International Prototype Metre

As a standard meter (French mètre of archives, Archive meter ' ) is defined as the physical scale of the August 1, 1793 first introduced in France dezimalmetrischen length unit meters.

In the intention of the bourgeois Dezimalmeterdefinition one meter should be the ten-millionth part of the quarter of the meridional circumference of the earth, which is about the length of one seconds pendulum.

The term of the standard meter refers in particular to the second specimen of 1799, that the final dimension of platinum iridium, which embodied the unit of length to 1889. In many cases, but also of the international prototype of 1889 meters is called the standard meter.

Production of the first standard meter

On March 26, 1791, the Constituent Assembly in Paris decided to introduce a universal unit of length on a proposal from the Académie des Sciences ( Academy of Sciences). The new, not yet "Meter" said length dimension should be the ten-millionth part of the Erdmeridianquadranten ( distance from the pole to the equator). These should be the meridian arc from Dunkirk to Barcelona by two French astronomers Jean Baptiste Joseph Delambre and Pierre - Méchain, be re-measured, but this lasted into the turmoil of the French Revolution to 1798. 1791 was another proposed definition of Talleyrand and Jefferson, based on a second pendulum, discarded, since this method would have been influenced by local differences of the gravitational acceleration.

On August 1, 1793 under the reign of terror was this measure of length - on a proposal called Bordas meters - introduced by law in the National Convention, but with a provisional value of 443.440 Parisian lines, which is just under 1000.325 millimeters. As the basis of a first brass prototype was produced in 1795.

The second, " definitive " standard meter

After completion of the triangulation between Dunkirk and Barcelona on the Meridian expedition, a second so-called definitive standard meter was made ​​of platinum in 1799 and closed on June 22, 1799 in the French National Archives in a steel cabinet. Today, it is kept in a vault of the International Bureau of Weights and Measures ( BIPM) in Sèvres, near Paris.

However, the accuracy of which - with respect to the target of ten millionth part of the distance from the equator to the pole - with defined 443.296 Parisian lines, even lower than that of the so-called "provisional Meters", since this distance according to the WGS84 is about 10001.966 km. The adoption of this standard meter as the unit was decided on 20 May 1875 in the " International Meter Convention " of seventeen states.

International meter prototype of 1889 (third standard meter )

On September 26, 1889 the standard meter was replaced by the General Conference on Weights and Measures by a meter prototype of an alloy of 90 % platinum and 10% iridium. On this 102 cm long with normal X -shaped cross section (20 × 20 mm) stroke groups represented the length of one meter. It has been defined over the distance between the center lines of these line groups, - due to the thermal expansion of the material at a temperature of 0 ° C. This length definition had an accuracy of 10-7 and was three orders of magnitude more accurate than the standard meter in 1799. Copies of this meter prototype were given to the calibration institutes in many countries.

Possession of official copies of the prototype of 1889 in Germany

Simultaneously with the standard meter in Paris from 1889, so to speak, the number zero, thirty numbered copies of the third standard meter were still produced. The copies, disrespectfully called in Germany " stick " were raffled to the Member States. Germany received a copy of No. 18 since the Kingdom of Bavaria in 1870, was joined before the Empire as an independent member, it also participated in the raffle and received a copy of No. 7 During the Third Reich had to Bavaria his copy to the Physikalisch-Technische Reich (PTR ) Berlin exits. Because most PTR laboratories were relocated in 1943 from Berlin especially after Weida in Thuringia, both specimen 1949-1990 remained in the possession of the GDR. As West Germany now stood without any prototypes, it acquired in 1954, the copy # 23 of Belgium, which had also received two copies ( Flanders and Wallonia ). Two of the three copies ( the copies of Nos. 18 and 23) are now in the Physikalisch- Technische Bundesanstalt in Braunschweig. There was until 2001 a copy No. 7, before it was returned to the Free State of Bavaria and is kept since then at the Bavarian State Office of Weights and Measures in Munich.

Redefinition of the meter due to optics and timing

The meter prototype was not until 1960 that replaced, as the General Conference on Weights and Measures times the meter as 1,650,763.73 which defined the wavelength of the atoms of the nuclide 86Krypton the transition from state to state 5d5 2p10 emitted, propagating in the vacuum radiation. This accuracies of 10-8 have been achieved.

Since the earlier definitions of the meter in the SI system were relatively inaccurate on the basis of the International meter prototype or a particular wavelength compared to the measured with atomic clocks second, the decision was made on the basis of the second and the vacuum speed of light to redefine the meter. Since 1983, therefore, is the SI base unit meter defined as follows.

The " odd" value for the pre-defined vacuum speed of light was chosen to keep the deviations from the old system to a minimum, that is, a value calculated using the length of time has almost the same value as would result from a comparison with the standard meter. It is completely irrelevant to whether a path ( X) or a period (t ) are used as length measurement, since these two variables by the vacuum light velocity (c0 ) of the formula

Are linked. With the help of the vacuum speed of light can be converted to spatial and temporal quantities into one another. A light year is, for example, the distance that light travels in a terrestrial year: Approximately 9.4605 trillion kilometers.

It remains, however, that all changes to the definition since 1799, always striving only a higher precision. Never ever intends to amend the measure itself, for example to the original definition with respect to the distance from the pole to the equator to achieve more accurate.