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 Nx 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 n’”, n’’, at the points d 
and 6. Now itisan 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 d, 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 ts 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 SN, 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 SN; but it is 
equally obvious that such a movement cannot be austiig 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 
