Feature Articles Articles de Fond A (Not So) Brief History of the Transits of Venus by Daniel Hudon ([email protected])

“This great marvel which we have just with. Could the disk of the Sun itself be witnessed, fellow savants (it almost takes used as a background? In 1629, Kepler my breath away), is nothing less than the predicted that Venus would pass directly transit of Venus!” across the face of the Sun two years hence, in 1631, and that it would just miss in — Some Learned Tales for Good Old 1639. Because of the tilt of Venus’ orbit Boys and Girls, compared to Earth’s orbit, this is a rare Mark Twain, 1875 Figure 1b. — Observers at different latitudes event — it occurs in pairs separated by on Earth will measure different parallel tracks eight years, with more than a century ow is it possible to measure of Venus across the Sun. From precise timings between the pairs (see Table 1 and Figure of the duration of the transit, the angle that distances in the solar system? 2). After the 17th-century pair, the next the two terrestrial stations subtend at Venus Today, astronomers simply bounce wouldn’t be until 1761 and 1769. Observers H can be determined, and hence both the distance a radar signal off the planet Venus and to Venus and the scale of the solar system in this century will see transits next year, calculate the distance between Earth and (from known orbital parameters). in June 2004, and 2012. No one alive has seen a transit of Venus. the Sun using Kepler’s laws. But in the Table 1 18th century, astronomers had to be much Past and Future Transits of Venus more clever in their measurements. Like December 7, 1631 surveyors out to measure their December, 4, 1639 surroundings, astronomers set sail around June 6, 1761 the world with a surveyor’s method to June 3-4, 1769 measure the solar system. December 9, 1874 The surveyor’s method is called December 6, 1882 triangulation or parallax. By sighting an June 8, 2004 object from two widely separated positions June 6-7, 2012 and measuring how its image appears to shift against the background, the unknown distance to the object can be determined through basic geometry (see Figure 1a and 1b). It’s the same as holding your thumb at arm’s length: by measuring how its angular position changes first with one eye, then the other, and knowing the distance between your eyes, you can calculate the length of your arm. Figure 1a. — A rendition of the Transit of However, the method can’t be applied Venus by James Ferguson, 1778. Reprinted to measure the Sun’s parallax directly with permission from The Transit of Venus: because in the daytime, the Sun blocks the Quest to Find the True Distance of the out all the background stars — there’s Figure 2. — Past and future transit paths Sun by David Sellers (Magavelda Press 2001). nothing to compare the Sun’s position (Proctor 1874).

6 JRASC February / fevrier 2004 The 1631 transit occurred when it he issued a call-to-arms to astronomers that their refusal to continue could not was nighttime in Europe so there are no worldwide, “Therefore, again and again, “…fail to bring an indelible Scandal upon recorded observations. In the spring of I recommend it to the curious strenuously their Character, and probably end in their 1639, the promising young scientist, to apply themselves to this observation.”2 utter Ruin.”3 For good measure, the Society Jeremiah Horrocks, discovered that Kepler Halley further pointed out the desirability added the threat of court prosecution was wrong: Venus would transit across of making observations from multiple “with the utmost severity of the Law.”4 the Sun that year, and in only a few weeks widely separated stations, both to improve Mason and Dixon reluctantly time (Fernie 2002). Horrocks and another the observations and to guard against capitulated and set sail again two months Englishman, William Crabtree, were the the problem of one station being clouded later when the ship was repaired, this only two people to observe the transit. out. time having at least secured an escort. They lived 30 miles apart but had never Under the auspices of the professional As it took three months to round the tip met — they communicated by letter. Both scientific societies, it was now possible of Africa, they decided to stop and set up were so excited to see the small black dot to heed Halley’s call and mount major their observatory at Cape Town, South of Venus dwarfed by the bright disk of expeditions. Expeditions were sent to Africa. The fact that Bencoolen had been the Sun that they failed to make any useful many of the world’s far-flung places: captured by the French may have timings. Northern Canada and Siberia, South Africa contributed to their decision. Horrocks details Crabtree’s experience: and the South Pacific, Baja, Mexico, and On transit day, June 6, the sky was “But a little before the time of sunset…the the Indian Ocean. perfectly clear and Mason and Dixon Sun breaking out for the first time from During an age when travel was obtained valuable readings. This was the clouds, he eagerly betook himself to decidedly less comfortable, if not downright fortunate for the British because their his observation, and happily saw the most dangerous, the scale of the expeditions other Southern Hemisphere observer, agreeable of all sights, Venus just entered was truly impressive. More than 100 Neville Maskelyne, the Astronomer Royal, upon the Sun. He was so ravished with astronomers participated. For those who was sent to the island of Saint Helena this most pleasing contemplation, that traveling by sea, the normal problems of — located between the middle of the he stood viewing it leisurely, as it were; navigational errors, monsoons, and scurvy South Atlantic and the middle of nowhere and from an excess of joy, could scarce were exacerbated by the Seven Years’ War, — was completely clouded out. (Perhaps prevail upon himself to trust his own fought between France and Britain in that’s why Maskelyne’s liquor expenses senses.”1 Indeed, the surprise must have every hemisphere in the early 1760s. For topped out at £141, nearly half his total been great, for Kepler had thought the some it was the adventure of their lives. expenditure of £292.) Sun was much closer and that Venus For the less fortunate, it cost their lives. Mason and Dixon stayed on at Cape would cover one quarter of its disk. Both Town for a while to measure Earth’s gravity Horrocks and Crabtree suddenly got an The 18th-Century British and the longitude and latitude of Cape image of the immensity of the solar system. Expeditions: Mason and Dixon’s Town. The precision of their geodetic Horrocks dutifully filed a report anyway Trip to South Africa work didn’t go unnoticed, for two years and indicated that the event could be later they were summoned to the American useful for determining solar distance. Before gaining lasting fame for surveying colonies to survey the disputed During the subsequent decades the eastern United States in 1763, the Pennsylvania-Maryland border — casting astronomy got organized. National societies British team of Charles Mason and Jeremiah a line that bears their name to this day. formed that held regular meetings and Dixon set sail for Bencoolen (modern published papers and transactions. The Bengkulu), Sumatra in December 1760. Other 18th-Century Expeditions most important of these were the Royal They gained firsthand knowledge of the Society of London and the French Academy hazardous state of affairs, for within hours Transit fever reached the American colonies in Paris. of leaving port they were attacked by a too. The Governor of the Province of Edmund Halley, an esteemed member French frigate. With 11 dead and 37 Massachusetts gave a stirring appeal to of the Royal Society, published a paper wounded, they limped back to port and the House of Representatives on behalf in 1716 outlining how the upcoming promptly wrote to the Royal Society of John Winthrop, professor of mathematics transits could be used to find the Earth- threatening to quit. Not only was the and natural philosophy at Harvard, that Sun distance. Knowing he would probably Royal Society unsympathetic, they went this was a “[P]henomenon which has be dead by the time of the next transits, so far as to warn the rattled astronomers been observed but once before since the

1 J. Donald Fernie, The Whisper and the Vision: The Voyages of the Astronomers, p. 10. 2 www.dsellers.demon.co.uk/venus/ven_ch8.htm 3 Fernie 1976, p. 16. 4 Ibid.

February/ fevrier 2004 JRASC 7 Creation of the world.”5 Winthrop was in Vienna, but despite collecting available so much baggage, whether it was essential duly equipped with observational data and publishing the best value of the astronomical equipment or not. The instruments and assistants and sailed to solar parallax for his time, the last two problem was finally rectified by the St. John’s, Newfoundland in the Province- decades of Hell’s life were seriously affected intervention of the French Academy. He sloop “Massachusetts” (see the recent by the initial suspicions over his data. was further delayed in the south seas JRASC article by Smith, 2003). Despite an The matter didn’t end with Hell’s when his ship met a hobbled French ship unabating plague of “venomous” insects, death. In 1823, when Johann Encke made whose captain demanded that they escort the team enjoyed clear weather and made a comprehensive evaluation of both the him back to Isle de France (today known useful timings of the end of the transit 1761 and 1769 transits, discussed further as Mauritius), a slowdown that cost Pingré (the beginning of the transit occurred below, he rejected Hell’s data. Ten years six or seven weeks. before sunrise in North America). later, Carl Littrow took the opportunity Arriving at Roderigue only a week Intrigue and adventure came in as director of the Vienna observatory before the transit, Pingré and his assistant various forms during the transit (Hell’s old position) to examine a worked ’round-the-clock to get their expeditions. Maximilian Hell, an Austrian rediscovered fragment of Hell’s original instruments in working order after the Jesuit and member of the French Academy, data sheets. Littrow claimed at last to long sea voyage, using turtle oil — from was renowned in Europe as a writer, have found evidence that Hell erased some the local delicacy — as a lubricant. With educator, and astronomy popularizer. In figures and corrected them in a slightly little time to spare, they built a crude 1755, he was named court astronomer different coloured ink. On the strength shelter to act as an observatory. “I think by Archduchess of Austria Maria Theresa of this purported evidence, Hell’s reputation there never was a more inconvenient and commissioned to set up an observatory was destroyed. one.”6 in Vienna. From there he made good It wasn’t until 1883 that American No matter: on transit day it was observations of the 1761 transit. astronomer Simon Newcomb, who figures cloudy. Undaunted, Pingré held out hope For the 1769 transit, Hell was invited prominently in the 19th-century transits, that the weather would clear. His patience by King Charles VII of Denmark and discredited Littrow’s evidence and paid off and he was able to obtain Norway to lead an expedition to the island exonerated Hell. Newcomb found that observations and timings for the end of station Vardö, located near Lapland north Hell’s changes were due to using a defective the transit. of the Arctic Circle. On transit day, Hell pen at the time of the observations, and With the transit over, Pingré’s much- and his assistants were so pleased to see further, that Littrow had been colourblind. prized letter seemed to act as a magnet the clouds part just before the transit for British ships because three weeks later began that they loudly celebrated afterwards The 18th-Century French one sailed into the harbour, sacked and by firing their ship’s cannon nine times Expeditions: Pingré’s Voyage to looted the small settlement and took and singing a Te Deum in gratitude. Hell Roderigue away Pingré’s ship as spoils of war. Pingré then stayed on for eight months to collect was stranded until another French ship additional scientific data for a proposed The French Academy launched several came along three months later — but not encyclopedia on arctic regions. expeditions for the 1761 transit. Alexander- before two more British ships arrived to Back in Paris, French Academy Gui Pingré, a prolific 50-year-old wreak more havoc. Finally, on his way members grew impatient with Hell’s delay astronomer and theologian, ventured out home again, Pingré had yet another run- in reporting his data and some suspected from Paris in November 1760 to the French in with British ships that this time captured him of waiting to hear other reports so island of Roderigue, east of Madagascar, his ship and escorted him into port in that he could adjust his data accordingly. in the Indian Ocean. Amongst his half- Lisbon. Though greatly esteemed as scholars, ton of baggage was a letter addressed to No doubt happy to see land again, academic opinion had recently turned the British Admiralty directing them not Pingré stuck to it and finished his journey against Jesuits because they were thought to interfere with his important expedition. by carriage. Despite the rough ride, at to have too much political power. The At a time when first contact between least he was rid of the British. Crossing insinuations ceased for a while when Hell warring ships was typically made by the Pyrennees into France, he noted with finally published his full observations in cannon fire, it’s hard to see what good some exasperation in his journal that he’d 1772, three years after the transit. This such a letter would do, but perhaps it been away 1 year, 3 months, 18 days, 19 was a year before the Jesuit Society as a provided moral support. hours, and 53 minutes. whole was suppressed and many Jesuits Pingré got off to a slow start. Arriving Back in Paris, Pingré resumed his were expelled from their respective at port with his considerable load, the work at the Academy7. One of his main countries. Hell maintained his position shipping agents refused to let him take interests was the problem of determining

5 Donald Fernie, American Scientist, Sept-Oct 1997. 6 Angue Armitage, The Pilgrimage of Pingré: An Astronomer-Monk of Eighteenth-Century France, p. 51. 7 Pingré was a free associate of the Academy. Scientists in Orders were barred from ordinary membership.

8 JRASC February / fevrier 2004 the longitude of a ship at sea. In 1767, he to Vienna. There he met and discussed flooded the town. The superstitious made a two-month voyage with the famed transit problems with the astronomer townspeople acted accordingly: they comet-hunter, Charles Messier, to test a Hell who was making his own preparations blamed the foreign astronomer for messing new marine chronometer. Subsequently, to observe it there. Upon reaching Warsaw, with the Sun. To quell the rising mob, the he tested another chronometer on a much he again switched modes of transport, local Governor posted guards for both longer voyage to Santo Domingo in what this time to horse-drawn sleds and made Chappe and his observatory. is now the Dominican Republic. From good time to St. Petersburg, arriving by The day before the transit, Chappe there he observed the 1769 transit of mid-February. had everything ready and he took a Venus at a picturesque coastal mountain But his Russian colleagues feared moment to reflect on the situation: “The site. With this data, he was able to calculate he wasn’t coming and had sent their own sky was clear, the Sun sunk below the one of the better values for the solar observers on ahead. Aware of the scientific horizon, free from all vapors; the mild parallax from that period. urgency of the expedition, and the glimmering of twilight, and the perfect onrushing spring, they quickly outfitted stillness of the Universe, completed my The 18th-Century French Chappe with an interpreter, guides, new satisfaction and added to the serenity of Expeditions: Chappe’s Journeys to giant sleds drawn by five horses abreast, my mind.”10 Siberia and Mexico plus supplies and provisions for his stay But the perfect weather didn’t last. at the remote outpost. In early March, By 10 p.m., the sky was completely clouded For widescreen cinematic drama, few Chappe was off again. A vivid imagining over. Naturally, Chappe feared his heroic expeditions can match that of Jean Baptiste is given by Donald Fernie: “One can picture expedition — and his honour in Chappe d’Autoroche who undertook a them racing for the Urals through the participating in this rare event — was 4000-mile trek to Tobolsk, Siberia, in the silence of the frozen countryside, great now in jeopardy and he grew increasingly dead of winter. A gifted Jesuit with a great clouds of snow rising from the horses’ despondent. He wrote: “In these dreadful enthusiasm for astronomy, Chappe gained flying hooves.”8 Had Dr. Zhivago been agitations I passed the whole night; I went a reputation as a skilled scientist beginning about an astronomer, this would have out and came in again every instant, and at the age of 25 when he observed a transit been a pivotal scene. could not continue a moment in the same of Mercury at the Paris Observatory with It was a month of steady winter position.”11 another French astronomer, J.B. le Gentil travel, often overnight, with sleep gained In the morning, Chappe’s hopes were (whose considerable adventures are detailed en route. Chappe wrote that it was anything revived as the clouds began to disperse. further below). Tobolsk was chosen because but a smooth ride: “had very little rest, The gradual improvement in the sky from there the transit would have the on account of the frequent shocks and seemed to affect his very being: “a pleasing shortest duration (Van Helden 1995). overthrows I met with.”9 Other problems satisfaction diffused itself through all my Chappe’s plan was to travel east from included his guides’ daily complaints frame, and inspired me with a new kind Paris to Vienna, then northeast through about the rapid pace — Chappe often of life…everything seemed to rejoice at Warsaw to St. Petersburg and finally across bribed them along with brandy. Through the return of a fine day…and as my hopes the vast Russian steppes. sheer determination, Chappe beat the became more sanguine, the joy of my Chappe might have dreamed of thaw — and the prospect of being mired mind was still more complete.”12 The today’s superhighways and automobiles forevermore in the Siberian mud. They governor and the archbishop came to with shock absorbers because during the rumbled into Tobolsk on April 10, 1761. visit, but the rest of the townspeople shut eight-day journey by carriage to Strasbourg, Chappe got to work immediately themselves up in their houses or in the near the German border, all of his and set up his observatory on a mountain churches. thermometers and barometers were out of town. He must have been pleased Chappe’s luck with the weather shattered and the carriages were damaged. to get settled and started on his scientific continued to improve and at last he was While the carriages were being replaced, program. Soon he determined the longitude ready: “I stood fixed with my eye to the Chappe industriously made himself a and latitude of his observatory, crucial telescope, wandering over the immense new set of instruments. data for the transit observations. space between us and the Sun a thousand To avoid a repeat of that ordeal, However, trouble now came from times in a minute…. The moment of the when he got to Ulm, Germany, he switched the spring thaw. This year it was unusually observation was now at hand; I was seized modes of transport and took a boat down early and severe, and the two local rivers with an universal shivering, and was

8 Donald Fernie, The Whisper and the Vision: The Voyages of the Astronomers, p. 34. 9 Jean-Baptiste Chappe d’Autoroche, A Journey to Siberia, p. 46. 10 Ibid., p. 80. 11 Ibid., p. 82. 12 Ibid., p. 82.

February/ fevrier 2004 JRASC 9 obliged to collect all my thoughts in order wish. I had full time to make accurate east coast of India, a full 14 months in not to miss it.”13 From there, things seemed and repeated observations for the setting advance of the transit. He intended to to go well, and Chappe made good of my clock. At last came the third of June, sail around the southern tip of Africa — observations. and I had the opportunity of making the the Cape of Good Hope — to Isle de France Chappe dispatched his data back to most compleat [sic] observations.”14 where he would catch another boat for Paris days later via mounted courier and This was his last journal entry. In India. Little did he know how familiar he stayed on another couple of months to the days after the transit, he cared for his was to become with Isle de France. He make additional observations of the region. colleagues who had caught the deadly arrived there in July 1760, after a four- He took a leisurely trip back to France, disease until he too fell ill. Despite fits of month voyage, and learned that because and a glimpse into his character is seen pain and fever, Chappe rallied himself to war had flared up between the French from his visit to Echaterinenburg, where view a lunar eclipse on June 18, as an and British at Pondicherry, no boats were he stopped to make some observations. independent longitude determination. travelling there. So he waited. Six months Evidently smitten with one of the local The epidemic that claimed three-fourths later, he was still waiting. Just as he was women, he hired a band and threw a party, of the village also claimed Chappe on about to give up and join Pingré in hoping to gain her attention. Unfortunately, August 1. Only one member survived to Roderigue, a few hundred miles to the he doesn’t report on the outcome of the bring the data back to Paris. east, a French frigate arrived on February event. Chappe also spent some time in Chappe’s team gathered some of the 19, 1761 bound for the coast of India. St. Petersburg and finally arrived back in best data of all and his words from the Local officials assured Le Gentil that Paris in November 1762. earlier 1761 transit have a lingering despite the monsoon winds, the ship By the time of the next transit in poignancy, “Pleasures of the like nature would easily make it to the coast of India 1769, Chappe wanted to go somewhere may sometimes be experienced; but at within two months — plenty of time to different — likely somewhere tropical. this instant, I truly enjoyed that of my make preparations for the transit. Le He decided on Baja, Mexico. After nearly observation, and was delighted with the Gentil decided to chance it. three months at sea crossing the Atlantic, hopes of its being still useful to posterity, Initially, they made good progress a lengthy hike across the breadth of Mexico when I had quitted this life.” but soon the favourable winds abandoned (in which Chappe and his colleagues them and they were blown away off course. travelled by litter), and a three week voyage The 18th-Century French Le Gentil wrote in his journal, “[W]e across the Gulf of California in which Expeditions: Le Gentil’s Epic wandered around for five weeks in the they were becalmed and saw their food, Voyages seas of Africa, along the coast of Ajan, in water, and time run perilously short, the Arabian seas.”16 In other words, they Chappe’s team at last arrived at a small If Chappe’s previous sled journey across wandered everywhere except towards village on the tip of Baja on May 19. As frozen Siberia was a scene from a cinematic their destination. the village was suffering from an epidemic epic, then the voyage of Guillaume Le Finally, on May 24, they came within of yellow fever, they took a considerable Gentil (full name: Guillaume-Joseph- sight of Mahé, on the west coast of India, risk when they decided to stay there. Hyacinthe-Jean Baptiste le Gentil de la directly across from Pondicherry. Here Chappe thought they wouldn’t have time Galasière) to the Indian Ocean was a they received news from another ship to find a new location and went ahead comedy of errors and a bounty of bad that Pondicherry was now in English with the preparations. It was a costly luck. As Helen Sawyer Hogg wrote once hands. To Le Gentil’s “great regret,” the decision. in this Journal, it “is probably the longest captain decided to return to Isle de France. Chappe recorded the following in lasting astronomical expedition in history. Consequently, when transit day (June 6) his journal: “Myself and all my train took In fact, it is quite possible that, except arrived, Le Gentil was aboard a rolling up our abode in a very large barn. I had for interplanetary travel, there will never ship in the middle of the Indian Ocean, half the roof taken off towards the south, be astronomical expeditions to equal in unable to make any reliable observations. and put up an awning, that could be spread duration and severity those made for that He dutifully observed the transit and out or contracted at will. All my particular pair of transits.”15 measured his longitude and latitude but instruments were fixed just as they were Le Gentil, a young member of the knew full well that his data was useless. to stand to observe the transit of Venus. French Academy, set out from Paris on Rather than make the long journey The weather favored me to my utmost March 26, 1760, for Pondicherry, on the back to France, Le Gentil was determined

13 Jean-Baptiste Chappe d’Autoroche, A Journey to Siberia, p. 83. 14 Doyce B. Nunis, The 1769 Transits of Venus, 1982. 15 Helen Sawyer Hogg, Out of Old Books: Le Gentil and the Transits of Venus, 1761 and 1769, Journal of the Royal Astronomical Society of Canada, volume 45, p. 37, 1951. 16 In Sawyer Hogg 1951, p. 41 and Fernie 1976, p. 42.

10 JRASC February / fevrier 2004 to make some useful scientific observations he wrote, he was now a veteran traveller: winds would change and clear the clouds of the region. He writes, “I resolved then “Sea voyages no longer cost me anything, from the sky. Instead, the weather got not to leave the Indian Ocean until this I had become so familiar with this worse. A freak squall blew in, piling the time [after the next transit in 1769], to element.”20 clouds together and completely obscuring make all the observations I could on He embarked on a Portuguese vessel the Sun when it rose. When the transit geography, natural history, physics, and was soon on his way to India again. was over, the winds calmed and the sky astronomy, navigation, winds, and tides.”17 En route, he mediated an argument between cleared — the Sun shone brilliantly for Indeed, 18th-century scientists were much the ship’s pilot and captain and took over the rest of the day. more broadly trained than those of today. the helm himself. Nevertheless, he described Le Gentil was so stupefied at his After a few years of this work, he began it as the finest of voyages and reached misfortune that it seems only fair to quote to think about the next transit. According Pondicherry in a mere 32 days. him at length. to his calculations, the best place to Le Gentil arrived at Pondicherry on “That is the fate that often awaits observe the transit would be in Manila, March 27, 1768. The Governor welcomed astronomers. I had gone more than ten Philippines. him with a feast that very night; it seemed thousand leagues [30,000 miles]; it seemed He dashed off a letter to the French he’d made the right decision. The next that I had crossed such a great expanse Academy informing them of his intentions day, the Governor invited him to choose of seas, exiling myself from my native and caught the next boat for Manila. His a spot for his observatory; he chose a land, only to be the spectator of a fatal satisfaction at moving on was evident in partially ruined palace (thanks to the cloud which came to place itself before his journal: “I finally left the Isle de France British), that, aside from being well situated, the Sun at the precise moment of my May 1, 1766, quite resolved to say good- still had a large gunpowder magazine in observation, to carry off from me the bye forever to that island.”18 He was soon its basement. fruits of my pains and of my fatigues…. to learn, however, that sometimes personal Over the months, Le Gentil occupied “I was unable to recover from my resolve just isn’t enough. himself by studying Indian astronomy astonishment, I had difficulty in realizing Le Gentil arrived in Manila in August and local customs. From Pondicherry, that the transit of Venus was finally over…. 1766 and began getting settled. Though the transit was to be visible first thing in At length I was more than two weeks in the climate appeared promising, Le Gentil the morning on June 4. As the clear a singular dejection and almost did not soon had doubts because the Spanish mornings of May passed, Le Gentil was have the courage to take up my pen to governor was not kindly disposed towards nearly beside himself with impatience. continue my journal; and several times the French and, on top of that, he ran the The night before the transit was perfectly it fell from my hands, when the moment place like a tyrant. Le Gentil’s doubts clear and Le Gentil observed the satellites came to report to France the fate of my became genuine worries when letters of of Jupiter with the Governor, using a operations….”22 introduction from the French Academy telescope sent by the now-friendly British To make matters worse, he soon arrived in July 1767; the governor rejected at Madras. learned that the skies had been clear in them as forgeries, saying that 14 months But his good fortune couldn’t last. Manila that day! was too short a time to receive a reply to He awoke at 2 a.m. and “saw with the Now, Le Gentil wanted nothing more his letter. greatest astonishment that the sky was than to return to Paris. In the world of An additional letter noted that Pingré, covered everywhere, especially in the Le Gentil, this was easier said than done. now safely returned to Paris — and perhaps north and north-east, where it was His departure from Pondicherry was wishing further seagoing adventures for brightening; besides there was a profound delayed by a recurring fever and dysentery his colleague — thought that Pondicherry calm. From that moment on I felt doomed, that prevented him from travelling. He would be a better site for observing the I threw myself on the bed, without being finally left Pondicherry, still ill, in March transit than Manila. By this time, able to close my eyes.”21 1770, making it only as far as his former Pondicherry was back in French hands, From there, his journal contains a home-away-from-home, Isle de France, so, rather than expose himself further long passage that would be familiar to where he decided he was too ill to continue. “to the caprice of him who governed,”19 anyone trying to observe a particular Here, his spirits were further dampened Le Gentil decided to have another attempt astronomical event. He veers back and by the death of an astronomer named at viewing the transit in India. After all, forth between “hope and fear” that the Veron, whom he’d met in India. Incidentally,

17 In Sawyer Hogg 1951, p. 42. 18 In Sawyer Hogg 1951, p. 43 and Fernie 1976, p. 43. 19 In Sawyer Hogg 1951, p. 90. 20 Ibid. 21 In Sawyer Hogg 1951, p. 131 and Fernie 1976, p. 48. 22 In Sawyer Hogg 1951, p. 132 and Fernie 1976, p. 49.

February/ fevrier 2004 JRASC 11 Veron had suffered the same misfortune alive.”25 He married, had a daughter, and exceedingly thick. When it lifted, Wales as Le Gentil for the 1761 transit — finding took up a quiet life writing his memoirs. spent much time counting ice floes: one himself stuck at sea. Le Gentil described Having met many untimely tempests in day 32, another 58. his death as “from a fever which he had his life, he mercifully died in 1792, months Upon arrival in Churchill, August acquired by his great zeal to observe before the great storm of the French 10, 1768, Wales writes about the “intolerably throughout the night on land when he Revolution descended upon Paris. troublesome” hordes of “moschettos” and was at the Moluccas.”23 Everyone seemed to fare better in sand-flies: “There are continually millions By July, Le Gentil thought he was the 1769 transits than poor Le Gentil. of them about one’s face and eyes, so that finally fit for travel and more than ready Mason and Dixon, who got off to such a it is impossible either to speak, breathe, to leave Isle de France for good. But it rotten start in 1761 for the Royal Society, or look, without having one’s mouth, nose, wasn’t until November that a ship was stayed closer to home for the 1769 event. or eyes full of them.”26 ready to take him. Two weeks into the They split up, with Mason venturing to For the first month, Wales and voyage, the ship met a hurricane that Ireland and Dixon to northern Europe Dymond busied themselves with building took down parts of its main masts. Unable and viewed it without incident. The Royal their observatory and making it secure to continue, the ship hobbled back to Isle Society sent out other expeditions, including for the winter. Once that was done, Wales de France. As if returning to the island that of William Wales to Hudson’s Bay, ceased keeping a journal “except of the wasn’t bad enough, here Le Gentil received and the most famous of all, that of Captain weather…which is, in reality, the only news that his heirs were spreading rumours Cook and the Endeavour, both described thing we have to keep a journal of here of his death and that the only thing holding below. in the winter season,”27 giving an indication up their taking possession of his estate of how little they had to occupy themselves. was a death certificate. The 18th-Century British Wales gives additional details in With renewed determination, he Expeditions: William Wales’ some “short memorandums,” where he left Isle de France on March 31, 1771 on Expedition to Hudson’s Bay writes of proudly donning his “winter a Spanish frigate. Around the Cape of rigging,” decking himself out head to toe Good Hope, the ship met “tempests upon Having heard about all the adventures in in furs furnished by the Hudson’s Bay tempests” but Le Gentil wrote that “My 1761, William Wales, who had recently Company28 and of sleepless nights due sole worry in the midst of all these storms computed lunar navigation tables for to the loud cracking of the cabin boards was the fear of being forced to see again Neville Maskelyne’s Nautical Almanac under the stress of the frost. Though the the Isle de France.”24 volunteered to observe the 1769 transit aurorae were unimpressive that year, the But the Spanish sailors were more for the Royal Society as long as the nights were cold enough to ice over a half- than capable and the ship arrived in Cadiz, destination was warm and not too far pint of brandy left in the open air in five Spain on August 1, 1771. Le Gentil finished out of the way. Naturally, he got the minutes. By February, the bedboards his journey on land, like Pingré before opposite. He was sent to Fort Churchill, dripped with icicles. Even so, when the him, and crossed the Pyrennees on October on the Hudson’s Bay, known even then clouds of “moschettos” returned in the 8. It was an absence of eleven years, six as the Polar Bear capital of the world. summer, Wales began to think that winter months, and thirteen days. As the shipping routes to the Hudson’s was “the more agreeable part of the year.”29 Le Gentil’s return was not entirely Bay would be frozen solid until early After more than a year of preparation happy. He immediately had a lengthy summer, it was necessary for Wales and and waiting, transit day, June 3, dawned court battle to regain part of his estate his assistant, Joseph Dymond, to sail in partly cloudy. At noon, the transit began that had been lost due to a careless late-spring 1768 and winter over in and the two astronomers differed in their manager, and he’d lost his seat at the Churchill. An agreement with the Hudson’s initial contact times of Venus on the disk French Academy — on whose behalf he’d Bay Company was reached to drop the of the Sun by 11 seconds, a result that taken his journeys in the first place. astronomers off and pick them up a year was a great disappointment to Wales. On the positive side, he gained some later. The journey across the North Atlantic They stayed in Churchill another three satisfaction from “hearing people recognize was unremarkable until they got to the months before sailing back to England, me and attest loudly that I was really Hudson Straits where the fog was with the great comet of 1769 (discovered

23 In Sawyer Hogg 1951, p. 133 and Fernie 1976, p. 50. 24 In Sawyer Hogg 1951, p. 174. 25 In Sawyer Hogg 1951, p. 177 and Fernie 1976, p. 53. 26 Helen Sawyer Hogg, JRASC, volume 42, p. 158; and Fernie 1976, p. 20. 27 In Sawyer Hogg 1952, p. 159. 28 Unfortunately, these were all confiscated by customs officials on his return to England. 29 In Sawyer Hogg 1952, p. 192 and Fernie 1976, p. 24.

12 JRASC February / fevrier 2004 by Messier) visible in the night sky. Robbed Britain, would surely raise the suspicions by the time the Endeavour sailed in August of favourable winds in the English Channel, of the other European powers. The transit 1768, similar chronometers were still very they made the final leg of the trip to was the perfect ruse. expensive and the ship went without. London via stagecoach. The Royal Society proudly proclaimed The Endeavour carried another Back home, Wales was so distressed that the transit would benefit navigation, scientist, Joseph Banks, a young aristocrat by his transit observations that he refused knowing full well that the size of the Solar who was devoting his life to science, to submit them to the Royal Society System had nothing whatsoever to do particularly botany. Banks, a formidable because they were inaccurate. However, with getting ships around the Earth. personality, travelled with an entourage the Society would not be denied. In March However, as navigation went before of assistants, including two illustrators 1770, Wales presented his results to the shipping, trade and profits, such boosterism for his botanical samples. He later became members of the Society and read a 50- was the only way to secure funding from President of the Royal Society and page manuscript of his journal excerpts the government for the expedition. Then, dominated science in late 18th-century detailing the various botanical, climatic, the Royal Society wrote a spirited, patriotic England. and scientific information he obtained. letter to their patron, King George III, At sea, Green was dismayed to find Happily, he was applauded for his efforts about the importance of the observations. out none of the naval officers knew the and now on his way to warmer climes: The King was good enough to chip in lunar observations method for determining Captain Cook recruited him to act as with the requested £4000 (equivalent to longitude. For four years, the Royal navigator for Cook’s second and third about £300,000 today). Greenwich Observatory had been voyages around the world. Wales then The Royal Navy agreed to loan a ship publishing the Nautical Almanac. What finished his career as a mathematics for the expedition but refused to have it was the point of publishing it, he grumbled, teacher in London and taught the likes be commanded by a mere civilian. For when naval officers didn’t know how to of Samuel Taylor Coleridge and Charles his part, Dalrymple refused to be a mere make appropriate observations. However, Lamb (Fernie 2002). In his essay, passenger and thus withdrew from the when shown, Cook quickly mastered the Recollections of Christ’s Hospital, Lamb entire expedition. Desperate to find a method. Evidently, Cook’s reputation for describes his schoolmaster, “There was commander for their ship, the Navy cast knowing the precise whereabouts of his in William Wales a perpetual fund of about until a man who had at least two ship was due in part to Green who humour, a constant glee about him, which things going for him was nominated. He enthusiastically took lunar observations heightened by an inveterate provincialism had charted the Gulf of St. Lawrence and at any opportunity. of north-county dialect, absolutely took had submitted observations to the Royal The Endeavour sailed west down away the sting of his severities.”30 Despite Society of a solar eclipse seen from the length of the Atlantic in nearly four all the “moschetto” stings, Wales seems Newfoundland (to better determine its months, took four attempts to cross the to have enjoyed his tenure as a world longitude). The man was James Cook. tumultuous Strait Le Mare at the tip of traveller and it is tempting to wonder Here the Navy hit an embarrassing Tierra del Fuego and passed Cape Horn how much of Coleridge’s Rime of the snag because Cook was not a on January 25, 1769. Ancient Mariner was inspired by Wales’ commissioned officer. Did they have no As part of the purpose of the stories. one of higher ranks, with some expedition was to find Terra Australis, astronomical abilities, who could lead Cook now sailed in a northwest direction, The 18th-Century British the expedition into uncharted waters? contrary to the winds and currents. The Expeditions: Lieutenant Cook’s Apparently not. So, Cook was promoted days passed on and no unknown continents Voyage to Tahiti to lieutenant — not to captain, that only were sighted. In his journal, Banks took came later — and given command of the a jab at armchair philosophers like For the Royal Society, the 1769 transit of HMS Endeavour. Dalrymple: “It is however some pleasure Venus coincided perfectly with their plans The official astronomer was Charles to be able to disprove that which does to explore the South Pacific. Alexander Green, an assistant at Greenwich (and not exist but in the opinions of theoretical Dalrymple, among others, was certain brother-in-law of William Wales) adept writers, of which sort most who have that it hid another continent, Terra Australis at finding longitude at sea solely based wrote [sic] anything about the seas without Incognita, the unknown southern land. on observations of the Moon and stars. having themselves been in them. They The idea of such a place had lurked in He sailed with Neville Maskelyne in 1763- have generally supposed that every foot geographers’ minds since Ptolemy had 4 to Barbados to test John Harrison’s of sea which they believed no ship had put it on his map in his Geography. But fourth marine chronometer — the device passed over to be land, though they had an exploratory expedition, with the aim that finally solved the problem of little or nothing to support that opinion of claiming newly discovered lands for determining longitude at sea. Interestingly, but vague reports.”31

30 Charles Lamb, Recollections of Christ’s Hospital. 31 J.C. Beaglehole, The Endeavour Journal of Joseph Banks, p. 240.

February/ fevrier 2004 JRASC 13 After three months on open water the mountains of Tahiti were sighted and the Endeavour landed at Matavia Bay on April 13, 1769. Before going ashore, Cook issued a set of rules to his men in order to promote the best relations with the island’s inhabitants. Foremost on the list was cultivating a friendship with the locals, while other rules regulated trade and responsibility. The last rule prohibited the exchange of “Iron, or anything that is made of Iron…for anything but provisions.”32 This last rule was necessary to literally keep the ship together. The Tahitians were a metal-less culture and thus held metal objects, such as nails, scientific instruments, and tools, in extraordinarily high regard. According to sailors on the Dolphin, which had landed in Britain just before the Endeavour sailed, Tahitian women were beautiful and uninhibited. They would trade sexual favours for a simple iron nail Figure 3. — Excerpt from Cook’s journal showing the “black drop” effect. Copyright James Cook — the very things that held wooden ships University. together. For men at sea months on end, such a price was so beguiling that they and placed in Cook’s tent, no one could the confusion of suspicion and search nearly pulled the ship apart to procure figure out how it could have gone missing. parties, a chief had been taken into custody. the costs of love. Cook wasn’t about to Normally diplomatic, Cook became livid Cook immediately released the man and jeopardize the rest of his expedition over because the instrument was crucial to days later made amends by presenting these dalliances and thus took the necessary the transit observations. He immediately him with an axe. steps to protect his ship. sealed the bay so that no one could escape As the transit day drew near, Green Soon after arrival, Cook and Green by canoe. and Cook made final preparations while observed the moons of Jupiter to establish Meanwhile, Green and Banks, who keeping an eye on the weather. They’d the longitude of Tahiti. Then, they set had already developed some rapport with had a mix of sunny and cloudy days and about building their observatory, which the Tahitians, made some discrete inquiries were understandably concerned. Cook they located at the northernmost end of and were soon hot on the trail. They dispatched a small party to a nearby island the bay. As the transit was the ostensible recovered one piece of it and this time it to improve their chances of success. raison d’être for the expedition, Cook was Banks who became livid because the Luckily, on June 3, the Sun broke didn’t want to take any chances with thief had clearly taken apart the quadrant through the dawn haze and, according instruments going missing, or worse, an and the likelihood of damage, or of not to Cook, “[the] day proved as favourable uprising, and thus had a fort built around recovering all the pieces, was great. In to our purpose as we could wish. Not a the observatory. front of a gathered, chattering crowd, he cloud was to be seen the whole day….”33 However, on May 2, a month before took out his two pistols to show his When the transit began, the team the transit, when the instruments were firepower. The demonstration had the made an important discovery: “We very brought into the finished observatory, desired results and the quadrant was distinctly saw an Atmosphere or Dusky the sturdy case for the astronomical returned piece by piece. Green confirmed shade round the body of the planet, which quadrant was opened and found to be that only minor pieces were now missing, very much disturbed the times of the empty. Where was it? Because it had only and that it could be made operable again. contact, particularly the two internal been brought ashore on the previous day Upon return, the two scientists found in ones.”34 Side by side and using telescopes

32 Peter Aughton, Endeavour, p. 65. 33 W.J.L. Wharton, Captain Cook’s Journal, p. 76. 34 Ibid. In fact, the atmosphere of Venus was first discovered by the Russian astronomer Lomonosov during the 1761 transit, though his priority wasn’t established until 150 years later when one of his papers was translated into German.

14 JRASC February / fevrier 2004 of the same power, Cook and Green “differed Like William Wales and Joseph 23 died in the voyage across the Indian from one another in observing the times Dymond on their journey home, they Ocean to Cape Town, South Africa, where of the contact much more than could be observed the great comet of 1769; Cook the ship landed on March 14, 1771. Included expected.”35 claimed its tail was an astonishing 42°! in the unfortunate death toll was Charles This became known as the “black Tupia saw it as a harbinger of war and Green, who had been battling health drop effect” (see Figure 3) and despite all feared his people would be invaded by problems over the many months at sea. the 1761 observations, neither Cook nor those of a nearby island. On April 29, Cook recorded the Green seems to have expected it. Due to After days and weeks on the open longitude in his log with the comment, Venus’ atmosphere, contact with the Sun’s seas, a stir of excitement was caused when “[have] now Circumnavigated the Globe disk was not distinct — it appeared like land was sighted. Could it be the unknown in a West direction.”36 Two months later, an oil drop that wouldn’t fully detach continent? No, it was New Zealand. The on July 13, 1771, three years after beginning from its source — making it difficult to Endeavour had removed the unknown its voyage, the Endeavour returned to obtain precise timings. Consequently, continent from another large chunk of England. Upon return, Banks began his they knew their results were suspect. uncharted ocean. own grand tour of the salons of London, After such a long voyage, Cook was On November 9, Green and Cook telling all and sundry of his numerous inevitably disappointed in the outcome observed a transit of Mercury from New botanical discoveries. Consequently, of its primary purpose. Zealand and used it to calculate their newspaper reports wrote about the voyage There was further intrigue that day. longitude. The Endeavour spent four as Banks’ own expedition, barely During the observations, the ship’s months charting New Zealand then Cook mentioning Cook and his many storeroom was broken into and a large ventured west to the coast of Australia navigational triumphs. quantity of nails was stolen. Evidently, where he had not one but two harrowing the transit provided enough distraction run-ins with the Great Barrier Reef. The Tallying Up I for other sorts of pursuits. Cook turned ship limped all the way to the nearest a blind eye to the fraternization between large port, Batavia (modern Jakarta, The 18th-century transit expeditions his crew and the local women for the sake Indonesia) for repairs. were truly an impressive effort. More than of morale but he couldn’t ignore thievery. By insisting on fresh food and water 120 observers from 62 separate stations When one sailor was caught with some for his crew whenever possible, Cook had around the world observed the 1761 transit, nails on him that day, he suffered two done more than any commander before while the 1769 transit was recorded by dozen lashes as punishment. him to keep his crew healthy and to keep 138 observers from 63 stations (Woolf Now it was time to complete the scurvy at bay. However, he couldn’t combat 1953). Once the data from the transits expedition. After three months on Tahiti, the diseases contracted at Batavia: malaria was published, it was analyzed time and the Endeavour raised anchor and set sail and dysentery. Seven crew members died again by astronomers as they tried to find on July 13, 1769. Though Cook nearly lost during the month-long stay and another the best value. For the 1761 expeditions, two men to desertion (and took extreme Table 2 the range of the solar parallax was 8.3˝ measures to have them returned), he to 10.6˝ (Dick et al. 1998; and see Tables A Range of Solar Parallax Values and the gained one, a local chief and priest named 2 and 3), considerably larger than expected. Corresponding Earth-Sun Distance Tupia. The wealthy Banks agreed to take The range was marginally reduced for responsibility for him in England, reasoning, the 1769 transits, in which values ran Solar Parallax Earth-Sun Earth-Sun in his most aristocratic way, that he could from 8.43˝ to 8.80˝. The French astronomer (arcsec) distance (km) distance (miles) keep him as a curiosity in the same way Lalande combined data from the two 8.3 158,500,000 98,500,000 his neighbours kept lions and tigers. Tupia transits to obtain a range of 8.55˝ to 8.63˝, 8.4 156,600,000 97,300,000 proved useful as an ambassador while corresponding to a distance of 153 ± 1 8.5 154,800,000 96,200,000 the Endeavour explored nearby islands. million kilometres (Pogge 2003). Halley 8.6 153,000,000 95,000,000 At sea again, the Endeavour was had thought the method would produce 8.7 151,200,000 94,000,000 now to continue its search for the unknown a precision of 1 part in 500, so this error, 8.8 149,500,000 92,900,000 continent — there were even sealed secret a factor of three larger than expected, 8.9 147,800,000 91,800,000 instructions from the Admiralty, which was cause for disappointment. 9.0 146,200,000 90,800,000 Cook now opened. From Tahiti, he was Many papers were published with 9.1 144,500,000 89,800,000 to sail south to 40° latitude and then mean values determined from different 9.2 143,000,000 88,800,000 westward until he either hit the unknown pairs of stations. But it wasn’t until the 9.3 141,500,000 87,900,000 continent or New Zealand. mathematician Karl Friedrich Gauss came

35 W.J.L. Wharton, Captain Cook’s Journal, 36 Ibid.

February/ fevrier 2004 JRASC 15 Table 3 around was an opportunity to use the Some Transit of Venus Observations nascent technique of photography. In 1874, Father S.J. Perry led a British Observer Date Parallax Error Mean Earth-Sun Mean Earth-Sun team of observers to Kerguelen Island, a (arcsec) Distance Error (km) Distance Error (miles) damp, chilly, windswept, and altogether Lalande 1771 8.55 to 8.63 153,900,000 to 95,600,000 to uninviting island that lies in the southern 1769 transit 152,400,000 94,700,000 Indian Ocean, closer to Antarctica than Pingré 1772 8.80 149,500,000 92,885,000 to either South Africa or Australia. 1769 transit Discovered by the French explorer Yves Encke 1824 8.5776 153,400,000 95,250,000 de Kerguelen-Trémarec in 1772, it often 1761 and goes by a nickname given it by Captain 1769 transits Cook, who stopped there on his third Harkness 1891 8.842 148,788,000 92,455,000 voyage around the world: Desolation 1882 transit, (0.0118) (199,600) (123,400) Island. Until a scientific base was set up American there in 1950, this remote, inhospitable photos island was home only to seals and penguins. Newcomb 1891 8.79 149,700,000 93,000,000 Perry was director of Stonyhurst 1761 and (0.051) (868,000) (540,000) Observatory, near Manchester, and gained 1769 transits respect from his contemporaries for his Stone 8.832 148,957,000 92,560,000 sunspot studies and his geodetic and 1882 transit, magnetic work (Ashbrook 1966). His British and expedition left England in May 1874 in Canadian two ships, the Volage and the Supply, results seven months before the December 9 Newcomb, 1895 8.800 149,500,000 92,898,000 transit. system of (0.0038) The team gathered in Cape Town constants where the naval lieutenants, according Modern IAU 1976 8.794148 149,597,870.691 92,955,859 to instructions by Airy, made a series of system of (0.000007) (0.030) practice observations. In addition to visual constants timings, they were to make photographic observations, so the four assistants had Adapted from Dick et al. (1998). Except for the final value, errors are “probable errors,” which their hands full with learning wet-plate are 74% of the “mean error” or “standard error” used today. and dry-plate photography. They rehearsed for two months before venturing on to up with the method of least squares early astronomy”37 and immediately set out a Kerguelen Island on October 8, 1874. in the 19th century that the heaps of data plan for observing the next transit of In his journal, Perry recorded his could be reliably analyzed (Fernie 1976). Venus in 1874. Soon, transit fever caught first bleak impressions of the island: snow In 1824, Encke used this method to obtain on around the world and it became a “as far as the eye could see.” Because spring a value of 8.5776˝ for the two transits matter of national pride to participate was still lingering in the Southern (Dick et al. 1998), equivalent to 153.4 in the observations. According to Agnes Hemisphere they had “pleasant prospects million kilometres. This value stood for Clerke, in her book A Popular History of of rambles in snow-shoes over rugged 38 a quarter century when new lunar motion Astronomy in the Nineteenth Century, hills and half-frozen marshes and bogs.” measurements indicated that it was too “Every country which had a reputation Upon landing at Morbihan Bay, the large. The solar parallax would have to to keep or to gain for scientific zeal was party unloaded 600 crates of equipment be measured again. forward to cooperate in the great and erected huts for living in and shelters cosmopolitan enterprise of the transit.” for the instruments. Weather was a big The 1874 and 1882 Transits Consequently, Russia led the way with concern — the average cloudiness was twenty-six expeditions, Britain twelve, 75% in December — so Perry sent two Mid-century, Astronomer Royal G.B. Airy the United States eight, France and teams to secondary sites around the bay called the measurement of the Earth-Sun Germany six each, Italy three, and Holland to improve their chances of success. distance “the noblest problem in one (Dick et al. 1998). New this time Lieutenant Cyril Corbet led one team and

37 Steven J. Dick et al. 1998, p. 226. 38 Joseph Ashbrook 1966, p. 341.

16 JRASC February / fevrier 2004 Lieutenant Goodridge another. report. He and his assistant differed by He continued to make expeditions: he Like Chappe, Le Gentil, and Wales as much as 15 seconds for their first observed the 1882 transit in Madagascar before him, Corbet kept a journal giving contact (of Venus to the Sun’s disk) timings and later died at sea in 1889, after us a vivid and colourful glimpse of the due to the nefarious black drop effect. completing solar eclipse observations in drama of the event. After making longitude Soon, heavy clouds moved in and though French Guiana (Gerard 1911; Kilburn and latitude measurements of their station, Corbet caught a glimpse of Venus leaving 2002). Corbet recorded the conditions: “We got the Sun’s disk, he wasn’t able to time it. The American effort was spearheaded a few observations in the evening, but it When the event was over, the team by Simon Newcomb, who recommended was terrible work in the high winds — treated themselves to a breakfast of Oxford the establishment of a government lamps flickering and blowing out, couldn’t sausages and a bottle of champagne. commission in 1870 and was an early hear the ticks of the clock or anything.”39 Meanwhile, Perry’s team had both a proponent of recording the transit At a mere 24 years of age, Corbet photographic and visual program. At their photographically. Newcomb’s biggest was already a Fellow of the Royal station, a single cloud obscured first concern was to accurately establish the Astronomical Society and keenly aware contact but the sky cleared and they got photographic plate scale in order to of the importance of the expedition. On good timings and photos of the end of minimize conversion errors (measurements December 6 he wrote: “Trying to keep the transit. Goodridge’s team had similar, on the photographic plate were linear calm and collected for the day after partial success. while the parallax measurements were tomorrow.”40 In fact, it seems his youthful After the transit, the teams re- angular). Because Venus was to look like zeal nearly got the better of him because gathered at the primary station and a small, circular sunspot, Newcomb the night before the transit he recorded compared notes, though this took a few recommended adopting a solar observation the following: days due to stormy weather. There was method perfected by Joseph Winlock at “Weather still bad and the barometer more work to do yet — Airy had given Harvard Observatory (Janiczek & Houchins very low and still falling, but I shall keep instructions to make more than a hundred 1974; Dick et al. 1998). The final design hoping, hoping, hoping for tomorrow. additional lunar observations to fine- was a horizontal telescope with a 40-foot Oh! to think it is so close — I feel funnier tune the longitude determination. However, focal length in which the Sun’s light was today than I have ever felt in my life, and the weather turned for the worse and it directed to the photographic plate by a I suppose really tomorrow morning will took three months to collect the necessary tilted, slowly moving mirror (known as be about the most unpleasant time of my observations — forcing the expedition a heliostat). life up to 11 o’clock, when one will know to go on half rations (Ashbrook 1966). Much of the instrument making one’s fate….”41 On February 27, 1875, the expedition set became the task of Alvan Clark and his It was a classic case of “butterflies sail back to England. Upon leaving the firm in Massachusetts. Clark had his in the stomach.” Understandably, he was island, Corbet recorded his wistful thoughts: hands full outfitting eight U.S. expeditions far too anxious to sleep that night and “We watched the dreary desolate with identical equipment, including the was up at 4:30 a.m. He waited until 6 island for ever so long till all the low land five-inch refractors for the visual o’clock before rousing his assistants and had sunk into the sea and we could see observations, the five-inch 40-foot “got their fat heads shaken out of them” the snow mountains only…. We were clear photoheliograph lenses, and the heliostat even though he described the weather as of the land by night, and all with light mirrors for the photographic program as “dubious, very.” hearts and full of happiness at getting well as chronographs for accurate time First contact was due at 6:30 a.m. away from Kerguelen at last after five measurement (Dick et al. 1998). This was and Corbet was not disappointed: “Oh! months of it, which sometimes seems an on top of the 26-inch refractor he was the happy moment, when from 6:00 am age, and at other times as nothing but a already commissioned to build for the to 6:30 I had been watching intently the mad whirling gap in one’s existence.”43 Naval Observatory. bottom of the Sun for an impression, and Unfortunately, both Corbet and Perry Beginning in May 1873, the teams I saw it — really and truly the happiest ultimately gave their lives to their work. gathered on the grounds of the Naval moment of my life.”42 It was exactly the A year after the transit, Corbet succumbed Observatory for a series of practice opposite of the “unpleasant time” that to a fever off the coast of Africa, cutting observations with an artificial sun and he had feared. short a promising career. Like Hell before Venus mounted on a building. Even Henry Corbet then kept a detailed observer’s him, Perry gained a reputation as a lecturer. Draper, one of the pioneers of

39 Maunder and Moore 2000, p. 66. 40 Ibid. 41 Ibid. 42 Ibid., p. 68. 43 Ibid., p. 69.

February/ fevrier 2004 JRASC 17 astrophotography, lent a hand for a few attempts to complete the data analysis stations in Canada and the United States. weeks. — a task that had fallen to him as secretary If professional interest was lacking, public In June 1874, the USS Swatara left of the commission. interest was at an all-time high. The New New York Harbour on a “milk run” to the Due to confusion about appropriation York Times reported that “A telescope Southern Hemisphere destinations. A of funds earmarked for this work, Newcomb was mounted on Broad Street, near the total of five parties were dropped off: was shortchanged $3000 and had to Stock Exchange, and the owner of this, Kerguelen Island, Tasmania (two parties), discharge his computers in 1876. The too, had all the business he could attend New Zealand, and Chatham Island (880 next year, new money was held up in a to.”44 Elsewhere in the city, some km east of New Zealand). The three legal dispute and Newcomb had to lay enterprising amateur astronomers set Northern Hemisphere parties travelled off his computers a second time. In 1879, up telescopes and made good money — to Nagasaki, Japan; Vladivostok, Siberia, an additional fiscal dispute caused a now the going rate was 10 cents a look! and Beijing, China. If anything, the predictable reaction: Newcomb let his (DeVorkin 1982) American expeditions were routine, with computers go a third and final time. For Though Newcomb doubted the few mishaps. Though travel had become Newcomb, this was the last straw and he usefulness of the transit observations in much more predictable, the weather had turned the work over to William Harkness. light of more recent methods, he led an not and on transit day the Southern William Harkness had developed expedition to Wellington, South Africa. Hemisphere stations were cursed with important equipment for the 1874 transit He set up in a garden of a seminary and poor weather much of the time. Like the and led an expedition to observe it from encouraged students and teachers alike British parties on Kerguelen Island, the Tasmania. Getting the transit data analyzed to partake in the observations. The teachers American party stationed there viewed and published became part of his life’s were women and some claimed to have only a portion of the transit. work. Meanwhile, the 1882 transit was made better observations than the Things were slightly better in the fast approaching. With no data published professional astronomers. Newcomb Northern Hemisphere. Unlike Chappe in by the Americans from their long-focus graciously wrote that “it was partly the Siberia, who battled the spring thaw, photographic method, European result of good fortune and partly due to Asaph Hall’s party in Vladivostok was astronomers began to suspect whether the quickening of the faculties which stuck fighting the Siberian winter. Gale it was superior, even though the British comes with intense interest,”45 though winds continually threatened to blow the had already admitted that their short- the women preferred to interpret their roof of their observatory off and lubricants focus photography method was a failure. success “as a tribute to the greater powers for the sidereal clock and heliostat froze. And, because the range of values obtained of their own sex.”46 Nevertheless, Newcomb The temperature difference between the from the visual contacts method for the gave them full credit for their observations inside of the photography house and 1874 transit was again intolerably wide in his report. outside was 30 degrees Celsius, plaguing (thanks in part to the black drop effect), the photography program with unsteady astronomers approached the 1882 transit air. with considerably less enthusiasm than In Beijing, James Watson caused a for the previous ones. stir among Chinese officials during his Other methods for determining the preparations when he discovered an solar parallax contributed to the asteroid. He diplomatically asked Prince disillusionment in the transit method, Kung, regent of the empire, to name the but with the next one not occurring for new minor planet. Today, the 139th asteroid, another 122 years, at the 11th hour, a “China’s auspicious star” or, Shui Hua “now or never” attitude prevailed and Hsing, is known by its contracted form, many countries hastily prepared Juewa (Ashbrook 1974). expeditions. For the Americans, partly Newcomb was optimistic about the through the efforts of Harkness, Congress results and thought the solar parallax finally approved funding for expeditions could be determined with a probable error four months before the transit. between 0.02˝ and 0.03˝ (Dick et al. 1998). It so happened that this transit was Figure 4. — Photo from the 1882 transit. Here he was sorely disappointed. Not only partially visible from North America, so Courtesy of the U.S. Naval Observatory Library that, he was soon to be frustrated in his there were many official and unofficial

44 DeVorkin 1982. 45 W.P. Koorts, The 1882 Transit of Venus: Observations from Wellington, South Africa, www.saao.ac.za/~wpk/tov1882/tovwell.html 46 Ibid.

18 JRASC February / fevrier 2004 For his part, Harkness observed the stations were set up from Winnipeg to embarassingly straightforward. Giant transit from Washington, D.C. where he Halifax and five of them enjoyed at least radio telescopes are used to fire a radar had the good fortune to view all four partial success — not bad for December beam towards Venus and the signal’s contacts. Three other American parties in Canada. The results were communicated return is timed by atomic clocks. had similar success so that in terms of to E.J. Stone, of Oxford, who used them Combining half the round-trip time with weather, the 1882 transit was much better to derive a solar parallax of 8.832˝, the speed of light gives the Earth-Venus observed, yielding better data and more corresponding to an Earth-Sun distance distance at that moment; this is photographs than the 1874 transit. One of 148,957,000 kilometres (92,560,000 transformed to the Earth-Sun distance of the 11 surviving photographic plates miles) (Fernie 1979). via Kepler’s laws. Based on these from the 1882 transit is shown in Figure measurements, in 1976, the International 4. In total, Harkness collected 1380 Tallying Up II Astronomical Union adopted the value measurable photographs from the various of 8.794148˝ ± 0.000007˝ for the solar American stations for the 1882 transit, Why weren’t better results obtained? constant, though the Earth-Sun distance, compared to only 221 measurable Precise timing of the contacts of Venus or the astronomical unit, is known to photographs for the 1874 transit. with the disk of the Sun was fraught with even greater precision: 149,597,870.691 The wealth of data swamped difficulties. Firsthand reports indicated km ± 0.030 km. With a precision of 1 part Harkness. He directed the measurement three major problems in the timings: (i) in 5 billion — like knowing the distance of the photographs, the time and latitude boiling of the image, (ii) a fuzzy ring between Vancouver and Toronto to within determination of each station and the surrounding Venus (too thick to be due 0.7 millimetres (Fernie 2002)! — this latest various subsidiary calculations that today to its atmosphere) and (iii) the notorious result has surely exceeded Halley’s wildest are done instantaneously by computer black drop effect (Bray 1980). Given these dreams. programs. In 1888, six years after the 1882 difficulties, one wit remarked to Sir George Thanks to their rarity, the transits transit, he finally published the results Airy, “You might as well try to measure of Venus provide a sort of “passing of the in the Astronomical Journal. He calculated the zodiacal light.”47 baton” through the generations. No one the solar parallax to be 8.847 ± 0.012˝ The first two effects were due to observed the 1631 transit and only two (Harkness 1888), a value that corresponded heating of the ground and parts of the people saw the next one, in 1639. The to a distance of 148,675,000 km (92,385,000 telescope by the Sun’s rays. Such heating 1769 and 1769 transits were observed by miles), with a probable error of 201,000 produces turbulent air currents that act perhaps a few hundred amateur and km (125,000 miles). He later revised this to change the telescope’s focus. Modern professional astronomers. The next pair, to 8.842 ± 0.0118˝ (Harkness 1891), solar telescopes are designed in such a in 1874 and 1882, was likely seen by corresponding to 148,788,000 km way as to eliminate these problems; 18th- thousands. Now, with television and the (92,455,000 miles), with a probable error and 19th-century astronomers found out Internet, the next transit in June 2004 of 199,600 km (123,400 miles). about the complications the hard way. could have an armchair audience of Harkness must have been pleased The “black drop” was first properly millions. to come up with a result when Newcomb described by Lalande in 1770 as a blurring In an address to the American couldn’t and then equally annoyed to see of the image due to normal terrestrial Association for the Advancement of Newcomb summarize results from a atmospheric smearing such that a meniscus Science in 1882, William Harkness gave variety of methods and give his results appears (Schaefer 2000). Diffraction within the following poignant words: low weight. It was Newcomb’s new value the telescope is also a contributing factor, “We are now on the eve of the second for the solar parallax from a variety of explaining why the 19th-century observers transit of a pair, after which there will be methods, 8.800˝, that was widely adopted who used larger aperture telescopes had no other till the 21st century of our era by astronomers. In fact, this was very less of a problem with the black drop than has dawned upon the earth, and the June close to the modern value. the 18th-century observers. A similar flowers are blooming in 2004. When the In Canada, Charles Carpmael, Director effect, due to the finite size of the eye’s last transit season occurred [1761 and of the Toronto Observatory, was in charge pupil, can be seen by looking at your 1769] the intellectual world was awakening of coordinating the 1882 Canadian transit thumb and index finger held very close from the slumber of ages, and that observations. He received a federal grant together near your eye. So, part of the wondrous scientific activity which has of $5000, which was mostly directed problem with the results was the initial, led to our present advanced knowledge toward acquiring good medium-sized overly optimistic expectations in the was just beginning. What will be the state telescopes (Sawyer Hogg 1982). These method itself. of science when the next transit season instruments no doubt greatly influenced Modern methods to calibrate the arrives, God only knows. Not even our local interest in astronomy. Thirteen Earth-Sun distance are almost children’s children will live to take part

47 Agnes Clerke 1902, p. 236.

February/ fevrier 2004 JRASC 19 in the astronomy of that day. As for Dick, S.J., Orchiston, W., & Love, T. 1998, Maunder, M., & Moore, P. 1999, Transit: When ourselves, we have to do with the Journal for the History of Astronomy, Planets Cross the Sun (Springer-Verlag: present….”48 29, 221 London) Fernie, D. 1979, JRASC, 73, 121 Nunis, D.B. ed. 1982, The 1769 Transits of Bibliographic Notes Fernie, D. 1976, The Whisper and the Vision: Venus: The Baja California Observations The Voyages of the Astronomers (Clarke, of Jean-Baptiste Chappe d’Auteroche, Part of the reason for this essay, on the Irwin and Company Ltd.: Toronto) Vicente de Doz, and Joaquin Velazquez eve of the next transit pair, was to bring Fernie, D. 2002, Setting Sail for the Universe: Cardenas de Leon (National History together some of the colourful tales and Astronomers and Their Discoveries Museum of Los Angeles County: Los journal excerpts that are scattered widely (Rutgers University Press: New Brunswick, Angeles) in books, magazines, and journals. The NJ) Pogge, R.W. 2000, Lecture 26: How Far to the best sources are Don Fernie’s two books, Gerard, J. 1911, in The Catholic Encyclopedia, Sun? The Venus Transits of 1761 and which describe the 18th-century transits Vol. 11, www.newadvent.org/ 1769, www-astronomy.mps. in warm detail. Interested members and cathen/p.htm ohio-state.edu/~pogge/ readers with access to back issues of Gillespie, C.C., ed. 1970, Dictionary of Scientific Ast161/Unit4/venussun.html the JRASC (that is, back issues that go Biography, Vol. 6 (Charles Scribner and Proctor, R., 1874, Transits of Venus: A Popular way back), are also encouraged to look Sons: New York), 233 Account of Past and Coming Transits. up Helen Sawyer Hogg’s Out of Old Books Harkness, W. 1888, AJ, 8, 108 Longmans Green, London. series for extensive and illuminating Harkness, W. 1891, PASP, 3, 46 Sawyer Hogg H. 1948, JRASC, 42, 153-159, journal excerpts from Wales and Le Janiczek, P.M., & Houchins, L. 1974, Sky & 189-193 Gentil. Telescope, December, 366 Sawyer Hogg H. 1951, JRASC, 45, 37-44, 89- Kilburn, K. 2002, Fr. Walter Sidgreaves (1837- 92, 127-134, 173-178, 1951 References 1919), www.u-net.com/ph/ Sawyer Hogg H. 1982, JRASC, 76, 362 astro-history/sidgreaves. Schaefer, B.E. 2000, American Astronomical Armitage, A. 1953, Annals of Science, 9, 47 htm Society Meeting 197, December 2000, Ashbrook, J. 1966, Sky & Telescope, 31, 340 Koorts, W.P. 1999, The 1882 Transit of Venus: abstract Aughton, P. 1999, Endeavour: The Story of Observations from Wellington, South Smith, F.R., 2003, JRASC, in press. Captain Cook’s First Great Epic Voyage Africa, www.saao.ac.za/~wpk/ Van Helden, A. 1995, in Planetary astronomy (Windrush Press: Moreton-in-Marsh) tov1882/tovwell.html from the Renaissance to the rise of Beaglehole, J.C., ed. 1963, The Endeavour Lamb, C. 1822, Recollections of Christ’s astrophysics, Part B: The eighteenth Journal of Joseph Banks (Angus and Hospital, Essays by Charles Lamb, and nineteenth centuries, ed. R. Taton Robertson: London) www.pinkmonkey.com/dl/ and C. Wilson (Cambridge University Bray, R.J. 1980, Proceedings of the Astronomical library1/essays.pdf Press: Cambridge) Society of Australia, 4, 114 MacDonnell, J.F., Maximillian Hell and His Woolf, H. 1953, Annals of Science, 9, 176 Chappe d’Auteroche, J.B. 1970, Journey into Mesmerizing Adventures, www. Siberia (Arno Press: New York) faculty.fairfield.edu/ Clerke, A.M. 1902, A Popular History of jmac/sj/scientists/hell. Astronomy During the 19th Century htm Daniel Hudon is an Assistant Editor with (Adam and Charles Black: London) Maor, E. 2000, June 8, 2004: Venus in Transit the JRASC. He teaches astronomy in the Core DeVorkin, D.H. 1982, Sky & Telescope, 64, 524 (Princeton University Press: Princeton) Curriculum at Boston University.

48 Quoted in Dick et al. 1998.

20 JRASC February / fevrier 2004