The Longitude Problem

This is an update of a story I first published in 2014.

The prize awarded was on a sliding scale, with a maximum of £20,000, a huge sum at the time, for a solution that could determine longitude to within 30 nautical miles.

The loss of so many ships and men shocked the Royal Navy and the British people, but it was no surprise. Navigation was difficult in all weathers at the time, because of the lack of an accurate method of determining position, and in particular Longitude. Although there was no proof that this was what caused the disaster, it led to Parliament establishing the prize.

So what was it that made the calculation of Longitude so difficult?

In the days before radio and GPS, calculating position was a combination of astronomical observation and accurate measurement of time.

Measuring Latitude was relatively easy.

In the Northern Hemisphere, mariners calculated it by sighting the North Star (Polaris) using a  sextant . The height of Polaris in degrees above the horizon was the latitude of the observer, within a degree or so.

In the Southern Hemisphere, Latitude could be calculated using the position of the Southern Cross (Crux), which is at a known angle from the South Pole.

The calculation of Longitude was a different matter. First it required a fixed point, or prime meridian (0°). In the early 1700’s the British Astronomer Royal started using the Greenwich Meridian, and this was generally accepted by the late 19th Century.

The calculation requires a precise measurement of the time at this prime meridian. The difference in the angle of the sun there at this time, and the angle of the sun at the navigator’s location is an indication of the longitude. (The Sun moves across the sky at 15° per hour).

Time measurement was the root of the problem. No timepiece existed that could provide the required level of accuracy on land, let alone on a rolling boat in the middle of the Ocean. The consensus was that such a timepiece may never exist.

The best solution available seemed to be astronomical, and this became known as the 'Lunar Distance Method'. It required the accurate measurement of the position of the moon from other celestial bodies such as the sun or recognized stars. By consulting a table of known distances at a specific date and time, the navigator could calculate the time at the prime meridian, and hence the longitude.

The disadvantage was that a comprehensive table of distances did not exist at this time (although people were working on it), but even with a table it sometimes required hours of work for the navigator to make the calculation.

The friction between the proponents of these two approaches would dominate development for the next 50 years.

John Harrison was a provincial clockmaker living at this time in the north of the county of Lincolnshire

Nevil Maskelyne was a Londoner, and much more of an establishment figure.

Back in Barrow it took five years for Harrison to build his first sea clock (later known as 'H1'), and it was like nothing seen before. Although large and heavy, weighing 75 lbs, it worked (it seemed at the time) almost magically. The design ran without lubrication, and compensated for temperature changes and the motion of a ship.

After testing it on the River Humber, Harrison took it to London to show it to the scientific community, and in 1736 it was prepared for its first sea trial.

It took Harrison 4 years to present his second clock ('H2'). Meanwhile, in 1737, he moved his family to Leather Lane in London, a short distance from George Graham and the Royal Society. He was to move twice more in the next 15 years.

The second clock was smaller, but heavier, and once again Harrison was not happy with it. It passed all of the tests short of a sea trial (which the Board was prepared to sanction), but Harrison found a design fault with the balances and would not release it.

He asked for more funds and time to develop his third clock.

Harrison worked on his third clock ('H3') for 19 years. Meanwhile, in 1749 he was awarded the Royal Society's Copley Medal "On account of those very curious Instruments, invented and made by him, for the exact mensuration of Time"

'H3' incorporated a number of technological advances (including one of the first uses of a bimetallic strip), and in many ways it could be considered a work of art. Once again Harrison was not completely happy with it, but deemed it worthy of sending to sea.

However, in 1753 John Jeffreys, another clockmaker and collaborator, presented him with a pocket watch incorporating many of Harrison's innovations. This worked so well that Harrison realized it presented a more practical solution to the Longitude problem.

He asked for more time ...

It is possible that Harrison was already working on his fourth submission when he withdrew 'H3'. This one was not a clock but a 'pocket' watch (although 5" across), and a masterpiece. Harrison professed himself satisfied, and ready for the next sea trial. This would be undertaken by his son William, who had been working with him for a number of years. 

Despite the success of the trial the Board decided, largely on technicalities, that the requirements for the Prize were not met, and ordered a second trial.

Maskelyne was appointed as an astronomer for the Royal Society to travel to the island of St Helena to observe the transit of Venus. An accurate measurement of this could be the first step in getting an accurate measurement of the Earth from the Sun, and then developing astronomical tables.

Bad weather stopped the observation, but during the voyage he tested out and refined what became known as the Lunar Distance method. On his return he proposed an idea for publishing tables of lunar distances on an annual basis. This became the 'Nautical Almanac', first published in 1766, and edited by Maskelyne.

For the second trial William Harrison was to sail to Barbados on HMS Tartar. Despite an apparent conflict of interest, Nevil Maskelyne was sent ahead to Barbados, as one of the representatives of the Board to oversee the trial. 

On his return, Maskelyne was announced as the new Astronomer Royal, and campaigned for H4 to be considered a 'fluke'. Harrison was awarded half of the prize (£10,000), but only on condition that he provided the design to other watchmakers. H4 was handed over to the Board for testing.

With his first Watch out of his control, Harrison proceeded to build a second one (H5).

Rather than present it to the Board, he handed this one over to King George III, a keen amateur scientist. After testing it at the King's Observatory at Kew, the King pressured Parliament to award a further sum of money, and this they did.

In the end Harrison received over £23,000 for his work on the Longitude problem, but officially he never won the Longitude Prize.

Through the first part of the 18th Century, while the Longitude problem was held hostage to Harrison's obsessiveness and Board of Longitude politics, the problem had not gone away ...

Despite his problems, Anson's voyage took him on around the world. Later he was to become First Lord of the Admiralty.

In 1775, Captain James Cook took a copy of Harrison's H4 watch on his second voyage of exploration, and heaped praise on it. He also made good use of Maskelyne's calculations, and the combination of the two methods showed the way forward for navigation.

Nevil Maskelyne had a distinguished career as Astronomer Royal.

Although he never submitted his own work for the Longitude Prize, it was recognized that the Lunar Distance Method was an easier short-term solution to the problem. Maskelyne continued to oversee the production of The Nautical Almanac, which was a standard tool of seafarers for many years, until more efficient (and affordable) versions of John Harrison-style Marine Chronometers supplanted it.

Maskelyne died in 1811. He is buried at Purton, just outside Swindon.

John Harrison died in 1776, and is buried in Chipping Barnet Churchyard in North London. A blue plaque is now at the site of the house in Red Lion Square.

The clocks were retained by the Royal Observatory, and were found mouldering behind a cabinet in 1920 by Rupert Gould, who spent years renovating them. They are now on display at the Observatory.

In recent years, the town of  Barrow-upon-Humber  has taken an interest in commemorating their most famous resident. This statue of John Harrison by Marcus Cornish was installed in the market place in March of 2020.