For many in Britain, the metric system and decimal measures are the same. Sunday’s once-in-a-century date provides an opportunity to consider the link between the two.
Since 1983, Metric Week in the US has been celebrated during the week that includes 10 October. It enjoys the support of the National Council of Teachers of Mathematics, recognising the way decimal measures facilitate the teaching of maths (or math, depending on which side of the Atlantic you live). And this year, the USA Science and Engineering Festival runs from 10 to 24 October, emphasising the link between science and engineering and decimal measures. As far as is known, no celebration is planned in the UK on 10 October – there may be those who would prefer to mark the anniversary of 12-3-1760.
Decimal relationships have in the past been the most controversial feature of the metric system. The Dozenal Society of Great Britain still argues in favour of a multiplier of twelve. Others say that ‘natural’ measures are more important: the size of a barleycorn or a man’s foot, the distance from King Henry I’s outstretched thumb to his nose or the area a horse can plough in a day. They believe ‘natural’ measures should govern the relationships between units of measurement. And there are others who prefer to be left to use the measures they are familiar with, no matter how complex, irrational and parochial these may be.
So how is it that preference for powers of ten is now possibly the most important feature of the world’s most widely used system of measurement?
The Age of Enlightenment produced some of the first suggestions for rational systems of measures. Bishop John Wilkins in England (1668) and Gabriel Mouton in France (1670) both proposed decimal systems of measures based on a universal standard of length. Mouton’s ideas were taken up by the French Academy of Sciences, and, as a result of revolution, people in France and then elsewhere in continental Europe had the opportunity to try them out. Old habits die hard, and the experiment was abandoned in 1812 – Napoleon had other more pressing matters on his mind. Reversion to the old measures was not possible – contemporaries estimated that under the cover of eight hundred names, ancien regime France contained a staggering 250 000 different units of weights and measures. So a compromise between traditional and metric measures was devised, known as mesures usuelles, which was based on metric units of measurement but used familiar subdivisions and multiples. Thus two metres became one toise equal to six pieds each equal to 12 pouces, and one kilogram became two livres each equal to 16 onces. The decimal principle had been dropped!
Even the founders of the United States hedged their bets with the world’s first decimal currency, which has cents and dimes, but also quarters.
Today the metric system, predominantly decimal, is the primary measurement system in 98% of the countries of the world. How did it survive the initial setback?
Before the French Revolution, the diversity of measures in the Low Countries had long frustrated administrators. Occupied during the time of Napoleon’s Empire, Holland, Belgium and Luxembourg had for a while enjoyed the benefits of a unified system of measures. Collapse of the Empire threatened complete metrical chaos. King William I of Orange saw the benefits of central administration of measures for a nation relying on trade, and ordered the decimal system of measures obligatory throughout the Low Countries by 1820. Uniformity, rather than simplicity, was his primary consideration.
France did not rejoin the metric nations until 1840.
Other factors aided the spread of the metric system in Western Europe, in particular in Italy and Germany. In Italy, the adoption of a common measure pointed towards the creation of an Italian nation state. Piedmont and Sardinia were the first to follow France in declaring the metric system obligatory in 1850. Over the next decade, other Italian city-states followed suit. In Germany, facing unification under the domination of Prussia, the metric system appealed to many of the German states because it favoured none. Prussia wanted the industrialised, prosperous, western states to agree to unification willingly. It agreed not to impose its own measures and instead to adopt the metric system as the natural, neutral standard sanctioned by science.
So far, the enactment of the metric system had followed from the political considerations of governments. These paid little regard to the needs of the governed, who would have to switch from the familiar to the new. Yet the subsequent popular adoption of the metric system followed quite a different pattern; it accompanied the expansion of networks of communication, transport, trade and education. Now the system’s principles of simplicity and logic, and those controversial decimals, became crucial to its widespread and often swift adoption. Particularly in the twentieth century, when the system broke out from its heartland of the countries of continental Europe and their present and former colonies, simplicity became important if governments were to persuade reluctant electorates to follow their lead.
There are still many obstacles to the metric system becoming, as its founders intended, ‘for all people, for all time’, and these are frequently discussed on Metric Views. However, decimals have become respectable at last and the metric system’s decimal principle, a handicap two centuries ago as we have seen, is now never seriously challenged. (I am not sure, though, whether we should welcome the decimal inches, not fractions, used to describe the screens of digital cameras, notebooks, laptops, monitors and TVs).
To the organisers in the USA of Metric Week and the Science and Engineering Festival, Metric Views sends greetings and good wishes, and hopes that success accompanies your efforts on 10-10-10 and the days thereafter.
(Metric Views acknowledges the assistance of “The measure of things” by Ken Alder, Abacus 2004, in the preparation of this article.)