TALBOT4319

Bridge of Earn ¹ Perthshire
August 7^th 1841

Dear Sir,

I have just received your very interesting Calotypes ² for which I return you many thanks. They not only give me a perfect notion of the art, but they prove that we have not been able even to approximate to it, altho’ we have made all the preliminary exp^ts you mentioned and followed rigorously your Instructions. We shall, however, make another trial, & I trust with better success.– I should like to know if you have tried the influence of electricity in accelerating the process, or the influence of a Red Glass in continuing the action. When the Calotype paper is placed damp in the Camera it could be electrified as easily as the Metallic plate. M^r Gray ³ and I tried the effect of Electricity yesterday at Kinfauns in producing a Daguerreotype ⁴ Copy of a Bust in common day light; but without the least success

I entirely concur with you in your observations on the conduct of the Council ⁵ of the Royal Society, ⁶ and I feel, as you do, that the trouble of remonstrance would be not compensated [sic] by success. At the same time I feel so much aggrieved that on public grounds I may possibly not spare the trouble, and when I have given you some acc^t of my case I think you will not advise me to break off my connexion with the Society without a public statement of the treatment I have experienced.

During my uninterrupted connexion with the Royal Society for 28 years, no attempt like the present was ever made to reject any of my papers, however little originality there might have been in several of them. D^r Young ⁷ could not understand the existence of two axes of Double Refraction which I discovered in 1818, and wished me to modify the Paper ⁸ containing an account of it. I resisted any change upon it, insisted upon an immediate answer whether or not it was to be printed as it stood, and reduced D^r Young to the necessity of begging an explanation of diff^t parts of my Paper. This I willingly gave, and satisfied him of the correctness of my views. On the present occasion, however, M^r Roberton ⁹ was writing me regarding the purchase of Daguerreotype Plates from M^r Lubbock; ¹⁰ and in a P.S. to his letter he said Your Paper On the Modification of the Colours of Thin Plates ¹¹ &c was ordered to be printed; your Paper on the Compensations of Polarised light ¹² not to be printed. This is the polite message sent me by the Council.

Now the Paper in question was the first of a series of three Papers the object of wh^h was to determine the Laws of the Polarisation of the Atmosphere which I have completely established, after much hard work. The 1^st Paper was intended to describe the principle and construction of a Polarimeter ¹³ for measuring degrees of Polarisation, an instrument never before thought of, & without which the Polarisation of the Sky cannot be studied. The Polariscope of Savart, ¹⁴ wh^h is merely a method of obtaining a system of rectilinear polarised fringes or bands was invented & used by me 15 years ago and described in my paper on the Amethyst. ¹⁵ This, as it were the Eyepiece of my Polarimeter, and by combining it with a bundle of Glass Plates, the effect of which is made variable in diff^t ways I obtain an instrument which when directed to partially polarised light indicates by an interruption of the bands when the partially polarised light is compensated by the Plates. – Thus the [illustration] system of bands AB is crossed with a neutral line MN where the light is common light, the bands on the side A being of an opposite character to those on the side B. This invention, to which I attach much value, could not have presented itself to any person but one who entertained the peculiar views which are given in my three papers of 1830; ¹⁶ but, tho’ this is the case, it does not depend upon these views, for it gives a numerical value of the degree of polarisation, upon the supposition that partially polarised light consists of a portion of light wholly polarised and another portion wholly unpolarised, and this value may be either in terms of the Angle of Incidence at which the reflexion or refraction is small, or the ratio’s of the quantities of Polarised & Unpolarised light. According to my views, which I have demonstrated in the paper, the numerical value is the change in the planes of polarisation, or the Rotation of the plane of light polarised ± 45^o to the plane of Incidence or Refraction.

This view of the constitution of common light, viz that it consists of equal portions of light polarised +45^o and -45^o to the plane of polarisation does not involve a physical truth. It is true only in reference to the action of reflecting and refracting surfaces which are equally inclined to the two rectangular planes, or in which the planes of Reflexion or Refraction bisect the right angle comprehended between the planes of polarisation.

Hence you will see that the Polarimeter is an entirely new Instrument not depending upon any theory whatever, and affording the only possible means of measuring the Polarisation of the Sky, or any other degree of polarisation. My 2^d Paper is on the Polarisation of light by rough & unpolished surfaces, ¹⁷ a subject not only entirely new; but explaining the strange fact that tho’ the light of the sky is reflected at the polarising angle of air it is only partially polarised like light reflected at angles of about 72^o and 40^o from a surface of Glass. Hence the error communicated by Arago, ¹⁸ which the Polarimeter alone could detect, of inferring the angle of complete Polarisation for Air from the crude observation that the polarisation of the sky seemed to be a maximum when the angle of Incidence was 45^o – 47^o.

My 3^d paper was to contain a large series of Observations on the polarisation of the sky ¹⁹ shewing that the Phenomena are related to two axes whose mutual Inclination constantly varied, namely the Solar axis or that passing thro’ the Sun and the Observer, and the Zenith axis which is a fixed one,– the one regulating the polarisation produced by Reflexion from the air, and the other that produced by transmission thro’ the strata and vapour planes of the atmosphere.

These researches, of which the above is a very meagre notice, appear to me the most important in which I have ever been engaged; and knowing my results to be entirely original, I can scarcely describe to you the collapse of all my faculties the which the reception of my first paper has produced, and the indifference to the further prosecution of the subject which it has occasioned

Excuse this heavy demand upon your Patience, and believe me to be

Ever Most Truly Yours
D Brewster

P.S. Altho’ I have dated my letter from this watering place yet I will thank you to address your letters to me as usual

^To Henry Fox Talbot Esq^r