On Electro-Dynamic Induction. 241 



rection the same as that of the primary current. In other cases the 

 magnetism was either imperceptible ormititis. With an arrange- 

 ment of two coils of wires around two glass cylinders, one within 

 the other, the same effect was produced. The magnetism was 

 less when the distance of the two sets of spires was smaller, indi- 

 cating, as it would appear, an approximation to a position of neu- 

 trality. These results are rather of a negative kind, yet they 

 appear to indicate the same change with distance in the case of 

 the galvanic currents, as in that of the discharge of ordinary 

 electricity. The distance however at which the change takes 

 place, would seem to be less in the former than in the latter. 



129. There is a perfect analogy between the inductive action 

 of the primary current from the galvanic apparatus and of that 

 from the larger electrical battery. The point of change, in each, 

 appears to be at a great distance. 



130. The neutralizing effect described in Sections TV and VI, 

 may now be more definitely explained by saying that when a 

 third conductor is acted on at the same time by a primary and 

 secondary current (unless it be very near the second wire) it will 

 fall into the region of the plus influence of the former, and into 

 that of the minus influence of the latter ; and hence no induction 

 will be produced. 



131. This will be rendered perfectly clear by Fig. 15, in 

 which a represents the conductor of the primary current, b that 

 of the secondary, and c the Fi„. ]5. 



third conductor. The char- ^ ^ 



acters + + +, &c., begin- + j 



+ ± 



ning at the middle of the 

 first conductor and extending + — 



downwards, represent the con- + "~ 



stant plus influence of the + "" 



primary current, and those -f — — , &c., beginning at the sec- 

 ond conductor, indicate the inductive influence of the secondary 

 current as changing with the distance. The third conductor, as 

 is shown by the figure, falls in the plus region of the primary 

 current, and in the minus region of the secondary, and hence in 

 it the two actions neutralize each other, and no apparent result 

 is produced. 



132. Fig. 16 indicates the method in which the neutralizing ef- 

 fect is produced in the case of the secondary and tertiary currents. 



Vol. xxxvui, No. 2.— Jan.-March, 1840. 31 



