History of the metre
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The history of the metre starts with the Scientific Revolution that is considered to have begun with Nicolaus Copernicus's publication of De revolutionibus orbium coelestium in 1543. Increasingly accurate measurements were required, and scientists looked for measures that were universal and could be based on natural phenomena rather than royal decree or physical prototypes. Rather than the various complex systems of subdivision then in use, they also preferred a decimal system to ease their calculations.
Giovanni Domenico Cassini, with the Paris Observatory in the background
The Meridian room of the Paris Observatory (or Cassini room): the Paris meridian is drawn on the ground.
Gravimeter with variant of Repsold-Bessel pendulum.
Triangulation of the Anglo-French Survey (1784–1790)
Paris meridian
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The Paris meridian is a meridian line running through the Paris Observatory in Paris, France – now longitude 2°20′14.02500″ East. It was a long-standing rival to the Greenwich meridian as the prime meridian of the world. The "Paris meridian arc" or "French meridian arc" is the name of the meridian arc measured along the Paris meridian.
Meridian Room (or Cassini Room) at the Paris Observatory, 61 avenue de l'Observatoire (14th arrondissement). The Paris meridian is traced on the floor.
The triangulation mesh of the Anglo-French survey 1784–1790
The West Europe-Africa Meridian-arc extending south from the Shetland Islands, through Great Britain, France and Spain to El Aghuat in Algeria, whose parameters were calculated from surveys carried out in the mid to late 19th century. It yielded a value for the equatorial radius of the Earth a = 6 377 935 metres, the ellipticity being assumed as 1/299.15. The radius of curvature of this arc is not uniform, being, in the mean, about 600 metres greater in the northern than in the southern part. The
One of the 135 Arago medallions. This one is located near the Louvre Pyramid.