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Christiaan Huygens was a brilliant scientist, but not a very nice man.

In her best-selling book  Longitude, Dava Sobell told the story of the ultimately successful efforts made in the England of the first half of the Eighteenth Century to measure longitude at sea using very accurate clocks, and also mentioned that attempts had been made in the second half of the Seventeenth Century to do the same thing. Huygens figured prominently in the account but there is much more to that part of the story than appeared in the book. It ended with a bitter feud between Huygens and Robert Hooke, but it began with an obscure Scottish nobleman.

Alexander Bruce, Lord Kincardine. Portrait by Johannes Mijtens.

Alexander Bruce, Second Earl of Kincardine, was one of the twelve members of the Committee that founded the Royal Society in 1660, but his presence there was probably due more to his long-standing friendship with Robert Moray, the Scots soldier of fortune who became a confidant of Charles II and was his main channel of contact with the scientific community, than to any scientific distinction. He was essentially an industrialist, at a time when such people were just beginning to appear, and his family had become rich from quarrying salt, stone and coal. He had long-standing connections with the Netherlands, and 1659 saw him supplying stone to Amsterdam for its new town hall and also allying himself with one of the richest families in the city by marrying Veronica van Aerssen van Sommelsdijck. It may have been on the same visit that he first met Huygens, who had produced his first pendulum clock two years earlier. The pair begun to collaborate on clock design.and it took almost five years for there to be a falling-out between them.

It was Huygens who first worked out the mathematical equations governing the motions of pendulums, but for him it was more than a mathematical exercise. Throughout his life he showed as much interest in profit as science, spending much of his time in legal actions over patents, and he knew that a reliable method of measuring longitude would have enormous commercial and military applications. The inventor of a means to do so would be rewarded with fortune as well as fame, and the most obvious way of succeeding was to develop a clock that could keep accurately to the time at a ship’s port of origin, despite being subject to the ship’s motions throughout the voyage. Only trivial calculations would be needed to convert the difference between this time and local solar time into a longitude. It was about the possible use of pendulum clocks at sea that Kincardine wrote to Huygens on 29 January 1664, at the beginning of the year in which both men turned thirty-five. In the letter, subsequently reproduceda in note headed “The Lord Kincardine’s observations of the pendulum clocks at sea, in 1662”  on pp 4-6 of the ‘Philosophical Experiments and Observations of the Late Eminent Dr. Robert Hooke, S.R.S.’,  Huygens was addressed as ‘My dear friend’ but there is no doubt from the contents that this ‘dear friend’ had seriously upset the writer.

The substance of Kincardine’s complaint revolved around a meeting between himself and Huygens in the Hague an unspecified (but evidently short) time earlier, and a meeting in London four months before that. On both occasions the problems of using pendulums on board ship had been discussed, and the substance of Kincardine’s complaint was that prior to the London meeting he and Huygens had been working on the problem almost independently, and that he had been the more successful of the two. Specifically, he said that while ‘There is no bodye can denye but that the first application of a pendula to a watch is yours, but I think that you can as little denye that without this additione of mine … that could not have been usefull at sea’. The nature of this ‘additione’ was not specified (presumably because both men were well aware of it) but at some stage the pair had agreed that Huygens should apply for a patent, either in his own name or in both their names. Kincardine was very clear that the agreement had been for a patent that would apply only in the Netherlands but by the time of writing Huygens was claiming universal rights.

The letter was probably never sent. It  is not in the voluminous Oeuvres Completes which contains so much of Huygens correspondence and which, for early 1664, does include a number of letters from Huygens to to his brother Lodewijk and to Robert Moray in England complaining that he had had no letters from Bruce. On 1 February he wrote to Lodewijk to say that he had not heard from his ‘Escossois’ and that he took that this to be a bad omen.

Historically, Kincardineis almost invisible and Huygens was one of the giants of early physics, and it is very easy to assume that it was Huygens who was in the right. A brief report of a sea trial published in the very first volume of the Royal Society’s Philosophical Transactions tends to support this, because Kincardine  is mentioned just once:

These watches having been first Invented by the Excellent Monsieur Christian Hugens of Zulichem, and fitted to go at Sea, by the Right Honourable, the Earl of Kincardin, both Fellows of the Royal Society, are now brought by a New addition to a wonderful perfection.

This leaves open the question of where the credit for the ‘new addition’ should be assigned, and Kincardine, in his letter to Huygens, is obviously suggesting that the improvements were his and were significant. For an indication of what they were the reading public had to wait until, in 1726, William Derham collected and published a final volume of Robert Hooke’s papers, twenty-three years after his death. Hooke wrote that

The Lord Kincardine did resolve to make some Trial what might be done, by carrying a Pendulum Clock to Sea; for which End he contrived to make the Watch Part to be moved by a Spring instead of by a Weight; and then making the Case of the Clock very heavy with Lead, he suspended it, underneath the Deck of the Ship, by a Ball and Socket of Brass, making the Pendulum but short; namely to vibrate half Seconds, and that he might be better inabled to judge the Effect of it, he caused two of the same Kind of Pendulum Clocks to be made, and suspended them both pretty near the middle of the Vessel, underneath the Deck; thus done, he caused them first to move parallel to one another, that is in the Plane of the Length of the Ship, and afterwards he turned one to move in a Plane at Right Angles with the former; and in both these Cases it was found by Trials made at Sea, at which I (i.e. Dr. Hook) was present, that they wold vary from one another, though not very much, sometimes one gaining and sometimes the other, but yet not so much but that we judged they might be of very good Use at Sea if some farther Contrivances about them were thought upon and put in Practice. This first Trial was made in the Year 1662; …..

The contents of this note are in part confirmed and in part contradicted by the correspondence between Christiaan Huygens and Kincardine and others, including his brother Lodwick and Lord Moray. Kincardine did take two modified pendulum clocks to sea in 1662, but only in the late December of that year, and the trial was not a success. It was made on the packet-boat in which he was travelling to Harwich from The Hague, where he had been visiting Huygens. The seas were rough, the boat was small and he was seasick. Foreshadowing a later and equally unsuccessful voyage made by Jean Richer with pendulums designed by Huygens, one of the clocks broke free and was damaged and no useful measurements were made with the other.

Derham gave no indication of when the note was written, but there is no suggestion that Hooke, who had just (in November 1662) been appointed Curator of Experiments to the Royal Society, took part in the first trial.  Lia Jardine records him as writing, again in 1674, that:

In February or march 1664 as I remember my Lord Kingkarden having gotten another made here in England did together with my Ld. Brounker Sr. Ro Moray & my self make a further tryall of them with some of the Kings Pleasure boats but not with soe good successe as was expected one of the watches by the shaking of the boat in the carriage from white hall to Greenwich ceasing to goe, & the watches afterwards not keeping exact proportion to one another.

The January 1664 letter seems to have been Kincardine’s last serious attempt to claim any credit. He may well have decided that to pursue the topic would take up more of his time than his business interests would allow, and he might well not have wished to get into a serious conflict with members of a family that were closely allied to his wife’s. He might also, by this time, have concluded that the chances of success were minimal. From this point on it was Hooke rather the Kincardine who disputed priority with Huygens, and that was one of his biggest mistakes, on a par with his disputes with Isaac Newton. With the ascent of the Dutch King William to the British throne, the Huygens family became powerful in Britain as well as the Netherlands, and they took no prisoners.