While Mr. Fox Talbot was engaged in these very elegant discoveries in England, M. Daguerre had brought to perfection and made public that admirable process by which he has compelled Nature permanently to engrave her own works; and thus the talents of France and England have been combined in bringing to perfection this useful art. Copper, plated with silver, was successfully employed by M. Daguerre for copying nature by the agency of light. The surface of the plate is converted into an iodide of silver, by placing it horizontally with its face downwards in a covered box, in the bottom of which there is a small quantity of iodine which evaporates spontaneously. In three or four minutes the surface acquires a yellow tint, and then, screening it carefully from light, it must be placed in the focus of a camera obscura, where an invisible image of external objects will be impressed on it in a few minutes. When taken out, the plate must be exposed in another box to the action of mercurial vapour, which attaches itself to those parts of the plate which had been exposed to light, but does not adhere to such parts as had been in shadow; and as the quantity of mercury over the other parts is in exact proportion to the degree of illumination, the shading of the picture is perfect. The image is fixed, first by removing the iodine from the plate by plunging it into hyposulphite of soda, and then washing it in distilled water; by this process the yellow colour is destroyed, and in order to render the mercury permanent, the plate must be exposed a few minutes to nitric vapour, then placed in nitric acid containing copper or silver in solution at a temperature of 61-1/4° of Fahrenheit for a short time, and lastly polished with chalk. This final part of the process is due to Dr. Berre, of Vienna. Nothing can be more beautiful than the shading of these chiaroscuro pictures when objects are at rest, but the least motion destroys the effect; the method therefore is more applicable to buildings than landscape. Colour is wanting; but the researches of Sir John Herschel give reason to believe that even this will ultimately be attained. The most perfect impressions of seaweeds, leaves of plants, feathers, &c., may be formed by bringing the object into close contact with a sheet of photographic paper, between a board and plate of glass; then exposing the whole to the sun for a short time, and afterwards fixing it by the process described. The colours of the pictures vary with the preparation of the paper, by which almost any tint may be produced. In the chromatype, a peculiar photograph discovered by Mr. Hunt, chromate of copper is used, on which a dark brown negative image is first formed, but by the continued action of light it is changed to a positive yellow picture on a white ground; the farther effect of light is checked by washing the picture in pure water.