400 OBSERVATIONS AND EXPERIMENTS 



Thus, with increasing resistance of the experimental circuit, the 

 ratio between the effects of both halves actually approaches to 

 unity. There would be no reason for this if the different strengths 

 of the shocks of the two halves were occasioned by difference of 

 electro-motive force, and we may therefore conclude that the less 

 activity of the posterior half of the organ is due to greater 

 resistance. 



I succeeded in demonstrating the superiority of the anterior over 

 the posterior half of the organ in another very instructive manner. 

 I fixed two zinc saddles on to one of the fish at such a distance 

 from each other, that they corresponded to the poles of the organ, 

 and I made a third saddle movable in such a way that it could 

 divide the distance between the two first (125 mm.) in any desired 

 proportion. The middle saddle was connected by the frog-inter- 

 rupter with the one terminal A, and the two other saddles were 

 connected with the other terminal B of the galvanometer, the 

 thermo-bobbins of which (2,12, turns) were close up. With this 

 arrangement, each of the two sections of the organ sent a current 

 in an opposite direction through the galvanometer. I now tried to 

 give such a position to the middle saddle that both currents should 

 be equal, or that the mirror should remain at rest. The results of 

 the experiments are shown in the following table, in which a de- 

 flection in the direction of the anterior half is denoted positive and 

 of the posterior negative : 



62'5 : 62-5 ..................... Positive deflection, not measurable. 



50 : 75 ..................... + 42 scale divisions. 



45 : 80 ..................... +22; -3; +23. 



40 : 85 '. .................... Strong negative deflection. 



The ratio 45 : 80 seemed nearest to that sought. In order to 

 learn to what extent the equilibrium found was complete, the 

 effect of the anterior section, 45 mm. long, and of the posterior, 

 80 mm., was measured separately, with only 53 turns. The former 

 was found = 4- 48, or multiplied into 4 = + 192 ; the latter = - 

 34, or multiplied into 4 H -- 136 sc. Equilibrium was certainly at- 

 tained as nearly as possible, when the difficulty of the experiment 

 is considered. 



This experiment acquaints us with the equator of the organ, or 



