&.*. 



^Hor 



Figure 2. — "Galvanometer"' was the name given by 

 Bischof to this goldleaf electrostatic instrument in 1802, 

 18 years before Ampere coupled the word with the use 

 of Oersted's electromagnetic experiment as an indicating 

 devii I-. 



announcement of the magnetic effects of a voltaic 

 circuit, on July 21, 1820. 9 



Oersted's Discovery 



Man) writers have expressed surprise that with all 

 the use made of voltaic cells after 1800, including the 



enormous cells that produced the electric arc and 

 vaporized wires, no one for 20 years happened to 

 see a deflection of any of the inevitable nearby compass 

 needles, which were a basic component of the scien- 

 tific apparatus kept by any experimenter at this time. 

 Yet so it happened. The surprise is still greater when 

 one realizes that many of the contemporary natural 

 philosophers were firmly persuaded, even in the 

 absence of positive evidence, that there must be 

 a connection between electricity and magnetism. 

 Oersted himself held this latter opinion, and had been 

 seeking electromagnetic relationships more or less 

 deliberately for several years before he made his 

 decisive observations. 



His familiarity with the subject was such that he 

 fully appreciated the immense importance of his 

 discovery. This accounts for his employing a rather 

 uncommon method of publication. Instead of sub- 

 mitting a letter to a scientific society or a report to 

 the editor of a journal, he had privately printed a 

 four-page pamphlet describing his results. This, 

 he forwarded simultaneously to the learned societies 

 and outstanding scientists all over Europe. Written in 

 Latin, the paper was published in various journals 

 in English, French, German, Italian and Danish 

 during the next few weeks. 10 



In summary, he reported that a compass needle 

 experienced deviations when placed near a wire 

 connecting the terminals of a voltaic batter)-. He 

 described fully how the direction and magnitude of 

 the needle deflections varied with the relative posi- 

 tion of the wire, and the polarity of the battery, and 

 stated "From the preceding facts, we may likewise 

 collect that this conflict performs circles . . . ." 

 ( )ersted's comment that the voltaic apparatus used 

 should "be strong enough to heat a metallic wire red 

 hot" does not excuse the 20-year delay of the 

 discovery. 



Beginnings of Electromagnetic 

 Instrumentation 



The mere locating of a compass needle above or 

 below a suitably oriented portion of a voltaic circuit 

 created an electrical instrument, the moment Oersted's 

 "effect" became known, and it was to this basic 



Hi ,i 1. / / .. a 1 xrca EJfectum Confliclus Electrki 



in Acum M/niiuhuim 1 ( :< ipei ih.iuen, July 21, 1820). 



111 lull details of Oersted's work and publications are in Oersted 

 tin-/ ih, Discovery oj Electromagnetism (Bern Dibner's Burndy 

 Library Publication No. 18), Norwalk, Connecticut, 1961. The 

 original Latin version and first English translation are repro- 

 duced in his ( 1928), vol. 34, pp. 435-444. 



126 



BULLETIN 240: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



