Magazine article The Spectator

How the Metre Become Master

Magazine article The Spectator

How the Metre Become Master

Article excerpt

THE MEASURE OF ALL THINGS by Ken Alder Little, Brown, L15.99, 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-Franqois-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. …

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