"At this rate of progress, very soon," answered the exile, after glancing at the map. "We should be at the foot of the Ural mountains in a few hours, and across them in the night. Then we will be in Siberia."

And he was right, for just as supper was being served, Ned, who had been making observations with a telescope, exclaimed:

"These must be the Urals!"

Mr. Petrofsky seized the gla.s.s.

"They are," he announced. "We will cross between Orsk and Iroitsk. A safe place. In the morning we will be in Siberia--the land of the exiles."

And they were, morning seeing them flying over a most desolate stretch of landscape. Onward they flew, covering verst after verst of loneliness.

"I'm going to put on a little more speed," announced Tom, after a visit to the storeroom, where were kept the reserve tanks of gasolene. "I've got more fluid than I thought I had, and as we're on the ground now I want to hurry things. I'm going to make better time," and he yanked over the lever of the accelerator, sending the Falcon ahead at a rapid rate.

All day this was kept up, and they were just making an observation to determine their position, along toward supper time, when there came the sound of another explosion from the motor room.

"Bless my safety valve!" cried Mr. Damon. "Something has gone wrong again."

Tom ran to the motor, and, at the same time the Falcon which was being used as an aeroplane and not as a dirigible, began to sink.

"We're going down!" cried Ned.

"Well, you know what to do!" shouted his chum. "The gas bag! Turn on the generator!"

Ned ran to it, but, in spite of his quick action, the craft continued to slide downward.

"She won't work!" he cried.

"Then the intake pipe must be stopped!" answered the young inventor.

"Never mind, I'll volplane to earth and we can make repairs. That magneto has gone out of business again."

"Don't land here!" cried Ivan Petrofsky.

"Why not?"

"Because we are approaching a large town--Owbinsk I think it is-the police there will be there to get us. Keep on to the forest again!"

"I can't!" cried Tom. "We've got to go down, police or no police."

Running to the pilot house, he guided the craft so that it would safely volplane to earth. They could all see that now they were approaching a fairly large town, and would probably land on its outskirts. Through the gla.s.s Ned could make out people staring up at the strange sight.

"They'll be ready to receive us," he announced grimly.

"I hope they have no dynamite bombs for us," murmured Mr. Damon. "Bless my watch chain! I must get rid of that Nihilist literature I have about me, or they'll take me for one," and he tore up the tracts, and scattered them in the air.

Meanwhile the Falcon continued to descend.

"Maybe I can make quick repairs, and get away before they realize who we are," said Tom, as he got ready for the landing.

They came down in a big field, and, almost before the bicycle wheels had ceased revolving, under the application of the brakes, several men came running toward them.

"Here they come!" cried Mr. Damon.

"They are only farmers," said the exile. He had donned his dark gla.s.ses again, and looked like anything but a Russian.

"Lively, Ned!" cried Tom. "Let's see if we can't make repairs and get off again."

The two lads frantically began work, and they soon had the magneto in running order. They could have gone up as an aeroplane, leaving the repairs to the gas bag to be made later but, just as they were ready to start, there came galloping out a troop of Cossack soldiers. Their commander called something to them.

"What is he saying?" cried Tom to Mr. Petrofsky.

"He is telling them to surround us so that we can not get a running start, such as we need to go up. Evidently he understands aeroplanes."

"Well, I'm going to have a try," declared the young inventor.

He jumped to the pilot house, yelling to Ned to start the motor, but it was too late. They were hemmed in by a cordon of cavalry, and it would have been madness to have rushed the Falcon into them, for she would have been wrecked, even if Tom could have succeeded in sending her through the lines.

"I guess it's all up with us," groaned Ned.

And it seemed to; for, a moment later, an officer and several aides galloped forward, calling out something in Russian.

"What is it?" asked Tom.

"He says we are under arrest," translated the exile.

"What for?" demanded the young inventor.

Ivan Petrofsky shrugged his shoulders.

"It is of little use to ask--now," he answered. "It may be we have violated some local law, and can pay a fine and go, or we may be taken for just what we are, or foreign spies, which we are not. It is best to keep quiet, and go with them."

"Go where?" cried Tom.

"To prison, I suppose," answered the exile. "Keep quiet, and leave it to me. I will do all I can. I don't believe they will recognize me.

"Bless my search warrant!" cried Mr. Damon. "In a Russian prison! That is terrible!"

A few minutes later, expostulations having been useless, our friends were led away between guards who carried ugly looking rifles, and who looked more ugly and menacing themselves. Then the doors of the Russian prison of Owbinsk closed on Tom and his friends, while their airship was left at the mercy of their enemies.

CHAPTER XIX

LOST IN A SALT MINE

The blow had descended so suddenly that it was paralyzing. Tom and his friends did not know what to do, but they saw the wisdom of the course of leaving everything to Ivan Petrofsky. He was a Russian, and he knew the Russian police ways--to his sorrow.