But we must now turn tom neighbouring country, France. In 1813, 3I. Niepee, of Chalons on the Saone, was engaged in a task Identical in conception with that of Wedgwood. He was endeavouring, by means of bituminous varnishes and metal plates, to fix permanently the images of the camera, and he succeeded to a remarkable extent. His experiments were carried on until 1827, in which year he presented a memoir with specimens to the Hoye' Society of London ; brit, as he kept his processes secret, no notice was taken of his labours. Ni6pce returned to Franco dispirited. Ile there, however, continued his experiments, making pictures on a surface of bitumen laid upon a metal plate, which be afterwards engraved by ordinary engraver'. acid. The rationale of his process is this :—Light is capable of harden her a bituniirema surface in such a way that the usual eolventa of bitumen no longer act readily upon the altered part of the surface, end then fore only the shaded portions of a partially illuminated plate would yield to such selventa as the mineral naphthas, for example, furnish. But when a metal plate had been partially laid bare by the removal of the bitumen in the shadows, nothing was easier than to etch such a plate by aqua fortis, and this was what Nitpce did. A thus made and prints from it were in the posseesion of the late ir. Hobert Brown, of the British 31useum. It is to be hoped that they are placed in the Museum itself. 31. Ni6pco named his art .Jraj l ?I.
In 1829 31. Niepee became acquainted with a31. Dap erre [DAeIIEnnE, L J. 31., In Moo. Div.], who was noted for his diommio paintings, and who was, it is alleged. also engaged upon methods for fixing the images of the career". A deal 11 rartnership was executed between the two experiment:diet., and they jointly pursued their labours until the death of Niiper, In July, 1833. A new arrangement was then made between Lis mai, 31. !alder° Niepcc and Daguerre.
At length came the memorable year 1839, when the whole scientific' and artistic world was startled at the announcement that objects could be made to draw their own pictures with in accuracy and minuteness quilts unattainable by hand. In January, 1839, theefirst specimens by Daguerre wore shown, but the process was withheld until the month of July. This enabled Mr. Fox Talbot to secure to himself the merit of priority of publication of a method by which sun-drawn pictures could be successfully produced. lie, on the 18th of January, com municated to the Hovel Society a paper, entitled 'Some Account of the Art of Photogenre Drawing, or the Promo by which Natural Objects may be made to delineate themselves without the Aid of the Artist's Pencil.' And on the 21st of February In the same year, ho gave another communication on the method of preparing seusitivo paper and of fixing the images obtained. That the two experi
mentalists, Talbot and Dsguerre, were independent discoverers is evident from the dissimilarity of their preemies ; the light and camera Omura being the only menu strictly iu common.
Mr. Talbots method consisted in washing letter-paper over repeat edly with alternate solutions of salt and nitrate of silver ; at a certain stage a surface was obtained which gave images under the influence of the camera, and these images were fixed by Immersion In a strong solution of salt and water, in which the unaltered parts of the chloride of silver were soluble. This process was net very sensitive, and was therefore set aside by Mr. Talbot's later discoveries of 1840.
Let us now examine the nature of Daguerre's process called the Daguerreotype. A plate of silvered copper is highly noliehed, and then exposed to the vapour of the chemical element Iodine, which imparts to the plate a aeries of colours, depending on the quantity of iodine absorbed. The exposure to the vapour was carried on until the plate Resumed a rosy tint, or simply a deep orange-yellow, bordering on rod. The plate was now sensitive, and had only to be exposed at the focus of the camera obscure in order to obtain a picture of any strongly illuminated object. Some minutes were necessary even in full sun shine. The plate was then withdrawn into the darkened room in which it had been prepared, and there it was exposed to the vapour of heated mercury, which has the wonderful property of attaching itself only to those parts of the iodised plate which have been exposed to light ; and tide deposit takes place in proportion to the original intensity of light of the image. Thus a picture was produced which represented in shades of black and white the original optical imago seen on the ground-glass screen of the camera.
A solution of the hypoeulphite of soda was used to fix the image by removing the compound of iodine and silver which still veiled in some degree the shadows on the plate. Subsequently M. Fizeau improved the appearance- of Daguerreotypes by imparting to them a warm tinge by a thin film of gold which was thrown down upon the image by a spontaneous electro-chemical action.
The original Daguerreotype process was not sufficiently sensitive to be used in portraiture. To Mr. Goddard, who deserves reward, we owe the great improvement of the introduction of a second chemical agent, which now enables us to make pictures in a second of time. In 1640 Mr. Goddard combined bromine with iodine, and at once published the result in the ` Athenmum journal. In the dull weather Cf November of that year, lie obtained portraits in a few seconds; Daguerre's process requiring many minutes, even in a strong light. Mr. Claudet, at relater date, used chlorine with iodine for a similar end; but the bromine is still used in preference.