492 



NATURE 



[June i6, 192 i 



Oersted— the Discoverer of Electro- magnetism.^ 



ON July 21, 1820, Hans Christian Oersted, of 

 Copenhagen, announced his great discovery 

 to the world in a circular letter in Latin, " Experi- 

 menta circa effectione conflictus electrici in acum 

 magneticam." He describes in detail the ap- 

 paratus he employed, emphasising the fact that 

 "the galvanic circle must be complete, and not 

 open, which last method was tried in vain some 

 years ago by very celebrated philosophers," gives 

 a list of distinguished men who had witnessed the 

 new effect, and then writes : — 



"Let the straight part of this wire" — i.e. the 

 wire uniting the two poles of the battery — "be 

 placed horizontally above the magnetic needle, 

 properly suspended and parallel to it ; if necessary 

 the uniting wire is bent so as to assume a proper 

 position for the experiment. Things being in 

 this state, the needle will be moved, and the end 

 of it next the negative side of the battery will 

 go westward. If the distance of the uniting wire 

 does not exceed three-quarters of an inch from 

 the needle, the declination of the needle makes an 

 angle of about 45°. If the distance is increased, the 

 angle diminishes proportionally ; the declination 

 likewise varies with the power of the battery." ^ 

 A later communication ^ states that " he discovered 

 by continual experiments during a few days the 

 fundamental law of electro-magnetism, viz, that 

 the magnetical effect of the electric current has 

 a circular motion around it." 



The Royal Danish Society of Sciences is cele- 

 brating the centenary of Oersted's discovery by 

 the issue of a collected edition of his scientific 

 papers, and the work before us is an essay by 

 Mrs. Kirstine Meyer, forming the first volume 

 of the collection. 



H. C. Oersted was born at Rudkjobing 

 in 1777- His father was an apothecary, 

 and Hans Christian and his younger brother, 

 A. C. Oersted, afterwards a distinguished jurist, 

 received their early education from a German wig- 

 maker and his wife, who taught them to read and 

 speak German, but whose knowledge of arith- 

 metic was limited to addition and subtraction ; an 

 older schoolfellow taught them multiplication ; a 

 friend of the family, division. From their eleventh 

 and tenth years respectively they helped their 

 father in his pharmacy. In 1794 they went 

 to Copenhagen to finish their preparation for 

 their first academic examination, which they 

 passed with honours. As undergraduates 

 they were admitted to Elers College, founded in 

 1691, which still provides free residence and 

 a small scholarship for needy students. They 

 went through the university course together 

 with distinction, studying mathematics and 

 chemistry, and being greatly interested in philo- 



* " Scientific Life and Works of H. C. Oersted." Bv Kirstine Meyer. 

 (From H. C. Oersted: "Scientific Pagers," vol. i.) Edited by the Royal 

 Danith Society of Sciences. Pp. clxvi, (Copenhagen : Andr. Fred. H^st 

 and .Son, 1920.) n-.r^ 



* Thomson's " Annuls of Philosophy," vol. xvi. (1820), translated from a 

 Latin account sent by the author. ,',^«; 



3 " Edinburgh Encyclopaedia," vol. xvili. (1830), ' *"", 



NO. 2694, VOL. 107] 



sophy. Kant's teaching was then expounded in 

 Copenhagen by Prof. Riisbrigh, and his lectures 

 markedly influenced them. The lectures on astro- 

 nomy and physics attracted H. C. Oersted to the 

 study of science ; his brother became distinguished 

 for his philosophical writings; but throughout 

 Hans Christian's life we can trace the effect of his 

 early philosophical studies in his work. In 

 1798 he writes : "I promised you in our last con- 

 versation to give you an account in letters of the 

 systematic part of chemistry. ... I keep my 

 promise with pleasure both for your sake and for 

 that of science, which you know I find so much 

 pleasure in communicating to others." The same 

 year the brothers became members of the editorial 

 staff of a short-lived journal, a philosophical reper- 

 torium, the chief object of which was to defend 

 Kant's works. 



As regards experimental work, the elder Oersted 

 was limited mainly to the chemical training re- 

 ceived in pharmacy where he was employed ; the 

 university had no physical equipment. He was 

 helped, however, by Prof. Manthey, professor of 

 chemistry, and owner of the Lion Pharmacy. 

 Manthey was abroad during 1800 and 1801, and 

 Oersted managed his pharmapy. Volta's discovery 

 of the galvanic battery had just been published, 

 and Oersted's earliest experiments were con- 

 nected with the behaviour of various forms 

 of cells and with the testing of a theory, 

 advanced by Ritter, to account for the de- 

 composition of water by a current : that water 

 plus nesfative electricity produced hydrogen, while 

 water plus positive electricity produced oxygen. He 

 measured his currents for these experiments by 

 the aid of a voltameter arranged to collect in a 

 graduated tube the products of the decomposition. 



In 1801 Oersted had hopes of a professorship or 

 readership in the university, but he was then 

 looking forward to the prospect of a journey 

 abroad, rendered possible by a grant from "Cap- 

 pel's Travelling Legacy " ; and in a letter to 

 Manthey he says that he would rather resign any 

 post than give up the prospect of the journey. 

 He started in the summer of 1801, and was away 

 until the end of 1803. For a time the world was 

 at peace. Napoleon was First Consul ; the war 

 between France and Austria was stayed tem- 

 porarily by the Peace of Lun^ville (February, 

 1 801). The victory of the Nile, 1798, and of 

 Aboukir Bay, 1801, ruined the French plans for 

 an attack on India through Egypt, while access 

 to the Baltic and the defeat of a combination 

 of the Northern Powers against England 

 were secured by Nelson's victory at Copenhagen 

 in April, 1801. The Peace of Amiens followed in 

 March, 1802, and intercourse between men of 

 science of all nations was at once renewed. To 

 us, in 192 1, the rapidity with which this took 

 place is somewhat surprising. 



Oersted went first to Weimar. At Gottlngen he 

 was introduced to Ritter, \vhose electrical re- 



