In June 1792 -- in the dying days of the French monarchy, as the world began to revolve around a new promise of Revolutionary equality -- two astronomers set out in opposite directions on an extraordinary quest. The erudite and cosmopolitan Jean-Baptiste-Joseph Delambre made his way north from Paris, while the cautious and scrupulous Pierre-François-André Méchain made his way south. Each man left the capital in a customized carriage stocked with the most advanced scientific instruments of the day and accompanied by a skilled assistant. Their mission was to measure the world, or at least that piece of the meridian arc which ran from Dunkerque through Paris to Barcelona. Their hope was that all the world's peoples would henceforth use the globe as their common standard of measure. Their task was to establish this new measure -- "the meter" -- as one ten-millionth of the distance from the North Pole to the equator.
The meter would be eternal because it had been taken from the earth, which was itself eternal. And the meter would belong equally to all the people of the world, just as the earth belonged equally to them all. In the words of their Revolutionary colleague Condorcet -- the founder of mathematical social science and history's great optimist -- the metric system was to be "for all people, for all time."
We often hear that science is a revolutionary force that imposes radical new ideas on human history. But science also emerges from within human history, reshaping ordinary actions, some so habitual we hardly notice them. Measurement is one of our most ordinary actions. We speak its language whenever we exchange precise information or trade objects with exactitude. This very ubiquity, however, makes measurement invisible. To do their job, standards must operate as a set of shared assumptions, the unexamined background against which we strike agreements and make distinctions. So it is not surprising that we take measurement for granted and consider it banal. Yet the use a society makes of its measures expresses its sense of fair dealing. That is why the balance scale is a widespread symbol of justice. The admonition is found in the Old Testament: "Ye shall do no unrighteousness in judgment, in meteyard, in weight, or in measure. Just balances, just weights, a just ephah, and a just hin, shall ye have." Our methods of measurement define who we are and what we value.
The men who created the metric system understood this. They were the preeminent scientific thinkers of the Enlightenment, an age which had elevated reason to the rank of "sole despot of the universe." These savants -- as the investigators who studied nature were known in those days -- had a modern face looking toward our own times, and an older face glancing back toward the past. In their own minds, of course, they were not two-faced; it was their world which was two-faced, with its burdensome past obstructing progress and a utopian future waiting to be born.
The savants were appalled by the diversity of weights and measures they saw all around them. Measures in the eighteenth century not only differed from nation to nation, but within nations as well. This diversity obstructed communication and commerce, and hindered the rational administration of the state. It also made it difficult for the savants to compare their results with those of their colleagues. One Englishman, traveling through France on the eve of the Revolution, found the diversity there a torment. "[I]n France," he complained, "the infinite perplexity of the measures exceeds all comprehension. They differ not only in every province, but in every district and almost every town...." Contemporaries estimated that under the cover of some eight hundred names, the Ancien Régime of France employed a staggering 250,000 different units of weights and measures.
Copyright © 2002 by Ken Alder.
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