ing oil into the crank case by means of a pump, and
a second pump circulated the cooling water.

Another good example of this type of engine was the Eole, which had
eight opposed pistons, each pair of which was actuated by a common
combustion chamber at the centre of the engine, two crankshafts being
placed at the outer ends of the engine. This reversal of the ordinary
arrangement had two advantages; it simplified induction, and further
obviated the need for cylinder heads, since the explosion drove at two
piston heads instead of at one piston head and the top of the cylinder;
against this, however, the engine had to be constructed strongly enough
to withstand the longitudinal stresses due to the explosions, as the
cranks are placed on the outer ends and the cylinders and crank-cases
take the full force of each explosion. Each crankshaft drove a separate
air-screw.

This pattern of engine was taken up by the Dutheil-Chambers firm in
the pioneer days of aircraft, when the firm in question produced seven
different sizes of horizontal engines. The Demoiselle monoplane used
by Santos-Dumont in 1909 was fitted with a two-cylinder,
horizontally-opposed Dutheil-Chambers engine, which developed 25 brake
horse-power at a speed of 1,100 revolutions per minute, the cylinders
being of 5 inches bore by 5.1 inches stroke, and the total weight of the
engine being some 120 lbs. The crankshafts of these engines were usually
fitted with steel flywheels in order to give a very even torque,
the wheels being specially constructed with wire spokes. In all the
Dutheil-Chambers engines water cooling was adopted, and the cylinders
were attached to the crank cases by means of long bolts passing through
the combustion heads.

For their earliest machines, the Clement-Bayard firm constructed
horizontal engines of the opposed piston type. The best known of these
was the 30 horse-power size, which had cylinders of 4.7 inches diameter
by 5.1 inches stroke, and gave its rated power at 1,200 revolutions per
minute. In this engine the steel cylinders were secured to the crank
case by flanges, and radiating ribs were formed around the barrel
to assist the air-cooling. Inlet and exhaust valves were actuated by
push-rods and rockers actuated from the second motion shaft mounted
above the crank case; this shaft also drove the high-tension magneto
with which the engine was fitted. A ring of holes drilled round each
cylinder constituted auxiliary ports whic