Technikatörténeti szemle 10. (1978)

A MÉRÉS ÉS A MÉRTÉKEK AZ EMBER MŰVELŐDÉSÉBEN című konferencián Budapesten, 1976. április 27–30-án elhangzott előadások II. - Kind, D.: Az elektromos mértékegységek fejlődése a SI rendszerben

the metre and the second to the wavelength and the frequency of specified atomic transitions, the ampere to the magnetic field constant fi

0

, which gets a constant value by the definition of the ampere. All derived electrical units can be expressed as products of powers of the base units, having only integer exponents, for instance: 1 Q = 1 m

2 kg s3 A2 1 V = 1 m

2 kg s-3 A-1 The uncertainty of the realization is at present: 4 • 10~

9 for the metre 8 • 10-9 for the kilogram 1,5» 10~

13 for the second 3 • 10~

8 for the ampere Here the entry for the kilogram is giving the uncertainty at the comparison of the national standard with the international prototype of the kilogram. New measuring methods as the application of the Josephson effect for maintaining the unit of voltage did lead, for instance, to an improvement of the reproducibility to better than 1 part in 10'. Further improvements can also be expected from precision measurements of the fundamental physical constants (13). W. Jaeger concludes his historical representation of the electrical units in 1932, as the development to an International System of Units of the Metre Convention has been already imminent, with resignation (10): "Perhaps, we will soon stand on the brink of the grave of the 'international' electrical units. That would be a curious circular course! At the time of the Paris Congress one started from the absolute measures and tried to establish empirical units corresponding to them as accurately as possible. After having adopted the resolutions, one has tried to determine the relation of these international measures to the absolute units by very precise measurements, and now, one is perhaps prepared to discard the imperial international measures completely. Then all the trouble and work as well as the various congresses would have been entirely s uperfluous. Herein is lying after all a certain tragedy". In the meantime, the decisions were made long ago and the SI has become a reality; certainly there will develop improvements of this system, but there will be no abandonment of the SI. I am sure, the above-cited author would, considering what has been achieved today, incline to the opinion that all the efforts for the international electrical units were necessary investments for the future. LITERATURE 1. IEC-Publication 164: Recommendations in the field of quantities and units used in electricity; Genf 1964 2. Stille, U.: Messen und Rechnen in der Physik; Vieweg, Braunschweig 1961