364- Mr. Faraday on Magneto-electric Induction ; 



render their sum equal or greater than the sum of the forces 

 on the other side, or that towards the circumference. If the 

 sum of the forces be equal, then the pole will be somewhere in 

 the line / z, as at 5, fig. 8, and will have no tendency either 

 towards the centre or the circumference, though its tendency 

 to move with the disc or above it remains the same. Or if the 

 sum of the forces be greater on the side d, fig. 9, than on the 

 side c, then the pole will be in the position 2, fig. 8, and 

 will be impelled outwards in the direction of the radius, in 

 conformity with Arago's results. 



Besides this cause of alteration in the motion of the pole 

 parallel to the radius, and which is dependent on the position 

 of the pole near the circumference, there is another cause that 

 occurs, I apprehend, at the same time, and assists the action of 

 the first. When the pole is placed towards the edge of the 

 disc, the discharge of the currents excited behind is thrown 

 against the side of the edge, from the absence of conducting 

 matter; thus, in fig. 10, instead of having the regular form 

 of the figures 7 and 8, the currents are deflected in their 

 course towards the circumference, while they have all neces- 

 sary latitude for their movement in the parts towards the cen- 

 tre ; this of itself would cause the point of greatest force to fall 

 a little nearer the centre than the projection of the axis of the 

 magnetic pole, and assist in placing the pole in the position 2, 

 fig. 8. I have such confidence in this opinion, that though 

 I have not had opportunity to make the experiment myself, 

 yet I venture to predict, that if instead of employing a revolving 

 disc, a lamina or plate of metal, five or six inches broad, as 

 A, B, C, D, fig. 9, were caused to move in a rectilinear di- 

 rection conformably to the arrow, under a magnetic pole si- 

 tuated at a, the pole would have a tendency to move forward 

 with the metal as well as above, but neither towards the right 

 nor left ; while if the pole were placed above the point b, it 

 would be directed towards the edge A B ; or if it were placed 

 above c, it would have a tendency to move towards the edge 

 CD. 



Having thus replied to the question, " What other hypo- 

 thesis" ?, &c. proposed by the authors of the memoir at p. 293, 

 I shall continue my examination of the memoir itself. At p. 

 294? the error relative to the nature of the currents, that is 

 their supposed inversion, is repeated. The effect described is 

 sure enough with a helix, and some particular forms of appa- 

 ratus ; but the simple and elementary current generated by the 

 passage of a wire in front of a magnet is not reversed when the 

 metal wire recedes. (F. 171.111. 92.) 



At p. 295 is the supposition that when the rotation is slow 



