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Never trust a pirate: Christiaan Huygens’s Longitude Clocks

Updated Monday, 26th October 2015

As a tribute to the historian Lisa Jardine, who died on October 25th, we're republishing her essay on the shady history of 17th Century timekeeping.

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On 13/23 January 1665 Sir Robert Moray, courtier and confidant to King Charles II, and sometime President of the Royal Society in London, wrote to the talented young mathematician and horologist Christiaan Huygens at The Hague:

At last Captain Holmes has returned, and the account he has given us of the experiment with the pendulum clocks leaves us in absolutely no doubt as to their success. He left the island of Saint Thomas, which is under the Line, accompanied by four vessels. In order to pick up the correct wind for his return he was obliged to steer towards the West and to sail for six hundred leagues without changing his course, after which, finding a favourable wind, he steered towards the coast of Africa, heading directly North North-East. But when he had sailed four or five hundred leagues in this direction, the Masters of the three ships under his command, fearing that they would run out of water before they reached their pretended destination, proposed that they should steer a course towards Barbados. In pursuit of which the Captain, having brought them all together with their Journals [log books] they were found to be at odds with the calculations of the Captain, one by 80 leagues, the other by 100 and the third by 120. For the Captain calculated using his pendulum clocks that he was hardly more than 30 leagues away from the Island of Fuego, which is one of the islands of Cape Verde, from which the three Pilots estimated that they were still at a considerable distance. And because the Captain had total confidence in the clocks, he insisted that they continue in his proposed route, and the following morning the Island of Fuego appeared just as he has judged would happen.

Christiaan Huygens was the man who patented that great breakthrough in accurate timekeeping, the pendulum clock, in 1657. For over a year he had been awaiting the outcome of a series of sea-trials of his clocks, to establish whether they might keep time with sufficient precision to allow an horological solution to the calculation of longitude. These had been undertaken by Robert Holmes on a voyage to the Guinea Coast of Africa sponsored by the Royal African Company. Huygens had written repeatedly to Moray for news of the trials, hence that ‘At last’ at the beginning of Moray’s letter.

Professor Lisa Jardine Creative commons image Icon The Royal Society under CC-BY-SA licence under Creative-Commons license Lisa Jardine

On 5 February Huygens wrote to a close friend, Jean Chapelain, to tell him of his successful application to the States General for a Dutch patent for his longitude clock, based on Holmes’s testimony.

On his return, Captain Holmes has lodged his report concerning the usefulness of pendulum clocks, which goes far beyond my expectations. I could never have imagined that clocks of this first, preliminary mode of construction could have succeeded so well, and I had reserved my principal hopes for the new ones. But since these have already been so successful, and that the others are even more precise, I feel entitled to believe that the discovery of true longitude will shortly reach its final perfection. . . . The pendulum clocks are a success. The Estates General want to see the clock at their Assembly.

Moray’s account of Holmes’s remarkable success with the pendulum clocks was published immediately, almost verbatim, in the Royal Society’s Philosophical Transactions and in French in the Journal des sçavans, together with extracts of his letter to Chapelain. I say almost verbatim, because at several points in the narrative phrases have been inserted: ‘having there adjusted his Watches’, ‘having a great confidence in the said Watches’.

The same account translated into Dutch eventually featured as the unique account of a sea-trial of pendulum clocks to be included in Huygens’s landmark book on pendulum clocks, the Horologium Oscillatorium, published in 1673. It formed the basis for Huygens’s determined efforts to secure a patent for his ‘longitude clock’ in Holland, France and England.

Right down to the present day, it is the spectacular success of these trials which is invoked as the crucial evidence, on the basis of which Huygens’s pendulum-clock timekeepers take their place as a significant step along the path from the theoretical aspiration to determine longitude at sea using a precision clock, to the realisation of that dream with John Harrison’s longitude timekeeper.

The problem is that Sir Robert Holmes (as he later became) was not known as a person of integrity. Quite the contrary: Major Robert Holmes, as he was at the time of the Guinea sea-trials, was somewhat notorious, as a notable villain. Or at least, he is infamous as the hot-tempered, violent and uncontrollable naval commander whose unprovoked attacks on Dutch shipping and seizure of Dutch goods were directly responsible for starting both the second and third Anglo-Dutch wars.

Holmes had served under Prince Rupert and James, Duke of York, and eventually rose to the rank of Admiral. In 1664, on the very voyage on which he was ostensibly testing the Huygens clocks, he sacked the Dutch trading-stations along the coast of Guinea one by one, seizing goods and property and laying waste the Dutch settlements. On his return he was twice imprisoned in the Tower of London (on 9 January and 14 February 1665), for having gone beyond orders or for failing to bring back adequate amounts of booty (it is not quite clear which). His actions led directly to the Dutch declaring war on 22 February 1665 (by announcing that they would retaliate against any British shipping in the Guinea region), at which point Holmes was released and pardoned, in order to command His Majesty’s forces.

In August 1666, Holmes attacked and destroyed by fire 150 East Indiamen in the Vlie estuary and sacked the town of Westerschelling on adjacent Terschelling Island. In 1672, Holmes and Sir Frescheville Holles attacked the Dutch East India Company convoy returning from Smyrna in the English Channel, seizing its cargo of salt and Oriental luxuries, thereby precipitating the third Anglo-Dutch war of that year.

Samuel Pepys was afraid of Holmes (‘an idle, proud, conceited, though stout fellow’), and on several occasions expressed reluctance at having to deal with him on matters of naval discipline. After the second Dutch war Holmes was rewarded for his exploits with the Governorship of the Isle of Wight; he eventually became extremely rich and much more respectable.

It was Huygens himself who first smelled a rat regarding Holmes’s report of the spectacularly successful performance of the ‘pendula’. On 6 February 1665 (the day after his upbeat letter to his friend Chapelain), in his first response to Moray, Huygens, after expressing his delight at the dramatic outcome of the trials, added a small caveat:

I have to confess that I had not expected such a spectacular result from these clocks. To give me ultimate satisfaction, I beg you to tell me what you and your colleagues at the Royal Society think of this Relation [of Holmes’s], and if the said Captain seems a sincere man whom one can absolutely trust. For it must be said that I am amazed that the clocks were sufficiently accurate to allow him by their means to find such a tiny island [as Fuego]. 

On 6 March, Huygens was still pressing Moray for ‘something of the detail of what you have learned from Mr Holmes, principally in order to know how the clocks behaved in a storm, and if in that climate rust did not eventually cause them to stop’. The matter of Holmes’s trustworthiness was raised at the 8 March meeting of the Royal Society (at which Huygens’s concerns were raised, and the letter of 6 March read):

It was affirmed by several of the members, that there was an error in [Holmes’s] relation, as to the island named therein; and that it was not the island of Fuego, which the Major’s ships had touched in order to water there, but another thirty leagues [90 nautical miles] distant from it.

Samuel Pepys (recently elected a Fellow) was ‘desired to visit the Major, and to inquire farther concerning this particular for the satisfaction of the society’. In practice this meant visiting Holmes in the Tower, where he was still imprisoned for his conduct towards the Dutch settlements at Guinea, during his voyage. On 14 March Pepys attended ‘a farewell dinner which [Sir John Robinson, Lieutenant of the Tower] gives Major Holmes at his going out of the Tower’, ‘Here a great deal of good victuals and company’.

On 3/13 March Moray responded again to Huygens’s pressing him for further detail from Holmes. He still had no concrete data from Holmes, but on the basis of conversations with one of his sea captains, he himself volunteered some significant corrections to the original account given:

I am due to dine with Mr Holmes tomorrow, and it is my intention to try to get his account in writing, which he promised me when we last parted. However, I have spoken to another officer of one of the ships which were with him, who was himself on the Major’s ship until they reached the island of Saint Thomas, and is indeed the person who had care of the Clocks, and from whom we had the first report on them 14 or 15 months ago [during an earlier voyage].

‘I do not blame [Major Holmes] for this’, he insists. But again, ‘There remains one further objection that I know of which reduces the accuracy of this experiment, which is the precise location of the Island of Fuego [which Holmes has miscalculated]’ – not exactly a ringing endorsement of Holmes’s story.

On 15 March, both Pepys and Moray reported to the Royal Society on their dealings with Holmes. Pepys had spoken to the master of ‘the Jersey ship’ – that is, Holmes’s own vessel.

The said master affirmed, that the vulgar reckoning proved as near as that of the watches, which [the clocks], added he, had varied from one another unequally, sometimes backward, sometimes forward, to 4, 6, 7, 3, 5 minutes; as also that they had been corrected by the usual account. And as to the island, at which they had watered, the said master declared, that it was not Fuego, but another 30 miles distant from the same westward.

According to the Master of Holmes’s ship, then, there was not much to choose between the old way of calculating longitude, and that using the new clocks. Moray, who had spoken to Holmes himself, corrected ‘some mistakes in the number of the leagues formerly mentioned’ (informed of these errors, Huygens expressed the hope that they would be corrected in any future edition of works on longitude clocks which included this important testimony – and indeed, the figures in the printed versions of Holmes’s story have been altered from those in Moray’s original letter to Huygens). Holmes’s Master also confirmed that the ships had not watered on Fuego, ‘yet they had made that island at the time, which the Major had foretold, and were gone from thence to another, more convenient, for watering’.

At the very next meeting of the Royal Society, on 22 March, ‘Mr Pepys was desired to procure the journals of those masters of ships, who had been with Major Holmes in Guinea, and differed from him in the relation concerning the pendulum watches.’17 Nothing further was heard, however, of discrepancies between the ship’s journals and his ‘relation concerning the pendulum clocks’. Had that convivial dinner a week earlier perhaps predisposed Pepys to draw a veil over the matter? In any case, by this time England was at war with Holland, and Holmes himself was in charge of English naval hostilities.

Holmes’s account of his trials of Huygens’s longitude clocks has been firmly lodged on the record ever since, as an exact account of the astonishing success of these critical sea-trials of Huygens’s pendulum clocks.

However, a presentation copy of Holmes’s journal of his two Guinea voyages survives in the Pepys Library at Magdalene College, Cambridge. It is presumably the copy Pepys procured, as instructed by the Royal Society, to validate Holmes’s narrative. It has gone unnoticed by scholars, in the context of the Holmes trials of Huygens’s longitude clocks on that very voyage.

Holmes’s journal is extremely full and specific. It is also rather well written – Holmes has a nice line in racy narratives, particularly where bombarding and plundering Dutch merchant ships is concerned. Day by day he chronicles the progress of his band of ships – the Jersey, the Brill, the Golden Lyon and the Expedition. Only once in the course of the entire journal does he mention the pendulum clocks, and it is hard to see how they could have been kept going steadily, given a series of buccaneering adventures and naval battles with Dutch East Indiamen in which (for instance) Holmes’s topmast and mainsail were shot away.

Here is a taste of Holmes’s swashbuckling style, and a reminder of the combative nature of his maritime ventures, as preserved in a letter he included in his Guinea voyages journals written from Lisbon on his return journey:

Since my Letters from Cape Coast wee have taken in Aga & Anamaboa the former by storm, and after promiseing Quarter to the Flemins & taken possession our men being somewhat greedy of Plunder, the Flemins treacherously blew up the Powder & withall 80 or 90 whites and Blacks which the Blacks rewarded by cutting of all their heads; At my Return from the Coast all things were in a good Posture, & well settled. I haue with me here the Golden Lyon, the Crown and Brill which I hope to man here & carry them for Engl[an]d. I know not how my Actions vpon the Coast of Guyny are resented at Court, nor how my Condicon stands.

So what does Holmes’s journal tell us about the ‘experiment’ he conducted with Huygens’s timekeepers?

In July 1664, Holmes was on San Thome, reprovisioning and rewatering. He set out for home on 11 August. For more than a month strong currents, contrary winds and becalmings bedevilled him. By the third week of September they were well and truly lost on the open seas. There is indeed a full sequence of entries relating to Holmes and his fellow captains getting lost and running short of water, which does, uniquely in the entire journal, mention ‘pendula’ (this fair copy of the journal was prepared for James, Duke of York, the future James II). It was with great reluctance that Holmes’s companions agreed to turn eastwards. It was three days before they sighted land, during which time variable winds took them in several different directions. As Pepys had learned, they did not land on Fuego, but some time later on another of the Cape Verde Islands, St Vincent. In the matter of the accuracy with which the ‘pendula’ enabled Holmes accurately to predict his eastwards landfall, he had, at the very least, greatly exaggerated. But once Holmes’s misleading report, with its bravura claims for the pendulum clocks, was on the record in England, France and Holland, and publicly unchallenged, Huygens’s claim to priority in relation to longitude timekeepers was assured. The account was prominently reprinted in 1673 in the Horologium Oscillatorium, and then followed within the year by the announcement from Paris of the balance-spring watch. Huygens’s impressive sequence of horological innovations – pendulum clock (1658), longitude pendulum timekeepers (1665) and balance-spring regulator (1674) – entitled him to precedence over others working close to him, and assured his lasting reputation as the pre-eminent figure in the field. The team of clock-makers, experimentalists and clock-enthusiasts, including Alexander Bruce, Lord Brouncker, Robert Hooke and Robert Moray, who had contributed significantly to his successes, faded from the record, their claims to some part of the credit, or even to feature in the story, overlooked and forgotten. Today, highly respected historians of science quote the Holmes story as the clinching evidence for Huygens’s success with pendulum clocks to establish longitude with accuracy.

By the time the Horologium Oscillatorium appeared, ostentatiously dedicated to the French king, Louis XIV, however, the Fellows of the Royal Society were of the opinion that Huygens was overstating his personal claims for priority. Immediately, strong protests were lodged by the most senior members of the Royal Society. The President, Lord Brouncker, the elder statesman of the Society, John Wallis and Sir Christopher Wren all wrote to Huygens, pointing out to him – with chapter and verse – of the contributions made to his unfolding horological theory and practice by English practitioners and virtuosi. They reminded Huygens that Robert Hooke’s circular pendulum had been demonstrated and discussed at several meetings, that Alexander Bruce’s modifications to the marine timekeepers had been crucial to their success, that Brouncker and Huygens had together debated the tautochronism of the cycloidal pendulum at length, that Wren had rectified the cycloid ahead of Huygens. All of these contributions were inadequately acknowledged in Huygens’s work, or (in the case of Hooke) not at all.


On 27 June 1673, the Secretary of the Royal Society Henry Oldenburg himself urged Huygens to be more generous in his acknowledgements:

Allow me to say, that being entirely impartial and resolved to give everyone his due, insofar as I understand the matter, I find that our Philosophers here are not inclined to claim discoveries made by others. But neither will they or anyone else take from them their inventions, or suppress what is truly theirs. . . .

You would wish me, I am sure Sir, to speak thus candidly, and so that you understand the mood of our mutual friends, who never miss an opportunity to speak well of your talents. . . . If candour reigned everywhere, what friendships might we be able to establish amongst the learned, and what advantages might the public derive?

‘Friendships amongst the learned’, I suggest, captures the kind of Royal Society-based international collaboration which underpinned Anglo-Dutch and Anglo-French cutting-edge research on longitude timekeepers in the 1660s. Given such a strong sense of a collaborative environment, it is no wonder that Hooke and his colleagues believed that their research and development had made a significant contribution to Huygens’s horological innovations, and felt cheated when he announced his ‘eureka’ moment, and the perfection of the balancespring watch in 1675.

Since the discovery of the so-called ‘Hooke Folio’ in January 2006, we can add some further documentary evidence (more substantial than Holmes’s at least) to this story.

In the transcriptions Robert Hooke makes from the Journal Books and Oldenburg’s rough papers in the recently rediscovered Hooke Folio Hooke particularly highlights moments when he demonstrated key technical points at Society meetings in the presence of Huygens; he notes Oldenburg’s omissions from the minutes, his failures to record key technical points made. Most dramatically, Hooke has removed two items from Oldenburg’s autograph rough minutes for critical Society meetings, and added them as evidence to his own body of transcriptions. One of these concerns Hooke’s demonstration of the isochronous properties of a circular pendulum, the other is four pages of rough minutes recording Hooke’s demonstration of a spring-regulated watch to the Society in June 1670, and the details of its mechanism.

We were already aware of transcriptions in Hooke’s hand of parts of two letters from Moray to Huygens, which Hooke had copied out from the Society’s letterbooks, as evidence of Moray’s letting slip vital clues to the isochronous nature of springs as demonstrated by Hooke, to Huygens. Now we find Hooke assiduously assembling the history of his contributions to what I am calling the collaborative venture of early longitude clocks and spring-regulated precision timekeepers. Taken all together, however, the volume of notes Hooke has assembled does not add up to evidence of a conscious betrayal, and I think that in the end Hooke knew this. As he puts together his dossier of occasions on which information passed from the Royal Society to Huygens (either in person, or via Moray or Oldenburg), nothing new actually emerges, either to prove once and for all that Hooke had been ‘betrayed’, or to clinch Hooke’s own independent priority in spring-regulated timekeepers.

Indeed, I would like to think that in the course of assembling the Hooke Folio in the late 1670s, painstakingly sifting back through the documentation of ten action-packed years of scientific activity at the Royal Society, Hooke finally saw clearly the extended, collaborative Anglo-Dutch character of the whole longitude timekeeper affair, and understood the injustice of priority and acclaim being accorded to Huygens, above all the other international co-participants.

Hooke, unlike many others, down to the present day, was certainly clear that the excitement surrounding those supposedly sensational trials of Huygens’s longitude pendulum clocks in 1664–5 was ill-founded, and that Holmes had tampered with the evidence. So since it is Hooke (even more than Alexander Bruce) who tends to get overlooked in the telling of the story of clocks and the quest for longitude, let me give him the last word here.

In an unpublished lecture of around 1676 (now in the British Library), Hooke, recapitulating the trials of the Bruce–Huygens clocks in which he had himself participated in early 1664, wrote:

In february 1664 as I remember my Lord Kingkarden having gotten another [pendulum clock] made here in England did togethe[r] wth. my Ld. Brounker Sr . Ro Moray & my self make a further tryall of them wth. some of ye Kings Pleasure boa[ts] but not wth. soe good successe as was expected. . . . They were afterwards sent by Sr . Robert Holmes to Guinny and an account returnd thereof somewt . like that printed by Hugeinus giving indeed a very favourable account of their performan[ce] but concealing all their faileurs & miscarriages whereas another person that was in the same ship gaue a relation very differing. which relation was concealed & the other printed.

This essay was originally published as part of Temptation In The Archives: Essays In Golden Age Dutch Culture by Lisa Jardine and published by UCL Press. The book is released under CC-BY-NC-ND. You can read and download the original, with footnotes and references, at





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