e two smaller sizes are single crank engines
with seven and nine cylinders respectively, and the larger sizes are
of double-crank design, being merely the two smaller sizes
doubled--fourteen and eighteen-cylinder engines. The inlet and
exhaust valves are located in the cylinder head, and both valves are
mechanically operated by one push-rod and rocker, radial pipes from
crank case to inlet valve casing taking the mixture to the cylinders.
The exhaust valves are placed on the leading, or air-screw side, of the
engine, in order to get the fullest possible cooling effect. The rated
power of each type of engine is obtained at 1,200 revolutions per
minute, and for all four sizes the cylinder bore is 4.13 inches, with
a 5.5 inches piston stroke. Thin cast-iron liners are shrunk into
the steel cylinders in order to reduce the amount of piston friction.
Although the Le Rhone engines are constructed practically throughout
of steel, the weight is only 2.9 lbs. per horse-power in the
eighteen-cylinder type.

American enterprise in the construction of the rotary type is perhaps
best illustrated in the 'Gyro 'engine; this was first constructed with
inlet valves in the heads of the pistons, after the Gnome pattern, the
exhaust valves being in the heads of the cylinders. The inlet valve in
the crown of each piston was mechanically operated in a very ingenious
manner by the oscillation of the connecting-rod. The Gyro-Duplex engine
superseded this original design, and a small cross-section illustration
of this is appended. It is constructed in seven and nine-cylinder sizes,
with a power range of from 50 to 100 horse-power; with the largest size
the low weight of 2.5 lbs.. per horse-power is reached. The design is
of considerable interest to the internal combustion engineer, for it
embodies a piston valve for controlling auxiliary exhaust ports, which
also acts as the inlet valve to the cylinder. The piston uncovers the
auxiliary ports when it reaches the bottom of its stroke, and at the end
of the power stroke the piston is in such a position that the exhaust
can escape over the top of it. The exhaust valve in the cylinder head is
then opened by means of the push-rod and rocker, and is held open until
the piston has completed its upward stroke and returned through more
than half its subsequent return stroke. When the exhaust valve closes,
the cylinder has a charge of fresh air, drawn in through the exhaust
valve, and the further motion