9
SCIENTIFIC SOCIETY
Christiaan Huygens returned to Paris in October 1660, travelling with an ambassadorial mission sent to congratulate Louis XIV on the successful arrangement of his marriage to the infanta Maria Theresa, which was designed to bring peace between France and Spain. If he momentarily doubted his new-found standing as one of the leading minds of the age, then he must have been reassured to overhear a man on the Delfshaven ferry speaking in respectful tones of the clocks of Huygens.
Once in the city, he embarked on a frantic round of social calls and cultural engagements, happy to be back to civilization. His brother Constantijn wrote immediately demanding to know the fashions for the winter season. Christiaan replied in great detail – suits of ‘mouse-grey cloth’ with white canions, ‘but not as big as they were before’ – but still his brother wanted to know more. Christiaan took up lodgings at the Hôtel de Venise on the rue du Bussy in the Saint-Germain district and began to make adjustments to his style of living appropriate to his status. A personal carriage was too great an expense, so he planned to buy a sedan and employ porters when he needed it, once or twice a day, ‘for there is no way of going by foot’.
Many of the friends he made during his first visit to the city five years earlier had maintained a lively correspondence with him since then, always eager to learn of his further successes in observing Saturn and designing clocks. His first call was to his greatest champion, the poet Jean Chapelain. Perhaps his gushing wonderment at Huygens’s scientific ideas now found at least a little reciprocal admiration from Huygens, who had recently prepared his father’s verse collection, Koren-bloemen, for publication. As he made his rounds, Huygens carefully noted when people he called upon were out (‘point trouvé’) so he would remember to try again. His circle of correspondents expanded, too, as Chapelain and others introduced him to new French colleagues. Even the renowned mathematician Pascal at last made Huygens’s acquaintance; he found it ‘a surprise and extreme joy’, and expressed the hope that they would become friends. But a few were disappointed not to be able to meet him at all. Fermat wrote: ‘I learn with joy but not without a little jealousy that my friends in Paris have the honour of having you for some while. I assure you, Monsieur, that if my health were strong enough for journeys, I would with great pleasure join in their good fortune.’
For Huygens, these months provided a vital opportunity to compare theories, observe demonstrations and take part in experiments with true equals, who valued his contribution as he valued theirs. At the home of the physicist Jacques Rohault, for instance, he ‘saw experiments made with mercury which confirmed the weight of air, and how that which surrounds us is always elastic’. He also experienced the habitual peril of the reputed scientist when an eager astrologer forced his book on him: it was ‘quite mad’. In addition, he made numerous practical enquiries of clock-makers, lens-grinders and instrument manufacturers in the city. He attended music recitals, comedies and the ballet, where he inspected the design of the stage equipment. He glimpsed the king at mass in the chapel of the Louvre. By the end of December, two months after his arrival and after several requests, he managed to see Marie Perriquet, but they did not dine alone.
Huygens also began to attend the meetings of the informal Montmor academy. It had always been a source of excitement at the meetings when Chapelain was able to read out some scientific news from the absent Huygens. This was never more so than in March 1658, when, having carefully won over a dubious Huygens, Chapelain was permitted to reveal the contents of the Dutchman’s earlier secret communication offering strong evidence that Saturn was surrounded by a ring rather than orbited by close-lying moons or other strange appendages. By acting as the impresario behind such revelations, Chapelain prepared the ground well, ensuring that Montmor would heartily welcome Huygens to the circle, and assuring Huygens in turn that his confidentiality would be respected in discussions about both his clocks and Saturn. Huygens was more relaxed about the latter than the former, where he had good reason to fear that others were working on similar innovations, and where he hoped to obtain a privilege that would safeguard his commercial rights in France.
The troublesome Roberval raised difficulties in both areas. When he saw the correspondence with Chapelain in which Huygens described Saturn in new detail, he claimed that Huygens was merely repeating his own ideas, which the two had supposedly discussed in 1655. However, because Huygens had taken the precaution of coding his discovery in an anagram with an earlier date, it was clear that the priority was his, and Roberval was forced to back down. In addition, Roberval was said to have devised his own clock, as he told Chapelain, who passed the word on to a worried Huygens. Chapelain tried doggedly to prise further details of the design out of Roberval, but after several months was able to glean only that ‘it is still very imperfect’. This threat, too, came to nothing.
But now Huygens was present in person. On 2 November, less than a week after his arrival in Paris, he dined with Chapelain at Montmor’s house. He attended most of the Tuesday evening meetings at Montmor’s from then until his departure in March. He saw for himself Montmor’s paintings, drawings by Dürer, toys, magnets, and ‘Little bottles in water which rise and fall without one seeing how’. Huygens wrote to Lodewijk that the meetings typically numbered twenty or thirty ‘illustres, including state counsels and other blue ribbons’. But his first impressions of proceedings were not favourable. He must have described one of the first meetings that he attended in less than flattering terms to his brother Constantijn (the letter is lost), because Constantijn replied drily: ‘We laughed a great deal about this fine gathering at Monsieur de Montmor, and what happened in this synod of illogicality when you were there, leaving us with a not very honourable opinion of the comprehension of these Gentlemen Academicians who have the patience to listen to the prattle of pedants for hours on end on subjects of nullity.’
Fortunately, perhaps, Montmor was not the only host in town, nor the only follower of Descartes, and Huygens also attended other regular salons, including a number organized by women learned in science and philosophy, as well as more informal gatherings. Even before his arrival, Montmor’s academy had explicitly attempted to steer discussion towards things that could be unambiguously known and towards practical advancements. But it was clearly not able to go far enough with its existing members and leadership to suit Huygens, who found it overly rhetorical in its deliberations compared to what he knew of what was then the only other scientific society, Leopoldo de’ Medici’s Accademia del Cimento in Florence.
Chapelain’s announcement of Huygens’s further descriptions of Saturn in 1658 illustrates the academy’s difficulty in attempting to limit discussion to things that could be definitely known. Chapelain reported back to Huygens that
although everybody did not agree with your interpretation as something completely certain, the majority nevertheless deemed it most probable and infinitely praised your sagacity and judgement in a matter so far removed from the reach of the senses, rejoicing to see you so perceptive and so reasoning at such a young age as yours, promising so much for other mathematical discoveries in the future.
As we have seen, the precise nature of the form or forms around Saturn remained highly debatable even after publication of the Systema Saturnium in 1659, and Huygens was obliged to continue defending his interpretation against those of astronomers in Paris and elsewhere in Europe.
One of the most important new contacts that Huygens made as a result of his correspondence with French colleagues was Pierre Petit, the cartographer to Louis XIV and a superintendent of fortifications. As a military engineer, he possessed the eye for mechanical detail that many in the Montmor circle plainly lacked, but he was also interested in questions of mathematics and astronomy. He was in addition a manufacturer of automata, the elaborate mechanical toys that became something of a craze in France at this time. He was thus perfectly equipped to discuss the most detailed aspects of Huygens’s designs for telescopes and clocks. His letters to Huygens were typical engineer’s reports, long and detailed and precise in their use of language, and their conversations together must have had some of the same tenor.
But there was another reason for Huygens to want to spend time with Petit – he had a beautiful daughter, Marianne. Huygens first visited Petit on 16 January, when Petit showed him his observatory and lent him his treatise on a proposed River Seine canal. Thereafter, he was at the house frequently until his departure from Paris, spending days on end working on a portrait of Marianne. As he drew and painted, they got to know one another a little, and Marianne learned enough about his outlook on life to declare that he was ‘heretical’ in his views, a pronouncement that gave Huygens pause for thought. When at last the portrait was done, Huygens was dissatisfied with his efforts, certain that he had failed to capture Marianne’s beauty.
During these weeks, Huygens was in limbo while he awaited news of arrangements being made by his father for him to travel on to London. He returned the harpsichord he had rented and began a long round of adieux. Chapelain asked him to enquire how John Milton was faring (Milton had been briefly imprisoned for anti-royalist agitation upon the restoration of Charles II). One morning, he awoke to the news that the Louvre was burning and went with friends to watch as the fire destroyed parts of the historic palace. Huygens had grown to feel thoroughly at home in Paris, and now dreaded moving on. It was not only the prospect of awful food and political instability that put him off England. (Cromwell’s corpse had just been exhumed to be ‘hanged and quartered, and afterwards his head triumphantly fixed to the top of a pole’, as his brother Constantijn reported.*) He wrote to Lodewijk: ‘I do not suppose that in England, even though I know the language very well, I could amuse myself so well as here where I have made a great number of acquaintances, whose wishing to learn from one another gives me every kind of pleasure.’
After a delay for the weather, Christiaan Huygens departed France by packet-boat and arrived, ‘accompanied by porpoises’, in Dover on 30 March 1661. He continued onward to London by ferry and carriage, idly noting as he passed through Chatham and Gravesend the number of English frigates lying at anchor.
He was following in the footsteps of his anglophile father and his brothers Constantijn and Lodewijk. But Christiaan had his own reasons to visit London, which was then second only to Paris in natural philosophy. Having previously sent copies of his treatises on Saturn and clocks to selected correspondents, here too he found that his reputation preceded him. On 11 April,† the English diarist John Evelyn recorded: ‘I dined with that great mathematician and virtuoso, Monsieur Zulichem, inventor of the pendule clock, and discoverer of the phenomenon of Saturn’s annulus: he was elected into our Society.’ In fact, Huygens was formally elected to the Royal Society of London only in 1663; Evelyn’s overcompensation here gives some indication of the enthusiasm with which Huygens was received.
Nothing about London could match Paris. After he had been there for a couple of months, he wrote to Lodewijk:
I . . . don’t find the stay in London as delightful as it seems you found it when you always swore you wanted so much to return there. I foresee that we shall have a big argument about that, for I will always maintain that the stink of the smoke is unbearable, and most unhealthy, the city badly built, the streets narrow and poorly paved, with nothing but mean buildings, and finally that piazza and all the common [Covent?] garden is not much and nothing compared to what one sees in Paris. The people there are melancholic, the persons of circumstance civil enough but hardly sociable, the women very shabby and not at all as witty or lively as in France: but perhaps everything was otherwise when you were there, and there is the suggestion that after the re-establishment of the court, some manners will return. I can say anyway that I have had dealings with the most decent people, most of whom have travelled in France and elsewhere, who have treated, entertained and supported me overall most nobly.
In this short time, Huygens visited Windsor and Oxford. In London itself, he called on clock-makers and ascertained the price of telescopes. But much of his time was taken up with visits to and from the leading natural philosophers. He attended the scientific meetings at Gresham College in Bishopsgate, and met many of the founders of what would become the Royal Society, including Sir Robert Moray, a Scottish soldier and diplomat with an interest in engineering projects who had good contacts with many French savants; Alexander Bruce, the Earl of Kincardine, another Scot, who would collaborate with Huygens in developing seagoing clocks; the English astronomer Sir Paul Neile, whose thirty-five-foot telescope was deployed at Gresham College; the royal cryptographer and mathematician John Wallis; and the Irish mathematician William Brouncker, who would become the society’s first president.
Huygens must have been especially pleased to make the acquaintance of the astronomer and geometer Christopher Wren (his architectural career was yet to take off at this time). In 1658 Wren had proposed one of the more plausible models to explain the appearance of Saturn, but graciously gave way when he learned of Huygens’s conception of a planetary ring, instantly recognizing both its visual appeal and its mathematical credibility. He also met several times with Henry Oldenburg, a German-born theologian whose linguistic skills would equip him to become the ‘foreign secretary’ of the Royal Society and a vital conduit between natural philosophers in Britain and elsewhere in Europe.
Many of these encounters took place at the foot of a telescope or at the laboratory bench. For Huygens, the evident Baconian dedication to observation and experiment must have made a striking contrast with the airy theorizing of some members of Montmor’s group. Neile’s thirty-five-foot telescope, Huygens found, ‘does not seem as distinct as mine of 22’, and he promised to have his lenses brought over from The Hague so that they might be compared. Bruce and Moray repeated the demonstration of Prince Rupert’s drops staged at Gresham College the month before Huygens’s arrival in London, allowing Huygens to discover more about the curious glass beads in addition to what he had doubtless already gleaned from his father. ‘I learned that the glass tears which break are made by dipping in cold water and quickly pulling them out.’ He inspected other men’s pendulum clocks, too. Following a meeting with Wallis at Gresham College, they went out to observe an experiment to test whether artillery pieces begin to recoil before the projectile flies out – ‘which was verified’. As he had found in Paris, his scientific fame came at a price. A clergyman came to visit him, presumably to question him on some question of astronomy or physics – ‘a right pedant’, Huygens found him.
More stimulating for Huygens was the opportunity to attend a demonstration of the air pump made by Robert Hooke for the Irish chemist and physicist Robert Boyle. Huygens observed the response of animals and objects placed in the vacuum generated by the device, and the following day received a visit from Boyle during which the two men ‘discoursed for a long time’. The conversation inspired Huygens to set about constructing his own air pump when he returned to The Hague, which was to prove a crucial action in advancing pneumatic science.
On 3 May, Huygens passed up the opportunity to be present at the coronation of Charles II, preferring instead to observe a similarly rare event – the transit of Mercury – with the telescope-maker John Reeves. Knowing his father would be appalled that he had missed the ceremony, he gathered enough information to be able to describe the anointment by the Archbishop of Canterbury, the diamond-encrusted crown and the crowds of people inside and outside Westminster Abbey crying out in acclamation. ‘All this by report, for I, however, was with Reeves to observe Mercury in the Sun, as I did. Being 30 years since M. Gassendi saw the same thing.’ His father seems to have excused his son for his omission; he wrote to literary friend: ‘He amused himself, I think, while others witnessed the excessive pomp of the coronation. But you will not hear without laughing what he tells me in these terms . . .’
Meanwhile, Huygens’s friends in France were eager to have his critical opinion of work that they had only heard about in vague reports. He had hardly been in London a month before Thévenot wrote to him: ‘I imagine that you will have been shown many curious experiments in the London academy . . . I would say it is a great advantage to have seen all these fine things with eyes as knowledgeable as yours and to know your assessment of them.’
Huygens had arrived in Paris as an exotic foreigner, a celebrated astronomer and marvellous inventor, and had quickly become a fully engaged and accepted participant in its learned gatherings. In London, he became something in addition: a scientific intelligencer and a usefully neutral agent who could be relied upon to say as he found. His record of achievement and great proficiency across disciplines – mathematics, astronomy, mechanics – meant that he was equipped better than anybody to form an accurate picture for his French colleagues of the state of scientific development in England, and likewise to acquaint the English with the latest thinking in France.
Chapelain believed that Montmor’s academy, running in an informal way since 1657, had inspired the English to follow with their own society at Gresham College. Now, he felt that the scientific progress the English were making in many fields could be used to galvanize renewed efforts in Paris. He told Huygens: ‘It seems our Academy is warming up by the emulation that they [the London savants] give it, and the wish is to turn to experiments in preference to all other activity where there is the mind to do it.’ A similar effect was observed at the Accademia del Cimento in Florence. Such virtuous circles made it possible to compare observations and experimental results more effectively between scientific centres in different countries. They also made it easier to compare experimental methods and the design of instruments, which was perhaps of even greater significance for the progress of science. These comparisons depended not only upon a sustained international exchange of letters, but also increasingly upon the physical presence of expert practitioners, whose witnessing of, and sometimes active engagement in, the design and conduct of experiments gave them a practical knowledge not always communicable even in the most detailed letter.
All the time he was in England, Huygens was mindful of how the science he saw practised there might be emulated in France. He may not have held London in high regard at first, but the men who assembled at Gresham College clearly had much to teach the Montmor circle. Years later, when he was living in Paris, he told a visitor of his belief that the members of the Royal Society were ‘an assembly of the Choisest Witts in Christendome’. He reported back to Chapelain on his visit to London with the clear objective of trying to steer his French colleagues towards a more rigorous experimental approach, but his initiative received an obstinate rebuff.
Huygens had hoped to return directly to France after his stay in England, accompanying his father and brother Lodewijk on business for the House of Orange, but he was obliged to return home to represent the family at another no doubt tedious wedding of some cousins. He busied himself at home in The Hague with a typically eclectic set of investigations, observing Saturn, grinding new lenses with Constantijn, making calculations of the pendulum, modifying Boyle’s air pump and thinking about musical theory.
He gave Lodewijk a letter to take to Marianne Petit, expressing the hope that she remembered the man who came and drew her, and assuring her that he ‘goes over in his memory everything that is beautiful in your face, and charming in your conversation’. But it seems that the sketches Huygens made of her in the hope that a painter might use them to make her portrait had caused her some embarrassment. After delivering the letter, Lodewijk, duly struck by her beauty, reported back to his brother that she wanted them destroyed. Christiaan wrote back: ‘I told you that Mademoiselle P. was more beautiful than in the drawing I showed you, and you have seen too well to judge otherwise. However I will not do what she wishes me to do with these portraits, although in every other thing I would wish to render complete obedience.’
On 1 August 1661 Christiaan Huygens received a visit from Henry Oldenburg, who was passing through The Hague on his way back to London from his home city of Bremen. Oldenburg was able to inspect Huygens’s telescope, and to review his plans to build an air pump like the one he had seen Boyle demonstrate at Gresham College. The two men also spent some time discussing the reproductive habits of the crayfish, because Oldenburg was carrying with him a new natural history of the animal by Sir Kenelm Digby, who claimed to have generated the young by distilling the putrid remains of the adults. Huygens found the work ‘admirable but I admit that I have trouble believing it’.
Oldenburg and Huygens were kindred spirits. Adept in several languages, curious about all manner of natural phenomena and accustomed to the etiquette of court life, each was eventually able to rise to a senior position in the early scientific societies of Europe in a country other than that of his birth. Both believed that progress would come faster if there was dialogue between investigators everywhere. Though Oldenburg made no important observations and performed no experiments himself, he was to prove one of the most significant figures in the development and spread of scientific ideas during the second half of the seventeenth century.
Heinrich Oldenburg, as he was once known, had set out from Bremen for London first in 1653 as a civic envoy commissioned to negotiate the release of a Bremen trading ship carrying a cargo of French brandy, which had been seized by the English during the First Anglo-Dutch War. He settled in England, working as a tutor, as he had done in the Netherlands and elsewhere on the continent, until Robert Boyle employed him as an assistant. He travelled again to France and Germany in his new capacity and became well acquainted with the leading natural philosophers in both countries, including members of the Montmor circle, whom he doubted would ever be able ‘to produce any great matter in point of Tubes [telescopes] or chymistry or any mechaniques’.
Oldenburg was elected to the future Royal Society in December 1660 and listed – with equal status, not as a foreign member – among the forty founding names. As one of two secretaries of the society, he had many duties to perform, salaried initially by the wealthy Boyle. He attended the weekly meetings and recorded the minutes. He served as a translator, especially of English work into Latin, so that it might be more readily understood abroad, but also of scientific news that he received from his German contacts into English. He also launched the Philosophical Transactions, which quickly became the official journal of the society.
But his most important task was to oversee the scientific communications of more than thirty regular correspondents in the British Isles and on the continent. In addition to Christiaan Huygens and his father, these included the Danzig astronomer Hevelius, Boulliau and Petit in Paris, the telescope-maker Cassini and the physician Malpighi in Italy, and the microscope pioneers Swammerdam and Leeuwenhoek as well as Spinoza in the Netherlands. It was arduous work, involving the hand copying of their often long and detailed letters, as well as writing to colleagues summarizing the recent work of others in whom they might be interested. These progress reports typically comprised a short paragraph on each person’s work and would cover a wide range of topics. A typical letter to Huygens, for example, included intelligence on new observations of Saturn from Italy, on Hooke’s work on pendulum clocks, on Barrow’s forthcoming book on optics and on Wren’s progress with lenses.
Oldenburg soon adapted his role into a more subtle one that made greater use of his diplomacy. He became a vital intermediary, able to effect introductions that would prove significant for the progress of science. For example, in later years, he introduced Huygens to Leibniz and, with the help of the Huygenses, brought Leeuwenhoek’s work with the microscope to the attention of the Royal Society. He helped experimenters obtain the materials they needed. From his broad knowledge of progress in many fields, he was often able to advise his correspondents when another already had the priority for a particular discovery, or when an experiment had already been performed, so that they might avoid unnecessary duplication. His secretarial duties involved much chasing of tardy and hesitant writers, and his judicious persistence saw to it that much work which might never have been finished or published was in fact added to the body of scientific knowledge. He developed a useful ability to handle both the arrogance of overconfident claimants to this or that new discovery and the offence of those who felt themselves cheated, and duly found himself having to moderate numerous, often international, disputes between rival scientists. (Huygens was to experience his share of these disputes.) Here, his skill often lay in advising agitated correspondents on ways to respond temperately, thereby defusing tensions between them.
Oldenburg was put on his mettle especially during times of international conflict when letters were often rerouted or intercepted. An ignorant official might easily construe the scientific and mathematical content of Oldenburg’s typical correspondence as being of military value or in some form of code. During the Second Anglo-Dutch War, therefore, Oldenburg asked Huygens to address his letters to ‘Monsieur Grubendol’ (a decidedly pregnable anagram of his name), and gave him a new address from which items could be forwarded without the risk that Oldenburg might be accused of spying for the enemy. Huygens, like most of Oldenburg’s scientific correspondents, did what he could to ignore the exigencies of war, and Oldenburg repeatedly expressed peaceful sentiments in his letters to Huygens: ‘I wish always an end to the war and the plague, with an unequalled passion, so as to re-establish study and good relations.’
Perhaps, though, Oldenburg’s elaborate precautions merely encouraged the suspicion that he might be a spy. When the Dutch launched the audacious Raid on the Medway in June 1667, torching a number of English warships and towing away others including the flagship, HMS Royal Charles, the government feared that an intelligence failure was to blame, and suspects were indiscriminately rounded up. Oldenburg was imprisoned in the Tower of London, accused of ‘dangerous desseins and practices’ because of his copious foreign correspondence. Samuel Pepys, a fellow of the Royal Society as well as a senior official on the Navy Board, wrote in his diary that Oldenburg had been held for ‘writing news to a Virtuoso in France with whom he constantly corresponds in philosophical matters’. Although Oldenburg had other correspondents in France, if the concern was the leak of intelligence to the Dutch, then this can only refer to Christiaan Huygens, who was living in Paris at the time. After two months, Oldenburg was released without charge or apology, and promptly resumed his former duties.
Huygens’s professional association with Oldenburg, augmented in its later stages by a personal friendship struck up by his father while staying in London in 1671, lasted until the German’s sudden death from ague in 1677. With that, a link was broken between scientists everywhere, and especially between scientists in Britain and their continental counterparts. Oldenburg left behind him the visionary prospect of an international network in which it was understood that the best hope for the advance of science lay in speedy, concise, honest and civil communications between like-minded participants irrespective of their nationality. No other personality emerged with the combination of scientific, linguistic and diplomatic abilities to continue what Oldenburg had started, before rising nationalism and a succession of European wars made such a thing seem hopelessly idealistic. The connection was arguably not reforged until the foundation of international scientific associations in the twentieth century.*
Huygens had returned home from London in May 1661 with Boyle’s description of the air pump. He was keen ‘to do some yet new experiments in the vacuum, and to have the pleasure of trying some of those which are in his book’. The air pump was an exciting invention for both practical and theoretical reasons. The nature of the vacuum, and whether it was truly an utter void, was a topic of lively speculation not only by scientists, but also by philosophers, theologians and lawyers. Control of the vacuum promised to lead to improved technology for pumping out mines and polder land. It was ‘seventeenth-century “Big Science”’.
Huygens followed Boyle’s instructions closely, paying particular attention to the airtight seals where different parts of the apparatus were joined. However, he found it hard to get parts made with the necessary precision by his errant instrument-maker, and early results were not encouraging. ‘The pump does not work,’ he wrote to Constantijn in October in a short letter that also included notification of the family wedding that had prevented him from returning to Paris. ‘The tube was so uneven in width that little or no air could be worked from the bottle.’ After another month, however, he dared to make some modifications to Boyle’s design, and found that the bladder used to show the goodness of the vacuum in the bottle would remain inflated overnight – ‘which Mr. Boyle was not able to effect’.
He was then able to repeat many of the experiments he had seen Boyle perform in London, for example demonstrating the rapid boiling of water in the vacuum, and showing, by placing an alarm watch inside the evacuated chamber, that the transmission of sound was greatly impaired. He bought some mice and birds, and then in triumph sent the corpse of one bird, ‘which died in the same way as described by Monsieur Boyle’, to Lodewijk in Spain. Huygens had greatly admired Boyle’s rigorous experimental approach, which stood in marked contrast to some of the scenes he had witnessed in France and to the English Hobbes, who had long held a fascination with the vacuum but who remained ill-equipped as a scientific investigator.* He was soon emboldened to bring his own further work with the air pump to Boyle’s attention. Boyle was pleased to find that Huygens’s objections to his work were ‘soe few, as well as soe judicious’, and made a positive response to Huygens’s suggestions.
At the Royal Society, however, members were unable to replicate the improvements Huygens had made, despite his letters describing what he had done, and even the visit of an emissary sent by Oldenburg to view the apparatus directly. It was not until Robert Hooke was made ‘curator of experiments’ at the society, and Huygens himself came over from The Hague in 1663, that the London air pump could be made to work well enough to repeat Huygens’s new experiments.
Many scientists lack the ‘green fingers’ needed for building apparatus and carrying out successful experiments that Hooke and Huygens clearly both possessed, and Huygens remained the only investigator who succeeded in building an air pump independently of Boyle’s original. But even he resented the time eaten up by the temperamental device, and sometimes pretended it was broken so that he did not have to set up another demonstration. His achievement was nevertheless an important next step in validating Boyle’s experimental results, spreading them on the continent, and establishing a robust theory of air and the vacuum. Huygens himself had initially disagreed with Boyle’s suggestion that the pressure exerted by a given mass of air is inversely proportional to its volume (the relationship now known as Boyle’s law), but he was obliged to change his thinking when confronted by his own experimental results.
What happens, though, if the volume of air is infinitely expanded and the pressure falls to zero? This was the broader context of experiments with the air pump ever since Torricelli had invented the barometer by creating a vacuum in a tube of mercury in 1643. What actually occupied the void thus created? Descartes and his followers, including Huygens, believed some form of ‘subtle matter’ must be present, but others, including Pascal and Roberval, were prepared to believe that the space was truly empty. The potential emptiness of the void created by the vacuum pump raised important theological questions, because of the belief that any space not filled by God’s spirit might be occupied by the Devil. The philosopher Hobbes could conceive of a vacuum in a physical sense. (He imagined two bodies pulled apart to leave a space between them. Did they then still touch? Of course not; therefore the vacuum exists.) But he strongly resisted the idea in a metaphysical sense, believing that the void left behind created a space for political dissension.
Boyle and Huygens were not much interested in such sophistry. However, another of Huygens’s experiments with his own air pump introduced a new confusion. During the winter of 1661–62, Huygens placed a Torricellian tube of water (a filled glass tube inverted and placed in a larger open container of water) inside the chamber of his vacuum apparatus. As the air was evacuated from the chamber, he noticed that bubbles began to form in the tube, and as they rose to the top the water was gradually pushed out. This observation could be explained by Boyle’s theory, which predicted that the level of the water in the tube would gradually fall to the level in the larger container. Alternatively, it could more simply be due to the release of air naturally dissolved in the water. Huygens therefore repeated the experiment using water that had been purged of air by prolonged suction. This time, the tube of water remained full as the air in the chamber around it was pumped out. A tube of mercury, on the other hand, did behave in accordance with Boyle’s theory. The ‘anomalous suspension’, as Huygens termed it, of the water column appeared to suggest that it might contain within it some additional, unknown ‘subtle fluid’ responsible for the unexpected behaviour.
Experiments with the air pump were always challenging, and Boyle had run across various ‘hydrostatical paradoxes’ before as he refined his experimental setup. But when he tried to replicate Huygens’s experiment, he was unable to get the same result. The apparent fact of the new ‘discovery’, and his respect for Huygens, the only other person who had been able to construct a functioning air pump, led Boyle to fear that Huygens now had the superior apparatus and technique. This latest development seemed to put Boyle’s law in jeopardy and his scientific credibility on trial. Boyle, who, along with Oldenburg, had done so much to crystallize the rules for dealing with disputed claims in science, now found himself with a personal opportunity to see how well the rules worked in practice.
There was no falling out on this occasion, but the matter was resolved to both men’s satisfaction only when Huygens visited the Royal Society again in 1663. With Huygens personally present, and even then with Hooke’s involvement too, Boyle was finally able to repeat the Dutchman’s work with success. The fact that both men fully understood at this relatively early date the importance of being able to replicate experimental results in order to establish scientific facts must surely have helped to overcome any tensions between them. Both could now agree that water behaved differently from mercury in the Torricellian tube, even if they could not explain why. (Later, Newton was able to explain ‘anomalous suspension’ as an effect of capillary action.)
This outbreak of scientific concord may well have been the most pleasing aspect of the visit for Huygens. But there was an official accolade awaiting him too, as, on 22 June 1663 (OS), just one month after the admission of its first fellows, Huygens himself was elected to the Royal Society.*