On Elleciro-Dynamic Induction. ; 231 
planation is also applicable to all the other cases of neutralization, 
even to those which take place between the conductors of the 
several orders of currents. 
95. The same principle explains some effects noted in refer- 
ence to the induction of a current on itself. If a flat coil be 
connected with the battery, of course sparks will be produced by 
the induction, at each rupture of the circuit. But if in this con- 
dition another flat coil, with its ends joined, be placed on the first 
coil, the intensity of the shock is much diminished, and when the 
several spires of the two coils-are mutually interposed by wind- 
ing the two ribands together into one coil, the sparks entirely 
disappear i in the coil transmitting the battery current, when the 
ends of the other are joined. 'To understand this, it is only ne- 
cessary to mention that the induced current in the first coil is a 
true secondary current, and it is therefore neutralized by the action 
of the secondary in the adjoining conductor; since this tends to 
produce a current in the opposite direction. 
96. It would also appear from the perfect neutralization which 
ensues in the arrangement of the last paragraph, that the induced 
current in the adjoining conductor is more powerful than that of 
the first conductor; and we can easily see how this may be. The 
two ends of the second coil are joined, and it thus forms a perfect 
metallic circuit ; while the circuit of the other coil may be consid- 
ered as partially interrupted, since to render the spark visible the 
electricity must be projected, as it were, through a small distance 
of air. 
97. We would also infer that two contiguous secondary cur- 
Tents, produced by the same induction, touhl partially counteract 
each other. Moving in the same dissotiog: they would each tend 
to induce a current in the other of an opposite direction. This 
is illustrated by the following experiment: helices No. 1 and 2 
Were placed together, but not united, above coil No. 1, so that 
they each might receive the induction; the larger was then grad- 
ually removed to a greater distance from the coil, until the inten- 
Sity of the shock from each was about the same. When the ends 
of the two were united, so that the shock would pass through the 
body from the two together, the effect was apparently less than 
With one helix alone. The result, however, was not as satisfac- 
tory as in the case of the other experiments; a slight difference 
in the intensity of two shocks could not be appreciated with per- 
fect certainty. 
