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The Green Meridian — Part 1: History - Chuck Fisher's LiveJournal [entries|archive|friends|userinfo]
From Bay Area to Barcelona

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The Green Meridian — Part 1: History [ Wednesday, 12 Dec 07 | 10:29 ]
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[My Location |El Masnou (Barcelona) España]
[My Mood |geekygeeky]

El monòlit del Meridià Verd

Nearly a year ago I received a flyer from the Ajuntament about the Inaugurat el monòlit del Meridià Verd.

The inaugration of the monolith of the Green Meridian where it reaches the Sea along the Ocata beach here in El Masnou. This sent me scurrying to Wikipedia to learn about the Green Meridian and it’s importance in the history of science.

The Green Meridian or Paris Meridian is a meridian line running through Paris, now longitude 2°20′14.025″ east. It was a long-standing rival to Greenwich as the prime meridian of the world. We all know which meridian won that rivalry. The Green Meridian was used to determine the length of the meter.

The Metric System

The metric system is a decimalized system of measurement based on the meter and the gram. One goal of the metric system is to have a single unit for any physical quantity. All lengths and distances, for example, are measured in meters, or thousandths of a meter (millimeteres), or thousands of meters (kilometers), and so on. There is no profusion of different units with different conversion factors, such as inches, feet, yards, fathoms, rods, chains, furlongs, miles, nautical miles, leagues, etc. Only three countries use non-metric measurement systems; Liberia, Myanmar, and the United States.

(Metrication in the United States has been unsteady. In some fields, the metric system has been used in the United States since the early 1800s. The use of metric units has been gradually increasing for many years, but much of the public momentum has been lost since the 1980s, except in schools, science, and manufacturing.)

The definition of the meter

In the eighteenth century, there were two favored approaches to the definition of the standard unit of length. One suggested defining the meter as the length of a pendulum with a half-period of one second. The other suggested defining the meter as one ten-millionth of the length of the Earth's meridian along a quadrant, that is the distance from the equator to the north pole.

In 1791, the French Academy of Sciences selected the meridional definition over the pendular definition because the force of gravity varies slightly over the surface of the Earth, which affects the period of a pendulum. In order to establish a universally accepted foundation for the definition of the meter, measurements of this meridian more accurate than those available at that time were imperative.

The Bureau des Longitudes commissioned an expedition led by Delambre and Pierre Méchain, lasting from 1792 to 1799, which measured the length of the meridian between Dunkerque and El Masnou. This portion of the meridian, which also passes through Paris, was to serve as the basis for the length of the quarter meridian, connecting the North Pole with the Equator. So, the circumference of the Earth through the poles is approximately forty million meters. Even though, during the years of the measurement, hostilities broke out between France and Spain, the development of such a standard was considered of such value that Spanish troops escorted the French team while in Spanish territory to ensure their safety.

Next: The Green Meridian today