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22 face of the stone, while it is repelled by the hard greasy matter in the transferred lines. The inking roller is then applied to the stone with a contrary result; the moistened surface repels the greasy ink, but the transferred lines attract and retain it. When an impression on paper is taken, the only part of the paper which receives ink is that part which touches the transferred lines. The theory of lithography is based upon the repulsion between grease and water. Lithographic printing is chemical printing.

Lithography is the most scientific and the most flexible of all methods of printing. It can imitate fairly, and it often reproduces with accuracy, a line engraving on steel, a drawing in crayon, the manuscript of a penman, or the painting in oil of an artist. By the aid of photography, it can repeat, in an enlarged or diminished size, any kind of printed work. It has many advantages over copper-plate and xylography. For some kinds of work, like autograph letters and rude diagrams, engraving is unnecessary; the design may be written with oily ink on paper, and can then be transferred direct from the written copy to a stone without the aid of a graver. The transferring process is another peculiarity of this art which allows the lithographer to duplicate small designs with greater facility and economy than a similar duplication could be effected by the stereotyper of types. These advantages are counterbalanced by one great defect: lithography is not a quick method of printing. The usual performance of the lithographic hand press when applied to ordinary work, is about four hundred impressions per day; on the steam press, the performance is about five thousand impressions per day.

The arts of lithography and copper-plate are useful and beautiful methods of printing, but they do not make books and newspapers. The necessity which compels them to