The eighteenth century expedition in Tornio River Valley to determine the shape of Earth by Frenchman Pierre Maupertuis

During the years 1736 and 1737 the French-Swedish expedition to determine the shape of the Earth was conducted, led by French mathematician, philosopher and astronomer Pierre Louis Maupertuis (1698-1759). The purpose of the Maupertuis expedition was to perform measurements to determine whether the Earth was round or flattened at its poles. Another similar expedition was sent to the Equator in the area of today’s Republic of Ecuador.

Maupertuis was one of the leading philosophers and scientists of the Age of Enlightenment from the French Academy of Sciences.

Accompanying Maupertuis on his expeditions were Alexis Claude Clairaut, Charles Étienne Louis Camus and Pierre Charles Le Monnier, all astronomers themselves. As was usually the case during the Age of Enlightenment, the members of the expedition were multidisciplinarians. In addition to astronomy, they were all particularly interested in mathematics. The expedition also included Reginald Outhier, and Swedish scientists Anders Celsius and Anders Hellant. Celsius, who is one of the best known scientists in Swedish history, was professor of astronomy at Uppsala University. Hellant was born in Pello.

The expedition of Maupertuis in Lapland not only left its mark in scientific history, but also on traditional knowledge in the Tornio River Valley.

In addition to measuring degrees, the expedition members were also forced to come to terms with the challenging natural conditions of the Arctic. A baseline covering 14.3 kilometres was measured on the frozen Tornionjoki River, using which the length of a degree of arc of the meridian was calculated using triangulation. The southernmost measurement site was the Tornio Church steeple and the northernmost was the Kittisvaara Mountain, located around four kilometres north of the Pello municipal centre. A monument, called Maupertuis Memorial, was erected on Kittisvaara Mountain in 1956 to commemorate the expedition and is today a popular tourist destination.

Another monument to the Pierre Louis Maupertuis Expedition was also erected in Aavasaksa (Ylitornio) south of Pello. In addition e.g. Pello’s very popular shopping centre for tourists, Vihreä Pysäkki, has a room showcasing the Maupertuis Expedition.

Upon returning home Maupertuis reported that the length of one degree was defined in Lapland as being 57,437.9 toise (a French unit of measurement equalling 1.949 metres). This finding, compared to the value of 57,060 at a site close to Paris, showed that the Earth is flattened at its poles. Although the measurements were later found to contain significant errors, they were still in the right direction and were scientifically revolutionary in a number of ways. With the findings obtained on his expedition, Maupertuis and his group of scientists were able to prove that Newton’s theory was indeed correct; the Earth is flattened at the poles.

The degree measurement findings of this French-Swedish expedition had huge significance for numerous scientific disciplines and fields of technology, such as with the making of nautical charts. During this Age of Enlightenment in eighteenth century France, the nation was one of the world’s leading superpowers, and Maupertuis became a true national hero in scientific circles. When he returned home, Maupertuis was invited to become a member of nearly every science academy in Europe.

Pierre Louis Moreau de Maupertuis on Wikipedia
Anders Celcius on Wikipedia

Maupertuis Foundation (page only in Finnish):