CONSTRUCTION DIRECTIONS.
In laying out this valve-motion, it is necessary to make the center or fulcrum F of the lever E coincide, when the crank is at either extreme stroke, with the center on which the slot-link JK vibrates: then these two centers coinciding when the engine stands at lead (that is, at either end of the stroke), the slot-link JK, which is, in fact, the reversing agent, may be put forward or backward through all degrees, without moving the valve, which thus has constant lead at all grades of expansion.
If, however, it is desired to give increasing or decreasing lead in the grades of expansion, this may be given by varying the coincidence of these two centers accordingly, or by under-correcting or over-correcting the action of the lever E, by varying the position of D on the link B.