The metre (Commonwealth English) or meter (American English) (symbol: m) is the SI base unit of length. It is defined as the length of the path travelled by light in an absolute vacuum during a time interval of 1/299,792,458 of a second. Commonwealth English is intended as a collective term for the perceived standard English language used in the Commonwealth of Nations1, applying in theory to Australian English, British English, Caribbean English, Canadian English, Hiberno-English (Irish English)2, Hong Kong English3, Indian English (includes Pakistani English), formal Malaysian English, New Zealand... American English (AmE) is the dialect of the English language used mostly in the United States of America. ... The SI system of units defines seven SI base units: physical units defined by an operational definition. ... 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... 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 (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength. ... For other uses, see vacuum cleaner and Vacuum (musical group). ... A watch Attempting to understand time has long been a prime occupation for philosophers, scientists and artists. ... Look up second in Wiktionary, the free dictionary. ...

Adding SI prefixes to metre creates multiples and submultiples; for example kilometre (1000 metres; kilo- = 1000) and millimetre (one thousandth of a metre; milli- = 1 / 1 000). An SI prefix is a prefix that can be applied to an SI unit to form a decimal multiple or submultiple. ... For the techno single by Moby, see Thousand (single). ...

SI prefixes applied to the metre

The metre may be used with SI prefixes. 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. ...

Conversions

1 metre is equivalent to:

• exactly 1/0.9144 yards (approximately 1.0936 yards)
• exactly 1/0.3048 feet (approximately 3.2808 feet)
• exactly 10000/254 inches (approximately 39.370 inches)

This article is about the unit of measure known as the yard. ... This article is about a foot as a unit of length. ... Mid-19th century tool for converting between different standards of the inch An inch is an Imperial and U.S. customary unit of length. ...

History

The word metre is from the Greek metron (μετρον), "a measure" via the French mètre. Its first recorded usage in English is from 1797. Measure can mean: To perform a measurement. ... The English language is a West Germanic language that originates in England. ...

In the 18th 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 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. In 1793, France adopted the metre, with this definition, 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. Simple gravity pendulum assumes no air resistance and no friction of/at the nail/screw. ... Periodicity is the quality of occurring at regular intervals (e. ... Look up second in Wiktionary, the free dictionary. ... On the earth, a meridian is a north-south line between the North Pole and the South Pole. ... 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. ... It has been suggested that gravitation be merged into this article or section. ... Earth is the third planet from the Sun. ...

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.

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 would maintain comparisons between them and non-metric measurement standards. This organisation 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 the melting point of ice. Template:USgov Template:Nist http://www. ... General Name, Symbol, Number krypton, Kr, 36 Chemical series noble gases Group, Period, Block 18, 4, p Appearance colorless Atomic mass 83. ... Cherenkov effect in a swimming pool nuclear reactor. ... The Metre Convention (or Convention of the Metre, or Convention du Mètre in French, its original language) of 1875 is an international treaty that established what is now known as the SI system. ... 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. ... Road to Sèvres, Jean-Baptiste Camille Corot, 1855-1865. ... The international prototype, made of platinum-iridium, which is kept at the BIPM under conditions specified by the 1st CGPM in 1889. ... The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures (CGPM, sometimes written in English Conférence Générale des Poids et Mesures). ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Atomic mass 195. ... General Name, Symbol, Number iridium, Ir, 77 Chemical series transition metals Group, Period, Block 9, 6, d Appearance silvery white Atomic mass 192. ...

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, when the eleventh CGPM defined the metre in the new SI system as equal to 1,650,763.73 wavelengths of the orange-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. 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 (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength. ... 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. ... The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures (CGPM, sometimes written in English Conférence Générale des Poids et Mesures). ... The International System of Units (abbreviated SI from the French language name Système International dUnités) is the modern form of the metric system. ... The wavelength is the distance between repeating units of a wave pattern. ... The colour orange occurs between red and yellow in the visible spectrum at a wavelength of about 620–585 nanometres. ... Red is any of a number of similar colors 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. ... Legend: γ = Gamma rays HX = Hard X-rays SX = Soft X-Rays EUV = Extreme ultraviolet NUV = Near ultraviolet Visible light NIR = Near infrared MIR = Moderate infrared FIR = Far infrared Radio waves: EHF = Extremely high frequency (Microwaves) SHF = Super high frequency (Microwaves) UHF = Ultrahigh frequency VHF = Very high frequency HF = High frequency... General Name, Symbol, Number krypton, Kr, 36 Chemical series noble gases Group, Period, Block 18, 4, p Appearance colorless Atomic mass 83. ... Properties An atom (Greek άτομον from ά: non and τομον: divisible) is a submicroscopic structure found in all ordinary matter. ... For other uses, see vacuum cleaner and Vacuum (musical group). ...

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: A watch Attempting to understand time has long been a prime occupation for philosophers, scientists and artists. ... 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.

Timeline of definition

• May 8, 1790 — 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.

• March 30, 1791 — 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 (one-fourth the polar circumference of the earth).

• 1795 — Provisional metre bar constructed of brass.

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

• September 28, 1889 — The first 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.

• October 6, 1927 — 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.

• October 20, 1960 — 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.

• October 21, 1983 — The seventeenth CGPM defines the length to be distance travelled by light in vacuum during a time interval of 1/299 792 458 of a second.

May 8 is the 128th day of the year in the Gregorian Calendar (129th in leap years). ... 1790 was a common year starting on Friday (see link for calendar). ... During the French Revolution, the National Assembly (French: Assemblée nationale) was a transitional body between the Estates-General and the National Constituent Assembly that existed from June 17 to July 9 of 1789. ... Simple gravity pendulum assumes no air resistance and no friction of/at the nail/screw. ... Periodicity is the quality of occurring at regular intervals (e. ... Look up second in Wiktionary, the free dictionary. ... March 30 is the 89th day of the year in the Gregorian Calendar (90th in Leap years). ... 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. ... On the earth, a meridian is a north-south line between the North Pole and the South Pole. ... 1795 was a common year starting on Thursday (see link for calendar). ... Brass is the term used for alloys of copper and zinc in a solid solution. ... December 10 is the 344th day (345th in leap years) of the year in the Gregorian calendar. ... 1799 was a common year starting on Tuesday (see link for calendar). ... June 23 is the 174th day of the year (175th in leap years) in the Gregorian Calendar, with 191 days remaining. ... 1799 was a common year starting on Tuesday (see link for calendar). ... September 28 is the 271st day of the year in the Gregorian calendar (272nd in leap years). ... 1889 (MDCCCLXXXIX) was a common year starting on Tuesday (see link for calendar). ... The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures (CGPM, sometimes written in English Conférence Générale des Poids et Mesures). ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Atomic mass 195. ... General Name, Symbol, Number iridium, Ir, 77 Chemical series transition metals Group, Period, Block 9, 6, d Appearance silvery white Atomic mass 192. ... October 6 is the 279th day of the year (280th in Leap years). ... 1927 (MCMXXVII) was a common year starting on Saturday (link will take you to calendar). ... A degree Celsius (°C) is a unit of temperature named after the Swedish astronomer Anders Celsius (1701-1744), who first proposed a similar system in 1742. ... diurnal (daily) rhythm of air pressure in northern Germany (black curve is air pressure) Atmospheric pressure is the pressure above any area in the Earths atmosphere caused by the weight of air. ... October 20 is the 293rd day of the year (294th in leap years) in the Gregorian Calendar, with 72 days remaining. ... 1960 (MCMLX) was a leap year starting on Friday (link will take you to calendar). ... The wavelength is the distance between repeating units of a wave pattern. ... For other uses, see vacuum cleaner and Vacuum (musical group). ... Electromagnetic radiation can be conceptualized as a self propagating transverse oscillating wave of electric and magnetic fields. ... General Name, Symbol, Number krypton, Kr, 36 Chemical series noble gases Group, Period, Block 18, 4, p Appearance colorless Atomic mass 83. ... Properties An atom (Greek άτομον from ά: non and τομον: divisible) is a submicroscopic structure found in all ordinary matter. ... October 21 is the 294th day of the year (295th in leap years) in the Gregorian Calendar, with 71 days remaining. ... 1983 (MCMLXXXIII) was a common year starting on Saturday of the Gregorian calendar. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength. ... Look up second in Wiktionary, the free dictionary. ...

See also

• Metric system
• SI
• SI prefix
• Conversion of units for comparisons with other units
• Orders of magnitude (length)
• Speed of light

The International System of Units (symbol: SI) (for the French phrase Syst me International dUnit s) is the most widely used system of units. ... The International System of Units (abbreviated SI from the French language name Système International dUnités) is the modern form of the metric system. ... An SI prefix is a prefix that can be applied to an SI unit to form a decimal multiple or submultiple. ... This article lists conversion factors between a number of units of measurement. ... Categories: | ... Cherenkov effect in a swimming pool nuclear reactor. ...

External links

• History of the metre at the U.S. National Institute of Standards and Technology (NIST)
• Timeline of history of the metre at the NIST
• Bureau International des Poids et Measures - Lengths