in a Letter to M. Gay-Lussac. 283 



words, for the correction of the errors committed in the ex- 

 periments might have been left to time. 



Messrs. Nobili and Antinori write (Annales, vol. xlviii. 

 p. 4-28.), " Mr. Faraday considers M. Arago's magnetism of 

 rotation to be entirely connected with the phenomenon which 

 he discovered ten years ago. He ascertained THEN, according 

 to the statement in the notice, that by the rotation of a metallic 

 disc under the influence of a magnet, electric currents may be 

 produced in the direction of the radii of the disc in sufficiently 

 considerable quantities to render the disc a new electrical ma- 

 chine. We are entirely ignorant how Mr. Faraday discovered 

 this fact, and we know not how a result of this nature could 

 remain so LONG generally unknown, and, so to speak, FOR- 

 GOTTEN in the hands of the discoverer," &c. 



Now / never said what is here imputed to me. In my 

 letter to M. Hachette, quoted at the head of the notice, I 

 gave a short account of what I had recently discovered, and 

 read before the Royal Society on the 24th of the preceding 

 month. This notice may be found at page 402 of the same 

 number of the Annales, and is as follows : " The fourth part 

 of the memoir treats of M. Arago's equally curious and ex- 

 traordinary experiment, which, as is known, consists in ma- 

 king a metallic disc revolve under the influence of a magnet. 

 Mr. Faraday considers the phenomenon which is manifested 

 in this experiment as intimately connected with that of mag- 

 netic rotation which he was so fortunate as to observe ten 

 years ago. He has ascertained that by the rotation of the 

 metallic disc under the influence of a magnet, electric currents 

 may be formed in the direction of the radii of the disc, in 

 sufficient number to render the disc a new electrical ma- 

 chine." 



I never either said, or intended to say, that I had obtained 

 these electric currents by the rotation of a metallic disc, at an 

 epoch previous to the date of the memoir that I was then en- 

 gaged in writing; but I said that the extraordinary effect dis- 

 covered by M. Arago was connected in its nature with 

 the electro-magnetic rotation I had discovered several years 

 before, both being due to a tangential action ; and that by 

 the rotation of a disc near a magnet I could (at the time I was 

 writing) cause currents of electricity to escape, or have a tend- 

 ency to escape in the direction of the radii, thus rendering 

 the disc a new electrical machine; and this I think is fully 

 proved in the part of my memoir of which I gave a sketch : 

 it may be seen in the Annales, vol. 1. p. 65 118. 



I am extremely desirous of explaining this error, because I 



