Faraday to Jean-Baptiste-André Dumas   9 January 1846

Royal Institution | 9 January 1846

My very dear friend

The kindness of your letter¹ has deeply affected me and I should have written the same day but that I was in the midst of a short series of lectures at this place which I could not neglect²[.] For all your kind wishes I earnestly thank you and I really do believe that I have strived the more to deserve your good thoughts since I knew that I had them so that you may perhaps even be helping science a little in thinking favourably of me. I am not always sure that what I think good, (being the result of my exertions) is good, but this I am sure of; that your praise makes me strive the more: - and this is not so much that I care for praise on its own account as that I care for the praise which comes from you.

I am a little taken by surprise & startled by your expression of a wish so honorable to me as that I would send some account of my late experiments to the Academy. Our Royal Society which is rather antique in some of its customs, and whose policy I do not on the whole approve of, have a great jealousy of its Fellows sending communications any where but to their meetings, or if sent to the meeting sending them any where else before they are published in the Transactions. I received a few hints about the notes I sent you respecting condensed gases³. Otherwise I should have sent you before this some brief notice of my recent experiments. When I received your last letter therefore I resolved to ascertain from one of the Secretaries the feeling of the Council (having long since ceased to take part personally in the management of the affairs) and the evening before last I saw Dr. Roget⁴. He told me it was against all rule and quoted to me a case in which Fox Talbot having sent a paper to the Royal Society afterwards sent a communication to the Academy which appearing in the Comptes Rendus caused that his paper was not printed in the Transactions⁵. This may be all right as it is the old custom but it hardly consists with slow publication, and it prevents me from doing that which would be a great delight to me and what is more if accepted by the Academy would be a great honor[.] Besides which it causes that a number of accounts hastily gathered up by the ear go abroad and any error they may contain remains uncorrected until the Memoire itself appears[.]

Still I must tell you a little. If the lines of magnetic force generated either by a powerful electro-magnet or a helix be sent through a transparent body parallel to a polarized ray of light passing through it at the same time the polarized ray is rotated. The effect takes place with all transparent liquid bodies and with all transparent solid bodies not possessed of double refracting powers - occurring in different degrees with different substances. In this effect I see a magnetic action on the ray of light but many of my friends here (who however have had no opportunity of considering all the facts in the paper⁶) think the effect by no means proves so much: so that you see though I hold my opinion as yet I may be wrong. The ray is rotated to the right hand if the magnetic force be in one direction or if the current in the helix go round it in one direction and to the left hand if the direction of the magnetic or electric force be reversed. The direction of the rotation is essentially dependant upon the direction of the magnetic or electric force and hence a difference between this rotation & any possessed by quartz, sugar, oil of turpentine &c of the following extraordinary kind. Place side by side a portion of water in a helix and a tube containing oil of turpentine: - if the oil have right-handed rotation send an electric current through the helix clock or right hand fashion and the water in the tube will also have right handed rotation and both will in this respect agree. Now leaving the tubes helice & current entirely alone let the polarized ray be sent in the contrary direction through the tubes & let the observer go to the other end of them to observe it. He will still find the oil of turpentine rotates the ray to his right hand - but not so the water it will rotate the ray to his left hand the rotation being absolutely tied to the direction of the electric current going round it & which seen from this end passes left hand fashion[.] Or if instead of water, oil of turpentine be in the helix, & the current of electricity of such force as to produce a rotation of the ray equal to that which the oil possesses; then, examined by a ray passing in one direction, its rotating power seems doubled; whereas if examined by a ray passing in the other direction, its rotating power is annihilated. This is the chief result on which I rest my opinion against that of my friends (or rather some of them.)

Passing from this subject to the Magnetic condition of matter, I find that all matter in the solid or liquid (& perhaps in the gaseous) state is affected by the magnet but not all as Iron; Matter magnetic as Iron is attracted by the magnet & an elongated portion points in the direction of the lines of magnetic force; but matter not magnetic, as Iron is repelled by the magnet and an elongated portion of it points across the lines of magnetic force. Water, Alcohol, Ether, oil, wood, flesh, blood, & a thousand other things, have this magnetic rotation, but perhaps the best are heavy glass, phosphorous, Antimony & bismuth. Perhaps you may remember that, (I think nearly 30 years ago) M. Le Baillif of Paris shewed the repulsion of a magnet by Antimony & bismuth. I recollected the fact generally & inserted it in my paper⁷[.] De la Rive has more lately⁸ referred me to the account of it in the Bibliotheque Universelle⁹. - Having called matter not magnetic as iron, diamagnetic I have kept this name to express this new magnetic condition, and so to sum up, I may say that, every solid or liquid substance possesses, & is subject to magnetic power, being either magnetic or diamagnetic in its nature[.]

Out of this property & its investigation, grows a multitude of curious conditions for which I must refer you to the papers which I will send you as soon as I can¹⁰. Amongst others I have ascertained this point. All the ordinary compounds of magnetic metals are also magnetic - thus, not only are the peroxides of Iron magnetic, as Becquerel¹¹ & others¹² have shewn but all the salts of Iron are magnetic & all the solutions of the salts if sufficiently strong to counteract the diamagnetic force of the water or alcohol used as a solvent. In this way I have been able to ascertain that Cerium is a magnetic metal for its salts are. So also are the salts of Chromium & Manganese. But I must stop & refer you to the two papers you will presently receive as soon as our R.S. prints them. In the mean time I am at work.

My dear wife thanks you most heartily & begs to be remembered to Madame Dumas in which pray join me. In reference to your observation that she ought to be happy, she thinks, Madame Dumas will be conscious of a happiness which they enjoy far beyond any thing that fame can give and it is my firm persuasion that both you & I are sharers in that happiness & the knowledge of it. Still the other is also pleasant perhaps more so than it ought to be.

My brother in law¹³ who was here half an hour ago begged me to thank you for your remembrance of him, with his sincere respects and hopes that before the year was out he should see you in England. Speak of me to M. Arago & say how gratefully I am his on every recurrence of his idea to my mind.

Ever Dear Dumas Yours Affectionately M. Faraday