and its Effects. 137 



traversed the two primary coils one after the other, the induction 

 coils, however, were separate, and A was allowed to give sparks, 

 whilst B remained unclosed, and without a soft iron core; the 

 introduction of the latter into B lueakened the sparks of A, and 

 the subsequent metallic closing of B reproduced their former 

 strength. From this it follows that two complete instruments, 

 combined one after the other, mutually disturb one another, and 

 the total effect is not equal to the sum of the effects which each 

 would produce with the same intensity of galvanic current. 



Further, if the above experiment be modified so that the 

 current traverses the primary coils of A and B placed alongside 

 one another, then the insertion of the soft iron core into B 

 increases the sparks of A, and the subsequent metallic closing of 

 B again destroys this increase. 



Hence, when many induction coils are connected one after the 

 other, so as to form a single coil, it is advisable to allow the cur- 

 rent to traverse the primary coils of these instruments side by side. 

 With respect to the cause of these phfenomena, it is no doubt 

 to be sought in the extra or inner induction current. The outer 

 induction current, with which we are at present solely concerned 

 and which is produced by breaking the inducing current, has the 

 same direction as the latter ; whereas the extra current, which is 

 at the same time excited in the inducing circuit, developes a 

 contrary current in the induction wire, whose tendency is to 

 weaken the first induction current, and the more so the stronger 

 the extra current, which latter is especially strengthened by the 

 soft iron core. 



Consequently, when the primary coils of A and B are con- 

 nected one after the other, it is clear that the insertion of the 

 soft iron core into that of B will strengthen the extra current in 

 that of A, and therefore weaken the induction current of the 

 latter instrument. 



By connecting the instruments side by side, a closed circle is 

 at once formed by tliem, and the extra current produced by the 

 insertion of the soft iron core into B acts against that in A, and 

 may therefore, when both are equal, completely neutralize it, 

 when the outer induction current of A will be necessarily 

 strengthened. Without the circle formed by this combination, 

 i. e. in the wire leading back to the voltaic battery, the two extra 

 currents act, of course, in the same direction and strengthen one 

 another, in consequence of which the sparks at the current- 

 breaker are still very active. 



By tlie metallic closing of B, the action of its soft iron core 

 only will be neutralized. Metallic coverings act similarly, though 

 under certain circumstances they may also act in an opposite 

 manner. 



Phil. Mag. S. 4. Vol. 10. No. Gl. Aug. 1855. L 



