COPYING MACHINE, any one of a number of contrivances by which one or more copies of a letter or other document may be made. Perhaps the best known is the copying press. The letter is written with °copying ink,° a writing fluid containing some gummy sub stance which prevents the ink from soaking into the paper. A sheet of bibulous tissue paper moistened with water to a certain degree is laid on the face of the writing, a sheet of oiled paper is laid on the tissue paper and the letter is placed between boards and put into a press, the platen of which is screwed down tightly. A few seconds' contact of the damp tissue paper with the writing transfers sufficient of the ink from the original to the tissue to make a perfect copy. A number of letters simi larly treated may be copied by one operation of the press, and by the use of very thin tissue and longer impression three or four good copies of a letter may be taken. Among copying processes are many that are perhaps rather methods of reproduction in bulk instead of copying in a more limited way, being somewhat akin to printing. Among these are lithography (q.v.) and the mimeographic process. The
mimeograph consists of a stylus, moving over a sheet of tissue paper, coated on one side with some sensitive material. This paper is placed on a steel plate, upon the surface of which are cut intersecting corrugations. When the stylus is moved over the paper, it presses the latter down pn the corrugations and these pierce the paper along the line of writing. The paper is then placed on a perforated cylinder; ink is forced through the perforations of the cylinder and paper is fed to the cylinder, as in any small printing press. The ink coming through the perforated line on the special paper makes a print on the sheets of paper fed to the cylinder and an indefinite number of copies may be struck off. The paper film is also adapted so that it may be placed on an ordinary typewriter, the ink ribbon of the latter is removed and the • stencil is cut by the type bars operated in the ordinary manner. The stencil is then placed on the printing cylinder and copies made in the manner described above for the stencil cut by the stylus.