practically at a standstill. All that the
balloonist could do in controlling his balloon was to make it ascend or
descend at will; he could not guide its direction of flight. No doubt
pioneers of aeronautics early turned their attention to the problem of
providing some apparatus, or some method, of steering their craft.
One inventor suggested the hoisting of a huge sail at the side of the
envelope; but when this was done the balloon simply turned round with
the sail to the front. It had no effect on the direction of flight of
the balloon. "Would not a rudder be of use?" someone asked. This plan
was also tried, but was equally unsuccessful.

Perhaps some of us may wonder how it is that a rudder is not as
serviceable on a balloon as it is on the stern of a boat. Have you ever
found yourself in a boat on a calm day, drifting idly down stream, and
going just as fast as the stream goes? Work the rudder how you may, you
will not alter the boat's course. But supposing your boat moves faster
than the stream, or by some means or other is made to travel slower than
the current, then your rudder will act, and you may take what direction
you will.

It was soon seen that if some method could be adopted whereby the
balloon moved through the air faster or slower than the wind, then the
aeronaut would be able to steer it. Nowadays a balloon's pace can be
accelerated by means of a powerful motor-engine, but the invention of
the petrol-engine is very recent. Indeed, the cause of the long delay in
the construction of a steerable balloon was that a suitable engine
could not be found. A steam-engine, with a boiler of sufficient power
to propel a balloon, is so heavy that it would require a balloon of
impossible size to lift it.

One of the first serious attempts to steer a balloon by means of engine
power was that made by M. Giffard in 1852. Giffard's balloon was
about 100 feet long and 40 feet in diameter, and resembled in shape
an elongated cigar. A 3-horse-power steam-engine, weighing nearly 500
pounds, was provided to work a propeller, but the enormous weight was so
great in proportion to the lifting power of the balloon that for a time
the aeronaut could not leave the ground. After several experiments the
inventor succeeded in ascending, when he obtained a speed against the
wind of about 6 miles an hour.

A balloon of great historical interest was that invented by Dupuy du
Lonie, in the year 1872. Instead of using steam he employed