_R_, to which motion is given by a connection _x_, with an eccentric on the
engine shaft. When once set, therefore the movement of the exhaust valves
is constant, and they will always be opened and closed at the same point of
the stroke. Connected with the rocking plate _R_, and on opposite sides of
its centre, the same as the exhaust valve connections, there are two
levers, vibrating on a centre _c_, of which one only is shown, as it covers
the other; to the upper ends of these levers pawls are attached, one end of
which rests on the stems or rods connected with the handles _s, s'_, of the
steam valves; on these stems there are notches against which the pawls
strike, and as the levers vibrate inward they push back the stems and
thereby open the valves, and this continues for the whole length of the
inward motion of the levers, or till the outer extremities of the pawls
come in contact with the end of the short lever _l_, which, pushing down
the outer end of the pawls, relieves the stems at the other ends, and the
valve stem returns to its place through the force of springs attached to
the outer extremities of the valve stems _a_, are cylindrical guides to the
valve stems, at the inner extremities of which are air cushions. The lever
_l_ is connected directly with the governor. As the balls rise, they
depress the extremity, which comes in contact with the pawls sooner, and
thereby shut the valves earlier; and on the contrary when the balls are
depressed, the valves remain open longer; as the pawls come in contact with
the stems always at one point, the steam valves open constantly, but are
closed at any point by the relief of the pawls, according to the speed of
the governor.

Fig. 71 represents, partly in section and partly in plan, the cylinder,
steam chests, valves, &c., of one of the Woodruff & Beach high pressure
Engines, Wright's patent.

Fig. 72 represents, in elevation, the cam shaft, to the upper end of which,
not shown in the drawing, is attached the ordinary centrifugal governor.
The cylinder, steam chests, valves, &c., being similar to those of other
engines, need no special notice; but the cam for opening and closing the
steam valves, fig. 72, requires particular attention, as it embodies a
beautiful and simple device for cutting off the steam with certainty at any
part of the stroke, the motion being produced automatically by the action
of the governor on this cam, throwing it more or less out of centre wi