"is commonly modeled as a sphere flattened 0.336% along its axis. This makes the Equator 0.16% longer than a meridian (a great circle passing through the two poles). The IUGG standard meridian is, to the nearest millimetre, , one arc-minute of which is , explaining the SI standardization of the nautical mile as , more than less than the geographical mile. The sea-level surface of the Earth (the geoid) is irregular, so the actual length of the Equator is not so easy to determine. ""Aviation Week and Space Technology"" on 9 October 1961 reported that measurements using the Transit IV-A"
"on the circumference of the Earth, explaining the advantages of a system based on nature. Mouton's publication appeared two years after John Wilkins, then president of the Royal Society, published a similar proposal. His suggestion was a unit, the ""milliare"", that was defined as a minute of arc along a meridian arc, and a system of sub-units, dividing successively by factors of ten into the ""centuria"", ""decuria"", ""virga"", ""virgula"", ""decima"", ""centesima"", and ""millesima"". The ""virga"", 1/1000 of a minute of arc, corresponding to 64.4 Bologna inches, or ~2.04 m, was reasonably close to the then current unit of length, the"
"of 10 hours to the day, 100 minutes to the hour and 100 seconds to the minute - introduced in 1793. Instead of the seconds pendulum method, the commission – whose members included Lagrange, Laplace, Monge and Condorcet – decided that the new measure should be equal to one ten-millionth of the distance from the North Pole to the Equator (the quadrant of the Earth's circumference), measured along the meridian passing through Paris. Apart from the obvious consideration of safe access for French surveyors, the Paris meridian was also a sound choice for scientific reasons: a portion of the quadrant"
"Metre The metre (British spelling and BIPM spelling) or meter (American spelling) (from the French unit ""mètre"", from the Greek noun μέτρον, ""measure"") is the base unit of length in some metric systems, including 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 second. The metre was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole – as a result the Earth's circumference is approximately 40,000 km today. In 1799, it was"
"astronomer, published the book ""Observationes diametrorum solis et lunae apparentium"" in which he proposed a decimal system of measurement of length for use by scientists in international communication, to be based on the dimensions of the Earth. The milliare would be defined as a minute of arc along a meridian and would be divided into 10 centuria, the centuria into 10 decuria and so on, successive units being the virga, virgula, decima, centesima, and the millesima. Mouton used Riccioli's estimate that one degree of arc was 321,185 Bolognese feet, and his own experiments showed that a pendulum of length one"
"arc). Although not an SI unit for either time or angle, the minute is accepted for use with SI units for both. The SI symbols for ""minute"" or ""minutes"" are min for time measurement, and the prime symbol after a number, e.g. 5′, for angle measurement. The prime is also sometimes used informally to denote minutes of time. One of the earliest known uses of the minute (and the second) is found in John of Sacrobosco's ""Computus"" (ca. 1235), where he used them when discussing the length of the tropical year. No earlier records for the origin of the minute"
"Meridian arc In geodesy, a meridian arc measurement is the distance between two points with the same longitude, i.e., a segment of a meridian curve or its length. Two or more such determinations at different locations then specify the shape of the reference ellipsoid which best approximates the shape of the geoid. This process is called the determination of the figure of the Earth. The earliest determinations of the size of a spherical Earth required a single arc. The latest determinations use astro-geodetic measurements and the methods of satellite geodesy to determine the reference ellipsoids. Those interested in accurate expressions"
"were the names of units of measure that were in use at the time. In 1670, Gabriel Mouton published a proposal that was in essence similar to Wilkins' proposal, except that his base unit of length would have been 1/1000 of a minute of arc (about 1.852 m) of geographical latitude. He proposed calling this unit the virga. Rather than using different names for each unit of length, he proposed a series of names that had prefixes, rather like the prefixes found in SI. In 1790, Thomas Jefferson submitted a report to the United States Congress in which he proposed"
"metric measures, and describe the ""direction"" of the local normal to the reference ellipsoid of revolution. This is ""approximately"" the same as the direction of the plumbline, i.e., local gravity, which is also the normal to the geoid surface. For this reason, astronomical position determination – measuring the direction of the plumbline by astronomical means – works fairly well provided an ellipsoidal model of the figure of the Earth is used. One geographical mile, defined as one minute of arc on the equator, equals 1,855.32571922 m. One nautical mile is one minute of astronomical latitude. The radius of curvature of"
"of a foot"" and ""sub-divided into lots of one mile square each, or 850 and 4-10ths of an acre"". The Danish and German geographical mile (""geografisk mil"" and ""geographische Meile"" or ""geographische Landmeile"", respectively) is 4 minutes of arc, and was defined as approximately 7421.5 metres by the astronomer Ole Rømer of Denmark. In Norway and Sweden, this 4-minute geographical mile was mainly used at sea (""sjømil""), up to the beginning of the 20th century. Geographical mile The geographical mile is a unit of length determined by 1 minute of arc along the Earth's equator. For the 1924 International Spheroid"
"by Spain. In Ecuador, they split into two groups, traveling overland through rain forests, arriving in Quito in June 1736. Bouguer, La Condamine, Godin and their colleagues measured arcs of the Earth’s curvature on the Equator from the plains near Quito to the southern city of Cuenca. These measurements enabled the first accurate determination of the size of the Earth, eventually leading to the establishment of the international metric system of measurement. La Condamine established the length of a pendulum beating seconds on the Equator near Quito, and he proposed this for the universal unit of measure. He had a"
". It is approximately equal to one milliradian ( ). A mil measuring of a revolution originated in the imperial Russian army, where an equilateral chord was divided into tenths to give a circle of 600 units. This may be seen on a lining plane (an early device for aiming indirect fire artillery) dating from about 1900 in the St. Petersburg Museum of Artillery. Degree (angle) A degree (in full, a degree of arc, arc degree, or arcdegree), usually denoted by ° (the degree symbol), is a measurement of a plane angle, defined so that a full rotation is 360"
"of seven seconds per day. British astronomers have long used the Royal Observatory as a basis for measurement. Four separate meridians have passed through the buildings, defined by successive instruments. The basis of longitude, the meridian that passes through the Airy transit circle, first used in 1851, was adopted as the world's Prime Meridian at the International Meridian Conference on 22 October 1884 (voting took place on 13 October). Subsequently, nations across the world used it as their standard for mapping and timekeeping. The Prime Meridian was marked by a brass (later replaced by stainless steel) strip in the Observatory's"
"of the quarter meridian as the unit of length, and named it ""metre"". Initially a ""provisional"" value was used, based on the old meridian measurement by Lacaille (1740). In 1793 the commission defined the unit of mass as a cubic decimetre of distilled water at 0 °C, and gave it the name ""grave"". Two supplemental unit names, gravet (0.001 grave), and bar (1000 grave), were added to cover the same range as the old units, resulting in the following decimal series of units: milligravet, centigravet, decigravet, gravet, centigrave, decigrave, grave, centibar, decibar, bar. The mass of a unit volume of"
"degree of the meridian arc with a margin of error of only 4%, when the current error at the time varied between 7 and 15%. Jean Picard performed the first modern meridian arc measurement in 1669–1670. He measured a baseline using wooden rods, a telescope (for his angular measurements), and logarithms (for computation). Jacques Cassini later continued Picard's arc (Paris meridian arc) northward to Dunkirk and southward to the Spanish border. Cassini divided the measured arc into two parts, one northward from Paris, another southward. When he computed the length of a degree from both chains, he found that the"
"Nautical mile A nautical mile (also known as an air mile) is a unit of measurement defined as exactly . Historically, it was defined as one minute of latitude, which is one sixtieth of a degree of latitude – i.e. since a minute of a degree is x = , the Earth's polar circumference is approximately 21,600 nautical miles. It is a non-SI unit which today has a continued use in both air and marine navigation, and for the definition of territorial waters. There is no single internationally agreed symbol. While using M itself, the International Bureau of Weights and"
"Quito. When an International Commission for Weights and Measures was convened in Paris to settle the true length of the metre, it adopted on 22 June 1799 a standard metre based on the length of a pendulum beating seconds on the Equator as established by La Condamine and his colleagues in 1742. They completed their survey measurements by 1739, measuring the length of a meridian arc of three degrees at the Equator. They did this in spite of earlier news that the expedition to Lapland led by Maupertuis had already finished their work and had proven that the Earth is"
"should have been, the metre has always been based on the length of the bar rather than the half meridian. The SI unit of area is the square metre (m), but when the metric system was first introduced in 1795, the unit of land measure was defined as the ""are"", being 100 m (or the area equivalent to that of a square having sides of 10 m). This measure was only used in a few countries, but the hectare (100 ares or 10,000 m), is a non-SI unit that has been catalogued as being acceptable for use with the SI"
"The length of 1 minute of latitude is (1.00 nautical miles), while the length of 1 second of latitude is (see nautical mile). In 1687 Isaac Newton published the ""Philosophiæ Naturalis Principia Mathematica"", in which he proved that a rotating self-gravitating fluid body in equilibrium takes the form of an oblate ellipsoid. (This article uses the term ""ellipsoid"" in preference to the older term ""spheroid"".) Newton's result was confirmed by geodetic measurements in the 18th century. (See Meridian arc.) An oblate ellipsoid is the three-dimensional surface generated by the rotation of an ellipse about its shorter axis (minor axis). ""Oblate"
"of latitude is not constant, but about at the poles and at the Equator, with a mean value of . Other countries measure the minute of arc at 45 degrees latitude, giving the nautical mile a length of . In 1929, the international nautical mile was defined by the First International Extraordinary Hydrographic Conference in Monaco as precisely 1,852 metres. Imperial units and United States customary units used a definition of the nautical mile based on the Clarke (1866) Spheroid. The United States nautical mile was defined as based in the Mendenhall Order foot of 1893. It was abandoned in"
"meridian arc comprised between Dunkirk and Barcelona) by Delambre and Méchain. In 1860, the Russian Government at the instance of Otto Sturves invited the Governments of Belgium, France, Prussia and England to connect their triangulations in order to measure the length of an arc of parallel in latitude 52° and to test the accuracy of the figure and dimensions of the Earth, as derived from the measurements of arc of meridian. In order to combine the measurements, it was necessary to compare the geodetic standards of length used in the different countries. The British Government invited those of France, Belgium,"
") is known as the geographical mile. Nautical mile A nautical mile (also known as an air mile) is a unit of measurement defined as exactly . Historically, it was defined as one minute of latitude, which is one sixtieth of a degree of latitude – i.e. since a minute of a degree is x = , the Earth's polar circumference is approximately 21,600 nautical miles. It is a non-SI unit which today has a continued use in both air and marine navigation, and for the definition of territorial waters. There is no single internationally agreed symbol. While using M"
"France adopted this definition of the metre as its official unit of length based on provisional results from this expedition. However, it was later determined that the first prototype metre bar was short by about 200 micrometres because of miscalculation of the flattening of the Earth, making the prototype about 0.02% shorter than the original proposed definition of the metre. Regardless, this length became the French standard and was progressively adopted by other countries in Europe. Earth's circumference Earth's circumference is the distance around the Earth, either around the equator () or around the poles (). Measurement of Earth's circumference"
"Introduction to the metric system The metric system was developed during the French Revolution to replace the various measures previously used in France. The metre (sometimes spelled ""meter"" in American English) is the unit of length in the metric system and was originally based on the dimensions of the earth, as far as it could be measured at the time. The litre (also spelled ""liter""), is the unit of volume and was defined as one thousandth of a cubic metre. The metric unit of mass is the kilogram and it was defined as the mass of one litre of water."
"a geoid, which literally means ""Earth-shaped"". Despite these issues, in 1793 France adopted this definition of the metre as its official unit of length based on provisional results from this expedition. However, it was later determined that the first prototype metre bar was short by about 200 micrometres because of miscalculation of the flattening of the Earth, making the prototype about 0.02% shorter than the original proposed definition of the metre. Regardless, this length became the French standard and was progressively adopted by other countries in Europe. The expedition was fictionalised in Denis Guedj, ""Le mètre du Monde"". Ken Alder"
"latitude is 1 nautical mile. The example above would be given as 40° 11.25′ (commonly written as 11′25 or 11′.25). The older system of thirds, fourths, etc., which continues the sexagesimal unit subdivision, was used by al-Kashi and other ancient astronomers, but is rarely used today. These subdivisions were denoted by writing the Roman numeral for the number of sixtieths in superscript: 1 for a ""prime"" (minute of arc), 1 for a second, 1 for a third, 1 for a fourth, etc. Hence the modern symbols for the minute and second of arc, and the word ""second"" also refer to"
"Minute The Minute is a unit of time or angle. As a unit of time, the Minute is most of times equal to (the first sexagesimal fraction) of an hour, or 60 seconds. In the UTC time standard, a minute on rare occasions has 61 seconds, a consequence of leap seconds (there is a provision to insert a negative leap second, which would result in a 59-second minute, but this has never happened in more than 40 years under this system). As a unit of angle, the minute of arc is equal to of a degree, or 60 seconds (of"
"one, based on a measurement at the latitude of Paris, the French decided to use the length of a meridian of the Earth instead of a seconds pendulum. This and other developments changed what had promised to be an internationally developed system into a strictly French project. Jefferson wrote, ""The element of measure adopted by the National Assembly excludes, ""ipso facto"", every nation on earth from a communion of measurement with them."" The Senate continued to consider Jefferson's two proposals, along with a number of new proposals, for several years. In 1795 a bill titled ""An Act directing certain experiments"
"of the angle (and time due to Earth's fairly regular rotation, approximately equal to the time) between the observation of two objects at the same, or similar declination. The hour circles (meridians) are measured in hours (or hours, minutes, and seconds); one rotation (360°) is equivalent to 24 hours; 1 hour is equivalent to 15°. An astronomical meridians follow the same concept and, almost precisely, orientation of a meridian (also known as longitude) on a globe. Hour circle In astronomy, the hour circles, which together with declination and distance (from the planet's centre of mass) locate any celestial object, is"
"Geodetic Latitude: 25° 20′ 08.29″ Distance in kilometres: 2,821.853 ± 0.012 Struve Geodetic Arc The Struve Geodetic Arc is a chain of survey triangulations stretching from Hammerfest in Norway to the Black Sea, through ten countries and over 2,820 km, which yielded the first accurate measurement of a meridian. The chain was established and used by the German-born Russian scientist Friedrich Georg Wilhelm von Struve in the years 1816 to 1855 to establish the exact size and shape of the earth. At that time, the chain passed merely through two countries: Union of Sweden-Norway and the Russian Empire. The Arc's"
"kilometers of distance at the equator; 1 centigrad of arc equaled 1 kilometer; 0.1 cc (centi-centigrads) of arc equaled 1 meter. The Gradian is sometimes used in surveying in some parts of the world. Subdivisions of the gradian used in surveying can be referred to as c (short for centigrad) and cc (effectively centi-centigrad), where 1 c = 0.01 grad and 1 cc = 0.0001 grad. Gradian The gradian is a unit of measurement of an angle, equivalent to formula_1 of a turn, formula_2 of a degree, or formula_3 of a radian. The gradian is defined as formula_4 of the"
"the mesures usuelles system, such that 1m was exactly toise. The Russian verst was 1.0668km. The Swedish mil was 10.688km, but was changed to 10km when Sweden converted to metric units. Metre The metre (British spelling and BIPM spelling) or meter (American spelling) (from the French unit ""mètre"", from the Greek noun μέτρον, ""measure"") is the base unit of length in some metric systems, including 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 second. The metre was originally defined"
"Arabic mile The Arab, Arabic, or Arabian mile (, ""al-mīl"") was a historical Arabic unit of length. Its precise length is disputed, lying between 1.8 and 2.0 km. It was used by medieval Arab geographers and astronomers. The predecessor of the modern nautical mile, it extended the Roman mile to fit an astronomical approximation of 1 minute of an arc of latitude measured along a north-south meridian. The distance between two pillars whose latitudes differed by 1 degree in a north-south direction was measured using sighting pegs along a flat desert plane. There were 4000 cubits in an Arabic mile."