The METRIC SYSTEM is an internationally agreed decimal system of
measurement . It was originally based on the _mètre des Archives _
and the _kilogramme des Archives _ introduced by the French First
Republic in 1799, but over the years the definitions of the metre and
the kilogram have been refined, and the metric system has been
extended to incorporate many more units. Although a number of variants
of the metric system emerged in the late nineteenth and early
twentieth centuries, the term is now often used as a synonym for "SI"
or the "
The metric system has been officially sanctioned for use in the
Although the originators intended to devise a system that was equally accessible to all, it proved necessary to use prototype units in the custody of national or local authorities as standards. Control of the prototype units of measure was maintained by the later French governments until 1875, when it was passed to an international intergovernmental organisation , the General Conference on Weights and Measures (CGPM). From its beginning, the main features of the metric system were the standard set of interrelated base units and a standard set of prefixes in powers of ten. These base units are used to derive larger and smaller units that could replace a huge number of other units of measure in existence. Although the system was first developed for commercial use, the development of coherent units of measure made it particularly suitable for science and engineering. The uncoordinated use of the metric system by different scientific
and engineering disciplines, particularly in the late 19th century,
resulted in different choices of base units even though all were based
on the same definitions of the units of the metre and the kilogram .
During the 20th century, efforts were made to rationalise these units,
and in 1960, the
CONTENTS * 1 Features * 1.1 Universality
* 1.2
* 1.3 Realisability and replicable prototypes * 1.3.1
* 1.4 Coherence * 2 History * 2.1 Original metric system * 2.2 International adoption * 2.3 International standards * 3 Variants * 3.1 Centimetre-gram-second systems
* 3.2 Metre-kilogram-second systems
* 3.3 Metre-tonne-second systems
* 3.4 Gravitational systems
* 3.5
* 4 Relating SI to the real world * 5 Usage around the world * 5.1 Variations in spelling * 5.2 Conversion and calculation incidents * 6 Conversion between SI and legacy units * 7 Future developments * 8 See also * 9 Notes * 10 References * 11 External links FEATURES Although the metric system has changed and developed since its
inception, its basic concepts have hardly changed. Designed for
transnational use, it consisted of a basic set of units of
measurement, now known as base units .
UNIVERSALITY Chinese road sign listing distances on an expressway in eastern Beijing . Although the primary text is in Chinese, the distances use internationally recognised characters. At the outbreak of the
The metric system was designed to be universal—in the words of the
French philosopher
When the French Government first investigated the idea of overhauling
their system of measurement, the concept of universality was put into
practice in 1789: Maurice de Talleyrand , acting on Condorcet's
advice, invited
In languages where the distinction is made, unit names are common nouns (i.e. not proper nouns). They use the character set and follow the grammatical rules of the language concerned, for example _"kilomètre"_, "_kilómetro_", but each unit has a symbol that is independent of language, for example "km" for "kilometer", "V" for "volts" etc. DECIMAL MULTIPLES Main article: metric prefix In the metric system, multiples and submultiples of units follow a
decimal pattern, a concept identified as a possibility in 1586 by
METRIC PREFIXES IN EVERYDAY USE TEXT SYMBOL FACTOR POWER exa E 7018100000000000000♠1000000000000000000 1018 peta P 7015100000000000000♠1000000000000000 1015 tera T 7012100000000000000♠1000000000000 1012 giga G 7009100000000000000♠1000000000 109 mega M 7006100000000000000♠1000000 106 kilo k 7003100000000000000♠1000 103 hecto h 100 102 deca da 10 101 (none) (none) 1 100 deci d 0.1 10−1 centi c 0.01 10−2 milli m 0.001 10−3 micro μ 6994100000000000000♠0.000001 10−6 nano n 6991100000000000000♠0.000000001 10−9 pico p 6988100000000000000♠0.000000000001 10−12 femto f 6985100000000000000♠0.000000000000001 10−15 atto a 6982100000000000000♠0.000000000000000001 10−18 * v * t * e A common set of decimal-based prefixes that have the effect of
multiplication or division by an integer power of ten can be applied
to units that are themselves too large or too small for practical use.
The concept of using consistent classical (
In the early days, multipliers that were positive powers of ten were given Greek-derived prefixes such as _kilo-_ and _mega-_, and those that were negative powers of ten were given Latin-derived prefixes such as _centi-_ and _milli-_. However, 1935 extensions to the prefix system did not follow this convention: the prefixes _nano-_ and _micro-_, for example have Greek roots. During the 19th century the prefix _myria-_ , derived from the Greek word μύριοι (_mýrioi_), was used as a multiplier for 7004100000000000000♠10000. When applying prefixes to derived units of area and volume that are expressed in terms of units of length squared or cubed, the square and cube operators are applied to the unit of length including the prefix, as illustrated below. 1 mm2 (square millimetre) = (1 mm)2 = (0.001 m)2 = 6994100000000000000♠0.000001 m2 1 km2 (square kilometre ) = (1 km)2 = (1000 m)2 = 7006100000000000000♠1000000 m2 1 mm3 (cubic millimetre) = (1 mm)3 = (0.001 m)3 = 6991100000000000000♠0.000000001 m3 1 km3 (cubic kilometre) = (1 km)3 = (1000 m)3 = 7009100000000000000♠1000000000 m3 Prefixes are not usually used to indicate multiples of a second greater than 1; the non-SI units of minute , hour and day are used instead. On the other hand, prefixes are used for multiples of the non-SI unit of volume, the litre (l, L) such as millilitres (ml). REALISABILITY AND REPLICABLE PROTOTYPES The METRE was originally defined to be one ten millionth of the
distance between the
The base units used in the metric system must be realisable , ideally
with reference to natural phenomena rather than unique artefacts .
Each of the base units in SI is accompanied by a _mise en pratique_
published by the
In the original version of the metric system the base units could be
derived from a specified length (the metre) and the weight of a
specified volume ( 1⁄7003100000000000000♠1000 of a cubic metre)
of pure water. Initially the _de facto_ French Government of the day,
the _Assemblée nationale constituante_ , considered defining the
metre as the length of a pendulum that has a period of one second at
45°N and an altitude equal to sea level . The altitude and latitude
were specified to accommodate variations in gravity ; the specified
latitude was a compromise between the latitude of London (51° 30'N),
Paris (48° 50'N) and the median parallel of the
The available technology of the 1790s made it impracticable to use
these definitions as the basis of the kilogram and the metre, so
prototypes that represented these quantities insofar as was
practicable were manufactured. On 22 June 1799 these prototypes were
adopted as the definitive reference pieces, deposited in the _Archives
nationales_ and became known as the _mètre des Archives _ and the
_kilogramme des Archives _. Copies were made and distributed around
France. :266–269 These artefacts were replaced in 1889 by the new
prototypes manufactured under international supervision. Insofar as
was possible, the new prototypes were exact copies of the original
prototypes, but used a later technology to ensure better stability.
One of each of the kilogram and metre prototypes were chosen by lot to
serve as the definitive international reference piece with the
remainder being distributed to signatories of the
Other Base Units None of the other base units rely on a prototype – all are based on phenomena that are directly observable and had been in use for many years before formally becoming part of the metric system. The second first became a _de facto_ base unit within the metric
system when, in 1832,
The CGS absolute unit of electric current , the abampere , had been
defined in terms of the force between two parallel current-carrying
wires in 1881. In the 1940s, the International Electrotechnical
Commission adopted an MKS variant of this definition for the ampere ,
which was adopted in 1948 by the
When the mole and the candela were accepted by the
COHERENCE Main article:
Each variant of the metric system has a degree of coherence—the various derived units are directly related to the base units without the need for intermediate conversion factors. For example, in a coherent system the units of force , energy and power are chosen so that the equations _force_ _= mass_ _× acceleration_ _energy_ _= force_ _× distance_ _power_ _= energy_ _÷ time_ hold without the introduction of unit conversion factors. Once a set of coherent units have been defined, other relationships in physics that use those units will automatically be true. Therefore, Einstein\'s mass-energy equation , _E_ = _mc_2, does not require extraneous constants when expressed in coherent units. The CGS system had two units of energy, the erg that was related to mechanics and the calorie that was related to thermal energy ; so only one of them (the erg) could bear a coherent relationship to the base units. Coherence was a design aim of SI resulting in only one unit of energy being defined – the joule . In SI, which is a coherent system, the unit of power is the "watt ," which is defined as "_one_ joule per second". In the US customary system of measurement, which is non-coherent, the unit of power is the "horsepower ", which is defined as "550 foot-pounds per second" (the pound in this context being the pound-force ). Similarly, neither the US gallon nor the imperial gallon is _one_ cubic foot or _one_ cubic yard— the US gallon is 231 cubic inches and the imperial gallon is 277.42 cubic inches. The concept of coherence was only introduced into the metric system in the third quarter of the 19th century; in its original form the metric system was non-coherent—in particular the litre was 0.001 m3 and the are (from which the hectare derives) was 100 m2. However the units of mass and length were related to each other through the physical properties of water, the gram having been designed as being the mass of one cubic centimetre of water at its freezing point. HISTORY Main article:
In 1585 the Flemish mathematician
One of the earliest proposals for a decimal system in which length ,
area , volume and mass were linked to each other was made by John
Wilkins , first secretary of the
In pre-revolutionary Europe, each state had its own system of units
of measure. Some countries, such as
Initially
ORIGINAL METRIC SYSTEM The French law of 18 Germinal, Year III (7 April 1795) defined five units of measure: * The _mètre _ for length * The _are_ (100 m2) for area * The _stère _ (1 m3) for volume of stacked firewood * The _litre _ (1 dm3) for volumes of liquid * The _gramme _ for mass. This system continued the tradition of having separate base units for geometrically related dimensions, e.g., _mètre _ for lengths, _are_ (100 m2) for areas, _stère _ (1 m3) for dry capacities, and _litre _ (1 dm3) for liquid capacities. The _hectare _, equal to a hundred _ares _, the area of a square 100 metres on a side (about 2.47 acres ), is still in use. The early metric system included only a few prefixes from _milli _ (one thousandth) to _myria _ (ten thousand). Originally the _kilogramme_ , defined as being one _pinte_ (later renamed the _litre_) of water at the melting point of ice, was called the _grave_; the _gramme_ being an alternative name for a thousandth of a _grave_. However, the word _grave_, being a synonym for the title "count ", had aristocratic connotations and was renamed the _kilogramme_. The name _mètre_ was suggested by Auguste-Savinien Leblond in May 1790. : 92
INTERNATIONAL ADOPTION Main article:
Areas annexed by
In 1817, the
The _
By 1920, countries comprising 22% of the world's population, mainly English-speaking, used the imperial system or the closely related US customary system; 25% used mainly the metric system and the remaining 53% used neither. In 1927, several million people in the
INTERNATIONAL STANDARDS In 1861 a committee of the British Association for Advancement of
Science (BAAS) including William Thomson (later Lord
On 20 May 1875 an international treaty known as the _Convention du
Mètre_ (
*
In 1881 first International Electrical Congress adopted the BAAS
recommendations on electrical units, followed by a series of
congresses in which further units of measure were defined and the
VARIANTS A number of variants of the metric system evolved, all using the _Mètre des Archives_ and _Kilogramme des Archives_ (or their descendants) as their base units, but differing in the definitions of the various derived units. VARIANTS OF THE METRIC SYSTEM QUANTITY CGS MKS MTS distance, displacement, length, height, etc. (_d_, X, _l_, _h_, etc.) centimetre (cm) metre (m) metre mass (_m_) gram (g) kilogram (kg) tonne (t) time (_t_) second (s) second second speed, velocity (_v_, V) cm/s m/s m/s acceleration (_a_) gal (Gal) m/s2 m/s2 force (_F_) dyne (dyn) newton (N) sthene (sn) pressure (_P_ or _p_) barye (Ba) pascal (Pa) pièze (pz) energy (_E_, _Q_, _W_) erg (erg) joule (J) kilojoule (kJ) power (_P_) erg/s watt (W) kilowatt (kW) viscosity (_µ_) poise (p) Pa·s pz·s CENTIMETRE-GRAM-SECOND SYSTEMS The centimetre gram second system of units (CGS) was the first
coherent metric system, having been developed in the 1860s and
promoted by Maxwell and Thomson. In 1874, this system was formally
promoted by the British Association for the Advancement of Science
(BAAS). The system's characteristics are that density is expressed in
g/cm3, force expressed in dynes and mechanical energy in ergs .
METRE-KILOGRAM-SECOND SYSTEMS The CGS units of electricity were cumbersome to work with. This was
remedied at the 1893 International Electrical Congress held in Chicago
by defining the "international" ampere and ohm using definitions based
on the metre , kilogram and second . In 1901,
The
METRE-TONNE-SECOND SYSTEMS The metre-tonne-second system of units (MTS) was based on the metre,
tonne and second – the unit of force was the sthène and the unit of
pressure was the pièze . It was invented in
GRAVITATIONAL SYSTEMS Gravitational metric systems use the kilogram-force (kilopond) as a
base unit of force, with mass measured in a unit known as the hyl ,
_Technische
INTERNATIONAL SYSTEM OF UNITS Main articles:
The 9th
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
The formal definition of
RELATING SI TO THE REAL WORLD Main article:
Although SI, as published by the CGPM, should, in theory, meet all
the requirements of commerce, science and technology, certain units of
measure have acquired such a position within the world community that
it is likely they will be used for many years to come. In order that
such units are used consistently around the world, the
* NON-SI UNITS ACCEPTED FOR USE WITH THE INTERNATIONAL SYSTEM OF
UNITS (TABLE 6). This list includes the hour and minute, the angular
measures (degree, minute and second of arc) and the historic metric
units, the litre , tonne and hectare (originally agreed by the
USAGE AROUND THE WORLD Further information:
_ This article MAY OVERUSE OR MISUSE COLOR, MAKING IT HARD TO UNDERSTAND FOR COLOR-BLIND USERS. Please remove or fix instances of distracting or hard-to-read colors. See the category page and WP:COLOR for guidelines. (February 2015)_ Countries by date of metrication. Colours red to green show the pattern of metrication from 1795 to 1998. Black identifies countries that have not adopted the metric system as the primary measurement system. White identifies countries that already used the metric system at the time they gained their independence The usage of the metric system varies around the world. According to
the US Central Intelligence Agency's _Factbook _ (2007), the
In the
In the countries of the
Some other jurisdictions, such as Hong Kong, have laws mandating or permitting other systems of measurement in parallel with the metric system in some or all contexts. VARIATIONS IN SPELLING The SI symbols for the metric units are intended to be identical, regardless of the language used but unit names are ordinary nouns and use the character set and follow the grammatical rules of the language concerned. For example, the SI unit symbol for kilometre is "km" everywhere in the world, even though the local language word for the unit name may vary. Language variants for the kilometre unit name include: _chilometro_ (Italian), _Kilometer_ (German), _kilometer_ (Dutch), _kilomètre_ (French), _χιλιόμετρο_ (Greek), _quilómetro/quilômetro_ (Portuguese), _kilómetro_ (Spanish) and _километр_ (Russian). Variations are also found with the spelling of unit names in
countries using the same language, including differences in American
English and British spelling . For example, _meter_ and _liter_ are
used in the
CONVERSION AND CALCULATION INCIDENTS The dual usage of or confusion between metric and non-metric units has resulted in a number of serious incidents. These include: * Flying an overloaded American International Airways aircraft from
CONVERSION BETWEEN SI AND LEGACY UNITS Main article:
During its evolution, the metric system has adopted many units of measure. The introduction of SI rationalised both the way in which units of measure were defined and also the list of units in use. These are now catalogued in the official SI Brochure. The table below lists the units of measure in this catalogue and shows the conversion factors connecting them with the equivalent units that were in use on the eve of the adoption of SI. QUANTITY DIMENSION SI UNIT AND SYMBOL LEGACY UNIT AND SYMBOL Conversion factor
Power _L_2_MT_−3 watt (W) (erg/s) horsepower (HP) Pferdestärke (PS) 10−7 745.7 735.5
Potential difference _L_2_MT_−3_I_−1 volt (V) international volt abvolt statvolt 7000100034000000000♠1.00034 10−8 7002299792500000000♠2.997925×102
Electric resistance _L_2_MT_−3_I_−2 ohm (Ω) international ohm abohm statohm 7000100049000000000♠1.00049 10−9 7011898755200000000♠8.987552×1011 Electric conductance _L_−2_M_−1_T_3_I_2 siemens (S) international mho (℧) abmho statmho 6999999510000000000♠0.99951 109 6988111265000000000♠1.112650×10−12
Dynamic viscosity _ML_−1_T_−1 (Pa·s) poise (P) 0.1 Kinematic viscosity _L_2_T_−1 (m2·s−1) stokes (St) 10−4
activity _T_−1 becquerel (Bq) curie (Ci) 7010370000000000000♠3.70×1010 Absorbed dose _L_2_T_−2 gray (Gy) roentgen (R) rad (rad) ≈0.01 0.01 Radiation dose equivalent _L_2_T_−2 sievert roentgen equivalent man (rem) 0.01
The SI Brochure also catalogues certain non-SI units that are widely used with the SI in matters of everyday life or units that are exactly defined values in terms of SI units and are used in particular circumstances to satisfy the needs of commercial, legal, or specialised scientific interests. These units include: QUANTITY DIMENSION UNIT AND SYMBOL EQUIVALENCE
FUTURE DEVELOPMENTS Main article:
After the metre was redefined in 1960, the kilogram was the only SI base unit that relied on a specific artefact. After the 1996–1998 recalibrations a clear divergence between the international and various national prototype kilograms was observed. At the 23rd
* in addition to the speed of light, define four constants of
nature—Planck\'s constant , an elementary charge , Boltzmann
constant and
The
SEE ALSO *
*
* Category:
*
NOTES * ^ _A_ _B_ _C_ _D_ _E_ _F_ The following abbreviations are taken from the French rather than the English language * SI: _Le Système international d\'unités_ * CGPM: _Conférence générale des poids et mesures_ * CIPM: _Comité international des poids et mesures_ * BIPM: _Bureau international des poids et mesures_ * CIE: _Commission Internationale de l\'Eclairage_ * ^ Non-SI units for time and plane angle measurement, inherited
from existing systems, are an exception to the decimal-multiplier rule
* ^ Now called the _degree Celsius_
* ^ An extremely learned or scholarly person –
REFERENCES * ^ _A_ _B_ _C_ _D_ _E_ _F_ _G_ _H_ _I_ _J_ _K_ _L_ _M_ _N_ Alder, Ken (2002). _The Measure of all Things—The Seven-Year-Odyssey that Transformed the World_. London: Abacus. ISBN 0-349-11507-9 . * ^ _A_ _B_ 29th Congress of the United States, Session 1 (13 May 1866). "H.R. 596, An Act to authorize the use of the metric system of weights and measures". Archived from the original on 5 July 2015. Retrieved 27 October 2011. * ^ _A_ _B_ Palaiseau, JFG (October 1816). _Métrologie universelle, ancienne et moderne: ou rapport des poids et mesures des empires, royaumes, duchés et principautés des quatre parties du monde_. Bordeaux. pp. 71–460. Retrieved 30 October 2011. * ^ "pint". Encyclopædia Britannica. 2013. Retrieved 4 April 2013. * ^ _A_ _B_ _C_ _D_ International Bureau of Weights and Measures
(2006), _The
* ^ Good, Michael. "Some Derivations of E = mc2" (PDF). Archived
from the original (PDF) on 7 November 2011. Retrieved 18 March 2011.
* ^ "Horsepower".
EXTERNAL LINKS _ Wikiversity has learning resources about USING THE METRIC SYSTEM _ * CBC Radio Archives For Good Measure: Canada Converts to Metric
* U.S. Metric Association
* v * t * e CURRENT GENERAL *
SPECIFIC * Apothecaries\'
*
NATURAL |

Time at 25056884.216667, Busy percent: -84.45482100551

***************** NOT Too Busy at 25056884.216667 3logs/periodic-service_log.txt