Voltaic Induction. 31 



The deflection may be supposed to be equally good in soft iron, 

 but that the coercive force is feeble, so that the rotation soon ceases ; 

 whereas, in unmagnetic metals, it is probable that there is neither 

 deflection nor coercion, and that in consequence of this difference, 

 they can receive magnetic induction only by an extraneous motion, 

 either of the magnet or the metallic body, so as to imitate the deflec- 

 tion. 



Upon this inequality of the inductive process at the opposite sides 

 of every particle, rests my hypothesis ; I shall, therefore proceed to 

 notice its application to unmagnetic metals, more particularly. 



That motion is necessary for voltaic induction is now demonstrated 

 beyond a doubt. Ampere* has satisfactorily shown that when one he- 

 lix, connected with a voltaic battery (and therefore highly charged with 

 magnetism in an active state of motion both around and along the circuit 

 wire) is introduced within another helix, connected with the galvanom- 

 eter, no currents are produced in the latter, while at rest; but, upon 

 the slightest movement along the axis either to or from the galvanom- 

 eter helix, they become at once apparent and continue during the 

 motion. Upon entering the helix and upon leaving it, opposite cur- 

 rents are produced ; a fact that cannot well be explained by refer- 

 ence to the current of the battery, which never changed. M. Fara- 

 day, as far as I understand his views, supposes that during the 

 approach, the galvanometer helix gains what he calls electric tension, 

 producing a current of one denomination, and that upon reversing 

 the motion, this tension is either destroyed by re-action or reversed, 

 so as to occasion a current of an opposite character. Observations 

 from so sagacious an inquirer are not to be viewed negligently, but 

 I hope to make it apparent that such opposite currents admit of expla- 

 nation without the necessity of adopting so purely hypothetical a con- 

 dition of matter. Considering the magnet and electro-dynamic 

 cylinder to effect magnetic induction upon similar principles, I shall 

 confine my illustrations to the former. 



Let N, fig. 4, represent the north pole of a magnet and N;r, Na?' f 

 NV lines of action. Now if we imagine two particles of copper 

 a a' to be placed between them, but at rest, these forces must act 

 with equal energy upon all the opposite surfaces, supposing no deflec- 

 tion to take place ; and, as all of them operate from the same point 

 N, no magnetic induction sufficient to occasion rotation, can ensue. 



* Annates de Chhnie, &c. December, 1831. 



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