The Search for a More Perfect Kilogram
October 4, 2011 8:12 AM Subscribe
The official SI definition of a kilogram is "equal to the mass of the international prototype," a cylinder of nine-tenths platinum and one-tenth iridium, forged in the 1880s. "Le Grand K," as the prototype is affectionately known, is the basis not only for the measurement of mass and volume, but of force, energy, and luminosity—and since the 1940s, Le Grand K has been losing weight. Now scientists are trying to redefine the kilogram in terms of fundamental constants—and in doing so, perhaps fulfill the 18th-century promise of a universal, fundamental system of measurement "for all people, for all time."
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