On , T. C. Mendenhall, then Superintendent of Weights and Measures, with the approval of the Secretary of the Treasury, decided that the international metre and kilogram would in the future be regarded as the fundamental standards of length and mass in the United States, both for metric and customary weights and measures. This decision has come to be known as the Mendenhall Order.
The following text is abridged from the 1976 edition of the National Bureau of Standards Special Publication 447, Weights and measures standards of the United States: A brief history by Lewis V. Judson. NIST has a virtual room in its museum about the Mendenhall Order.
The Mendenhall Order
(Photo from National Academy of Sciences)
On , T. C. Mendenhall, then Superintendent of Weights and Measures, with the approval of the Secretary of the Treasury, decided that the international metre and kilogram would in the future be regarded as the fundamental standards of length and mass in the United States, both for metric and customary weights and measures. This decision, which has come to be known as the Mendenhall Order, was first published as Bulletin No. 26 of the Coast and Geodetic Survey, approved for publication , under the title, Fundamental Standards of Length and Mass; it was republished in 1894 under the same title, as appendix No. 6—Report for 1893 of the Coast and Geodetic Survey, to give it a more permanent form
. In appendix No. 6 there was included as an addendum to the text of Bulletin No. 26 a section headed Tables for Converting Customary and Metric Weights and Measures, comprising some text, five customary-to-metric conversion tables, and five metric-to-customary conversion tables.
As a matter of interest and record, the full text of appendix No. 6 of the Report for 1893 of the Coast and Geodetic Survey, with the exception of an editorial footnote and the ten conversion tables, is reproduced below.
The Mendenhall Order initiated a departure from the previous policy of attempting to maintain our standards of length and mass to be identical with those of Great Britain, and thereafter there was a small difference between the British and the United States yards, a difference which may have been negligible in 1893 but which became of real importance as the British Imperial Yard bar gradually changed in length and as the requirements for greater accuracy in measurements increased.
When the United States yard was first adopted in 1832, it was defined as a particular interval on the Troughton bar, through which it was related to the British yard standard. The intention was to fix the United States yard as equal to the British yard.
When the “Imperial” system of weights and measures was established by the British in 1824, the Imperial Yard was defined in terms of a specific yard standard and a particular bar was legalized as the Imperial standard. In 1834, that bar was so damaged in the burning of the Houses of Parliament that replacement was necessary; a new bar was constructed, and in 1855 this bar was legalized as the new Imperial Standard Yard. In the course of the years this bar proved to be insufficiently stable in length and was found to be shortening by measurable amounts.
For a time, efforts were made by United States authorities to maintain equivalence between the United States and British yards. Such efforts were abandoned, however, in 1893, when the Mendenhall Order defined the United States yard in terms of the International Prototype Metre.
The difference between the United States and the British yards, prior to the 1959 actions of both governments in recognizing the new International Yard, reached a maximum value in the order of 0.000 13 inch, the United States yard being the longer.
The case of the pound was slightly different as will be seen from the record of the values assigned to it with respect to the kilogram.
The United States law of 1866 that made the use of the metric system permissive, carries the relation, 1 kilogram = 2.2046 avoirdupois pounds, an equation now believed to have been intended as sufficiently accurate for commercial purposes but not as a precise definition of the relationship between basic units. This value resulted from a rounding off of the results of an 1844 comparison made in England between the British pound and the Kilogram of the Archives which gave the relation, 1 pound = 0.453 592 65 kilogram; this relation was used in Great Britain and in the United States for years. Expressed reciprocally, this relation becomes, approximately, 1 kilogram = 2.204 621 61 pounds.
In the Coast and Geodetic Survey Report for 1893 that contained the Mendenhall Order, the kilogram-avoirdupois pound relationships are variously stated as follows:
| 1 pound avoirdupois | = | 1⁄2.2046 kg |
| 1 pound avoirdupois | = | 1⁄2.20462 kg |
| 2.204 622 34 pounds avoirdupois | = | 1 kilogramme |
| 1 avoirdupois pound | = | 453.592 427 7 grammes |
A comparison made in 1883 between the British Imperial Standard Pound and the International Prototype Kilogram resulted in the relation 1 Imperial Pound = 0.453 592 427 7 Kilogram; this relation was accepted in both Great Britain and the United States, but uniformity between the two countries ended in 1889 when Great Britain officially adopted a rounded-off value, making the relation, 1 Imperial Pound = 0.453 592 43 Kilogram. From its founding in 1901 until , the National Bureau of Standards recognized and used the relation 1 pound avoirdupois = 0.453 592 427 7 kilogram.
This uncertainty as to the precise values of the units of length and mass in common use, the yard and the pound respectively, was caused by inadequacies of the standards representing them. The bronze yard No. 11, which was an exact copy of the British imperial yard both in form and material, had shown changes when compared with the imperial yard in 1876 and 1888 which could not reasonably be said to be entirely due to changes in No. 11. Suspicion as to the constancy of the length of the British standard was therefore aroused. Neither the troy pound of the mint nor the copies of the imperial yard in the possession of the Office of Weights and Measures were satisfactory standards. The mint pound is made in two pieces, the knob being screwed into the body; hence its density can not be determined by weighing in water on account of danger of leakage. Moreover, it is made of brass not plated, and therefore liable to alteration by oxidation.
On the other hand, the new metres and kilograms represented the most advanced ideas of standards, and it therefore seemed that greater stability in our weights and measures as well as higher accuracy would be secured by accepting the international metre and kilogram as fundamental standards.
Time proved the wisdom of this action, and therefore when the National Bureau of Standards was established in , it fully accepted the decision made by the Office of Weights and Measures in 1893 to adopt the metre and kilogram as fundamental standards.
Text of The Mendenhall Order of
The following copy of the Mendenhall Order is from the 1976 edition of the National Bureau of Standards Special Publication 447, Weights and measures standards of the United States: A brief history by Lewis V. Judson.
Fundamental Standards of Length and Mass
While the Constitution of the United States authorizes Congress to fix the standard of weights and measures
, this power has never been definitely exercised, and but little legislation has been enacted upon the subject. Washington regarded the matter of sufficient importance to justify a special reference to it in his first annual message to Congress (January, 1790), and Jefferson, while Secretary of State, prepared a report, at the request of the House of Representatives, in which he proposed (July, 1790) to reduce every branch to the decimal ratio already established for coins, and thus bring the calculation of the principal affairs of life within the arithmetic of every man who can multiply and divide.
The consideration of the subject being again urged by Washington, a committee of Congress reported in favor of Jefferson’s plan, but no legislation followed. In the meantime the executive branch of the Government found it necessary to procure standards for use in the collection of revenue and other operations in which weights and measures were required, and the Troughton 82-inch brass scale was obtained for the Coast and Geodetic Survey in 1814, a platinum kilogramme and metre, by Gallatin, in 1821, and a troy pound from London in 1827, also by Gallatin. In 1828 the latter was, by act of Congress, made the standard of mass for the Mint of the United States, and, although totally unfit for such purpose, it has since remained the standard for coinage purposes.
In 1830 the Secretary of the Treasury was directed to cause a comparison to be made of the standards of weight and measure used at the principal custom-houses, as a result of which large discrepancies were disclosed in the weights and measures in use. The Treasury Department, being obliged to execute the constitutional provision that all duties, imposts, and excises shall be uniform throughout the United States, adopted the Troughton scale as the standard of length; the avoirdupois pound, to be derived from the troy pound of the Mint, as the unit of mass. At the same time the Department adopted the wine gallon of 231 cubic inches for liquid measure and the Winchester bushel of 2150.42 cubic inches for dry measure. In 1836 the Secretary of the Treasury was authorized to cause a complete set of all weights and measures adopted as standards by the Department for the use of custom-houses and for other purposes to be delivered to the governor of each State in the Union for the use of the States, respectively, the object being to encourage uniformity of weights and measures throughout the Union. At this time several States had adopted standards differing from those used in the Treasury Department, but after a time these were rejected, and finally nearly all the States formally adopted, by act of legislature, the standards which had been put in their hands by the National Government. Thus a good degree of uniformity was secured, although Congress had not adopted a standard of mass or of length, other than for coinage purposes, as already described.
The next and in many respects the most important legislation upon the subject was the act of , making the use of the metric system lawful throughout the United States and defining the weights and measures in common use in terms of the units of this system. This was the first general legislation upon the subject, and the metric system was thus the first, and thus far the only, system made generally legal throughout the country.
In 1875 an international metric convention was agreed upon by seventeen Governments, including the United States, at which it was undertaken to establish and maintain at common expense a permanent international bureau of weights and measures, the first object of which should be the preparation of a new international standard metre and a new international standard kilogramme, copies of which should be made for distribution among the contributing Governments. Since the organization of the Bureau, the United States has regularly contributed to its support, and in 1889 the copies of the new international prototypes were ready for distribution. This was effected by lot, and the United States received metres Nos. 21 and 27 and kilogrammes Nos. 4 and 20. The metres and kilogrammes are made from the same material, which is an alloy of platinum with 10 per cent of iridium.
On , the seals which had been placed on metre No. 27 and kilogramme No. 20 at the International Bureau of Weights and Measures, near Paris, were broken in the Cabinet room of the Executive Mansion by the President of the United States in the presence of the Secretary of State and the Secretary of the Treasury, together with a number of invited guests. They were thus adopted as the national prototype metre and kilogramme.
The Troughton scale, which in the early part of the century had been tentatively adopted as a standard of length, has long been recognized as quite unsuitable for such use, owing to its faulty construction and the inferiority of its graduation. For many years, in standardizing length measures, recourse to copies of the imperial yard of Great Britain had been necessary, and to the copies of the metre of the archives in the office of weights and measures. The standard of mass originally selected was likewise unfit for use for similar reasons, and had been practically ignored.
The recent receipt of the very accurate copies of the International Metric Standards, which are constructed in accord with the most advanced conceptions of modern metrology, enables comparisons to be made directly with those standards, as the equations of the national prototypes are accurately known. It has seemed, therefore, that greater stability in weights and measures, as well as much higher accuracy in their comparison, can be secured by accepting the international prototypes as the fundamental standards of length and mass. It was doubtless the intention of Congress that this should be done when the international metric convention was entered into in 1875; otherwise there would be nothing gained from the annual contributions to its support which the Government has constantly made. Such action will also have the great advantage of putting us in direct relation in our weights and measures with all civilized nations, most of which have adopted the metric system for exclusive use. The practical effect upon our customary weights and measures is, of course, nothing. The most careful study of the relation of the yard and the metre has failed thus far to show that the relation as defined by Congress in the act of 1866 is in error. The pound as there defined, in its relation to the kilogramme, differs from the imperial pound of Great Britain by not more than one part in one hundred thousand, an error, if it be so called, which utterly vanishes in comparison with the allowances in all ordinary transactions. Only the most refined scientific research will demand a closer approximation, and in scientific work the kilogramme itself is now universally used, both in this country and in England.
In view of these facts, and the absence of any material normal standards of customary weights and measures, the Office of Weights and Measures, with the approval of the Secretary of the Treasury, will in the future regard the International Prototype Metre and Kilogramme as fundamental standards, and the customary units — the yard and the pound — will be derived therefrom in accordance with the Act of . Indeed, this course has been practically forced upon this Office for several years, but it is considered desirable to make this formal announcement for the information of all interested in the science of metrology or in measurements of precision.
T. C. Mendenhall,
Superintendent of Standard Weights and Measures.
Approved:
J. G. Carlisle,
Secretary of the Treasury.
April 5, 1893.
[United States Coast and Geodetic Survey. — Office of Standard Weights and Measures — T. C. Mendenhall, Superintendent.]
TABLES FOR CONVERTING CUSTOMARY AND METRIC WEIGHTS AND MEASURES.
Office of Standard Weights and Measures,
Washington, D.C., .
[Ed. note: In 1959 the definitions of the yard, pound, and nautical mile were revised — see the refinement of values for the yard and the pound (which, of course, also affected the inch, foot, ounce, etc.) and the adoption of the International Nautical Mile — so the values shown below from 1894 are obsolete. Also, the definitions of the metre and litre were refined since the definitions shown below.]
The yard in use in the United States is equal to 3600⁄3937 of the metre.
The troy pound of the mint is the United States standard weight for coinage. It is of brass of unknown density, and therefore not suitable for a standard of mass. It was derived from the British standard troy pound of 1758 by direct comparison. The British avoirdupois pound was also derived from the latter and contains 7,000 grains troy. The grain troy is therefore the same as the grain avoirdupois, and the pound avoirdupois in use in the United States is equal to the British pound.
2.20462234 pounds avoirdupois = 1 kilogramme.
In Great Britain the legal metric equivalent of the imperial gallon is 4.54346 litres, and of the imperial bushel 36.3477 litres.
The length of a nautical mile, as given below, is that adopted by the United States Coast Survey many years ago, and defined as the length of a minute of arc of a great circle of a sphere whose surface is equal to the surface of the earth (the Clarke spheroid of 1866).
| 1 foot | = | 0.304801 metre, 9.4840158 log. |
| 1 fathom | = | 1.829 metres. |
| 1 Gunter’s chain | = | 20.1168 metres. |
| 1 square statute mile | = | 259.000 hectares. |
| 1 nautical mile | = | 1853.25 metres. |
| 1 avoirdupois pound | = | 453.5924277 grammes. |
| 15432.35639 grains | = | 1 kilogramme. |
* * * * *
By the concurrent action of the principal Governments of the world, an International Bureau of Weights and Measures has been established near Paris. Under the direction of the International Committee, two ingots were cast of pure platinum-iridium in the proportion of 9 parts of the former to 1 of the latter metal. From one of these a certain number of kilogrammes were prepared; from the other a definite number of metre bars. These standards of weight and length were intercompared without preference, and certain ones were selected as international prototype standards. The others were distributed by lot, in September, 1889, to the different Governments, and are called national prototype standards. Those apportioned to the United States were received in 1890 and are in the keeping of this office.
The metric system was legalized in the United States in 1866.
The International Standard Metre is derived from the Metre des Archives, and its length is defined by the distance between two lines at 0° centigrade on a platinum-iridium bar deposited at the International Bureau of Weights and Measures.
The International Standard Kilogramme is a mass of platinum-iridium deposited at the same place, and its weight in vacuo is the same as that of the Kilogramme des Archives.
The litre is equal to a cubic decimetre, and it is measured by the quantity of distilled water which, at its maximum density, will counterpoise the standard kilogramme in a vacuum, the volume of such a quantity of water being, as nearly as has been ascertained, equal to a cubic decimetre.
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