Contents

About the Book

About the Author

Also by Andrea Wulf

Title Page

Dedication

Epigraph

Author’s Note

Maps

Dramatis Personae

Prologue: The Gauntlet

PART I: Transit 1761

1. Call to Action

2. The French Are First

3. Britain Enters the Race

4. To Siberia

5. Getting Ready For Venus

6. Day of Transit, 6 June 1761

7. How Far to the Sun?

PART II: Transit 1769

8. A Second Chance

9. Russia Enters the Race

10. The Most Daring Voyage of All

11. Scandinavia or the Land of the Midnight Sun

12. The North American Continent

13. Racing to the Four Corners of the Globe

14. Day of Transit, 3 June 1769

15. After the Transit

Epilogue: A New Dawn

Picture Section

List of Observers 1761

List of Observers 1769

Selected Bibliography, Sources and Abbreviations

Suggested Further Reading

Picture Credits

Acknowledgements

Notes

Index

Copyright

About the Book

On two days in 1761 and 1769, astronomers cast their eyes to the skies to witness a rare sight: Venus travelling across the face of the sun. The two transits were to become the most significant astronomical events in scientific history, as by recording the path of Venus and comparing results, these men hoped to calculate the dimensions of our solar system – one of the most pressing quests of the Enlightenment. For the first time, scientists from across the globe came together – despite wars, savage weather and bitter rivalries – to measure the universe.

Chasing Venus recounts the extraordinary expeditions that set off on a race around the world to observe the transits, and the triumphs and misfortunes that befell them. Overcoming enormous obstacles to make their observations, these astronomers were pioneers: helping to discover new lands, animal and plant species, and to map the world as we know it today.

Featuring a cast of some of the most recognisable names in world history – Edmond Halley, Benjamin Frankin, James Cook, Mason and Dixon, and Catherine the Great, among others – Chasing Venus is a thrilling adventure story, a tale of obsession and personal tragedy, and an inspiring account of Enlightenment science and discovery.

About the Author

ANDREA WULF was born in India and moved to Germany as a child. She trained as a design historian at the Royal College of Art and is the author of The Brother Gardeners (longlisted for the 2008 Samuel Johnson prize and winner of the 2010 American Horticultural Society Book Award) and The Founding Gardeners, and is the co-author of This Other Eden: Seven Great Gardens and 300 Years of English History (with Emma Gieben-Gamal). She has written for the New York Times, the Guardian, the Wall Street Journal, the Los Angeles Times and many others. She lives in London.

Also by Andrea Wulf

The Founding Gardeners:

How the Revolutionary Generation

Created an American Eden

The Brother Gardeners:

Botany, Empire and the Birth of an Obsession

This Other Eden: Seven Great Gardens and

300 Years of English History

(with Emma Gieben-Gamal)

To Regan

‘The planet Venus drawn from her seclusion, modestly delineating on the sun, without disguise, her real magnitude, whilst her disc, at other times SO lovely, is here obscured in melancholy gloom’

Jeremiah Horrocks

‘We must show that we are better, and that science has done more to humankind than divine or sufficient grace’

Denis Diderot

Author’s Note

In the interests of clarity and consistency I have retained in the maps and in the text certain place names of the viewing stations as the transit astronomers referred to them in the eighteenth century. Instead of the modern ‘Puducherry’, for example, I have used ‘Pondicherry’; ‘Bencoolen’ instead of ‘Bengkulu’; ‘Madras’ instead of ‘Chennai’; ‘Constantinople’ instead of ‘Istanbul’. In some rare cases where the old names have fallen completely out of use, I have taken the modern name: ‘Jakarta’ instead of ‘Batavia’, for example. Please refer to the ‘List of Observers’ for a full list of the historic and contemporary names.

Dramatis Personae

Transit 1761

Britain

France

Sweden

Russia

America

Transit 1769

Britain

France

Sweden

Russia

America

Denmark

Prologue

The Gauntlet

The Ancient Babylonians called her Ishtar, to the Greeks she was Aphrodite and to the Romans Venus – goddess of love, fertility, and beauty. She is the brightest star in the night sky and visible even on a clear day. Some saw her as the harbinger of morning and evening, of new seasons or portentous times. She reigns as the ‘Morning Star’ or the ‘Bringer of Light’ for 260 days, and then disappears to rise again as the ‘Evening Star’ and the ‘Bringer of Dawn’.

Venus has inspired people for centuries, but in the 1760s astronomers believed that the planet held the answer to one of the biggest questions in science – she was the key to understanding the size of the solar system.

In 1716 British astronomer Edmond Halley published a ten-page essay¹ which called upon scientists to unite in a project spanning the entire globe – one that would change the world of science forever. On 6 June 1761, Halley predicted, Venus would traverse the face of the sun – for a few hours the bright star would appear as a perfectly black circle. He believed that measuring the exact time and duration of this rare celestial encounter would provide the data that astronomers needed in order to calculate the distance between the earth and the sun.

The only problem was that the so-called transit of Venus is one of the rarest predictable astronomical events. Transits always arrive in pairs – eight years apart – but with an interval of more than a century before they are then seen again.^fn1 Only once before, Halley said, in 1639, had an astronomer called Jeremiah Horrocks observed the event. The next pair would occur in 1761 and 1769 – and then again in 1874 and 1882.

Halley was sixty years old when he wrote his essay and knew that he would not live to see the transit (unless he reached the age of 104), but he wanted to ensure that the next generation would be fully prepared. Writing in the journal of the Royal Society, the most important scientific institution in Britain, Halley explained exactly why the event was so important, what these ‘young Astronomers’² had to do, and where they should view it. By choosing to write in Latin, the international language of science, he hoped to increase the chances of astronomers from across Europe acting upon his idea. The more people he reached, the greater the chance of success. It was essential, Halley explained, that several people at different locations across the globe should measure the rare heavenly rendezvous at the same time. It was not enough to see Venus’s march from Europe alone; astronomers would have to travel to remote locations in both the northern and southern hemispheres to be as far apart as possible. And only if they combined these results – the northern viewings being the counterpart to the southern observations – could they achieve what had hitherto been almost unimaginable: a precise mathematical understanding of the dimensions of the solar system, the holy grail of astronomy.

Halley’s request would be answered when hundreds of astronomers joined in the transit project. They came together in the spirit of the Enlightenment. The race to observe and measure the transit of Venus was a pivotal moment in a new era – one in which man tried to understand nature through the application of reason.

This was a century in which science was worshipped, and myth at last conquered by rational thought. Man began to order the world according to these new principles. The Frenchman Denis Diderot, for example, was amassing all available knowledge for his monumental Encyclopédie. The Swedish botanist Carl Linnaeus classified plants according to their sexual organs, and in 1751 Samuel Johnson imposed order upon language when he had compiled the first English dictionary. As new inventions such as microscopes and telescopes opened up previously unknown worlds, scientists were able to zoom in on the minutiae of life and gaze into infinity. Robert Hooke had peered through his microscope to produce detailed engravings of magnified seeds, fleas and worms – he was the first to call the basic unit of biological life a ‘cell’. In the North American colonies Benjamin Franklin was experimenting with electricity and lightning rods, controlling what until then had been regarded as manifestations of divine fury. Slowly the workings of nature became clearer. Comets were no longer viewed as portents of God’s wrath but, as Halley had shown, predictable celestial occurrences. In 1755 the German philosopher Immanuel Kant suggested that the universe was much larger than his contemporaries believed and that it consisted of uncountable and gigantic ‘Welteninseln’³ – ‘cosmic islands’, or galaxies.

Humankind believed it was marching along a trajectory of progress. Scientific societies were founded in London, Paris, Stockholm, St Petersburg, and in the North American colonies in Philadelphia, to explore and exchange this new-found knowledge. Observation, enquiry and experimentation were the building blocks of this new understanding of the world. With progress as the leading light of the century, every generation envied the next. Whereas the Renaissance had looked back upon the past as the Golden Age, the Enlightenment looked firmly to the future.

Halley’s idea of using the transit of Venus as a tool to measure the heavens was born out of developments in astronomy over the previous century. Until the early seventeenth century man had observed the sky with his naked eye, but technology was slowly catching up with the reach of his ambitions and theories. Astronomy had changed from a science which mapped stars to one which sought to understand the motion of planetary bodies. In the early sixteenth century Nicolaus Copernicus had proposed the revolutionary idea of the solar system with the sun rather than the earth at the centre, and the other planets moving around it – a model that had been expanded and verified by Galileo Galilei and Johannes Kepler in the early seventeenth century. But it was Isaac Newton’s groundbreaking Principia, in 1687, which had defined the underlying universal laws of motion and gravity that ruled all and everything. As astronomers gazed at the stars, they were no longer in search of God but of the laws governing the universe.

By the time Halley called upon his fellow astronomers to view the transit of Venus, the universe was regarded as running like a divinely created clockwork according to laws which humankind had only to comprehend and compute. The position and movements of planets were no longer seen as ordained arbitrarily by God but as ordered and predictable, and based on natural laws. But man still lacked the knowledge of the actual size of the solar system – an essential piece of the celestial jigsaw puzzle.

Understanding the dimensions of the heavens had ‘always been a principle⁴ object of astronomical inquiry’, the American astronomer and Harvard professor John Winthrop said in the transit decade. Already in the early seventeenth century Kepler had discovered that by knowing how long it took for a planet to orbit the sun, the relative distance between the sun and the planet could be calculated (the longer it took a planet to orbit the sun, the further away it was).^fn2 From this he had been able to work out the distance between the earth and the sun relative to the other planets – a unit of measurement that became the basis for calculating comparative distances in the universe.^fn3 Astronomers knew, for example, that the distance between the earth and Jupiter was five times that of the distance between the earth and the sun. The only problem was that no one had as yet been able to quantify that distance in more specific terms.

A 1759 depiction of the Ptolemaic and Tychonic planetary systems

Eighteenth-century astronomers had a map of the solar system, but no idea of its true size. Without knowing how far the earth really was from the sun, such a map was all but useless. Venus, so Halley believed, was the key to unlocking this secret. As the brightest star in the sky, Venus became the perfect metaphor for the light of reason that would illuminate this new world and extinguish the last vestiges of the Dark Ages.

Unlike most astronomers whose lives were ruled by the repetitive labour of their nightly observations, Halley had embarked on a far more exciting career – which was probably why he could envisage a global army of swashbuckling astronomers. Not only had he spent one and a half hours in a diving bell⁵ submerged almost twenty metres deep in the Thames, he had also undertaken three expeditions⁶ to the South Atlantic as the first European to map the southern night sky with a telescope. Halley ‘talks, swears, and drinks⁷ brandy like a sea captain’, a colleague said, but he was also one of the most inspired scientists of his age. He had predicted the return of the eponymous Halley’s Comet, produced a map of the southern stars and convinced Isaac Newton⁸ to publish his Principia.

Knowing that he would not be alive to orchestrate the global cooperation to view Venus’s transit – a fact that Halley lamented ‘even on his death-bed’⁹ whilst holding a glass of wine¹⁰ in his hand – all he could do was to place his trust in future generations and hope that they would remember his instructions half a century hence. ‘Indeed I could wish¹¹ that many observations of this same phenomenon might be taken by different persons at separate places’, he wrote. ‘I recommend it therefore¹², again and again, to those curious Astronomers who (when I am dead) will have an opportunity of observing these things’.

Halley was asking his future disciples to embark on a project that was bigger and more visionary than any scientific endeavour previously undertaken. The dangerous voyages to remote outposts would take many months, possibly even years. Astronomers would be risking their lives for a celestial event that would last just six hours and be visible only if weather conditions permitted it. The transit would be so short that even the brief appearance of clouds or rain would make accurate observations difficult or even impossible.

Edmond Halley’s drawing of Venus entering and exiting the sun during the transit

In preparation for it, scientists would need to secure funding for the best telescopes and instruments as well as for travel, accommodation and salaries. They would have to convince their respective monarchs and governments to support their individual efforts and would have to coordinate their own observations with those from other countries. Nations locked in battle would have to work together in the name of science for the first time ever. From many dozens of locations, hundreds of astronomers would have to point their telescopes to the sky at exactly the same moment in order to see Venus’s progress across the burning disc of the sun.

And perhaps even more challenging still – though less exhilarating – they must then share their findings. Each observer would have to add his or her observations to the pool of international data. No single result would be of any use without the others. In order to calculate the distance between the sun and the earth, astronomers would have to compare the figures and consolidate the different data into one definitive result. Timings obtained across the world using a disparate range of clocks and telescopes would somehow have to be standardised and made comparable.

The transit of Venus observations were to be the most ambitious scientific project that had ever been planned – an extraordinary undertaking in an era when a letter posted in Philadelphia took two to three months to reach London, and when the journey from London to Newcastle¹³ was six days. It took a great leap of the imagination to propose that astronomers should travel thousands of miles into the wildernesses far north and south, laden with instruments weighing more than half a ton.

Their idea of calculating exact distances in space was a bold concept too, considering that clocks were still not accurate enough to measure longitude precisely, and there was as yet no standardised measurement on Earth: an English mile was a different length from a mile in German-speaking countries – which also varied between northern Germany and Austria. A ‘mil’ in Sweden was more than ten kilometres, in Norway more than eleven, while a French league could be three kilometres but also as much as four and a half. In France alone there were 2,000 different units of measurement¹⁴ – which varied even between neighbouring villages. In light of this, the idea of merging hundreds of observations taken by astronomers across the world to find one common value seemed outrageously ambitious.

The scientists, who were to leave their observatories in the learned centres of Europe to view Venus from remote outposts of the known world, made for strange adventurers too. At first sight they might not have looked like heroic explorers, but as they chased Venus across the globe they did so with extraordinary intrepidity, bravery and ingenuity. On 6 June 1761 and again on 3 June 1769, several hundred astronomers all over the world pointed their telescopes towards the sky to see Venus travel across the sun. They ignored religious, national and economic differences to unite in what was the first global scientific project. This is their story.

^fn1 Because the orbits of Venus and earth have different inclinations, Venus usually passes above or below the sun (and therefore cannot be seen from the earth). The periods between the pairs of transits alternate between 105 and 122 years. The first transit of Venus observed by an astronomer was on 4 December 1639. The next transits were on 6 June 1761, 3 June 1769, 9 December 1874 and 6 December 1882. There was no transit in the twentieth century but two in the twenty-first – on 8 June 2004 and 6 June 2012. It will be another 105 years until the transit of 11 December 2117.

^fn2 This was Kepler’s third law which said that ‘the square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit’. In simpler terms it means that Kepler had provided a mathematical formula which could be used to calculate the relative distances in the solar system by using the radius of a planet and the time it took to orbit the sun.

^fn3 The distance between the earth and the sun became the base unit for measuring distances in the universe – it is 1 AU (1 Astronomical Unit). As such the distance between Jupiter and the sun was 5 AU and between Earth and Venus 0.28 AU.

Part 1

Transit 1761

1

Call to Action

BY THE MID-EIGHTEENTH century, at the beginning of the transit decade, the commercial empires of the European countries stretched across the globe. International travel was possible along the established trade routes to distant destinations in the East and West Indies,^fn1 Africa and Brazil. Britain controlled much of the eastern seaboard of the North American continent as well as parts of India, some Caribbean islands and Sumatra in Indonesia. France counted among her possessions Canada and Louisiana as well as plantations in India, sugar-producing colonies such as Haiti and St Lucia, and some islands in the Indian Ocean, while the Dutch organised much of their East India trade from Jakarta and ports at Galle in Sri Lanka and the Cape of Good Hope in South Africa.

But voyagers would also face great dangers: since 1756 much of Europe had been embroiled in the Seven Years’ War. The political conditions made the transit expeditions perilous enterprises. As scientists from France, Britain, Sweden, Germany, Russia and elsewhere were planning their international cooperation, their armies were fighting bloody battles against each other in the forests of Saxony, on the coast of the Baltic Sea, in the wilderness of the Ohio valley and in India. Rival fleets criss-crossed the oceans from Guadeloupe to Mauritius, engaging in attacks as far away as Pondicherry and Manila but also closer to home in the Mediterranean and the Atlantic.

The war had its origins in the old European conflicts between the Hohenzollerns in Prussia and the Habsburgs in Austria, and in the ongoing imperial contest between Britain and the House of Bourbon which ruled France and Spain. Britain and Prussia were fighting against France who was allied with Russia, Austria and Sweden. Not only political power was at stake, but also trading and commercial ventures: possession of the North American colonies, of India, the slave trade in West Africa and the valuable sugar-producing islands of the West Indies. As Europeans expanded their world, so did their warfare. It was the first global war – tearing apart Europe and its colonial outposts across the world. It was amid these turbulent times that the astronomers would have to travel on their ambitious quest.

On 30 April 1760, seventy-two-year-old Joseph-Nicolas Delisle, the official astronomer to the French Navy,^fn2 walked to a meeting of the Académie¹ des Sciences in Paris. Every Wednesday, academicians who studied in the fields of mathematics and astronomy assembled there to discuss experiments, projects and current research. Delisle only had a short distance to travel. The Académie’s rooms were in the Louvre, about a mile across the Seine from his small observatory at the Hôtel de Cluny, the administrative centre of the Royal Navy. The streets were narrow but, as Benjamin Franklin remarked a few years later, ‘fit to walk’² and kept clean by daily sweeping. They were lined with large houses and busy with people on foot and in coaches. Men and women hawked their wares from stalls – everything from brooms to oysters and from eggs to cheese and fruit. Cobblers, knife grinders and pedlars shouted at the passers-by, offering their services. People ‘of all sorts³ & condition’ mingled here, one traveller noted in surprise – from pickpockets to a ‘Prince of Blood⁴’. It was, Franklin said, ‘a prodigious Mixture⁵ of Magnificence and Negligence’ – others were harsher and called it the ‘ugliest, beastly town⁶ in the universe’.

Delisle crossed the river by the Pont Neuf, a sturdy stone bridge famed as the haunt of performers, quacks and tooth-pullers. The bridge was to the city, one Parisian said, ‘what the heart⁷ was to the body: the centre of movement and circulation’. Turning left, Delisle faced the imposing facade of the Louvre at the next corner.

France at that time was ruled by Louis XV, a king who had succeeded to the throne in 1715 at the age of five. He adored astronomy, and regularly attended scientific demonstrations in Versailles, even allowing himself to become electrically charged. His great-grandfather Louis XIV had founded the Académie des Sciences⁸ in Paris in the previous century to promote science (and its practical uses) and the glory of his reign. Over the past century, academicians had met there to discuss a wide range of scientific subjects, from the study of insects and comets to practical inventions such as hydraulics to power the fountains in Versailles or pumps to clean harbours. The Académie was the most important scientific institution in the country and its members were the best scientists – to be elected as a ‘membre de l’Académie’⁹ was the greatest scientific honour and the academicians wore their title proudly like a badge of nobility.

The paper that Delisle was about to present would place the academicians at the nexus of the greatest scientific project that had ever been planned. He was going to ask his colleagues to take up the gauntlet thrown down by Edmond Halley forty-four years previously: to set in motion an international collaboration to observe the transit of Venus due to occur one year later, on 6 June 1761.

Halley¹⁰ had propounded the revolutionary idea that Venus’s transit could be used as a natural astronomical instrument – almost a celestial yardstick. If several people around the world were simultaneously to watch the entire transit from different places as far apart as possible, he explained, they would each see Venus traversing the sun along a slightly different track – dependent upon the observers’ locations in the northern or the southern hemispheres. Venus’s path would be shorter – or longer – across the sun according to each viewing station.

With the help of trigonometry, these different tracks (and the differences in the duration of Venus’s transit) could then be used to calculate the distance between the sun and the earth. It was an ingenious method because the passage did not have to be ‘measured’ but only timed – by noting the exact moment of Venus’s entry and exit of the disc of the sun. The only equipment the observers would need was a decent telescope with coloured or smoked lenses (to protect against the sun’s glare), and a reliable clock.

The different tracks of Venus across the sun as viewed from stations in the northern and southern hemispheres during the transits of 1761 and 1769. Locations in the south would experience the longer duration in 1761 and the shorter in 1769.

Since Halley’s call to action in 1716, astronomers had tried to find other ways of measuring the solar system. In the early 1750s French astronomers had attempted to calculate the distance between the moon and the earth with observations taken simultaneously from Cape Town and Berlin. By observing the moon from these two locations and with the help of triangulation, they had hoped to measure the heavens prior to the transit of Venus – but the results had not been accurate enough. For years Delisle¹¹ had believed that he could utilise Halley’s method for the more frequently occurring transits of Mercury – he and other astronomers had observed several of those – but he had eventually realised that Mercury was too close to the sun. Only Venus’s transit would provide the opportunity to make the calculation.

The task of coordinating the transit observations from many different places on the globe would demand a very particular sort of individual – one so tenacious, persistent and determined that he would be able to unite competitive astronomers and even warring nations. There was no one better suited than Delisle himself. He was an obsessive man, with little time for anything other than the pursuit of science, dedicating his life to the stars. Possessed of an encyclopaedic knowledge and a ferocious work ethic, he was one of the most respected astronomers in Europe. He had worked for twenty-two years in St Petersburg where he had introduced the study of astronomy to Russia, set up an observatory and trained astronomers. He had also turned his journey to Russia into a Grand Tour – not of art and architecture but of scientific men. In London, he had met the ageing Halley¹² in 1724 and discussed the transit of Venus. Now an elderly widower, Delisle was based in Paris and spent most of his time between the Collège de France, where he taught astronomy and lived, and his observatory at the Hôtel de Cluny just opposite.

Not only had Delisle devoted his own life to astronomy, but he also acted as hub for the exchange of information between other members of Europe’s scientific community. The volume of his correspondence with foreign astronomers was prodigious, though not everybody agreed with his operating methods. The Swedish ambassador in Paris had been so harried for scientific information without ever receiving anything back that he called Delisle ‘greedy’.¹³ The French astronomer had the reputation to ‘pester all and¹⁴ sundry’ for observations but to keep his own a secret. He was ‘a devouring gulf¹⁵ which yields back nothing’, Jérôme Lalande, one of Delisle’s former pupils, complained. Maybe Delisle¹⁶ was sometimes a bit parsimonious with his own results, but he certainly ‘devoured’ all the information he could about the transit and used his persuasive, if not obstinate, personality to rally the world behind this endeavour.

In the years leading up to the transit, Delisle had studied Halley’s¹⁷ astronomical tables, concluding that the British astronomer had been slightly wrong – not in his prediction or call to action but in his choice of the best locations from which to observe the transit. The success of the measurements would depend on making the right choices of viewing stations. As Delisle presented his plan and explained where Venus would appear, his fellow academicians were taken on an imaginary voyage around the world – from Pondicherry in India to Vardø in the Arctic Circle, from Peking to Paris. Halley had predicted that the transit as seen from Hudson Bay on the North American continent would be eighteen minutes shorter than in the East Indies, but, ‘I have found’,¹⁸ Delisle told his fellow academicians, ‘very different results from those of Mr Halley’. According to his own predictions, Delisle claimed that the transit would only be two minutes shorter in Hudson Bay – not enough to aid their calculations¹⁹ – and in any case most of it would occur during the night.

The greatest difference in timings could be achieved if locations in the northern and southern hemispheres would be paired up. Delisle suggested that Tobolsk in Siberia would be an ideal choice, as would the Cape of Good Hope – the length of duration of the transit as viewed from these positions would differ by more than eleven minutes. To make the selection easier, he also presented a map of the world – his so-called ‘mappemonde’.²⁰ Having originally trained to become a surveyor,²¹ Delisle had combined his map-making skills with his astronomical knowledge and produced a map that was shaded in different colours to show where the transit could best be seen. In the blue zone observers would only be able to see Venus entering the sun, in the parts of the world which were coloured yellow only the exit would be visible, but in the red area the entire transit could be seen.

As the scientists examined the map, they could immediately see the best locations, though it also became clear that many of these were far away and would be difficult to reach. The full transit would be visible in China, India and the East Indies as well as near the Arctic Circle, in northern Scandinavia and Russia – with the Siberian location experiencing the shortest transit and the East Indies the longest.

Delisle’s²² presentation to his colleagues at the Académie in Paris was part of a much wider campaign. He had printed his map and explanations of the transit to send them to his international contacts – more than 200 scientists and astronomers in Amsterdam, Basle, Florence, Vienna, Berlin, Constantinople, Stockholm, St Petersburg, and many cities in France.^{fn3 23} At the same time French newspapers advertised and described the map, bringing the discussion of the transit into the public domain. Delisle proved to be a worthy disciple of Halley. His mappemonde had been received by every able astronomer in Europe and published in several scientific journals. Delisle could think of nothing else – his apartments at the Collège de France in Paris became the control room of the project and the clearing house for all communications related to it.

Until Delisle asked his fellow astronomers to mount transit expeditions, most of them had lived lives that were an endless round of dull routine: spending cold nights under the open sky or engaging in complex computations.^fn4 Though they gazed into the universe day after day and night after night, their own world was rarely extended beyond the confines of their observatories. The only distraction, as one father suggested to his astronomer son, were ‘books of voyages’²⁵ because ‘travels would divert and improve’. The job description for the assistant astronomer at the Royal Observatory in Greenwich was depressingly honest: they were looking for men who were ‘indefatigable hard working²⁶ & above all obedient drudges’ – not exactly characteristics and requirements normally associated with globetrotting voyagers and heroic explorers.

A mappemonde from 1770. Delisle’s version would have had regions coloured to represent the visibility of the transit.

It was an audacious endeavour, and now, with his petitions sent and little more than a year left before the transit, it was time for Delisle to coordinate the observations and to decide who would be going where. As the commercial reach of the European countries extended across the globe, it made sense to use their existing colonial trade routes in order to travel to the more remote locations. Already Halley²⁷ had suggested exploiting the imperial possessions of each country, advising the English to travel to Hudson Bay and to India, the French to their plantation in Pondicherry and the Dutch to their trading port of Jakarta – and Delisle agreed.

For the astronomers the transits promised the possibility of scientific revelations and a new understanding of the universe, but they also knew that there were other opportunities presented by the project which they could use to their advantage. If the observers stationed across the world succeeded, the measurements they took would also help improve navigation – essential for any trading empire and naval power. For in tandem with growing empires and Enlightenment ideals, the eighteenth century also became the nursery of capitalism. As new import and export markets mushroomed all over the world, accurate navigation became a branch of science that brought wealth and power. This fact, Delisle was sure, would help convince monarchs and governments to fund at least some of the expeditions.

With the Dutch East Indies as the most distant location and one of the most important viewing stations in the world, Delisle wrote to an acquaintance and fellow astronomer at The Hague²⁸ in the Netherlands, asking about the possibility of conducting an observation from the Dutch colony. At the same time he continued to canvas support closer to home, begging the French Secretary of State and King Louis XV to pay for a French expedition to Jakarta, pretending that he already had the full cooperation²⁹ of the Dutch. The gamble didn’t quite pay off. Delisle’s acquaintance in The Hague had bad news, reporting that the Dutch were only willing to arrange passage for a French observer on a Dutch vessel, but that was all. The Netherlands were unwilling to sponsor any expeditions because ‘the usefulness of astronomy³⁰ to mankind was not sufficiently appreciated in Dutch society’, he noted despondently.

Delisle, however, had come up with a solution. As his mappemonde clearly showed, there were many places where one could observe Venus either entering or exiting the face of the sun. If astronomers used Halley’s method³¹ of ‘duration’ (which required the astronomers to see the entire path of Venus across the sun), only a few places across the world would be suitable – many of which, like Jakarta, were far away and difficult to reach. Delisle’s new strategy would allow observers to view either the entry or the exit times of Venus, rather than having to see the entire transit. According to Delisle, an observation of the entry or exit time at one location could be combined with another from a distant location – as long as they were taken in similar latitudes and the exact difference between the places in longitude and latitude was known. Astronomers would be able to merge the data after the transit and still calculate the distance between the earth and the sun.

With Delisle as the project’s prime mover, it was unsurprising that the French were the first to mount an expedition. On 26 March, five weeks before Delisle had dispatched his mappemonde across Europe, one of his former pupils acted on his plan and set sail from Brest,³² a port on the Atlantic coast of France, on his way to India.

Born in 1725 in a little town in Normandy to ‘a not very well-to-do³³ gentleman’, Guillaume Joseph Hyacinthe Jean-Baptiste Le Gentil de la Galaisière was the first in the race. He had originally pursued an ecclesiastical career in Paris before being distracted by the intellectual stimulation on offer in the metropolis. Once he had heard Delisle lecture on astronomy, Le Gentil³⁴ turned to science. Instead of praying or getting into ‘vain’ theological arguments,³⁵ he now preferred to observe the ‘heavens’.³⁶ He found work at the Royal Observatory in Paris and became a member of the French Académie des Sciences. Like Delisle, he had observed the transit of Mercury in 1753, but had quickly turned his attention to the more useful and rarer transit of Venus, writing about it and then offering to travel to Pondicherry³⁷ in India where the entire transit would be visible.

At the end of 1759, Le Gentil had received permission³⁸ to travel to Pondicherry. The combined might of science, politics, and economics – the president of the Académie in Paris, the French Secretary of State and the Controller-General of Finances – were convinced of the importance of the mission and had supported it fully. With promises from the French East India Company, who controlled the trading port at Pondicherry, to provide Le Gentil with passage on one of their vessels, his voyage had been organised within a few weeks. The Compagnie des Indes was, according to Le Gentil, ‘always zealous’³⁹ when it came to ‘useful’ projects.

Two other French astronomers were also keen to travel: Jean-Baptiste Chappe d’Auteroche and Alexandre-Gui Pingré, who like Le Gentil were also members of the French Académie. Both had volunteered with ‘great eagerness’⁴⁰ to accept an invitation from the Imperial Academy of Sciences in St Petersburg to travel to Tobolsk in Siberia. It had been decided to send the thirty-eight-year-old Chappe to Russia and the forty-eight-year-old Pingré⁴¹ to another destination, to be agreed upon in due course. Chappe had long been known to Delisle for his precise astronomical calculations and skilful observations and Pingré was one of the most respected astronomers in Paris. Both were regarded as ‘worthy’⁴² of the honour and the ‘perfect’ candidates for the appointment – or so at least the members of the Académie thought. They were certainly brilliant astronomers, but also corpulent and middle-aged – not exactly the epitome of daring adventurers. Nevertheless they were ready to face the dangers of the long voyages. France was prepared to chase Venus … but Britain was following close behind.

* * *

On 5 June 1760, five weeks after Delisle had presented his mappemonde at the Académie in Paris, the fellows of the British Royal Society made their way to Crane Court, a little cul-de-sac off Fleet Street in London, for their weekly meeting.⁴³ Wealthy fellows arrived in their own carriages, while others walked along the muddy streets or hailed one of the thousands of hackney coaches⁴⁴ that choked the narrow lanes. Some called for a sedan chair⁴⁵ to be carried quickly through the busy city by porters, who rushed so fast that they often knocked over pedestrians who failed to jump out of their way. They passed the glittering shopfronts on the Strand and Fleet Street. Here, tourists remarked, the shops were ‘made entirely of glass’⁴⁶ and ‘one shop jostles⁴⁷ another’. Behind the windows precious wares were displayed, a spectacle of objects that testified to Britain’s reach across the globe as well as to her manufacturing prowess. In the evening the flickering light of thousands of candles illuminated shiny silver teapots, political cartoons, new telescopes and heaps of delicate lace. Pyramids of pineapples and grapes competed with diamonds and other precious gems, enticing shoppers to empty their purses.

Every day Londoners were serenaded in the crowded streets⁴⁸ by an orchestra of voices and sounds that seemed never to stop – fiddlers playing at the street corners, chimes from the church towers and cries from the street vendors – even during the night they could hear the ‘Watchman’s hoarse Voice’⁴⁹ calling the time and the state of the weather.

When the fellows had climbed the stairs to their meeting room, they excitedly exchanged the latest scientific news and gossip. Their president sat in a large armchair at one end of the long table with a portrait of their royal patron, King George II, behind him, and a marble bust of former president Isaac Newton opposite. As always, it took a moment for all the fellows to settle on the benches and for the chatter to quieten down. Like the Académie in France, the Royal Society⁵⁰ was Britain’s most important scientific forum. Since its foundation in the 1660s ‘for the improvement of naturall⁵¹ knowledge by Experiment’, it had become the nexus of British scientific enquiry and Enlightenment thinking. At their weekly Thursday meetings the fellows heard about diving bells and botanical taxonomy, saw exploding dogs, ‘electrified’ people, and conducted sheep-to-man blood transfusions as well as learning about comets, fossils, and the latest pendulum clocks. Experiments were conducted, results discussed and letters were read that had been received from other scientifically minded people, friends and foreigners alike.

The headquarters of the Royal Society at Crane Court in London

On 5 June, once the attendance had been noted, one of the fellows stood up to read a letter that he had received from Paris, the ‘Memoire presented by Mr de⁵² Lisle to the Society’ and the ‘map of the world’ that depicted the locations from where to see ‘the approaching passage of Venus’. It would set in motion a chain of events which would preoccupy the Royal Society for more than a decade, for when the fellows had finished studying the mappemonde and the transit proposal, they took up Delisle’s suggestion enthusiastically.

Only two weeks later, it was decided that the Council of the Royal Society should choose observers and ‘proper places’⁵³ from which to view the transit of Venus. But with only a year left to reach the far-flung destinations – as well as having to organise funds, instruments, and employ astronomers – time was running out. The Council ‘unanimously’ chose⁵⁴ two locations: the remote island of St Helena in the South Atlantic Ocean, the most southerly territory under British control; and a site to be decided upon in the East Indies. The choice lay between Bencoolen (today’s Bengkula) on the island of Sumatra, which like St Helena was under the control of the British East India Company, or possibly Jakarta ‘if it were not attended⁵⁵ with uncertainty’, for it was a Dutch possession. In the East Indies the whole transit would be visible while St Helena would only be graced with the exit which, according to Delisle’s method, was good enough. The great advantage of St Helena was that it was in the southern hemisphere and therefore the perfect counterpart to viewing stations in the far north.

With the decision made there was a flurry⁵⁶ of activity. Some fellows were asked to estimate the expeditions’ expenses and to compile lists of the instruments that would be needed. Others were tasked with collecting information on weather conditions in St Helena and the East Indies. Good weather was essential – it would be pointless sending astronomers to the other end of the globe to gaze at a cloudy sky. Most importantly, a delegation was dispatched to enquire of the directors of the British East India Company ‘what assistance might⁵⁷ be expected from them’.

The Company’s involvement was vital. Founded more than 150 years previously as a cartel of merchants who pooled resources to create a monopoly in order to control the supply of goods to their advantage, the Company had gradually expanded. It consisted of a network of colonial outposts that laced the globe, competing with the East India companies of other European countries such as the Dutch or the French. With funds low and timing tight, it made sense to tap into the existing trading network of the empire. If the East India Company proved willing, the Royal Society hoped that astronomers could travel on their vessels, stay in the Company’s compounds, and generally make use of the existing infrastructure in these faraway locations.

On 3 July,⁵⁸ four weeks after they had read Delisle’s letter, the Royal Society’s Council reconvened to hear the results of the enquiries: the former governor of Bencoolen had provided the necessary information⁵⁹ on the climate there and the meeting with the directors of the East India Company had been a great success, one fellow reported. The directors agreed to do all ‘in their Power’⁶⁰ to assist the project. There would be no problem, they said, in arriving in St Helena in time. Though it was one of the remotest islands in the world, a lone speck of land in the middle of the South Atlantic, it was an important stopover where vessels replenished their food stores on the East India Company trading route. The voyage would take about three months and commercial sailings were scheduled within this time frame. It would be easy for an observer team to sail on an East Indiaman^fn5 and the directors were also happy to provide accommodation in St Helena (though the Royal Society would have to pay for the privilege).

Reaching the East Indies, however, would prove more difficult. There was no company vessel that would reach Bencoolen before 6 June 1761. The directors instead recommended that the Royal Society should contact the Dutch to arrange passage on a ship to their trading port Jakarta, ‘which (most likely)⁶¹ will arrive in time’. Meanwhile, the directors had also dispatched letters to their employees in India with instructions⁶² on how to observe the transit. After this report another fellow explained that the instruments⁶³ for the expeditions⁶⁴ could not be hired as they had hoped, but would have to be purchased.

Having jotted down all the likely expenses, the Royal Society calculated that they would need a budget of £685 to send an astronomer with an assistant to St Helena, and approximately double that for two observers to go to the East Indies. The cost of the St Helena expedition was almost seven times the yearly salary of the Astronomer Royal and far too much for the Royal Society’s small budget – therefore it was decided to write to the Treasury, pleading for funding. Although astronomers across Europe realised the collection of data would have to be a collaborative effort in order to succeed, they also knew that governments and monarchs would be more likely to finance these expeditions if they could be convinced of a national benefit. The Royal Society’s petition to the Treasury and king appealed to patriotism, and stressed that the honour of the nation should be upheld in this endeavour.

England, the fellows of the Royal Society claimed, had a duty to participate. Not only had the original idea for this project been that of an Englishman, ‘Dr Halley, his Majesty’s⁶⁵ late Astronomer Royal’, but the only man who had ever observed a transit of Venus before, had also been an English astronomer – Jeremiah Horrocks in 1639.^fn6 More than that, the French and other European nations were about to run away with the prize, the fellows emphasised, for they are ‘now sending proper⁶⁶ persons to proper places’. The more observations were made, the greater the advantages to science and by extension the participating nations. With the whole world looking to England, the fellows insisted, surely the Treasury would want to answer this ‘general Expectation’.⁶⁷ For the advancement of astronomy and the glory of the nation, they needed the funds to dispatch their own observers. The strategy worked, and on 14 July, less than two weeks after their petition was sent, the Royal Society received the news that King George II ‘had been graciously⁶⁸ pleased’ to grant the money.

On the same day, without any further ado, twenty-seven-year-old astronomer Nevil Maskelyne was appointed⁶⁹ as the principal observer of the expedition to St Helena. The unmarried Maskelyne^70fn77273have