This being clearly excessive, let us next see what will occur if the
lever arm, CH, be reduced as in the diagram to CK. The edge of the
cut-off valve will then be at N; it instantly begins to close the port.
CN, but not so rapidly as the main valve opens the port, AB.

The former motion increases in rapidity, while the latter decreases;
therefore at some point they will become equal in velocity, and the
openings of the two ports will be the same; and the question is, Will
this maximum effective port area give a sufficient supply of steam?

This diagram is the same as the one actually used in the engine under
consideration, in which it was required to follow a minimum distance of
5 inches in the stroke of 22. Under these conditions it is found that
the actual port opening for that point of cutting off is three-fifths of
that allowed when following full stroke, whereas the speed of the piston
at the time when this maximum opening occurs is less than half its
greatest speed.

This, it would seem, is ample; but we now find the eccentric, K, no
longer in the right position for backing; when the engine is reversed it
ought to be at, P, the angle, POL, being equal to the angle, KOL. By
leaving it free, therefore, to move upon the shaft, by the means above
described, through the angle, KOP, the desired object is accomplished.
The real eccentricity is now reduced in the proportion of OK to OH,
while the lengths of the cut-off valves, and what is equally important,
their travel over the back of the main valve, are reduced in the
proportion of CK to CH, in this instance nearly one-half; a gain quite
sufficient to warrant the adoption of the expedient.

The third, and perhaps the most notable, peculiarity is the manner of