Thinking allowed — 02 December 2011

Once you have slogged up what must be the steepest hill in London and stood with your back to General Wolfe’s statute admiring the view the next port of call is standing with your feet either side of the Prime Meridian outside The Royal Observatory in Greenwich. There you get some childish excitement of having one foot in the Eastern hemisphere, while the other is in the Western hemisphere.

It marks the point as the sun passes overhead that it is noon Greenwich Mean Time and GMT is the standard time that every clock in the world and beyond is synchronised, even in space the International Space Station wakes up to GMT.

England has always been at the forefront of horology, the first known mechanical clock in Europe was made in 1283 for Dunstable Priory and the oldest working clock in the world can be found at Salisbury Cathedral, still going strong after 625 years. Anyone with the slightest interest in timekeeping would have heard of John Harrison who invented the first reliable ship’s chronometer which allowed sailors to locate their exact position. Latitude (the distance north or south of the equator) could be established by the position of the sun at midday or the position of the stars, but for longitude a navigator needs to compare the time on board ship with the time at the home meridian, an hour’s difference meant you were 15° east or west from that home point. Harrison’s clocks which were accurate to within 0.06 seconds every day and their use established England as the world’s foremost seafaring nation. An excellent account of the race to find a means of measuring longitude has been written by Dava Sobel in her bestselling book Longitude.

From that point it was logical that a standard time should have been established. But it wasn’t until 1840 with the advent of the railways that everyone worked to the same time. Before then every town recorded noon as when the sun was overhead where they stood, making Plymouth 17 minutes behind London in its timekeeping, and necessitating rail passengers having to reset their watch at every town, this of course made nonsense of timetables.

But where to base the position for measuring time? The obvious choice was Greenwich, home of the Royal Observatory since 1675 and keeper of the most accurate astronomical records in the world. By 1880 GMT had been officially adopted by the Government and towns such as Oxford and Bristol who had stubbornly refused to change had to comply. Four years later at the International Meridian Conference in Washington under pressure from England it was agreed that Greenwich would be the zero point for longitude and world GMT was born.

As the supreme sea power England had seemed, at least by us, to be the best choice, but one country refused to accept the Conference’s decision. Ignoring the outcome at Trafalgar the French declared that they were following Paris Mean Time. Then after 20 years of bureaucratic shenanigans that our Gallic friends are famous for, they announced that the new official time for France would be Paris Mean Time retarded by nine minutes and 21 seconds, thus obviating the need to utter the word Greenwich.

By the 1920s electric clocks had been invented giving rise to the suspicion that the Earth’s rotation was irregular. Subsequently our watch of choice – the quartz – and the atomic clocks which are accurate to within one second in 20 million years have confirmed the Earth’s contrary nature.

The Sun’s gravitation and our sister planet, the Moon – which of course gives us our tides – and surprisingly our molten core sloshing around, causes our planet to adjust its spin and slowing it down.

This doesn’t cause a problem to a farmer or for that matter a cabbie with The Knowledge, but can wreck havoc on GPS systems. Every few years a leap second has to be introduced to compensate for this lag, the last was in 2008.

This tweak has not satisfied our friends the European bureaucrats and the French ever anxious to defeat us (you would have thought changing the Eurostar from Waterloo to St. Pancras would have been enough), argue that introducing a leap second carries an element of risk, insisting that atomic clocks should determine time. Next month at the French-based Bureau of Weights and Measures it is proposed to drop the use of Greenwich Mean Time and introduce France’s version of timekeeping. Would it then revert to Paris Mean Time?

This would mean days measured by the rising and setting of the Sun would become longer than what your records and future generations could find themselves going to work at four in the morning. Inserting a minute occasionally to the day is France’s way of correcting this problem; they argue there is less room for error by inserting a minute rather than one second as is the case at present.

Apart from losing that joy of straddling the meridian at Greenwich, if this plan goes ahead, it would be the first time in human history that there was no connection with the time of our clocks and the rotation of the Earth.

Our only consolation might be the BBC, ever anxious to adopt metric, telling its announcers to start the Shipping Forecast: “And now the Shipping Forecast, issued by the Met Office on behalf of the Maritime and Coastguard Agency at 23.30 PMT”.

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