SCIENCE IN THE NEWS DAILY
The Kilogram, Reinvented
from IEEE Spectrum
Once a year, three officials bearing three separate keys meet at the bottom of a stairwell at the International Bureau of Weights and Measures, in Sèvres, France. There they unlock a vault to check that a plum-size cylinder of platinum iridium alloy is exactly where it should be. Then they close the vault and leave the cylinder to sit alone, under three concentric bell jars, as it has for most of the past 125 years.
This lonely cylinder is the International Prototype of the Kilogram, known colloquially as Le Grand K, and it is the last remaining physical object to define a unit of measure. It's a quaint throwback to a time when people compared the ocean's depth to the span of a man's outstretched arms and the second to a tiny fraction of a year.
Now we fix our rulers to the speed of light and our clocks to a spectral property of cesium. By thus linking measurement to fundamental and unchanging phenomena, scientists have paved the way for GPS satellites, gravity-wave detectors, and many other precision technologies that simply wouldn't have been possible before.
Subscribe to Our Content!
Visit our RSS Feeds page to choose among 13 customized feeds, or create a free My AmSci account to request an email notice whenever a specified author, department or discipline appears online.
A free daily summary of the latest news in scientific research. Each story is summarized concisely and linked directly to the original source for further reading.
An early peek at each new issue, with descriptions of feature articles, columns,
and more. Every other issue contains links to everything in the latest issue's table of contents.
News of book reviews published in
and around the web, as well as other noteworthy happenings in the world of science books.
To sign up for automatic emails of the
Update and Scientists' Nightstand issues, create an
online profile, then sign up in the
My AmSci area.
Science in the Media
Magazines and Web Sites:
The Science-Media Intersection: