valuable to propel automobiles. Santos-Dumont's success in aerial
navigation is due largely to the gasoline motor, which generated great
power in proportion to its weight.

A gasoline motor works by a series of explosions, which make the noise
that is now heard on every hand. From the gasoline tank, which is always
of sufficient capacity for a good long run, a pipe is connected with a
device called the carbureter. This is really a gas machine, for it turns
the liquid oil into gas, this being done by turning it into fine spray
and mixing it with pure air. The gasoline vapour thus formed is highly
inflammable, and if lighted in a closed space will explode. It is the
explosive power that is made to do the work, and it is a series of small
gun-fires that make the gasoline motor-car go.

All this sounds simple enough, but a great many things must be
considered that make the construction of a successful working motor a
difficult problem.

In the first place, the carbureter, which turns the oil into gas, must
work automatically, the proper amount of oil being fed into the machine
and the exact proportion of air admitted for the successful mixture.
Then the gas must be admitted to the cylinders in just the right
quantity for the work to be done. This is usually regulated
automatically, and can also be controlled directly by the driver. Since
the explosion of gas in the cylinder drives the piston out only, and
not, as in the case of the steam-engine, back and forward, some
provision must be made to complete the cycle, to bring back the piston,
exhaust the burned gas, and refill the cylinder with a new charge.

In the steam-engine the piston is forced backward and forward by the