After the bitterly cold winter of 1788–9, and the subsequent drought that sent food prices through the roof, the old regime was overthrown through the French Revolution.
Cassini III had passed away three years previously, and it was the fourth-generation Cassini, Jean-Dominique, who was now close to completing the project. The survey was finished; all that remained was to publish the last fifteen maps. But the revolutionaries had other ideas–the new French Republic was under threat from neighbouring countries, and the need for maps was great. The head of the French Army’s engineering corps was also afraid that Cassini’s maps might result in sensitive information falling into enemy hands: ‘His map may be good or bad. If it is good, it will have to be banned, and if bad, it would hardly deserve favour.’ The National Convention decided to confiscate the map and hand it over to the Dépôt de la Guerre. Cassini was heartbroken. ‘They took it away from me,’ he wrote in his memoirs, ‘before it was entirely finished and before I had added the final touches to it.’ In 1794, Cassini was thrown in prison, only just managing to avoid losing his head to the guillotine before being released a few months later.
Technically, the map was never completed. The Dépôt de la Guerre allowed the project to lie fallow right up until 1804, when Napoleon Bonaparte, at this time at war with practically all of Europe, wrote to his military chief of staff: ‘If we had stuck to making maps on Cassini’s scale, we should already have the whole Rhine frontier. […] All I asked was that the Cassini map be completed.’ The Dépôt de la Guerre appointed twelve engravers to update the old copper plates and print new editions, and the last maps of Brittany were finally published in 1815. But by then, sixty-seven years after it was started, the map was out of date, and Cassini’s map was archived–not because a new king ordered that this be done, nor because the map failed to correspond to the ideology of a new republic, but because of what a modern nation quite rightly needs: an updated survey.
THE ORDNANCE SURVEY | The Napoleonic Wars also influenced the production of maps on the other side of the Channel. The British had established their mapping agency, the Ordnance Survey, in 1791, and began publishing maps from 1801. But in 1810, when Great Britain had been at war with France for almost twenty years, the publication of maps was deemed too great a threat to national security. Public maps were withdrawn from the market the following year, and would not become available again until Napoleon was well and truly defeated at the Battle of Waterloo in 1815.
Just thirty years earlier, the triangulation of Great Britain had been started as a result of a French invitation–in typical French fashion, this was made both as an insult to and in recognition of the British. In 1783, Cassini de Thury wrote to Joseph Banks, president of the Royal Society, stating that it would be interesting to know the exact difference in longitudes and latitudes between Europe’s most renowned observatories–Paris and Greenwich. Although the latitudes and longitudes were regarded as well-known, Thury wrote, it was still the case that the English and French calculations were not concurrent to a worrying degree. Particularly doubtful, Thury believed, was Greenwich’s position–and the solution was to perform a joint British–French triangulation across the Channel.
The British had started discussing the triangulation of their territory not long after the French had started to triangulate theirs. With support from the Royal Society, cartographer John Adams had measured a baseline in 1681, but just seven years later was complaining about the lack of support to continue the work, and all later mapping had been carried out using the old methods, with significant inaccuracies as a result.
Nevertheless, many members of the Royal Society were irritated by Thury’s invitation. How dare the French imply that the British were unsure about where their own observatory was located! Nevil Maskelyne, British Astronomer Royal at Greenwich, didn’t bother to dignify Thury’s suggestion with a response, but an old notebook shows that he cared enough to initiate his own secret experiment to calculate the distance between the two observatories.
Banks, on the other hand, was not so easily offended, and took the request to William Roy, an officer who had been on many military surveys, and who saw in the letter a golden opportunity to remedy the British mapping situation and finally get started with triangulation. That same summer, Roy had measured a baseline on his own initiative–the plan being to start the triangulation of London and the surrounding areas on his own.
Two thousand freshly minted pounds from George III enabled Roy to start a new and accurate triangulation of the area where Heathrow Airport is situated today–Hounslow Heath. But the summer of 1784 proved to be an exceptionally wet one–the wooden measuring rods shrank and expanded so much in the rain that they eventually became useless. A friend of Roy’s suggested that they might be able to obtain new glass measuring rods, and on 2 August, two months after they had started work with the wooden rods, they started over again. At the end of the month, the result was clear: 27,404.7 feet. ‘There never has been so great a proportion of the surface of the Earth measured with so much care & accuracy,’ Roy declared.
In September 1784, Cassini de Thury’s death resulted in his son, Jean-Dominique, taking over the French side of the project, but this would not be started until three years later, as it took the British this long to create the world’s most sophisticated theodolite.
In July 1787 the British started triangulating from Roy’s baseline on Hounslow Heath, sighting Banstead Church, Windsor Castle, Hanger Hill Tower and St Ann’s Hill in Chertsey, Hundred Acres, Norwood, Greenwich and Severndroog Castle. Eventually, they had created a network of triangles across Sussex and Kent to Botley Hill and Wrotham Hill, but the work progressed slowly. ‘General Roy is at some distance from London… but from what I hear, he has not reached very far yet,’ wrote a Briton to the French, and it was decided that both sides would head straight to the coast to start the collaboration.
Cassini and Roy met in Dover in September, and agreed that ‘white lights [with] extraordinary brilliance’ should be attached to the surveying flagstaffs to illuminate them through the thick fog that often hung over the Channel. Over the next three weeks, the French and British alternately lit signals and conducted observations that criss-crossed the Channel, between Dover Castle and the windmill at Fairlight Head on England’s south coast, and the Montlambert hilltop, Cap Blanc Nez, Dunkirk tower and the Notre-Dame church in Calais, all on the northern coast of France.
By the middle of October the measurements were completed, and Britain and France had been trigonometrically bonded. But what about Greenwich’s position? Maskelyne’s secret experiment to measure the distance between the two observatories had reached a longitudinal distance of 9 minutes and 20 seconds–Roy calculated the difference to 9 minutes and 19 seconds, and this largely agreed with the results of the French astronomers.
Some view the establishment of the Ordnance Survey in 1791 as being due to the British fear of France after the revolution–the need for good maps with which to defend the nation. ‘But the truth is not quite so simple,’ writes Rachel Hewitt in Map of a Nation: A Biography of the Ordnance Survey. Hewitt believes that ‘the Paris–Greenwich triangulation had laid the groundwork’ at a time when the Anglo-French relationship was more benign, and that George III ‘was an enthusiastic sponsor of Enlightenment and nationalistic endeavours […] and the mapping project pricked his interest.’ The Ordnance Survey was also indebted to the Society of Arts’ attempt ‘to make accurate Maps of Districts, till the whole Island is regularly surveyed’ and the many map-makers’ widespread acceptance of triangulation as the most accurate technique for large areas.
THE FLAGSTAFF | The town of Kongsvinger is situated along one of the few easily accessible roads between Norway and Sweden–that which runs from Oslo to Magnor and Eda, and from there into the gently rolling landscape of Värmland. Construction of the fortifications here was started in 1673 to secure the ferry landing on the River Glomma and the surrounding areas against Swedish troops. In the summer
of 1779, the two lieutenants Johan Jacob Rick and Ditlev Wibe arrive in Kongsvinger to put the town on the map. ‘The survey shall hereafter be supported by astronomically determined points […]. Lieutenants Rick and Wibe have therefore been trained by Professor Bugge in Copenhagen and shall take over this work,’ wrote General von Huth.
Using the cutting-edge new instruments they have brought with them from Copenhagen–two surveyor’s transits used to measure the angle from one point to another, two pendulum clocks and two seven-foot-long telescopes–the lieutenants perform the necessary astronomical calculations to find out the exact latitude and longitude of their current position. The fortress’s flagstaff will have the honour of marking Norway’s prime meridian. The light summer nights make celestial observations difficult, but they manage to calculate a latitude for the flagstaff of around 60 degrees, 12 minutes and 11 seconds north based on observations of the clearest stars and the movements of the Sun. On 14 June, they observe the time of a solar eclipse in order to determine the longitude. Throughout the autumn, however, they struggle with bad weather, which prevents them from observing a single lunar eclipse of the stars or eclipse of Jupiter’s moons, and they therefore never obtain a good enough basis on which to establish an astronomically calculated prime meridian. Their observations and the baseline they established through the use of smoke signals and by taking measurements across the ice do, however, provide them with enough information to undertake further observations across the country. And now they must move northwards.
Equipped with a large officers’ tent, two smaller tents for assistants, four canteens, four metal pots with lids, four saddlebags containing provisions and a pass that entitles them to free transport with the local farmers, the lieutenants set out on their journey north. From 1779 to 1784, during the summer months, Rick and Wibe measure the latitudes and longitudes of a broad range of mountaintops and church spires as they construct an increasing network of triangles along the border, erecting small observatories where no appropriate premises in which to set up their instruments can be found.
During the winters, they make observations at Halden, Oslo, Kristiansand and Copenhagen to find the latitude and longitude values at each of these locations, and establish new baselines on frozen lakes to avoid minor errors becoming magnified as they work. In January 1781, they measure a six-kilometre-long line across the Osensjøen lake, in March the same year a seven-kilometre-long line across Mjøsa, the following year a seven-kilometre-long line at Femunden and in 1785 a final line at Jonsvatnet, south-east of Trondheim. Their assignment was complete–a strategic area of Norway had been mapped using the most accurate and most scientific method of the age.
Danish cartographer Christian Jochum Pontoppidan was the first person to use this new information when he published a new map of southern Norway in the same year that Rick and Wibe completed their work. In the introduction to his Geographisk Oplysning til Cartet over det sydlige Norge i trende Afdeelinger (Geographical Information to Accompany the Map of Southern Norway in Three Sections), he writes that ‘the survey, which was undertaken by Captain Rick and Lieutenant Wiibe in the years 1780, 81, 82, 83 and 84 using trigonometric operations, and which stretched from Kongsvinger to Egge church in the bailiwick of Inderøen,’ has been one of the ‘most distinguished aids’ he has ever used. He also used von Langen’s forest survey and the border survey from 1752 to 1759. The result is an effective and accurate map, which would become the new template for maps of southern Norway. Andreas Bureus’s map from 1626, and its presentation of Norway as envisaged by someone outside the country, had finally been superseded.
THE TRANSIT OF VENUS | Rick and Wibe suggest to Professor Bugge that the next stage of their project should be the mapping of the Norwegian coast from Trondheim towards the south, and in 1785 a royal decree determines ‘that the Norwegian coast and all islands and rocks beyond the same from Haltenø–the outermost point of the northern reaches of Trondheim–and to Fredrikshald shall be surveyed, since good sea charts are so sorely lacking.’ The Danish-Norwegian shipping industry has boomed due to the country’s neutrality during the American War of Independence, in which France, the Netherlands, Spain and German states have participated–so the need for good nautical charts is great.
Bugge prepares a detailed set of instructions for the surveyors: ‘When Trondheim’s meridian becomes the prime meridian in the surveying of the entire Norwegian coast, to which all the longitudes of stations along the coast shall refer, it will be of the utmost importance to accurately establish Trondheim’s longitude, which as yet remains unknown.’
Bugge is well aware of the problem. He visited Trondheim twenty-four years earlier to observe a transit of Venus–a phenomenon in which Venus is seen passing across the surface of the Sun. As early as the year 1716, British astronomer Edmond Halley had calculated that transits of Venus would take place in 1761 and 1769, and then not occur again until over 100 years later. At this time, knowledge of the distances between the Earth and the Sun and Venus respectively, and therefore the size of the solar system, comprised little more than vague assumptions, and so Halley recommended that the transit of Venus should be observed from many different locations around the world. The various times at which the planet crept across the face of the Sun would provide the figures necessary for calculating the distances, and they would also be able to be used to work out longitude values. On the day before the first transit, 6 June, 200 astronomers from various countries had travelled to the edges of the world, including Siberia, Madagascar and Saint Helena, taking their instruments with them. The transit of Venus that took place in 1761 was the world’s first collaborative scientific project.
But Venus behaved strangely; the planet did not simply move across the Sun’s surface as anticipated. The observers noticed that it became oval in shape, before becoming round again when it had moved a good way towards the centre of the solar disc. It was also difficult to know when the transit had actually started, and this is evident in the results from Trondheim. Bugge obtained results that differed from those of another observer stationed in the same place to undertake the same task–their recorded times at which Venus was first visible against the Sun’s surface differed by two whole minutes. At the time, many believed the phenomenon offered proof that Venus had an atmosphere, but today scientists believe that this was due to disturbances in the atmosphere of the Earth.
Ten years after Carl Joachim Pontoppidan published the map Det Sydlige Norge (southern Norway), he also published the map Det Nordlige Norge (northern Norway). In his Geographical Explanation of the Map of Northern Norway in Two Parts, published in 1795, he wrote: ‘The mainland of the county of Nordland consists of a narrow stretch, where the distance between the border and the coast varies, from 6, 8, 12 to 16 geographical mil. Finnmark’s greatest distance from the border in the north to the sound between Jelmsøen and the mainland is 35 mil.’
The next transit of Venus was estimated to take place eight years later, on 3 June 1769, and Copenhagen seized the opportunity to attract the most distinguished experts to the city. A letter was dispatched to Hungarian priest Maximilian Hell, the royal imperial astronomer in Vienna, inviting him to travel to Vardø and observe the transit of Venus from there. As a Jesuit, Hell would not usually be permitted to enter Denmark-Norway, but given the prestigious nature of the project, the law was set aside on this occasion. King Christian VII would pay all Hell’s expenses.
Hell and a colleague set out from Vienna on 28 April 1768, and arrived in Vardø seven months later. Once there, they set up an observatory as an extension of the bailiff’s house. Luck was with them on the day–the skies cleared just before Venus entered the Sun’s disc, before clouding over for the next six hours, and then clearing once again just in time for Hell to observe and record Venus’s exit.
Hell compared his results with those the British captain James Cook had obtained in Tahiti in the Pacific, as well as the measurements taken at Hudson Bay in Canada by British mathematician Willia
m Wales, and calculated the Earth’s distance from the Sun to be 151.7 million kilometres–not far off the true distance of 149.6 million kilometres.
Back home in Vienna, Hell drew four maps: one of southern Norway, one of the northern counties, one of the county of Finnmark and one of the municipality of Vardø. The map of Vardø was printed and published, but only test prints were made of the maps of southern Norway and Finnmark–the map of the northern counties was never even engraved, because the copper engraver Hell worked with died. When he received the test prints for review, Gerhard Schøning created a list of place names that had been spelled incorrectly, but believed that the map of southern Norway, based on Wangensteen’s map, represented a significant step foward, and that the map of Finnmark was also a clear improvement on previous maps. ‘That the locations of many places are more correctly described here than previously, all the places to which P: Hell himself has been, is clearly evident,’ wrote Schøning. Today, we know nothing about either of the test prints–only the map of Vardø has survived, and so it is difficult to say whether Hell’s maps helped to improve any later maps of Norway.
MAPPING THE COAST | Rick and Wibe settle down in Trondheim to calculate the city’s longitude value, converting a building just south of the city’s cathedral into an astronomical observatory. In the summer of 1785 they are provided with a transit instrument–a large telescope specially created for observing the transits of stars–and mount it on a pine column inside the observatory. But despite the column being driven two metres into the ground, the winter’s bitterly cold temperatures cause the column to move, and the observers have to accept the telescope’s position when it finally stabilises slightly to one side of the meridian through the cathedral they are currently working to establish.
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