Slough
Dec 4/39

My dear Sir

I do not know whether I ever thanked you for your obliging comm^{n <1>} of M. Biot’s message. If not let me now acquit myself of this debt. I am afraid too that a letter of yours of much longer date (Sep 12) ^<2> remains yet unreplied to – and as in that letter a point is alluded to as to publication I would gladly know whether you consider those remarks to apply now that it is known that Daguerre himself is the patenter of his own process ^<3> – as in that case, I would yet keep quiet what slight facts have occurred to me respecting photographic processes – whereas if otherwise I am rather desirous now, to throw them off and thus get rid of the subject – not because I am tired of it, but because its future pursuit would trench upon my astronomical work to which it must be now a matter of duty with me to devote my entire attention to the exclusion of all other even more attractive subjects. If I My intention was if you think the objection on the score of the patent removed – to draw up a short paper for reading to the R. Society ^<4> –

and Your coloured rings produced by vapour of Iodine are very beautiful. By the way By the way have you noticed those which form on mercurial solutions exposed to air. Mercurial salts are affected also by light but in a mode rather enigmatical.

I shall be very glad to know your mode of acting on glass without fluoric acid which you offer to communicate.

Last full moon I got in 55 minutes, by light condensed by an aplanatic double lens 3ⁱⁿ aperture & 6ⁱⁿ focus – a very dark spot almost black. I used your Salted paper I think it would have required 5 or 6 seconds of Sunshine to have produced an equal darkness.

Your remarks on the Daguerrotype are quite in accordance in one respect with mine I mean the excessive sharpness & moon-lighty or frost-edged effect of chimneys &c against the sky. I cannot account for it. Your other remark as to the relative brightness of objects is very singular and cannot but depend on some interesting relations not yet made out. It has not struck me. There is no end to the Caprices of this subject but your experiment with the unsensitive oil C as applied to the 2 papers A & B strikes me as the oddest of all.

I have been trying a few combinations with a view to facilitating the Camera-photog^ing with paper which is certainly susceptible of great development.

1^st Sensitive papers will not keep (at least I have none that will not darken by time in obscurity) and to prepare them when travelling is very difficult & troublesome. – Now I find that by reserving the Nitrate of Silver for a last wash, this may be obviated, as the paper when prepared all but that last wash will of course keep white ad infinitum Thus then I proceed. The paper is first washed with acetate of Lead (Saturated Solution) and dried 2^d. With a solution consisting of 40 parts water, 2 parts muriate of Soda and 1 part Hydrobromate of Potash* & dried. It is now ready for the travellers use and may be exposed to air & light ad libitum. – To use it, have ready a wash of Nitrate of Silver SG 1·25 – 1·20. Wash it rapidly over with a brush well dipped – (shading it as much as possible) & apply it face foremost against a plate of glass to which it will apply closely and adhere. Ap Wet the back & apply another glass behind it & then expose it wet in the Camera having duly adjusted the focus by trial on unprepared paper so treated. – As soon as the image is completed throw the paper into water (or keep it in the dark till water can be got) and dry it in the dark after which fix with Hyposulphite of Soda – the only liquid I find never to fail.

I will now only mention one point more which I think may be of great service to travellers under conceivable circumstances – viz. that in place of fixing the photograph on the spot it may be by a certain application A totally obliterated instanter – And after remaining as white paper in his portfolio, or exposed to air and sun ad libitum ^<5> for an indefinite time – the image may be recalled in an instant and fixed [illegible deletion] by a brushing it over with another liquid B. – I have some idea that two images may be made to coexist on the same paper both invisible and either of which may be thus recalled at pleasure without the other, but I have not yet satisfied myself of its practicability. –

I remain My dear sir Yours very truly
JFW Herschel

*The addition of Hydrobrom of Potash to Mur. Soda gives great additional sensitiveness in the first moment & where the paper has got a shade on it it absorbs the incident rays better & so gives the Mur Soda its full effect. The Bromuretted silver alone is rapidly affected at first but the action is not proportional to the time. I have some very curious results as to the action of the spectrum on this salt which is quite unique.

H. F. Talbot Esq
Lacock Abbey
near Chippenham
Somerset Wilts

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Notes:

1. See Doc. No: 03971.

2. See Doc. No: 03932.

3. On 14 August 14 1839, patent agent Miles Berry obtained a Writ of the Privy Seal for a New or Improved Method of Obtaining the Spontaneous Reproduction of All the Images Received in the Focus of the Camera Obscura, specification to be enrolled six months later. Berry was acting on behalf of Louis Jacques Mandé Daguerre (1787–1851), French artist, showman & inventor who wished to patent his invention in England. WHFT had advised Herschel to refrain from publishing any improvements in photography, to prevent Berry, or in this case Daguerre, claiming those improvements as his own in enrolling the specification.

4. This would become, John Frederick William Herschel, ‘On the Chemical Action of the Rays of the Solar Spectrum on Preparations of Silver and Other Substances, Both Metallic and Non-metallic, and on Some Photographic Processes,’, Philosophical Transactions of the Royal Society of London, 1840, pp. 1–59.

5. At liberty.