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
ance attributed world wide to this prbceeding. Wilhelm Weber [figure 4], who gained special merits regarding the electrical units by his eminent theoretical and experimental work, could not participate in the Congress due to his state of health. Already in 1873, that means 8 years before the Paris Congress, there had appeared Maxwell's famous book A Treatise on Electricity and Magnetism, in which electrodynamics is described so ingeniously and completely. In this book already physical quantities are introduced as the product of „the numerical value and the name of the concrete unit". For practical applications there was, however, needed not only a unified representation of the electrical units but also a representation which could be realized with accuracy and by modest means. Here the unit for electric resistance takes a central rank; to that Maxwell is writing: ,,In the present state of electrical science, the determination of the electric resistance of a conductor may be considered as the cardinal operation in electricity, in the same sense that the determination of weight is the cardinal operation of chemistry. The reason of this is that the determination in absolute measure of other electrical magnitudes, such as quantities of electricity, electromotive forces, currents, etc., requires in each case a complicated series of operations" and „must be repeated for every new determination because it is impossible to preserve a unit of electricity, or of electromotive force, or of current, in an unchangeable state, so as to be available for direct comparison." Consequently the International Electrical Congress of 1881 dealt particularly with an internationally unified representation of the units ohm, volt, and ampere for the quantities electric resistance, voltage, and current, intending however a linkage to the electromagnetic (e.m.) CGS system. On the base of a standard introduced by Werner von Siemens already in I860, it was decided that the ohm is represented by the electric resistance of a column of mercury of 1 mm 2 crosssection and of a length, still to be determined exactly, at the temperature of 0 °C. The questions raised in 1881 initiated comprehensive activities of interested scientists in several countries. They also gave a main impulse to the foundation of the first national standardizing laboratory, the Physikalisch-Technische Reichsanstalt (PTR) in Berlin in 1887, whose first president became Hermann von Helmholtz. Werner von Siemens, who particularly furthered the PTR, wrote as the foundation of the PTR was at first delayed (9): „Thus it is the responsibility of the Reich to take care of the installation of an institution for electrical metrology and calibration. It must be regarded as a great want that this has not yet been achieved. At present there are settled contracts on millions of value on the base of electrical measures which are not yet determined legally. It arises the danger that this lawlessness regarding the electrical measures will lead to great legal insecurity and many lawsuits." As a further remarkable event should be mentioned the International Electrical Congress of 1893 in Chicago. There agreement was reached on definitions relating to the CGS system and simultaneously on rules for the realization of the representation of the following units: : , :
