the upper one just closing the exhaust; the low-pressure pistons are at
half stroke, that in sight exhausting, the opposite one, which cannot be
seen in this view, taking steam.

In Fig 2 the shaft has turned through one-eighth of a revolution; in
Fig. 3, a quarter turn; Fig. 4, three-eighths of a turn. Another eighth
turn brings two parts into position represented by Fig. 1, except the
second pair of cylinders now replace the first pair. The bearings, KL,
support the two shafts and act as stationary valves, against which faces
formed on the cylinders revolve; steam and exhaust ports are provided in
the faces of K and L, and two ports in the revolving faces, one to each
cylinder. The point at which steam is cut off is determined by the
length of the admission ports in K and L. The exhaust port is made of
such a length that steam may escape from the cylinders during the whole
of the return stroke of pistons.

Fig. 5 shows the complete engine. It will be seen that the engine is
entirely incased in a box frame, with, however, a lid for ready access
to the parts for examination, one great advantage being that the engine
can be worked with the cover removed, thus enabling any leakage past the
pistons or valve faces to be at once detected. The casing also serves to
retain a certain amount of lubricant.

The lubrication is effected by means of a triple sight-feed lubricator,
one feeder delivering to steam inlet, and two serving the main shaft
bearings.

Figs, 6 and 7 are an end elevation and plan of the same engine. There is
nothing in the other details calling for special notice.