WEIGHTS AND MEASURES The Metric System Source: Bureau of Standards, U. S. Department of Commerce The International Prototype Meter is kept at the International Bureau of Weights and Measures. By definition the meter now bears no definite relation to the earth's quadrant, but is the length of a certain platinum-iridium bar when supported in a definitely specified manner, at the temperature of melting ice, and at standard atmosphere pressure (760 millimeters of mercury). The kilogram is independently defined as the mass of a definite platinum-iridium standard, the International Prototype Kilogram, which is also kept at the International Bureau of Weights and Measures. The liter is defined as the volume of a kilogram of water, at standard atmospheric pressure, and at the temperature of its maximum density, approximately 4° C. The meter is thus the fundamental unit on which are based all metric standards and measurements of length and area, and of volumes derived from linear-measurements. Comparison of Metric and Customary Units From 1 to 9 A supplementary definition of the meter in terms of the wave length of light was adopted provisionally by the Seventh General (International) Conference on Weights and Measures, in 1927. According to this definition, the relation for red cadmium light waves under specified conditions of temperature, pressure, and humidity is-1 meter-1 553 154.13 wave lengths. This corresponds to a wave length (cadmium red) of 6 438.469 6x10 millimeters. The kilogram is the fundamental unit on which are based all metric standards of mass. The liter is a secondary or derived unit of capacity or volume. The liter is larger by about 27 parts per million than the cube of the tenth of the meter, i.e., the cubic decimeter-that is, 1 liter=1.000 027 cubic decimeters. All lengths, areas, and cubic measures in the tables are derived from the international meter, the basic relation between units of the customary and the metric systems being: 1 meter=39.37 inches. All capacities are based on the equivalent 1 liter equals 1.000 027 cubic decimeters. The decimeter is equal to 3.937 inches in accordance with the legal equivalent of the meter given above. The gallon referred to in the tables is the United States gallon of 231 cubic inches. The bushel is the United States bushel of 2 150.42 cubic inches. These units must not be confused with the British units of the same name which differ from those used in the United States. The British gallon (277,420 cubic inches) is approximately 20 percent larger, and the British bushel (2 219.36 cubic inches) is 3 percent larger than the corresponding units used in this country. All weights are derived from the International Kilogram, as authorized in the Mendenhall Order of April 5, 1893. The relation used is 1 avoirdupois pound-453.592 427 7 grams. volume occupied by the mass of 1 kilogram of pure A liter (liter) is a unit of capacity equal to the water at its maximum density (at a temperature of 4° C, practically) and under the standard atmospheric pressure (of 760 mm). It is equivalent in volume to 1.000 027 cubic decimeters. A bushel (bu) is a unit of capacity equal to the volume of 2 150.42 cubic inches. This is the socalled stricken or struck bushel. A heaped bushel for apples of 2 747.715 cubic inches was established by the U. S. Court of Customs Appeals on Feb. 15, 1912, in United States v. Weber (no. 757). A heaped bushel, equivalent to 14 stricken bushels, is also recognized. |