the link can be laid down as before, that is, from _c″_ and _d″_ as centres and with the length of the eccentric-rods as a radius arcs, _f″_ and _g″_, are drawn. Then with the paper template the positions of the centres of the link-pins in these arcs are determined and marked, and from them with the length of the eccentric rods as a radius, two intersecting arcs, _v″_, _w″_, are drawn, whose intersection gives the centre of the link from which its centre line, -4 -4, is drawn. This will give the position of the rocker-pin for another point of the stroke. In a similar manner its position can be determined for any number of points of the stroke, from which the position of the valve can easily be determined and laid down on the diagram for the motion-curve as was described in the answer to Question 44. Of course the valve will be moved from its middle position the same distance that the rocker-pin is,[54] only in an opposite direction. In order to lay down the position of the valve on the diagram for motion-curves, it is, therefore, only necessary to draw it in the same relative position as that of the rocker-pin which is given by the point of intersection of the center line of the link with the path in which the rocker-pin oscillates. To construct the motion-curves it is necessary to determine the positions of the valve for different points of the stroke and mark them on the horizontal lines which represent the respective positions of the piston. Curves are then drawn through these points, either by hand or by constructing templates. The more points there are determined, the more accurate will be the curves. It is, therefore, best to lay down the position of the valve for each inch of the stroke of the piston. They should also be drawn full size, which of course was impossible for the illustrations which are given herewith. [53] In order to get the engraving within the required limits, the diagram is drawn with a connecting-rod only 5¹⁄₂ instead of 7 feet. The latter is the length used in previous illustrations. [54] This will be the case when the two arms of the rocker are of the same length, as they usually are. Sometimes, though rarely, they are of different lengths. QUESTION 192. _Is there any other method of drawing these motion curves?_