Metre

Metre - Wikipedia, the free encyclopedia
Historically, the metre was defined by the French Academy of Sciences as the ... 1.2 Prototype metre bar. 1.3 Standard wavelength of krypton-86 emission ...
en.wikipedia.org

metre - Wiktionary
metre (plural metres) (Commonwealth) The rhythm or measure in verse and musical composition. ... Retrieved from "http://en.wiktionary.org/wiki/metre" ...
en.wiktionary.org

meter: Definition from Answers.com
meter n. ( Abbr. m ) The international standard unit of length, ... The metre was originally defined by a prototype object meant to represent 1?10 ...
www.answers.com

Van Metre Homes
... YOUR HOME. HOMEOWNERS. REALTORS. ABOUT US. CONTACT US © 2006 Van Metre Homes | Privacy Statement | Site Directory | Site Designed ... Ecendant Interactive ...
vanmetrehomes.com

Warning: mkdir() [function.mkdir]: Permission denied in /home/webs/affiliatelib2/CacheManager.php on line 12

Warning: mkdir() [function.mkdir]: No such file or directory in /home/webs/affiliatelib2/CacheManager.php on line 12

Warning: fopen(/home/templatecore2cache//*cluesnet.com/66/66c8ece1c5cc384559d50f442bddb9c6e5ce7044.tc2cache) [function.fopen]: failed to open stream: No such file or directory in /home/webs/affiliatelib2/CacheManager.php on line 130

Warning: fwrite(): supplied argument is not a valid stream resource in /home/webs/affiliatelib2/CacheManager.php on line 131

Warning: fclose(): supplied argument is not a valid stream resource in /home/webs/affiliatelib2/CacheManager.php on line 132

The metre American English meterSee American and British English spelling differences(symbol: m) is the SI base unit of length in the International System of Units (SI). The metre was originally defined by a prototype object meant to represent the distance between the Geographical poles and the Equator. Today, it is defined as of a Speed of light.

Because it is the base unit of length in the SI, all SI units which involve length (such as area or speed) are defined relative to the metre. Additionally, due to the metre being the only SI base unit used to measure a vector (e.g. displacement), all vector units are defined relative to the metre. However, decimal multiples and submultiples of the metre— such as kilometre (1000 metres) and centimetre (0.01 metres)— can be formed by adding SI prefixes to metre (see #SI prefixed forms of metre below).

Etymology The word wikt:metre is from the Greek metron (), "a wikt:measure" via the French mètre. Its first recorded usage in English meaning this unit of length is from 1797.

History Meridional definition In the eighteenth century, there were two favoured approaches to the definition of the standard unit of length. One suggested defining the metre as the length of a pendulum with a half-period (physics) of one second. The other suggested defining the metre as one ten-millionth of the length of the Earth's meridian (geography) 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.

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 (geography) 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 the 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. So, the circumference of the Earth through the poles is approximately forty million metres.

Prototype metre bar 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 when constructed, distribute national metric prototypes, and maintain comparisons between them and non-metric measurement standards. This 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 of an alloy of ninety percent platinum and ten percent iridium, measured at 0 degrees Celsius

Standard wavelength of krypton-86 emission In 1893, the standard metre was first measured with an interferometer by Albert Abraham Michelson, the inventor of the device and an advocate of using some particular wavelength of light as a standard of distance. By 1925, interferometry was in regular use at the BIPM. However, the International Prototype Metre remained the standard until 1960, when the eleventh General Conference on Weights and Measures defined the metre in the new SI system as equal to 1,650,763.73 wavelengths of the orange (colour)-red emission line in the electromagnetic spectrum of the krypton-86 atom in a vacuum. 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. Resolution 1 of the seventeenth CGPM (1983): Definition of the metre

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. Today's best determination of the wavelength of the relevant transition in 127I2 used for this purpose is λ = 632 991 212.58 fm with an estimated relative standard uncertainty (U) of 2.1 × 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) NIST-F1 Cesium Fountain Atomic Clock. Consequently, a practical realisation of the metre is usually delineated (not defined) today in labs as 1 579 800.762 042(33) wavelengths of helium-neon laser light in a vacuum.

Timeline of definition

1790 May 8 — The National Assembly (French Revolution) decides that the length of the new metre would be equal to the length of a pendulum with a half-period (physics) of one second.

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 (geography) along a quadrant through Paris, that is the distance from the equator to the north pole.

1795 — Provisional metre bar constructed of brass.

1799December 10 — The French National Assembly specifies the platinum metre bar, constructed on 23 June 1799 and deposited in the National Archives of France, as the final standard.

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.

1927October 6 — The seventh CGPM adjusts the definition of the length to be the distance, at 0 °Celsius, between the axes of the two central lines marked on the prototype bar of platinum-iridium, this bar being subject to one standard atmospheric 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.

1960October 20 — The eleventh CGPM defines the length to be equal to 1,650,763.73 wavelengths in vacuum of the electromagnetic radiation corresponding to the transition between the 2p10 and 5d5 quantum levels of the krypton-86 atom.

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.

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.{{SI multiples].|n=|mc=|m=|c=|k=|xd=decimetre|xmc=[micrometre (micron)]|xn=[nanometre|xda=[decametre|xk=[kilometre-->

Equivalents in other units {||-style="font-size:125%;padding-left:0px;"!colspan="5" style="text-align:left;"|Metric unit
expressed in non-SI unit !colspan="5" style="text-align:left;"|Non-SI unit
expressed in metric unit|-|1 metre ||≡ ||style="text-align:right;"|10−4 ||Norwegian/Swedish mil|||1 Norwegian/Swedish mil||≡ ||style="text-align:right;"|104 ||metres|||-|1 metre ||≈ ||style="text-align:right;"|39.37 ||inches]||≡ ||style="text-align:right;"|0.0254 ||metres|||-|1 centimetre ||≈ ||style="text-align:right;"|0.3937 ||inch|| |1 inch||≡ ||style="text-align:right;"|2.54 ||centimetres|| |-|1 millimetre ]||[Ångström|| |-|1 nanometre ||≡ ||style="text-align:right;"|10||Ångström|| |1 Ångström||≡ ||style="text-align:right;"|100 ||picometres|| |}

See also

SI (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

Notes References

Bureau International des Poids et Mesures. The BIPM and the evolution of the definition of the metre. URL accessed on 2006 June 3.
Resolutions of the CGPM. URL accessed on 2006 June 3.
Penzes, William B. at the U.S. National Institute of Standards and Technology Precision Engineering Division (2005 December 29). Time Line for the Definition of the Meter. URL accessed on 2006 June 3.
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. URL accessed on 2006 June 3.
Definitions of the SI base units. URL accessed on 2006 June 3.
Historical context of the SI: meter. URL accessed on 2006 June 3.

External links

Official BIPM definition of 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)

metre from FOLDOC
metre < unit > (US "meter") The fundamental SI unit of length. From 1889 to 1960, the metre was defined to be the distance between two scratches in a platinum-iridium bar kept in ...

Metre - Wikipedia, the free encyclopedia
The metre or meter [1] is a measure of length. 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 ...

Cath Kidston - Fabric by the Metre
Cath Kidston has a great range of homeware, clothing, accessories and outdoor products. The home furnishings range is inspired by textured floral prints perfect for modern ...

Cath Kidston - Oilcloth by the metre
Cath Kidston has a great range of homeware, clothing, accessories and outdoor products. The home furnishings range is inspired by textured floral prints perfect for modern ...

IMYM - Metre Yacht Restoration, Sale, Racing and Transportation
International Metre Yacht Management (IMYM) are specialists in the sale, restoration, racing, surveys and transportation of modern and traditional classic, wooden metre yachts.

Definition: metre from Online Medical Dictionary
The Online Medical Dictionary is a searchable dictionary of definitions from medicine, science and technology.

Universal Marina
METRE SHED ... The Willment Group 2008: site by dock93.com

First Metre
First Metre ... In a world where computers dominate business activity it is easy to overlook the power of the human brain.

Home

metre.org
Metre.org belonged to my daughter until she relinquished it in favour of a new domain (to be revealed).