System of Measurement

1. System of Measurement

2. Origin of the Metric System • Gabriel Mouton, the vicar of St. Paul's Church in Lyons, France, is the “founding father” of the metric system • He proposed a decimal system of measurement in 1670. • Mouton based it on the length of one minute of arc of a great circle of the Earth (now called a nautical mile, 1852 meters). • He also proposed the swing-length of a pendulum with a frequency of one beat per second as the unit of length (about 25 cm)

3. The Metric System • The political sponsor of weights and measures reform in the French Revolutionary National Assembly was the Bishop of Autun, better known as Talleyrand • The French Academy appointed several committees to carry out the work of developing a usable system of weights and measures for France-

4. The Metric System • One of the committees recommended a decimalized measurement system based upon a length equal to one ten-millionth of the length of a quadrant of the earth's meridian (i.e., one ten-millionth of the distance between the equator and the North Pole).

5. The Metric System • In 1790, in the midst of the French Revolution, the National Assembly of France requested the French Academy of Sciences to “deduce an invariable standard for all the measures and all the weights.” • The Commission appointed by the Academy created a system that was, at once, simple and scientific. • The unit of length was to be a portion of the Earth's circumference. Measures for capacity (volume) and mass were to be derived from the unit of length, thus relating the basic units of the system to each other and to nature. • Furthermore, larger and smaller multiples of each unit were to be created by multiplying or dividing the basic units by 10 and its powers. • This feature provided a great convenience to users of the system, by eliminating the need for such calculations as dividing by 16 (to convert ounces to pounds) or by 12 (to convert inches to feet).

6. In 1889, a new international prototype was made of an alloy of platinum with 10 percent iridium, to within 0.0001 National Prototype Meter No. 27 ca. 1875-1889  NIST Museum Collection

7. Meter • The meter is the length of the path traveled by light in vacuum during a time interval of 1/299 792 458 of a second. • Note that the effect of this definition is to fix the speed of light in vacuum at exactly 299 792 458 m·s-1.

8. Kilogram • The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram.

9. At the end of the 18th century, a kilogram was the mass of a cubic decimeter of water. In 1889, the 1st CGPM sanctioned the international prototype of the kilogram, made of platinum-iridium, and declared: This prototype shall henceforth be considered to be the unit of mass.

10. The Metric System • The initial metric unit of mass, the “gram,” was defined as the mass of one cubic centimeter — a cube that is 0.01 meter on each side — of water at its temperature of maximum density. For capacity, the “litre” (spelled “liter” in the U.S.) was defined as the volume of a cubic decimeter — a cube 0.1 meter on each side.

11. Second • The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. • The unit of time, the second, was defined originally as the fraction 1/86 400 of the mean solar day. The exact definition of "mean solar day" was left to astronomical theories.

12. The Metric System • The standardized structure and decimal features of the metric system made it well suited for scientific and engineering work. Consequently, it is not surprising that the rapid spread of the system coincided with an age of rapid technological development. In the United States, by Act of Congress in 1866, it became “lawful throughout the United States of America to employ the weights and measures of the metric system in all contracts, dealings or court proceedings.”

13. SI • The SI was established in 1960 by the 11th General Conference on Weights and Measures (CGPM, Conférence Générale des Poids et Mesures). • The CGPM is the international authority that ensures wide dissemination of the SI and modifies the SI as necessary to reflect the latest advances in science and technology.

14. SI prefixes and their etymologies • Prefix Symbol Factor Numerically Name • Giga G 109 1 000 000 000 billion** • Mega M 106 1 000 000 million • Kilo k 103 1 000 thousand • Centi c 10-2 0.01 hundredth • Milli m 10-3 0.001 thousandth • Micro μ 10-6 0.000 001 millionth • Nano n 10-9 0.000 000 001 billionth**

15. Some examples and relationships among units • 1 mL = 1 cm3 • 1 milliliter is the same volume as 1 cubic centimeter. • 1 mL of water has a mass of approximately 1 g • The mass of 1 milliliter of water is approximately 1 gram. • 1 L of water has a mass of approximately 1 kg • The mass of 1 liter of water is therefore approximately 1 kilogram. • 1 m3 of water has a mass of approximately 1 t • There are 1000 liters in a cubic meter, so the mass of 1 cubic meter of water is approximately 1000 kilograms or 1 metric ton.