The professor, having made a careful examination of the ship to see that everything was in order, showed Jack and Mark how to steer the craft, and how to start, stop, raise and lower it from the conning tower or the engine room.
Then he let them practice a bit, and two more delighted boys there never was, as they sent the craft ahead up or down, starting and stopping her with a few turns of a wheel or lever.
"You may want to know how to run her some day in an emergency," said
Amos Henderson. "No telling what will happen."
"We hope nothing will," spoke Jack.
"There's no telling," prophesied the inventor.
For several days the ship moved ahead at moderate speed. The machinery, excepting for some minor accidents, worked smoothly. The gas bag did not leak, which was the accident most dreaded, and it was not necessary to run the gas generator, which proved a saving of the valuable chemical from which the lifting-vapor was produced.
Now and then, when in need of water, the craft was lowered to the earth in a secluded spot near a stream or lake, and the tanks were filled for drinking and washing purposes. But so far, from the time of the hasty flight, no one on the earth had spoken to the voyagers. Nor, so far as was known, had their presence been noted, though the black speck in the sky might have furnished plenty of talk all over the country for those who observed it. The weather was pleasant, but it was noticed that it was constantly growing colder.
One morning Jack, who was the first up, stuck his head out of the cabin door before he had finished dressing. He quickly popped back again.
"Whew!" he exclaimed. "Colder than Greenland!"
"What's that about Greenland?" asked the professor, who had just awakened.