FIG Working Week 2000, 21-26 May, Prague

Struve Arc

by Seppo Härmälä

Key words: Dimensions of the Earth Ellipsoid, Historical Triangulation, The Aims of the Struve Arc, Struve Arc as a historical Memorial.


The Background of the Measurement

In the first part of the 19th century the shape and size of the Earth were not very well determined. The computed dimensions were based on measured short arcs only. This left the accuracy uncertain. Then a new arc of 25 degrees of latitude offered a firmer basis to compute the dimensions and subsequently the geodetic measurements.

The project would hardly have been possible without the international political situation. Due to the Napoleonic wars the importance of good maps was felt in Russia. The west boundary of Russia as agreed in the Vienna Congress in 1815 coincided well with the site of the planned arc. Obviously, the military needs for mapping helped to bring the resources the project needed.

The Russian-Scandinavian Meridian Arc Measurement

This is the proper name for the project although it is shorter to call it the Struve Chain. It honours also the central person of the project. The Estonian astronomer Wilhelm Struve was the initiator and responsible geodesist as well as the publisher of the results of the Russian-Scandinavian meridian arc measurement.

Outwardly the Struve arc gives an impression of a carefully designed project, However, it has been built piece by piece. The first two parts were measured one by Struve himself between Högland and Jakobpils and the other by the Estonian general Tenner simultaneously and quite independently. Then in the year 1828 it was found out that the ends were close to each other and so a connection was made. This was the first part of the chain measured in the years 1816 - 1830.

After this Struve and Tenner started to extend the chain, Struve northwards and Tenner southwards. Tenner continued in 1830 - 1844 his high quality triangulation as far as to Ismail, located near the mouth of the river Danube.

Struve had a more complicated task. At first the measurement across autonomous Finland was not difficult. Moreover, he could leave the practical implementation to a Finnish astronomer Woldstedt. Later political steps were needed. The chain was joined in the north to that part carried out by Sweden as their share. In Sweden the responsibility for the work was given to the astronomer N. H. Selander. There the chain followed first the old Maupertuis arc half of it on the Swedish side and the other half at the Finnish side of the boundary. Further north there was a new political problem. Norway belonged to the Swedish realm but had her own administration. Consequently, the rest of the chain up to the Barents Sea was measured under the responsibility of Christopher Hansteen as far as the northernmost point at Fuglenes.

The Value of the Struve Chain 

The value of the Struve chain has several aspects. The measurements have been astonishing accurate in spite of the early era. There are no remarkable differences in comparison with the latest measurements. The points of the chain have, in general, been monumented very carefully in the solid rock where possible. The results of the work have been documented in detail, together with the applied methods, the observations, the descriptions of the points and the results of the computations. In this respect the volumes by Struve make a remarkable example to the documentation of measurements.

Due to the aforementioned facts the Struve Chain has been an example to the later triangulations. All these measurements, partly initiated by Struve, gave a fine opportunity to determine the size and shape of the earth. Consequently, the foundation of map-making gained a solid basis for calculations and presentations.

In addition, the well marked and well documented points of the chain have been a good beginning for extended measurements. Some parts of the chain have been in use over one hundred years since the establishment of the Struve Arc. It belongs to the most remarkable accomplishments in the history of map-making.


Scientific Conference in Tartu gave August 28, 1993 the resolution No 1:

"Considering the scientific, historical and practical importance of the measurement of the arc of meridian through Tartu, made by F.G..W. Struve,

Urge the governments of those countries that still possess relics of that enterprise to take all possible steps to preserve those relics, including an approach to UNESCO to declare them to be World-Heritage sites."

Corresponding resolutions have since been made later in FIG Congresses. Practical steps have been taken later, especially in Finland in addition to that share taken on by FIG.. At the same time the International Institution for the History of Surveying & Measurement (a permanent body within FIG) has worked hard to achieve the preservation of the Struve points and to get the aforementioned declaration of UNESCO.

This requires close cooperation from all ten countries involved before a case can be put to UNESCO. However, if a submission can be achieved by the end of this year then it is hoped that some definite progress will be able to be reported to the FIG Congress of 2002 in Washington.

The desired World-Heritage declaration provides, that the included Struve points are already protected in those countries where they are situated. Do your best and follow the advice of Mr. Jim Smith.

Seppo Härmälä
Katajanokankatu 7 B 15
FIN-00160 Helsinki

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