How the metre became master
Douglas Johnson
THE MEASURE OF ALL THINGS by Ken Alder Little. Brown, .115.99, pp. 466, ISBN 0316859893
\When did the French Revolution begin? Many dates are suggested, but one that seems reasonable is 8 August 1788. It was then that the King announced the summoning of the Estates-General. Deputies to this institution were elected during March and April 1789 and the elections were accompanied by the preparation of lists of grievances (the cahiers de doleances).
Ken Alder calls our attention to these choruses of complaint and tells us that thousands of them uttered a united call: 'one law, one king, one weight and one measure'. From the Paris region came the demand that France be governed 'by a single set of weights and measures'. For a long time, there had been those who sought to reform a system whereby measures varied from province to province, from town to town, from parish to parish. Royal administrators, the army, the Encyclopaedia, all had inveighed against this great confusion. The Revolution, whether it saw itself as creating a unified state or whether it thought of peace spreading from France across the whole world, believed in a uniformity that would coincide with fraternity.
The story that is told by Ken Alder, a historian of science who teaches at the Northwestern University in Illinois, is that of a remarkable attempt, during some of the most dramatic years of the Revolution (1792 to 1799), to establish the metric system in France and to get it adopted in Europe. It concerned two astronomers, Jean-Baptiste-Joseph Delambre and Pierre-Francois-Andre Mechain. They were given the task of measuring the world by surveying the French meridian from Dunkirk to Barcelona and thereby determining a unit of length based on this measurement. This would be the metre, one ten-millionth of the distance from pole to equator. In practical terms, a uniform system of measures would facilitate the free movement of grain. In ideological terms, since the earth belonged to all mankind, the metre would symbolise the brotherhood of man.
Both men came from poor backgrounds and had, by chance, encountered France's greatest astronomer, Lalande. Mechain, who was from Picardy, born in 1744, had collected certain astronomical instruments that he had been forced to sell, thereby arousing Lalande's interest. He was given work studying coastlines and discovering comets. He became a member of the Academic des Sciences, was appointed to the Paris Observatory and, during 1787 and 1788, took part in a lengthy exercise comparing the Greenwich and Paris Observatories.
Delambre, who was from Amiens, born in 1749, earned a living in Paris by teaching sons of the elite while educating himself. He attended Lalande's lectures at the College Royal and was encouraged by him to study mathematics and astronomy. In February 1792, he was elected to the Academic des Sciences, and when certain leading astronomers refused to take part in the meridian mission on 5 May, Delambre was appointed. Mechain was to take the area south of Paris and go to Spain. Delambre was to go north. They practised the science of geodesy, which measures the size and shape of the earth. They used the method of triangulation, establishing a set of triangles where they knew all the angles and where every two triangles shared at least one side. Hence they could calculate the lengths of all the sides.
Ken Alder tells the story of the two men at work. This is a straightforward and clear narrative of what happened. But an enormous amount of research has gone into this book. French national and departmental archives along with the archives of the Observatoire and the Academic des Sciences are listed along with certain Delam
bre papers that are in Utah and California, while Mechain sources exist in Paris and Copenhagen. Parts of the narrative raise important questions. Should Delambre have tried to conceal certain mistakes made by Mechain that he discovered in his colleague's notes after his death in 1804? And, in any case, what is a mistake in scientific terms? Alder's approach to his subject is correct. This is the story of one of the most important moments in the applied science of the 18th century.
Many disasters occurred, whether it was bad weather making surveying impossible, Mechain's accident with a recently invented water-pump, or the hostility of local populations to unknown men arriving in their midst with mysterious instruments. The authorities did not help. Church spires that would have been ideal for surveying were destroyed or transformed by cast-iron liberty bonnets; France and Spain went to war; in December 1793, the Committee of Public Safety dismissed Delambre because he was not endowed with republican virtues or with abhorrence of kings; and time was wasted until a General Calm relaunched the measurement of the meridian and re-appointed Delambre.
Nor was Napoleon always helpful. As the most junior member of the Academic des Sciences, he admired Delambre and took part in what was perhaps the first international scientific meeting, discussing the metric system, in 1798. In September 1801, he made the metric system obligatory throughout France. But in 1812 he rescinded the metric system and spoke scornfully of those who had tried to foist it on France and other countries. (Alder presents some evidence suggesting that Napoleon could not think in terms of the new units.) This was the problem. No one was prepared to give up their traditional measurements and their particular ways of doing things. It was not only ignorant peasants, not only cunning tradesmen who feared the opening up of markets. It was also the educated citizens, whether officials, military men or physicians.
And the French had been subjected to many changes. Alder tells the story of a woman protester (a story that might interest today's English anti-metric campaigners). She complained to a judge, but she found that she had to call him 'Citizen'. She could not explain what had happened to her on a Sunday, in a week, in April, because none of these words existed in the revolutionary calendar, and when she said that she had bought an 'aune' or two 'ells' of cloth and did not refer to the metre, she was expelled from court and denounced as an aristocrat.
Mechain, a melancholy man, is remembered for his discovery of several comets. Delambre, a determined worker, went on to write the story of the expedition and the history of astronomy in France. He died in 1822. A street in Montparnasse is named after him.
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