Paris Meridian - Origin

Origin

In the year 1634, France ruled by Louis XIII and Cardinal Richelieu decided that Ferro's 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 (outside of Anglo-America) 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).

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.