69 Albert St. Regents Park | Jan. 13th 1858
My dear Dr. Tyndall,
You have not remembered quite rightly the views I expressed about the dark bands, or fixed lines, of the solar spectrum and the bright lines of electric spectra.1 As to the former you were right. I said that I thought it most probable that they were a phenomenon of gaseous absorption produced by the atmosphere partly of the sun partly of the Earth. But as to the bright lines you have substituted for my views, from imperfect recollection, something utterly different. In the former case light is the rule, a dark line the exception; but here light is the exception, and we have isolated bright lines. There is nothing whatsoever to lead us to suppose that the generally wanting light ever existed. Everything tends to show that in the voltaic arc (not the incandescent poles) ponderable matter sets the ether in vibration in a manner analogous to a finite number of notes of particular pitch.
It is well known that alloys exhibit simultaneously the bright lines due to the several metals of which they are composed; and it is just what one would expect in accordance with the view I have explained.
What put the explanation which you supposed to be mine of the bright lines into your head was probably an indistinct recollection of a very remarkable experiment of Foucault’s2 which I mentioned to you, in which he shewed that the voltaic arc between charcoal points3 was at the same time a source of light giving out the bright line (darker line) D and an absorbing medium extinguishing light of that particular refrangibility4 (not, observe, all light except that agreeing in refrangibility with D). I mentioned I believe what I regarded as an illustration of this experiment of Foucault’s derived from the analogy of sound.
My wife5 desires me to say that she is much obliged to you for the ticket.6 We hope to be present at the lecture.
Yours very truly | G. G. Stokes
P.S. I presume you would like the 21st for your day at the R.S.7 and believe it is the same subject that you are to bring forward at the R.I.
RI MS JT/1/S/219
RI MS JT/1/TYP/4/1361–2
bright lines of electric spectra: possibly a reference to a lecture Stokes gave at the RI on 18 February 1853, and published as ‘On the Change of Refrangibility of Light, and the exhibition thereby of the Chemical Rays’, Proc. Inst. Roy., 1 (1851–4), pp. 259–64. Stokes’s paper on the same subject ‘On the Change of Refrangibility of Light’, Phil. Trans., 142 (1852), pp. 463–562, had earned him the RS’s Rumford Medal in 1852.
very remarkable experiment of Foucault’s: Jean Bernard Léon Foucault (1819–68), a French physicist, published a note on his experimental observation in the 7 February 1849 number of L’Institut, journal universel des sciences et des sociétés savantes en France et à l'étranger, 17 (1849), pp. 44–6. Reprinted as L. Foucault, ‘Note sur la lumière de l’arc voltaique’, Annal. Chim. et Phys., 58 (1860), pp. 476–8. Also see G. G. Stokes, ‘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 (1860), pp. 193–7.
charcoal points: see letter 1440, n. 20.
refrangibility: the ability of light (or other rays) to be refracted (OED).
My wife: Mary Stokes (née Robinson, 1823/24–99), married on 4 July 1857. Together they had five children.
the ticket: on 22 January 1858, Tyndall lectured at the RI, ‘On Some Physical Properties of Ice’.
your day at the R.S.: presumably Stokes was mistaken in stating that he believed Tyndall’s subject for the RS on 21 January was the same as his subject at the RI on 22 January. Tyndall read Samuel Haughton’s paper on rock cleavage at the RS on 21 January 1858. See letter 1449, n. 6.
Please cite as “Tyndall1481,” in Ɛpsilon: The John Tyndall Collection accessed on