Metric system

Delambre and Méchain measured the meridian from Dunkerque and Barcelona between 1792 and 1798. However between these dates the French Revolution progressed to the stage where the Académie des Sciences was abolished in August 1793 but before that Borda, Lagrange and Laplace had computed a provisional value for the metre based on the survey carried out by Cassini de Thury in 1740. The metric system was passed into law by the National Assembly and a metre bar together with a kilogram weight were dispatched to the United States in the expectation that they would adopt the new measures. Congress hesitated because the standards were provisional. Britain became hostile to the metre as did Germany which wanted a standard based on the pendulum.

An International Commission began work in September 1798 to replace the provisional values with precise ones computed from the data collected by Delambre and Méchain. By June of the following year the Commission had produced a platinum bar which became the official definition of the metre, and in September 1799 the metre was required by law to be used in the Paris region. However, as one might expect, introducing the new measure was easier said than done. Part of the problem was that Greek and Latin prefixes like kilo- and centi- had been proposed to help make the new system internationally acceptable but were strongly disliked in France. It was also a law which was essentially impossible to enforce and, again as one might expect, many traders took the opportunity to cheat their customers. Teaching the metric system became compulsory in schools and the hope was that at least the next generation would accept it even if the current generation would not.

In November 1800 an attempt was made to make the system more acceptable by dropping the Greek and Latin prefixes and reinstating the older names for measures but with new metric values. In September of the following year it became illegal to use any other system of weights and measures anywhere in France but it was largely ignored. It did not last long for, on 12 February 1812, Napoleon returned the country to its former units. The metre standard was still used in the sense that a fathom was declared to be 2 metres, there were 6 feet in a fathom and 12 inches in a foot.

Now, despite this retrograde move, Napoleon had a major effect on the spread of the metric system. French conquests of the Low Countries had seen the metric system introduced there and, on the defeat of Napoleon and the restoring of monarchy in those countries, they retained the system. The decimal metric system was required to be used by law in the Low Countries in 1820. In 1830 Belgium became independent of Holland and made the metric system, together with its former Greek and Latin prefixes, the only legal measurement system. Perhaps the fact that the French had scrapped the system they invented helped its acceptance in other European countries. In 1840 the French government reintroduced the metric system but it took many years before use of the old measures died out.

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