"Standard gauge
Jean-Baptiste-Joseph Delambre (1749-1822)
Pierre-François-Andre Mechain (1744-1804)
It was under Louis XVI that the impetus was given in France to the introduction of a standardized measure of length, - the meter, which was to be derived from one intangible quantity, the circumference of the earth, the circumference of a meridian, a circle passing through both poles. and crosses the equator twice perpendicularly. If every circle counts such a meridian 360 degrees, that is 360 x 60 minutes, which in this case are called 'latitudes' and 'minutes of latitude'. In the first place, it was a matter of determining the total length of those 21600 minutes in a common measure of length.
When the engineers Delambre and Méchain set to work in the second half of the 18th century, they, like Eratosthenes had done in his day, sought as starting points two places, which must be on the same meridian and at a measurable distance from each other. They found it in Dunkirk and Barcelona.
By means of astronomical observations, they determined the number of minutes of latitude between those cities. A much more extensive work was the measurement of the mutual distance, linea recta, in a usual measure of length. This was first done - directly with measuring chains over the ground - on a 'base' between two high - mutually well observable - points in Melun and Lieusaint. From this basis, the progressive method of triangulation was applied, long known as 'triangulation': had the angles alternately measured and the lengths of the sides of adjacent triangles calculated in turn, with the final result being the linear distance. Dunkirk-Barcelona.
From the illustration, which clarifies the triangulation, it can also be read how the new unit of length was subsequently derived from a quarter of the meridian length, ie from a quarter of the earth's circumference. This made the Earth's circumference - it was thought - determined to be exactly 40,000 kilometers, but that this beautiful round number was not completely correct, it turned out later, after the discovery of the flattened shape of the Earth. There are deviations from 9 to 76 kilometers, and for the same reason the nautical mile, equal to the length of one minute of latitude, is not everywhere 1852 meters long. This is an average."
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"The Green Meridian
The impetus for this project under the supervision of Paul Chemetov was the transition to the new millennium. It was decided to follow the route of the 0-meridian again, whereby the calculation of the distance from Dunkirk to Barcelona, ??carried out by Delambre and Mechain around 1800, led to the standard meter. Condorcet (then member of the Academy of Sciences, and of the Constituent Assembly) commented: "Pour tous les hommes, pour tous les temps".
In this project, started on November 25, 1999, it was decided to plant long-lived trees on the route of the 0 meridian, to compensate for the clear-cutting caused by the storms of winter (1999). In addition, bronze plaques have been placed in the bottom. Planting the trees and placing the bronze plaques on the Paris meridian turned out to be not always feasible in reality, due to local circumstances, road network, safety and the like. It was therefore mainly about encountering the meridian at all kinds of locations.
On July 14, 2000, the "Incredible Picnic" took place in all 337 towns and cities in France that lie on the meridan, organized by Mission 2000, the organizing committee of the millennium celebration."
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