The Measure of All Things: The Seven-Year Odyssey and Hidden Error that Transformed the World (review)

The Measure of All Things is just what it claims to be: a page-turner about the definition of the meter. What's next, steamy romances about the development of the Erlenmeyer flask? If as entertaining and well written as Ken Alder's latest book, I hope so. Apparently, a discovery in the archives put him on the trail of a remarkable story. Browsing through thousands of pages of records from the 1792 meridian expedition—formulas, logbooks, diagrams, calculations, maps—Alder happened upon a note by the astronomer Jean-Baptiste-Joseph Delambre in which he admitted to suppressing details and deceiving the public about the expedition. "I can still remember the shock I felt on reading these words," Alder writes (p. 6). From there, some fine sleuthing uncovered important materials in Santa Barbara, California, and Provo, Utah. Together, these documents revealed a fascinating story of scientific error and cover-up, of deception and self-doubt, that lies just beneath the surface of Delambre's imposing two-volume tome, Base du système métrique décimal.

Alder structures his narrative around the ventures and misadventures of Delambre and Pierre-François André Méchain, the two astronomers charged with measuring the meridian arc from Dunkirk to Barcelona. Armed with the latest in precision equipment, Méchain and Delambre set out from Paris in the summer of 1792. They traveled in opposite directions: Méchain went south and Delambre went north. Of course, these were not quiet times, and what was initially supposed to be a journey of about seven months turned into a seven-year pilgrimage. The two savants encountered foul weather, shabby bell towers, hostile villagers, and a host of other difficulties as they triangulated their way through the French and Spanish outback. According to Alder, though, the expedition was delayed by more than merely external obstacles; it was hampered by the deception, doubt, and self-loathing occasioned by a crucial error in Méchain's measurements.

The error that "transformed the world" cannot be understood apart from the Borda repeating circle, a cumbersome piece of equipment that Méchain lugged with him over the Pyrenees, across the Belearic Islands, and pretty much everywhere else he went. The principle behind the Borda repeating circle, as one might guess from its name, was repetition. Its design, described wonderfully by Alder, allowed geodesists to improve precision by multiplying the number of readings that could be made on a given angle. The Borda circles, intended to "eliminate virtually all error," produced measurements of unprecedented precision (p. 56). But the repeating circle may also have been responsible for the crucial error that tortured Méchain and nearly destroyed the meridian expedition. Arrested by the Spanish and confined to quarters in Barcelona during 1793, Méchain made some ten thousand observations to determine the precise latitude of his hotel there. He had wanted to account for a small anomaly in some earlier results, but the new latitude measurement now revealed "a stunning discrepancy" (p. 121). Méchain's error, and the actions it inspired—delay, deceit, and some serious tinkering with the data—drive the narrative the rest of the way.

Though written for a popular audience, The Measure of All Things skillfully incorporates many insights and arguments from recent historiography of science. Familiar themes from the work of Theodore Porter, Lorraine Daston, and M. Norton Wise percolate through the well-crafted layers of Alder's narrative. He frequently combines these themes with a bit of psychological speculation to explain why the characters behaved as they did. "Precision is an obsession, and the sharp edge of Méchain's exactitude was cutting him up inside" (p. 213). This is generally persuasive stuff, but it sometimes runs the risk of becoming history of science...