The pressure is produced by a lever six to twelve feet long, fastened to the scraper below and to a spring (an elastic board) above. It is connected with a tread, and when forced down, presses with the desired force on the scraper and so on the plate. The board holding the lever overhead must be partially movable like a spring because the lever describes a part of a circle on the plate below. Hence the pressure at the beginning and end of the impression is not so great as in the middle, and great care in choice of wood and manufacture is demanded to give the spring board the necessary elasticity and power combined. I have found a board of young dried pine the best, the dimensions being six feet long, eight inches wide, and two inches thick, provided that the fibres all ran lengthwise. It is not always possible to find a good board at once. Often I have found that the difference between two boards made a great difference in the effectiveness of two presses otherwise exactly the same. The scraper arm consists of two parts, of which the shorter one, to which the scraper is fastened with a screw, is only one and one quarter feet long. The other part is as long as the height of the press permits. The higher a lever press is, the better is it, because then the circular motion described by the scraper wood approaches a straight line more and more, so that the press exercises a more uniform pressure during all stages of the impression and is easier to handle. The second illustration shows this kind of press in the moment when the impression has been finished, the printing-frame opened, and the scraper arm swung back again. The printing-frame is much like a book-printing frame, and is furnished inside with a second small frame which holds the paper, being furnished with small springs or strings. When the frame has been turned over the stone, the paper must be at least half an inch from the stone to avoid smutting, which will occur if it touches. The paper must not touch the stone till pressure is applied, and then only on the spot pressed downward by the scraper. As soon as both parts of the scraper arm are in a straight line, so that they form practically one piece, the scraper wood is pulled down and the printer draws it toward himself over the printing-frame and the stone plate. At this time the following is to be observed:--