A vote will be taken today at the International Bureau of Weights and Measures to decide whether the kilogramme should cease to be benchmarked against "Le Grand Kilo," a physical object stored under three bell jars in a French vault.

Dr James Poskett comments on how a decision by the French revolutionary government in 1795 led to the kilogramme becoming Europe's standard measure of mass:

“From the French Revolution to Brexit, the history of the kilogram is the history of European science in microcosm. The kilogram was first introduced by the French revolutionary government in 1795, a symbol of a more enlightened and rational future. Following the Napoleonic Wars, the kilogram spread across Europe, but Britain remained aloof.

“Parliament was asked multiple times in the nineteenth century to decide on whether the kilogram system should be adopted in Britain. Leading scientists, including Lord Kelvin, James Clerk Maxwell, and George Airy, made the case that Britain should adopt the same units of measurement used across Europe. But the proposals were rejected.

“In 1875, following years of war and revolution in Europe, the International Bureau of Weights and Measures was set up. This formalised the kilogram as a standard unit in seventeen countries, creating a shared scientific culture. British representatives attended the meeting, but initially refused to sign up to the deal. However, under increasing pressure from scientists back home, the British government joined the International Bureau of Weights and Measures in 1884. A few years later, in 1889, the International Prototype Kilogram was manufactured. It still sits in a Parisian vault to this day.

“Despite signing up to the treaty, Britain continued to use the old imperial system of measurement both for trade (and sometimes for scientific work) right throughout the twentieth century. It was only after joining the European Economic Community in 1973 that the metric system became mandatory. Even then, adoption was slow and controversial.

“The International Bureau of Weights and Measures is an independent organisation, not a part of the European Union. But the kilogram is tied to a long history of European integration. And so there is something heartening about the news that the kilogram is about to be redefined. The political future is uncertain. But scientists, meeting this week in Paris, continue to strive for some kind of certainty.”

• Dr James Poskett is Assistant Professor in the History of Science and Technology at the University of Warwick

16 November 2018

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