The international standard for distance measure, except for the USA

Views of the physical standard metre, a platinum-iridum bar (Courtesy NIST, Dept of Commerce, USA)

In America, when talking lengths and distances from there to here, we typically speak feet and miles, of course. As is well known even by us parochial Americans, however, nearly everywhere else in the world, they speak in terms of what we incorrectly call the “metric” system, the Systeme Internationale.

The basic unit of linear measurement in the SI is the metre (or meter as we have it in English grammar). The word itself ultimately derives from the Greek word metron, meaning simply “measure”.

The history of the derivation of the metre is quite interesting. As it happened, the measurement itself was determined by the French Academy of Sciences in 1791, using what was called the “meridional” approach, which determined the metre to be one ten-millionth of the distance along a true meridian connecting the Pole and the Equator (the other competing method was the “pendular” approach, where the metre equalled the length of a pendulum with a half-period of one second–the force of gravity tends to vary slightly over the earth’s surface, making a standardization somewhat hard to come by). Thus, the circumference of the earth could be stated in this system as forty million metres.

Over time the standard itself was kept in a physical form: a platinum iridium bar was used (pictured) and the meter was set as the distance between the ends of this bar as measured at the melting point of ice. The bar was first produced by the International Bureau of Weights and Measures in 1889, and was used for the standard until 1989, when a more universal and reproducilbe standard was settled on: the speed of light. Currently, the metre is defined as the distance travelled by light in a vacuum in 1/299,792,458th of a second. Conversely, this makes the speed of light 299,792,458 metres per second.

References:

[1] Wikipedia’s article on “Metre”

P.J. Linstrom and W.G. Mallard, Eds., NIST Chemistry WebBook, NIST Standard Reference Database Number 69, June 2005, National Institute of Standards and Technology,Gaithersburg MD, 20899 ([2] http://webbook.nist.gov).