From John Frederick William Herschel   July 21 1861

Collingwood July 21. 1861.

My dear Sir

Accept my best thanks for your valuable paper the Bakerian Lecture on the diathermancy &c of Gases¹—which is an immense step in the Physics of Aeriform Bodies. —Also for your two lectures on Scientific teaching and on Solar Chemistry.²

On this latter allow me to regret that while naming Talbot & Miller,³ as having early described the bright bands peculiar to certain flames you have omitted to notice the results which I obtained as early as 1822 and described in a paper printed in the Transactions of the RS Edin⁴ for that year and the further indications of a similar nature in §’s 520–524 of my treatise on Light in the Encycl. Metropol published in 1827.⁵ In that Treatise §520 mention is made of Brewster’s & Talbot’s results and those of “others” (pursuant to a principle adopted throughout that article of never citing my own works—but in some such oblique form of expression). Of the indications given in the subsequent Sections, whatever is not to be found in the then published papers of Brewster & Talbot is my own—and the expression used in §524 “the colours thus communicated by different bases to flame afford in many cases a ready & convenient way of detecting extremely minute quantities of them &c” taken in conjunction with the distinct announcement of Bright lines appropriate to certain of them might have led an enquiring person at an earlier period than the present to much that is now so strikingly brought out. I was then so circumstanced as to be unable to prosecute the enquiry but I always considered it a very promising one—and you will excuse me if I say that I do think it a little hard, seeing that every other name connected with the subject—Brewster, Talbot, Miller, Masson, Willingen, Plücker, Wheatstone, Foucault, Stokes, Thomson,⁶ is mentioned in this admirable lecture (which must have created quite a sensation and will be accepted as a resumé of the history of the subject) mine should never once have been alluded to. —

On the general subject of Kirchoff’s theory of the absorption of the peculiar coloured light of a body by the flame of that body there occurs to me a remark which may or may not be worth your consideration. —You (or Kirchoff) assimilate this absorptive action to that of glass on heat emanating from bodies heated below incandescence. —You say that it only does not transmit the rays because it disperses them—i.e. so much is scattered quaquaversum that little is shot forward directly. —Granted. —But apply this to the Sun—quaquaversum means in all directions outwards into space. (Inwards & backwards also—but this will be re-absorbed & radiated out again—so that ultimately all will find its way out in some direction or other). —Now the totality of these quaquaversum radiations amounts to a radiation quaquaversum of the totality—ie to an emanation some how or other (however circuitously) from the Sun’s general spherical surface equally in all directions into Space of the whole light just as if it had never been absorbed.

There is a little paper w[hic]^h I sent to the Lond & Edin Phil Mag printed in their 3^rd series Vol 3 N^o 18 Dec. 1833⁷ on the absorption of light (by coloured media) which perhaps may be found to contain something in point on this matter.

Excuse this rambling letter & believe me yours very t[rul]y | JFW Herschel

PS.¹ Vegetable colours are bleached by those rays which they reflect most abundantly not those which they absorb in preference

P.S.² Is it not rather startling to assume that molecules which are particularly fitted to vibrate in one rigidly definite time & which are in the air of such vibration should yet par excellence stifle & destroy vibrations in that identical definite time when propagated into them ab extra? It is clear there is a link wanting in the chain of the argument.

RI MS JT/1/H/94

RI MS JT/1/TYP/2/505–6

Royal Society Letters (RMD 5 August 2011), 23_335 (this is Tyndall’s own transcription)