by Seppo Härmälä
Key words: Dimensions of the Earth Ellipsoid, Historical
Triangulation, The Aims of the Struve Arc, Struve Arc as a historical
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
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
Katajanokankatu 7 B 15
Tel. + 358 9 629 566
THE BACKGROUND OF THE MEASUREMENT
The seeds of the Struve Arc were sowed by the Great French
Revolution. Many traditional habits were replaced by new systems. Especially old
measures were toppled by a new metric system. It was quite simple to stipulate
that one quarter of a meridian makes 10 million metres. But how long was the
meridian? Some determinations were made, the longest between Barcelona and
Dunkerque. First they yielded a prototype of the new unit, the Legal Metre.
However, it was based on quite inadequate measurements and calculations.
The best possible result from the early arc measurements was
derived by a Finnish astronomer Walbeck. He applied for the first time the
method of least squares to compute the dimensions of the earth ellipsoid.
However, a more reliable knowledge of the dimensions was still missing owing to
the limited number and limited length of measured arcs.
As another result of the French Revolution wars were raging
around Europe and yet wider. The Napolenic wars stretched from Nordkapp to Cairo
and from Moscow to the Atlantic Ocean. After wars that lasted a quarter of a
century Napoleon was defeated. This resulted in the Vienna Conference which set
out to bring order back to Europe. Even while negotiations were taking place
Napoleon escaped from Elba and started new wars. He was defeated a second time
and only then was the Conference able to continue. By 1815 international
boundaries were established in Europe and steps taken that were supposed to
prevent any further revolutions or uprisings.
Then the general feeling among the rulers was quite restless
in Europe. They did not trust on a lasting peace and tried to get prepared for
new wars. The mapping for military purposes was appreciated and all steps to its
promoting were advanced.
The proper framework for the topographic mapping was a
problem at that time. As a lower order framework polygonic traversing was
available. The higher order was more complicated. The astronomic observations
were too difficult to the density needed in traversing, especially due to the
determinations of the longitude. In addition, the coordinate system required
still the final word of ellipsoid dimensions.
Especially in Russia both needs were felt deeply, the need of
fundaments of geodetic surveys and the fundaments of map grids. Every attempt to
foster new knowledge of them was favoured. The proposal of the Estonian
astronomer Wilhelm Struve to Czar of Russia combined both elements. In addition,
the Czar Alexander the First was in favour of higher education and science and
so Struve met deep wishes and so got all the resources he needed.
The way was open to an arc measurement along the west
boundary of Russia to serve the scientific aims, to develop the basis of
geodetic framework and to start the topographic mapping.
In the year 1814 Director Lindenau of the Seeberg observatory
has proposed an arc measurement following the west provinces of Russia. He
presented the proposal to Wilhelm Struve and to Carl von Tenner independently.
This was the beginning.
THE RUSSIAN-SCANDINAVIAN MERIDIAN ARC MEASUREMENT
This is the proper name for the project although it is
shorter to call it the Struve Arc. Geographically it runs across Russia and
Scandinavian countries. The name Struve honours 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.
Besides Wilhelm Struve, Carl von Teller belongs to the
remarkable names of the arc measurement history. He was an Estonian general in
the Russian army and had the responsibility of trigonometric and topographic
works in Kurland. To the same time they bouth carried out arc measurements
separately and independently. Struve got his permit and resources from the Czar
and von Tenner his permit from Prince Wolkonsky. Outwardly the Struve Arc gives
an impression of carefully designed project. However, it has been built piece by
Struve measured a triangle chain along the meridian of Tartu
from Hogland (Suursaari) to Jekabpils and von Tenner along the meridian of
Vilnius from Belica to Birzai The ends of both chains were not far from each
other. In 1828 Struve and von Tenner agreed to connect the chains. As a result
they got in 1831 an arc of 8° 02,5´ equipped with three base-lines and five
astronomical stations with latitude and azimuth observations. It was a fine
result for that time, but still more was coming.
The problem of the longitude determining was the reason to
assume the astronomic position of Tartu or Vilnius as a zero meridian. Then the
latitudes and azimuths could give longitudes to the other points in relation to
the zero meridian.
When the first arcs were completed Struve and von Tenner
started to extend the combined chain, Struve northwards and von Tenner
southwards. Von Tenner continued in 1830 - 1844 the triangulation chain as far
as to Ismail, located near the mouth of the river Danube. Three more base-lines
were measured and three astronomical stations.
Struve had a more complicated task. The first leg across
autonomous Finland was not politically difficult. Moreover, he could leave the
practical implementation to a Finnish astronomer Woldstedt. Later political
steps were needed and the necessary agreements made.
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, western points at the Swedish side and the eastern ones at the Finnish side
of the boundary.
Continuing further to 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. This finished the field work. The northern part included four
additional astronomical stations and four base lines.
Considering especially the difficulties of transportation in
the first part of the 19th century the work has been immense. The
total length between the ends of the long chain covered 25° 20’ 08,29"
of latitude or 2821,854 metres when converted from the toise-unit. The unit of
length applied in the measurements was the French fathom, the toise. To modern
people the metres are more illustrative.
However, the amount of work is not the only merit. Taking the
instrument and observation techniques of that time into account the achieved
accuracy was amazing. Co-ordinate transformations between some Struve points and
coinciding new points measured applying the best methods about one century
later, have revealed an unexpected quality. The discrepancies were of the order
of some centimetres, maybe one or two decimetres. One lost Struve point was
found when measured from a nearby new triangulation point. It was about one
decimetre from the computed site. Perhaps the accuracy of the modern methods
deserve the admiration.
Another remarkable item of the Struve Arc is the
monumentation of the stations. They were marked on the solid rock by drilling a
hole. The hole was filled with lead and on the top of the lead was a plate of
brass. In the course of time the plates have disappeared first. Most of them
were found missing in 1890s already. Later the lead has been digged out, maybe
to be made shots for the hunters. However, nobody has been able to take along
the holes in his pockets. The monumentation belongs probably to the merits of
A still more amazing feature of the Struve Arc is the
documentation. Struve gathered all the material of the measurements and made a
final report. After some busy years everything was published in three volumes.
This tome belongs to the most valuable literary historical products of the time.
It gives a very carefully drawn history of the accomplishment of Struve Arc in
THE VALUE OF THE STRUVE CHAIN
The Struve chain brought several benefits. The long and
accurate chain gave a fine addition to the determination of the ellipsoid.
Further it had plenty of indirect influence. The principles of the work were
published in all details. Then the Arc could be used as a good example. Even the
personal contacts were important. For instance, Struve had an influence to the
measurement of the parallel arc along the latitude of 52° and Tenner tied its
end to the Struve Arc. Many chains were measured in different continents in the
following years. Some results of these works can be seen in the development of
the computed dimensions of the earth.
|| 6376 896
|| 6377 397
|| 6378 249
|| 6378 388
|| 6378 180
|| 6378 160
Here are some examples of generally used values. Very clearly
the mutual agreement has become better since the publishing of Struve Arc and
succeding measurements. This has given a good start to the uniformed mapping,
its framework and the map projection systems.
Indirectly it has also helped assuming the metric system. It
became quite generally accepted on principle in the international agreement in
the year 1875. It is true, the length of the base unit does not depend any more
of the deterimination of the earth dimensions. However, their good
determinations have given some good will to the system.
The part of the Struve Arc has been remarkable to the
framework for mapping. Strong chains with permanent marking and good
documentation have ever since belonged to the basic work in many countries. Base
lines and astronomical stations distributed along the triangulation chains have
become a part of good triangulation. These principles have then been followed
for nearly two hundred years until the GPS has completely changed the methods.
Thus Struve Arc can be considered as the Mother of Triangulations.
Struve Arc has not served tringulations as an example only.
Its points have been starting points to many new triangulations and travesrses
in the course of a century. Still up to sixties in the 20th century
Struve Arc was the only connection of coordinates between South and North
Finland. An additional advantage has been the careful trigonometric levelling
along the chain
All in all, the Struve Arc makes an early and exceptional
incident in the history of geodesy. It has served scientific and practical aims
and stays as a memorial to get preserved.
About the time in sixties when the Struve arc was sent to the
well-earned retirement a new interest in the chain was arisen in Finland. In
connection of the new co-ordinate system comparisons were made to the modern
triangulation. Because it revealed unexpected accuracies, it started
investigations of the material more thoroughly. The more was learned the more
respect and admiration was felt.
Professor Petrelius had checked the stations in three
excursions in the years 1886, 1888 and 1889 and had made a catalogue of his
findings. At that time only few points were missing. Now a new search was
started. The task to make an inventory of the points was entrusted to Mr. Aarne
Veriö. He has taken the issue carefully and has collected plenty of
information. Doing this he has realized that the preservation of the remaining
sites is very important to the honour, the Struve Arc deserves. In this sense he
had prepared a paper to present it at the Tartu scientific conference. Due to
his sickness he could not arrive to the conference. However the paper was
presented and his idea on the UNESCO declaration to preserve the relics as a
The Scientific Conference in Tartu assumed the idea and 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
Corresponding resolutions have since been made later in FIG
Congresses. Consequently 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
It is quite natural that in Finland the interest was high.
There are more Struve stations situated in Finland than in any other country,
probably more still identified, too. In addition their practical significance
has been very important. Aarne Veriö has worked hard to advance the matter.
Director General of the National Survey Organization, Mr. Jarmo Ratia has
contacted the directors of relevant organizations along the Struve Arc and urged
them to join the project.
The desired World-Heritage declaration provides, that the
included Struve stations are already protected in those countries where they are
situated. The task is not easy because the legislation deviates from one country
to another. For instance in Finland it is still unclear whether to apply the
rules of planning or nature conservation. Similar problems may arise anywhere.
However, a close co-operation of all ten countries involved and Mr. Jim Smith,
General Secretary of the International Institution for the History of Surveying
& Measurements is really worth while before the case can be put to UNESCO.
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.
There is still one more aspect to be discussed. As mentioned
before, the tome by Struve where the Arc was documented, belongs to the history
of surveying. It is valuable and it is interesting. Unfortunately the book is
now a rarity, seldom found in the libraries. It is uncertain whether it is found
in every involved ten countries. It is true, it has been reprinted already once
in Russian in the year 1957 in Moscow. No doubt, it must also be out of print.
It would be a cultural achievement to reprint the tome. Still
better if it would be in English to get more readers. In French it could be a
facsimile product. Perhaps International Association of Geodesy could support
the idea. It is worth thinking of this idea.
Struve F G W : Arc du Méridien de 25° 20’ entre
le Danube et la Mer Glaciale mésure depuis 1816 jusqu’en 1850. 3
vol St.Petersburg, 1860
Struve F G W: Arc of Meridian (in Russian). Moscow, 1957
Harsson B G et al. The Russian-Scandinavian
Meridian Arc Measurements 1816 – 1852, FIG Congress, Melbourne
Donner, Petrelius: Das Aufsuchen von Dreieckspunkten in
Finnland, Helsinki 1889
Petrelius, A: The Search for Triangulation Stations in Finland
in 1889. Helsinki
Veriö A: The Struvean Triangulation Stations today (in
Veriö A: One and Half Centuries from the
Measuring of the Struvean Chain. Helsinki 1970
Veriö A: The Later Phases and Utillizing of the Northern Part
of the Struvean Chain. Tartu 1993
Smith J The Struve Geodetic Arc
Smith J The Struve Meridian Arc (in French) Revue XYZ, 1999
Dr. Seppo Härmälä
18 April 2000