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Glasgow - WT feels 'very strongly inclined towards Faraday's view that the substance of a diamagnetic is polar like oxygen or iron, when near a magnet, but that it is less so than the surrounding medium'. John Tyndall 'is in error if he still supposes that either his experiments or Weber's, or any others yet made affords a test as to whether this hypothesis, or true hypothesis that bismuth and the like, have a polarity the reverse of that of iron in the same circumstances. The resultant external force between a diagmagnet and paramagnet is demonstrably the same which ever hypothesis is true; and those experiments are solely indicative of resultant external force' [see WT to James Forbes, 19 March 1857]. Perhaps Faraday doubted Weber's [Wilhelm Weber] experiment gave any other result and he certainly doubted the truth of the interpretation put on Weber's results. 'Tyndall's repetition of Weber's experiment I believe convinced Faraday that the result was genuine'. WT has written a short article in the Cambridge and Dublin Mathematical Journal in May 1846, which 'contains principles and mathematical expressions, founded solely on what Faraday told me in his first paper, which lead in the most obvious way to the determination of all such forces as those which Weber and Tyndall observed'. WT describes what a (mechanical) explanation of electromagnetic induction would entail. Regarding 'Ampere's [André Ampere] theory of real motions in minute circular orbits or vortices, with axes on the whole set in the directions of the line of force, to account for magnetism, I think it is probably true. The magnetic optic discovery seems explicable on no other hypothesis. Since Foucault's [Jean Foucault] exhibition at Liverpool I have been much disposed to look on the gyroscope as an illustration of a magnet. It is of course difficult to see how a current ([?] of matter flowing) through a straight wire can induce among the thermal motions in the surrounding medium, eddies of which the axes are circles in planes perpendicular to the wire; and how eddies in a steel bar magnet with their axes on the whole parallel to its length can induce among the surrounding thermal motions, eddies rooted to the steel at each end...Still it is not beyond expectation that a definite mechanical explanation of such influences may be invented'. If this is done it simply shows that magnetic attraction is a product of pressure along the axes of eddies, caused by centrifugal force. An 'explanation of electromagnetic induction would have to be looked for by considering mechanically the effects produced by moving as whole, pieces of matter among the particles of which these are vortical motions with determined sets'. WT does 'not see how a momentary recoil in the surrounding matter can account for electromagnetic induction'. Nevertheless 'there may be lateral action at or near the boundaries of the conductor in its interior with a reaction causing the external induced current'. WT thinks 'Faraday must be right in supposing both electric action to be conducted through matter and by means of the matter through which it is conducted'. 'Is it credible that matter can act where it is not? Were not those of the schoolmen who demonstrated a universal Plenum right?' WT wonders whether WW can come up with any epithets for recent developments in electrostatics: 'I would like to be able to distinguish between systems in which the electricity to be tested is tried by one, and by two, independently electrified bodies'. He would also like names to distinguish electrometers.

Glasgow - WT [later Lord Kelvin] attended Michael Faraday's lecture on Gravitation, and spoke to both him and John Tyndall: 'I made a slight attack on Tyndall by asking him to explain to me the distinction between a viscous solid and a plastic solid. He said that before the end of a year it would be very clear. Which ever word is the most appropriate is the best expression of your theory as I have always understood it. As to the clear and porous alternate layers proving the veined structure, I do not know whether you lay much stress on the explanation Tyndall quotes as yours. It may be true what Tyndall says - that it is occasioned by pressure but that is no explanation'. Many writers have assumed that pressure is the cause of the clearage in slate mountains: 'It is a real thing proved if Tyndall or any one else can prove the clearage surfaces to be perpendicular to the lines of maximum compression'. In diamagnetics WT holds that Weber [Wilhelm Weber] and Tyndall have illustrated by experiment conclusions deducible (and which I deduced in 1846) from Faraday's forces experienced by bismuth; that they have established no new conclusion'. Faraday does not seem to perceive the relation with Weber's phenomena and even doubts Weber's results; 'Tyndall's repetition of Weber's experiment (described in the Phil. Trans.) confirmed the results and removed the possibility of such doubts as Faraday had temporarily raised. Not one of these experiments touches the ultimate nature of the magnetic effect experienced by the substance of a piece of bismuth, since the resultant external action is necessaily the same whether air in the surrounding medium is unpolarised and bismuth severly, or the surrounding medium and the substance of the bismuth both polarised directly (like a 'paramagnetic') but the surrounding medium more so than the bismuth'. Many of Tyndall's experiments simply prove things that did not require proving: 'In reality no testing experiment has ever been made to distinguish between two hypothesis: and I agree (I believe) with Faraday in thinking the second the more probable of the two true (I had a good deal of this in a letter to Tyndall which he published in the Phil. Mag. April 1855)'. WT has been occupied chiefly with electrometers and electroscopes in the apparatus room.