Messes. Editors.—On page 59, No. 8, this Vol., Scientific American, there is an account of Randolph Appel's process of producing copies of printed books, 'c. The said process has been known to me for at least twenty years, and during that time I have made many experiments upon various kinds of substances, such as leather, horn, ivory, brass, copper, iron, zinc, silver, 'c., I also claim part of the honor for reproducing printed matter without the re-setting of type, making new en- « gravings, 'c. I am in possession ot a large number of impressions on paper taken from printed books, papers, engravings, 'c., which were taken directly from the paper surface without transferring them to metal surfaces ; any amount of impressions may be taken in this way without injury to the original. The following is a description of a process by which any desirable impression may be etched upon common tin plate:—Take a piece of tin plate (or tinned iron) which is new, clean, and free from spots and marks, cut it somewhat larger than the original subject from which it is desirable to make the etching or engraving, next take hold of the plate by one corner with a pair of pliers, and subject it to the heat of a spirit lamp, holding it in a horizontal position and continue the heat by moving the plate over the flame until the tin thereupon has thoroughly melted, when it must bl:> withdrawn and held in the same position until the metal hardens again; it may now be cooled in water and polished with flour of emery or the like. All kinds of grease must be avoided; when thoroughly polished moisten the design with a solution of the nitrate of silver prepared in the following manner :—Take a half dollar (American coin) and dissolve it into an ounce and a half of strong nitric acid, diluted slightly with water to quicken the operation (the water should be hot), when the silver coin is found to be entirely dissolved place the contents into a half pint glass and fill up the remainder with pure cold water; the solution is now ready tor use, and must be placed into a separate vessel in small quantities and applied with a soft brush to the paper; care must be taken never to immerse the brush into the larger portion of the liquid, for in case there should be more than one impression required or taken from the same design, the second would be apt to precipitate the silver in solution and it would require the hand of a practical chemist to restore it-to its tormer condition. When the paper of the design has been thoroughly moistened with the above solution, place it between folds of blotting paper to free it from all superfluous moisture, now place the plate in a press face upward, and the design upon it face downwards, and lay two or three tolds of cotton, flannel, or woolen cloth upon the same, and then apply pressure by screw or otherwise, and then remove the paper quickly from the plate by taking hold of it by one corner. If the whole has been properly conducted, it will be found on examination that the plate has acquired a beautiful and uniform etching over the whole surface, and oftentimes it will require no further etching, but should it happen that the process is incomplete or unsuccessful, heat the plate and repeat the process as before, and if it is required to deepen the impression, heat the plate slightly, face upward, so as to harden the surface, then, when cold, moisten the surface by pouring pure water thereupon, holding it in a horizontal position so as to retain a quantity of the water, and next pour upon the surface nitric acid diluted in the proportion of one part of acid to eight of water. This being an extremely « delicate operation, it requires to be conducted with the utmost care, or the whole design will be destroyed. David Baldwin, Godwinville, N. J. [We have received a number of impressions—rather copies—of pictures, printed matter, 'c., from our correspondent, the said copies having been taken without being transferred to metal. We have never seen any anastatic proofs which we considered equal to the originals