{ W.R. Dick Geodeet 6(30) 2002 25-27 }

Wilhelm Struve and the Europäische Gradmessung

W.R. Dick

Institut für Angewandte Geodäsie, Aussensteile Potsdam, Postfach 60 08 08, D-14408 Potsdam, Deutschland

1857. aastal reisis W. Struve läbi Euroopa, õhutades teadlasi mõõtma Maa paralleelikaart Iirimaalt Uuralini. A. von Humboldt saavutas selleks Preisimaa valitsuse toetuse, kes suunas tööd korraldama geodeedi kindral J.J. Baeyeri. Mõõtmised teostati laiusel 52° ja nende lõpetamine toimus Rahvusvahelise Geodeesia Liidu egiidi all.

In 1861 the Prussian general and geodesist Johann Jacob Baeyer (1794-1885) proposed his famous plan for arc measurements covering the area of Europe (Baeyer 1861a, 1861b). The most important point in his proposal was the idea of establishing a general net of triangulations instead of lines of triangles along parallels and meridians. This plan was received with great interest both by the Prussian government and abroad. It immediately led to the Mitteleuropäische Gradmessung (Association pour la mesure des degres dans I'Europe centrale) - soon renamed into Europäische Gradmessung (Association pour la mesure des degres en Europe), later Internationale Erdmessung (Association geodesique internationale), and finally taken over by the Association Internationale de Geodesie (Buschmann and Kautzleben 1987, Völter 1963).

However, only little is known about the way how Baeyer came to his plan. I will demonstrate here Wilhelm Struve's activities in 1857 concerning the measurement of an arc of parallel in latitude 52° (Längengradmessung in 52° Breite), as well as the following developments up to 1861. It will be seen that there is a direct way from this arc of parallel to the Mitteleuropäische Gradmessung, and that W. Strave played a major role in the prehistory of this project.

In 1857 Baeyer published the results of his connection between the Prussian and Russian triangulations at Thorn and Tarnowitz (Baeyer 1857). A similar work he had already done between 1832 and 1834 together with Friedrich Wilhelm Bessel. Encke and Struve acted as referees for the new connection and found the results to be of high quality. Struve's detailed report was published as an annex to Baeyers paper (Struve 1857). The conclusion of this report contains a proposal for an arc of parallel in latitude 47 1/2° between Brest and Astrachan, the geodetic material for which, i.e. several triangulations, Struve saw to be ready. More generally, he drew attention to the fact, that there existed already a continuous European network of triangulations between Hammerfest in the north, Cap Marco in the south, Valentia in the west, and Astrachan in the east (Struve 1857, p.441f.). It seems to me, that Baeyer got the idea of a European network from this report by Struve, or even from earlier discussions with him. In the preface to his 1857 publication Baeyer wrote, that the importance of connecting the Russian triangulations with that of Western Europe, and thus of establishing a continuous network of triangulations covering the whole Europe, was obvious, and was always considered by the Russian geodesists as an important aim of their operations (Baeyer 1857, p.III).

In summer and autumn 1857 Wilhelm Struve travelled through Europe, both for recreation after illness and for negotiations about his proposal of the international arc of parallel from Ireland to the Ural (Batten 1988). His previous plans for an arc of parallel in latitude 47 1/2° failed since there was a lack of exact triangulations at this latitude in Western Europe (Novokshanova-Sokolovskaya 1967), but a similar arc of parallel at mean latitude 52° seemed to be possible. From France and England Struve arrived at Berlin in November. On 11 November Alexander von Humboldt (1769-1859) transmitted to him an invitation of the Prince of Prussia, later Wilhelm I, for the next day. Most probably, during this audience Struve officially offered his plan to Prussia. The following day, on 13 November, Struve described his wishes concerning the involvement of Prussia in a written statement and sent it to Humboldt, who added his own proposition and transmitted it on 14 November to the Prince. Six days later Struve received an official answer by the Prussian war minister von Waldersee, in which the minister offered him the support of Prussian government, and agreed to charge general Baeyer with the necessary pieces of work (Humboldt 1857; Waldersee 1857; see also Helmert 1893).

Soon after this travel Wilhelm Struve fell into serious illness, from which he never completely recovered. His duties were taken over by his son Otto Struve, who later also became the Russian deputy for the arc measurement organisation. In February 1858 Otto Struve wrote a letter to Humboldt, in which he described his father's illness, adding that the Tsar (i.a. Alexander II) promised his protection for the projected arc of parallel, but that due to the illness preparational work could not yet been done (O. Struve 1858).

The most important person in this project became Baeyer, who in summer of 1857 had been dispensed from his military duties due to strong tensions with the Prussian general staff, becoming free for mainly scientific work. The above mentioned letter of Waldersee shows that Baeyer and Struve were in contacts concerning the arc of parallel, but other documents about this are so far not known to me. Baeyer had a very high opinion of Wilhelm Struve. He called him the "finest and most skilful observer ever being" (Baeyer 1861b, p. 15).

On 4 December 1857 Baeyer was asked to prepare an estimation of expected expenses. In March 1858 he got two lieutenants at his disposal for the needs of the arc measurement. This staff remained nearly unchanged during the first years of the Mitteleuropäische Gradmessung. For the year 1858 Baeyer wrote a first annual report about Struve's arc measurement, as he called it. Such reports he compiled also for the years 1859 and 1860. In the archive file after these hand-written reports immediately follows his Entwurf zu einer Mitteleuropäischen Gradmessung. The next paper is called Annual report on Struve's and the Central European arc Measurement for 1861 (Baeyer 1858-1861). Thus, there is a straight line from Struve's arc of parallel to the Mitteleuropäische Gradmessung with respect to organization.

A practically unknown document shows the intellectual connection between the two projects. In a notice about the history of the Europäische Gradmessung written by Baeyer in 1878 for the just

established Scientific Council of the Geodetic Institute at Berlin (Baeyer 1879), he gave the following reason for his idea: For the arc of parallel old triangulations made in the twenties with the 8"-theodolite by Reichenbach should be used. As a pupil of Bessel and knowing the 15"-theodolite by Ertel, Baeyer thought about better measurements. So he looked for additional reasons beside the arc of parallel to ask for a continuation of the financial support for triangulations in the sense of arc measurements and coast survey. This led him to the idea of leaving the principle of arc measurements along parallels or meridians and, instead of this, investigating the curvature of large parts of the Earth.

It is not quite understandable, why Baeyer needed additional arguments beside the arc of parallel. I suggest that there were also other reasons for his idea, namely his conflicts with the Prussian general staff. It is not the place here to discuss this. The main point here is that there were intellectual connections between Struve's project and Baeyer's proposal of 1861. Another indication of Wilhelm Strave's influence on Baeyer I see in the fact, that prior to Baeyer's participation in Struve's international project he thought mainly in national dimensions. His first own project, proposed in 1856, was that of better triangulations in East Prussia (Baeyer 1868). In 1856 he also thought about an arc in parallel, but just between Helgoland and Trunz, the south end of Bessel's arc measurement (Baeyer 1873). His work in connecting the Prussian and Russian triangulations was also more of local kind with respect to the practical work to be done. Struve's arc in parallel was the first properly international project in which Baeyer took part, teaching him to think in international dimensions.

However, Baeyer's idea itself, i.e. the investigation of regional and local anomalies of the figure of the Earth and their physical reasons, was really new and went far behind what Struve had proposed. But the impulse came from Struve's project and his ideas of a European network.

From these facts I conclude that Wilhelm Struve may be considered as one of the intellectual fathers of the Europäische Gradmessung.

Acknowledgements. I am much indebted to Dr. Ernst Buschmann (Potsdam) for very useful hints to published and unpublished sources, for interesting discussions and for a critical reading of the manuscript. I also thank Dr. C. Suckow of Humboldt-Forschungsstelle Berlin for making me available the transliterations of Humboldt's correspondence with W. and O. Struve, as well as the Brandenburgisches Landeshauptarchiv for the permission to use the files of the former Geodetic Institute of Potsdam.

References

BLHA = Brandenburgisches Landeshauptarchiv, Bez.Pdm., Rep. 465, AdW, ZI für Physik der Erde, Aktenstück Nr.

1. Baeyer, J.J. 1857, Die Verbindungen der Preussischen und Russischen Dreiecksketten bei Thorn und Tarnowitz, Berlin.

2. Baeyer, J.J. 1858-1861, [Jahresberichte] BLHA A 231.

3. Baeyer, J.J. 1861a,     Entwurf    zu    einer Mitteleuropäischen Gradmessung. Berlin (Reprinted in: [J.J.Baeyer;]    Zur    Entstehungsgeschichte    der europäischen Gradmessung.Berlin 1882, p. 1-5).

4. Baeyer, J.J. 1861b, Ueber die Grosse und Figur der Erde. Eine Denkschrift zur Begründung einer mitteleuropäischen Gradmessung. Berlin.

5. Baeyer, J.J. 1868, Mein Entwurf zur Anfertigung einer guten Karte von den östlichen Provinzen des Preussischen Staates. Berlin.

6. Baeyer, J.J. 1879, Einige geschichtliche Notizen. In: Verhandlungen des Wissenschaftlichen Beiraths des Königlichen Geodätischen Instituts zu Berlin im Jahre 1878. Berlin, S.25.

7. Batten, A.H. 1988, Resolute, and Undertaking Characters: The Lives of Wilhelm and Otto Struve. Dordrecht, p. 156.

8. Buschmann, E., Kautzleben, H. 1987, Erdmessung - 125 Jahre erstes internationales geodätischen Programm. Vermessungstechnik 35, H.4., S. 110-115.

9. Helmert, F.R. 1893, Die Europäische Längengradmessung in 52 Grad Breite von Greenwich bis Warschau, I. Heft. Hauptdreiecke und Grundlinienanschlüsse von England bis Polen. Berlin, p.l.

10. Humboldt, A.v. 1857, [Letters of 11, 14, and 20. Nov. 1857 to W. Struve]. Archives of the Russian Academy of Sciences, St. Petersbourg, F. 703, op. 1, No. 56, L. 212, 214, 215. (Transcription at Humboldt-Forschungsstelle, Berlin).

11. Novokshanova-Sokolovskaya, Z.K. 1967, Kartograficheskie i geodezicheskie raboty v Rossii v XIX - nachale XX v. Moskva, pp. 52 and 96.

12. Struve, O. 1858, [Letter of 20 Feb. 1858 to A.v. Humboldt]. Archives of the Russian Academy of Sciences, St. Petersbourg, F. 286, op. 1, No. 210, L. 7-8. (Transcription at Humboldt-Forschungsstelle, Berlin).

13. Struve, W. 1857, Ueber die in den Jahren 1852-1854 ausgeführte Verbindung der geodätischen Arbeiten in Russland und Preussen. In: Baeyer 1857, pp. 406-422

[dated Pulkowo, 21/9 June 1857].        

14. Völter, U. 1963, Geschichte und Bedeutung der Internationalen Erdmessung. Veröffentlichungen der Deutschen Geodätischen Kommission, Reihe C, H. Nr. 63.

15. Waldersee, v. 1857, [Letter of 19 Nov. 1857 to W. Struve]. BLHA A 379.