ART. II.-1. A Description of the Autotype Facsimiles of the Frescoes by Michael Angelo Buonarroti, in the Sistine Chapel, Rome. By C. BRUCE ALLEN. London: 1870.

2. Wonders of European Art. By LOUIS VIARDOT. Illustrated with Sixteen Reproductions by the Woodbury Permanent Process. London: 1870.

3. On Photozincography and the Photographic Processes employed at the Ordnance Survey Office, Southampton. By Captain A. DE C. SCOTT, R.E., under the direction of Colonel Sir HENRY JAMES, R.E., F.R.S. London: 1862. 4. Art Pictorial and Industrial. Illustrated by the Heliotype Process. London: 1870.

5. Micro-Photography. By T. HIGGINS, Esq. Liverpool. A NY real scientific discovery, however barren in practical bearing it may appear at the moment, is certain, in the long run, to lead to many other inventions, and to set in motion other appliances, which heretofore only seemed to be awaiting the new influence. The machinery, so to speak, rests idle for the want of some cog or spring to complete its action. Among the more recent examples of a latent want, the supply of which has given a start to many a new art, and has revolutionised others, may be considered Photography. The instantaneous draughtsman, ever ready, working with absolute truth both by night and day (for by the addition of highly sensitive paper the aid of the sun can now be dispensed with), catches and registers the scientific data of the astronomer and the meteorologist, seizes the wonders, and renders patent to the eye the hidden world opened up to us by the photo-microscopist; and where there is excess of light which blinds the human eye, Sol paints himself with his own beam, with lineaments so accurate from day to day, that the scientific watcher is only now beginning to discover the changes that are taking place in the great luminary.

When Fox Talbot and Daguerre simultaneously discovered the power of the pencil of light to paint an image on a tablet as quickly as it flashes upon the retina of the eye, great were the predictions of the part the new discovery would play in the field of science and art; but the wildest anticipations have already been surpassed in less than forty years since the original discovery, and every day is adding to the number of the wonders it is opening before us. It is our purpose in this paper to sketch with a light hand the many valuable arts and

the curious appliances which this beautiful discovery has suggested to the scientific worker, the artist, and the manufacturer. So rapid are the changes, and so great from day to day are the improvements, that we can only treat it as a progressive art, capable of almost unlimited extension.

The most important adaptation of photography is, as might be expected, to the pictorial and printing arts. But it was very speedily discovered by Mr. Fox Talbot that beautiful as were the productions of the camera, the original photograph contained within itself the elements of its own destruction. The instability of the metallic salts of which it is composed, is only too sure, sooner or later, to lead to its gradually fading away; and many of us who possess portraits of those we fondly cherish, have experienced with regret this gradual progress of an evitable decay. In an article by the editor of the British Journal of Photography,' in the Popular Science Review,' the reason of this unfortunate instability in the new art is thus alluded to:

'The blacks of photographic prints on ordinary unsized paper consist of silver. To aid in the proper fixing of a photograph, or destroying its future sensitiveness to light, hyposulphate of soda in solution is employed. The action of this salt on the silver in the pores of the paper is of an extremely complex nature, and long washing is requisite to secure its removal. If not thoroughly removed, an action continues to be exerted which ultimately results in the destruction of the picture, the blacks of which are converted into a sulphide of silver. But the sulphurous gases with which the atmosphere is impregnated, joined with the complex effects produced by the albumen (with which photographic paper is usually prepared), acting on the silver in a manner not yet clearly understood, exert a destructive influence on photography. The introduction of gold-toning has mitigated this evil to a considerable extent; but an inspection of some recent pictorial productions of photographers of reputation suffices to show that it still exists, notwithstanding the known care taken by them to obviate it.'

It may easily be conceived that Mr. Fox Talbot was fully alive to this shortcoming in his great invention, and as long ago as 1852, was anxious to find some means by which permanence could be given to sun-pictures. In casting about to find some means by which engraved plates could be taken directly from the photographic negative, his attention was directed to a discovery made by Mr. Mongo Ponton a short time before, apparently by accident-that bicromate of potash became darker in colour when exposed to the light; the photogenic quality of this salt at once struck his acute mind as the means of solving the problem. After many experiments he found that bicromatised gelatine or gum upon exposure to light

became insoluble in water, and that a plate could be prepared with this material, from which all those parts debarred from the light might be dissolved away. This discovery was the germ of numerous allied processes which have revolutionised the engraver's art, and which cannot fail to have a most important effect upon the illustrations of our literature, and indeed upon pictorial art generally, inasmuch as we need no longer depend upon line engraving, woodcutting, or lithography, nature herself reproducing her own drawings at a cost infinitely less than we have hitherto paid for inferior productions of the human hand.

Among the numerous patents that have been taken out of late years for utilising by this means the sunbeam as an engraver, we name as practically established the different processes known as Autotype, Woodburytype, and Heliotype. We wish to refer to these three processes first as the only ones capable of giving, with commercial success, copies of photographs, pictures, and drawings whose delicacy of halftone in a graduated tint is their chief beauty, and this cannot be produced with equal success by line engraving, lithography, or mezzotinto.

The process of relief-printing or Woodburytype, which we shall describe, as it is only known to the initiated and the trade, is a very curious art, totally unlike any method of engraving or copying previously known. As we have said before, the process is based upon the photographic qualities of the bicromate of potash, which, when mixed with a certain proportion of gelatine, dissolves away when placed in hot water in exact proportion to the amount of light that has been permitted to penetrate to it, through a glass photographic negative. Let us suppose some of this prepared dark brown gelatine poured upon a plate of glass so as to form a film; this film being dried in a dark room, is now placed under a glass negative and exposed to light. After an exposure of an hour, the prepared film upon which the picture is invisibly copied, is placed in hot water face upwards, and then it will be seen that all the gelatine upon which the light has not acted dissolves away, and the picture comes out in relief, the elevations or raised parts being in proportion to the penetrating power of the light through the negative. This raised picture in gelatine is then dried by a gentle heat. These gelatine film pictures keep for any length of time, and may be laid by in the portfolio with impunity. Of course these films are not suitable to be printed from, as they would render impressions in masses of black and white, without gra

dations of colour or half-tones. The picture is now in cameo, whereas it is required to be in intaglio. In order to reverse the plate in this desired manner, when the process was first established, Mr. Woodbury thought to accomplish it by an electrotype deposit of copper. This, although a perfectly successful method, was found to be too tedious, and the method now employed is the most singular part of the process. Every boy knows that he can fire a tallow-candle through an inch deal-board; the scientific man also knows that by the process of nature printing,' as it is termed, the softest details of a leaf, even the down on the thistle, can by hydraulic pressure be impressed upon a metal plate so that it can be printed from. Our knowledge of this extraordinary quality of a soft material to impress a harder one, may take away from the astonishment that otherwise would be felt by the statement that the gelatine mould hardened by crome alum, when placed in an hydraulic press, in contact with a plate composed of type metal and lead, impresses a most perfect reverse of itself upon the plate. The amount of hydraulic pressure depends of course on the size of the plate, extending from 50 to 200 tons on the square inch. It might be imagined that the gelatine would be flattened by such enormous force, but this is not so; on the contrary, it will allow five or six impressions on metal to be taken without losing any of its sharpness, and as each operation does not take more than a minute, no time is lost in the operation. From these metal jelly moulds' the object represented is printed in the following manner:-A portion of gelatine tinted usually of a dark colour, or with any permanent pigment, is placed in a liquid state in the centre of the intaglio mould of the picture, which is then placed in a press made like a shallow box with a hinged lid; a thick plate of glass at the bottom, and a similar one on the top, are perfectly adjusted so as to bring their two planes to a true level. Å sheet of paper is then laid upon the mould, the lid is folded down, and the pool of gelatine ink is squeezed into the mould, the superfluity escaping over the edges of the paper. Nearly a minute is allowed to let the gelatine ink set; when this is done, the lid is raised and the picture is found fixed to the paper in relief, in fact like a jelly just turned out of a mould. But this projection only remains for a short time, the picture as it dries shrinking flat to the paper. The lights and shades are given by the amount of colouring matter in the gelatine; where there have been high projections, of course there has been most colour entangled, representing deep shadows; where the film has been slight or in little colour, half-tones are

represented; and where the pressure has squeezed away all the coloured gelatine, there are white lights. A wash of crome alum is added to fix the image and prevent its washing off in warm water, which it would otherwise do. The delicacy of pictures rendered from the photograph is most marvellous ; it would be impossible to surpass the delicacy and beauty of the half-tones, or to approach nearer to the clear softness of the photograph of which it is a perfect facsimile. Of course any colour may be given to the gelatine vehicle; the fugitive colours, however, such as the aniline dyes are inadmissible, as they are themselves liable to fade, and thus the very object of the process would be defeated, as they would be as perishable as the photograph, which the relief process is intended to preserve.

Already some excellent specimens of its work have issued from the press, among which we may mention Viardot's 'Wonders of European Art,' which contain sixteen impressions by this process, with eleven woodcuts, and the contrast between the two is sufficiently striking to even the uninitiated in art. Crossing the Stream' by Claude, gives the golden haze of the Italian distance with a delicacy which is perfectly unapproachable by any system of engraving, whilst the shadows possess a depth which leaves nothing to be desired. Again, the copy of Vandyck's noble portrait in the Louvre of Charles I. habited in Cavalier costume, is an exquisite example of its power to render the tenderest details and the most powerful shadows with wonderful effect. The ink used, or rather we should say the pigment, is of a very warm dark chocolate tint and of a flowing character, which gives a rich glow to all the shadows, contrasting powerfully with the harsh blacks of the woodcuts in the same volume. The small expense at which these delicate copies can be made, will, we fancy, give the process a great advantage in the illustration of books. The only drawback, as far as we can see to its being applied to cheap literature, is the necessity to mount the prints upon card, or other stiff paper, their borders being destroyed by the nature of the process, which, as we have before stated, spills all the superfluous ink over the margin, consequently trimming and mounting are necessary. Unless this difficulty is overcome, we fear the process will be confined to the more expensive class of works. At the present moment the size of the prints produced is limited by the size of the hydraulic press, which is comparatively small, but we understand this size is about to be increased.

The action of light is necessary to produce the chemical effect