MKSA units |
The unit of length - the meter |
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The meter was originally defined (by the French) 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 Sevrés near Paris. In 1960 it was internationally agreed that the fundamental unit of length, the meter, should be redefined again in terms of the orange-red spectral line of Krypton 86. This replaced the standard meter, still kept at that time in Sevrés along with the standard kilogram. 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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