the general
plan shown in Figs. 1 and 2.

[Illustration: Figs. 1-2 IMPROVED STEAM ENGINE.--BY PROF MACCORD.]

The first of these relates to the arrangement of the right and left
handed screw, above mentioned, and of the device by which it is rotated.

Usually, the threads, both right handed and left handed, are cut upon
the cut-off valve stem itself, which must be so connected with the
eccentric rod as to admit of being turned; and in most cases the valve
stem extends through both ends of the steam chest, so that it must both
slide endwise and turn upon its axis in two stuffing boxes, necessarily
of comparatively large size.

All this involves considerable friction, and in the engine under
consideration an attempt has been made to reduce the amount of this
friction, and to make the whole of this part of the gear neater and more
compact, in the following manner:

Two small valve stems are used, which are connected at their lower ends
by a crosstail actuated directly by the eccentric rod, and at their
upper ends by a transverse yoke. This yoke, filling snugly between two
collars formed upon a sleeve which it embraces, imparts a longitudinal
motion to the latter, while at the same time leaving it free to rotate.

This sleeve has cut upon it the right and left handed screws for
adjusting the cut-off valves; and it slides freely upon a central
spindle which has no longitudinal motion, but, projecting through the
upper end of the valve chest, can be turned at pleasure by means of a
bevel wheel and pinion. The rotation of the spindle is communicated to
the sleeve by means of two steel keys fixed in the body of the latter
and projecting inwardly so as to slide in corresponding longitudinal
grooves in the spindle.

Thus the point of cutting off is varied at will while the engine is
running, by means of the hand wheel on the horizontal axis of the bevel
pinion, and a small worm on the same axis turns the index, which points
out upon the dial the distance followed. These details are shown in
Figs. 3, 4, and 5; in further explanation of which it may be added that
Fig. 3 is a front view of the valve chest and its contents, the cover,
and also the balance plate for relieving the pressure on the back of the
main valve (in the arrangement of which there is nothing new), being
removed in order to show the valve stems, transverse yoke, sleeve, and
spindle above described. Fig. 4 is a longitudinal section, and Fig. 5 is
a transve