Slough.
Mar 18/39
Dear Sir,
Many thanks for the specimens of your sensitive paper <1> – It really deserves the name, and in fact so far surpasses my expectation from any trials I had made that I cannot help congratulating you on your hitting on so very valuable and curious a discovery.
I handed over all my best specimens of copies of engravings to the R.S. <2> and owing to want of Sun yesterday or today I have none worthy of sending to Baron Humboldt. <3> but I thank you much for your offer.
In the last No of the Annales de Chimie there is a Chemical paper <4> which contains a hint which I think may turn out to be the key to Daguerre’s process. <5> The curious habitudes of Chlorine in relation to Carbon & hydrogen under the influence of Light have long been known – and in a note to the “Notice” I handed into the RS on Thursday, allusion is made to these reactions as a possible mode of “photogeny”– Well. Monssr Regnaults paper above alluded to mentions one reaction so marked & vivid [illegible deletion] not only under sunshine but in daylight that it seems hardly possible it should not become available some-how or other
The Experiment is this
Take of the oily liquid produced by action of Chlorine on Olefiant gas – quantum sufficiis <6> put it in a shallow dish & pour over it a stratum of water – Then place it in an atmosphere of Chlorine. This will be copiously absorbed and a liquid is produced which is permanent in the dark but decomposes as above described in the light. –
Now. NB. The “oily liquid” has also been called chloric ether and as you mentioned “muriatic ether” in a late letter as one of Daguerre’s re-agents this seems to strengthen the suspicion that we are to look in this direction for his process.–
Yours very truly
JFW Herschel
Notes:
1. On the 21 March, WHFT presented the process of his Bromine paper to the Royal Society, it was published as ‘Note Respecting a New Kind of Sensitive Paper’, Proceedings of the Royal Society of London, v. 4 no. 37, 1837–1843, p. 134.
2. These were to illustrate Herschel’s 14 March 1839 paper, ‘Note on the Art of Photography or the Application of the Chemical Rays of Light to the Purposes of Pictorial Representation’, read before the Royal Society 12 March, 1839, withdrawn from publication. The twenty-three examples were bound in a booklet which is now in the NMeM, Bradford (1943–40). Several are illustrated in Schaaf, ‘Sir John Herschel’s 1839 Royal Society Paper on Photography’, History of Photography, v. 3 no.1, January 1979, pp. 47–60.
3. Alexander von Humboldt (1769–1859), German scientist.
4. Henri Victor Regnault (1810–1878), was first a professor of chemistry at the École Polytechnique, then a professor of physics at the College de France, and so was a colleague of Jean Baptiste Biot. He became an accomplished photographer with the calotype process. This paper was written when he was Engénieur des Mines, ‘De l’Action du Chlore sur les Éthers Hydrochloriques de L’alcool et de l’esprit de bois, et de plusieurs points de la Théorie des Éthers’, Annales de Chimie et Physik, v. 71, 1839, pp. 353–430.
5. That is, the daguerreotype.
6. In sufficient quantity.
7. That is, Alexander Humboldt.
8. True cyanates do not feature in photographic chemistry, being uncommon and rather unstable; he meant potassium ferricyanide.