In Celsius’ footsteps, by Ian Hembrow

Retracing the route of the 1736-37 Arctic Circle expedition to establish the shape of the Earth

A daily blog by SIS member and travel grant recipient Ian Hembrow on a research trip to Lapland for his biography of the Swedish astronomer and mathematician Anders Celsius (1701-1744).

Thursday 5 May 2022

The thick winter ice is just beginning to break up on the River Torne as it reaches and empties into the Baltic Sea in the Gulf of Bothnia on the border between modern Finland and Sweden. The cracks starting to snake across the surface are a reminder that we live on a dynamic planet – one that’s constantly being shaped and altered by the immense forces of gravity, magnetism, volcanism and climate.

The river – Europe’s longest free-flowing waterway without locks, dams or any other human-made intervention – is also what brought a small but intrepid band of French and Swedish scientists here in June 1736. Their mission, decreed and bankrolled by France’s young King Louis XV, was to help settle the great scientific debate of the age – the exact shape and form of the Earth.

The twenty-five-year-old king had already dispatched a similar expedition to Peru a year earlier. The logic was that by precisely measuring the distance of degrees latitude at the equator and as far north as possible then comparing the results, it would be possible to determine whether the planet was a perfect sphere, or as great natural philosophers like Newton and Cassini had theorised, it was slightly deformed. The big question was whether that difference was at the planet’s waistline – squeezing it into an elongated lemon shape, or at the poles making it flatter, more like an orange.

My friend Mark and I arrived in Tornio at the mouth of the river in the late evening, still light of course at this time of year. In case we were in any doubt, the final stage of our journey – a two-hour propeller plane flight north from Helsinki – proved we were entering a very different realm. Far below us, Baltic pack ice stretched into the distance, with the tiny dot of an ice-breaking ship bravely battling to keep open a narrow, navigable channel.

This is why the eighteenth-century Earth-measuring scientists had to come here in midsummer – arriving just in time to make their first astronomical observations from the elegant, birch-shingled bell-tower of Tornio Church on the longest day of 1736. The adjacent steeple became the southernmost marker on a latticework of observation and triangulation points stretching northwards up the river valley. Their objective was to survey and measure one degree of latitude – roughly 95km along the meridian running through Tornio.

The expedition was led by the flamboyant French mathematician and royal court-favourite Pierre Louis Moreau de Maupertuis. But we’ve come to focus on another of the party, Anders Celsius – the man whose name still lives on in the one-hundred-point (‘centi-grade’) temperature scale he invented and bequeathed to the post-Enlightenment world.

It was good fortune and coincidence that led to Celsius being part of the study. At the time King Louis was commissioning his expeditions, the thirty-two-year-old Swede had arrived in Paris as part of his Grand Tour of Europe’s great scientific capitals. His mix of astronomical, mathematical and geodesic surveying experience was exactly what De Maupertuis needed to achieve the desired results. Plus of course it was useful that he and another member of the party – one of Celsius’ students, Anders Hellant, spoke Swedish and knew something of their Arctic destination.

All of this is what brought us to the council chamber on the top floor of Tornio’s modern City Hall, with magnificent views of the icy river and its thickly wooded valley. Ilkka Halmkrona, head of education for the Tornio region spoke with passion and pride about not just the city’s important history, but also its unique status as a cooperative, open-border centre for business, industry, culture and tourism with its Swedish twin settlement Haparanda on the opposite riverbank. In an era of division and conflict it was refreshing to witness such enthusiasm for internationalism and clear evidence of its benefits.

Next we heard from Veli-Markku Korteniemi – an impressively energetic Finnish academic and entrepreneur, Chair of the Maupertuis Foundation and someone with a deeply personal reason to keep the story of the 1736-37 expedition alive. Eight generations ago, his family owned and ran a remote but well-appointed guest house where most of the scientific expedition stayed, working on their calculations during the dark and frozen months of winter.

Alongside us was Jarno Niskala, an affable and committed social scientist leading a project to commemorate another, even more ambitious scientific enterprise a century later. In 1842, the Torne Valley once again became the focus of international attention as a segment of the Struve Geodetic Arc – a 2,800km line of survey triangles passing through ten countries, from Norway to Ukraine’s Black Sea coast.

This UNESCO-heritage path and world-changing exercise are now brought to life through an excellent virtual reality exhibit at Tornio Museum, which we visited before heading off to see the real thing. Two hours later, a strenuous march through deep snow and stony outcrops took us to the 189m top of Mt Kaakamavaara – the next point on both the Maupertuis and Struve meridians.

While we were still puffing and perspiring from a rugged climb, the incredible physical and logistical achievement of these pioneer scientists came into fresh perspective. With our modern binoculars, it was just possible to see the Tornio Church steeple to the south and another key landmark, Mt Niemivaara, a little bump on the horizon in the opposite direction.

Maupertuis’s team had to row upstream against a strong current, lug heavy wooden and brass instruments through dense forest up to this point, fell hundreds of trees to clear the summit (all the time plagued by vicious biting mosquitoes and flies), and then be able to accurately measure angles and observe stars. It was an astonishing feat. And more astounding still is that the party – supported by a troop of tough Finnish soldiers and some local Lapps – did this for all eight of the principal measuring points in just 63 days.

Even with modern access, equipment, machinery and communications this would be a mammoth task. And in itself, the valley route was a hastily-concocted ‘Plan B’. De Maupertuis had originally intended to use a series of islets at the mouth of the river for the survey, but these proved to be much too low and flat for the purpose. So Celsius and his companions had to draw on their collective initiative to adapt and act quickly, before the ice returned.

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Friday 6 May 2022

Our itinerary took us to two more hilltops – Aavasaksa, where the brightly-painted but crumbling ghost of the Imperial Lodge sits, patiently waiting for a Russian Tsar who never came, and Luppiovaara, overlooking a straight stretch of frozen river. This is where, after waiting for the cold and dark of winter, Celsius led his companions out onto the ice to measure a 14km baseline, from which they could then calculate all the other distances.

With just a few hours of daylight and the shimmering, ethereal Northern Lights to illuminate their work, the group split into two teams, starting from each end of the line and laying 30-foot-long, birch poles end-to-end to measure the distance. It took them ten, brutal and freezing days, vividly described by the expedition’s leader:

‘Judge what it must be to walk in snow two feet deep, with heavy poles in our hands, which we must be continually laying upon the snow and lifting again; in a cold so extreme, that whenever we would take a little brandy, the only thing that could be kept liquid, our tongues and lips froze to the cup and came away bloody.’²

But the scientists proved their mettle. When the two teams compared their results, they differed by just ten centimetres. It was a prodigious undertaking and outcome in fearsome conditions.

For this part of our day, we met Tuomo Korteniemi: the younger brother of Veli-Markku and a journalist and publisher who first founded the Maupertuis Foundation. From Luppiovaara on the Swedish side of the river he directed us to the Arctic Circle monument at Juoksengi.

The exact position of this line (the southern limit of continuous daylight at the summer solstice) constantly wobbles around because of the Earth’s tilt and the influence of the sun, moon and planets. But at roughly 66° 33’ it’s an eerily atmospheric place. A stainless steel depiction of the globe stands surrounded by the flags of the eight Arctic countries – with the Russian pole now conspicuously empty…

Saturday 7 May 2022

Over to Finland again to meet Miia Kallioinen and Janne Tolvanen – two young colleagues from the Pello mayor’s office giving up their weekend to act as our guides. They took us first to the ultimate destination of Celsius and his fellow scientists, Mt Kittisvaara, at the northern end of the expedition’s survey chain.

We crunched through snow as the rocky path wound between slender trees and a dark green carpet of bilberry and lingonberry plants just emerging to greet the spring sunshine. As we rounded a bend, a squat stone pyramid appeared – indicating the place where the scientists built a wooden observatory to house the huge sector and portable zenith custom-built for the trip by London’s master instrument maker George Graham.

For me too, this felt like an arrival. The culmination of five years’ fascination and study of the modest young Swede with the familiar name who brought his team – and us – to this place. I left the other three and walked away into the trees for a while, listening to the breeze and birdsong. I tried to imagine the experiences and feelings of the expedition members who came here, desperately hoping that the precision of their work would satisfy their own instincts, the scientific establishment and King Louis back in the opulence of Paris.

I paused at prominent rocks – unmoved since they were deposited by glaciers – and ran my palms across their surfaces, crusted with pink, green and white lichens. And I thought about how Celsius and his fellow scientists had probably done the same.

Back down from the mountain, Miia and Janne took us to two other landmarks – a memorial stone to Celsius’ student Anders Hellant, who was just 20 years old when he returned to this his hometown. He was born where another stone now stands near to the river. It marks the site of the Korteniemi guest house, where Veli-Markku and Tuomo’s ancestors sheltered the exhausted scientists and helped them to recover from their exertions.

Some remnants of this compound might still be visible if it were not for the terrible destruction wrought by retreating Nazi forces as they left Finland in autumn 1944. In a literal application of ‘scorched earth’ tactics, they burned and obliterated everything in this part of Lapland: homes, barns, forests, bridges and crops, so that nothing remained for the Finnish population.

The Korteniemi house was just one casualty of these events, and a sadness seemed to hang over the place as I walked down towards the riverbank. A few small buildings now dot the area – not unlike those shown in the drawing from Celsius’ time, with Mt Kittisvaara a silent, sorrowful sentinel above.

But a lovely surprise awaited us at the end of our tour around Pello – a late lunch in the town’s special Maupertuis dining room, where the walls are tastefully decorated with prints of the expedition and reproductions of seminal equations, formulae and graphs. Very tasty too was the traditional homemade dark, malted rye Kalja beer we were served – a kind of non-alcoholic-stout-meets-dandelion-and-burdock, which is almost a meal in itself.

Sunday 8 May 2022

A day off from the serious research as we headed further north, the scenery quickly taking on a more remote and blasted feel than any we’d encountered before. We saw our first wild reindeer – a silver- and pewter-coated adolescent grazing peacefully at the side of the road – and several sturdy-looking black-tailed capercaillies scuttling across in front of us.

We headed for Pajala, about 60km up the valley, where the Torne is joined by the even bigger River Muonio pouring down from the far north on the border with Norway. On the way, we stopped at Kengis Bruk – a dramatic set of cascades and rapids. It’s another place with a strong connection to Celsius.

Here, four decades before the Maupertuis expedition, Celsius’ maternal grandfather Anders Spole visited and stayed while on his own astronomical and botanical adventure to Lapland. It was partly from hearing and reading about his grandfather’s exploits that Celsius had suggested this region for the 1736 expedition. Today, Kengis is a magnet for salmon fishing, with 20kg-plus monsters more than a metre long often hauled from the dark, peaty pools beneath the waterfalls.

Monday 9 May 2022

Our final day of travel and investigation. We drove south, heading off the main highway onto an unmade road that took us many kilometres into the surrounding lakes and forests, to visit Mt Niemivaara.

More reindeer lifted their heads to gaze at us from the surrounding trees. One walked straight down the track and skipped past with a barely audible clicking of its flattened hooves. There were no signs or marked paths, so when the car could go no further we just stopped and struck out for the top.

It was easier going than some of the other ascents, but Niemivaara has its own peculiarities: sheer stone walls cut with deep fissures and promontories that we had to negotiate our way around. And just before the summit a massive boulder field demanded careful steps and a few leaps of faith. We wondered again how Celsius and his companions had managed when this was even rougher and completely unknown territory.

At the top of the hill we were rewarded with a stunning view of Lake Ajankijärvi – still frozen from end to end. Once again, De Maupertuis’s eighteenth-century description closely matched what we saw and felt:

‘The beautiful lakes that surround this mountain, and the many difficulties we had to overcome in getting thither, gave it the air of an enchanted island in a romance. On one hand you see a grove of trees rise from a plain, smooth and level as the walks of a garden, and on the other you have rocks so perpendicular, so high and so smooth that you would take them for the walls of an unfinished palace rather than for the work of nature. We had been frighted with stories of bears that haunted this place, but saw none. It seemed rather a place of resort for fairies and genii than for bears.’

Stopping by a towering pile of freshly cut pine and birch trunks on our way down, the air was filled with sweet, fragrant resin and sizeable black butterflies suddenly roused into busy flight by the light and warmth. I peeled back the bark of a log to uncover the pure white wood underneath. This was an important part of the expedition’s method of creating summit markers that could be easily seen from far away.

In an unplanned instant, this simple act connected me once more to the brave and brilliant band of scientists who came here so long ago.

Tuesday 10 May 2022

I leave Lapland with a far greater understanding of who the members of the 1736-37 expedition were, and of what they did, why, how and where. Having followed in his footsteps, I feel closer to my subject Anders Celsius. And after standing where he stood and seeing and hearing what he saw and heard, I am even more in awe of his qualities and capabilities – both as a scientist and as a man.

Before they even departed Finland for France in spring 1737, and years before the few survivors of the Peru expedition returned, De Maupertuis, Celsius and the rest of their team were confident that they had solved the great puzzle about the shape of the Earth.

It took some time and effort to persuade the sceptics, but their painstaking measurements conclusively showed that the planet is a slightly flattened ellipsoid – about 40 kilometres fatter than it is tall.

The River Torne was our constant companion throughout this trip – a dominant, surging presence always in view, its colour, form and texture changing by the hour. Thanks to Celsius, his colleagues and their adventures in its majestic, snaking valley we know today that our planet is an orange not a lemon.

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[1] This and other drawings taken from Journal D’un Voyage Au Nord, En 1736 & 1737 written by expedition member Abbé Réginald Outhier. Sadly the artists’ names are not recorded.

[2] Maupertuis P L M de, Clairaut A C, Camus C E L, Le Monnier P C, Outhier R, Celsius A. The figure of the earth, determined from observations made by order of the French king at the Polar Circle, London, 1738

Measuring a potato planet, by Ian Hembrow

Research grant recipient Ian Hembrow reports on a fascinating study trip to learn about 18th century surveying methods from SIS’s Nicolàs de Hilster.

At the start of 2022 I was thrilled to receive a grant from the Society to support my project to write a biography of the Swedish scientist Anders Celsius (1701-44). Best known of course for his centigrade temperature scale, Celsius made an array of other discoveries and breakthroughs in a stellar career cut tragically short by his death from tuberculosis aged just forty two.

In particular, he played a vital role in settling the great scientific debate of his age about the shape of the Earth, taking part in a perilous winter expedition to the Arctic Circle in 1736-37 to measure the exact distance of one degree of latitude (see figure 1). Comparing the results with a parallel expedition to the equator proved Newton’s theory that the planet is an oblate ellipsoid, slightly flattened at its poles by the centripetal force of its spin. The Earth, they showed, is shaped like an orange – roughly 43km broader than it is tall.

Keen to find out how Celsius and his companions made their measurements I reached out to the SIS network for help to understand the methods and equipment they used in the frozen north. Surveyor and collector Nicolàs de Hilster answered my call, inviting me to visit him in the Netherlands to do some hands-on study. It turned out to be an enthralling and memorable trip.

When I entered Nicolàs’ home, a short train ride west from Amsterdam, I noticed a laptop with what appeared to be an image of the sun surrounded by tables of flickering data. Some sort of astronomical website I thought. But no, this was actually the live-feed from Nicolàs’s own observatory perched on top of the house! I followed my host up the spiral stairs to discover his amazing creation: a cluster of powerful telescopes mounted within a beautiful wooden dome – all hand-crafted from scratch by Nicolàs (see figure 2). The instruments included a custom-made Galilean-type refractor intentionally made to replicate the imperfections of 17^th century lenses.

Nicolàs attached a special filter to one of telescopes and invited me to look directly at the sun. Unsurprisingly, I saw a bright, fiery orange ball. “Now adjust that knob and you’ll be able to see some solar flares,” he advised. And sure enough, as I fine-tuned the focus, little looping swirls appeared around the edge of the image, clearly moving in real time.

“Wow!” I said. “How big are they?” “About five times the size of Earth,” replied Nicolàs. I was stunned and nearly moved to tears by the magnificence of what I was seeing.

The observatory though was simply the tip of a very big iceberg. I went on to admire an astounding collection of surveying instruments and devices – from the simplest sighting sticks to massive, high-specification theodolites, an enormous library and two gorgeous bespoke ‘de Hilster’ sun-dials mounted on the walls outside.

After a fine lunch kindly prepared and served by Nicolàs’s wife Ria, we loaded up the truck with a collection of sextants and measuring rods and headed out into the polder nearby – flat countryside criss-crossed by drainage ditches giving way to sand dunes up towards the nearby North Sea coast. Ever prepared, Nicolàs had found a spot where we could ‘tour the horizon’, first using a modern ‘total station’ instrument (see figure 3) and then a handheld, brass sextant.

My heart sank when it was explained to me that geodetic sextants use the 400-point Gradian system, rather than the more familiar (to me at least) 360 degrees of geometry. But I needn’t have worried, because once I’d got the hang of how to use the heavy brass device – merging the direct and mirrored images of adjacent sighting points like church spires and telephone masts – I managed to take and call out full-circle readings from our location (see figure 4). Nicolàs noted down the numbers at each point and then pulled out his phone to check their accuracy against the digital results.

Thanks to the expert tuition and supervision, my readings added up to 399.49 grad – just 0.51 of a grad out. Nicolàs smiled and declared this was “acceptable for a first attempt,” before going on to explain how even a small difference like this soon multiplies up to a huge margin of error when applied over the sorts of distances Celsius had to measure.

Back at the house, Nicolàs then showed me the inherent difficulties of using measuring rods to gauge accurate distances. The 1736-37 expedition members used thirty-foot-long wooden poles laid continuously end-to-end on a frozen river surface. But even on the flat floor of a modern building the kinks and dips of a twelve-foot sectioned rod were obvious to the naked eye. Our planet is of course not entirely smooth, so surveyors have to take account of all the slumps and bumps in their way. “Remember Ian,” said Nicolàs, “the Earth is not a true ellipsoid – it’s a potato!”

The key to surveying accuracy, I learned, is to measure, measure and measure again – using multiple base lines and repeated calculations to obtain the best possible answer. And, Nicolàs reminded me, measuring the linear distance was only the start of the job – Celsius then had to do some complex astronomical sightings to determine their precise latitude.

That will have to wait for another time and visit…

My sincere thanks to Nicolàs and Ria for making me so welcome and treating me to such an extraordinary day.

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In early May 2022 Ian is retracing the route of the 1736-37 expedition in Swedish and Finnish Lapland. Watch out for his report of that trip.