Engraving representing the use of the new measures (litre, kilo and meter). By L.F. Labrousse, 1795 • WIKIMEDIA COMMONS While traveling through France on the eve of the Revolution, the British agronomist Arthur Young was stunned by the incredible diversity of measurements he encountered on his way:"They differ not only for each province, but each canton, and almost for every city,” he rightly lamented. Because behind the 800 existing denominations were hidden no less than 250,000 different values... Leaving on new bases Forced to realize that such a lack of uniformity favored arbitrariness and hindered communication and trade, the scholars of the Age of Enlightenment were quick to advocate reforms consisting in unifying systems of weights and measures to facilitate trade. trade and science between countries. The Italian Tito Livio Burattini, for example, recommended adopting a unit corresponding to the length of the pendulum beating the second, thus dusting off an old idea of Galileo. He met with even greater success when he coined the name "metre" for her. The Enlightenment had few illusions about the future of such a reform. Appalled by the scattering of weights and measures, the encyclopaedists Diderot and D'Alembert had themselves given up all hope of bringing order to it. The French Revolution gave them the opportunity they had been waiting for to break with tradition and rebuild society on new foundations. The scholars of the Enlightenment had tried, without success, to bring order to the thousands of values that coexisted in 18th century France. The long-awaited upheaval occurred on August 4, 1789, the night when privileges were abolished. On the night of August 4, 1789, three weeks after the storming of the Bastille, the abolition of privileges also abolished the seigniorial monopoly of weights and measures, thus triggering a shower of citizen proposals. A few months earlier, the eminent astronomer Jérôme de Lalande had already advocated a very simple solution:to make Paris units compulsory throughout the territory. Any other era could have chosen Jérôme de Lalande's proposal, but the circumstances were exceptional. For Talleyrand, the adoption of the Parisian measures “did not yet respond sufficiently either to the importance of the object, or to the expectations of enlightened and difficult men”. The only solution for this standard of measurement to be thought of as a good offered “to all times, to all peoples”, in the words of Condorcet, was that it be extracted from nature. This is therefore the request that Talleyrand addressed to the National Assembly. The same base unit Consultations ensued to think about the future system of measurement:its different units (length, surface, weight, etc.) would all derive from the same basic unit and would proceed by powers of 10. This basic unit would be baptized "meter “, a “name so expressive, […] almost so French” to the ears of the mathematician Auguste-Savinien Leblond, while its subdivisions would begin with a Latin prefix (decimetre, centimeter, millimetre) and its multiples with a Greek prefix (decametre, hectometre, kilometer). Once the proposal was adopted, the chemist Antoine Laurent de Lavoisier concluded:“Never has anything greater and simpler, more coherent in all its parts come from the hands of men. » To establish the basic unit of this new system, the National Assembly and the Academy of Sciences decided to create a Commission of Weights and Measures bringing together some of the greatest scientists of the time, such as the surveyor Gaspard Monge , the astronomer and mathematician Pierre-Simon de Laplace and the philosopher and mathematician Condorcet. But where would she get this "meter" from? After studying various possibilities, the Commission determined that it would correspond to the ten millionth part of the distance separating the North Pole from the equator, which it would calculate by measuring the arc of meridian linking Dunkirk to Barcelona via Paris. The astronomers Jean-Baptiste Delambre and Pierre Méchain would share the measurement of this distance, one starting from Dunkirk and the other from Barcelona. They completed their mission in 1799, and the decimal metric system was adopted on December 10 of the same year. Napoleon has the “usual measures” adopted Having become First Consul of the Republic, Napoleon Bonaparte declared:“Conquests come and go, but this will continue. This hard-won science victory was slow to bear fruit, however. Deeply rooted, the use of the old units persisted in commerce. Powerless in the face of inertia, the imperial government finally gave in:on February 12, 1812, in the midst of preparations for the Russian campaign, the “usual measures” were adopted. This system claimed to maintain the official use of the metric system, while bringing it closer to the Parisian measures of the Old Regime:for example, it reinstated the use of the toise, however increasing its length to 2 m instead of 1.949 m. Also read:Napoleon, between shadow and light These new measures met with no more success than the metric system, and the standards of the Ancien Régime made their return under the Restoration. Banished to Saint Helena and wounded in his pride, Napoleon attacked the Enlightenment, deriding its excessiveness:“They believed that it was not enough to do good for forty million men; they wanted to involve the universe in it. » A global distribution It was not until 1837 that King Louis-Philippe decided to claim the heritage of the Revolution and modernize the country by revoking the "usual measurements" in favor of the metric system. But France had already lost its status as a pioneer in this field:invaded by Napoleonic troops, the Netherlands, Belgium and Luxembourg had preceded it for twenty years. In 1820, King of the Netherlands William I st had indeed formalized the adoption of the metric system, which the young independent Belgium decided 10 years later to keep. The meter finally seemed to fulfill the function for which it had been designed:to promote national unification and international exchanges. Also read:China, empire of great inventions The adoption of the metric system contributed both to strengthening national and international ties, as illustrated by the Spanish colonial empire. France had also appealed to Spain by placing the end of the arc of the meridian in Barcelona, at the castle of Montjuïc, and by having recourse to a Spanish commission headed by the mathematician and sailor Gabriel Císcar . Worried about the revolutionary outbreak, the Spanish monarchy initially declined this invitation to join the metric system, which was only adopted in 1849 by a law of Isabella II, and took a few decades to supplant the old measures. The adoption of the meter by societies around the world did not immediately follow its inclusion in their legal framework, but it gradually accompanied the development of education, transport and commerce. Over the past two centuries, the metric system has thus imposed itself in most countries of the world, with the exception of three irreducible territories:Burma, Liberia and the United States. Find out more Measuring the world. The incredible story of the invention of the meter, K. Alder, Flammarion (Champs), 2015. Stallions hung in the streets In 1795, while waiting for the exact measurement of the meter entrusted to Jean-Baptiste Delambre and Pierre Méchain, a provisional meter is adopted. To familiarize the population with this new measure, leaflets, posters and conversion tables were distributed, and between February 1796 and December 1797, 16 marble standard meters were installed in the busiest places in Paris. two of which are still visible today. An assumed mistake When measuring the arc of the meridian, Pierre Méchain made a mistake that he kept secret:to obtain the length of the meridian between the pole and the equator, the Méchain and Delambre meter was missing 0.2 mm. This value will nevertheless be adopted as the measurement of the definitive meter.
