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The metre is the basic unit of length in the . It is defined as the length of the path travelled by light in absolute vacuum during a time interval of 1/299,792,458 of a second. It is equal to 10000/254 inches, approximately 39.37 inches. The symbol of the metre is m. Metre is also spelled meter in American English
millimetre << centimetre << decimetre << metre << decametre << hectometre << kilometreA kilometre ( American spelling: kilometer (symbol: km is a unit of length equal to 1000 metres. It is approximately equal to 0. 621 miles, 1094 yards or 3281 feet. Slang terms for kilometre include " klick" (or "click") and "kay". Click" is also used for
The word itself is from the GreekThe Greek language ( /Elini'k{/) is an Indo-European language which has existed from around the 14th century BC in the Cretan inscriptions called Linear B. Mycenaean Greek of this period is distinguished from later Classical or Ancient Greek of the 8th ce metron (μετρον), "a measureMeasure can mean: To perform a measurement. In mathematics, a measure is a way to assign non-negative real numbers to subsets of a given set, in order to "measure their sizes or probabilities". See measure (mathematics) for a treatment of the concept." via the FrenchFrench le francais la langue francaise is one of the most important Romance languages, outnumbered only by Spanish and Portuguese. French is the 11th most spoken language in the world, spoken by about 77 million people (called Francophones) as a mother to mètre. Its first recorded usage in EnglishThe English language is a West Germanic language, originating from England. It is the third most common "first" language (native speakers), with around 402 million people in 2002. English has lingua franca status in many parts of the world, due to the mil is from 1797Events January 3 The Treaty of Tripoli (a peace treaty between the United States and Tripoli) is signed at Algiers. January 7 The parliament of the Repubblica Cisalpina adopts the Italian Tricolore as official flag: here starts the story of the Flag of It.
In the eighteenth century, there were two favored approaches to the definition of the standard unit of length. One suggested defining the metre as the length of a pendulumA gravity pendulum is a weight on the end of a rigid rod, which, when given some initial lift from the vertical position, will swing back and forth under the influence of gravity over its central (lowest) point. A torsion pendulum consists of a body suspe with a half- periodA period is an arbitrary interval of time. The word is applied to many different concepts: generally, in science, the time taken for one complete cycle of an alternating quantity. The period of oscillation of a wave is the time taken for the wave to compl of one second. The other suggested defining the metre as one ten-millionth of the length of the earth's meridian along a quadrant (one-fourth the polar circumference of the earth). In 1791, the French Academy of Sciences selected the meridional definition, using the meridian of Paris, over the pendular definition because of the slight variation of the force of gravity over the surface of the earth, which affects the period of a pendulum. In 1795, France adopted the metre as its official unit of length. Although the first prototype metre bar was short by a fifth of a millimetre due to miscalculation of the flattening of the earth, this length became the standard. So, the circumference of the Earth through the poles is approximately forty million metres.
In the 1870s and in light of modern precision, a series of international conferences were held to devise new metric standards. The Treaty of the Metre ( 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 organization would preserve the new prototype metre and kilogram when constructed, and would maintain comparisons between them and the basic units of other, nonmetric, weights and measures. This organization created a new prototype bar in 1889, establishing the International Prototype Metre as the distance between two lines on a standard bar of an alloy of ninety percent platinum and ten percent iridium.
In 1893, the standard metre was first measured with an interferometer by Albert A. Michelson, the inventor of the device and an advocate of using some particular wavelength of light as a standard of distance. By 1925, interferometry was in regular use at the BIPM. However, the International Prototype Metre remained the standard until 1960, when the eleventh General Conference on Weights and Measures (CGPM: Conférence Générale des Poids et Mesures) defined the metre in the new SI system as equal to 1,650,763.73 wavelengths of the orange- red emission line in the spectrum of the krypton-86 atom in a vacuum.
To further reduce uncertainty, the seventeenth CGPM of 1983 replaced the definition of the metre with its current definition, thus fixing the length of the metre in terms of time and the speed of light:
Note that this definition exactly fixes the speed of light in a vacuum at 299,792,458 metres per second. Definitions based on the physical properties of light are more precise and reproducible because the properties of light are considered to be universally constant.
The original international prototype of the metre is still kept at the BIPM under the conditions specified in 1889.