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

also introduced into the law—resulting from international comparisons of the absolute determinations of the ohm. Two important events, which must be mentioned in connection with the development of the electrical units, are the foundation of the National Physical Laboratory (NPL) in Teddington, Great-Britain, in 1900 and of the National Bureau of Standards (NBS) in Washington, USA, in 1901. The work for the international electrical system of units, already being successfully under way in these and other countries, has been continued and intensified in these institutions. From the deficiency of the Chicago resolutions of 1893 and the differences in the legislation on the electrical units in the various countries followed the urgent necessity to come anew to an international agreement. This became particularly obvious at the International Electrical Congress held in St. Louis, USA, in 1904, at which the constitution of the International Electrotechnical Commission (I EC) was initiated. The national standardizing laboratories, responsible for the maintenance of the electrical units, were charged to make efforts to reach a common proposal for new international resolutions. At the suggestion of S.W. Stratton, director of the NBS, the then president of the PTR, Emil Warburg, invited representatives of the various national standardizing laboratories and several scientists, who had dealt especially with the electrical units, to an International Conference in Berlin—Charlottenburg in the PTR in October 1905. This Conference got, due to its inofficial character, rarely known, although important preliminary decisions for the later development had been achieved; therefore it shall be shortly described here. Under the chairmanship of E. Mascart (France), among others, the following scientists discussed suitable resolutions regarding the representation of the international electrical units: H.S. Carhart (USA), E. Gerard (Belgium), R.T. Glazebrook (Great Britain), V. von Lang (Austria) as well as F. Kohlrausch and E. Warburg (Germany). The guests were surprised by a proposal of the PTR that those countries interested in rules for electrical metrology should constitute an „International Bureau for Electrical Measures", which in analogy to the Bureau International des Poids et Mesures (BIPM) at Sevres should establish and disseminate mercury standards for the ohm. Likewise the meanwhile developed Weston cadmium cell could be established as voltage standard and disseminated. This Bureau should be affiliated to one of the already existing national standardizing laboratories. With regard to the level reached in Germany in establishing mercury standards and also easily transportable manganin resistors, PTR was proposed as location for the Bureau in the discussions. However, the guest participants of the Conference, were not prepared to agree to the German proposal. Therefore this matter was not persued any longer at that time. It was decided to recommend only two base units, i.e. the ohm, defined in terms of a mercury resistance, and the ampere, defined in terms of the electrolytical deposition of silver. The unit volt for the electromotive force was defined by Ohm's law, introducing the Weston cell as voltage standard. A linkage to the ,.absolute" CGS system was not mentioned any more. An official congress should only be held after a satisfying agreement had been reached for the determination of units from the experimental work under way in the national standardizing laboratories. The foreseen International Conference on Electrical Units and Standards was finally held in London in 1908, in which 46 delegates from 26 countries participated,