Faraday to Charles-Gaspard De La Rive   12 September 1821

Royal Institution | Sept. 12th, 1821.

My dear Sir

I was extremely gratified the other day on receiving your very kind letter and also your beautifull little apparatus. I owe you many thanks for them and have been using the latter I hope you will say with some effect¹[.] I have not seen Mr. Prevost² so have not heard any news of your delightful place except what your letter contains but I trust all is well[.]

I am much flattered and encouraged to go on by your good opinion of what little things I have been able to do in science and especially as regards the chlorides of carbon³[.] I put a copy of my paper on them into the hands of Dr. Ure for you some time since⁴[.] He intended to visit Geneva & I trust long ere this you will have seen him and the paper. You will probably have seen since that was printed that Mr. Phillips and myself have described a new chloride of carbon so that now there are three of these interesting bodies and I anxiously look for a fourth⁵[.] A short account is in the Annals of Philosophy Aug 1821 which I presume you have seen⁶[.] I expect in a few days to have a copy of the paper to send you. In saying this I may express how much I should be gratified if you could and would point out a way whereby I may send you such or any other papers in the quickest & safest manner. Can I do it by Treuttel & Wurtz⁷ the Booksellers or how? For I am so much flattered by your kindness that I shall always intrude my papers on to it if I may be allowed. I have not seen M Prevost or M Macaire⁸.

Sir H Davys paper is not yet printed and I hardly know what it is for Sir H. left town for the country almost before his ideas were put into order on the subject on which he was working⁹[.]

You partly reproach us here with not sufficiently esteeming Amperes expts on Electro-magnetism¹⁰[.] Allow me to extenuate our opinion a little on this point. With regard to the experiments I hope and trust that due weight is allowed to them but these you know are few and theory makes up the great part of what M Ampere has published and theory in a great many points unsupported by experiments when they ought to have been adduced[.] At the same time M Amperes experiments are excellent & his theory ingenious and for myself I had thought very little about it before your letter came simply because being naturally sceptical on philosophical theories I thought there was a great want of experimental evidence¹¹.

Since then however I have engaged on the subject and have a paper in our Institution Journal which will appear in a week or two and that will as it contains experiment be immediately applied by M Ampere in support of his theory much more decidedly than it is by myself. I intend to enclose a copy of it to you with the other & only want the means of sending it¹².

I find that all the usual attractions and repulsions of the Magnetic needle by the conjunctive wire are deceptions the motions being not attraction &c or repulsions nor the result of any attractive or repulsive forces but the results of a force in the wire which instead of bringing the pole of the needle nearer to or farther from the wire endeavours to make it move round it in a never ending circle and motion whilst the battery remains in action[.] I have succeeded not only in shewing the existence of this motion theoretically but experimentally and have been able to make the wire revolve round a magnetic pole or a magnetic pole round the wire at pleasure[.] The law of revolution and to which all the other motions of the needle and wire are reducible is simple and beautiful[.] Conceive a portion of connecting wire north and south the north end being attached to the positive pole of a battery the south to the negative[.] A north Magnetic pole would then pass round it continually in the apparent direction of the sun, from east to west above & from west to east below[.] Reverse the connections with the battery & the motion of the pole is reversed[.] Or if the south pole be made to revolve the motions will be in the opposite directions as with the North pole[.] If the wire be made to revolve round the pole the motions a [MS torn] according to those mentioned. In the apparatus I used there were but two plates and the direction of the motions were of course the reverse of those with a battery of several pair of plates and which are given above[.] Now I have been able experimentally to trace this motion into its various forms as exhibited by Amperes helix¹³ &c & in all cases to shew that the attractions & repulsions are only appearances due to this circulation of the pole, to shew that dissimilar poles repel as well as attract and that similar poles attract as well as repel and to make I think the analogy between the helix & common bar magnet far stronger than before[.] But yet I am by no means decided that there are currents of electricity in the common magnet. I have no doubt that electricity puts the circles of the helices into the same states as those circles are in that may be conceived in the bar magnet but I am not certain that this state is directly dependent on the electricity, or that it cannot be produced by other agencies and therefore until the presence of Electrical currents be proved in the magnet by other than magnetical effects I shall remain in doubt about Amperes theory.

I have no room here to describe my results more particularly to you but you shall have them as soon as I can possibly send them and I hope they will meet your approbation[.] Allow me to say how much I am indebted to your little ring apparatus for information as I went on and also to say that I have as well by that as by other means been enabled to repeat and confirm an experiment of Amperes that had been doubted by great men here namely the direction of a curve by the magnetism of the earth¹⁴[.]

Wishing you all health & happiness & waiting for news from you[.]

I am My dear Sir | Your Very Obliged & grateful | M. Faraday