"What are you going to do?" asked Dick.

"I'm going to tilt the craft suddenly at an angle that would turn her over if it were not for the stabilizer," was the answer.

Dick looked at the barograph, or height-recording gage. It registered thirty-eight hundred feet. They had gone up a considerable distance in making their experiments.

"Maybe you'd better wait," suggested the young millionaire, pointing to the hand of the dial, "until we go down a bit."

"No," decided the aviator. "If she's going to work at all she'll do it up at this distance as well, if not better, than she would five hundred, or one hundred feet, from the ground."

"But it might be safer—" began Paul.

"There won't be any danger—it will work, I'm sure of it," said Mr. Vardon, confidently.

The gyroscope which was depended on to keep the airship on a level keel at all times, or at least to bring her back to it if she were thrown to a dangerous angle, had been set in motion as soon as the start was made. The big lead wheel, with the bearings of antifriction metal, was spinning around swiftly and noiselessly. Once it had been started, a small impulse from a miniature electrical motor kept it going.

"Now," said Mr. Vardon, issuing his orders, "when I give the word I want you all suddenly to come from that side of the cabin to this side. At the same time, Dick, you will be at the steering wheel, and I want you to throw her head around as if you were making a quick turn for a spiral descent. That ought to throw her nearly on her beams' end, and we'll see how the gyroscope works. That will be a good test. I'll stand by to correct any fault in the gyroscope."

They were all a little apprehensive as they ranged themselves in line near one wall of the cabin. The airship tilted slightly as all the weight came on one side, just as a big excursion steamer lists to starboard or port when the crowd suddenly rushes all to one rail. But, on a steamer, deck hand are kept in readiness, with barrels of water, and these they roll to the opposite rail of the boat, thus preserving the balance.