Struve Geodetic Arc
On 15 July 2005 the UNESCO World Heritage Committee inscribed a new name on its list of important sites – the Struve Geodetic Arc. This is a triangulation network observed between 1816 and 1855 which stretched from near North Cape in Norway to the Black Sea. In today’s geography it passes through ten countries, namely Norway, Sweden, Finland, Russian Federation, Estonia, Latvia, Lithuania, Belarus, the Republic of Moldova and Ukraine.
The Struve Geodetic Arc is the first survey scheme and also the first such scientific and technological landmark to be entered on the World Heritage List and it joins a select list of less than 900 such listed sites around the world. Whereas one is used to seeing ancient buildings, stunning scenery and famous archaeological sites as Heritage monuments the Struve Arc is but a series on marks in the ground barely covering a square metre or so each. However taken as a whole the Arc was, for its time, a major scientific achievement using state-of-the-art instrumentation to achieve amazing accuracies straddling such a vast distant and several countries. Much smaller similar schemes preceded it and longer and more accurate ones succeeded it but it was a veritable milestone in the quest to determine accurate values for the parameters of the earth.
Arc measurement is the determination of the linear length of a section of meridian (line of longitude) on the earth together with the astronomical determination of the positions of the two end points. Whilst it should theoretically follow exactly along such a line of longitude in practice this is not essential, and indeed would be impractical, and appropriate corrections can be made. The terminal points of the Struve Arc are at Fuglenaes, latitude 70º 40’ 12” N and longitude 23º 39’ 48” E, and Staro-Nekrassowka, latitude 45º 19’ 54” N and longitude 28º 55’ 41” E. Hence it is said to run more or less along the 26º E line of longitude for a distance of 2820 km.
The use of such a scheme was particularly designed to assist in the accurate determination of the size and shape of the earth. It was an extraordinary example of scientific collaboration among scientists from different countries and of collaboration between monarchs for a scientific cause. Additionally it formed the basis upon which long required accurate mapping of the areas concerned could be based.
The historic monument is defined by the initial preservation of 34 of the 265 main survey stations involved. The ten countries involved, with encouragement and help from the International Institution for the History of Surveying & Measurement (IIHSM), a Permanent Group within the International Federation of Surveyors (FIG), cooperated since 1954 in the recovery, verification, monumentation and documentation of the selected points. These were chosen (a) to give a spread of preserved points along the whole arc, (b) to be representative of all countries, (c) that could be verified as original points (d) were reasonably accessible to the public (e) were in such positions that if restored, they would not by liable to imminent destruction by building developments and (f) were generally in areas where the local population were keen to take such a monument under their wing for its up-keep.
Where possible the most prominent sites have been selected including the obelisks at each terminal, the Tartu Observatory in Estonia (known at the time as Dorpat) which served as the origin of the scheme and the point in the tower of Alatornio church. The church itself has remained unchanged since the time of the measurements. Other points take a variety of forms such as drill holes in rock, cairns and crosses chiselled rock.
F G W Struve (1793-1864), after whom the arc gets its name, was born in Altona, Holstein and died in Pulkova, Russia. He married twice and had 18 children. By age 20 he became Professor of Mathematics and Astronomy at Dorpat. His involvement in the survey of Livonia was the start of almost 40 years work on the meridian arc. He founded Pulkova astronomical observatory, then the best in the world, and of the Russian Geographical Society. The other principal name associated with the arc was that of the Russian military officer Carl F Tenner (1783-1859). In 1816 he became Head of the vast Russian triangulation work in western provinces of the Empire. He had started in 1817, on his own initiative, a triangulation scheme to the south of Livonia. After Struve and Tenner became acquainted with each others activities they joined forces. Some of the route in the northern parts covered similar territory to that surveyed in 1735 by Maupertuis when observing his much shorter scheme that was is particularly remembered, with a similar expedition to Peru, 1735-1745, for solving once and for all the controversy between Newton in England and the Cassinis in France, regarding the shape of the earth i.e. was it a prolate (flattened at the Equator) or oblate (flattened at the Poles) spheroid. The latter version was proven to be correct.
With the achievement of World Heritage Monument status for this arc what enhancements are possible? Monuments can be extended at any later date and a “monument” such as the Struve arc can be extended southwards as far as South Africa.
This is feasible because (a) in the 1930s a join was made from the Struve Arc in Belarus to Crete and (b) the Arc of the 30th Meridian through East Africa stretches from near Port Elizabeth to near Cairo but in the 1950s a connection was made across the Mediterranean Sea to Crete. Hence there exists a connection that would extend the whole arc to one of 105º. Such an extension would though involve a further 20 or so countries and would be no small task.