NIEPCE AND DAGUERRE.

29

(34.) In a paper dated the 5th December, 1829, M. Niepce communicated to M. Daguerre the particulars of

plus que de la témérité de ma part à donner à quelques résultats prématurés une importance qu'ils sont encore loin de mériter; et si j'ose vous les communiquer, Monsieur, avec tout l'abandon de la confiance, c'est pour ne rien vous laisser ignorer de ce qui se rattache à des recherches auxquelles vous voulez bien prendre un si vif et si constant intérêt. Dans quelques mois d'ici je les poursuivrai, je l'espère, avec de nouvelles garanties de succès, pourvu que la saison me soit moins défavorable que l'an passé; et je me bornerai d'abord à une seule application de mes procédés, à fin d'arriver plus promptement au but. Si j'ai ce bonheur là, Monsieur, vous pouvez compter sur mon empressement à vous le faire savoir.

No. 9.

N. NIEPCE.

Monsieur,

Paris, 3me Février, 1828. Depuis votre départ j'ai fait deux tableaux, un pour le Diorama, et l'autre pour l'exposition du musée, ce qui m'a occupé toute l'espace du tems, ce qui fait que je n'ai pu donner aucune suite à mes recherches.

Quant à vous, Monsieur, je vois avec peine que vos occupations vous ont détournées de votre intéressante découverte, et que vous n'avez trouvé en quelque sort que découragement en Angleterre. Mais, consolez-vous: il n'est pas possible qu'il en soit de même ici; surtout, si vous arrivez au résultat que vous avez droit d'espérer, je puis vous assurer qu'on ne verra pas cela avec la même indifférence. Je me ferai un véritable plaisir, si cela peut vous être agréable, de vous indiquer les moyens d'en tirer de meilleure partie. Je ne puis vous dissimuler que je brûle du désir de voir vos essais d'après nature; car si ma découverte a pour base un principe plus incompréhensible, il n'en est pas moins que vous êtes bien plus avancé dans les résultats, ce qui doit nécessairement vous encourager.

M. NIEPCE.

DAGUERRE.

Specimens of Heliography given by M. Niepce to the late Francis Bauer, Esq., of Kew, and now in the possession of Dr. Robert Brown, of the British Museum.

1. A design 5 by 4 inches longways, on a pewter plate 6 by 5 inches; it is stated at the back to have been taken from a print about 2 feet long. The picture represents the ruins of an abbey: in a pro per light it is very distinct.

the process employed by him, and they entered into an agreement to pursue, for their mutual benefit, the researches which they had respectively begun. As many parts of this process of M. Niepce's, and some of his remarks, are curious and interesting, I shall devote a brief space to a few extracts from this communication:*

"The discovery which I have made," says M. Niepce, "and to which I give the name of Heliography, consists in producing spontaneously, by the action of Light, with gradations of tints from black to white, the images received by the camera obscura.

"Light, in its state of composition and decomposition, acts chemically upon bodies. It is absorbed, it combines with them, and communicates to them new properties. Thus it augments the natural consistency of

2. A view 7 inches by 6 inches longways, on a pewter plate 8 by 61 inches; it is stated on the back to have been N. Niepce's first successful experiment of fixing permanently the image from nature. The view is of a court-yard seen from an upper window. It is less distinct than the former; the outlines of the black portions are bordered by a white fringe, whiter than the adjacent parts. The surfaces on which the pictures appear are metallic, but are blacker, and reflect more light than the under pewter surfaces; the colour appears to be that of lead or platinum. No. 1. has experienced no injury. No. 2. is covered in some parts with minute brown spots.

3. A design 4 by 5 inches upright, on a pewter plate 8 by 5 inches, from a print, the subject "Christ bearing the Cross:" every line is beautifully distinct.

4. A copy from a print of a head 6 plate 7 by 5 inches, etched by an after good impressions of the plate.

by 5 inches, upright, on a process, with two extremely

5. An impression from a plate 8 by 7 inches: the design is a landscape and ruin, 6 by 4 longways. The lines are beautifully distinct in parts.

Besides the above, M. Niepce presented a beautiful specimen to Mr. Cassells of Richmond, the subject of which appears to be the same as No. 5. It is also understood that M. Niepce presented some plates to the late Sir Everard Home.

See History and Practice of Photogenic Drawing, by M. Daguerre, translated from the original by T. S. Memes, LL.D. London, 1839.

NIEPCE'S HELIOGRAPHY.

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some of these bodies: it solidifies them even, and renders them more or less insoluble, according to the duration or intensity of its action.

"The substance which has succeeded best with me, and which concurs most immediately to produce the effect, is asphaltum or bitumen of Judea, prepared in the following manner: I about half fill a wine-glass with this pulverised bitumen. I pour upon it, drop by drop, the essential oil of lavender, till the bitumen can absorb no more. I afterwards add as much more of the essential oil, as will cause the whole to stand about three lines above the mixture, which is then covered and submitted to a gentle heat, until the essential oil is fully impregnated with the colouring matter of the bitumen. If this varnish is not of the required consistency, it is to be allowed to evaporate slowly, without heat, in a shallow dish, care being taken to protect it from moisture, by which it is injured, and at last decomposed. A tablet of plated silver is to be highly polished, on which a thin coating of the varnish is to be applied cold, with a light roll of very soft skin; this will impart to it a fine vermillion colour, and cover it with a very thin and equal coating. The plate is then placed upon heated iron, which is wrapped round with several folds of paper, from which, by this method, all moisture has been previously expelled. When the varnish has ceased to simmer, the plate is withdrawn from the heat, and left to cool and dry in a gentle temperature, and protected from a damp atmosphere.

"The plate thus prepared may be immediately submitted to the action of the luminous fluid, in the focus of the camera. But even, after having been thus exposed a length of time sufficient for receiving the impressions of external objects, nothing is apparent to show that these impressions exist. The forms of the future picture remain still invisible. The next operation then is to disengage the shrouded imagery, and this is accomplished by a solvent."

This solvent consists of a mixture of one part, by volume, of the essential oil of lavender, and ten of oil of white petroleum. A vessel being procured of a sufficient size, enough of this solvent to cover the plate is poured in. "Into this liquid the tablet is plunged, and the operator, observing it by reflected Light, begins to perceive the images of the objects to which it had been exposed gradually unfolding their forms, though still veiled by the supernatant fluid, continually becoming darker from saturation with varnish. The plate is then lifted out, and held in a vertical position till as much as possible of the solvent has been allowed to drop away." The pictured tablet is now carefully washed by being placed upon an inclined plane, over which a stream of water is carefully poured.

It should be observed that the Light solidifies the varnish, and renders it less soluble than the parts upon which the shadows have fallen. In the same communication M. Niepce says, "It were, however, to be desired that, by blackening the plate, we could obtain all the gradations of tones from black to white; I have therefore turned my attention to this subject, and employed at first liquid sulphate of potash (sulphuret of potassium?). But when concentrated it attacks the varnish; and if reduced with water, it only reddens the metal. This twofold defect obliged me to give it up. The substance which I now employ is iodine, which possesses the property of evaporating at the ordinary temperatures." It will be seen that the Daguerreotype process, which derives its name from its discoverer, consists in the application of iodine to silver plates, which is decomposed by the influence of Light.

(35.) It appears probable, that the discovery of the Daguerreotype was owing to some observations of Daguerre's, on the changes produced by Light on those silvered plates covered with films of iodine. M. Daguerre, however, appears to imply the contrary, in a note which

DAGUERRE'S EXPERIMENTS.

33

however, appears to imply the contrary, in a note which he has appended to M. Niepce's paper. This heliographic process was exceedingly tedious and uncertain. An exposure of two or three hours was necessary to produce an impression from an engraving, even under the influence of a bright sun; and in the camera obscura, the plate was left under the influence of strong Light for six or eight hours, and sometimes even longer, before a tolerable picture could be produced. M. Daguerre materially modified and improved this process. The resin of the essential oil of lavender, dissolved in alcohol, was found by him to be more susceptible of change than the bitumen; and instead of washing the plate with the solvent recommended by M. Niepce, which often removed all the varnish from it, he exposed the tablet to the vapour of petroleum, by which a much more certain effect was produced.

(36.) A correspondence between M. Niepce and M. Daguerre has been published, which sufficiently proves, that to the latter the sole merit of the discovery of the process which bears his name is due. In 1831-2, M. Niepce indeed regrets that, at the recommendation of M. Daguerre, he had lost so much time in experiments on iodine. "I repeat it, Sir," he says, "I do not see that we can hope to derive any advantage from this process, more than from any other method which depends upon the use of metallic oxides," &c. &c. In another letter he speaks of a decoction of thlapsi* (shepherd's purse), fumes of phosphorus, and particularly of sulphur, as acting on silver in the same way as iodine, and that caloric produced the same effect by oxidising the metal, "for from this cause proceeded in all these instances this extreme sensibility to light." We may perceive, from these remarks, that although M. Niepce may not have been fortunate enough to discover the exquisitely sensitive method of M. Daguerre, he must have submitted to experiment a great variety of substances

* Thlapsi Bursa-pastoris (Linn.), Capsélla Bursa-P. (De Candole.)

D