metre | science dictionary |

<unit>

The fundamental SI unit of length.

From 1889 to 1960, the metre was defined to be the distance between two scratches in a platinum-iridium bar kept in the vault beside the Standard Kilogram at the International Bureau of Weights and Measures near Paris.

This replaced an earlier definition as 10^-7 times the distance between the North Pole and the Equator along a meridian through Paris; unfortunately, this had been based on an inexact value of the circumference of the Earth.

From 1960 to 1984 it was defined to be 1650763.73 wavelengths of the orange-red line of krypton-86 propagating in a vacuum.

It is now defined as the length of the path traveled by light in a vacuum in the time interval of 1/299,792,458 of a second.

2. A measure of length, equal to 39.37 English inches, the standard of linear measure in the metric system of weights and measures. It was intended to be, and is very nearly, the ten millionth part of the distance from the equator to the north pole, as ascertained by actual measurement of an arc of a meridian. See Metric system, under Metric.

American spelling: meter

(01 Apr 1998)

metr-, metra, metratonia, metratrophy < Prev | Next > met repressor operator complex, metria

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