For all people, for all time


Why not "export" the metric system?

Indeed, even before it was born, one was concerned about having the whole world benefit from the advantages of the new system. Beeckman was seeking an "invariable measure for people in all places and all times". Burattini wanted that "all civilized people in the world use the same measures and weights in spite of the different languages and habits". In his speech of 1790, Talleyrand - possibly with some second thoughts - suggested to associate the British government and scientists in the determination of "the natural unit of measures and weight". At the same time one looked with attention at George Washington and Thomas Jefferson's endeavors to amend the US system of measures. The republican wars shelved the proposals but in 1795 the Committee for public education invited the young Republic of Batavia (now the Netherlands) "to spread beyond the boundaries of the French territory the system of uniform and decimal measures". Furthermore in 1798 international (i.e. European) commissions were called in to check the meter and kilogram standards.

The result may be surprising: France was not the first state to become "metric": Belgium and the Netherlands were awarded the first place.

A keen interest for the French system

Then came the first universal expositions: London in 1851, Paris in 1855 and again in 1867. In these technological show-rooms of nations jumping into the industrial revolution, one began to dream of a system of uniform measures that would ease trade and science relations. The French system, coherent, with its decimal ratios, did appear as the system of the future.

French government convenes an international conference

As it did in 1840 the French government, informed by the Bureau des Longitudes of Paris, seizes the opportunity: by a note of 16th November 1869 the Foreign Affairs Minister of Napoleon III directs the ambassadors to invite governments to dispatch scientists to a meeting in Paris of an International Committee of Meter, aiming at considering how to give to the metric system the universal scope intended from its inception on.


Through working group meetings, lobby discussions, plenary sessions, the Conference proceeds. And by 20th May 1875, plenipotentiaries of 17 countries out of those participating sign, on behalf of their governments, the International Metric Convention, soon called Convention du Mètre. Which countries did not sign? Greece and the Netherlands, albeit already metric, perhaps worrying about the consequences of the Convention; and... Great Britain. But the United States of America did sign enthusiastically! As soon as December of that year, the first national ratifications were solemnly received at a ceremony in Château of Versailles and the Treaty could come in force at the planned date of 1st January 1876.


France had the glory - the chairmanship of the General Conference (CGPM). But also the charge to put at the disposal of the Bureau (BIPM) a decent building. The price tag was not to high to put a term to three-quarters of a century of endeavors to export the product of the Revolution.

The International Bureau of Weights and Measures

I recall that I was very proud to be taught at school that the global standards of meter and kilogram, made of iridized platinum (I did not know what it meant, but I found the term very pleasant) were deposited at the Pavilion of Breteuil in France. If I believe my grand-children, it seems that this is no longer taught; quite regrettable... The International Bureau of Weights and Measures - BIPM in all languages in the world - was indeed the first international organization to be hosted by France. At that time there were not so many international organizations!

The international prototypes

From the series of standards made, the CIPM selected after many tests a specimen of the Meter and a specimen of the Kilogram; they were officially presented by the Committee to the 1st CGPM in 1889 which accepted them as international prototypes. Since that time, their names are written with a capital letter... They were then deposited in a cave underneath the Pavilion of Breteuil, 9 meter below the surface: the Kilogram under a three-layer glass bell under vacuum, the Meter in a metal case. Three keys - one less than for the cabinet that held the Archives meter and kilogram - are needed to enter the cave: one is kept by the Chairman of the CIPM, another by the BIPM Director, the last one by the President of Archives of France. Why such a profusion of precautionary measures? Simply because any manipulation entails the risk of altering the prototypes characteristics: for example dust particles could adhere to the surface of the Kilogram in spite of its perfect polish, or conversely some metal particles could be torn out by rubbing, and this could change its mass in intolerable proportions - a few thousands of milligrams. Thus are they taken out as less often as possible, four times in hundred years, in 1899, 1911, 1939 and 1946, and "standards" are used, as exact and accurate, but they are not the prototypes.

CGPM is in charge of keeping the system up to date: the International System (SI) is now in force, with units meeting the various needs . Most of these units bear names derived from scientists.

Amongst these 32 names, just one lady: our great Marie Curie (1867-1934). Yet the curie was replaced in 1975 by the becquerel. The law on equal opportunity was not yet in force... Let us be comforted by the fact that Antoine Henry Becquerel (1852-1908) was a French physicist who shared in 1903 a Nobel prize with Pierre and Marie Curie. No more names from the Arabic or Eastern civilizations. There is no such thing as a unique History...

However the system has lost the initial simplicity.

Astronomers for example say that Neptune is far from the sun by 30 astronomic units; that our galaxy has a diameter of 30 000 parsecs; that the Spiral Nebula stands at 2 millions of light-years. Fine, but same values could well be expressed in SI units, respectively 4.5 Tm (terameters), 300 Em (exameters) and 21 Zm (zettameters). More correct, certainly less poetic. Similarly oceanographers quantify oscillations of El Niño stream in sverdrups, from the name of the Norwegian explorer and geographer H. U. Sverdrup. They could as well speak of hm3/s (cubic hectometers per second) or, even simpler, millions of m3/s. In the field of nuclear physics, effective areas are measured in barns, a barn equating 1 fm2 (you grasped it right: a square femtometer). Textile manufacturers express thread thickness in tex (a tex being the diameter of a 1000 meter long thread having a mass of one gram), but the retail textile market still uses the denier, equal to 1/9th of a tex. There is also the diopter of opticians, simply the inverse of the distance in meters. Finally energy of explosions is rated in TNT tons: in pure SI a ton of TNT is roughly equivalent to 4 Gigajoules; this does not speak to anybody, whilst everyone may visualize the damages made by a ton of trinitrotoluene explosive...





United Kingdom

United States