e base, and back to the main large oil pump cylinders.
By means of these small pump pistons a constant quantity of oil is kept
in the motor, and the oil is continually being freshened by means of the
new oil coming in. All the oil pipes are very securely fastened to the
lower half of the crank case, and some cooling of the oil is effected
by air passing through channels cast in the crank case on its way to the
carburettor.

A light steel manifold serves to connect the exhaust ports of the
cylinders to the main exhaust pipe, which is inclined about 25 degrees
from vertical and is arranged to give on to the atmosphere just over the
top of the upper wing of the aeroplane.

As regards carburation, an automatic air valve surrounds the throat of
the carburettor, maintaining normal composition of mixture. A small jet
is fitted for starting and running without load. The channels cast in
the crank chamber, already alluded to in connection with oil-cooling,
serve to warm the air before it reaches the carburettor, of which the
body is water-jacketed.

Ignition of the engine is by means of two Bosch ZH6 magnetos, driven at
a speed of 2,175 revolutions per minute when the engine is running at
its normal speed of 1,450 revolutions. The maximum advance of spark is
12 mm., or 32 degrees before the top dead centre, and the firing order
of the cylinders is 1,5,3,6,2,4.

The radiator fitted to this engine, together with the water-jackets,
has a capacity of 25 litres of water, it is rectangular in shape, and is
normally tilted at an angle of 30 degrees from vertical. Its weight is
26 kg., and it offers but slight head resistance in flight.

The radial type of engine, neglected altogether in Germany, was brought
to a very high state of perfection at the end of the War period by
British makers. Two makes, the Cosmos Engineering Company's 'Jupiter'
and 'Lucifer,' and the A.B.C. 'Wasp II' and 'Dragon Fly 1A' require
special mention for their light weight and reliability on trials.

The Cosmos 'Jupiter' was--for it is no longer being made--a 450
horse-power nine-cylinder radial engine, air-cooled, with the cylinders
set in one single row; it was made both geared to reduce the propeller
revolutions relatively to the crankshaft revolutions, and ungeared;
the normal power of the geared type was 450 horse-power, and the total
weight of the engine, including carburettors, magnetos, etc., was only
757 lbs.; the engine speed was 1,850 revolution