MAY, 20 1875: THE METRE CONVENTION IN PARIS

International Committee for Weights and Measures

Today, Joseph de Ca'th Lon wants to talk about the metre, in its 142nd anniversary, and about its importance in our societies as a measure of distance.

The Metre Convention, Convention du Mètre or the Treaty of the Metre is an international treaty that was signed in Paris on 20 May 1875 by representatives of 17 nations. 

The treaty set up an institute for the purpose of coordinating international metrology and for coordinating the development of the metric system. The treaty also set up associated organizations to oversee the running of the institute. 

Initially it was only concerned with the units of mass and length but, in 1921, at the 6th meeting of the General Conference on Weights and Measures (CGPM), it was revised and its mandate extended to cover all physical measurements. 

In 1960, at the 11th meetings of the CGPM, the system of units it had established was overhauled and relaunched as the International System of Units (SI).

More information: Bureau International des Poids et Mesures (BIPM)

Membership of the convention is restricted to countries who have diplomatic relations with France, but in 1999 the category of associate membership was introduced for those nations that wished to partake in the calibration and measurement aspects of the CIPM Mutual Recognition Agreement (CIPM-MRA) program without taking part in the activities of the BIPM.

Second CGPM, Pavillon de Breteuil, Paris

In England in 1215, clause 25 of the Magna Carta set out the standards of measure that were to be applied throughout the realm prefixed. The wording of the clause emphasised that There is to be a single measure ... throughout our realm. 

Five centuries later, when in 1707 England and Scotland were united into a single kingdom, the Scots agreed to use the same units of measure that were already established in England. 

During the eighteenth century, in order to facilitate trade, Peter the Great, Czar of Russia adopted the English system of measure.

Abuse of units of measures were one of the causes of the French Revolution and its reform was one of the items on the agenda of National Assembly. Talleyrand, an influential leader of the Assembly invited British and American participation in the establishment of a new system, but in the event, the Assembly went it alone and introduced the metre and the kilogram which were to form the basis of the metric system, manufacturing prototypes which, in 1799, were lodged with Archives.

More information: French Metrology

Between 1850 and 1870, a number of countries adopted the metric system as their system of measure including Spain, many South American republics and many of the Italian and German states, the Netherlands had adopted the system in 1817. In 1863, the International Postal Union used grams to express permitted weights of letters.

Mesure d'un Arc du Grand Méridien

In 1867, at the second general conference of the International Association of Geodesy held in Berlin, the question of international length standard aroused with the concern for combining the measurments made in different countries in order to determine the size and shape of the earth. 

The conference recommended the adoption of the metric system and the creation of an international metre commission.

In the 1860s, inspections of the prototype metre revealed wear and tear at the measuring faces of the bar and also that the bar was wont to flex slightly when in use. In view of the doubts being cast on the reproducibility of the metre and the kilogram and the threat that a rival standard might be set up, Napoleon III invited scientists from all the world's nations to attend a conference in Paris. 

In July 1870, two weeks before the conference was due to start, the Franco-Prussian War broke out. Although the delegates did meet, without a German delegation, it was agreed that the conference should be recalled once all the delegates, including the German delegation, were present. France was defeated in the war, Napoleon went into exile and Germany and Italy, now unified nations, adopted the metric system as their national system of units, but with the prototype copy of the kilogram and metre under the control of the Third French Republic. 

In 1872 the new republican government reissued the invitations and in 1875 scientists from thirty European and American countries met in Paris.

More information: NPL

 Rhyme, that enslaved queen, that supreme charm of our poetry, 

that creator of our meter. 

Victor Hugo