I 



Extra Currents through the Electric Spark. 175 



tween the points i and k was a bridge 

 of German- silver wire ; and the point 

 k was moreover connected by the I* 1 "" 

 conducting-wire / with the water- a O 

 pipe in the house, and was thus placed 

 in conducting communication with 

 the earth. When the disk AB was 

 rotated, sparks passed between b and 

 d as well as between / and g, and the 

 needle made a deflection. The re- 

 sistance in the wire h was infinitely 

 small, compared with that of the rheo- 

 stat m and in the spark between/ 

 and g. Hence the induction-currents 

 formed in the coils of the galvanome- 

 ter passed almost exclusively through 

 the bridge h ; and as they were equal 

 in quantity while opposite in direc- 

 tion, their action upon the needle 

 was of course imperceptible. This 

 would not have been the case if the 



bridge h had not existed, and the currents had had to pass through 

 the spark between / and g ; for this, as will afterwards be shown, 

 acts like an electrical valve — that is, transmits one current but 

 stops the other. Polarization-experiments showed, moreover, that 

 the current obtained arose from the spark between/ and g } and not 

 from the induction of the discharge-current in the galvanometer- 

 coils ; for in these experiments the galvanometer was removed, 

 and there was no other spiral in the conductions ; so that there 

 could be no induction. After the galvanometer, as previously 

 shown, had been so much improved that the bridge h could be 

 removed without disadvantage, I investigated more closely the 

 phenomena in question ; and as the results obtained seem to offer 

 some interest, I will give them here. 



At the time the galvanometer was made I also had a coil con- 

 structed for making induction-experiments, which in all respects 

 was like the coil of the galvanometer. The wooden frame had 

 the same dimensions ; the wire covered with gutta percha was of 

 the same kind ; and the number of windings in both coils was 

 the same, namely forty. Hence under the same circumstances 

 both coils must exert the same inductive actions. If the vol- 

 taic resistance in the rheostat m was called 100, it was found 

 that the resistance in each of the coils was 4*5, and the resist- 

 ance in the two conducting-wires from the joints c and e to 

 the galvanometer amounted to about as much. The following 

 experiments were made with this coil, which in the sequel will 

 be called R : — 



