Prime Meridian (French version)

Before the agreement to use Greenwich as Prime Meridian – in 1884, there were several other meridians which of course led to confusion, especially at sea. A major competitor to Greenwich was the French version. During the different conferences that were held to decide on a global common meridian, the French accepted to give up theirs on one condition; to have the meter accepted as a universal measurement - not yet quite achieved!

The French meridian was officialised in 1667 and has its starting point at the Observatoire (Paris 14th), finished in 1672 (three years before Greenwich!). The building which is exactly in a north-south axe had as architect, Claude Perrault, brother of Charles Perrault (author of Little Red Riding Hood, Sleeping Beauty, Puss in Boots, Cinderella, Bluebeard, Hop o’ My Thumb…). It’s the world’s oldest still active observatory. I have not found a clear explanation for the choice of the place of the Observatoire. It’s interesting to see that it’s exactly in the axe of the then already exisiting Palais de Luxembourg, built on the initiative of Marie de Medici (Henry IV’s widow), who was much interested in astrology. You find the same north-south axe around the Invalides, built at the same period as the Observatoire.The “Da Vinci Code” refers to this axe, the “Rose Line”. Actually the French meridian passes well the Louvre, but not exactly where the pyramid is, whereas the St. Sulpice church is well out of the axe.To find the trace of the axe, the “Da Vinci Code” refers to the 135 “Arago plates”, 12 cm (= 4,7 inches, - the meter is not yet adapted all over) bronze disks which were placed along the axe in 1994. You still find most of them along the streets – but some have disappeared; nice pieces of collection.(Arago was a 19th century French astronomer and politician.) The axe is in Paris also visualised in the park just behind the Observatoire and by the so called “mires”, one at Montmartre (north) and one in the Montsouris Park (south). You can read that they were erected in 1806 during the reign of….- the name of Napoleon has disappeared.The meter was “invented” by the French Academy of Sciences in 1793, based on researches made at the Observatory, as being one ten-millionth of the length of the meridian. (Nowadays it’s equal to the distance traveled by light in vacuum during a time interval of 1/299 792 458 of a second or something similar!)

The Greenwich Mean Time (GMT) is today officially replaced by an international time reference, UTC, maintained by a number of atomic clocks around the world.