In poetry, the rhythmic pattern of a poetic line. Various principles have been devised to organize poetic lines into rhythmic units. Quantitative verse, the metre of Classical Greek and Latin poetry, measures the length of time required to pronounce syllables, regardless of their stress; combinations of long and short syllables form the basic rhythmic units. Syllabic verse is most common in languages that are not strongly accented, such as French or Japanese; it is based on a fixed number of syllables within a line. Accentual verse occurs in strongly stressed languages, such as the Germanic; only stressed syllables within a line are counted. Accentual-syllabic verse is the usual form in English poetry; it combines syllable counting and stress counting. The most common English metre, iambic pentameter, is a line of 10 syllables, or 5 iambic feet; each foot contains an unstressed syllable followed by a stressed syllable. Free verse does not follow regular metrical patterns. Seealso prosody.
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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 (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". However, the American English spelling is "meter", which is officially endorsed by the United States.
The word metre is from the Greek metron (μέτρον), "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 order to establish a universally accepted foundation for the definition of the metre, measurements of this meridian more accurate than those available at that time were imperative. The Bureau des Longitudes commissioned an expedition led by Delambre and Pierre Méchain, lasting from 1792 to 1799, which measured the length of the meridian between Dunkerque and Barcelona. This portion of the meridian, which also passes through Paris, was to serve as the basis for the length of the half meridian, connecting the North Pole with the Equator.
However, in 1793, France adopted as its official unit of length a metre based on provisional results from the expedition as its official unit of length. Although it was later determined that the first prototype metre bar was short by a fifth of a millimetre due to miscalculation of the flattening of the Earth, this length became the standard. The circumference of the Earth through the poles is therefore slightly more than forty million metres.
In the 1870s and in light of modern precision, a series of international conferences were held to devise new metric standards. The Metre Convention (Convention du Mètre) of 1875 mandated the establishment of a permanent International Bureau of Weights and Measures (BIPM: Bureau International des Poids et Mesures) to be located in Sèvres, France. This new organisation would preserve the new prototype metre and kilogram standards when constructed, distribute national metric prototypes, and maintain comparisons between them and non-metric measurement standards. The organization created a new prototype bar in 1889 at the first General Conference on Weights and Measures (CGPM: Conférence Générale des Poids et Mesures), establishing the International Prototype Metre as the distance between two lines on a standard bar composed of an alloy of ninety percent platinum and ten percent iridium, measured at the melting point of ice.
Note that this definition had the effect of fixing the speed of light in a vacuum at precisely 299,792,458 metres per second. Although the metre is now defined in terms of time-of-flight, actual laboratory realisations of the metre are still delineated by counting the required number of wavelengths of light along the distance. An intended byproduct of the 17th CGPM’s definition was that it enabled scientists to measure the wavelength of their lasers with one-fifth the uncertainty. To further facilitate reproducibility from lab to lab, the 17th CGPM also made the iodine-stabilised helium-neon laser “a recommended radiation” for realising the metre. For purposes of delineating the metre, the BIPM currently considers the HeNe laser wavelength to be as follows: λHeNe = 632.99139822 nm with an estimated relative standard uncertainty (U) of 2.5 × 10–11. This uncertainty is currently the limiting factor in laboratory realisations of the metre as it is several orders of magnitude poorer than that of the second (U = 5 × 10–16). Consequently, a practical realisation of the metre is usually delineated (not defined) today in labs as 1,579,800.298728(39) wavelengths of helium-neon laser light in a vacuum.
Timeline of definition
SI prefixed forms of metre
SI prefixes are often employed to denote decimal multiples and submultiples of the metre, as shown in the table below.
Two spellings of the name of the unit are common in English: metre (British) and meter (American). The most recent official brochure about the International System of Units (SI) was written in French by the International Bureau of Weights and Measures, in 2006. A British English translation was included, to make it "more widely accessible".
In 2008, an American English translation was published by the U.S. National Institute of Science and Technology.
Equivalents in other units
Within this table, "inch" means "international inch".
expressed in non-SI unit
expressed in metric unit
1 Norwegian/Swedish mil