h the piston uncovered at the
inner end of its stroke, and these were of considerable assistance not
only in expelling exhaust gases, but also in moderating the temperature
of the cylinder and of the main exhaust valve fitted in the cylinder
head. A water-cooled Clement-Bayard horizontal engine was also made, and
in this the auxiliary exhaust ports were not embodied; except in this
particular, the engine was very similar to the water-cooled Darracq.

The American Ashmusen horizontal engine, developing 100 horse-power, is
probably the largest example of this type constructed. It was made with
six cylinders arranged on each side of a common crank case, with long
bolts passing through the cylinder heads to assist in holding them down.
The induction piping and valve-operating gear were arranged below the
engine, and the half-speed shaft carried the air-screw.

Messrs Palons and Beuse, Germans, constructed a light-weight,
air-cooled, horizontally-opposed engine, two-cylindered. In this the
cast-iron cylinders were made very thin, and were secured to the
crank case by bolts passing through lugs cast on the outer ends of
the cylinders; the crankshaft was made hollow, and holes were drilled
through the webs of the connecting-rods in order to reduce the weight.
The valves were fitted to the cylinder heads, the inlet valves being of
the automatic type, while the exhaust valves were mechanically operated
from the cam-shaft by means of rockers and push-rods. Two carburettors
were fitted, to reduce the induction piping to a minimum; one was
attached to each combustion chamber, and ignition was by the normal
high-tension magneto driven from the halftime shaft.

There was also a Nieuport two-cylinder air-cooled horizontal engine,
developing 35 horse-power when running at 1,300 revolutions per minute,
and being built at a weight of 5.1 lbs. per horse-power. The cylinders
were of 5.3 inches diameter by 5.9 inches stroke; the engine followed
the lines of the Darracq and Dutheil-Chambers pretty closely, and thus
calls for no special description.

The French Kolb-Danvin engine of the horizontal type, first constructed
in 1905, was probably the first two-stroke cycle engine designed to
be applied to the propulsion of aircraft; it never got beyond the
experimental stage, although its trials gave very good results. Stepped
pistons were adopted, and the charging pump at one end was used to
scavenge the power cylinder at the other ends of th