_Answer._ The admission and the cut-off will then occur at the same points of the stroke, but the ports will not be opened so wide. This is illustrated in fig. 143, in which the paths of two eccentrics having the same throw as those in fig. 142 are represented. The centre, _a_, of the larger eccentric is represented in the same position in fig. 143 as in fig. 142. If a line is drawn from the centre of the larger eccentric to that of the axle, and if the centre, _h_, of the smaller eccentric is located on the intersection of this line with the circle representing its path, then the smaller eccentric will have the same angular advance, but the linear advance measured by the distance _o t_ will be only ⁵⁄₈ in. If the valve have the same lap as in fig. 142, its steam edges at the beginning of the stroke, if the small eccentric is employed, will occupy the position represented by the dotted lines _A_ and _B_. If these edges are cut off, as shown by the full lines and shading, then the valve will have the same lead as in fig. 142. It is obvious, too, that if the smaller eccentric has the same angular advance it will reach the point _v_, at which, with the reduced lap, the steam will be cut off, at the same time that the centre, _a_, of the large eccentric will reach _p_, at which point it cuts off the steam with the valve having the large lap. There is, however, this difference in the distribution, that in the one case the valve opens the port a distance equal to _t s_, and in the other a distance equal to _r b_. As _o t_ is equal to the linear advance of the small eccentric, or ⁵⁄₈ in., and _o s_ to half the throw of the eccentric, or 1³⁄₄, _t s_ is equal to 1³⁄₄ - ⁵⁄₈ = 1¹⁄₈ in. The distance _r b_, as shown above, is equal to 2¹⁄₂ - ⁷⁄₈ = 1⁵⁄₈ in., so that the effect produced upon the admission of using an eccentric with a small throw and corresponding amount of lap is, that the ports are not opened so wide as with an eccentric having a larger throw. [Illustration: _Fig. 145._ Scale ³⁄₁₆ in. = 1 foot.] QUESTION 235. _How do eccentrics with a short throw, and valves with a corresponding amount of lap, affect the admission with a link motion as compared with eccentrics having a larger amount of throw and greater lap of valve?_ _Answer._ The chief difference is that the ports are not opened so wide for the same period of admission. Thus in fig. 144 is a series of motion-curves drawn with a model of a link motion like that illustrated in fig. 103. The eccentrics had 5 in. throw, and the valve ⁷⁄₈ in. lap outside and ¹⁄₁₆ in. inside. Fig. 145 represents a series of curves, drawn with the same arrangement of valve-gear, excepting that the eccentrics had 3¹⁄₂ in. throw and the valve ¹⁄₂ in. lap. In both cases the curves represent the motion of the valve when cutting off at the same point of the stroke. The following table will show the relative amount of opening of the port.