Weights and Measures, General Conferences on

international conferences of representatives of member countries of the metric convention, which meet not less often than once every six years to discuss and adopt necessary measures for the dissemination and improvement of the metric system. The conferences report on the work of the International Committee on Weights and Measures and on the work of the International Bureau of Weights and Measures for the period between the conferences, adopt decisions on metrology, and hold new elections for half of the membership of the international committee.

Up to 1970, 13 conferences have been held, in which a number of important decisions have been adopted. The first conference, held in 1889, established an international prototype of the meter and the kilogram. The second conference (1895) confirmed the meaning of the meter in length of light waves on the basis of the work done at the International Bureau of Weights and Measures by the American scientist A. Michelson and the French scientist R. Benoit. The third conference (1901) clearly delineated the concept of mass and weight and adopted a value for the normal acceleration of free fall. The sixth conference (1921) revised the Metric Convention of 1875 and greatly broadened the work of the International Bureau of Weights and Measures. The seventh conference (1927) established the relation between the meter and the wavelength of a red line of cadmium and introduced the international practical temperature scale. The eighth conference (1933) charged the International Bureau of Weights and Measures to set a length of time for converting from international electrical units to absolute units, a conversion completed by Jan. 1, 1948. The ninth conference (1948) adopted a new definition of the unit of luminous intensity, the candela, through the luminescence of a full radiator (black-body) at the freezing point of platinum. The tenth conference (1954) established a thermodynamic temperature scale with one reference point and the basic unit of the International System of Units (SI). The 11th conference (1960) confirmed the SI and adopted a definition of the meter from the length of a lightwave and an astronomical definition of the second as a definite fraction of the tropical year. The 13th conference (1967) adopted a definition of the second through the emission periods of the atom ¹³³Cs.