80 



ELECTRO-MAGNETISM. 



marked n, s, 'respectively, succeeding 

 each other in a regular order of alter- 

 nation round the wire. But this hypo- 

 thesis cannot be a faithful representa- 

 tion of the phenomena ; for it is found 

 on experiment that the action of the 

 conducting wire upon a magnetized 

 needle is exactly the same in every part 

 of its circumference. If the wire be 

 vertical, for instance, its effect is the 

 same in all azimuths, and has no rela- 

 tion to any rectangular planes passing 

 through the axis of the wire. 



(256.) With this correction, the hypo- 

 thesis that a conducting wire acts as if 

 a series of minute magnets were placed 

 in succession round its circumference, 

 with their opposite poles facing each 

 other, will account for a large class of 

 phenomena. It explains why a com- 

 pass needle assumes its peculiar position 

 at right angles to the axis of the wire, 

 in obedience to the directive influence of 

 that particular portion of the imaginary 

 series of magnets which is the nearest to 

 the needle, ^see Jig. 150; and also the 

 mutual attraction between the needle 



and the wire under these circumstances. 

 It also explains the other fundamental 

 fact in the science ; namely, the mutual 

 actions exerted between two conducting 

 wires : for when the currents are passing 

 in the same direction in both the wires 

 as in A and B, fig. 151, the polarities 



Fig. 151. 



*^A>** J / c^* 9 * 



*2i \f* \S 



J L I 



j\ S* 



of the minute magnets on the sides adja- 

 cent to one another will be reversed, and 

 they will consequently attract one an- 

 other. The contrary will happen when 

 the currents are passing in opposite 

 directions in the two wires, as in A and 

 C ; for then the polarities of the mag- 

 nets belonging to each, which are ad- 

 joining to each other, are the same in 

 kind, and, therefore, repulsive of each 

 other. 



(257.) But there is still one class of 

 phenomena which the hypothesis we 

 are considering is totally inadequate to 

 explain ; that comprising the rotatory 

 movements either of magnets or of con- 

 ductors, and which movements may be 

 maintained with uniform velocity not- 

 withstanding the retardation from fric- 

 tion, or the impediments of a resisting 

 medium ; exhibiting, in fact, the extra- 

 ordinary spectacle of a really perpetual 

 motion. The supposition of a series of 

 magnets encircling the conducting wire 

 will not account for this continued mo- 

 tion; for it is certain that no actual 

 combination of magnets, nor even any 

 conceivable arrangement of magnetic 

 particles, could ever, consistently with 

 the known laws of magnetic action, 

 produce any approach to perpetual ro- 

 tation. In order to obtain such move- 

 ments, the agent from which the force 

 emanates must itself be in motion, and 

 must revolve round the axis of the wire, 

 while traversing it from end to end, with 

 the utmost rapidity. Such was the pe- 

 culiar kind of movement, partly longitu- 

 dinal, and partly circular, which Dr.Wol- 

 laston attributed to the electro -magnetic 

 agent, and which he termed its verti- 

 ginous motion. 



(258.) A further emendation must, 

 therefore, be made in the hypothesis in 

 order to adapt it to the phenomena, by 

 supposing that the two magnetic fluids, 

 which accompany the electric fluids, 

 when the latter are set in motion, and in 

 a state of conflict, (if we choose to adopt 

 the phraseology of Oersted,) acquire a 

 vertiginous motion in opposite direc- 

 tions transversely to the axis of the con- 

 ductor ; that is, the boreal fluid revolving 

 in one direction, and the austral fluid 

 in the other; these determinations being 

 given to them by the direction in which 

 the electric fluids are moving in the 

 conductor, dependent, of course, upon 

 the relative positions of the poles of the 

 voltaic apparatus from which they pro- 

 ceed. There will result from this pecu- 

 liar kind of movement, not only all the 

 effects that we have just seen to be the 

 consequence of quiescent circles of 

 magnets, but also those of a rotatory 

 nature, which nothing but an agent in 

 motion could produce. The tangential 

 action of a conductor upon a magnet is 

 a necessary consequence of the trans- 

 verse motions of the magnetic fluids in 

 the conductor; and the rotation of a 

 magnetic pole round that conductor, or 

 conversely, the revolutions of the con- 



