Prototype metre bar and kilogram massIn 1799, the first definitive prototype metre bars (mètre des Archives) and kilograms were constructed in platinum. This followed the legal definition of the metric system by the French National Assembly on 7 Apr 1795, that was itself established during the famous measurements of the Earth's meridian between Dunkerque and Barcelona. The definitive protype replaced a provisional metre prototype bar constructed by Lenoirthat had been accepted as a standard for the metre on 9 Jun 1795. The use of a metal bar to define the standard meter continued until replaced on 14 Oct 1960 by a definition based upon a number of wavelengths of light from a certain spectroscopic light source. By 20 Oct 1983, that was replaced with a new definition based on the speed of light.« |
