on various Electro-d^tiamic Phaenomena. 369 



me when I read M. Nobili's work ; in which, moreover, there 

 are researches upon vai'ious circumstances of electro-dynamic 

 phaenomena which abound in interest. 



You have plainly shown, sir, that the result of all the expe- 

 riments described in that work entirely agrees with that de- 

 ducible from my mode of explaining electro-dynamic pha:no- 

 mena. I must, however, add two observations to those you have 

 already made on that subject. The first relates to my having 

 asserted in a letter to Mr. Faraday dated April 18th, 1823, that 

 the mutual action of two complete circuits, or of two assem- 

 blages of complete circuits, cannot produce the continuous ro- 

 tatory movement in one of those two ciicuits or assemblages. 

 (See my JRccueil cV Observations Ji^lectro-dynamiques, p. 366.) — 

 You have great reason, as well as M. Nobili, to reproach me 

 with having stated in that passage (of a letter written in great 

 haste), in too general a sense, a fact which is only true of com- 

 plete circuits, or assemblages of complete circuits, which are 

 solid ; i. e. of invariable form in their whole extent. That it is 

 true in that case, will be easy for you to ascertain ; because in 

 every position of two complete circuits, where one tends to 

 impart to the other a motion of continuous rotation, it happens 

 that whenever that motion takes place, the moveable complete 

 circuit supports itself upon the other, and that the motion 

 cannot continue without one of the two circuits having, where 

 they meet each other, a liquid portion that the other can cross. 

 But if I was wrong in that passage of my letter to Mr. Faraday, 

 in not explaining that restriction, by saying " complete solid 

 circuits, and of an invariable form in their whole extent," it 

 was because I thought that the first glimpse of that passage 

 wouhl show that I meant to speak only of that sort of circuit ; 

 for the experiment of Mr. Faraday himself (where a magnet 

 turns continually round a vertical conductor) has been known 

 to me for a length of time ; and it is evident from my for- 

 mula, that in that case the continuous motion of rotation must 

 take place, whether the electrical current do or do not cross 

 the magnet, provided the mercury in which it is set up can 

 open to let the magnet pass ; in a word, provided the fixed 

 circuit be in a liquid part. I was, moreover, led to think that 

 what I said relative to the impossibility of producing a motion 

 of continuous rotation by their mutual action would be con- 

 fined to solid complete circuits, as that restriction omitted in 

 my letter to Mr. Faraday was explained most completely in 

 two places of my Reciieil. 



At page 235 of that collection of observations I have thus 

 explained myself: " As soon as I saw, about the end of Octo- 

 ber 1821, the work of Mr. Faraday, in which he published, a 

 Vol.66. No. 331. Nov. 1825. " 3 A short 



