TALBOT4342

Dear Sir,

I was yesterday favoured with your most agreeable packet of Talbo-types, ¹ which my friends insist upon calling them, not only from a desire of doing honour to the Inventor, but from a love of symmetry, and also to avoid the trouble of explaining the meaning of êáëïò ² which some of them cannot do. It must be Talbo-type and Daguerreo-type ³ whether you will or no; and you must put up with the affront the best way you can.

Major Playfair ⁴ D^r Adamson ⁵ and myself are quite enchanted with the new specimens, and all agree in opinion that in a short time The Talbotype will supplant the Daguerreotype. My two friends are wholly absorbed in the subject, & having got the finest Cameras ever made, both with single and double achromatic Lenses, they will never give up till they master the process.

As they distrust all their materials they are most anxious that you should desire your Chemist to send here, either to Major Playfair or me, a fair quantity of the materials including Paper, & request them to apply for payment to Mssrs Robert Small and Co^y Old Jewry London. When you speak of the aperture of your Lens do you mean the diameter of the Stop, or the diameter of the Lens. In our Cameras the stop, for keeping back the bad rays is less than ½ the diam^r of the Lens.

In the Royal Society ⁶ affair I have only submitted the matter to the Revision of the Council, and will take no further step without consulting you.

If your plan, which I think good, of giving a privilege to those who have contributed three ⁷ acceptable papers, sh^d be considered reasonable, I who have contributed above 30 without one of them being challenged, & to which all the Medals given by the R.S. have been awarded, have certainly some claim to a favourable reception of my 31^st Paper. – The part of my Paper objected to is the part supporting the view contained in my Papers of 1830 ⁸ to which the Royal Medals were awarded.

I have stated in the Ency. Brit. Art Optics that the fringes observed by you are identical with mine. My discovery was that when the Retarding plate was on the Red side of the Spectrum no fringes were produced, and I determined the general laws of the phenomena. These seemed to indicate a polarity in prismatic light or light refracted into its elements by Refraction.

M^r Airy ⁹ in his 2^d Paper ¹⁰ decidedly concludes that my fringes are quite New & were not seen either by you or him, and he makes you say that your fringes were equally well seen whether the Retarding Plate was on the Red or the Violet side. You never said so, & your statement that you never tried the exp^t is precisely what I expected. – Since I wrote you I have completely discovered their origin. I can project them upon Paper & refer them all to known principles; – but I still cannot without assuming polarity give a good reason why they disappear under the circumstances; unless what is pro^ble that they are developed by prismatic action in the same manner as the Newtonian rays See Newt. Opt. ¹¹ V^l II P^t I Obs. 23 & 21 P^t II Expts of Feb. 7. The fringes in Question are the Intensive or white & Black ones formed in the shadow of the edge of the Retarding plate acting as a screen, & have nothing to do with Apertures of Telescopes or pupils. Their phenomena are most curious, & exceedingly perplexing in the investigation. Airy is in a most extraordinary predicament in having written two elaborate & triumphant Papers which describe something & explain nothing, his experimental being as bad as his non-theoretical Philosophy.

I am glad to be able to solve your difficulty regarding the Double line D, which greatly perplexed me in my former exp^ts. The yellow light is not entirely homogeneous that is having one definite refrangibility. The rays coincide in part with the two lines of D, but they compose a spectrum like the Annexed which is a [illustration] most interesting sight. I discovered long ago a small black line mn in the Solar spectrum within the double line D, & it has its counterpart in a white line in the Salted wick Spectrum, but it is very difficult to recognise. There are other thin white lines at a, b, c, c being seen only in strong light. The Space between the two lines of D is dark, but the space Db is luminous tho' faint, and bc is extremely feeble.

I think I have discovered that similar lines & groups of lines recur in the spectrum; but the tracing of them is difficult. I have found two extraordinary groups of lines of the very same character on the less refrangible sides of Á and â thus [illustration]

The bands from b to a gradually widen from b to a, & give the spectrum the appearance of being scooped out at from a to b. At sunset the bright space between bb & A is absorbed and also the portion bâ , bâ , so that A is converted into a black band AââA. – on the left side of B there is also a bright Space, then a darkish band n, then a bright band oo, then about 13 equidistant & exceedingly sharp dusky lines. At present the whole space Bmnm is one dark line, oo being persistent and bright. I have discovered large & deep lines and bands beyond A , as far as B is from A and farther. I shall look immediately at your exp^t in the Phil Mag. v. IX p. 403. ¹²

Believe me to be Ever Most Faithfully y^rs
D Brewster

S^t Leonards
S^t Andrews
Octr 14^th 1841

H.F. Talbot Esq^r
Lacock Abbey
Chippenham
31 Sackville Street ¹³
London