[this is Herschel's draft of his reply to WHFT's letter of 25 July See Doc. No: 04314 - the letter as sent has not been located.]

Dear Sir

The Publication of D^r Brown’s res^{r <1>} in the Trans RS Edin^<2> seem to indicate some degree of enquiring into the authenticity of his expts – Nevertheless the discovery is vastly too important not to undergo a very minute scrutiny before it is received. I have not rec^d the Volume & have no idea of the nature of the exp^ts 5 parts from 30 or 16 per cent of Silica is too palpable a quantity to remain long in doubt as its origin. All of course will depend on the evidence by which it is proved that the results stated to be Silica & Silicates are really so, or new products into which Azote may enter from the Cyanogen giving rise to a degree of inertness that may afford a semblance to Silica. – Especially also as the Iron is transformed, –) it is not improbable that we may have got among a set of compounds combinations of some new compound radical. – But till I have seen the acct of the Expts – this is all talking at random.

I am quite ashamed to say that I have not yet repeated the Calotype Expt. ^<3> But I have been preparing a parcel of reports for the B. Association ^<4> and other work which has prevented my doing anything towards getting my chemical preparations into action or doing any thing that requires the use of any reagents except such as happen to be ready at hand in a few loose bottles turned up out of a sort of chaos in which state all my chemical concerns have been ever since I left Slough having never had time to unpack & establish them. – All I have done in the Photographic way has been with vegetable substances needing no preparations & no additions other than the contents of those same loose bottles which happened to be at hand or extempore makeshifts of the rudest kind. However in this desultory way I blundered not long since on a curious enough imitation in vegetable photography, of your Calotype – a specimen of which I enclose ^<5> (a very poor one, for I made the trial only on a spoiled picture). The picture being first impressed, and visible (in which point it is not like the Calotype) was then totally discharged – leaving white paper. – This being exposed to light by very slow degrees recovered its former intensity. About 24 hours diffused light suffices (as for sun we have had none of late). Air also in darkness developes [sic] the picture but very much more slowly and feebly – [illegible deletion]

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Notes:

1. Samuel Brown (1817–1856), chemist.

2. Royal Society of Edinburgh.

3. The experiment of exposure by moonlight in Doc. No: 04293.

4. The British Association for the Advancement of Science.

5. Enclosure not located.