Faraday to Julius Plücker   14 December 1848

Royal Institution | London | 14 Decr. 1848

My dear Sir

Though I date from London yet I ought to say in strict truth that we are at Brighton for the sake of rest & health: - but I received your kind letter¹ in London & shall return thither again in a week or so. It makes me very happy to think that you enjoyed your trip to England and did not consider your excursion to the Association at Swansea lost time. All these minglings do great good, but I am getting too old now to take much part in them. In fancy I enjoy the thought of seeing Germany, but I doubt now whether I shall ever realize the imagination - and indeed the disturbed state of the country is not such as to tempt one².

I have been at work lately and though my first results seemed in striking contrast with yours on the repulsion of the optic axes of crystals yet I come more and more to the conclusion that the power active in both sets of effects are the same. I find that if a crystal of bismuth or antimony or arsenic or a crystalline fragment be subjected to the power in the Magnetic field, it is strongly affected & points i.e that there is a line in the crystal which tends to place itself in the Magnetic axis or in the line joining the two Magnetic poles. When this line is placed vertical in a magnetic field having horizontal lines of force then the crystal is in this respect indifferent. This line I have called the Magnecrystallic axis - it is strikingly distinguished from the optic axis line because it is axial. If a crystallized plate of bismuth i.e. one having uniform crystallization through[out] be experimented with, this line or the Magnecrystallic axis will be found to be perpendicular to the chief cleavage planes. If this plate be suspended by the edge the cleavage planes will point or face toward the magnetic poles - but if it be suspended so that this plane is horizontal then the plate does not point at all. Any part of the edge of the plate may then be made to point towards the magnetic poles simply by depressing or raising it above the level, for the vertical plane perpendicular to the inclined plane will always be coincident with the magnetic axis simply because the Magnecrystallic axis of the crystal lies in that plane[.]

I have sent two papers to the Royal Society³ which have been read & will I hope shortly be printed & I will send you copies of them as soon as I can.

Mr Taylor has not yet given us your papers in the English dress but I know they are in print & must be out shortly for I have seen copies of the first two which will appear in the next No. of the Scientific memoirs⁴. It is a great grief to me that I cannot read German & profit by the beautiful record of Science which Poggendorf[f] gives to the world. But my memory loses power continually & I am obliged to husband the little powers of recollection that I have left least my head should give way altogether. It aches sadly now but will improve I hope. Writing or thinking makes it feel weary[.]

I am My dear friend |Most truly Yours | M. Faraday

Professor Plucker | &c &c &c

Address: Professor Plücker | &c &c &c | University | Bonne | Germany