Paris
le 14 juin 1841

Monsieur

Conformement à votre intention j’ai communiqué à l’academie, lundi dernier votre procédé, tant désiré, pour confectionner le papier Sensible que vous appelez calotype. l’académie a entendu cette communication avec beaucoup d’interêt; et vous la pourrez voir dans le compte rendu qui a paru hier.^<1> J’ai pris soin que les nombres que vous indiquez fussent imprimés bien exactement. pour cela j’ai revu moi meme la premiere épreuve; et comme je partais pour la campagne j’ai confié la revision de la mise en page à un de mes confreres qui m’a promis d’y donner toute son attention. j’espère ainsi que tout sera transcrit exactement.

Craignant de ne pas etre moi meme assez exercé a la production des tableaux photogeniques pour bien employer les echantillons de votre papier que vous m’aviez envoyés, je les ai remis à un de mes plus jeunes confreres, M^r Regnault, ^<2> Physicien aussi habile que savant chimiste, qui avait fait deja, pour son propre plaisir, des épreuves daguerriennes qui ont réussi tres heureusement. vous pouvez ainsi etre assuré que ces echantillons seront employés avec toute espece de soin, d’habilete et d’interêt.

Voulant temoigner combien ce genre d’invention me semble [utile pour les] voyageurs, j’ai pris la liberte de joindre à votre communication quelques indications que je crois pouvoir etre utiles pour en ameliorer l’emploi. lune[sic] de [illegible deletion] consisterait à donner aux objectifs des chambres noires, des courbures specialement appropriees[sic] à la concentration des radiations qui se trouveront agir le plus efficacement. une autre [illegible deletion] a pour but d’accelerer, et probablement d’ameliorer les effets produits, en n’exposant le papier que pendant quelques secondes aux radiations emanées des objets que l’on veut reproduire; et a continuer l’action ainsi commencée, en exposant ensuite ce même papier hors de la presence des objets, à la radiation solaire ou atmospherique sous un verre rouge. si vous lisez nos comptes rendus, vous avez pu voir que ce mode de continuation a été découvert par un de nos jeunes physiciens M^r Edmond Becquerel. ^<3> Et, dans le rapport que nous avons fait à l’academie M^r Arago ^<4> et moi, sur ses expériences, nous avions insisté sur signalé l’importance qu’il y aurait à réaliser cette application sur les epreuves dagueriennes. je crois vous avoir mandé cela dès que nous eumes connaissance de cette découverte; et, si je ne me trompe, je vous engageais à essayer Si elle ne S’appliquerait pas aussi à votre papier Sensible. j’ai aujourdhui peu de doutes à cet égard. car maintenant, à l’aide de ce procedé, on fait d’admirables portraits daguerriens, en faisant seulement poser les personnages pendant quelques secondes seulement; et je crois que déja cette application a été transportee à Londres. tout porte donc à croire qu’elle réussira egalement sur votre papier. et Si vous éprouvez quelques difficulté pour les épreuves que vous appelez positives, peut être les resoudriez vous par le même moyen. je desirerais de tout mon cœur qu’il en fut ainsi, et, du moins l’essai merite d’être fait. car, pour les portraits par exemple, il y a un avantage infini à ne tenir le personnage fixe que pendant quelques secondes. vous trouveriez facilement à Londres de ces verres rouges que l’on emploie pour les experiences d’optique. il faudra seulement les eprouver vous même, par le prisme, [illegible deletion] dans une chambre fermee, ou pendant la nuit, afin de vous assurer que la lumiere d’une bougie ou d’une lampe à courant d’air, ^<5> transmise à travers leur substance, ne Contient [illegible deletion] Sensiblement que des rayons rouges. car alors il parait que ces verres ne laissent passer aussi que les rayons invisibles, de cette même refrangibilité.

maintenant, je vais prendre la liberté de solliciter de votre obligeance un service scientifique qui me serait d’un grand secours, s’il vous etait possible de me l’accorder. j’ai découvert dernierement dans les cristaux d’alun [illegible deletion] où il entre de l’ammoniaque, un nouveau mode de polarisation qui s’opere dans le passage de la lumiere entre leurs lames constituantes; et que j’ai appelé, par cette raison la prolongation lamellaire. il me parait jetter le plus grand jour sur les phénomenes singuliers découverts par le D^r Brewster ^<6> et J. F. Herschel ^<7>dans l’apophyllite; comme aussi sur ceux que le D^r Brewster à trouvés dans l’analcyme. ^<8> J’ai bien eu à ma disposition un certain nombre de cristaux d’apophyllite pyramidale, ou en tables, qui m’ont servi à constater cette application. mais je n’ai pas eu, comme le D^r Brewster l’avantage d’avoir des cristaux complets et il n’en existe pas un seul de ce genre, dans nos collections publiques, d’ailleurs tres pauvres en général pour la minéralogie. je Suis encore moins favorisé pour l’analcyme, n’en ayant de limpide que de simples fragmens, et pas un seul cristal complet à travers lequel je puisse faire passer la lumière. comme vous avez fait, vous même, beaucoup d’expériences sur la polarisation, auriez vous par hazard en votre possession de pareils cristaux soit d’apophyllite soit d’analcyme? et, dans ce cas, auriez vous l’extreme bonté de me les’ prêter pendant quelques semaines pour les etudier? jen aurais le plus grand soin; je n’aurais aucun besoin de les tailler, et je les rendrais parfaitement intacts. si cela est en votre pouvoir, vous me rendrez un service dont je serai tres reconnaissant, et que le seul interet des sciences me fait prendre la liberté de solliciter de vous.

J’ai l’honneur d’etre avec la consideration la plus distinguee Monsieur Votre très humble et obeissant serviteur
J. B. Biot

P.S. M^r Wheatstone ^<9> m’a remis de votre part de tres beaux dessins photogeniques, où nous avons surtout admire le caractere frappant de la figure de votre domestique, ouvrant la portiere de votre voiture. ^<10> cest une chose Singuliere que la difference de vivacité avec laquelle certains objets, les blancs par exemple impressionnent le papier comparativement à d’autres! il est bien remarquable aussi de voir les feuilles vertes, celle du lierre, par exemple, n’agir que par leurs seuls reflets speculaires! que de particularites physiques ne reste t’il pas à découvrir, ou à expliquer dans ce mode d’action!

A Monsieur
Monsieur H. Fox Talbot, membre de
la societe Royale de Londres &c &c
Lacock Abbey
Chippenham
England

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Translation:

Paris.
14 June 1841

Sir

In accordance with your intention, I informed the academy last Monday of your much anticipated process for making Sensitive paper which you call the calotype. The academy listened to this announcement with a great deal of interest; and you will be able to see it in the compte rendu which was published yesterday. I ensured that the numbers which you indicated were printed exactly. In order to do this I personally corrected the first proof; and since I was leaving for the country, I entrusted the revision of the layout to one of my colleagues who has promised me that he will give it his undivided attention. I therefore hope that everything will be transcribed exactly.

Since I feared that I was not myself sufficiently practised in the production of photogenic pictures to make good use of the samples of your paper which you had sent me, I handed them over to one of my younger colleagues, Mr Regnault, as skilled a Physicist as he is a learned chemist. He had already made some daguerrian proofs for his own enjoyment, which were very successful. Consequently, you can rest assured that these samples will be used with the greatest care, skill and interest.

Since I wanted to show how this type of invention seems to me for travellers, I took the liberty of enclosing a few indications with your announcement, which I believe can be of use in improving it in practice. One of them would consist in giving a curvature to the lenses of the camera obscura, which is specially suited to the concentration of the most effective radiation. Another is designed to accelerate, and probably improve the effects which are produced, by exposing the paper only for a few seconds to the radiation from the objects which are to be reproduced; and to continue the action begun in this way by then exposing this same paper, in the absence of the objects, to the solar or atmospheric radiation under a red glass. If you read our comptes rendus, you will have been able to see that this method of continuation was discovered by one of our young physicists, Mr Edmond Becquerel. And, in the report on the experiments, which Mr Arago and I gave to the academy, we had indicated the importance of carrying out this application on daguerrian proofs. I think that I informed you of this as soon as we were aware of the discovery. And if I am not mistaken, I urged you to see if it could also be applied to your Sensitive paper. I have few doubts upon this matter today. For, with the help of this process, admirable daguerrian portraits are now being made requiring people to pose for only a few seconds; and I think that this application has already reached London. Consequently, everything suggests that it will be equally successful on your paper, and if you experience some difficulty with the proofs which you call positives, you could possibly resolve them by the same means. I wish it with all my heart, and it at least deserves to be attempted. For, as far as portraits are concerned for example, there is an infinite advantage in keeping the person still for no more than a few seconds. You would easily find in London some of these red glasses, which are used for optical experiments. You need only test them yourself, with the prism in a closed room, or at night, so that you can ensure that the light from a candle or a chimney lamp which is transmitted through their substance noticeably only contains red rays. For, it seems that these lenses also only allow invisible rays to pass through them, which are of this same refrangibility.

I will now take the liberty of asking you to be so kind as to grant me a scientific favour which would help me a great deal if it were possible for you to agree to it. I have recently discovered a new method of polarisation in alum crystals in which there is ammonia, which operates in the passage of light between their constituent lamellae; and which I have called, for this reason, lamellar prolongation. It seems to me that it throws the most light on the remarkable phenomena which were discovered by Dr Brewster & J. F. Herschel in apophyllite, as well as those which Dr Brewster has found in analcime. I had a certain number of crystals of pyramid-shaped apophyllite at my disposal, or slabs which I used to observe this application. But, unlike Dr Brewster, I did not have the advantage of having complete crystals, and not one crystal of this type exists in our public collections, which are, moreover, very poor in general for mineralogy. I am at an even greater disadvantage for analcime since the only perfectly transparent analcime I have is merely in the form of fragments, and I have not a single complete crystal through which I can make light pass. Since you have yourself conducted many experiments on polarisation, would you by any chance have similar crystals in your possession, either of apophyllite or of analcime, and if so, would you be so kind as to lend them to me for a few weeks in order to study them? I would take the utmost care of them. I would not need to cut them at all, and would return them to you perfectly intact. If this is in your power, you will be doing me a favour for which I will be very grateful and which I am only taking the liberty of asking you in the interest of science.

I have the honour to be with the deepest respect, Sir Your very humble and obedient servant
J. B. Biot

P.S. Mr Wheatstone gave me some very beautiful photogenic drawings from you in which we particularly admired the striking figure of your servant when he opened the door of your carriage. It is an extraordinary thing to see the difference in intensity with which certain objects, whites for example, stand out on the paper compared to others! It is also very remarkable to see the green leaves, such as those of the ivy, acting only with their own specular reflections. How many physical characteristics are still to be discovered or explained in this form of action!

To M^r H. Fox Talbot,
Member of the Royal Society of London &c &c
Lacock Abbey
Chippenham
England <

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Notes:

1. "Lettre de M. Talbot à M. Biot, sur la confection de papiers sensibles," Comptes Rendus hebdomadaires des séances de l' de l'Académie des Sciences, v. 12 no. 23, 1^st sem, 1841, 7 June 1841, pp. 1055-1058. See Doc. No: 04263.

2. 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.

3. Alexandre Edmond Becquerel (1820–1891), physicist.

4. Dominique François Jean Arago (1786–1853), French physicist, astronomer & man of science.

5. The most common lamp of this type was the Argand lamp.

6. Sir David Brewster (1781–1868), Scottish scientist & journalist.

7. Sir John Frederick William Herschel (1792–1871), astronomer & scientist.

8. For several years beginning in 1819, Sir John Frederick William Herschel (1792–1871), astronomer & scientist, and Sir David Brewster (1781–1868), Scottish scientist & journalist, exchanged many letters, experiments and thoughts on the deviations they had discovered in the conventional Newtonian spectral scale. Although they originally intended to publish their results jointly, several irreconcilable differences in their theories emerged. See Herschel, ‘On Certain Remarkable Instances of Deviation from Newton’s Scale in the Tints Developed by Crystals with One Axis of Double Refraction on Exposure to Polarized Light’, Edinburgh Philosophical Journal, v.4, 1820–1821, pp. 334–344. Brewster, ‘On a new species of Double Refraction, accompanying a remarkable structure in Analcime’, Edinburgh Philosophical Journal, v.10, 1824, pp. 255–259.

9. During 1839 and 1840, WHFT and Sir Charles Wheatstone (1802–1875), scientist, developed a design for an electromagnetic locomotive. In 1841, they entered into an agreement for the specific purpose of funding Wheatstone’s work, resulting directly in his patent for ‘Improvements in producing regulating and applying Electric Currents’, in which WHFT provided more than £400 of funding. They met frequently and corresponded on this topic as well as photography, and Wheatstone would have, on numerous occasions, received specimens of photogenic drawing.

10. This portrait, called ‘The Footman’, Schaaf 2507, in WHFT’s manuscript negative list, was taken 14 October 1840. See Larry J. Schaaf, The Photographic Art of William Henry Fox Talbot (Princeton: Princeton University Press, 2000), p. 99.