The Observatory archives are located in the southeastern octagon, where the papers of the meridian expedition fill twenty cartons. They include thousands of pages of computation in logbooks and on scraps of paper, along with maps, protocols, diagrams, and formulas that comprise the seven years of calculation which went into the making of a single number: the length of the meter. Leafing through one of Méchain's logbooks, I found an extended commentary written and signed by Delambre.
I deposit these notes here to justify my choice of which version of Méchain's data to publish. Because I have not told the public what it does not need to know. 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. I have carefully silenced anything which might alter in the least the good reputation which Monsieur Méchain rightly enjoyed for the care he put into all his observations and calculations.
I can still remember the shock I felt upon reading those words. Why was there more than one version of Méchain's data? What exactly had been hidden from the public? Part of the answer lay in the one carton that had not been deposited with the rest, but stored separately by Delambre and placed by him under seal as a special precaution. Inside, there are no logbooks or calculations. Instead there are letters, dozens of letters between Delambre and Méchain, as well as letters between Delambre and Madame Méchain. Had I stumbled, amid all these dusty calculations, on a scandal of intrigue and deception? Reading through these letters, I began to realize that I had discovered something much more interesting: a tale of scientific error and the agonizing choices it forced upon men and women of integrity. In the margin of Méchain's last letter to Delambre, mailed from the abandoned monastery of Saint-Pons in the remote Montagnes Noires (the Black Mountains) of southern France, Delambre had scribbled a final explanatory note.
Though Méchain more than once begged me to burn his letters, his mental state, and my fear that he would one day turn against me, led me to keep them in case I ever needed to use them to defend myself....[B]ut I thought it prudent to place them under seal so that they could not be opened unless someone needed to verify the extracts I published in the Base du système métrique.
The remaining clues to the mystery lay elsewhere, scattered not only across France and the sources Delambre preserved, but also in the records of the savants' many correspondents in Spain, Holland, Italy, Germany, Denmark, England, and the United States, including a cache of Delambre's papers which had mysteriously vanished from a French archive -- along with the garbage, said the archivists -- to find its way, via a London auction house, to the library of Brigham Young University in Provo, Utah. And finally, I tracked down something long presumed lost: Delambre's own copy of his magisterial work, the Base du système métrique décimal.
Those volumes are located today in the private home of David Karpeles, a collector of rare books and manuscripts in Santa Barbara, California. There, on the title page, in his angular hand, Delambre had inscribed Napoleon's grand prophesy: "'Conquests will come and go, but this work will endure,' words of Nap. Bonaparte to the author of the Base." Yet the title page was not the only page on which he had recorded his marginal comments.
Together, these documents reveal a remarkable story. They reveal that Méchain -- despite his extreme caution and exactitude -- committed an error in the early years of the expedition, and worse, upon discovering his mistake, covered it up. Méchain was so tormented by the secret knowledge of his error that he was driven to the brink of madness. In the end, he died in an attempt to correct himself. The meter, it turns out, is in error, an error which has been perpetuated in every subsequent redefinition of its length, including our current definition of the meter in terms of the distance traveled by light in a fraction of a second.
Copyright © 2002 by Ken Alder.
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