Thus, the meter was intended to equal 10-7 or one ten-millionth of the length of the meridian through Paris from pole to the equator. However, the first prototype was short by 0.2 millimeters because researchers miscalculated the flattening of the Earth due to its rotation. Still this length became the standard. In 1889, a new international prototype was made of an alloy of platinum with 10 percent iridium, to within 0.0001, that was to be measured at the melting point of ice. In 1927, the meter was more precisely defined as the distance, at 0°, between the axes of the two central lines marked on the bar of platinum-iridium kept at the International Bureau of Weights and Measures (BIPM), and declared Prototype of the meter by the 1st General Conference on Weights and Measures (CGPM), this bar being subject to standard atmospheric pressure and supported on two cylinders of at least one centimeter diameter, symmetrically placed in the same horizontal plane at a distance of 571 mm from each other.

Posted: July 11th, 2008 under Main.
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The meter is the unit of length in the International System of Units (SI). It is one of the seven SI base units. The origins of the meter go back to at least the 18th century. At that time, there were two competing approaches to the definition of a standard unit of length. Some suggested defining the meter as the length of a pendulum having a half-period of one second; others suggested defining the meter as one ten-millionth of the length of the Earth’s meridian along a quadrant (one-fourth the circumference of the Earth). In 1791, soon after the French Revolution, the French Academy of Sciences chose the meridian definition over the pendulum definition because the force of gravity varies slightly over the surface of the Earth, affecting the period of the pendulum.

Posted: July 11th, 2008 under Main.
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