the cylinder from heat. The pistons of the two cylinders are connected
by rods, D, to opposite cranks on the shaft, E. This shaft, by means of
bevel gear, F, works a revolving cylindrical valve, G, situated in a
casing between the two cylinders. The lowest part of this casing is
supplied with combustible gas and with air, in proportions capable of
being regulated by stopcocks or valves. The highest part of the casing
communicates with a discharge-pipe; and the middle part of it with a
reservoir which can be cut off from communication by a stopcock, so that
the charge in the reservoir may be retained when the engine is stopped.
The middle space of the hollow valve, G, communicates, by a number of
holes, with the middle space of the slide casing. It also, by means of a
port at its lower part, communicates alternately with the annular spaces
of the two cylinders; this communication in each case being made when
the piston is performing the latter part of its downstroke. The interior
of the slide also, by means of a second port at its upper part,
communicates alternately with the tops of the two cylinders; this
communication being in each case made while the piston is performing the
first portion of its downstroke. During the upstroke of each piston the
slide, by means of another port, makes communication alternately to each
cylinder from the bottom of the slide casing, and by means of a fourth
port make communication alternately from each cylinder to the top of the
slide casing. In the passage connecting the top of the slide casing
to each cylinder is placed a regenerator, consisting of a number of
perforated metal plates or sheets of wire gauze.

[Illustration: SIEMENS' GAS PRODUCER AND GAS MOTOR. Fig 1.]

In order that gas of poor quality or gas diluted with a large proportion
of air may be utilized, an igniting arrangement is employed which
operates as follows: I is a vessel containing a supply of hydrocarbon