The metre, symbol: m, is the basic unit of distance (or of "length", in the parlance of the physical sciences) in the International System of Units. The internationally-accepted spelling of the unit in English is "metre", although the American English spelling meter is a common variant. However, both American and non-American forms of English agree that the spelling "meter" should be used as a suffix in the names of measuring devices such as chronometers and micrometers. The SI system of units defines seven SI base units: fundamental physical units defined by an operational definition. ... personal space, proxemics. ... In general English usage, length (symbols: l, L) is but one particular instance of distance – an objects length is how long the object is – but in the physical sciences and engineering, the word length is in some contexts used synonymously with distance. Height is vertical distance; width (or breadth... The International System of Units (abbreviated SI from the French phrase, Système International dUnités) is the most widely used system of units. ... The English language is a West Germanic language that originates in England. ... American English or U.S. English is the form of the English language used mostly in the United States of America. ... A chronometer is a clock designed to have sufficient long-term accuracy that it can be used as a portable time standard on a vehicle, usually in order to determine longitude by means of celestial navigation. ... A micrometer is a widely used device in mechanical engineering for precisely measuring thickness of blocks, outer and inner diameters of shafts and depths of slots. ...

A metre is defined as the length of the path travelled by light in an absolute vacuum during a time interval of exactly 1/299,792,458 of a second. This definition does not change the size of the unit (see History below), but it was introduced to take into account recent developments in measurement techniques whereby length and time can be reproduced with very high accuracy — in the case of time, to an accuracy of 10¹³. One metre is equal to approximately 39.37 inches (3.28 feet). In general English usage, length (symbols: l, L) is but one particular instance of distance – an objects length is how long the object is – but in the physical sciences and engineering, the word length is in some contexts used synonymously with distance. Height is vertical distance; width (or breadth... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye, or in a more general sense, any electromagnetic radiation in the range from infrared to ultraviolet. ... See vacuum cleaner for information on the home appliance. ... 8:17 am, August 6, 1945, Japanese time. ... This article is about the unit of time. ...

History

The means of defining the metre has changed over time:

• 1793: 1/10,000,000 of the distance from the pole to the equator.
• 1795: Provisional metre bar constructed in brass.
• 1799: Definitive prototype metre bars constructed in platinum.
• 1889: International prototype metre bar in platinum-iridium, cross-section X.
• 1960: Krypton spectrum: 1650763.73 wavelengths in vacuum of the radiation corresponding to the transition between levels 2p10 and 5d5 of the krypton-86 atom.
• 1983: Speed of light definiton: Length travelled by light in vacuum during 1/299792458 of a second.

The word itself is from the Greek metron (μετρον), "a measure" via the French mètre. Its first recorded usage in English is from 1797. 1793 was a common year starting on Tuesday (see link for calendar). ... The equator is an imaginary line drawn around a planet, halfway between the poles. ... 1795 was a common year starting on Thursday (see link for calendar). ... Brass is an alloy of copper and zinc. ... 1799 was a common year starting on Tuesday (see link for calendar). ... General Name, Symbol, Number Platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10 , 6, d Density, Hardness 21. ... 1889 was a common year starting on Tuesday (see link for calendar). ... General Name, Symbol, Number Iridium, Ir, 77 Chemical series transition metals Group, Period, Block 9, 6, d Density, Hardness 22650 kg/m3, 6. ... 1960 was a leap year starting on Friday (link will take you to calendar). ... General Name, Symbol, Number krypton, Kr, 36 Chemical series Noble gases Group, Period, Block 18 (VIIIA), 4 , p Density, Hardness 3. ... 1983 is a common year starting on Saturday of the Gregorian calendar. ... Cherenkov effect in a swimming pool nuclear reactor. ... This article is about the unit of time. ... Measure can mean: To perform a measurement. ... The English language is a West Germanic language that originates in England. ... 1797 was a common year starting on Sunday (see link for calendar). ...

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 of one second. The other suggested defining the metre as one ten-millionth of the length of the earth's meridian along a quadrant (one-fourth the polar circumference of the earth). In 1791, the French Academy of Sciences selected the meridional definition, using the meridian of Paris, over the pendular definition because of the slight variation of the force of gravity over the surface of the earth, which affects the period of a pendulum. (17th century - 18th century - 19th century - more centuries) As a means of recording the passage of time, the 18th century refers to the century that lasted from 1701 through 1800. ... A gravity pendulum is a weight on the end of a rigid rod (or a string/rope), which, when given an initial push, will swing back and forth under the influence of gravity over its central (lowest) point. ... A period is an arbitrary interval of time. ... This article is about the unit of time. ... On the earth, a meridian is a north-south line between the North Pole and the South Pole. ... 1791 was a common year starting on Saturday (see link for calendar). ... The French Academy of Sciences (Académie des sciences) is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French scientific research. ... The Eiffel Tower has become a symbol of Paris throughout the world. ... Gravitation is the tendency of masses to move toward each other. ...

International Prototype Metre standard bar made of platinum-iridium. This was the standard until 1960, when the new SI system used a krypton-spectrum measurement as the base. In 1983 the current metre was defined by a relationship to the speed of light in a vacuum. (NIST)

In August 1793, the Republican Government in France decreed that the standard unit of length would be 10 ^{- 7} of the earth's quadrant passing through Paris and that the unit be called the metre. Five years later the survey of the arc was completed and three platinum standards and several iron copies were made. Subsequent analysis showed that the length of the earth's quadrant had been incorrectly surveyed resulting in the first prototype metre bar being short by a fifth of a millimetre (due to miscalculation of the flattening of the earth), instead of altering the length of the metre to maintain the 10 ^{- 7} ratio, the metre was redefined as the distance between two marks on a bar. So, the circumference of the Earth through the poles is only approximately forty million metres. Template:USgov Template:Nist http://www. ... The International System of Units (abbreviated SI from the French phrase, Système International dUnités) is the most widely used system of units. ... General Name, Symbol, Number krypton, Kr, 36 Chemical series Noble gases Group, Period, Block 18 (VIIIA), 4 , p Density, Hardness 3. ... Cherenkov effect in a swimming pool nuclear reactor. ... As a non-regulatory agency of the United States Department of Commerce’s Technology Administration, the National Institute of Standards (NIST) develops and promotes measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life. ... 1793 was a common year starting on Tuesday (see link for calendar). ... Earth, also known as the Earth or Terra, is the third planet outward from the Sun. ...

In the 1870s and in light of modern precision, a series of international conferences were held to devise new metric standards. The Convention du Mètre (Treaty of the Metre) 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, and would maintain comparisons between them and the national standards for the metre and the kilogram. This organisation created a new prototype bar in 1889, establishing the International Prototype Metre as the distance between two lines on its standard-issue bar of an alloy of ninety percent platinum and ten percent iridium. 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. By 1925, interferometry was in regular use at the BIPM. However, the International Prototype Metre remained the standard until 1960. The original international prototype of the metre is still kept at the BIPM under the conditions specified in 1889. Events and Trends Technology The invention of the telephone (1876) by Alexander Graham Bell. ... The Convention du Mètre of May 20, 1875 is an international treaty that established what is now known as the SI system of units. ... 1875 was a common year starting on Friday (see link for calendar). ... The Bureau International des Poids et Mesures (International Bureau of Weights and Measures, or BIPM) is a standards organization, one of the three organizations established to maintain the SI system under the terms of the Metre Convention. ... Sèvres is a commune of the Hauts-de-Seine département in France. ... The international prototype, made of platinum-iridium, which is kept at the BIPM under conditions specified by the 1st CGPM in 1889. ... 1889 was a common year starting on Tuesday (see link for calendar). ... General Name, Symbol, Number Platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10 , 6, d Density, Hardness 21. ... General Name, Symbol, Number Iridium, Ir, 77 Chemical series transition metals Group, Period, Block 9, 6, d Density, Hardness 22650 kg/m3, 6. ... 1893 was a common year starting on Sunday (see link for calendar). ... Interferometry is the applied science of combining two or more input points of a particular data type, such as optical measurements, to form a greater picture based on the combination of the two sources. ... Albert Abraham Michelson. ... The wavelength is the distance between repeating units of a wave pattern. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye, or in a more general sense, any electromagnetic radiation in the range from infrared to ultraviolet. ... 1925 was a common year starting on Thursday (link will take you to calendar). ... Interferometry is the applied science of combining two or more input points of a particular data type, such as optical measurements, to form a greater picture based on the combination of the two sources. ... 1960 was a leap year starting on Friday (link will take you to calendar). ... 1889 was a common year starting on Tuesday (see link for calendar). ...

The eleventh General Conference on Weights and Measures (CGPM: Conférence générale des poids et mesures) in 1960 defined the metre in the new SI system as equal to 1,650,763.73 wavelengths of the orange-red emission line in the spectrum of the krypton-86 atom in a vacuum. The Conférence générale des poids et mesures (General Conference on Weights and Measures or CGPM) is one of the three organizations established to maintain the SI system under the terms of the Metre Convention (1875). ... The International System of Units (abbreviated SI from the French phrase, Système International dUnités) is the most widely used system of units. ... The colour orange occurs between red and yellow in the visible spectrum at a wavelength of about 620-585 nanometres. ... Red is a color at the lowest frequencies of light discernible by the human eye. ... 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 with the nearby frequencies. ... The electromagnetic spectrum encompasses all possible wavelengths of electromagnetic radiation. ... General Name, Symbol, Number krypton, Kr, 36 Chemical series Noble gases Group, Period, Block 18 (VIIIA), 4 , p Density, Hardness 3. ... Properties For alternative meanings see atom (disambiguation). ... See vacuum cleaner for information on the home appliance. ...

To further reduce uncertainty, the seventeenth CGPM of 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: 1983 is a common year starting on Saturday of the Gregorian calendar. ... 8:17 am, August 6, 1945, Japanese time. ... Cherenkov effect in a swimming pool nuclear reactor. ...

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.

Note that this definition exactly fixes the speed of light in a vacuum at 299,792,458 metres per second. Definitions based on the physical properties of light are more precise and reproducible because the properties of light are considered to be universally constant.

Orders of magnitude

• A decimetre (American spelling: decimeter, symbol: dm) is a measurement of distance equal to ten centimetres or 1/10 metre. Although considered obsolescent, Canada uses it as the metric measurement for the loading of ships (see Plimsoll line) because measurement in centimetres is too precise.
  • Cubic decimetres are a common measurement of volume, equal to 1 litre, which is often used in chemistry and other sciences, for example when specifying molarity.
• A centimetre (American spelling: centimeter, symbol: cm) is one-hundredth of one metre
• A millimetre (American spelling: millimeter, symbol mm) is equal to one thousandth of a metre.
  • 1 mm is equal to about 0.03937 inches
  • The level of rainfall is also reported as millimeters as measured with a rain gauge.
• A micrometre (American spelling: micrometer, symbol µm) is defined as one millionth of a metre (1×10⁻⁶ m)
  • The symbol "um" is sometimes used, when the µ and μ are not available, e.g. when using a typewriter.
  • The micrometre is a common unit of measurement for wavelengths of infrared radiation.
  • Some people (especially in astronomy and the semiconductor business) use the old name micron and/or the solitary symbol µ for the same thing, even though it is officially discouraged. They were official in 1879–1967.
  • A micrometer is also a name for a measuring instrument.
• A nanometre (American spelling: nanometer, symbol: nm) is 1.0×10⁻⁹ metres
  • commonly used in measuring the wavelengths of visible light (400 nm to 700 nm), ultraviolet radiation and gamma rays; amongst other things.
  • In older (e.g. 1958) texts, the nm is sometimes denoted "mµ" for "millimicron", based on the old term "micron" for a micrometre. Double prefixes are not allowed in SI, and this is never seen in modern writing or speech.
• Picometre (American spelling: picometer, symbol: pm) is equal to 10⁻¹² of a metre.
  • It is commonly used in measuring atomic-scale distances; atom diameters are in the range from ~30 to 600 pm.
• Femtometre (American spelling: femtometer, symbol:fm) is equal to 10⁻¹⁵ (femto) of a metre.
  • It is commonly used in measuring the diameter of atomic nuclei. The diameter of an atomic nucleus is up to about 15 fm. Neutrons and protons are about 1 fm in diameter.
  • In the parlance of particle physicists, a femtometre is often called a fermi (same symbol), after the physicist Enrico Fermi.
• Attometre (American spelling: attometer, symbol: am) is equal to 10⁻¹⁸, or 1 quintillionth (atto-) of a metre.
  • An electron's radius is thought to be about 1 am.
• Zeptometre (American spelling: zeptometer, symbol: zm) is equal to 10^-21 (zepto-) of a metre.
• Yoctometre (American spelling: yoctometer, symbol: ym) is equal to 10^-24 (yocto) of a metre.

American English or U.S. English is the form of the English language used mostly in the United States of America. ... A centimetre (American spelling: centimeter, symbol: cm) is an SI unit of length. ... The Plimsoll line is the mark on the hull of a ship that shows where the waterline is when the ship is loaded to full capacity according to the condition of the water at the point of loading. ... A cubic decimetre (symbol dm³) is an SI derived unit of volume. ... The litre (or liter in US) is a metric unit of volume. ... Chemistry (in Greek: χημεία) is the science of matter and its interactions with energy and itself (see physics, biology). ... This page refers to concentration in the chemical sense. ... American English or U.S. English is the form of the English language used mostly in the United States of America. ... American English or U.S. English is the form of the English language used mostly in the United States of America. ... Mid-19th century tool for converting between different standards of the inch An inch is an Imperial unit of length. ... A rain gauge is a type of instrument used by meteorologists to gather and measure the amount of falling precipitation, rain. ... American English or U.S. English is the form of the English language used mostly in the United States of America. ... Micro sign (µ, ) is the Unicode character U+00B5. ... This Smith Premier typewriter, purchased around the end of the 19th century, was found abandoned in the Bodie ghost town. ... Measurement is the determination of the size or magnitude of something. ... The wavelength is the distance between repeating units of a wave pattern. ... Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. ... Astronomy is one of the few sciences where amateurs can still play an active role, especially in the discovery and monitoring of transient phenomena. ... A semiconductor is a material which has an electrical conductance which is between that of an insulator and a conductor. ... A micrometer is a widely used device in mechanical engineering for precisely measuring thickness of blocks, outer and inner diameters of shafts and depths of slots. ... American English or U.S. English is the form of the English language used mostly in the United States of America. ... Measurement is the determination of the size or magnitude of something. ... The wavelength is the distance between repeating units of a wave pattern. ... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ... Note: Ultraviolet is also the name of a 1998 UK television miniseries about vampires. ... This article is about electromagnetic radiation. ... American English or U.S. English is the form of the English language used mostly in the United States of America. ... Properties For alternative meanings see atom (disambiguation). ... American English or U.S. English is the form of the English language used mostly in the United States of America. ... Femto is a prefix (see all prefixes) to a unit and means that it is 10-15 times this unit, or, one quindecillionth (European) or one quadrillionth (American). ... Properties For alternative meanings see atom (disambiguation). ... Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939. ... Properties In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... Enrico Fermi (September 29, 1901 – November 28, 1954) was an Italian physicist most noted for his work on beta decay, the development of the first nuclear reactor, and for the development of quantum theory. ... American English or U.S. English is the form of the English language used mostly in the United States of America. ... Atto- (symbol a) is an SI prefix to a unit and means that it is 10-18 times this unit. ... Properties The electron is a subatomic particle. ... American English or U.S. English is the form of the English language used mostly in the United States of America. ... Zepto (symbol z) is a prefix in the SI system of units denoting a factor of 10-21. ... American English or U.S. English is the form of the English language used mostly in the United States of America. ... Yocto (symbol y) is a SI prefix in the SI system of units denoting a factor of 10-24. ...

Unicode

Unicode has symbols for "cm" (㎝), for square centimetre (㎠) and for cubic centimetre (㎤); also, for "mm" (㎜), for square millimetre (㎟) and for cubic millimetre (㎣); however, they are useful only with East Asian fixed-width CJK fonts, because they are equal in size to one Chinese character. In computing, Unicode is the international standard whose goal is to provide the means to encode the text of every document people want to store in computers. ... CJK is a collective term for Chinese, Japanese, and Korean, which comprise the largest of East Asian languages. ... 漢字 in Traditional Chinese and other languages. ...

References

• A Dictionary of Scientific Units - including dimensionless numbers and scales. 5th Edition 1986. H.G. Jerrard and D.B. McNeill.

See also

• 1 E0 m
• SI
• SI prefix
• Orders of magnitude
• Conversion of units for comparisons with other units
• Planck length

To help compare different orders of magnitude this page lists lengths between one metre and ten metres. ... The International System of Units (abbreviated SI from the French phrase, Système International dUnités) is the most widely used system of units. ... An SI prefix is a prefix which can be applied to any unit of the International System of Units (SI) to give subdivisions and multiples of that unit. ... An order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. ... This article lists conversion factors between a number of units of measurement. ... The Planck length is the natural unit of length, denoted by . ...

External links

• History of the metre at the U.S. National Institute of Standards and Technology (NIST) (http://physics.nist.gov/cuu/Units/meter.html)
• History of the metre at the International Bureau of Weights and Measures (BIPM) (http://www.bipm.org/en/si/history-si/evolution_metre.html)
• Timeline of history of the metre at the NIST (http://www.mel.nist.gov/div821/museum/timeline.htm)
• Bureau International des Poids et Measures - Lengths (http://www1.bipm.org/en/scientific/length/)