f optics and angles, but, the professor declares,
most assuredly a fact.

[Illustration: HOW THE EARTH LOOKS WHEN VIEWED FROM A HEIGHT OF ONE
MILE.

(Photographed from a balloon.)]

Never before these talks did I realize how busy an aeronaut is, how much
there is to do in a balloon. Besides attending to valve-cords and
ballast there is the barometer to keep your eyes on, for by it alone can
you know your altitude. Around moves the needle slowly as you rise,
slowly as you fall, one point for a thousand feet. Rising or falling,
you know the worst or the best there. Sometimes the needle sticks, the
barometer will not work, and you must cast overside pieces of
tissue-paper to see by their rise or fall if you are going up or down.
By your senses alone you cannot tell whether you are rising or falling,
or your distance from the earth. That is most deceiving. Then you must
have your watch ready to reckon your speed, so many thousand feet up or
down in so many seconds, and your map spread out (nailed to a board, and
that lashed fast), to tell where you are, and your compass out to fix
the north and south points, for a balloon twists slowly all the time,
twists one way going up and the other way coming down. Nobody knows just
why this is, unless it be the unequal drawing of the seams as the
fabric swells and shrinks.

"I always keep the mouth of my balloon within easy reach," said the
professor, "and play with it as an engineer does with his
throttle-valve. Sometimes I even tie it shut when I am sailing, but that
is dangerous."

"Why dangerous?"

"Because the balloon might ascend suddenly, and the expanding gas burst
it."

"Can you see up into the balloon," I asked, "through the mouth?"

"Of course you can, and a beautiful sight it is. You look up through a
round window, twenty inches or so in diameter, into the great bag,
swelled out fifty or sixty feet in diameter, and perfectly tight, so
that every line and veining of the net shows plainly through the silk in
exquisite tracery, and wherever the sun strikes it you see a spread of
gold and amber melting away in changing colors to the shaded parts. The
balloon seems to be perfectly empty, perfectly still, yet it swings you
upward and upward like a live thing. You get to feel that your balloon
is alive."

"Does it make any noise?"

"Usually not. Now and then there is a creaking of the basket or a rustle
of fabric, as you pass from one wind current to another, but as