How it began
During the French Revolution, the task of devising a new system of measurement was given to the nation's leading scientific thinkers, who wanted a uniform set of measures based on reason and on nature. The meter was to be one ten-millionth of the distance from the North Pole to the equator along the Paris meridian. In 1792 two astronomers set out from Paris to measure the meridian arc: Jean-Baptiste-Joseph Delambre went north to Dunkirk and Pierre Méchain south to Barcelona. The system was first realized in practice in 1799.
Before it existed
Before the Revolution, weights and measures varied not only from nation to nation but within nations. In France alone, an estimated 250,000 different units of weights and measures were in use under the Ancien Régime. An ell of cloth generally equaled the width of local looms, and arable land was often measured in days, the area a peasant could work in that time.
How it works
The system is decimal, with units related by multiples and fractions of ten. The meter was based on the dimensions of the Earth, and the kilogram on the mass of a liter of water, which is a cubic decimeter. The meridian arc was measured by triangulation between Dunkirk and Barcelona and then extrapolated to the full distance from pole to equator. Reference copies of both units were made in platinum.
How it spread
Standard meter bars were placed around Paris to introduce the new unit, and one survives on the facade of the Ministry of Justice on Place Vendôme. The metrication of France and much of Europe was complete by the 1850s. The 1875 Treaty of the Metre led to the distribution of meter and kilogram artifacts and created an international body, the CGPM, to oversee the system.
Who pushed back
The survey, planned for one year, took seven. The astronomers worked through political upheaval, were met with suspicion and animosity, and were injured on the job. Once the system was defined, people were reluctant to give up old measures that were bound up with local customs and economies. France reverted for a period to customary measures because the metric system was unpopular.
Where it stands today
In 1960 the CGPM launched the International System of Units, the SI. According to the BBC, the metric system is the official system of measurement for every country except the United States, Liberia, and Myanmar, and it is used even there for purposes such as global trade.
