In an article in today's Sydney Morning Herald, Marcus Storm reports that
at the 104th meeting of the International Committee for Weights and
Measurements (CIPM), which was held last week in Paris, that they
were satisfied after years of experiment that they found a new
method to define the kilogram.
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Originally Posted by Marcus Storm Sydney Morning Herald
The current definition of the kilogram is based on the "International Prototype", or Le Grand K.
It is a cylindrical lump of platinum-iridium alloy sitting in a vault in the Pavillon de Breteuil, Sevres, near Paris. Six other near-identical alloy masses were made with it in 1889 to establish an international standard for the kilogram.
The problem is that after 126 years the seven kilogram masses no longer weigh the same: they are out by about 60 micrograms. And because the International Prototype is deemed the standard, it is unclear whether it has become lighter or the others heavier. Most likely it is Le Grand K losing mass through minute amounts of radioactive decay or atoms leaving the artefact from handling or in the form of gas.
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Quote:
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Originally Posted by Marcus Storm, Sydney Morning Herald
The metric system now encompasses seven base units: mass (kilogram), distance (metre), time (seconds), electric current (ampere), temperature (Kelvin), substance (mol) and luminosity (candela).
Of those seven, six are based on universal constants of nature. For example, a metre is defined as the length of the path travelled by light in a vacuum during a time interval of 299,792,458ths of a second.
The kilogram has been the hold-out.
To shift from Le Grand K, two methods have been developed.
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Article here -
http://www.smh.com.au/technology/sci...16-gkbg9s.html