of the piston causes a partial vacuum;
by the time the piston reaches bottom dead centre the piston-valve has
moved up to give communication between the cylinder and the crank case,
therefore the mixture is drawn into the cylinder. Both the piston valve
and exhaust valve are operated by cams formed on the one casting, which
rotates at seven-eighths engine speed for the seven-cylinder type, and
nine-tenths engine speed for the nine-cylinder engines. Each of these
cams has four or five points respectively, to suit the number of
cylinders.

The steel cylinders are machined from solid forgings and provided with
webs for air-cooling as shown. Cast-iron pistons are used, and are
connected to the crankshaft in the same manner as with the Gnome and Le
Rhone engines. Petrol is sprayed into the crank case by a small geared
pump and the mixture is taken from there to the piston valves by radial
pipes. Two separate pumps are used for lubrication, one forcing oil to
the crank-pin bearing and the other spraying the cylinders.

Among other designs of rotary aero engines the E.J.C. is noteworthy,
in that the cylinders and crank case of this engine rotate in opposite
directions, and two air-screws are used, one being attached to the end
of the crankshaft, and the other to the crank case. Another interesting
type is the Burlat rotary, in which both the cylinders and crankshaft
rotate in the same direction, the rotation of the crankshaft being twice
that of the cylinders as regards speed. This engine is arranged to
work on the four-stroke cycle with the crankshaft making four, and the
cylinders two, revolutions per cycle.

It would appear that the rotary type of engine is capable of but little
more improvement--save for such devices as these of the last two engines
mentioned, there is little that Laurent Seguin has not already done in
the Gnome type. The limitation of the rotary lies in its high fuel and
lubricating oil consumption, which renders it unsuited for long-distance
aero work; it was, in the war period, an admirable engine for such
short runs as might be involved in patrol work 'over the lines,' and
for similar purposes, but the watercooled Vee or even vertical, with
its much lower fuel consumption, was and is to be preferred for distance
work. The rotary air-cooled type has its uses, and for them it will
probably remain among the range of current types for some time to come.
Experience of matters aeronautical is sufficient to