410 Prof. E. Edlund on the Theory 



this condition, we may imagine, in the calculation of the mag- 

 nitude of the induction, that the magnetic pole is at rest, and 

 that the element of the circuit actually moves with a velocity 

 equal in magnitude and direction to the resultant of the 

 original velocity, and of a velocity equal to that of the magnet 

 but in the opposite direction. 



§5. 



1. I now propose to make use of what has been said in the 

 preceding pages for the explanation of the experiments men- 

 tioned above in § 2. 



When the jacket only is in rotation, whilst the magnet and 

 the wire are at rest, it is evident that the electromotive force 

 ought to be produced in the jacket. The old theory and that 

 which I am expounding agree in this respect. But this 

 agreement ceases when we pass to the second case, that where 

 the magnet and the jacket are put into rotation about the 

 axis of the former. We will suppose at first the magnet and 

 the jacket in rotation in the same direction and with the same 

 angular velocity. In this case the two may be considered as 

 united ; and it is not possible, according to the old theory, to 

 produce an electromotive force in the jacket ; but the induc- 

 tion ought (always in accordance with the same theory) to 

 take place in the metallic wire at rest. But it is of course 

 impossible to admit that induction may take place in the wire 

 from the fact that the jacket is in motion ; and in the case 

 where an induction is caused by it, that this induction ought 

 to be due to the rotation of the magnet. But, as was remarked 

 above, the magnet may be put into rotation either in the one 

 direction or the other without consuming other work than that 

 necessary to overcome the torsion of the thread by which the 

 magnet is suspended, or the friction against the angles which 

 support it. But such a consumption of work has nothing to 

 do with the production of electricity. It is possible never- 

 theless that the induced current offers some slight obstacle to 

 the rotation, although this obstacle may be too small to be 

 perceptible. The old theory, that the production of the 

 induced current takes place without the consumption of me- 

 chanical force, cannot, consequently, be correct. According 

 to my theory, on the contrary, the rotation of the magnet 

 in this case is without appreciable importance in the forma- 

 tion of the current ; for the reason that, in virtue of well- 

 known experiments, the resulting induced current does not 

 offer any sensible obstacle to the rotation. By far the most 

 important part of the induction is produced in the jacket 

 altogether as if the magnet were at rest. The rotation of the 



