It is estimated that up to a quarter of a million different units of measurement were in use throughout France at eve of the Revolution in 1789, and that these differed not only from trade to trade but also from town to town. The difficulties in trade, science and taxation that arose from these inconsistent systems prompted the French Academy of Sciences to investigate the reform of weights and measurements, although scientists across both Europe and America had discussed the advantages of a universal system of measurement for over a century.
Having decided that units in the new decimal system should be based on the natural world, the Academy defined the metre as one ten millionth of the distance between the North Pole and the Equator. However, since this distance had never been calculated, the astronomers Jean Baptiste Joseph Delambre and Pierre Méchain led an expedition to measure the length of the meridian arc between Dunkirk and Barcelona as a basis for it. They completed their survey in 1798 and presented their findings the following year, having created both a reference metre and kilogram from platinum. The latter was calculated as the mass of a cube of water at 4°C, where each side of the cube measured 0.1 metres. This volume was also defined as a litre.
Although France was the first country to adopt the new metric system, it was abolished by Napoleon in 1812. By the time it was reinstated in 1840, however, numerous other countries had begun to adopt the system and its universal units soon spread to become the dominant form of measurement around the world.