"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 you drift along there is perfect stillness. I know nothing like the peace of a balloon sweeping in a storm. You feel like a disembodied spirit. You have no weight, no bonds; you fly faster than the swiftest express train. More than once Carlotta has raced a train going fifty miles an hour and beaten it."
"Is there danger to a balloon in a thunderstorm?"
"Apparently not, but it is terrifying to be in one. You seem to be at the very point where the lightning starts and the thunder-crash is born. All about you are roarings and blinding flashes, and it rains up on you and down on you, and in on you from all sides. While I never heard of a free balloon being struck by lightning, it is a common thing for operators on the ground even in fair weather to get shocks of atmospheric electricity down the anchor ropes of captive balloons."
Our talk drifted on, and the professor told of exciting times reporting the great yacht races from captive balloons (with reporters turning seasick in the plunging basket), and remarkable phenomena observed from balloons and double colored shadows of balloons (called parhelions) cast on clouds, and wonderful light effects, as when a marveling aëronaut looks down upon a sea of silver clouds bathed in sunshine and through black clefts sees a snowstorm raging underneath.
I was surprised to learn that at very great altitudes, say above three miles, the voice almost fails to serve, or, rather, the rarefied air loses in great part its power of voice transmission, so that in the vast silent spaces of the sky one aëronaut must literally shout to another in the same basket to make himself heard. One would say that the great, calm heavens resent the chattering intrusion of noisy little men.