meter, abbr. m, fundamental unit of length in the metric system. The meter was originally defined as 1/10,000,000 of the distance between the equator and either pole; however, the original survey was inaccurate and the meter was later defined simply as the distance between two scratches on a bar made of a platinum-iridium alloy and kept at Sevres, France, near Paris. More recently, it has been defined as the distance light travels through a vacuum in 1/299,792,458 of a second. The meter is now the legal standard of length for most of the world, other standards, such as the yard, being defined in terms of the meter.

meter, in music, the division of a composition into units of equal time value called measures, and the subdivision of those measures into an underlying pattern of stresses or accents (see measure). Meter is usually indicated by a time signature, a fraction whose numerator indicates the number of beats in a measure and whose denominator indicates the note value that is the unit of beating. The time signature may be changed at any point in the composition, and frequent changes of meter occur in much 20th-century music. In music of the 18th and 19th cent., however, the same meter is usually adhered to throughout a section or movement in a composition. See rhythm. For meter in poetry, see versification; for meter as a unit of measure, see metric system.

Short pipe with a constricted inner surface, used to measure fluid flows and as a pump. The effects of constricted channels on fluid flow were first investigated by Giovanni Battista Venturi (1746–1822), but it was Clemens Herschel (1842–1930) who devised the instrument in 1888. Fluid passing through the tube speeds up as it enters the tube's narrow throat, and the pressure drops. There are countless applications for the principle, including the carburetor, in which air flows through a venturi channel at whose throat gasoline vapour enters through an opening, drawn in by the low pressure. The pressure differential can also be used to measure fluid flow (see flow meter).

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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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