Sunday, 19th May
My dear Mr Stokes.
Being engaged so much in lecturing and other matters just now, my mind is thrown a little out of gear, and indeed my time so filled that I could not, when I received them, devote the attention they deserved to your remarks on my paper:1 —I have looked over them again this morning and have felt much interested by them.
As far as I can revive my impressions2 I figured the propagation of heat thro’ a solid in this way: —Imagine a prism, say of rock crystal, with a source of heat applied to one of its terminal surfaces, a definite amount of motion being thus imparted to the terminal superficial stratum of molecules. The question is how is this motion disposed of?
I suppose one portion of it (A) to be in the first instance communicated to the ether which divides the stratum from its next neighbour; a portion of this portion being transferred to the molecules of the second stratum, thus assisting conduction.
I suppose a second portion (B) to be transferred directly, which is pure conduction.
The second portion of (A) I suppose to be transmitted to the ether external to the prism, and thus lost as regards conduction.
The larger the ratio of A to B the greater I suppose is the loss just alluded to, and the shorter the distance to which the motion can be transmitted from particle to particle thro’ the mass. In fact the motion is not there to be transmitted, having been wasted in space. Bad conduction is the diversion of the motion from the molecules to the ether.
I suppose the ratio of A to B to depend mainly upon the form of the molecule. If it be smooth, round and heavy, (A) will be less and (B) greater than if it be rough or pitted, and specifically light.
Supposing, the terminal stratum of our prism once set in motion, that the source of heat is suddenly withdrawn, the stratum being permitted to exhaust its motion; a portion of the latter would be communicated to the ether behind the stratum, and there take the form of radiant heat.
It appears to me that the copiousness of this radiation would depend on precisely the same quality as that which renders the component A large, or which in other words diminishes conduction.
Thomson refers to you3 in connexion with Bunsen & Kirchoff.4 I want to know more about this matter, for I have a dim remembrance that once as I sat at your side in the Philosophical Club5 you mentioned Foucault’s experiment6 to me in connexion with the subject of Fraunhofer’s lines.7 Do you remember this conversation? Can you refer me to any thing published on the subject? Of course I shall be only too willing to act on Thomson’s suggestion.
very truly yours | John Tyndall
RI MS JT/1/T/1421
RI MS JT/1/TYP/4/1468–9
your remarks on my paper: see letters 1780 and 1782.
As far as I can revive my impressions: this refers to the difference of opinion between Tyndall and Stokes on the relationship between radiation and conduction of heat. See letter 1780, n. 6 and letter 1781, n. 8.
Thomson refers to you: William Thomson.
Bunsen & Kirchoff: Tyndall was preparing his Friday Evening Discourse on 7 June ‘On Solar Chemistry’, Proc. Roy. Inst., 3 (1858–62), pp. 387–96, in which he gave full credit to Kirchhoff for discovering the relationship between the dark lines in the solar spectrum and the bright lines in the spectra of heated metals.
Philosophical Club: an elite dining club of the Royal Society, established after the reforms to the Royal Society in the 1840s, in addition to the existing Royal Society Club. Tyndall had been elected in 1855. See T. E. Allibone, The Royal Society and its Dining Clubs (Oxford: Pergamon, 1976).
Foucault’s experiment: Stokes had written a letter to the Philosophical Magazine in which he reported an observation that Foucault had made to him: ‘On the Simultaneous Emission and Absorption of Rays of the same definite Refrangibility; being a translation of a portion of a paper by M. Léon Foucault, and of a paper by Professor Kirchhoff’, Phil. Mag., 19 (February 1860), pp. 193–7. Foucault’s paper was published in L’Institut for 7 February 1849, having been brought forward at a meeting of the Philomatic Society on 20 January. Kirchhoff’s communication ‘On Fraunhofer’s Lines’, dated 20 October 1859, was made to the Academy of Sciences in Berlin on 27 October and printed in the Monatsberict, p. 662.
Fraunhofer’s lines: see letter 1595, n. 10.
Please cite as “Tyndall1783,” in Ɛpsilon: The John Tyndall Collection accessed on