Fabian Carl Ottokar von Feilitzsch to Faraday   3 December 1850

Honourable Sir!

If the exhibition of a new theory conditionates likewise a progress in science, because the apparitions alredy known are comprised under one point of sight engaging to new essays to prove or to disprove them - then I dare hope to have made by my efforts one though but little an advance in that branch, that you Sir the great discoverer of diamagnetism have opened. I dared not so assure you of my unbounded esteem, to express you, of what a veneration I am penetrated by following your disinterested indeavours in that science that I love over all, and of which I have made the task of my life,- before I could not put to your feets a little work so unimportant it might be. I wish so vehemently to give you a mark of my deference, that I can not wait longer, to manifest the awe with which I look up to you, might you pardon to such feelings and kindly excuse, that I take now the liberty, to dedicate you this little work.-

I could not be entirely satisfied by that theoretical contemplation of the nature of the diamagnetism, that you and after you M[ess]rs Reich¹, Poggendorff², Weber³ et Plücker⁴ have settled⁵. This theory asked the hypothesis: that in every molekule of a magnetical substance by exterial induction the magnetism is in such manner distributed, that to the inducing Southpole is turned a Northpole, and to the inducing Northpole a Southpole; but that in diamagnetical substances the distribution takes in such a manner place that in every molekule to the inducing Southpole a Southpole and to the inducing Northpole a Northpole is turned too. Or what is the same thing, that the currents of the theory of Ampère in the magnetical substances are in a contrary direction moved as in the diamagnetical substances. I tried rather to explicate myself the apparitions by an hypothesis that Mr. van Rees F had explained; consequently I suppose, that in magnetical as in diamagnetical substances the polarity of the molekules have the same direction, but so that all the Northpoles are turned to the Southpole, and all the Southpoles to the Northpole of the inducing Magnet, only whith that difference, that in a bar of magnetical substance the intensity of the distribution of the molekules increases from the ends to the midst, while it decreases in a bar of diamagnetical substance from the ends to the midst. The currents of Ampère in magnetical substances would be consequently more feebly directed in every particles that is situated next one of the centres of excitation, as in one more distant, but in diamagnetical substances they would be more strongly directed.

These suppositions are permitted, if we attribute to the two groups of substances a diverse resistance against the magnetical excitation (a different Coërcitiv-power). The particles of a magnetical body have a very little Coërcitiv-power, thus the distribution of magnetism must take place in such a manner, that the magnetism dispensed by the primitive excitation in every particle acts distributing on his part on the others, and particulary on the neighbouring particles. Because the molekules are situated very near one to the other, it is to be thought that this part of magnetism is stronger, than that of the primitive excitation. But in the diamagnetical bodies the Coërcitiv-power is so important, that this portion of magnetism, that takes place by the excitation of the molekules one to the other, is more feeble, than that which is produced by the primitive excitation. A bar of magnetical or diamagnetical substance can we excite in two manners, either from the ends to the midst, or from the midst to the ends

A. The excitation from the ends to the midst is done usually thereby, that a bar is suspended between two magnetpoles.

1., To its Coërcitiv-power so important that the effect of the molekules to each other can be neglected, then every particle that is nearer to the magnetpole will be more strongly excitated than that next neighbouring and more distant particle.

Do we such observe two neighbouring particles near the exterial Southpole then will the more near exert a Southpole with the intensity s, the more distant will turn to a Northpole with the intensity n’, but in such a manner that n’<s. But outwardly works this two excitated magnetisms with the difference of their power s-n’, but this is in our case southpolar, consequently of the same kind, as the excitating Southpole. The contrary will take place near the Northpole, so that the disengaged magnetism, extended over the bar, grows southpolar on that half which is turned to the Southpole, but northpolar on the other half, that is turned to the Northpole. A substance, where this takes place is diamagnetical, it puts itself equatorial.

2., Is the bar of a magnetical substance therefore so qualified, that the separating action of the molekules on each other must be taken in consideration than can it grow so strong, that the molekules in the midst of the substance are more strongly magnetical, than towards the ends. Do we observe once more two such particles near the exterial Southpole, of the intensity s<1> so will the next avert a Southpole of the intensity s<1> from this exterial Southpole, but the more distant turn towards it a Northpole of the intensity n<1>‘; but in such a manner, that n<1>‘>s<1> outwardly works both with the intensity n<1>‘-s<1>, but this is northpolar, therefore of a contrary nature, as the excitating Southpole. The contrary shall take place near the Northpole, so that the disengaged magnetism, extended over the bar, grows northpolar on the half that is turned towards the Southpole, but southpolar on that half, that is turned towards the Northpole. A substance, where this takes place is magnetical, it puts itself axial.

3., Besides of this observed disengaged magnetism must be yet considered that magnetism, that grows disengaged on the final surface of the bar and that can not be compensated by the neighbouring particles. But this is always of a contrary nature than the excitating neighbouring pole. For magnetical bodies does it support the effect of the disengaged magnetism extended over the bar; in diamagnetical bodies acts it in the contrary, and it is to be thought, that even it is preponderating. Perhaps might this be cause of the feeble magnetism, that you were finding in the Platin, Paladium and Osmium⁶.-

B., An excitation from the midst to the ends takes place, if we do lay a bar in an electrical spiral. But in this case all the substances must gain an equal polarity as the iron[.]

To prove that, I puted a thick bar of Bismouth in a very strongly acting spiral, which were excitated by 4 cells of Mr. Grove every one of twelve <square> inch of platin plate. I set this spiral on a side near a little declinations-needle suspended on a silk-thread and I compensated its effect by a magnet of steel, that I dislocated as long on the other side of the needle, as it was returned to its first place. Did I withdrew the bismuth bar out of the spiral, than the needle declined in favour of the compensating magnet, but if I puted it again in the spiral, then the needle declined in favour of the spiral. Unlucky the poor fortune of the physical establishment of our university did not allow, to prove also other substances, than the bismouth, but I schall supply this defect as soon as it is do be done; but you will allow me the consequence:

that the diamagnetismus and the magnetismus are only modifications of the same power, that are produced partly by the different Coërcitiv power of the substances, partly by the different manner of excitation.

Transporting the former in the theory of Ampère I startled, because it has teached hitherto only: Currents, that are parallel and directed in the same way, attracts themselves, but if they are parallel but not directed in the same manner they are repulsive; therefore that a current, moving in the sense of a hand of a watch, in a spiral produces a Southpole on the entrance point in the spiral, but a Northpole on the egression point. But hitherto one has only constructed spirals, where the currents in every winding schows an equal intensity.

But I tried, to construct spirals in such a manner as these, which I have adjointed⁷. One of them is in such a way constructed that on two copper wires are solderd to each of them 15 thin threads spined over with silk. With all this 15 threads is the first winding layed backwards over the copperwire; the second winding is only winded with 14 threads, during that the fifteenth moves itself along the axis etc. Consequently has every of the 15 windings a thread less, and the ends of all the other threads have the direction of the axis. Are soldered in the midst the lasted ends of the 2. 15 threads and are the two thick threads without touching themselves, in each manner bowed, that they can be suspended in the little cups of the apparatus of Ampère, than a current, passing by the spiral, will divide itself in such a manner, that it is the most strong on the exterial ends of the spiral, but decreases more and more to the midst. If the winding of the spiral took place in the direction of the hand of a watch, then must the end of it, where the current enters, grow a Southpole: but a Northpole, kept parallel of the spiral, will it repulse. Only the final winding will be attracted and is representing this disengaged magnetism of the final surface. The second spiral is winded like this, only with that difference, that the strongest windings are laying in the midst and the feelblest near the ends. This spiral will be attracted of the Northpole of a magnet over the half in which the current moves at first, but the other half will be repulsed by it. Of the third spiral at last have all the windings the same strength, over all the extension, it is indifferent against a magnetpole, that is not to[o] near, and only their last ends are attracted or repulsed.

Therefore it is permitted to enlarge the theory of Ampère in this manner

If an electrical current passes through a spiral in the direction of a hand of a watch, and

a., if the current is more feeble in every winding that is nearer to the

midst of the spiral, then that half is attracted by a Southpole, in which enters the current excepted the first winding,

b., but if the current is more strong in every winding that is nearer to

the midst of the spiral, then that half is repulsed by a Southpole, in which enters the current including the first winding[.]

The contrary will be adopted for that half in which deserts the current and likewise for the Northpole of the magnet opposed.

In consequence of this extension of the theory of Ampère, it is easy to transfer them in the opinions above produced. In the molecules of magnetical and diamagnetical bodies are to find electrical currents: By the magnetism they will be in such a way directed, that they put themselves parallel of the exterial acting currents. In the diamagnetical bodies is opposed a very great resistance to the direction of these currents of molekules, therefore will their intensity decrease from the centre of the excitation; these bodies will comply with the opinion that is given in a., they will be repulsed. But in magnetical bodies acts the currents of the molekules, that are diverted by exterial influence, on their part also directing on the neighbouring currents of molekule, and in such a manner, that these currents are the most energical directed in the midst of the bar, but are more feebly directed near the ends. These bodies comply with the opinion given in b., they will by attracted and puts themselves axial.

But I fear to tire you, would I transfer the opinions that I have explained on the different apparitions, that followed to the your discovery of the diamagnetism. The apparitions of the minglings of magnetical and diamagnetical substances; the predominating attraction or repulsion of the axis of the crystals; the apparitions of the magne-crystallic axis; the currents of induction that gives a bar of Bismuth exhibited by Mr Weber:- all this apparitions follows by themselves by plain adaptions.-

I ask your pardon, Sir, that I have dared to write you in your own language, that I know so very imperfectly: but I hope I have not to much deformed the sense of what I would express.

I have the honour to be Sir, your most humble servant | Dr. von Feilitzsch | Professor of the university of | Greifswald

Greifswald in Prussia, | 3 Dec. 1850

F cfs. Memoirs of the Netherlandish Institution Vol 12⁸.