January 7, 1839 is a key and controversial date in the history of photography. That day, François Arago (1786-1853) made a statement of “applied physics” entitled “fixation of the images that form at the focus of a dark room”.

The context

As we told you here, the French Louis Mandé Daguerre (1787-1851), after his association with Joseph Nicephore Niepce (1765-1833) and the death of last, presents the fruit of their joint work to François Arago.

The latter, a scientist and a French politician, proposes to present this discovery to the Paris Academy of Sciences.

This organization, found in 1666, has for mission to

devote to science development and advise government authorities in this area.

This double vocation has been reinforced over time, with the evolution of knowledge. Today, academicians exercise their missions, vis-à-vis the state and vis-à-vis foundations, in committees or working groups set up by the Academy.

Académie des Sciences de Paris

It is therefore January 7, 1839 that François Arago presents the “discovery” of Daguerre.

Fixing the images that form at the focus of a dark room

Here is the report of the meeting. The original text is in the archives of Academy of Sciences preserved and digitized by the National Library of France (BnF)

M. Arago took the floor to give the Academy a general idea of the fine discovery which M. Daguerre had made, and on which the greater part of the public had until now only mistaken notions.

Everyone, says Arago, knows the optical apparatus called dark room or dark room, and the invention belongs to J.-B. Porta; everyone has noticed with what clarity, with what truth of forms, color and tone, the external objects will reproduce on the screen placed at the focus of the large lens which constitutes the essential part of this instrument; everyone after having admired these images, abandoned themselves to regret that they could not be preserved.

This regret will now be irrelevant: Mr. Daguerre has discovered particular screens on which the optical image leaves a perfect impression; screens in which everything contained in the image is reproduced even in the most minute details, with an accuracy, with an incredible finesse. In truth, it would be no exaggeration to say that the inventor discovered the means of fixing the images, if his method retained the colors; but, we must hasten to say so to undeceive a part of the public, there is in the paintings, in the copies of M. Daguerre, as in a drawing in black pencil, as in a engraving with the chisel, or even better (the assimilation will be more exact), as in a black or aquatinta engraving, than white, black and gray, as light, darkness and half-tones . In a word, in the dark room of M. Daguerre, light itself reproduces the forms and proportions of external objects, with an almost mathematical precision; the photometric ratios of the various white, black, gray parts are exactly preserved; but halftones represent red, yellow, green, etc., because the method creates drawings and not color tables.

The principal products of his new methods, which M. Daguerre has put before the eyes of three members of the Academy, MM. from Humboldt, Biot and Arago, are a view of the large gallery which joins the Louvre to the Tuileries; a view of the City and towers of Notre-Dame; views of the Seine and several of its bridges, views of some of the barriers of the capital. All these pictures support the examination with a magnifying glass, without losing any of their purity, at least for the objects which were motionless while their images were being made.

The time required for the execution of a sight, when one wishes to arrive at great vigours of tone, varies with the intensity of the light and, consequently, with the hour of the day and with the season. In summer and at midday, eight to ten minutes are enough. In other climates, for example, in Egypt, one could probably limit oneself to two or three minutes.

The process of M. Daguerre has not only required the discovery of a substance more sensitive to the action of light than all those of which physicists and chemists have already been occupied. It was necessary to find still the means of removing this property at will; this is what M. Daguerre did: his drawings, when he has finished them, can be exposed to full sun without any alteration.

The extreme sensitivity of the preparation of which M. Daguerre makes use is not the only character by which his discovery differs from the imperfect attempts which had been made beforehand to draw silhouettes on a layer of chloride of silver. This salt is white, the light darkens it, the white part of the images thus goes black, while the black portions, on the contrary, remain white. On Mr. Daguerre’s screens, the drawing and the object are all the same: white is white, halftone is half-tone, black is black.

Mr. Arago has tried to bring out all that the invention of Mr. Daguerre will offer resources to travelers, all that will draw today, especially, the learned societies and the private individuals who deal with so much zealous of the graphic representation of architectural monuments spread throughout the various parts of the kingdom. The ease and accuracy which will result from the new processes, far from detracting from the interesting class of draughtsmen, will procure them an extra occupation. They will certainly work less outdoors, but much more in their workshops.

The new reagent also seems to provide physicists and astronomers with very valuable means of investigation. At the request of the Academicians already mentioned, Mr. Daguerre cast the image of the Moon, formed in the center of a mediocre lens, on one of its screens, and left an obvious white imprint on it. In making a similar experiment with silver chloride, a commission of the Academy composed of MM. Laplace, Malus and Arago, did not obtain any appreciable effect. Perhaps the exposure to light was not prolonged enough. In any case, Mr. Daguerre was the first to produce a sensitive chemical modification using the light rays of our satellite.

The invention of Mr. Daguerre is the result of a hard work of several years, during which he had for collaborator his friend, the late Mr. Niepce, Châlons-sur-Saône. In seeking how he could be compensated for his pain and his expenses, this distinguished painter was quick to recognize that a patent of invention would not lead to the goal: once unveiled, his processes would be available to everybody. It seems indispensable, therefore, that the Government should directly compensate M. Daguerre, and that France, then, nobly endow the whole world with a discovery which can contribute so much to the progress of the arts and sciences. M. Arago announced that he would address a request to the Ministry or to the Chambers, as soon as M. Daguerre, who proposed to introduce him to all the details of his method, proved to him that to the admirable The results obtained are such a striking demonstration, this method joined, as announced by the inventor, the merit of being economical, of being easy, of being able to be used everywhere by travelers.

“M. Biot declares that he associates himself completely with the exhibition which M. Arago has just made, the astonishing results obtained by M. Daguerre. Having had the advantage of seeing them several times, and hearing M. Daguerre recount some of the many experiments he has made on the optical sensitivity of the preparation he has managed to compose, M. Biot thinks with M. Arago will furnish us with new and desirable means of studying the properties of one of the natural agents which we are most interested in knowing, and that so far we have had so little means of putting ourselves to independent tests. of our feelings. And he can not express his thought better about this invention than by comparing it to an artificial retina put by M. Daguerre at the disposal of physicists. ”

Compte rendu des séances du l’Académie des Sciences – séance du Lundi 7 janvier 1839 – Présidence de M. Chevreul

The presentation before the Academy of Sciences is remarkable in many ways.

Let us immediately evade the question of the paternity of the invention. In his remarks, Arago mentions the collaboration between Niépce and Daguerre. However, Niépce is qualified as “collaborator” of Daguerre, and not partner. This qualifier is enough to dispossess the descendants of Niepce “compensation” indicated by Arago in favor of Daguerre. Does Daguerre minimize the role of Niepce? did Arago know the nature of the collaboration between the two men? Unanswered questions.

Regarding the rest of the elements of this statement, it is interesting to note some less polemical elements.

The colour ?

In the first lines, the question of color and black & white is evoked. Arago states that the method would have the power to “fix the images” if it “kept the colors”. The scientist clearly understands that the invention is not yet complete. For the record it will be necessary to wait until the second half of the 19th century to see the color appear, we will come back to it in another article.

The technique ?

All stages of film photography are presented; exposure, stop bath and fixative. And they do not differ from current black and white processes. Of course, this is a direct, “positive” method of exposure. The exposed surface becomes the photograph; unlike transfer methods that require developing and then making a draw.

Uses ?

Finally, the uses imagined by Arago of photography cover practically all current uses; Architecture, science, travel and personal photos are presented by the scientist. Only “forgetfulness”, the press photo is not mentioned.

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