In the closing years of the eighteenth century, France and Britain enjoyed a period of external peace that their scientific communities put to good use by finding an objective common to the leading academic institutions: the Académie royale des sciences in France, and the Royal Society in England. This was not an entirely new concept; the novelty was that the objective would be brought about by teams from each side working outside their own borders. It was part of both nations' long-running search for a means of establishing longitudes on land and at sea. The specific objective, however, was confined to establishing the accurate difference in longitude between the meridian of Greenwich Observatory and that of the Observatoire de Paris. Previous astronomical measurements, derived from the times of certain eclipses or transits as recorded at each observatory, were acknowledged to be inaccurate.
During the 1770s two methods of finding longitude, which required the observer to know the difference between local time and the time at his principal meridian, were nearing success: the ‘lunar distance method’ and the ‘chronometer method’. A third method of establishing differences of longitude had already been proved on land, but not hitherto between two countries separated by water; this was by triangulation. The great map of France, which had been generated under the direction of the Cassini family, successive heads of the Paris Observatory since shortly after its foundation in 1667, had established longitudes across France, with outreach observations in Flanders and at Vienna, encouraging César-François Cassini de Thury (1714–84), third of the dynasty and known for convenience as Cassini III, to dream of a global network.
Given this achievement, it was not surprising that Cassini de Thury was the first to express the idea that the ultimate goal of geodesy would be to extend the French network to encircle the planet. Yet he regretted that a lesser but more essential distance had not been established, that between the meridians of Greenwich and Paris. Their proximity should make this triangulation a straightfoward exercise and at the same time make the result valuable to other geodesists. Cassini could even envisage in practice an achievement with as yet no European equivalent, and it was in this sense that in October 1783 the Académie royale des sciences presented his proposal as a Mémoire which was forwarded through diplomatic channels to King George III:
Mémoire sur la jonction de Douvres à Londres par M.Cassini de Thury, Directeur de l'Observatoire Royal, de la Société Royale de Londres, &. &. &:
Il est intéressant pour le progrès de l'astronomie que l'on connoisse exactement la différence de Longitude et de Latitude des deux plus fameux observatoires de l'Europe et quoique les observations astronomiques faites depuis un siècle offrent un moien assez exact pour parvenir à cette recherche il paroit cependant que l'on n'est pas d'accord sur la longitude de Greenwich à onze secondes près et sur sa latitude à quinze secondes.
L'on a reconnu par les opérations trigonométriques exécutées en France au Nord et au Pérou que sur l'étendue d'un degré du méridien ou de 57 000 toises l'on se trompoit a peine de dix toises ce qui a été prouvé par des Bases mesurées a l'extrémité de suites de triangles, ainsi sur la distance de Douvres à Londres qui est de 49800 toises ou environ on pourroit se tromper de 120 toises qui répondent à onze secondes de longitude.
M. Cassini a déjà publié dans le Livre de la méridienne vérifiée les opérations par lesquelles l'on a déterminé la distance de Calais à la grosse tour de Douvres de 18241 toises par un 1er triangle et de 18243 par un 2e triangle: on aurait cette distance avec une plus grande exactitude en observant les angles conclus à Douvres qui sont fort aigus.
M. Cassini ne doute point que ce projet ne soit agréé d'un souverain qui aime les sciences et qui non content des découvertes du célèbre Cook vient d'ordonner un second voyage autour du monde et que la Société Royale ne charge un de ses membres de l'exécuter et dans le cas ou ses occupations l'empêcheroit de s'y livrer qu'elle ne permît à Mr Cassini de s'en charger. L'honneur qu'elle lui a fait de l'associer à un corps aussi respectable seroit un titre pour lui accorder sa confiance.
M. Cassini a découvert des côtes de France plusieurs objets sur les côtes d'Angleterre qui seront visibles de Douvres et sur cette première Base on etabliroit une suite de quelques triangles jusqu'à Londres dont le nombre et la grandeur dépendroit de l'exposition des objets compris dans la direction de Douvres à Londres.
Pour joindre les triangles de la Méridienne à ceux de Snellius en Hollande en 1762, il a prolongé la perpendiculaire de Paris jusqu'à Vienne en Autriche. La branche qui s'étendra jusqu'à Londres sera la troisième et formera la jonction des deux plus belles Villes de l'Europe.1
Although this somewhat presumptuous offer to ‘interfere’ in English science inevitably ruffled feathers in the Royal Society, the President, Sir Joseph Banks (1743–1820),
considered the operation as doing honour to our scientific character, & benefit to astronomy, & I have no doubt but that we have people enough in the RS able & willing to undertake it. If his Majesty will permit me to ask the advice of the Council of the RS, I shall be enabled, I hope, in a short time to give in a plan, estimate & names of proper people for his Majesty's information.2King George authorized Banks to proceed, providing £2000 for the undertaking and the purchase of instruments, notably a large theodolite built to a new design by Jesse Ramsden (1735–1800), a leading London instrument maker.3
By passing Cassini de Thury's memoir to Banks rather than to Nevil Maskelyne (1732–1811), his Astronomer Royal, the King effectively ensured that the triangulation would be undertaken by his Royal Engineers under General William Roy (1726–1790). Roy was probably the author of an unsigned document ‘On the advantages that are likely to arise from the operations on Hounslow Heath’4 in which, like Cassini, he too foresaw the interconnection of bases in other countries, leading to the general dimensions and true figure of the Earth.
Banks sent an informal copy of the memoir to Charles Blagden (1748–1820) (pictured in the frontispiece to this issue), his friend and at the time Secretary of the Royal Society5. Blagden was not impressed, as he wrote to Banks on 18 October:
M. Cassini's memoir does not show the workmanship of a very able hand. With regard to the longitude it is possible that no astronomical method might determine it so exactly as a suite of triangles, though I believe that it is not strictly the case, and that occultations of fixed stars by the moon, carefully observed at both places, would give their difference of longitude nearer than any actual measurement. But what does he mean by the latitude? Can he possibly suppose that our instruments at Greenwich will not determine this as well as any they have in the Observatory at Paris? Observations across such a tract of sea as lies between the nearest coasts of England and France, are subject to many sources of inaccuracy, which must always distract from the confidence to be placed in them. … All this is weak, and indeed frequent conversations with M. Cassini the elder while I was in Paris convinced me that he is a man of very modest intellects, supported principally by the stock of representation acquired to the family by his illustrious grandfather. The younger Cassini, however, seems to possess more acuteness, and has, I think, good ideas upon some subjects, such as the accuracy of instruments, but he is not the person who offers to conduct this business, and probably could not even be spared from the observatory to attend his father, yet the scheme must be executed, but certainly among ourselves, without foreign assistance, notwithstanding the difficulties, which I foresee will attend the choice of persons just now.6
About one year later, Banks passed Cassini's memoir to Nevil Maskelyne for comment. Maskelyne was particularly irritated by Cassini's reference to the disagreement between the French and British values for latitude and longitude between their respective observatories, but he must have known earlier about its content. Before the memoir officially reached him, he secretly sent his assistant Joseph Lindley by post-chaise and sailing ship to Paris and back in September–October 1785, carrying seven watches by John Arnold (1736?–1799), including two ‘box watches’ or chronometers. This exercise yielded a difference of longitude of 9′ 19.8″, close to the values yielded by the astronomical method and subsequently by Roy's triangulation.7
On 11 May Banks responded (in French) to Cassini's memoir, informing him that the King had authorized the Royal Society to direct the provision of a baseline supporting a triangulation network to Dover, where it would join the French network, in order to link the two observatories. It was necessary to construct new instruments, there being none sufficiently accurate made hitherto in England. A baseline would be established near London in preparation for the triangulation, which would commence in the following summer under the direction of General Roy.8
Cassini de Thury, seeing matters progressing in the desired direction, lost no time in replying to Banks, urging that during the summer Roy should send his engineers to establish the points of intervisibility on both coasts. Cassini himself had sighted several windmills on the English coast, and he hoped that from one of these it would be possible to see both Calais and Dover.9
Cassini could certainly rejoice that his proposal was to be adopted, because at that time the geodetic method was not universally favoured. Triangulation had reigned supreme in France ever since Jean Picard (1620–1682) had employed it to measure 1° of the meridian between Paris and Amiens in 1669–70. The combination of geodesy and astronomy had produced results benefiting the Cassini family since Gian-Domenico Cassini (1625–1712), Cassini I, had been recruited by Jean–Baptiste Colbert (1619–83), principal minister to Louis XIV, to direct his new Observatory, in operation from 1672. For his grandson, Cassini de Thury, the year 1783 marked the achievement of the triangulation required for his Carte particulière et générale de la France begun in 1747 and was the occasion of the publication of La Description de la France, the account of those operations. The copy sent to the Royal Society therefore served to summarize the experience gained by the Cassini family since the first concept of a general map of France in 1681 and the establishment of the Paris Méridienne,10 as well as to justify and support the new project. In the Description Cassini referred to the 19 bases measured across the kingdom and claimed that the difference between two triangulated bases seldom exceeded two toises.11 The results matched those achieved by the best astronomical observations and confirmed the excellence of trigonometry for the most accurate geographical work. The opposite view could, however, be upheld, and indeed was argued by Maskelyne and Blagden.
Rapid exchanges of correspondence testify to the concern taken by each side in its preparations. However, the British decision to converse in French led to some misunderstanding in Paris; Banks's letter of 14 June proposed that in future each side should write in its own language. Choosing his words with elegance and diplomacy, Banks dealt with certain points such as which country's name would take precedence—a matter that depended on the choice of a communicating language; he recalled the scientific stake, and expressed hopes for success to both parties. These sentiments did not exclude an afterthought perhaps inspired by Blagden's severe criticism of Cassini's memoir, and we may read between the lines his implied message: ‘You have certainly priority in directing the work but should your engagements oblige you to pass the work over to someone else we would not see that as inconvenient.’ This suggests that Banks and Blagden both recognized the proven geodetic competence and the suitability in this field of Cassini de Thury's son Jean-Dominique Cassini (1748–1845), Cassini IV (figure 1). Matters were resolved more swiftly than they might have imagined, because the elder Cassini was struck down with smallpox and he died in September 1784. Cassini IV inherited the Directorship of the Observatory and took over the Anglo-French project.12
Even before his official appointment, Cassini IV expressed his willingness to cooperate, sending his letter through the hands of Count de Montmorin, Minister of Foreign Affairs.13 All this was doubtless to Blagden's satisfaction and augured well for the future, although for the moment Banks could not respond to Cassini's urgency to proceed with the geodetic stations on the southern coast of England. General Roy and the new director of the Observatory would thus be the principal characters in the Anglo-French project. Roy had his own reasons for wanting to be involved; these were linked both with his own declining state of health and his wish to take advantage of an enterprise whose outcome was dear to his heart. He set about planning his procedures and obtaining instruments and apparatus. Cassini IV, who had been well educated and had travelled to Newfoundland, had seen his own universe expand beyond land-based cartography. Now he had to wait for the English to authorize action.
Roy spent the summer months of 1784 laying a baseline across five miles of Hounslow Heath, a desolate and uncultivated area to the southwest of London. After various trials with deal rods (their lengths affected by humidity) and then with glass tubes (accurate but difficult to manipulate), Roy adopted a steel chain made by Ramsden. The base measurement was completed by August. Thereafter Roy awaited delivery of his new instrument.
The years 1785 and 1786 passed with no word from London. Only in 1787 did the project begin to take shape. Blagden and Roy, both upset by delays in the delivery of the new theodolite, took advantage of Cassini's expressed desire for Foreign Membership of the Royal Society to establish personal relationships before the cross-Channel triangulation. Blagden, whose French was both excellent and elegant, summarized the history and present situation in a letter to Cassini on 22 May 1787, explaining the delay in obtaining Ramsden's instrument and hoping that it would soon be ready. Meanwhile, arrangements could be made for the actual cross-Channel part of the junction. He noted that many years had passed since Cassini de Thury had marked the signal points on the French coast, and the Académie's help might be needed to locate their exact positions.14 To handle English sensitivities, Blagden was determined to set out exactly each party's role in the operations, but his tone was warm and it was clear that he welcomed Cassini's promotion to his father's position. In similar vein, on 29 June he reiterated the various roles and warned that no progress was likely before the autumn. He then departed on a visit to the west of England; on his return he found to his surprise that the theodolite had been delivered and that Roy was already at work in the field.
Ramsden's theodolite was a remarkable work of precision engineering, for such large instruments could not simply be scaled up from the small theodolites normally used in the field (figure 2). Although Ramsden had been pressing the advantages of circular instruments over quadrants, this was the first order that had come his way, and the task of designing such a novel instrument must have taken many hours with pencil and paper, then with wooden models. Its horizontal circle, 3 feet in diameter, was divided to 10 minutes of arc, and by means of two micrometer microscopes could be read to 1 second of arc. Two achromatic telescopes were provided, each of 36 inches focal length, and 2½ inches aperture, with various eyepieces, and for night work the circle could be illuminated through the horizontal axis of rotation. The theodolite came with its ancillary tackle of stand, steps, stools, pulleys, ropes, tent and canopy, weighing as much again as the instrument. The whole assemblage was transported in a specially adapted canopied four-wheeled carriage drawn by two, and sometimes four, horses.
Crossing the water
It had been obvious, as the summer passed with no sight of the theodolite, that Roy would not complete his triangulation from Hounslow to Dover before the season ended. However, by 21 August everything had changed for the better. Blagden conferred with Roy, who agreed to suspend his triangulation at Wrotham Hill, near Maidstone, Kent, and to hasten to Dover to set up the cross-Channel junction while Blagden invited Cassini to proceed to the French coast.15
Thus informed, Cassini dealt with the political niceties. The supervision was taken over by the Baron de Breteuil, Secretary of State to the King, who announced that King Louis XVI, an enthusiast for geography, was taking a great interest. On 9 June the astronomer and geodesist Pierre François André Méchain (1744–1804) was named as Cassini's assistant and the sum of 7000 livres was assigned to cover expenses, including Cassini's request for the purchase of a repeating circle 1 foot in diameter. This was the new measuring instrument that had been conceived by Jean Charles de Borda (1733–99) and constructed by the instrument-maker Étienne Lenoir (1744–1832) (figure 3). Each observation was repeated on different sectors of the divided circle, and by averaging these values the instrument's accuracy matched that given by single observations on Ramsden's 3-foot instrument.
Its appearance was perhaps an unexpected but happy consequence of Ramsden's delay in delivering his theodolite, which so upset Roy. Cassini remarked that despite the short time for preparation, their instrument delivered results as accurate as those of the English instrument.16 Perhaps, given the origin of the project in 1783, we should understand that the recent delivery of Borda's repeating circle came at exactly the right moment to be of such advantageous service to the French team. Commenting after several years’ experience, Legendre emphasized the originality of its principle and its ease of use.17
The French team was now complete and all matters settled. The decision to suspend the triangulation at Wrotham Hill had been agreed, and in his letter of 7 September Roy notified Cassini of their proposed meeting, with the final arrangements:
I am extremely glad to find that the proposition which I made for transferring the operation directly to the coast, meets with your approbation and that of your colleague. It is indeed very doubtful whether I shall be able to compleat the whole series this season; but the two coasts being connected the remaining intermediate Triangles situated between the first and second Base may be executed at any other more convenient time.
I will not fail, Sir, to have the honour of meeting you at Dover by the 20th of this month, where in concert with Dr Blagden (who will afterwards pass to Calais) we will settle the plan of co-operation for the Junction of the two coasts. I can assure you, Sir, that I rejoice in this opportunity of forming an acquaintance with two Gentlemen of such distinguished Talents, & I have the honour to be Sir,
A new base of 28 535 feet (just under 5 miles; 8.698 km) was measured, running northwest from the coast across Romney Marsh, from which eight triangles were set out along the coast to Dover; here two principal points, one at Dover Castle, the other on high ground at Fairlight Down, near Hastings, were intervisible with three points on the French coast: Calais, Cap Blanc-Nez and Montlambert (figure 4). These five points carried four triangles; the French later set out six more triangles, extending north to Dunkerque. Two manuscript documents provide detailed information on proceedings: ‘Voyage sur les côtes de Calais et de Douvres pour la jonction des Observatoires de Paris et de Greenwich’ and the proceedings of the operations presented to the Académie des sciences at the Easter 1788 session under the title ‘De la jonction des Observatoires de Paris et de Greenwich et précis des travaux géographiques exécutés en France qui y ont donné lieu’.19
Cassini left Paris on 17 September and with Méchain and Legendre arrived at Calais on 20 September. There they welcomed the astronomer Giuseppe Piazzi (1746–1826) from Palermo, who had been permitted to join the French team. The crossing planned for 23 September was delayed by extremely bad weather, but the gales swept away certain prejudices in demonstrating the care and attention that the English sailors bestowed on their lady passengers, as Cassini tells us.20
The voyagers barely had time to recover before Roy came to welcome them. A favourable impression was immediate.21 Roy invited everyone to repair to the castle that dominated the town. Cassini found it ‘antique and half-ruined’ but this was a passing detail in comparison with the spectacle that greeted them, namely the first sight of the great theodolite.22
The technical business began at 10 o'clock the next morning.23 The plan of campaign involved the emplacement of light signals on the French side, at the same points used by Cassini de Thury for his map of France. These were set on high ground or on prominent buildings, namely the tower at Dunkerque, the church of Notre-Dame at Calais, Cap Blanc Nez, and Montlambert, the hilltop behind Boulogne. This method was not new but had become more effective with the use of Bengal lights,24 whose brief but powerful flares were visible during the daytime as well as at night. It was agreed that the timing should allow reciprocal observations each quarter of an hour, always in the same sequence, starting at 6.30 a.m. at Calais.
The three Frenchmen, accompanied by Blagden, set out on the return voyage on 25 September. Roy provided sufficient lights and reflectors for both parties, and over the following days the French team set these up as agreed. Duties were shared out, with Blagden stationed at Calais, Legendre at Dunkerque, Méchain at Montlambert, and Cassini at Cap Blanc Nez. Roy's angles would converge on this headland, the closest point to England, and on that at Montlambert.25
On 29 September the measurement of angles began. The season was already far advanced and meteorological conditions were unfavourable for a project that involved the sighting of distant signals. Mists and fog would certainly have delayed operations if the method proposed by the English team had been less effective. In the event, the powerful Bengal lights could be seen at considerable distances.
As time passed, the observations multiplied. On days when even the Bengal lights were invisible, the teams turned to other tasks such as levelling to establish heights of the various observing stations above the sea level at low tide. Despite some dreadful weather during the 17 days on which the signals were fired, Roy's team had seen almost all the French signals. Cassini's men had seen most of the English signals, perhaps even sighting on one occasion a light from 40 miles away despite the intervening sea mist. Cassini was confident that success was within their grasp.
On 17 October the collaboration ended. Everyone gathered at Calais to bid farewell to Blagden on his return to England. But neither team had entirely finished: Roy needed to bring his chain of triangles to Dover, and the French surveyors were not content to rely on the earlier triangulation, which had served for mapping the region of which sheets 5 (St Omer) and 22 (Boulogne) had been published in 1758. Cassini realized that the guard-house at Cap Blanc Nez, which had served for his father's signal, had been rebuilt in a different location and that position of the original station was now lost. Cassini returned to Dunkerque and, encouraged by the efficiency of the Borda circle, established a fresh network of triangles, back to the Paris Méridienne, continuing, despite further appalling weather, until it was completed on 12 November. On 30 April 1789 Cassini, Legendre and Méchain were elected as Foreign Members of the Royal Society.
Roy set about closing the gap in triangulation between the coast and Wrotham Hill. He dealt with five of the remaining seven stations before increasingly stormy weather made observations from steeples or hilltops positively dangerous, bringing operations to a close on 2 November. The theodolite was returned to Ramsden for sundry repairs and modifications. The 1788 season was Roy's last in the field. His remaining time was spent on calculations and writing up his account of the exercise, delivering his report in instalments to the assembled members of the Royal Society during the early months of 1790. In failing health, he departed to the warmer climes of Lisbon, leaving his assistant Isaac Dalby (1744–1824) to work on the proofs of his paper. He returned to London in April 1790 and, having all but completed the paper, died on 1 July that year.
It would be difficult to imagine two scientific instruments destined for the same purpose more unlike in size and practice than Ramsden's theodolite and Borda's repeating circle. The circle had proved itself during the cross-Channel operation, its handiness enabling it to make the final measurements under the most difficult weather conditions. Under the same conditions, Roy, with his cumbrous and weighty theodolite, had been unable to complete his chain of observations to Dover, requiring a further year in the field to achieve his objective.
The results: publications and their immediate translations
An account of the works undertaken on the French side was published in 1790 as Exposé des opérations faites en France en 1787 pour la jonction des observatoires de Paris et de Greenwich par MM. Cassini, Méchain et Legendre, membres de l'Académie Royale des Sciences (figure 5). The subtitle of the work testified to the importance of the instrument employed throughout the operation: Description et usage d'un instrument propre à donner la mesure des angles, à la précision d'une seconde. Taking into account concepts relating to the flattening of the Earth, the calculations produced two results to define the separation of the meridians of Greenwich and Paris: 9′ 20.6″ and 9′ 18.6″. This latter, considered the most probable, was very close to that of 9′ 18.8″ produced by Roy. In his preface, Cassini explained that his account could have appeared in 1789 but he had decided to await publication of the English results. Despite the unfavourable political situation he hoped to find an interested readership.26
Roy had submitted his proposal to King George III, who had funded the project. His manuscript with its drawings is now in the British Library, bound in MS Kings 270, ff. 4–5. This proposal and the full report of his work were read over several meetings of the Royal Society and then published in Philosophical Transactions.27 Roy was seriously unwell by the time he wrote up his full report. He sent the text for printing when he returned in April and worked through the proofs, making corrections, but errors and infelicities remained.28
The articles in Philosophical Transactions were intended for the Society's Fellows, but such was the general interest that the articles and their plates were republished in 1799,29 with a lengthy preface by Roy's successor in the field, William Mudge (1762–1820), and Dalby, summarizing the history of the project. A ‘preface’ by Charles Blagden explained the reasons for the errors in Roy's text and the care taken by Dalby to make sure that the values now agreed with the original computations. Roy's description of the setting-out of the Hounslow base, and his account of the triangulation, published in Philosophical Transactions in 1785 and 1790, were translated into French by the civil engineer Gaspard-Clair-François-Marie, Baron Riche de Prony (1755–1839), who chanced to have been in England while the survey was in progress, as Description des opérations faites en Angleterre pour déterminer les positions respectives des observatoires de Greenwich et de Paris (1791).
The importance of future collaboration
Without waiting for their publication, and carried away by the enthusiasm generated by the repeating circle, Cassini and Borda began comparing the results obtained by the circle with similar observations made with the mural quadrant at the Observatory. They concluded that the use of the circle for observing the meridian altitude of stars was as promising as its use in geodesy. The Journal des Sçavans, whose publication had been less disrupted by political events than the Mémoires of the Académie, published in 1791 an account by Cassini of these trials under the title ‘Mémoire sur l'application du cercle entier à l'observation des hauteurs méridiennes des astres’. It announced the arrival of a new instrument that gave a fresh momentum to French geodesy.
In the years between 1792 and 1799 Delambre and Méchain remeasured an extended Méridienne, spanning Dunkerque to Barcelona, confident that Borda's new circle would deliver a more reliable value. When the post-Revolutionary government decided to replace the ancient multiplicity of local measures by a national standard, the new metre was set at one ten-millionth of a meridian quadrant of the globe as calculated from this extended arc. In addition to this glorious episode, many other studies were planned or undertaken throughout the Empire, although the results did not always reach the height of the ambitions expressed in those troubled times. From 1802 there were proposals for a new general map of France, which would remedy the inadequacies of the Cassini map. This project was put in hand in 1817.
It was also in 1817 that the French and English scientists resumed the relations that, to their regret, had been interrupted by events. Joseph Banks was still ready to play his part. The same ambition to measure the flattening of the Earth now held sway among a larger group, including Jean-Baptiste Biot (1774–1862). Referring to the operations undertaken during the first half of the eighteenth century, Biot declared that matters had remained static for 50 years, but now, with astronomical instruments becoming more perfect, and the methods of observation more general and accurate, it was hoped to resolve remaining uncertainties relating to the flattening of the Earth. The Académie, inheritor of these great works, determined to resume them with every means of ensuring their success.
In France, the success of the first junction of the meridians of Paris and Greenwich by trigonometry had justified this new enthusiasm. In England, the political situation between the two countries worsened after 1789, with renewed fears of invasion on the southern coast, where Roy's triangulation had laid bare the inaccuracies of the old maps. The Triangulation Survey was revived under William Mudge, assisted by Isaac Dalby. They carried the triangulation westwards, commencing what was to become a national cartographic survey, henceforth the Ordnance Survey. Precision was all, and in 1823–25 François Arago and Henry Kater remeasured the separation between the Paris and Greenwich observatories.
We greatly appreciate the support and assistance we have received from the librarians at the Paris Observatoire and at the Royal Society. We are also grateful to Suzanne Débarbat, Danielle Fauque and Anthony Turner for their helpful comments and suggestions while this paper was in preparation.
One contribution of 3 to a Special Feature on ‘Franco-British interactions in science in the seventeenth and eighteenth centuries’.
- Received July 7, 2008.
- Accepted July 25, 2008.
- © 2008 The Royal Society