Extra Currents through the Electric Spark. 177 



11 was inserted between g and e, by which there was obtained 



27-8 

 27-8 



Mean . . 27*8 

 After removing R there was once more observed 



'o 



40-3 

 41-3 



Mean . . 40*8 



In this case also the deflection was diminished by the induc- 

 tion-currents. It is easily ascertained that it was the currents 

 B which traversed the spark between / and g with greater facility. 

 By introducing the coil R into the circuit the resistance was a 

 little increased. To convince myself that this was not the cause 

 of the diminution in the deflection of the magnetic needle, a few 

 experiments were made in which the resistance of the rheostat 

 when R was interposed was so much diminished that the total 

 resistance was a little less than when R was removed. But 

 these experiments gave just the same results as the above. The 

 small alteration in the resistance had therefore no perceptible 

 influence upon the result obtained. The experiments were made 

 in such a manner that the place where the spark was formed 

 was removed from the position indicated by the figure, a little 

 towards n, while the rheostat took its place between c and e. But 

 in this case also the deflection was lessened in the same manner 

 as before by the induction-currents. 



It may at first sight appear unexpected that in one case the 

 currents A, but in the other the currents B, should be able more 

 easily to traverse the spark. Yet closer consideration shows that, 

 in one view, A in the first and B in the second experiment have 

 a common character, upon which some stress must here be laid. 

 In the first case it is the current A which traverses the spark in 

 the same direction as the electrical discharge, while in the second 

 it is the current B. It follows hence, that of the induction- cur ■- 

 rents formed by electro-induction , those which endeavour to tra- 

 verse the spark in the same direction as the discharge also penetrate 

 it most readily. 



That the induction -currents which are formed in the coil of 

 the galvanometer itself also diminish the deflection of the needle, 

 necessarily follows from what has preceded, and scarcely needs 

 any proof. Yet it was very easy to demonstrate this experi- 

 mentally in the following manner. In front of the galvano- 

 meter a German- silver wire was inserted between the points i 

 and k, the resistance of which was thrice that of the resistance 

 in the coil of the galvanometer. Hence, of the currents which 



