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.
Abstract
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.
Measures
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
FINLAND
E-mail: seppo.harmala@kolumbus.fi
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