The Mendenhall Order marked a decision to change the fundamental standards of length and mass of the United States from the customary standards based on those of

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

to metric standards. It was issued on April 5, 1893, by

Thomas Corwin Mendenhall Thomas Corwin Mendenhall (October 4, 1841 – March 23, 1924) was an American autodidact physicist and meteorologist. He was the first professor hired at Ohio State University in 1873 and the superintendent of the United States Coast and Geodeti ...

, superintendent of the

United States Coast and Geodetic Survey The United States Coast and Geodetic Survey ( USC&GS; known as the Survey of the Coast from 1807 to 1836, and as the United States Coast Survey from 1836 until 1878) was the first scientific agency of the Federal government of the United State ...

, with the approval of the

United States Secretary of the Treasury The United States secretary of the treasury is the head of the United States Department of the Treasury, and is the chief financial officer of the federal government of the United States. The secretary of the treasury serves as the principal a ...

John Griffin Carlisle John Griffin Carlisle (September 5, 1834July 31, 1910) was an American attorney and Democratic Party politician from Kentucky. He represented Kentucky in the United States House of Representatives from 1877 to 1890, serving as the 31st Speake ...

. The order was issued as the Survey's ''Bulletin No. 26 – Fundamental Standards of Length and Mass''.

Standards before the order

In October 1834, the United Kingdom

Houses of Parliament The Palace of Westminster is the meeting place of the Parliament of the United Kingdom and is located in London, England. It is commonly called the Houses of Parliament after the House of Commons and the House of Lords, the two legislative ch ...

were destroyed in a

fire Fire is the rapid oxidation of a fuel in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. Flames, the most visible portion of the fire, are produced in the combustion re ...

, and the British standards of length and mass were also destroyed. "When the new imperial standards to replace them were completed in 1855, two copies of the yard and one copy of the avoirdupois pound were presented to the United States". These were superior to the yard then in use, so one of them was adopted as the United States national standard yard. These yards were taken to England and re-compared with the imperial yard in 1876 and 1888. The pound provided by the United Kingdom agreed with the United States mint pound, which remained the national standard according to Barbrow and Judson. Hockert claims the UK pound replaced the mint pound. These were the fundamental standards for customary length and mass measurements in the United States, but the Office of Weights and Measures had other standards for metric measurements.

Official recognition of the metric system

The Metric Act of 1866 was passed by Congress and allowed, but did not require, the use of the metric system. Included in the law was a table of conversion factors between the traditional and metric units. The United States Coast Survey (which in 1878 became the U.S. Coast and Geodetic Survey) Office of Weights and Measures had on hand a number of metric standards, and selected the iron

Committee Meter Metrication is the process of introducing the International System of Units, also known as SI units or the metric system, to replace a jurisdiction's traditional measuring units. U.S. customary units have been defined in terms of metric unit ...

and the platinum Arago Kilogram to be the national standards for metric measurement. The standard yard and pound previously mentioned continued to be the standards for customary measurements. A series of conferences in France between 1870 and 1875 led to the signing of the

Metre Convention The Metre Convention (), also known as the Treaty of the Metre, is an international treaty that was signed in Paris on 20 May 1875 by representatives of 17 nations: Argentina, Austria-Hungary, Belgium, Brazil, Denmark, France, German Empire, Ge ...

and to the permanent establishment of the

International Bureau of Weights and Measures The International Bureau of Weights and Measures (, BIPM) is an List of intergovernmental organizations, intergovernmental organisation, through which its 64 member-states act on measurement standards in areas including chemistry, ionising radi ...

, abbreviated BIPM after the French name. The BIPM made meter and kilogram standards for all the countries that signed the treaty; the two meters and two kilograms allocated to the United States arrived in 1890, and were adopted as national standards.

Reasons for the change

The imperial standard yard of 1855 was found to be unstable and shortening by measurable amounts. Also, the mint pound was found to be "likewise unfit for use". For several years before the Mendenhall order was actually issued, the Office of Weights and Measures was "practically forced" to use the metric standards because of their superior stability, and because they were better designed for carrying out precision comparisons. The Office found that the conversion tables in the 1866 law were satisfactory and used them to derive customary length and mass from the metric standards. The conversions were 1 yard = meter and 1 pound = kilogram. Therefore, the Mendenhall order amounted to a formal announcement of a change that had already occurred in practice. Another motivation for the order was that later that year, in August 1893, an

International Electrical Congress The International Electrical Congress was a series of international meetings, from 1881 to 1904, in the then new field of applied electricity. The first meeting was initiated by the French government, including official national representatives, le ...

would be held in connection with the World's Fair in Chicago. Associated with the Congress would be a "Chamber of Delegates", officially organized for the purpose of coming to an international agreement on units of electrical quantities. As Mendenhall wrote,

Refinement of the conversions

The definitions of 1893 remained unchanged for 66 years, but increasing precision in measurements gradually made the differences in the standards in use in English-speaking countries important. By the

international yard and pound The international yard and pound are two units of measurement that were the subject of an agreement among representatives of six nations signed on 1 July 1959: Australia, Canada, New Zealand, South Africa, the United Kingdom and the United States ...

agreement of July 1, 1959, Australia, Canada, New Zealand, South Africa, the United Kingdom, and the United States agreed that 1 yard = 0.9144 meter and that 1 avoirdupois pound = kilogram (but see U.S. survey foot).

Standards versus systems

Mendenhall ordered that the standards used for the most accurate length and mass comparison change from certain yard and pound objects to certain meter and kilogram objects, but did not require anyone outside of the Office of Weights and Measures to change from the customary units to the metric system.

References

* * Footnotes {{reflist, refs= {{cite web , title=Bronze Yard No. 11 , website=National Institute of Standards and Technology (NIST) , url=http://museum.nist.gov/object.asp?ObjID=17 , archive-date=26 August 1999 , access-date=8 May 2021 , archive-url=https://web.archive.org/web/19990826141236/http://museum.nist.gov/object.asp?ObjID=17 {{cite web , title=Imperial Avoirdupois Pound , website=National Institute of Standards and Technology (NIST) , url=http://museum.nist.gov/object.asp?ObjID=19 , archive-date=11 November 1999 , access-date=8 May 2021 , archive-url=https://web.archive.org/web/19991111114344/http://museum.nist.gov/object.asp?ObjID=19 Hockert, Carol. (21 July 2015).
Address to the National Conference on Weights and Measures to Commemorate Their 100th Meeting
. National Institute of Standards and Technology. {{cite web , title=Committee Meter , website=National Institute of Standards and Technology (NIST) , url=http://museum.nist.gov/object.asp?ObjID=12 , archive-date=26 August 1999 , access-date=8 May 2021 , archive-url=https://web.archive.org/web/19990826124504/http://museum.nist.gov/object.asp?ObjID=12 {{cite web , title=Arago Kilogram , website=National Institute of Standards and Technology (NIST) , url=http://museum.nist.gov/object.asp?ObjID=20 , archive-date=11 November 1999 , access-date=8 May 2021 , archive-url=https://web.archive.org/web/19991111114300/http://museum.nist.gov/object.asp?ObjID=20 {{cite web , title=National Prototype Meter No. 27 , website=National Institute of Standards and Technology (NIST) , url=http://museum.nist.gov/object.asp?ObjID=37 , archive-date=11 November 1999 , access-date=8 May 2021 , archive-url=https://web.archive.org/web/19991111111802/http://museum.nist.gov/object.asp?ObjID=37 {{cite web , title=Prototype Kilogram 20, replica , website=National Institute of Standards and Technology (NIST) , url=http://museum.nist.gov/object.asp?ObjID=38 , archive-date=11 November 1999 , access-date=8 May 2021 , archive-url=https://web.archive.org/web/19991111112604/http://museum.nist.gov/object.asp?ObjID=38 {{cite web , title=Fischer Transverse Invar Beam Comparator , website=National Institute of Standards and Technology (NIST) , url=http://museum.nist.gov/object.asp?ObjID=54 , archive-date=12 April 2000 , access-date=8 May 2021 , archive-url=https://web.archive.org/web/20000412110323/http://museum.nist.gov/object.asp?ObjID=54