The
metre or
meter[1] is the basic unit of length in the
International System of Units (SI). 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 one ten-millionth of the distance from the Equator to the North Pole through Paris. In 1983, the metre was redefined as the distance travelled by
light in
free space in
1/299,792,458 of a
second.
[2]The symbol for metre is m. Decimal multiples such as kilometre and centimetre are indicated by adding SI prefixes to metre.
The word metre is from the Greek µ?t??? (métron), "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.
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, a 'seconds pendulum'. 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.
