146 DOVE ON THE ELECTRICITY OF INDUCTION. 



rent. This assumption has gained probability by the discovery 

 of magneto-electricity, for every magnetic action of an electrical 

 current, when it is produced by some other means than an 

 electric current, gives rise to an electric current in an oppo- 

 site direction to that current which would itself have produced 

 it. The more numerous, however, the points of coincidence 

 in both departments are, the more necessary it is to point out 

 the phaenomena which appear to be incompatible with their 

 identity. 



In the first place, as regards the occurrence of magnetic po- 

 larity by the influence of an electric current, it results always 

 under such conditions as never give rise to electric currents. 

 For an electric current excites in a conductor placed by its 

 side another quickly subsiding electric current only when it 

 begins and when it ceases, not however during its continuance. 

 It produces magnetism, on the contrary, during the whole time 

 of its continuance, in a piece of iron placed by the side of it, 

 which attains its maximum in an appreciable space of time. 

 The peripherical electric currents, supposed hypothetically by 

 Ampere to surround the molecules of iron in order to explain this 

 magnetism, differ therefore, on the supposition that they are now 

 for the first time produced, from all known electric currents, 

 inasmuch as they are produced during the continuance of an 

 electric current, i. e. they occur under conditions where no 

 other electric currents could be excited. This difficulty is 

 avoided by the theory, on the ground, that existing currents cir- 

 culating round the molecules of iron are only directed and not 

 produced by the external current. But then the phaenomenon 

 that an electro-magnet returns to its unmagnetic state, when 

 the primary magnetizing current ceases, is without analogy in 

 the other departments, A polarized ray of light remains polar- 

 ized when it is removed from the active agency of the reflecting 

 or refracting substance : the oscillatory directions of the particles 

 of pether which have become parallel remain parallel when they 

 have once become so. For what reason then do the elementary 

 currents which have become parallel cease to be parallel when 

 the current which brought them into this pai-allel direction 

 ceases to flow ? for they themselves can have no tendency to di- 

 gress from their parallel direction. The cause of this phaeno- 

 menon, be it what it may, must nevertheless be, according to the 



