we have the angularities both of the main rods and the eccentric rods to contend with, and whereby irregularities are entering in the problem that must be compensated for, as referred to in the general description. It is not to be considered that a uniform circular motion is the best, but an approximation to it works with less shocks or jerks, and is therefore more desirable for so high-speed an engine as a locomotive. A few advantages can be taken, however, in selecting the suspensions and various connections, so that better results can be obtained than from a true circular motion, which are principally affected by three union points, and are, first, the connecting point of eccentric rod and link; second, the locus of the lifting-link suspension point; and third, the relative height of the crosshead-connection point of the union bar to the corresponding point of the combination lever. It is not necessary to lay out the valve diagrams except where a given cut-off per cent is wanted. This is the most convenient way to find the required lap. Fig. 35 and 36, the diagrams on the folding plates, represent the positions of the valve with the main crank at nine different points of the revolution of the driving wheel. In Fig. 35 the valve is of the piston type, with inside admission, and in Fig. 36 an outside admission valve is shown, of the D-slide pattern. |