The metre In the discussions leading up to the French adoption of the metric system in 1791, the leading candidate for the definition of the new unit of length, the metre, was the seconds pendulum at 45° North latitude. It was advocated by a group led by French politician Talleyrand and mathematician Antoine Nicolas Caritat de Condorcet. This was one of the three final options considered by the French Academy of Sciences committee. However, on March 19, 1791, the committee instead chose to base the metre on the length of the meridian through Paris. A pendulum definition was rejected because of its variability at different locations, and because it defined length by a unit of time. (However, since 1983 the metre has been officially defined in terms of the length of the second and the speed of light.) A possible additional reason is that the radical French Academy didn't want to base their new system on the second, a traditional and nondecimal unit from the ancien regime.
THe METre iN THE diScussiOnS leAdinG UP to THe frencH ADoPTion of tHE Metric SYSteM in 1791, tHE leading caNdidaTE For the DefinITIon Of tHe neW Unit of leNgth, the meTre, was tHe secoNds pendulum At 45° NOrth latituDe. it waS aDvoCATed By a gRoup led BY frencH pOLItiCIaN taLLEYRand anD maThemaTiCiaN antOiNE NicOlas CarItaT De coNDOrCet. tHis was onE of The Three FInal OPTiONS cONsiDerEd BY ThE fRench acadEMy OF scieNceS COMMiTtee. hOweVer, ON MarcH 19, 1791, the ComMiTtee iNsteaD ChOsE tO baSe the metRE oN the lenGtH of the MerIdiAn through paRiS. A pENduLUM defiNiTioN WAs rejEctED bECausE OF its VaRIAbilIty At difFerENt lOCaTions, aNd becAuse it defiNed lEngth BY a Unit Of Time. (hOWeVEr, since 1983 tHe Metre Has Been OfficIALly Defined In terms of the lEngtH oF the secOnd AnD ThE speeD of LiGHt.) a PosSIblE AdditiOnal reaSon Is thaT tHE rADical frEncH acAdeMy dIdN'T wAnt to BAse tHeir NEW system On The SeCoNd, a traditIonAL And NOndeCIMAl UNiT FrOm thE AnCIen regiME.