Le Mètre du monde

Following Dava Sobel’s success with Longitude, Denis Guedj here recounts the story of the creation of the metre. Pierre Méchain and Jean-Baptiste Delambre set out from the Tuileries on 24 June 1792 heading for Barcelona and Dunkerque respectively. The idea was for these two men to leave their destinations and to meet halfway in Rodez. By this process they could mesure an arc of the meridian, from which to derive the length of a quarter of that meridian, from the pole to the equator, and from this to take one ten-millionth as a base measure. It took them seven years. And indeed, partially in honour of their work, the French Year 2000 committee has planted trees all along the line from Dunkerque to Barcelona.