solvent, and the plate printed. There are a number of processes based on etching, like aquatint, crayon manner, stipple, soft-ground etching, and others, but a review, however brief, of all these kindred devices does not lie within the scope of these pages. We have now reviewed the relief processes, both dependent entirely on hand work, and the intaglio processes, engraving, dry-point, mezzotint, likewise relying upon manual power to prepare the plate for printing. In the etching group of intaglio devices, a chemical factor is called upon to lessen and accelerate the work of the hand. The last group to be considered, planographic processes, is based entirely upon chemical and physical action. The drawing to be reproduced is made with fatty crayon or ink upon a slab of a special variety of limestone; the stone is then treated with acidulated water, and with gummed water. As a result, when the stone is moistened, all those parts which have been drawn upon reject the water, but have an affinity for printing-ink, while the portions not drawn upon have an affinity for water and reject printing-ink, as long as they are kept moist. Neither by ridges nor sunken furrows, just from one plane surface,--hence the term “planographic,”--merely by the enmity of water and fatty ink are these lithographic impressions obtained. Plates of metal are often substituted for stone (zincography, algraphy), but the process always remains the same. It goes without saying that each of these three possibilities of printing necessitates presses of appropriate construction; thus, in the so-called _platten_ press, the pressure is exerted vertically upon the block by the flat metal plate which comes down upon it, on the same principle as in the letter-press familiar to us all. All intaglio plates are printed in _roller_ presses, in which the plate, laid on an iron bed, passes between two rollers, one above, one below, as in a clothes-wringer. The lithographic press, finally, has a traveling bed, which passes under a stationary flat piece of wood. During its passage under this wooden bar, the paper is firmly pressed down upon the stone, which would be crushed in the other types of presses.[2] [2] Lithographs made on metal plates may be printed in an intaglio press as well. After this summary review of the technique of prints, let us consider, with what brevity we may, the great phases of development of the graphic arts. II THE ORIGIN OF WOODCUT