The King of Siam’s Eclipse, 1868

A total eclipse of the sun in the mid-19th century led to the discovery of Helium and the death of Rama IV, the King of Thailand, a self-taught polymath who had predicted the event several years before and to a degree of accuracy exceeding his European contemporaries.

On August 18, 1868, the moon’s shadows swept across the earth from Yemen to Australia during a total solar eclipse in which the moon passes between the sun and the earth and its apparent size neatly covers the disc of our star. 

Such events (although not rare – a total eclipse happens on average every 18 months somewhere in the world) are a perfect opportunity to observe the corona, the outer part of the sun’s atmosphere, which is normally hidden by the brilliant light of the sun’s surface.

Eclipses therefore yield a wealth of scientific data and were intensely studied and eagerly awaited, particularly during the 19th century when men of science were actively gazing Heavenwards with ever-better instruments and making rapid progress in the fields of physics, chemistry, and astronomy.

The date and timing of the 1868 eclipse had been calculated two years before and the most accurate prediction (by two seconds) came not from the professional scientists of the day, but from a rather remarkable source – King Mongkut of the Far East Asian country of Siam, now modern-day Thailand.  In commemoration of his contribution, the Thai Astronomical Society and NASA, now name the 1868 event as "The King of Siam's eclipse".

The King, styled as Rama IV in the Thai dynasty, was a remarkable polymath.  Born in 1804, he ruled Siam from 1851 until his death, the same year as the eclipse.  He presided over the country at a time of increasing pressure from Western powers, greedy for colonial expansion.  Siam was rich in natural resources and the north was a perfect location for the lucrative cultivation of opium.  It is a testament to his diplomatic skill (he learned English well enough to translate treaty documents for his court) that he managed to keep his country independent when neighbouring Myanmar (then Burma) and Cambodia became European colonies.

He kept up a lively correspondence with Queen Victoria (addressing her as, “my dear sister”) and accorded a full state welcome to a letter that she sent, treating it with the same dignity as the person of the Queen herself.  Although Mongkut accepted unfavourable trade deals (such as the 1855 Bowring treaty which legalised opium export into Siam when previously he had forbidden the drug) he kept his country independent.  Siam was respected by the superpowers of the time who admired Siamese culture, customs and business acumen and the country’s acquisition of Western science and methods undermined their argument that colonisation was needed to bring “civilization”.

Outside of Thailand he is best known as the King in the 1951 Rodgers and Hammerstein musical “The King & I”, which was made into a film in 1957 with Yul Brynner playing the eponymous monarch.  The musical was based on the memoires of Anna Leonowens who had been a schoolteacher at his court in the 1860s when he wanted his 39 wives and concubines and 82 children to receive elements of a Western-stye education.

Mongkut spent almost the first thirty years of his life as a monk when he was passed over for succession to the throne in favour of a more experienced Prince.  It was during this period that he studied Latin, English, and Astronomy and became acquainted with Christian missionaries and foreign traders and sailors.  He rose to become the Abbot of a temple in Bangkok and even allowed a Christian friend to preach sermons there since he admired the morals and achievements of the foreign faith although its doctrine confused him.

A legacy of his intellectual curiosity and tolerance, his reign was one of modernisation and reforms with Siam emerging as a close partner of its Western allies.  One anecdote relates that he offered a herd of domesticated elephants to the US president James Buchanan, to be used as beasts of burden.  The US politely declines and pointed out that the weather might not suit the animals and that steam engines now served just as well.

The King’s enthusiasm for the 1868 solar eclipse (which he calculated accurately using a mix of Siamese and Western systems) was such that he had a special viewing pavilion built in the jungle at the village of Wakor, south of Hua Hin.  He judged this to be an optimal location from which to observe and invited various dignitaries and foreign representatives to accompany him. 

Many nations had had the same idea, and two expeditions had been sent from Germany to Aden, with others viewing in India and the Celebes Sea.  It was the first eclipse since the 1859 theory that bright lines in the spectrum of light would correspond to chemicals present within the sun.  This was tested and led to the discovery of a new element named Helium from the Greek “Helios” for sun.

Although King Mongkut’s own observations were a success, the eclipse viewing would ironically be his downfall.  He and his son caught malaria while in the jungle and six weeks later, back in Bangkok, the King died and his son, who survived the disease, succeeded him.

Today, his ashes are interred beneath the Buddha image of a small temple (by Thai standards), to the east of the Grand Palace in Bangkok.  A narrow alleyway gives access to a richly decorated chamber where, at the very back, and if you look closely, you can find a mural showing the King bent over a telescope and studying the eclipse that now bears his name, one small part of his unusual life and legacy to his country.