ively.

On the inside of each yoke, and opposite to its valve-toe, is a raised
piece, against which the closing piece (_t_) on the shell (_C'_) acts to
close the valves.

This shell (_C'_), as before noticed, has a spiral groove on its inside,
similar in all respects to that in the cam-shell (_C_); and being acted
upon in the same manner and through the same rod by the governor, it is
evident that the closing piece (_t_) on its outside will always hold the
same relation to the opening toe on the lower or cam-shell (_C_); and
whatever alteration is made in the one, a corresponding alteration takes
place in the other, thereby insuring the closing of the valves at the
proper time at every point of the variation of the cut-off.

When the several pieces above described are put together, the apparatus for
opening and closing the valves and producing the cut-off is complete, as
shown in fig. 72, and it operates as follows:

[Illustration: Fig. 71.]

[Illustration: Fig. 72.]

Motion is communicated by gearing from the crank-shaft to the bevel wheel
on the piece (_d_) on the end of the hub _D_, and is communicated to the
spindle of the governor, which is screwed into the socket on _D'_. As the
balls rise or fall, through change of centrifugal force due to the
variation in the speed of rotation, they raise or depress the governor-rod,
which passes through the spindle and the hubs _D'_ and _D_, and is attached
to the feathers, thereby raising or depressing the feathers, which, acting
on their respective spiral grooves, instantly alters the lift of the cam on
the shell (_C_), and brings the closing toe (_t_) on the shell (_C'_) into
proper position for closing, and so regulates the amount of steam admitted
to the cylinder.

[Illustration: Fig. 71.]

Consequently, any speed may be selected at which the load of the engine is
to move, and any variation from that will be instantly felt by the
governor, and corrected by this simple and beautiful device. There is no
jar in the working of the parts; the feathers move noiselessly in their
grooves; the governor rod moves up and down through the spindle and the
hubs _D_ and _D'_, and can be regulated by hand to give any required
opening of the steam ports to suit the work to be done. Any change in the
amount of work will then alter the speed of the engine, and so affect the
governor and cam, as before said.

It is unnecessary to insist on the great economy attained by using steam