Amid the ideological and religious upheavals of the last 200 years, the metric system has spread around the world as an exemplar of science and rationality. But in both its champions and detractors, it has evoked as much passion as reason.

Created beginning in 1790 by the French Academy of Sciences at the behest of the revolutionary National Assembly, the metric system reflected a century of measurement reform proposals. The meter was defined by a law of the National Convention in 1793 as one ten-millionth of a quarter-meridian, the distance from the earth's equator to one of its poles. Ken Alder of Northwestern University, studying records in Paris, found that the attempt to measure the meridian mixed painstaking detail with high adventure. It took two French astronomers seven years to measure the distance between Dunkirk, France, and Barcelona, Spain, and Alder's memorable account, The Measure of All Things, reveals that one of the men covered up for the other's fudged work. The astronomers knew the earth was slightly flat at the poles–Pierre-Louis Moreau de Maupertuis had proved Newton's prediction in 1736–but thought it otherwise uniform. Survey one meridian, they thought, and you've surveyed them all. They soon learned the lumpiness of reality.