Standard meter

Copy No. 27 of the original meter from 1889 for the United States

The original meter ( French mètre des archives , archival meter) is the measuring standard of the length unit meter , which was valid until 1960 . With the introduction of the metric system of units the meter was first ten-millionster part of the district of that circumference of the earth set of Paris and the north pole touches. The circumference of the earth was geodetically measured and the result was transferred to the distance between two markings on a metal rod. This metal rod was subsequently used to calibrate measuring devices and measuring rods for daily use and for national surveying .

The concept of the standard meter relates in particular to the second specimen (sample) in 1799, that the final dimensions of platinum iridium , which embodied the unit length to 1889th The international meter prototype from 1889 is also often referred to as the original meter .

Manufacture of the first original meter

On March 26, 1791, the constituent assembly in Paris decided to introduce a universal unit of length on the proposal of the Académie des sciences (Academy of Sciences). The new measure of length, not yet called “meter”, should be the ten millionth part of the earth's meridian quadrant (distance from the pole to the equator). For this purpose, the meridian arc from Dunkirk to Barcelona was to be re-measured by two French astronomers , Jean-Baptiste Joseph Delambre and Pierre Méchain , which, however , dragged on until 1798 during the turmoil of the French Revolution . In 1791 another proposed definition by Talleyrand and Jefferson , based on a seconds pendulum , was rejected because this method would have been influenced by local differences in the acceleration of gravity .

On August 1, 1793, under the reign of terror , this length measure - called Bordas meter - was legally introduced in the National Convention , but with a provisional value of 443.440 Parisian lines , which corresponds to almost 1000.325 millimeters. Based on this value, the first brass prototype was produced in 1795 .

The second, "definitive" standard meter

After the triangulation between Dunkirk and Barcelona on the meridian expedition was completed, a second so-called definitive original meter was made from platinum as a gauge block in 1799 and locked in a steel cabinet in the French National Archives on June 22, 1799. Today it is kept in a safe at the International Bureau of Weights and Measures (BIPM) in Sèvres near Paris. However, its end faces were damaged by the beginning of the 20th century at the latest.

However, its accuracy - with regard to the targeted ten millionth part of the distance from the equator to the pole - with defined 443.296 Parisian lines (corresponding to 1000.0001606 mm) - is even less than that of the so-called "provisional meter", since this distance according to the WGS84 is about 10001, 966 km. The adoption of this original meter as a unit of measurement was decided on May 20, 1875 in the " International Meter Convention " by seventeen states.

International meter prototype from 1889 (third original meter)

Computer- generated image International meter prototype , standard bars made of platinum-iridium. These were the length standards until 1960. ( NIST )

So far one had used gauge blocks , u. a. because these can be compared more easily and more precisely with other standards. This is offset by the serious disadvantage that the end faces can be damaged when copying by touching feeler levers or the like (as happened with the second master meter). As the standard meter from the September 26, 1889 General Conference on Weights and Measures by one meter prototype of an alloy of 90% platinum and 10% iridium was replaced, it therefore went to a Line measure through. On this 102 cm long standard with an X-shaped cross-section (20 mm × 20 mm) groups of lines represented the length of one meter. It is 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 thus three orders of magnitude more precise than the original meter from 1799. Copies of this meter prototype were given to calibration institutes in many countries.

Ownership of official copies of the prototype from 1889 in Germany

At the same time as the Paris original meter of 1889, the number zero, so to speak, thirty numbered copies of the third original meter were made. The copies, also disrespectfully called “sticks” in Germany, were raffled off to the member states. Germany received copy no. 18. Since the Kingdom of Bavaria had joined as an independent member in 1870, before the founding of the empire, it also took part in the raffle and received copy no. 7. During the Third Reich, Bavaria had to send its copy to the Submit the Physikalisch-Technische Reichsanstalt (PTR) Berlin. Because most of the PTR laboratories were relocated from Berlin mainly to Weida in Thuringia in 1943 , both specimens remained in the possession of the GDR between 1949 and 1990. Since West Germany was now without a prototype, it acquired copy No. 23 from Belgium in 1954, which had also received two copies (for Flanders and Wallonia). Two of the three copies (copies No. 18 and 23) are now in the Physikalisch-Technische Bundesanstalt in Braunschweig. Copy No. 7 was there until 2001, before it was returned to the Free State of Bavaria and has since been kept in the Bavarian State Office for Weights and Measures in Munich.

Overview of the whereabouts of the copies

number	Original destination country	Today's land of ownership	Repository
1	Italy
2	Switzerland
3	Norway
4th	France
5	Grand Duchy of Finland
6th	BIPM	BIPM	International Office for Weights and Measures Paris
7th	Bavaria	Germany	Bavarian State Office for Weights and Measures Munich
8th	France
9	Italy
10	Portugal
11	Russia
12	Flanders	Belgium
13	BIPM	BIPM	International Office for Weights and Measures Paris
14th	Hungary
15th	Empire of Austria
16	United Kingdom	United Kingdom	National Physical Laboratory Teddington
17th	Spain
18th	Prussia	Germany	Physikalisch-Technische Bundesanstalt Braunschweig
19th	Empire of Austria	BIPM	International Office for Weights and Measures Paris
20th	France
21st	United States	United States	National Institute of Standards and Technology
22nd	Japan
23	Walloon region	Germany	Physikalisch-Technische Bundesanstalt Braunschweig
24	Spain
25th	Mexico
26th	BIPM	BIPM	International Office for Weights and Measures Paris
27	United States	United States	National Institute of Standards and Technology
28	Russia
29	Sweden
30th	Serbia

Replacement of the original meter

See also : Meter # history of definition

With the advancement of measurement technology, the disadvantages of the ancient meter became more and more apparent: a physical object is never completely stable, but loses substance. Measurements can damage the object and can only take place where it is located.

At the beginning of the 20th century , Albert A. Michelson proposed the wavelength of light as an unchangeable, universally available length standard . In the 1950s, the Krypton 86 lamp became a light source of sufficient stability and precision. With regard to their wavelength, the meter was redefined in 1960. There was another change in 1983 when the speed of light became the reference value. The new definitions were chosen so that they corresponded as closely as possible with the original meter within the scope of the measurement accuracy. The original meter itself has not had a normal function since 1960 and is only of historical interest.

Web links

Wiktionary: Urmeter  - explanations of meanings, word origins, synonyms, translations

• Urmeter, Evolution on the official BIPM website
• ZDF Mediathek; Terra X: The Hunt for the Original Meter (January 27, 2016) (Documentary about the measurement of Delambre and Mechain 1792–1799)

Individual evidence

1. ↑ ^{a b} dimensions . In: Meyers Großes Konversations-Lexikon . 6th edition. tape 13 . Bibliographical Institute, Leipzig / Vienna 1908, p. 401–406 ( zeno.org [accessed July 4, 2018]).
2. ↑ The Earth according to WGS 84. ( Memento from January 24, 2015 in the Internet Archive ) calculated by Sigurd Humerfelt.
3. ^ Resolution 6 of the 11th CGPM (1960). In: bipm.org. Bureau International des Poids et Mesures, accessed June 22, 2019 . 
4. ^ Resolution 1 of the 17th CGPM (1983). In: bipm.org. Bureau International des Poids et Mesures, accessed June 18, 2019 .