able types produced are the Rolls-Royce and the Napier.
The first mentioned of these firms, previous to 1914 had concentrated
entirely on car engines, and their very high standard of production in
this department of internal combustion engine work led, once they took
up the making of aero engines, to extreme efficiency both of design and
workmanship. The first experimental aero engine, of what became known
as the 'Eagle' type, was of Vee design--it was completed in March
of 1915--and was so successful that it was standardised for quantity
production. How far the original was from the perfection subsequently
ascertained is shown by the steady increase in developed horse-power
of the type; originally designed to develop 200 horse-power, it was
developed and improved before its first practical trial in October of
1915, when it developed 255 horsepower on a brake test. Research
and experiment produced still further improvements, for, without any
enlargement of the dimensions, or radical alteration in design, the
power of the engine was brought up to 266 horse-power by March of 1916,
the rate of revolutions of 1,800 per minute being maintained throughout.
July, 1916 gave 284 horse-power; by the cud of the year this had been
increased to 322 horse-power; by September of 1917 the increase was to
350 horse-power, and by February of 1918 then 'Eagle' type of engine was
rated at 360 horse-power, at which standard it stayed. But there is no
more remarkable development in engine design than this, a 75 per cent
increase of power in the same engine in a period of less than three
years.

To meet the demand for a smaller type of engine for use on training
machines, the Rolls-Royce firm produced the 'Hawk' Vee-type engine of
100 horsepower, and, intermediately between this and the 'Eagle,' the
'Falcon' engine came to being with an original rated horse-power of 205
at 1,800 revolutions per minute, in April of 1916. Here was another case
of growth of power in the same engine through research, almost similar
to that of the 'Eagle' type, for by July of 1918 the 'Falcon' was
developing 285 horse-power with no radical alteration of design.
Finally, in response to the constant demand for increase of power in a
single plant, the Rolls-Royce company designed and produced the 'Condor'
type of engine, which yielded 600 horse-power on its first test in
August of 1918. The cessation of hostilities and consequent falling off
in the demand for extreme