290 Prof. E. Edlimd on Unipolar Induction. 



cylinder in such manner that one of the electrodes is in con- 

 tact with it in the vicinity of the poles of the magnet, and the 

 second electrode at a point situated between the two poles, 

 experience shows that the cylinder begins to rotate about the 

 magnet. The direction of rotation depends on that of the 

 current in the cylinder, and also on the situation of the poles. 

 As to the magnet itself, it remains perfectly motionless ; con- 

 sequently the galvanic current does not exert upon it any ro- 

 tatory action. It is therefore possible to turn the magnet 

 mechanically round its axis without the slightest obstacle being 

 offered by the reciprocal action of the magnet and current ; 

 the sole resistance to be surmounted in the mechanical rotation 

 of the magnet is occasioned by the friction in the sockets of 

 the axis, &c, a resistance which has nothing to do with the 

 current. In a previous memoir* I have demonstrated that, 

 according to the mechanical theory of heat, every phenomenon 

 of the sort mentioned w T ill be accompanied by a phenomenon 

 of unipolar induction. In fact, if the pile be removed and 

 replaced by a galvanometer inserted between the two above- 

 mentioned electrodes, and in contact with the cylinder, the 

 galvanometer indicates the rise of a current as soon as the cy- 

 linder is mechanically put in rotation. The electromotive 

 force here consists of the mechanical work necessary to over- 

 come the reaction of the magnet upon the current in that part 

 of the circuit which is set rotating. This species of induction 

 has received the name of "unipolar induction." The current 

 produced is proportional to the velocity of the cylinder. Of 

 course the simultaneous mechanical rotation of the magnet 

 produces no augmentation in the current generated by the 

 rotation of the cylinder, since this augmentation would be 

 made without the consumption of a corresponding amount of 

 mechanical work — which would be perfectly absurd. Pliicker 

 has also proved by experiment that in this case the rotation of 

 the magnet is incapable of producing a current. Here is an- 

 other reason : — It has been demonstrated by experiment that, 

 in the case in question, for the magnet a solenoid can be sub- 

 stituted, producing the same effectf . I have myself shown, 

 on a previous occasion^, that the rotation of the solenoid about 

 its axis cannot produce a unipolar induction current, whether 

 proceeding from a single fluid or from two fluids in transla- 

 tory motion. It is therefore, in this case, the rotation of the 

 cylinder about the magnet that gives rise to the observed uni- 



* Ofversigt of hongl. Vetensk.-Ahad. Vorh. 1877 ; Wiedemann's An- 

 nalen, vol. ii. p. 347. 



t Ofversigt, April 1877 ; Pogg. Ann. vol. clx. p. 604. 



t Ofversigt, Jan. 1877; Pogg. Ann. vol. clx. p. 617. 



