494 



NATURE 



[June i6, 192 i 



would appear to do less than justice to his master, 

 and has proved rather unfortunate, lending colour 

 to the impression that the whole discovery was 

 due to chance. This was far from being the case. 

 Oersted had for years been seeking a connection 

 between electricity and magnetism, and the dis- 

 covery was the result of his search. 



Not the least instructive part of Mrs. Meyer's 

 very interesting book is a series of sheets repro- 

 duced in facsimile from notes, mostly in his own 

 handwriting, found among Oersted's papers, 

 which give in detail the experiments with the 

 large battery during July, 1820. Not only 

 did he experiment with a straight wire, but 

 also with one bent into a loop so as to form one 

 complete turn of a circuit, which thus had 

 its north and south face. Oersted saw that 

 such a circuit acted like a magnet. The effect of 

 replacing the magnet by needles made of non- 

 magnetic material was tried, and it was found 

 that they were not disturbed by the current. 



The results, announced to all centres of scientific 

 activity, at once produced a great sensation. The 

 paper was published in various journals, and 

 among others in Schweigger's Journal for July, 

 1820, and the same number contains an 

 account of further experiments of importance. 

 Oersted showed in this second cornmunication 

 that the effects "do not seem to depend 

 upon the intensity of the electricity, but 

 solely on its quantity "- — in modern words, on 

 the current, and not on the e.m.f. of the supply. 

 Further, he showed, by suspending by a fine 

 torsion wire a small battery and the circuit through 

 which the current passed, that the effect is recip- 

 rocal : on bringing a magnet pole up to one face, 

 the circuit is repelled; on bringing the same pole 

 up to the other face, it is attracted. 



But while Oersted's experimental work is ad- 

 mirable and his demonstration complete, it is not 

 easy to follow his theoretical ideas. He speaks 

 continually of the "conflict of the electricities" 

 which constitutes a current. The positive and 

 negative electricities flowing in opposite ways 

 round the circuit come into conflict, and it 

 is through their struggle that the various 

 effects are produced. It would almost appear 

 as though he thought that the heat and 

 light radiated from a glowing conductor 

 needed some violence for their origin — vio- 

 lence provided by the struggle between the 

 positive and negative electricities. " He did not 

 consider," he writes himself, "the transmission 

 of electricity through a conductor as a uniform 

 stream, but as a succession of interruptions and 

 re-establishments of equilibrium in such a manner 

 that the electrical powers in the current were not 

 in equilibrium, but in a state of continual conflict." 

 To this conflict he attributes also the magnetic 

 action which originally he anticipated would be 

 radiated outwards from the wire, like heat and 

 light. Experiment proved otherwise ; the mag- 

 netic action showed itself effective in directions at 

 right angles to the wire, but he did not grasp 

 the idea of a current of electricity flowing in the 

 NO. 2694. VOL. 107] 



wire accompanied by a field of magnetic force 

 arranged in circles round the path of the current. 

 In his view, the electricity acted directly on the 

 poles of his magnet, and as the force was due to 

 the electric conflict, this conflict took place, not 

 only in the wire, but also throughout the surround- 

 ing space through which the electricity flowed in a 

 series of flat spirals encircling the wire itself. 

 There was a transference of electricity in the direc- 

 tion of the wire ; the path, therefore, of the current 

 could not be a circle in a plane normal to the 

 wire, but a spiral giving rise to a component of the 

 motion parallel to the wire. According to his 

 first ideas, though he modified these later, "nega- 

 tive electricity repels the north pole, but does 

 not act on the south pole," while positive elec- 

 tricity acts on the south pole, but not on the north. 



In 1828 Oersted writes thus, possibly after he 

 had become aware of Faraday's work : "The elec- 

 trical stream has a magnetic circulation about its 

 axis. Every act of decomposition due to an elec- 

 trical current in a given direction is accompanied 

 by a circulation. Through this electrical stream, 

 which, as I have shown elsewhere, is propagated 

 by alternations of positive and negative electricity, 

 there is brought about a series of charges and dis- 

 charges of particles in the direction of the stream, 

 and a circulation in planes at right angles to it." 



The importance of this discovery was recognised 

 everywhere. In Germany, at a somewhat later 

 date, an attempt was made by Gilbert and others 

 to lay stress on its accidental nature. "Was alles 

 Forschen und Bemiihen nicht hatte geben woUen 

 das brachte ein Zufall Herrn Professor Orsted in 

 Kopenhagen," he wrote in his Annalen in 

 October, 1920, and this view was accepted by 

 many of his contemporaries ; but elsewhere Oersted 

 received full and generous credit. The French 

 physicists, led by Arago and Ampere, took up 

 eagerly the investigation of the new phenomena, 

 and in a few months Ampere established the laws 

 of the mechanical action between electric currents. 

 "The whole theory and experiment," writes 

 Maxwell, "seems as if it had leaped full grown 

 and full armed from the brain of the ' Newton of 

 Electricity.' It is perfect in form and unassail- 

 able in accuracy, and it is summed up in a formula 

 from which all the phenomena may be deduced, 

 and which must always remain the cardinal 

 formula of electro-dynamics." Ampere's brilliant 

 work somewhat overshadowed Oersted's merit, 

 which, however, the French investigators fully 

 recognised. 



In England Sir Humphry Davy was the first 

 to repeat the experiments, using for the work 

 "the great battery of the London Institution, con- 

 sisting of 2000 plates of zinc and copper " ; he 

 showed at an early date that the arc between 

 two charcoal electrodes was altered in shape when 

 a magnet was brought near. In April, 182 1, 

 Faraday wrote an historical survey of the growth 

 of the subject up to date, stating that Oersted's 

 results "comprise a very large part of the facts 

 that are yet known relating to the subject," and 

 pointing out that his constancy in the pursuit of his 



