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National Geographic : 1977 Aug
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cubing a tenth of a meter to produce the liter. And a liter of water produced a basic unit of mass, the kilogram. For larger units, multiples on the basis of 10 were eventually provided, with Greek prefixes: thus dekameter for 10 meters, hectometer for 100, kilometer for 1,000, megameter for a mil lion, and so on. For subdivi sions, Latin prefixes were used: decimeter for a tenth of a meter, centimeter for a 100th, millimeter for a 1,000th, and micrometer for a millionth. Thus all the units were inti mately and uniformly related. For the first time the world had available a consistent, unified measurement system in which calculations would be easy no more unwieldy fractions, no more memorizing a host of con version factors. "Never has anything more grand and simple, more co herent in all its parts, issued from the hand of man," wrote Antoine Lavoisier, the most famous French scientist of the time. Over the decades the metric system has been modified and expanded into what is known today as SI, Le Systeme Inter national d'Unites. SI provides five other basic units besides the meter and the kilogram. For example, the unit for time is the second; the ampere is the basic unit for electricity; and for temperature the degree Celsius (formerly centigrade). For scientific use, temperatures are measured in kelvins start ing with absolute zero (-273.15 °C). A kelvin is equal to a degree Celsius. In addition, the meter has been redefined, for even greater accuracy, as 1,650,763.73 wavelengths of orange-red light emitted by the krypton-86 atom. Gradually at first, then ever more rapidly, the metric system took root in Europe in the 19th century. It spread to other con tinents until, today, 95 percent of the world's inhabitants speak its language. Only in the United States (and in Brunei, Burma, Liberia, and Yemen) is it not yet the system generally in use. Repeatedly our nation has approached metrication, but it has always backed away from full embrace. Nevertheless, by act of Congress, metric has been "legal" in the United States since 1866. Multiplication factor Prefix Symbol 1000000000000000000= 1018 exa 1 000 000 000 000 000 = 1015 peta 1 000 000 000 000 = 1012 tera 1000000000= 109 giga 1000 000 = 106 mega 1000= 103 kilo 100 = 102 hecto 10=10 deka 0.1 = 10- 1 deci 0.01 = 10- 2 centi 0.001 = 10- 3 milli 0.000 001 = 10- 6 micro 0.000 000 001 = 10- 9 nano 0.000 000 000 001 = 10- 12 pico 0.000 000 000 000 001 = 10- 15 femto 0.000 000 000 000 000 001 = 10-18 atto E P T G M k h* da* d* c* m n P f a Meaning (in USA) one quintillion times one quadrillion times one trillion times one billion times one million times one thousand times one hundred times ten times one tenth of one hundredth of one thousandth of one millionth of one billionth of one trillionth of one quadrillionth of one quintillionth of In other countries trillion thousand billion billion milliard milliardth billionth thousand billionth trillionth *While hecto, deka, deci, and centi are SI prefixes, their use should generally be avoided except for the SI unit-multiples for area and volume and nontechnical use of centimeters, as for body and clothing measurement. The prefix hecto should be avoided also because the longhand symbol h may be confused with k. 289 _ Metric (SI) prefixes
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