A Less-Remembered Gain of the French Revolution
It has to do with a ruler. No, not that kind.
When people are talking about the hardships of life under the ancien regime that existed before the French Revolution, weights and measurements are usually not what they have in mind. These are important, though. Imagine living in a country where even within the same region, measures vary by market day, leading to a "Tuesday measure" and a "Friday measure", and where there is a dizzying array of local measures—pouce, pied, coudée, aune, arpent, and more. It led to, to put it mildly, quite a headache for everyone involved. That was not to mention the rather bewildering ways some things were measured according not to physical features, but to a human method applied - for example, a journal was defined in different places as the amount of ground that a peasant could seed, or scythe, or plough, between sunrise and sunset.
Will I shock anyone if I tell you that the vague and fuzzy nature of these units of measure led to them being manipulated by landowners and merchants alike to the detriment of poor peasants? I suspect not.
It was not for nothing that one of the Cahiers de Doléances - literally, lists of grievances - presented to the monarch in 1789 was simply asking for an honest system of measurement.
The desire for a uniform decimal measurement system became a central pillar of the "regeneration" efforts following 1789, and the ideas promising clarity and equality.
Scientists, already working on reforms since 1787, were tasked by the Constituent Assembly in 1790 to lead this ambitious project. Initially, a commission including figures like Lavoisier and Laplace considered basing the unit of length on the length of a pendulum beating the second at 45 degrees latitude. However, after the English government declined to collaborate, the commission revised its decision in March 1791, opting for the "terrestrial meridian" as the reference.
Different teams were dispatched to conduct experiments and even expeditions to the purpose: Borda and Coulomb for pendulum measurements, and crucially, Jean-Baptiste Joseph Delambre and Pierre Méchain to measure an arc of this meridian from Dunkirk to Barcelona. Lavoisier and René-Just Haüy were tasked with determining the weight of water for the unit of volume, which would become the kilogram.
The measurement expedition, though it launched in 1792, faced immense difficulties. Delambre, working on the northern section from Dunkerque to Rodez, faced arrests and logistical nightmares alike. His orders, initially signed by Louis XVI, made him a target - some misunderstandings even led him to being accused of being a royalist agent by the locals. As a result, he only managed to complete his initial measurements around Paris by early March 1793. Méchain, operating in the faraway south of France - a world unto its own - and later even in Spain, tragically died of yellow fever before completing his segment.
Despite these ongoing and incomplete measurements, the National Convention, driven by the urgency of external and internal wars, provisionally established the metric system in August 1793. This move was seen as a "new means of cementing the unity of the Republic". New measures were named meter, gravet (the future gram), and cade (the future cubic meter). Lavoisier and Haüy continued their work on the kilogram, and the production of physical standards began.
However, the political turmoil continued to impact the project directly. In August 1793, the Royal Academy of Sciences, the very institution driving the metric reform, was suppressed. Even more dramatically, Lavoisier, a key figure in the research, was arrested in November 1793 and subsequently executed on May 8, 1794 - though, unlike some popular assumptions claim, that had nothing to do with the Republic’s supposed animosity towards scientific inquiry; his sad fate came about because he was a former tax collector (fermier général).
The adoption of a metric system was a major event, and one making surprising waves in popular culture - a large public information campaign to promote its benefits was launched, involving chansonniers, poets, and playwrights. Despite these efforts, the adoption was slow, with the physical standards for weight and length not ready until June 1799, only becoming obligatory in December 1801.
Napoleon's 1812 decree permitted the use of old measures, encouraging a de facto return to old habits (like frankly many of his decrees did for many aspects of life, including much more visceral ones, such as his banning of no-fault divorce a decade after the Revolution legalized it or reinstating slavery in the colonies). However, by that time the convenience of the new metric system born during the revolution was too self-evident, and it remained the sole system taught and used by administrators.
Say what you will, but I am certainly grateful to the Jacobins for supporting the metric system. Not sure I am quite as grateful for the kilogram - at least I rarely feel this way when I step on the scales…