Prof. E. Edlund on Unipolar Induction. 299 



of this force will be 



+ m»— s^L (E) 



Subtracting the expression (E) from the sum of (C) and 

 (D), we get, for the total electromotive force of the induced 

 current, 



kMv. 



This force, then, is independent of the distance between the 

 bar ac and the magnet, just as it is of their lengths. The 

 theoretic consideration, moreover, evidently requires that the 

 force be independent of the section of the conductor, and that 

 it have the same value, whether the brass cylinders ac and bd 

 are introduced both at the same time into the apparatus, or 

 only one at a time *. In the former case we have two elec- 

 tromotors ; but they are placed side by side and consequently 

 do not augment the electromotive force. The same fact pre- 

 sents itself here as when we connect each to each the po- 

 sitive poles and the negative poles of two ordinary piles : the 

 electromotive force is not changed ; but the resistance of the 

 combined pile is lessened by one half. Now the resistance in 

 the circuit oacs is extremely slight in comparison with that of 

 the galvanometer ; therefore the intensity of the current will 

 remain the same, whether the cylinders ac and bd be both in- 

 troduced into the apparatus or only one of them, and the dis- 

 tance at which they happen to be from the magnet will not 

 influence the result. This is proved by the following experi- 

 ments, made with an apparatus of this kind : — 



Galvanometer- 

 deflections, 

 scale-divisions. 



A single cylinder placed at 4*5 centims. f 36*0 

 distance from the magnet . . . . (37*5 



A cylinder on each side of the magnet, J J:' J: 

 placed at 4*5 centims. distance . . i Jfj; 



A single cylinder placed at 4*5 centims. ( 37*3 



from the magnet (38'0 



The mean of the two first and the two last observations is 

 37*2 ; and that of the three middle observations is 37*5. 



* Pliicker has inferred from some experiments that the induced elec- 

 tromotive force of a conductor is proportional to the section of the con- 

 ductor and dependent on its conductive power (Pogg. Ann. vol. lxxxvii. 

 p. 368). Examination of his experiments, however, shows that they by 

 no means authorize this conclusion. 



