Paris meridian

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 Paris meridian exactly bisecting the site north–south.

[6] Hitherto geodetic observations had been confined to the determination of the magnitude of the Earth considered as a sphere, but a discovery made by Jean Richer turned the attention of mathematicians to its deviation from a spherical form.

This fact, which was scarcely credited till it had been confirmed by the subsequent observations of Varin and Deshayes on the coasts of Africa and America, was first explained in the third book of Newton’s Principia, who showed that it could only be referred to a diminution of gravity arising either from a protuberance of the equatorial parts of the Earth and consequent increase of the distance from the centre, or from the counteracting effect of the centrifugal force.

This conclusion was totally opposed to the theoretical investigations of Newton and Huygens, and accordingly the Academy of Sciences of Paris determined to apply a decisive test by the measurement of arcs at a great distance from each other – one in the neighbourhood of the equator, the other in a high latitude.

Thus arose the celebrated French Geodesic Missions [fr], to the Equator and to Lapland, the latter directed by Pierre Louis Maupertuis.

Cesar-François Cassini de Thury (1714–1784) expressed the project to extend the French geodetic network all around the world and to connect the Paris and Greenwich observatories.

Biot and Arago published their work as a fourth volume following the three volumes of by Delambre and Méchain's "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).

[6][8] In 1879, Ibáñez de Ibero for Spain and François Perrier for France directed the junction of the Spanish geodetic network with Algeria.

[6][14] The triangulation of France was then connected to those of Great Britain, Spain and Algeria and thus the Paris meridian's arc measurement extended from Shetland to the Sahara.

[2] In 1860, the Russian Government at the instance of Otto Wilhelm von Struve invited the Governments of Belgium, France, Prussia and Britain to connect their triangulations 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.

[15] 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.

[17] During this period the International Geodetic Association gained worldwide importance with the joining of United States, Mexico, Chile, Argentina and Japan.

[18][21] The United States passed an Act of Congress on 3 August 1882, authorizing President Chester A. Arthur to call an international conference to fix on a common prime meridian for time and longitude throughout the world.

[20][6] In 1911, Alexander Ross Clarke and Friedrich Robert Helmert stated in the Encyclopædia Britannica : "According to the calculations made at the central bureau of the international association on the great meridian arc extending from the Shetland Islands, through Great Britain, France and Spain to El Aghuat in Algeria, a [the equatorial radius of the Earth] = 6,377,935 metres, the ellipticity being assumed as 1/299.15.

[21] The creation of the International Time Bureau, seated at the Paris Observatory, was decided upon during the 1912 Conférence internationale de l'heure radiotélégraphique.

Dominique Stezepfandts, a French conspiracy theorist, attacks the Arago medallions that supposedly trace the route of "an occult geographical line".

"[citation needed] Henry Lincoln, in his book The Holy Place, argued that various ancient structures are aligned according to the Paris meridian.

David Wood, in his book Genesis, 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 metres (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 sceptical 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.

[citation needed] The confusion between the Greenwich and the Paris meridians is one of the plot elements of Tintin book Red Rackham's Treasure.