Where International Standard Units Come From, Part Three: The Candela
NIST Photometer and Lumious Intensity Standard Lamp for Measuring Candela Courtesy of NIST This week, the origin and continued preservation of five of our favorite standard units of measure This week, Sam Kean takes a look at some ridiculously precise standards -- the meter, the second, and other international standard units -- and the role that elements have played in defining, redefining, and re-redefining them over the ages. Most of the seven base metric units were pretty consistent from the beginning. Scientists agreed on what each unit meant and were confident that people in different countries meant the same thing. The big exception to this consistency was the candela-the unit for the luminosity of light. As the name implies, candelas were based on the burning of candles, and scientists tried as hard as they could to define a standard candle. The English standard, for instance, called for candles made...