What do the United States, Myanmar, and Liberia have in common, as opposed to every other nation in the world? The answer is that they are the only nations not to have embraced the metric system. Inevitably, they will; their scientists all use it, and cars are made by it, and trading with other nations requires it. The inevitability of victory of the metric system is something Napoleon himself recognized: "Conquests will come and go," he declared, "but this work will endure." The work he spoke of was the defining of the meter, and it was a task begun in the final days of the French monarchy. In 1792, two French astronomers set out separately on the quest to make an accurate measurement of the globe, a measurement that would enable people to use the constant of the size of the globe as the foundation for rational weights and measures. Their plan was to measure enough of the distance of a north-south meridian through Paris that they would then be able to calculate the distance from the equator to the north pole, and one ten-millionth of that natural distance would be the meter. They aimed for unprecedented precision, and they got it, but they didn't get it exactly, for fascinating reasons all wonderfully told in _The Measure of All Things: The Seven-Year Odyssey and Hidden Error That Transformed the World_ (The Free Press) by Ken Alder.
It seems a simple task; a line of longitude from Dunkirk south to Barcelona would be mapped and calculated by triangulating high points, like mountains and steeples, along the line. In practice, it was devilishly, maddeningly, and lethally difficult. Weather, disease, the ravages of time, superstition, politics, and war all conspired to make the work of a few months stretch into years. The astronomer Delambre, heading north, was mistaken for an aristocrat, detained, and suspected of using a church tower as a royalist beacon. His partner Méchain, who took the southern route, had similar problems, and worse ones, as war with Spain erupted while he was in Spain. He had a fiendish obsession with exactitude, and made measurements of Barcelona's latitude by reckoning from the stars. Unfortunately, they were wrong due to refraction from the atmosphere, and Méchain knew they were wrong, but couldn't get them right. The knowledge of the error tortured him for the rest of his life. Méchain's error is not the error referred to in the book's subtitle. All the triangulation work had shown that the critics had been right from before the beginning, for the work could not produce a perfectly precise meter; the world was too irregular for that. The astronomers' work had produced, however, documentation of the more interesting fact of Earthly irregularity.
This story could not have been presented in a more dramatic and entertaining manner. An epic about the foundation of the metric system might seem to be impossible, but Alder has made the personalities interesting. He has also made clear the process of triangulation, the equipment required, and the scientific philosophy of what an error actually is. He has well described the history of the period, and the failures of the French Revolution, such as the calendar containing twelve months of three ten-day weeks each, or the clock with ten one-hundred minute hours in a day. Beside the origin of the admirable metric system of weights and measures, Alder has also given a brief history of how the world has adopted the system, which Americans ought to know about, since, with reluctance, we are having to use it more and more