Last updated

Metric seal.svg
Seal of the International Bureau of Weights and Measures (BIPM) – Use measure (Greek: ΜΕΤΡΩ ΧΡΩ)
General information
Unit system SI base unit
Unit of Length
Symbolm [1]
1 m [2] in ...... is equal to ...
    SI units    1000  mm
0.001  km
    Imperial/US units   1.0936  yd

3.2808  ft

39.37  in
   Nautical units   0.00053996  nmi

The metre (Commonwealth spelling) or meter (American spelling) (from the French unit mètre, from the Greek noun μέτρον, "measure", and cognate with Sanskrit mita, meaning "measured" [3] ) is the base unit of length in the International System of Units (SI). The SI unit symbol is m. The metre is defined as the length of the path travelled by light in a vacuum in 1/299 792 458 of a second. The metre was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole along a great circle, so the Earth's circumference is approximately 40000 km. In 1799, the metre was redefined in terms of a prototype metre bar (the actual bar used was changed in 1889). In 1960, the metre was redefined in terms of a certain number of wavelengths of a certain emission line of krypton-86. The current definition was adopted in 1983 and modified slightly in 2002 to clarify that the metre is a measure of proper length.



Metre is the standard spelling of the metric unit for length in nearly all English-speaking nations except the United States [4] [5] [6] [7] and the Philippines, [8] which use meter. Other Germanic languages, such as German, Dutch, and the Scandinavian languages [9] likewise spell the word meter.

Measuring devices (such as ammeter, speedometer) are spelled "-meter" in all variants of English. [10] The suffix "-meter" has the same Greek origin as the unit of length. [11] [12]


The etymological roots of metre can be traced to the Greek verb μετρέω (metreo) (to measure, count or compare) and noun μέτρον (metron) (a measure), which were used for physical measurement, for poetic metre and by extension for moderation or avoiding extremism (as in "be measured in your response"). This range of uses is also found in Latin (metior, mensura), French (mètre, mesure), English and other languages. Ultimately the word came from the sanskrit "mita", meaning "measured". [3] The motto ΜΕΤΡΩ ΧΡΩ (metro chro) in the seal of the International Bureau of Weights and Measures (BIPM), which was a saying of the Greek statesman and philosopher Pittacus of Mytilene and may be translated as "Use measure!", thus calls for both measurement and moderation. The use of the word metre (for the French unit mètre) in English began at least as early as 1797. [13]

History of definition

Meridian room of the Paris Observatory (or Cassini room): the Paris meridian is drawn on the ground. Obs-Paris-meridienne.jpg
Meridian room of the Paris Observatory (or Cassini room): the Paris meridian is drawn on the ground.

In 1671 Jean Picard measured the length of a "seconds pendulum" (a pendulum with a period of two seconds) at the Paris observatory. He found the value of 440.5 lines of the Toise of Châtelet which had been recently renewed. He proposed a universal toise (French: Toise universelle) which was twice the length of the seconds pendulum. [14] [15] However, it was soon discovered that the length of a seconds pendulum varies from place to place: French astronomer Jean Richer had measured the 0.3% difference in length between Cayenne (in French Guiana) and Paris. [16] [17] [18]

Jean Richer and Giovanni Domenico Cassini measured the parallax of Mars between Paris and Cayenne in French Guiana when Mars was at its closest to Earth in 1672. They arrived at a figure for the solar parallax of 9.5 arcseconds, equivalent to an Earth–Sun distance of about 22000 Earth radii. They were also the first astronomers to have access to an accurate and reliable value for the radius of Earth, which had been measured by their colleague Jean Picard in 1669 as 3269 thousand toises. Picard's geodetic observations had been confined to the determination of the magnitude of the Earth considered as a sphere, but the discovery made by Jean Richer turned the attention of mathematicians to its deviation from a spherical form. In addition to its significance for cartography, the determination of the Figure of the Earth became a problem of the highest importance in astronomy, inasmuch as the diameter of the Earth was the unit to which all celestial distances had to be referred. [19] [20] [21] [22]

Meridional definition

Paris Pantheon Pantheon de Paris, 16 January 2016.jpg
Paris Panthéon

As a result of the French Revolution, the French Academy of Sciences charged a commission with determining a single scale for all measures. On 7 October 1790 that commission advised the adoption of a decimal system, and on 19 March 1791 advised the adoption of the term mètre ("measure"), a basic unit of length, which they defined as equal to one ten-millionth of the distance between the North Pole and the Equator along the meridian through Paris. [23] [24] [25] [26] [27] In 1793, the French National Convention adopted the proposal. [13]

The French Academy of Sciences commissioned an expedition led by Jean Baptiste Joseph Delambre and Pierre Méchain, lasting from 1792 to 1799, which attempted to accurately measure the distance between a belfry in Dunkerque and Montjuïc castle in Barcelona at the longitude of the Paris Panthéon (see meridian arc of Delambre and Méchain). [28] The expedition was fictionalised in Denis Guedj, Le Mètre du Monde. [29] Ken Alder wrote factually about the expedition in The Measure of All Things: the seven year odyssey and hidden error that transformed the world. [30] This portion of the Paris meridian, was to serve as the basis for the length of the half meridian connecting the North Pole with the Equator. From 1801 to 1812 France adopted this definition of the metre as its official unit of length based on results from this expedition combined with those of the Geodesic Mission to Peru. [31] [32] The latter was related by Larrie D. Ferreiro in Measure of the Earth: The Enlightenment Expedition that Reshaped Our World. [33]

A more accurate determination of the Figure of the Earth would soon result from the measurement of the Struve Geodetic Arc (1816–1855) and would have given another value for the definition of this standard of length. This did not invalidate the metre but highlighted that progresses in science would allow better measurement of Earth's size and shape. [22]

International prototype metre bar

Creating the metre-alloy in 1874 at the Conservatoire des Arts et Metiers. Present Henri Tresca, George Matthey, Saint-Claire Deville and Debray Metre alloy.jpg
Creating the metre-alloy in 1874 at the Conservatoire des Arts et Métiers. Present Henri Tresca, George Matthey, Saint-Claire Deville and Debray

In 1867 at the second general conference of the International Association of Geodesy held in Berlin, the question of an international standard unit of length was discussed in order to combine the measurements made in different countries to determine the size and shape of the Earth. [34] [35] [36] The conference recommended the adoption of the metre in replacement of the toise and the creation of an international metre commission, according to the proposal of Johann Jacob Baeyer, Adolphe Hirsch and Carlos Ibáñez e Ibáñez de Ibero who had devised two geodetic standards calibrated on the metre for the map of Spain. [37] [34] [36] [38] Measurement traceability between the toise and the metre was ensured by comparison of the Spanish standard with the standard devised by Borda and Lavoisier for the survey of the meridian arc connecting Dunkirk with Barcelona. [39] [38] [40]

A member of the Preparatory Committee since 1870 and Spanish representative at the Paris Conference in 1875, Carlos Ibáñez e Ibáñez de Ibero intervened with the French Academy of Sciences to rally France to the project to create an International Bureau of Weights and Measures equipped with the scientific means necessary to redefine the units of the metric system according to the progress of sciences. [41]

Gravimeter with variant of Repsold pendulum Repsold.jpg
Gravimeter with variant of Repsold pendulum

In the 1870s and in light of modern precision, a series of international conferences was 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 was to construct and preserve a prototype metre bar, distribute national metric prototypes, and maintain comparisons between them and non-metric measurement standards. The organisation distributed such bars 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 90% platinum and 10% iridium, measured at the melting point of ice. [42]

The comparison of the new prototypes of the metre with each other and with the Committee metre (French: Mètre des Archives ) involved the development of special measuring equipment and the definition of a reproducible temperature scale. The BIPM's thermometry work led to the discovery of special alloys of iron-nickel, in particular invar, for which its director, the Swiss physicist Charles-Edouard Guillaume, was granted the Nobel Prize for physics in 1920. [43]

Artist's impression of a GPS-IIR satellite in orbit. GPS-IIR.jpg
Artist's impression of a GPS-IIR satellite in orbit.

As Carlos Ibáñez e Ibáñez de Ibero stated, the progress of metrology combined with those of gravimetry through improvement of Kater's pendulum led to a new era of geodesy. If precision metrology had needed the help of geodesy, the latter could not continue to prosper without the help of metrology. Indeed, how to express all the measurements of terrestrial arcs as a function of a single unit, and all the determinations of the force of gravity with the pendulum, if metrology had not created a common unit, adopted and respected by all civilized nations, and if in addition one had not compared, with great precision, to the same unit all the standards for measuring geodesic bases, and all the pendulum rods that had hitherto been used or would be used in the future? Only when this series of metrological comparisons would be finished with a probable error of a thousandth of a millimetre would geodesy be able to link the works of the different nations with one another, and then proclaim the result of the last measurement of the Globe. As the figure of the Earth could be inferred from variations of the seconds pendulum length with latitude, the United States Coast Survey instructed Charles Sanders Peirce in the spring of 1875 to proceed to Europe for the purpose of making pendulum experiments to chief initial stations for operations of this sort, in order to bring the determinations of the forces of gravity in America into communication with those of other parts of the world; and also for the purpose of making a careful study of the methods of pursuing these researches in the different countries of Europe. In 1886 the association of geodesy changed name for the International Geodetic Association, which Carlos Ibáñez e Ibáñez de Ibero presided up to his death in 1891. During this period the International Geodetic Association (German: Internationale Erdmessung) gained worldwide importance with the joining of United States, Mexico, Chile, Argentina and Japan. [39] [44] [45] [46] [47] [48]

Efforts to supplement the various national surveying systems, which begun in the 19th century with the foundation of the Mitteleuropäische Gradmessung , resulted in a series of global ellipsoids of the Earth (e.g., Helmert 1906, Hayford 1910 and 1924) which would later lead to develop the World Geodetic System. Nowadays the practical realisation of the metre is possible everywhere thanks to the atomic clocks embedded in GPS satellites. [49] [50]

Wavelength definition

In 1873, James Clerk Maxwell suggested that light emitted by an element be used as the standard both for the meter and for the second. These two quantities could then be used to define the unit of mass. [51]

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 length. 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 International System of Units (SI) as equal to 1650763.73 wavelengths of the orange-red emission line in the electromagnetic spectrum of the krypton-86 atom in a vacuum. [52]

Speed of light definition

To further reduce uncertainty, the 17th CGPM in 1983 replaced the definition of the metre with its current definition, thus fixing the length of the metre in terms of the second and the speed of light: [53]

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.

This definition fixed the speed of light in vacuum at exactly 299792458 metres per second (≈300000 km/s). [53] An intended by-product of the 17th CGPM's definition was that it enabled scientists to compare lasers accurately using frequency, resulting in wavelengths with one-fifth the uncertainty involved in the direct comparison of wavelengths, because interferometer errors were eliminated. 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. [54] For the purpose of delineating the metre, the BIPM currently considers the HeNe laser wavelength, λHeNe, to be 632.99121258 nm with an estimated relative standard uncertainty (U) of 2.1×10−11. [54] [55] [56] This uncertainty is currently one limiting factor in laboratory realisations of the metre, and it is several orders of magnitude poorer than that of the second, based upon the caesium fountain atomic clock (U = 5×10−16). [57] Consequently, a realisation of the metre is usually delineated (not defined) today in labs as 1579800.762042(33) wavelengths of helium-neon laser light in a vacuum, the error stated being only that of frequency determination. [54] This bracket notation expressing the error is explained in the article on measurement uncertainty.

Practical realisation of the metre is subject to uncertainties in characterising the medium, to various uncertainties of interferometry, and to uncertainties in measuring the frequency of the source. [58] A commonly used medium is air, and the National Institute of Standards and Technology (NIST) has set up an online calculator to convert wavelengths in vacuum to wavelengths in air. [59] As described by NIST, in air, the uncertainties in characterising the medium are dominated by errors in measuring temperature and pressure. Errors in the theoretical formulas used are secondary. [60] By implementing a refractive index correction such as this, an approximate realisation of the metre can be implemented in air, for example, using the formulation of the metre as 1579800.762042(33) wavelengths of helium–neon laser light in vacuum, and converting the wavelengths in a vacuum to wavelengths in air. Air is only one possible medium to use in a realisation of the metre, and any partial vacuum can be used, or some inert atmosphere like helium gas, provided the appropriate corrections for refractive index are implemented. [61]

The metre is defined as the path length travelled by light in a given time and practical laboratory length measurements in metres are determined by counting the number of wavelengths of laser light of one of the standard types that fit into the length, [64] and converting the selected unit of wavelength to metres. Three major factors limit the accuracy attainable with laser interferometers for a length measurement: [58] [65]

Of these, the last is peculiar to the interferometer itself. The conversion of a length in wavelengths to a length in metres is based upon the relation

which converts the unit of wavelength λ to metres using c, the speed of light in vacuum in m/s. Here n is the refractive index of the medium in which the measurement is made, and f is the measured frequency of the source. Although conversion from wavelengths to metres introduces an additional error in the overall length due to measurement error in determining the refractive index and the frequency, the measurement of frequency is one of the most accurate measurements available. [65]


Closeup of National Prototype Metre Bar No. 27, made in 1889 by the International Bureau of Weights and Measures (BIPM) and given to the United States, which served as the standard for defining all units of length in the US from 1893 to 1960 US National Length Meter.JPG
Closeup of National Prototype Metre Bar No. 27, made in 1889 by the International Bureau of Weights and Measures (BIPM) and given to the United States, which served as the standard for defining all units of length in the US from 1893 to 1960
DateDeciding bodyDecision
8 May 1790 French National Assembly The length of the new metre to be equal to the length of a pendulum with a half-period of one second. [31]
30 Mar 1791French National AssemblyAccepts 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 a great circle quadrant along the Earth's meridian through Paris, that is the distance from the equator to the north pole along that quadrant. [66]
1795Provisional metre bar made of brass and based on Paris meridan arc (French: Méridienne de France) measured by Nicolas-Louis de Lacaillle and Cesar-François Cassini de Thury, legally equal to 443.44 lines of the toise du Pérou (a standard French unit of length from 1766). [31] [32] [40] [50] [The line was 1/864 of a toise.]
10 Dec 1799French National AssemblySpecifies the platinum metre bar, presented on 22 June 1799 and deposited in the National Archives, as the final standard. Legally equal to 443.296 lines on the toise du Pérou. [50]
24–28 Sept 18891st General Conference on Weights and Measures (CGPM)Defines the metre as the distance between two lines on a standard bar of an alloy of platinum with 10% iridium, measured at the melting point of ice. [50] [67]
27 Sept – 6 Oct 19277th CGPMRedefines the metre as the distance, at 0  °C (273  K ), 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 10 mm (1 cm) diameter, symmetrically placed in the same horizontal plane at a distance of 571 mm (57.1 cm) from each other. [68]
14 Oct 196011th CGPMDefines the metre as 1650763.73 wavelengths in a vacuum of the radiation corresponding to the transition between the 2p10 and 5d5 quantum levels of the krypton-86 atom. [69]
21 Oct 198317th CGPMDefines the metre as the length of the path travelled by light in a vacuum during a time interval of 1/299 792 458 of a second. [70] [71]
2002 International Committee for Weights and Measures (CIPM)Considers the metre to be a unit of proper length and thus recommends this definition be restricted to "lengths ℓ which are sufficiently short for the effects predicted by general relativity to be negligible with respect to the uncertainties of realisation". [72]
Definitions of the metre since 1795 [73]
Basis of definitionDateAbsolute
1/10 000 000 part of the quadrant along the meridian, measurement by Delambre and Méchain (443.296 lines)1795500–100 μm10−4
First prototype Mètre des Archives platinum bar standard179950–10 μm10−5
Platinum-iridium bar at melting point of ice (1st CGPM)18890.2–0.1 μm (200–100 nm)10−7
Platinum-iridium bar at melting point of ice, atmospheric pressure, supported by two rollers (7th CGPM)1927n.a.n.a.
Hyperfine atomic transition; 1650763.73 wavelengths of light from a specified transition in krypton-86 (11th CGPM)19604 nm4×10−9 [74]
Length of the path travelled by light in a vacuum in 1/299 792 458 second (17th CGPM)19830.1 nm10−10

Early adoptions of the metre internationally

Triangulation near New York City, 1817. HasslerCollection 001.jpg
Triangulation near New York City, 1817.

After the July Revolution of 1830 the metre became the definitive French standard from 1840. At that time it had already been adopted by Ferdinand Rudolph Hassler for the U.S Survey of the Coast. [31] [75] [37]

"The unit of length to which all distances measured in the Coast Survey are referred is the French metre, an authentic copy of which is preserved in the archives of the Coast Survey Office. It is the property of the American Philosophical Society, to whom it was presented by Mr. Hassler, who had received it from Tralles, a member of the French Committee charged with the construction of the standard metre by comparison with the toise, which had served as unit of length in the measurement of the meridional arcs in France and Peru. It possesses all the authenticity of any original metre extant, bearing not only the stamp of the Committee but also the original mark by which it was distinguished from the other bars during the operation of standardising. It is always designated as the Committee metre" (French : Mètre des Archives ). [76] [15]

In 1830 President Andrew Jackson mandated Ferdinand Rudolf Hassler to work out new standards for all U.S. states. According to the decision of the Congress of the United States, the British Parliamentary Standard from 1758 was introduced as the unit of length. [77]

Another geodesist with metrology skills was to play a pivotal role in the process of internationalization of weights and measures, Carlos Ibáñez e Ibáñez de Ibero who would become the first president of both the International Geodetic Association and the International Committee for Weights and Measures. [39]

SI prefixed forms of metre

SI prefixes can be used to denote decimal multiples and submultiples of the metre, as shown in the table below. Long distances are usually expressed in km, astronomical units (149.6 Gm), light-years (10 Pm), or parsecs (31 Pm), rather than in Mm, Gm, Tm, Pm, Em, Zm or Ym; "30 cm", "30 m", and "300 m" are more common than "3 dm", "3 dam", and "3 hm", respectively.

The terms micron and millimicron can be used instead of micrometre (μm) and nanometre (nm), but this practice may be discouraged. [78]

SI multiples of metre (m)
ValueSI symbolNameValueSI symbolName
10−1 mdm decimetre 101 mdam decametre
10−2 mcm centimetre 102 mhm hectometre
10−3 mmm millimetre 103 mkm kilometre
10−6 mµm micrometre 106 mMm megametre
10−9 mnm nanometre 109 mGm gigametre
10−12 mpm picometre 1012 mTm terametre
10−15 mfm femtometre 1015 mPm petametre
10−18 mamattometre1018 mEmexametre
10−21 mzmzeptometre1021 mZmzettametre
10−24 mym yoctometre 1024 mYmyottametre

Equivalents in other units

Metric unit
expressed in non-SI units
Non-SI unit
expressed in metric units
1 metre1.0936 yard 1 yard0.9144metre
1 metre39.370 inches 1 inch0.0254metre
1 centimetre 0.39370inch1 inch2.54centimetres
1 millimetre 0.039370inch1 inch25.4millimetres
1 metre 1 × 1010 ångström 1 ångström1 × 10−10metre
1 nanometre 10ångström1 ångström100 picometres

Within this table, "inch" and "yard" mean "international inch" and "international yard" [79] respectively, though approximate conversions in the left column hold for both international and survey units.

"≈" means "is approximately equal to";
"≡" means "equal by definition" or "is exactly equal to".

One metre is exactly equivalent to 5 000/127 inches and to 1 250/1 143 yards.

A simple mnemonic aid exists to assist with conversion, as three "3"s:

1 metre is nearly equivalent to 3  feet 3 38 inches. This gives an overestimate of 0.125 mm; however, the practice of memorising such conversion formulas has been discouraged in favour of practice and visualisation of metric units.

The ancient Egyptian cubit was about 0.5 m (surviving rods are 523–529 mm). [80] Scottish and English definitions of the ell (two cubits) were 941 mm (0.941 m) and 1143 mm (1.143 m) respectively. [81] [82] The ancient Parisian toise (fathom) was slightly shorter than 2 m and was standardised at exactly 2 m in the mesures usuelles system, such that 1 m was exactly 12 toise. [83] The Russian verst was 1.0668 km. [84] The Swedish mil was 10.688 km, but was changed to 10 km when Sweden converted to metric units. [85]

See also


  1. "Base unit definitions: Meter". National Institute of Standards and Technology . Retrieved 28 September 2010.
  2. "Base unit definitions: Meter". National Institute of Standards and Technology . Retrieved 28 September 2010.
  3. 1 2 Monier Williams, M (2002). A Sankrit English Dictionary. Delhi: Motilal Banarsidass. p. 815. ISBN   81-208-0065-6.
  4. "The International System of Units (SI) – NIST". US: National Institute of Standards and Technology. 26 March 2008. The spelling of English words is in accordance with the United States Government Printing Office Style Manual, which follows Webster's Third New International Dictionary rather than the Oxford Dictionary. Thus the spellings "meter,"…rather than "metre," in the original BIPM English text...
  5. The most recent official brochure about the International System of Units (SI), written in French by the Bureau international des poids et mesures, International Bureau of Weights and Measures (BIPM) uses the spelling metre; an English translation, included to make the SI standard more widely accessible also uses the spelling metre (BIPM, 2006, p. 130ff). However, in 2008 the U.S. English translation published by the U.S. National Institute of Standards and Technology (NIST) chose to use the spelling meter in accordance with the United States Government Printing Office Style Manual. The Metric Conversion Act of 1975 gives the Secretary of Commerce of the US the responsibility of interpreting or modifying the SI for use in the US. The Secretary of Commerce delegated this authority to the Director of the National Institute of Standards and Technology (Turner). In 2008, NIST published the US version (Taylor and Thompson, 2008a) of the English text of the eighth edition of the BIPM publication Le Système international d'unités (SI) (BIPM, 2006). In the NIST publication, the spellings "meter", "liter" and "deka" are used rather than "metre", "litre" and "deca" as in the original BIPM English text (Taylor and Thompson (2008a), p. iii). The Director of the NIST officially recognised this publication, together with Taylor and Thompson (2008b), as the "legal interpretation" of the SI for the United States (Turner). Thus, the spelling metre is referred to as the "international spelling"; the spelling meter, as the "American spelling".
  6. Naughtin, Pat (2008). "Spelling metre or meter" (PDF). Metrication Matters. Retrieved 12 March 2017.
  7. "Meter vs. metre". Grammarist. Retrieved 12 March 2017.
  8. The Philippines uses English as an official language and this largely follows American English since the country became a colony of the United States. While the law that converted the country to use the metric system uses metre (Batas Pambansa Blg. 8) following the SI spelling, in actual practice, meter is used in government and everyday commerce, as evidenced by laws (kilometer, Republic Act No. 7160), Supreme Court decisions (meter, G.R. No. 185240), and national standards (centimeter, PNS/BAFS 181:2016).
  9. "295–296 (Nordisk familjebok / Uggleupplagan. 18. Mekaniker – Mykale)" [295–296 (Nordic Family Book / Owl Edition. 18. Mechanic – Mycular)]. Stockholm. 1913.
  10. Cambridge Advanced Learner's Dictionary. Cambridge University Press. 2008. Retrieved 19 September 2012., s.v. ammeter, meter, parking meter, speedometer.
  11. American Heritage Dictionary of the English Language (3rd ed.). Boston: Houghton Mifflin. 1992., s.v. meter.
  12. "-meter – definition of -meter in English". Oxford Dictionaries.
  13. 1 2 Oxford English Dictionary, Clarendon Press 2nd ed.1989, vol.IX p.697 col.3.
  14. texte, Picard, Jean (1620–1682). Auteur du (1671). Mesure de la terre [par l'abbé Picard]. Gallica. pp. 3–4. Retrieved 13 September 2018.[ verification needed ]
  15. 1 2 Bigourdan 1901, pp. 8, 158–159.
  16. Poynting, John Henry; Thomson, Joseph John (1907). A Textbook of Physics. C. Griffin. pp.  20.[ verification needed ]
  17. Picard, Jean (1620–1682) Auteur du texte (1671). Mesure de la terre [par l'abbé Picard]. pp. 3–5.
  18. Bond, Peter, (1948- ...). (2014). L'exploration du système solaire. Dupont-Bloch, Nicolas. ([Édition française revue et corrigée] ed.). Louvain-la-Neuve: De Boeck. pp. 5–6. ISBN   9782804184964. OCLC   894499177.CS1 maint: multiple names: authors list (link)
  19. Wikisource-logo.svg One or more of the preceding sentences incorporates text from a publication now in the public domain : Clarke, Alexander Ross; Helmert, Friedrich Robert (1911). "Earth, Figure of the". In Chisholm, Hugh (ed.). Encyclopædia Britannica . 8 (11th ed.). Cambridge University Press. p. 801.
  20. "Première détermination de la distance de la Terre au Soleil | Les 350 ans de l'Observatoire de Paris". Retrieved 14 May 2019.
  21. Buffet, Loriane. "Cassini, l'Astronome du roi et le satellite – Exposition virtuelle". (in French). Retrieved 14 May 2019.
  22. 1 2 "Nomination of the Struve geodetic arc for inscription on the World Heritage List" (PDF). Retrieved 13 May 2019.
  23. Tipler, Paul A.; Mosca, Gene (2004). Physics for Scientists and Engineers (5th ed.). W.H. Freeman. p. 3. ISBN   0716783398.
  24. ('decimalization is not of the essence of the metric system; the real significance of this is that it was the first great attempt to define terrestrial units of measure in terms of an unvarying astronomical or geodetic constant.) The metre was in fact defined as one ten-millionth of one-quarter of the earth's circumference at sea-level.' Joseph Needham, Science and Civilisation in China , Cambridge University Press, 1962 vol.4, pt.1, p.42.
  25. Agnoli, Paolo (2004). Il senso della misura: la codifica della realtà tra filosofia, scienza ed esistenza umana (in Italian). Armando Editore. pp. 93–94, 101. ISBN   9788883585326 . Retrieved 13 October 2015.
  26. Rapport sur le choix d'une unité de mesure, lu à l'Académie des sciences, le 19 mars 1791 (in French). 15 October 2007. Retrieved 25 March 2013.: "Nous proposerons donc de mesurer immédiatement un arc du méridien, depuis Dunkerque jusqu'a Bracelone: ce qui comprend un peu plus de neuf degrés & demi." [We propose then to measure directly an arc of the meridian between Dunkirk and Barcelona: this spans a little more than nine-and-a-half degrees."] p. 8
  27. Paolo Agnoli and Giulio D’Agostini,'Why does the meter beat the second?,' December, 2004 pp.1–29.
  28. Ramani, Madhvi. "How France created the metric system". Retrieved 21 May 2019.
  29. Guedj 2001.
  30. Alder 2002.
  31. 1 2 3 4 Larousse, Pierre (1817–1875) (1866–1877). Grand dictionnaire universel du XIXe siècle : français, historique, géographique, mythologique, bibliographique.... T. 11 MEMO-O / par M. Pierre Larousse.
  32. 1 2 Levallois, Jean-Jacques (1986). "La Vie des sciences". Gallica (in French). pp. 288–290, 269, 276–277, 283. Retrieved 13 May 2019.
  33. Robinson, Andrew (10 August 2011). "History: How Earth shaped up". Nature. 476 (7359): 149–150. Bibcode:2011Natur.476..149R. doi: 10.1038/476149a . ISSN   1476-4687.
  34. 1 2 Hirsch, Adolphe (1891). "Don Carlos IBANEZ (1825–1891)" (PDF). Bureau International des Poids et Mesures. p. 8. Retrieved 22 May 2017.
  35. "BIPM – International Metre Commission". Retrieved 26 May 2017.
  36. 1 2 "A Note on the History of the IAG". IAG Homepage. Retrieved 26 May 2017.
  37. 1 2 Ross, Clarke Alexander; James, Henry (1 January 1873). "XIII. Results of the comparisons of the standards of length of England, Austria, Spain, United States, Cape of Good Hope, and of a second Russian standard, made at the Ordnance Survey Office, Southampton. With a preface and notes on the Greek and Egyptian measures of length by Sir Henry James". Philosophical Transactions of the Royal Society of London. 163: 445–469. doi: 10.1098/rstl.1873.0014 .
  38. 1 2 Brunner, Jean (1857). "Comptes rendus hebdomadaires des séances de l'Académie des sciences / publiés... par MM. les secrétaires perpétuels". Gallica (in French). pp. 150–153. Retrieved 15 May 2019.
  39. 1 2 3 Soler, T. (1 February 1997). "A profile of General Carlos Ibáñez e Ibáñez de Ibero: first president of the International Geodetic Association". Journal of Geodesy. 71 (3): 176–188. Bibcode:1997JGeod..71..176S. doi:10.1007/s001900050086. ISSN   1432-1394. S2CID   119447198.
  40. 1 2 Wolf, Charles (1827–1918) Auteur du texte (1882). Recherches historiques sur les étalons de poids et mesures de l'Observatoire et les appareils qui ont servi à les construire / par M. C. Wolf... (in French). pp. C.38–39, C.2–4.
  41. Pérard, Albert (1957). "Carlos IBAÑEZ DE IBERO (14 avril 1825 – 29 janvier 1891), par Albert Pérard (inauguration d'un monument élevé à sa mémoire)" (PDF). Institut de France – Académie des sciences. pp. 26–28.
  42. National Institute of Standards and Technology 2003; Historical context of the SI: Unit of length (meter)
  43. "BIPM – la définition du mètre". Retrieved 15 May 2019.
  44. Ibáñez e Ibáñez de Ibero, Carlos (1881). Discursos leidos ante la Real Academia de Ciencias Exactas Fisicas y Naturales en la recepcion pública de Don Joaquin Barraquer y Rovira (PDF). Madrid: Imprenta de la Viuda e Hijo de D.E. Aguado. pp. 70–78.
  45. "Report from Charles S. Peirce on his second European trip for the Anual Report of the Superintendent of the U. S. Coast Survey, New York, 18.05.1877". Retrieved 22 May 2019.
  46. Faye, Hervé (1880). "Comptes rendus hebdomadaires des séances de l'Académie des sciences / publiés... par MM. les secrétaires perpétuels". Gallica (in French). pp. 1463–1466. Retrieved 22 May 2019.
  47. Torge, Wolfgang (2016). Rizos, Chris; Willis, Pascal (eds.). "From a Regional Project to an International Organization: The "Baeyer-Helmert-Era" of the International Association of Geodesy 1862–1916". IAG 150 Years. International Association of Geodesy Symposia. Springer International Publishing. 143: 3–18. doi:10.1007/1345_2015_42. ISBN   9783319308951.
  48. Torge, W. (1 April 2005). "The International Association of Geodesy 1862 to 1922: from a regional project to an international organization". Journal of Geodesy. 78 (9): 558–568. Bibcode:2005JGeod..78..558T. doi:10.1007/s00190-004-0423-0. ISSN   1432-1394. S2CID   120943411.
  49. Laboratoire national de métrologie et d'essais (13 June 2018), Le mètre, l'aventure continue... , retrieved 16 May 2019
  50. 1 2 3 4 "Histoire du mètre". Direction Générale des Entreprises (DGE) (in French). Retrieved 16 May 2019.
  51. Maxwell, James Clerk (1873). A Treatise On Electricity and Magnetism (PDF). 1. London: MacMillan and Co. p. 3.
  52. Marion, Jerry B. (1982). Physics For Science and Engineering. CBS College Publishing. p. 3. ISBN   978-4-8337-0098-6.
  53. 1 2 "17th General Conference on Weights and Measures (1983), Resolution 1" . Retrieved 19 September 2012.
  54. 1 2 3 "Iodine (λ ≈ 633 nm)" (PDF). Mise en Pratique. BIPM. 2003. Retrieved 16 December 2011.
  55. The term "relative standard uncertainty" is explained by NIST on their web site: "Standard Uncertainty and Relative Standard Uncertainty". The NIST Reference on constants, units, and uncertainties: Fundamental physical constants. NIST. Retrieved 19 December 2011.
  56. National Research Council 2010.
  57. National Institute of Standards and Technology 2011.
  58. 1 2 A more detailed listing of errors can be found in Beers, John S; Penzes, William B (December 1992). "§4 Re-evaluation of measurement errors" (PDF). NIST length scale interferometer measurement assurance; NIST document NISTIR 4998. pp. 9 ff. Retrieved 17 December 2011.
  59. The formulas used in the calculator and the documentation behind them are found at "Engineering metrology toolbox: Refractive index of air calculator". NIST. 23 September 2010. Retrieved 16 December 2011. The choice is offered to use either the modified Edlén equation or the Ciddor equation. The documentation provides a discussion of how to choose between the two possibilities.
  60. "§VI: Uncertainty and range of validity". Engineering metrology toolbox: Refractive index of air calculator. NIST. 23 September 2010. Retrieved 16 December 2011.
  61. Dunning, F. B.; Hulet, Randall G. (1997). "Physical limits on accuracy and resolution: setting the scale". Atomic, molecular, and optical physics: electromagnetic radiation, Volume 29, Part 3. Academic Press. p. 316. ISBN   978-0-12-475977-0. The error [introduced by using air] can be reduced tenfold if the chamber is filled with an atmosphere of helium rather than air.
  62. "Recommended values of standard frequencies". BIPM. 9 September 2010. Retrieved 22 January 2012.
  63. National Physical Laboratory 2010.
  64. The BIPM maintains a list of recommended radiations on their web site. [62] [63]
  65. 1 2 Zagar, 1999, pp. 6–65ff.
  66. Bigourdan1901, pp. 20–21.
  67. "CGPM : Compte rendus de la 1ère réunion (1889)" (PDF). BIPM.
  68. "CGPM : Comptes rendus de le 7e réunion (1927)" (PDF). p. 49.
  69. Judson 1976.
  70. Taylor and Thompson (2008a), Appendix 1, p. 70.
  71. "Meter is Redefined". US: National Geographic Society. Retrieved 22 October 2019.
  72. Taylor and Thompson (2008a), Appendix 1, p. 77.
  73. Cardarelli 2003.
  74. Definition of the metre Resolution 1 of the 17th meeting of the CGPM (1983)
  75. Centre, UNESCO World Heritage. "Struve Geodetic Arc". UNESCO World Heritage Centre. Retrieved 13 May 2019.
  76. Clarke, Alexander Ross (1873), "XIII. Results of the comparisons of the standards of length of England, Austria, Spain, United States, Cape of Good Hope, and of a second Russian standard, made at the Ordnance Survey Office, Southampton. With a preface and notes on the Greek and Egyptian measures of length by Sir Henry James", Philosophical Transactions, London, 163, p. 463, doi: 10.1098/rstl.1873.0014
  77. "e-expo: Ferdinand Rudolf Hassler". Retrieved 21 May 2019.
  78. Taylor & Thompson 2003, p. 11.
  79. Astin & Karo 1959.
  80. Arnold Dieter (1991). Building in Egypt: pharaonic stone masonry. Oxford: Oxford University Press. ISBN   978-0-19-506350-9. p.251.
  81. "Dictionary of the Scots Language". Archived from the original on 21 March 2012. Retrieved 6 August 2011.
  82. The Penny Magazine of the Society for the Diffusion of Useful Knowledge. Charles Knight. 6 June 1840. pp. 221–22.
  83. Hallock, William; Wade, Herbert T (1906). "Outlines of the evolution of weights and measures and the metric system". London: The Macmillan Company. pp. 66–69.
  84. Cardarelli 2004.
  85. Hofstad, Knut. "Mil". Store norske leksikon. Retrieved 18 October 2019.

Related Research Articles

Conversion of units is the conversion between different units of measurement for the same quantity, typically through multiplicative conversion factors.

The General Conference on Weights and Measures is the supreme authority of the International Bureau of Weights and Measures, the inter-governmental organization established in 1875 under the terms of the Metre Convention through which Member States act together on matters related to measurement science and measurement standards. The CGPM is made up of delegates of the governments of the Member States and observers from the Associates of the CGPM. Under its authority, the International Committee for Weights and Measures (ICWM) (French: Comité international des poids et mesures executes an exclusive direction and supervision of the BIPM.

Kilogram SI unit of mass

The kilogram is the base unit of mass in the International System of Units (SI), the current metric system, having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo in everyday speech.

Litre Unit of volume

The litre or liter is a metric unit of volume. It is equal to 1 cubic decimetre (dm3), 1000 cubic centimetres (cm3) or 0.001 cubic metre (m3). A cubic decimetre occupies a volume of 10 cm × 10 cm × 10 cm and is thus equal to one-thousandth of a cubic metre.

Metre Convention 1875 international treaty

The Metre Convention, also known as the Treaty of the Metre, is an international treaty that was signed in Paris on 20 May 1875 by representatives of 17 nations. The treaty created the International Bureau of Weights and Measures (BIPM), an intergovernmental organization under the authority of the General Conference on Weights and Measures (CGPM) and the supervision of the International Committee for Weights and Measures (CIPM), that coordinates international metrology and the development of the metric system.

International System of Units Modern form of the metric system

The International System of Units is the modern form of the metric system. It is the only system of measurement with an official status in nearly every country in the world. It comprises a coherent system of units of measurement starting with seven base units, which are the second, metre, kilogram, ampere, kelvin, mole, and candela. The system allows for an unlimited number of additional units, called derived units, which can always be represented as products of powers of the base units. Twenty-two derived units have been provided with special names and symbols. The seven base units and the 22 derived units with special names and symbols may be used in combination to express other derived units, which are adopted to facilitate measurement of diverse quantities. The SI system also provides twenty prefixes to the unit names and unit symbols that may be used when specifying power-of-ten multiples and sub-multiples of SI units. The SI is intended to be an evolving system; units and prefixes are created and unit definitions are modified through international agreement as the technology of measurement progresses and the precision of measurements improves.

SI base unit One of the seven units of measurement that define the Metric System

The SI base units are the standard units of measurement defined by the International System of Units (SI) for the seven base quantities of what is now known as the International System of Quantities: they are notably a basic set from which all other SI units can be derived. The units and their physical quantities are the second for time, the metre for measurement of length, the kilogram for mass, the ampere for electric current, the kelvin for temperature, the mole for amount of substance, and the candela for luminous intensity. The SI base units are a fundamental part of modern metrology, and thus part of the foundation of modern science and technology.

Metrology Science of measurement and its application

Metrology is the scientific study of measurement. It establishes a common understanding of units, crucial in linking human activities. Modern metrology has its roots in the French Revolution's political motivation to standardise units in France, when a length standard taken from a natural source was proposed. This led to the creation of the decimal-based metric system in 1795, establishing a set of standards for other types of measurements. Several other countries adopted the metric system between 1795 and 1875; to ensure conformity between the countries, the Bureau International des Poids et Mesures (BIPM) was established by the Metre Convention. This has evolved into the International System of Units (SI) as a result of a resolution at the 11th Conference Generale des Poids et Mesures (CGPM) in 1960.

History of geodesy Scientific discipline that deals with the measurement and representation of the Earth

Geodesy (/dʒiːˈɒdɨsi/), also named geodetics, is the scientific discipline that deals with the measurement and representation of the Earth. The history of geodesy began in pre-scientific antiquity and blossomed during the Age of Enlightenment.

Unit of length Reference value of length

A unit of length refers to any arbitrarily chosen and accepted reference standard for measurement of length. The most common units in modern use are the metric units, used in every country globally. In the United States the U.S. customary units are also in use. British Imperial units are still used for some purposes in the United Kingdom and some other countries. The metric system is sub-divided into SI and non-SI units.

The standard acceleration due to gravity, sometimes abbreviated as standard gravity, usually denoted by ɡ0 or ɡn, is the nominal gravitational acceleration of an object in a vacuum near the surface of the Earth. It is defined by standard as 9.80665 m/s2. This value was established by the 3rd CGPM and used to define the standard weight of an object as the product of its mass and this nominal acceleration. The acceleration of a body near the surface of the Earth is due to the combined effects of gravity and centrifugal acceleration from the rotation of the Earth ; the total is about 0.5% greater at the poles than at the Equator.

Units of measurement in France

France has a unique history of units of measurement due to the radical decision to invent and adopt the metric system after the French Revolution.

Paris meridian Meridian line running through the Paris Observatory in Paris, France

The Paris meridian is a meridian line running through the Paris Observatory in Paris, France – now longitude 2°20′14.03″ East. It was a long-standing rival to the Greenwich meridian as the prime meridian of the world. The "Paris meridian arc" or "French meridian arc" is the name of the meridian arc measured along the Paris meridian.

Angstrom Unit of length; equals 0.1 nanometre

The angstrom or ångström is a metric unit of length equal to 10−10 m; that is, one ten-billionth of a metre, 0.1 nanometre, or 100 picometres. Its symbol is Å, a letter of the Swedish alphabet.

History of the metre Origins and previous definitions of the SI base unit for measuring length

The history of the metre starts with the scientific revolution that began with Nicolaus Copernicus's work in 1543. Increasingly accurate measurements were required, and scientists looked for measures that were universal and could be based on natural phenomena rather than royal decree or physical prototypes. Rather than the various complex systems of subdivision in use, they also preferred a decimal system to ease their calculations.

Standard (metrology)

In metrology, a standard is an object, system, or experiment that bears a defined relationship to a unit of measurement of a physical quantity. Standards are the fundamental reference for a system of weights and measures, against which all other measuring devices are compared. Historical standards for length, volume, and mass were defined by many different authorities, which resulted in confusion and inaccuracy of measurements. Modern measurements are defined in relationship to internationally standardized reference objects, which are used under carefully controlled laboratory conditions to define the units of length, mass, electrical potential, and other physical quantities.

2019 redefinition of the SI base units Redefinition of the SI base units kilogram, ampere, kelvin, and mole

In 2019, the SI base units were redefined in agreement with the International System of Quantities, effective on the 144th anniversary of the Metre Convention, 20 May 2019. In the redefinition, four of the seven SI base units – the kilogram, ampere, kelvin, and mole – were redefined by setting exact numerical values for the Planck constant, the elementary electric charge, the Boltzmann constant, and the Avogadro constant, respectively. The second, metre, and candela were already defined by physical constants and were not subject to correction to their definitions. The new definitions aimed to improve the SI without changing the value of any units, ensuring continuity with existing measurements. In November 2018, the 26th General Conference on Weights and Measures (CGPM) unanimously approved these changes, which the International Committee for Weights and Measures (CIPM) had proposed earlier that year after determining that previously agreed conditions for the change had been met. These conditions were satisfied by a series of experiments that measured the constants to high accuracy relative to the old SI definitions, and were the culmination of decades of research.

History of the metric system

The history of the metric system began during the Age of Enlightenment with measures of length and weight derived from nature, along with their decimal multiples and fractions. The system became the standard of France and Europe within half a century. Other dimensions with unity ratios were added, and the system went on to be adopted across the world.

Outline of the metric system Overview of and topical guide to the metric system

The following outline is provided as an overview of and topical guide to the metric system – various loosely related systems of measurement that trace their origin to the decimal system of measurement introduced in France during the French Revolution.

Carlos Ibáñez e Ibáñez de Ibero 1st Marquis of Mulhacén

Carlos Ibáñez e Ibáñez de Ibero, 1st Marquis of Mulhacén, was a Spanish divisional general and geodesist. He represented Spain at the 1875 Conference of the Metre Convention and was the first president of the International Committee for Weights and Measures. As a forerunner geodesist and president of the International Geodetic Association, he played a leading role in the worldwide dissemination of the metric system. His activities resulted in the distribution of a platinum and iridium prototype of the metre to all States parties to the Metre Convention during the first meeting of the General Conference on Weights and Measures in 1889. These prototypes defined the metre right up until 1960.