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Prof. E. Edlund on the Theory 



A correct notion of the true cause and nature of unipolar 

 induction is of especial importance, because of the results 

 which may be deduced from it in the explanation of several 

 natural phenomena. I shall therefore attempt to show in the 

 following pages that the theory hitherto accepted for the phe- 

 nomena of unipolar induction is opposed to the principle of 

 the conservation of energy, and that therefore it must be ad- 

 mitted to be erroneous. I shall show moreover, in a manner 

 more complete than has previously been attempted*, that the 

 theory of the same phenomena which I advanced a few years 

 ago may be derived from the same principle, and that it ought 

 therefore to lead to certain results. 



§2. 



To fix ideas, let us start from a particular example which 

 may be considered as a typical example of unipolar induction 

 generally. Let s n be a cylindrical mag- 

 net having the south pole at s and the 

 north pole at n, and ab the section, in the 

 plane of the paper, of a jacket concentri- 

 cally surrounding the magnet, very easily 

 movable, like the magnet itself, and capable 

 of being put into rotation about the axis of 

 the latter. Let be da represent a metallic 

 wire pressing with its ends against the 

 upper and lower edges of the jacket, and 

 into which a galvanometer may be intro- 

 duced. Experiments made at various times 

 by different physicists have led, as is well 

 known, to the following results : — 



1. If the jacket only be put into rotation 

 in a direction opposite to that of the hands of a watch as seen 

 from above, we obtain an induced current in the direction 

 ab cola. If the rotation take place in the opposite direction, 

 the current will also go in the opposite direction. The inten- 

 sity of the current is proportional to the intensity of the 

 magnet and to the velocity of the jacket. 



2. If the magnet and the jacket are in rotation with the 

 same angular velocity, or, in other words, if they may be con- 

 sidered as relatively fixed, we obtain a current of the same 

 force and in the same direction as in the preceding case. The 

 magnet may be in rotation in any direction and with a greater 

 or less velocity at the same time as the jacket; the induced 



* Bulletin {Ofversigt) des travaux de VAcad. r. des Sciences de Suede 

 pour 1877 ; Wied. Ann. t. ii. p. 347 ; Memoires (Hcmdl.ngar) de VAcad. 

 r. des Sciences, t. xvi. 1878; Phil. Ma^. [5] vi. p. 289; Ann. de Chim. et 

 de Phys. tome xvi. p. 47 (1879). 



