‘But by reason of the motion of the Ship, the Variation of Heat and Cold, Wet and Dry, and the Difference of Gravity in different Latitudes, such a watch hath not yet been made”. And not likely to be, either, he implied’.  Isaac Newton cited, Dava Sobel, Longitude, Fourth Estate, London, 1998

‘And not likely to be’: However in 1736-7 just ten (10) years after Newton’s death (1727) H-1, an early model of John Harrison’s  marine watch  on a supervised timed voyage – England to Lisbon aboard HMS Centurian – proved to be a reliable time-keeper.

Accurate time-keeping was essential for the calculation of longitude at sea. Harrison a Yorkshire carpenter solved that problem. His  invention – a sea-going ‘pocket watch’ – gave a ship’s precise position when beyond sight of land.

‘John Harrison, the man who solved longitude in 1759’. Peter Ackroyd, Revolution, Macmillan, London, 2016

The Centurian voyage was typical of John Harrison’s long struggle for recognition.

‘He [Harrison] succeeded, against all odds, in using the fourth – temporal – dimension to link points on the three-dimensional globe’. Sobel. ibid.

‘The 1707 incident, so close to the shipping centres of England, catapulted the longitude question into the forefront of national affairs [and] underscored the folly of ocean navigation without a means for finding longitude’. Dava Sobel. ibid.

Throughout the centuries maritime disasters were common-place. In 1707, during  the reign of Queen Anne,  one of England’s worst recorded disasters occurred in the middle of the War of Spanish Succession (1701-14 ).

Gibraltar -1707, September 29:  Britain had captured ‘The Rock’ from Spain in 1704. Three (3) years later – September 1707 –  a fleet of twenty-one (21) English ships set sail from Gibraltar.

Portsmouth: Led by Admiral Cloudisley Shovell, overall Commander of British fleets aboard his flagship HMS Association, they were making  for Portsmouth their home base.

En-route Shovell’s vessels were battered by fierce gales. Dense sea-mist thrown up by recurring storms proved a nightmare for ships’ navigators making it all but impossible to plot a safe course.

Cornwell – October: To add to their woes nearing home, off the Cornish coast heavy cloud obscured the night sky.  No moon or stars made celestial navigation impossible.

Scilly Isles: In pitch darkness some sailing masters lost their bearings altogether and failed to recognise their proximity to the Isles of Scilly.

Four (4) vessels including HMS Association crashed onto rocks and sank with all hands including Admiral Shovell. Two (2) more  capsized. Overall mortality was reckoned at 1500 souls.

A lengthy investigation into the Cloudisley Shovell disaster concluded, due to prevailing weather conditions, ships’ navigators, limited only to ‘dead reckoning’ had been unable to determine their true position in relation to the lalnd.

‘The souls of Sir Cloudesley’s lost sailors – another thousand martyrs to the cause precipitated the famed Longitude Act of 1714, in which Parliament promised a prize of £20,000 for a solution to the longitude problem’. Sobel. ibid.


‘When John Harrison arrived in London in the summer of 1730, the Board of Longitude was nowhere to be found. Although that august body had been in existence for more than fifteen years, it occupied no official headquarters in fact, it had never met’. Sobel. ibid.

Another ten (10) years passed then came a second naval disaster of similar magnitude to that of Shovell’s off Cornwell.

‘Anson’s squadron took the Atlantic the old-fashioned way , on the strength of latitude readings, dead reckoning and good seamanship…A grand tragedy unfolded founded on the loss of their longitude at sea’. Sobel. ibid.

Nearly thirty (30) years previously -1714-  Parliament had offered a reward of £20,000, reckoned now at more than £400 millions and yet by 1740 the prize money, had not been awarded.

And this besides the strenuous efforts of John Harrison who, by 1740 had built three (3) versions of his mechanical H-1 ‘watch’. Persistent hounding by the commissars – Astronomer Royals – of Greenwich Observatory meant that when disaster overtook Admiral George Anson in 1740 ;‘the longitude clock stood on terra firma in Harrison’s home at Red Lion Square’. Sobel. ibid.


On the days before reliable time-keeping, the skies were used as a giant clock’.Vanessa Collingridge, Captain Cook, The Life, Death and Legacy of History Greatest Explorer, Random House, London, 2003

1740 – September: Although H-2 and H-3, improved models of Harrison’s initial chronometer, were available Commodore Anson in HMS Centurion, took his squadron of six (6) warships to sea ‘the old fashioned way’.

1741 – Cape Horn, March: Anson’s ships rounded Cape Horn in early March 1741. They were caught by gales so intense navigators had no idea where the squadron stood in relation to the land.

‘The old fashioned way’ Luna Tables and Star Catalogues may have been well suited to static land-based platforms. But much less so on a pitching deck in churning seas when dense cloud and black starless nights magnified a navigator’s problems.

In such circumstances ‘tedious’ complicated ‘difficult to execute’ calculations required four  (4) men with hand-held instruments. It was the reason many seamen lost an eye.

To make matters worse Anson’s squadron had been at sea far longer than intended. Many crew developed scurvy ‘killing 6 to 10 men every day’.

As time went on, there was never enough man-power to man the ships or repair sails shredded by ‘winds [that] carried rain, sleet and snow’.

Juan Fernandez: Finally the fleet reached Juan Fernandez where; ‘Anson helped carry the hammocks of sick sailors ashore, then watched helplessly as the scourge picked off his men one by one…until more than half of the original five hundred were dead and gone’.  Sobel. ibid.

Anson’s martyrs were added to Cloudisley’s lost souls. In part at least this was because the longitude prize money ‘a King’s ransom’ had unintended consequences.

£20,000 proved a heady brew when thrown amidst the warlocks of Greenwich Observatory whose intransigence was without doubt responsible for the loss of countless lives.


Complex Lunar Tables and Star Catalog had been devised a century earlier by Rev. John Flamsteed Britain’s first Astronomer Royal appointed  by King Charles II in 1675.  He held the post until his death in 1719.

Harrison like Flamsteed before him felt the cruel lash of greed and duplicity. Edmond Halley of comet fame, with the connivance of Isaac Newton, had purloined, plagiarised and published Flamsteed’s Star Catalog without permission or attribution.

In the mid 1760s battle-lines were drawn between moon and machine. The Observatory’s Rev. Nevil Maskelyne, Britain’s fifth Astronomer Royal, clung to outmoded thinking and old technology – Luna Tables – versus the mechanical sea-going clock. ‘See: Moon Versus Machine 

In 1765 one hundred (100) years after King Charles II founded Greenwich Observatory Maskelyne published the first edition of his major work –  The Nautical Almanac’..

He was certain theNautical Almanac’, based on the relationship between Sun, Moon and Stars as a means of calculating longitude on the high seas, would deliver him the ‘king’s ransom’.

John Harrison died in March 1776 aged ‘exactly eighty-three years’. Dava Sobel covers fully the extraordinary story of the persecuted Yorkshire carpenter whose invention, the marine chronometer, solved the problem of longitude. See: Cook, Harrison, Green – Three Yorkshire Men Walked Into A Bar – Maskelyne

‘A true-life thriller, jam-packed with political intrigue, international warfare, personal feuds and financial skullduggery’. Francis Wheen, Daily Mail.


‘The Board of Longitude was top-heavy with astronomers, mathematicians and navigators’. Sobel. ibid.

Longitude tells of Harrison’s painstaking efforts to perfect his ‘watch’ and of unending frustrations as he butted heads with the dictators of the Longitude Board.

Sobel catalogues the merciless persecution of Harrison by a succession of Astronomer Royals, James Bradley, Nathaniel Bliss and finally Rev. Nevil Maskelyne who held the position from 1765 to 1811. See: Malicious Maskelyne

‘Rarely have I enjoyed a book as much as Dava Sobel’s Longitude. She has an extraordinary gift of making difficult ideas clear’. Patrick O’Brien, Daily Telegraph (London).

For more details on Dava Sobel’s book, Longitude see:


‘In January 1772 William [Harrison’s son] wrote the king [George III] a poignant letter covering the history of his father’s hardships with the Board of Longitude and the Royal Observatory…the king is reported to have muttered under his breath “These people have been cruelly treated”. Sobel. ibid.

And where was Harrison’s chronometer in 1769 when Lieutenant James Cook RN sailed HMS Endeavour deep into the South Seas in search of the fabled Great South Land?

‘[H-4 [was] bolted to a window seat in the [Greenwich] Observatory’. Sobel. ibid.

James Cook and the crew of HMS Endeavour too ‘ha[d] been cruelly treated’. See: Captain Cook Caught Short

‘John Harrison, the man who solved longitude in 1759’. Peter Ackroyd, Revolution, Macmillan, 2016

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