As the world goes Venus-mad this week, spare a thought for the plucky astronomers sent to observe the transits of 6 June 1761 and 3 June 1769. Only two people had watched the previous transit in 1639 – the first ever observed – and astronomy had come a long way since then. Urged to make the most of this rare celestial event by English astronomer Edmond Halley, Britain, France and other nations organised expeditions to remote spots all over the globe. Some were famously successful. James Cook’s expedition to newly discovered Tahiti in 1769 was blessed with perfect conditions: “not a Clowd was to be seen the whole day and the Air was perfectly clear”. Not one to do things by halves, Cook also mapped the coast of New Zealand, claimed the east side of Australia for Britain and discovered a clutch of South Sea islands. For others, things didn’t go quite so smoothly…
EDMOND HALLEY knew he would be never see a transit of Venus. He was born 17 years after the transit of 1639 and he would be long dead by the time the next one came around. But the coming pair of transits offered astronomers their best chance of accurately determining the distance from the Earth to the sun, and so in 1716 Halley laid before the Royal Society a set of instructions for observing them and a list of the best places to watch from. He appealed to all nations to plan ahead so they could get observers in the right places at the right time.
When the time came, many astronomers made difficult and dangerous journeys. Some were caught up in diplomatic incidents. Others found themselves in even tighter spots. Charles Mason and Jeremiah Dixon were sent to Sumatra by the Royal Society to watch the 1761 transit. Unfortunately, the seven years war was in full swing, and only a day out of port their ship came under attack from a French frigate. With 11 dead and 37 injured, the ship fled back to port. Mason and Dixon decided they had had enough. The worthies back in London thought otherwise and threatened legal action if they refused to go on. They got as far as the tip of South Africa, and set up their telescope there.
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French astronomer Jean-Baptiste Chappe d’Auteroche was more determined. For the first transit, he travelled to Tobolsk in Siberia by road, river and finally, in the depths of winter, by sledge across the frozen vastness of Russia. He arrived as the spring thaw began, bringing the worst floods for years to the region. Superstitious and suspicious, the local people were convinced the deluge had something to do with this stranger messing with the sun. The governor gave Chappe an armed guard to protect him from the mob. Chappe was more worried about his telescopes and moved into his observatory “lest they should attempt to pull it down”.
He was even more worried about the weather. The night before the transit, there was fog. “The whole hemisphere was soon overspread with one single black cloud, which damped all my expectations and threw me into a state of despondency,” he wrote later. The next day, the cloud cleared just in time. Still he fretted. “I was seized with a universal shivering, and was obliged to collect all my thoughts, in order not to miss it.” He didn’t and his measurements were some of the best.
For the second transit, he went to the narrow peninsula of Baja California. This required an Atlantic crossing to Mexico, a trek across bandit-infested territory to the Pacific coast and then a hazardous voyage and a risky landing on a treacherous coast. When he reached his designated observation point near the remote Spanish mission of San José del Cabo, he found the place in the grip of an “epidemical distemper”. The disease was typhus and the local people were dying in droves.
Undeterred, Chappe began his preparations. “At last came the third of June, and I had an opportunity of making the most compleat observations,” he wrote in his notebook. Two days later, almost the whole party fell ill. Chappe tended the sick and the dying before succumbing. Astronomer to the last, he raised himself from his sickbed to observe an eclipse of the moon on 18 June, had a relapse and then died. Before he left Paris, a friend had ventured that the trip was too dangerous. Chappe replied that even if he knew he would die the day after the transit, he would still go. His results, sent back to France by one of the party’s few survivors, were the most precise made that year.
Guillaume-Joseph-Hyacinthe Jean-Baptiste Le Gentil de la Galaisière not only had the longest name of any of the would-be Venus-watchers, he also made the longest expedition. Yet, unlike his compatriot Chappe he failed to produce a single useful measurement. Le Gentil’s goal was Pondicherry, the capital of French India. He sailed to Mauritius in the Indian Ocean, but before he could find a ship to take him onwards hostilities had flared between the French and British in India. He began to despair and with time running out he was overjoyed when a French frigate arrived carrying urgent messages for Pondicherry. Bad weather forced the frigate to wander the ocean for weeks, and then when it finally neared its destination, word came that Pondicherry had fallen to the English. The ship headed back to Mauritius. On 6 June, Le Gentil was still at sea. “I observed the best I could the transit of Venus, its beginning and end,” he wrote later. But uncertain of his exact location and the precise time, his observations were worthless.
Determined to salvage something from his trip, Le Gentil spent several years mapping the east coast of Madagascar and observing the island’s people and natural history. By the time he had finished, there seemed little point in going home before the next transit. He decided to watch from the Mariana Islands, remote specks east of the Philippines. But in the Philippines he found that few ships ever visited the Marianas. Stuck in Manila, he made plans to observe the transit from there. But with the Spanish governor making things difficult, he finally decided to head back to Pondicherry, which was now back in French hands. This time his ship was endangered by a capricious captain and a petulant pilot, who argued then stalked off to their cabins to sulk – just as the ship entered a dangerous stretch of water.
Miraculously, the ship reached Pondicherry, and Le Gentil built his observatory among the ruins. From here, Le Gentil would be able to observe the second half of the transit and record the crucial time when Venus moved off the face of the sun early in the morning on 4 June. “During the whole of the month of May, until the third of June, the mornings were very beautiful,” he recounted later. At two the next morning, he looked outside. “I saw with the greatest astonishment that the sky was covered everywhere.” At 5 am, the wind got up and he dared to hope it might blow the cloud away. But the expedition was doomed. “At three or four minutes before seven o’clock, almost the moment when Venus was to go off the sun, a light whiteness was seen in the sky which gave a suspicion of the position of the sun, nothing could be distinguished in the telescope.” Shortly after 9, the clouds cleared and the sun shone brilliantly for the rest of the day.
Le Gentil was distraught. “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.”
Le Gentil’s misfortunes were not over yet. In Pondicherry, he heard that his relatives were trying to have him declared dead and divide up his estate. It took him another 18 months to reach France. He had been away 11 years, 6 months and 13 days. Although he reclaimed his estate, he lost most of his money and his coveted place in the French Academy. But his luck finally changed. He fell in love, married and had a daughter he doted on. And, unlike many friends, he avoided the guillotine – dying naturally in 1792 just before the revolutionaries caught up with him.
