Figure 38. — One of the first Weston cells used 

 by the National Bureau of Standards. 

 {USMM J1648J; Smithsonian photo 468^4.) 



Figure 39. — A model of Oersted's wire experi- 

 ment. {USNM 4yio6-A; Smithsonian photo 

 31 50 4' A.) 



The Electromagnet 



The first step towards the invention of an electro- 

 magnet was taken by Hans C. Oersted, a professor 

 of physics at Copenhagen who subscribed to the 

 widely diffused view of the GeriTian Naturphilosoph 

 that all the forces of nature were somehow related. 

 This belief seemed to Oersted to be borne out espe- 

 cially in the case of electricity and magnetism where 

 the attractions and repulsions followed the same 

 mathematical laws. Other speculators and experi- 

 menters had presented what they considered to be 

 proof of a relation between magnetism and electricity, 

 magnetism and light, and electricity and light; but 

 the proof rested on such dubious experiments that 

 most of the prominent scientists of the early 19th 

 century were justifiably skeptical of such an hypothesis. 

 But after many trials Oersted did find a relation 

 between magnetism and electricity when he dis- 

 covered that a current-carrying conductor, no matter 

 of what material it was made, would cause a magnetic 

 needle in its vicinity to orient itself at right angles to 

 the conductor (fig. 39). 



Oersted's brief notice ^* of his discovery was tested 

 within a few weeks by some of the world's leading 

 scientists — by Sir Humphrey Davy ^^ at the Royal Insti- 



tution in London; by Dominique Arago,^" one of the 

 editors of the Annales de Chimie et de Physique at the Aca- 

 demic des Sciences in Paris; by Auguste de la Rive, ^' 

 professor of chemistry at Geneva, Switzerland; by 

 J. S. Schweigger,*- professor of physics and chem- 

 istry at Halle and editor of the Journal Jilr Chemie und 

 Physik; and by L. W. Gilbert,''' professor of physics 

 at the university in Leipzig and editor of the Annalen 

 der Physik und der physikalischen Chemie. All of these 

 scientists confirmed Oersted's results. 



*8 Hans Oersted, Experimenta circa ejfeclum conflictus electrici in 

 acum magneticam, Hafniae, 1820 (also as an article in many 

 journals such as in Annales de chimie et de physique, 1820, vol. 14, 

 pp. 417-425, and "Neuere elektro-magnetische Versuche," 

 Schweigger's Jouraa/, 1820, vol. 29, pp. 364-369). 



59 "On the Magnetic Phenomena Produced by Electricity; 

 in a Letter from Sir H. Davy to W. H. WoUaston," Philosophical 

 Transactions, 1821, vol. Ill, pp. 7-19. 



™ Dominique Arago, "Extrait des seances de I' Academic 

 Royale des Sciences," Annales de chimie et de physique, 1820, 

 vol. 15, p. 80. 



61 Auguste de la Rive, "Notice sur quelques experiences 

 electro-magnetiques," Bibliotheque universelle, sciences et arts, 

 1821, vol. 16, pp. 201-203. 



"^J. S. Schweigger, "Zusaetze zu Oersted's elektro-magne- 

 tische Versuchen," Schweigger's jOT/raa/, 1821, vol. 31, pp. 1-6. 



63 Ludvifig Gilbert, "Untersuchungen ueber die Einwirkung 

 des geschlossenen galvanisch-elektrischen Kreises auf die 

 Magnetnadel," Annalen der Physik, 1820, vol. 66, pp. 331-391. 



256 



BULLETIN 228 : CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



