The automobile builders have a problem that troubles locomotive builders very little—­that is, compensating the difference between the speeds of the two driving-wheels when turning corners.  Just as the inside man of a military company takes short steps when turning and the outside man takes long ones, so the inside wheel of a vehicle turns slowly while the outside wheel revolves quickly when rounding a corner.  As most automobiles are propelled by power applied to the rear axle, to which the wheels are fixed, it is manifest that unless some device were made to correct the fault one wheel would have to slide while the other revolved.  This difficulty has been overcome by cutting the axle in two and placing between the ends a series of gears which permit the two wheels to revolve at different speeds and also apply the power to both alike.  This device is called a compensating gear, and is worked out in various ways by the different builders.

The locomotive builder accomplishes the same thing by making his wheels larger on the outside, so that in turning the wide curves of the railroad the whole machine slides to the inside, bringing to bear the large diameter of the outer wheel and the small diameter of the inner, the wheels being fixed to a solid axle.

The steam machine can always be distinguished by the thin stream of white vapour that escapes from the rear or underneath while it is in motion and also, as a rule, when it is at rest.

The motor of a steam vehicle always stops when the machine is not moving, which is another distinguishing feature, as the gasoline motors run continually, or at least unless the car is left standing for a long time.

As the owners of different makes of bicycles formerly wrangled over the merits of their respective machines, so now motor-car owners discuss the value of the different powers—­steam, gasoline, and electricity.

Though steam was the propelling force of the earliest automobiles, and the power best understood, it was the perfection of the gasoline motor that revived the interest in self-propelled vehicles and set the inventors to work.

A gasoline motor is somewhat like a gun—­the explosion of the gas in the motor-cylinder pushes the piston (which may be likened to the projectile), and the power thus generated turns a crank and drives the wheels.

The gasoline motor is the lightest power-generator that has yet been discovered, and it is this characteristic that makes it particularly 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.