The copies of the imperial yard had shown noticeable changes relative to the standard when subsequently compared, and this led to the belief that the imperial yard itself was not con stant. Shortly after the arrival of the na tional prototype metre, a careful determination of the relation of the imperial yard to the in ternational metre at the Office of Standard Weights and Measures showed that the rela tion differed from that legalized in 1866 by less than the uncertainty of the comparison, and it was decided to adopt the metre as the funda mental standard of length and to define the yard in terms of it. Not only is the constancy of the length of the imperial yard suspected. but in addition the lines, which are about 1-1000 of an inch wide, are much too broad for present requirements. On the other hand. the international metre and its copies satisfy the rigorous requirements of modern metrology. The kilogram was also declared to be the fun damental standard of weight. The present standards of the United States are, therefore, independent of the British standards and in part differ from them. The prevalent idea that the weights and measures in common use are identical with the British imperial system is. therefore, erroneous. The United States yard is slightly longer than the imperial yard and this inequality extends to all of its subdivisions and multiples. The present material standards of the United States are the national prototype metre No. 27 and the national prototype ktlo gram No. 20, received by the President of the United States on 2 Jan. 1890. These are ac curate copies of the international prototype metre and kilogram which are the fundamental standards of length and weight designed for the entire world. The latter standards are pre served at the International Bureau of Weights and Measures in accordance with the Interna tional Metric Convention of 1875, now by the leading countries of the world. countries jointly maintain and direct the work of this bureau through official representatives forming an international committee, composed of eminent scientific men.
The units of length and the derived units of area, volume and capacity are derived from the international metre in the ratio of 1 metre 39.37 inches (Law of 28 July 1866). Since 1893 the Office of Standard Weights and Measures and the Bureau of Standards which superseded that office have used the equivalent 1 yard°3600/3937 metre (by order approved 5 April 1893). This action fixed the values, in asmuch as the reference standards are as per fect and unalterable as human skill could make them. Besides the yard, the units of length most universally employed in the United States at the present time are the inch, foot and mile.
The •inch) is the 1-36 part of the yard and like it has been in use since ancient times. The name (derived from the Latin inicia, meaning the 12th part) occurs in A Saxon in the form of ynce. It probablyoriginated only as a convenient subdivision or the foot. Lengths shorter than one inch are commonly expressed in fractions of an inch. Two meth ods of subdivision are in common use: among builders and wood-workers it is customary to use the binary subdivisions, half quarter, eighth, etc., but machinists also divide the inch into
tenths, hundredths and thousandths. The inch is usually denoted by the symbol "; but bot anists use the symbol ' for the inch. The 'miner's inch' is a rather vague unit for the flow of water varying from 1.36 to 1.73 cubic feet per minute, and is the flow of water through a single square inch of orifice under varying beads of water. The 'inch or gauge of cream' is fixed by Iowa statute as equal to cese-half gallon.
The •foot• is legally defined as one-third of the yard or 12 inches. As its name implies it s as probably based on the length of the human foot Almost every nation, ancient and modern, has had a unit called the •foot,' its value differ ing somewhat, as might be expected with a unit of so crude an origin. Most countries, how vier. have now adopted the metric system, the fs.,ot being discarded as an official measure, though universally used in English countries. Lengths shorter than one foot are usually ex pressed in inches and fractions of an inch, but among surveyors and civil engineers it is quite common to use decimal fractions of the foot. The foot is generally denoted by the symbol ', bat botanists use the symbol • to denote feet. Some artisans use the foot and the inch but not the yard, others the yard and its binary di sisions, but not the foot or inch. Thus the foot and inch are used to the exclusion of the yard m building. while the yard and its binary sub divisions to the exclusion of the foot and inch in measuring cloth.
The •statute' or 'land mile* is the unit most commonly used for longer distances and is equal to 5.31O feet The name is from the Latin Rolle earneern, 1.000 paces, the Roman pace being a double step and consequently about five feet in length. This mile was used by the Anglo-Saxons. Almost every European nation has had a unit called the 'mile' but widely at variance with one another, ranging from about of the United States mile (Holland) up to seven United States miles (Norway). The old British statute mile was about 300 feet shorter than the United States mile but now is the same The following units of length are used in special work and are arranged in the order of their magnitude. Metric units are not included, as they are for the most part official only, and not generally in use in commercial and indus trial life See Mertic SYSTEM.
Mil (.001 inch) is used in electrical work, especially in indicating the cross section of The point (1-72 inch) is used in designating the sires of type, the point system designating the sines of type by the number of seventy-sec onds of an inch height of the type face. The em is a unit of measure used in composition and varies with the size of the typeusually as the square of the face line (1-12 inch) is little used, mechanics preferring to divide the inch into tenths, hun dredths and thousandths. It is used by printers aisd by botanists, the latter denoting the line by the symbol ". The line "button measure' is l-10 inch as defined in the tariff act.