38 



Voltaic Induction. 



the same extent. If, however, after having placed it as far as its 

 centre, between the poles, we raise or lower it until it passes quite 

 through, counter currents at first arise, because the magnetic forces 

 on the upper side of the magnet, act upon one surface of the coil- 

 wire, while those upon the lower side affect the opposite surface ; and 

 a uniformity of rotation does not commence until one quarter of the 

 coil is more influenced than the other. The maximum effect result- 

 ing from this arrangement therefore, never exceeds that which can 

 be produced by a uniformity of action upon one quarter of the coil. 



When, in addition to this interpolar position, a piece of soft iron is 

 made to pass through the centre of the coil, but without touching it, 

 the iron, by its approach to or contact with the magnet, acquires pow- 

 erful but temporary polar forces, which become highly developed 

 when we make it slide upwards or downwards from the magnet. 

 The latter motion adds so much to the promptitude of action, that we 

 obtain as strong a current with only one quarter of the coil, when we 

 make the armature slide quickly from the polar surface, as we do 

 with one half, when the armature is pulled off. 



Shortly after having become acquainted with Nobili's process for 

 obtaining sparks from the horse-shoe magnet, and long before Pixii's 

 improvement, or even Faraday's memoir reached me, I succeeded in 

 obtaining brilliant scintillations, and most unpleasant shocks, by anew 

 arrangement of the apparatus, and which I am here induced to notice 

 in consequence of a remarkable circumstance attending its action. 

 An account of it was published in vol. xxiv. No. 1. of this Journal; 

 but, for present purposes, a reference to the accompanying sketch 

 (fig. 6) will be sufficient. 



Fig. 6. 



The coil has the armature of soft iron passing through the centre, 

 and connected at one end, a, with it. The magnet is united to the 



