The connecting-bar H is in two parts, slotted and bolted together at H to admit of regulating the position of the cylinder.
No. 4 is a motion on a different principle; it is a French motion. It will readily be seen that the cylinder is driven out and in by the toothed wheel, which is wrought by a rack on the slide rod E. This slide rod works outside the framing of the machine, as is common in the French machines. One point must be observed about these motions—viz. that they must have a certain amount of dwell at the bottom of the stroke, or when the cylinder is in. The reason of this dwell will be explained further on, but the method of obtaining it may be given here. In the swan-neck motion (No. 1), any desired dwell can easily be obtained at either top or bottom by the length of the slot that is in a vertical direction, as when the stud is passing through this portion of the slot no motion is given to the cylinder. In the lever motions Nos. 2 and 3, as well as in No. 4, the dwell is got by the levers or arms passing the centres; in Nos. 2 and 4 it is by the lever or arm H passing the back centre, which may be considered as a crank; and in No. 3 it is the short lever C passing the centre that gives the dwell.
Fig. 20
Fig. 21
