ook--there's the coast of Europe!
How fast are we going now?"

"We were traveling at the rate of three miles a second at the peak."
Arcot answered. "Now it has fallen to two and a half."

Again Arcot turned his attention to his controls. "I'm going to try to
see what the ultimate ceiling of this machine is. It must have a
ceiling, since it depends on the operation of the generator to operate
the power-units. This, in turn, depends on the heat of the air, helped
somewhat by the sun's rays. Up we go!"

The ship was put into a vertical climb, and steadily the great machine
rose. Soon, however, the generator began to slow down. The readings of
the instruments were dropping rapidly. The temperature of the
exceedingly tenuous air outside was so close to absolute zero that it
provided very little energy.

"Get up some forward speed," Morey suggested, "so that you'll have the
aid of the air scoop to force the air in faster."

"Right, Morey." Arcot slowly applied the power to the forward propulsion
units. As they took hold, the ship began to move forward. The increase
in power was apparent at once. The machine started rising again. But at
last, at a height of fifty-one miles, her ceiling had been reached.

The cold of the cabin became unbearable, for every kilowatt of power
that the generator could get from the air outside was needed to run the
power units. The air, too, became foul and heavy, for the pumps could
not replace it with a fresh supply from the near-vacuum outside. Oxygen
tanks had not been carried on this trip. As the power of the generator
was being used to warm the cabin once more, they began to fall. Though
the machine was held stable by the gyroscopes, she was dropping freely;
but they had fifty miles to fall, and as the resistance of the denser
air mounted, they could begin to feel the sense of weight return.

"You've passed, but for the maneuvers, Dr. Arcot!" The Air Inspector was
decidedly impressed. "The required altitude was passed so long ago--why
we are still some miles above it, I guess! How fast are we falling?"

"I can't tell unless I point the nose of the ship down, for the
apparatus works only in the direction in which the ship is pointed. Hold
on, everyone, I am going to start using some power to stop us."

It was night when they returned to the little field in Vermont. They had
established a new record in every form of aeronautical achievement
except endurance! The altitude record, the spe