Article by Ed Snowdon

Whether you are a researcher gathering data, or a hobbyist taking photos from your back garden, astronomy has always required a certain amount of good luck. Instruments can be uncooperative, data can be lost or damaged, and of course there’s the ever-present threat of bad weather. This is nothing new, and the long history of astronomy is full of examples of things not quite going according to plan for even the most brilliant observers. However, few people can claim to have been dealt quite as bad a hand as one particular French astronomer who lived in the mid-late 1700s.

Guillaume Joseph Hyacinthe Jean-Baptiste Le Gentil de la Galaisière was born on the 12th of September 1725 in the small town of Coutances in Normandy. Despite early ambitions to join the Church, he eventually came to Paris to study astronomy under César-François Cassini de Thury, grandson of the famous Italian astronomer Giovanni Cassini. Le Gentil went on to join the French Royal Academy of Sciences and began a distinguished career, discovering several objects that would later be included in the Messier catalogue.

M32 was discovered by Le Gentil in 1749, it is a dwarf galaxy and a satellite to the Andromeda galaxy. Image credit: wikisky

The early 1760s was a very exciting time for the astronomers of Europe. A transit of Venus was due in 1761, which would also be only the second ever observed transit since the phenomenon was discovered in 1639. Edmond Halley (building on a theory by Scottish mathematician James Gregory) had proposed in 1716 that by observing and timing the transit from different locations around the world, the distance between the Earth and the Sun could be calculated more precisely than had ever been done before. Halley sadly died in 1742, but an international collaboration was put together to make the required observations. This was a truly enormous scientific project, especially by 18th century standards. Dozens of astronomers were dispatched to places as far-flung as Canada, Norway, the Cape of Good Hope, and Tahiti. Several participants died on their expeditions, and many of the others faced huge difficulties (one French astronomer, for example, had to be escorted to his assigned location in Siberia by armed soldiers due to attacks by superstitious locals). Guillaume Le Gentil for his part, was to make observations from the city of Pondicherry, a French colony on the south-east coast of India. He set sail from France on the 26th of March 1760.

He would not return for over eleven years.

A map of Le Gentil’s route to India, showing the various places he visited on his travels. Image credit: Helen Sawyer Hogg with further annotation by Apostolos Christou

The first leg of Le Gentil’s voyage seems to have passed without incident, although his later writings about his travels suggest he may have gotten pretty seasick. His ship took the long route around Africa and arrived at Isle de France (modern-day Mauritius) on the 10th of July 1760. It was here that the bad news began. Le Gentil learned that war had broken out in India between the French and British, and coupled with the oncoming monsoon season it was going to be very difficult to find any ships travelling from Isle de France to Pondicherry. To make matters even worse, Le Gentil contracted dysentery while he waited out the summer on the island, meaning even if he could find a ship he still might be too ill to travel. By February 1761, Le Gentil had practically given up and was making preparations to go and make his observations from a nearby island instead. Fortunately, on the 19th of February a ship arrived from France carrying an urgent message for the authorities in India. This persuaded the governor of Isle de France to send a ship to Pondicherry as quickly as possible, and Le Gentil was able to secure a place on board. Despite repeated assurances that the ship should be fast enough to get to his destination in time for the transit on the 6th of June, monsoon winds blew them completely off course. The final blow came when the ship managed to limp into harbour in Mahé, and the locals informed Le Gentil that Pondicherry had been captured by the British. Bitterly disappointed, Le Gentil agreed to return to Isle de France. They were still at sea when the day of the transit came; Le Gentil tried his best to make his observations regardless, but being unsure of his exact position and unable to steady his instruments on a rocking ship, any data he did manage to gather were effectively useless.

There was still some hope, however. Transits of Venus occur in pairs a few years apart, meaning that the next transit would happen in 1769, but the one after that would not occur until 1874. Le Gentil decided to simply stay in Isle de France and wait out the next 8 years before attempting his observations again. To pass the time, he undertook several expeditions around the Indian Ocean. This included spending time mapping the east coast of Madagascar and studying the customs of the indigenous people living there, as well as studying wind patterns and monsoons. By 1765, Le Gentil was beginning to plan ahead for the second transit. Given that the 1769 transit would also occur during monsoon season, he decided he would have a better chance of observing the transit elsewhere. He settled on Manila in the Philippines as his new destination and set sail on a Spanish ship on the 1st of May 1766, leaving Isle de France for what he expected to be the last time.

He arrived in Manila in August of 1766, and spent some time accurately determining the latitude and longitude of the city on behalf of the Spanish authorities. Le Gentil seems to have very much enjoyed his time in the Philippines, writing “Manila is without contradiction one of the most beautiful countries in all the seas of Asia”. He made several friends among the local church officials, whom he would remain in contact with for the rest of his life. However, one man who definitely did not befriend Le Gentil was the governor-general of the Philippines. Before leaving Isle de France, Le Gentil had written back to France asking for help in getting letters of recommendation from the king of Spain to make the journey to Manila easier. When these letters arrived about a year later and were presented to the governor, he decided that they had arrived too quickly and therefore must be forgeries. The governor continued to treat Le Gentil with hostility and suspicion throughout his stay in Manila. Eventually, afraid that the governor might try to arrest him or worse, Le Gentil resolved to finally head to Pondicherry after all, and set sail back to India in 1768.

On the 27th of March 1768, a full eight years and one day since he left France, Guillaume Le Gentil arrived in Pondicherry (which the British had given back to France in 1763). He stayed there for two years, passing the time by studying native Indian astronomical techniques from the local Tamil people. He was allowed to build a small observatory on top of a ruined fort that had been damaged in the recent war. The ruins were also being used as a powder store, making Le Gentil possibly the only astronomer to ever make observations while sitting above several tons of gunpowder.

A reproduction of Le Gentil’s original drawing of his observatory (the building to the right of the flag pole). Image credit: Helen Sawyer Hogg

Le Gentil made many observations in the months leading up to the second transit, often accompanied by the governor of French India, whom he had befriended. According to Le Gentil’s own writings, observing conditions were excellent for the whole of May. Even on the night before the transit, he writes “the weather was still of this same fineness the day before. At nine o’clock in the evening I observed with M. Law who was using the achromatic telescope, the emersion of the first satellite of Jupiter which we saw very well”. Le Gentil woke early on the morning of the 3rd of June, ready to finally make the observations that he had spent nearly a decade and travelled halfway around the world to see.

It was cloudy that day.

Le Gentil summed up his feelings in his writing: “That is the fate which often awaits astronomers. I had gone more than ten thousand leagues; it seemed that I had crossed such a great expanse of seas, exiling myself from my native land, only to be the spectator of a fatal cloud which came to place itself before the sun at the precise moment of my observation, to carry off from me the fruits of my pains and of my fatigues. […] At length I was more than two weeks in a singular dejection and almost did not have the courage to take up my pen and continue my journal; and several times it fell from my hands, when the moment came to report to France the fate of my operations”. To add insult to injury, while the skies in Pondicherry were overcast, the weather in Manila that day had been perfectly clear.

Even this wasn’t the end of Le Gentil’s bad luck. While observing comets in September, he fell ill with a fever and by December had also contracted Dysentery. He finally left Pondicherry by ship on the 1st of March 1770, but was too ill to continue all the way to Europe and so found himself once again stranded at Isle de France, where he was finally able to recover his health. The commissioner on the island attempted to persuade Le Gentil to go to Tahiti for some further work, but he was understandably not keen on the idea by this point. He departed Isle de France in November, only to be caught in a hurricane in early December which damaged the ship to the point that they were forced to return yet again. Le Gentil writes: “We arrived there January 1 1771, to the great astonishment of all the colony, since the last thing they expected to see was us again”.

After more months of delay, Le Gentil was finally able to board a Spanish warship bound for Cadiz. Still, the journey was not easy and they were plagued with constant storms. Le Gentil was understandably anxious about all this, writing: “My sole worry in the midst of all these storms was the fear of being forced to see again the Isle de France, that island which I had nevertheless loved very much; but the sight of it had become unbearable to me”. Fortunately this was a much sturdier ship with an experienced crew, and they successfully made it through the bad weather to reach the Cape of Good Hope. The remaining leg of the voyage passed more smoothly (excepting a tense encounter with a British warship that was resolved diplomatically via the gift of a large sack of potatoes), and Le Gentil arrived in Spain on the 1st of August. After resting for a while in Cadiz, he made his final return to France overland. He finally re-entered his native country on the 8th of October, describing it thusly: “The eighth, at sunrise, we passed the crest of the Pyrenees, and at last I set foot on France at nine o’clock in the morning, after eleven years, six months, and thirteen days of absence”. However, there was just one final bit of bad luck waiting for Le Gentil upon his repatriation.

He was dead.

At least, that’s what his colleagues, creditors, and heirs all believed. Le Gentil arrived in Paris to find that his wife had remarried, and his relatives had enthusiastically plundered his estate. Even worse, his position at the Academy of Sciences (on whose behalf he’d undertaken this whole journey) had been given away to someone else. He never did get all of his money back (or his wife for that matter), but he was at least able to get his position at the Academy restored after a few months of petitioning. On a happier note, Le Gentil was eventually able to settle down, remarrying to a second wife with whom he had a beloved daughter. He spent much of his later years writing memoirs and papers of his expedition. He eventually died of an acute illness in Paris in 1792 at the age of 67, sparing him from much of the horrors of the French Revolution. Jean-Dominique de Cassini, the son of Le Gentil’s old teacher, wrote in his eulogy: “In his sea voyages he had contracted a little unsociability and brusqueness, but without rudeness; because to his intimates he was gay, pleasant and agreeable. […] He was a good fellow member of the Academy, a very good husband, and an excellent father”.

The most recent transits of Venus occurred in 2004 and 2012, and the next one won’t be until 2117. Hopefully future astronomers hoping to observe it will have an easier time than monsieur Le Gentil.


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