Faraday to Julius Plücker   11 December 1849

Royal Institution | 11 Decr. 1849.

My dear Plucker

I received your last letter¹ a day or two ago and I think I have one before that to acknowledge dated August². I am very thankful to you for them & they are always a great pleasure. Your last views are very interesting but my head aches too much just now for me to say I have considered them and indeed they are fitted to remain in the mind for meditation again & again until by the growing up of facts they are developed confirmed & extended as the future progression of discovery may be. One part of your letter I do not quite understand where you say that it is a consequence of your theoretical views confirmed by experiments that the attraction of a given crystal by the poles of a magnet be only dependant of its exterior form but independant of the direction of its optical or crystallographical axes with regard to the poles of the magnet[.] For my own part I believe at present that the subjections of any crystal to the magnetic force depends upon its internal structure - or rather on the forces which give it its particular structure and that in any such crystal that line which coincides with the Magnetic axis may conveniently be called the Magnecrystallic axis. I do not suppose it necessary that the Magencrystallic axis should coincide either with the Crystallographical axis or with the Optic axis but I conclude that a very definite relation of these axis will in every case be found and that though they be convenient forms of expression in reference to three sets of phenomena that the ruling power is one and that when we properly understand it we shall see that one law will include all these phenomena and so all the forms of expression as axes &c by which we for the time represent them.

I have been at work endeavoring to establish experimentally any character of polarity in bismuth &c when in the magnetic field. I am sorry to say that I can get no stronger facts than those in my original paper and no stronger persuasion than that I gave in Par 2429, 2430³. Weber did me the honor to work upon this thought⁴. I believe I have obtained the effects he obtained in a far higher degree up to deflexions of 40˚, 50˚, or 60˚ but if they are the same they are not effects of polarity. I am just writing the paper⁵.

I shall see Mr. Grove in an hour or too [sic] and shall tell him you have his paper⁶.

Ever Yours Very Truly | M. Faraday

Profr. Plücker | &c &c &c

Address: Professor Plücker | &c &c &c | University | Bonn | on the Rhine