The
metre or
meter (from the Greek µ?t??? /?metron/)
[1] is a
unit of
proper length.
[2] 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. 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
1/10,000,000 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 (BIPM) as the distance travelled by
light in
free space in
1/299,792,458 of a
second.
[3]The BIPM does not distinguish between
quantum vacuum and
free space.
[4]The symbol for metre is m (never capital M). Decimal multiples and submultiples of the metre, such as kilometre (1000 metres) and centimetre (1/100 metre), are indicated by adding SI prefixes to metre (see table below).
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.
