Originally published as: Torge, W. (2012): 150 Years of International Cooperation in Geodesy: Precursors and the Development of Baeyer’s Project to a Scientific Organisation. ‐ Zeitschrift für Geodäsie, Geoinformation und Landmanagement (zfv), 137, 3/2012 Fachbeitra Torge, 150 Years of International Cooperation in Geodesy ... 150 Years of International Cooperation · in Geode.sy: Precursors and the Development of Baeyer's Project to a Scientific Organisation* Wolfgang Torge Summary ternationaler Kooperation wird ausführlicher eingegangen, Geodesy commemorates th is year the founda tion of the abschließend wird auf die spätere Erweiterung zur globalen "Mitteleuropäisc he Gradmessung", which started its activi­ Wissenschaftsorganisation und die immer stärker werdende ties 150 years ago. Originated from an initiative of the Prus­ Einbindung in die interdisziplinäre Geoforschung hingewiesen. sian General Baeyer, this regional geodetic project required international cooperation. Outstanding organization soon led Keywords: Are measurements, Earth figure, Genera l Baeyer, to a scientific body which continuously extended over the International Association of Geodesy, Mitteleuropäische globe and fin ally built a global network of geodetic scien ce, Gradmessu ng represented today by the "Internationa l Association of Geo­ desy" (lAG). The following paper first remembers the start of international The Origin of Modern Geodesy and Early cooperation at the beginning of modern geodesy, as real­ International Cooperation : 18th Century ized through the arc measurements of the 18th and the early 19th century. First attempts for arc measu rements covering Geodesy, by definition, requires in te rn ational collabora­ cen tral Europe then are fou nd in the firsthalf of the 19th cen­ tion on a global scale. Thi s becomes clearly visib le with tury - connected with the names of Zach, Schumacher, Gauß, the beginning of modern geoclesy, wh ich may be reck­ Müffl ing, Bessel and Struve, among others. Ba sed upon a onecl from the 171h century. The heli ocentric world system memorandum presented 1861, Baeyer proposed a coordinat­ with the annual revolution of the Earth araund the Sun ed proceeding and clearly defined the problemstobe solved. and the daily rotation of the Earth ha cl been accepted at This idea soo n led to a governmen tal supported project and an that time, and physics ancl astronomy postulate an Earth orga nization wh ich rapidly extended beyond the boundaries fi gure flattenecl at the poles (Perrier 1939, Bi alas 1982). of central Europe. Th is early phase of international coopera­ The corresponding Earth mo clel is basecl on the theory of tion is di scussed in more detail. Finally, the later extension of hycl rostatic equilibrium (Newton** 1687, Huygens 1690), this early structure to a global scientific organization and the the observecl polar flattening of Jupiter (Jean-Dominique increasing incorporation into interdiscipl inary geoscientific Cassini 1666). ancl the latitucle-clepenclence of gravity research is shortly described. found by pendulum measurements (Richer 1672/73, Hal­ ley 1677/78). This is a great challenge for geoclesy: to Zusammenfassung prove the polar flattening by geometric methocls and to in diesem Jahr gedenkt die Geodäsie der Entstehung ihrer in­ cl etermine the parameters of such an Earth moclel! For ternationalen wissenschaftlichen Vereinigung vor 150 Jahren. a rotational elli psoid, these parameters woulcl be the Auf Initiative des preußischen Generals Baeyer entstand die semi-major axis and the geometric flatteni ng. The arc 11Mitteleuropäische Gradmessung((, ein zunächst räumlich be­ measurement methocl known since an tiqui ty is avail­ grenztes Projekt. Die hierzu notwendige internationale Zusam­ ab le for this purpose. Triangulation introcluced by Snel­ menarbeit wird effektiv organisiert und führt- bei laufender lius ( 1614/15) offers an efficient proceclure to determine Erweiterung der Aufgabenstellung - schließlich zur globalen geocletic (ell ipsoiclal) differences in length, wh ile the cle­ Vernetzung der geodä tischen Wissenschaft, heute repräsen• tennination of latitucle, longitucle and azim uth can be tiert durch die 11 /nternationa/ Association of Geodesy(( (lAG). basecl on well-known astronomical methods. A First at­ Der folgende Beitrag erinnert zunächst an die mit Beginn der tempt in this direction is carried out by J.-D. Cassini and modernen Geodäsie einsetzende länderübergreifende Zu­ his son Jacques carrying out a triangulation ( 1683 - 1718) sammenarbeit bei den Gradmessungen des 18. und des frü• along the meridian of Paris. Dividing this meridian arc of hen 19. Jahrhunderts. Erste Gradmessungen in Mitteleuropa a·2o' extension into a northern and a southern patt and oder Ansätze hierzu finden sich dann in der ersten Hälfte des 19. Jahrhunderts- verbunden u. a. mit den Namen Zach, * Modifizierte und ins Englische übersetzte Fassung eines Vor­ Schumacher. Gauß, Miiffling, Besse/ und Struve. Baeyers Idee trages im Ra hmen des Festkolloquiums ., 150 Jahre Mitteleuro­ eines koordinierten Vorgehens mit klarer Aufgabendefinition päische Gradmessung in Sachsen• am 1. Juni 20 12 in Dresden. führt schließlich - auf der Grundlage einer 1861 vorgelegten •• Names written in italics refer to historical persons, with rel­ Denkschrift - zu einer zwischenstaatlichen Zusammenarbeit, evant years of important publications or surveys, and not to Iist die bald über Europa hinausreicht. Auf diese frühe Phase in- of references. 166 zfv 3/2012 137.Jg. Torge, 150 Years of International Coope rati on in Geodesy ... Fachbeitrag separate evaluation led to an Earth model elongated at 2 Central Europe at the Turn of the 19th Century: th e poles, with a negative· fl attening of - 1/95. Thi s result Military Triangulations and the Beginning of was in agreement with a few older arc measurements, Are Measurements bu t contradicted the hypothesis of an Earth ll attened at th e poles. The poli tical situation in centrat Europe is less favour­ This is the .beginning of the well -known dispute be­ able for large-scale triangulations of high standard. This tween the fo llowers of Newton (llattening at the poles) is due to the strong separation into local territorial units, and the Cassi nis (elongation at the poles) which is solved which is especially pronounced in Germany; for the his­ by the famous arc measuret1lents in Lapland (Maupertuis, tOty of geodesy in Germany we refer to Torge (2009). Cla irnut et al. 1736/37) .and in the Spanish Vice-Kingdom Among the remarkable exceptions are the triangul a­ of Peru - today Ecuador (La Co11dami11e, Bouguer, Godi 11 tions carried out in the dukedo m of Oldenbu rg (Georg et al. 1735- 1744), ini tiated and organized by the French Christiall vo 11 Oeder, 1781- 1785) and in th e princi pali ty, Academy of Sciences. The early co mbination of the Lap­ and later kingdom, of Saxony (Friedrich Ludwig Aster, land arc with the Pa ri ~ ri1eridian arc revised by Cassi 11 i 1780-18 11), both fo llowing the example of the geodetic de Thu1y and La Caille ( 1739/40) already yields a polar sutvey of Denmark ( 1762 - 1779) un der Thomas Bugg e. fl attening of 1/304. This is co nfirmed by th e combina­ An important intermedi ate phase occurs at the turn of the tio n of further arc measurements, although the ll atten ing 19'" ce ntu ry, with the extension of French influence over values vaty between 1/1 44 and 1/352. These grea t French centrat Europe through the Napoleonic wars. The military arc measurements not only require political agreements sutveys carried out by th e well -trained French engi neer­ between the countries in volved, but also are the begin­ geogra phers are based on triangulation, and shall extend ning of international participation at large-scale geodetic the French map of scale I : 86400 on the occup ied or al­ projects. The Lap land expedi tion, fo r instance, included lied countries. Triangul ation of the occupied German re­ the Swedish astronomer Celsius, and the Spanish navy gions left of the Rhine ( 1802- 1809) is connected with the officers Jorge Juan and A ntonio de Ulloa active ly co n­ name of Trc111c hot. The upper Rhine area is sutveyed by tributed to the measurements and the evalu ation of the He111y ( 1804), while Epailly performs a rapid triangul a­ Peruvian arc measurement. tion of Hannover ( 1805 - 1806), and Bo1111e establishes a The !arge differences found for th e tlattening (and nat­ first trigonometric network in the allied Bavaria ( 1801- ura lly also fo r the semi-major axis) of an Ea tt h ell ipsoid 1807). The Batavian Republic is triangulated by Krnye11 - led to first discussions on the figure of the Earth, starting l10jj ( 1802- 181 1) . All these triangulations are co nnected already in the 18'" century. ln the beginning it is tried to to the new arc measurement along the Pa ris mericlian keep the ellipsoidal Earth model, and to ex pl ain loca l and ( 1792 - 1798) carri ed out by Dela mbre and M echain in or­ later also large-scale deviati ons through the effects of der to defin e the metre as a natural unit of length, and topography, geology, and co ntinent-ocean distribution. thus refer to the geodeti c datum provid ed by the Paris Different strategies are proposed in order to solve this obsetvatoty. This is also va lid fo r the Prussian mi litary problem, including the red uction of loca l anomali es and triangulation of Westphalia ( 1795 - 1805) ca rried out un­ the introduction of a latitude- or longi tude-dependent der the direction of Colonel 110 11 Lecoq, in a period when tl attening parameter. Araund 1·800, the time is ri pe for Prussia had withd rawn from th e coalition against France. a new definition of the Ea rth fi gure, whi ch is introduced At the end of the Napoleo nic wa rs, Prussia reo rganized soo n after by Gauß, Besse/, ancl oth ers (see below).