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Ken Alder: The Epic Journey to Create the Meter

Before the French Revolution in the 1790s the world had no standard unit of measurement. In fact, France didn't even have a standard unit — it had 250,000 different measurement units. Each town had its own system of weights and measures, which made trade difficult and unequal.

But with the new regime came a new call for equal rights for all citizens, and thus the search for a standard unit of measure was set into motion. The unit? One ten-millionth of the distance between the North Pole and the equator along the meridian that cuts through France. The method? Measuring the meridian from the top of France to Barcelona and then using that measurement to extrapolate the rest of the distance. In 1792 two astronomers, Jean Baptiste Joseph Delambre and Pierre François André Méchain, set out to do just that.

Their journey — and mankind's journey to adopting scientific measurements — was the subject of the McCormick School of Engineering and Applied Science Dean's Centennial Seminar Series talk given Wednesday, Oct. 21 by Ken Alder, professor of history and the Milton H. Wilson Professor in the Humanities at Northwestern University. Alder is the author of the book on the subject, The Measure of All Things: The Seven-Year Odyssey and Hidden Error That Transformed the World.

Throughout the years of the expedition, Delambre took meticulous notes in his logbooks. Méchain, by contrast, kept his notes on loose-leaf paper, unsigned and undated-and in pencil. While taking his extensive latitude measurements in Barcelona in the winter of 1793 he discovered a discrepancy in his data, and fearing that he might be blamed for this, made a fateful decision to keep this problematic data secret. Only years later, after his death — and after the definitive meter had been built using his partial data — did his original measurements come into Delambre's hands. By then, with the meter already legally declared, Delambre decided to continue the cover-up. As he wrote in one of Méchain's logbooks: "I have suppressed all those details which might diminish its confidence in such an important mission, one which we will not have a chance to verify."

The result was a meter that was .2 millimeters short of the actual goal — a unit that was ten-millionth of the distance between the North Pole and the equator. Nevertheless, at a scientific conference the men's measurement was declared the standard unit. Full conversion to the system would take more than 100 years, and each country that adopted the system thereafter only did so during a period of political change.

Today the only countries that don't use the metric system are United States, Liberia, and Myanmar. Though it does not affect our everyday lives, it has had some crucial consequences. In 1998 the $330 million Mars Climate Orbiter was destroyed by atmospheric stresses and friction due to a navigation error that arose because a NASA subcontractor used imperial units instead of the metric system.

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