The metric system was developed from 1791 onwards by a group of scientists that was commissioned by the Assemblée nationale and Louis XVI of France to create a unified and rational system of measures.[9] The group, which included Antoine-Laurent Lavoisier (the "father of modern chemistry") and the mathematicians Pierre-Simon Laplace and Adrien-Marie Legendre,[10] used a number of principles first proposed by the English cleric John Wilkins in 1668[11] and the French cleric Gabriel Mouton in 1670.[12] On 1 August 1793, the National Convention adopted the new decimal metre with a provisional length as well as the other decimal units with preliminary definitions and terms. The law of 7 April 1795 (Loi du 18 germinal, an III) defined the terms gramme and kilogramme replaced the former terms gravet (correctly milligrave) and grave, and on 22 June 1799, after Pierre Méchain and Jean-Baptiste Delambre completed their survey, the definitive standard metre was deposited in the French National Archives. On 10 December 1799 (a month after Napoleon's coup d'état), the law by which metric system was to be definitively adopted in France was passed.


In 1832 Carl Friedrich Gauss implicitly defined a coherent system of units when he measured the earth's magnetic field in absolute units quoted in terms of millimetres, grams, and seconds.[14] In the 1860s James Clerk Maxwell and William Thomson (later Lord Kelvin), working through the British Association for the Advancement of Science formulated the concept of a coherent system of units with base units and derived units. The principal of coherence was successfully used to define a number of units of measure based on the centimetre–gram–second (cgs) system of units (cgs) including the erg for energy, the dyne for force, the barye for pressure, dynamic viscosity in poise and the kinematic viscosity in stokes.

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