360 Mr. Faraday on Magneto-electric Induction', 



the centre, the extent whence the force emanates will pass it ; 

 and as this part in excess is considered, though erroneously, 

 as inactive, the portion situated towards the circumference is 

 more powerful, and impels the pole towards the centre. 



Two or three slight objections present themselves to this 

 opinion, but they are nothing, so to speak, in comparison with 

 that which arises, when it is recollected, that in conformity 

 with the author's own ideas upon the action of currents, the 

 error with respect to the direction of those which are excited 

 near the pole obliges us to substitute attraction for repulsion, 

 as I have already shown when treating of the first of these 

 forces : consequently all the movements which are connected 

 with the third force would be in a direction contrary to those 

 that are actually presented ; and the theory which, when cor- 

 rected by experiments made with the galvanometer, indicates 

 such movements, must be abandoned. 



Page 292 of the memoir refers to Mr. Faraday's " second 

 law." As I have already said, I never stated those three as- 

 sertions as laws. I really regret extremely that a letter that 

 was never intended to convey minute details, but merely a few 

 facts, selected in haste from a multitude described previously 

 in the memoir read before the Royal Society, I regret that 

 this letter, which 1 never expected to see in print, should have 

 led the Italian philosophers into error. However, after having 

 examined anew all the facts, I do not see that I am in any de- 

 gree responsible for the error they have committed, as having 

 advanced fallacious results ; nor, as far as the memoir is con- 

 cerned, for not having given to the scientific world the most 

 complete details at the earliest period possible. 



I have not yet published my views as to the cause of the third 

 force described by M. Arago ; but as Messrs. Nobili and An- 

 tenori, when giving the hypotheses, which I justly regard as 

 inexact, say (p. 293.), "In fact, what other hypothesis can 

 reconcile the verticality that the needle preserves in the two 

 positions n, s, n", s", (fig. 4) with the fact of the repulsion from 

 below, above which raises the needle in the second position 

 s", w"?", I am induced to offer another hypothesis, premising, 

 however, that the directions and forms that I shall trace, as 

 those of the excited magneto-electric currents, are to be con- 

 sidered only as general approximations. 



If a piece of metal, large enough to contain without distor- 

 tion all the currents which may be excited in its whole extent 

 by a magnetic pole placed above it, be moved in a rectilinear 

 direction beneath the pole, then an electric current will move 

 across the direction of its motion, in the parts immediately 

 adjacent to the pole, and will return in the opposite direction 



