in a Letter to M. Gay-Lussac. 285 



them I should make alterations in some parts), that it will not 

 be necessary to refer to any experiments that are not therein 

 contained. 



It is not my intention further to animadvert upon Messrs. 

 Nobili and Antinori's first memoir. An English translation 

 of it appeared in the Philosophical Magazine*, to which I 

 added some corrections in the form of notes, copies of which 

 I had the honour of sending to you, and to the authors. My 

 present object is to compare the second part of their publica- 

 tions with the fourth part of my first memoir, and with parts 

 of the other memoirs, as a means of throwing light upon the 

 general principles. The intention of the two articles is to 

 explain Arago's phenomenon, and as fortunately they are 

 both contained in the fiftieth volume of the Annales, the^ may 

 be referred to with facility. The reference to my own papers 

 will be thus, (F. 111-.), and to those of Messrs. Nobili and 

 Antinori by a simple indication of the page of the Annales. 



At page 281, after a few general remarks, we read, " We 

 have recently verified, extended, and perhaps corrected in 

 some particulars the results of the English philosopher ; we 

 then said that magnetism of rotation found a real support in 

 the new facts developed by Mr. Faraday, and that, conse- 

 quently, the theory of such magnetism then appeared to 

 be so far advanced as fully to merit an effort to develope 

 the physical principles upon which it depends. It is to this 

 object that the present article is devoted" &c. Upon this ex- 

 tract I shall only remark, that exactly four months previously 

 I had said the same thing, in the memoir that I read before 

 the Royal Society, and had given, what I hope will prove, a 

 true and exact explanation of the philosophy of the effect 

 under consideration (F. 4 80.). 



At page 282 we read, " We have already noticed these 

 currents in our first researches, that is, in the first paper in- 

 serted in the Number for December" (p. 4 12.). But I had 

 ** already noticed these currents" four months earlier (F. 90.). 



At page 283 are described " galvanometrical explorers or 

 probes," which are nothing more than what! had previously de- 

 scribed under the name of collectors or conductors (F. 86, &c.). 



At the commencement of the investigation of the state of 

 Arago's revolving disc adjacent to a magnet, two relative po- 

 sitions of the plate and the magnet are chosen ; one called 

 (p. 284.) the " central arrangement," in which the magnetic 

 pole is placed vertically to the centre of the disc ; and the 

 other (p. 285.) the "excentric arrangement" in which the mag- 

 net acts beyond that point. 



[* Phil. Mag. and Annals, N.S. vol. xi. p. 401.] 



