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

D. KIND* ON THE HISTORY OF THE ELECTRICAL UNITS IN THE INTERNATIONAL SYSTEM OF UNITS Introduction The changeful development of the electrical units has already been represented in detail in international literature. As long as things were developing, mainly those scientists published their views, who took actively part in the solution of these as well important as difficult problems; and thus often controversial view points have been articulated with great emphasis. Today it is remaining only of historical interest, whether electrodynamics should be regarded as an independent domain of physics, for which special base units should be introduced, or not. This problem was decided definitely in favour of a so-called rationalized electrodynamic system with four base units by the world-wide adoption of the International System of Units (SI) containing as fourth base unit the ampere for the base quantity electric current. But also after the end of this development the electrical units have been reported on from a historical view in detail (1)—(7). Therefore, I should like to restrain myself to reporting on some decisive phases of the introduction of the electrical units at the end of the 19th and the beginning of the 20th century. In this connection I shall deal somewhat closer with contributions of the Physikalisch-Technische Reichsanstalt (PTR) without however neglecting in the least the really international character of the development. International Electrical Congress between 1881 and 1893 In the second half of the last century, the fast growing economical importance of electrotechnics furthered the insight in the necessity of an internationally unified system of electrical measurements. In fact, there were existing at that time in the various countries 12 different units of electromotive force, 10 different units of electric current, and 15 units of electric resistance. Going back to preparational work initiated by J. C. Maxwell [figure 1] and W. Thomson, the First International Electrical Congress was held in Paris in 1881. Among the 250 delegates from 28 countries there were well-renowned names as Rudolf Clausius, Marcel Deprez, Galileo Ferraris, Hermann von Helmholtz [figure 2], Gustav Kirchhoff, Ernst Mach, Werner von Siemens [figure 3], Sir William Thomson (Lord Kelvin). This is showing the signific* Physikalisch Teohnische Bundesanstalt Braunschweig, BRD. ,