History of the metre

In the aftermath of the French Revolution (1789), the traditional units of measure used in the Ancien Régime were replaced. The livre monetary unit was replaced by the decimal franc, and a new unit of length was introduced which became known as the metre. Although there was initially considerable resistance to the adoption of the new metric system in France (including a period of official reversion to customary units, mesures usuelles), the metre gained adoption in continental Europe during the mid nineteenth century, particularly in scientific usage, and was officially established as an international measurement unit by the Metre Convention of 1875.

The standard measures of length in Europe diverged from one another after the fall of the Carolingian Empire (around 888): while measures could be standardized within a given jurisdiction (which was often little more than a single market town), there were numerous variations of measure between regions. Indeed, as the measures were often used as the basis for taxation (of cloth, for example), the use of a particular measure was associated with the sovereignty of a given ruler and often dictated by law.

Nevertheless, with the increasing scientific activity of the 17th century came calls for the institution of a "universal measure" (as Englishman John Wilkins called it) or "metro cattolico" (Italian Tito Livio Burattini), which would be based on natural phenomena rather than royal decree, and would also be decimal rather than using the various systems of subdivision, often duodecimal, which coexisted at the time.

Wilkins' idea was to choose the length of a "seconds pendulum" (a pendulum with a half-period of one second) as the unit of length: such pendulums had recently been demonstrated by Christiaan Huygens, and their length is quite close to one modern metre (as well as to some other length units which were then in use, such as the yard). However, it was soon discovered that the length of a seconds pendulum varies from place to place: French astronomer Jean Richer had measured the 0.3% difference in length between Cayenne (in French Guiana) and Paris.

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