“Yes.”
“Then imagine the same airship seven miles in the air.”
“You’d freeze. Or if you didn’t you’d die from lack of oxygen.”
“Balloonists have gone that high. They were cold enough but they carried oxygen with them and didn’t die.”
“Well!”
“At seven miles in the air the air pressure is reduced one half. The forward speed of your airship, assuming that it is flying on the same angle, ought to be doubled. You’d be advancing at the rate of four hundred miles an hour.”
“I thought the buoyancy decreased with the pressure,” broke in Major Honeywell who had absorbed more or less of the terms of aeronautics.
“So it does,” explained Ned, “but the buoyancy of an aeroplane is due wholly to its rapid flight. If we are going at the rate of two hundred miles an hour and are then able to double this, we have compensation for the loss of half our buoyancy. So, all other things being equal, we have a theory that like a migrating bird, the higher we ascend, the faster our flight. And, one other thing. The faster you rise from the earth the less the force of gravity. At eight miles altitude, where the air pressure is one fourth that at the sea level, and where, mathematically,” he looked at the astonished editor mischievously, “the two hundred mile an hour aeroplane would be traveling at the rate of eight hundred miles an hour, it has already been calculated that the specific gravity of the airship would be two per cent less than at sea level. Do you understand what that means?”
“That the force of gravity would be less,” answered the editor.
“And that the centrifugal tendency would be greater,” continued Ned. “In other words there would be an appreciable inclination of the airship to fly away from the earth.”