POLYCIMOKE PRINTING, the art of printing in one or more colors at the same time. Although several attempts had been previously made to carry out this process, -Congreve, in 1620, was the first to do it successfully with metal plates. Sir William Congreve had seen Applegath's polychromatic block•printing press, by which very rude colored pictures were produced, and he conceived the idea of improving upon h, and doing it with metal. His plan is extremely simple, though requiring great nicety in carrying it out. First, the picture is outlined upon a metal plate; and supposing it intended to have two colors, then the details of only the chief color are completed upon it, and all the pans for the other color are cut out, and into those parts other plates are fitted, like the portions of a child's puzzle-map, but with very great exactness; and upon these the engraving for the parts of the second color are completed. When these are done, a thickness of type-metal is attached to the back of these interior pieces, so that they can be held separately, and pushed forward or drawn backward at pleasure. Then
they are so adjusted to the machinery of the press. that they are withdrawn when the first color-roller passes over the surface or the main plate, and are pushed forward beyond the face of the main plate, so as to receive the color of the second roller, which then passes over them without touching the first or main plate. Having received their colored ink, the secondary plates are again moved back to a perfect level with the other, so as to fcrm an entire plate, carrying two colors, which are thus, in the ordinary way, imprinted On the paper. Since sir William Congreve's patent very many improvements have been male, the principle, however, remaining the same, and it has now a very wide applica tion.