ON ELECTRO-DYNAMIC INDtTCTION. 325 



tends to induce a current in the adjacent conducting matter of a con- 

 trary direction. The same explanation 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 reference 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 condition 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 winding the two ribands together into one coil, 

 the sparks entirely disappear in the coil transmitting the battery cur- 

 rent, when the ends of the other are joined. To understand this, it is 

 only necessary 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 pro- 

 duce a current in the opposite direction. 



96. It would also appear from the perfect neutralization which en- 

 sues in the arrangement of the last paragraph, that the induced current 

 in the adjoining conductor is more powerful than that of the first con- 

 ductor ; 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 considered as partially in- 

 terrupted, since to render the spark visible the electricity must be pro- 

 jected, as it were, through a small distance of air. 



97. We would also infer that two contiguous secondary currents, 

 produced by the same induction, would partially counteract each other. 

 Moving in the same direction, they would each tend to induce a cur- 

 rent in the other of an opposite direction. This is illustrated by the 

 following experiment: helix No. 1 and 2 were placed together, but not 

 united, above coil No. 1, so that they each might receive the induc- 

 tion ; the larger was then gradually removed to a greater distance from 

 the coil, until the intensity 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 



