34 Voltaic Induction. 



If we place a metallic ring R R, fig. 4, near and parallel to the 

 north polar surface N, and then suddenly withdraw it, the outer 

 edge will undergo magnetic induction inasmuch as it intercepts the 

 polar forces N#Nx", while the opposite or inner edge, is passing out 

 of similar ones; hence north poles will be repelled from within the ring 

 towards x, x', as shown by the curved crosses ri 1 , n v , at the points d 

 and 6. Now it is an established fact in electro magnetism, that when- 

 ever a north polar force revolves from right to left over the current, 

 a positive current moves towards the observer ; the arrow on the 

 ring at e/, marks its advance. When, on the contrary, the north po- 

 lar force revolves from right to left under the current, the latter if 

 positive, moves from the observer. This is the case at the lower part 

 of the ring, as denoted by the arrow. The effect of withdrawing 

 the ring from the magnet, is therefore, to create a homogeneous cur- 

 rent through the ring, the direction of which corresponds fully with 

 the calculated results. If we now move the ring towards the mag- 

 net, the inner edge will receive the magnetic induction and thus lead 

 to the developement of a rotation and voltaic current the opposites 

 of the former. 



When the same ring is moved before the magnet in any direction 

 laterally, but still parallel to this position, fig. 4, there are opposite 

 currents produced in each half of it ; a fact in full accordance with 

 the explanation given for a similar motion of the particles a a', of the 

 same figure. In this instance all the forces upon one side of the 

 magnetic axis S N, will produce induction upon the inside of the 

 ring, while those upon the opposite side of this axis, produce the 

 same effect upon the outside; the action being in every case exerted 

 from the point N. 



Theoretically considered, therefore, no voltaic currents should 

 appear in the ring, when moved upwards, downwards, sidewise or in 

 any direction perpendicular to the magnetic axis S N ; but it is 

 equally obvious that such a movement cannot be sustained without 

 producing a preponderance of magnetic forces upon one side of the 

 axis, and these prevailing, will occasion weak currents. Thus, if we 

 move the ring downwards, the upper half circle, by getting more in 

 front of the magnet, receives its induction from very powerful forces 

 while the under portion is influenced by the more feeble ones. The 

 current is found, by appeal to experiment, to be very feeble, and 

 this makes the hypothetical indication the more probable. When we 

 place the ring so that only its upper margin stands opposite to the 



