fly-wheel. The stroke completed, the slide-valve, actuated by an
eccentric keyed to the driving shaft, returns backward and puts the
cylinders, B and C, in communication. The steam then expands and
drives the large piston to the right, so as to effect the second half
of the fly-wheel's revolution. The exhaust occurs through the valve
chamber, which, at each stroke, puts the large cylinder in connection
with the eduction port, M.

The volume of air included between the two pistons is displaced at
every stroke, so that, according to the position occupied by the
pistons, it is held either by the large or small cylinder. The
necessary result of this is that a compression of the air, and
consequently a resistance, is brought about. In order to obviate this
inconvenience, the constructor has connected the space between the two
pistons at the part, A', of the frame by a bent pipe. The air, being
alternately driven into and sucked out of this chamber, A', of
relatively large dimensions, no longer produces but an insignificant
resistance.

[Illustration: FARCOT'S SIX H.P. STEAM ENGINE.
Fig. 1.--Longitudinal Section (Scale 0.10 to 1).
Fig. 2.--Horizontal Section (Scale 0.10 to 1).
Fig. 3.--Section across the Small Cylinder (Scale 0.10 to 1).
Fig. 4.--Section through the Cross Head (Scale 0.10 to 1).
Fig. 5.--Application for a Variable Expanion (Scale 0.10 to 1).]

As shown in Fig. 5, there may be applied to this engine a variable
expansion of the Farcot type. The motor being a single acting one, a
single valve-plate suffices. This latter is, during its travel,
arrested at one end by a stop and at the other by a cam actuated by