_Answer._ Changing the travel of a valve with a link has a very similar effect to that produced by eccentrics of different throw--that is, the period of admission is increased with the throw of the eccentric and that for expansion lessened. This is shown clearly in both the motion diagram and the table. With the first curve and a travel of 2¹⁄₂ in. the steam is cut off at 8 in. for the backward stroke and 6³⁄₄ in. for the front, and with 5 in. travel steam is admitted during 20⁵⁄₈ in. of the backward and 20¹⁄₂ in. of the forward stroke. QUESTION 198. _How is the point of release or exhaust of the steam affected by the link?_ _Answer._ As the travel increases, it is delayed until later in the stroke. Thus, with 2¹⁄₂ in. travel the steam is exhausted or released from the cylinder during the backward stroke when the piston has moved 17 in., and on the return stroke at 16⁵⁄₈ in., whereas, with 5 in. travel of the valve, the release is delayed until 23¹⁄₈ in. of the stroke. An examination of the diagram and table will show very clearly the relation of the point of release to the travel. QUESTION 199. _How is the lead affected by the ordinary link motion?_ _Answer._ It is increased as the travel is diminished, as is shown in the table, and also by the inclination of the curves at the top and bottom of the diagram. [Illustration: _Fig. 129._ _Fig. 130._ _Fig. 131._ Scale ³⁄₄ in. = 1 foot.] QUESTION 200. _What is the cause of this change of the amount of lead?_ _Answer._ This can be best explained by reference to fig. 129, which represents a link with very short eccentric rods. If now the centre from which the link was drawn was in the centre of the axle _S_, and the eccentric straps embraced the axle instead of the eccentrics, their ends _c_ and _d_ would each describe the same arc, _a b_, parallel with the centre line, _x y_, of the link, and the latter could then obviously be raised and lowered without moving the rocker-pin at all. But the eccentric straps being attached to the eccentrics, as shown by the dotted lines, when the rods are raised or lowered they describe arcs, _c e_ and _g h_, from the centres _s_ and _t_ of the eccentrics, and not from the centre of the axle. When the link is raised then, the end of the upper rod obviously moves in the arc _c e_, and the top of the link is moved from the axle, as shown in fig. 130, a distance equal to the interval between the arc, _a b_, drawn from the centre of the axle, and _e f_, which the rod describes from the centre of its eccentric. When the link is lowered from back to mid-gear, a similar action takes place, as the end, _d_, fig. 130, of the lower rod describes an arc, _f g_, so that the whole link is thrown from the axle a distance equal to the space between the arcs described from the centre of the axle and the centres of the eccentrics. When the position of the eccentrics is reversed, as shown in fig. 131, the link is moved