The Torne Valley and the flattening of the earth, Sweden and Finland

The Torne Valley on the border between Sweden and Finland played a central role in the 18th century debate on the shape of the earth. A recommended starting point is the twin town Haparanda/Tornio (Haparanda is on the Swedish side, and Tornio on the Finnish side).

In the early 18th century, there was a debate among natural philosophers regarding the true shape of the earth. Isaac Newton and his followers believed the earth was slightly flattened at the poles, while Descartes and his supporters suggested it was prolonged at the poles. In order to find out which theory was correct, the French Academy of Sciences decided to send one expedition close to the equator and another close to the north pole. Each expedition would measure the length of a degree of the meridian, and by comparing the results, it would be possible to see whether Newton or Descartes was right. The expedition to the equator ended up in Mitad del Mundo in Peru (present day Ecuador), and the northbound expedition ended up in Torne Valley in Sweden (back then Finland was part of Sweden). The expedition to Sweden took place in 1736-37 and was led by the mathematician Pierre-Luis Moreau de Maupertuis. The Swedish astronomers Anders Celsius and Anders Hellant were also involved, as well as a team of assistants and workers.

The measurement of the meridian was done by using the triangulation method which has been common in geodesy. Starting in the town of Tornio, Maupertuis and his team travelled about 106 km up the Torne valley, where they set up a triangulation network consisting of eleven observation points on mountain tops. The southernmost point was the church tower in Tornio and the northenmost point was the Kittisvaara mountain. The base line of the triangulation network was 14,5 km and was set up on the ice of the Torne River between the Luppiovaara and Aavasaksa mountains. The base line was measured using eight spruce poles, each 30 feet in length, where two teams did the measurements by using four poles each. In the rest of the triangulation network, each observation point was constructed by clear-cutting the top of each mountain and then setting up a cone-shaped signal made of barked tree trunks, so that each signal could be observed from the neighbouring observation points. The angles between the observation points were measured using quadrants. Once they had measured the base line and all angles between the obervation points, they could calculate the length of the sides of each triangle. In order to find the direction of the meridian in relation to the triangles, they used a Graham zenith sector to measure the height of a star in the constellation Dragon from the end points in Kittisvaara and Tornio.

Map showing the triangulation network

Map showing the triangulation network.
Image in Public Domain.

Torne Valley was rather sparsely populated at this time, with only a few farms along the river banks in addition to the smaller villages of Pello and Turtola. When they were not busy working, the French crew socialised with the people, and there is even a romantic aspect of this expedition –two local girls, the Planström sisters, ended up travelling to France.

Even though the scientific result of the expedition was criticized for flaws, it was still a success, and when the Torne meridian degree was compared to the one in Peru, it was in favour of Newton’s theory. To further establish the true shape of the earth, another measurement of the meridian was done between 1816 and 1855 by Friedrich Georg Wilhelm von Struve. This time, the arc stretched from Hammerfest in Norway down to the Black Sea, including some of the same observation points which had been used by Maupertuis. In 2005, Struves geodetic arc was listed as a UNESCO world heritage.

Visitors to Torne Valley can find one monument by the church in Tornio and another monument in Kittisvaara. As a curiosity, the arms of the Finnish municipal Pello contains three stars which is a reference to the meridian measurements.

Further reading

The degree measurements by de Maupertuis in the Tornionlaakso Valley 1736-1737. [2013-06-26]

Terrall, Mary, The man who flattened the earth: Maupertuis and the sciences in the Enlightenment, Univ. of Chicago Press, Chicago, Ill., 2002

In addition, you may find at large libraries both Maupertuis own account of the expedition as well as the diary written by one of his crew members, Réginald Outhier. And if you can read Swedish, there is also a fictional novel by Olof Hederyd based on the fate of the two Planström sisters.