302 Prof. E. Edlund on Unipolar Induction. 



cial electromotive forces, or by the electric fluid being carried 

 along in the direction of motion of the conductor, is quite 

 immaterial. If we notwithstanding continue to regard the 

 unipolar phenomena as belonging to those of induction, we 

 shall be obliged to distinguish the following species of 

 magnetic induction : — 



1. Induction due to the action of the magnet upon the 

 induced circuit augmenting or diminishing, or in general un- 

 dergoing a variation. This may take place in the two follow- 

 ing ways : 



(a) The magnetic moment undergoes a change, while the 

 induced circuit and the magnet remain at rest, and conse- 

 quently do not alter their relative position ; 



(b) The magnet and the induced circuit approach towards 

 or recede from each other without the magnetic moment under- 

 going variation. 



2. Induction due to the circumstance that the conductor 

 moves in regard to the magnet without the distance from the 

 poles of the latter to the different points of the conductor ne- 

 cessarily varying, and without augmentation or diminution of 

 the magnetic moment — unipolar induction. 



These different species of induction may of course some- 

 times present themselves in combination, as the following ex- 

 ample shows. Let sn (fig. 7) be a magnet, and ab a metal 

 tube the axis of which coincides with the prolongation of the 

 axis of the magnet. If we increase, or if we diminish the 

 magnetic moment, there will arise in the tube induced cur- 

 rents of the species la. If we move the brass tube towards 

 or away from the magnet without modifying the magnetic 

 moment, induced currents will result of the species lb, but 

 also at the same time those of the species 2. On removing the 

 tube away from or approaching it to the magnet, the electric 

 molecules present in the tube are carried in the direction of 

 the movement, and thus form true electric currents, upon which 

 the magnet acts according to the known law of action between 

 a magnet and an electric current. It is easy to perceive 

 that these two kinds of currents proceed in the same direction; 

 but those of species 2 are so feeble in comparison with the 

 others, that they can hardly be observed at the same time with 

 them. In the last place, if the tube is put in rotation about 

 its axis, induced currents exclusively of species 2 tend to be 

 formed ; and they become appreciable if the two ends of the 

 tube be connected with the electrodes of a galvanometer. 



By making the theory which has just been expounded serve 

 for the explanation of the known cases of unipolar induction, 

 any one may convince himself that it gives for every case re- 



