This is an electronic reprint of the original article. This reprint may differ from the original in pagination and typographic detail. Sihvola, Ari Johan Jacob Nervander and the Quantification of Electric Current [Historically Speaking] Published in: IEEE Antennas and Propagation Magazine DOI: 10.1109/MAP.2020.3039803 Published: 01/02/2021 Document Version Peer reviewed version Please cite the original version: Sihvola, A. (2021). Johan Jacob Nervander and the Quantification of Electric Current [Historically Speaking]. IEEE Antennas and Propagation Magazine, 63(1), 123-128. [9347404]. https://doi.org/10.1109/MAP.2020.3039803 This material is protected by copyright and other intellectual property rights, and duplication or sale of all or part of any of the repository collections is not permitted, except that material may be duplicated by you for your research use or educational purposes in electronic or print form. You must obtain permission for any other use. Electronic or print copies may not be offered, whether for sale or otherwise to anyone who is not an authorised user. Powered by TCPDF (www.tcpdf.org) JOURNAL OF LATEX CLASS FILES 1 Johan Jacob Nervander and the quantification of electric current Ari Sihvola, Fellow, IEEE This article focuses on the developments in electromagnetism during the early 19th century. The discovery of electromag- netism by Hans Christian Ørsted in 1820 was a game-changing event which opened perspectives into deep understanding of physics and fundamental technical applications. In this paper, the principles to measure and quantify the electric current are given particular attention. Several scientists, like Schweigger, Poggendorff, Nobili, and Pouillet, contributed to the development of an instrument towards this purpose, the galvanometer. In this article, we put special emphasis on the researches by Johan Jacob Nervander, whose ”tangent bussol”, presented to L’Institute de France in Spring 1834, and later published in Annales de Chimie et de Physique, was a significant milestone in the instrumention of electrical engineering. Index Terms—history of electromagnetics, electric current, tan- gent galvanometer, tangent bussol, Ørsted, Pouillet, Schweigger, Nervander Fig. 1. Hans Christian Ørsted [1] honored by the airline company Norwegian (photo: A. Sihvola). I. INTRODUCTION:ØRSTED AND ELECTROMAGNETISM Uman understanding and exploitation of electrical and immediately Ørsted’s discovery and started to build on it. magnetic phenomena have a long history. For centuries H During the weeks after Arago’s seminar he worked intensively, these forces were considered to independent and separate. and established the quantitative laws of electrodynamics. However, after the invention of the voltaic pile, a battery, by These were later (1827) codified into his exposition on the Alessandro Volta in 1800, a continuous source of electricity mathematical foundations of electromagnetism [4], which has was available. This device offered the possibility to study been called by L. Pearce Williams—not unfairly—as the the effects of electric current: production of heat, radiation ”Principia of Electrodynamics” [5]. It is, however, essential of light, and chemical electrolysis. But indisputably the most to note the different emphases of the character of magnetism profound development was the discovery of electromagnetism: by the two scientists: while Ampere` reduced magnetic effects the creation of magnetic force by electric current. into macroscopic and microscopic electric currents, Ørsted This happened two hundred years ago. In 1820, Hans considered that magnetism should have an ontological status Christian Ørsted (Fig. 1) demonstrated and documented the in its own right [6]. connection between electricity and magnetism for the first time. His short letter Experimenta circa effectum conflictus Also other French scientists contributed to the understanding electrici in acum magneticam, dated 21 July 1820, spread out of the magnetic laws. To electrical engineering students, the fast through the scientific circles of the world and caused law named after Jean Baptiste Biot (1774–1862) and Felix a revolution in the understanding of the unified character Savart (1791–1841) is a fundamental one, analogous to the of natural forces. Ørsted lived, worked, and performed his Coulomb law in electrostatics. And again, this dates early, experiments in Copenhagen. And there, in Denmark, the from the year 1820, with the connection to Pierre-Simon bicentennial has duly been celebrated in 2020. For example, Laplace (1749–1827) who attached the field’s inverse-square the recent publication of the book Hans Christian Ørsted—the dependence on distance in the differental law to the inverse- Unity of Spirit and Nature [2], [3] illustrates several aspects distance dependence for the field due to a straight long current of the man and his work. wire [7]. What where the after-effects of the 1820 discovery? Ørsted’s Also in Great Britain, the discovery of electromagnetism letter reached soon the scientific community in Paris, where was immediately appreciated. Sir Humphry Davy and Michael Franc¸ois Arago demonstrated the electro-magnetic connection Faraday reproduced the experiments, and Davy, as the Pres- to the French academic circles in September 1820. And as ident of the Royal Society, secured the prestigious Copley the history goes, Andre-Marie´ Ampere` (1775–1836) absorbed Medal already for the same year 1820 to Ørsted [8]. In France, however, it took considerably longer before he was formally A. Sihvola is with the Department of Electronics and Nanoengineering, honored: the French Academie´ des Sciences elected Ørsted as Aalto University School of Electrical Engineering, Espoo, Finland, e-mail: ari.sihvola@aalto.fi correspondent in 1823, and finally in 1842, he became Foreign Manuscript received xx yy, 2020; revised Associated Member [9]. JOURNAL OF LATEX CLASS FILES 2 Further advances in electromagnetics took place soon. In This idea of a ”multiplier” as a source of electromagnetism 1831, Faraday was able to demonstrate the generation of dates from times shortly after Ørsted’s publication. It was electricity from magnetism, and it was Faraday’s Experimental known under the name ”Schweigger-Multiplikator” (Schweig- Researches [10], [11] that inspired J.C. Maxwell to formulate ger multiplier) to honor Johann S.C. Schweigger (1779–1857), his famous equations in 1860’s. On the continent, another professor of chemistry in the University of Halle in Saxony, direction in the search of a general framework of electro- present-day Germany [13]. The multiplier was used as a means magnetism can be traced from Ørsted and Ampere` towards to measure electric current. Simultaneously with Schweigger, Wilhelm Eduard Weber and his efforts to unification of electric similar multiplier arrangements were designed and built by and magnetic effects in the mid-19th century [12]. Johann Christian Poggendorff (1796–1877). But apart from the scientific understanding of electromag- The intensity of studies around the fascinating electromag- netics, there were several domains in which Ørsted’s discovery netic effect and race to uncover new properties around this would have enormous impact, like telegraphic communica- law of nature lead also to disputes of priority. The honor for tions, electrical machines, and measurement instrumentation the discovery of the very phenomenon was claimed by also to quantify the electric current, all obvious in retrospect. In other people, sometimes even in a very blunt manner as Fig. 3 the following, let us focus on this last application which began shows. to develop immediately after Ørsted’s communications in July True enough, the possible connection between electricity 1820. Although many people contributed to the progress in and magnetism had been considered before. Ørsted was af- the development of devices for electric current measurements, fected by German idealism and natural philosophy through the emphasis is mainly on the Finnish scientist Johan Jacob persons like Immanuel Kant, Johann Wilhelm Ritter, and Nervander and his tangent galvanometer, the instrument also Friedrich Wilhelm Joseph von Schelling. Indeed, one can called ”tangent bussol”. find obscure speculations in Schelling’s writings about the interaction between electricity and magnetism and conclusion that all magnetic phenomena can be put to correspond to II. SCHWEIGGER AND THE MULTIPLIER electric ones but not vice versa [15, p. 298]. The ethos in Ørsted’s search can also be appreciated in As everyone who teaches electromagnetics knows, demon- this philosophical vein. Looking for the electromagnetic effect strating the Ørsted effect can be done much more effectively was not a random trial-and-error exercise for him: a mental than using a straight current-carrying wire, like Ørsted has preconception is needed in order to be aware of the direction most probably done in his early experiments, see Fig. 2. from where to search and ”submit questions to Nature [...] this Instead of a wire held close to the compass, let the current is only possible for someone who already knows how to ask flow through a coil, a wire wound in a circle. A DC current such questions” [16], [17]. A true observation cannot happen loop is known to work as a magnetic dipole, and it makes by chance. a very efficient source of magnetism, in particular when its effect is multiplied by winding it into a coil of several rounds. The magnitude of the magnetic field decreases inversely with III. TOWARDS GALVANOMETER