The Struve Geodetic Arc Autor(en): Smith, J.R. Objekttyp: Article Zeitschrift: Vermessung, Photogrammetrie, Kulturtechnik : VPK = Mensuration, photogrammétrie, génie rural Band (Jahr): 98 (2000) Heft 5 PDF erstellt am: 09.10.2021 Persistenter Link: http://doi.org/10.5169/seals-235647 Nutzungsbedingungen Die ETH-Bibliothek ist Anbieterin der digitalisierten Zeitschriften. Sie besitzt keine Urheberrechte an den Inhalten der Zeitschriften. Die Rechte liegen in der Regel bei den Herausgebern. Die auf der Plattform e-periodica veröffentlichten Dokumente stehen für nicht-kommerzielle Zwecke in Lehre und Forschung sowie für die private Nutzung frei zur Verfügung. Einzelne Dateien oder Ausdrucke aus diesem Angebot können zusammen mit diesen Nutzungsbedingungen und den korrekten Herkunftsbezeichnungen weitergegeben werden. Das Veröffentlichen von Bildern in Print- und Online-Publikationen ist nur mit vorheriger Genehmigung der Rechteinhaber erlaubt. Die systematische Speicherung von Teilen des elektronischen Angebots auf anderen Servern bedarf ebenfalls des schriftlichen Einverständnisses der Rechteinhaber. Haftungsausschluss Alle Angaben erfolgen ohne Gewähr für Vollständigkeit oder Richtigkeit. Es wird keine Haftung übernommen für Schäden durch die Verwendung von Informationen aus diesem Online-Angebot oder durch das Fehlen von Informationen. Dies gilt auch für Inhalte Dritter, die über dieses Angebot zugänglich sind. Ein Dienst der ETH-Bibliothek ETH Zürich, Rämistrasse 101, 8092 Zürich, Schweiz, www.library.ethz.ch http://www.e-periodica.ch Histoire de la culture et de la technique The Struve Geodetic Arc Since 1994 the International Institution for the History of Surveying and Measurement - a Permanent Institution within FIG -, has been working on a project to get recognition "**B of the Struve Geodetic Arc as a UNESCO World Heritage Site. This arose from a resolution put to the FIG at its 1994 Congress in Melbourne. But what is the Struve Geodetic Arc and what, in this context, is a World Heritage Site? Before answering these questions it is necessary to fill in some of the background to the project and discuss the determination of the parameters of the earth in terms of its size and shape. Seit 1994 arbeitet die FIG-Arbeitsgruppe Vermessungsgeschichte (heute: International Institution for the History of Surveying and Measurement - a Permanent Institution within FIG) an einem Projekt zur Anerkennung der Meridianmessung vom Schwarzen Meer bis Hammerfest durch Friedrich Georg Wilhelm Struve (Struve Are) als Unesco-Welterbe. Das Projekt entstand aus einer Resolution am FIG-Kongress 1994 1: Friedrich Wilhelm Struve in Melbourne. Der Artikel beschreibt, was der «Struve Are» ist und wie er ein Unesco- Fig. Georg Welterbe werden kann. (1793-1864). Depuis 1994, le groupe de travail FIG «Histoire de la mensuration» (aujourd'hui: The problem International Institution for the History of Surveying and Measurement - a Permanent Prior to Eratosthenes, back to the time of Institution within FIG) s'occupe à élaborer un projet visant à la reconnaissance de la Pythagoras around 500 BC, it had been mesure du méridien entre la Mer Noire et Hammerfest par Friedrich Georg Wilhelm known that the earth was not flat but of Struve, comme héritage mondial de l'Unesco. Le projet est né d'une résolution du some spherical shape. Why spherical was congrès de la FIG de 1994 à Melbourne. L'auteur décrit ce qu'est «Struve Arc» et the next step after flat and not some other comment il peut devenir un héritage mondial de l'Unesco. shape is open to conjecture. At the time however the sphere was considered to be Dal 1994, la Institution for the History of Surveying and Measurement - un'istituzione the perfect shape, perhaps because of its permanente in seno alla FIG - sta lavorando ad un progetto per il riconoscimento regularity in all directions, and could well dell'Arco geodesico di Struve (la misurazione del meridiano dal Mar Nero fino a have been selected in this case just on that Hammerfest effettuata da Friedrich Georg Wilhelm Struve) quale patrimonio dell'umanità, assumption. The fact that it turned out to sotto l'egida dell'UNESCO. Questo mandato è scaturito da una risoluzione del be a correct choice would then, have been Congresso FIG del 1994 a Melbourne. Ma in cosa consiste l'Arco geodesico di Struve e pure luck. cosa si intende - in questo contesto - con patrimonio dell'umanità? Prima di rispondere The problem over the intervening a questi quesiti è necessario spiegare i retroscena del progetto e discutere la centuries has been to determine its exact fissazione dei parametri della Terra, cioè la sua dimensione e forma. shape and size. While it was considered to be a true sphere the problem resolved itself to one of just determining its size, but by the time of Isaac Newton in the might mention Fernel, Picard, the Cassinis, second half of the 17th century even the J. R. Smith Newton, Bouguer, La Condamine, La idea of a true sphere was being Caille, Maupertuis, Delambre, Mechain, questioned. (By «true sphere» and other terms Background Airy, Everest and many others. Notice how mentioned later, is meant the sea level many of these were Frenchmen. surface assumed continuous around the Since the time of Eratosthenes (c276 BC- The focus of this paper is another name, earth. In relation to the overall size of the d 95 BC)thedimensionsof the earth have that of F G W Struve, who made an earth the topography is insignificant). been determined from arc measurements. important contribution during the 19th Why was knowledge of these parameters In fact the theory developed by century. Such was the importance of the work of importance? This can be illustrated simply Eratosthenes remained in use until the era by Struve that it is the hope that some of by saying that if Christopher Columbus of satellite geodesy. Many famous names his survey points that still remain can be had known the true size of the earth, in the fields of astronomy, mathematics designated as world heritage monuments. he would not have gone where he did. By and surveying have been involved in the But more of him later. To put his working with a figure that was much too gradual improvement in both techniques, work in context some background detail small he had a distorted idea of the earth equipment and results. Among these one is necessary. he was navigating upon. It was almost as 322 i Mensuration, Photogrammetrie, Génie rural 5/2000 Kultur- und Technikgeschichte if he thought he was going round a tennis provements even by the late 15th century CK2CUMFEGEMC& ¦4*^.4 c- ball when in fact he was on a football. calculated values of the earth's size varied 3SO ¦ S Not only would he be using incorrect considerably and unfortunately the distances but incorrect directions as well [1 ]. value selected by Columbus was incorrect by about 25%. The measurement difficulty The problem of measuring accurately an /V\ Measure long lines object the size of the earth is not an easy / X One of the difficulties inali the early one yet the principle, first deduced by / /* measurements was that the linear distance Eratosthenes around 230 BC, has remained required had to be physically measured from the basis of all attempts until the advent 1 / Q-/ X end to end by whatever method was felt / of satellites. Although the method / appropriate. Each distance had to be of devised by Eratosthenes was based on the / the order of 60 miles (100 km). If much mathematics of a sphere it was later / / shorter distances only were used the possible to modify it to apply also to shapes •y accumulation of errors in the results would that were not quite true spheres. have been unacceptable. There were no Fig. 2: Principle of determining size of Whatever one is measuring it is advantageous tape measures then as we know them and earth as a sphere. to determine by direct measurement the methods were pacing, knotted ropes, as large a part of it as possible arcs that were not sections of great camel days journeys, the distance before resorting to extending a value by circles. travelled by horsemen in a given time and calculation. One has however to keep within Assuming a spherical earth, Eratosthenes variations on these. the bounds of practicality. For example, if said that if you measured the linear As far as the angular value was concerned you wanted to measure the circumference distance between two points on a particular this could be found by observing the stars of a football that would be done by line of longitude (also called a meridian or the shadows of obelisks but in either putting a tape measure around it. If on line as, for example, that of zero case the results were crude. the other hand it was required to measure longitude through Greenwich), and were the circumference of a large circular then able also to determine the angular The advent of triangulation roundabout it might be more practical to distance subtended at the centre of the It was not until the early 17th century that measure the length of an estimated quarter earth (see figure 2) between the same two a more convenient method, triangulation, of it and multiply the result by four, or points then the radius and other was developed in Holland and better alternatively determine the diameter and parameters of the earth could be easily measuring equipment became available. multiple up by p. When the structure or determined. Such an angle is not as While it still kept to the basic principle of figure involved becomes the size of the inaccessible as it might at first appear as it can Eratosthenes for measuring a very long earth then a small fraction, say 1°, might be found from star observations at each distance now an element of computation be the more practical amount to measure of the two points.