The unit of length - the meter |
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The meter was originally defined (In Paris) as one ten millionth of a quadrant of the Earth's polar circumference. (The distance from the equator to the North pole on a line through Paris). Subsequently it was redefined as the distance between two scratches on a platinum iiridium bar kept in a vault at Sevres near Paris. In 1960 it was internationally agreed that the fundamental unit of length, the meter, should be defined in terms of the orange-red spectral line of Krypton 86. This replaced the standard meter, which was defined in terms of a bar made of a platinum-iridium alloy kept in Paris France. In October 1983, the meter was again redefined by the International Bureau of Weights and Measures as being the length of the path traveled by light in a vacuum during a time interval of 1/299,792,458th of a second. This had the effect of defining the speed of light in terms of the meter and the second. |
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