C- (3,|£:30'-»■' '.""■ "<:» '"" "i 07M 5S5 0.946 353 28.349 5 0.4M 592 039 370 1 3 160 at 1093 61 '' mega (mEg a; ,,--, 001 = 10" cenli Isfn' li) 0091 = 10"'' mill! imffTl 0000 001 = 10'' mlco |m?kro| 0000000001 ; 10 ' nano |nSn 6) 000 000 001 ; 10- ; plco(o5'k0l 000 000 001 ; 10"" "cmlO (Itm I*) 0000000001 = IO""Blli>(Sl'wil REFERENCES eter ie »qu»re meter en | ..,,',■ Iiler 10001 cubic meter), illnoti , commonly used io measu*e lluid volume The standard (or the unit ot mass, the kilogram, Is a cylinder ol platinum-indium alloy kept by the Interna- tional Bureau ol Weights and Measures at Paris. A du- plicate in the custody ol the National Bureau of Stand- ards serves as the mass standard (or the United Slates. This Is the only base unit still defined by an artifact. ^g ^W u Pnou lair"""" The SI unit of force is the newton (N). One newton is the force which, when ifoBiou?"" applied to a 1-kilogram mass, will give the kilogram mass an acceleration ol 1 (meter per second) per second. 1 N = 1 kgtn/s* Wins ACCELERATION The SI unit for pressure Is the paical (P..| Ph 1N/nV The SI unit for work and energy of any kind Isthelouto (J). TIME The second is defined as the duration ot 9 1 92 63' 770 cycles ol the udialfon associated with a specilied transition ot Iho cesium-133 atom. II is realized by tuning an oscillator to the resonance frequency ol ceslumOM atoms as they pass through a system of magnets and a rr-sorianl cavity into a detector. or '*to<*. - only i The number of periods or cycles per second is called frequency The Si unit for frequency sine hertz [Hi! One h?r(z equals one cycle per second The SI unit lor speed's the meter per second (rn.'S) e (meter per Standard r r. i n ■ i time v '.WWB, ^nd WWVH. . .. ■ r the I .1 WWV and WWVH. on of 2 5 5 10 IS ant r n The SI uml ol voltage is the volt (V) ELECTRIC CURRENT □ their magnetic lields) of 2 * 10"' H=H- TEMPERATURE The ketvin is defined as trie trac- tion 1 '273.16 ot the thermody- namic lemperalure Ot the triple point of walpr The temperature K is called absolute zero". On the commonly used Celsius temperature scale, wa ■ ter Ireezes at about "C and boils ai about 100 "C.The 'C is delmed as an interval ol 1 K. and the Celsius tem- perature 'C is defined as 273.15 K 1 8 Fahrenheit degrees are equal to 1.0 *C or 10 K; the Fahrenheit scale uses 32 T as a temperature cor responding to °C. Tho standard temporrilure ol the Iripto point ol waler Is provided by a Special cell, an evacuated glass cylinder contain- ing pure waler When the cell is moled until a miinlle ol ice lorrns mound Ihe re- entrant well iho lemperalure at Ihe inter- face ol solid, liquid and vapOf is Z73 1C K Thermometers lobe calibrated are i ilaonl In Ihe reentrant welt. AMOUNT OF SUBSTANCE The mole Is the amount ot substance ol a system that contains as many elemen- When the mote is used, Ihe elementary enlllies must be specified and may be atoms, molecules, ions, electrons, othei particles, or specilied groups of such particles Tho SI unit of concentration (ol amount of substance) is the mole por cubic melor (mol/m 1 ). LUMINOUS INTENSITY The candela is Ihe luminous intensity, in a given direction, ol a source thai emits monochromatic radiation of frequency 540 * 1Q' ; hertz (Hz) and that has a radiant intensity in thai direction of 1/683 watt per steradian. PLANE ANGLE TWO SUPPLEMENTARY UNITS SOLID ANGLE Radiation at frequencies other than 540 • 10'-' H2 is also measured in candelas in accordance with the standard luminous efficiency. V(aJ, curve that peaks at 540 * 10'-' Hz (yellow green J. The steradian is the solid angle wiih ils vortex al Ihe center ol a sphoro that is subtended by an area ol Ihe spherical surface equal to that ol a square wilh sides equal in length lo the radius ,7 YARD 1, cEHn.no. '" 2 ° 3 ° " METER » » 70 eo and 19th centuries, the English system of weights and measures was spread to and established in many parts of the world, including the American colonies. However, standards still differed to an extent undesirable for commerce among the 13 colonies. The need for greater uniformity led to clauses in the Articles of Confederation (ratified by the origi- nal colonies in 1781) and the Constitu- tion of the United States (ratified in 1790) giving power to the Congress to fix uniform standards for weights and measures. Today, standards supplied to all the States by the National Bureau of Standards assure uniformity throughout the country. The Metric System The need for a single worldwide coor- dinated measurement system was recog- nized over 300 years ago. Gabriel Mou- ton, Vicar of St. Paul in Lyons, proposed in 1670 a comprehensive decimal meas- urement system based on the length of one minute of arc of a great circle of the earth. In 1671 Jean Picard, a French astronomer, proposed the length of a pendulum beating seconds as the unit of length. (Such a pendulum would have been fairly easily reproducible, thus facilitating the widespread distribu- tion of uniform standards.) Other pro- posals were made, but over a century elapsed before any action was taken. 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 ca- pacity ( volume ) and mass ( weight ) were to be derived from the unit of length, thus relating the basic units of the system to each other and to nature. Furthermore, the larger and smaller versions of each unit were to be created by multiplying or dividing the basic units by 10 and its powers. This fea- ture 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). Simi- lar calculations in the metric system could be performed simply by shifting the decimal point. Thus the metric sys- tem is a "base-10" or "decimal" system. The Commission assigned the name metre — which we spell meter — to the unit of length. This name was de- rived from the Greek word metron, meaning "a measure." The physical standard representing the meter was to be constructed so that it would equal one ten-millionth of the distance from the north pole to the equator along the meridian of the earth running near Dun- kirk in France and Barcelona in Spain. The metric unit of mass, called the "gram," was defined as the mass of one cubic centimeter (a. cube that is 1/100 of a meter on each sfde) of water at its temperature of maximum density. The cubic decimeter .(a cube 1/10 of a meter on each side) was chosen as the unit of fluid capacity. This measure was given the name "liter." Although the metric system was not accepted with enthusiasm at first, adop- tion by other nations occurred steadily after France made its use compulsory in 1840. The standardized character and decimal features of the metric system made it well suited to scientific and en- gineering work. Consequently, it is not surprising that the rapid spread of the Aoaoovnaosia For sule by the Suijerlntrudeiit of Documents. U.S. Govei Washington, D.C. 20402 - Price SI. 75 SI-30IA (METRIC HISTORY & CHART) nt Printing Offlct system coincided with an age of rapid technological development. In the United States, by Act of Congress in 1866, it was made "lawful throughout the United States of America to employ the weights and measures of the metric system in all contracts, dealings or court proceedings." By the late 1860's, even better metric standards were needed to keep pace with scientific advances. In 1875, an in- ternational treaty, the "Treaty of the Meter," set up well-defined metric stand- ards for length and mass, and estab- lished permanent machinery to recom- mend and adopt further refinements in the metric system. This treaty, known as the Metric Convention, was signed by 17 countries, including the United States. As a result of the Treaty, metric standards were constructed and distrib- uted to each nation that ratified the Convention. Since 1893, the interna- tionally agreed-to metric standards have served as the fundamental weights and measures standards of the United States. By 1900 a total of 35 nations — in- cluding the major nations of continental Europe and most of South America — had officially accepted the metric sys- tem. In 1971 the Secretary of Com- merce, in transmitting to Congress the results of a 3-year study authorized by the Metric Study Act of 1968, recom- mended that the U.S. change to predominant use of the metric system through a coordinated national pro- gram. The Congress responded by enacting the Metric Conversion Act of 1975. Today, with the exception of a few small countries, the entire world is using the metric system or is chang- ing to such use. The International Bureau of Weights and Measures located at Sevres, France, serves as a permanent secretariat for the Meter Convention, coordinating the ex- change of information about the use and refinement of the metric system. As measurement science develops more pre- cise and easily reproducible ways of de- fining the measurement units, the Gen- eral Conference on Weights and Meas- ures — the diplomatic organization made up of adherents to the Convention — meets periodically to ratify improve- ments in the system and the standards. In 1960, the General Conference adopted an extensive revision and sim- plification of the system. The name Le Systeme International d'Unitcs (Inter- national System of Units), with the in- ternational abbreviation SI, was adopted f ir this modernized metric system. Fur- er improvements in and additions to I were made by the General Confer- ice in 1964. 1968, 1971, 1975, and ,979.