ELECTRO-MAGNETISM. 



C2:V2.) The mutual action of electro- 

 dynamic cylinders on magnets is the 

 same as that of two magnets on each 

 other, so that in any experiment the one 

 may he Substituted for the other without 

 affecting the nature of the result. 



CHAPTER XII. 

 Theories of Electro- Magnetism. 



\.Electro- Magnetic Theory of Oersted. 

 (253.) THE discovery of the remark- 

 ahle phenomena of electro-magnetism 

 naturally gave rise to the invention of 

 a variety of hypotheses for their expla- 

 nation. Adopting the theory which 

 ascribes the electric phenomena to the 

 agency of two fluids, composing by their 

 union a neutral fluid, and exhibiting 

 their peculiar powers when that union 

 is decomposed, and when they are ob- 

 tained separately, Professor Oersted 

 conceived that a distinct class of effects 

 resulted during the act of their reunion ; 

 which was marked, not only by mecha- 

 nical agitations among the particles of 

 bodies, by the production of sound, by 

 the evolution of light, and by the dis- 

 engagement of heat, but. also by the 

 disturbance of the magnetic equilibrium. 

 These phenomena seemed to indicate 

 the occurrence of great and sudden 

 changes taking place in the conditions 

 of two powerful agents at the moment 

 of their coalescence, and suggested to 

 Oersted the idea that something ana- 

 logous to a shock takes place when the 

 fluids rush together from a distance. 

 During galvanic action, the separation of 

 the two electric fluids, proceeding with- 

 out intermission in one part of the ap- 

 paratus, and their reunion being in like 

 manner effected in perpetual sequence 

 along the conducting bodies which com- 

 plete^ the circuit, he conceived that a 

 continued series of electric shocks took 

 place throughout the whole line of con- 

 ductors ; a condition which he expressed 

 by the term Electric Conflict. 



(254.) If these views be correct, it 

 must follow that the electric fluids, 

 which, whether at rest or in motion, 

 have, when isolated, no apparent in- 

 fluence on magnetic bodies, acquire, 

 during their conflict, the power of af- 

 fecting these bodies. This hypothesis 

 was expressed by Oersted in the follow- 

 ing words : " The electric conflict acts 

 only on the magnetic particles of matter. 

 All non-magnetic bodies appear pene- 

 trable by the electric conflict, while 



magnetic bodies, or rather their mag- 

 netic particles, resist the passage of this 

 conflict. Hence they can be moved by 

 the impetus of the contending powers. 

 It is sufficiently evident that the electric 

 conflict is not confined to the conductor, 

 but dispersed pretty widely in the cir- 

 cumjacent space. 



" We may likewise collect that this 

 conflict performs circles ; for without 

 this condition, it seems impossible that 

 one part of the uniting wire, when placed 

 below the magnetic pole, should drive 

 it towards the east, and when placed 

 above it, towards the west (see $ 13, 

 figs. 1 and 2) : for it is the nature of a 

 circle that the motions in opposite parts 

 should have an opposite direction. Be- 

 sides, a motion in circles, joined with a 

 progressive motion, according to the 

 length of the conductor, ought to form 

 a conchoidal or spiral line ; but this, 

 unless I am mistaken, contributes no- 

 thing to explain the phenomena hitherto 

 observed. 



" All the effects of the north pole 

 are easily understood by supposing that 

 magnetic electricity moves in a spiral 

 line bent towards the right, and propels 

 the north pole, but does not act on the 

 south pole. The effects on the south 

 pole are explained in a similar manner, 

 if we ascribe to positive electricity a 

 contrary motion and power of acting 

 on the south pole, but not upon the 

 north*." 



(255.) The views entertained by Oer- 

 sted were very generally adopted by 

 philosophers who prosecuted the path 

 of discovery he had laid open. It was 

 the prevailing belief that electricity in 

 motion had magnetic properties, or 

 rather that it imparted to the body that 

 conducted it a species of transverse 

 magnetism. Some conceived that the 

 action resembled that of a series of 

 magnets placed around the axis of the 

 conductor, at riirht angles to each other, 

 their poles being situated in four lines 

 parallel to the axis, and forming a 

 square, as represented in Jig. 149, which 



Fig. 149. 



i: 



exhibits a section of the conducting 

 wire, and four magnets with their poles 



* Annals of Philosophy, vol. x vi. p. 2/6, 



