2 College, Glasgow | March 22, 1855
My dear Sir
I have no objection to the publication of any part of my last letter1 to you in the Philosophical Magazine, which you may think suitable. I wrote it very hastily, and I should be obliged by your making any remarks or corrections that may be required or that may occur to you; or allowing me to see a proof which I could return without delay if I receive it any day next week.
Since I wrote to you I have found that either iron filings or little pieces of very thin iron wire, mixed up with soft wax or dough, give a body which always places the line of compression perpendicular to the lines of force; doing so, & with great energy when suspended 4 or 5 inches from the centre of the field in a Ruhmkorf double electro-magnet,2 immediately on being pressed between the hands, over and over again in different directions. I was quite prepared for this in the case of the little pieces of iron wire; but I rather expected the opposite bearing when iron filings were used. The explanation in each case must be that the little fragments of iron get pushed into such positions by compression that they act upon one another inductively like the parts of a bar or row of fragments perpendicular to the line of compression, or like the parts of a set of bars or rows at small distances from one another but on the whole more nearly continuous perpendicular to than along the line of compression. Why this should be is quite obvious in the case of the little pieces of iron wire; but, though not unintelligible, it is not to me so obvious in the case of the iron filings. Both these cases exhibit a phenomenon opposed to that which you have I believe ascertained for paramagnetic substances in general, in a state of strain,3 and it follows that, although the effect of a state of strain by compression of the actual substance of a paramagnetic is, you find it to be, similar, as regards inductive capacity, to that which would exist in a compound solid composed of a number of small pieces of soft iron on the whole nearer one another along lines parallel to a certain direction than along lines perpendicular to that direction; yet as actual compression of a plastic medium containing fragments of soft iron mixed up with it does not produce the same effect on the resultant inductive capacity in the direction of compression, but in lines perpendicular to that of the compression.
I sent off to Professor Stokes4 a short time ago a short paper5 containing elementary demonstrations of some of the propositions regarding magnetic forces & the tendency of paramagnetics and diamagnetics as regards places of stronger and weaker force which have been already published as results of experiment, or as conclusions from mathematical analysis. It will probably be published before long, but I do not know in what journal.
Believe me, My dear Sir, | Yours very truly | William Thomson
RI MS JT/1/T/12
my last letter: Letter 1053, which was published in the April 1855 issue of the Phil. Mag. The present letter was a reply to letter 1060.
field in a Ruhmkorf double electro-magnet: The very strong magnetic field produced by high voltage electricity from a Ruhmkorff’s apparatus with two windings. The high voltage induction coil bears the name of Heinrich Daniel Ruhmkorff (1803–77), who appears not to have been the original inventor.
opposed to … paramagnetic substances in general, in a state of strain: Thomson was probably challenging the results that Tyndall had announced in his paper ‘On Diamagnetism and Magnecrystallic Action’, Phil. Mag., 2 (1851), pp. 165–88, esp. pp. 180–5.
Professor Stokes: William Thomson to G. G. Stokes, March 14, 1855; see letter 1076, n. 4.
a short paper: W. Thomson, ‘Elementary Demonstrations of Propositions in the Theory of Magnetic Force’, Phil. Mag., 9 (1855), pp. 241–8.
Please cite as “Tyndall1061,” in Ɛpsilon: The John Tyndall Collection accessed on