NOTES AND APPENDICES. 301 



It may therefore be said that the currents produced in con- 

 sequence of the displacement of the coils of a Gramme ring, 

 in relation to the two resultants corresponding with the two 

 neutral lines, are in the same direction as those evoked by 

 the passage of the spires of the coils before the inducing pole 

 in each half of the ring. 



In order to study the effects resulting from the polar in 

 versions, the experiment may be arranged as follows: on 

 one of the extremities of the iron rod provided with the in- 

 duction coil mentioned above, a permanent magnet is made 

 to slide perpendicularly to its axis. In this way the rod 

 undergoes successive inversions of its polarities, and it is seen 

 that not only is there produced by this a current more 

 powerful than the magnetization and demagnetization cur- 

 rents which result from the action of the pole of the 

 magnet, but also that this current is not momentary, and 

 appears to increase in energy until the inversion of the 

 poles is complete. The direction of this current varies 

 according to the direction of the movement of the mag- 

 netized bar, and if it is compared with that which results 

 from the magnetization or demagnetization of the magnetic 

 core under the influence of one or other of the poles of the 

 magnetized bar, it is observed that it is exactly of the same 

 direction as the demagnetization current caused by the pole that 

 has first acted; it is therefore in the same direction as the 

 magnetization current of the second pole ; and as, in the 

 movement performed by the magnet, the magnetic core is 

 demagnetized, in order to be again magnetized in the con- 

 exactly those we have analysed with the tangential movement of the coil, 

 somewhat resemble them, and the difference depends upon the currents, re- 

 sulting from the movements of the coil with regard to the magnets, being in 

 the direction contrary to those which result from the magnetization of the 

 rod, and giving rise to a rather feeble differential current, which shows that 

 the last action preponderates. On the other hand, the currents produced 

 from the middle of the rod to its free extremity, being no longer opposed by 

 the direct action of the magnet, possess all their energy. (See my paper on 

 this kind of actions in the Comptes Rendiis for the 24th February, 1879.) 



