:: First decisions to be taken during the French Revolution ::
A uniformity of weights and measures...

A uniformity of weights and measures

Inspired, among others, by shopkeepers, the registers of grievances of many cities, including Paris and Orleans, had required the government to settle the uniformity of weights and measures in the kingdom. All scientists supported these claims.

The issue of weights and measures was indirectly tackled in the French National Assembly for the first time on 15 March 1790. This decree – that the king sanctionned on 28 March – suppressed seigniorial privileges, of which a great number was collected "on the pretence of weights, measures, marks, supply or inspection of measure, or measurement of wares".

Later, Talleyrand, who was the delegate for the clergy, suggested the unficiation of measurements. He suggested adopting a "natural" unit, based, either on the length of the seconds pendulum at the 45° latitude, or on a fraction of the meridian.

The Assembly chose the pendulum. As they wanted "to make all France benefit forever from the advantage which must result from the uniformity of weights and measures", they voted the 8 May 1790 decree, which was sanctionned by the king on 22 August. This decree set the principle of standardization. Besides, it prompted the king to suggest to the king of England inviting the House of Commons to work with the French National Assembly. In that way, "representatives from the Academy of Science in Paris could meet in equal number with members from the Royal Society of London, to set the pendulum length, and to deduce from it an invariable pattern for all measures and all weights".

The offer made to England had no upshot. This country must have been too much attached to its traditional measures to consider adopting another system. Nevertheless, one has to admit that the declaration of war from France to England, as soon as February 1793, would have been an obstacle to the pursuit of a cooperation between scientists from these two countries.

However, the Academy of Science suggested, in its 19 March 1791 notice, the use of the length of a quarter of a terrestrial meridian instead of the length of a pendulum.

The Assembly came over to the Academy opinion with its 26 March 1791 decree - sanctionned by the king on 30 March : "by considering that, in order to achieve setting the uniformity of weights and measures, it is necessary to set a natural and invariable unit of measure, and that the only means of extending this uniformity to foreign countries and of committing them to a new measuring system, is to choose a unit which has nothing abitrary or peculiar to the situation of one people of the world […] [the Assembly] adopts the length of a quarter of a terrestrial meridian as a basis of the new system of measurements ; the processes that are necessary to set this basis - among others measuring a quadrant between Dunkirk and Barcelona - will soon be executed."

The measurement of the quadrant of the earth was left to the astronomers Delambre and Méchain.

The operation lasted from June 1792 to late 1798.

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