The challenges of measuring Mount Everest

As the Survey of India plans to remeasure Mount Everest, there is one mystery that endures—the role of a 19-year-old Indian mathematician in the discovery of the world’s highest peak


Swarna Subba Rao at the Shivalik range. Photographs by Priyanka Parashar/Mint
Swarna Subba Rao at the Shivalik range. Photographs by Priyanka Parashar/Mint

At 7,000ft above mean sea level, Hathipaon is far removed from the touristy din of Mussoorie, the Uttarakhand hill station 8km away. Another few hundred metres further up, a ridge stands like a frontier post—with the Shivalik hills in the south, the seemingly endless Gangetic plains at its base, and the concrete warren of Uttarakhand’s busy capital city, Dehradun, in front. Turn around, and the Himalayas are visible on the north-eastern horizon, in their primeval, snow-clad best.

It was here that the surveyor general of India, Britain’s George Everest, chose to settle down in 1833. An airy residence called Park House, a mini laboratory, an observatory and a bungalow that was christened Logarithm Lodge were his base for a little over 10 years.

A hill rises steeply, about 1,000ft, adjacent to the house. It is said that Everest would occasionally climb it for his observations. The hilltop offers views of the icy presence of Himalayan worthies like the peaks Bandarpunch, Kedarnath, Kamet, Trishul (West) and Nanda Devi. When I visited it in February, a rambunctious group from Panipat reached the hilltop, locally referred to as the George Everest peak, before me—recording their presence by stringing up a “flag” in the form of a handkerchief on the branch of a tree, delighting in the sunset hour and the view.

Everest, who wasn’t keeping good health, took advantage of the location to recuperate as he worked on one of the grandest geographical projects in human history, the Great Trigonometrical Survey of India (GTSI). The British authorities wanted him to be based in Calcutta (now Kolkata), then the capital, instead of Hathipaon. Everest, in his dual role as superintendent of the GTSI and the surveyor general, had his way, though he had to agree to a concession. Kolkata would continue to be the computational and administrative hub of the Survey of India (SOI); a separate office would be set up in the plains of Dehradun and Everest himself could remain close to his work at Hathipaon.

What was the work? In short, it was the measurement and mapping of India, an exercise both in geodesy and geography.

"There is no doubt that Sikdar was the chief computor at SOI’s Kolkata office when the measurement was done. George Everest saw enough “mathematical genius” in Sikdar to describe him as his “right arm”, eventually paving the way for the latter to inarguably be the first significant native Indian association with the peak"-

It was in 1800, a year after the British forces decisively defeated Tipu Sultan in the last of the Anglo-Mysore wars, that British surveyor and geographer William Lambton suggested a mathematical and geographical survey of peninsular India. Studying the arc of a meridian by measuring the distance between two points with the same longitude, may have been the primary motivation, but the colonial interest in understanding the lay of the land was implicit. Lambton’s project to establish the size of India, starting from the southernmost tip of peninsular India, 78 degrees east from Cape Comorin (now Kanyakumari), got the government’s approval soon.

The National Survey Museum in Dehradun.
The National Survey Museum in Dehradun.

In 1802, work began on this ambitious project with the establishment of a simple baseline. This involved triangulation. In his book The Great Arc: The Dramatic Tale Of How India Was Mapped And Everest Was Named (2000), historian John Keay explains triangulation as conceiving of three mutually visible reference points, usually on prominent hills or buildings, as the corners of a triangle. Knowing the exact distance between two of these points, and then measuring each of the angles made by the connecting sightline (an imaginary line-of-sight between points A and B) with those of the third point, could help establish the distance and position of the third point. One of the newly determined sides of this triangle would then become the base for a second triangle embracing a new reference point whose position would be determined in the same way. Another triangle would thus be completed and one of its sides would become the base for a third, and so on.

Slowly, the grid of triangles moved up from Kanyakumari, measuring heights and distances all the way north to Hyderabad, over 700 miles away. After Lambton’s death in 1823, his assistant, Everest, took over as GTSI superintendent. Between 1833 and 1843 (the years Everest moved to Hathipaon and he left India for good, respectively), the survey reached a critical stage. Banog, a hilltop that is just a short trek away from Hathipaon, was the terminal base station of the north-south arc starting from Kanyakumari.

Building on Lambton’s pioneering work, Everest would initiate geodetic innovations, such as changes to the theodolite—an instrument used for measuring angles between two points—concluding the Great Arc of the meridian survey in 1841—the longest measurement on the earth’s surface ever to be accomplished in human history.

Andrew Scott Waugh, who succeeded Everest as surveyor general in 1843, would use the results of Everest’s Great Arc as the base for a survey of the Himalayas. Though British interest was piqued by sightings of the perennially snow-capped mountains in Nepal, a country which didn’t allow outsiders, it was only in 1856 that Peak XV would be declared the highest point on earth.

In a story that some consider apocryphal, but one which is recounted in multiple books, Radhanath Sikdar, a 19-year-old Bengali mathematical “genius” who was handpicked by Everest as a computor at SOI’s Kolkata office, rushed into Waugh’s office exclaiming, “Sir! I have discovered the world’s highest mountain.” Keay rubbishes this story. He reasons that Waugh’s office was in Dehradun while Sikdar’s was in Kolkata, but admits that “it is quite probable that Sickdar’s (the spelling Britishers used) computations provided the first clear proof of XV’s superiority”. After a rigorous and painstaking study, the announcement was finally made at the Asiatic Society in Kolkata in 1856: Peak XV, rising 29,002ft above sea level, was indeed the roof of the world.

"The Survey of India’s proposal to remeasure Mount Everest will definitely try to infer if the peak has shrunk following the 2015 Nepal earthquake.... If this current mission is successful, I’ll be only the third person from India to announce the height of Everest."- Swarna Subba Rao

Waugh, a disciplined understudy of Everest, but without his magnetic personality, and forever beholden to his former boss, suggested the peak be named Mount Everest. Despite opposition from many quarters, including Everest himself, the name stuck. Local names like Chomolungma, Qomolungma and Sagarmatha fell into disuse.

Views of the Himalayas make the area around Everest’s house in Hathipaon a picnickers’ spot. The house itself remained a footnote till some years ago, when local authorities re-plastered the walls and applied a fresh coat of paint. Visitors have left their mark—almost every inch is marked by graffiti, including one bit that reads, “Who is Everest? Me Rupinder.” A small signboard outside the house outlines Everest’s contribution to our geographical understanding of India.

Everest himself had a late introduction to the Himalayas and there is no record of him ever being fascinated by their mystical, mesmerizing presence. Keay’s research tells us that he never offered his expertise to measure the height of the Himalayan peaks and scorned attempts by those who tried. In fact, Everest never set eyes on Peak XV.

A shrinking giant?

At SOI’s headquarters in Dehradun, a large, horizontal, framed photograph of Mount Everest and its surrounding peaks overlooks the office of Nitin Joshi, SOI’s geodetic and research branch director. The first measure of the mountain in 1856 is, understandably, the mightiest among SOI’s many accomplishments since it was set up 250 years ago. Fittingly, then, to mark the milestone year and its survival as the oldest scientific institution in India, SOI plans to remeasure Mount Everest. The current surveyor general of India, Swarna Subba Rao, announced this at the Geospatial World Forum in Hyderabad in January.

The photo of the Everest in the office of Joshi, who heads the technical team working on the current remeasurement plan, puts the height of the peak at 29,028ft. In 1956, 100 years after the first measurement, Rao says SOI used “indirect trigonometric methods” for a second round of surveying: the 26ft difference from the previous measurement underlined the efficacy of the measuring process used in the 19th century survey.

Since then, not unlike the competitive spirit evident in scaling the Everest, other countries too have attempted to measure the peak that straddles the border between Nepal and China. In the 1970s, a Chinese team put its height at 29,029.29ft. In 1999, an American expedition, using a global positioning system (GPS) device, found the height to be 29,035ft—yet again reiterating the credibility of the 1856 finding, which used traditional trigonometric methods and calculated the height from a distance to arrive within 33ft of the American figure that used modern technology. Though both the Indian- and American-measured heights of 29,028ft and 29,035ft, respectively, have been widely referred to as the height of Mount Everest, a 2005 Chinese survey created a stir when it found the height had come down to 29,017.16ft.

Even though the 2005 Chinese survey measured the actual height of the rock-head of the mountain and not its height with the ice cap at the summit, there has been a growing murmur in the scientific community that the Everest, considered to be part of a growing mountain range, might have shrunk in height following the 7.8 magnitude Nepal earthquake in 2015—an assertion that the proposed SOI survey will attempt to assess.

One needs to go back in geological time to understand this growing mountain range theory.

It is said that approximately 400 million years ago, there was a vast sea between India and Asia called Tethys, where the Himalayas now stand; the discovery of rocks with marine fossils like that of the sea lily at the pinnacle has confirmed this. Around 50 million years ago, India, as we know it now, moved away from the supercontinent, Gondwana, and started travelling north. Over 30 million years, the land mass travelled 4,000 miles (6,437km) north and collided with Asia. The impact resulted in the sea floor being raised abruptly, with the northern margins of India buckling and folding under pressure. Spread across 2,400km and home to 14 of the world’s highest peaks, the folds from the collision are now called the Himalayas. The Indian tectonic plate continues to push further into the greater Asian plate.

“The Survey of India’s proposal to remeasure Mount Everest will definitely try to infer if the peak has shrunk following the 2015 Nepal earthquake,” says Rao, sitting in Survey House, his official, colonial-era residence in a quiet corner of Dehradun. Even though no major and comprehensive scientific assessment work has been conducted since the Nepal earthquake, some members of the scientific community believe that the Everest, along with other peaks in the region, could even have moved sideways. Preliminary studies conducted over the years maintain that the Everest has been rising by 0.1 inches annually and sliding in a north-east direction by over an inch every year. “That is something we will consider as well,” says Rao.

On the day we meet, The Kathmandu Post carried an opinion piece by a former director general of Nepal’s survey department advising India to collaborate with Nepal and China on the remeasurement exercise. Since the announcement by Rao in Hyderabad, the international press, including the BBC, has quoted Nepalese officials as saying that no agreement has been reached on allowing an Indian team access to measure the Everest.

Rao, however, says the issue had come up at the 2016 annual meeting of the boundary working group that monitors the boundaries between India and Nepal. “Krishna Raj (director general of Nepal’s survey department) had agreed. (The) government of India is willing to bear the cost. We discussed technical issues, the inclusion of Nepalese officers in the expedition and the formalities will be completed through diplomatic channels. Meanwhile, we have already had some technical-level meetings with the Nepalese side. It will be a combined survey where the results too will be declared through a combined effort,” says Rao.

Having received “all the approvals in principle” from the Central government, the remeasurement proposal is currently awaiting the go-ahead from the Union ministry of external affairs. As things stand, a 30-member team will be formed: half of it will consist of officials, scientists and climbers from India and Nepal, the rest will be Sherpas; “without their help the mission can’t be successful,” says Rao of Sherpa support. “I’m proposing to measure by two methods. First, we want to send someone up the mountain with a GPS device to measure the peak using satellite technology. Simultaneously, we will be taking measurements on the same day from different locations on the ground also using the old trigonometrical method,” says Rao.

The combination of modern GPS technology and the traditional triangulation system will make for a “solid” round of surveying, he believes. “We will select five-six places for observation, including a couple in Nepal, and solve as many triangles as possible. The criterion is the angle and the ideal angle is one of 45-50 degrees from which one can see the Everest comfortably.”

One really understands the breadth of the triangulation method used for the GTSI in the 19th century when Arun Kumar, a soft-spoken man in charge of the library and SOI’s National Survey Museum in Dehradun, makes me pause before an extraordinary map of India, seemingly joined together by what looks like a triangular grid of necklaces.

It is while working on the north-east longitudinal series, under Waugh’s supervision in the mid-1800s, that British surveyors first spied the gleaming Himalayan peaks from the Gangetic floodplains of Bihar and Uttar Pradesh, places like Bhagalpur and Pilibhit, as well as from Darjeeling in West Bengal. One of the earlier records of Himalayan sightings, though, is by William Jones, a judge at the Calcutta high court. He would go on to pursue his interests as a linguist, historian, philologist and naturalist and found the Asiatic Society of Bengal in Kolkata in 1784.

Around sunset on 5 October 1784, Jones would get “a distinct view from Bhagilpoor (Bhagalpur) of Chumalary peak (Jomolhari in Bhutan)….” He went on to say that there was “abundant reason to think that we saw from Bhagilpoor the highest mountains in the world, without excepting the Andes”. It was because of Jones, Keay opines in The Great Arc, that the height of the Himalayas was added to the agenda of Orientalist research.

Open to the general public only on special days, Dehradun’s National Survey Museum is a treasure trove for geodesists, geographers, cartographers and researchers as well as those interested in the history of mapping mountains. Most of what is on display goes back to the GTSI days. Among handwritten letters by Everest, Colby compensation bars, chains and instruments used for measurement, are a couple of theodolites dating back to the 19th century. Photographs with captions of important personalities line the walls, while a shelf contains a starfish marine fossil found in the Himalayas. There are black and white photographs of Everest, Waugh, Sikdar, and surveyors at work. The GTSI men also braved an unfamiliar terrain of wild forests, infested with bandits and tigers. Many succumbed to malaria and typhoid; a frame at the museum lists the names of some of those who died.

In Kolkata, one would often cross a 75ft-high masonry tower a little north of Shyambazar. Neither a factory chimney nor a watch tower, the tall structure would be plastered with cinema posters or drying dung cakes. About a decade back, the authorities whitewashed it and pasted a brief history of the tower on it. It told us of its 1831-vintage, the time when Everest, then based in Kolkata, built it for work related to the GTSI. In his autobiographical book, High Exposure: An Enduring Passion For Everest And Unforgiving Places, mountaineer-film-maker David Breashears recalls seeing one such GTSI tower in the plains of Bihar, a place far removed from the Nepal Himalayas but from where, before air pollution dulled the scene, one could get a view of the Himalayas.

Standing in front of the triangulated map of India at the National Survey Museum, I wonder how the towers could have contributed to the measurement of Everest. Such towers (built where no other tall structures were available) did contribute, even if not directly, Kumar tells me.

For Peak XV was eventually calculated from six different places in the plains by surveyor J.O. Nicholson; each survey site was located well over 100km away from the actual peak. The average of the height readings measured from Jarol, Mirzapur, Janjipati, Ladnia, Harpur and Minai, where similar towers had been erected to make them intervisible for triangulation, and arguably calculated by Sikdar, read 29,002ft. Along with GPS technology, this model of deduction is being sought to be replicated by SOI.

“All the heights in our country are considered as above mean sea level (MSL), but GPS receivers give you a different height known as ellipsoidal height. The two heights don’t tally. To convert ellipsoidal height to MSL, we are trying to come out with a mathematical equation. That kind of equation is known as the Geoid Model, on which our director Nitin Joshi and the geodetic and research branch of the Survey of India is working,” Rao says. “We have worked on the Geoid Model for most of the country and now we want to extend it to the Himalayas also. If we extend it to Mount Everest and it is proved, my job becomes easy.

“The Survey of India-provided height of Mount Everest has been considered the most credible over the years and we have the oldest association with the peak,” the surveyor general continues. “If this current mission is successful, I’ll be only the third person from India to announce the height of Everest.

It will be a proud moment for the Survey of India in its 251st year, as well as for India.”

Radhanath Sikdar.
Radhanath Sikdar.

The mystery man

In 2011, Ashish Lahiri, a Kolkata-based author and independent researcher of the history of science, went looking for the grave of Radhanath Sikdar at Chandannagar, a former French colonial town more than 50km away from Kolkata. Sikdar, a Bengali-Christian, had retired to Chandannagar and died there in 1870. Though a small street there is named after him, his house has since been demolished to make way for an apartment building, says Lahiri.

In his search for Sikdar’s grave, Lahiri sought help from multiple sources. Some local club members eventually led him to a cemetery where they thought his grave might be. But the grave they pointed at did not have an epitaph. Lahiri had to give up the search for lack of credible evidence.

Though his role in the measurement of Mount Everest may be contested, there is no doubt that Sikdar was the chief computor at SOI’s Kolkata office when the measurement was done. Everest saw enough “mathematical genius” in Sikdar to describe him as his “right arm”, eventually paving the way for the latter to inarguably be the first significant native Indian association with the peak.

While a legendary explorer like Francis Younghusband would weigh in on the side of Sikdar, giving credence to the popular story of the young computor exclaiming that he had discovered “the world’s highest mountain”, Sikdar’s role was undermined by SOI historians like B.L. Gulatee, S.G. Burrard and R.H. Phillimore, and George Everest’s biographer J.R. Smith, who have all maintained that the computation work took place in Dehradun.

A diary containing letters written to George Everest by his subordinates at the museum.
A diary containing letters written to George Everest by his subordinates at the museum.

In the recent past, there have been two significant supporters of Sikdar—American journalist and climber Jon Krakauer, who, without going into much detail, credits Sikdar with the discovery in his best-selling book, Into Thin Air (1996), and Walt Unsworth, who goes into the Sikdar controversy with a detailed analysis in Everest: A Mountaineering History (1981), widely considered the most exhaustive account of the peak’s association with man.

In Everest: A Mountaineering History, Unsworth says, “Since the publication of the first edition a closer study of the evidence leads me to suspect that the computation of Everest’s height might have been by Sikhdar (Unsworth’s spelling) after all.” He doesn’t ignore contrarian evidence, including that of the widely respected survey historian Phillimore, even though the latter seems somewhat uncertain in his repudiation of Sikdar’s role.

Unsworth quotes a letter that Waugh wrote to Henry Thuillier in 1856, who was then in charge of SOI’s Kolkata office: “We have for some years known that the mountain is higher than any hitherto measured in India. In justice to my able assistant, J. Hennesy (Unsworth’s spelling), it is proper that I acknowledge that I am greatly indebted to him for his cordial cooperation in revising these computations.”

The George Everest house in Hathipaon.
The George Everest house in Hathipaon.

In the last paragraph of the chapter “The Height Of Everest”, Unsworth adds: “It seems to me that what Waugh is acknowledging in this letter is the fact that there already existed some previous calculations for Everest, perhaps preliminary and rough ones, and that Hennesy had revised these to produce a final published version. It could be that Radanath Sikhdar had made these preliminary calculations, and hence the confusion. Both Sikhdar and Hennesy had worked on the figures.”

After two short biographies of Sikdar, Sahitya Samsad published Lahiri’s new book, Radhanath Sikdar And Colonial Science: An Indian Surveys An Uncharted Terrain, in November. The book provides a detailed biographical sketch of Sikdar and includes previously unpublished notes, letters and documents sourced from the National Archives of India in Delhi.

I meet Lahiri on a winter evening at Boi-Chitra, an over 100-year-old photographic studio which, back in the day, competed with the famous European-owned studios in the city. The studio, located on the second floor of Albert Hall, Kolkata, now the College Street Coffee House, has been revived through the efforts of a group of well-wishers, including Lahiri. It seemed to be the perfect setting for a discussion on revisionist history.

Borrowing from his new book, Lahiri patiently outlines Sikdar’s commendable work in the areas of compensation for atmospheric refraction of light, a critical area in the computation of height, and mastering the ray tracing method introduced by Everest. Ray tracing was the determination of the direction between two points that would be intervisible if it were not for removable obstacles such as trees and huts, Lahiri explains.

Our conversation leads to the subject of Sikdar’s infamous fallout with Thuillier, who was many rungs his senior. After Thuillier made a technical blunder, Sikdar wrote an admonishing letter to him. This was in 1858, just after the rebellion of Indian sepoys had been quelled by the British, and here was “a native questioning the technical competence of a white man”, Lahiri wrote. Thuillier didn’t take well to this and reported the matter to the surveyor general. It was the ideal ground for a trial for insubordination, but Waugh, possibly because of Sikdar’s indispensability, took a kind view. The issue would be settled after Sikdar wrote a letter to Waugh apologizing for the harshness of his language, but not for the charge he had brought against his superior.

“Babu Radhanath Sikdar, distinguished head of the computing department of GTSI”, was acknowledged by Thuillier when he, along with another author, published The Manual Of Surveying For India in 1851. After Sikdar’s death, however, the third edition of the manual, published in 1875, dropped the acknowledgement. The first Indian to climb up the European hierarchy of SOI, Sikdar, Lahiri contends in his new book, had to overcome discrimination during his career, which Kumar of the SOI alludes to as well during our conversations.

Arun Kumar, a published author, is currently researching The Great Arc project as well as Sikdar. But when it comes to finding the most critical document—that of the final computation which eventually established Peak XV as the highest point on earth, along with the name of the person responsible for the calculation—both Lahiri and Kumar have drawn a blank.

Even as the SOI goes about its current mission to remeasure Mount Everest, Sikdar, and his role in the pioneering discovery, remain veiled in a mist.

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