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The Paris meridian is a meridian line running through the Paris Observatory in Paris, France—now longitude 2°20′14.03″ east. It was a long-standing rival to the Greenwich meridian as the prime meridian of the world.
In the year 1634, France ruled by Louis XIII and Cardinal Richelieu decided that the Ferro meridian should be used as the reference on maps, since this island is the most western position of the Old World. It was also thought to be exactly 20 degrees west of Paris.
A French astronomer, Abbé Jean Picard, measured the length of a degree of latitude and computed from it the size of the Earth during 1669–1670. In 1666, Louis XIV of France had authorized the building of an observatory in Paris to measure longitude. On Midsummer's Day 1667, members of the Academy of Sciences traced the future building's outline on a plot outside town near the Port Royal abbey, with Picard's meridian exactly bisecting the site north-south. French cartographers would use it as their prime meridian for more than 200 years.
Old maps from continental Europe often have a common grid with Paris degrees at the top and Ferro degrees offset by 20 at the bottom. Louis Feuillée also worked on this problem in 1724. It was later found that the actual island of El Hierro itself is in fact 20° 23' 9" west of Paris, but the Ferro meridian was still defined as 20 degrees west of Paris.
In the early 19th century, the Paris meridian was recalculated with greater precision by the astronomer François Arago, whose name now appears on the plaques or medallions tracing the route of the meridian through Paris (see below). Biot and Arago published their work as a fourth volume following the three volumes of "Bases du système métrique décimal ou mesure de l'arc méridien compris entre les parallèles de Dunkerque et Barcelone" (Basis for the decimal metric system or measurement of the meridian arc comprised between Dunkirk and Barcelona) by Delambre and Méchain.
In the second half of the 19th century, the results of Arago's survey of the Balearic Islands were lost. From 1865 to 1868, Carlos Ibáñez e Ibáñez de Ibero connected the survey of the Balearic Islands with that of the Iberian Peninsula. From 1870 to 1894 the Paris meridan arc was remeasured by Perrier and Bassot. The triangulation of France was connected to those of Great Britain, Spain and Algeria. In 1879, Carlos Ibáñez e Ibáñez de Ibero for Spain and François Perrier for France executed the junction of the Spanish geodetic network with Algeria and thus completed the measurement of the Paris meridian which extended from Shetland to the Sahara. This connection was a remarkable enterprise where triangles with a maximum length of 270 km were observed from mountain stations over the Mediterranean Sea.
Moreover the Paris meridian was linked with international collaboration in geodesy and metrology. Cesar-François Cassini de Thury (1714-1784) expressed the project to extend the French geodetic network all aroud the world. In 1783 the French Academy of Science presented his proposal to King George III. This led to the Paris and Greenwich observatories' connection by General William Roy and the first triangulation of Great Britain.
In 1860, the Russian Government at the instance of Otto Sturves invited the Governments of Belgium, France, Prussia and England to connect their triangulations in order to measure the length of an arc of parallel in latitude 52° and to test the accuracy of the figure and dimensions of the Earth, as derived from the measurements of arc of meridian. In order to combine the measurements it was necessary to compare the geodetic standards of length used in the different countries. The British Government invited those of France, Belgium, Prussia, Russia, India, Australia, Austria, Spain, United States and Cape of Good Hope to send their standards to the Ordnance Survey office in Southampton. Notably the standards of France, Spain and United States were based on the metric system, whereas those of Prussia, Belgium and Russia where calibrated against the toise, of which the oldest physical representative was the Toise of Peru. The Toise of Peru had been constructed in 1735 for Bouguer and De La Condamine as their standard of reference in the French Geodesic Mission, conducted in actual Ecuador from 1735 to 1744 in collaboration with the Spanish officers Jorge Juan and Antonio de Ulloa.
Alexander Ross Clarke and Henry James published the first results of the standards' comparisons in 1867. The same year Russia, Spain and Portugal joined the "Europäische Gradmessung" and the General Conference of the association proposed the metre as a uniform length standard for the Arc measurement and recommended the establishment of an International Bureau of Weights and Measures.
The Metre Convention was signed in 1875 in Paris and the International Bureau of Weights and Measures was created under the supervision of the International Committee for Weights and Measures. The first president of the International Committee for Weights and Measures was the Spanish geodesist Carlos Ibáñez e Ibáñez de Ibero. He also was the president of the Permanent Commission of the "Europäische Gradmessung" from 1874 to 1886. In 1886 the association changed name for the International Geodetic Association and Carlos Ibáñez e Ibáñez de Ibero was reelected as president. He remained in this position until his death in 1891. During this period the International Geodetic Association gained world wide importance with the joining of United States, Mexico, Chile, Argentina and Japan. In 1883 the General Conference of the "Europäische Gradmessung" proposed to select the Greenwich meridian as the prime meridian.
In 1884, at the International Meridian Conference in Washington DC, the Greenwich meridian was adopted as the prime meridian of the world. France and Brazil abstained. The French clung to the Paris meridian as a rival to Greenwich until 1911 for timekeeping purposes and 1914 for navigation. To this day, French cartographers continue to indicate the Paris meridian on some maps.
The competition between the Paris and Greenwich meridians is a plot element in Jules Verne's Twenty Thousand Leagues Under the Sea, published just before the international decision in favor of the British one.
The Arago medallions
In 1994 the Arago Association and the city of Paris commissioned a Dutch conceptual artist, Jan Dibbets, to create a memorial to Arago. Dibbets came up with the idea of setting 135 bronze medallions (although only 121 are documented in the official guide to the medallions) into the ground along the Paris meridian between the northern and southern limits of Paris: a total distance of 9.2 kilometres/5.7 miles. Each medallion is 12 cm in diameter and marked with the name ARAGO plus N and S pointers.
Another project, the Green Meridian (An 2000 — La Méridienne Verte), aims to establish a plantation of trees along the entire length of the meridian arc in France. Several missing Arago medallions appear to have been replaced with the newer 'An 2000 — La Méridienne Verte' markers.
In certain circles, some kind of occult or esoteric significance is ascribed to the Paris meridian; sometimes it is even perceived as a sinister axis. Dominique Stezepfandts, a French conspiracy theorist, attacks the Arago medallions that supposedly trace the route of "an occult geographical line"; to him the Paris meridian is a "Masonic axis" or even "the heart of the Devil."
Henry Lincoln, in his book The Holy Place, argues that various ancient structures are aligned according to the Paris meridian. They even include medieval churches, built long before the meridian was established according to conventional history, and Lincoln finds it obvious that the meridian "was based upon the 'cromlech intersect division line'." David Wood, in his book Genisis, likewise ascribes a deeper significance to the Paris meridian and takes it into account when trying to decipher the geometry of the myth-encrusted village of Rennes-le-Château: The meridian passes about 350 meters (1,150 ft) west of the site of the so-called "Poussin tomb," an important location in the legends and esoteric theories relating to that place. (A skeptical discussion of these theories, including the supposed "alignments," can be found in Bill Putnam and Edwin Wood's book The Treasure of Rennes-le-Château - A mystery solved.)
|Wikimedia Commons has media related to Paris Prime Meridien.|
- The Arago medallions on Google Earth
- Full Meridian of Glory: Perilous Adventures in the Competition to Measure the Earth: history of science book by Prof. Paul Murdin
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- Clarke, A. R.; James, Henry (1867-01-01). "Abstract of the Results of the Comparisons of the Standards of Length of England, France, Belgium, Prussia, Russia, India, Australia, Made at the Ordnance Survey Office, Southampton". Philosophical Transactions of the Royal Society of London. 157: 161–180. ISSN 0261-0523. doi:10.1098/rstl.1867.0010.
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- Torge, Wolfgang (2015). IAG 150 Years. Springer, Cham. pp. 3–18. doi:10.1007/1345_2015_42.
- "International Bureau of Weights and Measure Intergovernmental Organisation with headquarters located in Sèvres, France" (PDF). Bureau International des Poids et Mesures.
- Soler, T. (1997-02-01). "A profile of General Carlos Ibáñez e Ibáñez de Ibero: first president of the International Geodetic Association". Journal of Geodesy. 71 (3): 176–188. ISSN 0949-7714. doi:10.1007/s001900050086.