The sailor’s quest to pinpoint their location on the globe has a long and rich history as Dick Durham reports.
The dusted periwig, silken scarf and gold-fluted jacket cannot soften the blunt-featured face or contour of the paunchy body of Admiral of the Fleet, Sir Cloudesley Shovell. When you look at his portrait in the National Maritime Museum, Greenwich, UK, you are gazing upon a 17th Century no-nonsense English sailor.
You are confronted by a naval commander who rose through the ranks and, who, on the eve of his premature death, just seven years into the 18th Century, had a string of successful sea battles behind him.
As a respected commander in the Royal Navy, returning home from the Battle of Toulon, Shovell may have felt indomitable, but he was no fool. He knew that without the ability to measure longitude, no sailor could really ‘rule the waves.’ Dead reckoning – course and distance run – was an incomplete navigational tool.
But at that time, that’s all he had and as his fleet sailed for the Western Approaches. They were 40 miles north of their estimated position and powering on a dark autumn night straight for the Western Rocks which form a serrated barrier of granite in front of the Isles of Scilly.
His ship Association struck first, as witnessed by sailors on the one ship to survive. Three other ships also struck the reef and sank. Nearly 2,000 officers and men, including their commander, were drowned that night, in the then worst disaster to strike the Royal Navy. Yet it took seven years for a royal assent to be lodged in order to discover longitude at sea. In 1714 Queen Anne offered a reward of £20,000 – worth £1.5 million today – to meet the challenge.
Shovell’s fleet had laid a course longitudinally i.e. north-south on the globe. Latitude wasn’t that important to him as he and his officers all knew that the continent of Europe was off to starboard and that of America some 2,500 miles away to port. But without the means of determining longitude, his heading was important and relied on careful observation of the course steered, the distance run and the leeway made, all open to error.
Shipwrecks, due to navigational errors, had increased over previous centuries with the expansion of trade, overseas settlements and forts. In 1610 Galileo used a new invention, the telescope, to observe heavenly bodies and create a ‘celestial clock.’
But decades passed before Sir Isaac Newton deemed that the rolling deck of a ship was a hopeless platform from which to scientifically observe various planets. Calibrating the earth’s movement was continued on dry land, with observatories built in both Greenwich, London and Paris.
Meanwhile, mathematicians, astronomers and cartographers all continued to try to determine longitude.
Cartographers had drawn the globe into concentric rings. Those running east-west were deemed parallels, or latitude, starting at the equator at 0 degrees and running to 90 degrees north to the North Pole and 90 degrees south to the South Pole. The degrees are measured by imagining a plane from the centre of the globe to where that plane crosses the lines of parallel.
The lines running north-south were deemed meridians in the northern and southern hemispheres all the way from top to bottom: 360 degrees worth, right around the globe. Determining longitude required an accurate timepiece.
In 1735 a self-taught clock-maker, John Harrison, who had produced a timepiece accurate enough to only lose a second or gain a second every month, built another clock with swinging balances that he hoped would cancel out a ship’s pitch and roll.
Called H1, the clock was taken aboard HM ship Centurion in 1736 for a trial run to Lisbon and back. On the return voyage aboard another ship the Orford, Harrison determined the first bit of England sighted was The Lizard peninsula in southern Cornwall which the other officers had logged as The Start peninsula, 60 miles further east.
Harrison was right.
However, he was cheated out of the main prize, and the Admiralty Commissioners only gave him £250 and requested he build a better clock in order to be considered for the full reward. For the next 20 years Harrison worked on various iterations.
By 1761 his son, William, set off across the Atlantic to Jamaica with H4. Using the time-piece he correctly predicted a landfall at Madeira and before it was expected.
Once again, the Admiralty wasn’t satisfied, complaining the test wasn’t rigorous enough. Harrison argued with them, furious that by dragging their feet, rivals to the prize were now on the scene. The main competitor being Nevil Maskelyne who practised what was called the ‘lunar method’ on a voyage down the Atlantic to St Helena, observing the transit of Venus across the sun with a gadget called a sextant.
His calculations, using a nautical almanac, proved to be 9 per cent more accurate than those produced by dead reckoning. However, the Commissioners still believed the new system was not reliable enough to replace DR.
Harrison tweaked H4 making improvements and eventually the tight-fisted Commissioners coughed up half the original £20,000 – less monies already paid to the clockmaker. They promised to pay the remainder once Harrison could show H4 could be replicated and was not just a one-off.
By now an understandably cautious Harrison did not want to publish his technical calculations, before being paid out in full, for fear they would be plagiarised.
Finally, after much bad feeling, Harrison did begrudgingly receive compensation from the Treasury.
Thanks to Harrison, Greenwich and its Royal Observatory is the location for which the prime meridian starts. This is the line from which, since 1884, nearly all global positioning systems measure the start of longitude. Latitude’s 0 degrees has the equator from which to base measurement, however, longitude does not and so a north-south ‘equator’ had to be invented. It’s own nought begins at Greenwich.
As Emily Akkermans, Curator of Time at the Royal Observatory told Ocean Sailor, the observatory has a long history. Founded by Charles II in 1675, it was quickly realised that latitude was relatively easy to measure by observing the angle of the Sun or Pole Star above the horizon. This gave a position relative to the equator.
“Longitude was a particular problem as it could only be established by astronomical techniques.” Mathematicians realised that a difference in longitude was equivalent to the difference in time between two places, which could be measured locally using the Sun.
“The problem for navigators was knowing the time at a reference place which they could use to calculate a difference in time.”
But such calculations were complex and the Astronomer Royal at the Royal Observatory produced accurate star charts that could help. The other method was by carrying a portable precision timekeeper as mentioned above.
Emily said: “Today we rely on satellites, atom clocks, radio signals and quartz timekeepers to enjoy travel without relying on knowledge of the stars and time. We can thank Harrison, but also the astronomers, mathematicians, physicists, and engineers who contributed to the technologies that we use today.”
Royal Navy officers are still taught celestial navigation in case of disruption to, or failure of the GPS system.
The Royal Observatory will be open to the public again from April 2022. This is following a refurbishment of the famous Octagon Room in which the first Astronomer Royal laid down the basis for the theory which led to celestial navigation.
We would like to thank the excellent team at The National Maritime Museum for their support and images.
