464 Dr. Faraday's Researches in Electricity. 



ducting power of copper for electric currents, the gradual ac- 

 quisition and loss of magnetic power by the iron core of the 

 electro- magnet, and the production of those induced currents 

 of magneto-electricity which I described in the First Series of 

 these Experimental Researches (55. 109.). 



2328. The obstruction to motion on its own axis, when the 

 bar is subjected to the magnetic forces, belongs equally to the 

 form of a sphere or a cube. It belongs to these bodies, how- 

 ever, only when their axes of rotation are perpendicular or 

 oblique to the lines of magnetic force, and not when they are 

 parallel to it; for the horizontal bar, or the vertical bar, or 

 the cube or sphere, rotate with perfect facility when they are 

 suspended above the vertical pole (2246.), the rotation and vi- 

 bration being then equally free, and the same as the corre- 

 sponding movements of bismuth or heavy glass. The obstruc- 

 tion is at a maximum when the axis of rotation is perpendi- 

 cular to the lines of magnetic force, and when the bar or cube, 

 &c. is near to the magnet. 



2329. Without going much into the particular circum- 

 stances, I may say that the effect is fully explained by the 

 electric currents induced in the copper mass. By reference 

 to the Second Series of these Researches (160.), it will be 

 seen that when a globe, subject to the action of lines of mag- 

 netic force, is revolving on an axis perpendicular to these lines, 

 an electric current runs round it in a plane parallel to the 

 axis of rotation and to the magnetic lines, producing conse- 

 quently a magnetic axis in the globe, at right angles to the 

 magnetic curves of the inducing magnet. The magnetic 

 poles of this axis therefore are in that direction which, in con- 

 junction with the chief magnetic pole, tends to draw the globe 

 back against the direction in which it is revolving. Thus, 

 if a piece of copper be revolving before a north magnetic 

 pole, so that the parts nearest the pole move towards the 

 right-hand, then the right-hand side of that copper will have 

 a south magnetic state, and the left-hand side a north mag- 

 netic state ; and these states will tend to counteract the motion 

 of the copper towards the right-hand : or if it revolve in the 

 contrary direction, then the right-hand side will have a south 

 magnetic state, and the left-hand side a north magnetic state. 

 Whichever way, therefore, the copper tends to revolve on its 

 own axis, the instant it moves, a power is evolved in such a 

 direction as tends to stop its motion and bring it to rest. 

 Being at rest in reference to this direction of motion, then 

 there is no residual or other effect which tends to disturb it, 

 and it remains still. 



