Dear Sir,
I ought to have written you before this to have made you acquainted with our Progress with the Calotype; <1> but having got my large Prism from Munich <2> I have been so engrossed with the adjustment & use of it that I have had little leisure for any other pursuit. It is I believe the largest & finest that has ever been made; and when combined with the Solar Telescope (a non-achromatic one in which spherical aberration only is corrected), it has enabled me to make very accurate drawings of the Solar lines, and to resolve many obscure spaces into their linear elements.
I have also, with the same apparatus, repeated my Expt on the fringes of Refraction, of which Airy <3> has written so erroneously, and so incorrectly.
It was exceedingly rash to give the theory of phenomena which he himself had scarcely studied, and which when properly developed might put down the theory itself. The truth is Airy’s Paper of 1840 <4> is no explanation of all of the Fringes I studied, and I suspect he knew this himself. He refers to my two notices at Liverpool & Newcastle <5> for the phenomena, and the fringes & bands as there described are called “intensely black“, and “exceedingly black“ but the fringes explained by Airy are only obscure bands, in which a very great portion of the light is left. – In my Paper I say that they are seen in the Focus; – and he explains <6> only bands seen out of the Focus and disappearing in the Focus.
In his 2d Paper of 1841 he endeavours to get out of his difficulty by most unfair means. He describes the Case of the Intensely black fringes in the Focus, as one which he had omitted, and he acknowledges that the bands “seen by Mr Talbot and myself” to use his words were not black but merely dusky.
In order to get out of the puzzle he answers that there is “a small diffused image on the Retina whh is formed by the light coming from a single point, even when it is seen accurately in focus, and out of this light he manufactures by his undulatory shifts <7> a series of vivid black & bright bands to suit my observations.
His Corollary that the Interval between the bands increases by diminishing the Pupil or the Aperture of the Object Glass!! is wholly unfounded as they depend only, in a given Spectrum & a given part of it, on the thickness of the retarding Plate, and its inclination.
The following are two interesting properties of these fringes, the edge of the retarding being always kept in the same vertical plane with the fixed lens. When the edge is inclined towards the upper side of the Spectrum, the fringes are inclined to the Left, & when the edge is inclined towards the under side of the spectrum the fringes are inclined to the Right.
When the edge of the Plate is inclined away from the eye so as to approach the Spectrum, the interval between the fringes increases, & when the edge is brought towards the eye the interval diminishes; the interval having a mean value when the retarding plate is perpendicular to the axis of vision.
I have troubled you with these details in order to draw your attention to Mr Airy’s statements in which he uses your name, namely in the Phil. Trans. 1841 p. 226, 242, and 1841 p. 187 of the Paper, and to ask if you have made any communication to him or sent him any explanation of your Expt in the Phil. Mag. vol. X p. 364; <8> for it does not appear to me that your Paper justifies his statements. For example he says that the Bands seen by you are seen equally “whether the Mica be advanced from the Violet side or the Red side” p. 226. Now I know of no such bands produced by covering half the pupil. If you saw such bands they must have been the periodical bands of thin plates seen as well where the whole pupil was covered as when one half of it was.
I would like to know your opinion of the assumption in the 2d. Paper p. 5 of a diffused image. If such assumptions are admitted it will be easy for the Undulationists <9> to explain any thing.
I have had a correspondence with Mr Christie <10> on the subject of my ill-treated Paper. He refuses to give the name of the Reporter, as if any person need be ashamed of giving an honest scientific opinion; and he offers to lay any statement from me before the Council which he expects to meet on the 14th Octr “altho’ he sees no prospect of their rescinding their resolution”.
Believing, as I do, that Airy is the Reporter, & that his Report is influenced by personal feelings, I can see no alternative, but that of leaving the Society.
Dr Adamson <11> has been working like a Horse with your Calotype Process, I have often gone over the process with him. He has done only a few good Photographs. He finds it necessary to weaken the Gallo-nitrate; and we find it very difficult to fix the Positive Photographs altho’ we have got Whatmans Paper, <12> yet, from causes we cannot find out, the Photograph is often covered with large irregular white masses obviously arising from a defect in the Paper. I hear that the same difficulties have been experienced by several persons in Edinburgh who have abandoned the process on that account. I wish much you could send me a good Photograph of yourself.
I am Dear Sir, Ever Most Truly yrs
D Brewster
St Leonards
St Andrews
Octr 5th 1841
Henry Fox Talbot Esqr
Lacock Abbey
Chippenham
Wilts
Notes:
1. Important progress was being made on WHFT's calotype process - see see Roger Taylor and Mike Ware, "Pilgrims of the sun: The chemical evolution of the calotype," History of Photography, v. 27 no. 4, Winter 2003, pp. 308-319.
2. Made by Merz. [See Doc. No: 04470].
3. Sir George Biddell Airy (1801–1892), Astronomer Royal.
4. G. B. Airy, ‘On a New Apparent Polarity of Light’, British Association for the Advancement of Science, Report, 1840, part 2, pp. 3–5.
5. The British Association for the Advancement of Science met at Liverpool in 1837 and at Newcastle in 1838. D. Brewster, ‘On a new property of Light’, British Association for the Advancement of Science, Report, 1837, part 2, pp. 11–12; ‘An account of certain new phenomena of Diffraction’, British Association for the Advancement of Science, Report, 1838, part 2, p. 13.
6. Written over original ‘describes’.
7. Brewster held the Newtonian emission or corpuscular theory of light and opposed the undulatory [wave] theory.
8. WHFT, ‘An Experiment on the Interference of Light’, Philosophical Magazine s.3, v.10, n.62 (May 1837), p. 364.
9. Those who held the wave theory of light.
10. Samuel Hunter Christie (1784–1865), mathematician & Secretary of the Royal Society.
11. Dr John Adamson (1809–1870), physician and pioneer of photography. See A. D. Morrison-Low, ‘Dr John Adamson and Robert Adamson: An Early Partnership in Scottish Photography’, The Photographic Collector, v.2, 1983, pp. 198–214.
12. Whatman’s Turkey Mill paper, a hand-made writing-paper produced in Maidstone, Kent, was favoured by Talbot for photographic use. Its wove surface provided a uniform base for prints and a patternless density for negatives, and it had good wet-strength, although small variations in texture and chemical content could cause problems when the paper was used in photography. The gelatin size suited photographic chemistry better than the rosin used in some other papers, particularly Continental ones. It was generally watermarked with the year of manufacture and certain years were sought after.