Mendenhall Order

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The Mendenhall Order was the regulation by which the United States of America officially abandoned the national definitions for the basic unit of length, the yard, and the unit of mass, the avoirdupois pound, and related these definitions to the metric system. The ordinance was promulgated on April 5, 1893 by Thomas Corwin Mendenhall , Superintendent of the US Coast and Geodetic Survey with the approval of Treasury Secretary John Griffin Carlisle . It was published in Bulletin No. 26 - Fundamental Standards of Length and Mass des Surveys.

Standards before regulation

In October 1834, the Houses of Parliament in the United Kingdom were destroyed by fire, and the British standards for length and mass were also destroyed. When replacement standards were completed in 1855, two samples of the yard and one of the avoirdupois pound were given to the USA. A yard officially became the standard unit of length in the United States. Both yards were brought back to England in 1876 and 1888 and compared to the UK's Imperial Yard . The pound pattern transferred to the USA matched the pound of the US Mint (US mint); there are contradicting statements as to which of them became the national standard.

In any case, there were separate standards for length and mass in the Anglo-Saxon system of measurement and others for the metric system, which were kept by the Office of Weights and Measures of the US Coast and Geodetic Survey: the iron "Committee Meter" and the "Arago Kilogram" made of platinum.

First steps to the metric system

In 1866, the US Congress passed a law that allowed, but not required, the use of the metric system. This included a conversion table between traditional and metric units.

A series of conferences in France between 1870 and 1875 led to the signing of the Meter Convention and the establishment of the International Bureau of Weights and Measures , abbreviated to BIPM after the French name. The BIPM had meter and kilogram standards produced for all states that had signed the agreement; two yardsticks and two kilogram pieces for the USA arrived there in 1890, and replaced the Committee Meter and Arago Kilogram as national standards of the metric system.

Reasons for the change

The Imperial Yard standard of 1855 proved unstable: it was shortened by measurable amounts. The pound weight of the coin has also been found unsuitable. As a result, several years before the regulation was issued, the Office of Weights and Measures was practically forced to fall back on the metric standards because of their superior stability. In addition, these were better suited to carry out precision comparisons. The Office found the conversion tables from the 1866 Act to be correct and used them to derive length and mass in the Anglo-Saxon system of measurement from the metric normals.

The conversions were and

The Mendenhall Order was the formal act of declaring the conversion factors, which had been tried and tested in practice since 1866 and deliberately kept simple, the norm.

In the months that followed, it was found that the deviation from the British definition of the pound was unacceptable after all. The yard also deviated, but they stuck to it, but for the pound the British definition was adopted, which had more decimal places:

As of March 21, 1894, the equality of the British and the US pound was declared and the Office of Weights and Measures gave a conversion factor that was not completely correctly rounded:

The exact expression in brackets of the last digits (7989 ..) would have been correctly rounded to (80), but possibly corresponds to a British source.

Conversions improvement

The final stipulations of 1894 for the USA remained unchanged for 65 years, but improvements in measurement technology and increasing precision requirements in practice led to markedly different measurement results from the different definitions of the same basic units in the economies of the yard and the pound. Particularly in the movement of goods in the Commonwealth, this meant that precise standard and machine parts with fits such as ball bearings or dosing devices could no longer be exchanged at will. Scientific communication was also impaired, as research results were no longer reproducible and, for practical reasons, there was a threat that various high-tech disciplines and industries would increasingly publish their results and products in the metric system. In order to maintain the normative sovereignty in the technologically closed Commonwealth market, the Commonwealth countries Australia, Canada, New Zealand, South Africa and the United Kingdom established standardizations:

and

With effect from July 1, 1959, the United States of America defined that the US yard corresponds to the international yard and the US pound to the international pound . In countries where the yard and pound play a role in everyday life, these international definitions are also common.

Measurement standards and systems of measurement

Mendenhall decreed that the standards, on which the length and mass determinations were based, changed from certain yard and pound patterns to certain meter and kilogram patterns. On the other hand, no one outside the Office of Weights and Measures was induced to use the metric system instead of the Anglo-Saxon measurement system.

literature

Individual evidence

  1. ↑ a b c Barbrow & Judson 1976
  2. ↑ museum.nist.gov: Bronze Yard No. 11 ( Memento from February 4, 2012 in the Internet Archive )
  3. ↑ museum.nist.gov: Imperial Avoirdupois Pound ( Memento from September 29, 2006 in the Internet Archive )
  4. ↑ museum.nist.gov: Imperial Avoirdupois Pound ( Memento from September 29, 2006 in the Internet Archive )
  5. ↑ museum.nist.gov: Committee Meter ( Memento from September 26, 2006 in the Internet Archive )
  6. ↑ museum.nist.gov: Arago Kilogram ( Memento from September 29, 2006 in the Internet Archive )
  7. ↑ museum.nist.gov: National Prototype Meter No. 27 ( Memento from June 15, 2010 in the Internet Archive )
  8. ↑ museum.nist.gov: Prototype Kilogram 20, replica ( Memento from August 13, 2006 in the Internet Archive )
  9. ↑ museum.nist.gov: Photograph of Fischer Transverse Invar Beam Comparator ( Memento from September 29, 2006 in the Internet Archive )
  10. ↑ The Mendenhall Order of April 5, 1893 (Appendix 3, PDF file)
  11. ^ Mendenhall Order, page 2
  12. ↑ This system change has largely taken place with a delay to this day, since the other SI units (e.g. Newton, Watt or also natural constants) have prevailed and can only be used inconveniently and with losses with yards and pounds. The communication language is mostly English but with SI units. Even in the USA, high-tech products are now almost exclusively planned, manufactured and certified in SI units.
  13. ↑ Refinement of values ​​for the yard and pound at NIST ( Memento of October 30, 2013 in the Internet Archive ) (PDF file; 1.49 MB). Note that the old definition was indirectly retained in the US survey foot until further notice in the US land survey. The US Survey Foot has only become obsolete since the remeasurement of the reference point network was completed in the 1990s .

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