isplacing a foot of the air-ocean and to that
extent adding buoyancy.

"General Hazen and I," said the professor, "once planned that some day,
when we got an appropriation, we would go up in a balloon having a
capacity of, say, forty thousand cubic feet, but carrying at the ground
only ten thousand cubic feet of hydrogen--in other words, in a shrunken,
quarter-filled balloon. Of course as we rose and the air became rarefied
this hydrogen would expand against the decreasing air-pressure, and at a
height of two miles our original ten thousand feet of gas might have
swelled to twenty thousand feet, at five miles to thirty thousand feet,
and so on. The last ten thousand feet of expansion would have brought us
to no one knows what height, but certainly, we calculated, to the
greatest height ever reached by a balloonist."

He explained that the balloon record of seven miles claimed for
Glaischer and Coxwell, the English aeronauts, is not reliable, since the
barometer used in that famous ascension (it was made at Wolverhampton,
England, in 1862) could not register above five miles, and what was
accomplished beyond that height is matter of pure conjecture and must be
less than might be done by the Hazen-Myers plan, since Glaischer's
balloon (by a serious oversight) was started on its flight nearly full
of hydrogen, instead of nearly empty.

"Oh," exclaimed the professor, with regretful look, "why don't some of
our very rich men think of these things!"

IV

THE STORY OF A BOY WHO RAN AWAY IN A BIG BALLOON

ONE of the professor's hobbies is that gas-balloons are better and safer
than the hot-air kind, although the latter cost less to operate. Your
hot-air balloon goes up with a rush, but comes down again as soon as it
cools; and in the coming down lies the danger. A gas-balloon, on the
other hand, stays up as long as you keep gas in it, and the professor's
secret of varnishing holds gas like a trap.

As to the ordinary use of hot-air balloons for parachute dropping, the
professor has only condemnation. A parachute, says he, is a sin and a
disgrace--a thing to be prohibited by law. The parachute kills more
people every year (the professor still is talking) than many a battle,
and kills them in unpleasant ways: drops them on live electric wires,
which shock them to death; drops them in lakes, where they are drowned,
or in the ocean, where they are eaten by sharks; drops them in trees,
where they catch by their coat-