cases.

The highest speed ever attained on the sea was the forty-two miles per
hour of the unfortunate _Viper_, a turbine destroyer which developed
11,500 horse power, though displacing only 370 tons. This velocity would
compare favourably with that of a good many expresses on certain
railways that we could name. In the future thirty miles an hour will
certainly be attained by turbine-driven liners.

[7] Even at this speed the wheel has a circumferential velocity of
two-thirds that of a bullet shot from a Lee-Metford rifle. A vane
weighing only 250 grains (about 1/2 oz.) exerts under these conditions a
centrifugal pull of 15 cwt. on the wheel!

Chapter IV.

THE INTERNAL-COMBUSTION ENGINE.

The meaning of the term--Action of the internal-combustion
engine--The motor car--The starting-handle--The engine--The
carburetter--Ignition of the charge--Advancing the spark--Governing
the engine--The clutch--The gear-box--The compensating gear--The
silencer--The brakes--Speed of cars.

THE MEANING OF THE TERM "INTERNAL-COMBUSTION ENGINE."

In the case of a steam-boiler the energy of combustion is transmitted to
water inside an air-tight vessel. The fuel does not actually touch the
"working fluid." In the gas or oil engine the fuel is brought into
contact and mixed with the working fluid, which is air. It combines
suddenly with it in the cylinder, and heat energy is developed so
rapidly that the act is called an explosion. Coal gas, mineral oils,
alcohol, petrol, etc., all contain hydrogen and carbon. If air, which
contributes oxygen, be added to any of these in due proportion, the
mixture becomes highly explosive. On a light being applied, oxygen and
carbon unite, also hydrogen and oxygen, and violent heat is generated,
causing a violent molecular bombardment of the sides of the vessel
containing the mixture. Now, if the mixture be _compressed_ it becomes
hotter and hotter, until a point is reached at which it ignites
spontaneously. Early gas-engines did not compress the charge before
ignition. Alphonse Beau de Rochas, a Frenchman, first thought of making
the piston of the engine squeeze the mixture before ignition; and from
the year 1862, when he proposed this innovation, the success of the
internal-combustion engine may be said to date.

[Illustration]

[Illustration: FIG. 39.--Showing the four strokes that the piston of a
gas-engine makes during one "cycle."]

ACTION OF THE ENGIN