Faraday to Arthur-Auguste De La Rive   4 December 1845

Brighton | 4 Decr 1845

My dear friend

Your letter¹ which I received this morning was a very great gratification to me not more for the approbation which it conveyed than for the kindness with which I know it is accompanied. I count upon you as one of those whose free hearts have pleasure in my success and I am very grateful to you for it. I have had your last letter² by me on my desk for several weeks intending to answer it but absolutely I have not been able for of late I have shut myself up in my laboratory and wrought to the exclusion of every thing else. I learned afterwards that even your brother³ had called on one of these days & been excluded.

Well, a part of this result is that which you have heard and my paper was read to the Royal Society I believe last Thursday⁴ for I was not there and I also understand there have been notices in the Athenaeum⁵ but I have not had time to see them & do not know how they are done[.] However I can refer you to the Times of last Saturday (the 29 Nov.) for a very good abstract of the paper⁶. I do not know who put it in but it is well done though brief. To that account therefore I will refer you.

For I am still so involved in discovery that I have hardly time for my meals & am here at Brighton both to refresh & work my head at once and I feel that unless I had been here & been careful I could not have continued my labours. The consequence has been that last Monday⁷ I announced to our members at the Royal Institution⁸ another discovery of which I will give you the pith in a few words - the paper⁹ will go to the Royal Society next week and probably be read as shortly after as they can then find it convenient[.]

Many years ago I worked upon optical glass¹⁰ & made a vitreous compound of silica boracic acid & lead which I will now call heavy glass & which Amici uses in some of his microscopes¹¹ and it was this substance which enabled me first to act on light by magnetic and electric forces. Now if a square bar of this substance about half an inch thick and 2 inches long be very freely suspended between the poles of a powerful horse shoe electro magnet immediately that the magnetic force is developed the bar points but it does not point from pole to pole but equatorially or across the magnetic lines of force i.e. east & west in respect of the North & south poles. If it be moved from this position it returns to it & this continues as long as the magnetic force is in action. This effect is the result of a still simpler action of the magnet on the bar than what appears by the experiment & which may be obtained at a single magnetic pole. For if a cubical or rounded piece of the glass be suspended by a fine thread 6 or 8 feet long and allowed to hang very near a strong magneto-electric pole (not as yet made active) then on rendering the pole magnetic the glass will be repelled & continue repelled until the magnetism ceases. This effect or power I have worked out through a great number of its forms & strange consequences & they will occupy two series of the Experimental Researches¹². It belongs to all matter (not magnetic as iron) without exception so that every substance belong to the one or the other class. Magnetic or dimagnetic bodies. The law of action in its simpler <f>orm is that such matter tends to go from strong to wea<ker> points of magnetic force & in doing this the substance will go in either direction along the magnetic curves or in either direction across them. It is curious that amongst the metals is found bodies possessing this property in as high a degree as perhaps any other substance. In fact I do not know at present whether heavy glass or bismuth or phosphorus is the most striking in this respect. I have very little doubt that you have an electro magnet strong enough to enable you to verify the chief facts of pointing equatorially & repulsion if you will use bismuth carefully examined as to its freedom from Magnetism & making of it a bar about 1 1/2 inches long & 1/3 or 1/4 of an inch wide. Let me however ask the favour of your keeping this fact to yourself for two or three weeks and preserving the date of this letter as a record. I ought [not] (in order to preserve the respect due to the Royal Society) [to] write a description to any one until the paper has been received & even read there. After three weeks or a month I think you may use it guarding as I am sure you will do my right and now my dear friend I must conclude & hasten to work again. But first give my kindest respects to Madame de la Rive & my thanks to your brother for his call[.]

Ever Your Obedient & affectionate friend | M. Faraday

M Aug de la Rive | &c &c &c

Address: Professor | Aug. de la Rive | &c &c &c | Geneva