The Prime Meridian of the World.
In 1884 at the International Meridian Conference in Washington D.C., 26 countries voted to make Greenwich the Prime Meridian of the World. Only the French continued to recognize their own Paris Observatory meridian as 0 degrees until 1911 and even then still could not bring themselves to refer to 'Greenwich Mean Time' but to Paris Mean Time retarded by nine minutes twenty one seconds!
While Columbus and others before and after him, sailed the ocean blue along parallels of latitude, as latitude could be determined by length of day, height of Sun or north star at night, for the mariner, Longitude remained a matter of dead reckoning. The time a log thrown overboard took to be left astern measured speed and the ships navigator set the ships hour glass to 'local' time by the height of the sun at noon.
When dead reckoning was wrong, men died, as on October 22 1707. 'Dirty weather' Admiral Sir Clowdisley Shovel called the fog that his squadron had sailed in for twelve days returning to England victorious from a skirmish with the French. Concerned about their position, he called navigators from the five ships that made up his squadron together. The consensus was that they were west of the French Ile d'Ouessant requiring them to continue north before turning east to head up the English Channel. Twenty four hours later four of Admiral Shovels ships ran on the rocks of the (British) Scilly Isles, and 2000 men drowned. The error in navigation was in respect of latitude not longitude, the Ile d'Ouessant being some 100 miles south and fifty miles east of the Scilly Isles. If the dead reckoning by the squadrons navigators had been more accurate in respect of latitude, the squadron could have turned east to safely sail up the English Channel hours earlier and not continued north to end up on the rocks of the most western part of the British Isles.
However, the tragedy brought about Government action to do something and that was a decision to find a method to determine longitude.
The British Longitude Act of 1714, in the reign of Queen Anne, promised a prize of 20,000 english pounds for a solution to the longitude problem to anyone that could provide longitude to an accuracy of 1/2 degree. It was an immense amount of money at the time, the equivalent of millions of dollars today.
As Dava Sobel explains, "to know one's longitude at sea, one needs to know what time it is aboard ship and also the time at the home port or another place of known longitude-at that very same moment. The two clock times enable the navigator to convert the hour difference into geographical separation. Since the earth takes 24 hours to revolve 360 degrees, one hour marks 1/24 of a revolution or 15 degrees. And so each hour's time difference between the ship and starting point marks a progress of fifteen degrees of longitude to the east or west. Every day at sea, when the navigator resets his ships clock to local noon when the sun reaches its highest point in the sky, and then consults the home port clock, every hour's discrepancy between them translates into another fifteen degrees of longitude. One degree of longitude equals four minutes of time the world over, although in terms of distance, one degree shrinks from 60 nautical miles at the Equator to virtually nothing at the poles. Precise knowledge of the hour in two different places at once - a longitude prerequisite so easily accessible today from any pair of cheap wristwatches - was utterly unattainable up to and including the era of pendulum clocks. On the deck of a rolling ship such clocks would slow down, or speed up, or stop running altogether. Normal changes of temperature encountered en route from a cold country of origin to a tropical trade zone thinned or thickened a clocks lubricating oil and made its metal parts expand or contract with equally disastrous results. A rise or fall in barometer pressure, or the subtle variations in the Earth's gravity from one latitude to another, could also cause a clock to gain or lose time."
Galileo Galilei had thought he had solved the longitude problem by his charting the moons of Jupiter, the eclipse of the moons of Jupiter were so predictable that one could set a clock by them. The problem was that Jupiter and its moons could only be seen on a clear night and only for part of the year and needed a very steady base for the telescope, which was not possible on a ship at sea.
In 1616 Galileo was prohibited by the Catholic Church from doing further scientific work and later in his life forced, by the Inquisition, to 'recant'. He told colleagues that he 'was an old man and wouldn't have been able to take the torture', he used the excuse of age again in 1638 to turn down an invitation from Harvard University to be a visiting Professor, saying that at his age, the travel (not fear of torture there!) would be too much.
After Galileo died (in 1640) his longitude method became acceptable on land and was used by surveyors to redraw the maps of the world (earlier ones had seriously underestimated distances between continents), it now only remained to find longitude from the moving deck of a ship to take advantage of the improved world maps.
While some looked for 'meridians' in the sky, others looked to perfecting a ship's clock that would keep accurate time - would not lose or gain more than 3 seconds in 24 hours - on a six week voyage from England to the Caribbean - 2 minutes by journeys end - the half a degree of longitude required for the Longitude Act.
In 1675, Charles II had started the Royal Observatory at Greenwich and appointed John Flamsteed, Astronomer Royal, to get the help of the heavens in finding longitude at sea by calculating 'time' from the movement of the heavens. Flamsteed spent forty years plotting the stars in the sky.
By 1714 and the Longitude Act, the scene was set for a race between men of education (Astronomers) to provide time calculated from the heavens and men laboring with their hands (mechanic's) to create an accurate clock for ship use.
It turned out ultimately to be a battle between the 'establishment' led by the 5th Astronomer Royal, the Rev. Neil Maskelyne who had attended Westminster School and Cambridge (described by a contemporary as "rather a swot" and "a bit of a prig"), and John Harrison a carpenter turned clock maker, born in 1693.
Harrison had built his first pendulum clock entirely of wood when he was twenty. He later published his "Equation of Time" tables 'enabling a clock user to rectify the difference between solar or true time as shown on a sundial to the more regular "mean time" as measured by a clock'. The sun is actually a poor timekeeper as the difference between 'solar' and 'mean' time, widens and narrows, as the seasons change.
In retrospect, a pendulum clock by Harrison for Brocklesby Park Stables was his first step towards making a sea clock. This clock never needed oiling, has been running for 274 years, is friction free as parts are carved out of Lignum Vitae, a tropical hardwood that provides its own grease. Eliminate the need for oil in a clock, and you solve a major problem as oil gets thicker/thinner as temperature changes.
Temperature also affects the length of the pendulum increasing or decreasing the swing time, Harrison corrected this by what became to be called the 'gridiron' consisting of several alternating strips of brass and steel that compensated each other. His clocks had an accuracy of a second a month. He now turned his thoughts to a sea clock and the Longitude Prize. As no pendulum could work on a ship, it took him four years before he was ready to set off for London, two hundred miles to the south with his ideas and drawings for a pendulum free clock.
He met with Dr Edmund Halley who had become the 2nd Astronomer Royal (remembered today for 'his' Comet), Halley was a member of The Board of Latitude and knew the Board would not welcome a mechanical answer to what was regarded as an astronomical problem. But Halley was impressed with the drawings and sent Harrison to a London watchmaker who provided encouragement and a loan.
Harrison took five years to build his first sea clock H1, decided he could do better and H2 followed (which he was disgusted with), H3 took nineteen years, then followed H4. Then there were the sea trials, H1 had ventured only as far as Lisbon, H2 never went to sea, H3 would have gone to sea immediately on completion except for the inconvenience of the Seven Years war.
By this time Maskelyne was now the Astronomer Royal and also on the Board of Latitude and was reaching for the prize for himself with his lunar distance tables.
Sobel tells the story how justice eventually prevailed in Harrison's favor despite the machinations of the Rev. Maskelyne, George III had taken the Harrisons (Harrison had been joined by his son) under his aegis and directed his Prime Minister, Lord North, to correct the injustice.
Today, at the Greenwich Observatory outside London, home to the Rev. Maskelyne from 1765 to his death in 1811, you can view Harrison's clocks and they are fascinating.
By the time the Royal Commission was disbanded in 1828, it had paid out in excess of 100,000 pounds on determining a method of finding 'longitude', tax payers money for once well spent, British vessels were enabled to navigate the oceans of the world, first by lunar distance and then by ships chronometer, supporting the founding of an empire and a world power.
One cannot leave this time of Lord North and George III without quoting them. George III as he signed the papers giving Independence to the Colonies is alleged to have said "there they have their freedom, I wonder how long they can keep it!" Lord North (at the time of the American Revolution) had possibly a clearer view of the future, he said "If America should grow into a separate empire, it must cause a revolution in the political system of the world, and if Europe does not support Britain now, it would one day find itself ruled by America imbued with democratic fanaticism!"
But to return to the story, since the time of Ptolemy's (AD 150) the Prime Meridian has passed variously through the Azores, the Canary Isles, Cape Verde, Rome, Copenhagen, Greenwich, Jerusalem, St Petersburg (Russia), Pisa, Paris and Philadelphia.
In 1884 at the International Meridian Conference in Washington D.C., 26 countries voted to make Greenwich the Prime Meridian of the World. Only the French continued to recognize their own Paris Observatory meridian as 0 degrees until 1911 and even then still could not bring themselves to refer to 'Greenwich Mean Time' but to Paris Mean Time retarded by nine minutes twenty one seconds!
As time is longitude and longitude is time, Greenwich Mean Time is recognized throughout the world for navigation on Land, Sea, in the Air and in outer space.
Greenwich Observatory was designed by Commissioner Wren, while now a museum, the red ball (visible to ships in the Pool of London), at 12:55 hrs GMT still climbs halfway up the mast, pauses for three minutes, then ascends to the top, to drop precisely at 13:00 hrs GMT each day.
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