DIFFERENT MODES OF GENERATING CURRENTS. 53 



a current to which I have given the name of polar inversion 

 current, and which results from the inversions of magnetic 

 polarities to which the core is successively subject, by reason 

 of the movement of the inducer.* These two currents 



* In order that the origin of the currents which now play so important a 

 part in the new electric generators may be thoroughly understood, we shall 

 examine what takes place when a bar of soft iron surrounded by a magne- 

 tizing coil is brought near one of the poles of a permanent magnet, for 

 instance, near the north pole. At the instant of approach there will be pro. 

 duced a first current, a current of magnetization, whose direction will depend 

 upon which end of the bar is acted upon by the magnetic pole. This current 

 is due to the transformation of the bar into a magnet. If the magnet is with- 

 drawn, a current will again be induced in the direction opposite to the 

 former, and which will correspond with the demagnetization of the bar. 

 But if the pole of the magnet be brought near the middle of the bar, there 

 will be no current produced, because the bar itself will then form a magnet 

 with a consequent point, and the effect of the induction on the one side of 

 this point will be counteracted by that on the other side. The same effects 

 will ensue if the coil is deprived of the iron core. Now, it follows from this 

 principle that, if the iron bar surrounded by its coil be bent so as to form a 

 ri ig, neither currents of magetization nor of demagnetization can be obtained 

 by the approach or recession of the magnet, to what point soever it may be 

 directed, for the parts to the right and to the left of the point affected are then 

 polarized in the same manner. Nevertheless, if the magnet he moved 

 parallel to the axis of the bar, that is to say, circularly about the ring, it will 

 no longer be the same thing, and a current may be produced, due neither to 

 magnetization nor to demagnetization, but which will, under certain con- 

 ditions, last during the whole time the magnet is revolving in the same direc- 

 tion. This current may be the result of two different and simultaneous 

 actions, but in order that it may be manifested it will be necessary for the 

 coil to have a certain arrangement, for even if the induction be produced by 

 a single magnetic pole, the two opposite parts of the ring affected would 

 always be polarized in a different direction, and would give rise to contrary 

 currents. One of these actions is the result of the magnetic disturbance 

 produced in the core itself by the successive inversion of its polarities a 

 disturbance which must, as I have proved, give rise to a reaction analogous 

 to that observed when an effect of demagnetization is made to follow an 

 effect of magnetization under opposite conditions ; and as under such con- 

 ditions the resulting currents have the same direction, and in consequence 

 of the progressive motion of the inducer they follow each other without in- 

 terruption, a continuous current is the upshot, and this changes in direction 

 only when the direction of the movement of the inducing pole is changed. 

 The other action results from the motion itself of the magnetic inducing 

 system before the spires of the induced coil, or what amounts to the same 

 thing, f; om the motion of these coils before the inducing system. (Sice Note A. ) 



