On Electro- 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 fiat 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 fiat 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 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- 

 rents, produced by the same induction, would partially counteract 

 each other. Moving in the same direction, 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. 



