Distillations magazine

Unexpected Stories from Science’s Past
March 21, 2024 People & Politics

The Eclipse That Killed a King (and May Have Saved a Kingdom)

How the scientific prowess of King Mongkut of Siam helped stave off European incursion.

Daguerreotype of old man in royal clothing with infant child
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For most of history, humankind has been terrified of eclipses. The Vikings, the Maya, the ancient Chinese—they all trembled in fear, and understandably so. Imagine being an average farmer or herder and seeing the sun blotted from the sky with no warning. Terrifying stuff.

Given this fear, cultures around the world often linked natural disasters and untimely deaths to eclipses. Famous deaths that have been linked to eclipses include Charlemagne and his heir, Louis the Pious; the Prophet Muhammad’s son Ibrahim; and Jesus of Nazareth when the land was cast into darkness during his crucifixion.

Nowadays we’re likely to dismiss such links as superstition. Among astronomy buffs, however, the August 1868 solar eclipse in Southeast Asia is known as the King of Siam’s eclipse for its role in the death of King Mongkut, Rama IV, best known in the West as a character in the musical The King and I. But if the eclipse did lead to Mongkut’s demise, his deep love for astronomy helped save the kingdom itself from destruction.


Mongkut was born in Siam—modern-day Thailand—in 1804. The young prince was groomed for the throne from an early age and by all accounts enjoyed the royal life. Then, he gave it up—at least temporarily. At age 19, he entered a Buddhist monastery. Joining a monastery was a common step for young men, a way to teach them humility and discipline, comparable to modern princes attending military school. His sojourn as a monk seemed destined to be short-lived, however, when his father fell ill and died within a month of his ordination. Mongkut fully expected to assume the throne.

Except, life swerved on him. After his father’s death, royal advisors passed over young Mongkut in favor of his 36-year-old half-brother. Perhaps to avoid an ugly dynastic fight, Mongkut chose to remain a monk and maintain the austere lifestyle—begging for food, renouncing worldly possessions, avoiding contact with women. Quite a letdown for a prince.

Photograph of aged man in a white robe with hands together
Mongkut wearing a monk’s robe, undated.

Still, he made the most of his time. He led a series of reforms in Siam’s monastic orders, instilling discipline and tightening standards for conduct. He began studying European languages and cultures as well, partially in response to Great Britain and France’s growing aggression in Southeast Asia. Previous regimes had largely rebuffed European commercial interests in the country, but after the British defeat of Burma in 1826, and later China in 1842, Siamese rulers realized they could no longer ignore the West. To resist encroachment, Mongkut would have to understand the colonizers’ worldview. Among other things, he began studying Western geography and sciences, and was especially drawn to astronomy.

As an ancient kingdom, Siam had its own cosmology, including unique constellations. (Parts of what Westerners call Ursa Major, the great bear, they called crocodile stars.) The Siamese also used planets and stars to cast horoscopes, plot out their calendar, and determine the dates for religious holidays.

Mongkut, however, realized the monks in charge of the Siamese calendar were using outdated techniques and equipment, which led to poor and inaccurate results. Christian Europeans had experienced similar problems before reforming their calendars in the late 1500s. So Mongkut spearheaded a comparable reform. He began reading up on Western methods of tracking the sun and stars and eventually brought Siam’s Buddhist calendar up to date, rendering it more accurate and stable.

All the while, Mongkut waited to become king—although at several points his ascent seemed unlikely due to poor health. He lost all his teeth and at one point suffered a small stroke. Photographs from those years show him gaunt and white-haired, the right side of his face drooping from the stroke.

Finally, in 1851, his half-brother died. After 27 years as a monk, Mongkut ascended the throne at age 46. Mongkut married many times and eventually fathered 80 children beyond two he had sired as a teenager. The new king faced the serious task of keeping Siam independent from the British and French colonialists who were closing in on all sides, eager to carve the country up. He would have to tread carefully.

Monkut with his wife Debsirindra and children, before 1862. From the stereoscope series, Voyage de M. Iagor dans l’archipel Indien et dans le royaume de Siam.

Keeping his country independent would also require maintaining a strong home front, a challenge best highlighted by his dilemma regarding his children’s education. Many Westerners are dimly aware of this challenge due to the musical The King and I, whose plot revolves around the clash of two cultures: Mongkut wants to find a tutor to teach his children Western ways yet remains suspicious of most Westerners (especially missionaries), who he fears will convert his children to Christianity on the sly and undermine the kingdom. He eventually selects Anna Leonowens, a young widow from India who ran a school in Singapore, whose charm and influence help civilize him.

Unfortunately, that depiction has skewed how most Westerners view Mongkut, who actually enjoyed friendships with several missionaries. And while the king certainly put great value in preserving traditional Siamese ways, he knew far more about certain aspects of Western culture, especially science, than most colonialists. Indeed, the film’s depiction of a vain and brutish king was deemed so offensive that it’s still banned in Thailand today.

Photo portrait of an older women
Anna Leonowens, 1903.

The depiction of Leonowens was also ill-informed. In reality, she was most likely the daughter of a British soldier and an Anglo-Indian woman; she concealed her ethnicity throughout her life, probably to avoid prejudice. (Leonowens’s heritage was unknown when the musical was written.) Nevertheless, perhaps because she had a foot in both worlds, Asian and European, the real-life Anna proved a fine tutor, teaching Rama’s children Western ways without undermining their traditional values.

The weight of Mongkut’s royal duties could not stifle his interest in astronomy. When British officials visited his court in the mid-1850s, he quizzed them on the discovery of Neptune. Even more exciting, in the mid-1860s, Mongkut realized his kingdom would soon become the center of the astronomical world: on August 18, 1868, a solar eclipse would streak right across it.

Hearkening back to his days as a monk, Mongkut set out to calculate the exact time the eclipse would occur and how long the period of total darkness (the totality) would last in Siam. Such calculations were intricate business at the time, requiring demanding computations about the moon’s and sun’s precise speeds and paths through the sky. There were dozens of variables to juggle, and even a tiny mistake could throw off the entire result.

Map of Asia showing a blue arc across
Map of the path of the August 18, 1868, solar eclipse, from Archives des missions scientifiques et littéraires, 1868.

But Mongkut had learned his astronomy well. He determined that the “shadow cone” of maximum darkness would sweep across the small jungle village of Wakor in southern Siam. He calculated the length of totality as 6 minutes, 46 seconds. To check his result, he got in touch with some French astronomers in the region. They told him that he was off by only two seconds. Pretty impressive for an amateur.

Among officials in Siam, the eclipse provoked far less excitement. In fact, royal astrologers tried to dissuade the king from traveling to view the eclipse; his horoscopes for August 18 looked ominous. But Mongkut dismissed their advice. This was science, not superstition. He could not miss one of the great astronomical events of his lifetime.

The village of Wakor sat amid craggy mountains on a lush, low-lying floodplain. Mongkut brought his entire kingly retinue down, including his son, the heir apparent, as well as dozens of servants and a train of elephants. He was joined by a team of French astronomers and the inevitable French and British colonial officials who, like the bugs that swarmed this jungle village, seemed to pester him at every turn.

Old black and white photo a group of people in front of a building
Mongkut with foreign dignitaries at Wakor, August 1868.

Any tension between the camps was laid aside that day; everyone simply enjoyed the magic of the eclipse—the razor-sharp shadows, the sudden drop in temperature, the confused calls of monkeys and birds, the stirring of insects. Like no other event, an eclipse makes you aware that you’re on a celestial body—on a planet spinning amid other planets, at unfathomable speeds and distances. You stand in awe before the cosmos.

Mongkut was especially pleased. French astronomers had patted him on the back for a prediction that came within two seconds of their figure. But in truth, it was the professionals who were off; Mongkut’s estimated time of totality was dead right. He celebrated this triumph afterward with a feast that included buckets of champagne on ice, a decadent luxury in tropical Siam. It was truly one of the great days of his life.

Black and white photos of sun in eclipse
Photographs by British soldier and astronomer James Tennant of the 1868 eclipse, as seen from Guntoor, India.

Sadly, it would also prove one of the last days of his life. Because while he and the astronomers guzzled champagne and gorged on a royal feast, swarms of insects were feasting on them—including malaria-carrying mosquitos.

It’s impossible to pin down when exactly the fateful bite happened. But given that mosquitos are most active at dusk—and given that eclipses produce a false dusk that confuses animals—it’s possible it occurred during the king’s beloved eclipse, and even because of his beloved eclipse. Regardless, we know a mosquito bit Mongkut at some point during the trip to Wakor, and malaria microbes passed into his bloodstream.

Mongkut wouldn’t have noticed at first; malaria takes a few days to emerge. But when it does, there’s no mistaking it. The quaking chills, the roasting fevers, the bed-drenching sweats. A body-destroying cycle of hot and cold, hot and cold, over and over and over.

Mongkut wasn’t the only victim. Several British and French officials fell sick as well, as did the king’s son, Prince Chulalongkorn. But while most people pulled through, including the prince, Mongkut did not. Weak from 27 years of hardship as a monk, he died six weeks after the expedition. Ironically, Mongkut’s court astrologers had proved right—the eclipse had indeed been his doom. (In a further irony, despite his admiration of most Western science, Mongkut refused malaria medication even on his deathbed.)

But if a fascination with astronomy cost the king his life, it also helped save his kingdom. Again, British and French colonizers had been grabbing whatever land they could in Southeast Asia, with the British conquering Singapore, Burma, and Malaysia, and the French taking over Vietnam, Cambodia, and Laos. Siam sat smack in the middle of all of them, and both European powers were circling it hungrily.

Old black and white photo of elaborate Thai buildings
The temporary crematorium, or merumat, built to house Mongkut’s funeral pyre, ca. 1869.

Ultimately, though, neither country colonized Siam. This was due in part to the fact that Siam served as convenient neutral territory between the competing European belligerents—a buffer, in other words. But the other big reason was Mongkut’s passion for Western knowledge. Whenever he chatted to European officials about Neptune or eclipses, he struck them as very modern, very up to date. So did his children, thanks in part to their education under Anna Leonowens. His son and successor, Chulalongkorn, was also savvy about adopting Western innovations, instituting public health and sanitary reforms and helping establish the first railroads and electrical power plants in Siam.

In short, Mongkut and his heirs impressed the Europeans by playing on their prejudices of what modern leaders should do and say. As a result, the Westerners trusted Siam would play ball when it came to trade, alliances, and other matters, and therefore they largely left Siam alone. The kingdom remained proudly independent—one of the very few places never colonized by European powers.

It’s a truism that science and politics don’t mix well. Politics corrodes the independent judgment that makes science possible, and most politicians simply don’t (or can’t) think like scientists. But the King of Siam, Rama IV, was adept at both. And when his country was at stake, science proved to be just politics by other means.

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