Metre Convention
Metre Convention signatories | |
Member states | Associate states |
Former member states | Former associate states |
The Metre Convention (French: Convention du Mètre), also known as the Treaty of the Metre,
The treaty created the
The Metre Convention established a permanent organizational structure for member governments to act in common accord on all matters relating to units of measurement. The governing organs of the BIPM are:
- The General Conference on Weights and Measures (Conférence générale des poids et mesures or CGPM)—the plenary organ of the BIPM which consists of the delegates of all the contracting governments, and
- The International Committee for Weights and Measures (Comité international des poids et mesures or CIPM)—the direction and supervision organ composed of 18 prominent metrologists from 18 different member states
The headquarters or secretariat of the BIPM is at Saint-Cloud, France. It employs around 70 people and hosts BIPM's formal meetings.
Initially the scope of the Metre Convention covered only units of mass and length. In 1921, at the sixth meeting of the CGPM, convention was amended to its scope to other fields in physics. In 1960, at the eleventh meeting of the CGPM, its system of units was named the International System of Units (Système international d'unités, abreviateed SI).[2]
The Metre Convention provides that only nations can be members of the BIPM. In 1999, the CGPM created in the status of associate, to allow non-member states and economic entities to participate in some activities of the BIPM through their national metrology institutes (NMIs).
As of 13 January 2020[update], the CGPM had 62 members and 40 associates.
Membership in the CGPM requires payment of substantial fees. Being in arrears with these payments over a span of years has led to expulsion of some former members.
Background
Before the
Some of Charlemagne's units of measure, such as the pied du Roi (the king's foot) remained virtually unchanged for about a thousand years, while others, such as the aune (ell – used to measure cloth) and the livre (pound) varied dramatically from locality to locality. By the time of the revolution, the number of units of measure had grown to the extent that it was almost impossible to keep track of them.
In England in 1215, clause 25 of Magna Carta required that the same standards of measurement be applied throughout the realm. The wording of the clause emphasized that "There is to be a single measure ... throughout our realm".[3] Five centuries later, when in 1707 England and Scotland were united into a single kingdom, the Scots agreed to use the same units of measure that were already established in England.[4] During the eighteenth century, in order to facilitate trade, Peter the Great, Czar of Russia adopted the English system of measure.[5]
From 1668 to 1776 the French standard of length was the Toise of Châtelet which was fixed outside the Grand Châtelet in Paris. In 1735 two geodetic standards were calibrated against the Toise of Châtelet. One of them, the Toise of Peru was used for the French Geodesic Mission to the Equator. In 1766 the Toise of Peru became the official standard of length in France and was renamed Toise of the Academy (French: Toise de l'Académie).
Profusion of units of measures was a practical problem of importance before the French Revolution and its reform was one of the items on the agenda of
The Helvetic Republic adopted the metric system in 1803.[6] In 1805, a Swiss immigrant Ferdinand Rudolph Hassler brought copies of the French metre and kilogram in the United States. In 1830 the Congress decided to create uniform standards for length and weight in the United States.[citation needed] Hassler was mandated to work out the new standards and proposed to adopt the metric system. The United States Congress opted for the British Parliamentary Standard Yard of 1758 and the British Troy Pound of 1824 as length and weight standards.[citation needed] Nevertheless, the primary baseline of the U.S Survey of the Coast, which was renamed the United States Coast Survey in 1836 and the United States Coast and Geodetic Survey in 1878, was measured in 1834 at Fire Island using four two-metre iron bars constructed after Hassler's specification in the United Kingdom and brought back to the United States in 1815. All distances measured by the Survey of the Coast, Coast Survey, and Coast and Geodetic Survey were referred to the metre.
Between 1840 and 1870, a number of countries definitively adopted the metric system as their system of measure including France, Spain, many South American republics and many of the Italian and German states (the Netherlands had adopted the system in 1817).
In 1852 the Spanish Government was urged by the Spanish Royal Academy of Sciences to approve the creation of a large-scale map of Spain. The following year Carlos Ibáñez e Ibáñez de Ibero was appointed to undertake this task. All the scientific and technical material had to be created. Carlos Ibáñez e Ibáñez de Ibero and Frutos Saavedra Meneses went to Paris to supervise the production by Brunner of a four metres long measuring instrument which they had devised and which they later compared with Borda's double-toise No. 1, which was the main reference for measuring all geodetic bases in France and whose length was 3.8980732 metres.
In 1867 at the second General Conference of the International Association of Geodesy (German: Europäische Gradmessung) held in Berlin, the question of international standard of length was discussed in order to combine the measurements made in different countries to determine the size and shape of the earth.[8] The conference recommended the adoption of the metric system (replacing Bessel's toise, a copy of the Toise of Peru made in 1823) and the creation of an International Metre Commission.[8][9]
In the 1860s, inspections of the prototype metre revealed wear and tear at the measuring faces of the bar and also that the bar was wont to flex slightly when in use.[7] In view of the doubts being cast on the reproducibility of the metre and the kilogram and the threat that a rival standard might be set up, Napoleon III invited scientists from all the world's nations to attend a conference in Paris. In July 1870, two weeks before the conference was due to start, the Franco-Prussian War broke out. Although the delegates did meet (without a German delegation), it was agreed that the conference should be recalled once all the delegates (including the German delegation) were present. The International Metre Commission was established in Paris.[10]
Following the war, which resulted in Napoleon III's exile, Germany and Italy, now unified nations, adopted the metric system as their national system of units, but with the prototype copy of the kilogram and metre under the control of the
1875 conference
The principal tasks facing the delegates at the 1875 conference was the replacement of the existing metre and kilogram artefacts that were held by the French Government and the setting up of an organization to administer the maintenance of standards around the globe. The conference did not concern itself with other units of measure. The conference had undertones of Franco-German political manoeuvring, particularly since the French had been humiliated by the Prussians during the war a few years previously. Although France lost control of the metric system, they ensured that it passed to international rather than German control and that the international headquarters were in Paris.
Reference standards
The conference was called to discuss the maintenance of international standards based on the existing French standards rather than using French standards which, at that time, were 70 years old and which, through wear and tear, might not be exactly the same as when they adopted in 1799.
Prior to the 1870 conference, French politicians had feared that the world community might reject the existing metre as it was 0.03% (300 µm) shorter than its design length, ordering a new
Although the new standard metre had the same value as the old metre, it had an "X" cross-section designed by
The prototype metre was retained as the international standard until 1960 when the metre was redefined in terms of the wavelength of the orange-red line of
On 16 November 2018, the 26th General Conference on Weights and Measures (CGPM) voted unanimously in favour of revised definitions of some SI base units, in particular the kilogram.[18] The new definitions came into force on 20 May 2019, but do not change the metre.[19] [20]
International organization
The Convention created an international organization with two governing organs to facilitate the standardization of weights and measures around the world. The first, the CGPM provides a forum for representative of member states, the second, the CIPM is an advisory committee of metrologists of high standing. The Secretariat or Headquarters provides appropriate meeting and laboratory facilities in support of the CGPM and CIPM.[21]
The structure may be compared to a
General Conference on Weights and Measures
The
International Committee for Weights and Measures
The International Committee for Weights and Measures (Comité international des poids et mesures or CIPM) is made up of eighteen (originally fourteen)[24] individuals from a member state of high scientific standing, nominated by the CGPM to advise the CGPM on administrative and technical matters. It is responsible for the running of ten consultative committees (CCs), each of which investigates different aspects of metrology – one CC discusses the measurement of temperature, another the measurement of mass and so on. The CIPM meets annually at Saint-Cloud to discuss annual reports from the various CCs, to submit an annual report to the governments of member states in respect of the administration and finances of the BIPM and to advise the CGPM on technical matters as and when necessary. Each member of the CIPM is from a different member state – with France, in recognition of its work in setting up the convention, always having one seat on the CIPM.[25][26]
Secretariat of the BIPM
The Secretariat of the
Initially it had a staff of 9, falling to 4 once the initial batch of prototypes had been distributed;[27] in 2012 it had a staff of over 70 people and an annual budget of over €10 million.[28] The director of the BIPM is ex-officio a member of the CIPM and a member of all consultative committees.
Headquarters, language and protocol
The original treaty was written in French and the authoritative language of all official documents is French. Communication between the BIPM and member states is, in the case of France, via the French Foreign Minister and in the case of all other members, via the members' ambassador to France.[29]
The French government offered the treaty members the
Post-1875 developments
The science of metrology has progressed vastly since 1875. In particular the treaty was amended in 1921 with the result that many other international organizations have a forum within the CIPM to ensure harmonization of measurement standards across many disciplines. In addition, what were originally conceived as standards for the purposes of trade have now been extended to cover a large number of aspects of human activity including medicine, science, engineering and technology.
Extensions to the treaty (1921) and development of the SI
The metre convention was originally drawn up with the main purpose of providing standards of length and mass only. Standards relating to other quantities were under the control of other bodies – time was measured by
In 1901 Giorgi published a proposal for building a coherent set of units based on four base units – the metre, kilogram, second and one electrical unit (ampere, volt or ohm). In 1921 the convention was extended to permit the promotion of standards relating to any physical quantity which greatly increased the scope of the CIPM's remit and implicitly giving it freedom to exploit Giorgi's proposals. The 8th CGPM (1933) resolved to work with other international bodies to agree to standards for electrical units that could be related back to the international prototypes.[33] This was agreed in principle by the International Electrotechnical Commission at its congress in Brussels in 1935 subject to the choice of the fourth unit being agreed with, amongst others, the appropriate consultative committee of the CIPM.[34]
In 1948, three years after the end of the
The CIPM's draft proposal, which was an extensive revision and simplification of the metric unit definitions, symbols and terminology based on the MKS system of units, was put to the 10th CGPM in 1954. In the proposal the CIPM recommended that the ampere be the base unit from which electromechanical standards would be derived. After negotiations with the CIS and IUPAP, two further base units, the degree kelvin and the candela were also proposed as base units.[37] The full system and name "Système international d'unités" were adopted at the 11th CGPM.[38] During the years that followed the definitions of the base units and particularly the mise en pratique[39] to realize these definitions have been refined.
The formal definition of International System of Units (SI) along with the associated resolutions passed by the CGPM and the CIPM are published by the BIPM on the Internet and in brochure form at regular intervals. The eighth edition of the brochure Le Système international d'unités – The International System of Units was published in 2006.[40]
The Mutual Recognition Arrangements (CIPM-MRA)
During the 1940s, the United States government recognized the benefits of its suppliers keeping
International trade is hampered by one country not recognising the quality controls in place in other countries – often due to standards being different or being incompatible with each other. At the 20th CGPM (1995), it was recognized that although ad-hoc recognition of instrument calibration between cooperating countries had been taking place for a hundred years, a need had arisen for a more comprehensive agreement. Consequently, the CIPM was mandated to investigate the setting up of a
The CIPM-MRA scheme is to catalogue the capabilities of National Measurement Institutes (NMIs) such as NIST in the United States or the National Physical Laboratory in Britain whose calibration procedures have been peer-assessed. The essential points of CIPM-MRA are:[45]
- The agreement is only open to countries that have signed the Metre Convention, either as full or as associate members.
- A country may have more than one NMI, though only one NMI is chosen as the signatory organization.
- The measurement capabilities of NMI's will be peer-reviewed at regular intervals and each NMI will recognize the measurement capabilities of other NMIs.
- The BIPM maintains a publicly available database of the measurement capabilities of each NMI.
- NMI's
Subsequent to launch of the CIPM MRA and in response to a
Coordination of International Atomic Time
With the advent of the atomic clock it has been possible to define and measure International Atomic Time with sufficient precision that variations in the Earth's rotation can be detected. The International Earth Rotation Service monitors these changes relative to the stars at regular intervals and proposes leap seconds as and when these are needed. Currently there are over 200 atomic clocks in over 50 national laboratories around the world and the BIPM, in terms of the mandate given to it under the Metre Convention, coordinates the various atomic clocks.[48]
New SI
After 1960, when the definition of the metre was linked to a particular wavelength of light rather than the international prototype of the metre, the only unit of measure that remained dependent on a particular artefact was the kilogram. Over the years, small drifts which could be as high as 20×10−9 kilograms per annum in the mass of the international prototype of the kilogram were detected.[49] At the 21st meeting of the CGPM (1999), national laboratories were urged to investigate ways of breaking the link between the kilogram and a specific artefact.
Independently of this drift having been identified, the Avogadro project and development of the Kibble (or watt) balance promised methods of indirectly measuring mass with a very high precision. These projects provided tools that enabled alternative means of redefining the kilogram.[50]
A report published in 2007 by the Consultative Committee for Thermometry to the CIPM noted that their definition of temperature had proved to be unsatisfactory for temperatures below 20 K and for temperatures above 1300 K. The committee was of the view that the Boltzmann constant provided a better basis for temperature measurement than did the triple point of water, as it overcame these difficulties.[51]
Over the next few years the support for natural constants grew and details were clarified,[52][53][54][55][23] until in November 2018, the 26th General Conference on Weights and Measures voted unanimously in favour of revised definitions of the SI base units.[56][57] The 2019 redefinition of the SI base units came into force on the 144th anniversary of the convention, 20 May 2019.[19] [58]
Membership
The CGPM recognizes two classes of membership – full membership for those states that wish to participate in the activities of the BIPM and associate membership for those countries or economies
On 20 May 1875 representatives from seventeen of countries that attended the Conference of the Metre in 1875, signed the Convention of the Metre.[Note 3] In April 1884 HJ Chaney, Warden of Standards in London unofficially contacted the BIPM inquiring whether the BIPM would calibrate some metre standards that had been manufactured in Britain. Broch, director of the BIPM replied that he was not authorized to perform any such calibrations for non-member states. On 17 September 1884, the British Government signed the convention.[62] This number grew to 21 in 1900, 32 in 1950, and 49 in 2001. As of 13 January 2020[update], the General Conference membership was made up of 62 member states, 40 associate states and economies and four international organizations as follows (with year of partnership between brackets):[63]
Member states
Name | Year of partnership | Notes |
---|---|---|
Argentina | 1877 | |
Australia | 1947 | |
Austria | 1875 | Joined originally as Austria-Hungary |
Belarus | 2020 | Belarus was previously an Associate member since 2003 |
Belgium | 1875 | |
Brazil | 1921 | |
Bulgaria | 1911 | |
Canada | 1907 | |
Chile | 1908 | |
China | 1977 | |
Colombia | 2013 | |
Costa Rica | 2022 | |
Croatia | 2008 | |
Czech Republic | 1922 | Joined originally as part of Czechoslovakia |
Denmark | 1875 | |
Ecuador | 2019 | Ecuador was previously an Associate member since 2000 |
Egypt | 1962 | |
Estonia | 2021 | |
Finland | 1923 | |
France | 1875 | |
Germany | 1875 | Joined originally as the German Empire |
Greece | 2001 | |
Hungary | 1925 | |
India | 1957 | |
Indonesia | 1960 | |
Iran | 1975 | |
Iraq | 2013 | |
Ireland | 1925 | Joined originally as the Irish Free State |
Israel | 1985 | |
Italy | 1875 | |
Japan | 1885 | |
Kazakhstan | 2008 | |
Kenya | 2010 | |
Lithuania | 2015 | |
Malaysia | 2001 | |
Mexico | 1890 | |
Montenegro | 2018 | |
Morocco | 2019 | |
Netherlands | 1929 | |
New Zealand | 1991 | |
Norway | 1875 | Joined originally as part of Sweden and Norway |
Pakistan | 1973 | |
Poland | 1925 | |
Portugal | 1876 | |
Romania | 1884 | |
Russian Federation | 1875 | Joined originally as the Russian Empire |
Saudi Arabia | 2011 | |
Serbia | 1879 | Joined as the |
Singapore | 1994 | |
Slovakia | 1922 | Joined originally as part of Czechoslovakia |
Slovenia | 2016 | |
South Africa | 1964[66] | |
South Korea | 1959 | |
Spain | 1875 | |
Sweden | 1875 | Joined originally as part of Sweden and Norway |
Switzerland | 1875 | |
Thailand | 1912 | |
Tunisia | 2012 | |
Turkey | 1875 | Joined originally as the Ottoman Empire |
Ukraine | 2018 | |
United Arab Emirates | 2015 | |
United Kingdom | 1884 | |
United States | 1878 | |
Uruguay | 1908 |
Associates
At its 21st meeting (October 1999), the CGPM created the category of "associate" for those states not yet members of the BIPM and for economic unions.[67]
Country | Year of partnership |
---|---|
Albania | 2007 |
Azerbaijan | 2015 |
Bangladesh | 2010 |
Bolivia | 2008 |
Bosnia and Herzegovina | 2011 |
Botswana | 2012 |
Cambodia | 2005 |
Caribbean Community | 2005 |
Chinese Taipei[68] | 2002 |
Ethiopia | 2018 |
Georgia | 2008 |
Ghana | 2009 |
Hong Kong | 2000 |
Jamaica | 2003 |
Kuwait | 2018 |
Latvia | 2001 |
Luxembourg | 2014 |
Malta | 2001 |
Mauritius | 2010 |
Republic of Moldova | 2007 |
Mongolia | 2013 |
Namibia | 2012 |
North Macedonia[69] | 2006 |
Oman | 2012 |
Panama | 2003 |
Paraguay | 2009 |
Peru | 2009 |
Philippines | 2002 |
Qatar | 2016 |
Seychelles | 2010 |
Sri Lanka | 2007 |
Sudan | 2014 |
Syria | 2012 |
Tanzania | 2018 |
Uzbekistan | 2018 |
Vietnam | 2003 |
Zambia | 2010 |
International organizations
The following international organizations have signed the CIPM MRA:
- International Atomic Energy Agency (IAEA), Vienna, Austria (1999)
- Institute for Reference Materials and Measurements (IRMM), Geel, Belgium (1999)
- World Meteorological Organization (WMO), Geneva, Switzerland (2010)
- European Space Agency (ESA), Paris, France (2012)
Former member states
The following former members were excluded from the organization following failure to pay their arrears over a span of years and upon failing to provide any form of payment plan:[70]
- Cameroon was a member state from 1970[71] until 22 October 2012.[72]
- North Korea was a member state from 1982[73][71] until 2012[70]
- Dominican Republic was a member state from 1954[71] until 31 December 2014.[74]
- Venezuela was a member state from 1879 until 14 November 2018.[75]
- Yemen was an associate from 21 July 2014 until 1 January 2018.[76]
- Cuba was an Associate from 19 December 2000 until 31 December 2021.[77]
- Zimbabwe was an associate from 14 September 2010 until 1 January 2021, and was later reinstated as an associate on 8 February 2022.[78]
See also
- Outline of metrology and measurement
- Metrication
- History of the metre
- Seconds pendulum
- World Metrology Day
Notes
- ^ As of 2012, the only "economy" that was an associate member was CARICOM (Caribbean Community) – its membership comprising Antigua and Barbuda, Saint Kitts and Nevis, Barbados, Saint Lucia, Belize, Saint Vincent and the Grenadines, Dominica, Suriname, Grenada, Trinidad and Tobago and Guyana. Jamaica, although also a member of CARICOM, is an associate of the CGPM in its own right.
- ^ In the case of France, the French Foreign Minister
- Sweden and Norway, Switzerland, Ottoman Empire, United States and Venezuela.
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Further reading
- Chisholm, Hugh, ed. (1911). . Encyclopædia Britannica. Vol. 18 (11th ed.). Cambridge University Press.
- Kershaw, Michael. "The ‘nec plus ultra’ of precision measurement: Geodesy and the forgotten purpose of the Metre Convention." Studies in History and Philosophy of Science Part A 43.4 (2012): 563-576. online[permanent dead link]
- Quinn, Terry. "The Metre Convention and world-wide comparability of measurement results." Accreditation and quality assurance 9.9 (2004): 533–538.
- Stigler, S. The History of Statistics: The Measurement of Uncertainty before 1900 (1986).