Faraday to André-Marie Ampère   2 February 1822

Royal Institution | Feby 2nd. 1821

Sir

I am very much flattered by the letter you did me the honor to send me and by the present of the Expose¹ for which I beg leave to return you my best thanks[.] Having occasion to write to M Hachette I have promised to accompany my letter to him by this to you and venture a few observations on you[r] beautiful experiment of the rotation of the magnet &c &c². I repeated the experiment the day after I received your letter and using Hare’s³ calorimoter [sic] an instrument equivalent to a very large pair of plates⁴ instantly obtained the revolution[.] I found it convenient to cement a small piece of glass tube on the upper pole of the magnet which forming a cup to receive the mercury made contact very easy without the chance of touching the solid parts of the arrangement[.]

You mention your opinion that this experiment will be competent to decide the question whether the currents of electricity assumed by your theory exist round the axis of the magnet or round each particle from which I gather that the view you take of it differs from the one I at present have, since to me it seems a modification of the revolution of a wire round a pole. I presume much in differing from yourself on this subject and more in stating the differences to you but I do not hesitate a moment in concluding that in the true spirit of philosophy you are anxious to hear (or at least willing) even the doubts of one young in the subject if there be the smallest possibility that they will either correct or confirm previous views[.]

The rotation of the magnet seems to me to take place in consequence of the different particles of which it is composed being put into the same state by the passing current of electricity as the wire of communication between the voltaic poles, and the relative position of the magnetic pole to them. Thus the little arrows may represent the progress of the electricity; then any line of particles parallel to them except that line which passes as an axis through the pole (represented by a dot) will be in the situation of the revolving wire and will endeavour to revolve round the pole and as all the lines act in the same direction or tend to go one way round the pole the whole magnet revolves. That this is the way in which the magnet revolves is I think evident from the consideration above; from the revolution being in the same direction as with the wire and from the following analysis of the experiment[.] I took a piece of copper wire similar in form to the magnet and having floated it upright in mercury placed a little cap on the top to contain a globule of mercury and then connected the voltaic poles just as they were with the magnet then placing the pole of a strong magnet beneath the cup containing the mercury. it when exactly in a line with the axis of the wire made it rotate slowly on its own axis[.] In this experiment it appears to me that every thing was in the same state as in the former experiment except that the pole was removed out of the revolving mass but preserved in the line of its axis and the rotation of the wire on its own axis seems to me an effect produced exactly in the same manner as the rotation of the magnet on its axis[.]

I have been thus diffuse in giving my view of the rotation because if it be the true one I do not see how the experiment determines the position of the currents more than the one in which a wire rotates round a pole: perhaps however you have the same view of it but see explanations I do not. I regret that my deficiency in mathematical knowledge makes me dull in comprehending these subjects. I am naturally sceptical in the matter of theories and therefore you must not be angry with me for not admitting the one you have advanced immediately[.] Its ingenuity and applications are astonishing and exact, but I cannot comprehend how the currents are produced and particularly if they be supposed to exist round each atom or particle and I wait for further proofs of their existence before I finally admit them. Permit me to express my respect for your high philosophical character and to apologise for thus intruding on your time

I am Sir | Your Obliged & Humble Servant | M. Faraday

M. Ampere