The kilogram is the unit of mass it is equal to the mass of the international prototype of the kilogram. The meter is the length of the path traveled by light in vacuum during a time interval of 1/299 792 458 of a second. The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom. Present SI base quantities, base units, and definitions In the words of the Marquis de Condorcet, a new system of measurement “for all time, for all people” was born. Subsequently, in 1799, two platinum artifact standards for length and mass based on those definitions were deposited in the Archives de la République in Paris. and the kilogram the mass of 1 liter of distilled water at 4 ☌. International Bureau of Weights and Measures (BIPM), The International System of Units (SI), 8th edition (2006). Definitions for the units of volume and mass followed, with the liter being 0.001 m 3 3. Adler, The Measure of All Things, Simon & Schuster, New York (2002). The meter came from a perceived constant of nature: one ten-millionth of the distance along Earth’s meridian through Paris from the North Pole to the equator. the new system of weights and measures took as its starting point a single universal measure-the meter-and used it to define length, volume, and mass. Wilkins, An Essay towards a Real Character and a Philosophical Language, Royal Society, London (1668). Following an idea proposed a century earlier by John Wilkins, 1 1. Although the present International System of Units (SI, from the French Système International d’Unités) was officially established in 1960, its origin goes back to the creation of the metric system during the French Revolution.
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