cost of a steam engine using 9.9 pounds of coal per horse-power per
hour. Many similar exaggerated accounts of their economy in consumption
were circulated, and the public, on the strength of these figures,
bought.

It was understood that 17.6 cubic ft. of gas were required per
horse-power per hour, but it was found that as much as 105 cubic ft.
were often consumed. The discrepancy between the stated figures and the
actual performance of the engine was a disappointment to the using
public, and, as a result, the Lenoir engine got a bad name.

Hugon, director of the Parisian gas-works, who, together with Reithmann,
a watchmaker of Muenich, hotly contested Lenoir's priority to this
invention, brought out a modification of this engine. He cooled the
cylinder by injecting water as well as using a water-jacket, and used
flame instead of electric ignition. The consumption was now brought down
to 87.5 cubic ft.

At the second Parisian International Exhibition, 1867, an atmospheric
engine, invented by Otto & Langen about this time, was shown. In this
engine a free piston was used in a vertical cylinder, the former being
thrown up by the force of the explosion. The only work done on the
up-stroke was that to overcome the weight of the piston and piston rod,
and the latter being made in the form of a rack, engaged with a toothed
wheel on the axle as the piston descended, causing the fly-wheel and
pulley to rotate.

Barsanti and Matteucci were engaged in devising and experimenting with
an engine very similar to this some years before, but Otto & Langen, no
doubt, worked quite independently. Barsanti's engine never became a
commercial article; while Otto & Langen's firm, it is said, held their
own for ten years, and turned out about 4000 engines. In 1862 the French
engineer, Beau de Rochas, laid down the necessary conditions which must
prevail in order to obtain maximum efficiency. His patent says there are
four conditions for perfectly utilising the force of expansion of gas in
an engine.

(1) Largest possible cylinder volume contained by a minimum of surface.

(2) The highest possible speed of working.

(3) Maximum expansion.

(4) Maximum pressure at beginning of expansion.

These are the conditions and principles, briefly stated, that combine to
form the now well-known cycle upon which most gas engines work at the
present time.

It was not until 1876, fifteen years after these principles had been
enumerated, that Ot