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Document number: 4784
Date: 29 Mar 1843
Recipient: HERSCHEL John Frederick William
Author: TALBOT William Henry Fox
Collection: Royal Society, London
Collection number: HS 17:315
Last updated: 14th March 2012

29 March 1843

Dear Sir

Many thanks for the specimens, some of which I have retained as desired, but should be glad to have a memorandum of their nature, these are No 844 black, & 780 blue; both negative. <1>

With respect to the name “Celænotype” <2> it appears to me not sufficiently descriptive; for the positive Calotype process affords copies of Engravings equally sharp and black, & which might be mistaken for real engravings – But as your new process involves a very remarkable peculiarity viz. the change from negative to positive of the same photograph, I should wish the name given to it to be one allusive to that fact, and if you are not yet decided upon your nomenclature I would suggest that the above peculiarity might be concisely and clearly expressed by the name of Amphitype. The Greek name for “to change” [illegible deletion] is somewhat too long for convenient use (αλλασσειν) unless abbreviated into allotype; but the other is more classical.

I mentioned that we saw on the 24th besides the comet <3> a nebulous light involving the Pleiades – I find you regard this as the true Zodiacal light: but it still remains to me very obscure why the Z. light does not appear during total eclipses if it is really produced by the Sun’s atmosphere; and therefore I think this phenomenon must have its origin in our own atmosphere.

The slow changes which take place in your photographs during several months are certainly very remarkable; do not you think they might be hastened by constantly keeping them in a warm place, or in a reservoir filled with some gas or other?

Messrs Johnson & Wolcott <4> have made a new improvement in the Daguerreotype; I saw a specimen yesterday which I think the most perfect thing of the kind I have yet seen, and leaving little to be desired in the way of further improvement, if its execution be not attended with any unusual difficulties. A newspaper called the Illustrated London News contained a good woodcut of the Comet as seen at Blackheath on the 17th inst – quite like its appearance as I saw it on the 24th only that it was much fainter then. This seems a very remarkable comet, its tail grows faint without growing shorter, or materially shifting its place in the heavens. Is it going away from us nearly in a straight line?

Talking of comets, in my more mathematical days, I once found out the following simple theorem –

If the passage of a comet thro’ both its nodes is observed, these 2 observations suffice to determine the orbit rigorously, & by a very simple geometrical construction. Except the Inclination which remains indeterminate. The last circumstance renders this theorem a very peculiar one. I had afterwards reason to believe that my theorem was not altogether new, but I have since lost the memoranda I made on that point. The orbit is assumed parabolic.

I remain dear Sir Yours very truly
H. F. Talbot

Your No 4 appears to contain the elements of an excellent photogrc method, but to have been spoiled by an incautious use of the brush. Sir J. Herschel Bart


1. These are listed in Herschel’s Photographic Memoranda. 780 was accomplished on 10 August 1842: “10 Ammo Citr + 10 F3/2 CP no/precip. greenish paper covers 3 squares”. 844 was done on 16 January 1843: “(Acet L)1 + {(Ao C Iron ½ strength 1/12)1 + (Pern 1/6 strength)1}2”. HRHRC W0268.

2. See Doc. No: 04778.

3. The Great March Comet of 1834.

4. Alexander Simon Wolcott (1804–1844), and John Johnson developed a daguerreotype camera employing a concave mirror rather than a lens. They were granted an American patent, no.1582, 8 May 1840, and 18 March 1843 Wolcott alone was granted a British Patent, no.9672.