DEVELOPMENT of SI MEASURES

DEVELOPMENT of SI MEASURES

Post 258 ⇒   by Gautam Shah  →

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First International effort to develop a worldwide policy for weights and measures was made during May 1875. Some 17 countries signed a Metre Convention or Convention du Mètre, an international treaty to create a ‘permanent mechanism to recommend and adopt further refinements in the metric system’. This was directed towards defining what constitutes a standard measure unit, means to replicate it in great accuracy anywhere and any-time, and towards defining sub units for the main measures.

A decimal system of measurement was part of Wilkin’s philosophical language published in 1668

The metric convention was held at the time of heightened Industrial activity during the Industrial Revolution period across Europe and USA. Signatories of Treaty of Metric were: USA, Germany, Hungary, Belgium, Brazil, Argentina, Denmark, Spain, France, Italy, Peru, Portugal, Russia, Sweden, Norway, Switzerland, Turkey, Venezuela.

After the Convention du Mètre in France in 1875, a General Conference on weights and measures or Confèence gènvrale des poids et measures CGPM was organised in 1889. Eight CGPM, at rough intervals of 4 years, were held till 1933, followed by an inactive period due to world war II. These meetings gradually evolved a worldwide policy on the advice of scientists and metrologists (Metrology is science of measurements).

Conférence générale des poids et measures (CGPM), an intergovernmental conference of official delegates of member nations and the supreme authority for all actions. It continued the deliberations of Convention du Mètre.

Comité international des poids et measures (CIPM), consisting of selected scientists and metrologists, which prepares and executes the decisions of the CGPM and is responsible for the supervision of the International Bureau of Weights and Measures.

Bureau international des poids et measures (BIPM), a permanent laboratory and world centre of scientific metrology, the activities of which include the establishment of the basic standards and scales of the principal physical quantities and maintenance of the international prototype standards.

Pavillon de Breteuil in Sèvres was offered by French Government to house the BIPM. The pavilion was built in 1675, and was home to Emperor Napoleon III.

Hectic reconstruction activities began everywhere in the post world war II (1945) period. Major impediments to this effort were the differing National Standards. To allow free flow of raw materials, equipments and technology a platform of common Standards and Specifications was required. In 1946, delegates from 25 countries met in London to create a new organization, to facilitate the international coordination and unification of industrial standards. The new organization, Organisation internationale de normalisation, ISO, officially began operations on 23 February 1947, in Geneva, Switzerland.

The word ISO was selected to represent the organization in all languages, because it is derived from the Greek isos, meaning equal.

9th CGPM in 1948, meeting after 15 years gap due to WW II formally adopted a recommendation for writing and printing of measure unit symbols and numbers. The name Systeme International d’Unites (International System of Units), with the international abbreviation SI, was adopted for this New Metric System.

In 1960, the CGPM revised and simplified the measure system. Seven Base Units such as: meter (Length), kilogram (Mass), second (Time), ampere (Electric current), kelvin (Temperature), mole (Substance), and candela (Luminous intensity), were established.

Determination of the rod, using the length of the left foot of 16 randomly chosen people coming from church service. Woodcut published in the book Geometrei by Jakob Köbel (Frankfurt, c. 1536)

Acceptance of SI has been varied. For French and other European countries including their colonies, already using MKS system, adopting the new system (SI) was very easy. In 1965 Britain started using it. Canada, Australia, New Zealand, and South Africa quickly followed and soon exceeded the speed of change in Britain. In 1975, USA officially accepted the Metric system (in the form of SI system), but no specific schedule was set for the change over.

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