PRINTING.

553

when the machine is set in motion. The movement of the machine is neces-sarily intermittent, and is regulated so that the piece moves on a space exadtlyequal to the breadth of the block, and moves forward while the sieves aresupplied with colour from the rollers, 8, 8. This arrangement is produced bymeans of a dividing-wheel, 20. The wheels 21, keyed on the axle of thecylinder i, and having each the same number of teeth, are moved by a centralwheel with teeth in the same manner, and fixed behind the wheel 20. Thelatter receives an alternating movement from a rack, 24, fixed in a copperpiece, 25. This rises and falls alternately, and is keyed at its lower end toone of the spokes of the wheel 28. By altering the point of attachment tothe spoke the range of its movement is varied, more or fewer of the teeth ofthe wheel are allowed to pass, and the advance of the piece at each movement

Fig. 25.

is proportionately increased or lessened. It is further regulated by the ratchet-wheel, D. At each half-revolution the lever 22 raises the catch, and throwsthe wheels 21 out of gear during the next half turn; but as in workingthese wheels there would necessarily be a backward movement, this is pre-vented by a break, which consists of a pulley fixed on the shaft of the axle ofthe wheel 20, and a wire, which, after making a turn and a half or two turnson this shaft, is stretched by the weight 23, which offers a sufficient resistanceto any recoil. The slides are moved by the wheels 27 and 28 gearing withthe larger wheel 29. In order to regulate both the pressure and the amountof colour, the points of jundtion, 16 and 17, are moved to a greater or lessdistance from the point 15. The movement of the sieves is regulated by thecam, 11, 30, which moves them by means of a shaft to which they are keyed.