‘He [John Harrison] wrested the world’s whereabouts from the stars, and locked the secret in a pocket watch’. Dava Sobel, Longitude, Fourth Estate, London, 1998

Harrison H-4 Chronometer

Since earliest times Europe’s sea-faring nations England, Portugal, France, Spain, the Netherlands vied with each other to solve – the Holy Grail of Navigation – longitude – calculating with precision a ship’s position at sea while beyond sight of land.

1707 – Cornwell:  In heavy weather six (6) of Admiral Clowdisley Shovell’s ships lost their bearings off the Cornish coast and dashed to pieces against the Scilly Isles with the loss of 1500 lives.

1714  – Westminster: An enquiry into England’s first recorded 18th century maritime disaster resulted in legislation- The Act of Longitude 1714.

The Act established A Board of Longitude. Its task to invite submissions, evaluate their worth and award a prize of £20,000 to whom-so-ever solved the problem of determining longitude at sea.

The contest developed into a naked grab for cash to the detriment of the world’s seafarers.

A king’s ransom, reckoned now at more than £400,000,000, did much to delay recognition of the solution at the cost of countless lives.  See: Lotto and Longitude

‘John Harrison, the man who solved longitude in 1759’. Peter Ackroyd, Revolution, Macmillan, London, 2016 See: Lieutenant William Dawes & ‘The Eternal Flame’

In truth there were only two (2) viable contenders for the Longitude Prize.

The Nautical Almanac of Astronomer Royal Rev. Nevil Maskelyne a system of  Luna Tables  and Star Cataglog was the method favoured by a succession of Astronomer Royals.

‘The Board of Longitude was top-heavy with astronomers, mathematicians and navigators…the Reverend Nevil Maskelyne the fifth astronomer royal, who contested his [Harrison’s] claim to the [Longitude] prize money and whose [Maskelyne’s] tactics at certain junctions can only be described as foul-play’. Dava Sobel. ibid.

The other was a sea-going ‘pocket-watch’ the invention of an artisan, John Harrison a Yorkshire carpenter.

Portugal:  In 1736-7 aboard HMS Centurian John Harrison took his H-1 chronometer on a supervised time-trial voyage London to Lisbon. It performed within the guidelines required by the Board of Longitude.

1737 – 30 June: …a banner week for Harrison, because on the 30th [June 1737] the commissioners of the Board of Longitude convened for the very first time – twenty-three years after the board was created – citing his marvellous machine [H-1] as the occasion’. Sobel. ibid.

The prize money however  did not find its way to John Harrison. The might of one commissioner, Nevil Maskelyne however, was brought to bear on Harrison both personally and against his ‘marvellous machine’ the ‘pocket-watch‘See. Moon Versus Machine



‘As early as 1514, the German astronomer Johannes Werner struck on a way to use the motion of the moon as a location finder. The moon travels a distance roughly equal to its own width ever hour’. Dava Sobel. ibid.

Greenwich Observatory:  Luna Tables were the life’s work of Reverend John Flamsteed the first to hold the post.  Appointed in 1676 by King Charles 11. A succession of Astronomer Royals remained wedded to Luna Tables.

On Flamsteed’s death in 1719 Edmond Halley of comet fame was appointed Britain’s second Astronomer Royal.

Halley died in 1742. Then came James Bradley who held the position for twenty (20 years until his demise in 1762.

Next Nathaniel Bliss (1762-64) whose reign was shortened by ill-health. Bliss remained at Oxford University and did not take up residence at Greenwich. Charles Green acted as surrogate Astronomer Royal during Bliss’ absence.


1764 – Barbados:  In 1764, with Bliss too ill to travel, Green as Acting Astronomer Royal together with astronomer Rev. Nevil Maskelyne an official representative of the Board of Longitude, sailed to Barbados to asses yet again the accuracy of John Harrison’s ‘pocketwatch’.

At Barbados Green found H-4 ‘the perfect timekeeper‘. It satisfied all that was required by the Board of Longitude. Maskelyne had taken the opposing view. See: The Third Man – Charles Green

Greenwich – 1765: Not long after returning from Barbados, at the beginning of 1765, King George III announced Reverend Maskelyne ‘s appointment as Britain’s fifth Astronomer Royal.

On the 15th of March 1765 Green logged his final Observations and left the Observatory soon afterwards.

Nevil Maskelyne, negotiated a much more satisfactory salary than any of his predecessors and assumed his active role as Astronomer Royal in mid March 1765. He held the post until his death in 1811.

1765  Greenwich: Charles Green left the Observatory as Maskelyne began his long tenure (1765 -1811) as Britain’s Astronomer Royal. during which period he held a strangle-hold over everything related to the moon and stars. See: Moon Versus Machine. 


Tahiti – 1768: Yorkshire-man Lieutenant James Cook RN sailed for Tahiti to observe the Transit of Venus at the behest of the Royal Society  projected to take place in early June 1769. The Royal Society chose Charles Green a fellow Yorkshire man as their astronomer.

Cook having satisfied his obligation to the Royal Society was under ‘Secret Admiralty Instructions’ to search for the fabled Great South Land.

Not long before Cook sailed [for Tahiti] in HMS Endeavour Maskelyne had published his Nautical Almanac. 

‘The Almanac represents Maskelyne’s enduring contribution to navigation – and the perfect task for him too, as it embodied an abundance of excruciating detail’. Sobel. ibid.

Cook was given Maskelyne’s ‘tedious’ celestial Almanac but was denied Harrison’s ‘never-failing pocket-watch…[it] was bolted to a window-seat at the Observatory’. Dava Sobel. ibid. See: Captain Cook Caught Short


1771: Charles Green died not long after HMS Endeavour departed Batavia, present day Jakarta, on Captain Cook’s return to England from the ‘South Seas’. See: The Third Man, Charles Green











‘At the heart of Dava Sobel’s fascinating brief history of astronomy, navigation, and horology stands the figure of John Harrison and his forty-year obsession with building the perfect timekeeper’. Sobel, Longitude, Cited Cover Paperback Edition





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