This article is about the unit of length. For other uses of metre or meter, see meter (disambiguation).

The metre or meter^[1] is a measure of length. Inches redirects here To see the Les Savy Fav album see Inches. Length is the long Dimension of any object The length of a thing is the distance between its ends its linear extent as measured from end to end 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. The International System of Units (SI defines seven dimensionally independent SI base units. Length is the long Dimension of any object The length of a thing is the distance between its ends its linear extent as measured from end to end The metric system is a decimalised system of measurement. It exists in several variations with different choices of base units, though the choice of base units does 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. The French Academy of Sciences ( French: Académie des sciences) is a Learned society, founded in 1666 by Louis XIV at the Today, it is defined by the International Bureau of Weights and Measures as the distance travelled by light in absolute vacuum in ¹⁄_299,792,458 of a second. The International Bureau of Weights and Measures ( Bureau international des poids et mesures, in French) is an international Standards organization, one Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units

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 kilometre ( American spelling: kilometer) symbol km is a unit of Length in the Metric system, equal to one thousand A centimetre ( American spelling: centimeter, symbol cm) is a unit of Length in the Metric system, equal to one hundredth An SI prefix (also known as a metric prefix) is a name or associated symbol that precedes a unit of measure (or its symbol to form a Decimal multiple or

History

The word metre is from the Greek metron (μέτρον), "a measure" via the French mètre. 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. A pendulum is a mass that is attached to a pivot from which it can swing freely Frequency is a measure of the number of occurrences of a repeating event per unit Time. The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units 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. This article is about the geographical concept For other uses of the word see Meridian. 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. The French Academy of Sciences ( French: Académie des sciences) is a Learned society, founded in 1666 by Louis XIV at the Gravitation is a natural Phenomenon by which objects with Mass attract one another

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. The Bureau des Longitudes is a French scientific institution founded by decree of June 25 1795 and charged with the improvement of nautical Navigation Jean Baptiste Joseph chevalier Delambre ( September 19, 1749 Amiens - August 19, 1822 Paris) was a French Pierre François André Méchain ( August 16, 1744 &ndash September 20, 1804) was a French Astronomer and surveyor This article is about the geographical concept For other uses of the word see Meridian. Dunkirk ( French: Dunkerque, dœ̃kɛʀk or; Dutch:; is a harbour city and a commune in the northernmost part of France, in the Barcelona ( Catalan bəɾsəˈlonə Spanish baɾθeˈlona is the capital and most populous city of the Autonomous Community of Catalonia 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. Paris (ˈpærɨs in English; in French) is the Capital of France and the country's largest city The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is subject to the caveats explained below defined as the point in the northern The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the

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. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001

Prototype metre bar

Historical International Prototype Meter bar, made of an alloy of platinum and iridium, that was the standard from 1889 to 1960.

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. The Convention du Mètre of May 20, 1875 is an international treaty that established three organizations to oversee the keeping of metric standards The International Bureau of Weights and Measures ( Bureau international des poids et mesures, in French) is an international Standards organization, one Sèvres is a commune in the southwestern suburbs of Paris, 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. The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures ( CGPM, never GCWM Platinum (ˈplætɪnəm is a Chemical element with the Atomic symbol Pt and an Atomic number of 78 Iridium (ɪˈrɪdiəm is a Chemical element that has the symbol Ir and Atomic number 77

Standard wavelength of krypton-86 emission

In 1893, the standard metre was first measured with an interferometer by Albert A. Michelson, the inventor of the device and an advocate of using some particular wavelength of light as a standard of distance. Interferometry is the technique of using the pattern of Interference created by the superposition of two or more Waves to diagnose the properties of Albert Abraham Michelson ( December 19, 1852 &ndash May 9, 1931) was a Polish - American Physicist known In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 By 1925, interferometry was in regular use at the BIPM. Interferometry is the technique of using the pattern of Interference created by the superposition of two or more Waves to diagnose the properties of However, the International Prototype Metre remained the standard until 1960, when the eleventh CGPM defined the metre in the new SI system as equal to 1,650,763. The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures ( CGPM, never GCWM 73 wavelengths of the orange-red emission line in the electromagnetic spectrum of the krypton-86 atom in a vacuum. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. The colour orange occurs Red is any of a number of similar Colors evoked by light consisting predominantly of the longest wavelengths of Light discernible by the human eye in the wavelength A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range compared The electromagnetic (EM spectrum is the range of all possible Electromagnetic radiation frequencies Krypton (ˈkrɪptən or /ˈkrɪptɒn/ from kryptos "hidden" is a Chemical element with the symbol Kr and Atomic number 36 History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. The original international prototype of the metre is still kept at the BIPM under the conditions specified in 1889.

Standard wavelength of helium-neon laser light

To further reduce uncertainty, the seventeenth CGPM in 1983 replaced the definition of the metre with its current definition, thus fixing the length of the metre in terms of time and the speed of light:

The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second. For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of ^[2]

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 17^th 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 17^th 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: λ_HeNe = 632. 99139822 nm with an estimated relative standard uncertainty (U) of 2. 5 × 10^–11. ^[3] 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). ^[4] 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.

[edit] Timeline of definition

• 1790 May 8 — The French National Assembly decides that the length of the new metre would be equal to the length of a pendulum with a half-period of one second. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International The National Assembly of France is the lower legislative house under the French Fifth Republic. A pendulum is a mass that is attached to a pivot from which it can swing freely Frequency is a measure of the number of occurrences of a repeating event per unit Time. The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units

• 1791 March 30 — The French National Assembly accepts the proposal by the French Academy of Sciences that the new definition for the metre be equal to one ten-millionth of the length of the Earth's meridian along a quadrant through Paris, that is the distance from the equator to the north pole. The French Academy of Sciences ( French: Académie des sciences) is a Learned society, founded in 1666 by Louis XIV at the This article is about the geographical concept For other uses of the word see Meridian.

• 1795 — Provisional metre bar constructed of brass. Brass is any Alloy of Copper and Zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties

• 1799 December 10 — The French National Assembly specifies the platinum metre bar, constructed on 23 June 1799 and deposited in the National Archives, as the final standard. Events 1180 - First Battle of Uji, starting the Genpei War in Japan 1305 - The Flemish Year 1799 ( MDCCXCIX) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian calendar (or a The Archives nationales ( French for "National Archives" preserve the national Archives of the French state, apart from the archives of the

• 1889 September 28 — The first General Conference on Weights and Measures (CGPM) defines the length as the distance between two lines on a standard bar of an alloy of platinum with ten percent iridium, measured at the melting point of ice. The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures ( CGPM, never GCWM Platinum (ˈplætɪnəm is a Chemical element with the Atomic symbol Pt and an Atomic number of 78 Iridium (ɪˈrɪdiəm is a Chemical element that has the symbol Ir and Atomic number 77

• 1927 October 6 — The seventh CGPM adjusts the definition of the length to be the distance, at 0 °C, between the axes of the two central lines marked on the prototype bar of platinum-iridium, this bar being subject to one standard atmosphere of pressure and supported on two cylinders of at least one centimetre diameter, symmetrically placed in the same horizontal plane at a distance of 571 millimetres from each other. The Celsius Temperature scale was previously known as the centigrade scale.

• 1960 October 20 — The eleventh CGPM defines the length to be equal to 1,650,763. 73 wavelengths in vacuum of the radiation corresponding to the transition between the 2p¹⁰ and 5d⁵ quantum levels of the krypton-86 atom. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. Krypton (ˈkrɪptən or /ˈkrɪptɒn/ from kryptos "hidden" is a Chemical element with the symbol Kr and Atomic number 36 History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny

• 1983 October 21 — The seventeenth CGPM defines the length as equal to the distance travelled by light in vacuum during a time interval of ¹⁄_299,792,458 of a second. Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units

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. To help compare different Orders of magnitude, the following list describes various Lengths between 1 Scientific notation, also sometimes known as standard form or as exponential notation, is a way of writing numbers that accommodates values too large or small to be To help compare different Orders of magnitude, the following list describes various Lengths between 1 To help compare different Orders of magnitude this page lists Lengths shorter than 10&minus23 m (10 ym To help compare different Orders of magnitude this page lists Lengths between 10&minus21 m and 10&minus20 m (1 zm and 10 zm To help compare different Orders of magnitude this page lists Lengths between 10&minus18 m and 10&minus17 m (1 am and 10 am To help compare different Orders of magnitude this page lists Lengths between 10&minus15 m and 10&minus14 m (1 fm and 10 fm To help compare different Orders of magnitude this page lists Lengths between 10&minus12 m and 10&minus11 m (1 pm and 10 pm To help compare different Orders of magnitudes this page lists Lengths between 10&minus9 m (meter and 10&minus8 m (1 nm and 10 nm To help compare different Orders of magnitude this page lists some items with Lengths between 10&minus6 and 10&minus5 m (between 1 and To help compare different Orders of magnitude this page lists Lengths between 10&minus4 m and 10&minus3 m (100 µm and 1 mm To help compare different Orders of magnitude this page lists Lengths between 10&minus3 m and 10&minus2 m (1 mm and 1 cm To help compare different Orders of magnitude this page lists lengths between 10&minus2 m and 10&minus1 m (1 cm and 10 cm To help compare different Orders of magnitude this page lists lengths between 10&minus1 m and 1 m (10 cm and 1 m To help compare different Orders of magnitude this page lists lengths between one Metre and ten metres An SI prefix (also known as a metric prefix) is a name or associated symbol that precedes a unit of measure (or its symbol to form a Decimal multiple or

Equivalents in other units

Within this table, "inch" means "international inch". Scientific notation, also sometimes known as standard form or as exponential notation, is a way of writing numbers that accommodates values too large or small to be An ångström or angstrom (symbol Å) (ˈɔːŋstrəm Swedish: ˈɔ̀ŋstrœm is an internationally recognized non- SI unit of length equal

See also

• Metric system
• International System of Units
• Convention du Mètre
• SI prefix
• Conversion of units for comparisons with other units
• Orders of magnitude (length)
• Speed of light
• Metrication
• ISO 1 – standard reference temperature for length measurements

References

• Bureau International des Poids et Mesures. The metric system is a decimalised system of measurement. It exists in several variations with different choices of base units, though the choice of base units does The Convention du Mètre of May 20, 1875 is an international treaty that established three organizations to oversee the keeping of metric standards An SI prefix (also known as a metric prefix) is a name or associated symbol that precedes a unit of measure (or its symbol to form a Decimal multiple or Conversion of units refers to conversion factors between different Units of measurement for the same Quantity. To help compare different Orders of magnitude, the following list describes various Lengths between 1 Metrication (or metrification refers to the introduction of the SI metric system as the International standard for physical measurements—a long-term series International Standard ISO 1 specifies the standard reference Temperature for geometrical product specification and verification to be 20 °C, which The BIPM and the evolution of the definition of the metre. Retrieved 2006 June 3. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 350 - Roman usurper Nepotianus, of the Constantinian dynasty, proclaims himself Roman Emperor, entering
• ———. Resolutions of the CGPM. Retrieved 2006 June 3. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 350 - Roman usurper Nepotianus, of the Constantinian dynasty, proclaims himself Roman Emperor, entering
• Penzes, William B. at the U. S. National Institute of Standards and Technology Precision Engineering Division (2005 December 29). Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. Events 1170 - Thomas Becket: Thomas Becket Archbishop of Canterbury is assassinated inside Canterbury Cathedral by followers of King Henry II Time Line for the Definition of the Meter. Retrieved 2006 June 3. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 350 - Roman usurper Nepotianus, of the Constantinian dynasty, proclaims himself Roman Emperor, entering
• U. S. National Institute of Standards and Technology (October 2000). The NIST Reference on Constants, Units, and Uncertainty: International System of Units (SI):
  • SI base units. Retrieved 2006 June 3. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 350 - Roman usurper Nepotianus, of the Constantinian dynasty, proclaims himself Roman Emperor, entering
  • Definitions of the SI base units. Retrieved 2006 June 3. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 350 - Roman usurper Nepotianus, of the Constantinian dynasty, proclaims himself Roman Emperor, entering
  • Historical context of the SI: meter. Retrieved 2006 June 3. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 350 - Roman usurper Nepotianus, of the Constantinian dynasty, proclaims himself Roman Emperor, entering
  • Peter Mohr CODATA presentation October 2006
  • CODATA recommendations 2006

Notes

1. ^ See American and British English spelling differences
2. ^ Resolution 1 of the seventeenth CGPM (1983): Definition of the metre
3. ^ Citations: Time Line for the Definition of the Meter by the NIST; and these papers from a search at the BIPM database; particularly Optical Frequency - Maintaining the SI Metre by the National Research Council Canada
4. ^ NIST: NIST-F1 Cesium Fountain Atomic Clock. American and British English spelling differences are one aspect of American and British English differences.
5. ^ Based upon cutoff point of one million combined Google hits on the plural form of both the international and U. S. spellings. The bolded values returned an aggregate of between 3. 66 and 51. 4 million hits. Whereas the micrometer is also a device for measuring small distances, a search in September 2007 yielded over four million hits on the two variations of the micrometre. In comparison, the most common prefixed form of the metre that didn’t reach the cutoff threshold—the decimetre—yielded a total of only 322,000 hits even though it is often employed to explain the volume of a litre. The litre or liter (see spelling differences) is a unit of Volume.

External links

• National Research Council of Canada: Optical frequency - maintaining the metre
• Length—Evolution from Measurement Standard to a Fundamental Constant at U. S. NIST
• The History of the Meter By Tibo Qorl (Translated by Sibille Rouzaud)
• NIST:Definition of the meter and c