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Weber agreed with Tyndall that this may seem extremely artificial but stressed that he had made no new assumptions. He hoped that in time that mathematics might overcome the limitation to linear currents and the concept of channel-like current beds. In a footnote in Researches on Diamagnetism and Magnecrystallic Action in , Tyndall heartily endorsed Weber's view of this need for clarity in the description of the physical model. Tyndall's response, welcoming Weber's points, picked up only on the question of whether the diamagnetism of two bismuth particles lying in the line of magnetisation is diminished by their reciprocal action as Weber claimed rather than increased as Tyndall had claimed in the Bakerian Lecture.

Weber had stated that the effect was in any case very weak and might be affected by Tyndall's compression of the bismuth. Experiment, at this point, was unable to decide the facts.

An Elementary Treatise on Electricity by James Clerk Maxwell

It is amusing to see how many write to Faraday asking him what the lines of force are. But he has no exact knowledge himself, and in conversation with him he readily confesses this. In my next paper I shall have to say something of these lines of force. On 9 and 10 November Tyndall was attempting without success to repeat an experiment of Weber's which Faraday had also not been able to repeat. He gave Faraday a draft of his paper on 17 November, and was working on compression experiments during the week of 19 November.

Tyndall wrote to Thomson on 20 November offering assistance for Thomson's forthcoming Friday Evening Discourse and asking for some clarification over Thomson's theory of the magnetic field:. From your proof that the intensity of a magnetic field increases towards the centre of curvature Phil Mag April I should infer that if the lines of force were parallel straight lines the intensity at right angles to them would be constant.

I have a steel horse shoe magnet here in which the lines of force run sensibly parallel from leg to leg almost from top to bottom, yet such a field is not one of constant intensity, for the force increases [from] the bend towards the poles. When we examine such a field closely we even find that the lines of force are slightly curved, the centre of the curvature being towards the bend, and not towards the poles.

According to this the intensity increases as we recede from the centre of curvature…I have just finished a paper on polarity which I purpose sending to the Royal Society in a few days, I am now entangled in compression experiments. Thomson replied on 24 December, in a letter which Tyndall had published in Philosophical Magazine for January and also reprinted in Researches on Diamagnetism and Magnecrystallic Action. Tyndall replied to this letter:. The people at Red Lion Court [i.

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I took it back immediately and urged Francis strongly to publish it. This however he declares to be impossible this month. He may change his mind. The exchange illustrates Thomson's view of a consistent treatment of all magnetic and diamagnetic phenomena, conceptually and mathematically, while Tyndall was concerned to have a clearer physical picture.

A long letter to Grove of 5 December reveals both Tyndall's perception of constraints at the Royal Institution and the significance of his latest findings. From private continental letters I also infer the necessity of the enquiry. On 20 December, after dinner at the Philosophical Club, Stokes read the introduction to his paper and he was asked by the President to explain the experiments himself, which he did to the apparent satisfaction of everyone. Indeed von Feilitzsch did this and was unable to detect any effect.

The paper was refereed by Joule and Thomson. At this point, again, Tyndall's ability as an experimentalist showed itself. Using equipment designed by Weber he made a series of extremely sensitive experiments with copper, antimony and with insulators, using glass and six other materials, and found deflections to be permanent rather than temporary, which would be the case if there were a momentary induced current.

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In his terms this showed the polarity of a diamagnetic body as an insulator in addition to that of conductors. In this paper, primarily addressing Faraday's statement that the magne-crystallic force is neither attraction nor repulsion, he gave a clear explanation of the complex effects of attraction, repulsion and the effect of the resulting moments, or couples, in explaining the direction of movement of spheres and bars of substances in different magnetic circumstances.

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In particular, he showed that a recession from the pole can be due to differential attraction and repulsion, i. Throughout this time Tyndall demonstrated his skills as a systematic experimentalist which are more widely known through the subsequent work on radiant heat and spontaneous generation. His particular contribution to diamagnetism was to establish the physical facts unequivocally through experiment. His style was very much that of the systematist, meticulously controlling variables. In this he differed from Faraday, whose style might be described as dialogic; exploring and conversing with Nature.

Only two experimental notebooks survive from this period and they are relatively sketchy and untidy compared to those of later years. Yet the papers themselves, and especially the later Memoirs, demonstrate the clarity and skill with which he prepared and pursued his investigations. Tyndall was introduced by Grailich.

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He was polite and cold, and I reconciled myself to the fact. Both referees saw the paper as over-elaborate, and both queried its reference to Poisson's theory. Thomson commented that it was:. Tyndall's work on diamagnetism came to an end in ; no more significant progress in his terms could be made with the mathematical and theoretical understanding of the time, until the application of vector theory. Starting around almost as Tyndall finished his work, it was James Clerk Maxwell who made the major theoretical contribution, developing Faraday's field theory and Thomson's initial modelling of it, culminating in his great Treatise of Tyndall had intended to collect and publish all his work on experimental physics in , but an accident sustained by slipping over onto a block of granite above Bel Alp on 29 August prevented him from doing so, and required six weeks of recuperation with Lady Peel in Geneva.

I have already gone through those on diamagnetism. As he wrote to Helmholtz on 8 January:. I sent Tait the Memoir on Faraday, and he gave himself the trouble of reading it all through and of giving me his opinion upon it. Now you are Thomson's intimate friend, and I am anxious to do all just honour to Thomson: would you point out the places where you think his labours might be referred to? Weber wrote to Tyndall on 18 March , in a letter which encapsulates the different ways of visualising the phenomena:. I take the same interest as you in the beautiful and penetrating researches of Maxwell, and link it particularly to the electrodynamic theory of light that Maxwell has developed.

The proof of a medium , through whose molecular forces the effects could be determined precisely, which electric currents and electric charges exert on each other at a distance, would be very interesting in itself. The assumption of such a medium which really acts like this I take as just as admissible as the assumption of forces acting at a distance, from which these effects have until now been determined.

If indeed it were further shown that from the assumption of this medium the effects of light at a distance could also be determined at the same time, the alternative between the two assumptions would in my opinion be decided…As far as the medium itself is concerned, and the determination of the molecular forces effective within it, the agreement of the analytical expressions with the results of Faraday's experimental researches gives considerable confidence, even if we lack, as it appears to me, clear insight into the inner relationship between molecular forces and properties, which fundamentally is the case in general, where research into the inner molecular constitution of matter has led so far.

I would like to think that the transfer of the laws of action at a distance to molecular interactions, as C. Tyndall produced a second edition of Researches on Diamagnetism and Magnecrystallic Action in , in which he reprinted the six Memoirs but much less of the additional material; 7 items compared to 21 in the first edition, including removal of the items relating to correspondence with Thomson by now Sir William, who would become Lord Kelvin just before Tyndall's death.

Pasteur truly describes the art of experiment as beset with difficulty and danger. Both, by this time, had been dead for 20 years. So, towards the end of his life, and following all the developments of Thomson and Maxwell, Tyndall still saw the best interpretation of the phenomena of diamagnetism in his terms of polarity leading to attraction and repulsion of couples, rather than Faraday's field theory. A significant point at issue between Tyndall, Faraday and others was the concept of diamagnetic polarity.

How Earth Creates Its Magnetic Field

This came down to a matter of deciding what was meant by polarity and can be resolved in one sense in terms of the geometry of magnetism, now best described in terms of vector algebra. This was not available to Tyndall when he did his work, though it is developed from the concept, introduced by William Hamilton in of quaternions, mathematical entities formed of a scalar and the three components of a vector, which he never attempted to master later and which Thomson much disliked. Taking polarity first, it is not always clear what was meant by the term, and there were different understandings of it.

In electrostatics it is said that the forces of attraction or repulsion between two charges are polar; there is a straight line joining two charges or poles, about which there is cylindrical electrical symmetry. Tyndall believed he had established beyond doubt that diamagnetism was polar in his terms, but this cannot be disentangled from more fundamental concepts of matter, forces and fields.

Tyndall saw the structure of matter at the molecular level as critical to the mediation of force. Faraday, by contrast, saw force and the field as primary. So, at the molecular level substances are not in contact, and the channels between may differentially allow magnetic or other forces to be exerted.

Modern Views on Magnetism

In Faraday's terms, though, the lines of force represented something physically real, with continuous action understood in terms of forces filling space. Thomson, by contrast, imagined small magnetic elements each of which had anisotropy to produce that in a whole mass. Part I. Whatever the actual structures might be, their differences are posited to explain the differential transmission of heat or of magnetic forces in different directions related to underlying but unobservable structure; unobservable at least until the end of the 19 th century. From the outset of his experiments on diamagnetism, using cubes, discs, thin bars and reconstituted materials, squeezed in particular directions, Tyndall was exploring the molecular constitution and arrangements of substances underlying their overall mass.

A journal entry of Tyndall's describing a conversation with Faraday in October is instructive:. He Faraday does not deny the polarity of diamagnetic bodies but could not accept the experiment of Weber's as proving it… He did not coincide with the idea expressed in one passage of the memoir that force could not act upon force.

He would not say that it could but he was not quite clear that it could not. I said that with me the conception of force necessitated the conception of matter. Faraday's position on the ether, with respect to this argument, is discussed by Gooding. In a note in he stressed how Faraday had connected the force of magnetism with the luminiferous ether although it is doubtful if Faraday himself would have seen it like this , through his discovery of the rotation of polarised light by a magnet, and the importance of this understanding developed through the work of Thomson and Maxwell.

Faraday by contrast had developed a field theory, which was put into mathematical expression by Thomson and Maxwell. Airy, as an astronomer, could perhaps recognise a good action at a distance model, even if the distances involved in crystals were very small. Thomson and later Maxwell were in the second group of physicists with Faraday.

Thomson exploited the analogies between fluid flow, heat flow and electricity. Faraday, Thomson and Maxwell, unlike Tyndall, all had strong religious beliefs, and Gooding links the teleology and economy inherent in Faraday's interpretation to those beliefs. After Tyndall's experiments, it was not the facts that were in dispute but their interpretation. Faraday saw magnetic conductivity as relative, with diamagnetics having a lower conductivity than space and magnetics a higher, an assumption on which Thomson's first mathematical theory of diamagnetism was based.

For Faraday, ferromagnetics define the true polarity or direction of lines of force: other substances merely conduct this polarity. Faraday also had the argument from the early results that whereas a magnet polar would always set in one sense in a magnetic field, a diamagnet could set either way round.

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