The metre or meterSee American and British English spelling differences is a unit of length. It is the basic unit of length in the metric system and in the International System of Units (SI), used around the world for general and scientific purposes. Official brochures describing the SI were published by the Bureau International des Poids et Mesures (BIPM) (BIPM, 2006) and the National Institute of Standards and Technology (NIST) (Taylor and Thompson, 2008a and 2008b). NIST maintains a web site with the definitions of all SI units (NIST, December 2003).

Historically, the metre was defined by the French Academy of Sciences as the length between two marks on a platinum-iridium bar, which was designed to represent frac: 10,000,000 of the distance from the equator to the north pole through Paris. In 1983, it was redefined by the International Bureau of Weights and Measures as the distance travelled by light in absolute vacuum in frac: 299,792,458 of a second.

The symbol (not abbreviation) for metre is m (never capital M). Decimal multiples and submultiples of the metre, such as kilometre (1000 metres) and centimetre (frac: 100 metre), are indicated by adding SI prefixes to metre (see table]] below).

The spelling of the word recommended by the International Bureau of Weights and Measures is "metre".Bureau International des Poids et Mesures, 2006, p. 112. However, the American English spelling is "meter", which is officially endorsed by the United States.

History

The word metre is from the Greek metron ( ), "a measure" via the French mètre. It was first introduced in modern usage (metro cattolico) by Italian scientist Tito Livio Burattini in his work Misura Universale in 1675, in order to rename the universal measure unit proposed by John Wilkins in 1668. Its first recorded usage in English meaning this unit of length is from 1797.

Meridional definition

In the eighteenth century, there were two favoured approaches to the definition of the standard unit of length. One approach suggested defining the metre as the length of a pendulum with a half-period of one second. The other approach suggested defining the metre as one ten-millionth of the length of the Earth's meridian along a quadrant, that is the distance from the equator to the north pole. In 1791, the French Academy of Sciences selected the meridional definition over the pendular definition because the force of gravity varies slightly over the surface of the Earth, which affects the period of a pendulum.