R Institution | 8 Decr. 1848
My dear Sir
It is a fact that if a small bar of charcoal be suspended between the poles of a very strong Electromagnet, the charcoal will point equatorially but that if the magnet be weakened - or the poles opened out or the charcoal raised it will at a given distance or for a given weakness stand axially being in the first place affected as a diamagnetic body & in the second as a magnetic body. Hence Plucker concludes that the diamagnetic force increases & diminishes more rapidly than the magnetic force.
I have formed no final opinion on the conclusion he comes to. But this I think I know as a fact that no degree of power can make the magnetic & diamagnetic bodies change places or the individuals of the one class pass into the other.
In all the cases which Plucker mentioned to me, there was both a magnetic & a diamagnetic body present and I think he is now of opinion that that is necessary.
Since the paper of Pluckers to which you refer2 he has adopted rather strongly my supposition (2429.)3 that diamagnetic bodies may be polarized in the contrary way to iron or magnetic bodies having N & S poles opposite the corresponding N & S poles of the magnet. The proof he gives is brought from the action of a magnet or a piece of iron brought into the magnetic field[.]
I have similar phenomena produced in the case of crystals but I cannot in the one or the other case admit them as shewing polarity. I shew in my papers how they are a necessary consequence of the new direction given to the resultants of magnetic force.
Weber4 has I understand a proof of the supposition (2429) of another kind which he considers conclusive as to the correctness of the supposition but the paper is in German5 & I have not seen it yet in English6.
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But if a prismatic crystal of sulphate of iron whose length is 5 or 6 times its breadth be suspended in the magnetic field the poles being a certain distance apart it will point equatorially by magnecrystallic power. If the poles be much nearer it will point axially by Magnet power and for a certain distance included within very small limits it will point obliquely. This distance I have called n. Now n increases with increase in the length of the prism; diminishes with increase in the magnecrystallic dimension of the crystal - is not affected by the vertical dimension of the crystal - & is not affected by the strength of the Magnet[.] In a note which I gave into the R.S. last night7 I think I explain all this by the Polarity of the crystal as a magnetic body - and its mere axiality as a Magnecrystallic body[.]
The oblique set also I have dealt with and find reason to refer it to a small degree of obliquity in the Magnecrystallic axis as respects the length of the prism.
I have told Mr. Barlow that you will take the 19th8[.]
Ever My dear Sir | Most Truly Yours | M. Faraday
Revd. Dr. Whewell | &c &c &c
FARADAY, Michael (1846d): “Experimental Researches in Electricity. - Twenty-first Series. On new magnetic actions, and on the magnetic condition of all matter - continued”, Phil. Trans., 136: 41-62.
FARADAY, Michael (1849b): “Experimental Researches in Electricity. - Twenty-second Series (continued). On the crystalline polarity of bismuth and other bodies, and on its relation to the magnetic and electric form of force (continued)”, Phil. Trans., 139: 19-41.
SCHAFFER, Simon (1991): “The History and Geography of the Intellectual World: Whewell's Politics of Language” in Fisch and Schaffer (1991), 201-31.
WEBER, Wilhelm Eduard (1848): “Ueber die Erregung und Wirkung des Diamagnetismus nach den Gesetzen inducirter Ströme”, Pogg. Ann., 73: 241-56.
WEBER, Wilhelm Eduard (1849): “On the Excitation and Action of Diamagnetism according to the Laws of Induced Currents”, Taylor Sci. Mem., 5: 477-88.
Please cite as “Faraday2133,” in Ɛpsilon: The Michael Faraday Collection accessed on