The Day the World Discovered the Sun (6 page)

A second spectacle awakened the senses upon passing the stone fortress. As one contemporary put it, the bulk of the city was located “a good musket shot to the west of the castle.”
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And walking toward Cape Town's sea of thatched roofs and the company's sumptuous garden beyond, a brutish contradiction came into view that visitors from afar had fresh eyes to see.

While admirers like Linnaeus praised Cape Town as “paradise on earth,” it was also a city built, maintained, and run on an often unspeakably brutal institution of slavery. Gibbets around the town's periphery exhibited condemned slaves' maimed corpses and body parts.
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Mutiny onboard a ship might lead to executions, but the punishment of swift death looked merciful compared to the drawn-out and horrific ends revealed by these vulture-chewed charnel remnants.

From the porters who carried the expedition's gear to the servants in Tulbagh's entourage to the manpower that kept the bulk of this company town moving, the city's slaves also served as living mementos of conquered cultures to the north and east. Tribesmen from mainland southern Africa and Madagascar, as well as Indians, Ceylonese, and Indonesians, all made up the city's shackled population. Many slaves eked out their miserable lives in an overcrowded lodge near the castle, where the inhumane conditions (in some years the mortality rate was 20 percent) would have been unacceptable even in the Dutch East India Company's zoo farther inland.
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The zoo comprised a small portion of a forty-three-acre rectangular garden that practically defined the city. Sailors the world round may not have visited or even known of the Compagnies Garten. But if they sailed the Cape regularly, they had certainly feasted on its output. Mutton, beef, fruit, vegetables, bread, wine, and fresh water all flowed like manna—ensuring visitors like Mason and Dixon could scarcely want for good food and drink during their stay. And just east of Cape Town's cornucopia lay the company stables, beyond which city officials allowed Mason and Dixon to set up.
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As the rainy season approached, the men turned toward their final pretransit duty—constructing the observatory. The first two and a half weeks of Mason's meticulous Cape Town observer's log recorded just one night of stargazing. Had the duo wanted to calibrate their instruments, the skies didn't permit. It was cloudy, Mason notes, “nearly all the time.” Mornings especially, he said, “are very subject to thick fogs, which lie till 9 or 10 o'clock. But I hope our intentions will not be finally disappointed.”

Mason wrote back to his paymasters at the Royal Society on May 6 that Tulbagh had “supply'd us with necessaries for building an observatory, but the Dutch are so slow and so few speak English that I was very doubtful of getting it completed in time.”
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So instead, Mason and Dixon hired the
Seahorse
's six carpenters—men trained to patch leaky hulls and masts shot through with cannon fire—to build their tiny wooden shrine to the stars. The expedition's account books note a hefty cash outlay of £12, 6 shillings, 6 pence ($3,000 in today's money) going toward timber, a rare and expensive commodity on the Cape. The carpenters clearly knew how essential their services had become, and they charged accordingly. Their ten days of labor cost another £12, along with a hefty sum of £13, 16 shillings ($3,400) covering the costs of “victualing.”
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By May 18, the well-fed men had completed the twelve-foot-wide structure and set the observers' expensive pendulum clock onto boards sunk four feet in the ground. The whole structure was less than nine feet tall, with three feet occupied by a conical roof. The roof rotated
with a sliding aperture that enabled both telescope and quadrants to be pointed through the hole. Heedless visitors to the cramped space found ample opportunity to stub their toes and slam their head on the low door.

For five weeks, Mason glared at the skies. Clouds and rain cursed the explorers practically every day and every night when they tried in vain to point their telescopes at the planets and stars. The observatory was now fully ready, but the finest instruments in the world meant nothing if the weather refused to cooperate.

At dawn the next morning, June 6, the sun would rise with the Venus transit under way. Cape Town provided a window seat for only the second half of the planet's progress across the solar disk. The three hours immediately after sunrise would see Venus's ink spot shadow crawl up the rest of the sun's face and then disappear from the top edge, like a dog tick climbing and then falling from a lamp. This celestial spectacle—in conjunction with other transit measurements elsewhere on the globe—could still give the Royal Society the numbers it needed to triangulate the sun's distance.
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On the other hand, the society would hardly look kindly on a Venus transit mission to Bencoolen that never reached Bencoolen and then, even from its makeshift secondary observatory in Cape Town, returned home with nothing but tales from afar. If the skies on the morning of June 6 were like the cloudy skies every other morning during their Cape Town stay, these Royal Society hired hands could probably expect more love letters from the governing council like the one they'd sent to Mason on January 31.

But on the night of June 5, their fate took a turn. The clouds began to dissipate. Mason and Dixon, for only the second night of their entire Cape Town stay, were now free to do their job.

To the east, the star Antares—brightest star in the constellation Scorpio—rose above the jagged peaks of the Stellenbosch Mountains.
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The occasional whinny from the Dutch East India Company stables broke the studied silence of the most serious night in these men's lives. Mason trained his scope on Antares over the course of the night for thirty-two separate measurements of its height above the eastern, and later the western, horizon. At Mason's each recording of the star's altitude, Dixon read off the clock down to the half second. Clouds obscured four of the thirty-two measurements, however, as if reminding the astronomers how close to precipice they remained.

With the night chill and the seasonal offshore Cape winds buffeting the round-topped shanty, the observers took turns rotating their tiny dome to the other star they monitored throughout the night: Altair. Known to sky watchers as one of the three vertices in the “summer triangle,” this late-rising star—whose progress through the sky Dixon closely monitored—glimmered to the north over Table Bay.

Dixon completed his final measurement of Altair in the northwestern sky as the first fingers of dawn colored the bay's anchored ships in shades of marzipan. Mason and Dixon rotated their observatory roof toward the east. And so at 5:45
AM
on this morning of sweaty palms and adrenaline, they cast their fate with a turgid atmosphere.

The sun should have risen, Venus's transit already under way, glazing the top of Tygerberg Hill with the day's first hint of sunlight. But Mason logged in his journal, “The sun ascended in a thick haze and immediately entered a dark cloud.” The skies had turned sour again.

When he met them after their respective Venus transit experiences, Nevil Maskelyne had had little interest in hearing Mason and Dixon's stories of bad weather.

After spending another three months in Cape Town, the two explorers had arrived in October in the coastal town of the British-occupied island of St. Helena—one of the remotest islands on the planet, 1,100 miles west of the nearest African coastline and 1,900 miles northwest of the Cape. They'd come to assist Maskelyne, a fellow Royal Society explorer.

The twenty-nine-year-old Anglican curate had been holed up on this seven-mile-wide shard of volcanic rock for more than a year. Maskelyne's assistant, the navigator Robert Waddington, had left his boss behind soon after June 6. (The Royal Society had hired Waddington only to help with transit observations.) In fact, Waddington enjoyed a more productive time returning to England than he did during his St. Helena stay. Sailing home, Maskelyne's assistant so impressed the ship's captain with his lunar navigational skills that the captain refused any payment for Waddington's passage.

On the other hand, at dawn on June 6, Maskelyne and Waddington experienced much the same nervous anticipation that Mason and Dixon had known. Clouds flirted with the sun, occasionally blurring it or hiding it altogether. But Maskelyne and Waddington had also snuck in some measurements of an immersed Venus's varying distances from the sun's edge. Yet all was trivia unless the St. Helena observers could secure one crucial number: the exact time (down to the second) when Venus's silhouette touched the inside of the sun's edge. (In 1761 only the latter half of the Venus transit was visible in the south Atlantic. So lacking any ability to measure the complete duration of the transit, a different method of computing the sun's distance became necessary: one that compared from different observing stations on the globe the exact time of a single moment in the transit—in this case the instant when Venus first began exiting the sun's disk.)

Just a few minutes before Venus's shadow began to exit the sun, the whole proceeding disappeared from view. Maskelyne and Waddington watched, dumbstruck, as a cloud killed the purpose of their entire transatlantic adventure.

Mason and Dixon, on the other hand, had experienced just the opposite. Clouds obscured parts of Venus's middle passage across the sun. But Cape Town's skies cleared when the crucial moment arrived. Mason wrote “very clear” in his record of the moment of internal contact between Venus and the sun.

Maskelyne—none too modestly referring to himself as “our astronomer”—later wrote, “The cloudiness with which the island of St. Helena is so frequently infested . . . unfortunately deprived our astronomer of the important observation of the exit of the planet from the sun's body.” But, he added, “on this trying occasion he is said to have born his disappointment with so much fortitude as to have said he hoped to meet with better weather to observe the next transit.”
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Endowed with a squarish and sometimes snarly face, Maskelyne commanded an intimidating presence only heightened by his determined and singular focus. Maskelyne's claim of meeting such crushing failure with pluck and renewed determination may not be completely outlandish. Perhaps he ultimately was excited for Mason and Dixon's success. But the air surely weighed heavy at Mason's first meeting with Maskelyne at St. Helena.

Mason and Dixon's October arrival at Jamestown—a small (British) East India Company island way station—came with the fairer weather of late (Southern Hemisphere) spring. The rough, southeasterly winds of the open Atlantic mellowed into offshore breezes as Mason and Dixon's frigate rounded the bay and tucked into Jamestown's half-moon-shaped cove. The distant din of a ghost town awakening greeted the visitors, as country farmers flocked to port to engage in the chief economic activity this shut-in community could claim: trading and haggling with sailors from visiting ships.

The dock became a mini marketplace hawking fragrant baskets of produce—yams, bananas, grapes, and figs—and squawking hens and geese in exchange for calico, silk, or sugar. Every day as Mason came down to the waterfront to measure the tides (part of his daily routine
for Maskelyne), he came to learn the strange rhythms of an economy moored to the whimsy of passing ships.

He also came to know life working for a man at least as prone to drink as his underling, Dixon. The reverend's liberal purchase orders of casks of rum and claret and hogsheads of old porter
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for his St. Helena stay reveal a more liquid-based life of the spirit than what holy orders typically entail.

Maskelyne was certainly facing down a host of rich associative memories—if not quite spirits or ghosts—on this lonely island, too. Eighty-four years before on St. Helena, the legendary Edmund Halley had observed a transit of the planet Mercury (when Mercury briefly passed in front of the sun). “I very accurately obtained,” Halley told a 1716 meeting of the Royal Society, “with a good 24-foot telescope, the very moment in which Mercury, entering the sun's limb, seemed to touch it internally, as also that of his [i.e., Mercury's] going off.”

The problem was that Mercury was so small and so far away that it required both a sizable telescope and one of the world's finest astronomers to spot and track a Mercury transit. If only Mercury were bigger and closer to earth, Halley surmised, the most vexing problem in astronomy could be solved. But, of course, there is a planet that meets this description. So, Halley realized, Venus transits were the answer. At the time of the next transit, Halley proselytized in his writings and lectures, the great nations of the world should put multiple observers at different locations across the planet. Then they could combine their Venus transit measurements to discover the angular shift the sun makes against the sky when observed from different locations on earth. Given an accurate number for the sun's angular shift, or “solar parallax,” the physical distance to the sun was a schoolboy's geometry problem. However, the showstopper came when Halley calculated the date of the next Venus transit. The world would have to wait, he found, until 1761. The true dimensions of the solar system would next become visible only in the year of Halley's 105th birthday. On his deathbed in 1742, Halley
knew he was still a generation away from this watershed moment in human history.