EDITORIAL
Definitions for the purist
| The first 150 words of the full text of this article appear below. |
Since 1967, the international standard for a second has been defined as the time it takes for 9 192 631 770 oscillations of the microwave radiation corresponding to the transition between two hyperfine levels of the ground state of an atom of celsium-133. It sounds complex and an extremely accurate method for measuring time although a more recent proposal using a ytterbium standard is superior by a factor of more than a hundred times.
The origins of the metre go back to the late 18th century. At that time, there were two competing proposals for how to define a standard unit of measure, or metre. The astronomer Christian Huygens suggested that the metre be defined by the length of a pendulum having a period of one second; others favoured a metre defined as one ten-millionth the length of the earth’s meridian along a quadrant (one fourth the circumference of the
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(2005). Minerva. BMJ
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