402 OBSERVATIONS AND EXPERIMENTS 



came into play, for such uniformity is not to be thought of here. 

 Unfortunately I never repeated the experiment, and therefore a 

 certain obscurity is left in this respect also. 



9. On the influence of the length of the linings of the leading- 

 off covers upon the strength of the branch current in the 

 experimental circuit. 



A series of experiments have their place here, the object of 

 which was to determine the most favourable conditions for the 

 construction of the leading-off cover. The question is the length l 

 to be given to the linings. In Fig. 10, these have a medium 

 length which was given to them by guess. But the length of the 

 linings affects the strength of the branch current in the experi- 

 mental circuit in a two-fold way. First, its strength increases 

 with their surface, inasmuch as this increase of surface diminishes 

 the resistance of the circuit. Secondly, if we suppose the linings 

 not in electrical connexion to be applied to the electromotive 

 surfaces of the organ, it is clear that the tensions of the latter will 

 in part equalise themselves through the linings. Thus the strength 

 of the current in the experimental circuit will be directly pro- 

 portional to the mean tension of the surface touched by them, and 

 inversely proportional to the resistance of the experimental circuit. 

 Accordingly, it seems as though, when the resistance of the 

 experimental circuit is greater, shorter linings would be more 

 advantageous, and longer when the resistance is less: and in 

 order to obtain the strongest possible effect from the fish under 

 different circumstances, I undertook to decide this question by 

 experiment. 



Of two covers fitting the same fish, I provided the one with 

 short, the other with long linings. In the latter case, a gap of 

 only 8 mm. was left between them ; the short linings were about 

 2 cm. wide. With these linings it was easy to prove 2 the correct- 

 ness of the above conclusion. The great resistance here was a 

 tube 380 mm. long, j -4 mm. wide, filled with solution of sulphate 

 of zinc, and it was again necessary to push the bobbins of the 

 galvanometer close up (see above, p. 400). 



1 Comp. Ges. Abhandl., vol. i. p. 215. 



2 These experiments also were not performed until after the lecture in the 

 Academy, where I could only express the surmise that this would prove to be the 

 case. (Loc. cit. p. 104.) 



