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History: Scaling up

Andrew Robinson applauds a chronicle of metrication that balances physics with philosophy.

World in the Balance: The Historic Quest for an Absolute System of Measurement

W. W. Norton: 2011. 288 pp. £20 9780393072983 | ISBN: 978-0-3930-7298-3

The metric system of measurement was invented by French scientists in the early 1790s and imposed on the populace by the leaders of the French Revolution. For about a year, the revolutionaries even attempted to introduce a decimal clock, with each day divided into ten hours, each hour into 100 minutes and each minute into 100 seconds. Napoleon Bonaparte later congratulated the scientists: “Conquests will come and go, but this work will endure.”

The metric system was invented in France in the early 1790s but took 200 years to become dominant. Credit: THE ART ARCHIVE/ALAMY

Yet Napoleon himself refused to use metric units. In 1812, he ordered their official withdrawal. And, after falling from power in 1815, he attacked the system as a “stumbling block” to progress. Most of the French people also rebelled. Not until 1840 did the government again dare to make use of metric measures obligatory.

From France, the metric system spread haltingly around the globe, as World in the Balance documents. Robert Crease, a philosopher at Stony Brook University in New York, relates the history of measurement from ancient China to current debates over defining the kilogram by reference to physical constants. His respect for both the philosophical and physical aspects of measurement adds tension to his account.

Crease explains how growing industrialization and mechanization promoted the metre and suchlike. The advantages were also highlighted by events such as the Great Exhibition in London in 1851, which revealed the incompatibility of different national measurement systems, and by cheerleading editorials in Nature from the 1870s.

In 1875, representatives of 17 nations and empires met in Paris to sign the Convention of the Metre, “desiring international uniformity and precision in standards of weight and measure” and establishing the International Bureau of Weights and Measures (BIPM) at Sèvres. The United Kingdom and its colonies signed only in 1884, but in practice continued to use imperial measures for nearly another century. The Soviet Union officially went metric in the 1920s; Japan in the 1950s. The BIPM introduced the International System of Units (SI units, from the French) in 1960. Not until the final decades of the twentieth century did the metric system become dominant around the world.

Only the United States, Myanmar (Burma) and Liberia have yet to enact legislation to metricate. Even so, scientists and many of the public in the United States use the metric system daily. The third US president, Thomas Jefferson — Francophile, fanatical quantifier and admirer of the metric system — tried to convert his countrymen, but eventually gave up. “Shall we mould our citizens to the law, or the law to our citizens?” he wrote in an 1817 letter to John Quincy Adams, a future president who in 1821 reported to the US government on the feasibility of metrication.

Adams favoured the first option; but his report to Congress plumped for the second, and recommended retaining the existing system. Metrication, said Adams, would “affect the well-being of every man, woman and child”. The change would be too radical. The physicist and polymath Thomas Young, surprisingly omitted by Crease, gave the same advice to the British Parliament in the 1820s.

The most original section of the book concerns ancient China. Writing with the help of Chinese metrologists, Crease describes how the 12-note harmonic scale used in ritualized music helped to define the measurement system used at the imperial court. The ritual scale, known as the lülü, was supposedly devised by China's first emperor, Huang Di, in the third millennium BC. He sent a minister to the mountains to procure bamboo of a species revered for its regularity in length and thickness. From a piece 3.9 cun in length — the cun was the width of a thumb knuckle, or one-tenth of a chi, the 'Chinese foot' — Huang Di made a one-note flute, whose pitch became the lowest in the scale, known as the huangzhong. Eleven more bamboo flutes created the lülü.

Whatever the truth of this legend — the evidence suggests that the 12-note scale was actually introduced much later, some time before 400 BC — 12 pitch regulators were made in cast metal; the lengths were specified by regulation in chi, linking the basic unit of length with musical pitch. This system endured for more than 2,000 years and was not replaced until the 1920s, with the adoption of the metric system. In 1984, the country defined the chi to be one-third of a metre.

As a physicist, Crease is drawn to the drive for quantification, uniformity and precision in measurement — the main concern of his book. As a philosopher, he understands that there is more to quantification than these scientific virtues. The value of education and of scientific research, for example, cannot be measured wholly by examination results and citation indices. Nor can the fitting of clothes be entirely mechanized, as Crease concludes, after trying out various body scanners used by US retailers. Science cannot proceed without precise measurement, yet successful measuring systems cannot be divorced from everyday human dimensions.

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Correspondence to Andrew Robinson.

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Robinson, A. History: Scaling up. Nature 478, 32–33 (2011).

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