ニューヨーク・タイムズのインスタグラム(nytimes) - 11月29日 02時45分

Since 1889, Le Grand K — a sleek cylinder of platinum-iridium metal and the very definition of one kilogram of mass — has ruled from its underground vault in Paris. But now that rule has come to an end. In November, several dozen nations voted to overthrow Le Grand K and to redefine the kilogram and 3 other standard units of measure. The vote fulfills an 18th-century dream. Henceforth, all 7 units in the International System of Units will no longer be defined by material objects and instead will be defined only by abstract constants of nature. The “democratization of the units,” said Stephan Schlamminger, a NIST physicist, is now complete. The 4 new definitions — for the #kilogram, ampere, kelvin and mole — will officially take effect after World Metrology Day in May. @mattrothphoto took this photo of a one-kilogram sphere of single-crystal silicon.

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