enough to drive it a long distance, and yet must be almost
automatic in its workings. All of these things the modern motor car
accomplishes, but the struggle to make the machinery more efficient
still continues.

The three kinds of power used to run automobiles are steam, electricity,
and gasoline, taken in the order of application. The steam-engines in
motor-cars are not very different from the engines used to run
locomotives, factory machinery, or street-rollers, but they are much
lighter and, of course, smaller--very much smaller in proportion to the
power they produce. It will be seen how compact and efficient these
little steam plants are when a ten-horse-power engine, boiler,
water-tank, and gasoline reservoir holding enough to drive the machine
one hundred miles, are stored in a carriage with a wheel-base of less
than seven feet and a width of five feet, and still leave ample room for
four passengers.

It is the use of gasoline for fuel that makes all this possible.
Gasoline, being a very volatile liquid, turns into a highly inflammable
gas when heated and mixed with the oxygen in the air. A tank holding
from twenty to forty gallons of gasoline is connected, through an
automatic regulator which controls the flow of oil, to a burner under
the boiler. The burner allows the oil, which turns into gas on coming in
contact with its hot surface, to escape through a multitude of small
openings and mix with the air, which is supplied from beneath. The
openings are so many and so close together that the whole surface is
practically one solid sheet of very hot blue flame. In getting up steam
a separate blaze or flame of alcohol or gasoline is made, which heats
the steel or iron with which the fuel-oil comes in contact until it is
sufficiently hot to turn the oil to gas, after which the burner works
automatically. A hand air-pump or one automatically operated by the
engine maintains sufficient air pressure in the fuel-tank to keep a
constant flow.

Most steam automobile boilers are of the water-tube variety--that is,
water to be turned into steam is carried through the flames in pipes,
instead of the heat in pipes through the water, as in the ordinary flue
boilers. Compactness, quick-heating, and strength are the
characteristics of motor-car boilers. Some of the boilers are less than
twenty inches high and of the same diameter, and yet are capable of
generating seven and one-half horse-power at a high steam pressure (150