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Greg L/cc by-sa 3.0 [ay0yLmpwZw] Computer-generated image of Le Grand K. Greg L/cc by-sa 3.0 [ay0zLmpwZw] A replica of Le Grande K. National Institute of Standards and Technology/public domain [ay02LmpwZw] International Bureau of Weights and Measures in Paris. Olevy/cc by-sa 4.0 [ay0xLkpQRw] A replica of Le Grande K at the Cite des Sciences et de l'Industrie, Paris. Japs 88/cc by-sa 3.0 [ay00LmpwZw] Copy number K4, kept by the U.S. National Institute of Standards and Technology. U.S. government/public domain [ay01LmpwZw] Kilogram No. 20 (right) was a copy of the International Prototype Kilogram, used in the U.S. National Institute of Standards and Technology/public domain Been Here? 14 Want to Visit? 110 Le Grand K Copy Link Facebook Twitter Reddit Flipboard Pocket Related Stories The prototype and its copies will remain under lock and key--and under two bell jars. objects of intrigue So Much Used to Depend on a Small Metal Cylinder in a Vault in France The life and death of the physical prototype of the kilogram. Jessica Leigh Hester November 16, 2018 Top Places in France Pont du Gard Pont du Gard Vers-Pont-du-Gard, France --------------------------------------------------------------------- Jeannot's Floor Paris, France --------------------------------------------------------------------- The Duluc Detective Agency Paris, France See All From 1889 to 2019, the mass of a kilogram was defined by an object known as the international prototype kilogram (IPK) or, less formally, Le Grand K. A kilogram was a kilogram because of this object: a platinum alloy cylinder that sits in a vault on the outskirts of Paris. Le Grand K is located in an environmentally monitored safe in a lower vault in the basement of the International Bureau of Weights and Measures in Sevres, Paris. Housed under three bell jars, access to this precious cylinder requires three keys, operated independently, of which only two are kept in France. Since its creation in 1889 (it was forged in London before being taken to France), the cylinder has only been removed from its secure housing once every 40 years. This rare appearance only occurs so that its mass can be checked against sister copies, which are housed in locations across the globe. It's a delicate process, as hydrocarbons on fingertips or moisture in the air could contaminate the original's pristine surface, potentially causing tiny changes in mass to the world's definition of a kilo. But the original international prototype kilogram, by its very definition, could not change mass even if was subject to particulate change over time. It was, after all, the official kilogram, and therefore its mass was always one kilogram, even if it actually gains or loses mass. Its sister copies, however, are subject to measurable change in comparison to the original. Over the past century, the trend for most sister copies has been to gain mass relative to the original by varying amounts, although these amounts are unimaginably tiny. On average, the gain is around 50 micrograms (millionths of a gram) over 100 years. It's possible, of course, that the original was losing mass relative to its copies, or that it's a combination of both. Either way, it's no great cause for concern for most of us, as the change in mass is roughly the weight of a fly's wing. Still, for the men and women whose job it is to control and define these things, even the weight of a fly's wing is an unacceptable change. Something had to be done. A move was made to change how the kilogram is defined. And this is where it all gets very complicated. Rather than rely on a platinum cylinder in a bell jar in Paris, eggheads in the world of measurements decided to anchor the future kilogram to Planck's constant. This is a fixed quantity tied in with E=MC2 and quantum theory, specifying the amount of energy carried by a single particle of light, or photon. And that's just the most extremely simplified version. All this was carried out under the watchful eye of the General Conference on Weights and Measures (CGPM) and an international task force known as the Committee on Data for Science and Technology (CODATA) Task Group on Fundamental Constants (TGFC). Together, they came up with a value to redefine the kilogram in terms of the fundamental constants of nature. Update 2019: Le Grand K is no longer used to define a kilogram. Know Before You Go The International Bureau of Weights and Measures is situated in the Parc de Saint-Cloud, at Sevres, in the suburbs southwest of Paris. You can get there by taking Metro line 9 to Pont-de-Sevres, then bus number 171, 169, 179 or 426 to the second stop, Parc de Saint-Cloud. Visiting hours are not published, so you should email in advance to see if you can arrange a visit. A replica of the International Prototype Kilogram is on display at the Cite des Sciences et de l'Industrie (Science and Industry Museum) in Paris. marvelous maps and measures mathematics government instruments of science science Community Contributors Tony Dunnell Added by Tony Dunnell M g p f Edited by Martin, graingert, prvogelsang, firekira --------------------------------------------------------------------- Published August 29, 2018 --------------------------------------------------------------------- Edit this listing Make an Edit Add Photos --------------------------------------------------------------------- Sources * https://www.theguardian.com/science/shortcuts/2017/jul/26/ original-kilogram-le-grand-k-relegated-metric * https://www.scientificamerican.com/article/ the-kilogram-may-be-redefined/ * http://mentalfloss.com/article/31122/ not-so-perfect-kilogram-and-why-metric-system-might-be-screwed * https://www.scmp.com/business/article/2071765/ end-le-grand-k-lets-now-forget-importance-correct-measurement * https://www.sciencealert.com/ researchers-now-have-a-better-measurement-for-defining-a-kilogram * http://news.bbc.co.uk/1/hi/sci/tech/7084099.stm * https://www.nist.gov/si-redefinition/kilogram-present [blank-f2c3362333e2a7a073648cf7e50aa224b02674cd3b28b24000ca5cdc8980f] Avenue du Pavillon de Breteuil Saint-Cloud France 48.8293, 2.2201 View on Google Maps Visit Website Nearby Le Corbusier's Studio-Apartment 1.73 miles The Grande Lunette 1.75 miles Villa La Roche by Le Corbusier 2.58 miles Want to see fewer ads? Become a Member. Want to see fewer ads? Become a Member. Want to see fewer ads? Become a Member. Near This Place [blank-f2c3] Boulogne-Billancourt, France Le Corbusier's Studio-Apartment Experience architect Le Corbusier's modernist design for living in the home he designed for himself. The Grande Lunette at Meudon Observatory Meudon, France The Grande Lunette The largest refracting telescope in Europe is housed on the grounds of a former French castle. [blank-f2c3] Paris, France Villa La Roche by Le Corbusier Architect Le Corbusier built his friend a cubist house to match his impressive collection of cubist art. Musee Marmottan Monet, Paris Paris, France Musee Marmottan Monet Former hunting lodge of a duke who was an avid collector of impressionist works. Related Places NIST kilogram masses characteristic of the National Prototype Standard Gaithersburg, Maryland U.S. National Prototype Kilogram This golfball sized platinum iridium cylinder is the official starting point for all national weight calibrations [blank-f2c3] Uppsala, Sweden Anders Celsius's Thermometer The first thermometer made with the almost-universal temperature scale is backwards. [blank-f2c3] Paris, France The Last Original Standard Metre An overlooked marble is the only surviving in-place 18th century example of the measurement that changed how we define distance. The Liebniz Calculator. Hanover, Germany Leibniz's Stepped Reckoner An extraordinary mechanical calculator designed by the mathematician and philosopher Gottfried Leibniz. In partnership with KAYAK Plan Your Trip Random Place >> From Around the Web See Fewer Ads Become an Atlas Obscura member and experience far fewer ads and no pop-ups. Learn More Get Our Email Newsletter [ ] Thanks for subscribing! 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