astings of which the engine was made up are accounted for by
the necessity for considering foundry practice of the time, for in 1897
castings were far below the present-day standard. The crank-case of
this two-cylinder vertical Daimler engine was the only part made of
aluminium, and even with this no attempt was made to attain lightness,
for a circular flange was cast at the bottom to form a stand for the
engine during machining and erection. The general design can be followed
from the sectional views, and these will show, too, that ignition was by
means of a hot tube on the cylinder head, which had to be heated with a
blow-lamp before starting the engine. With all its well known and hated
troubles, at that time tube ignition had an advantage over the magneto,
and the coil and accumulator system, in reliability; sparking plugs,
too, were not so reliable then as they are now. Daimler fitted a very
simple type of carburettor to this engine, consisting only of a float
with a single jet placed in the air passage. It may be said that this
twin-cylindered vertical was the first of the series from which has been
evolved the Mercedes-Daimler car and airship engines, built in sizes up
to and even beyond 240 horse-power.

In 1901 the development of the petrol engine was still so slight that it
did not admit of the construction, by any European maker, of an engine
weighing less than 12 lbs. per horse-power. Manly, working at the
instance of Professor Langley, produced a five-cylindered radial type
engine, in which both the design and workmanship showed a remarkable
advance in construction. At 950 revolutions per minute it developed 52.4
horse-power, weighing only 2.4 pounds per horse-power; it was a very
remarkable achievement in engine design, considering the power developed
in relation to the total weight, and it was, too, an interruption in
the development of the vertical type which showed that there were other
equally great possibilities in design.

In England, the first vertical aero-engine of note was that designed
by Green, the cylinder dimensions being 4.15 inch diameter by 4.75
stroke--a fairly complete idea of this engine can be obtained from the
accompanying diagrams. At a speed of 1,160 revolutions per minute
it developed 35 brake horse-power, and by accelerating up to 1,220
revolutions per minute a maximum of 40 brake horse-power could be
obtained--the first-mentioned was the rated working speed of the engine
for con