40t Prof. E. Edlund on the Theory 



produced in the wire, but acting in the opposite direction, so 

 that the intensity of* the current becomes zero. 



4. The result indicated under No. 4 is explained in a similar 

 manner. 



The fact that, in the case given under No. 2, the induction 

 produced in the wire at rest when the magnet is in rotation 

 round its axis ought to be equal to that produced when the 

 magnet is at rest, but the wire enters into rotation in the op- 

 posite direction but with the same angular velocity about the 

 magnet, may, according to this theory, be explained as fol- 

 lows : — The lines of force, imagined by Faraday, are in rotation 

 with the same angular velocity as the magnet : and the electro- 

 motive force produced is proportional to the number of lines 

 of force which the conducting-wire traverses in a given time. 

 But since evidently the wire encounters an equal number of 

 lines of force, whether the magnet is in rotation and the wire 

 at rest, or whether it is the wire which rotates and the magnet 

 which is at rest, the induction, according to this hypothesis, 

 must be equal in the two cases. 



§3. 

 The only method by which we can give a certain explana- 

 tion of the origin of the currents in question is given us by 

 the mechanical theory of heat, a theory of which 1 have made 

 use for this purpose some time since. Let us introduce into 

 the conducting-wire bed a (fig. 1) a battery producing a cur- 

 rent, which passes through the closed circuit in the direction 

 abed a. In consequence of the action of the magnet upon 

 the current which traverses the jacket, it commences to move 

 in the direction, as seen from above, of the hands of a watch. 

 We may observe that here the magnet itself does not enter 

 into rotation. It may without appreciable resistance be turned 

 as much on the one side as on the other by an external force. 

 If now we reduce the jacket to rest by means of an interposed 

 obstacle, which we will call in this case the electromotive 

 force, denoting it by E, the resistance in the circuit itself being 

 denoted by m, and the intensity of the current by I ; and, 

 lastly, if we call A the calorific equivalent of the unit of work, 

 the sum of all the heat developed by the resistance in the 

 circuit will be equal to APm, and the heat consumed* in the 

 battery for the production of the current will be equal to AEI. 

 But, since these two quantities must be equal, since the cur- 

 rent has not produced any external work, we shall have 



PM-EI = 0. (1) 



* Memoires (Handling ar) de V Acad. r. des Sciences de Suede, t. xiv. 

 Pogg. Ann. t. clix. (1876) ; Phil. Mag. [5] vol. iii. 



