Cook, referenced in the article, took one of these duplicates on his second voyage (it was on his first that he tested Maskelyne's method), and declared it "our faithful guide through all the vicissitudes of climates". John Harrison died in 1776, one year after Cook returned and three years after receiving the second half of the longitude prize.

Also note that Astronomer Royal Nevil Maskalyne who is hailed in this article as the hero who "solved" the longitude problem, held a position on the very Board of Longitude that withheld the prize money and recognition rightfully due to Harrison. This article unfortunately seems to only further the historical prejudice against Harrison's remarkable achievement.

To learn more about Harrison's story, check out these three sources:

Dava Sobel's book Longitude (http://www.amazon.com/Longitude-Genius-Greatest-Scientific-Problem/dp/080271529X),

the BBC documentary (http://news.bbc.co.uk/2/hi/science/nature/241228.stm),

or the feature film based on Sobel's book (http://www.amazon.com/Longitude-Michael-Gambon/dp/B00004U2K1).

Additional Sources:

http://www.rmg.co.uk/harrison

http://www.rmg.co.uk/captain-cook

Art Hawley

A quibble. The International Dateline does not correspond with the 180 degree meridian throughout its entire length and is subject to politics. Note: "Kiribati's 1995 act of moving the international date line far to the east to encompass the Line Islands group, so that it would no longer be divided by the date line, courted controversy. The move, which fulfilled one of President Tito's campaign promises, was intended to allow businesses all across the expansive nation to keep the same business week. This also enabled Kiribati to become the first country to see the dawn of the third millennium, an event of significance for tourism." (Wikipedia)

Frank Reed

Wow! A genuinely excellent article on the origin of the Greenwich meridian highlighting the significance of lunars in that history starting way back in the late 18th century (and not merely repeating the story of the 1884 conference which largely confirmed the status quo). I teach a class in "longitude by lunars", and t's a real pleasure to see that you described the workload of lunars correctly. So many secondary sources repeat the mistaken notion that lunars ALWAYS took four hours to compute when, in fact, the computations only required somewhere between 15 and 30 minutes (depending on the method used) after the publication of the early Nautical Almanac and the accompanying Tables Requisite. My only quibble with this article would be your description of the International Date Line. There really is no official date line. Mariners at sea generally change the date at 180 degrees longitude, but that is just custom. Mapmakers have printed an "effective" date line since the late 19th century which serves as a tool in an "algorithm" for keeping track of the date change, but it's out there in the Pacific primarily because it's in the middle of nowhere and not really because it is opposite the Prime Meridian.

Andrew Booth

@Frank Reed Thank you Frank, I found your answer very interesting. I am one of those who has always believed that Harrison was treated very badly. However, I'm only an interested member of the reading public so I've only read whatever literature is available (such as Sobel's 'Longitude') which does tend to paint Harrison as a downtrodden victim and Maskelyne as mean and cold-hearted. It's good to view the events in a different light and realise the truth actually lies somewhere in the murky middle.

Regards, Andrew.

Andrew Booth

@Mark Chilton You're a little harsh there Mark! The British Empire was the major world power at the time and London was the most important city in the world. The observatory at Greenwich was the world's premier observatory so that's where the Prime Meridian was located. Nowadays wouldn't the US advocate the meridian being at New York? In fact the US tried to have the meridian changed to New York several times during the 19th Century. To suggest that the meridian was located in Greenwich with the intention to 'subjugate the non-European world in service.." or to "obliterate indigenous cultures, propagate the slave trade" etc is way off the mark and shows that you perhaps have some strange grudge to bear. Your views are quite unnecessary and have no place here as many around the world could assign those same objectives to the United States in the more recent past - or even today. It would be quite crass and unreasonable for anyone to do that.

Secondly, it's apparent that you don't really understand the history, context or subject anyway. You mention 'England' and the 'English Navy'. England, along with Wales and Scotland, became part of the United Kingdom of Great Britain and Ireland in 1707 following the Act of Union. Anything after that is 'British' and the 'English Navy' had long ceased to exist! You should therefore refer to 'Great Britain' or 'Britain' and the 'Royal Navy' for this time period. To use the term 'England' after 1707 simply shows ignorance.

Mark Cuson

@Mark Anderson Thanks for your clarifying comment! Now I understand where you're coming from, and I think it's a totally valid position to take. I would guess that you didn't want this article to be another Harrison vs. Maskelyne piece, but after reading it, I was under the impression that you had never heard of Harrison. Some of what you said in your comment would be great context in the article itself, so as to assure readers like myself that you know about Harrison but are in fact deliberately telling a different story.

Rebekah Higgitt

@James Muccioand @ Lee The Greenwich meridian was defined by the telescope used to make the key observations. What became the prime meridian was the line on which the Airy Transit Circle sat and still sits today.The GPS meridian is *based* on the Greenwich Meridian but is now worked out mathematically rather than being based on the physical location of a particular telescope. To find out more about why it is in a slightly different place, see http://www.rmg.co.uk/explore/astronomy-and-time/astronomy-facts/history/the-longitude-of-greenwich

Mark Chilton

@Andrew Booth @Mark ChiltonHarsh? Toward whom?

I chose my words carefully, so no, I don't think British would be a better word. The roles of Scotland and Wales in this story are quite incidental. Scotland itself was essentially colonized by England. So spreading the credit/blame across all of Britain would be a disservice to history in my opinion.

In any case, my point is fundamentally that the Prime Meridian is not arbitrarily located. It is in England for a reason. Imperialist impulses in London provided the resources for creating a system of longitudinal measurement, which resulted in the establishment of the Prime Meridian in Greenwich. What is wrong with acknowledging that reality?

19th and 20th century American desires for colonial domination differed little from those of the great European powers of the 18th century. And while I didn't know of efforts to move the Prime Meridian to New York, I don't find it surprising that there were such efforts. Indeed that underscores my point - that an underlying consideration in establishing the Prime Meridian was to define the rest of the world in egocentric terms.

It seems a little absurd to headline this column "How the Prime Meridian Changed the World" and then fail to acknowledge that one of the ways it changed the world was in furthering a dramatic transformation of the earth's population, economy, and landscape through the decimation of indigenous cultures and landscapes in favor of extractive industries intended to concentrate wealth in London . . . England . . . London, England.

Andrew Booth

@Mark Chilton @Andrew Booth Hi again Mark,

England did not attempt to colonise Scotland. Scotland requested union with England in 1706 due to the country being bankrupt and Scottish people starving. The main cause was Scotland's failed attempt to establish a trading colony in Panama to control trade with Spain, to the Pacific and between the Americas. The whole venture collapsed. All Scottish investors, including the Scottish government lost their money and the country went broke. Even today Scotland, wih just 5 million people and no major industry, would collapse in no time if it wasn't part of he UK. British money from London pays for Scottish hospitals, schools, police, defence, social services, welfare etc. We now see the same phenomena in Europe with other countries going bust - Ireland, Portugal, Greece etc. Scotland went bust in 1706 and it was the Act of Union that bailed out Scotland and fed the starving Scottish people.

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